Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-11-30
2004-04-06
Shosho, Callie (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S833000, C526S318400
Reexamination Certificate
active
06716912
ABSTRACT:
This invention relates to binders for water-resistant ink jet inks. More specifically, this invention relates to polymeric binders for use in ink jet ink applications, wherein the binder has suitable particle size, charge and glass transition temperature such that the resulting inks have good printability, do not clog the ink jet printer heads and form a water-resistant ink when applied to a print surface.
Certain ink jet inks comprise a liquid medium, a colorant, such as a pigment or dye, a binder or resin to aid in dispersing the pigment in the medium and to affix the colorant to the print surface. In order to create more durable print quality, particularly in terms of color-fastness and water- and rub-resistance of the printing ink, there has been interest in preparing ink jet inks in which the colorant is an insoluble pigment, rather than a water soluble dye. The latter are generally absorbed to some degree by the paper or other print medium, but due to their inherent water-solubility do not offer good waterfastness. Pigment-based inks are generally deposited on the surface of the print medium, making them susceptible to removal by water or abrasion. However, they are comprised of hard particles and do not form films. Nevertheless, these inks can exhibit improved waterfastness compared to dyes since they are inherently insoluble in water.
As a result of the physical properties of pigments, pigment based ink compositions have a tendency to dry smear, have low resistance to wet-rub and have low highlighter resistance. The term “dry smear,” as used herein, means applying abrasive pressure across the printed substrate and measuring any smear created thereby. The term “wet-rub,” as used herein, means applying a drop of water to the printed substrate followed by applying abrasive pressure across the printed substrate and measuring any smear created thereby; wet-rub differs from waterfastness because abrasion is used. The term “highlighter resistance,” as used herein, means applying abrasive pressure across the printed substrate with a commercially available highlighting marker and measuring any smear created thereby; an example of such marker is Sanford Corp. Major Accent brand highlighting markers. To solve this problem, the present invention was developed to provide a polymeric binder for use with a colorant to form an ink composition that improves the resistance of the printed ink to dry smear and wet-rub and provides better highlighter resistance when the ink is jetted onto the substrate. The binders of the present invention have been used in ink formulations which have demonstrated the ability to resist smearing upon dry smear and wet-rub as well as increased highlighter resistance.
Polymers have been added to inkjet ink compositions to improve durability, to improve print quality and to reduce color bleeding and feathering. However, the inclusion of polymers has resulted in increased printhead maintenance problems, including clogging of the nozzles and kogation, i.e. formation of film on or about the heater. Also, polymers may tend to form films on the nozzle plate. The addition of polymers to ink compositions also may cause decreased pigment dispersion stability and interference with bubble formation. Existing inventions have attempted to address the problems, such as kogation, clogging and other malfunctioning of the printhead, that result from the incorporation of polymers into ink compositions.
Satake et al., U.S. Pat. No. 5,814,685 (hereinafter referred to as “Satake”) disclose an ink composition in which pigment and a resin are dispersed in an aqueous medium. Satake further teaches that the resin is a polymeric core/shell material with a Tg of the core in the range of from −100 to 40° C., and a Tg of the shell in the range from 50 to 150° C., and an average particle size of 20 to 200 nm. Satake teaches that particle size greater than 200 nm causes increased maintenance problems.
Kappele et al., U.S. patent application Ser. No. 08/987,185, disclose wet-rub resistant ink compositions. Kappele teaches an ink composition utilizing specific copolymers and/or terpolymers as binders, which encapsulate or cover the colorants and form a film on the substrate when the ink is jetted.
Sacripante et al., U.S. Pat. No. 5,679,724, disclose an ink for inkjet printing including a pigment and an emulsifiable polymer resin. Further, Sacripante discloses a Tg range of 10 to 100° C., preferably 35 to 80° C. Sacripante teaches that if the Tg is too low, the print media becomes sticky.
Anton et al., U.S. Pat. No. 5,912,280, disclose an ink composition utilizing a core/shell emulsion polymer with a pigment as the colorant. Further, Anton teaches adding core/shell emulsion polymers to inks containing insoluble colorants in effective quantities to improve waterfastness. Anton illustrates a core/shell emulsion polymer containing two distinct phases having different Tg, i.e. one phase has a Tg above ambient temperature and the other phase has a Tg below ambient temperature.
Fujisawa et al., European Patent Application No. 704 303 A1, disclose an ink composition comprising a colorant, a thermoplastic resin and water. Fujisawa teaches that the thermoplastic resin has a Tg of 50 to 150° C. Fujisawa further teaches that the particle diameter of the thermoplastic resin is less than 300 nm, preferably 50 to 200 nm.
Kubota et al., European Patent Application No. 887 391, disclose an ink composition which comprises a colorant, an inorganic oxide colloid, an alkali metal hydroxide and an aqueous solvent. Kubota teaches including a resin emulsion having a particle size less than 150 nm, preferably 5 to 100 nm.
Nichols et al., European Patent Application No. 869 160 A2, disclose an inkjet ink formulation with colorant, vehicle and resin emulsion containing ionic carboxylic groups on the surface of resin emulsion particles to cause disassociation of the colorant and resin particles. The resin has 1 to 40 wt. % “carboxylic acid groups”, and Tg of 0 to 120° C. Exemplified embodiments of the resin include copolymers of butyl acrylate, methyl methacrylate and (meth)acrylic acid, with 3 to 20 wt. % acid, Tg of 53 to 95° C. and particle size of 63 to 235 nm, utilizing high Tgs and low particle sizes. The inks are said to have good water resistance, but the tests used only assessed passive water bleed, and did not assess the commercially critical wet-rub resistance or highlighter resistance.
As illustrated by Satake, Fujisawa and Kubota, prior research in this area teaches that smaller binder particles, generally less than about 200 nm average diameter, are preferred, presumably as a result of anticipating lowered maintenance problems such as clogging of the ink jet printhead nozzles. As illustrated by Sacripante and Fujisawa, prior research teaches that the apparent Tg of the binder should be significantly above ambient temperature (i.e., above about 25° C.) to avoid maintenance problems such as kogation.
As illustrated by Kappele and Anton, prior research teaches that resistance to wet-rub may be incorporated into inks by utilizing certain polymer resins or core/shell polymer emulsions.
As identified above, the challenge and problem presented by the prior art are to develop an inkjet ink binder which will remain dispersed in the complete inkjet ink formulation, will not clog the printer head nozzle or other aspects of the print mechanism, will form a film or other means to bind the ink jet pigment together and onto the surface of the paper or other print medium, and will provide a printed ink which is wet-rub, dry smear, scrub and highlighter resistant. The present invention solves all of these problems by use of a polymeric binder as described herein.
Contrary to accepted research and knowledge, the present invention provides a polymeric binder for an ink composition comprising a colorant and a polymeric binder wherein the polymeric binder has an average particle diameter of greater than 250 nm, a below ambient Tg in the range from −20 to 25° C., and an acid component content of 1% to 10% by weigh
Freeman Michael Bennett
Langenmayr Eric Jon
Madle Thomas Glenn
Rohm and Haas Company
Stauss Karl
LandOfFree
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