Abstract:
A method and an apparatus for producing a highly oriented yarn (HOY) wherein the yarn is withdrawn from the nozzle of a spinneret at a withdrawal speed of at least 6,500 m/min. The filaments forming the yarn are drawn during their solidification, so that a highly oriented molecular structure forms in the polymer. To withstand the withdrawal tension generated by the high withdrawal speed without overstressing the filaments, the filaments are assisted in their advance before they solidify such that prior to the solidification a tensile stress relief is effective on the filaments, and that during the solidification a reduced withdrawal tension is effective on the filaments while they are drawn.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of International Application No. PCT/EP99/08420 filed Nov. 4, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a method of producing a highly oriented yarn (HOY) from a thermoplastic material and a spinning apparatus for melt spinning a highly oriented yarn. 
     In the production of synthetic multifilament yarns from a thermoplastic melt in one process step, one distinguishes basically between partially drawn and fully drawn yarns. The partially drawn yarns, which are also described as preoriented yarns (POY), have a partially oriented molecular structure that requires a subsequent drawing in a second process step. In comparison therewith, fully drawn yarns (FDY) are suited for direct further processing without a subsequent drawing. The FDY yarns are drawn in the spinning process at a high ratio by means of draw systems, so that an aligned molecular structure is achieved in the polymer. 
     To produce a yarn with a highest possible orientation of the molecules of the polymer, methods are also known wherein the yarn is drawn at a high ratio while firming up directly before the solidification of the polymer. In these yarns, known as highly oriented yarns (HOY), a stress-induced crystallization leads to the orientation of the molecules in the polymer. In comparison with the FDY yarns, the known HOY yarns have a lower elastic limit. Depending on the method of further processing, this can lead, due to the force acting upon these yarns, to a permanent deformation and, thus, to an irregular dyeability. The known HOY yarns are totally unsuitable for methods of further processing, wherein major stress peaks act upon these yarns. 
     Although it is theoretically possible to increase the elastic limit of HOY yarns by increasing the withdrawal speed, there are physical limits set to this process, since in the melt spinning of HOY yarns, the filaments forming the yarn may have only a limited crystallinity during drawing to ensure a safe withdrawal without damage to the yarn. A too highly precrystallized filament is much too frozen in its structure to withstand, without being overstressed, the forces developing in the yield point. 
     EP 0 530 652 and U.S. Pat. No. 5,612,063, disclose an apparatus and a method for producing a synthetic yarn, wherein the filaments undergo a delayed cooling before their solidification. This further delays crystallization of the filaments, which leads to an increased elastic limit of the yarns. However, the known apparatus and method have the disadvantage that the length of the delayed cooling can be only very limited, since lacking stabilization of the filaments by the air flow represents within this region an increasing risk that the filaments stick together. 
     EP 244 217, and U.S. Pat. Nos. 5,141,700 and 5,034,182 propose to remove the filaments after passing through a pressurized cooling shaft from the cooling shaft by means of an air stream. This also achieves a delayed crystallization of the filaments. Likewise in EP 0 682 720, a delayed crystallization of the polymer is realized, in that an accompanying air stream is directed onto the filaments before solidification. 
     The apparatus and methods known in the state of the art are all aimed at producing a synthetic yarn at highest possible takeup speeds without its physical properties undergoing a substantial change. Thus, in these known methods, the decrease in elongation at higher withdrawal speeds is compensated by the delayed crystallization of the polymer in the spinning line. However, these methods are unsuitable for producing HOY yarns with higher elastic limits and with higher tenacities. 
     In the production of a highly oriented yarn, there exists the problem that the known yarns have too high elongation values and too low tenacity values. The elongation values of the yarn may be improved by increasing the withdrawal speed. An increase in the withdrawal speed, for example, in the apparatus disclosed in EP 0 530 652 and U.S. Pat. No. 5,612,063, is bound to lead to an increase in the withdrawal tension, which results, however, in that the filaments are overstressed during the drawing due to the low tenacity of the filaments. 
     It is an object of the invention to provide a method and a spinning apparatus for producing a highly oriented yarn (HOY), which exhibits elongation and tenacity values typical of a fully drawn yarn (FDY), and which can be produced with a high spinning reliability. 
     SUMMARY OF THE INVENTION 
