Abstract:
Known textile flat structures contain precious metal wire or they are composed completely thereof. In order to achieve high flexural and tensile strength, at the same time with high flexibility of the flat structure, the precious metal wire is configured as a precious metal cord having a plurality of cords or a plurality of individual precious metal wires or a combination of cords and individual precious metal wires, which are in each case laid around one another and/or twisted around one another.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Section 371 of International Application No. PCT/EP2013/051177, filed Jan. 23, 2013, which was published in the German language on Aug. 1, 2013, under International Publication No. WO 2013/110626 A1 and the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a sheet fabric which contains precious metal wire and is, in particular, a textile. 
         [0004]    2. Prior art 
         [0005]    The use of precious metal wire for producing knitted fabric, particularly netting of wires containing precious metal, has been known for catalyst applications for a long time. For instance, catalyst gauzes of platinum-rhodium wires having thicknesses between 60 μm and 120 μm are used for the catalysis of the ammonia combustion for nitric acid production. The catalytic action depends on the size of the freely accessible precious-metal surface, but at the same time a gas stream flowing through the catalyst gauze is to encounter a flow resistance that is as low as possible. The occupation density of the gauze having precious metal wire and the wire thickness are here relevant parameters. 
         [0006]    The known catalyst gauzes are made from precious metal wires, for example by machine weaving, knitting or other knitting work. In these manufacturing methods the flexural and tensile strengths and the ductility of the precious metal wires play a limited role. For instance, for knitting wires of specific platinum-rhodium, platinum-palladium-rhodium, palladium-nickel, palladium-copper, and palladium-nickel-copper alloys, only precious metal wires having diameters between 50-120 μm and tensile strengths between 900-1050 N/mm 2  are suited. Thick precious-metal wire reduces the flexibility of the gauze. 
         [0007]    Metal wires or metal threads are also used for many other applications. For instance, gas diffusion layers of textile fabric are used in fuel cells; this fabric is to show a high electrical conductivity and catalytic properties. Wires of platinum or ruthenium can be used for producing the fabric. 
         [0008]    To produce flexible shields against electromagnetic fields, for example in packaging material or in articles of clothing, it is known that copper wires are knitted, woven, machine-knitted, or needled into electrically conductive textile sheet fabrics as electrically conductive contacts. The metal threads used therein must be very thin to ensure flexibility for the textile. They are therefore almost invisible. 
         [0009]    In decoration production, precious metal wire is used for forming decorative elements in textiles and ribbons. To this end a certain thickness of the decorative element is needed to achieve a visual perceptibility and optically decorative effect. Thick threads or wires may however impair the mechanical properties of the sheet fabric, particularly the flexibility thereof. It is also known that metal threads are incorporated as authenticity or security features in banknotes or certificates. 
         [0010]    In the manufacture of the respective sheet fabric and also during its specific application, great forces may act on the metal wire. Therefore, special attention is normally paid to the flexural and tensile strength of the wire, but also to flexibility. These, however, are contradictory demands; it is difficult to satisfy the high demands made on strength and flexibility at the same time. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    It is an object of the invention to provide a sheet fabric which contains or is made of precious metal wire and which satisfies the high demands made on strength and flexibility. 
         [0012]    As for the aforementioned sheet fabric, this object is achieved according to the invention in that the precious metal wire is configured as a precious metal strand, which comprises a plurality of cords or a plurality of individual precious-metal wires or a combination of cords and individual precious-metal wires, which are in each case laid around one another and/or twisted around one another. 
         [0013]    A cord is here a normally loose, but friction- or form-fit combine of at least two, preferably at least four, and particularly preferably at least seven individual precious-metal wires. These individual precious-metal wires are either helically laid around one another and/or twisted around one another, as is generally known from wire and rope production. 
         [0014]    The precious metal strand comprises a plurality of, preferably at least four, particularly preferably at least seven, cords of such types, which are combined in a bundle in which the cords are connected in friction- or form-fit manner, or it comprises individual precious-metal wires or a combination of cords and individual precious-metal wires which are each laid around one another and/or twisted around one another. Particularly preferably, the precious metal strand comprises a bundle consisting of at least two cords that are each formed from a plurality of individual precious-metal wires, which are laid around one another and/or twisted around one another. 
         [0015]    Such a precious metal wire in bundle form—here called precious metal strand—exhibits a high tensile strength, as compared with an individual wire of precious metal having the same radial cross-sectional area, together with an increased flexibility, i.e. less flexural rigidity. These properties are equally observed in the sheet fabrics made from this precious metal strand or containing the precious metal strand. This means that the sheet fabric is more flexible and, as a rule, also firmer at the same precious-metal content—in comparison with a single wire. Moreover, at the same precious-metal content the strand is thicker and has a nobler appearance than an individual wire. 
