Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-12-20
2001-08-28
Jagannathan, Vasu (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C528S425000, C564S474000
Reexamination Certificate
active
06281268
ABSTRACT:
FIELD OF THE INVENTION
This application relates to a process for making an ink jet ink using an alcohol carrier and a particular dispersant to produce a dispersion characterized by nanometer-size pigment particles.
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.
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. 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 polymeric dispersing agents is that they tend to impart an undesirably high viscosity to the resulting inks. Thus, there is a continuing need for improved dispersing agents for pigmented inks, especially for non-aqueous inks.
Dispersing agents for non-aqueous ink jet inks previously used include metal salts of styrene-acrylic copolymers, metal salts of sulfonated styrene-acrylic copolymers, phosphonium salts or quaternary ammonium salts of styrene-acrylic copolymers.
U.S. Pat. No. 5,679,138 relates to a process for preparing an ink jet ink wherein the pigment particle size distribution obtained is quite small. There is a problem with this process, however, in that the carrier medium is limited to water. It would be desirable to provide ink jet inks which employ non-aqueous carriers in order to avoid paper deformation upon printing. However, dispersing agents commonly used for aqueous dispersions generally do not work in non-aqueous dispersions.
U.S. Pat. Nos. 5,837,046; 5,739,833 and 5,538,548 relate to ink jet inks containing various Disperbyk® dispersants used in a variety of carriers such as aliphatic hydrocarbons and dibasic esters. However, there is a problem with these dispersants in that they do not provide very low particle size dispersions when used with alcohol carriers.
It is an object of this invention to provide a method for making a non-aqueous, pigment dispersion for an ink jet ink 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 another object of this invention to provide a method for making a non-aqueous, pigment dispersion for an ink jet ink which employs a dispersant which enables the production of nanometer-size pigment particles.
SUMMARY OF THE INVENTION
These and other objects are achieved in accordance with this invention which relates to a process for making an ink jet ink comprising:
a) providing a dispersion containing a pigment, an alcohol carrier and an amine-terminated polyether dispersant;
b) mixing the pigment dispersion with rigid milling media less than 100 &mgr;m;
c) introducing the mixture of step (b) into a mill;
d) milling the mixture from step (c) until the pigment particle size is below about 100 nanometers;
e) separating the milling media from the mixture milled in step (d); and
f) diluting the mixture from step (e) to obtain an ink jet ink having a pigment concentration suitable for ink jet printers.
The dispersant used in the process of the invention is highly effective in reducing pigment particles to a size of less than about 100 nm when milled in the presence of very fine milling media. The resulting dispersion is characterized by nanometer-size pigment particles. The dispersing agents employed are useful with a wide variety of pigments.
DETAILED DESCRIPTION OF THE INVENTION
As noted above, the ink jet ink composition used in the process of the invention contains an amine-terminated polyether dispersant. The dispersant is preferably used in a ratio of dispersant to pigment from about 0.1:1 to about 5:1. In a preferred embodiment, the ratio of dispersant to pigment is from about 0.5:1 to about 2:1.
In a preferred embodiment of the invention, the amine-terminated polyether has the following formula:
where
R
1
, R
4
and R
5
each individually represents a substituted or unsubstituted alkyl group having from 1 to about 6 carbon atoms;
R
2
represents hydrogen or a substituted or unsubstituted alkyl group having from 1 to about 6 carbon atoms;
R
3
represents a substituted or unsubstituted alkyl group having from 1 to about 10 carbon atoms or a substituted or unsubstituted aryl group having from about 6 to about 10 carbon atoms;
x is from about 5 to about 100; and
y is from 1 to about 6.
In another preferred embodiment, R
1
, R
4
and R
5
in the above formula each individually represents methyl or ethyl. In another preferred embodiment, R
2
is methyl. In yet another preferred embodiment, R
3
is a methyl-substituted aryl group. In still another preferred embodiment, x is from about 15 to about 45 and y is 2. An example of these dispersants which is commercially available is Disperbyk® BYK 182 from BYK-Chemie, USA.
In the present invention, any of the known pigments can be used. Pigments can be selected from those disclosed, for example, in U.S. Pat. Nos. 5,026,427; 5,086,698; 5,141,556; 5,160,370; and 5,169,436, the disclosures of which are hereby incorporated by reference. The exact choice of pigments will depend upon the specific color reproduction and image stability requirements for the printer and application. The pigment must be totally insoluble in the carrier. For four-color printers, combination of cyan, magenta, yellow, and black (CMYK) pigments should be used. An exemplary four color set is bis(phthalocyanyl-alumino)tetraphenyl-disiloxane cyan, quinacridone magenta (C.I. Pigment Red 122), Hansa® Brilliant Yellow 5GX-02 (C.I. Pigment Yellow 74), and carbon black (C.I. Pigment Black 7).
As noted above, the pigment particle size obtained using this process is below about 100 nm. This figure is understood to mean the 50
th
percentile value (half of the particles have a particle size below that value and half are above). Particle size distributions can be measured on diluted millgrind samples (about 50:1) using a Leeds & Northrop Ultrafine Particle Analyzer (UPA).
The process of preparing inks from pigments commonly involves two steps: (a) a dispersing or milling step to break up the pigment to the primary particle, and (b) a dilution step in which the dispersed pigment concentrate is diluted with a carrier and other addenda to a working strength ink. In the milling step, the pigment is usually suspended in a carrier along with rigid, inert milling media less than about 100 &mgr;m. The dispersing agent is added at this stage. Mechanical energy is supplied to this pigment dispersion, and the collisions between the milling media and the pigment cause the pigment to deaggregate into its primary particles.
There are many different types of materials which may be used as milling media, such as glasses, ceramics, metals, and plastics. In a preferred embodiment, the grinding media can comprise particles, preferably substantia
Guistina Robert A.
Maskasky Karen E.
Romano, Jr. Charles E.
Cole Harold E.
Eastman Kodak Company
Jagannathan Vasu
Shosho Callie E.
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