INKJET RECEIVING MEDIUM AND PRE-TREATMENT
COMPOSITION FOR INKJET PRINTING
FIELD OF THE INVENTION
The invention relates to the field of inkjet printing. In particular
the invention relates to a composition to be applied to a receiver to enhance the
quality of inkjet prints printed with pigment-based ink, to inkjet recording media
treated with such composition, and to printing systems and methods using such
media.
BACKGROUND OF THE INVENTION
The present invention is directed in part to overcoming the problem
of printing on glossy or semi-glossy coated papers or the like with aqueous inkjet
inks. Currently available coated papers of this kind have been engineered over the
years to be compatible with conventional, analog printing technologies, such as
offset lithography, and may be designated as "offset papers." The printing inks
used in offset printing processes are typically very high solids, and the solvents
are typically non-aqueous. As a consequence, the coatings that are currently used
to produce glossy and semi-glossy offset printing papers, such as those used for
magazines and mail order catalogs, have been intentionally designed to be
resistant to the absorption of water. In fact, when these papers are characterized
by standard tests as to their porosity and/or permeability, they have been found to
be much less permeable than a typical uncoated paper.
In contrast to lithographic inks, inkjet inks are characterized by low
viscosity, low solids, and aqueous solvent. When such coated offset papers are
printed with inkjet inks that comprise as much as 90-95% water as the carrier
solvent, the inks have a tendency to sit on the surface of the coating, rather than
penetrate into the coating and/or underlying paper substrate.
Because the inks printed on a water-resistant receiver must dry
primarily by evaporation of the water without any significant penetration or
absorption of the water into the coating or paper, a number of problems are
encountered. One such problem is that the individual ink droplets slowly spread
laterally across the surface of the coating, eventually touching and coalescing with
adjacent ink droplets. This gives rise to a visual image quality artifact known as
"coalescence" or "puddling." Another problem encountered when inks dry too
slowly is that when two different color inks are printed next to each other, such as
when black text is highlighted or surrounded by yellow ink, the two colors tend to
bleed into one another, resulting in a defect known as "intercolor bleed." Yet
another problem is that when printing at high speed, either in a sheet fed printing
process, or in a roll-to-roll printing process, the printed image is not dried
sufficiently before the printed image comes in contact with an unprinted surface,
and ink is transferred from the printed area to the unprinted surface, resulting in
"ink retransfer."
In contrast to glossy offset papers, some coated papers for offset
lithography have matte surfaces that are very porous. While high-solids
lithographic inks remain on the surface, the colorant of aqueous inkjet inks on the
other hand tends to absorb deeply into the paper, resulting in a substantial loss of
optical density and as a consequence, reduced color gamut.
Recently high speed inkjet printing processes, including continuous
inkjet printing processes, have been developed that are suitable for high speed,
mid-volume printing and have become of interest to the commercial printing
industry. As commercial offset papers are manufactured in high volume, it would
be preferable to be able to use such offset papers themselves for commercial inkjet
printing purposes, to take advantage of economies of scale. For the several
reasons discussed above, however, the standard preparation of substrates for offset
lithographic printing renders them unsuitable for printing with aqueous inkjet
inks. Thus the need arises for inkjet-printable receivers providing the familiar
look and feel as well as economical cost of standard lithographic printing-grade
offset papers.
The requirements of commercial printing industry include, among
others, image quality in terms of high optical density, broad color gamut, sharp
detail, and minimal problems with coalescence, smearing, feathering and the like.
Operationally, the printing process strives for low environmental impact, low
energy consumption, fast drying, and so forth. The resulting print must exhibit
durability, resisting abrasion when dry or if wetted.
Simply omitting the water-resistant coating of a glossy lithographic
offset paper does not enable high-quality inkjet printing. Uncoated paper does not
maintain the ink colorant at the surface, but allows significant penetration of the
colorant into the interior of the paper, resulting in a loss of optical density and a
low-quality image. Moreover, ink penetrates non-uniformly into the paper due to
the heterogeneous nature of the paper, giving rise to mottle, which further
degrades the image.
Very high quality photopapers have been developed for desktop
consumer inkjet printing systems incorporating relatively high laydown inkreceiving
layers that are porous and/or permeable to the ink. However, such
coated photopapers are generally not suitable for high-speed commercial inkjet
printing applications for a number of reasons. The thick coatings result in a basis
weight that is unpractically heavy for mailing or other bulk distribution means.
Such receivers are not meant for rough handling or folding, which would result in
cracking of the coated layers. In general, these coated photopapers are too
expensive for high-speed inkjet commercial printing applications, such as
magazines, brochures, catalogs, and the like. This is because such coated
photopapers require either expensive materials, such as fumed oxides of silica or
alumina, to produce a glossy surface or very thick coatings to adequately absorb
the relatively heavy ink coverage required to print high quality photographs.
Multivalent metal salts are known to improve the print density and
uniformity of images formed on plain papers from inkjet printers. For example,
Cousin et al, in US Patent 4,554,181, disclose the combination of a water-soluble
salt of a polyvalent metal ion and a cationic polymer at a combined dry coat
weight of 0.1 to 15.0 g/m2, for improving the print density of images printed by
inkjet printers employing anionic dye-based inks.
Varnell, in US Patent 6,207,258, discloses the use of water-soluble
salts of multivalent metal ions combined with a polymeric sizing agent and a
carrier agent in a size press to improve the print density and uniformity of images
formed on plain papers from inkjet printers employing pigment colorants in the
ink set. The actual surface concentrations are not readily apparent from the
disclosure of the size-press application method.
Tanaka, et al, in US Patent 7,199,182, disclose an inkjet recording
material comprising an impervious substrate coated with at least 20 g/m2 of an
aqueous resin composition comprising a water soluble magnesium salt, an
aqueous polyurethane, and one or more of a cationic compound (such as a cationic
polymer), a nonionic water soluble high molecular weight compound (such as
acetoacetylated poly(vinyl alcohol) (PVA acac)), and a water soluble epoxy
compound.
Tran et al (US 201 1/0059272) describe anti-curl compositions for
inkjet receivers incorporating a water-soluble salt of a multivalent metal ion and a
cationic polymer typically applied in the size press in combination with an amine
oxide.
Sheng (US 2003/0203134) describes the use of a low friction
substance to be a component of an inkjet receiving layer in order to modify the
coefficient of friction of inkjet media and provide improved sheet feeding
performance. The low friction substances are emulsified forms of waxes, simple
organic polymers, silicone polymers, and fluoropolymers. The particle size is less
than 5 micrometers, preferably less than 1 micrometer. The examples shown have
slip aids present at approximately 4-5% of the total dry coat weight.
Ma et al. (US 6,779,884) describes a system for printing durable
inkjet images in which a slip component is applied over the previously printed
inkjet image.
Wang et al. (US 201 1/0091666) describes inkjet printable article in
which the ink-receiving layer is comprised of 60-95% by weight clays, kaolin,
calcium carbonate, or combinations of these particles.
Wang et al. (US 2012/0034398) and Wang et al. (US 8,092,873)
each describe an inkjet receptive coating layers comprising inorganic pigments as
the major component by weight and a coefficient of friction reducing agent. The
latter are described as having a particle size ranging from 0.1-2.0 micrometers,
and are comprised of polyethylene, paraffin, carnauba, polypropylene, or PTFE
waxes, or combinations of these.
Sargeant et al (US 5,700,582) describes a polymer matrix coating
for use as an inkjet receiver layer that avoids the problem of pigment ink cracking.
The polymers chosen are characterized by Tg, an integrity value, and a
swellability parameter. In addition, up to 15% by weight of the dry coating may
be comprised of water-insoluble pigments. These particles may be comprised of
organic materials including polyolefms, polystyrene, PTFE, and other materials.
