Ink compositions containing modified pigment particles

A process for preparing an ink composition suitable for ink jet printing processes which comprises:

• a. preparing modified pigment particles by:
• i. first mixing together in water a free radical polymerization initiator and a monomeric vinyl aromatic salt and heating the mixture under vacuum or inert atmosphere, thereby polymerizing the vinyl aromatic salt;
• and
• ii. subsequently adding to the polymerized vinyl aromatic salt pigment particles with an average particle diameter of from about 0.001 to about 10 microns, additional vinyl aromatic salt monomers, and, optionally, additional free radical polymerization initiator, thereby further polymerizing the vinyl aromatic salt and resulting in chemical grafting of the polymerized vinyl aromatic salt to the surfaces of the pigment particles;
• and
• b. admixing the modified pigment particles thus prepared with an aqueous liquid vehicle comprising water and a humectant to result in an ink having a viscosity of 10 centipoise or less.

A process for preparing an ink composition suitable for ink jet printing processes which comprises:

• a. preparing modified pigment particles by:
• i. first mixing together in water pigment particles with an average particle diameter of from about 0.001 to about 10 microns, a monomeric vinyl aromatic salt, and a free radical polymerization initiator and heating the mixture under vacuum or inert atmosphere, thereby polymerizing the vinyl aromatic salt;
• and
• ii. subsequently adding to the mixture additional vinyl aromatic salt monomers and, optionally, additional free radical polymerization initiator, thereby further polymerizing the vinyl aromatic salt, wherein the polymerized vinyl aromatic salt is chemically grafted to the surfaces of the pigment particles;
• and
• b. admixing the modified pigment particles thus prepared with an aqueous liquid vehicle comprising water and a humectant to result in an ink having a viscosity of 10 centipoise or less.