| 摘要 |
PURPOSE:To manufacture a high quality film with high productivity by a method wherein a mandrels, which display large bubble stabilizing effect and large effect to suppress the vertical movement of an expansion starting point develops by the change of atmospheric temperature and the like, are provided at an annular die. CONSTITUTION:Air is fed to a space from an air suction pipe 2 under the state that the upper end opening of a strut 6 is closed and a hole 7 is open. At the same time, molten resin tubular body 8 is extruded from an annular die 1. When the tubular body is expanded diametrically and pinched by sucking the air from the air suction pipe into a space 12 by opening the upper opening of the strut 6 after passing over a first and a second mandrels 4 and 5, an expansion starting point 9 is generated. When the location of the expansion starting point 9 is shifted to the central part of the second mandrel 5 by controlling the amount of cooling air supplied from an air cooling ring 3, the tubular body 8 contactingly passes over the first mandrel 4 and, after that, expands under the state that the tubular body before and after the expansion starting point 9 comes into contact with the second mandrel 5 but the tubular body at the expansion starting point 9 does not contact nothing. Accordingly, the swaying of the bubble after expansion is eliminated and the bubble is stably molded. Even when the delivery of the tubular body is increased, the swaying of the bubble is suppressed by increasing the amount of cooling air from the air cooling ring 3 and the productivity of the tubular film can be enhanced. |
