| 摘要 |
PROBLEM TO BE SOLVED: To provide a production method of oily ink for a ballpoint pen, the ink containing a pigment which reduces so-called ink dropping in a mass, such a phenomenon that ink depositing at the tip of a tip holder drops onto a paper surface to smear during writing.SOLUTION: The production method of the oily ink for the ballpoint pen includes: a step of heating a pigment dispersion liquid comprising a pigment, a resin having a molecular weight of 50,000 or less, and an organic solvent that dissolves both of the resin having a molecular weight of 50,000 or less and a resin having a molecular weight of 800,000 or more, at a temperature higher than the glass transition temperature of the resin having a molecular weight of 50,000 or less and lower than the decomposition temperature of the resin having a molecular weight of 50,000 or less, so as to improve the dispersion stability of the pigment; and then a step of adding the resin having a molecular weight of 800,000 or more to the dispersion to obtain the ink for a ballpoint pen. |
