| 摘要 |
1,190,028. Polyolefin films. SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ N.V. 26 Nov., 1968 [28 Nov., 1967], No. 54139/67. Addition to 1,093,018. Heading B5B. In a process for the manufacture of a polyolefin film, as shown in Fig. 1, a polyolefin is melt-extruded downwards from an extruder 1 having a vertical extrusion die provided with an annular extrusion orifice and an air inlet through which air for inflating the extruded tubular film 2 is supplied. The film is drawn downwards from the die through a body of cooling water 3 by means of a pair of nip rolls 5 by means of which the film is fully collapsed to the lay-flat form and leakage of air from the inflated portion of the film prevented. Mounted for rotation in the upper part of the tank are two parallel nickel-plated driven chilling rollers 4 rotating in the opposite directions shown by the arrows and spaced apart so as to partly collapse and support the film 2 as it enters the water 3, but without actually nipping the film. The surface of the water 3 in its cooling tank is maintained at a level such that the axes of rotation of the chilling rolls 4 lie approximately within the plane of the water surface. Each of the chilling rolls 4 is provided with a device 6 for maintaining an even distribution of cooling water on the roll surface. As shown in Fig. 2, a preferred form of such a device comprises a wiper in the form of a pad 7 of flexible absorbent material such as filter cloth, for example, some five inches wide, which extends lengthwise of each roll 4, the roll diameter being, for example, about ten inches. One side of the cloth pad 7 is supported by a backing strip 8 itself carried at each end by the sides of the tank, the cloth pad 7 extending away from the backing strip 8 so as to lie on the surface of the roll 4 in a position such that there is about one inch of roll surface between the trailing edge 7a of the cloth pad 7 and the line of first contact of the roll 4 with the tubular film 2. The cloth pad 7 is partly supported by a perforated pipe 9 which extends lengthwise of the roll 7 and lies beneath the cloth pad 7 in such a manner as to direct cooling water to the underside of the cloth pad 7 (as indicated by the sprays 10). A fabric scraper 11 is also provided in rotational advance of the cloth pad 7 for cleaning the chilling roll 4 prior to contact with the cloth pad 7. Instead of the device shown in Fig. 2, each chilling roll 4 may be provided with a water trough positioned a short distance above and extending lengthwise of the roll, the trough having at its base either a permeable pad which contacts the peripheral surface of the roll or a pair of rubber or fabric lips which contact the roll and are caused to part when the roll rotates to an extent which permits water to pass between the lips on to the peripheral surface of the roll. |
