Patent Publication Number: US-2006008644-A1

Title: Fabrics of mixed-polyester-ratio bi-component fibers

Description:
This is a non-provisional of U.S. application number 60/585,899 filed July 7, 2004, now pending.  
     FIELD OF THE INVENTION  
      The invention is directed to yarn comprising mixed polymer ratio bi-component fibers and to fabrics formed therefrom.  
     BACKGROUND OF THE INVENTION  
      Bi-component fibers formed by melt spinning a filament from two or more polymer components have previously been disclosed in the art and are well known for use in various applications, such as fabric and apparel production, stuffing for filled articles, and the like. The bi-component fibers result from coalescing two different polymer melts before or after passing the melts through a spinneret to produce fibers. Bi-component fibers may be obtained by extrusion of at least two different polymers through the same spinneret die opening in which the two polymers have different shrinking potentials. Such bi-component fibers have a latent crimping ability which can be developed during subsequent processing steps.  
      When a bi-component fiber is produced, its composition, denier, and other characteristics result in a particular type of helical crimp. When these fibers are wound into yarn, bi-component fibers all having the same component weight ratio all have the same helical crimp. This causes the fibers of the yarn to exhibit what is sometimes known as “follow-the-leader” crimp which results when the helices of many crimps all match up. In the subsequent production of fabric, this follow-the leader crimping can result in random filament direction reversals leading to areas of non-uniformity in the fabric.  
     SUMMARY OF THE INVENTION  
      Accordingly, it may be desirable to develop a yarn of bi-component fibers of varying crimp frequency in order to produce a yarn that contains fibers without matching crimps, avoiding follow-the-leader crimping.  
      A yarn and a fabric formed from the yarn are disclosed. The yarn comprises mixed ratios of polyesters, such as polyethylene terephthalate and polytrimethylene terephthalate, in which some filaments of the yarn are of different polymer ratios than other filaments. It is preferred that the yarns be spun with the desired mixture of ratios and that the differences in polymer ratios between the filaments of the yarn is at least about 10% absolute. The net overall weight ratio in the yarn is preferably in the range of about 55/45 to about 75/25 polyethylene terephthalate to polytrimethylene terephthalate. The number of filaments in each yarn does not need to be uniformly distributed. Fabrics can be formed from the yarn, such as by knitting or weaving. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a chart showing crimp frequency versus tension for three yarns of various bi-component fiber ratio.  
       FIG. 2  is a chart showing crimp frequency versus tension for a different set of yarns of various bi-component fiber ratio. 
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
      Exemplary embodiments of the invention are directed toward yarn and fabric knit from that yarn that comprises mixed polymer ratio bi-component fibers.  
      Bi-component fibers may be produced by melt-spinning polymers. By modifying various properties that affect crimping of individual fibers spun in a spinneret, a yarn can be produced with individual bi-component fibers of the yarn having different crimping frequency. One way of producing such a yarn may be accomplished by varying the, ratio of polymer components fed to individual orifices of a spinneret, resulting in bi-component fibers of varying component weight ratios. The various weight ratios in turn result in the bi-component fibers in the yarn having crimping frequencies that differ from other bi-component fibers in the same yarn.  
      The terms “bi-component filament” and “bi-component fiber” as used herein refer to any filament or fiber that is composed of two distinct polymers which have been spun together to form a single filament or fiber. As used herein the term “fiber” includes both continuous filaments and discontinuous (staple) fibers. By the term “distinct polymers” it is meant that each of at least two polymeric components are arranged in distinct substantially constantly positioned zones across the cross-section of the bi-component fibers and extend substantially continuously along the length of the fibers. Bi-component fibers are distinguished from fibers that are extruded from a homogeneous melt blend of polymeric materials in which zones of distinct polymers are not formed. The two distinct polymeric components useable herein can be chemically different or they can be chemically the same polymer, but have different physical characteristics, such as tacticity, intrinsic viscosity, melt viscosity, die swell, density, crystallinity, and melting point or softening point. One or more of the polymeric components in the bi-component fiber can be a blend of different polymers. Bi-component fibers useful in the current invention have a laterally eccentric cross-section, that is, the polymeric components are arranged in an eccentric relationship in the cross-section of the fiber. Preferably, the bi-component fiber is made of two distinct polymers and has an eccentric sheath-core or a side-by-side arrangement of the polymers.  
