| 摘要 |
1316411 Cooling extruded films AGFA-GEVAERT 1 June 1970 [4 June 1969 5 Sept 1969] 28315/69 and 44042/69 Heading B5B Polymeric films are produced by extruding molten polymeric material through a slot orifice to form a molten film and stretching the film longitudinally by drawing it away from the orifice towards a quenching drum at a linear rate greater than that at which it is extruded. Between the extrusion orifice and the quenching drum the film is in contact over its full width with a cooled control surface, e.g. a roller, the positioning of which, its temperature and the degree of frictional contact with the film being such that the extruded film is molten when contact is first made with the control surface but "necking-in" of the film is abruptly arrested on it. The control roller has a diameter less than half of the diameter of the quenching drum and is so located that the distance between the extrusion orifice and the point where the film touches the control roller is less than the distance between the orifice and the point where the film would first touch the quenching drum if it were placed as close as possible to the orifice and the same drawing angle retained. Fig. 1 shows an apparatus according to the invention. The molten polymer is pumped into the manifold 20 of the extrusion head 21, from which it is extruded as a film 25 through the orifice defined by the adjustable lips 22 and 23. The film is extruded downwards, deflected by control roller 24 through about 90 degrees of arc and then fed around quenching drum 26. A second quenching drum 27 and a roller 28 form a nip through which the film is then passed and finally, the film is drawn away over a drum 29 for further processing. The roller 24 and the drums 26, 27 are driven at a higher peripheral speed than that at which the film is extruded, thus causing the film to be stretched. This roller and these two drums, and their shafts, are hollow so that a liquid coolant, for example water, may cool the film to the desired extent. The surface of the roller 24 and the drums 26, 27 are formed of highly polished metal, to facilitate heat exchange. The effect of various parameters; the distances x 1 , y 1 , x 2 , y 2 , speeds V 1 , V 2 in Fig. 1, the temperature of extrusion, the stretch ratio, and the velocity of extrusion on the degree of necking-in and on the edge-loss is discussed. The process is intended mainly for use with polyethylene terephthalate, but other thermoplastics may be similarly treated. |
