Field of the invention
The invention relates to a coating composition comprising a radiation grafted
functionalized fluoropolymer. This coating is preferably in the form of a powder
coating. The coating can be used on inorganic substrates, especially un-primed
metals. The invention also relates to the coated inorganic substrate and to the use
of the coating composition to protect the inorganic substrate, especially from
corrosion.
The technical problem
Fluoropolymers, in particular poly(vinylidene fluoride) (PVDF), are used in
applications which require high resistance to heat, high resistance to chemicals
and good barrier properties to liquids and to gases. Thus, they are very useful for
protecting substrates. Furthermore, they have both excellent resistance to ageing,
in particular resistance to ultraviolet radiation, and very good resistance to
abrasion, so that they retain their protective properties for a long time.
However, it is known that fluoropolymers suffer from a problem of adhesion to
certain substrates, in particular metals or glass. The coating made of
fluoropolymer is then capable of becoming detached, which is harmful to the
protection of the substrate. Generally, the problem of adhesion is solved by the
application of a primer layer which has good adhesion to the substrate and which
makes possible binding to the polymer.
In the case of powder coatings containing fluoropolymers, in particular of PVDF,
several systems which make possible attachment of the PVDF to substrates are
known but their effectiveness is reduced because additives having poorer
resistances to heat or to chemical attacks have to be employed. Current
commercial PVDF coatings, that usually refer to a 70:30 mixture of a PVDF
polymer with an acrylic copolymer as resin binder along with other additives and
pigments, require a primer system for optimum adhesion. Yet, primers add an
additional step to the coating process. Furthermore, liquid primers typically contain
hazardous solvents, which can overshadow the environmental benefits of powder
coatings. Though powder primers are available, they still impose an additional
coating step. Powder primers also increase the overall coating thickness, which
may reduce impact resistance and flexibility.
There has been a continuing effort to switch from solvent-based coatings to
powder coatings to take advantage of the environmental, safety and productivity
benefits of a powder coating process. Current PVDF coatings are applied via a
solvent dispersion process. The solvents used are VOC's (Volatile Organic
Compounds), requiring expensive exhaust treatment (e.g. thermal oxidizer units).
Additionally, some solvents are flammable, toxic, and/or hazardous air pollutants
(HAPs). A powder version of PVDF coatings offers many safety and
environmental benefits. Some PVDF powder coating formulations have been
reported in the following documents: US 4770939, 9/13/88, to LABOFINA/SIGMA;
US 5229460, 7/20/93, to EVODEX though none has been commercially
successful to date.
The grafting of a graftable compound to a polymer chain is a well-known operation
which is already employed on a large scale to modify the physicochemical
properties of polymers. Thus, maleic anhydride is grafted to a polyolefin
(polyethylene, polypropylene) in the melt in an extruder. To do this, a radical
initiator, the decomposition temperature of which has to be carefully chosen, is
added to the molten blend. The grafting using a radical initiator to a fluoropolymer
which comprises hydrogen atoms in its structure is much more difficult. Thus, this
explains why the grafting of maleic anhydride to PVDF has not been described to
any great extent. Furthermore, the contents of maleic anhydride grafted to PVDF
are generally low and the grafting efficiency is therefore poor. A large portion of
maleic anhydride therefore remains ungrafted and has to be removed in another
stage. The technique of grafting by extrusion additionally uses high temperatures
and a high shearing which are capable of decomposing the fluoropolymer chains
and of releasing hydrofluoric acid, which may be troublesome if it is not carefully
removed. It has now been found that grafting using irradiation makes it possible to
obtain more efficient grafting than grafting using a radical initiator, and results in
excellent properties of protection from corrosion. The term "radiation grafted
fluoropolymer" is used for simplicity's sake in the rest of the specification for the
fluoropolymer that is modified by radiation grafting.
There is a need for a fluoropolymer coating that offers excellent adhesion to an
inorganic substrate, especially un-primed metals and an excellent protection.
Surprisingly it has now been found that a coating comprising a radiation grafted
fluoropolymer optionally blended with a non-functionalized fluoropolymer and/or
an acrylic polymer offers excellent adhesion to inorganic substrates, especially unprimed
metals, and excellent protection. As an additional benefit, said coating
composition may be in the form of a powder which also offers the advantages of
the powder coating process discussed above.
The present invention relates to a coating composition comprising a radiation
grafted fluoropolymer, preferably in the form of a powder coating composition,
offering a strong adhesion on an inorganic substrate and an excellent protection,
especially from corrosion.
The prior art
Application WO 98/20071 discloses the use of a fluoropolymer comprising an
inorganic filler for improving the protection of metal surfaces from corrosion. No
mention is made of fluoropolymer modified by grafting by irradiation.
Patent EP 0 976 544 discloses a fluoropolymer obtained by copolymerization of a
fluoromonomer carrying a polar group and of a fluoromonomer without a polar
group. This copolymer is used to coat metal, glass or ceramic surfaces. Not only
is no mention made of fluoropolymer modified by grafting by irradiation but the
copolymerization of a specific fluoromonomer requires that the manufacturing
process be adjusted.
Application EP 0 650 987 discloses a fluoropolymer to which a polar compound,
such as maleic anhydride, is grafted. The grafting is carried out in the melt using a
radical initiator. The polymer modified by grafting is applied directly to an inorganic
material after the grafting.
Application US 11/039979 describes an acrylic-modifed polyvinylidene fluoride
coating containing a polyepoxide, that can be applied to un-primed substrates.
In order to improve the adhesion to un-primed substrates, the PVDF coating
includes crosslinking functionality into the composition but at extra expense.
