Visualization of Curtain Coating Flows

Summary

In photograph, paper, and steel industries, some products are made by coating a liquid on a web-shaped base material.

In the coating process, the condition of the coating bead affects the coating face. Keeping the coating bead stable is an important task. If we can visualize the shape and flow of the coating bead, we can begin to determine more stable coating conditions. However, the coating bead is very small, spread out along the web and the web moves quickly. Therefore it is difficult to visualize the coating bead.

Currently in Prof. Scriven’s group at the University of Minnesota, visualization of the coating bead is being studied. Their method uses a glycerine-water solution, hydrogen bubbles and color dye. The coating types which they have tried are slide coating and slot coating.

In our experiment, we tried to visualize curtain coating flow. During curtain coating, the coating bead was less stable than that during slide coating or slot coating, because the coating die is farther apart from the coating bead. Therefore, its visualization needs a more highly clarifying technique. Moreover, we considered the influence of the web under several conditions of the coating bead.

In our results, we found some characteristic phenomena associated with the coating bead such as recirculating vortices and changing dynamic wetting lines.