     The above and other objects and advantages of the present invention are achieved by the provision of a method and apparatus wherein the melted thermoplastic material is extruded through a nozzle of a spinneret to form a plurality of downwardly advancing filaments, and such that the filaments solidify at a location spaced below the nozzle. The filaments are withdrawn from the nozzle under a withdrawal tension so as to cause the filaments to be drawn while being solidified, with the withdrawal tension being generated by a withdrawal speed of at least about 6500 m/min. In addition, the filaments are assisted in their advance before their solidification such that before their solidification the filaments are relieved from tensile stress and during solidification and drawing a reduced withdrawal tension is effective on the filaments. The filaments are also combined during their advance after their solidification, to form an advancing multifilament yarn, which is then wound into a package. 
     The invention is based on the recognition that overstressing of the filaments can occur in the process of the yarn formation. In high speed spinning, one observes no uniform rise of the yarn speed between the yarn exit from the spinneret and the solidification point of the filaments. After the filaments emerge from the spinneret, a relatively slow acceleration sets in initially, until the start of the stress-induced crystallization. Within few centimeters, the stress-induced crystallization leads to an acceleration of the filaments to the withdrawal speed. In this instance, the tenacity of the filaments must be greater than the forces necessary for the acceleration of the yarn, to avoid filament breakage. In accordance with the invention, the filaments are assisted in their advance before they solidify such that no significant additional tensile stresses resulting from frictional forces of the air act upon the filaments before they solidify. Thus, the filaments are relieved before their solidification, so that a reduced withdrawal tension is effective on the filaments while being drawn during their solidification. With that, one realizes on the one hand a high orientation of the molecules during drawing. On the other hand, a high withdrawal speed is made possible with a correspondingly high withdrawal tension. In this process, the withdrawal tension is generated by a withdrawal speed of at least 6,500 m/min. It has shown that it is thus possible to produce a highly oriented yarn with tenacity values greater than 4cN/dtex and an elongation in the range of 30%. 
     To assist the movement of the filaments before their solidification or to bring about a relief of the forces engaging on the filaments before their solidification, it is possible to apply basically two variants of the method according to the invention. In a first variant, the speed of the advancing yarns is increased before drawing by a higher injection speed in the extrusion of the filaments. In practice, this possibility can be used only to a certain extent due to the high pressure drops upstream of the spinneret. 
     In the second variant of the method, the air friction acting upon the filaments is influenced. To this end, the filaments advance after their extrusion through a cooling medium. Directly before the solidification of the filaments, a cooling medium stream is generated that assists the movement of the filaments. This measure effects a reduction of the air friction that exerts a braking effect on the filaments. The cooling medium in use is preferably air. 
     In a particularly advantageous embodiment of the method, the cooling medium stream has a flow velocity that is substantially the same as the speed of the advancing filaments before their solidification. Thus, no braking flow forces are operative on the filaments, so that the advancing speed of the filaments further increases. 
     For a further reduction of the tensile forces that are operative during the solidification, it is possible to generate the cooling medium stream with a flow velocity that is greater than the speed of the advancing filaments before they solidify. This permits production of highly oriented yarns of a great tenacity at even higher process speeds. 
     In a preferred embodiment of the method, for purposes of generating the cooling medium stream, the filaments advance through a constrictor and a diffuser. This allows to generate the cooling medium stream purposefully at one point over a very short distance of the spinning line. Preferably, the narrowest cross section of the constrictor is placed in the spinning line such that it is shortly before the solidification point of the filaments. This measure permits reducing a stress-induced preorientation within the filaments. The yarn firms up within a very short distance, which leads to a particularly high orientation of the molecule chains in the polymer. 
     In a particularly advantageous further development of the method, the filaments advance after their extrusion and before their solidification through a cooling shaft that connects to ambient air through an air-permeable cylindrical wall. Thus, a delayed cooling of the filaments is realized, so that the yield forces are advantageously influenced and lead to a further relief of the withdrawal tension. This measure is advantageous in two respects, since it permits on the one hand an increased withdrawal tension during the drawing of the filaments, and since on the other hand the delayed cooling substantially reduces a preorientation of the still molten filaments. 
