FLEXIBLE COATINGS FOR ELASTOMER SUBSTRATES
FIELD OF THE INVENTION
[0001] The present invention relates to weatherable coatings applied on exterior
surfaces of flexible substrate articles, particularly elastomeric or rubbery articles or
substrates containing such materials. In addition to providing protective film
properties, the coatings reduce heat buildup by directing heat away from the article
(emissive). The coatings can be applied to an elastomeric substrate either before or
after the substrate has been vulcanized.
BACKGROUND OF THE INVENTION
[0002] Engineered elastomeric products are designed to flex and bend, distort and
recover, and/or dampen forces including absorbing torque or vibration repeatedly
during their service life and are utilized in numerous industrial applications. For
example, elastomeric materials are utilized in the manufacture of tires, hoses, seals,
mountings such as engine mounts, dampers and insulating devices, and are
designed to exhibit hysteretic losses, and withstand heat, to name a few design
aspects. These and other articles shaped into myriad articles have many
established uses such as industrial machines and parts for vehicles. Many
elastomer products come into contact with heat from a variety of sources, such as
from internal combustion engines. Recent increases in operating temperatures, and
reduction of the size of vehicular engine compartments give rise to closer proximity
between heat sources and such molded parts as rubber hoses, plastic housings,
belts, various mounts, shrouds, seals, grommets, washers, spacers, covers, and
housings, etc.. Some of these articles are heat vulcanized, others are room
temperature vulcanized and still others are cured in a different manner and exhibit
characteristic flexing, elongation, rubbery elasticity, as thermoplastics or thermoset
materials.
[0003] All polymeric materials degrade on account of exposure to heat, light,
oxygen, ozone solvents, oils, and/or fuels. Elastomeric materials, and especially
natural and/or synthetic vulcanized rubbers are particularly known to degrade when
exposed to these agents, and there is a continuing search within industry to provide
elastomer articles that are resistant to such degradative elements.
[0004] U. S. Pat. No. 6,022,626 discloses coatings suitable for covering engine
mounts to protect the rubber substrate from oxygen, ozone and/or UV light,
especially when reaching temperatures of 220°F/104 °C, or more. The coatings
taught provide a polymer barrier from chemical or UV intrusion. In exposure to hot
environments, the polymers taught in U.S. Pat. No. 6, 022,626 may provide an initial
barrier against oxygen, ozone and UV radiation but lack durability to repeated flexure
over long periods of time. Once adhesion fails or the coating is breached by cracks,
degradative effects resume. Such coatings as taught in U.S. '626 also do not
provide emissive properties and do not deflect heat.
[0005] U.S. Pat. No. 5,314,741 to Roberts, et. Al. entitled "Rubber Article Having
Protective Coating" relates to polymeric articles which are coated with hydrogenated
synthetic rubbers or polymers obtained by hydrogenating an unsaturated polymer
which is a polymer of 1,3-butadiene and optionally one or more monoethylenically
unsaturated polymers.
[0006] Conventional polymeric stabilizers, UV absorbers and the like are used for
the rubber articles coated thereon, yet improved aging properties are desired even in
light of more harsh operating conditions.
[0007] Achieving sufficient permanent adhesion to the underlying rubber which
experiences repeated flexure or extension over long-term service life is further
needing improvement.
[0008] Alkyd, urethane, and enamel metallic paint finishes are well known for
providing sparkled metallic effects, are widely used as on automotive bodies. The
substrates are mainly metal or rigid plastic parts where flexure is limited or the paints
are expected to crack if impacted severely. Speckled- effect metallic coatings are
commonly provided on metal body panels, whereby 1% or less metallic pigments are
interspersed with coloring pigments, and oVercoated with clear finish. Likewise,
aluminized spray paints have been provided for applying to furniture, metal articles
and the like, however the film forming materials utilized, cure to form a coating of
very limited elongation, and would be unsuitable as coatings on flexible substrates
such as engineered rubber articles due to flex cracking and loss of adhesion not long
after placing the coating in service. Metal flake effect paints provide visual
aesthetics for appearance parts but do not provide heat emissive properties to any
extent useful for extending the useful long term service of engineered rubber
products under hot environments.
[0009] One method of rendering elastomeric materials resistant to corrosive
materials is to apply a protective coating to the elastomeric material. Various
corrosion-resistant coatings previously utilized for both flexible substrates (e.g.,
elastomeric substrates) and rigid substrates (e.g., steel, stainless steel, aluminum or
plastic) include polyurethanes, polysulfides and fluorocarbon elastomers. When
applied to rigid substrates, traditional corrosion-resistant coatings such as
fluorocarbon elastomers have been found to provide excellent resistance to oil and
fuel. However, when applied to flexible elastomeric substrates comprising natural
rubber and/or diene-type elastomers and mixtures, the fluorocarbon elastomers
suffer from poor fatigue resistance, poor low temperature characteristics, and poor
adhesion to these substrates.
[0010] Low molecular weight polyolefin or polyisoolefin based elastomers containing
a low level of chemically bound functionality such as an hydroxyl or an amine
bearing group are known for incorporation into urethane foams. Such elastomers
can be blended with and cured by an unblocked or blocked polyisocyanate. For
example, U.S. Pat. No. 4,939,184 discloses the preparation of flexible polyurethane
foams made by reacting a low molecular weight poiyisobutylene having two or three
terminal hydroxy groups with a polyisocyanate in the presence of a blowing agent.
[0011] U.S. Pat. No. 4,136,219 to Odarn relates to two methods or processes for
applying polyurethane paint to vulcanized rubber parts.
[0012] U.S. Pat. No. 4,670, 496 discloses tire sidewall striping paint as a coloring
indicia of any color, such as a dye, and preferably metallic particles are disposed in a
solution that contains unvulcanized diene rubber(s) and rubber vulcanization
accelerator. Crosslinkable silicone and/or modified EPDM may also be disposed in
the solution. The accelerator is essential for scavenging sulfur from the vulcanized
rubber substrate to provide auto-vulcanizing of the coating rubber. In order to
provide adequate adhesion for long term service as a coating for rubber articles, a
diene polymer containing more than 10% residual unsaturation after curing will
necessarily undergo degradation and embrittlement and will fail long before the
underlying substrate fails.
[0013] Diisocyanate containing free isocyanate groups has also been previously
proposed for curing copolymers of isobutylene and modified styrene containing
tertiary aminoalcohol groups in EPA 325 997. EPA 325 997 discloses diisocyanate
curing of polymers having a molecular weight of 700 to 200,000, and exemplifies
blends of up to about 30,000 weight average molecular weight (Mw) and about 8,600
number average MW (Mn), as measured by gel permeation chromatography.
[0014] A variety of bulk isocyanate-cured rubbers and mastics have been disclosed
in the 50's and 60's. Isocyanate reactive functional groups present in the elastomer
readily cure with NCO groups of the diisocyanate. As an example, U.S. Pat. No.
6,087,454 discloses a process to produce a cured bulk elastomer comprising
combining an elastomeric polymer, having an Mw of 60,000 or more and containing
hydroxyl and/or amine functional groups with a blocked polyisocyanate at a
temperature below the temperature that will unblock the isocyanate. The mixture is
cured by heating it to a temperature above the temperature that will unblock the
poiyisocyanate. This reaction can be effected at room temperature by the use of
unblocked isocyanates. Low molecular weight polyisobutylene containing hydroxy
functional groups are cured with a poiyisocyanate in the presence of a blowing agent
as is disclosed in U.S. Pat. No. 4,939,184.
[0015] U.S. Pat. No 4,774,288 discloses a hydrogenated copolymer of a conjugated
diene and an a,ß-unsaturated nitrile containing an active phenol-formaldehyde resin
vulcanization system. The disclosure is directed to the bulk vulcanizate, which is
characterized as having good compression set properties and a good resistance to
oils and good resistance to oxidative attack in air at elevated temperature aging
under oxidizing conditions, however no mention is made suggesting coatings could
be formed on flexible elastomeric substrates such as natural rubber and
polybutadiene which might provide useful properties.
[0016] U.S. Patent 5,314,955 discloses a coating composition consisting of (a) a
hydrogenated acrylonitrile-butadiene copolymer, (b) a phenolic resin, (c) a curing
component, and (d) a solvent. This coating solves many of the problems of adhesion
to rubber substrates combined with fatigue resistance and fuel resistance. One of
the drawbacks of this coating composition is that it requires a high temperature bake
to cure the coating and to promote adhesion to adjacent metal surfaces. A high
temperature baking conditions even for a coating requires heat soaking of the entire
article to be coated. Some parts such as helicopter rotor bearings would be
damaged by a high temperature bake, therefore coatings such as taught in '955 are
not practical to apply. The high temperature bake is also costly in production since it
adds a time delay and additional handling of the parts. There still exists a need for
improved protective coatings for flexible elastomeric substrates comprising typical
natural rubber and/or diene-type elastomers that are resistant to fatigue over a broad
temperature range, and that exhibit effective adhesion to the substrate, and that can
be cured at room temperature if this is a limiting factor in coating an article.
[0017] U.S. Pat. No. 6,156,379 discloses a conventional base-coat-clear coat paint
on metal surfaces, containing metal flakes in the base coat. The novel distinction is
based on bright pigments derived from finely divided vapor-deposited metal. The
metallic coating composition is applied over a base coating layer and a clear
topcoating layer is applied over the metallic coating layer. A metallic coating
composition is defined to consist essentially of the bright pigments and the solvent,
meaning that coating composition either contains no ingredient other than the flake
pigments and solvent, or a small amount of resin or additive such that the pigment
weight concentration if 95% or higher. Binders such as acrylic, polyamide, vinyl
chloride copolymers, urethane and polyesters are suggested. Such binders are not
recognized as suitable for coating on flexible substrates as these can not exhibit
100% elongation, and will fail from flex-cracking and adhesion loss after placing in
service.
[0018] U. S. Patent 5,314,741 discloses a coating composition including a latex of
highly saturated polymer such as hydrogenated nitrile rubber, highly saturated ;
styrene/butadiene copolymer, hydrogenated polybutadiene, or hydrogenated
styrene/vinyl pyridine/butadiene terpolymer. The coating is applied to a substrate
and cured in place to yield a desired coated article reportedly resistant to ozone,
oxygen, and UV light. Suitable curatives taught are zinc-sulfur cure packages.
Elevated temperatures are necessary to affect curing of these coatings. Moreover,
conventional vulcanizing systems high in sulfur content and low vulcanization
accelerator content, or semi-efficient vulcanizing system having a moderate dosage
of sulfur and vulcanizates accelerator known to the expert, and described e.g. in W.
Hofmann, Kautschuk-Technologie, Genter Verlag, Stuttgart, 1980 p. 64 and 254-255
have several drawbacks. Conventional vulcanizing coatings result in vulcanizates
with good resistance to dynamic stresses (flex life) are very sensitive to aging and
reversion. Semi-efficient vulcanizing systems usually give vulcanizates which have a
less of a resistance to dynamic stresses (flex life), but, in return, they are somewhat
more stable to aging and reversion (cf. R. N. Datta and W. F. Helt, Rubber World,
August 1997, p. 24, et seq.)
[0019] It has been observed by the present inventors that coatings based on highly
saturated elastomers utilizing vulcanizing chemistry suffer from loss of adhesion to
substrates such as blends of natural rubber and diene elastomers widely used in
rubber articles in the aforementioned articles, especially on automotive tires, hoses
and the like. A need still exists for an improved elastomeric protective coating for
flexible elastomeric substrates which provide improved adhesion to the surface of
elastomers, and improved flex-resistance as well as thermal emissive properties
enabling the reduction of heat transferred to the underlying polymer substrate. The
level of stress from heat under long-term service in engineered products is time and
temperature dependant. Any reduction in absorbed heat and any increase in the
release of heat within the elastomer can significantly extend the service/
performance life of the product. It would be industrially important to decrease the
rate of heat absorption, and increase the rate of heat dissipation of engineered
elastomer products in order to extend the useful working life of these articles.
SUMMARY OF THE INVENTION
[0020] One embodiment according to the invention is directed to a non-emissive
coating composition of the invention which is resistant to long-term fatigue and
temperature variability and provides for excellent adhesion to flexible elastomeric
substrates. The coating cures at room temperature. The coatings comprise a film
former polymer (Tg < 0 °C) containing less than 10% ethylenic unsaturation before
curing. In a preferred embodiment, the coating composition of the invention
comprises (A) a carboxylated hydrogenated acrylonitrile-butadiene copolymer, (X-
HNBR) (B) a curing component which contains at least one isocyanate group and a
group which forms crosslinks, and (C) a solvent. The coatings exhibit cured
elongation of at least 100% and remain bonded to the substrate after long-term
weathering. The preferred coating composition comprises 3 to 30 weight percent of
solids of (a) a carboxylated hydrogenated copolymer comprising a repeating units
from a conjugated diene, an unsaturated nitrile, and a carboxyl monomer and (b) a
curing component containing at least one isocyanate group and another group which
forms crosslinks, and (C) a solvent.
[0021] In another aspect, there is a method for coating a substrate comprising
applying the aforementioned solvent-based coating to the surface of a vulcanized
rubber substrate which is bonded to metal, drying the coating and allowing the dried
coating to cure at ambient conditions, optionally with application of heat. It is
preferred to provide the coating also onto the portion of exposed metal around the
periphery of the elastomer. The present invention provides coatings for elastomer-
metal composites with excellent adhesion to the elastomer substrate, resistance to
corrosive materials and resistance to flex- fatigue over a wide temperature range.
[0022] A further coating embodiment is an opaque, metal-filled emissive elastomeric
coating, devoid of rubber accelerator and curable at ambient temperature are -
provided. The coatings are in two parts which are mixed together at the time of
application to the substrate... The first part comprises a flexible film-forming polymer
exhibiting a Tg of less than 0°C and incorporated therein or thereon a functional
group which is reactive to an active hydrogen containing curing agent, or the
functional group is an active hydrogen-bearing group, and a liquid carrier. The
second or another part comprises a curing agent component containing either an
active hydrogen bearing group and a crosslinking group, or the curing agent
component contains a group reactive with active hydrogen and a crosslinking group,
and a carrier liquid and (a) from 10 to 100 parts by weight per 100 parts by weight of
film forming elastomer of thermally conductive metal particles having a particle size
average of from 2 to 10 µm or (b) from 20 to 150 parts by weight of thermal
conductive particles having an average particle size of 20 to 60 microns.
BRIEF DESCRIPTION OF THE ACCOMAPYING DRAWINGS
[0023] FIG. 1 is a plot of internal temperature versus time for a coated versus
uncoated rubber block exposed to an infrared heat source over 120 minutes.
[0024] FIG. 2 is a graphical representation of the effect of a 0.001' (0.00040 cm)
thermal conductive coating applied to naturat rubber on internal heat build under
radiant heat at 0, 10 and 20 phr of a thermal conducting pigment.
[0025] FIG. 3 is a graphical representation of the effect of a 0.001" (0.00040 cm)
thermal conductive coating applied to natural rubber on internal heat build under
radiant heat at 0, 10 and 20 phr of a thermal conducting pigment.
[0026] FIG. 4 is a graphical representation of the effect of a 0.001' (0.00040 cm)
thermal conductive coating applied to natural rubber on internal heat build under
radiant heat at 0, 20 and 50 phr thermal conducting pigment.
[0027] FIG. 5 is a graphical representation of the effect of a 0.001' (0.00040 cm)
thermal conductive coating applied to natural rubber on internal heat build under
radiant heat at 0, 20 and 50. phr thermal conducting pigment.
[0028] FIG. 6 is a graphical representation of the effect on the internal temperature
of natural rubber blocks coated using three different thermal conductive coatings
versus an uncoated block under radiant heat after 10 minutes.
DETAILED DESCRIPTION OF THE INVENTION
[0029] The coatings disclosed herein cure at ambient conditions and are resistance
to solvents and fuels, and have ozone resistance. The coatings comprise film
forming polymer and a specified amount of particulate metal filler. The film former
provides a film that is has at least 90% light transmission in the cured state, and
contains no more than about 90% unsaturation after curing. The 90+% light
transmissive film forming matrix provides low loss of heat reflectivity and thermal
transfer properties from the reflective metal particulate filler.
[0030] The coating results in reflection of significant heat from the underlying
conductive particles of the coating, while the coating adheres permanently and is
resistant to stress or environmental cracking or embrittlement. Such coatings
durably bond to molded rubber, TPE and plastic goods, such as pneumatic tires,
non-pneumatic tires, hoses, belts, mounts, shrouds, deflector panels, and the like,
especially where used near hot bodies, like engine blocks or other industrial
components emitting heat. The cured coatings are mar and scuff-resistant.
[0031] The coatings cure under ambient conditions after coating on flexible
substrates to typical dry film thickness (DFT) of from about 0.5 to 20 mils (12.7 µm-
508 µm). The coating is applied in liquid form using an aqueous or organic carrier
depending on the selected cure agent and film former as a solution substantially
devoid of water, or an aqueous dispersion. Faster curing can be obtained at
elevated heat conditions, with or without photonic energy, depending on availability
of curing conditions available. An advantage of the present invention having
ambient cure is that a final assembled engineered rubber product with a significant
thermal mass need not be heated to effect cure of the coating. The cured physical
properties of the metal-filled coating films include resistance to flex-fatigue over a
broad operating temperature range (-40°C - 150°C), resistance to degradation on
long-term exposure to high temperatures and ozone and include excellent adhesion
to flexible elastomeric substrates. The coating composition after curing at room
temperature exhibits more than about 50% elongation without distorting (full
recovery), and more typically elongate up to 100%, 200% or 300% without adhesion
loss, cracking, distortion or separation from the underlying flexing of the elastomer
substrate. The heat reflective surface maintains its integrity to repeated flexing and
the thermally conductive particles remain intact to provide a heat-emissive surface.
[0032] The coating compositions contain at least one film former polymer or
prepolymer which contains functional groups as cure sites for a curing agent without
the use of vulcanization chemicals. A curing agent is utilized typically from 5 to 100
(phr) parts per 100 parts of film former polymer. The thermal conductive metal
particles are specified hereinbelow in amounts on a weight basis depending upon
the average size of the metallic particles.
[0033] Examples of useful film forming polymers that contain active hydrogen
functional groups are disclosed herein. Polymers containing functional groups which
are reactive with active hydrogen containing cure agents are also disclosed. Film
forming polymers suitable herein include a-olefin elastomers, conjugated diene
elastomers, hydrogenated diene elastomers, fluoroelastomers, ethylene-
carboxylate, ethylene-propylene-diene elastomers, functionalized ethylene-vinyl
acetate, SB-diblock, SBS- and SIBS-triblock copolymers and hydrogenated versions
thereof, acrylic rubber, and polyurethanes are adaptable for use herein. Functional
groups can be provided in the film former by comonomers in the polymerizate, or by
post-polymerization methods known in the art by conventional means. The chemical
crosslinks between the curing agent and film forming polymer are an essential
feature of the invention for ambient curing, substrate adhesion and durability.
[0034] In a preferred embodiment, the coating composition of the invention
comprises a functionalized hydrogenated acrylonitrile-butadiene copolymer (A)
(functionalized HNBR), a curing agent (B) which contains at least one isocyanate
group, preferably a polyisocyanate, or isocyanate-functional prepolymer, or
isocyanato silane, or at least one multifunctional compound, oligomer, prepolymer
having an isocyanate group and a group which forms crosslinks, and (C) an organic
solvent. It is an important aspect of the present invention that the solvent of the
coating composition can be either water based or hydrocarbon based. Aqueous
coatings are provided which contain reduced levels of volatile organic compound
(VOC).
[0035] The coatings of the present invention are applied to elastomer substrates
either prior or subsequent to vulcanization of the elastomer substrate. In one aspect,
the present invention sets forth a method for coating a substrate comprising applying
the coating to a surface of an unvulcanized rubber substrate and drying the coating
at ambient or elevated temperatures, thereby curing the coating.
[0036] In another invention aspect, a method for coating a substrate is provided and
comprises a step of applying the coating to the surface of a vulcanized rubber
substrate which itself may optionally be bonded to a metal component, drying the
coating and allowing the dried coating to cure at ambient conditions, optionally with
application of heat, light or radiation. When necessary, it is preferred to provide the
coating also onto the portion of exposed metal around the periphery of the
elastomer.
[0037] The present invention provides exterior coatings for shaped or molded
polymeric articles such as elastomeric materials and elastomer-metal composites
with excellent adhesion to the elastomer substrate, resistance to corrosive materials,
resistance to heat build-up, and resistance to flex- fatigue over a wide temperature
range.
[0038] The coating is formed by a mixture of two liquid parts at the time of
application to the substrate. Part A contains a liquid solution or dispersion of a
functionalized polymer, and part B contains a liquid curing agent. When the parts
are combined, the ambient temperature curable embodiments have a typical pot life
of 30 minutes to one hour. The curable coating mixture of parts A and B contain
from 2 to 20% solids content. The viscosity can be controlled depending on the
selected components, and is less than 20,000 cps (Brookfield) such that the coating
can be sprayed, brushed or dipped.
POLYMER FUNCTIONALIZING METHODS
[0039] Functionalized elastomer film-formers used herein can be provided by several
routes, such as by copolymerization and in various methods to modify film forming
polymers by incorporation of functional groups to the polymer after polymerization.
The term "functionalized" means that an active hydrogen-bearing moiety as part of
an ethylenic unsaturated comonomer is copolymerized or, an active hydrogen
bearing compound is graft-linked, post-polymerization, The comonomer or grafted
compound becomes covalently bonded to the polymer structure, and provides a
group capable of reacting with an ambient temperature curing agent.
[0040] The film former is prepared using conventional approaches for incorporation
of an active hydrogen-bearing functional group on polymerized non-functional
elastomer such as by converting a functional group-bearing compound into a
suitable functional group precursor or the direct incorporation of a suitable precursor
radical as may be accomplished when the elastomer is in solution or in the molten
state via the "Ene" reaction, whereby an allylic hydrogen transfer to an enophile
followed by coupling between two unsaturated termini occurs, or via free-radical
addition across a carbon-carbon double bond in the molten state or in a dilute
solution with solvent. When the polymer is in the molten state, however, means
capable of imparting high mechanical shear, such as an extruder, will be used to
effect the desired reaction to incorporate the functional group to be converted or to
directly incorporate a suitable precursor radical. When the functional group to be
converted to a suitable precursor or the precursor radical incorporated directly is
incorporated via techniques such as metallation followed by reaction with a suitable
electrophile, on the other hand, incorporation will, preferably, be accomplished with
the polymer in solution.
[0041] Of the several methods available-for incorporation of a functional group or
functional group precursor, those methods tending to incorporate a single function
group or functional group precursor unit at each site of incorporation with minimal
coupling of the elastomer polymer such as the Ene reaction and the method
involving metallation followed by reaction with an electrophile are preferred. When a
functional group to be converted to a suitable precursor is incorporated into the
elastomer, conversion of the functional group to the precursor radical will also,
generally, be accomplished with the polymer in solution. In general, any of the
solvents known to be useful for preparing such elastomer polymers in solution may
be used to effect these reactions or conversions.
[0042] A variety of post-polymerization functionalization techniques are known which
provide heretofore non-functional addition polymers with coupted crosslinking cure
sites for use in the present invention. Hydroxyi groups are useful functional groups
for effecting the crosslinking reactions with curing agents used herein. U.S. Pat. No.
4,118,427 discloses hydroxyl-containing curable liquid hydrocarbon prepolymers by
ozonizing a high molecular weight saturated hydrocarbon polymer such as
polyisobutylene or ethylene-propylene rubber, followed by reducing the ozonized
material; e.g., by using reducing agents such as diisobutyl aluminum hydride, to form
the above-noted hydroxyl-containing liquid prepolymers having a substantially lower
molecular weight than the parent polymer
(A) FUNCTIONALIZED COMONOMERS
[0043] The curable film forming polymer employed herein can be formed by
copolymerization of elastomer-forming monomers together with functionalized
comonomers or by reaction of a polymer with a functional group containing monomer
or reactive compound. The incorporated reactive group subsequently cures the
polymer by reaction of the curing component as described herein. The curing
method utilizes reactions of a crosslinking agent with an active hydrogen-bearing
functional group or active hydrogen reactive group which crosslinks with the
corresponding reactive functional group on the copolymer or pendant on the
copolymer. It is convenient to introduce a functional group bearing comonomer
during polymerization of the film former polymer, as is conventionally practiced. The
various approaches of free radical addition copolymerization, anionic addition
polymerization, free-radical graftlinking, metathesis grafting, and hydrolytic grafting
are known in the art. The functional group containing polymers, or copolymers
include polymers characterized by their major constituents, such as a-olefin
elastomers, diene elastomers, hydrogenated diene elastomers, functionalized
fluoroelastomers, crosslinkable a-olefin copolymer elastomers, functionalized
acrylate or methaerylate acrylate copolymers, and ethylene-carboxylates, etc..
[0044] Preferred examples of rubbery copolymer elastomers include but are not
limited to anionic polymerized olefinic elastomers. Examples of anionic polymerized
olefinic rubbers include ethylene-propylene rubber, ethylene-propylene-diene
monomer rubber, polyisobutylene, or "butyl rubber", or any other polymer of isoolefin
optionally copolymerized with conjugated diene (such as isoprene), optionally
containing up to 30 wt. % or an a,ß-ethyienic unsaturated nitrile and/or styrenic
comonomer (such as styrene and/or alkyl substituted styrene), and the like.
Particularly preferred elastomers include isobutylene-isoprene copolymer,
isobutylene-para methylstyrene copolymer and the like.
[0045] A suitable pendant active hydrogen functional group is provided by methods
for forming amine-functionalized ethylene propylene diene monomer rubber (EPDM)
by the process described in U.S. Pat. No. 4,987,200. Likewise higher molecular
weight isobutyiene copolymers functionalized with hydroxy! groups can be produced
using the process described in EPA 325 997. Furthermore any commercially
available halogenated isobutyiene based polymer containing a low level of halogen
typically 0.5 to 2.0 mole % can be combined with an aikylamine or an amino alcohol
to produce the amine or the hydroxyl functional group respectively.
[0046] Functionalized elastomers having an weight average molecular weight of
1000 up to 200,000 and containing hydroxyl and/or amine functional groups are
known. Hydroxy terminated polyisobutylene are conventionally prepared by
introducing hydroxy groups into the terminal positions of cationically polymerized
isobutyiene by dehydrochlorinating, hydroborating and oxidizing chloro-terminal
polyisobutylene. Chloro terminated polyisobutylenes obtained by cationically
polymerizing an isobutyiene monomer are known. See Faust and Kennedy in, "Living
Carbocationic Polymerization: 111. Demonstration of the Living Polymerization of
Isobutyiene," Polym. Bull. 15:317-23 (1986), disclosing living carbocationic
polymerization of isobutyiene and quenching the living recipe with methanol and
other reagents such as amines.
[0047] Living polymerization methods are described in U.S. Pat. Nos. 5,350,819;
5,169,914; and 4,910,321 are preferred techniques to form the film forming polymer.
General conditions under which living polymerizations can be achieved, for example
using isobutyiene include: (1) an initiator such as a tertiary alkyl halide, tertiary alkyl
ether, tertiary alkyl ester, or the like; (2) a Lewis acid co-initiator which typically
comprises a halide of titanium, boron or aluminum; (3) a proton scavenger and/or
electron donor; (4) a solvent whose dielectric constant is selected considering the
choice of the Lewis acid and the monomer in accord with known cationic
polymerization systems and monomer.
Terminal Functional Polymers.
[0048] Active hydrogen groups or groups reactive with active hydrogen groups can
be incorporated at the terminus of film former polymers which are useful herein.
U.S. Pat. No. 5,448,100 discloses sulfonated telechelic polyisobtuyiene prepared by
the "inifer" (initiator-transfer agents) initiated carbocationic polymerization of
isobutyiene with Lewis acid to form polymer, followed end-quenching with acetyl
sulfate and precipitation by steam stripping or with methanol, ethanol, isopropyl
alcohol, or acetone. The polymerization preferably occurs in a chlorinated solvent,
most preferably in a mixture of solvents, such as methylene chloride, methyl
chloride, or an aliphatic or alicyclic compound containing five to ten carbon atoms.
The Lewis acid can be, for example, boron trichloride or titanium tetrachloride, or
other metal halide (including tin tetrachloride, aluminum chloride, or an alkyl
aluminum). End-quenching preferably occurs at a temperature between -90 ° to 0
°C, and most preferably at the polymerization temperature or at the decomposition
temperature of the complex . The molar ratio of polyisobutylene to acetyl sulfate is
preferably 1:1 or greater.
[0049] A film former polymer such as polyisobutylene can contain terminal silane
groups bearing a hydroxy and/or alkoxy group. These can be obtained by a known
route of dehydrohalogenating a poiyisobutylene polymer that contains tertiary
carbon-chlorine groups, followed by an addition reaction with an ethyienic
unsaturated silane. For example, chlorobutyl rubber having tertiary carbon-chlorine
bonds can be reacted with allyltrimethylsilane to give a poiyisobutylene having an
unsaturated group then reacted under addition conditions with platinum catalyst
using a hydrosiiane compound of the general formula

