Coating Colour Dewatering in Blade Coaters, 1993 Coating Conference Proceedings

Philippe Letzelter

Dan Eklund

A model for the dewatering of a coating colour is proposed, with the aim to theoretically quantify the structure, the porosity and the mean hydraulic diameter of an immobilised coating colour and by that mean be able to predict the dewatering behavior in a blade coater. The model, which has been developed under the assumption that filtration is the main dewatering mechanism, is based on a modified Hagen-Poisseuille equation and takes colour and machine parameters into account. The results showed that the type of particles present in the colour and the packing structure of the particles in the immobilised colour where the most important factors for the dewatering. The colour parameters and the influence of a simplified machine configuration on the dewatering behavior was also simulated. The results showed that the dewatering under the blade tip, especially for a roll applicator configuration, is small compared with the dewatering induced in the application zone. The results also showed that the sorption potential of the base paper, which in the free draws is the only source for the pressure potential required for dewatering to take place, could be of greater importance for the dewatering than is the pressure pulse induced under the blade tip.