Prediction of velocity and coat-weight limits based on filter-cake formation

A model is proposed to predict the maximum velocity at which a blade coater can operate before runnability problems occur. Many runnability problems seem to correlate with the dewatering of the coating. The model is based on fluid mechanics and considers the effects of (a) filter-cake formation on the sheet surface and (b) sheet roughness. The model shows that formation of a filter-cake can generate a large pressure pulse under the blade, which drives more fluid from the coating into the paper. The model predicts the maximum operating speed and the blade forces for a given coat weight and paper roughness. Comparison of model predictions with data from several researchers shows good agreement. The model provides a tool to optimize coating solids and web velocity for given coat-weight targets and paper properties.