| 摘要 |
PROBLEM TO BE SOLVED: To provide a film which is free from its stretching break and can be stretched at an area stretching magnification over a wide range of temperature, and further, shows high strength, wear resistance, dimensional stability and superb antistretching properties as well as a method for manufacturing the film. SOLUTION: This method for manufacturing a biaxially stretched polyester film includes a first-stage stretching step to concurrently biaxially stretch an unstretched cast film in the longitudinal and the crosswise direction at an area stretching magnification of 2-7 times within the temperature range of (glass transition temperature Tg+25) deg.C-(Tg+45) deg.C and a second-stage stretching step to concurrently biaxially stretch the cast film in the longitudinal and the crosswise direction at an area stretching magnification of 4-20 times within the temperature range of (Tg-15) deg.C-(Tg+10) deg.C following the first-stage stretching step. In addition, at least, either of the ratio R1 (IMD/ IND) of peak intensity (IMD, IND) in the longitudinal and the thickness direction or the ratio R2 (ITD/IND) of peak intensity (ITD/IND) in the crosswise and the thickness direction as measured by the laser Raman scattering method is 6 or more as the characteristics of this biaxially stretched polyester film. |
