EP0409752A1 - Method and machine for producing continuously an elastic yarn from elastane - Google Patents

Abstract

Process for the manufacture of an elastic yarn (21) based on elastane, characterised in that it consists continuously and in the same working position: - in a first step, in assembling, at a twist of less than five hundred (500) turns/metre (t/m) and without a twist resultant, a tensioned bare elastane yarn (12) with a partially drawn multifilament synthetic yarn (2); - then, in a second step, in subjecting this assembled yarn (20) to an additional drawing with heating (16) to supplement the residual drawing, on the one hand of the partially drawn multifilament yarn (2) and, on the other hand, of the tensioned elastane yarn (12); - and finally in rereeling (17, 18) the elastic yarn (21) obtained. Application: elastic yarn for stockings and tights.

Description

The invention relates to a method for the continuous production of an elastic yarn based on elasthane. It also relates to a machine for implementing this method.

It has been known for a very long time to manufacture elastic wrapped threads, in particular by the technique known as "simple wrapping". To do this, first of all the elasthane thread is stretched three to five times, then a so-called "wrapping" thread is wound around it in turns, preferably contiguous, in particular a textured thread. In practice, the wrapping twist which varies inversely with the title of the wrapping wire is of the order of a thousand to three thousand (1000 to 3000) turns / meter (t / m), since it is desired to obtain substantially turns contiguous. Also, when it is desired to make single yarns that are wrapped as thin as possible and with the minimum amount of bulk, such as the yarns that are sought for the manufacture of stockings, fairly thin elasthane yarns are commonly used, c that is to say of the order of ten to forty dtex, which are covered with a raw synthetic or textured thread by false twist of ten to thirty dtex, wrapped in twists of the order of one thousand five hundred ( 1500) turns per meter (t / m). Although this technique is very widely used, it nevertheless has certain notable disadvantages, such as the high cost price and the impossibility of obtaining windings without knot of appreciable weight.

In document FR-B-2 561 676 of the Applicants, a technique has been proposed which consists in guiding the stretched elasthane yarn with a multifilament synthetic yarn partially stretched with a wrapping twist of a third of the usual twist, then in a separate phase to complete this twist with a double twist spindle, and finally in a third phase, also distinct, to subject the wrapped yarn to additional residual hot stretching. This technique gives wrapped threads that are well suited to the production of stockings and tights where the finest threads are sought. However, to obtain a correct covering of the elastane thread and thereby protect it from scuffing, it is necessary to twist the thread at twists of the order of two thousand (2000) turns / meter (t / m). It follows that this technique, although developed, is still expensive.

It has also been proposed to knit (or weave) naked stretched elasthane yarns. Although proposed for a long time, this technique has not developed due to the too high manufacturing cost, resulting in particular from the high percentage of finished products (tights) of second choice.

The invention overcomes these drawbacks. It relates to a process and a machine for the continuous production on a single working position of an assembled elastane thread which is rapid, economical, and makes it possible notably to reduce the quantity of elasthane threads and consequently the price of this yarn, while increasing the fineness of the yarns made in this way, finesse which is more and more sought after in particular in the manufacture of stockings and tights. In addition, this improved technique makes it possible to use the yarns produced in this way at knitting speeds which are incommensurate with that used with bare yarns.

This improved process for the manufacture of an elastic thread is characterized in that it consists continuously and in the same working position:
- firstly, to be assembled at a twist of less than five hundred (500) turns / meter (t / m) and without torsional result, a bare elastane thread stretched with a partially drawn multifilament synthetic thread;
- Then, in a second step, subjecting this assembled yarn to additional hot drawing to complete the residual drawing, on the one hand of the partially drawn multifilament yarn, and on the other of the stretched elasthane yarn;
- And finally, to rewind the elastic thread obtained.

