Multilayer Calendering of Coextruded Sheets

Abstract

Coextruded multilayer plastic sheets used in the packaging industry are usually calendered between two rolls to reduce the original sheet thickness coming from the die. To meet certain thickness criteria for each layer as well as for the calendered sheet, the operating parameters, such as roll speeds, size, temperatures and minimum gap width, have to be specified. Due to the intractability of the prob lem by analytical methods, numerical methods have to be used. The Lubrication Ap proximation Theory (LAT) is employed and the solution is achieved by using a Newton-Raphson iterative scheme which determines both the unknown a priori flow domain and the interface locations for a combination of layers. The analysis provides the pressure distribution, separating force, torque, power consumption and tempera ture rise. Several cases of 2-, 3- and 9-layer calendering are presented and a design criterion of equal interfacial viscosities is put forward to determine the operating temperatures in the process