| 摘要 |
PURPOSE:To perform the heat treatment of a film without developing any process troubles such as flaw, break or the like of the film so as to obtain the target low heat shrinkage factor and flatness by a method wherein a biaxially stretched film is crosswise relaxation-treated at a relaxation factor lying in a specified range in a tenter and successively is lengthwise relaxation- treated at a relaxation factor lying in a specified range in the tenter under the state that both sides of the film are kept on being grasped with clips. CONSTITUTION:First, before a tenter 21, a film F is lengthwise unidirectionally stretched with a longutudinally stretching device. Secondly, the film is carried into the tenter 21 so as to be preheated and then stretched crosswise into a biaxially stretched film. Thirdly, the resultant biaxially stretched film is crosswise relaxation-treated at a relaxation factor of 0.1-10% in No.7 zone 37. Fourthly, the film is lengthwise relaxation-treated at a relaxation factor of 0.1-3% in No.8 zone 38. The lengthwise relaxation treatment is done under the state that similarly to the crosswise relaxation treatment both sides of the film are kept on being grasped with clips 23 or done by shortening the distance between the clips 23 adjoining to each other among the clips 23 arranged in large numbers. |
