Flat Dies for Film, Extrusion Coating and Sheet: A Design and Application Update, 1993 Polymers, Laminations & Coatings Conference Proceedings

H. Helmy

Many new developments took place over the past few years to improve the capabilities of flat film and sheet dies. The areas of development covered: improvements of gauge and layer thickness control for coextrusion applications, reducing the edge effects (edge bead) for film and coating applications, reducing the strain level across the sheet and advancing the design for manufacturing very wide film and sheet dies in the range of 8-10 meters. The developments entailed both the design of polymer flow passages as well as the mechanical design in the case of very wide dies and dies with edge bead reduction capability.

Flat film and sheet is produced on one of two generic type of dies, the T-shaped die with constant manifold and the coathanger-shaped die with a volumetrically reducing cross section. Both dies have been used for extrusion and coextrusion applications. The modifications and design enhancements of those two types of dies will be discussed here.