| 主权项 |
1. An ink composition comprising:
a pigment represented by Chemical formula 1a or Chemical formula 1b; a polymer comprising a structure unit having a diphosphonic acid group; a hydrosoluble solvent; and water, wherein when the pigment is represented by Chemical formula 1a, the pigment satisfies the relation 1: Y/X≦0.800, where X represents a peak intensity at a Bragg (2θ±0.2°) angle in a range of 2θ of from 5.5° to 6.0° and Y represents a peak intensity at a Bragg (2θ±0.2°) angle in a range of 2θ of from 26.5° to 27.5°, in a CuKα X-ray diffraction spectrum having a wavelength of 1.541 Å, where R each, independently represents hydrogen atoms, methyl groups, or chlorine atoms, wherein when the pigment is represented by Chemical formula 1b, the pigment satisfies the relation 2: Y′/X′≦0.200, where X′ represents a peak intensity at a Bragg (2θ±0.2°) angle in a range of 2θ of from 26.5° to 27.5° and Y′ represents a peak intensity at a Bragg (2θ±0.2°) angle in a range of 2θ of from 11.0° to 11.5°, in a CuKα X-ray diffraction spectrum having a wavelength of 1.541 Å, wherein the structure unit having a diphosphonic acid group is represented by Chemical formula 2 where R1 represents a hydrogen atom or a methyl group and M1+, M2+, M3+, and M4+ each, independently represent alkali metal ions, organic ammonium ions, or hydrogen ions. |
