Operability Coating Windows In Two-Dimensional Slot Coating Flow: Effect of Die Lip Configuration and Comparison with Viscocapillary Model

Slot coating, which is an indispensable process in industries manufacturing flat panel displays and Li-ion secondary batteries, can be susceptible to unexpected disturbances at high speeds, leading to many kinds of undesirable defects such as ribbing, rivulets, barring, and leaking. Operability coating windows for Newtonian liquid in coating bead flow region have been investigated in this study, focusing on the effect of slot die geometry. Employing finite element method for two-dimensional (2-D) Navier-Stokes model with free surface boundaries, various flow characteristics have been observed including upstream/downstream vortices by changing lip angle of both upstream and downstream dies. In addition, uniform coating region, free from leaking and bead break-up, have been determined by the position of upstream meniscus. The simplified viscocapillary model in this flow regime via lubrication approximation from 2-D model has been derived and tested, quantitatively corroborating 2-D results.