| 摘要 |
Filaments of stereoregular poly-2-olefines, especially isotactic polypropylene, are drawn between a feed roll and a draw roll, the filaments supplied to the feed roll being under tension, said tension causing substantially no alteration in length of the filaments and being insufficient to cause a distinct draw-point or "neck" to form. Such tension may be imparted to the filaments by means of a nip roll moving slower than the feed roll, or by a mechanical tension gate or hysteresis brake. Such tensioning devices may cause up to 15% stretching. Preferably the feed roll is heated, e.g. to about 75 DEG C., and the draw ratio is between 2:1 and 10:1. Between the feed and draw rolls the filaments may be passed over a plate heated to about 145 DEG C., and a scrubbing pin may be used to localize the draw point. Filaments prestretched according to the invention show improved break and lap levels in the subsequent stretching step.
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