FR2861091A1 - FLAT MULTIFILAMENTAL ELASTOMERIC WIRE, METHOD AND INSTALLATION FOR THE PRODUCTION THEREOF - Google Patents

Abstract

The invention relates to the manufacture of a multifilament elastomeric yarn (F), in particular of polyurethane, by wet spinning. During the wet spinning and before the multifilament yarn baking operation, the mutifilament yarn (F) is shaped so as to give it a flat cross section. More particularly, to shape the yarn, we make pass the filaments (f) at the outlet of the extrusion dies (5a), when they are still immersed in the coagulation bath, over a rotating shaping cylinder (7) which is at least partly immersed in the bath coagulation valve (6), the filaments being positioned relative to each other to form the required flat cross section.

Description

ELASTOMERIC MULTIFILAMENTARY FLAT WIRE, METHOD AND

  INSTALLATION FOR THE MANUFACTURE OF SAID THREAD

  Field of the Invention The present invention relates to a novel multifilamentary elastomeric flat section wire, its method of manufacture, and an installation for the manufacture thereof. The elastomeric yarn of the invention is advantageously used, for example but not exclusively, in the field of the manufacture of hygienic articles, and in particular diapers.

  PRIOR ART In the field of sanitary articles, and more particularly diapers, it is customary to incorporate elastic threads into the structure of the article. In the case of layers, elastics are inserted on the one hand at the waist and on the other hand at each leg passage, to ensure a better seal fecal barriers of the layer. These elastic threads must have sufficient recovery characteristics for the seal obtained to be optimal. It is also customary to integrate into the structure of the layer elastic elastomer yarns which make it possible to give the layer, at rest, an anatomical shape of a spoon.

  When traditional elastic threads having a round cross section are used, it is often found that the pressure exerted by the elastic threads on the skin of the wearer of the diaper is excessive, especially at the level of the legs, and causes a significant risk of marking. skin, or even irritation and / or injury to the skin of the wearer. This disadvantage is even more preponderant when the coucheculotte is intended to be in contact with sensitive skin, such as in particular a baby diaper.

  In order to overcome the above drawback, it is thus sought by the manufacturers of hygienic articles, and in particular of layers, to replace the round-section elastic threads with flat-sectioned elastic threads, which advantageously makes it possible to increase the contact area, and thus reduce the pressure exerted on the skin with the same tension.

  In the present text, and within the meaning of the invention, flat wire or flat cross-section wire means a wire whose cross section has two main axes: a major axis subsequently designated width (L) (larger dimension of the section) and a minor axis subsequently designated thickness (e) (smaller dimension of the section) which are substantially perpendicular. Preferably, and as a guide, it is considered that a wire has a flat section within the meaning of the invention, when the width (L) is at least five times greater than the thickness (e), and preferably at least less than ten times the thickness (e). As non-exhaustive examples, among the son of flat cross section, there are in particular son having a cross section substantially shaped rectangle, trapezoid, ellipse, oval, ....

  To date, it has already been proposed, in particular in the patent issued in the United States under number US 6 248 197 B1, to produce a multifilament yarn of elastomeric material, and in particular polyurethane, which is shaped, and which in certain forms proposed embodiments (see for example Figure 3A) has a flat cross section. According to the technique described in this publication, a yarn composed of several juxtaposed elastomer filaments is manufactured in a first step, and in a second step, an additional treatment of the constant multifilament yarn to heat and press the filaments is carried out subsequently, especially between suitable rolls so as to shape the multifilament yarn in cross-section. More particularly, in the embodiments described in the aforementioned publication, the intermediate multifilament yarn, before shaping, which is obtained at the end of the above-mentioned first manufacturing step is carried out according to a conventional process known as spinning. dry (dry spinning process).

  OBJECTS OF THE INVENTION The main object of the present invention is to provide a new elastomeric flat section wire, as well as a method and an installation for the manufacture of this wire.

  Another object of the invention is to provide a novel elastomeric flat section wire more particularly (but not only) to be used in the manufacture of hygienic articles and in particular diapers.

  SUMMARY OF THE INVENTION The first object of the invention is a method for manufacturing a flat elastomeric yarn which is of the multifilament type. According to this method, said multifilament elastomer yarn is manufactured according to the wet-spinning technique, and during wet spinning and before the usual operation of firing the mutifilamentary yarn, the mutifilamentary yarn is shaped so as to give it a flat cross section.

  The invention also relates to a wet spinning installation for the implementation of the method of the invention, and a mutifilamentaire elastomer yarn spun wet and having a flat cross section 2o.

