Changes in solid particle fractions of coating color in low- and high-speed blade coating

Changes in coating color composition in a recirculation loop of a coater can cause runnability and paper quality variability. Besides an increase in the coating color solids content, the average size of the solid particles increases as a result of depletion of fine materials or shear-induced aggregation. The mechanisms for changes in solid particle fractions of coating colors and control parameters are not well understood or documented. Previous work has investigated the role of coating color solids content and cohesion energy in particle segregation tendencies by using a low-speed laboratory coater. The current work extends the study to high-speed pilot-scale coating and compares the results to the laboratory-scale coater. It is proposed that similar results in regard to particle size segregation can be observed with both a low-speed laboratory coater and a high-speed pilot coater. The same parameters, such as solids volume fraction, control the particle size segregation regardless of the speed and the applicator type. If the solids volume fraction and the packing volume are high, the coating color cohesion energy is not of importance for particle segregation.