     This measure can be still further improved by a variant wherein the filaments advance directly after emerging from the spinneret through a heating zone, wherein an amount of heat is supplied to the filaments. 
     To operate the method with the least possible expenditure for apparatus, the withdrawal tension may be generated directly by the winding speed of a takeup device. 
     To produce, if possible, a qualitatively superior and uniform yarn, it is desirable to use a variant of the method wherein the withdrawal tension is defined by a feed system. The feed system is arranged upstream of the takeup device, so that fluctuations in the yarn tension due to the winding can advantageously not become effective in the spinning line. It is possible to produce the yarn with a very uniform withdrawal tension. 
     In accordance with the invention, it becomes possible to produce a highly oriented yarn with substantially similar properties to a fully drawn yarn by influencing the spinning line. In this connection, the spinning apparatus of the present invention has been found especially advantageous for carrying out the method. In accordance with the invention, a constrictor and a diffuser arranged on the outlet side of the constrictor form a cooling device. The constrictor effects a great acceleration of the air entrained by the filaments. In this process, the cooling air stream is accelerated to a maximum speed in the narrowest cross section. Directly after passing the narrowest cross section of the constrictor, the diffuser causes the cooling air to expand. Thus, the flow velocity of the air slows down, thereby assisting the filament movement for a very short time. A longer treatment zone that favors a preorientation is avoided. 
     A cooling cylinder composed of an air permeable tubular wall may be positioned between the spinneret nozzle and the constrictor. This helps ensure that no air turbulences develop that influence the advance of the filaments as they enter the constrictor. 
     In the variants of the method, wherein it suffices to reduce or avoid air frictions that slow down the advance of the filaments for producing a highly oriented yarn, it is preferred to construct the spinning apparatus with the diffuser connected to a vacuum generator. 
     In this connection, it is possible to avoid turbulence at the outlet end of the cooling device during the expansion of the air stream surrounding the filaments, by constructing the spinning apparatus so that the diffuser connects at its outlet end to an air permeable tubular screen cylinder and which is part of a vacuum chamber which is connected to the vacuum generator. Thus, entrained air is uniformly removed over the entire circumference of the filament bundle. 
     To realize in the production of the yarn a favorable flow profile, it has been found that the constrictor should have in its narrowest cross section a diameter from at least 10 mm to at most 40 mm. 
     To make available an adequate quantity of air in the spinning line and in particular in the center of the filament bundle for building up the air stream as well as for cooling the filaments, the cooling cylinder may be subdivided in the direction of the advancing yarn into several zones, with each zone having a wall with a different gas permeability. This configuration makes it possible to influence the quantity of air flowing into the cooling shaft irrespective of the filament speed and irrespective of the differential pressure between the cooling shaft and the surroundings. Thus, it is possible to exert a purposeful influence on the properties of the filaments. The quantity of air entering through the wall of the inlet cylinder is in this instance proportionally dependent on the gas permeability or porosity of the wall. Accordingly, in the case of a high permeability to gas, a larger quantity of air per unit time is admitted into the cooling shaft under otherwise constant conditions. Conversely, in the case of a low permeability to air of the wall a proportionately smaller quantity of air enters the spin shaft. The transition of the pas permeability from the one zone to the other is made preferably stepless to avoid greater differential flows. However, a stepped transition of the gas permeability is likewise possible. 
     In the production of the yarn, it is especially important that each filament in the spinning line be evenly treated until their combination into a yarn. The nozzle bores of the spinneret are preferably arranged in one or more annular lines of bores, with the bores of each line being equally spaced apart. This ensures that the flow generated in the constrictor is uniformly effective on each of the filaments. 
     In a further development of the spinning apparatus according to the invention, the yarn is withdrawn from the spinneret by means of a feed system. This allows to adjust the withdrawal tension and yarn tension independently of each other when the yarn is wound. Furthermore, it is possible to generate a highly uniform withdrawal tension. 
