Forces generated by web peeling for printing and coating applications

Abstract

The tensile forces that act on a web in printing and coating applications are important in situations where the web may delaminate or break. A model is proposed that uses lubrication expressions to describe the fluid flow in the thin fluid layer combined with a force balance on the web to describe the peeling event. A novel experimental method is described that measures the forces to separate a tensioned web from a surface with a viscous fluid between them. Forces are measured for various parameters such as viscosity, web tension, separation velocity, fluid volume, and fluid geometry. Dimensionless expressions are developed to correlate experimental results. Web deformation and forces are found to be influenced by a thin air film between web and bottom plate. These initial forces are found to be larger than later peeling forces unless something is done to allow air to flow between the web and the lower plate. Low web tension and stiffness are found to reduce the maximum force. The model predicts the measured forces within the expected accuracies. However, the model overpredicts the forces for large patch areas and thin films; this is likely caused by a cavitation mechanism or be three-dimensional flows for these large patch areas. Simplified expressions are generated to correlate the peeling forces for a wide range of experimental parameters.