| 摘要 |
PURPOSE:To provide the above film so that the film possesses uniform physical properties but bowing is little, by a method wherein heat shrinkable stress of a widthwise direction and a heat shrinkable factor of a widthwise direction of a thermoplastic resin stretched film which is oriented at least unidirectionally are specified. CONSTITUTION:A ratio sigma2/sigma1 of heat shrinkable stress sigma1 of a lateral (widthwise) direction of a film at a temperature higher by 70 deg.C than the glass transition temperature of the thermoplastic resin stretched film oriented at least in a lateral direction to heat shrinkable stress sigma2 of a lateral (widthwise) direction of the film at a temperature lower by 80 deg.C than the melting point should be 1.0 or less, preferably 0.9 or less. Then a heat shrinkable factor of a widthwise direction of the film is made into 5% or less at a temperature higher by 40 deg.C than the glass transition temperature. In addition, since the bigger a value of a ratio L/W of a length L of a cooling process for cooling of the film at the glass transition temperature or less between a lateral stretching and thermal fixation treatment to a film width W becomes, the more a reduction effect of a bowing phenomenon is improved, the ratio L/W is selected so as to become at least 1.0, preferably at least 2.0. |
