Biaxially oriented poly ethylene terephthalate film and process for their preparation

摘要

1433344 Polyethylene terephthalate film CELANESE CORP 18 July 1973 [19 July 1972] 34123/73 Heading B5B A biaxially oriented polyethylene terephthalate film having substantially equal tensile strengths in both longitudinal and transverse directions in the range of 38,000 to 50,000 p.s.i. and substantially equal tensile strengths at 5% elongation in the range 16,000 to 25,000 p.s.i., is made by extruding a melt of the polymer on to a cooled casting drum, longitudinally stretching the film 3À0 to 5À0 times, transversely stretching 3-2 to 5À2 times subject to the limitation that the transverse stretch ratio is greater than the longitudinal stretch ratio and heat setting the film at a temperature of 180‹ to 250‹ C. The film preferably has an intrinsic viscosity of 0À64 to 0À8 deciliter/gram in orthochloro phenol at 25‹ C., a modulus in excess of 600,000 p.s.i. and a breaking elongation of 600,000 p.s.i.