GB1196586A - Jet Drawing of Conjugate Filaments - Google Patents

Abstract

1,196,586. Jet drawing of conjugate filaments. E. I. DU PONT DE NEMOURS & CO. 30 Oct., 1967 [31 Oct., 1966], No. 48709/66. Heading B5B. A process for drawing conjugate filaments of linear synthetic polymers at high speed comprises forwarding a filament bundle under drawing tension through an enclosure and within the enclosure splaying the filament bundle by impinging thereon a jet of a singlephase gaseous fluid thereby substantially instantaneously to raise the temperature of the individual filaments above the second order transition point, and withdrawing the filaments from the enclosure. Filaments for drawing may be fed continuously to the enclosure from the filament forming step, or alternatively may be drawn from a spinning spool. Preferably, the drawing tension either is no more than 75% of that required to obtain the same draw ratio in a single step at a filament temperature of 25‹ C., or is such as to produce a draw ratio unobtainable at 25‹ C. Desirably, the drawing tension is no more than 65%, and especially no more than 60%, of that required to obtain the same draw ratio at a filament temperature of 25‹ C. The single-phase gaseous fluid may be supplied from a source under pressure of at least 25 p.s.i.g. Both components of the filaments being treated may be polyamides, or both components thereof may be polyesters. Where polyesters are treated, the filament bundle suitably reaches a temperature of at least 118‹ C. within the enclosure to produce a yarn with a boil-off shrinkage of less than 10%. and the preferred gaseous fluid is steam which suitably impinges on the filament bundle at a velocity of at least 500 ft/sec., and especially at at least sonic velocity. Polyamides are preferably treated at a filament temperature of at least 115‹ C. There is no maximum operable temperature provided the filaments are not heated above their stick temperature which is generally about 20‹ to 35‹ below the polymer melting point. Especially suitable polyamides and polyesters are listed. After the drawing step, the yarn may be moisturized, preferably prior to packaging to permit the yarn to regain its normal or equilibrium moisture content. In the apparatus of Fig. 1, undrawn filament yam 10 is unwound from a package 12, moistened over finish roll 14, passed between guide pins 16 and tensioned between driven feed roll 18 and draw roll 20, rolls 18, 20 being operated at differential peripheral speeds so that the filamentary structure will be drawn to several times its extruded length. From roll 20, the drawn filamentary structure passes between pins 22 to wind-up 24. In the zone between rolls 18 and 20, a jet device 26 of the type shown in Figure 2 is positioned. The yarn passes through the longitudinal enclosure 27, which communicates with the orifice of a jet conduit 28, disposed at all angle with the axis of passage 27. Device 26 is connected at 29 to a supply of a heated gaseous fluid. The arrangement of Fig. 3 is similar to that of Fig. 1, except that yarn 101 is spun from a spinneret 12<SP>1</SP> and the spinning and drawing occur without intermediate packaging. As shown, a tandem arrangement of two jet devices 26<SP>1</SP> may be provided in the draw zone. The jet devices of Figs. 4 and 5 may be substituted for the device 26 of Fig. 2. The device of Fig. 4 is similar to that of Fig. 2, except for the provision of two angularly disposed jet conduits 41, 42 discharging into the longitudinal passage 43. The jet device 50 of Fig. 5, which is especially suitable for polyamides, has an initial passage 51 through which yarn travels to expansion chamber 52, passage 53 and tail pipe 54. In chamber 52, heated fluid from four syminetrically disposed jet conduits 55 is jetted on to the yarn in intersecting relationship therewith. Alternative forms of jet may also be used. Alternatively, a device comprised of a pair of opposed flat plates between which the yarn travels as fluid is jetted thereon from an orifice in one of the plates is operable under certain conditions, the principal requirement being that the heated fluid must impinge on the yarn in an at least partially restricted zone, fluid expansion in that zone of contact or impingement contributing to a separation of the yarn bundle and to the substantially instantaneous increase in filament temperature which is essential to the process. Filaments so drawn may be subjected to a pre-crimping heat treatment, by passing the yarn through another jet supplied with heated air at 90 p.s.i.g. after it leaves the draw rolls. The pre-crimping jet is like the draw jet, except that the yarn path channel is expanded in a funnel-like crosssection to give an exit air velocity of about 60 ft. per min. The unheated " tension let-down rolls " are operated at a lower surface speed than the draw rolls, to permit the drawn yarn to relax in the jet, and then cool it, prior to wind-up. Significant crimp develops when this yarn is converted to fabric and then boiled off. An example of the treatment of a conjugate polyamide filament yarn is given.