Response of slot coating flow to gap disturbances: effects of fluid properties, operating conditions, and die configurations

Slot coating is perhaps one of the most successful film manufacturing methods and is used to produce a wide variety of products. It is a pre-metered method and ideal for high-precision coating: the steady-state thickness is precisely controlled by the flow rate fed to the die and the web speed. However, the coating method is surrounded by small-scale disturbances that can destroy film thickness uniformity. Among various disturbances, a periodic change of the coating gap, the so-called gap disturbance, is considered the most dangerous in previous studies, e.g., Romero and Carvalho (Chem Eng Sci 63(8):2161-2173, 2008), Tsuda et al. (AIChE J 56(9):2268-2279, 2010), and Lee and Nam (AIChE J, 2015). However, the effects of fluid properties, operating conditions, and die configurations on the slot coating flow under gap disturbances are not examined in detail. In this study, we revisit the computer-aided analysis of transient slot coating flow designed to predict the thickness variations under gap disturbance. Extensive computational predictions reveal important parameters for suppressing film nonuniformity that can be induced by gap disturbance.