Patent ID: 8309629

Claim:
An ink composition comprising a polymerization initiator, a polymerizable monomer, and a phosphoric acid group-containing polymer having a weight-average molecular weight in a range of from 10,000 to 30,000 and has a phosphoric acid group content of 0.4 meq/g to 3.6 meq/g, wherein the phosphoric acid group-containing polymer is a single polymer or a mixture of two or more polymers selected from the group consisting of a polyurethane resin having, as its skeleton, a product of reaction between at least one diisocyanate compound represented by the following Formula (1A) and at least one diol compound represented by the following Formula (1B); a polyester resin; a polyurea resin; and a (meth)acrylic resin represented by the following Formula (1-3): OCN—X 0 —NCO (1A) HO—Y 0 —OH (1B) wherein in Formula 1A and Formula 1B, X 0 and Y 0 each independently represents a divalent organic residue; and wherein in Formula (1-3), R represents a hydrogen atom or a methyl group; R 107 and R 108 each independently represents a hydrogen atom, sodium, potassium, an alkyl group or an aryl group; Z 1 represents a hydrogen atom or a univalent organic group; and W represents a divalent linkage group selected from the group consisting of a straight-chain having 1 to 20 carbon atoms, branched-chain or cyclic alkylene, a straight-chain, branched-chain or cyclic alkenylene having 2 to 20 carbon atoms, an alkynylene group having 2 to 20 carbon atoms, an arylene having 6 to 20 carbon atoms, —OC(═O)—,—OC(═O)Ar—, —OC(═O)O—, —OC(═O)OAr—, —C(═O)N(R)—, —C(═O)N(Ar)—, —SO 2 N(R)—, —SO 2 N(Ar)—, alkyleneoxy, polyalkyleneoxy, aryleneoxy, polyaryleneoxy, —C(═O)O—, —C(═O)O—Ar—, —C(═O)Ar—, —C(═O)—, —SO 2 O—, —SO 2 OAr—, —OSO 2 —, OSO2Ar—, —N(R)SO 2 —, —N(Ar)SO 2 —, —N(R)C(═O)—, —N(Ar)C(═O)—, —N(R)C(═O)O—, —N(Ar)C(═O)O—, —OC(═O)N(R)—, —OC(═O)N(Ar)—, —N(Ar)—, —N(R)—, —N + (R)(R′)—, —N + (R)(Ar)—, —N + (Ar)(Ar′)—, —S—, —SAr—, —ArS—, a heterocycle residue of 3- to 12-membered monocyclic or condensed ring containing at least one hetero atom, —OC(═S)—, —OC(═S)Ar—, —C(═S)O—, —C(═S)OAr—, —C(═S)OAr—, —C(═O)S—, —C(═O)SAr—, —ArC(═O)—, —ArC(═O)N(R)—, —ArC(═O)N(Ar)—, —ArC(═O)O—, —ArC(═O)S—, —ArC(═S)O—, —ArO— and —ArN(R)—, wherein R and R′ in the W linkage group each independently represents a hydrogen atom, a straight-chain or branched alkyl group, a chain or cyclic alkyl group, a straight-chain or branched alkenyl group, a chain or cyclic alkenyl group, a straight-chain or branched alkynyl group, or a chain or cyclic alkynyl group; and Ar and Ar′ each independently represents an aryl group.