Defects in multilayer plastic films I: Interface defects in extrusion

This paper deals with defects in multilayer plastic films in the extrusion process. A methodology to link process parameters and fluid rheology to onset of certain types of defects is developed. The defects considered include zigzag features that can form on the surface or interfaces in the extruded multilayer films, and parabolic and finger-like features that can form at the interfaces. The zigzag defects occur due to excessive shear and the parabolic and viscous-finger defects develop in response to flow perturbations. Novel approaches to predict the formation of the latter defects based on steady-state flow calculations are presented in this paper. Tendency of formation of parabolic defects can be evaluated based on steady-state calculations, and possibility of formation of viscous fingers can be explored based on energy considerations. It has also been shown that a process window can be developed by simultaneously considering the process requirements for elimination of these defects.