Patent ID: 6986808

Claim:
An ink composition comprising: (a) a liquid medium; (b) a pigment; (c) at least 0.1% by weight of the ink of an amphiphilic material having the formula R—O—Q n A − M + where R represents an alkyl, aryl, akyl-aryl or alkenyl group; Q represents a hydrophilic repeating unit of ethylene oxide or propylene oxide, wherein n>4; A − represents a sulfate, sulfonate or phosphate group; M + represents a cation such as potassium, sodium, lithium or ammonium; and where if the pigment is a modified carbon black with organic groups covalently bonded thereto, the amphiphilic material has the same charge as the modified carbon black; and at least 0.1% by weight of the ink of a second amphiphilic material, where the second amphiphilic material has the formula XQ n R′—Y—R where X represents hydroxyl or amino functionality; Q represents a hydrophilic repeating unit of ethylene oxide or propylene oxide, wherein n>4; R′ represents C 1 to C 6 alkyl functionality; Y represents oxygen, nitrogen or sulfur, and R represents an alkyl, aryl, alkyl-aryl or alkenyl group.