US2786737A - Wet spinning process - Google Patents

Description

March 26, 1957 s. G. HAWTIN ETAL 2,736,737

WET SPINNING PROCESS Filed March 27,":1951

Attorneys 2,786,737 WET SPINNING rnocuss Selwyn George Hawtin and John William Grebby, Spondon, near Derby, England, assignors to British Celanese Limited, a corporation of Great Britain Application March 27, 1951, Serial No. 217,816

Claims priority, application Great Britain March 28, 1950 6 Claims. (Cl. 18-54) This invention relates to the manufacture of artificial fibres by wet spinning methods and to the treatment of fibres with liquids.

in one method of wet spinning multi-filament yarns, the spinning solution is extruded through a spinning jet upwardly, for instance vertically upwards, into an upwardly flowing current of coagulating liquid. For example a solution of cellulose acetate in acetone may be extruded into and set in an upwardly flowing current of aqueous acetone. The current of coagulating liquid may be contained in a substantially vertical tube of fairly narrow diameter (referred to below as a setting tube), preferably attached to a somewhat broader base containing the jet and the inlet for the coagulating liquid. The coagulating liquid may overflow at the top of the tube or may escape through orifices near thetop of the tube, and may be led off forrecovery or re-use. The filaments leaving the setting tube are preferably carried upwards through the atmosphere for a further distance and may then be led, preferably round one or more guides, through a further air-run to a godet feeding to a winding device. The filaments leaving the body of coagulating liquid in the setting tube normally carry with them a column of coagulating liquid to a height depending inter alia on the number and denier of the filaments and the "speed at which they are travelling, and the abovementioned guide, or -the first guide if more than one is employed, is advantageously positioned well above the top of this column of coagulating liquid.

We have observed that when multi-filament yarns are made by the wet spinning method outlined above, the individual filaments remain separate, from each other during the whole of their travel through the body of the coagulating liquid, but come together at a point between the surface of the liquid and the first guide, forming a narrow cone. We have also observed that, at least over a considerable range of conditions, the height of the column of coagulating liquid carried up with the filaments is approximately the same as the height of the-cone, in other words, when or soon after the filaments have come together they no longer carry the column of coagulating liquid with them, though they are of course still quite wet. The'point of convergence ofthe filaments, he the apex of the cone formed by the filaments as they come together, we call the node. The bundle of filamerits above the node is hereinafter referred to as the yarn to distinguish it from the separatefilaments below the node.

We have found that'by applying a false twist to the yarn by a device situated above the node, the position of the node may be lowered, for example until it is at or below the surface of the coagulating liquid, and that when this is done the amount of coagulating liquid carried up by the filaments or yarn is reduced. If, as is preferred, the

2,786,737 Patented Mar. 26, 1957 node is forced right down to or below the surface of the liquid, the reduction in the amount of coagulating liquid carried up is very considerable. This has a number'of advantages, for instance it facilitates winding, makes possible a shorter air-run for the yarn, and reduces the amount of solvent which is lost, e. g. by evaporation, or which can be recovered only with considerable difliculty and expense.

The application of a false twist in this way hasa similar effect in other processes in which a number of filaments passing through a liquidate brought together to form a yarn at a point (in the absence of the twist) above the surface of'the liquid.

According'to the invention, therefore, in a process in which a number of filaments pass separately in nearly parallel paths upwardly through a liquid and come together to form a yarn at a point which is above-the surface of the liquid when the yarn is free from twist, the point at which the filaments come together is lowered by applying a false twist to the yarn. The invention also includes devices whereby the process can be carried out and the false twist applied.

The invention is of particular importance in connection with vertical upward wet spinning processes'of the general type already indicated, and will be described in more detail by reference to such a process and to a form of device'for carrying it out.

In a wet-spinning device constructed in accordance with the preferred form of the invention, the newly formed yarn passes first over a grooved pulley which is or can be fixedskew with respect to the natural plane of the yarn so as to cause the yarn when it first reaches the pulley to make contact with one side of the groove, and at a later stage in its passage over the pulley to make contact with the bottom of the groove. (By the natural plane of the yarn is meant the plane in which the yarn would travel were the pulley replaced by a perfectly smooth rod having its length substantially at right angles to the line of the yarnaproaching the pulley andthe line of the yarn leaving it.) The groove in the pulley must of course'be deep enough and narrow enough to cause the yarn to behave in the manner described when the pulley is suitablyfixed. lngeneral, the shallower and wider the groove the greater will -bethe angle at which the pulley must be set to producea giveneffect. We prefer to use a pulley having an approximately V-s'haped groove whose greatest width is not more than about 3 times, and especially not more than about twice, its depth. Preferably the pulley .is held in a mounting which can be turned about a horizontal axis, or at least about an axis having a considerable horizontal component, e. g. one set at 45 or less to the horizontal, to one side or to either side out of the natural plane of the yarn, for example it maybe held in a mounting which can be rotated'about-thc desired axis'and is provided with means whereby itmay be fixed in the desired position. Alternatively the pulley may for example be held in amounting which is pivoted about afvertica'l axis-lying in the natural plane of the yarn but outsidethe pulley.

