MULTILAYER EXTRUSION - EXPERIMENTS AND COMPUTER-SIMULATION

A mathematical model is presented for the computer simulation of multi layer flow of polymer melts in coextrusion. The proposed model can han dle an arbitrary number of layers. The viscosity of each layer is shea r-rate and temperature dependent. Given the material properties, die d imensions, and process conditions, the model determines the flow field throughout the die gap. Computer simulations and experimental data ar e presented for a three-layer polyester/EVA/polyester film coextrusion , with emphasis on the interfacial instability and its effects on opti cal properties of the film. The results are discussed in the context o f the critical interfacial shear stress criterion that has been propos ed by Schrenk, et al. (1) for the onset of interfacial instability. It appears that elasticity differences between layers contribute to the interfacial instability. It is conjectured that minimizing interfacial shear stress and matching elasticities of adjacent layers is an appro priate criterion in coextrusion analysis.