Extrude Undried PET With Low I.V. Loss

Vacuum-vented twin-screw extrusion of undried PET can produce sheet with I.V. similar to that obtained with predried PET on a single-screw extruder.

Vacuum-vented twin-screw extrusion of undried PET can produce sheet with I.V. similar to that obtained with predried PET on a single-screw extruder. So says Battenfeld Extrusionstechnik in Germany (represented here by American Maplan). Two twin-screw sheet lines are running undried PET at Faerch Plast A/S, a packaging firm in Holstebro, Denmark. The first line was installed in 2001 to produce up to 3300 lb/hr. The second arrived this year with capacity for 4400 lb/hr. These lines use 119-mm and 70-mm ZSK MegaCompounder Plus corotating twin-screws from Coperion Werner & Pfleiderer (U.S. offices in Ramsey, N.J.). Faerch was the beta test site for the Plus models, which were introduced commercially last year. They have extra-high torque and a special screw design, both of which are said to be essential to maintaining very high I.V. Higher torque allows the line to run more slowly with the same output, increasing residence time under vacuum by about 20%.