Patent ID: 7696263

Claim:
An ink composition comprising: a polymer complex having a block polymer bonded to pigment; and water, wherein said block polymer comprises repeating units of polyvinyl ether structure and two or more kind of different hydrophilic blocks, in which at least one of said two or more kind of different hydrophilic blocks is stimulus-responsive, wherein said block polymer is represented by one of the following formulae (II-a) to (II-e): wherein u, v, and w are independently from 1 to 10000, and wherein Me, Et, and i-Pr denote a methyl group, an ethyl group, and an isopropyl group, respectively, and wherein said polymer complex having a block polymer bonded to pigment is produced by bonding an activated polymerization terminal group of said block polymer with said pigment having a nucleophilic functionality which can react with said activated polymerization terminal group, which is a cation.