Incremental printing of symbolic information – Ink jet – Fluid or fluid source handling means
Reexamination Certificate
1998-12-21
2001-05-22
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Fluid or fluid source handling means
C347S105000, C347S098000, C106S031600
Reexamination Certificate
active
06234624
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method of using a dispersant for a pigmented ink jet ink.
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.
DESCRIPTION OF RELATED ART
U.S. Pat. No. 5,651,813 discloses the use of sodium N-methyl-N-oleoyl taurate dispersants in ink jet pigmented inks. However, there is a problem with these dispersants in that under some circumstances they produce images on glossy receivers which can exhibit unacceptable image quality defects. It would be desirable to produce a pigment dispersion which would produce inks that when printed onto glossy receivers have high D-max's, very good image quality, and do not exhibit any defects which would be noticeable to the customer. Furthermore, it would be desirable to have a dispersant which would be able to disperse a wide variety of pigments.
It would also be desirable to produce pigment dispersions with a low particle size in order to obtain better covering power and which would have less tendency to clog the ink jet nozzles.
It is an object of this invention to provide a method of using a dispersant for a pigmented ink jet ink which will enable the particle size of the dispersed pigment to be lower than that obtained using prior art dispersants. It is another object of this invention to provide a method of using a dispersant for an ink jet ink which will produce images which have a high D-max, and which are free of defects.
SUMMARY OF THE INVENTION
These 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-receptive substrates;
C) loading the printer with an ink jet ink composition comprising from about 0.5% to about 30% by weight of a pigment, a carrier and a hydrophobically capped oligomeric acrylamide dispersant in a ratio of dispersant:pigment from about 0.1:1 to about 5:1; and
D) printing on an ink-receptive element using the ink jet ink in response to the digital data signals.
Use of the dispersants in the invention will produce images which have a high D-max, and which are free of defects. The dispersing agents used in accordance with the invention are highly effective in reducing pigment particles to much less than one Jm in size during the milling process. These dispersions are also characterized by excellent colloidal stability, lack of flocculation and/or sedimentation. Finally, these dispersing agents are useful with a wide variety of pigments.
DETAILED DESCRIPTION OF THE INVENTION
Any hydrophobically capped oligomeric acrylamide dispersant may be used in the invention provided it produces the desired results. In a preferred embodiment of the invention, the hydrophobically capped oligomeric acrylamide dispersant has the formula (I):
or the formula (II)
or the formula (III)
wherein
each R
1
and R
2
independently represents a linear or branched alkyl, alkenyl or arylalkyl group having from 1 to about 30 carbon atoms, such as octyl, 2-ethylhexyl, decyl, dodecyl, octadecyl, octadecenyl, 3-phenylpropyl, 3-phenyl-2,2-dimethylpropyl etc.; with the sum of R
1
and R
2
comprising from about 8 to about 50 carbon atoms;
each R
3
independently represents hydrogen or a methyl group;
each X independently represents hydrogen or an alkyl group containing up to about 4 carbon atoms, such as methyl, ethyl or isopropyl etc.;
each Y independently represents hydrogen or an alkyl group containing up to about 4 carbon atoms, such as methyl, ethyl or isopropyl etc., or a hydroxylated or sulfonated alkyl group containing up to about 4 carbon atoms, such as tris(hydroxymethyl) or 2,2-dimethylethyl sulfonate, wherein the sulfonated alkyl group may contain an associated alkali metal such as sodium, or ammonium or alkylated ammonium counter ion;
each Z independently represents oxygen, NH, NR
1
or S;
m is an integer of from about 2 to about 80;
n is an integer of from 0 to about 80; and
p is an integer of from about 1 to about 6, preferably from about 1 to 2.
Examples of the hydrophobically capped oligomeric acrylamide dispersants useful in the invention include the following:
TABLE 1
Acrylamide
Dispersant
Chemical Structure
P-1
P-2
P-3
P-4
P-5
P-6
P-7
P-8
P-9
P-10
P-11
P-12
The hydrophobically capped oligomeric acrylamide dispersants useful in the invention may be prepared by methods similar to those in the examples hereafter and in Makromoleculare Chemie, (1992), 193(9), pages 2505-2517.
As noted above, the ink jet ink composition used in the method of the invention contains a hydrophobically capped oligomeric acrylamide dispersant in a ratio of dispersant:pigment from about 0.1:1 to about 5:1. In a preferred embodiment, the ratio of dispersant:pigment is from about 0.25:1 to about 2.5:1.
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 repro
Erdtmann David
Pitt Alan R.
Wear Trevor
Barlow John
Cole Harold E.
Eastman Kodak Company
Shah Manish
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