| 摘要 |
PURPOSE:To mold a film stably without oversucking or overpressing a bubble by reducing velocity of cool air passing between a tapered surface of a cylindrical lip and a bubble on the inner and outer sides resectively forming a cool air ring-shaped diffuser in an air ring. CONSTITUTION:An air ring 12 provided on the downstream side of a ring-shaped discharge outlet 11 of a molding die 10 is equipped with a ring-shaped auxiliary air diffuser 13 on the upstream side and a ring-shaped main air diffuser 14 on the downstream side. A bubble B, molten and soft, just after being extruded out of the ring-shaped discharge outlet 11, is controlled by a small volume of cool air coming upwardly out of the auxiliary discharge outlet 13 of the air ring 12 and flowing along the inner side cylindrical surface of an inner side cylindrical lip 18 so as not to expand in the radius direction, cooled down and stretched. The cool air coming out of said auxiliary air diffuser 13 is dispersed to the outside of the radial direction along a recessed cool air velocity reducing section 24 of the inner side cylindrical lip 18 and reduced in its rising velocity. Also, part of the cool air flowing along an inner side cylindrical surface 22 of an outer side cylindrical lip 19 in the main air diffuser 14 is dispersed along a cool air velocity reducing section 25 and reduced in its rising velocity. |
