Patent ID: 7479183

Claim:
An ink jet ink composition comprising water, a humectant, and composite pigment polymer particles, wherein said composite pigment polymer particles have a pigment phase and a polymer phase, said polymer phase comprising a polymer formed from a) an ethylenically-unsaturated monomer free of ionic charge groups and capable of addition polymerization to form a substantially water-insoluble homopolymer, and b) another ethylenically-unsaturated monomer capable of addition polymerization to form a substantially water-soluble homopolymer; said particles being formed in situ, wherein a portion of an addition polymerization initiator is added to an aqueous pigment mixture, wherein said aqueous pigment mixture contains no monomer which is used to form the polymer phase, and then adding a monomer mixture of subparagraphs a) and b) for forming the polymer phase to the pigment mixture in a continuous process the ink jet ink composition being stable as defined by said composite pigment polymer particles not increasing in mean particle size more than about 18% when said ink jet ink composition is incubated for one week at 60° C., wherein said composite pigment polymer particles have a mean particle size of less than about 80 nm and wherein the ratio of said pigment phase to said polymer phase is from about 30:70 to about 70:30.