EASILY TEARABLE BIAXIALLY ORIENTED POLYESTER FILM

摘要

PROBLEM TO BE SOLVED: To obtain a biaxially oriented film having low hygroscopicity, transparency, flavor retention and wet-heat-resistant dimensional stability and capable of giving a packaging material possessing linear tearability upon opening by mixing polyethylene terephthalate with modified polybutylene terephthalate containing a specified amount of polytetramethylene glycol. SOLUTION: A film made from a feedstock prepared by mixing polyethylene terephthalate (PET) with a modified PBT being polybutylene terephthalate containing 5-20wt.% polytetramethylene glycol units in a PET/modified PBT ratio of 70/30 to 95/5 by weight is biaxially oriented to obtain a polyester film which can be linearly torn in at least the longer direction. The modified PBT can be easily obtained by a method comprising adding polytetramethylene glycol to a PBT polymerization step and polycondensing it or by a method comprising melt-kneading them in an extruder.