Ink compositions

Details Ink compositions Ink compositions

1999-12-14

2003-11-11

Shosho, Callie (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C524S556000, C524S560000, C524S577000

Reexamination Certificate

active

06646024

ABSTRACT:

TECHNICAL FIELD
This invention relates to the field of ink compositions for ink jet printers.
BACKGROUND ART
The present invention relates to ink compositions for ink jet printers. More particularly, the present invention relates to ink compositions comprising a colorant and a polymeric binder.
Ink jet printing is a conventional technique by which printing is normally accomplished without contact between the printing apparatus and the substrate, or medium, on which the desired print characters are deposited. Such printing is accomplished by ejecting ink from the ink jet printhead of the printing apparatus via numerous methods which employ, for example, pressurized nozzles, electrostatic fields, piezo-electric elements and/or heaters for vapor phase bubble formation.
The ink compositions used in ink jet printing typically employ an aqueous carrier, usually water, colorants and low molecular weight water miscible materials. The colorants which may be employed include dyes and pigments. Pigments provide improved properties such as improved print quality, lightfastness and waterfastness. Unlike dyes, which penetrate into the substrate along with the other components of the ink, pigments tend to sit on top of the substrate. 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 using a cloth and measuring the optical density of the residual ink which lifts from the substrate onto the cloth; 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 an ink composition comprising a colorant and a polymeric binder 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 present invention has demonstrated the ability to resist smearing upon dry smear and wet-rub as well as increased highlighter resistance.
Polymers have been added to ink jet 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.
U.S. Pat. No. 5,814,685 to Satake, et al. (hereinafter referred to as “Satake”) discloses 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 glass transition temperature (Tg) of the core in the range of from −100° C. to 40° C., and a Tg of the shell in the range from 50° C. 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.
U.S. Pat. No. 6,063,834; filed Dec. 8, 1997 to Kappele, et al. and assigned to Lexmark International, Inc. (hereinafter referred to as “Kappele”) discloses 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.
U.S. Pat. No. 5,679,724 to Sacripante, et al. (hereinafter referred to as “Sacripante”) discloses an ink for ink jet printing including a pigment and an emulsifiable polymer resin. Further, Sacripante discloses a Tg range of 10° C.-100° C., preferably 35° C.-80° C. Sacripante teaches that if the Tg is too low, the print media becomes sticky.
European Patent Application No. 851 010 of inventor Anton, et al. (hereinafter referred to as “Anton”) discloses 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.
European Patent Application No. 704 303 of inventors Fujisawa, et al. (hereinafter referred to as “Fujisawa”) discloses an ink composition comprising a colorant, a thermoplastic resin and water. Fujisawa teaches that the thermoplastic resin has a Tg of 50 °-150° C. Fujisawa further teaches that the particle diameter of the thermoplastic resin is less than 300 nm, preferably 50-200 nm.
European Patent Application No. 887 391 of inventors Kubota, et al. (hereinafter referred to as “Kubota”) discloses 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 5-100 nm.
European Patent Application No. 869 160 A2 of inventors Nichols, et al. (hereinafter referred to as “Nichols”) discloses 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 of Nichols has 1 to 40 wt. % “carboxylic acid groups”, and Tg of 0° C. 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° C. to 95° C. and particle size of 63 nm to 235 nm, utilizing high Tgs and low particle sizes. Nichols asserts that the inks have good water resistance, however the tests of Nichols 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 inkjet 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 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 printhead nozzle or other aspects of the print mechanism, will form a film or other means to bind the 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 inven

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