Thinnest uniform liquid films formed at the highest speeds with reverse roll coating

Abstract

Reverse roll coating is probably the most widely used coating operation, much less investigated than its counterpart and inherently unstable forward roll coating. A new data to complement earlier work which was limited to large gaps and thus “thick” films is presented. The intention is to assess the feasibility of reverse roll coating to yield very thin films (<10 μm) at high speeds (>1 m/s) for application in the newer technologies, such as the production of solar cells and plastic electronics. The data obtained demonstrate this is possible but at the lowest permissible gap (25–50 μm) with low-viscosity fluids (∼7 mPa s). The study also developed a new understanding of how instabilities are controlled. It was seen that the size of the inertia forces generated by the applicator roller in relation to surface tension, as expressed by the Weber number and not the applicator Capillary number (viscous forces/surface tension) which is the critical parameter.