     To be able to produce in a spinning plant a plurality of parallel side by side yarns, the feed system preferably comprises two rolls which are partially looped by the advancing yarn, and with at least one of the rolls being driven. In this embodiment, a decrease in the yarn tension may be adjusted by means of the amount of looping by the yarn on the rolls. 
     To prevent a premature preorientation of the filaments, a heating device may be provided between the nozzle of the spinneret and the cooling cylinder for thermally treating the filaments. 
     Both the method and the apparatus of the present invention are suitable for producing highly oriented textile yarns of polyester, polyamide, or polypropylene. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following, several embodiments of the method as well as of the apparatus of the present invention are described in more detail with reference to the attached drawings, in which: 
     FIG. 1 shows a first embodiment of a spinning apparatus according to the invention; 
     FIG. 2 shows a further embodiment of a spinning apparatus according to the invention; 
     FIG. 3 is a top view of an embodiment of a spinneret; 
     FIG. 4 is a schematic cross sectional view of an embodiment of a cooling cylinder; and 
     FIG. 5 is a diagram of the tenacity of a yarn as a function of the withdrawal speed. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a first embodiment of a spinning apparatus according to the invention for spinning a highly oriented yarn. In this apparatus, a yarn  12  is spun from a thermoplastic material. To this end, the thermoplastic material is melted via a feed hopper  43  in an extruder  40 . The extruder  40  is driven via a drive  41  that connects for its control to a control unit  42 . The control may occur, for example, as a function of pressure. To this end, the control unit  42  connects to a pressure sensor  48  arranged at the outlet end of extruder  40 . From the extruder  40 , the melt advances through a melt line  47  to a distributor pump  44 . With respect to its delivery, the pump  44  is controlled by a drive  45  and a controller  46 . The distributor pump  44  delivers the melt via a melt line  3  to a heated spin head  1 . On its underside, the spin head  1  mounts a spinneret  2 . The spinneret  2  comprises on its underside a plurality of nozzle bores. Under pressure, the melt is extruded through the nozzle bores and emerges from the spinneret in the form of fine filament strands  5 . The filaments  5  advance through a cooling shaft  6  that is formed by a cooling cylinder  4 . To this end, the cooling cylinder  4  extends directly downstream of spinning head  1  and encloses the filaments  5 . Subjacent the free end of cooling cylinder  4 , in direction of the advancing yarn, is a constrictor  9 . In the direction of the advancing yarn, the constrictor  9  narrows the cooling channel  6 . In the narrowest cross section of constrictor  9 , a diffuser  10  is arranged. A seam  8  interconnects the constrictor  9  and diffuser  10 . In direction of the advancing yarn, the diffuser  10  leads to a widening of cooling channel  6 . At its end, the diffuser  10  terminates in a vacuum chamber  11 . In vacuum chamber  11 , a screen cylinder  30  extends in the extension of diffuser  10 . The screen cylinder  30  has an air permeable wall and extends through vacuum chamber  11  down to the underside thereof. In the underside of vacuum chamber  11 , an outlet opening  13  is arranged in the plane of the advancing yarn. On one side of the vacuum chamber  11 , a suction stub  14  terminates therein. Via suction stub  14 , a vacuum generator  15  arranged at the free end thereof connects to the vacuum chamber  11 . The vacuum generator  15  may be, for example, a vacuum pump or a blower, which generates a vacuum in the vacuum chamber  11  and thus in the diffuser  10 . 
     As seen in FIG. 1, the constriction  9  and the diffuser  10  are each frustoconical, with the angle of cone of the constrictor being greater than the angle of cone of the diffuser. 
     In the plane of the advancing yarn, downstream of vacuum chamber  11 , a lubrication device  16  and a takeup device  20  are arranged. The takeup device  20  comprises a yarn guide  19 . This yarn guide  19  indicates the beginning of a traversing triangle that forms by the reciprocal movement of a traversing yarn guide of a yarn traversing device  21 . Downstream of yarn traversing device  21  a contact roll  22  is arranged. The contact roll  22  lies against the surface of a package  23  being wound. A rotating winding spindle  24  winds the package  23 . To this end, the winding spindle  24  is driven via a spindle motor  25 . The drive of winding spindle  24  is controlled as a function of the rotational speed of contact roll  22  such that the circumferential speed of the package remains substantially constant during the winding. 
