Abstract:
Synthetic plastic fibers are enhanced by inclusions therein of micro-polyester particles ( 4 ), preferably sized or otherwise optimized to enhance surface ( 10 ) characteristics (abrasion resistance, hydrophilicity, coating receptiveness, increase dullness), reduce UV degradation. The synthetic plastic matrix is preferably polyester but can be any synthetic plastic. The invention is preferentially implemented in multi-component fibers (e.g. core ( 6 )-sheath ( 8 ) bi-component fibers ( 3 )) with the inclusions entirely or primarily in one or some, but not all such components. The PTFE inclusions, sizing, concentration, morphology can be adjusted to optimize their enhancing effects, reduce costs and enhance throughput of fiber production. Co-inclusions can be made with the PTFE including anti-microbial and/or coloring agents and with synergistic effects.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 60/495,583 filed Aug. 15, 2003, the contents of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     Synthetic fibers have been produced with various additives to achieve certain characteristics, such as pigment additives to obtain desired colors. Certain polymers present difficulties, however, in achieving optimal performance. Many polyesters such as, for example, PET (polyethylene teraphthalate), have poor ultraviolet (UV) resistance characteristics and are hydrophobic. Many PET polymers also suffer from poor abrasion resistance and have a tendency to pill during abrasion.  
       SUMMARY OF THE INVENTION  
       [0003]     Synthetic fibers such as polyester, polyolefins (e.g., polypropylene), nylon, acrylics and others in either mono-component or multi-component matrix configurations (e.g., core/sheath, two side-by-side or pie-wedge forms) can be significantly improved by the inclusion (or micro-inclusions) therein of PTFE (polytetrafluoroethylene) of appropriate particle sizes to improve UV resistance, increase the dullness (reduce sheen), modify the surface of the fibers to improve hydrophilicity, improve abrasion resistance, and as a processing aid to increase production outputs. In multi-component configurations, the PTFE inclusions may be incorporated into one, some or all of the components comprising the enhanced fiber. In core-sheath bi-component configurations, the PTFE particles are substantially all included in the sheath component so as to assure particle presence at or near the external surface of the fiber in order to obtain the optimum desired effect. It is also preferred to dimension the thickness of the sheath in such configurations to approximate the inclusion size.  
         [0004]     The present invention provides in various aspects the enhanced fibers themselves and woven and non-woven fabrics (and other derivatives) composed at least in part of the fibers, and methods of making the same.  
         [0005]     Methods in accordance with the present invention generally involve adding the PTFE particles to the PET or other synthetic plastic matrix fiber, but preferably concentrate the added PTFE particles near the fiber surface. The fibers may be produced by extrusion or other processes that result in striations and other voids at the fiber surface. This structure, together with the presence of the PTFE particles proximate the fiber surface, favors hydrophilicity, stain and water resistance and enhanced substrate conditions for bonding coatings mechanically and chemically, particularly PTFE coatings. Through these techniques, enhancement of fiber and/or fabric dullness and resistance to abrasion can be achieved.  
         [0006]     The concentrations, sizing, and regional placement (in a fiber and/or fabric) of inclusions are controllable during production to reduce UV degradation of the fibers and/or at a minimum the components of the multi-component fibers incorporating the inclusions. The enhancement of UV resistance by the composite fiber is enhanced when the PTFE particles have at least one cross-sectional length dimension about equal to a materially important wavelength (one responsible for UV degradation) within the UV spectral region (˜10-400 nm.) The UV resistance effects are enhanced when PTFE and inorganic pigment particles (e.g., titanium dioxide) are provided as co-inclusions.  
         [0007]     The present invention enhances the suitability of polyester fibers for such applications as convertible tops (as well as similar tops for boats, umbrellas, awnings, fabric shades as well as vehicle interiors), automobile carpeting and other similarly challenging carpeting, clothing (due to reduced sheen and wicking properties, making polyester fibers competitive with natural fibers) and like fabric applications such as table cloths and bedding, curtains. The PTFE particle sizing is preferably 0.1 to 1.0 μm for UV resistance, but on the order of 5-20μ (preferably about 15μ) for some of the heavy duty carpeting applications. The particles are preferably spherically or nearly spherically shaped when employed to enhance UV resistance. The enhanced fibers can be staple fibers or mono-filaments.  
