Abstract:
The invention relates to a yarn having regenerated cellulose fibers produced by a spinning process, in particular a wet-spinning process and in particular consisting thereof, and having flame-retardant characteristics brought about by a flame retardant means spun into at least one portion of the regenerated cellulose fibers, wherein the yarn as soon across the cross-section thereof has an inhomogeneous distribution of the flame retardant mean and has a weight displaced towards the outside in relation to the yarn center.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is a 35 U.S.C. § 371 national phase entry application of, and claims priority to, International Patent Application No. PCT/EP2013/002840, filed Sep. 20, 2013, which claims priority to German Patent Application No. DE 10 2012 018 814.5, filed Sep. 24, 2012, the disclosures of which are hereby incorporated by reference in their entirety for all purposes. 
       BACKGROUND 
       [0002]    The invention relates to a yarn, which comprises, and in particular consists of, regenerated cellulose fibers produced by a spinning process, in particular a wet-spinning process, from viscose, and which has flame-retardant characteristics produced via a flame retardant spun into at least one portion of its regenerated cellulose fibers, and to textile structures produced from such yarns, in particular textile fabrics. 
         [0003]    Such yarns have been known in the art for approximately 30 years. They are suitable, for several reasons, for use in textile fabrics for protective clothing (PPE (Personal Protection Equipment) sector). For one thing, this leads to cellulose fibers with improved wearer comfort compared to synthetic fibers, which is evidenced particularly in a higher capacity to absorb moisture. Moreover, cellulose, as a nonthermoplastic material, does not tend to undergo deformation, melting or increased clinging, even at elevated temperature. As a result of the flame-retardant characteristics, a sufficient resistance to the impact of fire is also achieved with such yarns having a sufficiently high flame retardant content, and, in particular, the combustion test according to DIN ISO 15025 is passed. If these flame protection characteristics are achieved by a spun-in flame retardant, said retardant remains permanently and such regenerated cellulose fibers are referred to as permanently flame-retardant below. The expression “flame-retardant” in flame-retardant characteristics first covers, in general, resistance to the action of flames and in particular also comprises resistance to the action of flames in that, after removal of the acting flame, the combustion is not promoted further. This corresponds approximately to an LOI of 25 or higher. 
         [0004]    In many cases, today, the commercially used regenerated fibers are staple fibers marketed under the trade names Lenzing® FR. With these staple fibers, it is also possible to combine other fibers made of wool and/or synthetic fibers that are resistant to high temperatures in the form of intimate mixtures, for example, for the purpose of reducing the costs of synthetic fiber yarns exclusively of high temperature-resistant synthetic fiber yarns. 
         [0005]    In spite of the advantages of flame resistance achieved with the yarns of the type explained at the start, it has nevertheless been shown that, in particular in the fire-fighting sector, satisfactory wearing properties have not yet been achieved, in particular if the fire fighting personnel is exposed for several minutes to very high temperatures. 
         [0006]    Due to these problems, the aim of the invention is to provide a yarn from which textile fabrics whose suitability for use under high stresses is improved can be prepared, particularly in the sector of protective clothing. 
         [0007]    This aim is achieved by providing the yarn of the type mentioned at the start, which is characterized essentially in that it has, seen over its cross section, an inhomogeneous distribution of the spun-in flame retardant with a weight that is displaced towards the outside in relation to the yarn center. 
