Trailing edge formation during slot coating of rectangular patches

Different products, such as adhesives, pharmaceutical patches, batteries, and fuel cell membranes, require coating discrete patches onto moving substrates. For coating rectangular patches, intermittent slot die coating is the preferred method. The patches can be obtained by rapidly starting and stopping the flow out of the coating die. Controlling the flow start-up and shutdown to produce sharp and uniform leading and trailing edges of each patch is challenging. Different ways to control the liquid feeding are used to optimize the process. Even if the start-up and shutdown of the feeding system are well designed, the transient flow in the coating bead contributes to the formation of nonuniform leading and trailing edges of coated patches. In this work, we analyze how the operating conditions, die geometry, and liquid properties affect the coating bead breakup process and the trailing edge configuration. The process is directly related to the contact line dynamics. The results show that the uniformity of the trailing edge of each coated patch can be improved by changing the die shoulder angle and wetting characteristics of the die surface.