Kao Corporation

Tetsuya Eguchi

Hirokazu Hyakuda

Yusuke Shimizu

Ryuma Mizushima

Koji Azuma

Hiroki Kawaguchi

The present invention relates to a pigment water dispersion containing pigment-containing water-insoluble crosslinked polymer A particles, a water-soluble basic compound and water, in which a water-insoluble crosslinked polymer A constituting the particles has a carboxy group and a crosslinked structure containing an ester group derived from a water-insoluble crosslinking agent, a saponification value of the water-insoluble crosslinked polymer A is from 170 to 300 mgKOH/g, and the water-soluble basic compound contains a water-soluble amine compound; a process for producing the pigment water dispersion; a water-based ink for ink-jet printing which contains the pigment water dispersion; and an ink-jet printing method using the water-based ink.

Aqueous pigment dispersion

The present invention relates to a water-based pigment dispersion containing a polymer dispersant and a pigment, the polymer dispersant being prepared by crosslinking a carboxy group-containing water-insoluble polymer (A) with a water-insoluble polyfunctional epoxy compound, in which carboxy groups of the water-insoluble polymer (A) are at least partially neutralized by an alkali metal compound, and the water-based pigment dispersion satisfies the following conditions 1 to 3. The water-based pigment dispersion of the present invention can exhibit excellent redispersibility capable of suppressing solidification of the pigment or the polymer in ink ejection nozzles and can ensure good storage stability under high-temperature conditions. The conditions 1 to 3 are as follows: Condition 1: a value calculated according to the formula: {[100&#x2212;(neutralization degree)&#x2212;(crosslinking degree)]/100}&#xd7;[acid value of water-insoluble polymer (A)] is from &#x2212;30 to 30 mgKOH/g: Condition 2: a value calculated according to the formula: [(neutralization degree)/100]&#xd7;[acid value of water-insoluble polymer (A)] is from 80 to 180 mgKOH/g; and Condition 3: a value calculated according to the formula: [(crosslinking degree)/100]&#xd7;[acid value of water-insoluble polymer (A)] is from 80 to 180 mgKOH/g.

The present invention relates to a water-based pigment dispersion having not only excellent storage stability capable of suppressing solidification of a pigment or the like in ink ejection nozzles, but also excellent ejection properties and fixing properties, while maintaining good water resistance of the pigment dispersion as an advantage attained by using the pigment therein. That is, the present invention relates to a water-based pigment dispersion including a pigment, a polymer dispersant and an aqueous medium in which the pigment is dispersed in the aqueous medium using the polymer dispersant, the polymer dispersant being a water-insoluble polymer including carboxy groups that are at least partially neutralized with an alkali metal hydroxide, and having a crosslinked structure obtained by reacting a part of the carboxy groups with a water-insoluble polyfunctional epoxy compound, said water-based pigment dispersion satisfying the following conditions 1 and 2: Condition 1: a value calculated according to the formula: {[100&#x2212;(neutralization degree)&#x2212;(crosslinking degree)]/100}&#xd7;(acid value of carboxy group-containing water-insoluble polymer) being from 32 to 130 mgKOH/g; and Condition 2: a value calculated according to the formula: [(neutralization degree)/100]&#xd7;(acid value of carboxy group-containing water-insoluble polymer) being from 48 to 144 mgKOH/g.

Water-based pigment dispersion

There is provided a water-based ink for ink-jet printing which is excellent in optical density when printed on any of a high-water absorbing recording medium and a low-water absorbing recording medium, spreading of the dot size on the low-water absorbing recording medium, and rub fastness. The present invention relates to a water-based ink for ink-jet printing, including pigment-containing water-insoluble polymer particles A, water-insoluble polymer particles B, an organic solvent C and water, in which the water-insoluble polymer particles A are constituted of a water-insoluble polymer (a) including a constitutional unit derived from an ionic monomer, a constitutional unit derived from an aromatic ring-containing hydrophobic monomer and a constitutional unit derived from a specific hydrophilic nonionic monomer; the constitutional unit derived from the hydrophilic nonionic monomer is present in an amount of not less than 13% by mass and not more than 45% by mass on the basis of whole constitutional units in the water-insoluble polymer (a); the organic solvent C includes one or more organic solvents having a boiling point of 90&#xb0; C. or higher in which a weighted mean boiling point of the organic solvent C which is weighted by contents (% by mass) of the respective organic solvents in the organic solvent C is 250&#xb0; C. or lower; and a content of the organic solvent C in the water-based ink is not less than 20% by mass.

Water-based ink for inkjet recording

The present invention relates to an ink jet printing method for printing images or characters on a recording medium using a water-based ink, in which the water-based ink includes pigment-containing water-insoluble polymer particles A, water-insoluble polymer particles B, an organic solvent C and water; the water-insoluble polymer particles A includes a water-insoluble polymer (a) containing constitutional units derived from an ionic monomer (a-1), an aromatic ring-containing hydrophobic monomer (a-2) and a specific hydrophilic monomer (a-3), the constitutional unit derived from the hydrophilic monomer (a-3) being present in an amount of from 13 to 45% by mass; the organic solvent C includes one or more organic solvents having a boiling point of 90&#xb0; C. or higher, and has an average boiling point of 250&#xb0; C. or lower as a weighted mean value; and the recording medium has a water absorption of from 0 to 10 g/m2 as measured in a pure water contact time of 100 ms. The ink-jet printing method is excellent in spreading of the dot size, optical density, gloss and rub fastness when printed on a low-water absorbing recording medium.

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Wakayama, Japan

Tetsuya Eguchi