Effect of Latex Volumetric Concentration on Void Structure, Particle Packing, and Effective Particle Size Distribution in a Pigmented Paper Coating Layer

A series of paper coating formulations was prepared by mixing calcium carbonate, ground to two particle size ranges, with latex binders of low and high glass transition temperature, each having different equivalent spherical particle diameters. These coating formulations were prepared by keeping the carbonate volume concentration constant, while the solids content in the mix was raised by the addition of the latex volume fraction. The viscosity of the coating formulations was measured by Brookfield viscometry. A disruption of particle packing in the wet phase, caused by the presence of the increasing latex volumetric concentration, was identified by viscosity measurements. The void structures of dry coating layers, prepared from the same mixes, were characterized by mercury porosimetry and were modeled using network simulation software that generates a simplified three-dimensional void network structure representative of the sample. The software model was also used to calculate the sizes of representative structural solid elements, which fit between the simulated voids, providing information not only of the pore space but also of the effective particle and/or agglomerate packing that generates that void space. Differences in the final dry structures of coating layers were observed and attributed to the disruption of the particle packing detected by the viscosity measurements.