         [0008]    Here, the invention is based on the finding that the above-explained suitability for use which is not entirely satisfactory is due to an insufficient dimensional stability of the textile fabric under prolonged exposure to heat. Owing to the inhomogeneous distribution of the spun-in flame retardant, an area close to the center of the yarn having a relatively lower or infinitesimal flame-retardant material content is produced, which improves the dimensional stability of the entire yarn. To that extent it is surprising that an improved quality of textile fabrics with respect to extreme heat exposure is achieved not by an increased flame retardant addition, but instead by a decrease in flame retardant relative to the total weight of the textile fabric. In the preferred phosphorus-containing flame retardants, ecological advantages are also achieved in addition to economical advantages. 
         [0009]    In this manner, it becomes possible that a fabric produced exclusively from such a yarn, after exposure to a temperature of 260° C. for ten minutes, undergoes a maximum dimensional change of less than 10%. The criteria presented in NFPA 1971 can be used in this context as testing criteria, for example. 
         [0010]    The high dimensional stability achieved according to the invention, in other words this specific resistance to hot air shrinkage, has certainly considerable practical consequences. One can imagine what would happen if, for example, gloves shrink under the action of heat to such an extent that after use they can no longer be taken off, or if a jacket during a fire-brigade deployment shrinks so that breathing is made difficult or impossible. 
         [0011]    The spun-in flame retardant could be added as a dispersion in the form of a particulate solid to the spinning composition. It is preferable to use a phosphorus-containing flame retardant, in particular, 2,2′-oxybis[5,5-dimethyl-1,3,2-dioxaphosphorinane] 2,2′-disulfide, also known under the trade name Exolit or Sandoflam. Here, a target phosphorus content relative to the cellulose is in the range of 2.5% or higher, preferably 2.8% or higher, moreover preferably 3.2% or higher, or even higher than 3.5%. 
         [0012]    It is preferable that the yarn has a core-sheath structure, wherein the sheath comprises a higher flame retardant content than the core. In particular for the case of a flame-retardant-free core, a quantitative core:sheath ratio of 4:5 or less, preferably 3:4 or less, in particular 2:3 or less, could be provided. Thus, the sheath itself can have a homogeneous flame retardant distribution, just like the core. For the flame-retardant-free core, the indicated quantitative ratios are suitable for meeting the standard of sufficient resistance against combustion (for example, according to combustion tests from EN ISO 11612 and EN ISO 469 with regard to EN ISO 15025), in particular if a textile fabric to be produced from the yarn comprises no additional components. If, in addition, as a mixing partner for the production of such a fabric, one uses flame-retardant fiber types which in themselves meet the high requirements of heat resistance tests, (for example, according to ISO 17493), the indicated ratio could also turn out to be 1:1 or higher. 
         [0013]    In a practical embodiment of the invention, the yarn is a hybrid yarn. Here it is moreover preferable that the core of the hybrid yarn comprises, or consists of, a cellulose multifilament. The core can here be flame-retardant-free with an LOI of 17. Here it is particularly preferable that the cellulose multifilament used for the core is spun according to modal methods that are known per se, that is to say the modified classic viscose method by means of which elevated resistance properties can be achieved. It is particularly preferable if this cellulose multifilament, in its production, parameter values for the quotient of elongation measured in percent and final pull off speed measured in meter per minute defined first process parameter is less than 2.5 or less than 2.0, preferably less than 1.67 or less than 1.5, in particular less than 1.3 or even than 1.25, but preferably greater than 0.75 and in particular preferably greater than 1.0. Moreover, it is preferable for the product of these two variables to be, on the one hand, greater than 3200, in particular greater than 3600 or in particular even greater than 4000; and, on the other hand, preferably less than 8000, in particular smaller than 7500 or even than 7000, in accordance with the parameter values of claims  14  to  17  of the unpublished Application PCT/EP2012/002069 of the same applicant. 