  Compared to the process of the prior art described in the aforementioned publication US 6 248 197 B1, in the method of the invention the flat shaping of the multifilament yarn is carried out as early as the spinning stage, and while the filaments have not been dimensionally stabilized by the traditional heating (drying and firing) operations of the spinning process. This avoids an additional step of shaping.

  It is one of the merits of the invention to have demonstrated that it was possible against all odds to make a flat elastomeric multifilament yarn having the required elastic properties, by the wet spinning technique, by forming this yarn. at the exit of extrusion dies and prior to its baking at a stage of manufacture where the filaments constituting the multifilament yarn have not yet been stabilized from a dimensional point of view.

  More particularly, the method of the invention advantageously comprises the following additional technical features, taken alone or in combination: to shape the yarn, the filaments are passed out of the extrusion dies, when they are still immersed in the coagulation bath, in contact with a rotary forming cylinder which is immersed at least partly in the coagulation bath, the 1 o filaments being positioned relative to each other so as to form the section flat transverse required, and at the outlet of the shaping roll, the filaments are passed between this shaping roll and a rotational accompanying member; the shaping roll preferably comprises at least one filament receiving and guiding groove, which preferably but not necessarily has a trapezoidal profile, and in which the filaments constituting the multifilament thread are positioned; the optional support member is preferably placed outside the coagulation bath; the optional support member is positioned at the periphery of the forming cylinder so as to tension the multifilament yarn at the output of the forming cylinder; the multifilament yarn is transferred by a rotary transfer member from the coagulation bath to a first washing unit, and the yarn is tensioned between the output of the shaping roll and the transfer member; more particularly, the tensioning of the yarn is preferably performed by deflecting the yarn in a segmented path between the shaping roll and the transfer member; the multifilament yarn is pressed on the surface of the transfer member to prevent the yarn from losing its flattened shape in cross section when changing direction; at the outlet of the extrusion die, the submerged filaments are pre-flattened in the coagulation bath; more particularly, the pre-flattening of the filaments in the coagulation bath is carried out by passing the filaments between two rods immersed in the coagulation bath; passing the bundle of filaments for forming the middle filament yarn between the teeth of a comb positioned immediately upstream of the forming cylinder; more particularly, the multifilament yarn is stretched as it passes through the first washing unit, this stretch being preferably at least 1: 1.5; the constituent elastomer filaments of the yarn are preferably made of polyurethane.

  More particularly, the multifilament yarn of the invention advantageously comprises the following additional technical characteristics, taken alone or in combination: a titration at least equal to 600 dtex, and preferably greater than or equal to 1300 dtex; a width (L) of at least 1 mm; the yarn is composed of polyurethane filaments; the yarn is composed of at least 40 filaments, and preferably at least 300 filaments having a diameter less than or equal to 0.15 mm, and preferably less than or equal to 0.13 mm.

Brief description of the drawings

  Other features and advantages of the invention will appear more clearly on reading the following detailed description of an installation for the production of multifilament yarns according to the invention and several examples of production of multifilament yarns in accordance with the invention. invention, which description is given by way of non-exhaustive and nonlimiting example of the invention, and with reference to the accompanying drawings in which: - Figure 1 schematically shows an installation for the production of multifilament son of the FIG. 2 is a sectional view of the shaping roll and the accompanying roll associated therewith; FIG. 3 is a plan view of the comb of the installation of FIG. 1 positioned upstream of the FIG. 4 is a photograph (taken by means of an optical microscope) of the section of a wire (referenced A) of the invention having a titrag 1350 dtex, Figure 5 is a photograph (taken by means of an optical microscope) of the section of a wire (referenced B) of the invention having a titration of 1450 dtex.

  Detailed description of the invention

  There is shown in Figure 1, an installation according to the invention, which allows the wet spinning multifilament son synthetic elastomer and having a flat cross section.

  This installation comprises the usual technical means found in the known installations and processes for the wet spinning of round section multifilament yarns, namely: a reservoir 1, containing a suitable quantity, in liquid form, of a polymer elastomeric (P) extrudable and melt-wet; this reservoir is replenished (feed duct 2) with said polymer P, by a production unit (not shown) of this polymer P; a main pump 3 serving to supply a set 4 of metering pump 4a with the polymer P contained in the tank 1.

  a unit T1 of extrusion / coagulation allowing the continuous manufacture of a multifilament yarn (F) a plurality of successive washing units T2, Tn whose function is to wash the multifilament yarn (F), a unit 8 finishing commonly referred WEF (Wet End Finish) having the function of applying to the wire F a liquid solution S to lubricate the wire and make it antistatic, a drying unit 9, for example of the type comprising a furnace of drums 9a with heating by steam and electricity on the last two drums, at least one drawing unit 10 followed by a cooking unit 11 (generally several successive drawing / cooking units are used), 1 o a unit 12 winding the multifilament wire for example on coils.