      Laterally eccentric bi-component fibers comprising two synthetic components that differ in their ability to shrink are known in the art. Such fibers form helical/spiral crimp when the crimp is activated by subjecting the fibers to shrinking conditions in an essentially tensionless state. The amount of crimp is directly related to the difference in shrinkage between the components in the fibers. When the multiple-component fibers are spun in a side-by-side conformation, the crimped fibers that are formed after crimp activation have the higher-shrinkage component on the inside of the spiral helix and the lower-shrinkage component on the outside of the helix. Such crimp is referred to herein as spiral crimp. Such crimp is distinguished from mechanically crimped fibers, such as stuffer-box crimped fibers, which generally have two-dimensional crimp.  
      The bi-component fibers used in exemplary embodiments of the present invention may typically be polyester bi-component fibers spun from various polyester components. By “polyester” is meant polymers in which at least 85% of the recurring units are condensation products of carboxylic acids and dihydroxy alcohols with linkages created by formation of ester units. This includes aromatic, aliphatic, saturated, unsaturated di-acids and di-alcohols. The term is also meant to include copolymers, blends, and modifications thereof.  
      Particularly suitable polyesters of the present invention include polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polypropylene terephthalate (PPT), and polybutylene terephthalate (PBT). These polyesters may be synthetically produced from any known method of polyester production. One typical process includes the condensation reaction of alkylene glycol and terephthalic acid to produce polyalkylene terephthalate.  
      By varying the polymer ratio fed to individual apertures of a spinneret, such as using the method described in U.S. Pat. No. 3,671,379 to Evans et al., a single spinneret may be used to produce multiple fibers, each having varying ratios of distinct polymers. These fibers can then be wound into a yarn of mixed ratio bi-component fibers without the need to separately wind other yarns together to form a larger yarn. The various bi-component fibers, or yarns of these fibers, having mixed component ratios, are combined to form a single yarn that may be used to knit fabrics.  
      The weight ratio of individual bi-component fibers of the yarn of the invention may be any weight ratio of one component versus the other, but typically the ratio is between about 75/25 to 25/75, more typically between about 70/30 to 30/70.  
      Regardless of the weight ratios of the individual fibers, the overall or net weight ratio of the components in the yarn is about 45/55 to about 75/25, wherein the first number represents the component having the repeating unit of smaller mass. Preferably, the overall net weight ratio is asymmetric, favoring higher amounts of the component having the smaller repeating unit, i.e. PET in preferred embodiments of the invention using a PET and PTT as components.  
      The weight ratios of one component versus the other may vary between the fibers within the yarn, thus creating the mixed-ratio bi-component fibers. The components of various filaments may typically differ by about 10 weight percent or more in any particular yarn. For example, a yarn might typically include multiple bi-component fibers of 30/70, 40/60, 50/50, 60/40 and 70/30, but not typically 30/70, 33/67, 50/50, 67/33, and 70/30. Differences of less than about 10 weight percerit may not produce bi-component fibers with sufficient differences in crimp frequency to achieved the most desired levels of avoiding follow-the-leader crimping.  
      Once the yarns are spun, they may be used to knit fabrics which have desirable characteristics, such as a smooth and silky touch.  
     EXAMPLES  
      Several yarns were produced. In each case, PTT and PET were used to spin bi-component fibers that were then wound into yarn. The PTT and PET polymer was fed at 60 degrees C., drawn at 90 degrees C., and annealed after drawing at 160 degrees C. with no letdown. The fibers were spun using a stacked plate spinneret and were coalesced post-spinning. The fibers were cooled using a cross flow quench and wound into yarn, which was drawn 3.75×(375% of the original length) at 2100 m/min.  
      Tenacity and crimp contraction of all of the yarn samples was measured.  
      Crimp contraction is measured as follows. A bi-component fiber is formed into a skein of 5000+/−5 total denier (5550 dtex) with a skein reel at a tension of about 0.1 gpd (0.09 dN/tex). The skein was conditioned at 70+/−2 degrees F. (21+/−1 degrees C.) and 65+/−2% relative humidity for a minimum of about 16 hours. The skein was hung substantially vertically from a stand, a 1.5 mg/den (1.35 mg/dtex) weight (e.g. 7.5 grams for a 5550 dtex skein) was hung on the bottom of the skein, the weighted skein was allowed to come to an equilibrium length for 15 seconds, and the length of the skein was measured to within 1 mm and recorded as “C b ”. The 1.35 mg/dtex weight was left on the skein for the duration of the test. Next, a 500 gram weight (100 mg/d; 90 mg/dtex) was hung from the bottom of the skein, and the length of the skein was measured to within 1 mm and recorded as “L b ”. Percent crimp contraction (CC) was calculated according to the formula 
 
