Topography and Gloss of Paper Coating Layers, 2006 TAPPI Advanced Coating Fundamentals Symposium

The aim of the work is to study the correlations of topography, morphology and optical properties between a coating substrate and different coating layers. Precipitated calcium carbonate (PCC) pigments were coated on a model substrate and various coating thicknesses (coating amounts) were compared. A versatile roughness analysis was carried out for the measured AFM topographical 3D images in three different length scales: 3, 10, and 50 µm. The results give novel detailed information about different topographical features of pigment coatings, e.g., surface porosity, effective surface area, kurtosis, and density of local summits. Even a relatively low coating thickness was found to be enough to cover and smooth the surface on large scale (50 μm) but was observed to increase the root-mean-square (RMS) roughness at small scale (3 μm). The gloss was observed to be quite linearly dependent on RMS roughness. Interestingly the gloss was also found to increase with decreasing skewness, i.e. increasing surface porosity. The results give promise for enhanced control of coating amount and preparation of surfaces with desired topographical and optical features.