Patent ID: 7695555

Claim:
An ink composition, comprising: a liquid vehicle; and a surface-modified pigment, wherein the surface-modified pigment includes: a pigment with an outer surface; anionic groups chemically grafted to the outer surface; and replacement cationic counter ions bound to the anionic groups, the replacement cationic counter ions being selected from the group consisting of N(C 2 H 5 ) 4 + , N(C 3 H 7 ) 4 + , N(C 4 H 9 ) 4 + , and combinations thereof; wherein the replacement cationic counter ions replace original cationic counter ions bound to the anionic groups, the replacement counter ions being larger in size, more hydrophobic, or both larger in size and more hydrophobic than the original counter ions in aqueous solution; and wherein the replacement cationic counter ions are configured to decrease separation of the pigment from the liquid vehicle in an inkjet printhead.