Patent ID: 7521491

Claim:
An oil-based ink for a ball-point pen comprising at least a colorant and a resin, as well as a solvent selected from alcohols, polyhydric alcohols and glycol ethers each having a vapor pressure at 25° C. of 0.001 mmHg or higher as a main solvent occupying 50% or more of the entire solvent, and satisfying at least one of the following (a) and (b): (a) comprising from 0.01 to 1.5% by weight of a high polymerization degree polyvinyl butyral with a polymerization degree of 900 (theoretical molecular weight of 60,000) or more, and (b) comprising a pigment as the colorant and polyvinyl butyral as a dispersant, said main solvent being polyhydric alcohol or glycol ether represented by the following chemical structural formula (1) where R 1 , R 2 , and R 3 each represents independently H or CH 3 .