Measuring coating layer shape in arbitrary geometry

Abstract

Coating processes are typically analyzed on systems with flat substrates, such as the Landau–Levich–Derjaguin configuration in dip coating. However, actual applications often exhibit a much wider variety of geometries. For example, dip coating is also employed as a batch process with three-dimensional substrates. After the batch dip coating process, the coating layer is likely to exhibit irregular geometries near the lower edge of the substrate; the substrate profile is not flat, and the fluid can form overhangs depending on process conditions and rheological properties. These irregularities make it impossible to define layer shape measures, such as average thickness and roughness, in traditional ways. In this study, we propose generalized measures to overcome this issue by using offset distance and curve similarity. Our measures can quantify the shape of the coating layers in arbitrary geometries and are, therefore, robust against irregularities. We applied our measures to analyze the formation of external electrodes on multi-layer ceramic capacitors by batch dip coating. Coating layer profiles during the process were acquired for the analysis using a simple machine vision technique. As a result, differences in the coating layer shapes between fluids with different rheological properties were quantified. The results show that our measures can be used to compare coating qualities in arbitrary geometries for designing optimal process conditions.