In contrast to incorporating surface modifying chemistry at the size
press during paper manufacturing, or coating of a relatively thick ink receiving
layer on a photopaper, further coating treatments may also be applied as coatings
on finished paper. Dannhauser et al (US 201 1/0279554), e.g., describe an inkjet
receiving medium including a substrate and having a topmost layer coated thereon
comprising an aqueous soluble salt of a multivalent metal cation and a crosslinked
hydrophilic polymer binder, for example acetoacetylated poly vinyl
alcohol. Xiang and Botros (copending, commonly assigned USSN 13/433,412)
describes an inkjet receiving medium comprising a substrate and having a topmost
layer coated thereon, wherein the topmost layer comprises one or more aqueous
soluble salts of multivalent metal cations, a cationic polyelectrolyte comprising
amidine moieties, and a second polymer which is distinct from the cationic
polyelectrolyte comprising amidine moieties and which is selected from the group
consisting of a polyamide-epichlorohydrin, a polyamine solution polymer, and a
waterborne or water-dispersible polyurethane. Significant improvements in
resistance to wet-rub and dry-rub defects may be achieved by use of such coatings
on finished paper, along with good image quality, including high optical density
and reduced mottle and coalescence.
Nigam, in US Patent 7,041,338 discloses a process of providing a
coated paper by utilizing a coating composition containing one or more
nitrogenous dye-fixing compound and a film forming binder, where the coating
composition may also include an organic or inorganic cross-linker, and where the
coating composition may be applied as a pretreatment (prior to printing),
simultaneously with printing, or as an after-treatment.
Pigmented inks have many advantages over dye-based inks when
they are printed on traditional paper designed for offset printing. It has been a
challenge, however, to produce water resistant images with water-based
pigmented inks so there will be no ink smearing when end-users turn the pages of
a book with wet fingers or water is in contact with printed matter.
Even with the advances made to date in rub resistance, the need
remains for more durable digital prints on offset paper to overcome the effects of
handling in production and in use by the consumer.
SUMMARY OF THE INVENTION
It is a primary objective of one embodiment of this invention to
enable the printing at high speed using aqueous inkjet inks, of glossy, semi-glossy
and matte coated lithographic offset papers with high image quality, high optical
density, and good physical durability, including resistance to wet or dry abrasion,
water-fastness, and resistance to smearing from subsequent highlighter marking.
The present invention in one embodiment provides a coating
composition for pre-treating a substrate prior to inkjet printing thereon,
comprising one or more aqueous-soluble salts of multivalent metal cations, and
particles comprised primarily of polymer having a Rockwell Hardness of less than
R90, where the composition has a solids content which comprises at least 30 wt%
of the one or more aqueous soluble salts of multivalent metal cations, and the
particles comprised primarily of polymer having a Rockwell Hardness of less than
R90 have a mode equivalent spherical diameter of at least about 2 micrometers.
In another embodiment, the present invention provides an inkjet
receiving medium comprising a substrate and having a topmost layer coated
thereon, wherein the topmost layer comprises one or more aqueous soluble salts of
multivalent metal cations, and particles comprised primarily of polymer having a
Rockwell Hardness of less than R90, where the topmost layer is coated at a dry
solids coat weight of from 0.1 to 5 g/m2 and comprises at least 30 wt% of the one
or more aqueous soluble salts of multivalent metal cations, and provides at least
0.01 g/m2 of particles comprised primarily of polymer having a Rockwell
Hardness of less than R90 and which have an equivalent spherical diameter of i) at
least about 2 micrometers and ii) at least 0.1 micrometer greater than the
minimum coated thickness of the topmost layer.
Another aspect of the present invention is directed to a method of
printing in which the above-described inkjet receiving medium is printed with an
inkjet printer employing at least one pigment-based colorant in an aqueous ink
composition, wherein the pigment-based colorant is stabilized using anionic
dispersants or is self-dispersed.
In a further embodiment, the present invention provides a printing
method comprising transporting an inkjet receiving medium of the invention by a
continuous inkjet printhead applying an inkjet ink onto the receiving medium
comprising at least one pigment based colorant in an aqueous ink composition,
and subsequently transporting the printed receiving medium through a drying
station.
Advantages of various embodiments of the invention include: high
printed image quality including high pigment density and color gamut, and low
grain and mottle; improved print durability to dry rub, wet abrasion, and
highlighter marking; ability to provide all surface types including glossy, semiglossy,
and dull matte; and extremely low coverage allowing easy application and
low cost.
DETAILED DESCRIPTION OF THE INVENTION
Inkjet receiving media in accordance with one embodiment of the
invention comprise a substrate and have a preferably continuous topmost layer
coated thereon, wherein the topmost layer comprises one or more aqueous soluble
salts of multivalent metal cations, and at least 0.01 g/m2 of particles comprised
primarily of polymer having a Rockwell Hardness of less than R90 and which
have an equivalent spherical diameter of at least about 2 micrometers. The
topmost layer may further optionally comprise polymer binder, and the particles
comprised primarily of polymer having a Rockwell Hardness of less than R90 and
having an equivalent spherical diameter of at least about 2 micrometers further
have an equivalent spherical diameter of at least 0.1 micrometer greater than the
minimum coated thickness of the topmost layer, which minimum thickness will
primarily be determined by the coated amount of any such binders contained in
the topmost layer. More preferably, the particles comprised primarily of polymer
having a Rockwell Hardness of less than R90 and having an equivalent spherical
diameter of at least about 2 micrometers further have an equivalent spherical
diameter of at least 0.5 micrometer greater than the minimum coated thickness of
the topmost layer. The invention further relates to a coating composition for pre
hearing a substrate prior to inkjet printing thereon to form such an inkjet receiving
medium, comprising one or more aqueous-soluble salts of multivalent metal
cations, and particles comprised primarily of polymer having a Rockwell
Hardness of less than R90, where the composition has a solids content which
comprises at least 30 wt% of the one or more aqueous soluble salts of multivalent
metal cations, and the particles comprised primarily of polymer having a
Rockwell Hardness of less than R90 have a mode equivalent spherical diameter of
at least about 2 micrometers, preferably from about 2 to 10 micrometers.
The topmost layer may preferably be coated at dry solids coat
weight of from 0.1 to 3 g/m2, and preferably comprises from 30-98 wt% (more
preferably from 50-90 wt%) of one or more aqueous soluble salts of multivalent
metal cations, from about 1-69 wt % (more preferably 10-50 wt% of polymer
binder, and from about 1 to 10 wt % particles comprised primarily of polymer
having a Rockwell Hardness of less than R90, preferably less than R75, and
having a mode equivalent spherical diameter of at least about 2 micrometers,
preferably from about 2 to 10 micrometers. The particles comprised primarily of
polymer having a Rockwell Hardness of less than R90 are further preferably
coated in an amount of from 0.01 up to and including 0.05 grams/m 2, more
preferably of from 0.02 up to and including 0.05 grams/m 2.
While the topmost layer of the receiving medium of the invention
is believed to improve the inkjet printing performance on a wide variety of
substrates, in a particular embodiment of the invention the substrate is one of a
glossy, semi-glossy or matte coated lithographic offset paper. While such coated
offset papers are designed for printing primarily with non-aqueous solvent-based
inks, providing a topmost layer in accordance with the present invention over such
coated offset papers has been found to enable inkjet printing with high image
quality including reduced mottle, high optical density, and good physical
durability, including resistance to wet or dry abrasion, water-fastness, and
resistance to smearing from subsequent highlighter marking. Such embodiment
employing a coated offset paper as the substrate of the inkjet receiving medium of
the invention thus enables advantageous inkjet receiving mediums manufactured
taking advantage of economies of scale in preparation of the medium substrate.