Patent US 6362295 describes an acrylic-modified polyvinylidene fluoride powder
coating is described. The powder can be applied to a substrate both with and
without a primer. The effectiveness of this system is lower than with a radiation
grafted fluoropolymer.
No mention is made, in these documents of the prior art, of a radiation grafted
fluoropolymer which can be used to form a coating on an inorganic substrate.
Brief description of the invention
The invention relates to a coating composition that comprises :
• at least one radiation grafted fluoropolymer
• optionally at least one non-functionalized fluoropolymer
• optionally at least one acrylic polymer.
The coating composition can be in the form in the form of pellets, in the form of a
powder or in solution. Preferably, the coating composition is in the form of a
powder for coating metals without the need tor a primer comprising a blend of:
• at least one radiation grafted fluoropolymer, and
• at least one non-functionalized fluoropolymer.
The invention also relates to a coated inorganic substrate comprising a layer of
the coating composition and wherein no primer is present between the coating
and the inorganic substrate. It further relates to a coated inorganic substrate
having a powder coating composition, directly adhered thereto, wherein no primer
is present between the powder coating and the substrate.
The invention further relates to a process for coating an inorganic substrate
without the use of a primer comprising the steps of:
a), applying on the substrate the powder coating composition; and
b). curing said applied powder coating.
The invention further relates to the use of the coating composition to protect an
inorganic substrate, especially from corrosion.
Detailed description of the invention
French patent application 04.11068 and US patent provisional applications
60/647196 and 60/702110 are all incorporated herein by reference.
The term fluoromonomer refers to an unsaturated monomer of formula (I):
in which X and X' can be, independently of one another, a hydrogen atom, a
halogen, in particular fluorine or chlorine, or a perhalogenated, in particular
perfluorinated, alkyl.
Suitable exemplary fluoromonomers for use according to the invention include, but
are not limited to, vinylidene fluoride (VDF, CH2=CF2), vinyl fluoride,
trifluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP) and
chlorotrifluoroethylene (CTFE). Mention may also be made of, 2-
chloropentafluoro-propene, perfluoroalkyl vinyl ethers, such as CF3-O-CF=CF2 or
CF3-CF2-O-CF=CF2, 1 -hydropentafluoropropene, 2-hydropentafluoropropene,
dichlorodifluoroethylene, trifluoroethylene, 1,1-dichlorofluoroethylene and
perfluoro-1,3-dioxoles, such as those described in US 4558142. Fluorinecomprising
diolefins can be mentioned as well, for example diolefins, such as
perfluorodiallyl ether and perfluoro-1,3-butadiene.
The term fluoropolymer refers to polymer and copolymers (including polymers
having two or more different monomers, such as terpolymers) containing at least
50 mole percent of fluoromonomer units. The polymers and copolymers are
obtained by the radical polymerization of at least one fluoromonomer of formula
(I). Unsaturated olefinic monomers not comprising fluorine, such as ethylene,
propylene, butylene and higher homologues, may also be used as comonomers.
The fluoropolymer is produced by processes known in the state of the art. The
fluoropolymer can be prepared in aqueous emulsion or in aqueous suspension.
The emulsion comprise, for example, a water-soluble initiator, such as an alkali
metal or ammonium persulfate or an alkali metal permanganate, which produce
free radicals, and also comprise one or more emulsifiers, such as alkali metal or
ammonium salts of a perfluorooctanoic acid. Other aqueous colloidal suspension
processes use initiators which are essentially soluble in the organic phase, such
as dialkyl peroxides, alkyl hydroperoxides, dialkyl peroxydicarbonates or
azoperoxides, the initiator being used in combination with colloids of the following
types: methylcelluloses, methylhydroxypropylcelluloses, methylpropylcelluloses
and methylhydroxyethylcelluloses. In particular, patents US 3553185 and
EP 0120524 disclose processes for the synthesis of PVDF by suspending VDF in
water and polymerizing it. Patents US 4025709, US 4569978, US 4360652,
US 626396 and EP 0655468 disclose processes for the synthesis of PVDF by
emulsifying VDF in water and polymerizing it.
Preferably, the fluoropolymer is a PVDF, that is a homo- or copolymer of VDF
containing by weight at least 50% VDF, advantageously at least 75% VDF and
preferably at least 85% VDF. PVDF is preferred as it provides very good chemical
and thermomechanical resistance and it is easily extruded. As regards the PVDF
copolymers, they are obtained through the copolymerization of VDF and at least
one comonomer selected from the group consisting of vinyl fluoride,
trifluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP),
chlorotrifluoroethylene (CTFE), 2-chloropentafluoro-propene, perfluoroalkyl vinyl
ethers, such as CF3-O-CF=CF2 or CF3-CF2-O-CF=CF2, 1-
hydropentafluoropropene, 2-hydropentafluoropropene, dichlorodifluoroethylene,
1,1-dichlorofluoroethylene and perfluoro-1,3-dioxoles, such as those described in
US 4558142. Fluorine-comprising diolefins can be mentioned as well, for
example diolefins, such as perfluorodiallyl ether and perfluoro-1,3-butadiene.
Preferably, the PVDF is a homo- or copolymer of VDF and HFP and/or TFE
and/or vinylidene trifluoride and/or CTFE. Preferably, it is a VDF/HFP copolymer.
Preferably, the PVDF has a melt viscosity between 1 and 8 kP measured at
230°C and 100s-1.
The PVDFs commercialized under the brand name KYNAR® can be used.
The definition of the fluoropolymer applies equally to the non-functionalized
fluoropolymer and to the fluoropolymer from which the radiation grafted
fluoropolymer is derived.