         [0014]    In principle, the sheath of the hybrid yarn could be formed by a simple plying and twisting of additional regenerated cellulose fiber. However, it has been found moreover that the above-explained very high dimensional stability is achieved particularly well if the yarn is a core spun yarn. The production of core spun yarns per se is known to the person skilled in the art. It can be carried out on suitable commercially available machines. In the context of the invention, it has been recognized that, in the case of core spun yarns, a higher hot air shrinkage, due to the spun-in flame retardant, in the fiber direction of the regenerated cellulose fibers of the winding, now no longer extends in the fiber direction of the core of the hybrid yarn, but extends transversely thereto, resulting in a lower hot air shrinkage in the yarn direction. 
         [0015]    The invention thus also discloses a hybrid yarn having a core made of regenerated cellulose fibers, which is entitled independently to be protected, and a winding comprising regenerated cellulose fibers made flame-resistant by means of a spun-in flame retardant, wherein, in particular, a textile fabric produced exclusively from the hybrid yarn, in the case of exposure to a temperature of 260° C. for ten minutes, undergoes a dimensional change of at most 10%, in particular at most 8%. The core of this core spun yarn itself here could even comprise a flame retardant, in particular in such a way as to shift the overall flame-retardant distribution. However, here too, the above-explained distribution with weight displaced towards the outside is particularly preferable. 
         [0016]    The quotient of the titer of the core and the titer of the cover yarn (or winding) is preferably 0.75 or less, more preferably 0.6 or less, in particular 0.5 or less. 
         [0017]    In addition, it is preferable that a (the) cover yarn of the hybrid yarn comprises, or consists of, a cellulose multifilament, in particular using the same viscose as that of the core, as a result of which the resulting mechanical and textile properties are as similar as possible. Such cellulose multifilaments are described, in particular, in the as yet unpublished patent Application PCT/EP2012/002069 which has already been mentioned above. They consist of a high-strength, permanently flame-retardant yarn based on regenerated cellulose. This yarn is also marketed under the trade name Viskont® FR and is particularly suitable for use as a lining, for example, in firefighting clothing, due to its very smooth surface, its high abrasion resistance and its high specific dry tear strength in the range from 28 to 30 cN/tex. 
         [0018]    Although the cover yarn of the hybrid yarn is preferable particularly in view of these characteristics, it would be entirely conceivable to form the cover yarn of the hybrid yarn on the basis of staple fiber yarns, even if as a result slight lower strength characteristics are achieved as a result, particularly in the abrasion behavior (Martindale, pilling tests). 
         [0019]    With regard to the already marketed Viskont® FR, it should also be noted that, in spite of a fair dimensional stability, this yarn by itself does not yet achieve a desired very high dimensional stability at very high temperatures. 
         [0020]    Moreover, it is preferable that the core spun yarn has a twist of 800 TPM or less, preferably 600 TPM or less, particularly preferably 400 TPM or less, but in particular of 200 TPM or more, preferably 250 TPM or more, in order to maintain, on the one hand, low grammages, and, on the other hand, sufficient fire protection and good structural integrity of the yarn. 
         [0021]    It is preferable, not only for the core (the central core), as already mentioned above, but also for the sheath (the cover yarn/the winding), that their regenerated cellulose fibers are spun according to the modal method. In spite of the spun-in flame retardant, the individual yarn used as winding as a result also has improved overall usage properties, for example, a higher wet modulus correlating with higher dimensional stability with regard to washing. 
         [0022]    With regard to the titer of the individual yarns for core and/or winding, it is preferable that this titer is 220 dtex or less, preferably 190 dtex or less, in particular 167 dtex or less. 
         [0023]    In addition to the yarn itself according to the invention, the invention also protects a textile fabric that comprises such a yarn, consists primarily of said yarn, or is formed purely from said yarn. Thus, mixtures with other yarn types can be used, for example, aramid. This textile fabric, in the case of a temperature load of 260° C. for 10 minutes of exposure time, should have a hot air shrinkage of less than 10%, preferably less than 8%, in particular less than 6%. 
