Patent ID: 8038782

Claim:
An ink composition comprising: a colorant represented by the following formula (I); water; a guanidine-based compound; and a colorless water-soluble planar compound having more than ten delocalized π-electrons within one molecule: wherein each of X m (m=1, 2, 3, 4) represents a carbon atom or a nitrogen atom; each of Y m (m=1, 2, 3, 4) represents a carbon atom or a nitrogen atom; each of A m (m=1, 2, 3, 4) represents a group necessary for forming, together with X m and Y m , either an aromatic hydrocarbon ring which may further form a condensed ring with another ring or a hetero ring which may further form a condensed ring with another ring; each of A m may have a substituent; each of the substituents of A m may further have a substituent; at least one of the substituents of A m and the substituents of the substituents of A m is ionic hydrophilic group; and M represents a hydrogen atom, a metal element, a metal oxide, a metal hydroxide or a metal halide, provided that the following conditions are satisfied: (i) at least one of the four rings, each of which comprises respective A m , X m and Y m , is a hetero ring; (ii) when all of the four rings, each of which comprises respective A m , X m and Y m , are a pyridine ring, both of atoms adjacent to X m and Y m in each pyridine ring are a carbon atom; and (iii) when all of the four rings, each of which comprises respective A m , X m and Y m , are a pyrazine ring, both of atoms adjacent to X m and Y m in each pyrazine ring are a carbon atom.