Abstract:
An electrically conductive fabric for use in articles of clothing worn for shielding against electromagnetic radiation includes a knit body with a first broad surface and an opposite, second broad surface where at least one of the surfaces includes a fleece or raised surface. The conductive fabric further includes stitch yarns of electrically conductive fibers and loop yarns comprising non-conductive fibers. The non-conductive fibers of the loop yarns are finished upon at least one of the first broad surface and second broad surface to form the fleece or raised surface, with electrically conductive fibers of the stitch yarns being embedded among the non-conductive fibers and between and spaced from the first and the second broad surfaces.

Description:
CLAIM OF PRIORITY  
       [0001]    This application claims benefit from U.S. Provisional Application No. 60/386,179, filed Jan. 25, 2002. The complete disclosures of all of the above-listed patents and patent applications are incorporated herein by reference. 
     
    
     
       TECHNICAL FIELD  
         [0002]    This invention relates to electrically conductive fabrics, and more particularly to electrically conductive fabrics suitable for use in clothing articles worn to provide shielding against electromagnetic radiation (EMI).  
         BACKGROUND  
         [0003]    Human exposure to electromagnetic radiation can be minimized through utilization of an EMI shield. Specially manufactured clothing or fabric comprised of conductive elements can be used to provide such shielding. Shielding can be provided to protect against electromagnetic radiation in clothing by providing the clothing fabric with a metallic coating or metallic electro-chemical deposition, or by incorporating surface-metallized or other conductive fibers into the fabric construction, or by forming the fabric from yarns or threads containing metallic fibers. While articles of fabric may be effective, at varying degrees, at shielding a wearer from EMI radiation, the articles need also be flexible and stretchy rather than too stiff or “boardy”. Such stiff or “boardy” clothing decreases a wearer&#39;s comfort level during wearing.  
         SUMMARY  
         [0004]    In one aspect, the invention features an electrically conductive fabric for use in articles of clothing worn for shielding against electromagnetic radiation. The electrically conductive fabric includes a knit body having two broad surfaces. On at least one of the broad surfaces, there is a fleece or raised surface. The knit body is made up of electrically conductive stitch yarns and non-conductive loop yarns that are knit together to form the body. The non-conductive fibers of the loop yarns are finished upon at least one of the broad surfaces to form the fleece or raised surface. Embedded among the non-conductive fibers are the electrically conductive stitch yarns, which are between and spaced from the broad surfaces.  
           [0005]    In another aspect, the invention features articles of wearing apparel comprising an electrically conductive fabric for shielding a wearer against electromagnetic radiation. The fabric includes a knit body having a first broad surface and an opposite, second broad surface. At least one of the broad surfaces has a fleece or a raised surface. The knit body is formed of stitch yarns and loop yarns where the stitch yarns include electrically conductive fibers and the loop yarns include non-conductive fibers. The non-conductive fibers are finished upon at least one of the broad surfaces to form the fleece or raised surface. The electrically conductive fibers of the stitch yarns are embedded among the non-conductive fibers, the conductive fibers being between and spaced apart from the broad surfaces.  
           [0006]    Implementations of these aspects of the invention may include one or more other features. For example, the loop yarns may overlap the stitch yarns on both the broad surfaces of the knit body forming a barrier of non-conductive material about the stitch yarn. By forming this protective barrier of non-conductive material, each of the broad surfaces can be finished to form the fleece or raised surface on both broad surfaces of the fabric body. Additionally, the stitch yarn may also comprise non-conductive fibers, including stretchy materials, to allow for varying distributions of electrically conductive elements along the knit body. The fleeced surface may also be formed upon the knit body in a manner to avoid damage to conductivity performance of the electrically conductive fibers of the stitch yarn.  
           [0007]    Additional implementations may include electrically conductive fibers of various materials including conductive, continuous filaments, staples, stainless steel fibers, silver-coated nylon yarns, polyester fibers, silver-embedded fibers and/or Nano-tube carbon particle-embedded fibers. The denier of the loop yarns and stitch yarns may also vary. The loop yarn may include spun yarns having a denier between about 40 denier to 300 denier. The stitch yarn may include a spun yarn or a filament yarn having a denier between about 50 denier to 150 denier. The stitch yarn may also include various stretchy materials such as spandex, for example, providing added comfort.  
