Operability coating window of dual-layer slot coating process using viscocapillary model

• Simplified viscocapillary model to describe dual-layer slot coating flow is derived.
• Operability windows are accurately determined from the viscocapillary model.
• This model is a fast and useful tool to predict dynamics in dual-layer slot coating.

The viscocapillary model for predicting the operability windows in a dual-slot coating process for two Newtonian liquids has been derived by means of a lubrication approximation technique from two-dimensional (2-D) Navier-Stokes equations. The flow rates per width and the pressure differences simplified in several sub-regions within the coating bead regime have been integrated together with approximations of the upstream and downstream menisci and the interlayer between the top and bottom layers. Coating limits or onsets for leaking and bead break-up defects have been determined on the basis of the position of upstream meniscus of the bottom layer as an indicator. Operability coating windows predicted from the viscocapillary model show a good agreement with those by 2-D CFD solver and experiments. In addition, the pressure profiles within the coating bead regime compared between the viscocapillary and 2-D models are qualitatively similar. This simplified model can be applied as a fast tool for usefully manipulating the stable operations in dual-layer slot coating systems.