Production process of purified pigments, and purified pigments

摘要

A process is disclosed for the production of a purified pigment, in which electrolyte ions and fine particles of the opposite polarity have been either completely or partly eliminated so that the purified pigment will not become a hard cake in a slurry state and will hardly undergo secondary aggregation even when dried. The purified pigment is obtained by bringing an aqueous dispersion of particles of the pigment into contact with an H-type cation-exchange resin or an OH-type anion-exchange resin, whereby counter ions are ion-exchanged to either lower or raise the pH of the aqueous dispersion. As a result, the dispersion stability of the pigment particles is destroyed, and only acidic or basic pigment particles are caused to sediment and are hence separated. A process for the production of a highly-classified purified pigment is also provided. An aqueous dispersion of pigment particles is used after con­ducting ion-exchange treatment and deflocculating the pig­ment particles. The aqueous dispersion is classified rely­ing upon differences in sedimentation velocity among the pigment particles. followed by ion-exchange treatment to destroy the stability of the aqueous dispersion.