Patent ID: 8403579

Claim:
A water-based ink composition for a ballpoint pen comprising a coloring agent dissolved or dispersed in an aqueous medium, a thickening inhibitor, and a shear thinning viscosity-imparting agent, wherein said aqueous medium contains water-soluble organic solvent in an amount of less than about 1%, wherein the thickening inhibitor is added together with the shear thinning viscosity-imparting agent, wherein said thickening inhibitor is composed of at least one compound selected from a group of compounds having a polyoxyethylene group and/or a polyoxypropylene group, polyvinyl pyrrolidone having an average molecular weight in the range of about 8,000 to 3,000,000, polyvinyl alcohol and cellulose ether or derivatives thereof, and wherein said sheer thinning viscosity-imparting agent is at about 0.1 to 5% by mass, said thickening inhibitor is about 0.5 to 15% by mass and a mixed mass ratio between said sheer thinning viscosity-imparting agent and said thickening inhibitor is about 1/1 to 1/30, and said water based ink composition has an enhanced dry-up resistance.