Abstract: A paper coating composition comprising a paper coating pigment and a protein adhesive. The protein adhesive contains a protein material and a dispersing agent, in an amount effective to adjust the pH of an aqueous solution containing the paper coating composition sufficiently to substantially solubilize the protein material, comprising a basic reagent containing a divalent cation and a cation binding agent. The cation binding agent is present in an amount effective to inhibit divalent cation induced gel formation and pigment flocculation.

Abstract: A polymeric or plastic pigment, useful as a partial replacement for the inorganic pigment conventionally employed in paper coating compositions is disclosed. The pigment comprises a copolymer of an animal or vegetable protein and a monomer havingh a glass transition temperature (Tg) greater than about 70.degree. C. polymerized in a surfactant free system. When employed in paper coating compositions the pigment provides a coating of improved gloss and ink holdout, as compared to a coating in which the pigment composition consists only of an inorganic material. Improved water resistance, improved water holding and a potential for reduction in the coating sticking to the calender during the paper finishing process are obtained as compared to conventional polymeric pigments.