Kao Corporation

Hiroki Kawaguchi

Yusuke Shimizu

Koji Azuma

Tetsuya Eguchi

Hirokazu Hyakuda

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.

Aqueous pigment dispersion

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.

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Wakayama, Japan

Hiroki Kawaguchi