| 摘要 |
PROBLEM TO BE SOLVED: To improve the dispersion stability of an organic pigment in a water medium, by bonding previously an amine modified group onto the surface of the organic pigment and adding a pigment dispersant having unneutralized anionic groups to the dispersion, thereby enhancing the fluidity and storage stability of organic pigment dispersions or water inks in which the organic pigment is used. SOLUTION: The organic pigment dispersion is formed by dispersing, in a water medium, an organic pigment onto the surface of which a modified group represented by formula I or II is bonded, and adding a pigment dispersant having unneutralized anionic groups. In the formulae I and II, R1 and R5 are each a 1-4C alkylene group; and R2, R3 and R4 are each hydrogen or a 1-3C alkyl group. The proportion of neutralized anionic groups is preferably 95% or less in the total anionic groups that the pigment dispersant contains. The unneutralized anionic groups that the pigment dispersant contains are preferably carboxylic and sulfonic groups. The modified group is bonded onto the surface of the organic pigment by treating the pigment with an aminated silane coupling agent.
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