AQUEOUS DISPERSION OF PIGMENT AND INK COMPOSITION PRODUCED BY USING THE SAME

PROBLEM TO BE SOLVED: To provide an aqueous dispersion of pigment having excellent dispersion stability and heat-resistance and provide an ink composition realizing stable ink ejection over a long period not only by piezo-type ink ejection but also by thermal ink ejection requiring storage stability of the ink at a high temperature and giving a glossy printed material having smooth surface. SOLUTION: The aqueous pigment dispersion contains (A) a diketopyrrolopyrrole pigment, (B) a pigment derivative produced by introducing a sulfonic acid group to a diketopyrrolopyrrole pigment, (C) water and (D) a water-soluble organic solvent. When the dispersion is diluted with water to the total concentration of (A) the diketopyrrolopyrrole pigment and (B) the pigment derivative of 10 ppm, the ratio of the peak absorbance of the absorption spectrum exhibiting the maximum absorbance in the peak absorbance of the absorption spectrum developed at the closest short wavelength side among absorption spectrum peaks in the wavelength range of 400-800 nm, i.e. the ratio of the peak absorbance of the absorption spectrum exhibiting maximum absorbance in the peak absorbance of the absorption spectrum at the closest short wavelength side is ≤1.27. COPYRIGHT: (C)2007,JPO&INPIT