Lithographic coated offset papers typically comprise a paper base
which has been coated with clay or the like and undergone surface calendering
treatment to provide a desired surface smoothness. The invention applies to the
use of both glossy and matte coated offset papers. Advantageously, the relatively
low coating weight of the topmost layer of the inkjet receiving medium of the
invention helps maintain the relative glossy or matte surface of the employed
substrate. Such coated offset papers employable as the substrate of the inkjet
receiving medium of the invention may be obtained from various commercial
paper manufacturers, including, e.g., International Paper, Sappi, New Page,
Appleton Coated, Abitibi - Bowater, Mohawk Papers, Verso, Mitsubishi, Norpac,
Domtar, and many others. Specific examples include, e.g., STERLING ULTRA
GLOSS paper (80 lb basis weight), a coated glossy offset paper for lithographic
printing manufactured by NewPage, and UTOPIA BOOK (45 lb. basis weight),
available from Appleton Coated, a coated matte offset paper.
In various embodiments, the substrate can be readily hydrophilic
and capable of adsorbing and transferring ink colorant to the substrate interior
prior to being coated thereon with the topmost layer of the invention, such as
wherein the substrate may be porous. Alternatively, the substrate can be
substantially impermeable to water or aqueous ink, such as a non-porous plastic
film. In a particular preferred embodiment, the invention is particularly useful
wherein the substrate comprises a relatively hydrophobic coated surface prior to
being coated thereon with the topmost layer, and the topmost layer provides a
continuous relatively hydrophilic surface.
While the invention is in certain embodiments directed towards the
use of coated offset papers as the substrate, the topmost layer of the invention may
also be used in combination with uncoated offset paper or other plain papers.
Further, the invention may also be used with any of those supports usually used
for inkjet receivers, such as resin-coated paper, polyesters, or microporous
materials such as polyethylene polymer-containing material sold by PPG
Industries, Inc., Pittsburgh, PA under the trade name of TESLIN, TYVEK
synthetic paper (DuPont Corp.), and OPPALYTE films (Mobil Chemical Co.) and
other composite films listed in US Patent 5,244,861. Opaque supports include
plain paper, coated paper, synthetic paper, photographic paper support, meltextrusion-
coated paper, and laminated paper, such as biaxially oriented support
laminates.
Biaxially oriented support laminates are described in US Patents
5,853,965, 5,866,282, 5,874,205, 5,888,643, 5,888,681, 5,888,683, and 5,888,714,
the disclosures of which are hereby incorporated by reference. These biaxially
oriented supports include a paper base and a biaxially oriented polyolefin sheet,
typically polypropylene, laminated to one or both sides of the paper base.
Transparent supports include cellulose derivatives, e.g., a cellulose ester, cellulose
triacetate, cellulose diacetate, cellulose acetate propionate, cellulose acetate
butyrate; polyesters, such as poly(ethylene terephthalate), poly(ethylene
naphthalate), poly( 1,4-cyclohexanedimethylene terephthalate), poly(butylene
terephthalate), and copolymers thereof; polyimides; polyamides; polycarbonates;
polystyrene; polyolefins, such as polyethylene or polypropylene; polysulfones;
polyacrylates; polyetherimides; and mixtures thereof. The kind of paper supports
listed above include a broad range of papers, from high end papers, such as
photographic paper to low end papers, such as the kind used for newsprint. In a
preferred embodiment, commercial offset-grade coated paper is used.
The topmost coating composition may be applied to both sides of
the substrate, or alternatively to only one side. The method employed to
accomplish this can be selected from a number of known techniques, including
but not limited to spraying, rod coating, blade coating, gravure coating (direct,
reverse, and offset), flexographic coating, size press (puddle and metered),
extrusion hopper coating, and curtain-coating. After drying, the resulting topmost
layer can be calendered to improve gloss, but in preferred embodiments extensive
calendering is not performed after coating the topmost layer so as to better
maintain the rub resistance advantage enabled by the invention.
In one embodiment, in which paper is used as the support, the
topmost layer can be applied in line as part of the paper manufacturing process. In
another embodiment, the topmost layer may be coated as a separate coating step
subsequent to the paper (or other substrate) manufacture. In a particular
embodiment, the topmost layer may be applied inline as part of the inkjet printing
operation, wherein such layer is applied to a substrate in a pre-coating station prior
to printing of inkjet inks. Such inline application may be performed by the
various coating processes identified above, or alternatively by a printhead
positioned inline with the ink-applying printheads. When a printhead is used to
apply the coating solution, the option exists of covering only the printed image
area with the coating material, rather than the entire area of the substrate. Pre-coat
application provides the advantage of eliminating color-to-color bleed during
imaging, since the colorants of the ink are fixed instantaneously as the ink
contacts the pre-coated substrate. Furthermore, with pre-coating, images appear
darker and have sharper edge definition, since the coating minimizes ink
penetration and allows more fixed colorant on the surface. Finally, while the precoat
material may optionally be dried completely before image printing, complete
drying of the pre-coated substrate may not be necessary. Therefore, drying can
alternatively be applied once after imaging, resulting in considerable savings in
energy.
The topmost layer of the inkjet receiving medium of the invention
includes an aqueous-soluble salt of a multivalent metal. Aqueous-soluble is
herein defined as at least 0.5 g of the salt capable of dissolving in 100 ml water at
20°C. The salt is preferably essentially colorless and non-reactive. More
preferably, the multivalent metal is a cation selected from Mg+2, Ca+2, Ba+2, Zn+2,
and Al+ , most preferably Ca+2 or Mg+2 in combination with suitable counter ions.
Examples of the salt used in the invention include (but are not
limited to) calcium chloride, calcium acetate, calcium nitrate, magnesium
chloride, magnesium acetate, magnesium nitrate, barium chloride, barium nitrate,
zinc chloride, zinc nitrate, aluminum chloride, aluminum hydroxychloride, and
aluminum nitrate. Similar salts will be appreciated by the skilled artisan.
Particularly preferred salts are CaCl2, Ca(CH3C0 2)2,MgCl2, Mg(CH3C0 2)2,
Ca(N0 3)2, or Mg(N0 3)2, including hydrated versions of these salts. Combinations
of the salts described above may also be used. The topmost layer preferably
comprises calcium ion equivalent to at least 0.05 g/m2 of calcium chloride, more
preferably equivalent to at least 0.1 g/m2 of calcium chloride.
The topmost layer further comprises particles comprised primarily
of polymer having a Rockwell Hardness of less than R90. Such particles may
comprise, e.g., various wax particles, and other sufficiently soft polymer particles.
Specific examples include polymer particles comprising, e.g., polyethylene,
poly(tetrafluoroethylene), polypropylene, ethylene bis-stearamide, synthetic
hydrocarbon waxes, carnauba wax, or a combination thereof. Preferably, the
particles are poly(tetrafluoroethylene) particles or wax particles having the
specified Rockwell Hardness. Rockwell Hardness values for many polymeric
materials are readily available (see, e.g., literature published on-line by Plastics
International (http://www.plasticsintl.com/sortable materials.php) ), and such
values can further be measured according to ASTM D785-5 1.
