Patent ID: 9453114
Filing Date: 2016-09-27
CPC Classification: B29C,B29D,B29K,B32B,C08J

Claim Text:
1. A method for producing a polyethylene terephthalate film comprising: (a) extruding and cooling a polyethylene terephthalate resin to provide a non-oriented polyethylene terephthalate sheet; (b) orienting the polyethylene terephthalate sheet in machine direction (MD) to give a MD orientated polyethylene terephthalate film; (c) orienting the MD oriented polyethylene terephthalate film obtained in step (b) in transverse direction (TD); (d) heat treating the resulting biaxially oriented polyethylene terephthalate film obtained in step (c); and (e) carrying out simultaneous relaxation by subjecting the heat treated polyethylene terephthalate film of step (d) to a MD relaxation at a ratio of 3-8%, while subjecting it to a TD relaxation at a ratio of 3-8% in a tenter, wherein in step (b), the polyethylene terephthalate film is oriented at 1-10 times in the MD while being passed through an IR heater zone heated to 600-900° C., and then is further oriented 1-3 times while being passed through an IR heater zone heated to 500-800° C., so that the total MD-orientation is made 1-10 times; the MD-oriented film is passed through a preheating zone, subjected to TD-orientation 1-10 times; wherein the polyethylene terephthalate film has a shrinkage of 0.4% or less at 150° C. for 30 minutes in the MD, a maximum shrinkage stress of 0.20 kg/mm wherein the polyethylene terephthalate film has a thickness of 50 to 350 μm.