| 摘要 |
PURPOSE:To form stably a tubular film having uniform thickness by a method in which a film being expanded after draw-starting point under a specific condition is directed to a draw-regulating ring and then redrawn in such a range that the lenth of all drawing zone is several times greater than the final expansion radius and the final draw ratio is a specific one. CONSTITUTION:If the vertical length of all drawing zone from draw starting point (a) to draw ending point (b) is l for the advancing direction of a film, vertical distance l1 is set at the position (c) meeting the formula. The two-stage drawing of the film is made until the final draw ratio in both vertical and crosswise directions becomes 2.5- 6 times under a condition meeting the inside diameter gamma1 of a draw-regulating ring and the formula and within a section where the vertical length of all drawing zone from the draw starting point to draw ending point is within the range of 0.5-5 times the final expansion radius. Since drawing speed in the early period of the starting of drawing can be greatly delayed, extreme increase of the yield-point strength at the starting time of drawing can be suppressed and also the orientation and crystallization in the early period of the drawing can be avoided. By the synergism of excellent both effects, the neck portion at the starting time of drawing can be very smoothly and uniformly drawn in stable shape. |
