A scanning electron microscope study of the surface structure of mineral pigments, latices and thickeners used for paper coating on non-absorbent substrates

We investigate the structure of coating layers prepared on non-absorbent substrates using a bench coater, composed of mineral pigments, latex binders and polymeric thickeners and dispersants, using scanning electron microscopy (SEM) that are typical of those used in paper coatings. The main aim of the study is to identify how systematic variations in the composition of the coating, including pigment type (calcium carbonate, clay), the glass transition temperature of the binder, and type (CMC, EHEC) and molecular weight of the polymeric thickener affect the surface features of the coating layer, including surface roughness and porosity and, consequently, gloss. The samples are investigated mainly in conventional high-vacuum SEM mode; however some studies are also performed with the environmental feature (ESEM mode) at higher pressures and humidities, in order to track dynamic changes due to drying and rewetting. The results are compared to those of recent measurements on the same systems obtained with atomic force microscopy (AFM), where the local latex film formation process has been carefully studied.