Influence of pigment packing behavior on the adhesive requirements of aqueous paper coatings

The amount of adhesive included in an aqueous paper coating formulation is critical to the performance and appearance of the final product. While the time-honored “weight ratios” are typically used to formulate pigmented coatings for paper, pigment volume concentration (or alternatively, % void volume) has been found to be much more useful in determining the interactions of pigments with the adhesive on the properties of such aqueous coatings. In this study, slurries of commercial kaolin clay and ground calcium carbonate pigments used in papermaking applications were blended and then centrifuged to determine the maximum packing efficiency of the pigments. Isolated films of coatings made from selected pigment blends and increasing levels of latex adhesive were tested for void volume percentage and tensile modulus. Based on these results, a regression equation between pigment interstitial space and the mechanical strength of different coating films was established.