Particle Motion Analysis of Oblate Spheroids in Complex Flow Geometries, 1999 Coating Conference Proceedings

Aldo Romagnoli

Douglas W. Bousfield

Department of Chemical Engineering

University of Maine

The orientation of kaolin pigments is expected to influence the ability of a coating to flow during the metering operation and the final properties of the coating layer. Delaminated kaolin pigments are known to produce operational problems during the coating process and usually require application at lower solids compared to other pigments. Orientation of pigments in the metered size press is not understood. This work provides a new computational tool to predict the orientation of oblate spheroids during the coating applications.

The motion of oblate spheroids in a coating geometery is simulated using a Stokesian dynamics technique. A commercial fluid dynamics package is used to calculate velocity fields for a blade coating operation and the exit of a metering size-press or roll coater. The velocity fields are used to estimate the long-range hydrodynamic forces and torques on the particles. The model calculates the trajectories, rotation, forces and torques on the particles. Process variables such as coat weight and particle aspect ratio are studied. In general, particles are found to be aligned with the web, but the blade coater produces more orientation than the metering size-press. Particles with low aspect ratio are found to have low orientation. Particles are forced together in the metering zone which may lead to processing issues.