Patent Publication Number: US-2006013990-A1

Title: Textile product comprising metal cords and non-metallic fibers, and a semifinished sheet comprising such textile product

Description:
The right of priority is claimed under 35 U.S.C. § 119 based on U.S. Provisional Ser. No. 60/577,198 filed Jun. 7, 2004, and European Application No. 04 102 533.9 filed Jun. 4, 2004, the entire contents of both applications, including the specification, drawings, claims and abstract, are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION  
      The invention relates to a textile product comprising metal cords and non-metallic fibers, and to a semifinished sheet comprising such textile product, which sheet may be molded into high impact resistant parts.  
     BACKGROUND OF THE INVENTION  
      Impact resistant molded parts, for example bumper beams, are usually made by molding semifinished sheets comprising a thermoplastic polymer matrix and reinforcing fibers, especially unidirectional glass fiber roving or glass fiber woven fabrics. It has turned out, however, that in many cases such parts are not sufficiently impact resistant, especially at high speeds.  
      Attempts have been made to introduce into molded parts additional reinforcements, for example metal elements such as steel cords.  
      U.S. Pat. No. 5,290,079 describes a bumper beam, the walls of which are formed from a thermoplastic resin having encapsulated glass fibers, and optionally containing a reinforcing web of ductile metal strands. Such bumper beams require the provision of an expensive two dimensional metal grid.  
      Similarly, WO 03/076 234 A1 describes an impact beam comprising a polymer matrix and metal cords. The polymer matrix may contain glass fibers which can be random, chopped, unidirectional, even present as a woven fabric, or a combination of those. In a preferred embodiment a polymer matrix sheet and metal cords or cord tapes are directly molded together to form the impact beam.  
      US 2002/0182961 A1 describes a fabric comprising steel cords and a thermoplastic polymer material, and optionally further comprising glass fibers. In one embodiment the steel cords in the fabric are arranged parallel. Shaped articles can be made from such fabric for example by a press forming process.  
      It has turned out, however, that in press forming processes, parallel steel cords become distorted so that they lose their parallel arrangement, or migrate along with the flowing polymer to positions in the produced polymer article, where the presence of the cords was not intended. This migration and distortion results in drastically decreased mechanical properties of the shaped article. The uncontrolled flow of the steel cords further leads to parts with very low production consistency, which does not allow the use of such parts for an industrial mass production.  
     SUMMARY OF THE INVENTION  
      It is a subject of the present invention to provide a textile product comprising metal cords and non-metallic fibers which overcomes the disadvantages of prior art. It is a subject of the present invention to provide a textile product which, when used as reinforcing element of a press molded polymer article, reduces or solves the problem of migration of the cords during pressing.  
      It is further a subject of the present invention to provide a semifinished sheet comprising textile product comprising metal cords and non-metallic fibers which overcomes the disadvantages of prior art. It is a subject of the present invention to provide a semifinished sheet comprising a textile product, which sheet when used as reinforcing element of a press molded polymer article, reduces or solves the problem of migration of the cords during pressing.  
      A textile product as subject of the invention comprises metal cords and at least one layer of non-metallic fibers. The textile product is characterized in that the metal cords are bond to this layer of non-metallic fibers by means of stitches.  
      The stitches may be provided by sewing the cords to the layer of non-metallic fibers, e.g. by using embroidering processes. Alternatively the stitches may be provided by knitting through the layer of non-metallic fibers, e.g. as when one use the Malimo- or Arachne production processes.  
      The layer of non-metallic fibers may be a woven, non-woven or knitted fabric of non-metallic fibers.  
      Alternatively, essentially parallel bundles of fiber roving or tapes or tows of essentially parallel non-metallic fibers may be used as a layer of essentially parallel fibers replacing the nonwoven or other textile fabric in an Arachne-process.  
      The term “textile fabric” is to be understood as a manufactured essentially planar structure made of fibers and/or yarns assembled by various means such as weaving, knitting, tufting, felting, braiding, or bonding of webs to give the structure sufficient strength and other properties required for its intended use.  
      The term “textile product” is to be understood as a combination of one or more textile fabrics and/or yarns, which are mechanically and/or chemically connected to each other, but which product has properties similar to properties of textile fabrics.  
      Possibly, additional bundles of fiber roving, the tapes or tows of essentially parallel non-metallic fibers may be linearly mixed with the metal cords. This mix of non-metallic fibers and metal cords are stitched or knitted to at least one layer of non-metallic fibers.  
      Alternatively, bundles of fiber roving, the tapes or tows of essentially parallel non-metallic fibers, providing the at least one layer of non-metallic fibers in the textile product, may be crosswise bonded to the metal cords. As an example the orientation of the metal cords may differ 90° of the orientation of the bundles of fiber roving, the tapes or tows of essentially parallel non-metallic fibers. Possibly, additional bundles of fiber roving, the tapes or tows of essentially parallel non-metallic fibers may be linearly mixed with the metal cords, which mix is then crosswise bonded to the bundles of fiber roving, the tapes or tows of essentially parallel non-metallic fibers of the layer or layers of non-metallic fibers.  