wherein R2 is a hydrogen atom, an alkyl group containing 1 to 20 carbon atoms, an
aryi group containing 6 to 20 carbon atoms, an arylalkyl group containing 7 to 20
carbon atoms or a triorganosiloxy group of the formula (R')3 SiO-- (in which each R'
independently represents a hydrogen atom or a substituted or unsubstituted
hydrocarbon group containing 1 to 20 carbon atoms), each X independently
represents a hydroxyl group or well-known hydrolyzable group, a is 0, 1, 2 or 3.
Alternatively a polymeric hydrosilane-terminal siloxane can be used.
Known hydrosiiane compounds include halogenated siianes such as trichlorosiiane,
methyldichlorosilane, dimethylchlorosilane, phenyldichlorosilane; alkoxysilanes such
as trimethoxysilane, triethoxysilane, methyldiethoxysilane, methyldimethoxysiiane,
phenyldimethoxysilane, etc.; acyioxysilanes such as methyldtacetoxysiiane,
phenyldiacetoxysilane, etc.; and ketoximate silanes such as
bis(dimethylketoximate)methylsiiane, bis(cyclohexylketoximate) methylsiiane, etc.
processes are described, for example, in Japanese Kokoku Publication Hei-4-69659,
Japanese Kokoku Publication Hei-7-108928, Japanese Kokai Publication Sho-63-
254149, Japanese Kokai Publication Sho-64-22904, and Japanese Patent
Publication 2539445.
Functionalized Hydrogenated Diene Elastomers
[0050] Functionalized hydrogenated diene copolymers suitable for use herein as the
film forming polymer are solvent soluble polymers preferably of a molecular weight of
about 50,000 and higher, more typically 200,000 to 500,000, and contain no more
than 10% conjugated diene segments by weight. These polymers are distinguished
from liquid, functionalized oligomers, such as reactive terminal-group functional liquid
polymers, e.g., ATBN and CTBN. The unsaturated functionalized polymer for
preparing the hydrogenated coating polymer comprises broadly, from 50 to 85
percent by weight of conjugated diene monomer units, 5 percent to 50 percent by
weight one or more non-conjugated, ethylenicalliy unsaturated monomer units, and 1
to 20 percent by weight of a functional comonomer or graft-linked compound bearing
a reactive crosslinking site. The preferred conjugated diene monomer units are
derived from 1,3-butadiene monomer, and the non-conjugated ethyienicaliy
unsaturated monomer units are derived from one or more ethyienicaliy unsaturated
monomers selected from unsaturated acrylic esters, methacrylic esters, nitrites such
as acrylonitrile and methacrylonitrile, and monovinyl aromatic hydrocarbons such as
styrene and alkylstyrenes, and vinylidene comonomers. Divinyl aromatic
hydrocarbons such as divinyl benzene, dialkenyl aromatics such as diisopropenyl
benzene are preferably absent. Other comonomers include alkyl (meth) acrylates
such as methyl acrylate, methyl methacrylate, ethyl acrylate, butyl acrylate, 2-
ethylhexyl acrylate or methacrylate, vinyi pyridine, and vinyl esters such as vinyl
acetate. The preferred functional comonomers are selected from unsaturated
carboxylic acids and esters thereof such as acrylic acid, methacrylic acid, crotonic
acid, itaconic acid, and maleic acid. The glass transition temperature of
functionalized diene elastomer film formers must not exceed -10°C , and preferably
is less than -25°C in order to provide acceptable flex-cracking/ flex-fatigue resistance
in the thermal conductive particle filled coating.
[0051] Carboxyl end groups can be formed on diene elastomer high polymers
containing -C-CH=CH-C- type unsaturation by a chain scission methods in which a
rubber ozonide is formed, and aldehyde end groups are oxidized to carboxyl groups
using peroxide or peracid. Alternatively hydroxyl end groups on the rubber ozonide
can be formed by reductive techniques by catalytic hydrogenation or by reducing
agents like metal hydrides or borohydrides, and the like. See for example British
Patent No. 884,448. Likewise, U. S. Pat. No. 4,118,427 discloses liquid hydroxyl-
containing curable liquid hydrocarbon prepolymers by ozonizing a high molecular
weight saturated hydrocarbon polymer such as polyisobujtylene or ethylene-
propylene rubber, followed by reducing the ozonized material; e.g., by using
reducing agents, preferably diisobutyl aluminum hydride, to form the above-noted
hydroxyl-containing liquid prepolymers of lower molecular weight than the parent
polymer.
[0052] Modification of a film-forming polymer by incorporation of mercaptoalcohol or
mercaptocarboxylate grafting compounds yield useful film formers in the present
invention. Suitable hydroxymercaptans and/or mercaptocarboxylic acid esters
containing hydroxyl. HS-R-OH compounds include those where R is a linear,
branched or cyclic C1-C36 alkyl group which can optionally be substituted by up to 6
further hydroxyl groups or can be interrupted by nitrogen, oxygen or sulfur atoms.
Mercaptocaboxylates such as HS-(CHR2)n-(C(O)OR3OH)m wherein R2 is hydrogen
or a C1 -C6 alkyl group, R3 is a linear, branched or cyclic C2 -C36 alkyl group which
can optionally be substituted by up to 6 further hydroxy! groups or can be interrupted
by nitrogen, oxygen or sulfur atoms, preferably -OH is primary, n is an integer from 1
to 5 and m is an integer from 1 to 2 are suitable.
[0053] Preferred hydroxymercaptans are mercaptoethanol, 1-mercapto-3-propanol,
1-mercapto-4-butanol, a-mercapto-to-hydroxyoligoethylene oxides, e.g., a-mercapto-
?-hydroxyoctaethylene glycol, or the corresponding ethylene oxide/propylene oxide
copoiyethers. Mercapto-ethanol and a-mercapto-?-hydroxyoligoethylene oxides are
preferred. Preferred mercaptocarboxyiic acid esters containing hydroxyl groups are
esters of mercaptoacetic acid, mercaptopropionic acid and mercaptobutyric acid with
ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, triethylene
glycol, tetraethylene glycol, octaethylene glycol, dipropylene glycol, tripropylene
glycol, tetrapropyiene glycol and N-methyldiethanolamine. The corresponding esters
of mercaptoacetic acid and 3-mercaptopropionic acid are particularly preferred.
Suitable types of elastomer film former base polymers reacted with the mercapto
compound include polymers of containing isobutylene, chloroprene, polybutadiene,
isobutylene/isoprene, butadiene/acrylonitrile, butadiene-acrylate copolymers, S-B
copolymers, butadiene-vinyjidene chloride-acrylate type copolymers provided the
degree of unsaturation is 10% or less. Methods for incorporation of mercapto
compounds are described in U. S. Patent 6,252,008 incorporated herein by
reference and suitable for use as the functional film former polymer herein. The
rubber contains in the region of 0.1 to 5 wt.% of bonded hydroxyl groups. The
molecular weight of the solution polymerized diene rubber containing hydroxyl
groups incorporated according to the method of U.S. 6,252,008 should lie in a range
that dilute solutions of 5 to15% solids can be obtained and be sprayable, brushable
or dippable, such as from 10,000 to 200,000 Mn (gel permeation chromatogragphy).
[0054] There are other known approaches for incorporating OH groups into the
suitable film forming polymers used herein, such as by addition reactions with
formaldehyde, reaction with carbon monoxide followed by hydrogenation, and
hydroboration followed by hydrolysis. Copolymerization using silanes containing an
ethylenic unsaturated group is a suitable method. Representative silane
comonomers include vinylsilane or allylsilane having a reactive silicon group.
Examples which may be mentioned include vinyltrichlorosilane,
vinylmethyidichlorosilane, vinyldimethylchlorosilane, vinyidimethylmethoxysilane,
divinyldichlorosilane, divinyldimethoxysilane, allyitrichlorosilane,
allylmethyldichlorosilane, ailyldimethylchlorosilane, allyldimethylmethoxysiiane,
diallyldichlorosilane, diallyldimethoxysilane, ?-methacryloyloxypropyltrimethoxysilane,
and ?-methacryioyloxypropylmethyldimethoxysilane.
[0055] The functionalized diene elastomer will be described as follows with respect
to a nitrile copolymer as the most preferred film former embodiment of the present
invention. A functionalized butadiene acryionitrile copolymer offers beneficial film
characteristics such as low temperature flexibility, oil, fuel and solvent resistance as
well as good abrasion and water-resistant qualities.
[0056] The present invention is most preferredly carried out with a functionalized
hydrogenated nitriie rubber (HNBR). The functionalization of HNBR with reactive
functionality provides methods for crosslinking the coating composition and obtaining
the essential level of adhesion to the elastomer substrates. Without adequate
adhesion to the elastomer substrate, coatings exhibit premature flex-cracking and/or
delamination . The functional groups for HNBR can be generally classified as
containing active hydrogen groups, ethylenic unsaturated groups or hydrolyzable
groups.
[0057] Curing of the HNBR can be effected through the addition of crosslinking
components mentioned herein, by exposure to moisture, heat (infra-red, thermal), by
UV radiation, or by e-beam radiation. Depending on the reactive functionality
incorporated into the diene copolymer. Some functionalized HNBR embodiments
mentioned herein below are self-curing without added crosslinker, and all can be are
cured with suitable crosslinking components added to the functionalized HNBR such
as but not limited to dinitrosobenzene, ZnO, gamma-POM, phenolic resoles,
multifunctional amine, polyisocyanates, polyacrylates, dicyandiamide ,
dicarboximides, and formaldehyde (or UF, MF) resins.
[0058] A functionalized HNBR can be prepared by a variety of ways known in the
art. Functional groups can be incorporated by the use of functional-group-containing
comonomers, or by the use of graft-linkable, functional-group-bearing compounds,
and by functionalization of NBR using metathesis, followed by hydrogenation of the
modified NBR to give functionalized HBNR or reaction of NBR with methyloiated
phenols followed by hydrogenation of the modified NBR to give functionalized
HBNR.
[0059] Functionalized HNBR containing active-hydrogen bearing functional groups
are preferred crosslinkable film formers in the curable emissive coating composition.
The presence of unsaturated groups (i.e., vinyl and disubstituted olefins, nitriles) in
the NBR provides reactive sites in which reactive functionality may be attached and
used for further crosslinking, post-polymer functionalization, and grafting reactions.
These reactive sites can be modified through either catalytic or non-catalytic
chemistries. Such modification can introduce any number of active-hydrogen
functional groups such as epoxides by epoxidation of olefinic sites. Epoxides are
readily converted to other functional groups through ring-opening reactions. For
example, glycols are produced by ring-opening with base, glycol ethers with
alkoxides or phenoxides, alcohols with carbanions or hydrides. In addition, epoxides
serve as crosslinkable sites using chemistry available to one skilled in the art. Many
other functional groups may be introduced by reaction of the backbone olefins:
hydroformylation (aldhehydes, alcohols, carboxyiic acids), hydrocarboxylation
(carboxylic acids), hydroesterification (esters), hydrosilylation (silanes),
hydroamination (amines), halogenation (haiogens), chlorosulfonylation (chlorine,
sulfonic acids), hydroboration (boranes, alcohols, amines). Examples of such
transformations have been reviewed by Tremont (McGrath, MP.; Sail, ED.;
Tremont, SJ. "Functionalization of Polymers by Metal-Mediated Processes," Chem.
Rev. 1995, 95, 381). The nitrile group of NBR elastomers also can be converted to
an amide by reaction with alcohols in an acid catalyzed process and to carboxyiic
acids through hydrolysis.
[0060] Crosslinking can be effected through the addition of a crosslinking
component, moisture, thermal, UV radiation, or e-beam radiation. Depending on the
reactive functionality attached to HNBR and its intended use, suitable crosslinking
components can be added to the functionalized HNBR such as dinitrosobenzene,
ZnO, gamrna-POM, resoles, multifunctional amine, isocyanates, acrylates, and
dicyandiamide. Particularly preferred crosslinking components are those
components known in the art for obtaining good bonds to elastomeric articles.
These components include DNB, ZnO, and QDO and can be added to enhance the
adhesion of the functionalized HNBR to a wide variety of elastomeric materials.
[0061] The reactive functionality incorporated onto the diene elastomer, includes, as
non-limiting examples, phenolic OH, aliphatic OH, amine, isocyanate, epoxy,
acrylate, siiyl ethers, siiyl chlorides, anhydrides, maieimides, and Diels-Alder
dieneophiles among the aforementioned functional groups.
[0062] The appropriate curing components and aids for the curing reactions are
well-known in the prior literature and patents in the adhesive and coating area for
curing the R.F. of this invention. For example, when the functional group on the
polymer is phenol, then isocyanate, dicarboximide, formaldehyde source, and
resoles are suitable curing agents that are useful for crosslinking the phenol-
functionalized HNBR. Likewise, amine functionalized HNBR can be crosslinked
using isocyanate or dicarboximide, formaldehyde source, and resoles, as examples.
Epoxy functionalized HNBR can be crosslinked and cured with appropriate amines
and dicyandiamide components, as is known in the art of Epoxy adhesive and
coatings. Isocyanate functionalized HNBR is of particular interest because it can be
crosslinked or cured by moisture or by the addition of other curative agents such as
amine or polyols. Incorporation of the isocyanate as part of the HNBR is particularly
desirable because it reduces that amount of free monomeric and therefore volatile
isocyanate and its reported health and safety issues. A latent isocyanate
functionalized HNBR can be prepared by reaction of an amine functionalized HNBR
(or NBR) with a diary! carbonate to give a urethane functionalized HNBR (or NBR).
Thermal cracking of the urethane forms the isocyanate functionalized HNBR (or
NBR) (For example, see: Kothandaraman, K.; Nasar, A.S. "The Thermal
Dissociation of Phenol - Blocked Toluene Diisocyanate Crosslinkers", J.M.S. - Pure
Applied Chem. 1995, A32, 1009; Wicks, D.A.; Wicks, Z.W. "Blocked Isocyanates 111:
Part A. Mechanisms and Chemistry", Progress in Organic Coatings 1999, 36, 148;
Mohanty, S.; Krishnamurti, N. "Synthesis and Thermal Deblocking of Blocked
Diisocyanate Adducts," Eur. Poiym. J. 1998, 34, 77). Maleimide functionalized
HNBR can be crosslinked either by the addition of a free radical initiator or by
Michael addition reactions. Maleimides are known crosslinking agents. Acrylate
functionalized HNBR are capable of both free radical, UV and e-beam curing.
Anhydride functionality can be cured using amines and components described in the
art for anhydride-epoxy adhesives. Silyl ether and chiorosilanes can be utilized in
moisture-cured embodiments at room temperature. Diels-Alder adducts are self-
curing or by the addition of a metathesis type catalyst.
[0063] Exemplary detail of the aforementioned graft methods for incorporating
functional groups on a film forming elastomer is the melt processing of molten film
forming elastomer with a polyfunctional graftlinkable material such as polyfunctional
acrylate, maleated polybutadiene, and metal salts of difunctional acrylates. For
example, an olefin elastomer such as EPDM can be masticated on a two roll mill,
with 5 parts of an acid scavenger such as zinc oxide, 1 part stearic acid, an
antioxidant and a peroxide followed by addition of 5 to 10 parts of a multi-ethylenic
unsaturated compound such as trimethylolpropane triacrylate, maleated liquid
polybutadiene, or zinc diacrylate to the flux roll.
[0064] Functionalized HNBR can be prepared by metathesis, followed by
hydrogenation of the modified NBR to give functionalized HNBR and (2) the reaction
of NBR with methyiolated phenols followed by hydrogenation of the modified NBR to
give functionalized HBNR.
[0065] A novel method for incorporating a reactive pendant functional group, such
as a carboxy, anhydride, hydroxy functionality is provided on a NBR elastomer as
follows:
Direct functionalization of any suitable unsaturated film former polymer usable
herein, and especially NBR, and is accomplished through the use of olefin
metathesis chemistry. Here, the olefin C=C double bonds are reacted with a catalyst
and a monomer. The olefin metathesis catalyst must be capable of catalyzing
metathesis reactions in the presence of nitrile functional groups. The monomer can
be any cycloolefin, olefin, or a,?-diene that is capable of undergoing an olefin
metathesis reaction (e.g., ring-opening metathesis polymerization [ROMP], cross-
metathesis, ring-opening-cross-metathesis, and acyclic diene metathesis
polymerization [ADMET]). These monomers are derivatized with groups bearing
functionality (e.g., carboxylic acids, amides, esters, anhydrides, epoxy, isocyanate,
silyl, halogens, Diels-Alder diene and dienophiles, etc.) to provide cure sites for
secondary crosslinking reactions of the cured film or to give new properties to the
polymer. Kinetically, the metathesis catalyst will likely attack the vinyl C=C bonds
first, however, their low levels in the HNBR copolymer may make attack at the
backbone C=C double bond competitive. Such attack on the backbone unsaturation
will likely cause a drop in molecular weight of the NBR, but the extent of such a
process can be minimized by using high NBR-to-catalyst levels. After reduction of
the modified NBR using for example the aforementioned catalytic hydrogenation
methods, a reactive modified HNBR polymer is obtained. The polymer can be
crosslinked using moisture, a, selected curing agent, or an external energy source
(UV or e-beam). One particular preferred advantage of metathesis catalysis is that it
provides a unique means of introducing reactive functionality into NBR under mild
conditions in water or in solvent. So even NBR latex can be modified with reactive
functionality without de-stabilizing the latex through metathesis catalyst. This feature
allows the functionalization of a variety of commercially well-known NBR polymers, in
solution or as aqueous dispersions, and latexes (water-based polymerizate),
followed by hydrogenation to yield functionalized HNBR.
Hydrogenated Protic Group terminated Diene polymers.
[0066] Hydrogenated hydroxy or carboxy terminated diene polymers, alone, or in
blends with different high molecular weight (10,000 Mn and above) film forming
polymers are also suitable as a curable film former used in the emissive coating of
the present invention. Substantially saturated polyhydroxylated polydiene polymers
are known and commercially available. These represent anionic polymerized
conjugated diene hydrocarbons, such as butadiene or isoprene, with lithium
initiators, and terminated with OH groups. The process steps are known as
described in U.S. Pat. Nos. 4,039,593; Re. 27,145; and 5,376,745, all of which are
hereby incorporated by reference for their disclosure of preparing polyhydroxylated
polydiene polymers. Such polymers have been made with di-iithium initiator, such as
the compound formed by reaction of two moles of see-butyllithium with one mole of
diisopropylbenzene. Such a polymerization of butadiene has been performed in a
solvent composed of 90% by weight cyciohexane and 10% by weight diethyl ether.
The molar ratio of di-initiator to monomer determines the molecular weight of the
polymer. The polymer is capped with two moles of ethylene oxide and terminated
with two moles of methanol to produce the dihydroxy polybutadiene. The
hydroxyiated polydiene polymer is hydrogenated where substantially all of the
carbon-to-carbon double bonds become saturated. Hydrogenation has been
performed by those skilled in the art by established processes including
hydrogenation in the presence of such catalysts as Raney Nickel, noble metals such
as platinum and the like, soluble transition metal catalysts and titanium catalysts as
in U.S. Pat. No. 5,039,755. Suitable polyhydroxylated polydienes are those available
from Shell Chemical Company in the U.S.A. under the trade designation of KRATON
LIQUID® POLYMERS, HPVM 2200 series products, and from ATOCHEMIE under
the PolyBD® mark. The high molecular weight polymers suitable in blends with the
hydrogenated hydroxyl butadiene polymers are not limited, and include for example
the aforementioned carboxy modified chlorinated polyethylene, chlorinated
polyethylene, polymers of epichlorohydrin, ethylene-acryiic copolymers, SBR, SBS,
nitrite rubber (NBR), SIBS, EPDM, EPM, polyacrylates, halogenated
polyisobutylene, and polypropylene oxide, among others mentioned herein, and
known. The weight proportion of liquid hydrogenated polybutadiene polyol to high
molecular weight film former is limited such that the percent of unsaturation in the
combination is less than 10% overall. Therefore where mixtures of the hydrogenated
polydiene polyol are made with unsaturated high polymers such as SBR, NBR, and
the like, the proportion of unsaturated polymer will be limited to maintain the overall
degree of saturation of at least 90%. Modified chlorinated polyolefins can include
those modified with an acid or anhydride group. Some examples of modified
chlorinated polyolefins are described in U.S. Pat. Nos. 4,997,882 (column 1, line 26
to column 4, line 63); 5,319,032 (column 1, line 53 to column 2, line 68); and
5,397,602 (column 1, line 53 to column 2, line 68), hereby incorporated by reference.
The chlorinated polyolefins preferably have a chlorine content of from about 10 to 40
weight percent, more preferably from about 10 to 30 weight percent based on the
weight of starting polyolefin. One suitable example of a modified chlorinated
polyolefin is the modified chlorinated polyolefin that has a chlorine content of from
about 10 to about 30 weight percent based on the weight of polyolefin, which is not
neutralized with an amine, and has an acid value in the range of about 50 to about
100.
Hydrogenated Block Copolymers
[0067] Suitable film formers adaptable according the invention are hydrogenated
styrene-butadiene-styrene block copolymers, hydrogenated styrene-isoprene-
styrene block copolymers, which are modified according to methods disclosed herein
above, adapted for chlorinated polyethylene, and elsewhere provide cure
functionality on the block copolymer for interaction with the curing agent. Some
elastomeric block copolymers containing carboxyl groups are available
commercially. Those,block copolymers which contain unsaturation can be
hydrogenated according to known hydrogenated methods, including methods
referenced herein.
Phenol Functional Elastomer
[0068] Functionalization of HNBR with phenol functionality can be carried out by the
combination of a methyiolated phenol and the NBR, followed by hydrogenation of the
phenol-modified NBR intermediate. Methyiolated phenols can form covalent bonds
with NBR and NBR copolymers by a variety of chemical reactions as reported in the
literature [A. Knop and L. Pilato, "Phenolic Resins Chemistry and Applications and
Performance" Springer-Verlag, New York 1985, Chapter 19 pg 288-297].
[0069] Various known isocyanate-reactive functional groups can be incorporated in
a functionalized elastomer film-forming polymer. The aforementioned carboxy-
functional, hydroxy-functional and amine functional elastomers are most readily
adaptable. Functional comonomers, like carboxy-funotional comonomers are readily
adaptable to form a copolymer of carboxylated hydrogenated nitrile rubber. For the
purposes of the present invention, the functionalized hydrogenated nitrile rubber can
be defined as a polymer comprising at least one diene monomer, nitrile monomer,
and a functional group-bearing compound such as a comonomer or a graftlinking
compound containing a functional group or a combination thereof. When the
abbreviation HNBR is utilized herein, it is to be understood that the term refers to
rubbers which can include diene monomer other than 1,3 butadiene, and
comonomers other than acryionitrile, unless specifically stated. It is also important to
note that additional monomers can be polymerized along with or grafted to the diene
monomer to form the functionalized HNBR. The additional monomers can, for
example, provide at least one functional group to facilitate crosslinking.
[0070] Functionalization of HNBR with phenolic functionality can be carried out with
the unsaturated un-hydrogenated polymer, or a partially hydrogenated XHNBR
polymer (80-97% hydrogenation level) by addition of methylol phenol or ether
derivative under heat and optionally catalyzed by suitable Lewis acid . Preferably an
ether blocking group is provided on the methylol phenol compound, facilitating ease
ofpost reaction hydrogenation. Addition can be through the nitrile or carboxyl
groups by ester formation, or by way of the aforementioned addition at allylic sites.
Preferably a metathesis reaction of an ethyienic unsaturated compound bearing a
phenol group can be done in solvent or water. Alternatively, an olefinic bearing
methylolated phenyl ether or phenol can be metathesized with NBR, followed by
hydrogenation. The phenol functionalized NBR is subsequently hydrogenated, A
methylolation reaction can be undertaken using a phenol functional NBR or HNBR
with formaldehyde to generate a methylolated phenol functionality in the NBR, or
with HNBR. Methylolated phenols can form covalent bonds with NBR and NBR
copolymers by a variety of chemical reactions as reported in the literature. See, A.
Knop and L Pilato, "Phenolic Resins Chemistry and Applications and Performance"
Springer-Verlag, New York 1985, Chapter 19, pg. 288-297. The following structural
diagrams illustrate functionalizing with a representative phenolic bearing compound.
[0071] While it is possible to combine any methylolated phenol with NBR, mono-
methylolated phenols are especially preferred. The combination of Mono-
methylolated phenols with NBR polymers yields phenol functionalized-NBR products
which are stable. After hydrogenation of the phenol-modified NBR according to
known procedures in the art (e.g. cat. hydrogenation), a stable phenol-modified
HNBR copolymer is obtained. The phenol-functionalized HNBR copolymer can be
crosslinked with a variety of well-known crosslinkers for phenolic resins including
those selected from dicarboximides, isocyanate, and formaldehyde source
(paraformaldehyde, gamma-POM, hexamethylene amine, phenolic resoles or
etherified phenols).
[0072] Methylolated phenol functionalized nitrile rubber (NBR) or hydrogenated
versions (HBNR) can be prepared by procedures known in the art. The phenol
functionalized NBR/HNBR can be prepared by either the mono-methylolated phenol
or by metathesis involving unsaturated monomer with the unsaturated NBR. The
methylolated phenol functionalized NBR/HBNR prepared by metathesis utilizes a
methylolated phenolic monomer with NBR. These materials are useful not only as
coatings in accordance with the present invention, but also as components of
elastomer-to-metal adhesives, autodepositing materials, RFL dips, and reactive
tougheners (e.g. epoxy adhesives) taking advantage of their unique curing, film-
forming, metal adhesion and compatibility properties. Methylolated phenol
functionalized NBR/HNBR are capable of self-curing (i.e. without an external curing
agent). Methylolated phenol functionalized NBR/HNBRderivatives are capable of
curing with other coating components, such as phenolic novolaks, active hydrogen
reactive or active hydrogen containing crosslinkers and rubber/elastomer toughening
agents. Methylolated phenol functional HNBR can be used with known vulcanizing
agents for rubber. The vulcanization reaction is based on the formation of either a
quinone methide or a benzyiic carbenium that is generated by the thermal or
catalytic activation of the methylolated phenols. The quinone methide intermediate
reacts by abstraction of allylic hydrogen. Alternatively, methyiolated phenols can
generate reactive benzyl carbenium ions under acidic catalyzed conditions which will
react with unsaturated polymers in the substrate.
[0073] When the reactive functional group on the HNBR is phenol, then isocyanate,
dicarboximide, formaldehyde source, and resole curing agents are useful for
crosslinking the phenol-functionalized HNBR to the elastomer substrate. Likewise,
amine-functionalized HNBR can be crosslinked using isocyanate or dicarboximide, a
formaldehyde source, and/or resoles, as examples. Epoxy-functionalized HNBR can
be crosslinked and cured with known curing agents, e.g., amines, amidoamines,
and/or dicyandiamide, well known in the art of Epoxy adhesives.
[0074] Isocyanate functionalized HNBR can be crosslinked or cured.by moisture or
by the addition of other curative agents such as amine or polyols. Incorporation of
the isocyanate as part of the HNBR is particularly desirable because it reduces that
amount of free monomeric and therefore volatile isocyanate and its reported health
and safety issues. Maleimide functionalized HNBR can be crosslinked either by the
addition of a free radical initiator or by Michael addition reactions. Ethylenic
unsaturated acryiate-functionalized HNBR is capable of both free radical, UV and e-
beam curing. Anhydride functional HNBR can be cured using amines and
components described in the art for anhydride-epoxy adhesives. Silyl ether and
chlorides are moisture curing. Diels-Alder adducts are self-curing or by the addition
of known metathesis catalysts.
[0075] To provide the ethylenically unsaturated nitrile-conjugated diene rubber with
at least 90% saturation, the nitrile rubber is hydrogenated by conventional means.
Generally any of the numerous known processes for hydrogenation can be utilized,
including but not limited to, solution hydrogenation and oxidation/reduction
hydrogenation. The hydrogenation serves to saturate at least 90% of the
unsaturated bonds of the rubber. When the degree of saturation is less than 90%,
the rubber's heat resistance is low, The more preferred degree of saturation of the
rubber is 95-99.99%.
[0076] The preferred conjugated diene monomers useful for preparing the
carboxylated acrylonitrile-butadiene copolymers which are further hydrogenated can
be any of the well-known conjugated dienes including dienes having from about 4 to
about 10 carbon atoms, such as, but not limited to, 1,3-butadiene; 2-methyl-1,3-
butadiene, 2,3-dimethyl-1,3-butadiene; 1,3-pentadiene; 1,3-hexadiene; 2,4-
hexadiene; 1,3-heptadiene; piperylene; and isoprene, with 1,3-butadiene presently
being preferred.
[0077] The unsaturated nitrite monomers copolymerized to form a carboxyiated
acrylonitrile-diene copolymer typically correspond to the following formula:

wherein each A is hydrogen or a hydrocarbyl group having from 1 to about 10 carbon
atoms. Examples of A groups include alkyl and cycloalkyl, such as methyl, ethyl,
isopropyl, t-butyl, octyl, decyl, cyclopentyl, cyclohexyl, etc., and aryls such as phenyl,
tolyl, xylyl, ethylphenyl, t-butylphenyl, etc. Acrylonitrile and methacrylonitrile are the
presently preferred unsaturated nitriies.
[0078] The HNBR of the present invention also includes functional group containing
monomers which are polymerized into the backbone of the HNBR, or functional
group containing compounds which have been grafted to the HNBR, or a
combination thereof.
[0079] Carboxyl group containing monomers are optionally utilized in the film-forming
elastomer used in the present invention. Carboxyl groups can be provided by a,ß-
unsaturated monocarboxylic acid monomers with 3 to about 5 C-atoms such as
acrylic acid, methacrylic acid and crotonic acid and/or other known carboxyl group-
containing monomers such as, but not limited to a,ß-unsaturated dicarboxylic acids
with 4 to about 5 or about 6 C-atoms, e.g., maleic acid, fumaric acid, citraconic acid
and itaconic acid, and anhydrides of these. The bound unsaturated carboxylic acid
may be present in an amount of from about 1 to about 10 weight percent of the
copolymer, with this amount displacing a corresponding amount of the conjugated
diolefin. Preferably, the monomer is an unsaturated mono- or di-carboxylic acid
derivative (e.g., esters, amides and the like). Functions of the carboxyl group-
containing monomers include serving as a crosslinking site and enhancing adhesion.
[0080] Additional, other functional comonomers can be copolymerized into the
backbone of the HNBR copolymer. Examples of the functional ethylenically
unsaturated monomers which are copoiymerizable with the nitriie monomers and the
conjugated diene monomers are: hydrazidyl-group containing ethylenic unsaturated
monomers, amino-group-bearing ethylenic unsaturated monomers, thiol-group
bearing unsaturated ethylenic unsaturated monomers, unsaturated carboxyiic acids
such as acrylic acid, methacryiic acid, itaconic acid and maleic acid and salts
thereof, alkyl esters of unsaturated carboxyiic acids such as various acrylates, for
example methyl acrylate and butyl acrylate; alkoxyalkyl esters of unsaturated
carboxyiic acids such as methoxy acrylate, ethoxyethyi acrylate, methoxyethyl
acrylate, acrylamide, and methacrylamide.
[0081] Also suitable as functional comonomers are various classes of monomers
such as N,N-disubstituted-aminoalkyl acrylates; N,N-disubstituted-aminoalkyl
methacrylates; N,N-disubstituted-aminoalkyi acrylamides; N,N-disubstituted-
aminoaikyl methacrylamides; hydroxyl-substituted-alkyl acrylates and hydroxyl-
substituted-alkyl methacrylates, N-alkylol substituted acrylamides such as N-
methylolacrylamide, N,N'-dimethylolacrylamide and N-ethoxymethylolacrylamide; N-
substituted methacrylamides such as N-methylolmethacrylamide, N,N'-
dimethylolmethacrylamide and N-ethoxymethylmethacrylamide especially where free
radical initiated copolymerization occurs in the presence of an alkylthiol compound
having 12 to 16 carbon atoms three tertiary carbon atoms.
[0082] As specific examples of the hydroxy-substituted-alkyl acrylate and hydroxy-
substituted-aikyl methacrylate comonomers, there can be mentioned hydroxymethyi
acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate,
3~ehloro-2-hydroxypropyi acrylate, 3-phnoxy-2-hydroxypropyl acrylate,
hydroxymethyi methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl
methacrylate, 3-hydroxypropyi methacrylate, 3-chloro-2-hydroxypropyl methacrylate
and 3-phnoxy-2-hydroxypropyl methacrylate. Of these, hydroxymethyi acrylate, 2-
hydroxyethyl acrylate, hydroxymethyi methacrylate and 2-hydroxyethyl methacrylate
are preferable.
[0083] The NBR copolymers are polymerized by reaction of the any of the
aforementioned exemplary conjugated dienes, unsaturated nitriie, and unsaturated
functional-group containing comonomers in the presence of a free radical initiator by
methods well known to those skilled in the art. Suitable free radical initiators are
beyond the scope of this disclosure, and are typically organic oxides, peroxides,
hydroperoxides, and azo compounds, etc., such as hydrogen peroxide, benzoyl
peroxide, cumene hydroperoxide, di-tert-butyl peroxide, ascaridole, acetyl peroxide,
tert-butyl hydroperoxide, trimethylamine oxide, dimethylaniline oxide,
isopropylperoxydicarbonate, diisobutylene ozonide, peracetic acid, nitrates,
chlorates, perchforates, azobisisobutyronitrile, etc.
[0084] Hydrogenation of nitrile rubber is known to the art and to the literature. For
example, a preferred commercially available X-HNBR (carboxylated-HNBR) is made
from a carboxylated nitrile-diene copolymer that is hydrogenated in two steps. It is
known that the C-C double bonds of the 1,2-vinyl-configured butadiene units in NBR
are hydrogenated very rapidly, followed by the 1,4-cis configured units. The 1,4-trans
configured butadiene units are hydrogenated comparatively slowly. The NBR
products used for hydrogenation are distinguished by a predominant proportion of
the 1,4-trans configured double bonds.
[0085] In the known 2-stage hydrogenation method, carbon-carbon double bonds
are first reduced, followed by reduction of the carbon-to-nitrogen bond. Other
techniques for hydrogenating acrylonitrile-butadiene copolymers are disclosed in, for
example, U.S. Pat. Nos. 4,581,417; 4,631,315; and 4,795,788; the disclosures of
which are incorporated herein by reference.
[0086] A partly or completely hydrogenated nitrile rubber (HNBR) is also described
in several specifications (for example DE-OS No. (German Published Specification)
2,539,132; DE-OS No. (German Published Specification) 3,329,974; DE-OS No.
(German Published Specification) 3,046,008 and 3,046,251; and European Patent
No. A-111,412).
[0087] Hydrogenation of X-HNBR latex can be carried out by known conventional
techniques. A carboxylated NBR polymer latex made conventionally using anionic
surfactants is combined with (1) an oxidant selected from the group consisting of
oxygen, air and hydroperoxides; (2) a reducing agent selected from hydrazine and
hydrates thereof; and (3) a metal ion activator; (b) and heating the mixture to a
temperature from 0 °C. to the reflux temperature of the reaction mixture. This
technique is taught in U.S. Patent No. 4,452,950, assigned to Goodyear Tire and
Rubber Co., herein incorporated by reference.
[0088] The most preferred acrylonitrile-butadiene copolymers are hydrogenated to
an extent such that the final product has an unsaturation level of from about 1 to
about 10 mole percent, and preferably from about 1 to about 5 mole percent.
[0089] A suitable carboxylated hydrogenated nitrile rubber (X-HNBR) is
manufactured by Bayer under a trade name of "Therban®", for example Therban KA
8889. X-HNBR may have an iodine value of preferably about 50% or less, more
preferably about 3 to 40%, most preferably from about 8 to 30%.
[0090] The crosslinker-reactive functional groups of the film former provided by the
aforementioned methods can be done either before or after hydrogenation. As
examples of the unsaturated compound having a functional group, may be
mentioned vinyl compounds having a functional group, and cycloolefins having a
functional group. The introduction of the functional group by the graft-modifylng
method can be carried out by reacting the HNBR with a functional group-containing
unsaturated compound in the presence of an organic peroxide. No particular
limitation is imposed on the functional group-containing unsaturated compound.
However, epoxy group-containing unsaturated compounds, carboxyl group-
containing unsaturated compounds, hydroxyl group-containing unsaturated
compounds, siiyl group-containing unsaturated compounds, unsaturated
organosiiicon compounds, etc. are mentioned for reasons of improvements of
crosslinking density and adhesion to substrates at a low modification rate.
[0091] Examples of the epoxy group-containing unsaturated compounds or epoxy
group-containing cycloolefins include glycidyl esters of unsaturated carboxylic acids
such as glycidyl acrylate, glycidyl methacrylate and glycidyl p-styryl-carboxylate;
mono- or polyglycidyl esters of unsaturated polycarboxylic acids such as endo-cis-
bicyclo[2,2.1]hept-5-ene-2,3-dicarboxylic acid and endo-cis-bicyclo[2,2,1]hept-5-ene-
2-methyl-2,3-dicarboxylic acid; unsaturated glycidyl ethers such as al!yl glycidyl
ether, 2-methyl-aiiyl giycidyl ether, glycidyl ether of o-aiiylphenoi, glycidyl ether of m-
ailylphenol and giycidyl ether of p-allylphenol; and 2-(o-vinylphenyl)ethylene oxide, 2-
(p-vinylphenyl)ethylene oxide, 2-{o-allylphenyl)-ethylene oxide, 2-{p-
allylphenyl)ethylene oxide, 2-(o-vinylphenyl)propylene oxide, 2-(p-
vinylphenyl)propylene oxide, 2-(o-allylphenyl)propylene oxide, 2-{p-aiiylphenyl)
propylene oxide, p-giycidylstyrene, 3,4-epoxy-1-butene, 3,4-epoxy-3-methyl-1-
butene, 3,4-epoxy-1-pentene, 3,4-epoxy-3-methyl-1-pentene, 5,6-epoxy-1-hexene,
vinylcyciohexene monoxide and aliyl-2,3-epoxycycIopentyl, ether. These epoxy
group-containing unsaturated compounds may be used either singly or in any
combination thereof.
[0092] As examples of the carboxyl group-containing unsaturated compounds, there
may be mentioned compounds described in Japanese Patent Application Laid-Open
No. 271356/1993, for example, unsaturated carboxylic acids such as acrylic acid,
methacrylic acid and a-ethylacrylic acid; and unsaturated dicarboxylic acid such as
maleic acid, fumaric acid, itaconic acid, endo-cis-bicyclo-[2.2.1]hept-5-ene-2,3-
dicarboxylic acid and methyl-endo-cis-bicyclo[2.2,1]hept-5-ene-2,3-dicarboxyfic acid.
As further examples of unsaturated carboxylic acid derivatives, may be mentioned
anhydrides, esters, halides, amides and imides of unsaturated carboxylic acids.
Specific examples thereof include acid anhydrides such as maleic anhydride,
chloromaleic anhydride, butenylsuccinic anhydride, tetrahydrophthalic anhydride and
citraconic anhydride; esters such as monomethyl maleate, dimethyl maleate and
giycidyl maleate; and malenyl chloride and malermide. Of the aforementioned, the
unsaturated dicarboxylic acids and anhydrides thereof are preferred for reasons of
easy introduction of the functional group by a graft reaction, and the like, with acid
anhydrides such as maleic anhydride and itaconic anhydride being particularly
preferred.
[0093] Examples of the hydroxyl group-containing unsaturated compounds for
incorporation into the film forming polymer include allyl alcohol, 2-allyl-6-
methoxyphenol, 4-allyloxy-2-hydroxybenzophenone, 3-allyloxy-1,2-propanediol, 2-
allyldiphenol, 3-buten-1-ol, 4-penten-1-ol and 5-hexen-1-oi.
[0094] Examples of the siiyl group-containing unsaturated compounds for
incorporation into the film former include chlorodimethylvinylsilane,
trimethylsilylacetylene, 5-trimethylsi!yl-1,3-cyclopentadiene, 3-trimethylsilylallyl
alcohol, trimethylsilyl methacrylate, 1-trimethylsilyloxy-1,3-butadiene, 1-
trimethylsiiyloxycyclopentene, 2-trimethylsiiyloxyethyl methacrylate, 2-
trimethylsilyloxyfuran, 2-trimethylsilyloxypropene, allyloxy-t-butyldimethylsilane and
allyloxytrimethylsiiane.
[0095] Examples of the unsaturated organosilicon compounds for incorporation
include trisalkoxyvinylsilanes such as trimethoxyvinylsilane, triethoxyvinylsilane,
tris(methoxyethoxy)vinylsilane. The alkoxy groups in such an unsaturated
organosilicon compounds can be hydroiyzed into silanol groups.
[0096] Examples of unsaturated sulfonic acid or phosphorus ester groups include 2-
(meth)acrylamido-2-methyl-1-propanesulfonic acid, 3-sulfopropyl (meth)acrylate, 2-
sulfoethyl (meth)acrylate, and 2-phosphoethyl (meth)acrylate. These comonomers
incorporated into a variety of vinyl-acrylate, acrylate or other flexible polymers having
a Tg of below 0°C as the film former polymer will cure in the presence of epoxy
resins, isocyanates, carbodiimides, amino resins, aminosilanes, and other
crosslinking agents reactive with acidic groups. Flexible, low Tg copolymers which
bear at least abut 2 mol % of sulfur and/or phosphorus-containing acid groups and
exhibiting an acid number of from 5 to 100, preferably from 10 to 85, and most
preferably from 10 to 30 are useful film-formers in accordance with the invention.
[0097] A graft-modified HNBR according to the present invention can be obtained by
graft-reacting one of the aforementioned ethylenic unsaturated compounds having a
functional group with the HNBR under generation of a radical. As methods for
generating the radical, may be mentioned (i) a method making use of an organic
peroxide, (ii) a method making use of a photo-induced radical generator, (iii) a
method by irradiation of energy rays, and (iv) a method by heating.
[0098] (i) Method making use of an organic peroxide: As the organic peroxide, for
example, organic peroxides, organic peresters, etc. may be preferably used. As
specific examples of such an organic peroxide, may be mentioned benzoyl peroxide,
dichlorobenzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-
di(peroxide benzoate)hexyne-3, 1,4-bis(tert-butyl peroxylsopropyl)benzene, lauroyl
peroxide, tert-butyl peracetate, 2,5-dimethyl-2,5-di(tert-butyl peroxy)hexyne-3, 2,5-
dimethyl-2,5-di(tert-butyl peroxy)hexane, tert-butyl perbenzoate, tert-butyl
perphenylacetate, tert-butyl perisobutyrate, tert-butyl per-sec-octoate, tert-butyl
perpivalate, cumyl perpivalate and tert-butyl perdiethylacetate. In the present
invention, azo compounds may also be used as the organic peroxides. As specific
examples of the azo compounds, may be mentioned azobisisobutyronitrile and
dimethyl azoisobutyrate. Of these, benzoyl peroxide, and dialkyl peroxides such as
dicumyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di(tert-butyl
peroxide)hexyne-3, 2,5-dimethyl-2,5-di(tert-butyl peroxy)hexane and 1,4-bis(tert-
butyl peroxylsopropyl)benzene are preferably used.
[0099] These organic peroxides may be used either singly or in any combination
thereof. A proportion of the organic peroxide used is generally within a range of
0.001 to about 10 parts by weight, preferably about 0.01 to about 5 parts by weight,
more preferably about 0.1 to about 2.5 parts by weight per 100 parts by weight of the
unmodified HNBR. When the proportion of the organic peroxide used falls within this
range, the rate of reaction of the functional group-containing unsaturated compound,
and various properties of the resulting functional group-containing polymer, are
balanced with one another at a high level. It is hence preferable to use the organic
peroxide within such a range.
[0100] No particular limitation is imposed on the graft-modifylng reaction, and the
reaction may be carried out in accordance with any of the methods known per se in
the art. The graft reaction can be conducted at a temperature of generally 0 to
400°C, preferably 60 to 350°C. The reaction time is generally within a range of 1
minute to 24 hours, preferably 30 minutes to 10 hours. After completion of the
reaction, a solvent such as methanol is added in a great amount to the reaction
system to deposit a polymer formed, and the polymer can be collected by filtration,
washed and then dried under reduced pressure.
[0101] (ii) Method making use of a photo-induced radical generator: The method
making use of the photo-induced radical generator is a method in which after the
photo-induced radical generator is added, the resultant mixture is exposed to
ultraviolet light to generate a radical, and any conventionally known method may be
used. The photo-induced radical generator may be any substance so far as it is
activated by irradiation of ultraviolet light. Specific examples thereof include carbonyl
compounds such as benzoin, benzoin methyl ether, benzoin isopropyl ether, benzoin
isobutyl ether, acetoin, butyroin, toluoin, benzyl, benzophenone, 2,2-dimethoxy-2-
phenylacetophenone, alpha-hydroxycyclohexyl phenyl ketone, p-isopropyl-.aipha.-
hydroxylsibutylphenone, alpha, alpha-dichloro-4-phenoxyacetophenone,
methylphenyl giyoxylate, ethylphenyl glyoxylate, 4,4-bis(dimethylaminophenone) and
1-phenyl-1,2-propandione-2-(o-ethoxycarbonyl).oxime; sulfur compounds such as
tetramethylthiuram monosulfide and tetramethylthiuram disulfide; azo compounds
such as azobisisobutyronitrile and azobis-2,4-dimethylvaleronitrile; peroxide
compounds such as benzoyl peroxide and di(t-butyl) peroxide; acylphosphine oxides
such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide. A proportion of the photo-
induced radical generator used is generally within a range of 0.001 to about 10 parts
by weight, preferably about 0.01 to about 5 parts by weight, more preferably about
0.1 to about 2.5 parts by weight.
[0102] Method by irradiation: The method by irradiation of energy rays is a publicly
known method in which active energy rays such as alpha-rays, beta-rays and
gamma-rays are irradiated to generate a radical. In particular, it is desired that
ultraviolet light be used from the viewpoints of efficiency, practicability and
profitability.
[0103] Method by heating: The radical generating method by heating is carried out
by heating in a temperature range of 100 to 390°C. Both publicly known solution
method, and melting and kneading method may be used. Of these, the melting and
kneading method using an extruder or the like by which shear stress is applied upon
heating is preferred from the viewpoint of reaction efficiency.
[0104] No particular limitation is imposed on the method for introducing the functional
group on the film former polymer. Examples thereof include (a) a method by
oxidation of unsaturated bonds, (b) the afore mentioned method by an addition
reaction of a compound containing at least one functional group in its molecule to
unsaturated bonds, (c) the methods mentioned herein of introducing an epoxy group,
carboxyl group, hydroxyl group, or aforementioned reaction of an olefinic bond of the
NBR or HNBR polymer with an unsaturated, preferably a monounsaturated,
carboxylic reactant, and the end group addition to living cationic initiated polymer.
Alternatively, the polymer can be halogenated using chlorine or bromine-containing
compounds. The halogenated polymer can then be reacted with the
monounsaturated carboxylic acid. The polymer and the monounsaturated carboxylic
reactant can also be contacted at elevated temperatures to cause the
aforementioned thermal "ene" reaction to take place. Alternatively, the
monounsaturated carboxylic acid can be reacted with the polymer by free radical
induced grafting. The functionaiized elastomer of the present invention can be
functionalized by contact with a hydroxy aromatic compound in the presence of a
catalytically effective amount of at least one acidic alkylation catalyst. The alkylated
hydroxy aromatic compound can then be further reacted to form a derivative by
Mannich Base condensation with an aldehyde and an amine reagent to yleld a
Mannich Base condensate. In yet another means to functionalize the polymer, the
polymer may be contacted with carbon monoxide in the presence of an acid catalyst
under Koch reaction conditions to yleld the polymer substituted with carboxylic acid
groups. In addition to the above methods of functionalization, the polymer of the
present invention can be functionalized by methods of air oxidation, ozonolysis,
hydroformylation, epoxidation and chloroamination, or the like by any other method
(for example, Japanese Patent Application Laid-Open No. 172423/1994).
Fluoroelastomer Film Former
[0105] Fluorocarbon elastomers (fluoroelastomers) as film forming polymers useful
herein are derived from hydrocarbons, including vinylidene fluoride, .
hexafluoropropylene and are commercially available from a number of suppliers. A
detailed discussion of the various types of fluoroelastomers is contained in an article
by R. G. Arnold, A. L Barney and D. C. Thompson that appeared in the July, 1973
issue of a journal entitled "Rubber Chemistry and Technology" (Volume 46, pp. 619-
652). A fluoroelastomer is distinguished from a thermoplastic fluoropolymer
principally by whether plastic deformation occurs upon stressing the fluoroelastomer
to 100% elongation. Fluoroplastics undergo deformation at 100% elongation and are
unsuitable coating materials for elastomeric substrates according to the present
invention.
[0106] The representative fluoroelastomers used herein include polymers derived
from one or more fluorinated monomers including 1,1-dihydroperfluorobutyl acrylate;
copolymers of vinylidene fluoride and chlorotrifluoroethylene; vinylidene fluoride and
hexafluoropropylene; vinylidene fluoride and hydropentafluoropropylene;
tetrafluoroethylene and propylene; and terpolymers of vinylidene fluoride,
hexafluoropropylene, and tetrafluoroethylene; vinylidene fluoride, tetrafluoroethylene
and perfluorovinyl ether; vinylidene fluoride, tetrafluoroethylene, and propylene;
vinylidene fluoride and hydropentafluoropropylene and tetrafluoroethylene. The
most preferred fluoroelastomer modified according to the invention is commercially
available under the Viton ® designation, such as a copolymer of vinylidenefluoride
and hexafluoropropylene, or a terpolymer of vinylidenefluoride, tetrafluoroethylene,
and hexafluoropropylene. Other suitable fluoroelastomers are available from
Dyneon under the FLOREL® mark, and from Ausimont under the TECHNIFLON®
mark.
[0107] A graft-functionalized fluoroelastomer embodiment film former utilized
herein is the reaction product of a fluoroelastomer polymer and a grafting agent
which contains a graft linking group which covalently bonds to the fluoroelastomer,
and at least one active hydrogen-containing group, e.g., hydroxyl, thiol, or
carboxyl group that undergoes bond formation to one of the reactive groups of the
curing agent. The graft-modified fluoroelastomer is combined with the curing
agent in admixture, within the time of the pot life (prior to gelation) of the
admixture, at the time of coating the elastomer substrate.
[0108] The grafting agent for the fluoroelastomer contains one graft-linking group
and one active hydrogen-bearing group; The preferred grafting agent contains a
primary amine group and one active hydrogen-containing group. Examples
include hydroxyamines, aminoisocyanate, such as (R2)2 NCH2 CH2 NCO, wherein
R2 is, for example, hydrogen or a hydrocarbyl group, hydroxyalkylamines,
aminocarboxylates, aminosiiane, amino silanol, aminothiols, and the like. Other
suitable grafting agents that do not contain a primary amine as the graft-linking
group are mercapto hydroxy, like mercaptoalcohols and mercaptosiianols,
mercaptothiols, and the like. The preferred grafting agents will graft to the
fluoroelastomer at relatively mild temperatures (<60°C) and can be monomeric,
oligomeric or polymeric, and contains at least one active hydrogen-containing
group and no more than one primary amine group, but can contain optionally
secondary or tertiary amine groups, or other groups not capable of graft-linking
and crosslinking the fluoroelastomer. An optional secondary amine is believed to
increase the rate of the graft reaction of the primary amine graft-linking groups to
the fluoroelastomer. Specific examples of grafting agents include the various
hydroxyalkyl amines, e.g. 3-amino-1-propanol, aminoalkyl siianols, e.g.,
aminoaikyl silane triol or precursor aminoalkyl-alkoxysiianes which include within
each molecule at least one basic nitrogen capable of catalyzing the hydrolysis of
the alkoxysilane groups to produce the reactive silane triol; amine-N-oxides,
amino(hydroxy) carboxylic acids, amido(hydroxy)amines, polyoxyalkylene
polyether mono(primary)amines, and amine-terminated polyols. Such amine-
terminal polyols can be made by the known aminating methods for the
polyaddition of alkylene oxides, such as for example ethylene oxide, propylene
oxide, butylene oxide, dodecyl oxide or styrene oxide onto amino-starter
compounds. Generally, the polyoi, such as a polyether polyol is aminated with
ammonia in the presence of a catalyst such as a nickel containing catalyst, e.g., a
Ni/Cu/Cr catalyst. The known methods are taught in U.S. Pat. No. 4,960,942;
U.S. Pat. No. 4,973,761; U.S. Pat. No. 5,003,107; U.S. Pat. No. 5,352,835; U.S.
Pat. No. 5,422,042; and U.S. Pat. No. 5,457,147, all incorporated herein by
reference. The starter compounds used are ammonia or compounds containing
amine groups and will provide in the reaction product no more than one primary
amino group, such as for example aliphatic polyamines such as ethylenediamine,
ethylenediamine oligomers (for example diethylenetriamine, triethylenetetramine
or pentaethylenehexamine), ethanolamine, 1,3-propylenediamine, N-(2-
Hydroxyethyl)ethylenediamine , 1,3-or 1,4-butylenediamine, 1,2-, 1,3-, 1,4-, 1,5-,
1,6-hexamethylenediamine, and the like. Suitable polyether blocks for the
poiyether-monoamines include polyethylene glycol, polypropylene glycol,
copolymers of polyethylene glycol and polypropylene glycol, poly(1,2-butylene
glycol), and poiy(tetramethylene glycol).
[0109] The preferred amino-hydroxy grafting agent compounds are compounds
having a molecular weight of less than about 1000, preferably 500, more
preferably less than 250. More preferable amino-hydroxy grafting agents contain
from 2 to 16 carbon atoms. With grafting agents having a molecular weight above
about 1000, the degree of flexibility and solvent resistance of the coating is
reduced. Examples of more preferred grafting agents include 3-amino-1-
propanol, 2-{2-aminoethylamino)ethanol and aminoalkyl silanol, e.g., aminopropyl
silane triol. The effective amount of grafting agent used in relation to the weight of
fluoroelastomer is from 1-20%, preferably from 2-10% by weight, more preferably
3 to 7% by wt.
[0110] Other exemplary grafting agents which provide hydroxyl-functionalized
fiuoroelastomers, although less preferred, include grafting hydroxyl-functional
ethylenic unsaturated compounds via a graft-addition reaction. Aforementioned
mercaptohydroxy and mercaptocarboxy compounds are suitable. Hydroxy or
carboxy group-containing ethylenic unsaturated monomers are suitable and include,
but are not limited to 2-hydroxyethyl (meth)acrylate, 1-hydroxypropyl (meth)acrylate,
2-hydroxypropyl (meth)acrylate, 2-hydroxyethyl vinyl ether, N-
methylol(meth)acrylamide, methaerylic acid, and maleic anhydride, and can be
grafted to the fluoroelastomer in the presence of a free radical initiator by techniques
known in the art of reactive processing of polymers, widely practiced in
thermoplastics such as polyolefins.
[0111] In another embodiment, a fiuorocarbon elastomer is graft-functionalized by an
addition reaction with a hydroxy(alkyl)mercaptan, aminothiol, or mercaptocarboxylic
acid optionally containing hydroxy group(s). Suitable mercaptans which yleld bound
hydroxyl groups for addition to fiuoroelastomers include hydroxymercaptans like
mercaptoethanol, hydroxyalkylmercaptans, such as 1-mercapto-3-propanol,
mercaptoethanolamine, 1-mercapto-4-butanol, a-mercapto- ?-hydroxyoligoethylene
oxides, e.g., a-mercapto, ?-hydroxyoctaethylene glycol, or the corresponding
ethylene oxide/propylene oxide copolyethers. Mercaptoaikoxy compounds which
yleld hydroxy groups upon hydrolysis include ?-mercaptopropyltrimethoxysilane, ?-
mercaptopropyltriethoxysilane, ?-mercaptopropylmethyldimethoxysilane, and ?-
mercaptopropylmethyldiethoxysiiane, to name a few. Suitable mercaptocarboxylic
acids and corresponding esters are the aforementioned mercaptoacetic acid, and
esters of mercaptoacetic acid, mercaptopropionic acid and esters, mercaptobutyric
acid and esters. Esterifylng compounds containing hydroxy groups include ethylene
glycol, propylene glycol, butylene glycol, diethylene glycol, Methylene glycol,
tetraethylene glycol, octaethylene glycol, dipropylene glycol, tripropylene glycol,
tetrapropylene glycol and N-methyldiethanolamine.
[0112] Mercapto-compounds, especially mercapto alcohols can be graft-linked in
effective amounts for subsequent curing to any hydrocarbon elastomer suitable
herein. Especially useful in the preparation of functionalized fluoroelastomer,
mercapto compounds can be incorporated under mild temperatures or at ambient
temperatures. The addition of the mercapto-compounds to graft to the
fluoroelastomer can be carried out optionally with a free radical initiator in solution at
a temperature above the decomposition temperature of the initiator, using for
instance, an azo initiator such as azobisisobutyronitrile and azobiscyclohexanenitrile,
a peroxide such as dilauroyl peroxide, benzpinacol siiyl ether, or photoinitiators in the
presence of UV or visible light. Diacyl peroxides, especially diiauroyl peroxide,
didecanoyl peroxide, di(3,3,5-trimethylhexanoyl) peroxide, disuccinoyl peroxide and
dibenzoyl peroxide, are suitable. An effective amount of free radical initiator, is 0.5 to
10 wt. %, based on wt. of mercapto-compound. A preferred marcapto compound is
mercapto alcohol, such as mercaptoethanol. An effective amount of starting
mercapto-compound is from 3% to 10% on wt. of fluoroelastomer, and is sufficient to
bond at a level of 1 % to 5 % by wt. of bound hydroxyl groups to the fluoroelastomer.
[0113] The more preferred fluoroelastomer grafting agents are those that will graft to
the fluoroelastomer at room temperature, such as 2-(2-aminoethylamino)ethanol
(NH2 -CH2 -CH2 -NH-CH2 -CH2 -OH)(CAS # 111-41-1) and aminopropylsiianetriol,
such as supplied in a 22-25% solution in water by Gelest, Inc. as SIA0608.0 (CAS #
29159-37-3).
Crossiinkable a-olefin copolymer elastomers
[0114] Poly(olefin/acrylic ester/carboxylate) copolymer film forming elastomers are
copolymers produced by polymerizing at least one a-olefin with at least one C1-C18
alkyl (meth)acrylate and, a minor amount of an unsaturated functional group-bearing
comonomer that is accessible to form crosslinks with such materials as
polylsocyanates, carbodiimides, and other agents. Functional group bearing
comonomers can comprise an ethylenic unsaturated group and a group bearing an
acid, hydroxy, epoxy, isocyanate, amine, oxazoline, diene or other reactive groups.
In the absence of such functionalized monomer, crosslinking sites can be generated
in an a-olefin-ester copolymer, e.g. by partial hydrolysis of pendant ester groups.
Suitable a-olefins for polymerization of such olefin copolymer film-forming
elastomers include ethylene, propylene, butene-1, isobutylene, pentenes, heptenes,
octenes, and the like including combinations. C1-C4 a-olefins are preferred and
ethylene is most preferred.
[0115] The functionalized comonomer provides copolymerized a-oiefin polymers
bearing an active hydrogen, halogen, or a group which can be converted, such as by
transamidation or hydrolysis to an active hydrogen-bearing group, or conversely, the
functionalized commoner contains a group that is reactive with crosslinking agents
bearing an active hydrogen group. The alkyl or alkoxy(meth)acrylate acids and
esters are exemplary functionalized comonomers. Concrete examples of alkyl
groups are a methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl
group, isobutyl group, sec-butyl group, t-butyl group, pentyl group, hexyl group, octyl
group, 2-ethylhexyl group and decyl group; cycloalkyl group such as cyclopentyl
group and cyclohexyl group; aryl group such as phenyl group and tolyl group; and
aralkyl group such as benzyl group and neophyl group.
[0116] Examples of alkoxy groups include methoxy group, ethoxy group, n-propoxy
group, isopropoxy group, n-butoxy group, isobutoxy group, sec-butoxy group, t-
butoxy group, pentoxy group, hexoxy group and octoxy group.
[0017] Suitable alkyl or alkoxy (meth)acrylates optionally incorporated with a-olefin
include methyl acrylate, ethyl acrylate, t-butyl acrylate, n-butyl acrylate, 2-ethylhexyl
acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethyle-
hexy acrylate, methoxy acrylate, ethoxyethyl acrylate, methoxyethyl acrylate,
acrylamide, and methacrylamide, and the like or a mixture thereof. Specific
examples of functional ethylenically unsaturated monomers which are
copolymerizable with the a-olefin monomers are; unsaturated carboxylic acids such
as acrylic acid, methacrylic acid, itaconic acid and maleic acid and salts thereof, alkyl
esters of unsaturated carboxylic acids such as methyl acrylate and butyl acrylate.
[0118] A preferred a-olefin-aerylic ester copolymer rubber comprises unsaturated
carboxylic acid monomer unit, such as acid units, e.g. derived from (meth)acrylic
acid or maleic acid, or anhydride units, e.g. derived from maleic anhydride or partial
ester units, e.g. derived from mono ethyl maleate. In a preferred embodiment the
polymer is a terpolymer of ethylene, C1 -C4 alkyl acrylate and an carboxylic
monomer unit; more preferably such terpolymer comprises at least about 30 mole
percent of ethylene, about 10 to about 69.5 mole percent mono ethyl maleate. In all
cases it is preferred that the a-olefin acrylate rubber be essentially non-crystalline
and have a glass transition temperature (Tg) below room temperature, i.e. below
about 20°C.
[0119] Other comonomers which contain a reactive group for adding functional acid,
hydroxy, epoxy;isocyanate, amine, oxazoline, diene or other reactive functional
groups include the diene monomers, such as non-conjugated dienes such as
alkylidenenorbomene, alkenylnorbomene, dicyclopentadiene,
methylcyclopentadiene and a dimer thereof and conjugated dienes such as
butadiene and isoprene. Examples of the dihydrodicyclopentadienyl group-
containing (meth)acrylate include dihydrodicyclopentadienyl (meth)acrylate and
dihydrodicyclopentadienyloxyethyl (meth)acrylate.
[0120] Further examples of functional comonomers include the N-alkylol and N-
aikoxy amides of a,ß-olefinically unsaturated carboxylic acids having from 4 to 10
carbon atoms such as N-methylol acrylamide, N-ethanol acrylamide, N-propanol
acrylamide, N-methylol methacrylamide, N-ethanol methacrylamide, n-butoxy
acrylamide and isobutoxy acrylamide, N-methylol maleimide, N-methylol maleamide,
N-methylol maleamic acid, N-methylol maleamic acid esters, the N-alkylol amides of
the vinyl aromatic acids such as N-methylol-p-vinyl benzamide, and the like and
others.
[0121] Other examples of functional comonomers bearing groups which are either
reactive with active hydrogens or themselves contain active hydrogen groups are
epoxy group-containing ethylenically unsaturated compounds including allyl glycidyl
ether, glycidyl methacrylate, and glycidyl acrylate. Specific examples of the active
halogen-containing ethylenically unsaturated compounds include vinylbenzyl
chloride, vinylbenzyl bromide, 2-chloroethyl vinyl ether, vinyl chloroacetate, vinyl
chloropropionate, allyl chloroacetate, allyl chloropropionate, 2-chloroethyl acrylate, 2-
chloroethyl methacrylate, chloromethyl vinyl ketone and 2-chloroacetoxymethyl-5-
norbomene. Specific examples of common carboxyl group-containing ethylenically
unsaturated compounds include acrylic acid, methacrylic acid, crotonic acid, 2-
pentenoic acid, maleic acid, fumaric acid and itaconic acid.
[0122] Examples of the other ethylenically unsaturated (meth)acrylic esters
comonomers include octyl methacrylate; cyano-substituted alkyl (meth)acrylates
such as 2-cyanoethyl acrylate, 3-cyanopropyl acrylate, and 4-cyanobutyl acrylate;
amino-substituted alkyl (meth)acrylates such as diethylaminoethyl acrylate; fluorine-
containing acrylates such as 1,1,1-trifluoroethyl acrylate; hydroxyl group-substituted
alkyl (meth)acrylates such as hydroxyethyl acrylate; alkyl vinyl ketones such as
methyl vinyl ketone; vinyl or allyl ethers such as vinyl ethyl ether and ally methyl
ether; vinyl aromatic compounds such as styrene, a-methylstyrene, chlorostyrene ad
vinyltoluene; vinylamides such as acrylamide, methacrylamide and N-
