Patent Publication Number: US-6342456-B1

Title: Polypropylene outdoor fabric

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     Fabrics for outdoor uses have been known for many years, such as for patio furniture covers, covers for other products that are stored outside, and for a wide variety of other uses. Cotton duck and synthetic fiber fabrics, including those made of acrylics and polyolefins (such as polypropylene) have been particularly popular. However some or all of these fabrics have suffered from a number of deficiencies, such as (depending upon the particular prior art cover or other outdoor fabric) lack of color durability, lack of resistance to soiling so that the fabric does not retain a new and fresh appearance for a very long period of time, poor hand, less than desirable water and oil repellancy, and less structural strength than desired. 
     In most conventional outdoor use fabrics, finer yarn is used in the warp and heavier yarn used in the filling during the weaving process. The traditional thinking is that heavier yarn used in the filling means lower picks per inch need be used to obtain the fabric than with a finer yarn, and thus weaving costs are kept to a minimum. For example a conventional outdoor use woven fabric has a plain weave with finer yarn in the warp and heavier yarn in the filling, and with about 40% of the filling yarns equally exposed to both the back and the face of the fabric, and about 12% coring to the center of the fabric. 
     According to the present invention a method of making a polypropylene base fabric for outdoor use, and the fabric, and outdoor use product made from the fabric, are provided which have numerous advantages compared to prior art constructions. One of the most significant advantages of the fabric/product according to the invention is enhanced hand. While hand is difficult to measure quanitatively, it is one of the most easily recognized characteristics of a fabric by a consumer. While shear stiffness and flexural rigidity are not exactly equal to hand, the product according to the invention has improved shear stiffness and flexural rigidity, which are indicative of improved hand. The fabric according to the present invention has a shear stiffness of comparable to less than 3.0 gf/cm*Degrees, and an overall flexural rigidity of comparable to less than 600, for a fabric having a weight of about 6.5 oz/sq. yd. 
     The fabric according to the invention uses yarns comprising or consisting essentially of polypropylene, UV inhibitor for color fastness when exposed to sunlight, and a fluorochemical or fluoropolymer which causes the fabric to be inherently water repellent, and maintains water repellancy after abrasion. Because of the polymer mix utilized, and the controlled weaving, washing and drying conditions utilized in production, products according to the invention are softer and smoother than otherwise obtainable. 
     That is products according to the present invention have color durability, and resist fading from exposure to at least 500 hours of simulated sunlight. The products have a soft, comfortable soothing and smoother finish than comparable outdoor fabrics. The fabrics of the invention stay dryer than comparable fabrics that are surface treated with a fluorochemical water and oil repellancy treatment. The fabrics of the present invention continue to resist staining after wear abrasion such as with sandpaper. The fabrics of the present invention also tend to clean easily. Dirt can frequently be shaken from these fabrics, which exhibit much lower soiling than comparable fabrics. Finally, the fabrics of the invention dry more quickly than comparable fabrics making them resistant to mildew and tending to stay new and fresh appearing for much longer periods than comparable fabrics intended for outdoor use. However, an antimicrobial material may be added if desired. 
     Contrary to conventional thinking, the fabrics according to the invention are made with the filling yarns predominantly exposed to the face and with either the heavier yarn used in the warp direction and the finer yarn in the filling direction, or yarns of equal size or denier in the warp and filling directions. Therefore the invention uses a higher picks to warp ratio than comparable fabrics. Since it is the filling that is subjected to finishing processes, and fabrics according to the invention have not only more filling exposed but more filling picks inserted than comparable fabrics, the hand is necessarily superior. 
     According to one aspect of the present invention a method of making a polypropylene base fabric for outdoor use, using yarn comprising or consisting essentially of polypropylene, UV inhibitor, and a fluorochemical, is provided. The method comprises: (a) Weaving the yarn using heavier yarn in the warp direction and finer yarn in the filling direction, or yarns of substantially equal size or denier in the warp and filling directions, to produce a fabric having a face, a center, and a back, with at least 50% of the filling yarns exposed to the fabric face. (b) Washing the fabric to scour off spin finish on the yarns. And, (c) drying the washed fabric at a temperature below the softening point of polypropylene using air flow and tension control. The method may also comprise (d) making the fabric into an outdoor use product (such as a furniture cover), and (e) using the outdoor use product so that the face of the fabric faces the sun. 
