Numerical study on oblique stretching of viscoelastic polymer film

Abstract

• Numerical format for oblique stretching of viscoelastic film is established. • The application scenarios of the membrane hypothesis are expanded. • Detailed numerical procedure and a complete numerical case are provided. • The influence of the y -direction stretching on thickness uniformity is investigated. Oblique stretching is a special approach for the fabrication of polymer film whose product is mainly used in the optical display field, such as compensation films, retardation films, et al. Nonetheless, the previous research reports on oblique stretching processing are still lacking, and the related numerical research is almost blank. This contribution uses the FEM (finite element method) to simulate the oblique stretching process of viscoelastic polymer film for the first time. The differential viscoelastic PTT (Phan-Thien and Tanner) model, one of the most realistic constitutive models is chosen. Furthermore, the polycarbonate melt was rheologically characterized and used as input material parameters in our simulations. Based on the membrane hypothesis and stabilization algorithms like DEVSS (discrete elastic viscous stress splitting), the specific numerical scheme is derived and the algorithm implementation is summarized. Finally, a complete numerical example of oblique stretching is demonstrated and compared with symmetric stretching. Based on the simulation results, the evolution of thickness and the influence of the y -direction stretching on thickness uniformity are further investigated.