| 摘要 |
PROBLEM TO BE SOLVED: To provide a biaxially stretched polyester film which shows excellence in not only flex pinhole resistance required for a packaging material but also stick pinhole resistance. SOLUTION: The biaxially stretched polyester film is a laminate film which comprises a polyester layer (1) composed of 60 to 90 mass% of a polyester resin (A) having an ethylene terephthalate unit as a major component unit and 40 to 10 mass% of a polyester resin (B) having a butylene terephthalate unit as a major component unit, and a polyester layer (2) containing less polyester resin (B) than the polyester layer (1) and being placed on each of both surfaces of the polyester layer (1), wherein the film has a surface orientation coefficient of 0.16-0.175 and shows an absolute value of the difference between a refraction index in the lengthwise direction and that in the widthwise direction of from 0.0001 to 0.01. COPYRIGHT: (C)2007,JPO&INPIT
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