| 摘要 |
PURPOSE:To obtain inexpensively the titled film that is excellent in evenness, lubricity and gluability, and can be used as magnetic tapes, etc., by stretching an unstretched polyester film longitudinally at a special temperature to adjust the bireflingent index, then stretching the film longitudinally under specified conditions, and finally stretching the film laterally. CONSTITUTION:An unstretched polyester film is stretched longitudinally in one step between rolls 5, 5' and a roll 6 at a temperature of 100-130 deg.C to adjust the bireflingent index DELTAn to 0.015-0.025. Then while the film is being heated by a heater 13 to 95-150 deg.C, the film is stretched in the same direction as above between rolls 9, 9' and a roll 10 so that the film may be stretched three times as much as the original state and may have DELTAn not more than 0.080 and a refractive index (n) not more than 1.600, and thereafter the film is stretched laterally to produce the intended biaxially oriented film. |