         [0016]    The precious metal strand consists of precious metal, or it contains a significant proportion (&gt;50% by wt.) of precious metal. “Precious metal” stands here for the elements of the platinum group: Os, Ir, Pt, Ru, Rh, Pd and Ag, Au. The flexibility-maintaining or -increasing effect can also be expected in the case of metal strands consisting of different metals, such as Cu, Fe, Ni, Ti, Co, Cr, Zr, Nb, Mo, Ta, W, Al, and alloys based on these metals, wherein particularly nonferrous metals and special steel should be mentioned. A certain proportion of such metal strands is therefore harmless to the sheet fabric according to the invention. 
         [0017]    The sheet fabric according to the invention is planar or it extends in three dimensional directions and can be made from fibers or wires or may consist of a workpiece shaped as a flat part, into which one or plural precious-metal strands are embedded. Due to its small internal stress these strands do not impair the geometrical shape of the sheet fabric or impair it to an insignificant extent, so that the structure maintains the desired bendability and flexibility, even in the case of a large cross-section of the precious metal strand. 
         [0018]    In a preferred embodiment of the precious metal strand, the cords, just like the individual wires, are either helically laid around one another and/or twisted around one another, as is known from wire rope or rope production. 
         [0019]    In the bundle, one or plural individual precious-metal wires may be incorporated into the precious metal strand apart from the cords. 
         [0020]    In a particularly preferred embodiment, it is provided that the precious metal strand consists of exactly seven cords which are laid around one another and/or twisted around one another, each being formed from exactly seven individual precious-metal wires, which are laid around one another and/or twisted around one another. 
         [0021]    Special-steel wires of such a buildup are known under the names “7×7” strand” or “7×7 strand”. 
         [0022]    As for a flexibility of the sheet fabric that is as high as possible and a surface of the precious metal that is preferably large in catalyst applications, the individual precious-metal wires used for producing the precious metal strands are as thin as possible and advantageously have a diameter ranging from 25 μm to 50 μm, preferably from 30 μm to 40 μm. 
         [0023]    In this context a precious metal strand has turned out to be useful when it comprises an envelope surrounding its radial cross-section and having a diameter in the range of 250 μm to 500 μm, preferably in the range of 300 μm to 400 μm. 
         [0024]    The sheet fabric is, for example, composed of constructional, functional and/or decorative threads which form a woven, knitted or knit-like fabric, embroidery, cording, crocheting, a felt or fulled material or a nonwoven. 
         [0025]    The constructional threads are, for example, the machine-formed threads of knitted or knit-like fabrics, the weft or warp threads in the case of woven fabrics, or possible connection or completion seams. 
         [0026]    Functional threads or decorative threads have a special optical, chemical or physical effect that may differ from that of the remaining threads, for instance in their electrical conductivity, the catalytic effect or their esthetic impression. Decorative threads may, for example, also serve the manufacture of visible seams that fulfill a mere design function. 
         [0027]    All or at least a part of the constructional, functional or decorative threads are formed from the precious-metal strand. 
         [0028]    An optical insertion of precious metal develops its esthetic effect in the sheet fabric only at an adequate thickness. With the thickness, however, internal stress and bending stiffness are also increasing and these may lead to an undesired deformation of the sheet fabric. The use of the precious metal strand according to the invention avoids this drawback, because this strand produces an insignificant internal stress because of its high flexibility, even in the case of thicknesses ensuring an adequate visual recognizability and decorative effect. Furthermore, at the same precious-metal weight one achieves a higher value due to the larger diameter, which in comparison with a wire of a corresponding thickness saves material costs. 
         [0029]    In a preferred embodiment, the sheet fabric is configured as a textile product in which at least a part of the constructional or functional threads consists of glass, ceramics, basalt, carbon, natural fibers, synthetic fibers, or combinations thereof 
         [0030]    The inorganic fibers, such as the fibers explicitly mentioned above that consist of glass, ceramics, basalt or carbon, are often brittle and may be provided with a coating of plastic so as to simplify processing into the textile sheet fabric. Irrespective of the above, it is normally advantageous—when the precious metal strand is used together with such fibers—to embed the textile fiber composite in a completing manner in a plastic matrix or to provide it subsequently with a plastic coat. Sprayable plastics such as epoxy resins, polyetheretherketone (PEEK), polyoxymethylene (POM), or styrene-acrylonitrile (SAN) are especially suited therefor. 
