TRANSPARENT BIAXIALLY ORIENTED POLYESTER FILM AND MANUFACTURING METHOD THEREFOR

摘要

PROBLEM TO BE SOLVED: To provide a transparent biaxially oriented polyester film which shows high adhesive force between constituent layers and high barrier properties with such advantages that the manufacturing cost of the film is low and it is free from problems in discarding and regeneration. SOLUTION: This transparent biaxially oriented polyester film is constituted of a base layer B formed of 80 wt.% or more of a thermoplastic polyester and at least one outer layer A. The outer layer A is composed of a copolymer or a mixture of the copolymer and a homopolymer and further, 90-98 wt.% of an ethylene 2,6-naphthalate unit, 10 wt.% or less of an ethylene terephthalate unit and 10 wt.% or less of alicyclic or aromatic diol and/or carboxylic acid. In addition, the outer layer A of the outer layer A is 0.7μm or more thick and less than 25% of the total thickness of the film. The second glass transition temperature (Tg2) of the polyester film is higher than the Tg2 of the base layer B and is lower than the Tg2 of the outer layer A.