Coating on a rough surface

Commercial products such as photographic materials and speciality papers manufactured by single or multilayer coating processes, all have some surface topographic structure. Nevertheless, for many materials, a uniform plane approximates their surface, and analyses of dynamic wetting, a fundamental physical process which determines coating process limits, usually assume this condition. It is demonstrated here that under certain combinations of coating process parameters, the maximum coating speed is not predicted even qualitatively by using this assumption. Furthermore, the experiments indicate that a second coating mechanism supersedes complete wetting and promotes extremely high coating speeds.