Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
2002-03-15
2004-06-01
Berman, Susan W. (Department: 1711)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C428S461000, C428S475800, C428S483000, C428S500000, C428S511000, C428S514000, C522S081000, C522S083000, C522S084000, C522S085000, C524S800000, C524S802000, C524S815000, C524S832000, C524S833000, C524S836000
Reexamination Certificate
active
06743514
ABSTRACT:
FIELD OF INVENTION
This invention pertains to radiation-curable aqueous compositions comprising a mixture of monomer, water-reducible oligomer, and water-insoluble cationically-modified latex. More particularly, the invention pertains to radiation-curable aqueous compositions that are suitable for use as ink jet printing receptive coatings and in the production of ink jet printable products.
BACKGROUND OF THE INVENTION
Ink jet printing is widely used to print on a variety of substrates (including paper, textiles, and plastic films). These substrates are often coated with a material that enhances their receptivity for the ink jet ink. In the case of aqueous dye-based inks, which comprise the majority of inks currently used in ink jet printing, two properties are of paramount importance. The first is an affinity for water, as the coating must absorb a large amount of water from the ink in order to obtain a print that is dry to the touch in few seconds. Inkjet ink formulations often contain over 90% water. Furthermore, the coating must maintain its physical integrity while absorbing all of this water. In other words, the receptive coating must be hydrophilic enough to absorb a large quantity of water without actually being water-soluble.
The second important property is dye fixation. The majority of aqueous inkjet inks are based on dyes rather than pigments. To obtain sharp prints with high color density, the dye molecules must be immobilized almost immediately upon contact of the ink with the substrate. Penetration of the dyes into the substrate will result in reduced color density, while lateral migration of the dye molecules will cause indistinctness in the image formed.
In order to obtain high water absorption, inkjet receptive coatings are traditionally formulated with both hydrophilic pigments (such as silica or alumina) and hydrophilic binders. While the most commonly used hydrophilic binders are polyvinyl alcohol (PVOH) and polyvinylpyrrolidinone (PVP), other suitable natural and synthetic polymers are known in the art (e.g., gelatin, starch, polyethylene oxide (PEO), hydroxyethylcellulose, carboxymethylcellulose, and the like). Those polymers that contain hydroxyl groups (such as starch, PVOH, and PEO) are often cross-linked with a compound such as glyoxal or glutaraldehyde to render them water-insoluble while maintaining their hydrophilicity.
The dyes that are commonly employed in aqueous inkjet inks are anionic, containing sulfonic acid groups. Thus dye fixation is usually accomplished by the employment of cationic polymers, although some highly polar nonionic polymers (such as PVP and polyethyloxazoline) have a limited amount of dye fixing capability. A water-absorbing material and a cationic polymeric mordant are employed in typical constructions of ink jet coatings.
The most widely used cationic dye fixative in ink jet receptive coatings is poly(diallyldimethylammonium chloride), although other water-soluble cationic polymers are known in the art. For example, U.S. Pat. No. 6,010,790 to Chen et al. teaches the use of poly(vinylbennylquaternary ammonium salts). Other examples of water-soluble cationic polymers are cationic starch, cationic polyvinyl alcohol, guanidine-formaldehyde resins, epichlorohydrin-polyamine condensates, and water-soluble cationic acrylic resins.
However, a problem exists with the use of both soluble dipolar polymers and soluble cationic polymers in that, unless these polymers are cross-linked in some way, their presence has a detrimental effect on the water resistance of the ink jet prints.
Radiation curing provides an alternative method of producing a crosslinked coating. Desired coating characteristics can be obtained by incorporating appropriate monomers into the coating formulation.
Radiation-curable resins undergo crosslinking reactions when exposed suitable radiation, including ultraviolet (UV), electron beam, and other known radiations. Both free radical addition polymerization of vinyl compounds and cationic addition polymerization of epoxides and of vinyl ethers are amenable to radiation curing.
UV-curable formulations are essentially a mixture of low molecular weight reactive pre-polymers and monomers that also act as diluents. For free radical polymerizations, pre-polymers can be selected from commercially available acrylates of polyester, polyurethane, and polyether or polyepoxide. Alternatively, cationically curable systems are formulated with vinyl ethers or polyepoxides. These two curing systems require different initiators: the first, a radical generator; and the second, a photoacid that generates protons on irradiation.
Conventional radiation-curable coatings are often formulated for use as protective coatings. Such coatings are highly hydrophobic, crosslinked coatings designed to be impervious to liquids and to resist staining and abrasion. In contrast, an ink jet receptive coating should be hydrophilic in nature in order to be absorptive and susceptible to staining with inks. As noted above, ink jet inks (which are typically dilute aqueous solutions of dyes) demand coatings that can handle a high fluid load. Therefore, it is desirable that inkjet receptive coatings be able to fix water-soluble dyes so that prints are rendered water-insoluble.
Radiation-curable inks have also been employed to print on largely nonporous substrates for display graphics and other purposes. Improved adhesion, abrasion resistance, waterfastness, and gloss characteristics are some of the advantages of this technology.
Certain methods of making curable, multifunctional pre-polymers, and their use in microporous and/or semi-interpenetrating network forms have been described. For example, PCT International Publication No. WO 99/42296 describes an ink jet coating that is composed of a semi-interpenetrating network of hydrophilic/hydrophobic polymers. The hydrophobic part, a conventional curable mixture of monomer/oligomer/initiator, and the hydrophilic part, a water-soluble polymer dissolved in it, complete an interpenetrating network upon curing. The cationic, water-soluble component functions as the ink-receptive element. These formulations have the disadvantage of having to use volatile monomers, although they eventually are rendered non-volatile after curing. In the technology described, the monomers are essential for viscosity control and as solvent carriers for the ink-receptive polyvinylpyrollidinone/polyvinyl acetate copolymer. European Patent Application No. 0738608A2 describes curable polymeric materials suitable for ink jet coatings and ink formulations composed of water-soluble cationic polymers with a pre-polymer/monomer mixture. However, these formulations are made homogeneous by using water-soluble organic solvents. In both of these technologies, the use of water-soluble polymers compromises waterfastness unless they are high molecular weight materials. The high viscosity of these formulations requires use of a co-solvent or monomer as a diluent.
Therefore, an object of this invention is to disclose radiation-curable, aqueous compositions.
Another object of this invention is to disclose radiation-curable, aqueous compositions that exhibit properties that allow them to be useful in producing ink jet printing coating formulations.
A further object of this invention is to disclose radiation-curable ink jet printing coatings.
Yet another object of this invention is to disclose ink jet printable products.
SUMMARY OF THE INVENTION
The objects of this invention are met by the use of radiation-curable aqueous compositions comprising a mixture of water-reducible oligomer, monomer, and water-insoluble cationically-modified latex. Upon curing, the oligomer component and the monomer component of the mixture react in a free radical polymerization reaction to produce a continuous matrix that embeds the discontinuous phase formed by the water-insoluble cationically-modified latex particles. While these latex particles are not water-soluble, they are sufficiently hydrophilic to function as water-dissipating elements. Thus the utilization of a cationica
Berman Susan W.
McDaniel Terry B.
MeadWestvaco Corporation
Reece IV Daniel B.
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