| 摘要 |
PROBLEM TO BE SOLVED: To easily prevent uneven longitudinal thickness from occurring by a method wherein heating is performed by making gradient for the widthwise heating amount of a film or by making the heating amount to both the end parts of the film larger than that at its central part at the starting of or just after its longitudinal stretching. SOLUTION: Three infrared heaters 26a, 26b, and 26c are disposed in the direction of the width of a film between a slow speed roller 23 and a high speed roller 24 and on the passing film. The heating amount of the center infrared heater 26a is set to be smaller than the heating amounts of the infrared heaters 26b and 26c on both the end part sides, resulting in making the ambient temperature on both the end part sides of the film higher than that at its central part. The region, to which the heating amount larger than that given to the central part is given, is set to be at least 1/6 of the width of the film. When two heaters are arranged in the direction of the width of the film, the heaters are arranged only to both the end part sides of the film without arranging a heater at the center of the film. Further, when five or more heaters are arranged, the capacities of the heaters are increased stepwise from the center towards the outsides of the film. |