           [0008]    Further implementations may include varying additional parameters of the fabric body. For example, the conductive fibers can have a resistivity between about 10 &#39; to 10 9  ohms/cm and/or the conductive fibers may only be used as the stitch yarn. Also, the number of conductive elements per unit length may vary depending on the particular application, for example, the fabric body may have 20 conductive fibers per centimeter. In addition to the spacing of conductive elements, it may be preferable, depending on the application, to position the fabrics in either a symmetrical pattern and/or an asymmetrical pattern along at least a portion of the fabric body. By varying at least one of the parameters noted above, a fabric body can be created that is tailored to a particular application.  
           [0009]    Implementations of aspects of the invention may also include finishing the loop yarns to create the fleece or raised surface by employing certain methods including napping, sanding, and/or brushing, as examples. Preferably, the fabric is formed using standard reverse plaiting circular knitting. Additionally, the conductive fabric can be treated to render the fabric, for example, either hydrophilic or hydrophobic. Furthermore, the conductive elements may form a mesh to provide an electrical connection between conductive fibers and/or the conductive fabric may include buses that connect conductive fibers. The buses may be formed of stitching of conductive yarn and/or of a narrow conductive fabric, as examples. The buses may be attached by, for example mechanical fasteners, such as snaps and/or the buses may be attached by stitching. The buses may be formed along edge regions of the fabric body and/or they may be spaced-apart along the body of the fabric.  
           [0010]    The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
       
    
    
     DESCRIPTION OF DRAWINGS  
       [0011]    [0011]FIG. 1 is a perspective view of an electrically conductive fabric of the invention particularly suited for use in clothing articles worn for personal protection or shielding against electromagnetic radiation (EMI).  
         [0012]    [0012]FIG. 2 is a somewhat diagrammatic perspective view of an article of clothing, in this embodiment, a coverall, formed of electrically conductive fabric of the invention, to be worn for personal protection, i.e., shielding, against electromagnetic radiation (EMI).  
         [0013]    [0013]FIG. 3 is a similar view of articles of clothing, in this embodiment, pants and a shirt, formed of electrically conductive fabric of the invention, to be worn for personal protection, i.e., shielding, against electromagnetic radiation (EMI).  
         [0014]    [0014]FIG. 4 is an end section view of the electrically conductive fabric of the invention, taken at the line  4 - 4  of FIG. 1.  
         [0015]    [0015]FIG. 5 is a side section view of the electrically conductive fabric of the invention, taken at the line  5 - 5  of FIG. 1.  
         [0016]    [0016]FIG. 6 is a perspective view of a segment of a circular knitting machine, and FIGS.  7 - 13  are sequential views of a cylinder latch needle in a reverse plaiting circular knitting process, e.g., for use in forming an electric heating/warming composite fabric article of the invention.  
         [0017]    [0017]FIGS. 14 and 15 are somewhat diagrammatic perspective views of other embodiments of the electrically conductive fabric of the invention. 
     
    
       [0018]    Like reference symbols in the various drawings indicate like elements.  
       DETAILED DESCRIPTION  
       [0019]    This patent application is related to U.S. application Ser. No. 09/296,375, filed Apr. 22, 1999; U.S. application Ser. No. 09/395,326, filed Sep. 13, 1999 (now U.S. Pat. No. 6,160,248, issued Dec. 12, 2000); U.S. application Ser. No. 09/468,627, filed Dec. 21, 1999 (now U.S. Pat. No. 6,215,111, issued Apr. 10, 2001); and U.S. application Ser. No. 09/703,089, filed Oct. 31, 2000; the complete disclosures of all of which are incorporated herein by reference.  
         [0020]    Referring to FIGS.  1 - 3 , the invention relates to an improved electrically conductive fabric  10  particularly suited for use in clothing, e.g., coveralls  12  (FIG. 2) or pants  14  and shirt or blouse  16  (FIG. 3), worn to provide personal protection or shielding against electromagnetic radiation (EMI).  
