Study of Latex Contributions to the Rheology and Coated Paper Properties of Ground Calcium Carbonate and Precipitated Calcium Carbonate Paper Coatings, 2000 Coating Conference Proceedings

J. F. Attal, M. J. Pollock, J. A. Roper III--A series of latex polymers spanning a wide range of compositional modifications were formulated in a ground calcium carbonate (GCC) and a precipitated calcium carbonate (PCC) paper coating. The main objective of this study was to increase our understanding of the impact of various latex parameters on coating rheology as well as their impact on the final coated paper properties for a GCC coating compared to a PCC coating. A second objective of this study was to investigate and compare the rheological behavior of latex alone and of paper coating formulations prepared with these latex polymers. A third objective was to study if differences in rheological behavior correlated to the end use paper coating performance. The rheology of the latexes and coatings was characterized using a combination of low deformation oscillatory flow and high shear continuous flow to generate a standard flow curve spanning the shear rate range from 0.001 to 100,000 s -1 . The rheology profile was characterized by a linear low shear region, followed by a typical shear thinning behavior and followed by a limiting Newtonian viscosity region. The flow curve data showed a very wide range of differences for the different latex polymers, which were tested at the same percent solids, and degree of neutralization. The differences between the latexes spread over four decades of viscosity in the low shear range and close to two decades in the high shear range. When the latexes were formulated with pigment these differences were much less pronounced and fell within a factor of five. PCC formulations had larger differences than the GCC formulations at low shear rates and several of the PCC formulations exhibited shear-thickening behavior at high shear rates. Small particle size latexes were beneficial in reducing the high-shear viscosities. The viscosity differences for the coating formulations did not correlate with those seen for the latexes alone. Also, no obvious correlation between the coated paper performance and the coating rheology was seen in this study.