As is known, a "partially drawn multifilament synthetic yarn" is a synthetic yarn which has undergone only partial drawing, that is to say only partial molecular orientation. Such threads are well known and are commonly called "POY" (pre-oriented yarn) or sometimes MOY (medium oriented yarn). Such threads are described in particular in document FR-A-2 151 896 or in its American correspondents USA 3 771 162 and 3 772 872 by DUPONT DE NEMOURS.

By "without torsional result", one indicates an assembled wire of which each wire would have a zero torsion if one removed the other wire.

In practice :
- the coating wire is a partially drawn polyamide wire, having a residual stretching rate of the order of 10 to 25%;
- the elastane thread is drawn in a ratio of three.

It is important that the first assembly twist is less than five hundred (500) turns / meter (t / m). Indeed, if we assemble with higher twists, on the one hand we unnecessarily increase the cost price without proportional improvement, and on the other hand and above all we affect the appearance of the finished products (tights). Advantageously, this twist for fine threads intended for the manufacture of stockings and tights, that is to say in which an elasthane thread of the order of twenty dtex is used, must be between one hundred and fifty and three hundred ( 150 and 300) turns / meter (t / m), advantageously close to two hundred and fifty (250) turns / meter (t / m).

The invention also relates to a machine for manufacturing such an elastic thread. This machine consisting of a plurality of working positions is characterized in that each position includes:
- a hollow spindle with a turntable, intended to receive a fixed winding of spandex thread, immobilized during the rotation of the tray;
- A means of feeding a multifilament wire partially stretched from a winding to the turntable of the hollow spindle;
- a means of drawing the elastane thread;
- A means for assembling the partially stretched multifilament yarn with the stretched elastane yarn without torsional result;
- a drawing train of the assembled yarn formed to complete the residual drawing of the multifilament yarn and of the stretched elasthane yarn, consisting of two pairs of rollers respectively for drawing and drawing;
- a heater arranged between the two pairs of rollers;
- A winding member of the elastic thread formed.

It is essential that the drawing of the assembled yarn is carried out hot to promote both the residual drawing of the multifilament yarn, and also to increase the elongation capacity of the elasthane core yarn.

In document FR-A-2 184 230 from one of the Applicants, a method of simple wrapping of a stretched elastane wire has been described by winding a coating wire in a helix when the false twist is blocked. , in particular by using a hollow spindle with a turntable on which the elasthane winding is immobilized, then heat treatment possibly continuously. Here, a standard multifilament yarn, that is to say fully drawn, is used, and the assembled yarn obtained has poor coverage by the coating yarn. This is the reason why this technique has not developed.

It was not easy to reconcile and then adapt the lessons of these two techniques described in the cited documents (FR-A-2 184 230 and 2 561 676), proof of the long time elapsed, especially since the first unexploited technique aimed at a continuous process, while the second exploited aimed at a discontinuous process. In addition and above all, bringing these two techniques together, however, by adapting them, makes it possible to successfully resolve a problem which has arisen for a very long time, namely obtaining an elastic thread assembled as thin as possible, capable of being knitted at high speed. Furthermore, surprisingly, the invention makes it possible, for the same result, that is to say for the same textile qualities, to reduce the quantity of elasthane yarn and consequently the incidence of this expensive raw material. on the cost price of the finished yarn. In this way, the wires produced in accordance with the invention can be can be successfully used in the manufacture of tights or stockings where great finesse is sought.

The manner in which the invention can be implemented and the advantages which result therefrom will emerge more clearly from the embodiment which follows in the light of the single appended figure, showing a characteristic working position in accordance with the invention.

From a spinning reel (1), a thread (2) of polyamide 6.6 POY (pre-oriented yarn) having a titer of seventeen dtex formed from six parallel elementary filaments is taken on the parade. This POY wire (2) after additional stretching makes it possible to obtain a standard fourteen dtexsix strand wire.

This coating wire (2) then passes through a tensioner (3), then enters the hollow axis (4) of a hollow spindle designated by the general reference (5), carried by a bearing (6) and driven tangentially by a belt (7). In known manner, the bearing (6) can be disengaged by moving the belt (7) away. The partially stretched coating wire (2) crosses the axis of the spindle (4), enters tangentially into the turntable (8) and forms a balloon (9) limited by the balloon stop barbin (10).

