| 摘要 |
PROBLEM TO BE SOLVED: To obtain a biaxially oriented polyester film excellent in stiffness, dimensional stability and productivity, having hardly any unevenness in the thickness and faults on the surface, and useful for magnetic recording packaging and the like by making the film include a specific polyester and polyetherimide, and bringing the glass transition temperature of the film into a specific range. SOLUTION: This film includes (A) a polyester consisting mainly of ethylene terephthalate unit and (B) polyetherimide at preferably 1-50 wt.% based on the whole weight, and its glass transition temperature range defined by the difference between extrapolation glass transition beginning temperature and extrapolation glass transition ending temperature is made to be >=25 deg.C but <60 deg.C. This film is obtained by charging the component A and at least one kind of the component B into an extruder, molding a thermoplastic resin sheet whose glass transition temperature range described above is preferably 15-40 deg.C, and drawing the sheet both in the longitudinal and cross directions to bring its total area magnification to preferably >=10.
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