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.

Effect of temperature and pressure on the interfacial morphology and bond strength of thermally laminated glycol-modified polyethylene terephthalate/styrene-co-butadiene block copolymer films and comparison with coextruded (polyethylene terephthalate/styrene-co-butadiene block copolymer/polyethylene terephthalate) and polyethylene terephthalate/styrene-co-butadiene block copolymer/polyethylene terephthalate films heated with applied pressure after extrusion

“…There are several reports [4][5][6][7][8][9] on the interfacial adhesive properties and interfacial instability of the coextrusion process. Addressing interfacial instability is critical for multilayer film quality in conventional multilayer coextrusion.…”

“…Addressing interfacial instability is critical for multilayer film quality in conventional multilayer coextrusion. [4][5][6][7][8][9][10][11][12][13][14][15] Fundamentally, when molten polymer layers are laminated, adhesion challenges may occur due to differences in the material and flow properties. [16][17][18] M.T.…”

“…[4][5][6][7][8][9][10][11][12][13][14][15] Fundamentally, when molten polymer layers are laminated, adhesion challenges may occur due to differences in the material and flow properties. [16][17][18] M.T. Martyn reported experimental studies and numerical modeling of the interfacial instability in the bilayer coextrusion flow of two low-density polyethylenes.…”