PURPOSE: To obtain a biaxially stretched inflation film having a high blow ratio by a water cooling type biaxial stretching method inflating and stretching a bubble by air-pressure forming while applying Venturi action thereto by a distribution cylinder.
CONSTITUTION: A non-inflated and non-stretched thermoplastic resin bubble (a) extruded from an annular molding die 3 in a molten state to be quenched is folded double by nip rolls 6, 6 to be heated by a heater 15. Compressed air is blown into the heated bubble through an air supply grooved roll 24 to inflate the bubble. Air is supplied to the outside of the bubble from an air cooling ring to cool the bubble and the bubble (b) ready to inflate is guided along the taper downstream ends of the distribution cylinders 17... of a cooling device 18. The bubble (b) is effectively cooled by the Venturi action generated when the air streams blown toward the bubble (b) from the open air exhaust ports 21... of the cooling device 18 flow through the gaps between the bubble (b) and the downstream ends of the distribution cylinders and stretching force is applied to the bubble (b) by the Venturi action to obtain a high blow ratio.
NORO MASATAKA
MATSUI TAKASHI
KOBAYASHI NORIYUKI
