| 摘要 |
PURPOSE:To obtain a biaxially oriented film whose part having balanced physical properties and high uniformity has been widened, by a method wherein a preheating zone is provided between a lateral orienting zone and a heat treatment zone and a heating temperature is controlled from a high temperature to a low temperature toward the central part from an end part under a state where both end sides of the film is held by a tenter. CONSTITUTION:Although a thermoplastic film uniaxially oriented in a longitudinal direction is oriented laterally by a tenter and made into a biaxially oriented film by applying heat treatment to the same, a temperature gradient varying from high temperature to low temperature from an end part to the center part of the film is applied to the film in a preheating zone and preheat treatment is applied to the same while keeping a film temperature of the center part at less than 90 deg.C after providing the preheating zone between a lateral orienting zone and a heat treatment zone in the tenter. Then the film temperature posterior to the lateral orientation is lowered, which becomes profitable for post treatment, by providing a neutral zone between the lateral orienting zone and preheating zone in the tenter. A part corresponding to the upper bottom of a trapezoid shows uniform physical properties in a widthward direction by applying preheat treatment to the film posterior to the lateral orientation. |
