Computational analysis of slot coating on a tensioned web

When a web (thin substrate with considerable flexibility) travels through a coating applicator in free span between the two supporting rollers, the gap between web and coating applicator is determined primarily by the hydrodynamic stresses in the coating flow and externally applied tension on the web. The elastohydrodynamic interaction between the tensioned-web deformation and the viscous liquid flow in the coating bead has not been extensively studied, in spite of its practical importance. A tensioned-web wrapped around a slot coater was analyzed here by finite-element computations. The externally applied tension on the web typically is much greater than the force due to hydrodynamic stresses. Hence, tension in the web is assumed to be constant in the process direction tangential to the web surface. By neglecting the bending and twisting moments as in the approximation of membrane theory, the shape of the flexible web is determined by a normal stress balance equation, quire similar to that of the free surface of coating flow with a constant surface tension. In this work, elastohydrodynamic effects in tensioned-web slot coating are examined with respect to variations of the liquid feeding rate and externally applied web tension, web wrap angle, and other variables.