The radiation grafted fluoropolymer is a fluoropolymer that has been chemically
modified by radiation grafting. The grafting is carried out in the bulk of the polymer
and not on its surface according to the following process:
a) melt-blending a fluoropolymer and at least one graftable compound;
b) the blend obtained is made in the form of granules or powder;
c) irradiating this blend in the solid state by irradiation (which can be a y or
p radiation) with a dose of between 1 and 15 Mrad, optionally after having
removed the residual oxygen; and
d) optionally removing the graftable compound that has not been grafted
and the residues liberated by the grafting, especially HF.
The blend is obtained by any melt blending techniques known in the art,
preferably using an extruder.
The irradiation is done with an electron or photon source. The radiation dose is
between 10 and 200 kGray, preferably between 10 and 150 kGray. Irradiation
using a cobalt bomb is preferred. During step c), it is preferable to prevent oxygen
from being present, for instance by flushing the fluoropolymer/graftable compound
blend with nitrogen or argon.
The graftable compound is grafted in an amount of 0.1 to 5% by weight (i.e. the
grafted graftable compound corresponds to 0.1 to 5 parts per 99.9 to 95 parts of
fluoropolymer), advantageously 0.5 to 5% and preferably 1 to 5%. The content of
grafted graftable compound depends on the initial content of the graftable
compound in the fluoropolymer/graftable compound blend to be irradiated. It also
depends on the grafting efficiency, and therefore on the duration and the energy
of the irradiation.
Step d) can sometimes be optional if the amount of graftable compound that has
not been grafted is low or not detrimental to the adhesion of the modified
fluoropolymer. Step d) may be carried out using techniques known to those skilled
in the art. Vacuum degassing may be applied, optionally heating at the same time.
It is also possible to dissolve the modified fluoropolymer in a suitable solvent, such
as for example N-methylpyrrolidone, and then to precipitate the polymer in a nonsolvent,
for example in water or else in an alcohol.
One of the advantages of this radiation grafting process is that it is possible to
obtain higher contents of grafted graftable compound than with conventional
grafting processes using a radical initiator. Thus, typically, with the radiation
grafting process it is possible to obtain contents of greater than 1% (1 part of
graftable compound per 99 parts of fluoropolymer), or even greater than 1.5%,
whereas with a conventional grafting process carried out in an extruder the
content is lower and sometimes is not feasible.
The radiation grafting takes place "cold", typically at temperatures below 100°C, or
even below 70°C, so that the fluoropolymer/graftable compound blend is not in the
melt state, as in the case of a "conventional" grafting process that is carried out in
an extruder. One essential difference with a "conventional" grafting process is
therefore that, in the case of a semicrystalline fluoropolymer (as is the case with
PVDF for example), the grafting takes place in the amorphous phase and not in
the crystalline phase, whereas homogeneous grafting is produced in the case of
grafting carried out in an extruder. The graftable compound is therefore not
distributed among the fluoropolymer chains in the same way in the case of
radiation grafting as in the case of grafting carried out in an extruder. The modified
fluoropolymer product therefore has a different distribution of the graftable
compound among the fluoropolymer chains compared with a product that would
be obtained by grafting carried out in an extruder. This makes it possible to obtain
better adhesion properties than grafting using a radical initiator.
The radiation grafted fluoropolymer exhibits the very good resistance to chemicals
and oxidation, and also the thermal mechanical strength of the fluoropolymer
before being grafted.
With regard to the graftable compound, this possesses at least one double
bond C=C, and at least one polar functional group that may be one of the
following functional groups:
- a carboxylic acid;
- a carboxylic acid salt;
- a carboxylic acid anhydride;
- an epoxide;
- a carboxylic acid ester;
- a silyl;
- an alkoxysilane;
- a carboxylic amide;
- a hydroxyl;
- an isocyanate.
It is also possible to envisage mixtures of several graftable compounds.
As examples of graftable compounds, we mention methacrylic acid, acrylic acid,
undecylenic acid, zinc, calcium or sodium undecylenate, maleic anhydride,
dichloromaleic anhydride, difluoromaleic anhydride, itaconic anhydride, crotonic
anhydride, glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether and
vinylsilanes, such as vinyltrimethoxysilane, vinyltriethoxysilane,
vinyltriacetoxysilane and y-methacryloxypropyltrimethoxysilane.
Preferably, to obtain good adhesion, an anhydride or else zinc, calcium or sodium
undecylenates will be chosen. These graftable compounds also have the
advantage of being solids, which makes it easier to introduce them into an
extruder. Maleic anhydride is most particularly preferred as it has a reactive group
that allows good adhesion on many types of substrates.
Because of the presence of a C=C double bond in the graftable compound,
polymerization of the graftable compound, to give polymer chains either grafted
onto the fluoropolymer, or free chains, that is to say those not attached to the
fluoropolymer, is not excluded. The term "polymer chain" is understood to mean a
chain-linking of more than ten units of the graftable compund. Within the context
of the invention, it is preferable to limit the presence of grafted or free polymer
chains, and therefore to seek to obtain chains with fewer than ten units of the
graftable compound. Chains limited to fewer than five graftable compound units
will be preferred, and those having fewer than two graftable compound units will
be even more preferred. Grafting only one compound unit is most preferred.
Likewise, it is not excluded for there to be more than one C=C double bond in the
graftable compound. Thus, for example, graftable compounds such as
allylmethacrylate, trimethylolpropane trimethacrylate or ethylene glycol
dimethacrylate may be used. However, the presence of more than one double
bond in the graftable compound may result in crosslinking of the fluoropolymer,
and therefore in a modification of the Theological properties, or even the presence
of gels, which is not desirable. It may then be difficult to obtain a high grafting
efficiency while still limiting crosslinking. Thus, the graftable compounds
containing only a single C=C double bond are preferred. The preferred graftable
compounds are therefore those possessing a single C=C double bond and at
least one polar functional group.
