Leveling of Coating Defects, 1991 Coating Conference Proceedings

The leveling of coating defects and irregularities is important to obtain high quality coated surfaces. A model, based on fluid mechanics, is proposed to predict the rate of leveling of surface irregularities on a paper base sheet. The influence of surface tension forces, body forces, flow into the base sheet, and drying are taken into account in the model. The formation of a filtercake on the basesheet and the shape of the coating layer is predicted in time. Small rectangular channels or notches of different depths are made in a blade of a Cylindrical Laboratory Coater to produce systematic coating defects. The final shapes of these defects with different drying conditions are measured to within a few microns with a stylus profilometer. The experiments probe the ability of the coating to flow on the paper basesheet after the blade. Absorption of vehicle into the base sheet was found to be more important that the rate of drying with regard to the amount of irregularity leveling. The theoretical predictions compare well with the experimental results.