Coating Onto a Prewet Substrate With Low Weber Number Liquid Curtain

In recent years, miniaturization and high precision of the LCD screen used for small display has been developed fast. The thin and high-precision film covering the LCD screen is manufactured by slide coating. In slide coating, however, the distance between the slot and the substrate is too small. On the other hand, curtain coating can avoid the influence of the mechanical disturbance and is also a good method for coating on rugged substrate. Nevertheless, curtain coating has not been applied to the LCD screen because the liquid curtain with small discharge, i.e. small Weber number, causes instabilities of the flow and the free surfaces. In the present study, we performed the experiment of the liquid curtain bridged between the exit of slot die and moving roller under very small Weber number (We ∼0.1). It is found that the surface waves are reduced by using a roller pre-wetted by mists and by changing the viscosity of the liquid. Also, the coating window can be drawn in a plane of surface tension and viscosity. Finally, we tried to explain these phenomena by analyzing the equations of liquid curtain.