Application of Talc in Calcium Carbonate-Containing Paper Coating Formulations

Talc has a platy structure with hydrophobic surfaces. There is weak cohesion between the crystal lattices within talc particles, hence it possesses the advantages of a very low frictional coefficient, softness, and low abrasiveness. Talc has been applied to paper coating mainly for low weight coated (LWC) gravure grade and matted art paper for offset printing. Although talc has been widely used in coating formulation in Europe, its application for the coating purpose in Asia still awaits development. The purpose of this study was to use 2 types of talc in place of kaolin clay in calcium carbonate-based coating formulations and investigation of their effects on coating colors and coated paper properties. We aimed to understand the feasibility of such applications and the potential contributions in elevating quality and lowering costs by doing so. The experimental design entailed keeping the ground calcium carbonate (GCC) in a typical art paper color formulation at 70 parts while varying the amounts of no. 1 clay substituted by talc at the 0, 25, 50, 75 and 100% levels. The coating color properties evaluated included solids content, pH, low-shear viscosity, water retention value etc. The coated paper was calendered once in a supercalender and the properties of the coated paper including brightness, opacity, gloss (at 75o), printed gloss (at 60 o), smoothness, coarseness, Leneta, picking resistance, RI wet ink absorption, RI dry picking, RI wet picking, RI drying time etc. were evaluated. The results indicate that technically talc could totally replace no. 1 clay, and the MS-500A grade had better performance. Among the color properties, talc decreased low-shear viscosity but at the cost of sacrificing water retention value to some extent. Among the coated paper properties, talc helped to improve printed gloss, smoothness, coarseness, IGT picking resistance, RI wet ink absorption, dry picking, and wet picking, but tended to decrease gloss and prolong ink drying time. Talc use showed no effects on the brightness and opacity of the coated paper and it is suitable for matte grade coated papers.