The 'amount'by which'the pulley is turned out ofthe natural plane of the-yarn determines the degree offalsc twist imparted to the yarn, and thus the degree by-which theno'de is fforced'down. 'Advantageously the yarn'in passing overthepulley changes its direction by about a right angle; thus 'a substantially "vertical path may be changed to onesubstaritially' horizontal. The yarn may then begiven such fufther' din-run ,as may in 'any particular'instancebe necessary, and then,ifdesireda'fterpassing 3 over one or more further pulleys or other form of guide, it may be passed round a godet and wound up, or twisted and wound up, for instance as a cap-spun bobbin.

One embodiment of this invention is illustrated in the accompanying drawing, wherein:

l is a side view of a wet-spinning apparatus,

131g. 2 is a front View of a pulley used in this apparatus, an

Fig. 3 is a side view of this pulley.

The device shown in the drawing has been found to be very suitable for upwardly wet spinning yarns of cellulose acetate by extruding an acetone solution of the cellulose acetate into a coagulating liquid consisting of an aqueous solution of acetone. The device comprises an extrusion chamber 1, a setting tube 2 of smaller diameter, suitable guides 3 and 4 comprising free-running grooved pulleys, and a godet 5 feeding to a winding device (not shown). The extrusion chamber 1 is cylindrical in shape, and near its lower end is provided with inlets 6 for the coagulating liquid, at a somewhat higher level a spinning jet 7 is mounted centrally in the chamber and facing upwards, and between the level of the inlets 6 for the coagulating liquid and the level of the jet face a horizontal perforated metal sheet 8 extends across the Whole of the free space in the chamber to reduce turbulence in the coagulating liquid. Above the jet face the cylindrical chamber 1 is joined, by a converging section 9, to the setting tube 2, which is mounted vertically above the jet face. At its open upper end the setting tube 2 is surrounded by a funnel 10 fitted with a lead-off 11 for liquid, by means of which the coagulating liquid as it overflows at the top of the setting tube 2 is collected and led off for recovery or reuse.

The first guide pulley 3 is freely mounted vertically above the open upper end of the setting tube 2 in a mounting 12 attached to a rod 13 which passes through and is held by a bearing block 14; the rod 13 can be rotated in the bearing block 14, so causing the mounting 12 holding the pulley 3 to turn about a horizontal axis, and may be fixed in any desired position by means of a set screw 15. The second guide pulley-4 is freely mounted in a fixed mounting 15 at the same level as but a considerable distance from the first pulley 3; beneath this second pulley 4 is the godet 5 and the winding up device, the whole ar rangement being such that the yarn 17 passes over the two pulleys and down to the godet, and in doing so runs through the atmosphere for several feet, say 5-15 feet, the best distance depending on various factors such as fyarn speed, yarn denier, and temperature.

By virtue of its swivel mounting the first of the free running pulleys can be turned about a horizontal axis out 'of the plane in which the yarn would otherwise lie, so causing the yarn reaching the pulley to make contact with one side of the groove. By adjusting the amount by which the pulley is so turned the node, i. e. the apex of the cone formed by the filaments as described above, can be forced down to or (as illustrated) below the level of the open end of the setting tube, so considerably reducing the amount of coagulating liquid carried up with the filaments or yarn.

The device illustrated can be modified by providing a positive drive to the first guide pulley 3. Although in most cases we prefer that the pulley should be free running, if only for the sake of simplicity, a positive drive may be used with advantage when spinning under conditions such that the tension in the yarn is very low. It is found that, for a given skew position of the pulley, the position of the node can be varied by changing the speed at which the pulley is driven.

While the invention has been described in connection with the manufacture of cellulose acetate yarns by a particular wet spinning process, it is applicable over a wider field. Thus it may be used in the wet spinning of multifilament yarns having a basis of a material other than cellulose acetate, whether it be another cellulose ester,

e. g. cellulose propionate; a cellulose ether, e. g. ethyl cellulose or a Water-soluble ether such as a methyl, hydroxy-ethyl, or sodium carboxy-methyl cellulose; or a non-cellulosic material, for example a polymerised vinyl halide, a co-polymer of a vinyl halide and a vinyl fatty acid ester such as vinyl acetate, or polyacrylonitrile or a co-polymer of acrylonitriie with another vinyl compound. In the process particularly described the coagula-ting liquid is an aqueous solution of a volatile solvent for the cellulose acetate, namely acetone, but it may in stead comprise a solvent of low volatility; thus in spinning cellulose acetate from acetone solution an aqueous solution of diethylene glycol diacetate may be used; in such a case no extended air-run is needed, and residual diethylene glycol diacetate may be subsequently removed from the yarn by washing. Again, While in the wetspinning device particularly described the filaments are set in a co-current of coagulating agent, a counter-current or transverse current may be used, or the filaments may be set in a large volume of coagulating agent which is changed at a suitable rate but which does not flow as a whole at any considerable speed in any direction. Either a single jet or a number of jets may be used in the one coagulating bath.