The preferred mode average equivalent spherical diameter (ESD)
particle size of the polymer particles is 2.0-10.0 micrometers, more preferably 3-6
micrometers. The applied laydown of these large polymer particles is preferably
deliberately kept low enough so as the gloss of the paper is not reduced due to
excessive light scatter; the exact laydown is a function of the polymer particle
size, but generally will be 0.1 g/m2 or less, preferably 0.05 g/m2 or less. It has
been found that the same coatweight of smaller polymer particles is less effective
than the larger particles in conferring dry rub protection, despite the much greater
numbers per unit area of the smaller polymer particles. By selecting particle
having a mode average particle size of greater than 2 micrometers, and more
preferably of from 2 to 10 micrometers, coating coverages may be employed
enabling both effective dry rub resistance as well as minimizing gloss reduction.
The size of the polymer particles is larger (at least 0.1 micrometer
larger and more preferably at least 0.5 micrometer larger) than the minimum
coated thickness of the topmost layer, which minimum thickness will be primarily
due to the presence of any optional binder in the applied treatment coating.
Optional binders include film forming water soluble and water dispersible latex
polymers. In a preferred embodiment, the binder polymer may comprise one or
more cationic polymer, either alone or in combination with other non-cationic
polymer binders. Examples of pre-coat compositions including polymer binders
useful for the compositions of the present invention have been described in US
patent application 201 1/0279554, and in copending, commonly assigned USSN
13/433,412, the disclosures of which are incorporated by reference herein.
Coating laydowns of these treatments are typically 1.0 g/m2 (dry) or lower,
preferably 0.5 g/m2 or lower, and electron microscopy cross-sections of such
treatments have revealed a very thin polymer film at the surface, which has been
measured to be only about 0.5 micrometers thick. Similar SEM cross-sections
have shown the thickness of a dried layer of ink, jetted at its maximum laydown,
is about 0.1 micrometer thick. Therefore, to provide good dry rub resistance, the
polymer particles employed in the present invention are selected so as to have a
particle size greater than the combined thicknesses of the applied thickness of the
binder layer plus the maximum thickness of the jetted ink layer(s) (i.e., at least 0.1
micrometer greater for a single ink laydown, and more preferably at least 0.5
micrometers greater to exceed the thickness of 4 inks at 100% laydown).
Preferred optional binders for use in the topmost layer in
accordance with one embodiment of the present invention include cross-linked
hydrophilic polymer binders as disclosed in Dannhauser et al (US 201 1/0279554),
alone or in combination with one or more additional binders. Such hydrophilic
polymer binder comprises a polymer capable of adsorbing water, and preferably is
capable of forming a continuous phase solution. Non-exclusive examples of such
materials include gelatin, starch, hydroxycelluloses, polyvinyl alcohol, polyvinyl
pyrrolidone, polyethylene imine, polyvinyl amine, and derivatives of these
materials. A preferred binder is Gohsefimer Z-320 from Nippon Gohsei, an
acetylacetate-modifed polyvinyl alcohol. The water-adsorbing hydrophilic
polymer in the topmost layer coating formulation of such embodiment is
crosslinked to improve the print resistance to abrasion while wet, as well as
provide increased cohesiveness of the coating upon drying. To provide desired
abrasion resistance and cohesiveness, the topmost layer preferably comprises at
least 0.02 g/m2 of cross-linked hydrophilic polymer binder. The identity and
amount of crosslinker will depend on the choice of polymer and its reactivity with
the crosslinker, the number of crosslinking sites available, compatibility with
other solution components, and manufacturing constraints such as solution pot life
and coating drying speed. Non-exclusive examples of crosslinker materials are
glyoxal, Cartabond TSI (Clariant), Cartabond EPI (Clariant), Sequarez 755
(Omnova), glutaraldehyde sodium bisulfate complex (Aldrich), Sunrez 700M
(Omnova), Sunrez 700C (Omnova), CR-5L (Esprix), bis(vinyl) sulfone, bis(vinyl)
sulfone methyl ether, adipoyl dihydrazide, epichlorohydrin polyamide resins and
urea-formaldehyde resins. In a particular embodiment, the cross-linked
hydrophilic polymer comprises a cross-linked aceto-acetylated polyvinyl alcohol
polymer, such as aceto-acetylated polyvinyl alcohol polymer cross-linked with a
glyoxal compound.
Preferred optional binders for use in the topmost layer of the
receiving medium in accordance with another embodiment of the invention further
includes a cationic polyelectrolyte comprising amidine moieties as described in
Xiang and Botros copending, commonly assigned USSN 13/433,412. Such
cationic polyelectrolyte polymers may also conventionally be referred to as
polyamidine or polyvinylamidine polymers, and are cationic macromolecules
having the structural unit shown b the general formula [1]:
Formula [1]
wherein R1 to R4 represent hydrogen atom of an alkyl group such as methyl group.
The cationic macromolecule having the structural unit represented by general
formula [1] can be prepared by copolymerization of acrylonitrile or
methacrylonitrile with N-vinyl-carboxylic acid amine, N-isopropenylcarboxylic
acid amide, N-vinylcarboxylic acid amide or N-isopropenylcarboxylic acid amide,
followed by hydrolysis of the obtained copolymer to obtain an amidine. There is
the possibility that the polyvinylamidine prepared as described above has
additional units comprising, e.g., a cyano group derived from acrylonitrile or the
like, carbamoyl group formed by hydrolysis of cyano group, and amino group
formed by hydrolysis of N-vinylcarboxylic acid amide unit or the like in addition
to the structural unit represented by general formula [1]. DIAFLOC KP7000
manufactured by DIA-NITRIX Company is an example of polyvinylamidine
cationic polymer available as a commercial product, which is reported to have the
following structure:
The topmost layer in such embodiment comprising a cationic polyelectrolyte
comprising amidine moieties further may include one or more second polymer
which is distinct from the cationic polyelectrolyte comprising amidine moieties
and which is selected from the group consisting of a polyamide-epichlorohydrin, a
polyamine solution polymer, and a waterborne or water-dispersible polyurethane.
Polyamide-epichlorohydrin polymers are water soluble cationic
polymers. A representative example of a polyamide-epichlorohydrin polymer
which may be used in the present invention is POLYCUP 172, available from
Hercules, Inc., which is of the formula:
-epichlorohydrin)
Polyamine solution polymers are water soluble cationic polymers.
A representative example of a polyamine solution polymer which may be used in
the present invention is CATIOFAST 159(A), available from the BASF company,
which is of the formula:
CATIOFAST 159 (A) (polyamine solution polymer)
Waterborne polyurethanes are dispersions of fine polyurethane
particles in aqueous medium. Such polymer particles may be of self-dispersable
sizes and compositions, or otherwise be treated with additional dispersing agents
to be made dispersible. A representative example of a waterborne polyurethane
polymer which may be used in the present invention is PRINTRITE DP-376,
available from Lubrizol, which is described by the manufacturer as an all aliphatic
waterborne polymer dispersion useful in textile, nonwoven, and paper
applications, and as a primer on various substrates used for aqueous inkjet printing
receivers to improve hydrophilic character.
The topmost layer of the receiving medium of the invention may
include additional polymer binders in addition to those specified above. In a
further particular embodiment, e.g., a silanol-modified polyvinyl alcohol polymer
may additionally be employed. A representative example of a silanol-modified
polyvinyl alcohol polymer which may be used in such further embodiment is
POVAL R-l 130, available from Kuraray Co., which is of the formula:
POVAL R-1 130
CH CH CH CH*
The above polymer binders may be used alone in combinations. Various further
polymer binders, including cationic polymers, and combinations thereof useful in
the present invention are exemplified in the examples below. To provide desired
abrasion resistance and cohesiveness, the topmost layer preferably comprises at
least 0.02 g/m2 , and more preferably at least 0.05 g/m2 , of combined weight of
polymer binders.
