A writing board ink composition containing a medium of, or based on, a lower alcohol solvent, wherein a diketopyrrolopyrrole pigment represented by the following formula [I] having a median Stokes diameter of not more than 0.2 µm, an alcohol-soluble polymer, a scraping agent and a surfactant are contained in the medium.
wherein R¹ and R² independently represent an unsubstituted or non-water-solubilizing substituent substituted phenyl group or naphthyl group; R³ and R⁴ independently represent hydrogen or a non-water-solubilizing substituent.
The writing board ink composition of the present invention remains stable for a long time while in pens even when the resin content is such that unclear writing and scrapability reduction can be avoided, since the pigment of ultrafine particle size is fast to lower alcohol solvents.
The present invention provides an aqueous black ink composition for a writing board which hardly causes thickening, coagulation of the pigment, decreasing of writing density due to sedimentation, clogging in a penpoint, and break in writing. The aqueous black ink composition comprises water, the oxidized carbon black obtained by oxidizing carbon black using hypohalogenous acid and/or salt thereof, a film forming agent, and a release agent.