Patent ID: 7297730

Claim:
An oil-based ballpoint-pen ink composition comprising at least a colorant, a solvent consisting essentially of an organic solvent, and a shear-viscosity reducing agent, wherein said organic solvent comprises not less than 50% by weight of an organic solvent having a vapor pressure of about 665 to 6650 Pa (5.0 to 50 mmHg) and being one or more solvents selected from the group consisting of aliphatic monohydric alcohols, and wherein said shear-viscocity reducing agent is selected from non-crosslinked acrylic copolymers of acrylic acid or methacrylic acid with acrylates represented by Formula (3) or methacrylates represented by Formula (4): wherein R 1 is an alkyl group having 1 to 12 carbon atoms wherein R 2 is an alkyl group having 1 to 12 carbon atoms, and wherein the ink viscosity at the shear speed of 3.84 s −1 is not less than about 10 mPa·s (20° C.) and the shear-viscosity reduction index is about 0.3 to 0.99.