Measurement of liquid film thickness on moving plate during dip-coating process

Abstract

Dip-coating can be used to obtain a relatively uniform film thickness on a substrate and is widely used in industry. The thickness of the liquid film is a very important parameter for the desired function. In this study, a laser focus displacement meter is used to measure the liquid film thickness. The thickness of liquid film coated on the withdrawing plate increases initially and then becomes constant as time passes. The liquid film of the constant film thickness zone is in good agreement with these two existing correlations. For the transition region where the liquid film thickness increases, a comparison of the profiles of dimensionless liquid film thickness shows that as the withdrawal speed increases, the profile of dimensionless liquid film thickness becomes more convex. However, at a capillary number higher than 0.1, the profiles are consistent within a certain range. It is confirmed that the profile of dimensionless liquid film thickness can be classified into a viscous dominant region and a surface tension dominant region, similar to the tendency of liquid film thickness in the constant film thickness region.