  Among all the polymers of elastomer type P capable of being wetted and known to those skilled in the art, the preferred polymers for the manufacture of a multifilament yarn of the invention are polyurethanes. More particularly, but not exclusively, among the known polyurethanes, those which are prepared from aromatic diisocyanate, for example 4,4'-diphenylmethane diisocyanate (MDI), of a linear polyether, for example polytetramethylene ether glycol (PTG), are preferably used. , and a 1,4-butadienol type alcohol (1,4 butylene glycol) commonly referred to as 40H.

  The extrusion / coagulation unit Ti comprises: an assembly 5 of extrusion dies 5a (spinnerets) which are immersed in a coagulation bath 6, and which are supplied continuously and in parallel with the required quantity of polymer P by the metering pumps 4a, a wire forming cylinder 7, whose function is firstly to combine, in the form of a single multifilamentary wire (F), the filaments (f) which are extruded in parallel in the coagulation bath 6 at the outlet of the dies 5a, and secondly to leave the multifilament yarn (F) of the coagulation bath 6.

  The coagulation bath 6 usually comprises distilled water, for example at a temperature of 60 ° C. to 80 ° C., mixed with a solvent such as DMF in a suitable amount (for example with a concentration of 20%), so that to evade the formation of a skin on the surface of each filament (f), and to allow a complete extraction of the solvent (DMF).

  Each washing unit T2 to Tn comprises an open reservoir containing a washing bath formed of distilled water, for example at a temperature of 80 ° C., and is equipped with two motorized rollers R1 and R2 which are partially immersed in the washing bath. and which allow the multifilament yarn (F) to scroll at a predetermined speed in the wash bath.

  Usually, for the transfer of the wire to the next unit, each unit T1, ... Tn is equipped at the output of a motorized transfer roller RT1, ... RTn.

  The modifications to the above-described wet spinning plant for manufacturing a flat-section elastomeric multifilament yarn of the invention will now be detailed.

  Modifications made to the wet spinning plant The wire shaping cylinder 7 is a motorized cylinder, for example made of stainless steel, comprising at least one peripheral groove 7a (one groove per wire) in which the filaments are joined ( f) from the extrusion dies 5a, and which preferably has in section a trapezoidal profile (Figure 2). In another alternative embodiment of the invention, the shaping roll may not have a groove and be constituted by a simple smooth surface cylinder in combination with two wire guides for guiding the filaments to the setting cylinder. in smooth form.

  In FIG. 2, the dimension (a) represents the larger trapezium base, and corresponds to the width of the open face of the groove at the surface of the shaping roll 7; the dimension (b) represents the base of smaller dimension of the trapezium, and corresponds to the width of the bottom of the groove 7a; Dimension (c) corresponds to the depth of the groove 7a.

  With reference to FIG. 1, the filaments (f) (in the form of a bundle of filaments) are fed from below into the groove 7a of the shaping roll 7 while still being immersed in the coagulation bath 6, and are positioned side by side in the groove 7a of the cylinder 7 so as to form the multifilament yarn (F). The trapezoidal shape of the groove 7a contributes to imparting the required flat cross-sectional area to the middle thread. The multifilament yarn (F) thus formed in the groove 7a is then removed from the coagulation bath 6 by the forming cylinder 7.

  At the periphery of this shaping cylinder 7, and outside the coagulation bath 6, is preferably (but not necessarily) mounted an accompanying rotary member, in the form of a roller 7 'rotatably mounted , of smaller diameter than the shaping roll 7, and which serves mainly the following function: - the accompanying roll 7 'makes it possible, at the output of the shaping roll 7, to give a first tension to the multifilament yarn (F) so as to maintain the flat shape in section of this wire.

  Preferably, the accompanying cylinder 7 'has an elastomer-type surface, and for example consists of a stainless steel cylinder coated on its periphery with a rubber surface coating.

  In the coagulation bath, upstream of the shaping roll 25 are additionally and optionally provided: a comb 12 having two staggered rows (FIG. 3) 12a, 12b of teeth 12c, and allowing upstream of the setting cylinder in form 7 to ensure pre-guidance of each bundle of filaments (f) for forming a multifilament yarn, 3o between the extrusion dies 5a and the comb 12, two rods 13a and 13 which are preferably fixed.