From this standpoint, an anhydride and also zinc, calcium and sodium
undecylenates constitute good graftable compounds as they have little tendency
to polymerize or even to give rise to crosslinking. Maleic anhydride is most
particularly preferred.
As regards the coating composition, it comprises :
• at least one radiation grafted fluoropolymer
• optionally at least one non-functionalized fluoropolymer
• optionally at least one acrylic polymer.
More particularly, the invention relates to a powder coating composition for
coating metals without the need for a primer comprising a blend of:
• at least one radiation grafted fluoropolymer, and
• at least one non-functionalized fluoropolymer.
The powder coating composition may further comprise also an acrylic polymer.
The coating composition comprises from 90 to 10 parts, preferably from 70 to 30
parts, of radiation grafted fluoropolymer per 10 to 90 parts, preferably per 30 to
70 parts, of the non-functionalized fluoropolymer and/or the acrylic polymer.
The non-functionalized fluoropolymer and the acrylic polymer may be present
either for reasons of cost or in order to obtain a compromise in physicochemical
and/or mechanical properties and better protection of the substrate. The choice
depends on the nature of the substrate to be protected and on the type of
protection envisaged. Thus, the coating composition may comprise the radiation
grafted fluoropolymer and :
• at least one non-functionalized fluoropolymer, or
• at least one acrylic polymer, or
• a combination of at least one non-functionalized fluoropolymer and at least
one acrylic polymer.
The coating composition may comprise only the radiation-grafted fluoropolymer
and the non-functionalized fluoropolymer, but preferably, an acrylic polymer is
also present. Thus, the coating composition preferably comprises a combination
of at least one non-functionalized fluoropolymer and at least one acrylic polymer.
The proportion of non-functionalized fluoropolymer should preferably be by weight
at least 70% of the non-functionalized fluoropolymer and the acrylic polymer. The
proportion of non-functionalized fluoropolymer should be by weight between 70
and 99%, advantageously between 80 and 95%, preferably between 80 and 90%,
with respect to the non-functionalized fluoropolymer and the acrylic polymer.
The non-functionalized fluoropolymer is chosen in the list of fluoropolymers given
above. It is preferably a PVDF homo- or copolymer.
It may be wise to combine a radiation grafted fluoropolymer with an nonfunctionalized
fluoropolymer which is different in nature, so as to obtain a
compromise in physicochemical and/or mechanical properties and consequently
better protection of the substrate. Thus, for example, the radiation grafted
fluoropolymer can be derived from a PVDF homo- or copolymer and the nonfunctionalized
fluoropolymer may be a tetrafluoroethylene homo- or copolymer.
Another example relates to the case where the radiation grafted fluoropolymer
and the non-functionalized fluoropolymer are two PVDF homo- or copolymers
having two different melt flow indices.
The MFI (abbreviation for Melt Flow Index) of the radiation grafted fluoropolymer
and of the unfunctionalized fluoropolymer is advantageously between 5 and
30g/10min (at 230°C under a load of 5kg) for a PVDF homopolymer and
between 5 and 30 g/10 min (at 230°C under a load of 5 kg) for a copolymer of
VDF and of HFP.
The acrylic polymer is chosen from the list of homo- or copolymers comprising at
least 50% by weight of an alkyl (meth)acrylate. Methyl methacrylate homo- and
copolymers (PMMA) comprising by weight at least 50%, advantageously at least
75% preferably at least 90% of methyl methacrylate are preferred. Mention may
be made, as examples of comonomers, for example, of alkyl (meth)acrylates,
acrylonitrile, butadiene, styrene or isoprene. Examples of alkyl (meth)acrylates are
described in Kirk-Othmer, Encyclopedia of Chemical Technology, 4th edition, in
volume 1, pages 292-293, and in volume 16, pages 475-478. Advantageously, the
acrylic polymer can comprise 0 to 20% by weight and preferably 5 to 15% of at
least one other alkyl (meth)acrylate, such as, for example, methyl acrylate and/or
ethyl acrylate. The acrylic polymer can be functionalized, that is to say that it
comprises, for example, acid, acid chloride, alcohol, anhydride and ureido
functional groups. These functional groups can be introduced by grafting or by
copolymerization. As regards the acid functional group, this is advantageously an
acid functional group contributed by the acrylic or methacrylic acid comonomer.
Two neighbouring acrylic acid functional groups can dehydrate to form an
anhydride functional group, which would not be a nuisance for the application.
The proportion of functional groups can be from 0 to 15% by weight of the acrylic
polymer comprising the optional functional groups. The acrylic polymer can also
optionally comprise from 5 to 30% by weight of impact additives well known to a
person skilled in the art.
A coating composition can be obtained by melt blending, preferably in an extruder:
• 20-50 parts of a radiation grafted fluoropolymer, preferably a radiation
grafted PVDF ;
• 20-50 parts by weight of a non-functionalized fluoropolymer, preferably a
PVDF;
• and 30 parts of an acrylic polymer, preferably a PMMA homo- or
copolymer.
So as to obtain a powder coating composition, the blend (in the form of pellets
when an extruder is used) is then cryogenically ground into a powder and
classified into a suitable particle size range for powder application, typically
between 1-100 urn, with a mean particle size between 25-75 urn. This will
produce a non-pigmented "clear coat" powder coating. Addition of suitable
pigments at the extrusion stage (at levels known by those skilled in the art of
powder coatings manufacture) will produce a pigmented powder coating after the
grinding process. This melt blending / grinding / classifying process is the
preferred method to practice this invention. A second method for pigmentation
involves dry blending of pigments with the "clear coat" powder. This second
approach is less preferable due to variation of dry pigment blending, but is
advantageous for preparing small batches of custom colors. Regardless, the melt
blending of all the polymer resin components (PVDF, radiation grafted PVDF,
PMMA) is the preferable blending method.
