| abstract |
A writing board ink composition comprises a medium formed of a lower alcohol solvent which contains an alcohol-soluble polymer, a scraping (erasing) agent, a surfactant and a diketopyrrolopyrrole pigment having a median Stokes diameter (ultrafine particle size) of not more than 0.2 mu m and represented by the following formula <IMAGE> [I] R1 and R2 independently represent an unsubstituted phenyl or naphthyl group of a non-water-solubilizing substituent substituted phenyl or naphthyl group, and R3 and R4 independently represent hydrogen or a non-water-solubilizing substituent. The writing board ink composition remains stable for a long time while in pens even when the resin content (alcohol-soluble polymer) is such that unclear writing and scrapability reduction (loss of scrapability or erasability) can be avoided, since the pigment of ultrafine particle size is fast to lower alcohol solvents. |