Numerical Analysis of Multilayer Forward Roll Coating: Power-Law Fluids

Abstract

Roll coating is at the heart of production of films which can be composed of many layers. The fluids may be Newtonian or shear-thinning, usu ally described by a power law. The fluids' rheology along with operating param eters, such as roll speeds, their size and minimum gap width, must be con sidered in order to achieve a desirable coating thickness. Numerical studies are undertaken based on the Lubrication Approximation Theory (LAT) for the isothermal analysis of forward roll coating of multilayer sheets, which are con sidered as slightly shear-thinning fluids (power-law indices > 0.6). The solu tion process is based on an iterative Newton-Raphson scheme. It provides the unknown a priori flow domain, interface locations for different layer combina tions, layer thicknesses after splitting, pressure and stress distributions, torque and power consumption. A parametric study based on power-law index ratios and consistency index ratios for double-layer sheets is presented. A case of a 3-layer roll-coated sheet is also examined.