Patent ID: 7198362

Claim:
An ink set comprising plural inks for inkjet, each one of the plural inks having a maximum absorption wavelength of one of from 500 to 580 nm and from 580 to 680 nm in an aqueous medium and a different absorbance, wherein based on an absorbance of a dye or a combination of dyes in an ink, which has a maximum dye concentration out of the plural inks, an absorbance of a dye or a combination of dyes in all another ink excepting the ink having a maximum dye concentration is from 1/20 to ½, and wherein when each one of the plural inks has a maximum absorption wavelength of from 500 to 580 nm in an aqueous medium, at least one of the plural inks having a maximum absorption wavelength of from 500 to 580 nm includes an azo dye having a chromophore represented by the following formula: [(heterocyclic ring A)-N═N-(heterocyclic ring B)] wherein the heterocyclic ring A and the heterocyclic ring B are the same or different, and the azo dye having a chromophore represented by the formula [(heterocyclic ring A)-N═N-(heterocyclic ring B)] is a colorant having an oxidation potential of more positive than 0.7 V (vs SCE); and when each one of the plural inks has a maximum absorption wavelength of from 580 to 680 nm in the aqueous medium, at least one of the plural inks having a maximum absorption wavelength of from 580 nm to 680 nm includes a dye represented by the following formula (I) and the dye represented by formula (I) is a colorant having an oxidation potential of more positive than 1.0 V (vs SCE): wherein X 1 , X 2 , X 3 and X 4 each independently represents —SO-Z, —SO 2 -Z, —SO 2 NR 1 R 2 , a sulfo group, —CONR 1 R 2 or —CO 2 R 1 and at least one of X 1 , X 2 , X 3 and X 4 is —SO 2 -Z or —SO 2 NR 1 R 2 wherein Z represents a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heterocyclic group, and R 1 and R 2 each independently represents a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heterocyclic group, provided that when multiple Zs are present, these may be the same or different, Y 1 , Y 2 , Y 3 and Y 4 each independently represents a monovalent substituent, provided that when multiple X 1 s, X 2 s, X 3 s, X 4 s, Y 1 s, Y 2 s, Y 3 s or Y 4 s are present, these may be the same or different, a 1 to a 4 and b 1 to b 4 represent the number of substituents of X 1 to X 4 and Y 1 to Y 4 , respectively, a 1 to a 4 each independently represents 0 or an integer of 1 to 4 but all are not 0 at the same time, b 1 to b 4 each independently represents 0 or an integer of 1 to 4, and M represents a hydrogen atom, a metal atom or an oxide, hydroxide or halide thereof.