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0008]     Other objects, features and advantages will be apparent from the following detailed description of preferred embodiments taken in conjunction with the accompanying figures, wherein:  
         [0009]      FIGS. 1-3C  are cross-section views of mono-component fibers and certain exemplary but non-limiting types of multi-component fibers, illustrating certain aspects of the invention;  
         [0010]      FIG. 4A  is a photomicrograph showing a PET upper fiber control and a PET lower fiber with PTFE inclusions visible at the surface; and  
         [0011]      FIG. 4B  is a photomicrograph showing the same control PET and PET/PTFE fibers tested for abrasion under similar conditions with better durability evident for the PET/PTFE fiber. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0012]     The present invention provides synthetic fibers enhanced with PTFE and fabrics made from same, as well a methods for producing the enhanced fibers.  
         [0013]     By adding fine particles of PTFE to a polymer such as, for example, polyesters (e.g., PET), polyolefins (e.g. polypropylene), nylon and acrylics during a melt stage of an extrusion or other melt stage, or by other means without melting, UV resistance and other properties of the fiber can be improved significantly. Selecting for introduction into the polymer PTFE particles in a range of size such that the particle size is in the range of the wavelength of the UV light to be resisted enhances the fiber&#39;s ability to withstand UV-induced degradation.  
         [0014]     Experiments were conducted to demonstrate this enhanced resistance to UV. Typical PET starts to degrade at 250 kilojoules (kJ) of exposure. PTFE particles in the range of 0.2 to 0.5 μm (microns) were added to the PET in the range from about 0.8 to about 2.5% by weight. At 2 wt-% (% by weight of the fiber) PTFE, UV stability in excess of 1200 kJ was achieved (far in excess of the most stringent automotive requirements). Although mono-component fiber  2  having PTFE inclusions  4  therein, such as illustrated in  FIG. 1 , performs extremely well, employing a bi-component configuration (such as illustrated in  FIG. 2A ) wherein the PTFE inclusions  4  are contained in a sheath  8  surrounding a core  6  comprising 40 wt-% of the fiber, the quantity of PTFE required to achieve the same effectiveness was reduced to 0.8 wt-%, corresponding to a 60% reduction in cost for the same performance. It should be noted that exact adherence to the values provided here are not required to produce an effective PTFE-enhanced synthetic fiber.  
         [0015]     Tests were also performed with no PTFE inclusions. By adding PTFE, in conjunction with inorganic pigments, such as titanium dioxide, the UV resistance was enhanced by 20-50%, providing a fiber superior to all other synthetic fibers with respect to this desirable property. Applications for such enhanced fibers include: convertible tops, awnings, outdoor furniture, automotive fabrics, instrument panels, marine fabrics, and the like.  
         [0016]     From an aesthetic viewpoint in addition to technical reasons, it is desirable to produce fibers with a dull appearance that do not appear to reflect light or to be shiny. By adding PTFE particles of nominal size from about 0.2 to 0.5 microns, a fiber with a very dull appearance was produced. The fibers ranged from 0.5 to 3 wt-% PTFE. Once again, the mono-component fiber was acceptable, but by using the core/sheath bi-component approach with the sheath  8  ranging from 20 to 60 wt-%, a significant cost reduction can be obtained. Further, by approximately matching the thickness of the sheath  8  and the dimension of the PTFE particles, even higher efficiencies could be obtained.  
         [0017]     By adding PTFE to the sheath  8  of a core/sheath fiber  3 , the external surface  10  of the fiber  3  is modified (with cracks or striations  12  on the sheath  8 ) to enhance hydrophilic properties. These “cracks” or striations improve the ability to wick moisture along the length of the fiber (i.e., roughly normal to the cross-sectional view of the fiber presented.) Fibers were produced in the range from about 0.8 to 20 denier with a sheath from 20 to 60%-wt. The best results occurred using PTFE nano-particles in that range of 0.1 to 0.5 microns. The concentration in the sheath of the PTFE ranged from 0.3 to 5 wt-%.  
         [0018]     When using other additives in the fibers, such as silver, copper, or zinc as antimicrobial particles, it is desirable to create striations in the surface that will allow the antimicrobial particles to have greater surface exposure. This is optimized by manufacturing a core/sheath fiber that has both antimicrobial and PTFE particles restricted to the sheath  8 . Tests were performed in which sheath component ranged from 30 to 70 wt-% of the fiber. In the case of silver in a dissolvable glass, the rate of silver release was enhanced four-fold making it ideal for applications in bandages for direct wound care. The fibers can be made into woven and non-woven fabrics usable as wipes to combat germs and mildew on walls, furniture and utensil surfaces. The present invention overcomes the tendency of PET to flow over antimicrobial particles and form a skin, limiting release. The cracks or striations of the PET/PTFE enhance the release of the anti-microbial additives without gross, excessive release.  
