| 摘要 |
<p>1306686 Extruding nets NETLON (PTA) Ltd 19 April 1971 [9 April 1970] 17008/70 Heading B5A [Also in Division D1] An extruded tubular plastics net comprises an inner layer of parallel orientated strands 1 extending in a helix around the tube, an outer layer of similar strands 2 extending in an opposite helix, the two layers being unconnected at their crossing points 6, and a third layer of more orientated and attenuated strands 3 joined to the outer side of the inner layer strands 1 and to the inner side of the outer layer strands 2 along lines of connection points parallel to the tube axis X-X. Each third set strand 3 follows a looped untensioned path between connection points. The inner and outer strands are extruded from die slots 15, 16 in counter-rotating die lips 10, 11, respectively, whilst strands 3 are extruded from smaller slots 17 in stationary die lip 12. Twice the number of slots 17 as slots 15 or 16 gives the net shown, in which the third strands cross strands 1, 2 on both sides of each crossing point 6. Alternatively strands 3 cross on one side only of every crossing point 6 if the number of slots 17 is equal to the number of slots 15 or 16. The net is passed into a cooling bath then stretched by take-up rollers to produce molecular orientation in the strands, particularly in strands 3, using the apparatus of Specification 836,555. The suitable thermoplastics are nylon, polyesters, polyvinyl chloride and copolymers thereof with vinyl acetate or vinylidine chloride, polyolefins and cellulose acetate.</p> |