         [0024]    Here, the cloth can be one wherein the yarn according to the invention is used at least as warp yarn. On the other hand, the textile fabric could also be a knitted fabric. 
         [0025]    The textile fabric preferably has a grammage of 300 g/m 2  or less, preferably 250 g/m 2  or less, and in particular of 200 g/m 2  or less. As a result, it is possible to achieve good wearing comfort and at the same time satisfactory usage properties. 
         [0026]    Other constituents of the textile fabric are conceivable, in particular as long as the above hot air shrinkage and the flame resistance are not significantly lowered. For example, aramid could be used as weft yarn in the case of a cloth. 
         [0027]    If the textile fabric is a cloth, it is not subjected to further limitation with regard to the type of its structure. For example, twill weave of various types can be used, but linen weaves as well, and satin, rip, or Jacquard weaves can also be used. 
         [0028]    With regard to the suitability for use, it is moreover preferable if the textile fabric has an abrasion resistance of at least 80,000 cycles, preferably at least 90,000 cycles, in particular at least 100,000 cycles under a load of 12 kPa (measured according to Martindale EN ISO12947-1, 2). 
         [0029]    With regard to possible applications, knitted fabrics made of the yarn according to the invention can be used for flame-resistant gloves, for example. The cloths according to the invention, as already explained, can be used for clothing in the PPE sector, for example, for clothing for fire-fighting and military personnel, personnel in white rooms, foundries, furnaces and other professional groups at high risk of exposure to heat. 
         [0030]    Additional possibilities for use of the textile fabric according to the invention also exist in technical applications in which heat resistance is required, for example, for cladding and covering materials in interiors, cars, aircraft or ships, for filter materials, coverings, etc. 
         [0031]    In addition to fabrics, applications that can also be considered for the yarn according to the invention are strings, ropes and cables well as the use as individual threads. 
         [0032]    Other characteristics, details and advantages of the invention result from the following description of embodiment examples in reference to the appended figures, wherein 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]      FIG. 1  shows a diagrammatic representation of a weave for an example cloth of the invention, and 
           [0034]      FIG. 2  shows a comparison of strength properties achievable by means of multifilament regenerated fibers in comparison to intimate mixtures of staple fibers as warp of a cloth. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]    A first example of a yarn according to the invention is a hybrid yarn, whose core is formed by the yarn Viskont HT dtex 67f38 S90, which is produced from the cover yarn Viskont HTFR dtex 167 f60 S90 in S600 and has a titer of 234 dtex. The core here is flame-retardant-free, so that the flame retardant distribution consists the form of a step function with a step between core and winding from zero to the flame retardant concentration of the cover yarn Viskont HTFR. 
         [0036]    This yarn is used as warp yarn for a cloth structure formed from a heterogeneous mixture. The weft consists of 20 tex/1 aramid. As structure, a twill weave 2/1 with a warp density of 30 Fd/cm and a weft density of 22 Fd/cm is used, see the diagrammatic representation of the weave in  FIG. 1 . 
         [0037]    The cloth produced was washed at 60° C. for 15 minutes and dried in the tumbler at 90° C. for 40 minutes. The resulting grammage was 187 g/m 2 . The material was not dyed for the intended use (lining for fire-fighting jackets). However, such dyeing would have no effect on the test results provided below. First, for the cloth, the dimensional change in percent in the longitudinal and transverse directions in the case of exposure to heat at 260° C. for 10 minutes is determined. The percentages were −5% for the longitudinal direction and −0.5% for the transverse direction, as can be seen in Table 1 below. Moreover, the cloth was also studied at this temperature for possible ignition and/or melting, with a negative result (measurement procedures from NFPA 1971, EN ISO 11612 (for heat resistance according to ISO 17493 at 260° C.)). 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Behavior in heat of the example cloth according to the invention 
               