         [0031]    Carbon fibers are commercially available in different diameters. They consist of individual fibers having diameters around 5-8 μm, of which 1000 are each time combined into strands, so-called “rovings.” Roving types of 1K to 12K are particularly suited for use with precious metal strands according to the invention, where K stands for 1000 individual fibers. 
         [0032]    In a particularly advantageous embodiment of the sheet fabric according to the invention, fibers of carbon and/or glass with precious metal strand form a flat textile composite. 
         [0033]    This textile composite stands out for a particularly high strength and flexibility. It can be provided as a dry semi-finished product of fiber composite, for example in roll form. 
         [0034]    For applications where an enhanced bending stiffness or form accuracy of the sheet fabric is of importance, for example in technical shaped parts, the textile composite may also be impregnated with a polymerizable, flowable matrix material, such as a resin. After shaping and curing of the matrix material the desired shaped part is obtained. 
         [0035]    Alternatively, or in addition, the textile composite may also be covered with a film made from a polymerizable matrix material. After shaping and curing the film forms a dense smooth surface layer on the fiber composite. 
         [0036]    With a view to ease of processability, the diameters of the fibers of carbon and/or glass and of the precious metal strand are ideally identical. Deviations of the diameters by not more than 20%, based on the respectively larger one of the two diameters, are however acceptable. 
         [0037]    Textile composites according to the invention of precious metal strand and carbon fibers have turned out to be particularly useful. 
         [0038]    Natural fibers or synthetic fibers, which may also be (spun) threads, preferably consist of linen, hemp, jute, sisal, coconut, cotton, wool, animal hair, silk, viscose, modal, cupro, acetate, polyester, polyamide, polyimide, aramid, polyacrylnitrile, polytetrafluoroethylene, polyethylene, polypropylene, polyvinylchloride, or polyurethane. 
         [0039]    In such a textile product, which is made from different fiber or wire materials, the problem of distortion frequently arises already during production or also in the course of the intended use, if the fibers or wires are too different in their flexibility and bending stiffness. Moreover, when rigid wires are incorporated, this is detrimental to the flexibility of the whole sheet fabric. These difficulties are avoided by the invention, because the flexibility and bending stiffness of the precious metal strand can be easily adapted to the given requirements by way of the bundle form and size. Moreover, the precious metal strand also exhibits high flexibility in the case of a comparatively large cross-section and thereby produces a small internal stress within the textile product. As a result, it can also be processed in combination with fiber or wire materials of an entirely different kind in a reproducible manner into distortion-free flexible textile products. 
         [0040]    In a preferred embodiment, the textile product is configured as a garment. In this case, the precious metal strand only forms a part of the textile and serves, for example, as a functional or decorative element in the form of a thread or a connection, decoration or completion seam. 
         [0041]    As an alternative, the sheet fabric may also be made of paper, leather, fur, plastic, or fiber-reinforced carbon in which the precious metal strand is embedded as a functional or decorative element. 
         [0042]    The sheet fabric is here present as a planar or three-dimensionally shaped workpiece from a flexible base material in which one or plural precious-metal strands are incorporated. In this type of sheet fabric, the above-discussed problem of distortion or loss of flexibility will also arise when wires are incorporated that have a very different bending stiffness in comparison with the base material. The flexibility and bending stiffness of the precious metal strand produces a small internal stress within the sheet fabric and can be adapted through the bundle shape and size in a simple manner to the given requirements. 
         [0043]    In addition, the precious metal strand has, for instance, functions for ensuring the security and genuineness of documents, such as certificates or banknotes, or for meeting optical and esthetic requirements, such as markings or optically appealing embedding in flat constructional parts or as completion or decoration seams in leather or fur articles. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0044]    The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In a schematic representation: 
           [0045]      FIG. 1  is a radial cross-sectional view of a 7×7 precious metal strand according to an embodiment of the invention; 
           [0046]      FIGS. 2 to 4  are cross-sectional views of particularly suited precious metal strands according to further embodiments of the invention; 
           [0047]      FIGS. 5 to 12  are plan views of examples of textile fabric having precious metal strands incorporated thereinto and having different shape and function; 
           [0048]      FIG. 13  is a plan view of a case cover for a mobile phone into which decorative threads of precious metal strand are incorporated according to an embodiment of the invention; and 
           [0049]      FIG. 14  is a plan view of an embodiment of the sheet fabric according to the invention in the form of a leather case having a connection seam and an emblem of precious metal strand. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0050]    The precious metal strand  1  shown in  FIG. 1  consists of 7×7, i.e. 49, individual wires of 18K 5N pink gold, each having a diameter of 35 μm. Seven of these individual wires  2  are respectively combined in a hexagonal arrangement (having internally centered precious metal wire  2   a ) to form a cord  3 , and seven of the cords  3  are bundled in turn also in a hexagonal arrangement (having internally centered cord  3   a ) to form the precious metal strand  1 . 
