WATER-BASED PIGMENT INK COMPOSITION FOR WRITING TOOL

PURPOSE: To obtain an ink composition excellent in pigment dispersibility and stability with time by adding a specific amount of an alkylpyrrolidone to an ink composition comprising a pigment, a dispersing agent and a water-soluble solvent. CONSTITUTION: The ink composition comprising (A) a pigment, (B) a dispersing agent, (C) water and a water-soluble solvent is mixed with (D) 0.05-5wt.%, preferably 0.1-3wt.%, of a 4-20C alkylpyrrolidone (e.g. n-octylpyrrolidone, n- dodecylpyrrolidone). The component A, the component B, the component C, the water-soluble organic solvent and the component D are preferably used in a ratio of 25-20%, 1-20%, 70-40%, 10-30% and 0.05-5%, respectively. For example, 10% of carbon black, 20% of polypropylene glycol, 3% of a styrene- maleic acid resin (neutralized with ammonia), 0.1% of n-octylpyrrolidone and 66.9% of water are mixed and dispersed.