Troubleshooting coextrusion film problems by considering process–property relationships*

Abstract

Coextrusion of plastics into a multilayer film is a complex process where many processing and structure design factors affect performance. As a result, problems can be difficult to troubleshoot. We describe issues involving estimating properties from monolayer films, achieving good interlayer adhesion and minimizing curl. Multilayer film properties such as gas permeation and bending stiffness cannot be estimated from simply adding up the properties of monolayer films of the individual layers. Properties may also differ from their monolayer analogs due to differences in stress and temperature history during coextrusion. Some combinations of polymers may not be possible to make due to flow instabilities. Many polymers used in multilayer films do not adhere well to one another. Tie resins have been developed to promote adhesion, but many factors affect their peel strength performance, including fabrication parameters. More so than monolayer films, coextrusion films are prone to curling or rolling up on themselves. Factors such as differential shrinkage during quenching play a role. This paper explores some of the recent advances in the science of coextrusion and how this knowledge can be used to address these issues.