In accordance with further preferred embodiments of the
invention, the topmost layer is coated on the substrate at dry solids coat weight of
from 0.1 to 5 g/m2, preferably from 0.1 to 3 g/m2, more preferably from 0.2 to 2
g/m2, even more preferably from 0.2 to 1.5 g/m2, and most preferably from 0.2 to
less than 1.0 g/m2, and such layer preferably comprises from 30-98 wt%, more
preferably 50-90 wt%, of one or more aqueous soluble salts of multivalent metal
cations, from about 1-69 wt % (more preferably 10-50 wt%) of polymer binder,
and from about 1 to 10 wt % particles comprised primarily of polymer having a
Rockwell Hardness of less than R90 and having a mode equivalent spherical
diameter of at least about 2 micrometers, preferably from about 2 to 10
micrometers. The particles comprised primarily of polymer having a Rockwell
Hardness of less than R90 are further preferably coated in an amount of from 0.01
up to and including 0.05 grams/m2. Such combination of relatively low total solid
laydown and relatively high multivalent metal salt concentration in a topmost
coating composition, along with use of the specified combination of polymer
particles and optional polymer binders, surprisingly has been found to enable
improved inkjet printing performance when printing pigment-based aqueous inks
on a variety of substrates, including coated offset papers as discussed above.
The topmost layer coating formulation may further comprise
additional optional components, such as additional inorganic or organic particles,
though it is preferred that the coating solid laydown and relative concentration
preferences of the invention still be met. These can include, but are not limited to,
kaolin clay, montmorillonite clay, delaminated kaolin clay, calcium carbonate,
calcined clay, silica gel, fumed silica, colloidal silica, talc, wollastinite, fumed
alumina, colloidal alumina, titanium dioxide, zeolites, or organic polymeric
particles such as Dow HS3000NA.
Another aspect of the invention is directed to a method of printing
in which the above-described receiver is printed with an inkjet printer employing
at least one pigment-based colorant in an aqueous ink composition. Preferably,
the pigment-based colorants are stabilized using anionic dispersants. Such
dispersants can be polymeric, containing repeating sub-units, or may be
monomeric in nature. The present invention is particularly advantageous for
printing periodicals, newspapers, magazines, and the like. The printing method
may employ a continuous high-speed commercial inkjet printer, for example, in
which the printer applies colored images from at least two different print heads,
preferably full-width printheads with respect to the media, in sequence in which
the different colored parts of the images are registered.
One type of printing technology, commonly referred to as
"continuous stream" or "continuous" inkjet printing, uses a pressurized ink source
that produces a continuous stream of ink droplets. Conventional continuous inkjet
printers utilize electrostatic charging devices that are placed close to the point
where a filament of working fluid breaks into individual ink droplets. The ink
droplets are electrically charged and then directed to an appropriate location by
deflection electrodes having a large potential difference. When no print is desired,
the ink droplets are deflected into an ink-capturing mechanism (catcher,
interceptor, gutter, etc.) and either recycled or disposed of. When print is desired,
the ink droplets are not deflected and allowed to strike a print medium.
Alternatively, deflected ink droplets may be allowed to strike the print media,
while non-deflected ink droplets are collected in the ink capturing mechanism.
Typically, continuous inkjet printing devices are faster than droplet
on demand devices and produce higher quality printed images and graphics.
However, each color printed requires an individual droplet formation, deflection,
and capturing system. Such continuous inkjet printing devices employ a highspeed
inkjet receiving medium transport system capable of transporting at least
one of roll-fed or sheet fed receiving medium, in combination with a continuous
inkjet printhead for image-wise printing of inkjet ink onto the receiving medium
and a drying station for drying of the printed image. Use of a topmost layer in
accordance with the present invention in such a high speed continuous inkjet
printing device advantageously enables an aqueous pigment-based printed inkjet
image to be initially stabilized upon the surface of the receiving medium until the
printed image can be dried in the device drying station to result in improved image
quality, especially when printing on substrates comprising relatively hydrophobic
coated offset papers or aqueous ink impermeable plastic films.
Examples of conventional continuous inkjet printers include US
Patent 1,941,001 issued to Hansell on Dec. 26, 1933; US Patent 3,373,437 issued
to Sweet et al. on Mar. 12, 1968; US Patent 3,416,153 issued to Hertz et al. on
Oct. 6, 1963; US Patent 3,878,519 issued to Eaton on Apr. 15, 1975; and US
Patent 4,346,387 issued to Hertz on Aug. 24, 1982.
A more recent development in continuous stream inkjet printing
technology is disclosed in US Patent 6,554,410 to Jeanmaire, et al. The apparatus
includes an ink-drop-forming mechanism operable to selectively create a stream
of ink droplets having a plurality of volumes. Additionally, a droplet deflector
having a gas source is positioned at an angle with respect to the stream of ink
droplets and is operable to interact with the stream of droplets in order to separate
droplets having one volume from ink droplets having other volumes. One stream
of ink droplets is directed to strike a print medium and the other is directed to an
ink catcher mechanism.
The colorant systems of the inkjet ink compositions employed in
accordance with one embodiment of the invention may be dye-based, pigmentbased
or combinations of dye and pigment. Compositions incorporating pigment
are particularly useful. Pigment-based ink compositions are used because such
inks render printed images having higher optical densities and better resistance to
light and ozone as compared to printed images made from other types of
colorants. A wide variety of organic and inorganic pigments, alone or in
combination with additional pigments or dyes, can be in the present invention.
Pigments that may be used in the invention include those disclosed in, for
example, US 5,026,427; 5,086,698; 5,141,556; 5,160,370; and 5,169,436. The
exact choice of pigments will depend upon the specific application and
performance requirements such as color reproduction and image stability.
Pigments suitable for use in the invention include, but are not
limited to, azo pigments, monoazo pigments, di-azo pigments, azo pigment
lakes, b-Naphthol pigments, Naphthol AS pigments, benzimidazolone pigments,
di-azo condensation pigments, metal complex pigments, isoindolinone and
isoindoline pigments, polycyclic pigments, phthalocyanine pigments,
quinacridone pigments, perylene and perinone pigments, thioindigo pigments,
anthrapyrimidone pigments, flavanthrone pigments, anthanthrone pigments,
dioxazine pigments, triarylcarbonium pigments, quinophthalone pigments,
diketopyrrolo pyrrole pigments, titanium oxide, iron oxide, and carbon black. In
accordance with one embodiment of the invention, colorants comprising cyan,
magenta, or yellow pigments are specifically employed. The pigment particles
useful in the invention may have any particle sizes which can be jetted through a
print head. Preferably, the pigment particles have a mean particle size of less
than about 0.5 micrometer, more preferably less than about 0.2 micrometer.
Self-dispersing pigments that are dispersible without the use of a
dispersant or surfactant can be used in the invention. Pigments of this type are
those that have been subjected to a surface treatment such as
oxidation/reduction, acid/base treatment, or functionalization through coupling
chemistry. The surface treatment can render the surface of the pigment with
anionic, cationic or non-ionic groups such that a separate dispersant is not
necessary. The preparation and use of covalently functionalized self-dispersed
pigments suitable for inkjet printing are reported by Bergemann, et al., in US
6,758,891 B2 and US 6,660,075 B2, Belmont in US 5,554,739, Adams and
Belmont in US 5,707,432, Johnson and Belmont in US 5,803,959 and
5,922,1 18, Johnson et al in and US 5,837,045, Yu et al in US 6,494,943 Bl, and
in published applications WO 96/18695, WO 96/18696, WO 96/18689, WO
99/51690, WO 00/05313, and WO 01/51566, Osumi et al, in US Patents
6,280,513 Bl and US 6,506,239 Bl, Karl, et al, in US 6,503,31 1 Bl, Yeh, et
al, in US 6,852,156 B2, Ito et al, in US 6,488,753 Bl and Momose et al, in
EP 1,479,732 Al.
