Viscoelastic Stress Analysis of Wound Rolls of Plastic Films

Abstract

In the industrial winding process of plastic films, the existence of air interlayer in film rolls leads to some roll defects, such as lateral slide, wrinkling and blocking, and the occurrence of such defects is strongly influenced by the interlayer pressure of the roll. With increasing demands for higher quality of film rolls without such defects, it is of vital importance to determine the optimal process conditions such as winding torque, nip and tension. For that purpose, an accurate estimation of the internal stress fields in film rolls is essential. This paper presents a new theoretical approach to the prediction of transient viscoelastic stress distributions, where a generalized Maxwell viscoelasticity and nonlinear compressibility of films are taken into account. Moreover, the effect of air-entrainment at the roll inlet is discussed based on the theory of elasto-hydrodynamic lubrication. The numerical solutions for the stress distributions agree fairly well with the corresponding experimental results of winding tests using an in-house pilot reel, and they show the significant influence of the viscoelasticity of a plastic film upon the stress level.