Patent ID: 7077894

Claim:
An inkjet ink set comprising at least two inks, wherein at least one ink contains a betaine compound and at least one other ink contains a nonionic surfactant, and (A) the betaine compound is a compound represented by one of formulae (5) and (7), R—N-(L-COOM 1 ) 2 (7) wherein M 1 is an alkali metal cation or a hydrogen atom, at least one of R 1B to R 3B and L in the formula (5) contains a group having 8 or more carbon atoms, and at least one of R and L in the formula (7) contains a group having 8 or more carbon atoms; and (B) the at least two inks contains a dye represented by one of formulae (C1), (M1), (Y1) and (BK2), wherein Y 1 , Y 2 , Y 3 and Y 4 each independently represents a hydrogen atom, a halogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an aralkyl group, an aryl group, a heterocyclic group, a cyano group, a hydroxyl group, a nitro group, an amino group, an alkylamino group, an alkoxy group, an aryloxy group, an acylamino group, an arylamino group, a ureido group, a sulfamoylamino group, an alkylthio group, an arylthio group, an alkoxycarbonylamino group, a sulfonamido group, a carbamoyl group, a sulfamoyl group, a sulfonyl group, an alkoxycarbonyl group, a heterocyclic group, an azo group, an acyloxy group, a carbamoyloxy group, a silyloxy group, an aryloxycarbonyl group, an aryloxycarbonylamino group, an imido group, a heterocyclic thio group, a phosphoryl group, an acyl group, a carboxyl group or a sulfo group, and wherein X 1 , X 2 , X 3 and X 4 in the formula (CI) each independently represents —SO-Z c , —SO 2 -Z c , —SO 2 NR 1c R 2c or —CONR 1c R 2c wherein each Z c independently represents an alkyl group, a cycloalkyl group, an alkenyl group, an aralkyl group, an aryl group, or a heterocyclic group; and R 1c and R 2c each independently represents a hydrogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an aralkyl group, an aryl group, or a heterocyclic a 1 +b 1 =4 group.