Topography and gloss of precipitated calcium carbonate coating layers on a model substrate

This work investigates the correlation of topography, morphology, and optical properties between a rough substrate and the coatings covering it. A model substrate (YUPO((R)) film, "synthetic paper") was coated with increasing amounts of rod-like precipitated calcium carbonate (PCC) pigment. A versatile roughness analysis was carried out for measured atomic force microscopy (AFM) topographical 3-D images at three different length scales: 3, 10, and 50 mu m. The results give novel detailed information about various topographical features of pigment, coatings, e.g., surface porosity, effective surface area, kurtosis, and density of local summits. A relatively low coating thickness covered and smoothed the surface on large scale (50 mu m), but increased the root mean-square (RMS) roughness at small scale (3 mu m).The TAPPI 75 degrees gloss linearly depend on RMS roughness within the gloss-roughness window for the studied coatings. Gloss also increased with decreasing skewness, i.e., increasing surface porosity, although this was found to be scale dependent. These results give promise for enhancing control of coating amount and preparing surfaces with desired topographical and optical features.