Preferably, the PVDF has a melt viscosity between 1 and 8 kP (measured at
230°C and 100 s"1). Preferably, the radiation grafted PVDF is derived from a
PVDF homopolymer. Preferably, maleic anhydride is grafted onto the PVDF.
Preferably, the PMMA is a copolymer of methyl methacrylate and ethyl acrylate
comprising between 1 and 10% of ethyl acrylate. Preferably, the PMMA has a
molecular weight between 30000 and 100000 g/mol.
Preferably, the coating composition further comprises one or more additives. The
additives may be, but are not limited to, pigments, fillers, extenders, plasticizers,
impact modifiers or additives to improve aging resistance, and UV stabilizers.
The UV stabilizer is preferably of a high molar mass (> 200 g/mol), so as to
prevent it from dissipating or evaporating. As an example, it can be a UV stabilizer
of benzotriazole, oxalic acid, benzophenone, HALS or hindered amine type. More
specifically, it can be, as examples, 2-[3,5-di(a,a-dimethylbenzyl)-2-
hydroxyphenyljbenzotriazole, 2-(3,5-di(t-butyl)-2-hydroxyphenyl)benzotriazole, 2-
(3-(t-butyl)-5-methyl-2-hydroxyphenyl)-5-chlorobenzotriazole, 2-(3,5-di(t-butyl)-2-
hydroxyphenyl)-5-chlorobenzotriazole, 2-(3,5-di(t-amyl)-2-
hydroxyphenyl)benzotriazole, 2-ethoxy-2'-ethyl oxalic acid bisanilide, 2-ethoxy-5-(tbutyl)-
2'-ethyl oxalic acid bisanilide, 2-hydroxy-4-(n-octoxy)benzophenone,
bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, bis(1,2,2,6,6-tetramethyl-4-
piperidyl) sebacate, dimethyl-2-(4-hydroxy-2,2,6,6-tetramethyl-1 -piperidyl) ether or
1-[2-3-(3,5-di(t-butyl)-4-hydroxyphenyl)propionyloxy]-2,2,6,6-Ttetramethylpiperidine.
Preferably, when the coating composition comprises
anacrylic polymer, the UV stabilizer is chosen from UV stabilizers which are
compatible with the acrylic polymer. The UV stabilizer, when present, is
advantageously present in the coating composition in the amount of from about
0.1 to about 10 parts by weight per 100 parts of polymer(s). While for most
applications the preferred range is from about 1 to about 5 parts by weight
pigment per 100 parts of polymer(s).
The coating composition may be pigmented or non-pigmented. If pigmented, the
pigments may be inorganic or organic and include, but are not limited to titanium
dioxide, silica, iron oxides of various colors, mixed metal oxides of various colors,
various silicates, talc, diatomaceous earth, mica, clay, zinc oxide, zinc sulfide,
zirconium oxide, carbon black, leafing and non-leafing metallic pigments,
molybdate orange, calcium carbonate and barium sulfate. The pigment
component, when present, is advantageously present in the composition in the
amount of from about 0.1 to about 50 parts by weight per 100 parts of polymer(s).
While for most applications the preferred range is from about 5 to about 20 parts
by weight pigment per 100 parts of polymer(s).
The additives may be present in the individual polymers before blending or may
be added after the polymers have been blended.
As regards the form of the coating composition and the process to apply it,
the coating composition can be in the form of pellets, in the form of a powder or in
solution. When the coating composition is in the form of pellets, any melt blending
technique known to a person skilled in the art, for example by using an extruder,
followed by any pelletizing technique known to one skilled in the art, can be used.
When the coating composition is in the form of a solution, the solution is prepared
by dissolving in a solvant (for example in N-methylpyrrolidone) the polymers either
individually or after preblending. The polymers that are dissolved may be in the
form of pellets or in the form of powders.
When the coating composition is in the form of powders, the polymers may be
blended prior to powderization, or may be dry blended after individual
powderization. Any technique of powderization, such as by spray drying, freeze
drying, cryogenical grinding, non-cryogenical grinding, ultrasonication, or other
methods known to one skilled in the art, can be used.
The blending step may be carried out in any order. For instance, when the coating
composition comprises a radiation grafted fluoropolymer, a non-functionalized
fluoropolymer and an acrylic polymer, all polymers may be blended together, for
instance in an extruder, or there may be a preblending step involving the nonfunctionalized
fluoropolymer and the acrylic polymer, prior to blending such blend
with the radiation grafted fluoropolymer.
The coating composition can be applied directly to the substrate in the molten
state, in solution or in the powder state. Application in the molten state can be
carried out by coating, rolling or spread coating.
Preferably, the coating composition is in the form of a powder and the coating
composition is applied in the powder state by any known conventional application
method which will provide an uniform coating. Typical techniques are fluidized
bed, thermal spray, or preferably electrostatic coating. The coating may be
applied to one or more surfaces of the substrate. After application, the coating is
subjected to curing at a temperature above the melt temperature of the coating
composition, preferably between about 220°C and 250°C.
The thickness of the applied coating depends on the nature of the substrate to be
protected. Generally the final coating thickness is between 10 and 5000 urn,
preferably, between 10 and 1000 urn, and more preferably between 10 and
500 urn. Each layer (that is the coating composition and the optional layer(s)
made of acrylic polymer) can have a thickness between 10 and 5000 urn.
