Leveling of surface defects in thin films of pigmented coatings

Leveling of surface irregularities in thin films of pigmented coatings was investigated. Artificially induced defects in a pilot scale coater trial we re analyzed using a high-speed video camera, surface profilometry and optic al microscopy. The influence of the defect geometry, rheological properties of the pigment suspension, substrate properties and process conditions was studied. The leveling rate of the defects was found to depend on both the elasticity and the viscous resistance of the coating suspension. Numerical simulations suggested that final dry widths of the defects were determined by immobilization of the uniform coating layer next to the defects.