THE LEVELING OF COATING DEFECTS WITH SHEAR THINNING RHEOLOGY

A one-dimensional model is proposed to predict the leveling of coating defects or irregularities on a planar surface. Though shear thinning rheology is the focus of this paper, any viscous non-Newtonian rheolog y can be included in the model. Surface tension, gravity and viscous f orces are accounted for in the model. A novel numerical technique is p resented to obtain solutions of the model. Results agree with a full t wo-dimensional solution of the flow held obtained with a spectral elem ent method. A new dimensionless group is identified which indicates th e significance of shear-thinning theology. Defects are made with a not ched blade used to coat pigmented liquids on polymer films. The defect shapes are obtained at different times by drying under infrared. The dried surface is characterized with a stylus profilometer. The surface profiles and the final amount of leveling compare well with the model predictions. Copyright (C) 1996 Elsevier Science Ltd