Predicting the cause of operational anomalies in blade coating

Blade coating is a high speed (20ms-1) coating operation that involves thesqueezing of shear thinning coating slurry between a base paper substrate and asteel metering blade. The gap between the blade and the paper can be as small as1&\#956;m and mineral pigments in the slurry can become trapped, giving rise tostreaks and scratches on the coating surface. The objective of the researchpresented herein is to develop a model for simulating the process of blademetering and to use the model to investigate operational anomalies connected tothe process. The effects of specific variables were studied notably; blade shapeand backing roll stiffness. Virtual experimentation was undertaken to study thedeformation of the paper surface, the coating colour thickness and the position ofthe stagnation point (where pigments may gather). The choice of blade type wasfound to have a highly localised influence on the area close to the nip. Thebacking roll stiffness was shown to be one of the most important parameters inblade metering. Lowering the stiffness decreases the coating thickness andpushes the stagnation point further away from the heel region.