     In the preferred embodiment, (a) is practiced to provide about 50-70%, preferably about 68-70%, of the filling yarns exposed to the fabric face, and about 6-10%, preferably about 8%, in the center, and about 20-40%, preferably about 22-24%, on the back. Typically (b) is practiced using water and detergent. Also typically (c) is practiced using a tenter frame, and at a temperature of between about 270-280 degrees F., and with an air flow of between about 4000-5100 cfm. 
     In the practice of the invention, typically (a)-(c) are practiced to produce a fabric having a shear stiffness of comparable to less than 3.0 gf/cm*Degrees, and an overall flexural rigidity of comparable to less than 600, for a fabric having a weight of about 6.5 oz/sq. yd. (a) through (c) are also typically practiced to produce a fabric having a weight between about 6-7 ounces per square yard, and to produce a fabric having a warp tear strength, pursuant to ASTM D117, of greater than 90, and a filling tear strength of greater than 26. That is (a)-(c) are practiced to produce a fabric having hand at least 10% better than if (a) were practiced using finer yarn in the warp and heavier yarn in the weft and about 44% of the filling yarns on each the face and back, and about 12% in the center. 
     According to another aspect of the present invention an outdoor object cover is made from a fabric produced from the method described above. The invention, according to another aspect, also comprises a woven fabric made of yarns consisting essentially of polypropylene, UV inhibitor, and fluorochemical air textured yarn, heavier yarn in the warp direction and finer yarn in the filling direction, or yarns of equal size or denier in the warp and filling directions, having a face, a center, and a back, with at least 50% of the filling yarns exposed to the fabric face. The woven fabric according to the invention preferably has about 68-70% of the filling yarns exposed to the fabric face, and about 8% in the center, and about 22-24% on the back; has a weight of between about 6-7 oz/sq. yd.; has a warp tear strength, pursuant to ASTM D117, of greater than 90, and a filling tear strength of greater than 26; and has a shear stiffness of comparable to less than 3.0 gf/cm*Degrees, and an overall flexural rigidity of comparable to less than 600, for a fabric having a weight of about 6.5 oz/sq. yd. 
     It is the primary object of the present invention to provide a highly advantageous outdoor use fabric in a simple, yet effective, manner. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a box diagram schematically illustrating the practice of an exemplary method according to the present invention; 
     FIG. 2 is a side schematic view of an outdoor use fabric produced according to the present invention; and 
     FIG. 3 is a schematic perspective showing an outdoor use product made from the fabric of FIG. 2 serving as an outdoor furniture cover. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     FIG. 1 schematically illustrates the practice of an exemplary method according to the present invention. The method starts with yarns, shown schematically at  10  in FIG. 1, that are produced as schematically illustrated at  11 . The yarns  10  utilized according to the invention include polypropylene  12 , UV inhibitor  13 , and fluorochemical  14 . The preferred fiber is that prepared by RAM Extrusions, Inc. of Dalton, Ga. comprising or consisting of a polypropylene polymer plus a UV inhibitor and a fluorochemical, preferably PMA FX-1801 supplied by the 3M Company, as well as color additives if desired. RAM mixes the polymer composition with the additives and then extrudes the composition into a continuous filament form. RAM applies a typical spin finish to assist in downstream processing. RAM then air textures the thus formed yarn, to produce the yarns  10  used according to the invention. 
     The advantageous yarns  10  are woven, as schematically illustrated at  15  in FIG. 1, to provide a high weft face. That is weaving step  15  is practiced so that the fabric  16  (see FIG. 2) produced by the weaving stage  15  has no less than 12 harness dobbies [a type of loom harness control] in which the filling yarns  17  are primarily exposed to the face  18 , with less filling yarns  17  exposed to the back  19 , or coring to the center  20 . The preferred denier range for the warp yarn is about 300 to 800, and about half that (e.g. about 150-400) for the filling yarn. For example, stage  15  is practiced using a yarn  10 , e.g. 650 denier, in the warp direction, and a yarn  10 , e.g. 325 denier, in the filing direction, or by using about 325 denier in both the warp and filling directions. While stage  15  is practiced so that at least 50% of the filling yarns are predominantly exposed to the face  18  of the fabric  16 , preferably stage  15  is practiced so that between about 50-70%, most preferably about 68-70%, of the filling yarns  17  are exposed to the face  18 , and between about 20-40%, most preferably about 22-24%, to the back  19 , with only about 6-10%, most preferably about 8%, coring to the center  20 . Stage  15  is also preferably practiced so that the fabric  16  has a weight between about 6-7 ounces per square yard, e.g. about 6.5 ounces per square yard, although heavier or lighter fabrics can be produced. 
