Influence of Dynamic Rheological Behavior on Final Coating Properties: Part 2- Dynamic Suspension Rheology and Coating Structure Consolidation, 1999 Coating Fundamentals Symposium Proceedings

Hideaki Nisogi, Douglas W. Bousfield, Pierre LePoutre

The dynamics of the elastic modulus after steady shear of a coating suspension is reported. For the coating suspension including a synthetic thickener, the elastic modulus, G’, increases rapidly within the first 20 seconds but then approaches a plateau. These results indicate the recovery of some network structure. A logarithmic equation fits the elastic modulus as a function of time. When the coating suspension is applied on a plastic substrate, the dry coating bulk was not affected by the drying rate. However, for the plastic film cases, the most rapid drying was still over six seconds: this time is longer than the time where the most significant change in elastic modulus occurs.

When the coating is applied on cellophane, a water absorbing substrate, it is immobilized in less than six seconds and the void fraction is lower than that on the plastic film. We hypothesize that the structure in the suspension is destroyed by shear during application and does not have time to rebuild before the setting. This rapid setting gives a lower void fraction of the dry coating layer. Particle motion modeling reveals that van der Waals attractive forces are not strong enough to hold particles together during blade coating. This indicates that during blade coating, particle network structures are broken down by the blade. Therefore, the dynamics of setting compared to structure recovery may influence the final coating structure.