Novel: Low-stress extrusion process
A new low-stress extrusion process for making film and sheet of very high optical quality is believed to be the first to use a free surface to form plastic film. The sheet is formed by flowing resin out of a long slot that runs along the top of the die. Resin then flows down two sides of the die and meets at the bottom, forming a low- stress film of molten plastic. The molten film is clamped and supported on both edges as it cools. Because the sheet of plastic isn’t formed between metal surfaces, the polymer chains aren’t oriented and the surface is very smooth.
The patented SFO (Stress-Free Optical) process is similar to that used to make optical glass. It is available for licensing from Rohm & Haas Co., Philadelphia. It targets plastic films and rigid substrates for LCDs, electroluminescent displays, optical windows and films, data-storage media, and other applications. Rohm & Haas has used the process to make developmental acrylic and PC films up to 20 in. wide and 1 mm thick.