Numerical Modeling of Drying Thin Film Coating with a Surface-Wiping Process

The drying of thin film coating with a surface-wiping process was modeled numerically. A one-dimensional diffusion equation for a PVAc-toluene system was solved by taking into account temperature/concentration-dependent diffusion coefficients and solvent vapor pressures to obtain solvent concentration profiles. The numerical results revealed a peak in the concentration profile at a particular thickness in the wiping process due to diffusion of solvent from the wiping layer to the coating. The resultant increase in residual solvent contents gives rise to a significant drop in solution boiling point, leading to the occurrence of boiling periods during drying.