Eastman Kodak: PET Barrier Screw With Internal Vacuum Vent
Conventional two-stage single screws for processing PET powder typically have an internal vent channel, but now the concept has been applied to a barrier screw. Recently patented by Eastman Kodak Co., USA (U.S. Patent No. 6,164,810, issued Dec. 26, 2000), the screw design has a small vent hole located within about two diameters from the end of the feed section, between a pumping and barrier flight. It vents volatiles out the back of the screw through an axial bore. Walls in the flow channel divert polymer so it does not flow into the small single vent hole. This design can be used to process PET powder into film. Before now, barrier screws were used only with PET pellets, not powder, because pellets let volatiles escape back out the feed throat. Eastman’s vented barrier screw reportedly permits higher throughputs of PET powder. The vented barrier screw can also be used for other hygroscopic resins like ABS.