methylolacrylamide; and ethylene, 'propylene, vinyl chloride, vinylidene chloride, vinyl
fluoride, vinylidene fluoride, vinyl acetate, alkyl fumarate, etc.
Acrylic Elastomers
[0123] Functionalized acrylate elastomers are suitable if the glass transition
temperature is below -10°C, and are defined as addition polymers derived from a
major amount (greater than 50 wt. % on total polymer weight) of one or more
copolymerizable a,ß-ethylenic unsaturated ester monomers having the general
structure
where R1 is hydrogen or methyl; R2 represents C1-C20 aikyl, C2-C7 alkyl, C2-C7
alkoxyalkyl, C2-C7 alkylthioalkyl, C2-C7 cyanoalkyl, and a minor amount of active
hydrogen-group bearing comonomer or active bearing group graft-linked functional
site. The acrylates are available in solid bale, and as emulsions or latexes from a
variety of commercial sources. Minor amounts of up to about 35% on total acrylate
rubber weight, of hardening or Tg increasing comonomers , e.g. methyl
methacrylate, acrylonitrile, vinyl acetate, vinylidene chloride and/or styrene, to name
a few, can be included. Desirably, the functional group bearing comonomer having
active hydrogen or a group reactive with active hydrogen containing curing agent is
an unsaturated monocarboxylic acid (e.g. acrylic or methacrylic acid) or
polycarboxylic acid (e.g. itaconic, citraconic acid, etc.) or anhydrides of
polycarboxylic acids.
[0124] Specific examples of suitable acrylic or methacrylic monomers alone and in
combinations include methyl acrylate, ethyl acrylate, butyl acrylate, butyl
methacrylate, ethylhexyl acrylate, and the like. A preferred copolymer comprises
one or two different copolymerizable monomers each having structure (I) in which R1
is hydrogen; and, R2 is C4 -C8 alkyl, or C2 -C8 alkoxyalkyl, either of which may
contain a primary, secondary or tertiary C atom. Examples of more preferred C4 -C8
alkyl acrylates are n-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, isoamyl
acrylate, hexyl acrylate, 2-methylpentyl acrylate, n-octyl acrylate, and 2-ethylhexyl
acrylate; of preferred C4 -C8 alkoxyalkyl acrylates are methoxy acrylate, and
ethoxyethyl acrylate; of a preferred alkylthioalkyl acrylate is methylthioethyl acrylate;
of preferred C2 -C7 cyanoalkyl acrylates are cyanoethyl acrylate and cyanoproyl
acrylate; and mixtures of two or more of the foregoing may be used.
[0125] Preferred active hydrogen bearing comonomers for acrylic elastomers
include many of the above mentioned functional comonomers bearing active
hydrogens, some of which are repeated here include comonomers containing
carboxylic anhydride, carbonamide, N-substituted carbonamide, aldehyde, alkyl and
aryl keto, hydroxyl radicals, allylic chlorine radicals, methylol, maleimide, bis-
maliimide, alkyl N-methylol, phenolic methylol, thiol radicals, amino radicals,
isocyanate radicals, alkoxyalkyl radicals, oxirane radicals, and the like. The a,ß-
unsturated hydroxy carboxylic acids or anhydrides of dicarboxylic acids are
preferred. If the polymers are only copolymers of acrylate ester and carboxylic acid
or anhydride comonomers, they desirably have from about 90 to about 98 mole
percent repeat units from acrylate ester, more desirably from about 92 to about 97 or
98 moie percent of the ester and from 2 to 10% of carboxylic acid or anhydride, more
preferably 3 to 8% of carboxylic acid or anhydride.
[0126] Exemplary functional comonomers incorporated randomly during addition
polymerization of film former polymer include glycidyl methacrylate, acrylic and
methacrylic acids, maleic anhydride, N-alkyl maleimide, acrylamide, N-alkoxyalkyl
acrylamides such as N-isobutoxymethyl acrylamide, N-hydroxymethyl acrylamide
and the like, methyl vinyl ketone, acrolein, vinyl isocyanate, hydroxyalkyl acrylates
such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate and the like. Also
included are mixtures of two or more such functional monomers.
[0127] Included in acrylic elastomers are the so-called core-shell polymers.
The rubbery copolymers useful in soft-shell copolymers include copolymeric
compositions of at least one acrylic monomer whose homopolymer Tg is below -
10°C, and a second copolymerizable functional monomer. These monomers can be
polymerized in the presence of minor proportions of monovinyl or vinylidene
monomers set forth above such as for example styrene, acrylonitrile, methyl
methacrylate and the like, in a proportion with the low Tg acrylic comonomer(s)
selected so as to not raise the Tg of the resulting acrylic copolymer above about
-10°C.
[0128] The shell copolymer is an addition polymer and may be varied over a wide
composition range, however, for most purposes the copolymer will comprise from
about 99.9 to about 95 wt% of at least one rubbery monomer and from about 0.1 to
about 5 wt.% of second copolymerizable functional monomer. The preferred shell
copolymers are copolymers of an alkyl acrylate and 2-hydroxyethyl methacrytate.
[0129] The elastomeric coatings of this invention based on sequential polymerized
functionaiized addition polymers may exhibit two glass transition temperatures, one
of which is below 0°C, and one above 0°C. The amount of rubbery shell copolymer
component as well as the proportion of hard component and rubbery component
may be varied however, for most purposes the ratio of rigid copolymer component to
rubbery shell copolymer component is less than 1, meaning the amount of rubbery
component is in a major proportion of greater than 50 wt. %, and preferably from 60
wt% to 80 wt%.
[0130] Dual (halo, carboxy) functionaiized acrylic addition polymers are also useful
as the film-former for organic solvent-borne embodiments of the invention and
comprise repeating units from acrylic ester monomers or monomer mixtures and
which exhibit a glass transition temperature in the elastomer less than -20 °C. The
functional group is provided from a combination of from about 0.1% to about 30%,
preferably from 0.2% to about 15% by weight of an active halogen-containing
comonomer and from about 0.1% to about 20% by weight of a carboxyl-group
containing comonomer. In the preferred level of halogen-containing comonomer, the
halogen content is from about 0.1% to about 5% by weight of the functionaiized
acrylic rubber. The halogen groups of the halogen-containing comonomer can be
chlorine, bromine, or iodine. Chlorine containing comonomers are preferred from an
economic, availability and safety basis.
[0131] Examples of halogen containing comonomers are vinyl chloroacetate, vinyl
bromoacetate, allyl chloroacetate, vinyl chloropropionate, vinyl chlorobutyrate, vinyl
bromobutyrate, 2-ehloroethyl acrylate, 3-chIoropropyl acrylate, 4-chlorobutyl acrylate,
2-chloroethyl methacrylate, 2-bromoethyl acrylate, 2-iodoethyl acrylate, 2-chloroethyl
vinyl ether, chioromethyl vinyl ketone, 4-chloro-2-butenyl acrylate, vinyl benzyl
chloride, 5-chloromethyl-2-norbornene, 5-a-chloroacetoxymethyl)-2-norbornene, 5-
(a,ß-dichloropropionylmethyl)-2-norbornene, and the like. The preferred monomers
are vinyl chloroacetate, allyl chloroacetate, 2-chloroethyl acrylate, 2-chloroethyl vinyl
ether, vinyl benzyl chloride, 5-chloromethyl-2-norbornene, and 5-
chloroacetoxymethyl-2-norbomene.
[0132] A preferred active hydrogen bearing comonomer for acrylic rubber is present
from about 0.1% to about 20% by wt, preferably from 0.2% to about 10%, more
preferably from 2% to about 6% by weight of at least one carboxyl group-containing
comonomer. The carboxyl comonomer is preferably monocarboxylic, but can be
polycarboxylic. Preferred carboxyl comonomers contain from 3 to about 8 carbon
atoms. Examples of such preferred comonomers are acrylic acid, methacrylic acid,
ethacrylic acid, ß, ß-dimethylacrylic acid, crotonic acid, 2-pentenoic acid, 2-hexenoic
acid, maleic acid, fumaric acid, citraconic acid, mesaconic acid, itaconic acid, 3-
butene-1,2,3-tricarboxylic acid, and the like. The most preferred carboxyl
comonomers are the monocarboxylic acid monomers such as acrylic acid,
methacrylic acid, itaconic acid, and the like.
[0133] The functional group-containing comonomers are incorporated as introduced
above most conveniently during the addition polymerization of acrylate elastomers.
Polymerization by way of suspension, emulsion, solution, and bulk methods are
suitable. These polymerizations are initiated using free radical initiators. The
emulsion polymerization method is preferred. Various conventional soaps,
emulsifiers, and surfactants, known to the art and to the literature can be utilized in
emulsion polymerized functional acrylate rubber synthesis. The weight average
molecular weight of the dual- functionalized acrylate elastomer is generally in excess
of 100,000. Commercial grades of functionalized acrylic rubber are available from
Zeon Chemicals under the HYTEMP® mark.
[0134] A variety of a,ß-urisaturated C2-C8 alkyl ester copolymer latexes containing
active hydrogen functional groups are known and available from a variety of
commercial sources. A preferred acrylic rubbery latexes are available from
Noveon® under the HYCAR mark, and Rhoplex® ex. Rohm and Haas. An emulsion
polymerized copolymer of n-butylacrylate, acrylonitrile, N-methylol acrylamide and
itaconic acid, exhibiting a Tg of less than 20°C is a preferred acrylic film former for
use in aqueous coating embodiments.
Crosslinkable a-Olefin Copolymers
[0135] Poly(olefin/acrylic ester/carboxylate) copolymer are thermoplastic in the
uncured state and are suitably flexible for use herein. These are principally
copolymers produced by polymerizing at least one a-olefin with at least one C1 -C18
alkyl (meth)acrylate and a minor amount of an unsaturated protic functional group-
bearing comonomer that is accessible to form crosslinks with such materials as
poiylsocyanates, carbodiimides, and other curing agents. Functional group bearing
comonomers can comprise an ethylenic unsaturated group and a group bearing an
acid, hydroxy, epoxy, isocyanate, amine, oxazoline, diene or other reactive groups.
In the absence of such functionalized monomer, crosslinking sites can be generated
in an a-olefin-ester copolymer, e.g., by partial hydrolysis of pendant ester groups.
Suitable a-olefins for polymerization of such olefin copolymer film-forming elastomers
include ethylene, propylene, butene-1, isobutylene, pentenes, heptenes, octenes,
and the like including combinations. C2 -C4 a-olefins are preferred, and ethylene is
most preferred.
[0136] Other examples of functional comonomers bearing active hydrogen groups
are epoxy group-containing ethylenically unsaturated compounds including allyl
glycidyl ether, glycidyl methacrylate, and glycidyl acrylate. Specific examples of the
active halogen-containing ethylenically unsaturated compounds include vinylbenzyl
chloride, vinylbenzyl bromide, 2-chloroethyl vinyl ether, vinyl chloroacetate, vinyl
chloropropionate, allyl chloroacetate, allyl chloropropionate, 2-chloroethyl acrylate, 2-
chloroethyl methacrylate, chloromethyl vinyl ketone and 2-chloroacetoxymethyl-5-
norbomene. Specific examples of the carboxyl group-containing ethylenically
unsaturated compound include acrylic acid, methacrylic acid, crotonic acid. 2-
pentenoic acid, maleic acid, fumaric acid and itaconic acid.
[0137] Examples of ethylenically unsaturated (meth)acrylic ester comonomers
include octyl methacrylate; cyano-substituted alkyl (meth)acrylates such as 2-
cyanoethyl acrylate, 3-cyanopropyl acrylate, and 4-cyanobutyl acrylate; amino-
substituted alkyl (meth)acrylates such as diethylaminoethyl acrylate; fluorine-
containing acrylates such as 1,1,1 -trifluoroethyl acrylate; hydroxyl group-substituted
alkyl (meth)acrylates such as hydroxyethyl acrylate; aJkyl vinyl ketones such as
methyl vinyl ketone; vinyl or aliyl ethers such as vinyl ethyl ether and ally methyl
ether; vinyl aromatic compounds such as styrene, a-methylstyrene, chlorostyrene ad
vinyltoluene; vinylamides such as acrylamide, methaerylamide and N-
methylolacrylamide; and ethylene, propylene, vinyl chloride, vinylidene chloride, vinyl
fluoride, vinylidene fluoride, vinyl acetate, alkyl fumarate, etc.
[0138] A preferred olefin/acrylic ester copolymer rubber comprises unsaturated
carboxylic acid monomer units, such as acid units, e.g. derived from (meth)acrylic
acid or maieic acid, anhydride units, e.g. derived from maleic anhydride or partial
ester units, e.g. derived from mono ethyl maleate. In a preferred embodiment the
polymer is a terpolymer of ethylene, C1 -C4 alkyl acrylate and an carboxylic
monomer unit; more preferably such terpolymer comprises at least about 30 mole
percent of ethylene, about 10 to about 69.5 mole percent mono ethyl maleate. In all
cases it is preferred that the a-olefin acrylate rubber be essentially non-crystalline
and have a glass transition temperature (Tg) below about 20°C. Ethylene-
carboxylate copolymers are available commercially under the VAMAC® mark.
[0139] When the acrylic acids and acrylates are part of the a-oiefin copolymer
backbone, transamidation reactions may be made in melt processing techniques
which are known to produce pendant hydroxyl functionality such as by employlng an
aminoalcohol, e.g., 2-amino-1-ethanol. A further reaction by the pendant hydroxyls
may occur, i.e., transesterification with another acrylate linkage, resulting in
crosslinking and an increase in product viscosity:
Polyurethanes
[0140] A castable film former comprising a curable urethane can be utilized as the
film former component. The active hydrogen functionalized polymer is a saturated
prepolymer and is cured with an aliphatic polylsocyanate. The cured glass transition
temperature of the poiyurethane is limited to below 0°C and is lightly crosslinked by
inclusion of a triol, tetraol or higher OH functionality. Therefore the chain extending
polyols are limited to those such as hydroxy terminated hydrogenated polybutadiene
polyol homopolymers and copolymers exhibiting a glass transition temperature of
0°C or less, polyTHF, polyester diols, polypropylene glycols and the like, of which
are familiar to those skilled in the art and commercially available. Conventional
curing agent and catalyst is employed. U.S. Pat. No. 4,669,517 discloses a suitable
method to apply emissive poiyurethane to a prepared post-vulcanized rubber surface
for obtaining excellent bonding of the poiyurethane. The method for preparing a
post-vulcanized surface is applicable for applylng a castable poiyurethane emissive
coating. Cyanuric acid is applied to the rubber surface which contains incorporated
therein a polybutadiene polyol, prior to application of the poiyurethane reaction
mixture which contains the thermally conductive metal particles. The poiyurethane
reaction mixture cures at ambient temperatures.
Acrylourethanes.
[0141] Urethane modified acrylic materials conforming to the requirements of the
film former as set forth herein are also contemplated. These may be adapted to be
cure activated by moisture, heat or light. The glass transition temperature of such
urethan modified acrylates must be °C or less and comprised of a major amount of
C2-C8 acrylic or methacrylic esters. An example of preferred urethane-modified
acrylic resins usable in the present invention is, in the case of the urethane-modified
acrylic resin represented by formula (I), an acrylic copolymer produced by
copolymerizing 60 to 70 moles of methyl-, ethyl-, or butyl- acrylate with 10 to 50
moles of methacrylic acid and 30 to 80 moles of 2-hydroxymethyl methacrylate.
Some or all of the hydroxyl and carboxyl groups are capped in a reaction with a,ß--
ethylenic unsaturated isocyanate, for example, methacryloyloxyethyl isocyanate (2-
isocyanate ethyl methacrylate). This material is moisture curable, and curable by UV
by incorporation of a conventional photoinitiator. In mosture curable acrylourethane
embodiments, it is preferred that at least 10 mole%, preferably at least 50 mofe% of
the hydroxyl groups from the 2-hydroxyethyl methacrylate units have been reacted
with the methacryloyloxyethyl isocyanate. The a,ß-ethylenic unsaturated isocyanate
is preferably based upon the reaction product of an isocyanate and hydroxyl-
containing monomers, such as N-methylolacrylamide, N-methylolmethacrylamide, 2-
hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-
hydroxypropyl methacrylate, 4-hydroxybutyl acrylate, and 4-hydroxybutyl
methacrylate, may be used optionally with 3-aminopropyl triethoxy silane,3-
aminopropyl trimethoxy silane, 3-aminopropyl methyl dimethoxysiiane or 3-
aminopropyl methyl diethoxy silane, primary secondary amines such as N-(2-
aminoethyl)-3-aminopropyl trimethoxy silane, secondary amines such as N-methyl-
or N-phenyl-3-aminopropyl trimethoxy silane, condensed aminoalkyl siianes such as
bis(3-aminopropyl) tetramethoxy or tetraethoxy disiloxane NH2 (CH2 )3--Si(OCH3)2 -
O—(CH3 O)2 Si-(CH2 )3 NH2, pofyglycolether-modified aminosilanes such as that sold
under the Trademark "Dynasylan 121" and triamino functional propyl trimethoxy
siianes such as "Dynasylan TRIAMO" available from Huls AG. Similar siianes having
two or three silicon atoms can also be used.
Maleated Elastomeric Materials
[0142] Various polymer blends, alloys and dynamically vulcanized composites of
maleated addition polymers based on polyethylenes, such as maleated
polypropylenes, maleated styrene-ethylene-butene-styrene-block copolymers,
maleated styrene-butadiene-styrene block copolymers, maleated ethylene-propylene
rubbers, and blends thereof can be utilized as the functionaiized film-forming
elastomer in accordance with the invention. The maleated elastomers are dissolved
in an appropriate organic solvent system and mixed with the thermally conductive
metal particles which are preferably predispersed in a portion of the solvent used.
Ethylene Vinyl Ester Copolymers
[0143] Film forming, solvent soluble, OH-functional ethylene copolymers are
available in various grades which contain carboxyl or hydroxyl functional groups and
are also suitable as the film former used herein. Conventionally, some of these
polymers are used as cross-linkable hot melt adhesives, however these polymers
are readily adaptable for ambient temperature cured emissive coating films herein
even though the elevated temperature cohesiveness is relatively low. The ethylene
vinyl ester polymers containing hydroxyl functionality can be adapted for use in the
emissive coating composition and cured with unblocked isocyanates and provide
sufficient properties for certain environmental temperatures not exceeding the
temperature at which the cured coating will flow. An ethylene vinyl acetate
copolymer containing OH groups is based on a polymer having monomeric units
ethylene and of vinyl alcohol, and optionally vinyl acetate, the melt viscosity being
preferably from 4 to 40 Pa.s at 180°C. Ethylene vinyl alcohol copolymers have
preferably at least 5 wt % of vinyl alcohol units. One example is a terpolymer
(viscosity 20 Pa.s at 180° C, MFR at 125 °C. under 325 gm load of 6.4 gm/10 min)
with 10% vinyl alcohol, 88.75% ethylene and 1.2 wt % vinyl acetate. The m.p. is
101.5 °C. (by DSC). Another terpolymer contains 13.7 wt % vinyl alcohol, 82.3%
ethylene and 4.0 wt % vinyl acetate (viscosity 5.8 Pa.s at 180 °C, MFR at 125°C
under 325 gm (cf. 30.4 gm/10 min, DSC m.p. 91.degree. C).
[0144] Film formers of a mixture or interpenetrating network containing partly
functionalized polymer, and partly non-functionalized polymer types are suitable for
use herein. Blendable with functionalized polymers are olefinic rubber polymer as
random or block copolymers, e.g., SBS, EBS, EPM and EPDM, hydrogenated
polydiene copolymer, acrylic rubber, and others of the aforementioned film formers.
As an example, a non-functionalized polymer film former can be blended with a
partially hydrolyzed ethylene vinyl acetate polymer in a proportion of from 10-90
wt.% to 90-10 wt.%, respectively, and cured with any of the suitable curing agents
disclosed herein, and equivalents thereof.
Functionalized EPM and EPDM Elastomers
[0145] Functionalized EPM and EPDM elastomers are suitable film forming
elastomers used as the film former in the emissive coating. These comprise two or
more a-monoolefins, copolymerized with a polyene, usually a non-conjugated diene
comonomer. Useful polyenes include 5-ethylidene-2-norbornene; 1,4-hexadiene; 5-
methylene-2-norbornene; 1,6-octadiene; 5-methyl-1,4-hexadiene; 3,7-dimethyl-1,6-
octadiene; 1,3-cyclopentadiene; 1,4-cyclohexadiene; dicyclopentadiene; 5-vinyl-2-
norbornene, etc.; or a combination thereof. Preferred polyenes for the EPM and
EPDM functionalized elastomers are 5-vinyl-2-norbomene, 5-ethylidene-2-
norbomene and 1,4-hexadiene. Functional groups can be incorporated by the
aforementioned conventional routes, and by the metathesis route disclosed herein.
[0146] In one aspect of the methods disclosed in this invention a particularly useful
scheme for the production of polymers containing organic acid functionality such as
carboxyl functionality, aliphatic or aromatic hydroxyl functionality, and the like and
inorganic acid functionality such as sulfonic acid functionality, phosphoric acid
functionality and the like is provided.
[0147] One such scheme is illustrated below for EPM and EPDM rubber, for
incorporating pendant carboxyl, hydroxyl or non-sterically hindered pendant olefinic
functionality.
wherein n represents a conventional number of repeating ethylene units for EPDM
sold commercially, m represents a conventional number of propylene repeating
units, o represents a number of conventional diene monomer repeating units, and p
represents the number of repeating units of maleated dicyclopentadiene ranging
from 1 to 100.
[00148] The same approach as illustrated above for modifylng EPDM can be utilized
for incorporating a functional group in a conjugated diene polymer, such as a
butadiene-acrylonitrile copolymer containing vinyl unsaturation.
(B) Curing Agent Component
[0149] The ambient temperature curing agent is a multifunctional curing component
containing either (1) at least one group bearing active hydrogen and a crosslinking
group which is the same active hydrogen group or a different corssiinking group, or
(2) at least one groups that is reactive with an active hydrogen group and a
crosslinking group which is a group reactive with an active hydrogen group or a
different crosslinking group. In the case of castable polyurethane or urethane
acrylate (acrylo-urethane), the curing interaction is between a polyol optionally with
?-curing polyamine and a polylsocyanate or polylsocyanate prepolymer and or
ethylenic unsaturated groups on the acrylated portion. The curing component is
selected from polylsocyanate, chain extended polylsocyanate, polymeric isocyanate-
polyol adduct, a polycarbodiimide, multifunctional oxazoline, multifunctional
oxazine, multifunctional imidazoline, phenolic novolak, phenolic resole, amino resin,
and amino(alkoxy)silane. The preferred curing component contains at least one
isocyanate group, or a group bearing an isocyanate group, or a functional group
reactive crosslinking group, or combinations thereof. The curing component is used
at a level generally of from about 3 to about 30 wt. parts, desirably from about* 5 to
about 25 wt. parts, and preferably from about 10 to about 20 wt. parts per 100 wt.
parts of a functionalized addition polymer, or in the case of a castable polyurethane,
in a stoichiometric amount based upon the equivalent weight of the polyol
components.
[0150] Suitable curing agents include monomeric polylsocyanates such as aliphatic
or aromatic diisocyanates containing from 2 to 40 carbons. Exemplary
polylsocyanates include ethylene diisocyanate, trimethylene diisocyanate,
hexamethylene diisocyanate, propylene-1, 2-diisocyanate, ethylidene diisocyanate,
cyclopentylene-1, 3-diisocyanate, the 1,2-, 1,3- and 1,4-cyclohexylene diisocyanates,
the 1,3- and 1,4-phenylene diisocyanates, diphenylmethane diisocyanates,
polymethyleneisocyanates, the 2,4- and 2,6-toluene diisocyanates, the 1,3- and 1,4-
xylylene diisocyanates, bis(4-isocyanatoethyl) carbonate, 1,8-diisocyanato-p-
methane, 1-methyl-2, 4-diisocyanatocyclohexane, the chlorophenylene
diisocyanates, naphthalene-1,5-diisocyanate triphenylmethane-4,4', triisocyanate,
isopropylbenzene-alpha-4-diisocyanate, 5,6-bicyclo[2.2.1] hept-2-ene diisocyanate,
5,6-diisocyanatobutylbicyclo [2.2.1] hept-2-ene. Exemplary commercial products are
trimethylhexamethylene diisocyanate available from VEBA, heptadecyl (C17)
diisocyanate, DDI 1410 an aliphatic C-36 diisocyanate available from the Henkel
Corporation of Minneapolis, Minn and Isonate® 143L diisocyanate, a modified
diphenylmethane diisocyanate (MDI) available from Upjohn Corp. Further urethane
components are isophorone diisocyanate available from VEBA and Desmodur® N
an aliphatic triisocyanate available from Mobay. Desmodur® N is more particularly
defined as the reaction product of 3 moles of hexamethylene diisocyanate and water
having an isocyanate equivalent weight as later defined of 191. Other adducts or
prepolymers of the polylsocyanate include Desmodur® L and Mondur® CB which
are the adducts of tolylene diisocyanate (TDI).
[0151] Examples of alicyclic polylsocyanates include 1,3-cyclopentene diisocyanate,
1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 1-isocyanato-3,3,5-
trimethyl-5-isocyanatomethyl-cyclohexane (isophorone diisocyanate, IPDI), 4,4'-
methylenebis(cyclohexyl isocyanate), methyl-2,4-cyciohexane diisocyanate, methyl-
2,6-cyclohexane diisocyanate and 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane)
and polylsocyanates (e.g., 1,3,5-triisocyanatocyclohexane. Polymeric isocyanates
are preferred crosslinking agents used for curing the emissive coating. Liquid;
polymeric isocyanates are more preferred and are also widely available. The term
"liquid" is defined as a liquid at ambient temperature, or at elevated temperature, or a
solution of polylsocyanate in a solvent for the poiylsocyanate. Poiylsocyanates
containing from 10 to 50% reactive NCO groups which are liquid at ambient
temperature, or are liquefied at up to about 70°C, or soluble in carriers or diluents
are readily adapted for use in the present invention. Numerous types of liquid
isocyanates are described in, for example, U.S. Pat. Nos. 3,644,457, 3,883,571,
4,229,347, 4,055,548, 4,102,833, 4,332,742, 4,448,904, and 4,490,301.
[0152] A useful liquid polylsocyanate is prepared through the reaction with various
hydroxyl functional materials. These reactions can be catalyzed using an
organometallic or tertiary amine. Useful hydroxy compounds are aliphatic alcohols
containing about 1 to 36 and preferably 4 to 16 carbon atoms. Non-limiting examples
of aliphatic alcohols are cycloaliphatic alcohols, aliphatic alcohols containing
aromatic groups, aliphatic alcohols containing groups that do not react with
isocyanates e.g., ether groups and halogens such as bromine and chlorine. Specific
non-limiting examples of aliphatic alcohols are 2-methyl-1-propanol, cetylalcohol,
cyclohexanol, 2-methoxy-ethanol, and 2-bromoethanol. Branched aliphatic alcohols
having relatively molecular weights up to 150, are most preferred.
[0153] Exemplary liquid adducts of isocyanates compounds include a reaction
product of solid 4,4'- and/or 2,4'-diphenylmethane diisocyanate with a branched
aliphatic dihydroxy compound in a molar ratio of 0.1 to 0.3 mol of dihydroxy
compound per mol of diisocyanate. Another exemplary liquid MDI-based compound
is a reaction product of MDI with mixtures of monoalcohol, poiy-1,2-propylene ether
glycols and a triol. Another exemplary liquid polylsocyanate is the reaction product
of an alcohol or thiol having an average functionality of from about 1.5 to about 4 and
an average equivalent weight of at least about 500 with at least 2 equivalents per
hydroxyl and/or thiol equivalent of an organic polylsocyanate wherein about 20% of
the initially formed urethane or thiourethahe groups are converted to allophanate
and/or thioallophanate groups.
[0154] Blocked isocyanates, which are known, can be adapted in the practice of
forming the coatings where a heating step is used for curing the coating. Suitable
blocking agents for reaction with the organic mono- or poiylsocyanates are those
isocyanate-reactive compounds, for example, phenols, lactams, oximes, imides,
alcohols, pyrazoles, and the like. The reaction of the organic poiylsocyanate and
the blocking agent can be carried out by any of the methods known in the art. The
reaction can be carried out in bulk or in inert solvent at temperatures of, for example,
about 50-120° C. For completely-blocked isocyanates, equivalent ratios of
isocyanate-reactive groups to isocyanate groups of 1/1-2/1 or higher can be utilized.
Completely blocked isocyanates are preferredly used herein, but the ratio can be
adjusted if only a partially-blocked poiylsocyanate is desired.
[0155] The aqueous coating containing functionalized elastomer and crosslinker
dispersed therein is utilized shortly after preparation. In the aqueous based coating
embodiments employlng poiylsocyanate curing agents such as by the use of an
aqueous dispersed poiylsocyanate these materials are known and disclosed, for
example, in U.S. Pat. No. 5,202,377. Exemplary emulsifiable polylsocyanates
taught in the '377 patent comprise a hydrophilic tertiary isocyanate functional
oligomer rendered hydrophilic by partially reacting with a hydrophilic polyether.
Other water dispersible isocyanates suitable for aqueous-based embodiments
according to the invention are known. U.S. Pat. No. 4,663,377, teaches an
emulsifiable poiylsocyanate mixture comprising (a) a hydrophilic isocyanate-
functional oligomer and (b) a poiylsocyanate. A non-limiting example is the reaction
product of an aliphatic poiylsocyanate with a mono- or polyhydric, nonionic
polyalkylene ether alcohol having at least one polyether chain containing at least 10
ethylene oxide units. Water dispersible isocyanates which are preferred are based
upon aliphatic and alicyclic isocyanates.
[0156] Coating compositions can be formed by combining (i) the water dispersible
crosslinkers, such as carbodiimide or poiylsocyanate with (ii) the separate aqueous
solutions, emulsions or dispersions of the functionalized elastomer polymer
containing reactive functionality. Alternatively, the aqueous composition containing
the functionalized elastomer can be combined with a separate aqueous dispersion
containing the crosslinker such as is taught in U.S. Pat. No. 5,466,745 for the
diisocyanate embodiment. The coating can be prepared by admixing the elastomer
in aqueous medium with a non-aqueous, emulsifiable composition comprising an
unblocked polylsocyanate crosslinking agent and a surface active isocyanate-
reactive material. This alternative will introduce some volatile organic components
when selecting solvents known as VOC, however there are other solvent diluents
that can be used that are not considered VOC. A known procedure can be followed
by (i) admixing an unblocked hydrophobic isocyanate and diluent with a mixture of a
surface active isocyanate-reactive material and water to form a water-in-oil emulsion,
then (ii) adding this emulsion to the aqueous medium containing the elastomer in
proportions and under conditions to invert the isocyanate emulsion into an oil-in-
water emulsion.
[0157] Specific examples of commercial diisocyanates that may be mentioned, are
1,6-hexane diisocyanate (commercially available, for example, under the trade
designation HMDI from Bayer), isophorone diisocyanate (commercially available, for
example, under the trade designation IPDI from Huls), tetramethylxylene
diisocyanate (commercially available, for example, under the trade designation m-
TMXDI from Cytec), 2-methyl-1,5-peniane diisocyanate, 2,2,4-trimethyl-1,6-hexane
diisocyanate, 1,12-dodecane diisocyanate and methylene bis(4-cyelohexyl
isocyanate) (commercially available, for example, Desmodur® W from Bayer), and
higher functional isocyanates such as a biuret of 1,6-hexane diisocyanate
(commercially available, for example, as Desmodur® N from Bayer), an isocyanurate
of 1,6-hexane diisocyanate (commercially available, for example, as Desmodur® N-
3390 from Bayer), an isocyanurate of isophorone diisocyanate (commercially
available, for example, as Desmodur® Z-4370 from Bayer), a reaction product of
tetramethylxylene diisocyanate and trimethylol propane (commercially available, for
example, as Cythane® 3160 from Cytec), and a reaction product of one mole of
trimethylol propane and 3 moles of toluene diisocyante (commercially available, for
example, as Desmodur® L from Bayer). The amount of di- or poiylsocyanate
included should be from 3 to 30 phr. Preferably the amount is from 8 to 15 phr.
[0158] Another class of crosslinking component which can be employed to cure the
functionalized film former and form siloxane crosslinking, are the various known
organosilanes. A preferred organosilane is an isocyanatosilane which contain an
isocyanate group and one or more groups capable of forming crosslinks with the
silane and/or film former, such as a hydrolyzable group, hydrazidyl, thio, halogen,
hydroxy, alkoxy, and other ?-reactive substituents on the group bonded to silicon
through a carbon atom, such as acyloxy, mercapto, amino, phenolic, and glycido.
The silanes may contain a vinyl group; a vinyl-containing group; another isocyanate
group; another isocyanate-containing group; an ureido group; an ureido-containing
group; an imidazole group; or an imidazole-containing group. Such compounds are
known in the art.
[0159] The reactive siiane curing agents used herein will provide ambient curable
emissive coatings in amounts on a weight basis of from 25 to 150 parts of siiane
curing agent per 100 wt. parts of film former and wherein the film former contains
no more than 10 wt. % of functional groups which cure with the curing agent. The
siiane curing agents can be monomeric, tetravalent silanes or bis, or oligo-
derivatives containing at least two silicone bonded groups, of the same or different
coreactive groups depending upon the chosen functional groups on the film forming
polymer. One such type of curing group is a hydrolyzable group, or group that
interacts with the acidic or basic functional groups on the film former polymer. The
silicone bonded group is an active hydrogen bearing group coreactive with the
functional group on the film former polymer, or the silicone bonded group is
coreactive with active hydrogen bearing groups on the film former polymer. These
organosilane compounds are known and available from a number of commercial
sources.
[0160] Representative preferred hydroxyalkyl group-containing silanes have the
general structure:
wherein R is a divalent aliphatic, cycloaliphatic or aromatic radical having from 1 to
20 carbon atoms, and is preferably an alkylene radical having from 1 to 9, most
preferably 2 to 4 carbon atoms; R1 is a monovalent aliphatic, cycloaliphatic or
aromatic radical having from 1 to 20 carbon atoms, and is preferably selected from
the group consisting of alkyl radicals having from 1 to 4 carbon atoms, cycloalkyl
radicals having from 4 to 7 ring carbon atoms, and aryl radicals having 6, 10, or 14
nudear carbon atoms and optionally one or more substituent aikyl groups having
from 1 to 4 carbon atoms; R2 is a monovalent aliphatic, cycloaliphatic or aromatic
organic radical containing from 1 to 8 carbon atoms, and is preferably selected from
the group consisting of methyl, ethyl, propyl and butyl, and R3—O—R4, and where
R3 is an alkylene group having from 1 to 4 carbon atoms (methyl, ethyl, propyl, butyl)
-C=(0)-R, and R4 is an aikyl group having from 1 to 4 carbon atoms; and a is zero
or 1, preferably zero.
[0161] Aminofunctional siianes are preferred for curing carboxy-functional film
formers and include those having the structure (B)