 CC= 100×( L   b − C   b )/ L   b    (1) 
 
      The test is performed on several samples and the results are averaged.  
     EXAMPLE 1  
      A first yarn was produced by commingling two yarns. Each yarn contained fibers of a unitary weight ratio of components for all filaments in the yarn. One yarn was a 150 denier PTT/PET yarn, which was then commingled with a 100 denier PTT/PET yarn. Each yarn was spun with 34 filaments. Thus, the resulting commingled yarn had a total of 68 filaments, with a denier per filament (dpf) of 250 divided by 68, or about 3.7. Tenacity for the commingled yarn was about 4 g/denier, with a maximum elongation of about 20%. Crimp contraction of the commingled yarn was about 60%.  
     EXAMPLE 2  
      A second yarn was produced in the same manner as generally described above, except that this 34 filament yarn included a mixed filament ratio from 70/30 to 30/70 weight percent of PET and PTT. The overall weight percent of PET to PTT in the yarn was about 50/50. The yarn was drawn 3.75×. Tenacity for the mixed filament ratio yarn was about 3.5 g/denier, with a maximum elongation of about 20% Crimp contraction was measured at about 45%.  
     EXAMPLE 3  
      A third yarn was produced in a manner identical to the yarn of Example 2, with the only exception that the yarn was drawn 4×. Tenacity, elongation and crimp contraction were all measured at about the same value as the yarn of Example 2.  
      To evaluate yarns of mixed ratios, the crimp frequency of individual filaments having varying weight ratios was charted versus applied tension as shown in  FIGS. 1 and 2 .  
       FIG. 1  shows an analysis of three filaments comprising PET and PTT. The weight ratios vary between 30/70, 40/60, and 50/50. Crimp frequency, measured in the number of crimps per inch, is plotted on the y-axis as measured against increasing tension from 0 to .01 g/ denier, in 1 mg/denier increments. Tensions typically seen in fabrics tend to be about 2 to 4 mg/denier. Over this range, the difference in crimp frequency between the 40/60 and 50/50 versions are about 4-5%, while the difference between the 30/70 and 50/50 mixture filaments is about 16-27%.  
       FIG. 2  also demonstrates test results of three bi-component filaments comprising PET and PTT, but in this case, the 40/60 filament is substituted with a 70/30 filament. In this range, the crimp frequency versus tension of the two yarns with the same, but inverted weight percents tend to show little difference in crimp frequency versus tension, but maintain the 16-27% difference versus the 50/50 mixture;  
     EXAMPLE4  
      A fourth yarn sample was created with 34 separate fibers. The spinneret was adjusted to produce individual fibers in the yarn of various weight ratios as shown below in Table 1, wherein the weight ratio is shown in PET/PTT. The overall net weight percent of PET to PTT in the yarn was about 51/49.  
                                                           TABLE 1                       Weight   25/75   30/70   35/65   40/60   45/55   50/50   55/45   60/40   65/35   70/30   75/25       Ratio                  #   4   2   2   2   4   4   4   2   4   2   4       filaments                  
 
     EXAMPLE 5  
      Fabrics were produced by knitting yarns of mixed-ratio bi-component fibers. Fabric was knit using a 24 feed circular knit machine with 255 inches per revolution to prepare a single jersey fabric. The fabrics were dyed at 212 degrees F., followed by drying at 250 degrees F. and heat set at 330 degrees F. Fabric properties are shown below in Table 2. “W×F” is an abbreviation for “warp by fill,” measured in number of yarns per inch. Fabric weight is measured in units of ounces per square yard of fabric.  
                       TABLE 2                       Fabric   W × F   Fabric weight                  1   50 × 60   4.74       2   42 × 56   5.62                  
 
      These fabrics had improved characteristics that included a smooth and silky touch.  
      The present invention is not to be limited in scope by the specific embodiments described herein. Indeed, various modifications of the present invention, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such modifications are intended to fall within the scope of the following appended claims. Further, although the present invention has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present invention can be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present invention as disclosed herein.