As regards the substrate to be coated, the latter is an inorganic substrate
comprising a layer of the coating composition wherein no primer is present
between the coating and the inorganic substrate. The invention further relates to a
coated inorganic substrate, especially an un-primed metal, having directly
adhered thereto the coating composition, preferably the powder coating
composition. The invention thus relates to a coated inorganic substrate having a
layer of the coating composition directly adhered thereto, wherein no primer is
present between the coating and the inorganic substrate.
All variants described above for the coating composition apply also for the coated
inorganic substrate.
According to a specific form of the invention, it is possible to add to the coating
according to the invention at least one layer comprising at least one acrylic
polymer. Said layer is directly attached to the layer of the coating composition.
The acrylic polymer is chosen from the same list of acrylic polymers as previously
given. The acrylic polymer of this layer can optionally also be modified by a
compatible non-functionalized fluoropolymer chosen from the same list of fluoropolymers
as that given above and can optionally comprise a UV stabilizer.
The layer of acrylic polymer thus comprises from 100 to 10 parts of acrylic
polymer per 0 to 90 parts of non-functionalized fluoropolymer. This layer can also
comprise a UV stabilizer, the content of which can vary from 0 to 10% by weight
with respect to the acrylic polymer optionally modified by the fluoropolymer.
According to the invention, it may therefore be possible to find a protective coating
with a single layer of acrylic polymer or else with several different layers, for
example two different layers of acrylic polymer.
The inorganic substrate may be a metal, glass, quartz, ceramics, concrete or
silicon. Preferably, it is selected from the group consisting of metal, concrete and
ceramics. Preferably, the metal is un-primed and is aluminum or steel (this
includes also stainless steel). In the case of aluminium, the alloys of the 2000,
3000, 5000 and 6000 series of the Aluminum Association Inc. Register are
included.
The term "metal" also covers other types of metals, for example, iron, copper,
aluminium, titanium, lead, tin, cobalt, silver, tungsten, nickel or zinc. The term
"metal" also covers the mixtures of these metals and their alloys. Possible alloys
are steels, such as, for example, carbon, nickel, chromium, nickel/chromium,
chromium/molybdenum or silicon steels, stainless steel, cast iron or Permalloy.
Alloys of aluminium are, for example, aluminium/magnesium, aluminium/silicon,
aluminium/copper/nickel/magnesium or aluminium/silicon/copper/nickel/
magnesium alloys. Copper alloys are, for example, brass, bronze, silicon bronze,
silicon brass or nickel bronze. Nickel alloys are, for example, nickel/magnesium
(nickel D), nickel/aluminium (nickel Z) or nickel/silicon alloys, Monel, or Hastelloy.
Aluminium alloys also include aluminium oxides, as well as, for example,
aluminium/copper, aluminium/silicon, aluminium/manganese or
aluminium/copper/nickel/manganese alloys.
The metal substrate can be subjected beforehand to a physical and/or chemical
pretreatment, the purpose of which is to clean the metal surface and to promote
the adhesion of the coating. The possible pretreatments are as follows: alkaline
degreasing, degreasing by solvents, such as trichloroethylene, brushing, shot
blasting, phosphatizing, chromium plating, anodizing (for example, for aluminium
and its alloys), chromium anodizing, silanization, abrasion, pickling and in
particular sulphochromic pickling. A possible pretreatment can consist in applying
an adhesion promoter. Adhesion promoters have been described by Cassidy P.E.
in the review Ind. Eng. Chem. Prod. Res. Development, 1972, Volume 11, No. 2,
p. 170-177, or by Kinlock A.J. in J. Mat. Sci., 1980, 15, p. 2141-66. Mention may
be made, by way of examples, as possible chemical pretreatments, of Alodine
NR1453, Alodine NR2010, Accomet C or Safeguard 6000. The pretreatment can
also consist of a combination of these various pretreatments, in particular the
combination of a physical pretreatment and of a chemical pretreatment.
20
In the case where the substrate to be coated is a metal, it can exist in various
forms and geometries, such as, for example, in the form:
• of an elongated surface, such as, for example, a sheet, a plate or a leaf,
• of a hollow body, such as, for example, a receptacle, a container, a
bottle, a carboy or a chemical reactor,
• of a pipe, of an elbow, of a valve, of a punch or of a pump,
• of a yarn, strand, cable or stay,
• of an electrode.
The protective coating according to the invention lends itself particularly well to the
protection of flexible metal pipes for the extraction and/or the transportation of
gases and hydrocarbons in the oil and gas industries. This is because the
materials which are used in these industries are brought into contact with
particularly aggressive substances (such as hydrocarbons, strong acids, solvents,
inorganic and organic bases, and the like).
The term "glass" covers any type of glass, for example silica-soda-lime glass,
borosilicate glass, ceramic glass or lead glasses. Reference may be made to the
list of glasses given in Ullmann's Encyclopedia, 5th edition, volume A12,
pages 382-383, Table 9.
Applications of the coating composition
The coating composition can be used to protect the inorganic substrate. It offers
UV resistance, exterior durability, abrasion resistance and/or impact resistance.
It also offers protection from corrosion. Each substrate may undergo corrosion
which is specific to it. Thus, in the case of a metal, there exist several types of
corrosion depending on the nature of the metal and of the aggressive medium to
which it is subjected. Corrosion can thus be localized or non-localized, by pitting,
intergranular, under stress, and the like. In the chemical industry in particular,
metal components are often subjected to highly corrosive media (for example
acids, such as sulphuric acid, hydrochloric acid, nitric acid, hydrobromic acid or
hydrofluoric acid, bases, such as sodium hydroxide or potassium hydroxide, highly
corrosive gases, such as fluorine, bromine, chlorine or ammonia, and the like). In
everyday life, metal components may be subject to atmospheric corrosion (under
the effect of the combination of air and water) or else to salt corrosion (in a marine
environment, for example).