  The filaments (f) coming from the extrusion dies 5a are, at the outlet of dies, collected in the form of a bundle of filaments (a bundle of filaments (f) being intended to subsequently form a multifilament yarn). Each bundle of filaments (f) passes between the two rods 13a and 13b in a substantially flat S-shaped path. Those skilled in the art will judiciously adapt the spacing between these two rods. These two rods 13a and 13b allowing a first flattening on both sides of each bundle of filaments for forming a wire.

  Then each bundle of filaments (f) is guided by the comb 12 towards a groove 7a of the forming cylinder 7, passing between two teeth of each row 12a, 12b of the comb 12. Referring to Figure 3 , in a specific embodiment given by way of indication and not limitation of the invention, the distance (d) between the two rows 12a, 12b of teeth of the comb 12 was 17mm, and the spacing (p) between two teeth 12c each row was worth 14mm.

  Between the cylinder 7 / roller assembly 7 'and the first transfer roller RT1 is further interposed a rotary means 14 for tensioning the middle filamentary wire in its upward portion to the transfer roller RT1. In the particular example illustrated, this rotary tensioning means 14 is composed of three rods 14a, 14b and 14c of small diameter, which are preferably fixed. If necessary, in another variant, these rods could be rotatable. The three rods 14a, 14b, 14c are positioned and spaced relative to each other so that the multifilament yarn (F) follows a segmented path between the shaping roll 7 and the first transfer roll RT1, which allows to apply on the wire (F), in its ascending portion, a tension allowing the wire to maintain its flattened shape in cross section. The rods 14a to 14b could be replaced by any equivalent means allowing tensioning of the wire. In another variant (not shown), the rods 14a to 14c could for example be replaced by a fixed C-shaped guide profile or equivalent.

  In another variant embodiment of the invention, it is conceivable to eliminate the accompanying roll 7 '. In this case, there is a risk that the filaments (f) constituting the yarn (F) will undergo relaxation at the outlet of the coagulation bath 6, which would detrimentally lead to losing the flattened shape in cross section of the yarn (F). ). To avoid this risk, in the absence of an accompanying roll 7 ', it is recommended to increase the tension applied on the wire by the rods 14a, 14b, 14c (or any other equivalent means) by judiciously adjusting the positions of the stems relative to each other.

  Preferably, but not necessarily, in the particular example of FIG. 1, a rotary tensioning means 14 'similar to the means 14 previously described is also mounted on the upward portion of the multifilament yarn (F) between the cylinder R2 of the first washing unit T2 and the transfer roller RT2 between said unit T2 and the following washing unit T3.

  At the periphery of the first transfer roller RT1 between the extrusion / coagulation unit and the first washing unit T2 is further mounted a rotary pressing member 15, in the form of a small diameter pressing roller, and mounted free in rotation. Preferably, a roll of stainless steel coated with a rubber coating is used. This pressure roller 15 in combination with the transfer roller RT1 makes it possible to apply on the wire (F) a sufficient pressure which at least allows the wire to maintain its flat section during the change of direction of the wire (from its ascending portion to its downward portion), or even get a better flattening of the wire. Instead of a single pressure roller 15, several (at least two) pressure rollers judiciously disposed at the periphery of the first transfer roller RT1 could be used.

  Preferably, upstream of the finishing unit 8 (WEF) are mounted two fixed rods 13'a and 13'b similar to the rods 13a and 13b and making it possible to improve the flattening of the multifilament yarn before the drying operations and cooking.

  Examples of multifilament yarns of the invention As non-exhaustive and non-limiting examples of the invention, two types of polyurethane multifilament yarns, referred to hereinafter as A and B, have been produced by means of the installation of the Figure 1 previously described. In both cases, these were yarns composed of polyurethane filaments obtained from MDI, PTG and 40H. The main data relating to the manufacture and properties of these two examples of multifilament yarn A and B of the invention are summarized in Table (I) below. The manufacturing data below are those relating to the new elements of the invention. In particular, the operating parameters (temperatures, draw ratio) of the units 9, 10 and 11 respectively for drying, drawing and cooking are not indicated because these parameters are set in the usual manner and known to man. of the trade, and moreover these parameters are identical for the two types of yarn A and B. It should also be emphasized that the heating of the multifilament yarn in the drying units 9 and cooking 10 allows to fix the yarn.

