Abstract:
Insulating flame-resistant woven fabrics have been discovered which have a non-pilling pile on the back side of the fabric to provide an insulating layer of stagnant air and have long wear life.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to the general field of fabrics, and to the particular area of flame-resistant fabrics.  
         BACKGROUND  
         [0002]    It is well known in the prior art that woven fabrics can be finished by abrading one or both surfaces to obtain a soft surface texture resembling a suede leather or prewashed fabric as is explained in U.S. Pat. Nos. 4,918,795, 4,863,775, 4,837,902 and the teachings are entirely incorporated herein by reference. The sueded or washed feeling in the fabric is created by raising the fibers of the constituent material while at the same time nicking or splitting some of the raised ends to soften the filaments. Another patent, U.S. Pat. No. 5,468,545 teaches that flame-retardant treated fabrics can be made durable by blending small amounts of thermoplastic fibers with cotton. Efficient ways of flame-retarding fabrics made from blends of cotton and thermoplastic fibers with tetrakis (hydroxymethyl) phosphonium compounds (THP) are described in U.S. Pat. Nos. 4,909,805 and 5,480,458. While improvement in hand and thermal protection can be achieved, sanding enhances the formation of small balls as fiber ends freed by sanding pull loose and entangle when garments are worn or washed. When synthetic fibers are incorporated in fabrics to increase wear life, these strong fibers hold the cotton balls on the sanded surface producing an unsightly appearance and reducing the effectiveness of the insulating layer. A number of methods for reducing pilling are well known which involve weakening the synthetic fibers with or without temporarily immobilizing them as explained in U.S. Pat. No. 5,468,545 and the teachings are incorporated entirely herein by reference. Knit fabrics have long been used to make pile fabrics because some knit structures lend themselves to forming loops, which can be cut without loosing fabric integrity. Knits are not the subject of this disclosure.  
         SUMMARY OF THE INVENTION  
         [0003]    This invention provides cotton/thermoplastic fiber blend flame-resistant fabrics with an insulating pile on the backside that is non-pilling. It has been discovered that woven 3×1 and 4×1 twill and sateen fabrics that contain 15-30% nylon in the warp and 100% cotton on the fill side can be sanded on the fill side without inducing pilling and without a significant reduction in wear life provided that the final sanded fabrics have a tear strength of no less than 3 lbs when fabrics are torn across along the warp direction to break the yarns.  
           [0004]    Woven fabrics of this invention have a 3×1 or 4×1 twill or sateen construction and have an insulating pile on the back made up primarily of sanded fill yarns, 15-30% nylon in the warp yarns, 100% cotton yarns in the fill direction, a fill tear strength of at least 3 lbs and contain at least 1.0% phosphorus by weight of the fabric due to flame-retardant contained therein.  
         DETAILED DESCRIPTION OF THE INVENTION  
         [0005]    This invention adds enhanced thermal protection to long wear life flame-resistant woven fabrics by sanding the backside of 3×1 or 4×1 twill or sateen cotton blend fabrics which contain a very narrow range of nylon in the warp and by limiting the strength loss due to sanding such that the tears along the warp direction which break the fill yarns require at least 3 lbs to propagate.  
           [0006]    The staple fibers used herein are textile fibers having a linear density suitable for wearing apparel, i.e., less than 10 decitex per fiber, preferably less than 5 decitex per fiber. Still more preferred are fibers having a linear density of 1 to 3 decitex per fiber and length from 1.9 to 6.3 cm (0.75 to 2.5 in). Crimped fibers are particularly good for textile aesthetics and processibility.  
           [0007]    It is important to use nylon in the warp because it has the best fatigue life of all of the commercially available thermoplastic fibers and is capable of maintaining the integrity of the warp much better than other fibers, such as polyester, when the garment is abraded by normal wash and wear conditions. The warp yarn pinches the fill yarns at crossover points and slows down the rate at which the broken ends in the sanded fill yarns come free and the fabric breaks. With less than 15% nylon in the yarns, normal wash and wear fatigue will quickly loosen the grip of the warp yarns and subsequently the fill yarns weakened by sanding will break prematurely and the warp yarns will follow so that holes are formed. With more than 30% nylon in the warp, the fabrics lose a significant part of their flame-resistance. The fill must be 100% flame-retardant treated cotton because sanding nylon blend yarns will cause pilling and the fabric will burn once the nylon fibers are raised and have increased access to oxygen.  