Glass can be corroded by hydrofluoric acid or else concentrated basic solutions,
such as, for example, concentrated sodium hydroxide solutions. Silicon can be
corroded by bromine, chlorine or gaseous hydrobromic acid.
The applications of the coated substrates are primarily decorative where long term
UV resistance, exterior durability, abrasion resistance and/or impact resistance
are required. Typical examples are architectural exterior metal building parts
(window frames, door frames, roofing, wall panels, aluminum extrusions, and the
like) and automotive components. Use as functional coatings (for corrosion and/or
wear resistance, for example) is also possible.
Examples
The following examples further illustrate the best mode contemplated by the
inventors for the practice of their invention and are intended to be illustrative and
not in limitation thereof.
The products used were the following:
PVDF:KYNAR®710
acrylic resin : PARALOID® B-44 (with Mw 140000 g/mol).
pigments : SHEPHERD BROWN 39
KYNAR® ADX 111 : modified PVDF containing 1% grafted maleic anhydride
obtained according to the operating method described below, starting with a
KYNAR® 710, a PVDF homopolymer of MFI = 20 g/10 min at 230°C / 5 kg.
KYNAR® ADX 111 was prepared as follows. A blend of KYNAR® 710 PVDF (from
Arkema) and of 2 wt% maleic anhydride was prepared. This blend was prepared
using a twin-screw extruder operating at 230°C and 150 rpm with a throughput of
10 kg/h. The granulated product thus prepared was bagged, in aluminium-lined
sealed bags, and then the oxygen was removed by flushing with a stream of
argon. These bags were then irradiated by y radiation (Co60 bomb) at 3 Mrad (10
MeV acceleration) for 17 hours. A 50% grafting level was determined, this level
being checked after a step of dissolving the material in N-methylpyrrolidone and
then precipitation in a water/THF mixture (50/50 by weight). The product obtained
after the grafting operation was then placed in a vacuum overnight at 130°C in
order to remove the residual maleic anhydride and the hydrofluoric acid released
during the irradiation. The final grafted maleic anhydride content was 1%
(determined by infrared spectroscopy on the C=O band at around 1870 cm"1).
The aluminum panels were supplied with a chromate pretreatment ("chromated"
aluminum panels) and were rinsed with acetone prior to use.
Example 1:
A powder blend was prepared using pre-formulated PVDF-acrylic powder coat
and grafted PVDF by dry blending as follows: A sample of formulated PVDFacrylic
powder coating (a formulation consisting of the acrylic resin 24-27 parts,
PVDF resin 56-63 parts, and pigments 10-20 parts, melt blended then cryoground
; the powder has a mean size of 45 urn and a distribution between 10 and
100 urn) of which 70 parts are blended with the modified PVDF (KYNAR® ADX
111) 30 parts using a dry blender mill. This homogeneous powder blend is ready
for application.
The dry powder blend was applied to an unprimed chromated aluminum panel by
electrostatic spray. The powder coated panel was then baked in a convection
oven at 450°F for 10 minutes. A very smooth, defect free coating resulted. The
coating was tested by the following methods: cross-hatch adhesion (AAMA 2605-
98 7.4.1.1) direct and reverse impact (AAMA 2605-98 7.5.11 & NCCA 4.2.6),
cross hatch adhesion/reverse impact (NCCA 4.2.1.0), boiling water/cross hatch
adhesion (AAMA 2605-98 7.4.1.3) and boiling water/cross hatch adhesion with
reverse impact (a combination of AAMA 2605-98 7.4.1.3 and NCCA4.2.1.0). This
coating passed those tests satisfactorily, with no cracking, peeling, or coating pulloff
with tape.
Example 2 (comparative):
An aluminum panel was coated with the PVDF-acrylic powder coating of Example
1 that did not contain any KYNAR® ADX 111. This coating passed the cross hatch
adhesion, direct impact, and indirect impact tests. However, after boiling water
exposure, adhesion failure was noted both in the cross hatch adhesion and
especially in the cross hatch adhesion/reverse impact tests. Chips of the paint
were pulled off by tape, and coating delamination occurred in the reverse impact
test.
Example 3 (comparative)
The powder formulation of Example 2 (without any KYNAR® ADX 111) was
applied to a panel to which a powder epoxy primer had been applied. Initial
adhesion was good, but after boiling water exposure, coating delamination
occurred in the cross hatch/reverse impact test.
Thus, as shown with examples 1-3, the grafted KYNAR® resin significantly
improves the adhesion of KYNAR-acrylic powder coatings.
Example 4
A dry powder blend was prepared by mixing 50 parts of KYNAR® 710 powder
(melt viscosity 4-8 kP at 230°C, 100 s'1), 25 parts of KYNAR® ADX 111 and
parts of an acrylic copolymer of methylmethacrylate and ethylacrylate
(PARALOID® B-88) methylmethacrylate 95%, ethylacrylate 5%) in a powder
blender. The powder has a mean size of 45 urn and a distribution between 10
and 100 urn. The mixed blend was applied to chromated aluminum panels by
electrostatic spray and baked by heating at 480°F for 10 minutes. The clear
coating was tested by the same methods described in Example 1. This coating
passed all the adhesion tests, with no coating loss by tape pull-off.
