Abstract: Disclosed is a water based ink composition for a rollerball pen that includes at a least colorant, a water-soluble organic solvent, water, a shear thinning viscosity property-providing agent, a lubricant, and a bubble suppressant. The ink composition includes a phosphate-ester based surfactant having a structure of general formula 1 as the lubricant, and an erythorbic acid or a derivative thereof as the bubble suppressant (n represents an integer of 1 or more, R represents an alkyl group having carbon numbers of 12 to 15, and R? represents H or R—(C2H4O)n—).

Abstract: In order to obtain an ink for oil-based ballpoint pens and an oil-based ballpoint pen which are excellent in handwriting sharpness, handwriting dryness, handwriting and feeling of writing, an ink composition includes an oil-soluble dye, water, an organic solvent whose vapor pressure at 20° C. is 0.5 mmHg or more and which dissolves the water, and an organic solvent whose vapor pressure at 20° C. is 0.1 mmHg or less and which dissolves the organic solvent whose vapor pressure at 20° C. is 0.5 mmHg or more. A total of these three components is 20 to 75% by mass based on an entire mass of the ink composition. A content of the water is 3.0 to 15.0% by mass based on the entire mass of the ink composition. An ink viscosity at 20° C. is 100 to 5,000 mPa·s. The water and the other components are formulated, mixed and stirred to produce the ink. A ballpoint pen refill with low vapor permeability is used.

Abstract: An ink composition for oil-based ballpoint pens is comprised of a solvent, a colorant and an anti-corrosive wetting agent. The solvent is a water containing water-in-oil-type organic solvent. The colorant is a combination of a dye and a pigment, wherein the pigment is dispersed in the ink with a nonionic surfactant. The anti-corrosive wetting agent is a phosphate based surfactant. An oil-based ballpoint pen using the above ink is also included.