         [0021]    Referring next to FIGS. 1, 4 and  5 , the improved electrically conductive fabric  10  of the invention, suitable for use in clothing to be worn for personal protection or shielding against electromagnetic radiation (EMI), consists of a fabric body  20  formed, e.g., by reverse terry circular knitting with electrically conductive elements  22  incorporated into the fabric as the stitch yarn and extending generally between edge regions  24 ,  26  of the fabric to provide shielding. Non-conductive yarns  28  are incorporated as stitch yarn  40  and loop yarn  42 , the loop yarns overlaying the stitch yarns at the technical face  30  and forming loops  44  (FIG. 7) at the technical back  32  of the fabric body  20 . The fibers of the non-conductive yarns  28 , preferably of the loop yarn  42 , are then napped at the technical face  30  and technical back  32  to form a layer of fleece  46 ,  48  at each face, which keeps the electrically conductive shielding elements  22  away from the wearer&#39;s skin, including for enhancement of wearer comfort, and also protects the electrically conductive elements  22  from physical abrasion. According to the invention, the napping of fibers of non-conductive yarns  28  at the technical face  30  and technical back  32  is also performed in a manner to avoid damage to the conductivity of the electrically conductive elements  22 . In preferred embodiments, the electrically conductive elements  22  of the stitch yarn  40  may be continuous filaments or may be a blend of staples (conductive or conductive and nonconductive) of relatively short length, e.g., stainless steel yarn/fibers, silver-coated nylon yarns, or polyester or other synthetic fibers with silver or Nano-tube carbon particles embedded therein. An example is BEKITEX® textile yarn made out of nylon fibers and stainless steel fibers, available from N. V. Bekaert S. A., of Zwevegem, Belgium.  
         [0022]    Referring also to FIGS.  6 - 13 , in a preferred embodiment, the fabric body  20  is formed by joining a stitch yarn  40  and a loop yarn  42  in a standard reverse plaiting circular knitting (terry knitting) process, e.g. as described in “Knitting Technology,” by David J. Spencer (Woodhead Publishing Limited, 2nd edition, 1996), the entire disclosure of which is incorporated herein by reference. Referring again to FIGS. 1, 4, and  5 , in the terry knitting process, the stitch yarn  40  forms the technical face  30  of the resulting fabric body  20  and the loop yarn  42  forms the opposite technical back  32 , where it is formed into loops  44  extending over the stitch yarn  40 . In the fabric body  20  formed by reverse plaiting circular knitting, the loop yarn  42  is preferentially exposed outwardly from the planes of both surfaces  30 ,  32  and, on the technical face  30 , the loop yarn  42  covers the stitch yarn  40 . As a result, during napping of the opposite fabric surfaces to form a fleece, the loop yarn  42  protects the electrically conductive elements  22  knitted into the fabric body  20  in the stitch yarn position.  
         [0023]    The loop yarn  42  forming the technical back  32  of the knit fabric body  20  can be made of any synthetic or natural material. The cross section and luster of the fibers or the filament may be varied, e.g., as dictated by requirements of the intended end use. The loop yarn  42  can be a spun yarn made by any available spinning technique, or a filament yarn made by extrusion. The loop yarn denier is typically between 40 denier to 300 denier. A preferred loop yarn is a 200/100 denier T-653 Type flat polyester filament, e.g. as available commercially from E. I. duPont de Nemours and Company, Inc., of Wilmington, Del.  
         [0024]    The stitch yarn  40  forming the technical face  30  of the knit fabric body  20  can be also made of non-conductive yarn, such as synthetic or natural materials in a spun yarn or a filament yarn. The denier is typically between 50 denier to 150 denier. A preferred yarn is a 70/34 denier filament textured polyester, e.g. as available commercially from UNIFI, Inc., of Greensboro, N.C.  
         [0025]    The resistivity of the electrically conductive elements  22  can be selected in the range, e.g., of from about 10 3  ohms/cm to about 10 9  ohms/cm on the basis of end use requirements of the fabric  10 . However, electrically conductive elements  22  performing outside this range can also be employed, where required or desired.  
         [0026]    As mentioned above, in a preferred method of the invention, the fabric body  20  is formed by reverse plaiting on a circular knitting machine. This is principally a terry knit, where the loops formed by the loop yarn  42  cover the stitch yarn  40  on the technical face  30 . The electrically conductive elements  22  are incorporated into the knit fabric body  20  formed on the circular knitting machine at a predetermined spacing or distance apart, D (FIG. 5). In a fabric body  20  of the invention, the spacing, D, is typically a function, e.g., of the requirements of EMI shielding desired in the clothing articles to be formed. For example, the spacing of electrically conductive elements  22  may be the range of about 0.02 inch (i.e., with about  50  electrically conductive elements/inch or about  20  electrically conductive elements/cm). However, other spacing may be employed, depending on the conditions of intended or expected use, including the conductivity of the electrically conductive elements  22 . The electrically conductive elements  22  may be spaced symmetrically from each other, or the electrically conductive elements  22  may be spaced asymmetrically, with varying spacing, if desired.  
