| 摘要 |
PURPOSE:To stabilize the frost line of bubble and consequently enhance the quality of the film concerned by a method wherein the domain ranging from an air ring for cooling the neck part of bubble and its upper part above the frost line is surrounded with an inverted conical net and the surroundings of the net are cooled to a certain temperature. CONSTITUTION:Bubble 7 is formed by extruding molten thermoplastic elastomer composition through the annular orifice 11 of a die. At this time, the diameter of the bubble 7 just after extrusion is small due to low melt tension, resulting in forming the so-called neck part 71. In the neck part 71, the bubble 7 is stretched mainly in longitudinal direction (MD). Next, the bubble 7 expands itself abruptly so as to have the predetermined bubble diameter. In the expansion part 72, the bubble 7 is stretched not only in MD but also in lateral direction (TD). Near the almost upper end of the expansion part 72, a frost line is present and the thermoplastic elastomer composition turns into cooled and solidified state here. The bubble is further cooled with a second cooling ring 3 and a third cooling ring 4, both of which are provided in a bubble region 73, which lies above the frost line 74. |
