Method of processing polyester film

摘要

In making a film of amorphous polyester resin by the extrusion and subsequent flattening of a tubular film, the polyester film is heated and flattened at a temperature above the glass temperature of the resin of which the film is made but below the sticking temperature of the film. "Glass temperature" is synonymous with second order transition temperature. The polyester resin may be an ethylene terephthalate-ethylene isophthalate copolyester with 90%-30% of the former and 10%-70% of the latter, preferably with 90%-40% ethylene terephthalate and 10%-60% ethylene isophthalate, and especially with 75%-60% terephthalate and 25%-40% isophthalate. The polyester resin may alternatively be an ethylene terephthalate-2, 2-bis [4(-b -hydroxyethoxy) phenyl]propane terephthalate with 90%-30% of the former and 10%-70% of the latter, and especially the 60/40 copolyester with 60% of the former and 40% of the latter. The process is generally applicable to linear condensation polyester resins with glass temperatures above 50 DEG C. (list given). In an example, a granulated 75/25 ethylene terephthalate-ethylene isophthalate copolyester resin is advanced as shown via hopper 2 and screw worm 3 into barrel 4, which is heated to from 204 DEG C. at its entrance to 226 DEG C. at its end just before filter 5. The resin is compressed and fused in barrel 4 and advanced through filter 5 into head 6 and die 7 to form a tube 8. Air or other gas is introduced via 9 to expand the tube, which is cooled in quench tube 11, held at 24 DEG C. by cooling fluid circulated through shell 12. The tube then passes to heating tube 15, held at 60 DEG -66 DEG C. by a heating fluid circulated through shell 16, is flattened by the rolls 19 and 20, which are surrounded by the oven 21 held at 71 DEG C. (above the glass temperature of the resin but below the sticking temperature of the film), and passes to the windup rolls. Specifications 766,290 and 877,539 are referred to.