Effect of Inorganic Pigments on Polymer Interdiffusion in a Low-Tg Latex Film

There is a continuing need to lower costs of coated paper production while at the same time maintaining or improving paper quality. To reach this goal, one would like to have the knowledge necessary to design the structure of the coating in a way that optimizes the use of latex as a pigment binder. For this purpose, one needs a deeper understanding of the role of the latex binder in the coating. We approach this problem by trying to understand how a large amount of pigment in the coating formulation affects the coalescence of latex particles and the subsequent polymer diffusion that enhances the mechanical properties. We carried out fluorescence resonance energy transfer (FRET) measurements on latex films that allowed us to follow the extent of interparticle polymer diffusion as a function of time after the latex/pigment dispersion dried. The initial energy-transfer quantum efficiency data indicate that neither precipitated calcium carbonate (CaCO 3 ) nor silica (SiO 2 ) promotes coalescence of the latex particles. CaCO 3 has little effect on the rate of polymer interdiffusion up to 80 wt %, whereas even a small amount of 25-nm silica particles has a significant influence.