     After weaving at  15 , the fabric  16  is washed, as indicated schematically at  21  in FIG. 1, to scour off the spin finish on the yarns  10  which was applied during the production stage  11 . The washing stage  21  preferably is practiced utilizing water and detergent, and at a temperature and conditions which effectively remove the vast majority of the spin finish. Removing the spin finish enhances the water and all the oil repellancy of the resultant woven fabric  16 . For example stage  21  may be practiced using a Kuster washer equipped with automatic tension control on steam/dwell chambers in multi-pass wash boxes, allowing open width, wrinkle free, controlled tension processing. 
     After stage  21  the fabric  16  is dried, as indicated schematically at  22 , using tension and air control, as indicated schematically  23 . Typically the stages  22 ,  23  are practiced together, for example, in a conventional tenter frame with a low profile housing, circulated hot air, cold water exit cooling, and computerized process control including automatic tension control from entry to exit of the tenter frame. 
     Processing in stages  22 ,  23  is typically practiced to dry at low temperature, that is keeping the tenter frame temperature below the softening point of polypropylene, which is about 290°-300° F. The desired temperature range for frame finishing of polypropylene is between about 270-280° F. Width-wise tension is preferably controlled by the fabric construction and the tenter rail settings. Length-wise tension is preferably controlled by the use of overfeed rollers and the frame tension control system utilizing a combination of sonic, infrared and load cells. Air flow is preferably controlled by circulating fans with inverters to control motor load and rpm, and the desired air flow range is between about 4000-5100 cfm (e.g. about 4060-5075 cfm). 
     As indicated at stage  24  in FIG. 1, the fabric exiting the tenter frame is made into an outdoor product of any conventional construction, such as the furniture cover illustrated schematically at  25  in FIG.  3 . Then, as illustrated schematically at  26  in FIG. 1, the product  25  is used outdoors in a functional manner. For example as illustrated in FIG. 3 the product  25  is illustrated covering an outdoor chair  27 , or for covering a snowmobile, car, woodpile, bicycle, or any other outside object. The stage  24  is practiced so that the front face  18  of the fabric  16  from which the product  25  is made faces the sun, as schematically illustrated in FIG.  3 . 
     The fabric  16 , and product  25 , according to the present invention have high color durability. Color durability is measured by light fastness, and the fabric/products  16 ,  25  according to the present invention resist fading from exposure to at least 1000 hours of simulated sunlight, typically over 1,000 hours. The fabric/products  16 ,  25  according to the invention also have improved pilling. Soil resistance is also excellent, as measured by oil and water drop (alcohol) repellancy. 
     The fabric  16 , and products  25 , according to the present invention have a shear stiffness of comparable to less than 3.0 gf/cm*Degrees, and an overall flexural rigidity of comparable to less than 600, for a fabric having a weight of about 6.5 oz/sq. yd. The fabric  16  and products  25  also have a warp tear strength, pursuant to ASTM D117, of greater than 90, and a filling tear strength of greater than 26. The fabric  16  and products  25  according to the invention also have a hand at least 10% better than if stage  15  were practiced using finer yarn in the warp and heavier yarn in the weft and about 40% of the filling yarn on each of the face and back and about 12% on the center (that is a conventional construction). 
     The fabric  16  according to the present invention has been tested compared to commercially available 100% acrylic and 100% polypropylene commercial products. A summary of the results of one such test are provided in Table 1 below. In the Table, Sample #1 is a 100% acrylic commercial product with post-fabric production fluorochemical treatment, Sample #2 a 100% polypropylene commercial product, and Sample #3 is a product produced according to the present invention, made from the RAM yarn described above consisting essentially of polypropylene with a UV inhibitor and a fluorochemical that is air texture by weaving so that heavier yarn is in the warp direction and finer yarn in the filling direction with about 69% of the filling yarn exposed to the face, about 8% in the center, and about 23% on the back, washed with water and detergent to remove substantially all of the spin finish on the yarns, and dried in a conventional tenter range at a temperature of about 275° F. with an air flow of about 4500 cfm. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE I 
               