               
                 at 260° C. 
               
             
          
           
               
                   
                 Longitudinal/ 
                 Dimensional change 
                 Ignition 
                 Melting 
               
               
                   
                 transverse 
                 % 
                 y/n 
                 y/n 
               
               
                   
               
             
          
           
               
                   
                 L 
                 −5 
                 n 
                 n 
               
               
                   
                 Q 
                 −0.5 
                 n 
                 n 
               
               
                   
               
             
          
         
       
     
         [0038]    Moreover, the combustion behavior of the cloth was investigated (combustion test according to ISO 15025, relevant for the requirements of EN ISO 11612 and of EN ISO 469 (protective clothing for combating fire)). The results are reproduced in Table 2 and they also confirm in that regard the quality of the cloth according to the invention. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Combustion behavior of the example cloth. 
               
             
          
           
               
                   
                 Flame 
                   
                   
                   
                   
                   
                 Particle 
                   
               
               
                   
                 reaches the 
                 Afterflame 
                   
                 Afterglow 
                 Hole 
                 Particle 
                 ignites filter 
               
               
                 Longitudinal/ 
                 upper edge 
                 duration 
                 Afterglow 
                 duration 
                 formation 
                 detachment 
                 paper 
               
               
                 transverse 
                 [y/n] 
                 [s] 
                 [y/n] 
                 [s] 
                 [y/n] 
                 [y/n] 
                 [y/n] 
                 OK [y/n] 
               
               
                   
               
               
                 L 
                 N 
                 0 
                 n 
                 0 
                 n 
                 n 
                 n 
                 y 
               
               
                 Q 
                 N 
                 0 
                 n 
                 0 
                 n 
                 n 
                 n 
                 y 
               
               
                   
               
             
          
         
       
     
         [0039]    With regard to strength properties, a tensile test (according to EN ISO 13934-1) was also carried out, the result of which is reproduced in Table 3. 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Strength of the example cloth. 
               
             
          
           
               
                   
                   
                 Strength 
               
               
                   
                 Orientation 
                 [N] 
               
               
                   
               
               
                   
                 Warp 
                 810.2 
               
               
                   
                 Weft 
                 483.4 
               
               
                   
               
             
          
         
       
     
         [0040]    Finally, in Table 4, the Martindale abrasion behavior of the example cloth is also reproduced (abrasion test according to Martindale EN ISO 12947-1, 2). Here, values of &gt;100,000 cycles under a load of 12 kPa were reached. This extraordinarily high abrasion resistance is entirely surprising, if one considers that similar materials made exclusively of Viskont® are approximately in an order of magnitude between 40,000 and 70,000 cycles. The good result is predominantly attributed to the structure of the yarn according to the invention. 
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Martindale abrasion behavior of the example cloth. 
               
             
          
           
               
                   
                 Evaluation 
                 Overall 
               
             
          
           
               
                 Cycles 
                 Sample 1 
                 Sample 2 
                 Sample 3 
                 results 
               
               
                   
               
             
          
           
               
                 5000 
                 few slubs 
                 roughened 
                 few slubs 
                   
               
               
                 10,000 
                 roughened 
                 roughened 
                 roughened 
                   
               
               
                 15,000 
                 roughened 
                 roughened 
                 roughened 
                   
               
               
                 20,000 
                 rough., very slight thin f. 
                 rough., very slight thin f. 
                 rough., very slight thin f. 
                   
               
               
                 30,000 
                 rough., very slight thin f. 
                 rough., very slight thin f. 
                 rough., very slight thin f. 
                   
               
               
                 40,000 
                 rough., very slight thin f. 
                 rough., very slight thin f. 
                 rough., very slight thin f. 
                   
               
               
                 50,000 
                 rough., very slight thin f. 
                 rough., very slight thin f. 
                 rough., very slight thin f. 
                   
               
               
                 60,000 
                 rough., very slight thin f. 
                 rough., very slight thin f. 
                 rough., very slight thin f. 
                   
               
               
                 70,000 
                 rough., very slight thin f. 
                 rough., very slight thin f. 
                 rough., very slight thin f. 
                   
               
               
                 80,000 
                 rough., thin f. 
                 rough., thin f. 
                 roughen, thin f. 
                   
               
               
                 90,000 
                 rough., thin f. 
                 rough., thin f. 
                 roughen, thin f. 
                   
               
               
                 100,000 
                 rough., thin f. 
                 rough., thin f. 
                 roughen, thin f. 
                   
