Incremental printing of symbolic information – Ink jet – Medium and processing means
Reexamination Certificate
2000-04-26
2002-06-18
Hess, Bruce H. (Department: 1774)
Incremental printing of symbolic information
Ink jet
Medium and processing means
C347S106000, C428S195100, C523S160000
Reexamination Certificate
active
06406143
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an ink jet printing method employing graft copolymers as pigment ink stabilizers.
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 lightfastness. 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. In general, dispersions suffer from poor colloidal stability due to particle agglomeration and/or sedimentation, thus limiting the usefulness of the dispersions in inks.
Although a wide variety of dispersing agents are known for pigmented ink jet inks, they are not without certain problems. For example, many dispersing agents are very selective as far as being able to disperse pigments to sub-micron size. In many instances, each class of pigments may require a specific dispersing agent. Another problem encountered with some dispersing agents is that the resulting inks suffer from unacceptable image quality properties. This can include unacceptable coalescence, banding, bleeding, densities, or other defects seen on the final printed image. Yet another problem with many commercially available dispersants is that they yield dispersions with very low surface tensions. Thus, there is a continuing need for improved dispersing agents for pigmented inks.
EP 0 889 102 relates to a dispersing agent of a styrene/maleic anhydride (SMA) copolymer, a reaction product of the SMA copolymer and an alcohol, or a combination of the SMA copolymer and the SMA copolymer/alcohol reaction product. There is a problem with this dispersing agent, however, in that it is not effective at high humectant levels and at high temperatures.
U.S. Pat. No. 5,948,843 relates to a lithographic printing ink containing a dispersing agent of a reaction product of an SMA copolymer and an alcohol as a pigment dispersant. There is a problem with this dispersing agent, however, in that it is not effective at high humectant levels and at high temperatures.
It is an object of this invention to provide an ink jet printing method employing a dispersant for a pigmented ink jet ink which will be effective at high humectant levels at high temperatures.
SUMMARY OF THE INVENTION
This and other objects are achieved in accordance with this invention which relates to an ink jet printing method comprising the steps of:
A) providing an ink jet printer that is responsive to digital data signals;
B) loading the printer with ink jet recording elements;
C) loading the printer with an ink jet ink composition; and
D) printing on the ink jet recording element using the ink jet ink in response to the digital data signals;
wherein the ink jet ink composition comprises from about 0.5% to about 30% by weight of a pigment, a carrier, a humectant and a dispersant in a ratio of dispersant:pigment from about 0.1:1 to about 5:1; the dispersant being a graft copolymer having the following formula:
wherein
R is H, halogen, an alkyl group of from about 1 to about 15 carbon atoms or an aryl group of from about 6 to about 18 carbon atoms;
R
1
is H, an alkyl group of from about 1 to about 15 carbon atoms, an aryl group of from about 6 to about 18 carbon atoms, arylalkyl, or a polydimethylsiloxane;
X
1
is H, Na or K;
X
2
is NH or O;
R
2
and R
2
′ are H or CH
3
;
R
3
is H, CH
3
, C
2
H
5
or C
3
H
7
;
x is from about 30 to about 90 weight ratio;
y is from 0 to about 30 weight ratio; and
z and z′ are from about 3 to about 50.
The dispersants employed in the invention are effective at high humectant levels at high temperatures.
DETAILED DESCRIPTION OF THE INVENTION
In a preferred embodiment of the invention, the graft copolymer is prepared from poly(styrene-co-maleic anhydride) and either poly(ethylene oxide-co-propylene oxide) or poly(ethylene oxide). In another preferred embodiment, the mole % maleic anhydride of the poly(styrene-co-maleic anhydride) is from about 20% to about 40%. In another preferred embodiment, the molecular weight of the poly(styrene-co-maleic anhydride) is from about 1000 to about 3000 and the number average molecular weight of the poly(ethylene oxide-co-propylene oxide) or poly(ethylene oxide is from about 500 to about 3000. In still another preferred embodiment, the poly(ethylene oxide-co-propylene oxide) and poly(ethylene oxide) are amine-terminated. In yet still another preferred embodiment, the mole % ethylene oxide of the poly(ethylene oxide-co-propylene oxide) is from about 30% to about 90%.
The polymers employed in the invention are graft copolymers comprising a hydrophobic backbone and a hydrophilic side chain. In a preferred embodiment of the invention, the hydrophobic backbone is poly(styrene-co-maleic acid) or an ester of poly(styrene-co-maleic anhydride), and the hydrophilic side chain is a homo- or co-polymer of ethylene oxide and propylene oxide.
The hydrophobic portion of the polymer helps the adsorption of polymer onto the surface of the pigment while the hydrophilic portion of the polymer helps the solubility of the polymer in the pigment ink composition.
Graft copolymers employed in this invention can be prepared by two methods. The first method is to react a copolymer of poly(styrene-co-maleic anhydride) with the hydroxy- or amine-terminated copolymer or homopolymer of ethylene oxide and propylene oxide. The second method is the copolymerization of styrene, maleic acid or half ester of maleic acid, with a reactive monomer containing poly(ethylene oxide) or copolymer of ethylene oxide and propylene oxide. The first method is preferred because of ease of synthesis.
Poly(styrene-co-maleic anhydride) is commercially available from Aldrich Co. or from Elf Atochem Co. (SMA resin) or can be prepared from radical polymerization. Radical polymerization is well known in the art and can be found in R. Lenz, “Organic Chemistry of Polymerization”. To control the molecular weight, chain-transfer agents may be used. Narrow molecular weight distribution (Mw/Mn<1.5) is preferred. To control the molecular weight distribution, Atom Transfer Radical Polymerization (ATRP) or Group Transfer Polymerization(GTP) are preferred.
In addition to styrene, substituted styrenes can also be used in the invention. Examples of a substituted styrene include p-methyl styrene, p-t-butyl styrene, p-chlorostyrene, p-bromostyrene, o-chlorostyrene, o-br
Chen Tien-teh
Stapleton Russell A.
Cole Harold E.
Eastman Kodak Company
Grendzynski Michael E.
Hess Bruce H.
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