Coated paper microstructure: particle shape - microstructure interrelations

Model coatings with differing pore structures were prepared based on precipitated calcium carbonate (PCC), ground calcium carbonate(GCC) and kaolin. Corresponding numerical model structures were also constructed. The physical coating layers were assessed with high-resolution Focused Ion Beam (FIB). The FIB images of the coating structures were analyzed with modern image analysis techniques, including a Maximal Inscribed Sphere(MIS) approach and gradient analysis. The proposed approach was the basis for producing new information about the microscopic properties of paper coatings, assessing also the interrelations between the particle shapes and the corresponding microscopic pore structures. The results indicate that the statistics calculated for the numerical coating structures was found to be in reasonable agreement with that of the experimental data. The PCC and the kaolin samples had the highest and lowest porosity, respectively. Such differences, which were also detected when quantifying the pore shapes, are attributed to the different particle shapes. The study demonstrated that the fundamental knowledge generated from the image analysis on the experimental 2-D sections and the numerical models can be used to improve our mechanistic understanding of the links between pigments, coating structure and paper/printing performance.