         [0051]    The precious metal strand  1  is produced with the help of a standard cording machine in that seven individual precious-metal wires  2  are drawn off by a draw-off mechanism from coils and twisted around one another with an adjustable lay length with the help of a rotor into a cord  3 . Seven sub-pieces of the cord  3  produced in this manner are bundled in the same way into the precious metal strand  1 . 
         [0052]    The envelope  4  of the precious metal strand  1  produced thereby, which envelope surrounds the cross-section, has a diameter of 330 μm. Based on the cross section, the precious metal strand  1  shows an excellent flexibility together with a high tensile strength. 
         [0053]      FIG. 2  shows a 1×7 precious metal strand according to the invention in a radial cross-section;  FIG. 3  shows a 1×19 precious metal strand; and  FIG. 4  shows a 3×7 precious metal strand. 
         [0054]    The cross-sectional view of  FIG. 2  schematically shows a precious metal strand having 1×7 design. It consists of seven individual wires helically stranded with one another. This is a particularly simple design of a precious metal strand. 
         [0055]      FIG. 3  schematically shows a 3×7 design of a precious metal strand, consisting of 21 individual precious-metal wires. Seven of these individual wires  2  are respectively combined in a hexagonal arrangement (having internally centered precious-metal wire  2   a ) into a cord  3 , and three of the cords  3  are in turn bundled into the precious metal strand. 
         [0056]      FIG. 4  schematically shows a precious metal strand having 1×19 design. This strand consists of 19 individual precious-metal wires  2  which are combined in a hexagonal arrangement (having internally centered precious-metal wire  2   a ) into a cord  3 . 
         [0057]      FIGS. 5 to 12  schematically show fabric types for which a precious metal strand within the meaning of the invention can be advantageously used with other textile threads. The precious metal strand  51  is shown in all figures in a dark gray hatching; the other textile thread  52  in white color. The precious metal strand  52  is used as a weft thread or as a warp thread or, as shown in the figures at the right side ( FIGS. 6 ,  8 ,  10 , and  12 ), as weft and warp thread. The weft thread direction S and the warp thread direction K are illustrated in all examples in the same manner and with reference to the directional arrows K and S (shown above and to the left in  FIG. 5 ). 
         [0058]      FIG. 5  schematically shows a first embodiment of a simple canvas fabric having precious metal strand  51  as weft thread and warp from other threads  52 . 
         [0059]      FIG. 6  schematically shows a second embodiment of a simple canvas fabric having precious metal strand  51  partly as weft thread and as warp thread, mixed with respectively other threads  52 . 
         [0060]      FIG. 7  schematically shows a fabric 4×4 in a twill weave having precious metal strand  51  as weft thread and warp from other textile threads  52 . 
         [0061]      FIG. 8  also shows a fabric 4×4 in a twill weave having precious metal strand  51  as weft thread and as warp thread, mixed with respectively other threads  52 . 
         [0062]      FIG. 9  also shows a fabric 2×2 in a twill weave having precious metal strand  51  as weft thread and warp from other threads  52 . 
         [0063]      FIG. 10  also shows a fabric 2×2 in a twill weave having precious metal strand  51  as weft thread and as warp thread, mixed with respectively other threads  52 . 
         [0064]      FIG. 11  schematically shows a modification of the fabric shown in  FIG. 9  in 2×2 twill weave. The precious metal strand  51  serves here as weft thread, but lies on a side of the fiber bundle in the warp. The warp threads consist of carbon fibers  52 . 
         [0065]      FIG. 12  corresponds to a modification of the fabric shown in  FIG. 10  in 2×2 twill weave. The precious metal strand  51  serves here as weft and warp thread, but is positioned on a side of the fiber bundle in the warp. The warp threads consist of carbon fibers  52 . 
         [0066]    A few examples of the use of precious metal strands are indicated hereinafter within the scope of the manufacture of a sheet fabric according to embodiments of the invention. 