The invention may also be applied to processes other than wet-spinning, in which a number of separate filaments pass through a liquid and are then wound up as a single yarn; the filaments may be single continuous filaments, or may each be made up of a number of single continuous filaments or of staple fibre. Such processes may have as their object either to alter the properties of the material in some way, e. g. to dye it or to shrink it, or to apply a removable coating or other substance to the surface of the filaments, e. g. a size or anti-static dressing or (in the case of thermoplastic materials) a softening agent or plasticiser. The degree of false twist applied may be such as to reduce to a minimum the amount of liquid adhering to the yarn, or to adjust it to some desired value above the minimum. The application of the invention is not restricted to processes in which, in the absence of the false twist, the filaments or yarn carry with them a column of the coagulating or treating liquid.

If desired, instead of the false twist a true twist to a similar degree may be inserted in the yarn, but this will usually be much less convenient.

Having described our invention, what we desire to secure by Letters Patent is:

1. A process for the production of yarn by the wet spinning method, which comprises extruding a spinning solution into a setting liquid to form a number of filaments, drawing the filaments by a yarn forwarding means upwardly in nearly parallel paths through and once for all out of the liquid under conditons such that they come together to form a yarn at a point which would be between the surface of the liquid and the yarn forwarding means were the yarn free from twist, and changing the direction of travel of the yarn by passing it over a grooved pulley fixed skew with respect to the natural plane of the yarn, the said pulley being the first structure with which the yarn makes contact after the filaments have left the setting liquid, and the shape of the groove and the position of the pulley being such that the yarn when ittreaches the pulley makes contact with one side only of the groove and at a later stage in its passage over the pulley makes contact with the bottom of the groove, whereby a false twist is applied to the yarn and the point at which the filaments come together is lowered.

2. Process according to claim 1, wherein the groove in the pulley is of approximatey V-shaped section having its greatest width at the most three times its depth, and the plane of the pulley is rotated out of the natural plane of the yarn about an axis at an angle of 0 to 45 to the horizontal. g 7 Q I 3. Process according to claim 2, wherein the pulley is free running. I i

References Cited in the file of this patent UNITED STATES PATENTS Schrenk Aug. 7, 1934 Dickie et al Dec. 31, 1935 Oppenlaender Feb. 8, 1938 Polak May 9, 1944 Whisnant Jan. 30, 1951

Claims (1)

1. A PROCESS FOR THE PRODUCTION OF YARN BY THE WET SPINNING METHOD, WHICH COMPRISES EXTRUDING A SPINNING SOLUTION INTO A SETTING LIQUID TO FORM A NUMBER OF FILAMENTS, DRAWING THE FILAMENTS BY A YARN FORWARDING MEANS UPWARDLY IN NEARLY PARALLEL PATHS THROUGH ONE ONCE FOR ALL OUT OF THE LIQUID UNDER CONDITIONS SUCH THAT THEY COME TOGETHER TO FORM A YARN AT A POINT WHICH WOULD BE BETWEEN THE SURFACE OF THE LIQUID AND THE YARN FORWARDING MEANS WERE THE YARN FREE FROM TWIST, AND CHANGING THE DIRECTION OF TRAVEL OF THE YARN BY PASSING IT OVER A GROOVED PULLEY FIXED SKEW WITH RESPECT TO THE NATURAL PLANE OF THE YARN, THE SAID PULLEY BEING THE FIRST STRUCTURE WITH WHICH THE YARN MAKES CONTACT AFTER THE FILAMENTS HAVE LEFT THE SETTING LIQUID, AND THE SHAPE OF THE GROOVE AND THE POSITION OF THE PULLEY BEING SUCH THAT THE YARN WHEN IT REACHES THE PULLEY MAKES CONTACT WITH ONE SIDE ONLY OF THE GROOVE AND AT A LATER STAGE IN ITS PASSAGE OVER THE PULLEY MAKES CONTACT WITH THE BOTTOM OF THE GROOVE, WHEREBY A FALSE TWIST IS APPLIED TO THE YARN AND THE POINT AT WHICH THE FILAMENTS COME TOGETHER IS LOWERED.

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