           [0008]    Fill yarns must cross over at least 3 or 4 warp yarns in order to shield the cotton/nylon warp yarns from the sander when the fabric is rubbed on the backside. Twills and sateen of 3×1 or 4×1 construction are suitable for this purpose whereas plain weave or fabrics of 2×1 construction are not. Fabrics of a style which allows too much exposure of the warp yarns on the backside will lose warp tensile and tear strength upon sanding and styles wherein the yarn crossover points of warp and fill are too far apart will weaken and have poor wear life after sanding as the broken fibers will fall out.  
           [0009]    While sanding will not cause fabrics of the invention to pill during washing or wearing or cause significant warp damage, it will cause strength loss in the fill direction. In order to keep normal garment stress from tearing the garment, the fill strength must not be reduced below 3 lbs during the sanding operation. Sanding can occur at any stage in the production of the fabric, greige, after flame-retarding treatment or after the fabric has been compressively shrunk, such as by Sanforization.  
           [0010]    Fabrics must be flame-retardant treated in order to meet the objective of the invention which is to provide fabrics with flame-resistance and enhanced thermal insulation.  
           [0011]    At least two satisfactory commercial products are available. One is          Pyroset          TPO, a THPS/urea precondensate of tetrakis (hydroxymethyl) phosphonium sulfate and Urea available from Freedom Chemical Company, Charlotte, N.C. The other is THPC/urea prepolymer condensate of tetrakis (hydroxymethyl) phosphonium chloride and urea sold by Albright and Wilson. While these compounds are ammonia cured, other phosphorus flame-retardant chemicals may also be used which involve heat treatment for curing.  
         Measurements  
         [0012]    Tear strength of fabrics was measured using the American Society for Testing Materials (ASTM) test D1424, Elmendorf tear. Tensile strength was measured using ASTM-D5035-95, strip tensile. Fabric pieces were folded and sewn together at cut edges with the fill face on the inside of the fabric to simulate a sewn garment. Sewn pieces were washed 75 times and examined for pilling on the inside. Pilling was determined by empirical analysis and rated as non-pilling, moderate, substantial. Holes or significant fiber loss from abrasion were used to determine wear life. 
       
    
    
     EXAMPLE 1  
       [0013]    Woven fabric was made as a 3×1 twill having in the warp 25% of polyhexamethylene adipamide (6,6 nylon) fibers and 75% cotton. The fill was 100% cotton. The fabric was prepared, dyed and flame-retardant treated such that it contained 2.5% phosphorus. The fabric was compressively shrunk to loosen the structure. It was then sanded on the fill side using a conventional multi-roll sander with fine grit sandpaper. A noticeable pile was generated on the backside of the fabric. Fill tear strength was reduced from 7 to 5 lbs. Warp tear and tensile strength was reduced less than 15%. Sewn fabric pieces washed and dried 75 times showed no signs of pilling and wear.  
       EXAMPLE 2  
       [0014]    The same woven fabric described in Example 1 was sanded after flame-retardant treatment to create an insulative pile. Fill strength was reduced from 7 to 4 lbs. Warp tear and tensile strength was reduced less than 15%. The fabric was compressively shrunk to reduce shrinkage. Fabrics washed and dried 75 times showed no signs of pilling or wear. Comparative Example A not of this invention was made by sanding such that fill strength was reduced to 2 lbs. Warp tear and tensile strength was reduced less than 15%. Sewn fabric pieces washed and dried 75 times had holes.  
       EXAMPLE 3  
       [0015]    Woven fabric was made as a 4×1 sateen having in the warp 25% of polyhexamethylene adipamide (6,6 nylon) fibers and 75% cotton. The fill was 100% cotton. The fabric was prepared, dyed and flame-retardant treated such that it contained more than 2% phosphorus. It was compressively shrunk. It was then sanded on the fill side using a conventional multi-roll sander with fine grit sandpaper. Fill tear strength was reduced to 4 lbs. Warp tear and tensile strength was reduced less than 15%. Sewn pieces washed and dried 75 times showed no signs of pilling and had minimal wear. Comparative Example B not of this invention was made by sanding a 100% flame-resistant cotton fabric of similar construction to reduce fill strength to 4 lbs. After 75 washes the sewn piece had holes.  
         [0016]    It is understood that while certain forms of the present invention have been illustrated and described herein, it is not to be limited to the specific forms or arrangements of parts described and shown.