Understanding coating strength at the molecular and microscopic level

Insufficient coating strength can lead to various problems in printing and converting of pigment-coated paper and paperboard. The loss in strength, especially in the presence of printing liquids, can result from poor adhesion between the binder and the coating pigments. Experiments and numerical simulations were used to better understand the microscopic and molecular level interactions between the latex-binder and dispersant-covered coating pigments used in paper coating. Micromechanical simulations were carried out to identify the microstructural variables most influential to strength. Several new pigment dispersing agents were synthesized with the reversible addition-fragmentation chain transfer copolymerization technique, and their dispersing effect and influence on dry and wet strength of pigment coating were evaluated. Molecular level interactions between binders, coating pigments, and various functional groups used in the dispersants were studied with molecular modeling. Furthermore, dynamic mechanical thermal analysis was used to examine the influence of both commercial and novel dispersants on the pigment-latex interactions. Some of the novel dispersants synthesized and tested show promise in improving the wet strength of the coating while providing as good as or better dispersing effect when compared to a sodium polyacrylate–based commercial dispersant.