     In the spinning apparatus shown in FIG. 1, a polymer melt is delivered to spin head  1  and extruded via spinneret  2  to a plurality of filaments  5 . The takeup device  20  withdraws the filament bundle. In so doing, the filament bundle advances at an increasing speed through cooling shaft  6  inside cooling cylinder  4 . Subsequently, the filament bundle is sucked into the constrictor  9 . The constrictor  9  connects via diffuser  10  to the vacuum generator  15 . Thus, due to the vacuum action, ambient air surrounding the outside of cooling cylinder  4  is sucked into the cooling shaft  6 . The quantity of air entering the cooling shaft  6  is proportionate to the gas permeability of wall  7  of cooling cylinder  4 . The inflowing air leads to a precooling of the filaments, so that the surface layers of the filaments firm up. Due to the narrowest cross section in seam  8 , the airflow is accelerated under the action of vacuum generator  15  such that an airflow counteracting the movement of the filaments is reduced or avoided. Thus, the filaments are assisted in their movement, so that during the drawing of the filaments in the solidification region, only a reduced withdrawal tension is effective. The relief of the withdrawal tension is dependent on the extent to which the braking air friction is compensated. In this connection, it is attempted to accelerate the flow velocity, if possible, to the range of the filament speed. 
     Shortly downstream of seam  8 , the filaments are solidified. As they continue to advance in diffuser  10 , the filaments are further cooled. To generate as little turbulences as possible in the outlet region of diffuser  10  and, thus, a possibly constant flow profile, the air stream is introduced via the diffuser into the screen cylinder  30  that extends inside vacuum chamber  11  and connects to the vacuum generator  15 . The air is then sucked out and removed from vacuum chamber  11  via suction stub  14 . The filaments  5  emerge from the underside of vacuum chamber  11  through outlet opening  13 , and advance into the lubrication device  16 . The lubrication device  13  combines the filaments to a yarn  12 . To increase cohesion in the yarn, the yarn could be entangled in an entanglement nozzle before being wound. In the takeup device  20 , the yarn  12  is wound to the package  23 . 
     FIG. 2 shows a further embodiment of a spinning apparatus according to the invention. The basic construction of the spinning apparatus of FIG. 2 is substantially the same as that of FIG.  1 . To this extent, the foregoing description of FIG. 1 is herewith incorporated by reference. Only differences in the construction of the spinning apparatus of FIG. 2 are described. 
     In the spinning apparatus shown in FIG. 2, a heating device  31  directly arranged on spin head  1  extends between spinneret  2  and cooling cylinder  4 . The heating device  31  may be, for example, a radiation heater or a cylindrical resistance heater. The additional heating device  31  permits thermal treatment of the filaments after their extrusion through the nozzle bores of spinneret  2 , so that a delayed cooling occurs. 
     Furthermore, the spinning apparatus shown in FIG. 2 comprises a feed system  17  between lubrication device  16  and takeup device  20 . The feed system is formed by two driven rolls  18 . 1  and  18 . 2 . The yarn  12  loops in S-shape about the driven rolls. Thus, the yarn  12  is withdrawn from spinneret  2  by feed system  17  and takeup device  20 . The circumferential speed of rolls  18 . 1  and  18 . 2  is greater than the winding speed, thereby decreasing the tension in the yarn between the feed system  17  and the takeup device  20 . In the present embodiment, the looping angle on the rolls is invariably predetermined. However, it is also possible to make rolls  18 . 1  and  18 . 2  adjustable, so that different looping angles can be adjusted. The essential advantage of the additional feed system of the spinning apparatus of FIG. 2 lies in that the fluctuations in the yarn tension resulting from the traversing movement can propagate only to the feed system. The withdrawal tension in the spin zone remains unchanged, which leads to a uniform yarn formation. 
     FIG. 3 is a top view of an embodiment of a spinneret  2 , as could be used, for example in the spinning apparatus of FIG. 1 or FIG.  2 . In this embodiment of spinneret  2 , nozzle bores  33  are annularly arranged in a line of bores  34 . In the line of bores  34 , the nozzle bores  33  are arranged in spinneret  2  in equally spaced relationship. Further nozzle bores are arranged in a second line of bores  36  concentric with the line of bores  34 . The nozzle bores  33  of both lines of bores  34  and  36  are offset from one another, so that the nozzle bores of the inner line of bores  36  come to lie between two adjacent nozzle bores of the outer line of bores  34 . This arrangement of bores encloses a center inlet region  35  that has no nozzle bores. With this configuration, it is accomplished that with the use of a frustoconical constrictor and a frustoconical diffuser a flow profile is generated in the narrowest cross section that is effective substantially uniformly on each individual filament. As is known, the flow profile of a circular body traversed by a flow exhibits in its center a maximum flow velocity that decreases toward the peripheral regions. Thus, the annular arrangement of the nozzle bores in spinneret  2  permits advancing the filaments advantageously in zones, wherein the flow velocity generated by the constrictor is uniform. 
