GB564584A - Improvements in or relating to fibres, threads, and yarn made from polymers and interpolymers of ethylene - Google Patents

Abstract

The heat-shrinkage of threads, filaments, and the like made of ethylene polymers or interpolymers is reduced, after they have been treated to orientate the micelles of the polymer, by heat-setting the threads while preventing contraction at a temperature above the desired initial shrinkage temperature but below the melting point of the polymer until there is no further appreciable reduction in tension, and then shrinking the threads by heating in the relaxed condition at a temperature at least as high as the desired initial shrinkage temperature but below the temperature of the heat-setting operation. The threads may be oriented by hot or cold stretching. During the heat-setting operation the threads may be held at constant length or may be extended by drawing to slightly less than the break elongation. The process may be modified by hot drawing unoriented threads at a slow rate so that they are heated for a sufficiently long time to be heat-set in the oriented condition. The heat-setting treatment may be carried out when the threads are wound tightly round bobbins and the ends are tied, and the shrinking may be effected by suspending the threads in skeins in a heating medium. The process may be carried out continuously by running the previously oriented filaments over three consecutive rolls, while heat is applied between the first and second rolls, e.g. from a heated block, and slightly less heat is applied between the second and third rolls. The first two rolls are run at the same speed and the third is run at a lower speed to allow the heat-set filaments to shrink. Crimped fibres may be obtained by combining a crimping operation with the heat-setting operation, e.g. by using a mandrel of appropriate shape. The heat-setting and the shrinking operations may be carried out with the threads immersed in a hot liquid. In an example, yarns wound on bobbins are immersed for 5 minutes in an aqueous solution of sodium chloride at 108 DEG C. The bobbins are removed and cooled and the yarns are skeined. The skeins are then suspended in water at 92 DEG C. and allowed to relax. Specifications 471,590, 472,051, 497,643 and 511,054; and 8070/40 (as open to inspection under Sect. 91) are referred to.