Improvements in or relating to the production of films

摘要

In a process for the downward extrusion of thermoplastic tubular film and reduction of its wall thickness by inflating and drawing, the inflated tube is passed through a passage-way of circular section, at least at its entrance, down the walls of which flows a cooling liquid in contact with the external surface of the tubular film. The cooling liquid is preferably supplied from a reservoir which surrounds the passageway and in addition the walls of the passageway may be hollow and be chilled by liquid circulating therethrough. Cold water or a refrigerant may be used as the cooling liquid. The films may be of linear superpolyamides and linear superpolyesters such as polyethylene terephthalate. As shown, a tubular film 2 is extruded from nozzle 1 and is inflated by air introduced through pipe 3. The inflated tube passes into a passage-way 6 bounded by wall 7 down the interior of which flows cooling liquid from bath 4. The wall 7 is surrounded by a barrier 8 having orifices 11 for the passage of cooling liquid, the height of the barrier being adjustable by means of its threaded mounting 10. The tubular film then passes between a pair of flat plates 12 hinged to the bottom of bath 4; the plates are of metal which may be highly polished, etched or coated with polytetrafluorethylene. The nip rollers 13 are driven at adjustable speed and one is preferably rubber coated. The flattened film is drawn off through a bath 15 having an adjustable outlet 16, although it is not necessary for bat 15 to contain any water, other than water entrained by the film. If desired, the tubular film may be slit by a knife before it reaches nip rollers 13, in which case the nip rollers and knife are immersed in the bath, the water pressure being sufficient to confine the air within the inflated portion of the tube.