Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2000-09-22
2002-09-17
Green, Anthony J. (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S410000, C106S411000, C106S412000, C106S413000, C106S494000, C106S495000, C106S496000, C106S497000, C106S498000
Reexamination Certificate
active
06451103
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a self-dispersible aqueous pigment dispersion having easy dispersibility in an aqueous system and excellent dispersion stability over time, and a method for preparing the same. Further, the present invention relates to an inkjet recording liquid produced from the aqueous pigment dispersion, which provides excellent light-resistance, water-resistance and hue of printed image, and simultaneously reveals excellent discharge stability at the nozzles of ink-jet printer.
2. Description of the Prior Art
Conventionally, aqueous ink and aqueous paints have been prepared using a surfactant, dispersing agent, or dispersing resin for dispersing a pigment in water. In the case of a surfactant, a foaming problem exists, and co-use of a de-foaming agent is necessary for improving foaming property. However, the co-use of the surfactant and other additives leads to problems in balance of ink properties, such as compatibility of the de-foaming agent and the surfactant, and a leveling problem in drying after printing. In the case of a dispersing resin, extremely effective dispersion stabilizing effect is recognized owing to the resin, in the ink or paint of relatively high viscosity. However, in the case of dispersion having relatively low viscosity, dissolution of the resin into the solvent imparts a significant influence on the viscosity of the dispersion, giving limitation to lowness of viscosity.
On the other hand, there have been conventionally suggested methods in which the surface of a pigment powder is chemically modified for achieving sufficient dispersion property of the pigment. As industrially effected examples, surface treatments to carbon black utilizing gas phase or liquid phase process are found. The gas phase method aims at manifestation of a polar functional group by oxidation treatment such as ozone treatment and plasma treatment. The liquid phase method is used when further intense treatment is required than in the oxidation treatment usually conducted by the gas phase method, and uses a stronger oxidation agent such as nitric acid, sodium nitrite, sodium hypochlorite, permanganate, and the like. By conducting these treatments, dispersing a pigment into an aqueous system is possible without using a dispersing agent and resin. Their application range has been enlarged, therefore. However, in these cases, a demerit of high production cost is present due to features of the treating processes, and further, application of the technology to an organic pigment is impossible, resulting in limitation of use range.
Further, there have been known methods in which a pigment derivative is specifically used as a dispersing agent. Pigment particles are surface treated by the derivative in these methods. Namely, the pigment derivative treating method is a method in which an acidic group or basic group is introduced as a substituent into a compound of the same kind as a pigment to be dispersed, to give a pigment derivative, which is allowed to be adsorbed onto the pigment particles surface to increase its polarity, to improve its wetting property, and therefore, to enhance the dispersibility of pigment particles. However, these methods have problems that bleeding and color mixing tend to occur when the paint or ink produced therefrom is actually applied onto matter for painting or printing. Also, these methods have such a fatal problem unsolved, namely thixotropic characteristics of the system, that dispersed particles may easily happen to flocculate even if the dispersion of particles has been once attained. This has made it difficult for us to achieve a stable dispersion of pigment particles only by using a pigment derivative. Various trials have been made on addition of a surfactant, organic solvent and other additives to this dispersion system to improve the property, however, there have been actually no basic solution found. Rather, these additional additives make the disperse system complex and results in the troubles such as dewetting (crawling) during drying a coated film, etc.
Regarding their applications, recording liquid for inkjet printing, which has so proliferated in recent years, is one example for practical use of such aqueous coloring materials prepared by dispersing a dye or pigment in an aqueous system. As inkjet recording liquid, one which is prepared by dissolving a water-soluble dye in an aqueous solution composed of a glycol-based solvent and water has been conventionally used. However, the resulting recorded article has a problem of poor water-resistance since the recording liquid contains a water-soluble dye, and for improving this problem, a recording liquid prepared by dispersing an organic pigment in an aqueous medium has been developed. However, it is extremely difficult, as described above, to disperse a pigment in the form of a minute particle in an aqueous system and maintain the dispersed condition stably, unlike a dye which is dissolved in an aqueous system. In addition, high resolution of recent inkjet printing has made the nozzle diameter extremely minute. Accordingly, the particle size of a pigment used in the recording liquid is also required to be made finer, consequently, high dispersion of minute particles, which is a higher dispersion technology than that of the conventional ones, is needed. Further, properties naturally required for a recording liquid such as discharge stability from printer nozzles, re-dispersibility, color developing property after printing, and the like should also be maintained together, and under actual condition, simultaneous satisfaction of the properties required for an inkjet recording liquid has not been accomplished.
SUMMARY OF THE INVENTION
Accordingly, the primary object of the present invention is to provide a self-dispersible aqueous pigment dispersion having excellent storage stability over time. Another object of the present invention is to provide a pigment type inkjet recording liquid which manifests discharge stability at nozzles, and has sufficient color-reproducing range when printed, and has excellent water-resistance and light-resistance without bleeding and color mixing as above-mentioned.
The present invention disclosed herein is a self-dispersible aqueous pigment dispersion comprising an aqueous solution, particles of a pigment and a water-soluble pigment derivative, said particles being dispersed in the aqueous pigment dispersion in a concentration within the range from 2 to 25 wt. % based on the amount of the aqueous pigment dispersion, wherein a part of the water-soluble pigment derivative is adsorbed on the surface of the particles of the pigment to form dispersed particles comprising the particles of the pigment adsorbed by said part of the pigment derivative, and the remaining parts of the water-soluble pigment derivative are free in the dispersion without being adsorbed on the surface of the pigment in a concentration less than the critical flocculation concentration on which flocculation is initiated on said particles of the pigment dispersed under said concentration.
The water-soluble pigment derivative preferably comprises a compound in which an acidic functional group or salt thereof has been introduced into the skeleton of the pigment molecule. In this case, the acidic functional group is preferably a carboxylate group or sulfonate group.
In the pigment dispersion of the present invention, the dispersed particles preferably have an average particle diameter of 10 to 300 nm. Furthermore in the present invention, it is preferable that the particles of the pigment are dispersed in the aqueous pigment dispersion in a concentration within the range from 15 to 20 wt. % based on the amount of the aqueous pigment dispersion, and the viscosity of the aqueous pigment dispersion is 3 to 20 cps.
Regarding the pigment derivative, according to the present invention, said part of the aqueous pigment derivative adsorbed on the surface of the pigment is preferably in an amount ranging from 0.01 to 1.5 mmol/g based on the amou
Iguchi Tsukasa
Kato Mikiya
Mochizuki Akimitsu
Uemura Toshiyuki
Green Anthony J.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Toyo Ink Mfg. Co. Ltd.
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