| 摘要 |
PURPOSE:To obtain the film which has uniform physical properties along a width direction and is useful for a magnetic disk, etc., by heat treating a biaxially oriented thermoplastic resin film twice in a normal direction and a reverse direction at each specified temperature and compensating a bowing effect. CONSTITUTION:When the biaxially oriented film composed of a thermoplastic resin (e.g., a polyethylene terephthalate) is heat treated in two steps, the temperature range which is 40 deg.C higher than the glass transition point Tg of the thermoplastic resin and 60 deg.C lower than the melting point Tm of said resin is selected as a foregoing step heat treatment temperature T1 and a heat treatment is performed, the biaxially oriented film being made to run under a tension, then the film is once taken up by winding. Next, the film is rewound and is made to run in a reverse direction to the running direction of the foregoing step, being restrained at its both side edges and the later step heat treatment is performed at the heat treatment temperature T2 ranging from T1+20 deg.C to T1+100 deg.C (provided that T2 is below Tm-8 deg.C), thereby obtaining the desired film. |
