| 摘要 |
<p>1,170,639. Thermoplastic nets. E.I. DU PONT DE NEMOURS & CO. 23 May, 1967 [23 May, 1966], No. 23834/67. Heading B5B. [Also in Divisions A1 and D1] A net of intersecting strands of a thermoplastic resin which has been drawn along one axis only, in which the intersections are uniplanar, integrally moulded and substantially non-oriented, the strands between the sections being oriented, each intersection having a strength at least 50% of that of the strength of a strand entering that intersection and wherein the strands and intersections form diamondshaped apertures, may be made by forming from the molten resin a web which includes a plurality of strands extending parallel to the length of the web, each strand being joined to its adjacent strands by alternating longitudinally spaced intersections, said intersections being thicker than the strands, the strands being joined by a film which is thin relative to the thickness of the strands, the cross-sectional area of an intersection being at least 1À25 times that of two strands, cooling and solidifying the web, heating the web to remove said film, longitudinally drawing the web to lengthen the strands without drawing the intersections, transversely opening up the web to form the net in which the strands and intersections form diamond-shaped apertures, and finally heat stabilizing the net so formed. The web may be formed by extrusion casting of a molten resin on to a suitably patterned chill roll while maintaining a pressure-seal between roll and die, e.g. using the apparatus described and claimed in Specification 1,170,640. The thin film joining the strands may be 0À001-0À003 inch thick, and be removed by a blast of very hot air (700-800‹ C.) prior to quenching. Many suitable resins are listed, working temperatures being given for high and low density polyethylene, polypropylene, polystyrene, PVC and nylon 66.</p> |