      As an example, the metal cords my be provided as warp and/or weft inlay in a warp knitted textile fabric, being the textile product as subject of the invention.  
      The non-metallic fiber layer may be provided as essentially parallel bundles of fiber roving or tapes or tows of essentially parallel non-metallic fibers, provided as inlay in the direction perpendicular to the metal cords in this warp knitted fabric.  
      A textile product as subject of the invention has as an advantage that, when it is used to provide a polymer article comprising such textile product, the metal cords are held in place during the press molding process. They don&#39;t tend to distort or migrate along with the molten polymer material.  
      The metal cords may be present all essentially parallel to each other, or as two or more groups of metal cords, all cords of a group being essentially parallel to each other. The metal cords of the first group may be inclined in regard to the metal cords of the second group over an angle θ, which is preferably in the range of 10 to 170°, such as, as an example 90°.  
      The metal cord preferably used for an impact beam as subject of the invention, are of a type which can absorb relatively high amounts of impact energy but also other metal cords may be used.  
      Examples here are: 
          multi-strand metal cords e.g. of the m×n type, i.e. metal cords, comprising m strands with each n wires, such as 4×7×0.10 or 3×3×0.18; the last number is the diameter of each wire, expressed in mm.     compact cords, e.g. of the 1×n type, i.e. metal cords comprising n metal wires, n being greater than 8, twisted in only one direction with one single step to a compact cross-section, such as 1×9×0.18 or 1×12×0.18; the last number is the diameter of each wire, expressed in mm.     layered metal cords e.g. of the l+m (+n) type, i.e. metal cords with a core of l wires, surrounded by a layer of m wires, and possibly also surrounded by another layer of n wires, such as 2+4×0.18; the last number is the diameter of each wire, expressed in mm.     single strand metal cords e.g. of the 1×m type, i.e. metal cords comprising m metal wires, m ranging from two to six, twisted in one single step, such as 1×4×0.25; the last number is the diameter of each wire, expressed in mm.     Open metal cords e.g. of the m+n type, i.e. metal cords with m parallel metal wires surrounded by n metal wires, such as disclosed in U.S. Pat. No. 4,408,444, e.g. a metal cord 2+2×0.25; the last number is the diameter of each wire, expressed in mm.        

      All cords as described above can be equipped with one or more spiral wrapped wires to increase the mechanical bond of the cords in the polymer matrix, and/or to bundle the n single parallel crimped or non-crimped but plastically deformed wires if the cord is provided using such parallel wires.  
      Preferably however, the metal cord used in the context of the present invention may be a metal cord with a high elongation at fracture, i.e. an elongation exceeding 4%, e.g. an elongation between 5% and 10%. High elongation metal cord has more capacity to absorb energy.  
      Such a metal cord is: 
          either a high-elongation or elongation metal cord (HE-cords), i.e. a multi-strand or single strand metal cord with a high degree of twisting (in case of multi-strand metal cords: the direction of twisting in the strand is equal to the direction of twisting of the strands in the cord: SS or ZZ, this is the so-called Lang&#39;s Lay) in order to obtain an elastic cord with the required degree of springy potential; an example is a 3×7×0.22 High Elongation metal cord with lay lengths 4.5 mm and 8 mm in SS direction;     or a metal cord which has been subjected to a stress-relieving treatment such as disclosed in EP-A1-0 790 349; an example is a 2×0.33+6×0.33 SS cord.     as an alternative or in addition to a high elongation metal cord, the metal cord may be composed of one or more wires which have been plastically deformed so that they are wavy. This wavy nature additionally increases the elongation. An example of a wavy pattern is a helix or a spatial crimp such as disclosed in WO-A1-99/28547.        

      According to the required properties of the impact beam as subject of the invention, all metal cords may be identical, or alternatively, different metal cords may be used to provide the impact beam.  
      The metal elements used to provide these metal cords may have a diameter, being a diameter of a radial cross section of the metal elements, which is equal or larger than 100 μm, more preferred larger than 125 μm e.g. more than 150 μm or even more than 175 μm. All metal elements of a metal cord may have the same diameter, or the diameters of the metal elements may differ from each other.  
      Preferably, the optical diameter of the metal cord is larger than 200 μm, or even larger than 250 μm, such as larger than 300 μm or more. The optical diameter of the metal cord is to be understood as the diameter of the smallest imaginary circle, encompassing the radial cross section of the metal cord.  
      Most preferably steel cords are used to provide the impact beam as subject of the invention. Presently known steel alloys may be used to provide the steel cords. Preferably, the steel cords are subjected to a stress relieving thermal treatment, e.g. by passing the steel cord through a high-frequency or mid-frequency induction coil of a length that is adapted to the speed of the steel cord during production. It was observed that, increasing the temperature to more than 400° C. for a certain period of time, a decrease in tensile strength of the steel cord (a reduction of approximately 10%), but at the same time, an increase of the plastic elongation of the cord before rupture of more than 6% may be obtained. Such steel cords are hereafter referred to as stress relieved steel cords.  