  In Table (I), parameters (17) and (18) are average values measured over a plurality of samples.

  The parameter (18) [mean thickness (e)] has also been calculated on the basis of several samples, and is an approximate value given as a guide for comparing the order of magnitude of the thickness with the section width of the sample. wire, being specified that the thickness of the wire varies more or less on the section according to the more or less homogeneous distribution of the filaments (f) over the width of the wire. By way of illustration, in Figure 5, the thickness values (el; e2; e3) were (89.64pm, 67.33pm, 77.51pm).

  In general, for the same yarn titration, the more the filaments have a small diameter and are numerous, and the distribution of the filaments over the width (L) of the yarn is homogeneous. Given titration, to improve the regularity in thickness (e), it is therefore desirable to increase the number of filaments and reduce their diameter.

  It will be noted in Table (I) that the wire during manufacture is subjected to considerable stretching when it passes through the first washing unit T2 (speed of the first roller R1 of T2 of the order of 24 m / min and speed of the second R2 roll T2 of the order of 42 m / min), a draw ratio of the order of 1 / 1.75. This stretching contributes to the maintenance of the flattened section of the middle filament yarn. Preferably, this draw ratio is more generally superior. or equal to 1 / 1.5. In its most general scope, the invention is however not limited to this particular limit value of 1 / 1.5. In other embodiments covered by the invention, the draw ratio could be less than this ratio of 1 / 1.5 Subsequently, the yarn does not undergo stretching as it passes through the following washing units (T3 to Tn ).

  TABLE (1) Wire A Wire B 1 Titration (dtex) 1350 1450 2 Number of filaments (f) / wire (F) 300 300 3 Number (n) of unit Ti, T2, ... Tn 11 11 4 Diameter ( in mm) 0.13 0.13 circular holes of the die head Diameter Dl (in mm) of the 165 165 shaping cylinder (7) 6 a (mm) 12 12 7 b (mm) 6 6 8 c (mm) 7 7 9 Speed (in m / min) of cylinder 24.1 Shaping 24.6 (7) Diameter D2 (in mm) of 55 55 accompanying cylinder (7 ') 11 thickness (in mm ) of the rubber coating of the accompanying cylinder (7 ') 12 Diameter (in mm) of the 8 8 tension rods (14a, 14b, 14c) and the rollers (13a, 13b) 13 Diameter (mm) of the cylinders 165 165 transfer (RT1 to RTn) and cylinders (R1) and (R2) 14 Speed (in m / min) of the first 24.1 24.6 transfer cylinder (RT1) and the first roller (R1) of T2 Speed ( in m / min) of 41.7 41.7 transfer rolls (RT2, .... RTn) 16 Speed (in m / min) of the second 41.7 41.7 roll (R2) of T2 and rollers (R1 and R2) units T3, ... Tn 17 Width average (L) of the yarn in 2000 2200 cross section (, um) 18 Average thickness (e) of the yarn in 80 90 cross section (, um)

Claims (34)