Pigment-based ink compositions employing non-self-dispersed
pigments that are useful in the invention may be prepared by any method known
in the art of inkjet printing. Dispersants suitable for use in the invention in
preparing stable pigment dispersions include, but are not limited to, those
commonly used in the art of inkjet printing. For aqueous pigment-based ink
compositions, particularly useful dispersants include anionic surfactants such as
sodium dodecylsulfate, or potassium or sodium oleylmethyltaurate as described
in, for example, US 5,679,138, US 5,651,813 or US 5,985,017.
Polymeric dispersants are also known and useful in aqueous
pigment-based ink compositions. Polymeric dispersants include polymers such
as homopolymers and copolymers; anionic, cationic or nonionic polymers; or
random, block, branched or graft polymers. The copolymers are designed to act
as dispersants for the pigment by virtue of the arrangement and proportions of
hydrophobic and hydrophilic monomers. The pigment particles are colloidally
stabilized by the dispersant and are referred to as a polymer dispersed pigment
dispersion. Polymer stabilized pigment dispersions have the additional
advantage of offering image durability once the inks are dried down on the ink
receiver substrate.
Preferred copolymer dispersants are those where the hydrophilic
monomer is selected from carboxylated monomers. Preferred polymeric
dispersants are copolymers prepared from at least one hydrophilic monomer that
is an acrylic acid or methacrylic acid monomer, or combinations thereof.
Preferably, the hydrophilic monomer is methacrylic acid. Particularly useful
polymeric pigment dispersants are further described in US 2006/0012654 Al and
US 2007/0043144 Al, the disclosures of which are incorporated herein by
reference.
Inkjet inks printed onto inkjet receiving media in accordance with
the invention may contain further addendum as is conventional in the inkjet
printing art. Polymeric dispersed pigment-based aqueous inkjet ink formulations
suitable for use in particular embodiments of the present invention include those
described, e.g., in U.S. Patent Publication Nos. US201 1/0123714,
US201 1/0122180, US20 10/0302292, and US20 10/0304028, the disclosures of
which are incorporated by reference herein in their entireties.
The inkjet ink compositions printed onto inkjet receiving media in
accordance with the invention further may comprise polymer additive which is
distinct from any dispersant which may be used to disperse the pigment particles.
The polymer additives can act as ingredient binders which may form films and
further increase printed image dry physical or wet durability. These polymers may
be classified as water-soluble polymers, water-reducible polymers or waterdispersible
polymeric particles, and include nonionic, anionic, and amphoteric
polymers. Representative examples of water soluble polymers include, polyvinyl
alcohols, polyvinyl acetates, polyvinyl pyrrolidones, carboxymethyl cellulose,
polyethyloxazolines, and polyamides. Representative examples of water-reducible
polymers include alkali soluble resins, polyurethanes (such as those found in U.S.
Patent No. 6,268,101), polyacrylic acids, styrene-acrylic methacrylic acid
copolymers (such as Joncryl® 70 from BASF Corp., TruDot® IJ-4655 from
MeadWestvaco Corp., and Vancryl® 68S from Air Products and Chemicals, Inc)
and polymers exemplified in U.S. Patent No. 6,866,379 and U.S. Patent
Application No 2005/0134665 Al. Examples of water dispersible polymeric
particles used in inkjet inks are styrene-acrylic copolymers sold under the trade
names Joncryl® (BASF Corp.), Ucar™ (Dow Chemical Co.), Jonrez®
(MeadWestvaco Corp.), and Vancryl® (Air Products and Chemicals, Inc.);
sulfonated polyesters sold under the trade name Eastman AQ® (Eastman Chemical
Co.); polyethylene or polypropylene resin emulsions and polyurethanes (such as
the Witcobonds® from Witco Corp.). These polymeric particles are preferred
because they are compatible in typical aqueous-based ink compositions, and
because they render printed images that are highly durable towards physical
abrasion, light and ozone.
Particularly preferred polymers for use in the black, cyan, magenta
and yellow inks of the ink sets employed in embodiments of the invention are
water soluble polyacrylate co-polymers and polyurethane latex binder co
polymers, which may be used alone or in mixtures. The water soluble polyacrylate
polymers can be either addition polymers or condensation polymers, both of which
are well known to those skilled in the art of polymer chemistry. Polyurethane latex
binders may be formed from at least one monomer comprising at least two
hydroxyl groups and at least one carboxyl group and another monomer comprising
at least two isocyanate groups. Water-dispersible polyurethanes are disclosed as
binders in pigmented inks in U.S. Patent No.6,533,408, and particularly useful
polyurethanes for pigmented inkjet inks which exhibit good jetting performance
and good resulting image durability are described in U.S. Patent Application No.
2004/0085419A1, the disclosures of both are incorporated herein by reference.
While any useful quantity of a polyurethane latex binder can be employed, the
cyan, magenta, yellow, and black inks of the ink set employed in embodiments of
the invention in a preferred embodiment each preferably comprise between 0.1 and
5% by weight, and more preferably present at between 0.5 and 3% by weight of a
polyurethane latex binder.
EXAMPLES
Example 1:
Treatment solutions TS- 1.1 and TS-1.2 are comprised of the same
components, but in different proportions. These are described in the Table 1.1
below:
Table 1.1
parts dry active
ingredient
component TS-1.1 TS-1.2
The coating experiment outlined below examined changes in surfactant package,
crosslinker level, and replacement of cross-linked methylmethacrylate polymer
matte bead particles (Kodak MP1, 4 micrometer average particle size) with
Lancol796 (Lubrizol, PTFE wax powder, 6 micrometer average particle size) on
dry rub resistance. Cross-linked methylmethacrylate polymer has an estimated
Rockwell hardness of R100, and PTFE has an estimated Rockwell hardness of
R58, based on literature published on-line by Plastics International
(http://www.plasticsintl.com/sortable materials .php) . The solutions were coated
on Sterling Ultragloss (NewPage) offset paper using a lab-scale extrusion hopper
coating machine. Dry rub resistance was measured by printing the coated sample
using a KODAK PROSPER continuous inkjet pilot printer with a KODAK
PROSPER polymeric dispersant dispersed pigmented inkset wherein the inks
included polyurethane polymer latex for added print durability. The printed
samples were dried for 3 days at ambient conditions. Then, a 100% black density
patch was rubbed with a 2"x4" piece of bond paper beneath a 4 lb. weight for 10
back and forth cycles using a Sutherland rub tester. Dry rub resistance was
characterized by measuring the % density loss in the abraded black patch (less is
better). The Table 1.2 below summarizes the results.
Table 1.2
dry rub
%
density
Surfactants (all expressed as % active by weight total coating solution):
A=0.1% Agitan299 antifoamant (Munzing)
B=0.3% Agitan299 antifoamant (Munzing)
C=0.5% DaPro7580 antifoamant (Elementis Specialties) +0.1% Surfynol440
surfactant/wetting agent (Air Products)
D=0.35% DaPro7580 antifoamant (Elementis Specialties) +0.1% Surfynol440
surfactant/wetting agent (Air Products)
E=0.2% DaPro7580 antifoamant (Elementis Specialties) +0.1% Surfynol440
surfactant/wetting agent (Air Products)
Note that all coatings containing Lancol796 with particle size and
Rockwell hardness in accordance with the present invention show significantly
improved dry rub resistance, regardless of solution component ratios, cross-linker
level, or surfactant package. Also note that the size of the matte/wax particle is
not the sole determinant of dry rub resistance, as the similar sized cross-linked
PMMA beads having a higher Rockwell hardness did not perform as well.