wherein R, R1, R2 and a are as previously defined for (A); and R5 is selected from
the group consisting of hydrogen, monovalent aliphatic radicals having from 1 to 8
carbon atoms, monovalent cycloaliphatic radicals having from 4 to 7 ring carbon
atoms, phenyl, alkaryl radicals having 6 nuclear carbon atoms and containing one or
more substituent aikyl groups having from 1 to 4 carbon atoms, and the group R7—
NH—R6— , wherein R6 is selected from the group consisting of divalent aliphatic,
cycloaliphatic and aromatic radicals having from 1 to 20 carbons, there being
preferably at least two carbon atoms separating any pair of nitrogen atoms, with R6
being preferably an alkylene group of 2 to 9 carbon atoms; and R7 being the same
as R5 and preferably is hydrogen.
[0162] Mercaptofunctional siianes include those having the structure ( C)

wherein R, R1, R2 and a are as previously defined for (A);
[0163] Organosilane compounds useful herein include those contain as a
substituent on the Si atom an organic chain having from 1 to 20 carbon atoms, at
least one extractable hydrogen atom which is preferably attached to a functional
group separated from the silicon atom by a chain of at least 3 interconnected carbon
atoms.
[0164] The preferred organosilane is an isocyanatosilane. Examples of
commercially available isocyanato-alkoxy silanes which are suitable herein include
gamma-isocyanatopropyltrimethoxysiiane, available as Silquest ® ?-5187 from OSi
Specialties Group, a Witco company (OSi), and gamma-
isocyanatopropyltriethoxysiiane, available as Silquest® A-1310, also from OSi.
[0165] Representative names and pseudonyms for organosilanes containing active
hydrogen groups are hydroxypropyltrimethoxysilane, hydroxypropyltriethoxysilane,
hydroxybutyltrimethoxysilane, ?-aminopropyltrimethoxysilane ?-
aminopropyltriethoxysiiane, methylaminopropyltrimethoxysilane, ?-
aminopropyltripropoxysilane, ?-aminoisobutyltriethoxysilane, ?-
aminopropylmethyldiethoxysilane, ?-aminopropylethyldiethoxysilane, ?-
aminopropylphenyldiethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane,
propyltrimethoxysilane, butyltrimethoxysiiane, isobutyltrimethoxysilane,
hexyltrimethoxysilane, octyltrimethoxysilane, decyltrimethoxysilane,
cyclohexyltrimethoxysiiane, cyclohexylmethyltrimethoxysilane, and the like.
[0166] Also suitable as the curing agent are hydroxy silanes having an (Si-OH
bond), optionally as either partially neutralized silanediols or silanetrfols. The
silanols preferably contain at least one nucleophile connected to silicon through a
first connecting group. As used herein, the term "partially neutralized" means that at
least some of the siianol groups are in the form of mono-, di-, or tribasic alkali metal
salts, more particularly lithium, sodium, or potassium salts. The extent of
neutralization is that amount sufficient to inhibit no more than 50% of the
condensation of condensable groups of the siianol, but provide enough interaction
between the siiane with the film forming polymer to form linking bridges but not gel
the film forming polymer when part A and part B are combined. The curing agent
can be a partially neutralized siianol represented by the structure D:

where n is 1, 2, or 3; m is 0, 1, or 2; p is 0 or 1, preferably 0, with the proviso that
m+n+p=3; R is the first connecting group; M+ is an alkali salt forming metal; Y is a
group that contains a nucleophilic moiety; and R' is a linear, branched, or cyclic C1-
C8 -alkyl group, preferably methyl or ethyl, more preferably methyl. Connecting
group R in D is preferably a linear, branched, or cyclic alkylene group, or arylene
group, or a combination thereof, and may contain one or more heteroatoms, which
may themselves be nucieophilic. More preferably, X is a C2 -C6 -alkylene group or --
R'--NH--R'", where each R' is independently a C2 -C4 -alkylene group.
[0167] Examples of suitable nucleophile groups include amines, phenols,
mercaptans, and carboxylates, with primary and secondary amines and mercaptans
being preferred, primary and secondary amines being more preferred, and primary
amine being most preferred. A specific example of partially neutralized
aminosilanetriols are typically potassium or sodium salts of 3-aminopropyl-siiane triol
and N-(2-aminoethyl)-3-aminopropyl-silanetriol.
[0168] The more preferred organosilane curing agent will have at least one silicone
bonded group that contains a substituted or unsubstituted alkylamino group and
alkoxy groups bonded to silicone capable of forming network crosslinks on
condensation of the organosilane. The amine group may be in the free unblocked
form or as a blocked amino group. Blocking of the amine group can be provided by
reaction with methyl isobutyl ketone or methyl amyl ketone. The preferred groups
reactive with the silane compound are preferably a C1-C4 alkoxy groups. Examples
of curing components include but are not limited within the class of aminosilanes are
aminopropyltriethoxy or -methoxy silane and aminoethylaminopropyltriethoxy or -
methoxy silane, 3-aminopropyl triethoxy silane, 3-aminopropyl trimethoxy silane, 3-
aminopropyl methyl dimethoxysilane or 3-aminopropyl methyl diethoxy silane, a
silane containing primary secondary amines such as N-{2-aminoethyl)-3-aminopropyl
trimethoxy silane, secondary amines such as N-methyl- or N-phenyl-3-aminopropyl
trimethoxy silane, condensed aminoalkyl silanes such as bis(3-aminopropyl)
tetramethoxy or tetraethoxy disiloxane, NH2 (CH2)3 -Si(OCH3)2 -O-(CH3 0)2 Si-(CH2)3
NH2, polyglycolether-modified aminosilanes such as that sold under the Trademark
"Dynasylan 121" and triamino functional propyl trimethoxy silanes such as
"Dynasylan TRIAMO" available from Huls AG. Similar silanes having two or three
silicon atoms can be used.
[0169] A preferred combination of an aminoalkyl trialkoxy silane and a fluoroalkyl
trialkoxy silane exhibits improved color stability (non-yellowing) on heat aging of the
cured coating.
[0170] Fluoroalkyl silanes useful in admixture with another silane containing active
hydrogens, and most preferably in mixture with an aminosilane curing agent in the
invention generally have a formula E:

where R1 is a monofluoridated, oligofiuoridated, or perfluoridated alkyl group with 1
to 20 C atoms or a monofluoridated, oligofiuoridated, or perfluoridated aryl group, Y
is a CH2 , O, or S group, R2 is a linear, branched, or cyclic alkyl group with 1 to 8 C
atoms or an aryl group, and R is a linear, branched, or cyclic alkyl group with 1 to 8
C atoms or an aryl group, y is 0 or 1, and m is 0 or 1,
Specific examples of some of the fluoroalkyl silanes as representative include 3,3,3-
trifluoropropyl trimethoxy silane, 3,3,3-trifluoropropyl methyl dimethoxy silane, 3,3,3-
trifluoropropyl methyl dimethoxy silane, 3,3,3-trifluoropropyl cyciohexyl dimethoxy
silane, 3,3,3-trifluoropropyl phenyl diethoxy silane, and
heptadecatrifiuorodecyl trimethoxysilane CF3(CF2) 7CH2CH2Si(OCH3).
[0171] Amino resins utilized in amounts of less than 10 wt.% on weight of the film
former can be used as curing components where acid catalyzed heated conditions
can be used. The amino resins refer to any material in the broad class of materials
based on the reaction of formaldehyde with urea, melamine, benzoguanamine, or
acetylguanamine, and the like. Such compounds are well known and described in,
for example, "Kirk-Othmer Encyclopedia of Chemical Technology", 3rd Ed., Volume
2, pages 440-469, Wiiey-lnterscience, 1978.
[0172] Curing agents containing at least two ethylenically unsaturated double bonds
each activated by an adjacent electron-withdrawing groups and capable of Michael
addition when the functional groups on the film forming polymer are suitable and
known, e.g. maleic dianhydrides and fumaric dianhydrides.
[0173] Examples of other suitable curing components are the carbodiimides.
The polyfunctional carbodiimides exhibit suitable reactivity with functional group-
containing elastomers used in the present invention. N-acylurea groups form
between carboxylic sites. Carbodiimide linkages can also be formed between a
carboxyl group and other functional groups contained in the functionalized
elastomer, such as hydrazidyl, amino and/or thiol groups. Polyfunctional
carbodiimides can be obtained from polylsocyanates using phospholine oxide as
catalyst as is described, for example, in U.S. Pat. No. 2,941,966. Water dispersible
carbodiimides can be formed by the addition of hydrophilic polyamines or polyols
and carbodiimides containing isocyanate groups, by reacting the reactants in the
presence of from 0.01 to 3% by weight, based on the reaction mixture, of a Sn
catalyst as is taught in U.S. Pat. No. 4,321,394. The re-arrangement products can
be produced at temperatures as iow as 25-150° C, using such catalysts as
tin(II)acetate or dibutyl tin diacetate. The hydroxyl-bearing compounds are preferred
hydrophilic groups and include polyols containing from 2 to 8 hydroxyl groups, and
especially those having a molecular weight in the range from 800 to 10,000.
Exemplary polymeric polyols include for example, polyesters, polyethers,
polythioethers, polyacetals. Hydrophilic polyfunctional carbodiimides containing
hydrolyzabie silane groups with polyfunctional carbodiimides, are also suitable,
especially for aqueous coating embodiments in accordance with the invention as are
taught in U. S. Patent 5,258,481.
[0174] Examples of suitable carbodiimide compounds used in the present invention
are N,N'-dicyclohexylcarbodiimide, 1 -ethyl-3-(3'-dimethylaminopropyl)carbodiimide,
N-ethyl-N'-(3-d!methylaminopropyl)-carbodiimide, N'-diisopropyl-carbodiimide, N'N'-
di-tert-butylcarbodiimide 1-cyclo-hexyl-3-(4-diethylaminocyclohexyl)carbodiimide,
1,3-di-(4-diethylaminocyclo-hexyl)carbodiimide, 1 -cyclohexyl-3-
(diethylaminoethyl)carbodiimide, 1 -cyclohexyl-1 -cyclohexyl-3-{2-morphonlinyl-(4)-
ethyl)carbodiimide 1-cyclohexyl-3-(4-diethyl-aminocyclohexyl)carbodiimide, and the
like. There are a variety of commercially available solvent soluble and water
dispersible carbodiimides. Carbodiimide compounds are commercially available
from Union Carbide Corp., USA under the UCARLNK® designation.
(C) CARRIER LIQUID
[0175] The coatings are applied in a carrier liquid. A carrier liquid can be either one
or more organic solvents, or water, predominantly, although minor amounts of one
can be contained in the other for introducing materials, ?-solvating, dispersing, such
that, the carrier can comprise a minor proportion of solvent, or ?-solvent along with
a major proportion of water, as an example. The coating compositions of the present
invention are preferably applied to an elastomeric substrate in the form of a solution
using one or more organic solvent carriers. For the purposes of the present
invention, the term solvent can broadly be defined as a carrier for the other
components of the composition, wherein the solvent is capable of dissolving or
maintaining the component in a substantially dispersed state or mixture. Preferred
solvents include water based latexes and/or non-HAP (Hazardous Air Pollutant) or
non-VOC, or non-HAP, non-VOC organic solvents.
[0176] Non-HAP solvents include methyl acetate, n-butyt acetate, t-butyl acetate,
acetone, ethyl acetate, isopropyl acetate, isobutyt acetate, tetrahydrofuran, n-methyl
pyrrolidone, aliphatic hydrocarbons such as heptane, dimethylformamide, diisobutyl
ketone (DIBK), methyl isoamyl ketone, monochlorotoluene, para-
chlorobenzotrifiuoride (PCBTF), and vm&p naphtha. A combination of acetone and
DIBK is the preferred non-HAP solvent mixture. Acetone, methyl acetate, and para-
chlorobenzotrifluoride (PCBTF) alone or in any combination are the preferred
solvents for HAP, and VOC compliant coatings. Among the HAP solvents which are
photochemically reactive in the atmosphere are hexane, xylene, toluene, MEK, and
MIBK. Toluene, xylene, MEK and MIBK are the preferred solvents when HAP and
VOC compliance is not critical.
[0177] One such category of solvent useful as the carrier vehicle for the coating
composition of the present invention can essentially be any organic solvent or other
material known to dissolve acrylonitrile-butadiene copolymers. Examples of organic
solvents useful in the present invention include ketones such as methylethyl ketone,
methylisobutyl ketone, and diisobutyl ketone; acetates such as butyl acetate;
toluene, xylene and their derivatives; nitropropane; and ethylene dichloride.
[0178] The organic solvent of solvent-based embodiments according to the
invention is typically utilized at about 70% to about 97% by weight of the total coating
composition (solvent, functionalized HNBR, curing component, thermal conductive
particles and optional components. Preferably solvent comprises from about 85% by
weight to 95% by weight. Accordingly the coating composition has a total nonvolatile
solids content ranging from about 3 to about 30% percent, and preferably from about
5 to about 15%.
[0179] Often, it is highly desirable and environmentally advantageous to utilize water
as the carrier. The invention is enabled by utilization of latex polymers prepared by
emulsion polymerization as well as aqueous converted dispersions of polymer solids,
as follows. A solid bulk elastomer film former can be converted to a dispersion by
dissolving in a suitable organic solvent or mixture of organic solvents. EExamples of
organic solvents include, but are not limited to, any of the organic solvents listed
above, and preferably methyl ethyl ketone, methyl isobutyl ketone, and methyl
isopropyl ketone. The solvent, which can be a solvent mixture, preferably has a low
water-solubility and optionally forms an azeotrope with water at a solvent content of

more than about 50%, or a boiling point below about 95ºC, and at least below the
boiling point of water. The polymer solution as continuous phase is treated by
introducing a surfactant, followed by addition of water. Mixing techniques known in
the art can employ anionic, cationic, nonionic, or amphoteric emulsifiers, including
mixtures. The aqueous organic solvent mixture is mixed under high shear and a
phase inversion takes place wherein water become the continuous phase. The
solvent is stripped off, typically by heating below the boiling point of water, and
generally below 95ºC. The curing component and additional components, if any, are
added to the latex, preferably shortly before coating.
[0180] An example of a further suitable procedure for preparing an aqueous based
latex of a X-HNBR rubber is described in U. S. Patent No. 4,826,721, herein
incorporated by reference. The rubber component is dissolved in a solvent such as
3-chloro-toluene. An emulsifier such as abietic (rosin type) acid derivatives and
dehydro abietic acid derivatives is also added. Water was also added to the
composition. The composition was emulsified and subsequently the solvent is freed
utilizing rotary evaporation, preferably under reduced pressure. X-HNBR latex is
also available from Nippon Zeon of Japan. The aqueous latex coating compositions
employed according to the present invention generally have solids content 30 to 50
percent by weight.
[0181] The emmissive coating compositions of the present invention cure to form
substantially clear or transparent matrix elastomer. The transparency is essential in
order to provide transmission of incident radiant heat to the underlylng thermally
conductive metallic particles, which emit heat back through the coating surface.
Rather than conducting heat into the coated substrate, a surprising level of heat
reflectance was observed in monitoring the temperature below the surface of the
article. This emissive property is observed even for low surface area shaped
substrates, although the reduction in substrate temperature is expected to be also
directly proportional to the ratio of surface area to volume of the underlylng shaped
article.
[0182] At a low level, optional tinting compounds such as dyes or organic pigments
can be incorporated. Colored coatings provided in accordance with the invention
provide outstanding color and coating physical properties for long-term weathering
uses. An extensive list of organic pigments suitable for adding to emissive for
tinting can be found in the current volume of the Rubber Blue Book, published by
Lippincott & Peto Publications and well known to those versed in the art of
formulating elastomers. Organic colors as typically used, can be incorporated for
different coloring effects. The non-pigmented organic colorants leave the coating
transparent but with a color or shade.
[0183] inorganic metal oxide pigments, especially micronized (diameters of 0.5
microns or less) can be included at up to 2.0 weight parts per 100 parts by weight
of elastomer film former, e.g., titanium is possible without interfering substantially
with the emissive properties of the coating can be used. Pigments can be mixed
into the solid polymer using a Banbury mixer or a two-roll mill. The rubber containing
the pigment is then dissolved in the solvent. Alternatively, the pigment may be
dispersed in the liquid solvent and then added to the solvated polymer blend. This is
the preferred method for adding aluminum flakes. An exemplary solvent dispersion
of aluminum flake comprises 50 parts of aluminum flake and a blend of 55 parts
ethylene glycol and 45 parts ethylene glycol monobutyl ether.
Metal Conductor Particles
[0184] In the embodiment coatings which further contain heat emissive properties,
a minimum surface coverage in the coating is essential in order to provide effective
emissive properties. The term "particles" is inclusive of irregular shapes, granular
shapes, leafy shapes or complex assorted shapes. Heat reflective pigments are
available in many forms, as fine-grain solids, or leafs, in dry powder form or
dispersion or as pastes in solvent or plastieizer, e.g., mineral spirit. Flakes derived
from finely divided vapor deposited films are suitable. Thermally conductive metal
particles include finely divided irregular particles, or leafy particles of brass, titanium,
silver, or aluminum. Included are metal-coated particles/metal coated films which
are preferably introduced as leafing or non-leafing aluminum flakes. Leafing flakes
such as leafing aluminum particles or flakes are available commercially with a
coating, e.g., stearic acid, and when applied to a surface, the particles orient in an
interleaved structure parallel to the surface of the finished emissive coating. Metallic
particles of a particle size average of 5 to 25 urn employed at a level of at 10 to 100
parts by weight per 100 parts by weight of film forming elastomer when cast in a thin
film of 5 mils (0.01 cm.) provide effective radiant energy emmissivity and yet provide
sufficient flex-fatigue resistance in the coating so as to not undergo stress-cracking.
Stress cracking causes loss in emissive performance. Metal particles having an
average particle size of 25 to 100 microns must be employed at a level of at least 20
parts and up to 150 weight parts per 100 parts by weight of film former to provide
sufficient radiant heat emissivity without stress cracking. Aluminum flakes are
typically available in an average particle size of less than about 300 microns in
diameter. The maximum diameter of the metallic particles with high aspect ratio is
rather indeterminate with two major dimensions (width and length) and one minor
dimension (thickness) which may be multiples or orders of magnitude smaller than
the two major dimensions. Reliance is on supplier specifications to characterize the
average particle size. Preferably, aluminum flakes have a number average particle
size of about 1 to about 100 microns, more preferably between 5 and 60 microns,
and still more preferably between 10 and 45 microns. Preferred aluminum particles
are flakes of a size such that 99.9% pass through 325 mesh screen, i.e., a diameter
of less than about 45 microns, most preferably from 8 and 35 and especially from 10
and 20 microns in average particle size.
[0185] The leafing metal flakes can be introduced as a dry flake rather than the
paste of aluminum and solvents having at least about 40 wt-% aluminum flake and
more preferably about 60 to 70 wt-% aluminum flake as described in U.S. Pat. No.
5,045,114. The metal particles are employed in the aforementioned quantity in
relation to the film forming polymer in order to exhibit emissive performance. The
preferred amount of metal particles is in a range of from 15 to 30 parts by weight per
100 parts by weight of film former. This proportion of includes consideration of
surface additives, e.g., surfactants, or adhesion promoter, e.g., silanes.
[0186] The coating composition of the present invention may contain other optional
ingredients such as, a nitroso compound, ZnO, and QDO, maleimides, antioxidants
and sub-micron sized particulate reinforcements. The total amount of optional
additive shoud not exceed about 15 parts per 100 parts of the functionalized film
forming polymer. Specific examples of particulate reinforcements useful in the
invention include precipitated silica, and fumed silica. Flatting agents, which are well
known to the art, can be utilized in effective amounts to control the gloss of the cured
coating and include, but are not limited to, silicates. Optional silica having a particle
size less than 700 nanometers, more typically from 20 to 200 nanometers. Sub-
micron-sized particulate reinforcement does not affect the transparency of the film
former to any noticeable effect on reducing the emissive properties of the coating
and may be utilized in various amounts not to exceed 20 parts per 100 parts by
weight of the functionalized elastomer film forming polymer.
[0187] The coating composition may be prepared by simply mixing the ingredients
by hand with a spatula or the like or by mechanical mixing or shaking. The coating
composition is typically applied to an elastomeric material and/or other substrate by
dipping, spraylng, wiping, brushing or the like, after which the coating is allowed to
dry for a period of time typically ranging from about 30 minutes to 2 hours, preferably
from about 45 minutes to 1 hour. The coating composition is typically applied to form
a dry layer on the substrate having a thickness ranging from about 0.1 to 5 mils (2.54
l^m - 127 jim), preferably from about 0.5 to 1.5 mils (12.7 - 38.1 u.m). In the cured
state unsupported or supported coating films can elongate at least 100% of the
original length, and preferably can elongate up to 200%, more preferably up to 300%
without cracking.
[0188] The coating compositions can be applied to substrates which have been
vulcanized or to un-vulcanized or uncured substrates and ?-cured therewith, at
elevated temperatures if necessary.
[0189] The gloss of the cured coated substrate which does not significantly reduce
transparency therefore can be manipulated at least by utilizing different amounts of
solvent, controlling the evaporation rate and/or incorporating various known
pigments and/or flatting agents. It has been found that with respect to organic
carrier-based coatings, a relatively quick or rapid evaporation produces a flatter or
less glossy surface than a more prolonged cure rate. The cured coatings of the
present invention can impart to a substrate a gloss generally from about 3% to about
70% at a 60 degree angle when measured using a Byk-Gardner Micro TRI
Glossmeter per ASTM D-523 and D-2457. The desirability on the gloss wiil vary
according to the use, with camouflage colors being desirable at low gloss levels and
decorative coatings being desired at medium to high gloss levels. For example, the
coating compositions can be beneficially utilized to impart an aesthetically pleasing
appearance to a tire sidewall, such as a "metallic wet" look. The resulting gloss of
the cured coating can be effectively controlled to produce a desired surface, finish, or
appearance on a substrate.
[0190] The coating composition will cure within about 2 to 24 hours in ambient air
conditions, including room temperature. The cure can be accelerated by exposing
the coating to elevated temperatures, but this is not required.
(D) Flexible Substrates
[0191] Coating compositions of the present invention are able to coat flexible
substrates, such as the myriad molded elastomeric materials in pre-cured or post-
cured condition. The coating is applied to the entire exterior surface thereof. The
coating compositions can be applied to shaped or molded articles such as those
made from thermoplastic vulcanizates or thermosettabie rubber. The coating
composition of the present invention is particularly suitable for coating cured rubber
engine mounting devices which are comprised of vulcanized elastomeric parts that
have been bonded to metal parts.
[0192] An engine mount structure, comprises a base layer formed from natural
rubber, optionally bonded to and/or formed around one or more metal mounting
members such as for securing with bolts to the vehicle structure and the engine
housing. The base layer is susceptible to degradation caused by heat, oxidation,
ozone attack or ultraviolet radiation. The emissive coating is sprayed or dipped and
conforms to the contours of the mount where applied and allowed to fully cured after
being applied to said base layer, wherein the emissive coating is applied to the base
layer such that the operating or equilibrium temperature internal to the rubber portion
of the mount, when placed in service, is reduced by at least 30 °F (16°C), more
preferably at least 50°F (27 °C), and most preferably at least 75°F (41.6 °C).
[0193] The preferred emissive coating compositions are particularly effective as
coatings on cured elastomers that have limited oil and solvent resistance. Such
elastomers include natural rubber, styrene butadiene rubber, polybutadiene rubber,
ethylene propylene and ethylene propylene diene rubber, polylsobutylene-isoprene
rubber, polychloroprene, low acrylonitrile content (< 35 wt.%) nitriie-butadiene
rubbers; and the like. The coating composition may also be used over rigid
substrates such as metals, plastics, ceramics, and composites. Examples of
thermoplastic and/or thermosetting substrates include, but are not limited to, flexible
polyvinyl chloride, PVC-elastomer alloys, like PVC-Nitrile; adhesion promoted or
modified polyolefins such as compounded polyethylene and polypropylene; flexible
polyesters like PBT, flexible or rubbery polyurethane-, polyurea-, polyurea- rim; fiber
reinforced flexible plastics, and cellular vinyl and polyurethane. The coatings are
particularly useful for bonded rubber mounts which contain both elastomeric and
rigid components. A substrate is considered flexible if the elongation of the substrate
material is greater than 25%.
[0194] Further examples of commonly available flexible substrates which can be
coated with the compositions of the present invention include, but are not limited to,:
tires, bumpers, wiper blades, vibration isolators, rubber mounts, rail track pad
fasteners, helicopter rotor bearings, chassis mounts, wiper frames, gaskets, heels,
shoe soles, printing rolls, belts, hoses, fuel tanks, rubber moldings, TPO or TPE
molding, facias, and flexible engineered rubber products. In addition to emissive
properties the coatings provide improved resistance to oils, solvents, oxygen, ozone
and UV light.
[0195] The coating composition of the present invention can be applied to one or all
sides of a substrate. It is to be understood that occasionally it may be effective for
heat dissipation to only coat one side or surface of a substrate which is oriented to a
heat source. As stated above, it is advantageous to coat the surfaces of a substrate
which are exposed to light, air, oils, and solvents. Obviously, surfaces of a substrate
which are not in contact with the same do not necessarily have to be coated. The
coating preferably is a continuous coating in film form which completely covers the
intended surface of a substrate. The coating is of the aforementioned thickness to
cover the desired surface to be protected, but not overly thick-to materially alter the
mechanical properties of the substrate.
[0196] Tire(s) can be coated with a composition of the present invention. It is to be
understood that the coating compositions can be utilized to cover the entire outside
and/or inside surfaces of a tire. Furthermore, it may also be desired to only coat
certain portions of a tire such as the sidewall, tread or the like. Tires generally
comprise a tread, a pair of sidewalls which abut the tread in the shoulder regions, a
fabric reinforced rubber carcass of generally toroidal shape and one or more plies for
supporting the tread and sidewalls, and a circumferential fabric reinforced belt of one
or more plies, positioned between the carcass and the tread. Tires generally also
include a pair of circumferentially extending bundled wire beads which are
substantially inextensible, wherein the carcass extends from one bead to the other
and the side edges may be wrapped around the beads as shown. Tires may also
include a pair of apex components, preferably of a stiff construction and having a
triangular cross section in the region of the beads, and a pair of stiff chaffer
components which are positioned in the bead region. The above listed components
of the tire are conventional, but it is to be understood that additional parts not listed
may be included and parts listed above may be omitted. Tires may also include an
inner liner which can be applied to the inner surface of the tire to improve air
impermeability. Any tire component or components can be coated with the
compositions of the present invention. Preferably, the tread and/or sidewall regions
are coated.
PREPARATION OF ELASTOMER SUBSTRATE FOR COATING
[0197] The elastomeric surface or substrate to be coated may optionally be
pretreated with a chlorinating agent such as sodium hypochlorite and hydrochloric
acid. The use of various chlorinating agents to prepare elastomeric materials for
application of a coating composition is well known in the art. One example of a
chlorinating agent is commercially available from Lord Corporation under the
CHEMLOK® mark such as 7701. The chlorinating agent may be applied to the
surface of the elastomeric material by brushing, dipping, spraylng, wiping, or the like,
after which the chlorinating agent is allowed to dry. Chlorinating agents tend to be
very volatile and typically dry within a matter of seconds or minutes.
[0198] The coating compositions of the present invention have the surprising ability
to form a tenacious bond to flexible elastomeric parts alone, and also to metal
components where these are affixed adjacent to the elastomeric part. It is desirable
to provide the elastomeric coating over both elastomer and metal so that the
boundary between the elastomer and metal can be adequately protected by the
coating composition. The present invention is therefore distinguished from many
traditional protective coating compositions which only have the ability to bond to one
type of substrate to be protected.
[0199] The following examples are provided for purposes of illustrating the present
invention and shall not be constructed to limit the scope of the invention which is
defined by the claims.
[0200] Example 1
[0200] The following example was prepared using Zetpol 2220, an X-HNBR polymer
produced by Zeon Chemical having a 36% acrylonitrile content with 5 mol percent
unsaturation. A suitable commercial substitute is Therban® KA 8889.
[0201] An elastomer coating solution was prepared as follows:

X-HNBR carboxylated hydrogenated nitrile-butadiene 100.0
[0202] This formulation was dissolved in Methyl Isobutyl Ketone (MIBK, CAS No.
108-10-1) to a solids content of 12.0% by weight.
[0203] To 40 grams of solution, of bis-[isocyanatopheny] methane (diisocyanate),
53% in xylene was added at 0.1 g, 0.5 g and 1.0 g levels. At 0.1 g. diisocyanate
level, the solution cured at room temperature in less than 16 hours. At 0.5 g, the
solution cured in 30 minutes.
[0204] To 40 grams of solution, 3-isocyanatopropyltriethoxysilane, CAS # 24801-88-
5, was added at 0.3, 0.7, 1.0, and 1.3 gram quantities. At all levels, the coating
composition starts to cure within 45 minutes to one hour and was fully cured in less
than 16 hours.
Fuel Resistance Testing
[0205] The coating were tested on a 55 durometer natural rubber compound
(A135Q) which had been treated with Chemlok® 7701. The coating was then
compared against commercial fluorocarbon coating PLV-2100, and a commercial
HNBR SPE XV coating taught according to US patent 5,314,955 and an uncoated
control.
[0206] When immersed in Jet A fuel for 24 hours at room temperature, the following
volume % swell results obtained are:
Control Uncoated 192.9%
Control PLV 2100 0.1%
Control HNBR SPE XV 33.6%
Example Coating with bis-[isocyanatopheny] methane 2.2%
Example Coating with 3-isocyanatopropyltriethoxysilane 2.3%
ADHESION TESTING
[0207] Rubber adhesion was tested by bonding two one-inch-wide strips together,
and by pulling in a 180° peel. The rubber strips were made from a 55 durometer
commercial natural rubber compound (A135Q) which had been treated with
Chemlok® 7701. An approximate two-inch-long section was coated; each strip was
placed in contact with each other and a 472g weight applied to ensure intimate
contact. The weight was left in place for ten minutes. After 8 days drylng time, each
strip was pulled apart in the Tinius Olsen® tensile tester. The following table records
the results.