               
               
                 110,000 
                 several f. torn 
                 several f. torn 
                 2 f. torn 
                   
               
               
                   
                 105,000 
                 105,000 
                 105,000 
                 105,000 
               
               
                   
               
             
          
         
       
     
         [0041]    Another embodiment example is a hybrid yarn which is also made in the form of a core spun yarn. The core here forms a nonpermanently flame-retardant yarn dtex 110 f6 S90, the cover yarn or winding made of a permanently flame-retardant yarn dtex 110 f46 S90. 
         [0042]    A cloth formed exclusively from this hybrid yarn 220 dtex, in the case of a nonpermanently flame-retardant to permanently flame-retardant yarn ratio of 40:60 here, for example, undergoes a shrinkage at 260° C. with 10 minutes of exposure time of less than 6%, both for the warp and for the weft (structure twill 3/1, cloth density warp 34 FD/cm, weft 23 FD/cm). 
         [0043]    An even lower hot air shrinkage was achieved with the same hybrid yarn in the case of a linen structure with a cloth density 24 FD/cm and weft 18 FD/cm. Here, a shrinkage of less than 5% (weft) and less than 2% (warp) was achieved. In this second embodiment example, the same combustion behavior as indicated in Table 2 for the first embodiment example was also achieved. 
         [0044]    But such hybrid yarns with a ratio of nonpermanently flame-retardant to permanently flame-retardant yarns of more than 40:60 are still entirely capable of exhibiting very little shrinkage even at 260° C. However, in the case of a considerably higher ratio, additional flame-retardant or flame-resistant fibers should be used for producing textile fabrics, since the flame protection effect of the hybrid yarn alone in that case no longer reliably ensures an afterflame duration (ISO 15025) of zero. 
         [0045]    As comparison example, another cloth is presented, which is formed 100% from an FR filament, dtex 290, warp and weft structure 225 g/m 2 . In Table 5, the hot shrinkage process of this structure is represented for two samples at two temperatures. It can be seen that at 180° C., only a very small percentage shrinkage occurs, which also meets the standard EN ISO 11612. However, at even higher temperatures, these low values cannot be maintained. 
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Shrinkage behavior of a cloth made of 100% FR filament, dtex 290, warp and weft 
               
               
                 structure, 225 g/m 2  at 180° C. and 260° C. 
               
             
          
           
               
                   
                 Starting size 
                 Final size [cm] 
                 Shrinkage [%] 
               
             
          
           
               
                 Method 
                 Sample 
                 longitudinal 
                 transverse 
                 longitudinal 
                 transverse 
                 longitudinal 
                 transverse 
                 Total 
               
               
                   
               
             
          
           
               
                 180° C. 
                 1st 
                 14.8 
                 15.0 
                 14.7 
                 14.7 
                 0.7 
                 2.0 
                 1.3 
               
               
                   
                 2nd 
                 14.9 
                 14.6 
                 14.8 
                 14.4 
                 0.7 
                 1.4 
                 1.0 
               
               
                 260° C. 
                 1st 
                 14.9 
                 15.0 
                 13.1 
                 13.3 
                 12.1 
                 11.3 
                 11.7 
               
               
                   
                 2nd 
                 14.8 
                 14.8 
                 12.8 
                 13.5 
                 13.5 
                 8.8 
                 11.1 
               
               
                   
                 3rd 
                 14.9 
                 15.0 
                 13.2 
                 13.3 
                 11.4 
                 11.3 
                 11.4 
               
               
                   
               
             
          
         
       
     
         [0046]    As already mentioned above, the use of multifilament regenerated fibers is preferable compared to staple fibers or intimate mixtures of staple fibers. In a comparison of the strengths at identical grammage, higher strength values from 20% to 30% in the warp are achieved, if it consists of multifilament regenerated fibers and not of intimate mixtures of staple fibers. This is represented in  FIG. 2 , which, to that extent, does not relate to the fabric according to the invention itself, but serves to explain the background for particularly preferred embodiments of the invention.