Abstract
Plastic film is often passed through roll-to-roll manufacturing processes such as coating, printing and slitting to convert to industrial products. The film is made into wound roll on the final stage of the process to ease handling and storage. And then it is usually transported and heat-treated under the various temperatures, which could be different from winding temperature. As a result, wound roll defects such as slippage and wrinkling occur, and then it leads to a risk of an economic loss. For preventing these problems, it is necessary to understand and predict the internal stress. In above situation, the internal stress may vary over time due to thermal strain and creep strain of the film. Furthermore, it is known that load stress and the temperature affect creep. Therefore, this paper describes a thermal-viscoelastic winding model considering the thermal elasticity and the viscoelasticity. To perform the numerical calculation of the internal stress which are radial and circumferential stress, an unsteady conduction analysis in radial direction was applied to evaluate time change of the in-roll temperature. The creep compliance change was measured by compression and tensile creep tests under various load stress and temperature conditions to investigate the creep behavior of a polypropylene film as test film. From the experimental results, magnitude of the change was affected by these conditions. In order to apply the effect into winding model, an empirical formula was obtained based on the experimental results. It was possible to estimate the creep compliance values on arbitrary stress/temperature condition and was expressed by generalized Voigt model. The predicted values generally correspond to the experimental values.
