PARTICLE MOTION ANALYSIS AT THE EXIT OF A BLADE COATER

The motion of particles at the exit of a blade coater has been simulat ed using a Stokesian dynamics technique. The velocity field in the vic inity of the blade tip was obtained with a finite element method. This velocity field is used to calculate the long-range hydrodynamic force s for the particle motion model. Surface-particle hydrodynamic interac tions are calculated with an image particle placed opposite the free s urface to produce a stress-free region at the interface. Surface tensi on forces, not the blade surface, are found to keep large particles aw ay from the top layer of the coating. In addition, large particles can push small particles near the top surface as the flow field changes f rom simple shear to plug flow after the blade. The analysis thus point s to a mechanism by which small latex binder particles can be concentr ated at the surface of the coating layer Such a concentration of binde r often is associated with print quality problems in the form of print mottle.