         [0019]     Some previously developed fibers exist that have been superficially treated with a wide range of PTFE coatings such as Teflon® and Scotchguard®, but such fibers usually suffer from poor durability after repeated washings or exposure to rain and the elements. By adding PTFE particles to a polymer melt for example, during an extrusion or co-extrusion process, chemical bond sites at the striations are made available for the external PTFE coatings to adhere to, in order to improve the coating bonding. Manufacturing processes for forming mono-component and multi-component fibers such as those described in U.S. Pat. No. 6,723,428 may be employed in forming the PTFE-enhanced fibers of the present invention.  
         [0020]     Applications of PTFE-enhanced fibers include apparel, convertible tops, awnings and other fabric usages stated above, which are attributable to the enhanced competitiveness of PET-based fabrics in comparison to natural fabrics, acrylic and nylon. PTFE particles ranging from 0.2 to 15 microns were tested with excellent results. While mono-component fibers perform satisfactorily, greater efficiency and effectiveness has been achieved in bi-component fiber configurations of the core/sheath type, especially when the thickness of the sheath closely matched the PTFE particle size. The PTFE particles may be fully included as in the mono-component fiber configuration of  FIG. 1  (with homogeneous inclusions or gradation thereof, lightest at the center.) Alternatively, the PTFE particles may be included in one or more of the components  14 , 16  in multi-component fiber configurations, such as the bi-component fibers illustrated in  FIGS. 2B-2C . Note that the term bi-component embraces the core/sheath configuration as well as side-by-side fiber configurations, and that the PTFE inclusions  4  may be restricted to one component and/or be interspersed with other additives, such as anti-microbial particles  18  and/or other particles  20 , such as inorganic pigments, flame retarding particles, and the like. Either or both of the components  14 , 16  may also be composed of PET or another polymer such as described above.  
         [0021]     With reference to  FIGS. 3A-3C , enhanced fibers in accordance with the present invention may take a variety of shapes and be comprised of more than two components. Fibers can be extruded as ovals ( FIG. 3B ) or even as flat ribbons ( FIG. 3C ) and indeed the invention can be applied to sheet forms of plastics including laminates. Enhanced fibers of the invention and woven or non-woven fabrics thereof can be integrated with film. Enhanced fibers of the invention can be mixed with non-enhanced fibers or fibers of different degrees of enhancement in some applications for example, to design an article having greater UV resistance and/or abrasion resistance in one portion than another.  
         [0022]     Testing demonstrated that incorporating larger PTFE particles (5-15 microns) in a fiber dramatically improves the abrasion resistance of the fiber. Non-woven carpets were produced that were made from PTFE-enhanced polyester fibers. These fibers exhibited anti-abrasion characteristics 30-50% greater than untreated polyester. When these fibers were then blended with polyester in a ratio of 70 wt-% PTFE-enhanced PET and 30 wt-% PP (polypropylene), test results demonstrated an additional 20% performance improvement. The preferred embodiments employed a core-sheath configuration wherein the sheath thickness was roughly 1.7 times the nominal PTFE particle size to concentrate the particles at or near the external surface of the sheath. For example, if 10 micron particles were to be employed, a sheath thickness of between 15 and 20 microns was most suitable. The net result were carpets that exceeded the performance of standard tufted nylon carpets with an approximate 25% cost savings. The total combination of stain resistance and abrasion resistance will make a commercial carpet that can withstand adverse conditions in high traffic areas.  
         [0023]     The PTFE additive can be used in all synthetic fibers such as nylon, polyester, polypropylene, and acrylic. Polyester showed the greatest improvement and durability because it has relatively low raw material costs and is compatible with most product applications. Deniers can range from 0.8 to 60 denier with cut lengths from 7 mm. to 180 mm.  
         [0024]     It will now be apparent to those skilled in the art that other embodiments, improvements, details, and uses can be made consistent with the letter and spirit of the foregoing disclosure and within the scope of this patent, which is limited only by the following claims, construed in accordance with the patent law, including the doctrine of equivalents.