Mineral pigments for paper: structure, function and development potential (Part II)

Beginning with the crystallographic structures of kaolin, talc and calcite, the dominant morphologies of white pigments typically used in the paper industry are discussed in relation to their specific functions as fillers and coating pigments. Control of particle size, its measurement and the response of different minerals to comminution are discussed with particular reference to the effects on pigment packing characteristics. The practical application of pigments in aqueous systems and the inherent demands for dispersion and stabilisation are outlined. Functional aspects of coverage and optical performance are dominant in the increasing market demand for improved paper properties of printability, uniformity and brightness, and the basis for these properties are summarised. Practical observation of ink-on-paper interactions using rheological methods in combination with in-situ ink tack measurements are shown to provide a direct measure of offset ink solids content and viscosity during the initial stages of absorption after printing. Based on fundamental studies of surface pores and the absorption dynamic of fluid imbibed into porous network systems the article outlines the link with printability and briefly presents the way forward to some potential strategies to meet the emerging technological demands of the printing media of the future.