         [0027]    Also as mentioned above, a preferred position of the electrically conductive elements  22  is in the stitch position of the circular knitted construction. The electrically conductive elements  22  may then be knit symmetrically, i.e., at a predetermined distance, D, apart, in each repeat, i.e., the electrically conductive elements  22  can be in stitch position at any feed repeat of the circular knitting machine. If desired, e.g., in order to maximize EMI shielding, the electrically conductive elements  22  may be used entirely as the stitch yarn  40 . Alternatively, the feed position may be varied, and the electrically conductive elements  22  may be knit asymmetrically, with the elements more closely or widely spaced, e.g., as desired or as appropriate to the intended product use. Again, the specific number of feeds, and the spacing of the electrically conductive elements  22 , is dependent on the end use requirements.  
         [0028]    Furthermore, the shielding provided by the fabric at a given electromagnetic frequency can be optimized by varying certain parameters such as the conductivity of the conductive elements, the gauge of the knitting machine and the distribution of the conductive elements in the fabric construction. For example, the resistivity of the conductive elements can be varied between 10 3  ohms/cm to 10 9  ohms/cm and/or the gauge of the knitting machine can be varied between 12 to 40. As noted above, the distribution of the electrically conductive elements may be symmetrical or asymmetrical, depending on the end use requirements. Additionally, the spacing of the electrically conductive elements may be increased or decreased. By varying knitting parameters, an EMI shielding fabric, such as an article of clothing, can be created having varying shielding effects along the fabric body.  
         [0029]    Preferably the knitted fabric body  20  incorporating the electrically conductive elements  22  is next subjected to finishing. During the finishing process, the fabric body  20  may go through processes of, e.g., sanding, brushing, napping, etc., to generate a fleece  46 ,  48 . The fleece  46 ,  48  may be formed on one face of the fabric body  20 , e.g., on the technical back  32 , in the loop yarn  42 , or, preferably, a fleece  46 ,  48  may be formed on both faces of the fabric body  20 , including on the technical face  30 , in the overlaying loops  44  of the loop yarn  42  and/or in the stitch yarn  40 . In either case, the process of generating the fleece  46 ,  48  on the face or faces of fabric body  20  is preferably performed in a manner to avoid damage to the electrically conductive elements  22  that are part of the construction of the fabric body  20 . In particular, the fleece  46 ,  48  is formed in a manner that avoids damage to the electrically conductive elements  22  that would result in a reduction in conductivity, or would sever the electrically conductive elements  22  completely, which could result in loss of electrical flow, and shielding, in a region of the clothing. The fabric body  20  may also be treated, e.g., chemically, to render the material hydrophobic or hydrophilic.  
         [0030]    Referring to FIG. 14, electrical connection between electrically conductive elements  22  may be provided by formation of buses  50 ,  52  along the edge regions  24 ,  26  of the fabric body  20  and/or spaced-apart in the body, e.g., as described in Rock et al. U.S. Pat. 6,373,034, issued Apr. 16, 2002, the complete disclosure of which is incorporated herein by reference, and/or by joining of elements of fabric  20  at clothing seams, e.g., as described in Dordevic U.S. Pat. No. 5,103,504. The buses  50 ,  52  may be formed by stitching a conductive yarn along the body to connect the conductive elements, or a bus element, e.g. a narrow strip of conductive fabric, may be attached to the fabric, e.g. with mechanical fasteners, such as snaps, or by stitching. Referring to FIG. 15, the electrically conductive elements may also have the form of a mesh or grid  200 , preferably with electrical interconnection achieved at intersections  202  of warp and weft electrically conductive elements  204 ,  206 , respectively, in the fabric body  20 ″.  
         [0031]    A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, the textile structure can contain a stretchy material, such as spandex, as an example, in the stitch yarn at various predetermined spaced-apart locations throughout the fabric to further improve the comfort level. Further, any type of yarn may be employed.