     FIG. 4 shows an embodiment of a cooling cylinder, such as could be used in the spinning apparatus of FIG. 1 or FIG.  2 . The cooling cylinder  4  has a wall  7  constructed of a perforated sheet element with two different perforations  29  and  26 . An upper zone at the end of the cooling cylinder, which faces spinneret  2  contains a perforation  29  with a small diameter. The perforation in the upper zone leads to a schematically illustrated inflow profile  28 . The inflow profile  28  that is symbolized by arrows, provides a measurement for the air quantity entering the cooling shaft  6 . The perforation  29  is identical within the upper zone. Thus, the quantity of air increases as the distance from the spinneret becomes greater due to the vacuum action in constrictor  9  and due to the increasing filament speed. 
     In a lower zone that is formed at the end facing constrictor  9 , the wall  7  contains a perforation  26  with a larger opening cross section. As shown by symbolized inflow profile  27 , a larger quantity of air will enter the cooling shaft  6  in the lower zone. Likewise here, one notices the tendency that the quantity of inflowing air increases as the distance from the spinneret becomes greater. 
     The inflow profile shown in FIG. 4 above the wall of the cooling cylinder is especially suitable for realizing a slow and slight precooling of the filaments. This leads in particular to a very uniform cross section of the yarn. With that, it is possible to adapt the air quantity to the heat treatment of the filaments. It is possible to influence advantageously both precooling and the formation of the cooling stream. 
     The method of the invention permits production of HOY yarns, which have physical properties that permit direct further processing. Thus, properties are obtained that otherwise are ascribed only to FDY yarns. Typical elongation and tenacity values of FDY yarns are about 30% and &gt;4 cN/dtex. In comparison therewith, Table 1 shows two polyester yarns that were produced by the method of the present invention. In this process, the variant of the method was applied as results from the arrangement of the spinning apparatus of FIG.  2 . The withdrawal speed was set to 7,500 m/min. To assist the advance of the filaments, an air stream was generated in the constrictor that reached a velocity of about 2,500 m/min. Despite the high withdrawal speeds, tenacity values were obtained that were clearly higher than 4 cN/dtex. With yarn deniers of 55 dtex and 83 dtex, the elongation was respectively 34% and 30%. Both yarns distinguished themselves by a very good modulus ratio. The boiling shrinkage of 3% to 2.8% was satisfactory. 
     FIG. 5 illustrates a diagram, wherein the tenacity of a polyester yarn is plotted as a function of the withdrawal speed. Two curves are shown that are indicated by lower-case characters a and b. In both cases, a polyester yarn with a denier of 83 dtex was spun. The tenacity curve identified by a shows the tenacity of a yarn produced by a process known from the state of the art. As shown, tenacity starts to fall shortly before reaching the withdrawal speed of 6,500 m/min and drops as the withdrawal speed increases. The drop in the breaking tenacity shows the overstress of the yarn in this process. The filaments are overstressed in the yield point, since in this point an already too highly crystallized and thus structurally frozen yarn is to be still drawn. Thus, in the method of the prior art, individual filament breaks occur already effective a speed &gt;6,500 m/min. 
     The tenacity curve identified at b shows the course of the tenacity of a polyester yarn that was produced by the method of the present invention. Despite the high withdrawal speed, one can note a steady increase in tenacity. Thus, the invention makes it possible to produce a highly oriented yarn at greater withdrawal speeds, while maintaining a spinning reliability even at withdrawal speeds &gt;7,500 m/min. Therefore, by suitable measures, even appreciably higher withdrawal speeds can be realized for producing a highly oriented yarn. 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Polymer 
                 PET 
                 PET 
               
               
                   
                   
               
             
             
               
                   
                 Denier (dtex) 
                 55 
                 83 
               
               
                   
                 Number of filaments 
                 24 
                 36 
               
               
                   
                 Withdrawal speed (m/min) 
                 7500  
                 7500  
               
               
                   
                 Air velocity (m/min) at 
               
               
                   
                 outlet of constrictor 
                 2500  
                 2500  
               
               
                   
                 Elongation (%) 
                 34 
                 30 
               
               
                   
                 Tenacity (cN/dtex) 
                 4, 15 
                 4, 2 
               
               
                   
                 Uster (%) 
                 1, 4  
                  0, 87 
               
               
                   
                 Boiling shrinkage (%) 
                  3 
                 2, 8