Example 2 :
Treatment solution TS-2 is comprised of 9.9 parts CaC12 salt
(Oxychem), 1.0 parts Catiofastl59A polyamime polymer (BASF), 0.25 parts
PrintRite DP376 polyurethane latex(Lubrizol), and 0.2 parts guar gum thickener
(TIC Gums). This was coated at 0.65 g/m2 dry laydown on Sterling Ultragloss
offset paper using a lab-scale extrusion hopper coater. The coated paper was
printed and tested for dry rub as described in Example 1, and shows very poor dry
rub resistance. Additional coatings were made with similar solutions that
contained Lanco 1796 PTFE wax (Lubrizol, 6 micrometer average particle size) or
Lanco 1799 PTFE wax (Lubrizol, 4 micrometer average particle size). The Lanco
waxes were added at levels so as provide 0.01, 0.02, and 0.04 g/m2 to the dry
coatings. When these coatings were printed and tested for dry rub resistance,
dramatic improvements in dry rub resistance were observed for these formulations
relative to the base TS-2 solution. This is summarized in the Table 2.1 below:
Ta l 2 1
Example 3:
Treatment solution TS-3 is comprised of 50 parts CaC12
(anhydrous, Oxychem), 22 parts Z320 modified polyvinyl alcohol (Nippon
Gohsei), 9 parts Raycat56 cationic styrene-acrylic latex (Specialty Polymer, Inc.),
4.7 parts Polycupl72 crosslinker (Ashland). A series of matte particles and waxes
of varying composition, size, and laydown were added to TS-3 as described in the
table below and coated to assess their impact on dry rub resistance. Matte particles
MP1, MP2, and MP3 were made at Kodak; Lanco 1796 and Lanco 1799 were
obtained from Lubrizol Advanced Materials, Inc.; CoatOSil DSA 6 was obtained
from Momentive Performance Chemicals, Inc.; Hydrocerf 9174, Fluoropure
Ultrafme 50CW, and nanoFlon W50C were obtained from Shamrock
Technologies, Inc.; Acumist A6 was obtained from Honeywell. The sizes of the
particles were measured in water/surfactant dispersions using a Horiba LA-920
particle size analyzer; the mode ESD particle size is reported. Rockwell hardness
values were estimated based on literature published on-line by Plastics
International (http://www.plasticsintl.com/sortable_materials.php); the hardness
for CoatOSil DSA6 was estimated to be -R100 from the description of the
manufacturing procedure (US57890517). All these solutions were coated on
Sterling Ultragloss (NewPage) offset paper using a lab-scale extrusion hopper
coating machine with 0.1% Olin 10G (dry weight relative to solution weight)
added to each coating solution as a spreading agent. After drying, the coatings
were printed on a KODAK PROSPER continuous inkjet print stand using standard
KODAK PROSPER polymeric dispersant dispersed pigmented inks. A test patch
of black ink printed over yellow ink was subjected to dry rub testing as described
in Example 1. The amount of retained black ink was used to quantify dry rub
resistance. This was calculated by measuring the visual densities of the black over
yellow color patch before and after the dry rub test, the visual density of an
unrubbed yellow color patch, and calculating the % visual density lost using the
following equation:
%Dvis lost = 100 x{Dvis(K/Y before rub) - Dvis(K/Y after
{Dvis(K/Y before rub) - Dvis(Yonly)}
Results are summarized in the Table 3.1 below.
Table 3.1
Black
over
est. Dmin Yellow Dynam.
particle Rockwell mode- Gloss dry rub CoF
matte/wax la do n R measured (%Dvis (sled/
pi + 0.002gsm
Fluoropure
3.23 Ultrafme 50CW PTFE 0.002 58 0.3 67.8 60.7% 0.332
pi + 0.005gsm
Fluoropure
3.24 Ultrafme 50CW PTFE 0.005 58 0.3 68.9 46.7% 0.328
pi + 0.032gsm
Fluoropure
3.25 Ultrafme 50CW PTFE 0.032 58 0.3 61.1 12.8% 0.316
pi + 0.001gsm
nanoFLON
3.26 W50C PTFE 0.001 58 0.4 68.3 65.7% 0.348
pi + 0.005gsm
nanoFLON
3.27 W50C PTFE 0.005 58 0.4 67.5 57.6% 0.331
pi + 0.027gsm
nanoFLON
3.28 W50C PTFE 0.027 58 0.4 63.9 23.2% 0.298
pi + 0.01 lgsm
3.29 Acumist A6 oxidized PE 0.01 1 55 8.2 66.3 0.4% 0.326
pi + 0.032gsm
3.30 Acumist A6 oxidized PE 0.032 55 8.2 65.0 -0.4% 0.283
pi + 0.108gsm
3.31 Acumist A6 oxidized PE 0.108 55 8.2 61.6 -0.2% 0.267
Note the greatly improved dry rub resistance from the larger PTFE
particles and the Acumist A6 (oxidized PE) particles. However, not all large
particles provide good dry rub resistance; the methylmethacrylate, silicone
microresin, and polystyrene particles are examples of this. Note that these less
effective particles have Rockwell hardness values greater than R90. Also of note
is that smaller PTFE particles are less effective at conferring dry rub resistance
relative to equal laydowns of larger PTFE particles. This is unexpected; at
constant coatweight, the number of larger particles should decrease as a function
of the (particle size) 3. However, it is desired that the dry laydowns of these
particles be kept low enough (-0.0 1-0.05 g/m2) so as to minimally reduce the
gloss of the coating.
The dynamic coefficient of friction of the coatings was measured
using a brushed stainless steel sled against the coated paper surface. Comparison
of these values to the %Dvis lost metric for dry rub shows coefficient of friction is
not a satisfactory property for predicting dry rub resistance. For instance, samples
3.14 through 3.16 have a coefficient of friction comparable to or even lower than
samples 3.8 through 3.10, yet the dry rub resistance is noticeably poorer for the
former samples. Similarly, samples 3.23 through 3.28 all have coefficient of
friction values equal or lower than samples 3.8 through 3.13, yet samples 3.23
through 3.28 have poorer dry rub resistance.
A multiple linear regression analysis of the data in Table 3.1 shows
a strong correlation of improved dry rub resistance with increasing particle size
and softer particles. Further analysis shows decreasing coating gloss to be
strongly correlated with increasing particle laydown. A softer, more deformable
particle (lower Rockwell hardness) thus is required for the desired dry rub
resistance of the printed image, combined with a larger particle size to provide
sufficient spacing between the print and the plain paper abradant with its relatively
rough topography. Sufficient numbers of particles must be present to maintain
this spacing, yet not so many as to cause significant light scatter from the coating
surface which will decrease coating gloss. A preferred embodiment of the
invention is the use of 0.01 to 0.05g/m 2 of particles of Rockwell hardness less than
R 90, more preferably less than R75, with a mode particle ESD size of at least 2
micrometers, more preferably at least 3 micrometers, and most preferably 3 to 10
micrometers. A more preferred embodiment employs 0.02 to 0.04g/m 2 of such
particles.
