Patent GB-1190042-A (GB)
Title: The Making of Tubular Film of Thermoplastic Synthetic Polymeric Material
IPC: B29C48/10
Filed: 1967-07-17
Abstract: 1,190,042. Films. OKURA KOGYO K.K. 17 July, 1967 [25 Oct., 1966], No. 32833/67. Heading B5B. In an extrusion apparatus as shown, thermoplastic synthetic polymeric material melted in extrusion device A is forced out of annular orifice 2 in an extrusion die 1 to form a liquid state tubular film. The film is cooled from its inner surface by cooling liquid 3 and from its outer surface by cooling liquid 4, and after passing mandrel 5 and having been cooled completely the film is taken up by rollers 6 and passes to wind-up. Cooling liquid 3 passes into an upper chamber of mandrel 5 through inlet tube 7, and passes from the upper chamber through exit orifice 8 of the mandrel. This cooling liquid passes between the film and the mandrel 5, contacting and so cooling the film, and re-enters the mandrel through a suction orifice 9 in a lower chamber of the mandrel. The liquid leaves the mandrel through exit tube 10 and is cooled in a cooling chamber and pumped back into the mandrel through inlet tube 7 to continue its circulation cycle. Mandrel 5 tapers upwardly and so there is a space between the film and the mandrel at the upper part of the mandrel, through which the cooling liquid 3 passes. Suitably, the radial extent of this space is from 2 to 10 mm. Mandrel 5 may be of metal having a smooth surface, and the surface may be formed with spiral grooves to lessen friction, the mandrel surface being also coated with some elastic material if desired. Cooling liquid 4 enters basin 13 through inlet 12 and pours out from outlet 13. The height of outlet 14 can be adjusted up and down so that the level of the free surface of cooling liquid 4 can be changed. The level of cooling liquid 3 may be adjusted by adjusting the circulating volume of the cooling liquid 3. Thus by increasing the circulating volume the level of the liquid surface is raised, and by decreasing the volume the level is lowered. Thus the respective levels of the cooling liquids 3 and 4 may be adjusted independently of each other. The level of cooling liquid 3 is maintained the same as, or up to 30 mm. higher than, the level of cooling liquid 4 and better stability and smaller changes in the diameter of the film are thus obtained. Cooling liquids 3 and 4 are inactive to the thermoplastic synthetic polymeric material, and have low-boiling points. Water may be used for both cooling liquids 3 and 4. If desired, the liquid-state tubular film may be pre-cooled by blowing cool air over it before cooling with the cooling liquids 3 and 4. The process is particularly useful in the manufacture of thick continuous tubular film of thermoplastic synthetic polymeric materials that require cooling rapidly because the liquid-state tubular film may be cooled very rapidly from both its inner and outer surfaces; polyethylene film is specified. The process may also be used in the manufacture of thin tubular film of high quality, since variation in the tube diameter is kept to a minimum. In the manufacture of tubular film from thermoplastic synthetic polymeric materials that do not require cooling rapidly, the invention may be used to produce even, thick tubular films of high stability rapidly and with high efficiency because of the rapid cooling.