| 摘要 |
1,157,245. Tubular polyethylene films. OSTERREICHISCHE STICKSTOFFWERKE A.G. 8 April, 1968 [20 April, 1967], No. 16882/68. Heading B5B. A process for the manufacture of tubular polyethylene films having a rough surface, comprises extruding the molten polymer through an annular die, inflating the material which issues therefrom in the form of a tube by means of compressed air which is blown in to give a bubble of lesser wall thickness than that of the tube on issuing from the annular gap, which bubble is closed off by means of two rollers, and is cooled in the inflated state, the molten polymer being cooled immediately before it issues from the annular gap, from at least the outside, by keeping the annulus of the die which surrounds the molten polymer at a temperature 100‹ to 180‹ C. Preferably, the molten polymer is cooled from both inside and outside, the temperature of the die on the inside of the molten polymer being suitably 140‹ to 150‹ C., and the temperature of the die on the outside of the molten polymer is suitably from 155‹ to 165‹ C. Polyethylene manufactured by the high pressure process is preferred. In Fig. 1, which shows a preferred blowing head of a side-fed die, the annular gap 1 is cooled by a flow of coolant through outer cooling spiral 2 and inner cooling spiral 3, via inlets and outlets 4 and 5 respectively . An inner mandrel 6 is provided with an air pipeline 7, and the molten polymer enters the blowing head at 8. Cooling can equally well be applied to a blowing head with a central feed, as shown in Fig. 2. If cooling not only outside the annular gap but also inside the annular gap is to be provided, the pipeline supplying the coolant must be passed through one of the spider bars which hold the inner mandrel of the blowing head. Thus in Fig. 2, 1 denotes the annular gap, 2 the outer cooling spiral and 3 the inner cooling spiral, which spirals are fed with coolant through inlets and outlets 5 and 4 respectively. The inlet and outlet 4 for the inner cooling spiral 3 passes through spider bars 9 and 10 respectively, 6 is again the inner mandrel and 7 the air pipeline, and 8 denotes the position of entry of the molten polymer into the blowing head. An example describes the production of film from high pressure polyethylene having a roughened internal and external surface and hence no tendency to block. |
