Patent GB-1158815-A (GB)
Title: Improvements in or relating to synthetic textile yarn and method of making same
IPC: D01D5/42
Filed: 1968-03-25
Abstract: 1,158,815. Film fibrillation. HERCULES Inc. 25 March, 1968 [30 March, 1967; 10 Oct., 1967], No. 14354/68. Heading B5B. [Also in Division D1] A bulky synthetic yarn has a spun-like appearance and a relatively soft hand comprising a plurality of continuous longitudinnally-oriented filaments of substantially uniform cross-section along the length thereof, the yarn comprising filaments having opposed side edges and a minimum thickness at the side edges and a maximum thickness intermediate the side edges, and a plurality of fibrils integral with the filament along the side edges and extending laterally therefrom to a free end, the fibrils having a thickness corresponding to the thickness of the filament at the opposed side edges. Preferably, the maximum thickness of each of the filaments is substantially at the transverse mid-point thereof and the thickness decreases in both directions therefrom to a minimum thickness at the side edges. Such yarn may be made by providing a film strip that is highly oriented uniaxially and has a plurality of spaced parallel striations longitudinally aligned with the axis of orientation and webs integral with and extending between the striations, and directing on to the film strip at a point intermediate the guides and in a direction substantially normal to the strip of film a fluid jet having a jet velocity sufficient to effect separation of the film strip along the webs with the formation of fibrils from the webs thereby reducing the strip of film to a plurality of individual filaments consisting of individual striations together with a portion of the web at each side edge thereof and fibrils integral with the filaments at the side edges and extending laterally therefrom. Specified materials include polyethylene, polypropylene, copolymers of ethylene and propylene, polyamides, polyesters, mixtures thereof including graft copolymers, and blends, laminates and other combinations. In apparatus as shown, polvmer melt is extruded from the die 4 of extruder 2, and the extruded strip 5a is immediately melt-drawn, and quenched in a quench tank 6 containing a liquid, suitably water. The quenched film strip 5 passes around rolls or bars 7 to a pair of feed rolls 8 that effect the melt draw of the film strip, suitably to a draw ratio of 3 : 1 to 10 : 1. The film may then be wound up on roll 9, or alternatively the film strip 5 can be led directly to the subsequent processing. The die 2 is suitably of the form shown in Fig. 3, which extrudes a striated film of the form shown in Fig. 4, which after melt drawing assumes the form shown in Fig. 5. As shown in Fig. 2, the melt-drawn film strip 5 is now pulled from film roll 9 by a set of low-speed feed rollers 10, and between the low-speed feed rollers 10 and a set of high-speed draw rollers 11, the film strip is directed over a heated drum 12, outer rollers 13 and 14 and a cold drum 15. The heated drum is maintained at a temperature sufficient for heating the film strip to the optimum orienting temperature for a particular material which, e.g. may be about 130‹ C. for polypropylene. The cold drum 15 is maintained at ambient temperature, and the high-speed draw rollers 11 are operated at a peripheral speed relative to the low-speed feed rollers 10 to provide the desired draw ratio, e.g. up to about 15 : 1, and with a melt draw ratio of about 4 : 1, this is preferably about 6 : 1 or 8 : 1. Drawing of the film strip occurs between the hot drum 12 and the first idler roll 13, and the appearance of the oriented film strip is shown in Fig. 6. After drawing, the strip 16 is cooled by the cold drum 15. The oriented filmstrip 16 is pulled from the delivery end of the draw rollers 11 by a pair of feed rollers 17. Between rollers 11 and 17, fibrillation device 18 separates the film strip 16 as shown in Fig. 5 into a yarn 19 as shown in Fig. 7, consisting of a bundle of individual continuous filaments. From rollers 17, the yarn 19 is taken up into yarn package 20. Fibrillation device 18 comprises a cylinder 21 having guides 22 in the opposite ends thereof and an air tube 23 in the side wall thereof. Guides 22 have the form of plugs inserted into the ends of the cylinder and have central bores that serve as the guides for the incoming film strip 16 and the outgoing yarn 19. Fig. 3 shows in cross-section a portion of one set of die lips 24 for the die 4. Die lips 24 have a matched series of opposed die grooves 25 equally spaced along the length thereof and separated by intermediate die faces 26. Thus the film strip 5a comprises a plurality of substantially rounded filament-forming strips 27, referred to as the striations and which are arranged in spaced parallel relation and are interconnected by integral webs 28. As shown in Fig. 7, film strip 16 has been split longitudinally of webs 32 into a plurality of filaments 33. Figs. 9 and 10 show on an enlarged scale a typical filament 33 of the yarn 19. This filament comprises an individual striation together with a portion of web on each side thereof which web portions terminate in side edges 34 and which constitute the edges along which the webs have been slit to separate the respective filament 33 from its adjacent filaments on the film. As the filaments 33 are all continuous and not broken, the tensile strength of the yarn is determined by the polymer characteristics and is not dependent upon the degree of twist in the yarn. Accordingly, twisting of the yarn is only necessary to the level required to establish coherence of the yarn. Hence the yarn can be made loose and bulky. The fibrils 37 which extend laterally relative to filaments 33 tend to support the filaments in spaced relation to increase the bulk of the yarn relative to a comparable yarn of equal twist but without the fibrils. In a modification, a flat sheet or tube is extruded and subsequently slit into strips of the desired width. In another modification, a die of the form shown in Figure 11 is used for making a single striated film.