| 摘要 |
PURPOSE:To obtain a biaxially stretched film excellent in heat shrinkability by applying longitudinal stretching to a bubble over a short section by nip rolls in addition to the stretching of the bubble due to air in longitudinal and lateral directions. CONSTITUTION:Air is blown in a thermoplastic resin bubble (e) extruded from an annular molding die (d) in a molten state. The bubble (e) is subjected to inflation molding under such a condition that b/a is 1.5-10 when the diameter of the bubble at the crystallizing temp. of the used thermoplastic resin is set to (a) and the final diameter of the expanded bubble is set to (b) to obtain an oriented film (f) which is, in turn, folded double. This oriented film (f) folded double is longitudinally stretched by 1.2-5 times by utilizing the peripheral speed difference between nip rolls 18,19. The blow ratio of the oriented film obtained by inflation molding is pref. 6-22 times. As the used thermoplastic resin, polyethylene, polypropylene, an ethylene/vinyl acetate copolymer, an ethylene/acrylic acid copolymer and the like are designated. |
