Process Stability in Multilayer Sheet Extrusion

Calendering of multi-layer sheets is an excellent process for production of sheets and films for thermoformable feedstocks. The quality of the sheet surface and throughput rate are strongly affected by thermal and adhesive properties of constituent materials and temperatures of individual layers and nip-rolls. We conducted a set of experiments that allows us to relate process conditions to sheet quality and develop mathematical functions for process optimization. In addition, we have developed a physics-based model to calculate transient thermal distribution in the sheet and adhesive strength between rolls and sheet surface. Model predictions of temperature are in good agreement with actual surface temperature measurement. The model can be used to relate quality characteristics to thermal gradients and adhesive strength and can become a useful tool for development the of optimum process envelope for highest throughput.