               
                   
                   
               
               
                   
                 Property 
                 Sample #1 
                 Sample #2 
                 Sample #3 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Tensile 
                   
                   
                   
               
               
                   
                 LT (−) 
                 0.78 
                 0.78 
                 0.78 
               
               
                   
                 WT (gf* cm/cm 2 ) 
                 3.55 
                 5.97 
                 7.40 
               
               
                   
                 RT (%) 
                 55.42  
                 54.02 
                 44.94 
               
               
                   
                 EMT (%) 
                 1.81 
                 3.07 
                 3.77 
               
               
                   
                 Shear Stiffness 
               
               
                   
                 G (gf/cm * Degree) 
                 3.16 
                 5.61 
                 2.10 
               
               
                   
                 2HG (gf/cm) 
                 1.80 
                 11.82 
                 4.14 
               
               
                   
                 2HG5 (gf/cm) 
                 15.22  
                 &gt;20.00 
                 11.60 
               
               
                   
                 Bending Rigidity 
               
               
                   
                 B (gf* cm 2/ /cm) 
                 too stiff 
                 too stiff 
                 too stiff 
               
               
                   
                 2HB (gf* cm/cm) 
                 too stiff 
                 too stiff 
                 too stiff 
               
               
                   
                 Surface 
               
               
                   
                 MIU (−) 
                  .022 
                 0.23 
                 0.27 
               
               
                   
                 MMD (−) 
                 0.23 
                 0.32 
                 0.30 
               
               
                   
                 SMD (micron 
                 14.74  
                 18.08 
                 9.84 
               
               
                   
                 Compression 
               
               
                   
                 LC (−) 
                 0.03 
                 0.03 
                 0.03 
               
               
                   
                 WC (gf* cm/cm 2 ) 
                 0.31 
                 0.13 
                 0.20 
               
               
                   
                 RC (%) 
                 51.04  
                 49.92 
                 53.46 
               
               
                   
                 EMC (%) 
                 40.46  
                 25.60 
                 26.63 
               
               
                   
                 Thickness (mm) 
                 1.01 
                 0.78 
                 0.88 
               
               
                   
                 Weight (oz/yd 2 ) 
                 7.79 
                 6.57 
                 6.56 
               
               
                   
                 Flexural Rigidity 
               
               
                   
                 Overall Rigidity 
                 843.47  
                 738.99 
                 469.05 
               
               
                   
                 Length of Overhang 
               
               
                   
                 Warp (cm) 
                 8/03 
                 7.25 
                 8.75 
               
               
                   
                 Filling (cm) 
                 6.83 
                 7.48 
                 4.78 
               
               
                   
                   
               
            
           
         
       
     
     When evaluating the results in Table 1 please note that a higher EMT value indicates greater extensibility, or that the sample possesses a higher degree of stretchability. A higher G value indicates greater stiffness to the shearing motion (lower G is softer/more pliable). A higher B value indicates greater bending rigidity. A higher SMD value indicates a rougher fabric surface. A higher RC value means a higher percent recovery from being compressed. 
     During the testing, as exhibited by the summary of results of Table 1, the materials were too stiff to bend on a KES bending tester, therefore the reported stiffness results were obtained from the cantilever test. 
     Sample #1, which is heavier and thicker, is more compressible (higher EMC, percent thickness with maximum force compared to initial thickness with no force in compression test). It is least extensible in the tensile test (lowest EMT). It has highest flexural rigidity, which may be expected since it is thicker than the other samples. 
     Sample #3 is smoothest (lowest SMD) but has a little higher surface friction (higher MIU) which may be associated with the greater surface contact of friction probe with a smother surface sample. it is most shearable (lowest G), and has a little edge on other samples in elongation/stretch in the tensile test. It is also judged to be most bendable (lowest flexural rigidity). 
     Sample #2 does not appear to have any outstanding attributes in mechanical hand properties. It has a much higher degree of shearing stiffness (highest G) than the other samples. It is about twice as stiff to bending as the others. 
     The fabric  16  was also tested, again with respect to the same two commercial fabrics, as indicated in Table 2 below. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Sample #1 
                 Sample #2 
                 Sample #3 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Tear Strength 
                 warp 
                 70 
                 75.2 
                 110.8 
               
