Consolidation of coating colors: Experimental studies

Various methods to study the consolidation of coating layers have been used both in the laboratory and pilot scales. Common laboratory methods include a Standard water retention device and a rheometer equipped with an immobilizing cell. Approximate hydrodynamic radii of co-binders and thickeners were estimated from viscosity measurements. Gloss and diffuse reflection or scattering measurements have been applied to detect the critical concentrations during coating layer and coated paper drying. According to our results, the Standard water retention device and the immobilization cell gave the same information, when dewatering was considered. The immobilization cell measurement also provided the immobilization solids. Approximate hydrodynamic radii of different co-binders and thickeners greatly varied and their movement relative to pigment in consolidating coatings was consequently different. On-line gloss and scattering measurement at the drying section of a pilot coater showed that it was impossible to detect the first critical concentration of the coating color, whilst it was easy to detect the second critical concentration.