The spindle (5) carries a winding (11) of elasthane wire (12), for example a wire marketed by DUPONT DE NEMOURS under the registered trademark LYCRA of twenty two dtex (mono or multifilamentary). During the rotation of the turntable (8), this winding (11) is fixed. The elasthane wire (12) is strongly stretched by the braking that the tensioner exerts on it, while it is pulled up by the positive roll call from the first roll (14) of the drawing train. The elastane yarn (12) thus elongated enters the barb (10) where it is assembled with the yarn (2) with the effect of false twisting, but without the result of twisting. The assembled yarn obtained (20) then enters a drawing train formed by two pairs of rollers or capstans, respectively of call (14) and drawing (15) to undergo a complementary drawing intended to complete the drawing. residual on the one hand, multifilament yarn (2) partially stretched and on the other hand, stretched elasthane yarn (12).

To facilitate this drawing and the elongation properties of the finished wire, this additional characteristic drawing is carried out hot, that is to say by passing through a known thermal oven (16).

The finished elastic assembled thread (21) is returned by known means (17) in the form of a coil (18). In a practical embodiment, the coating wire (2) is a polyamide 6.6 POY wire. of seventeen dtex - six strands capable, after drawing, of forming a standard wire of fourteen dtex - six strands. The elasthane core thread (12) is a LYCRA thread (registered trademark EI DUPONT DE NEMOURS) of twenty-two dtex, which is stretched after passing over the tensioner (13) by about three times to be brought to seven dtex. The speed ratio between the two capstans (14) and (15) is adjusted to around 20% and the temperature of the oven (16) to 160 ° C.

There is thus obtained an elastic assembled thread (21) consisting of an elasthane thread of about six dtex, approximately rectilinear, covered in a regular manner, but not contiguous by turns of polyamide 6.6 of fourteen dtex - six strands. The final title of this thread (21) is twenty dtex, which was very difficult to obtain economically to date. This yarn is ideal for making stockings and tights on high-speed knitting machines.

Claims (4)

1 / Process for the manufacture of an elastic yarn (21) based on elasthane, characterized in that it consists continuously and in the same working position:
- firstly, to be assembled at a twist of less than five hundred (500) turns / meter (t / m), and without the result of twisting, a stretched bare elasthane thread (12) with a partially drawn multifilament synthetic thread (2 );
- Then, in a second step, subjecting this assembled yarn (20) to additional hot drawing (16) to complete the residual drawing, on the one hand of the partially drawn multifilament yarn (2), and on the other part of the stretched elastane thread (12);
- And finally, to rewind (17,18) the elastic thread (21) obtained. 2 / A method according to claim 1, characterized in that the multifilament yarn (2) is a partially drawn polyamide yarn, having a residual stretching rate between 10 and 25%. 3 / Method according to one of claims 1 and 2, characterized in that the elastane yarn (12) is drawn in a ratio of three. 4 / Machine for manufacturing an elastic thread (21) based on elasthane constituted by a plurality of working positions, characterized in that each position comprises:
- a hollow spindle (5) with a rotating plate (8), intended to receive a fixed winding (11) of elasthane wire (12), immobilized during the rotation of the plate;
- a means (1,3) for feeding a multifilament yarn partially stretched (2), from a winding (1) to the turntable (8) of the hollow spindle (5);
- a means of drawing (13) of the elastane wire (12);
- A means (10) for assembling the partially stretched multifilament yarn (2) with the stretched elasthane yarn (12) without torsional result;
- a drawing train (14,15) of the assembled wire (20) formed to complete the residual drawing of the multifilament wire (2) and the stretched elasthane wire (12), consisting of two pairs (14,15) rollers (14) and drawing (15) respectively;
- a heating member (16) disposed between the two pairs of rollers (14,15);
- A winding member (17,18) of the elastic thread formed (21).

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