       EXAMPLE 1 
       [0067]    The precious metal strand  1  is inserted as warp thread into a net-like fabric having weft threads consisting of carbon fibers. The precious metal strand  1  gives the net a high strength with low flexural rigidity. 
       EXAMPLE 2 
       [0068]    The low flexural rigidity can also advantageously be noticed in another use of the precious metal strand  1  according to the invention, namely when used as a decorative or functional element in a textile garment, such as a jacket of synthetic fiber material into which the precious metal strand  1  is incorporated. 
       EXAMPLE 3 
       [0069]      FIG. 13  schematically shows a case cover  110  for a mobile telephone. The cover is designed as a flat, slightly curved component having a bulge  114 . The case cover  110  consists of a mixed fabric of interwoven carbon fibers  111  and precious metal strands  112  of gold wires having an individual wire diameter of 35 μm, which are stranded with one another into a 7×7 strand. 
         [0070]    For the manufacture of the case cover the mixed fabric is embedded into a polymerizable epoxy synthetic resin  113  which fully fills the fiber interspaces and which is transparent after curing. 
         [0071]    After curing, a dimensionally stable component is obtained that still shows a certain elastic flexibility. In the mixed fabric produced according to the fabric type “canvas,” the black carbon fibers  111  and the gold-colored precious metal strand  112  form an optically appealing striped pattern. 
       EXAMPLE 4 
       [0072]    A watch dial has a border and markings for the hour display. It consists of a fiber-reinforced plastic component of carbon fiber fabric into which pink-gold strands are woven. These consist of gold wires, each having a diameter of 50 μm, which are bundled into the form of a 3×7 strand. The pink-gold strands form the border, and the hour markings the dial. The mixed fabric of carbon fibers and pink-gold strands is impregnated with transparent epoxy synthetic resin and cured. 
       EXAMPLE 5 
       [0073]    An eyeglass frame consists of a fiber-reinforced plastic of interwoven precious metal strand from a silver alloy and aramid fibers (Kevlar®). The silver strands have a diameter of 40 μm each and are stranded into a 7×7 strand. The fabric of silver strand and aramid fiber is embedded into a transparent epoxy synthetic resin, as described with reference to Example 4. The silver strand forms an easily recognizable decorative emblem in the temples of the eyeglass frame. 
       EXAMPLE 6   
       [0074]    A decorative strip for use in a car compartment forms a flat curved component. It consists of a fiber-reinforced plastic which is composed of a 7×7 precious metal strand of gold fibers having a fiber diameter of 35 μm and carbon fibers and synthetic resin. The mixed fabric of gold-fiber strand and carbon fiber is embedded into a synthetic resin, as described with reference to Example 4. In the mixed fabric produced according to the fabric type “twill,” the gold-fiber strands form an optically appealing herringbone pattern. 
       EXAMPLE 7 
       [0075]    In the same way as described with reference to Example 4 for a watch dial, an instrument panel for an automotive vehicle is made from a reinforced-fiber plastic component which consists of a carbon fiber fabric into which platinum strands are woven. These consist of platinum wires having a diameter of 25 μm each, which are bundled as 7×7 strand. The platinum strands form the borders and markings of instrument displays. The mixed fabric of carbon fibers and platinum strands is impregnated with transparent synthetic resin and cured. 
       EXAMPLE 8 
       [0076]      FIG. 14  schematically shows a leather case  120  consisting of an upper part  121  and a lower part  122  sewn thereto, each consisting of black leather. The connection seam  123  is made from a precious metal strand of 18K pink gold 5N. The strand consists of individual wires having a diameter of 35 μm; these are stranded with one another into a 7×7 strand. 
         [0077]    The visible seam  123  of precious metal strand decoratively stands out from the black leather. Moreover, an emblem  124  is crocheted into the upper part  121  of the case with the same strand. 
       EXAMPLE 9 
       [0078]    A lighter holder is made from a tubular semi-finished product. The semi-finished product consists of a fiber composite of palladium strand and copper strand. Both the palladium strand and the copper strand are each made from individual wires having a diameter of 50 μm; these are bundled into a 3×7 strand. Precious metal strand and copper strand form a mixed fabric of metal strips of different colors that form a decorative pattern. 
         [0079]    The tubular semi-finished product obtained thereby is supplied on a roll and is bent in a green state—before curing of the synthetic resin—into a tubular sleeve via a mandrel. The sleeve obtained after curing of the synthetic resin matrix has a dense smooth surface and forms a lighter holder in which stripes of silver-colored palladium and reddish-golden copper are alternating in an optically appealing way. 
         [0080]    It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the invention as defined by the appended claims.