[0208] Metal adhesion was tested in shear by bonding a one-inch wide rubber strip
to a one-inch metal coupon with one square inch of overlap. The rubber strips were
made from a 55 Durometer natural rubber compound (A135Q) which had been
treated with Chemlok® 7701, The metal coupons were 304 stainless steel.
Stainless was chosen because it is known to be a difficult substrate to bond to. After
coating, each was placed in contact with each other and a 472g weight applied to
ensure intimate contact. The weight was left in place for ten minutes. After 8 days
drylng time, each specimen was pulled apart in the Tinius Olsen tensile tester.
Coating Type Adhesion Results, psi
Control PLV 2100 16.78
Control HNBR SPE XV 19.23
Example Coating with bis-[isocyanatopheny] methane 18.2
Example Coating with 3-isocyanatopropyltriethoxysilane 18.5
Ozone Resistance
[0209] Ozone testing was done using a dynamic ozone test (ASTM-D3395) at 50
pphm ozone at 104 °F (40 °C).
[0210] Specimens were based on a 55 durometer commercial sulfur-cured natural
rubber/polybutadiene blend protected with antiozonant wax and an alkyl-aryl
phenylene-diamine antiozonant (M122N). Under dynamic conditions, it appears that
the carboxylated hydrogenated coating is more effective as an ozone barrier than the
HNBR coating SPE XV.
Elapsed time until initial cracking:
Control Uncoated 6.5 hrs.
Control HNBR SPE XV 6.5 hrs.
Example 1 Coating with bis-[isocyanatopheny] methane was uncracked at 28 hrs.
Example 1 Coating with 3-isocyanatopropyltriethoxysilane was uncracked at 28 hrs.
[0211] Besides having low adhesion values, the PLV 2100 coating cracks and
delaminates from the rubber surface after flexing. Unpierced DeMattia flex
specimens (made from a 55 durometer natural rubber compound) were coated with
these same coatings and flexed in accordance with ASTM D-813. The PLV-2100
coating was severely cracked and delaminated, exposing the substrate in less than
4000 cycles. Both the baked HNBR SPE XV and Example 1 ran 80,000 cycles at
which point the natural rubber substrate was cracked. There was no sign of
delamination in either of the Example coatings. This base formulation when
provided with the effective amount of thermal conducting metaiiic exhibits as good
performance as tested above and further provides emissive properties.
[0212] Example 2
The following example was prepared using an X-HNBR polymer available from
Bayer AG under the Therban® mark as Therban® KA 8889.
An elastomer coating solution was prepared as follows:

X-HNBR carboxylated hydrogenated nitrile-butadiene 100.0
[0213] This formulation was dissolved in Methyl Isobutyl Ketone (iVHBK, CAS No.
108-10-1) to a solids content of 15.0% by weight
33 phr of aluminum flake having an average particle diameter of 16 microns were
added to the coating solution.
[0214] To 97.5 wet wt. parts of solution, 2.5 wet wt. parts of bis-[isocyanatopheny]
methane (diisocyanate)(Casabond® TX, 53% in xylene) was added.
[0215] A cured block of natural rubber 3" x 3" x 0.5" (7.6 cm.x 7.6 cm x 1.2 cm)
having a Durometer A of 65 was coated to a dry film thickness of about 1 mil.
[0216] A hole was drilled 1.5 in. (3.8 cm.) and a thermocouple inserted for
monitoring temperature in the center of the block. The block was placed under a 250
watt infrared lamp, suspended 8" (20 cm. From the rubber block. The control block
was uncoated. Temperature recordings were made using a Cole-Parmer Dual J-T-
E-K Thermocouple Thermometer Model 91100-40 at the time intervals below.
[0217] The uncoated specimen began smoking within the first 10 minutes of
exposure to the heat source.
[0218] DeMattia Flex specimens were coated with the coating material used ii
example 2 in accordance with ASTM D-813, After 77,000 cycles with no signs c
cracking or delamination were observed in the coating. Cracks occurred in th<
rubber substrate and coating was split where the substrate crack occurred
Adhesion was excellent, and failure only observed in the underlylng substrate
indicates that the maximum level of coating integrity is obtained.
[0219] The results illustrated in FIG. 1 represent a repeat of Example 2 coated
specimen with a 16 inch, 3 speed fan running at low speed, blowing across the
specimens from 9.5 feet away and the infra-red lamp positioned 4 inches from
specimens. Under air movement simulating actual automotive
[0220] Example 3 - Functionalized HNBR Water Based Latex
Water based functionalized HNBR latexes were prepared according to the present
invention. A 41% solids carboxylated-HNBR latex, 404EXPLTX005 also sold as
Latex B from Zeon Chemical was utilized. The following compositions were
prepared.
2 Bayhydur® 302 (1,6-HDI) available from Bayer Corporation
[0221] DeMattia Flex specimens were sprayed with the latex/isocyanate combination
as listed above. The DeMattia specimens were wiped with MIBK and treated with
Chemlok® 7701, and the coating was applied to the specimens by spraylng. All
specimens ran 80,000 cycles with no signs of cracking or delamination. Adhesion is
excellent.
[0222] Ozone testing was done using a dynamic ozone test (ASTM-D3395) at 50
pphm ozone at 104 °F.
[0223] Specimens were based on a 55 durometer commercial sulfur-cured natural
rubber/polybutadiene blend protected with antiozonant wax and an alkyl-aryl
phenylene-diamine antiozonant (M122N). Observations were made at 2 hour
intervals.
Time to observed edge cracking
A. uncoated control 4.0 hrs.
B. coated with Chemisat® LCH7302X, a non-functionalized HNBR
2 hours
C. coated with Chemisat® LCH7302X non-functionalized HNBR with 5.0 parts per
hundred by weight of Bayhydur® 302 (1,6-HDI))
4.0 hours
D. coated with Carboxylated HNBR 404EXPLTX005
10 hours
E. coated with carboxylated Latex 404EXPLTX005 with 5.0 parts per hundred by
weight of 1,1,6-HDI
22.0 hours
Chernisat® LCH7302X is an HNBR Latex currently produced by Zeon Chemical,
formerly produced by Goodyear Chemical Company.

[0225] Alglo® 400 and the aluminum paste 586 are supplied by Toyal America, Inc.
and the Stapa® Metallux 214 is supplied by Eckart Amerlba L P. Aluminum Paste
565 and Stapa® Metallux 2156 were also used. Both leafing and non-leafing
aluminum pigments of varylng particle sizes may can be used to obtain different
visual effects. The compounded elastomers were each dissolved in solvent to 10%
solids content. They were readily blended with tinting colorants to different tinted
shades conventionally according to the known art of color matching. On the other
hand, a mixture of 90% Silver 3 and 10% green gives a silver color with a hint of
pastel green.
[0226] A blend of copper conductive powder from Caswell with silver2 (Example 4F)
gave a metallic gold color.
[0227] Example 5 - CONTROL
A control example using a coating cured according to U.S. Pat. No. 5,314,741 of
hydrogenated copolymer of acrylonitrile and butadiene in organic solvent using zinc-
sulfur curing as taught therein was applied to a peroxide cured natural rubber
substrate.
Coating Composition

[0228] The ingredients except HNBR were mill mixed and then dissolved to a 10%
solution in MIBK solvent. The coating composition was prepared by mixing the solid
rubber on a two roll mill followed by dissolving HNBR in solvent One inch wide
specimens of sulfur-cured natural rubber sheet were washed with isopropyl alcohol
prior to applylng the coating composition.
[0229] The coating composition was applied to the surfaces of the natural rubber
substrate specimens. The coating thickness was approximately 1 mil dry. Two
coated, uncured strips were placed together with the coated sides against each
other. The coatings were dried for 24 hours at room temperature. Some of the
specimens were baked in an oven for fifteen (15) minutes at 307° F (152°C) to cure
the coatings. This gave as the product coated natural rubber tensile sheets having
thereon coatings, approximately 2 mil thick and bonded together. The bonded
specimens were pulled apart in peel and the force required to separate them was
recorded.
Uncured coating (dried but not baked) 0.6 lbs peel strength
Cured coating (baked 15 minutes at 307F) 1.9 lbs peel strength
[0230] These adhesion levels to the rubber substrate as cured and uncured coatings
are unacceptably low and result in flex fatigue and cracking on elastomer substrates
subjected to flexing.
[0231] Examples 6
A clear base coating was made by dissolving X-HNBR elastomer (Therban KA-8889
from Bayer AG) in MIBK to a solids content of 5% by weight. To 99.25 wet wt. parts
of solution, 0.75 wet wt. parts of bis-[isocyanatopheny] methane (diisocyanate), 53%
in xylene (Casabond TX,) was added. Thermal conductive aluminum pigments
were added to the clear coating solution in various weight percents based on the
weight of the polymer.
[0232] Cured blocks of natural rubber 3" x 3" x 0.5" (7.6 cm.x 7.6 cm x 1.2 cm)
having a Durometer A of 65 were coated to dry film thickness of about 1 mii (0.0004
cm).
[0233] Holes were drilled 1.5 in. (3.8 cm.) into the center of the block and
thermocouples were inserted for monitoring temperature in the center of the block.
The blocks were placed under a 250-watt infrared lamp, suspended 4" (10 cm.) from
the rubber block. The control block was uncoated. Temperature recordings were
made against time using a Cole-Parmer Dual® J-T-E-K Thermocouple Thermometer
Model 91100-40. No fan was used in this experiment.

[0234] Example 6A
STAPA® Metallux® 2156 (Eckart America LP.) ) 70% solids, non-leafing, 16
micron avg. dia.
Coated Rubber Block using STAPA Metallux 2156
10phr 20phr
[0238] Example 7
Three similar coatings were made using a fluoroelastomer, a water based XHNBR
latex, and a polyurethane, respectively. The fluoroelastomer base coating was made
by mixing the following formulation and then dissolving it in MIBK to a solution having
a solids content of 30%.
[0239] Example 7A
Viton® A-100 (DuPont) 100.0 PHR
Magnesium Oxide (Maglite D) 1.0
Calcium Hydroxide Technical Grade 2.0
Metallux® 2156 (Eckart America LP.) 10.0
Aluminum Paste 586 (Toyal America) 5.0
To 120.0 grams of the dissolved solution, 1,8 grams of N-(2-
hydroxyethyl)ethylenediamine was added. After 4 hours, 5.0 grams of 3-
isocyanatopropyltrie^hoxysilane was added along with an additional 25 grams of
MIBK.
[0240] Example 7B
The XHNBR Latex was made by starting with Latex B from Zeon Chemical (41%
solids content). To 100.0 grams of Latex B, 20.0 grams of Sparkle Silvex® 760-20-A
(Silberline®) and 5.0 grams of the water dispersible polylsocyanate Bayhydur® 302
(Bayer) were added.
[0241] Example 7C
The polyurethane was made by adding 7.0 grams (21.8 phr on urethane solids) of
Aluminum Paste 586 (ex. Toyal America) to 100.0 grams of Chemglaze® V021
clear, moisture curable polyurethane at 32% solids by weight, having a viscosity of
115 cps, a cured Tgof below 0°C, and cured tensiie strength of approx. 3000 p.s.i.
with 350% ultimate elongation.
[0242] Cured blocks of natural rubber 3" x 3" x 0.5" (7.6 cm.x 7.6 cm x 1.2 cm)
having a Durometer A of 65 were coated to dry film thicknesses of about 1 mil using
the coatings of examples A, B and C.
[0243] Holes were drilled 1.5 in. (3.8 cm.) into the center of the tested blocks and
thermocouples were inserted for monitoring temperature in the center of the block.
The blocks were placed under a 250-watt infrared lamp, suspended 3" (7.5 cm.) from
the top surface of the rubber block. The control block was uncoated. Temperature
recordings were made at against time. The surface temperature was monitored
using an Omegascope® Model OS530 Series non-contact infrared thermometer.
The internal temperature was monitored using a Cole-Parmer Dual J-T-E-K
Thermocouple Thermometer Model 91100-40. No fan was used in this experiment
[0244] The results comparing the surface temperature of the uncoated control and
coated specimens based on Example 7A, 7B and 7C are graphically illustrated in
FIG. 6
[0245] Example 8
Room temperature curable reflective coating formulations were made as follows:

[0246] KBM 7803 is Heptadecatrifluorodecyl trimethoxysilane CF3(CF2)
7CH2CH2Si(OCH3)3 and is commercially available from Shinetsu Silicones.
A 6"x6"x0.75" natural rubber pad (65 durometer) was coated with each of the
coatings. After the coatings were cured, they were exposed to an infrared lamp
suspended 6" above the coatings. The surface temperature was monitored using a
Cole-Parmer® Dual J-T-E-K Thermocouple Model 91100-40 at the time intervals
indicated below. Immediately after exposure, the pads were subjected to heating in
an oven at 350°F for 7 more minutes to accelerate discoloration.

Discoloration- aging at 350°F/175 °C: Severe Minimal
[0248] Emissive coatings based on hydrolyzable mixture of aminoalkyl
trialkoxysilane and fluoroalkyl trialkoxysilane demonstrate rapid cure and reduced
discoloration after heat aging.
[0249] While in accordance with the patent statutes the best mode and preferred
embodiment have been set forth, the scope of the invention is not limited thereto, but
rather by the scope of the attached claims. -
1. An ambient temperature curable, 2-part liquid coating composition
comprising in one part (a) a flexible film-forming polymer exhibiting a Tg of
lets than 0ºC and incorporated therein a functional group which is reactive to
an active hydrogen containing curing agent, or said fonctional group is an
active hydrogen-bearing group, said polymer containing less than 10%
ethylenic unseturetion, and in another of said 2-parts, a curing component
reactive with the functional group of the film forming polymer and comprising
at least one group selected from aminofuncttonal silanes, roercapco-unctionat
snanes, hydroxyalkyl group containing silanes, hyfroxysilenes, amties, sayl
ether, melefitids, and carbodiimidos end a carrier liquid.
2. The composition as claimed in claim 1 further comprising and (a)
from 10 to 100 parts by weight per 100 parts by weight of Mm forming
polymer of thermeHy conductive metal particles having e particle size average
of from 2 to 10 urn or (b) from 20 to 150 parts by weight of thermal
conductive particles having an average particle size of 20 to 60 microns.
3. The coating as cleaned in claim 1 wherein said film former is a
hydrogenatad random or block dlene copolymer having a molecular weight of
about 20,060 to 200,000.
4. The coating as cleaned in claim 1 wherein said film forming polymer
is carboxylated HNBR.
5. The coating as claimed in claim 1 wherein the film forming polymer is a
functionelized acrylic rubber.
6. The coating as claimed in claim 1 wherein said film former is derived
from an ethylenically-unsatureted monomer and an a,ß- unsaturated
carboxylk acid.
7. The coating as claimed in daim 1 wherein said functional group on said
film forming polymer is selected from the group consisting of sulfonic acid,
sulfonic acid derivatives, chlorosulfonic acid, vinyl ethers, vinyl esters, primary
anunes, secondary arrunes, ternary amines, mono-carboxylicc acids,
dicarboxylic adds, partially or fully ester derivatited mono-carboxylic acids,
partially or fully aster derivetized dicarboxylk acids, anhydrides of dicarboxylic
acids, cyclic imides of dicarboxzylic acids, ionomeric derivatives thereof, and
combinations thereof.
8. Tha coating composition as claimed in claim 1 whereto said fttrn former is
a hydrogenated diene elastomer comprising methylol functional groups.
9. The coating composition as claimed in claim 6 wherein said film former is
a hydrogenated diene elastomer comprising phenolic methylol functional
groups.
10. The coating as claimed in claim 1 wherein said mm former is the thermal
cracked reaction product of en amine functionlized HNBR with a diaryl
carbonate.
11. The coating as claimed in claim 5 wherein said filrn former comprises a
terporymer of ethylene, C1 -C4 alkyl acrylate and a carboxylic acid monomer
unit.
12. The coating as claimed in claim 5 wherein said film former comprises at
least 30 mole percent of ethylene, and from 10 to about 70 mole percent
mono ethyl maleate.
13.The coating as claimed in cliam 1 wherein said film former is a
carboxylated, block copolymer derived from an elastomer and selected from
the group consisting of hydrogenets d styrene-butadiene-styrene block
copolymers, and hydrogenated styrene-isoprerie-styrene block copolymer.
14. The coating as claimed in claim 1 wherein the film forming elastomer is a
poly a-olefin-ecrylic ester-acrylic carboxylate terpolymer.
15. The coating as claimed in claim 1 wherein said film former is a
hydrogenated nitrite butadiene polymer containing hydroxyl groups.
16.The coating as claimed in claim 1 wherein said Mm former is a mixture of
hydrogenated hydroxyl butadiene and a film former selected from the group
consisting of carboxy modified chlorinated polyethylene, chlorinated
polyethylene, pofyepichiorohydrin, poly ethylene-ecrylic acid, SBR, SSS, NBR,
SIBS, EPDM, EPM, pofyacryletes, hafogenated pofyleobutylene and
polypropylene oxide and wherein the total proportion of unseturation in said
mixture is not more than 10% overall.
17. The coating as claimed In claim 1 wherein said film former comprises
hydroxyl groups incorporeted by freating a hydrocarbon polymer under
ozonizetion conditions to form an ozonized saturated hydrocarbon polymer
followed by reducing the ozonized saturated hydrocarbon polymer.
18. The coating as claimed in clean 1 wherein said film former contains
carboxyl groups incorporated by treating a saturated hydrocarbon polymer
under ozonization conditions to form an ozonized saturated hydrocarbon
polymer followed by reducing the ozonized saturated hydrocarbon polymer.
19. The coating as claimed in claim 1 wherein said film forming polymer
comprises two or more a-monoolefins- and a non-conhugted diene
comonomer and incorporated thereon are functional groups selected from the
group consisting of carboxylic, anhydride, epoxy, phosphoric, sulfonic,
sulfonate, sulfinate, hdyroxy, epoxy, isocyanate, amine and oxazoMne groups.
20. The coating as claimed in claim 1 wherein said film former comprises
hydroxy terminated polyteobutylene prepared by introducing hydroxy groups
into the terminal positions of cationlcally polymerized isobutylene by
dehydrocMorineting, hydroborataig and oxidizing chloro-terminet
poly isobutylene.
21. The coating compostion as claimed in claim 1 wherein said curing agent is
in 2-parts and comprises a redcuction-oxidation curing system comprising a
multifunctional ethylenic unsaturated compound, an oxidizing agent and a
reducing agent.
22. The coating composition as claimed in claim 1 wherein said film former
comprises a chlorinated polyolefin modified with an acid or anhydride group.
23. A method for coating a rnolded elesotmer articles, said article optionally
affixed to a shaped metal article, comprising spraylng, dipping or brushing a
solvent-based, metallic pigment filled, room temperature curing elestemeric
film forming coating to the surface of said molded elestomer article, said
coating comprising a curing agent, at least 10 wt.% of thermally conductive
particles and a film-forming polymer exhibiting a Tg of lees than 0°C and
incorporated therein a factional group which is reactive to an active
hydrogen containing curing agent, or said functional group is an active
hydrogen-bearing group, said polymer containing less than 10% ethylene:
unsaturatton.
24.The method as claimed in claim 23 wherein said elastomer article
comprises an elastomer selected from the group consisting of natural rubber,
styrene butadiene rubber, polybutediene rubber, ethylene propylene rubber,
ethylene propylene diene rubber, potylsobutylene-isoprene rubber,
porychforoprene, and taw acrylonitrite content (<35%) nitrite-butadiene
rubber.

An ambient temperature curable, 2-part liquid coating composition
comprising in one part (a) a flexible film-forming polymer exhibiting a Tg of less
than 0°C and incorporated therein a functional group which it reactive to an
active hydrogen containing curing agent, or said functional group is an active
hydrogen-bearing group, said polymer containing less than 10% ethylenic
unsaturation, and in another of said 2-parts, a curing component reactive with
the functional group of the film forming polymer and comprising at least one
group selected from aminofunctional silanes, mercapto-functional silanes,
hydroxyalkyl group containing silanes, hydroxysilanes, amines, silyl ether,
maleimids and carbodiimides and a carrier liquid.