  A method of manufacturing a flat multifilament elastomeric yarn, characterized in that said multifilament elastomer yarn (F) is made by wet spinning, and in the course of wet spinning and prior to the spinning operation. baking the multifilament yarn, the intermediate filament yarn (F) is shaped so as to give it a flat cross section.   2. Method according to claim 1 characterized in that to form the wire, the filaments (f) are passed out of the extrusion dies (5a), when they are still immersed in the coagulation bath, on a rotating shaping cylinder (7) which is immersed at least partly in the coagulation bath (6), the filaments being positioned relative to each other so as to form the required flat cross-section.   3. Method according to claim 2 characterized in that at the output of the shaping roll (7), the filaments (f) are passed between the shaping roll (7) and an accompanying member (7). 20).   4. Method according to claim 2 or 3 characterized in that the forming cylinder (7) comprises at least one groove (7a) for receiving and guiding the filaments, in which the filaments (f) constituting the multifilament yarn are positioned. (F).   5. Method according to claim 4 characterized in that the groove (7a) has a trapezoidal profile.   6. Method according to claim 3 or 4 characterized in that the accompanying member (7 ') is placed outside the coagulation bath (6).   7. Method according to one of claims 2 to 6 characterized in that the accompanying member (7 ') is positioned at the periphery of the forming cylinder (7) so as to tension the multifilament wire ( F) at the outlet of the forming cylinder (7).   8. Method according to any one of claims 1 to 7 characterized in that the multifilament yarn (F) is transferred by a rotary transfer member (RT1) of the coagulation bath (6) to a first washing unit (T2) and in that the thread is tensioned between the output of the shaping roll (7) and the transfer member (RT1).   9. The method of claim 8 characterized in that the tensioning is performed by deflecting the wire in a segmented path between the shaping cylinder (7) and the transfer member (RT1).   10. Method according to any one of claims 1 to 9, characterized in that the multifilament yarn (F) is transferred by a rotary transfer member (RT1) of the coagulation bath (6) to a first washing unit (T2 ), and in that the multifilament yarn is pressed on the surface of this transfer member.   11. A method according to any one of claims 1 to 10 characterized in that extrusion die outlet (5a) is pre-flattened filaments immersed in the coagulation bath.   12. The method of claim 11 characterized in that the pre-flattening of the filaments in the coagulation bath is achieved by passing the filaments between two rods immersed in the coagulation bath (6).   13. Method according to any one of claims 2 to 12 characterized in that the bundle of filaments (f) intended to form the wire (2) mutifilamentaire passes between the teeth (12c) of a comb (12) positioned immediately upstream of the forming cylinder (7) 14. Process according to any one of Claims 1 to 13, characterized in that the multifilament yarn undergoes stretching as it passes through the first washing unit (T2).   15. The method of claim 14 characterized in that the stretching is at least 1 / 1.5.   16. Method according to any one of claims 1 to 15 characterized in that the filaments (f) constituting the wire (F) are polyurethane.   17. Spinning plant for the manufacture of a flat multifilament elastomeric yarn according to the method referred to any one of claims 1 to 16 characterized in that it is constituted by a wet spinning installation, equipped with means for setting in the form of the mutifilamentary wire (F) for imparting to the intermediate filamentary wire (F) a flat cross section before the firing operation of the wire.   18. Installation according to claim 17, characterized in that the shaping means comprise a rotary forming cylinder (7) which is immersed at least partly in the coagulation bath (6).   19. Installation according to claim 18 characterized in that the shaping means comprise a rotational support member (7 ') positioned at the periphery of the forming cylinder (7).   20. Installation according to claim 18 or 19 characterized in that the forming cylinder (7) comprises at least one groove (7a) for receiving and guiding the filaments (f) constituting the multifilament yarn (F).   21. Installation according to claim 20 characterized in that the groove (7a) has a trapezoidal profile.   22. Installation according to one of claims 19 to 21 characterized in that the accompanying member (7 ') is placed outside the coagulation bath (6). 23. Installation according to any one of claims 18 to 22 characterized in that it comprises first transfer means 30 (RT1) for transferring the multifilament wire to a first washing unit (T2), and in that it comprises means (14) for tensioning the thread (F) between the output of the shaping roll (7) and the first transfer means (RT1).   24. Installation according to claim 23 characterized in that the tensioning means (14) of the wire are positioned so as to undergo a path segmented to the wire between the forming cylinder (7) and the first transfer means (RT1).   25. Installation according to any one of claims 17 to 24 characterized in that it comprises first transfer means (RT1) for transferring the multifilament wire to a 1 o first washing unit (T2), and in that it comprises a pressing means (15) for pressing the multifilament wire on the surface of the first transfer means (RT1).   26. Installation according to any one of claims 17 to 25, characterized in that it comprises, at the outlet of extrusion dies (5a), means for pre-flattening of the filaments immersed in the coagulation bath (6). . 27. Installation according to claim 26 characterized in that pre-flattening means comprise two rods (13a, 13b) immersed in the coagulation bath (6) and for pre-flattening the filaments (f) by subjecting them to S-shaped path 28. Installation according to any one of claims 18 to 27 characterized in that it comprises a comb (12) positioned immediately upstream of the forming cylinder (7).   29. Installation according to any one of claims 17 to 28 characterized in that it comprises means (1, 2, 3, 4) for feeding extrusion die (5a) with polyurethane.   30. Molyilamentary elastomeric yarn spun wet and having a flat cross section.   31. Thread according to claim 30 characterized in that it has a titration at least equal to 600 dtex, and preferably greater than or equal to 1300 dtex.   32. Wire according to claim 30 or 31 characterized in that it has a width (L) at least equal to 1 mm.   33. The yarn according to any one of claims 30 to 32, characterized in that it is composed of polyurethane filaments.   34. Thread according to any one of claims 30 to 33 characterized in that it is composed of at least 40 filaments (f), and preferably at least 300 filaments having a diameter less than or equal to 0.15 mm, and preferably less than or equal to 0.13 mm.