Example 5 (Comparative)
A dry powder blend was prepared by mixing 70 parts of polyvinylidenefluoride
powder (melt viscosity 4-8 kp at 230°C, 100 s"1) and 30 parts of an acrylic
copolymer (Paraloid B-88) of methylmethacrylate and ethylacrylate
(methylmethacrylate 95% by weight, ethylacrylate 5%) in a powder blender. The
powder has a mean size of 45 urn and a distribution between 10 and 100 urn. The
mixed blend was applied to chromated aluminum panels by electrostatic spray
and baked by heating at 480T for 10 minutes. The clear coating was tested by
the same methods described in Example 1. This coating passed all the adhesion
tests, except for reverse impact/boiling water and reverse impact/cross
hatch/boiling water. In these tests, chips of the polymer coating were removed by
tape pull.
The following examples further illustrate the presence of the additional acrylic
polymer layer. There may be only a single layer of an acrylic polymer:
inorganic substrate / layer of the coating composition / layer of an acrylic
polymer
Illustrative examples:
• metal/PVDF homo- or copolymer grafted by maleic anhydride/methyl
methacrylate homo- or copolymer
• metal/PVDF homo- or copolymer grafted by maleic anhydride/50 to 90%
methyl methacrylate homo- or copolymer + 10 to 50% PVDF homo- or
copolymer
• metal/PVDF homo- or copolymer grafted by maleic anhydride/50 to 90%
methyl methacrylate homo- or copolymer + 10 to 50% PVDF homo- or
copolymer with 4% of 2-hydroxy-4-(n-octoxy) benzophenone with
respect to the blend of the two polymers
Structures of this type are highly suitable for protecting aluminium.
There may be two different layers of acrylic polymer:
inorganic substrate / layer of the coating composition / layer of an acrylic
polymer / another layer of acrylic polymer
Illustrative examples:
• metal/PVDF homo- or copolymer grafted by maleic anhydride/50 to 90%
methyl methacrylate homo- or copolymer + 10 to 50% PVDF homo- or
copolymer/methyl methacrylate homo- or copolymer
• metal/PVDF homo- or copolymer grafted by maleic anhydride/50 to 90%
methyl methacrylate homo- or copolymer + 10 to 50% PVDF homo- or
copolymer with 4% of 2-hydroxy-4-(n-octoxy) benzophenone with
respect to the blend of the two polymers/methyl methacrylate homo- or
copolymer
• metal/PVDF homo- or copolymer grafted by maleic anhydride/50 to 90%
of a copolymer comprising 75% of methyl methacrylate and 25% of
ethyl acrylate + 10 to 50% of a PVDF homo- or copolymer with from 1 to
5% of Tinuvin 234 with respect to the blend of the two polymers/10 to
50% of a methyl methacrylate homo- or copolymer + 50 to 90% of a VF2
homo- or copolymer
Structures of this type are also highly suitable for protecting aluminium.

WE CLAIM:
1. Coating composition comprising from 90 to 10 parts of at least one radiation grafted fluoropolymer per 10 to 90 parts of at least one non-functionalized fluoropolymer and at least one acrylic polymer.
2. Coating composition as claimed in claim 1, wherein said composition is in the form of a powder for coating metals without the need for a primer.
3. Coating composition as claimed in any of the previous claims, in which the coating composition comprises from 70 to 30 parts, of radiation grafted fluoropolymer per 30 to 70 parts, of the non-functionalized fluoropolymer and/or the acrylic polymer.
4. Coating composition as claimed in any of the previous claims, in which the proportion of non-functionalized fluoropolymer is by weight at least 70% of the non-functionalized fluoropolymer and the acrylic polymer.
5. Coating composition as claimed in any of the previous claims, in which the the proportion of non-functionalized fluoropolymer is by weight between 70 and 99%, advantageously between 80 and 95%, preferably between 80 and 90%, with respect to the non-functionalized fluoropolymer and the acrylic polymer.
6. Coating composition as claimed in any of the previous claims, in which the non-functionalized fluoropolymer or the fluoropolymer from which the radiation grafted fluoropolymer is derived, is any polymer or copolymer containing at least least 50 mole percent of fluoromonomer units derived from fluoromonomer (I):
(Formula Removed)
in which X and X' can be, independently of one another, a hydrogen atom, a halogen, in particular fluorine or chlorine, or a perhalogenated, in particular perfluorinated, alkyl.

7. Coating composition as claimed in any of the previous claims, in which the fluoropolymer is a homo- or copolymer of VDF containing by weight at least 50% VDF, advantageously at least 75% VDF and preferably at least 85% VDF.
8. Coating composition as claimed in any of the previous claims, in which the fluoropolymer is a homo- or copolymer of VDF and HFP and/or TFE and/or vinylidene trifluoride and/or CTFE.
9. Coating composition as claimed in any of the previous claims, in which the graftable compound that is radiation grafted onto the fluoropolymer possesses at least one double bond C=C, and at least one polar functional group that may be one of the following functional groups:

- a carboxylic acid;
- a carboxylic acid salt;
- a carboxylic acid anhydride;
- an epoxide;
- a carboxylic acid ester;
- a silyl;
- an alkoxysilane;
a carboxylic amide;
- a hydroxyl;
an isocyanate.
10. Coating composition as claimed in Claim 9, in which the graftable compound is an anhydride or zinc, calcium or sodium undecylenates.
11. Coating composition as claimed in any of claims 9 or 10, in which the graftable compound is maleic anhydride.
12. Coating composition as claimed in any one of Claims 1 to 9, in which the acrylic polymer is chosen from the list of homo- or copolymers comprising at least 50% by weight of an alkyl (meth)acrylate.
13. Coating composition as claimed in any of the previous claims comprising one or more additives selected from the group consisting of pigments, fillers, extenders, plasticizers, impact modifiers,

additives to improve ageing resistance, and UV stabilizers.
14. The coating composition as claimed in any of the previous claims, as and when used as a coating for protection of inorganic substrate.