               
                 ASTM D117 
                 fill 
                 23 
                 24 
                 31.4 
               
               
                 (Trapezoidal) 
               
               
                 Tensile Strength 
                 warp 
                 245 
                 257 
                 315 
               
               
                 ASTM D5034 
                 fill 
                 107 
                 186 
                 115 
               
               
                 Wyzenbeek Abrasion 
                   
                 heavy 
                 heavy 
                 slight 
               
               
                 Resistance 
                   
                 frosting 
                 frosting 
                 frosting 
               
               
                 ASTM D4157 (Wire) 
                   
                 no fiber 
                 no fiber 
                 no fiber 
               
               
                   
                   
                 breakage 
                 breakage 
                 breakage 
               
               
                 Spray Test 
                 orig 
                 50 
                 0 
                 100 
               
               
                 AATCC 22 
                 1x 
                 50 
                 70 
                 100 
               
               
                   
                 3x 
                 50 
                 70 
                 100 
               
               
                 Roughing and Pilling 
                   
                 3 
                 4 
                 4 
               
               
                 ASTM D3512 - modified 
               
               
                 Seam Slippage 
                 w/f 
                 40 
                 43 
                 51 
               
               
                 ASTM D434 
                 f/w 
                 26 
                 51 
                 35 
               
               
                 Brush Pilling 
                   
                 5 
                 3.5 
                 5 
               
               
                 ASTM D3511 
               
               
                 120° F. Wash Shrinkage 
                 warp 
                 −2.80T 
                 −2.13% 
                 −2.60% 
               
               
                 AATCC 135 (1, IV, B) 
                 fill 
                 −0.33% 
                 −0.67% 
                 −2.40% 
               
               
                 Oil Repellancy 
                 orig 
                 4 
                 0 
                 3 
               
               
                   
                 1x 
                 1 
                 0 
                 1 
               
               
                   
                 3x 
                 0 
                 1 
                 0 
               
               
                 Water Drop 
                 orig 
                 7 
                 0 
                 6 
               
               
                   
                 1x 
                 3 
                 0 
                 3 
               
               
                   
                 3x 
                 3 
                 2 
                 5 
               
               
                 Oil after Abrasion 
                 orig 
                 0 
                 0 
                 3 
               
               
                   
                 1x 
                 2 
                 0 
                 0 
               
               
                   
                 3x 
                 0 
                 0 
                 0 
               
               
                 Water after Abrasion 
                 orig 
                 0 
                 0 
                 6 
               
               
                   
                 1x 
                 3 
                 1 
                 3 
               
               
                   
                 3x 
                 1 
                 1 
                 4 
               
               
                 Resistance to Fungi 
                   
                 light 
                 traces 
                 none 
               
               
                 ASTM G-21 
                   
                 (10-30%) 
                 (&lt;10%) 
               
               
                   
               
            
           
         
       
     
     All seam slippage values are for thread breakages (no slippage). The resistance to fungi was tested on slightly different (although not significantly different) versions of the Sample #3 fabric according to the invention. 
     It will thus be seen that the fabric  16  according to the invention has enhanced properties desirable for outdoor product  25  use, including lower shear stiffness, lower overall rigidity, and higher tear and tensile strength, as well as having excellent color durability, resistance to staining after wear abrasion such as with sandpaper, easy cleanability, and faster drying, making the product  25  more resistant to mildew and tending to stay new and fresh appearing for longer periods of time. 
     In the above description, where ranges are recited it is to be understood that the invention encompasses all narrower ranges within the broad range recited. For example the range of 20-40% includes 21-39%, 26-40%, 29-33%, and all other narrower ranges within the broad range. 
     While the invention has been herein shown and described in what is presently conceived to be the most practical and preferred embodiment it will be apparent to those of ordinary skill in the art that many modifications may be made thereof within the scope of the invention, which scope is to be accorded the broadest interpretation of the appended claims so as to encompass all equivalent methods and products.