WATER-BASED PIGMENT DISPERSION AND INK COMPOSITION USING THE SAME

PROBLEM TO BE SOLVED: To provide a water-based pigment dispersion excellent in disperse stability and heat resistance and further to provide an ink composition capable of realizing stable discharge of ink over a long period not only in piezo system, but also in thermal system in which storage stability of ink at high temperature is required. SOLUTION: The water-based pigment dispersion comprises (A) an organic pigment, (B) a pigment derivative in which a sulfonic acid group is introduced into the organic pigment and/or a pigment derivative in which a sulfonic acid group is introduced into a pigment having the same chemical structure as a part of chemical structure which the organic pigment (A) has, (C) water and (D) a water-soluble organic solvent. In the water-based pigment, surface tension of the water-based pigment dispersion at 25°C is 25-60 mN/m and a sulfate ion concentration, contained in the water-based dispersion when concentration of a solid content composed of the organic pigment (A) and the pigment derivative (B) in the water-based pigment dispersion is 4 wt.%, is ≤50 ppm. COPYRIGHT: (C)2006,JPO&NCIPI