Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
1999-12-27
2001-06-19
Klemanski, Helene (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031870, C106S031890
Reexamination Certificate
active
06248163
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an additive for a pigmented ink jet ink to improve printing reliability.
BACKGROUND OF THE INVENTION
Ink jet printing is a non-impact method for producing images by the deposition of ink droplets on a substrate (paper, transparent film, fabric, etc.) in response to digital signals. Ink jet printers have found broad applications across markets ranging from industrial labeling to short run printing to desktop document and pictorial imaging. The inks used in ink jet printers are generally classified as either dye-based or pigment-based.
A dye is a colorant which is molecularly dispersed or solvated by a carrier. The carrier can be a liquid or a solid at room temperature. A commonly used carrier is water or a mixture of water and organic co-solvents. Each individual dye molecule is surrounded by molecules of the carrier. In dye-based inks, no particles are observable under the microscope. Although there have been many recent advances in the art of dye-based ink jet inks, such inks still suffer from deficiencies such as low optical densities on plain paper and poor light-fastness. When water is used as the carrier, such inks also generally suffer from poor water fastness.
In pigment-based inks, the colorant exists as discrete particles. These pigment particles are usually treated with addenda known as dispersants or stabilizers which serve to keep the pigment particles from agglomerating and settling out of the carrier. Water-based pigmented inks are prepared by incorporating the pigment in the continuous water phase by a milling and dispersing process. Pigmented inks require a water soluble dispersant in the pigment slurry during the milling process. Such a dispersant is necessary to produce a colloidally stable mixture and an ink that can be “jetted” reliably without clogging the print head nozzles.
Dispersing agents in an ink jet ink have the dual function of helping to break down pigments to sub-micron size during the milling process and of keeping the colloidal dispersion stable and free from flocculation for a long period of time.
A requirement in wide format ink jet printers is the delivery of at least 500 ml of ink through a printhead before nozzles begin to fail to fire ink droplets. Reproducible quantities of ink delivered prior to print cartridge failure (ink reliability) and particle size stability, over time, have been problems encountered with ink jet inks containing pigments as colorants and anionic dispersants.
U.S. patent application Ser. No. 09/351,614, filed Jul. 12, 1999, (Docket79666HEC) entitled “Color Pigmented Ink Jet Ink Set” discloses a typical ink jet pigmented ink. However, there is a problem with print cartridges containing those inks in that the print reliability over an extended period of time is not as good as one would desire.
U.S. Pat. No. 5,833,744 relates to an ink jet ink containing a surfactant which may be an aromatic sulfonate such as sodium dodecylbenzene sulfonate. However, there is a problem with using sodium dodecylbenzene sulfonate in that the print reliability over an extended period of time is not effective with all pigments, as will be shown hereinafter.
It is an object of this invention to provide an additive for a pigmented ink jet ink which would improve the print reliability. It is another object of this invention to provide an additive for a pigmented ink jet ink which would be useful with a variety of pigments.
SUMMARY OF THE INVENTION
These and other objects are achieved in accordance with this invention which relates to an ink jet ink composition comprising from about 30 to about 90% by weight of water, from about 0.5 to about 30% by weight of a pigment, from about 0.05 to about 2% by weight of an aromatic sulfonate or disulfonate comprising sodium p-toluenesulfonate, disodium 2,5-dihydroxybenzene-disulfonate monohydrate, sodium p-hydroxybenzenesulfonate or sodium p-aminobenzenedisulfonate, and from about 10 to about 50% by weight of a humectant comprising a polyhydric alcohol.
Use of the aromatic sulfonates or disulfonates in the inks of this invention greatly increases the amount of ink that may be delivered before print nozzles begin to fail.
DETAILED DESCRIPTION OF THE INVENTION
As noted above, the ink jet ink composition of the invention contains the aromatic sulfonate or disulfonate at a concentration of from about 0.05 to about 2.0 weight percent. In a preferred embodiment, the concentration of is from about 0.075 to about 0.5 weight percent.
In the present invention, any of the known organic pigments can be used. Pigments can be selected from those disclosed, for example, in U.S. Pat. Nos. 5,026,427; 5,085, 698; 5,141,556; 5,160,370 and 5,169,436, the disclosures of which are hereby incorporated by reference. The exact choice of pigment will depend upon the specific color reproduction and image stability requirements of the printer and application. For four-color printers, combinations of cyan, magenta, yellow and black (CMYK) pigments are used. In a preferred embodiment, the pigment set is cyan pigment, C.I. Pigment Blue 15:3; quinacridone magenta, C.I. Pigment Red 122; C.I. Pigment Yellow 155; and carbon black, C.I. Pigment Black 7. The ink jet ink composition of the invention contains the pigment at a concentration of from about 1% to about 5% by weight of the ink jet ink composition.
A humectant is added to the composition of the invention to help prevent the ink from drying out or crusting in the orifices of the ink jet printhead. Polyhydric alcohols useful in the composition of the invention for this purpose include, for example, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, tetraethylene glycol, polyethylene glycol, glycerol, 2-methyl-2,4-pentanediol, 1,2,6-hexanetriol and thioglycol. As noted above, the humectant is employed in a concentration of from about 10 to about 50% by weight. In a preferred embodiment, diethylene glycol or a mixture of glycerol and diethylene glycol is employed a concentration of between 10 and 20 wt.%.
A co-solvent can also be employed in the composition of the invention. The selection of a co-solvent depends on the requirements of the specific application, such as desired surface tension and viscosity, the selected pigment, drying time of the pigmented ink jet ink, and the type of paper onto which the ink will be printed. Representative examples of water-soluble co-solvents that may be selected include (1) alcohols, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, t-butyl alcohol, iso-butyl alcohol, fur furyl alcohol, and tetrahydrofurfuryl alcohol; (2) ketones or ketoalcohols such as acetone, methyl ethyl ketone and diacetone alcohol; (3) esters, such as ethyl acetate, ethyl lactate, ethylene carbonate and propylene carbonate; and (4) sulfur-containing compounds such as dimethyl sulfoxide and tetramethylene sulfone.
Ink Preparation
A preferred method for making the inks of the invention is disclosed in U.S. Pat. No. 5,679,138, the disclosure of which is hereby incorporated by reference. In general, it is desirable to make the pigmented ink jet ink in the form of a concentrated mill grind, which is subsequently diluted to the appropriate concentration for use in the ink jet printing system. This technique permits preparation of a greater quantity of pigmented ink from the equipment. The mill grind can be diluted with either additional water or water-miscible solvents to make a mill grind of the desired concentration. By dilution, the ink is adjusted to the desired viscosity, color, hue, saturation density and print area coverage for the particular application.
Jet velocity, separation length of the droplets, drop size and stream stability are greatly affected by the surface tension and the viscosity of the ink. Pigmented ink jet inks suitable for use with ink jet printing systems should have a pH in the range of 5 to 9. Anionic and cationic surfactants may be used in the composition of the invention as disclosed in U.S. Pat. Nos. 5,324,349; 4,156
Cole Harold E.
Eastman Kodak Company
Klemanski Helene
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