Example 4 :
Varying types of PTFE waxes were added to a treatment solution
TS-4 comprising 8.75% CaC12, 5.0% Catiofast 159A solution (50% solids
polyamine solution polymer, BASF), 0.63%> Printrite DP376 (40%> solids
polyurethane latex, Lubrizol), 0.01% each Agitan731 and Agitan299 (defoamants,
Munzing), 0.1% Metolat 725 (surfactant, Munzing), and 0.2% Kordek MLX
(biocide, Dow Chemical). These were applied to Sterling Ultra gloss offset paper
(NewPage) by hand coating with a #2.5 wound wire rod and dried with a hot air
gun. KODAK PROSPER polymeric dispersant dispersed pigmented inks
including polyurethane polymer latex for added print durability were applied to
the above coatings by handcoating with a #2.5 wound wire rod followed by drying
with a hot air gun. Black ink was applied in this way alone and over a previously
and similarly coated yellow ink. After drying, the printed areas were tested for
dry rub resistance as described in Example 1. The results are summarized in the
following Table 4.1.
Table 4.1
* based about 5.0 micron wet coating with #2.5 wired rod
Improved dry rub performance was obtained for the larger wax polymer particles
relative to equal coat weights of the smaller wax polymer particles.
Example 5 :
Another series of hand coatings were made using the same
procedures as described in Example 4. These coatings tested different treatment
solutions TS-5.1 to TS-5.7, that are described in the Table 5.1 below. Note parts
5.2, 5.4, 5.5, 5.6, and 5.7 have large wax polymer particles (Hydrocerf 9174)
added to the formulations. Dry rub was tested as described in earlier examples on
Dmax black-only patches and on Dmax black printed over Dmax yellow patches.
Table 5.1
Component Source ingredient
Ticaxan Xanthan EC TIC gums Xanthan gum
Catiofast 159(A) BASF Polyamine solution polymer (cationic)
Poval -1130 Kuraray silanol modified polyvinyl alcohol
Polycup 172 Ashland Polyamide-epichlorohydrin (crosslinker)
PrintRite DP376 Lu brizol Polyurethane
Hydrocerf 9174 Shamrock dispersion of 4 micron PTFE
Hydrocerf 797 Shamrock dispersion of 6 micron high MW PE and PTFE
KP7000 Esprix polyamidine-based polymer
The addition of the large polymer particles in accordance with the present
invention provides improved dry rub performance to a variety of treatment
solutions.
CLAIMS:
1. An inkjet receiving medium comprising a substrate and having a
topmost layer coated thereon, wherein the topmost layer comprises one or more
aqueous soluble salts of multivalent metal cations and particles comprised
primarily of polymer having a Rockwell Hardness of less than R90, where the
topmost layer is coated at a dry solids coat weight of from 0.1 to 5 g/m2 and
comprises at least 30 wt% of the one or more aqueous soluble salts of multivalent
metal cations, and provides at least 0.01 g/m2 of particles comprised primarily of
polymer having a Rockwell Hardness of less than R90 and which have an
equivalent spherical diameter of i) at least about 2 micrometers and ii) at least 0.1
micrometer greater than the minimum coated thickness of the topmost layer.
2. The inkjet receiving media of claim 1, wherein the topmost layer
is coated at a dry solids coat weight of from 0.1 to 3 g/m2.
3. The inkjet receiving media of claim 2, wherein the topmost layer
comprises from 30-98 wt% of the one or more aqueous soluble salts of
multivalent metal cations, from 1-69 wt % of polymer binder, and from 1 to 10 wt
% of the particles comprised primarily of polymer having a Rockwell Hardness of
less than R90.
4. The inkjet receiving media of claim 3, wherein the topmost layer
comprises a cationic polymer.
5. The inkjet receiving media of claim 4, wherein the one or more
multivalent metal salts comprise a calcium salt.
6. The inkjet receiving media of claim 5, wherein the topmost layer
comprises calcium ion equivalent to at least 0.10 g/m2 of calcium chloride.
7. The inkjet receiving media of claim 2, wherein the topmost layer
is coated at a dry solids coat weight of from 0.2 to 2 g/m2.
8. The inkjet receiving media of claim 2, wherein the topmost layer
is coated at a dry solids coat weight of from 0.2 to 1.5 g/m2.
9. The inkjet receiving media of claim 2, wherein the topmost layer
is coated at a dry solids coat weight of from 0.2 to less than 1.0 g/m2.
10. The inkjet receiving media of claim 1, wherein the substrate is
capable of adsorbing and transferring an aqueous ink colorant to the substrate
interior prior to being coated thereon with the topmost layer.
11. The inkjet receiving media of claim 1, wherein the substrate
comprises a relatively hydrophobic surface prior to being coated thereon with the
topmost layer, and the topmost continuous layer provides a continuous relatively
hydrophilic surface in comparison to the relatively hydrophobic substrate surface
prior to being coated.
12. The inkjet receiving media of claim 1, wherein the substrate is
a coated offset paper.
13. The inkjet receiving medium of claim 1, wherein the particles
comprised primarily of polymer having a Rockwell Hardness of less than R90
have a mode equivalent spherical diameter of at least about 2 micrometers.
14. The inkjet receiving medium of claim 1, where the topmost
layer comprises 0.01 to 0.05 g/m2 of particles comprised primarily of polymer
having a Rockwell Hardness of less than R90 and having a mode equivalent
spherical diameter of from 2 to 10 micrometers.
15. The inkjet receiving medium of claim 1, wherein the topmost
layer provides 0.01 to 0.05 g/m2 of particles comprised primarily of polymer
having a Rockwell Hardness of less than R90.
16. The inkjet receiving medium of claim 1, wherein the topmost
layer provides 0.01 to 0.05 g/m2 of particles comprised primarily of polymer
having a Rockwell Hardness of less than R75.
17. The inkjet receiving media of claim 1, wherein the one or more
multivalent metal salts comprises a cation selected from Mg+2, Ca+2, Ba+2, Zn+2,
and Al+3.
18. The inkjet receiving media of claim 1, wherein the one or more
multivalent metal salts comprise CaCl2, Ca(CH3C0 2)2,MgCl2, Mg(CH3C0 2)2,
Ca(N0 3)2, or Mg(N0 3)2, or hydrated versions of these salts.
19. A method of printing in which the inkjet receiving media of
claim 1 is printed with an inkjet printer employing at least one pigment-based
colorant in an aqueous ink composition wherein the pigment-based colorant is
stabilized using anionic dispersants or is self-dispersed.
20. The method of claim 19, comprising transporting the inkjet
receiving media by a continuous inkjet printhead applying the ink composition
onto the receiving medium, and subsequently transporting the printed receiving
medium through a drying station.
2 1. The printing method of claim 20 in which the inkjet printer is a
continuous inkjet printer and the inkjet printer applies colors from at least two
different print heads in sequence in which different colored parts of an image
printed on the inkjet-receiving medium are registered.
22. A coating composition for pre-treating a substrate prior to
inkjet printing thereon, comprising one or more aqueous-soluble salts of
multivalent metal cations, and particles comprised primarily of polymer having a
Rockwell Hardness of less than R90, where the composition has a solids content
which comprises at least 30 wt% of the one or more aqueous soluble salts of
multivalent metal cations, and the particles comprised primarily of polymer
having a Rockwell Hardness of less than R90 have a mode equivalent spherical
diameter of at least about 2 micrometers.
23. A coating composition according to claim 22, wherein the
solids content comprises from 30-90 wt% of the one or more aqueous soluble salts
of multivalent metal cations, from 10-69 wt % of polymer binder, and from 1 to
10 wt % of the particles comprised primarily of polymer having a Rockwell
Hardness of less than R90.
24. A coating composition according to claim 22, wherein the
solids content comprises from 50-98 wt% of the one or more aqueous soluble salts
of multivalent metal cations, from 1-49 wt % of polymer binder, and from 1 to 10
wt % of the particles comprised primarily of polymer having a Rockwell Hardness
of less than R90.
25. A coating composition according to claim 22, wherein the one
or more multivalent metal salts comprises a calcium salt.