Patent ID: 6933330

Claim:
A water-based ink comprising: (A) a coloring material; and (B) an aqueous dispersion of polymer particles comprising a water-insoluble graft copolymer comprising an acrylic polymer side chain (P) and a salt-forming group (Q), wherein the acrylic polymer side chain (P) is a (co)polymer consisting essentially of: at least one monomer represented by the following formula (1), CH 2 ═C(R 1 )COOR 2 (1) wherein R 1 is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and R 2 is an alkyl group having 1 to 20 carbon atoms; and optionally at least one comonomer selected from styrene, acrylonitrile and vinyl acetate, and wherein the content of the monomer represented by the formula (1) in the (co)polymer is not less than 60% by weight wherein the graft copolymer has a nonionic polymer side chain (R) comprising: (I) a polymer made of at least one monomer represented by the formula (2): CH 2 ═C(R 1 )COO(R 3 O) n R 4 (2) wherein R 1 is as defined above; R 3 is a divalent hydrocarbon group having 1 to 30 carbon atoms, which may have a heteroatom; R 4 is a hydrogen atom or a monovalent hydrocarbon group having 1 to 30 carbon atoms, which may have a heteroatom; and n is a number of 1 to 60; (II) a polymer made of at least one monomer represented by the formula (3): CH 2 ═C(R 1 )CON(R 5 )(R 6 ) (3) wherein R 1 is as defined above; and each of R 5 and R 6 is independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms; (III) a copolymer made of at least one monomer represented by the formula (2) and at least one monomer represented by the formula (3); or (IV) a group represented by the formula (4): —(R 3 O) m R 4 (4) wherein R 3 and R 4 are as defined above; and m is a number of 3 to 60 wherein the content of said nonionic polymer side chain (R) is 10 to 35% by weight of said graft copolymer.