| 摘要 |
1,138,008. Tubular polyolefin films. OSTERREICHISCHE STICKSTOFFWERKE A.G. 10 May, 1967 [25 May, 1966], No. 21689/67. Heading B5B. In a process for the manufacture of tubular films of olefin homopolymers or copolymers or mixtures which contain such olefin polymers as the main constituent, in which the material issuing as a tube is expanded by means of air pressure to a bubble of reduced wall thickness which is closed by two nip rolls, and the bubble is externally cooled by a ring-shaped cooling device, there is externally applied a reduced pressure of 100 to 1000 mm. of water below atmospheric pressure on the inflated tubular film in the region of the cooling device. Said pressure may be 300 to 400 mm. of water, and the cooling device may be fed with water or other cooling liquid. The preferred starting material for the manufacture of the tubular film is polypropylene or a mixture principally consisting thereof. In apparatus as shown, an extrusion die 1 is provided with a tube-shaped probe 2 for supplying a blowing gas into the interior of the tube and a cooling ring 3 which surrounds the inflated tubular film, the cooling ring being, on its inner face, which is either completely smooth, or, optionally, roughened, provided with grooves 5 which run at rightangles to the axis of the ring and which are connected through bores 6 with an externally welded-on semi-circular cross-section tube 7 which runs parallel to the grooves over the whole circumference and is supplied with suction nipples 8, which are connected to a suction pump by means of vacuum pipe lines. The cooling ring is provided with an outlet 10 for the cooling liquid. Suitably, the number of bores is very large, and each groove is suitably provided with 40 to 60 bores distributed uniformly over the circumference of the cooling ring 3. The internal chamber of the cooling ring may be provided with a dividing wall in the position of the said grooves so that the internal chamber is sub-divided into two or more chambers which can be fed separately with cooling liquid. Thus the first zone may be supplied with water, and the second with a cooling liquid at a lower temperature. In operation, the tubular film issues from the extruder 1, is inflated by means of the blow tube 2, and the bubble which is thereby produced is led through an entry 11 to a pair of nip rolls 12 and is closed off by the nip rolls. The bubble is externally cooled by the cooling ring 3, whose internal space 9 is supplied with water or cooling brine through supply lead 4. The use of reduced pressure in the zone of external cooling enables the draw-off speed of the tubular polyolefin film to be increased, and in the manufacture of polypropylene films it is possible to achieve films with significantly enhanced physical properties. |
