It is extruded into clear and colored film and sheeting for a variety of food and medical packaging uses, and it also finds application in the field of graphic arts. PET has been used for years in crystalline form suitable for use at elevated temperatures. PET pellets, usually supplied in crystalline state, can be converted by various techniques into finished products having crystalline, amorphous, or oriented properties. Accordingly, different technical considerations are required as downstream conversion processes are varied to achieve final product characteristics. 9921 and 9921W polyesters are slower to crystallize than homopolymer PET and thus offer greater latitude in thermoforming thick sheet and deep draws.
PET adapts well to in-line extrusion, thermoforming, and trimming operations.
PET must be thoroughly dried prior to extrusion. All additives must be thoroughly dried before use with polyesters. Additive feeders have an advantage in that they can be adjusted, as required, while the line is in operation. A silicone emulsion coating can be applied to either one or both sides of extruded sheeting to retain the excellent optical qualities of polyesters while providing denest properties. Silicone coating cannot always be used when secondary operations such as printing are required.