      Possibly, the metal cords may be coated with a polymer coating layer, such as a layer out of e.g. polyolefin, polyamide fiber, thermoplastic polyester, polycarbonate, polyacetal, polysulfone, polyether ketone, polyimide or polyether imide.  
      The non-metallic fibers are preferably glass fibers, poly-aramide fibers, poly(p-phenylene-2,6-benzobisoxazole) fibers, carbon fibers, mineral fibers such as basalt fibers or natural fibers such as flax or hemp. The non-metallic fibers may be mixed with polymer fibers like polyolefin fibers, polyamide fibers, thermoplastic polyester fibers, polycarbonate fibers, polyacetal fibers, polysulfone fibers, polyether ketone fibers, polyimide fibers or polyether imide fibers.  
      The non-metallic fibers may be mixed with polymer fibers like polyolefin fibers, polyamide fibers, thermoplastic polyester fibers, polycarbonate fibers, polyacetal fibers, polysulfone fibers, polyether ketone fibers, polyimide fibers or polyether imide fibers.  
      The metal cords are bond to the non metallic fiber layer using a yarn, which is preferably made out of glass fibers, poly-aramide fibers, poly(p-phenylene-2,6-benzobisoxazole) fibers or thermoplastic polyester fibers or a combination of these fibers.  
      Possibly more than one layer of non-metallic fibers are bond to the metal cords by means of stitches. As an alternative, the textile product may comprise additional layers of fibers being laminated to the layer of non metallic fibers with metal cords stitched to it.  
      It is further a subject of the invention to provide a semifinished sheet comprising a polymer matrix and a textile product as subject of the invention, comprising metal cords and at least one layer of non-metallic fibers, for which the metal cords are bond to this at least one layer of non-metallic fibers by means of stitches. The non-metallic fibers are preferably glass fibers, poly-aramide fibers, poly(p-phenylene-2,6-benzobisoxazole) fibers, carbon fibers, mineral fibers such as basalt fibers or natural fibers such as flax or hemp. The non-metallic fibers may be mixed with polymer fibers like polyolefin fibers, polyamide fibers, thermoplastic polyester fibers, polycarbonate fibers, polyacetal fibers, polysulfone fibers, polyether ketone fibers, polyimide fibers or polyether imide fibers.  
      For the polymer matrix all thermoplastically moldable polymers are suitable, for example polyolefins, polyamides, linear polyesters, polycarbonates, polyacetals, polysulfones, polyether ketones, polyimides and polyether imides. Especially preferred are propylene polymers having a melt index MFI (2.16 kg/212° C.) between 20 and 300 g/10 min, preferably homopolypropylene and graft copolymers of propylene and maleic anhydride or acrylic acid. The same applies to the thermoplastic polymers in the commingled fibers and hybrid fabrics.  
      This polymer matrix may be provided to the textile product by means of melt impregnation using a double belt process. The textile product is laminated at a temperature preferably above the melting temperature of the used polymer matrix to obtain a full impregnation of the reinforcing fibers, being the metal cords and non metallic fibers.  
      As an alternative, especially for polymer matrices being thermoplastics with a high melt viscosity or a low thermo-stability under oxygen, the polymer matrix can be introduced as fibers out of polymer matrix material, being mixed with the non metallic fibers and/or the metal cords. The mixing can be done by commingling of fibers out of polymer matrix material and the non metallic fibers or by weaving of hybrid fabrics out of fibers out of polymer matrix material and non mletallic fibers. The fibers out of polymer matrix material are then being molten in the double belt press and the so obtained molten polymer matrix is then used to impregnate the non metallic fibers and the metal cords, similar to as in case of the melt extrusion process.  
      The textile product may be laminated with additional layers of non metallic fibers like glass fibers, poly-aramide fibers, poly(p-phenylene-2,6-benzobisoxazole) fibers, carbon fibers, mineral fibers such as basalt fibers or natural fibers such as flax or hemp, depending on the requirements of the target application. These additional layers may also comprise oriented fibers or non oriented fibers, the latter hereafter referred to as “random distribution layer”.  
      These additional layers, possibly random distribution layers, of non metallic fibers may also be melt-impregnated or alternatively comprise fibers out of polymer matrix material out of polyolefins, polyamides, thermoplastic polyesters, polycarbonates, polyacetals, polysulfones, polyether ketones, polyimides and polyether imides, and this to the required amount as needed for the application. In this case the random distribution layers may be mixed fiber fleeces made by carding or airlay processes.  
      Preferably, a semifinished sheet as subject of the invention comprises a polymer matrix and a textile product comprising bundles of fiber roving, the tapes or tows of essentially parallel non-metallic fibers, providing the at least one layer of non-metallic fibers in the textile product, being crosswise bonded to the metal cords. As an example the orientation of the metal cords may differ 90° of the orientation of the bundles of fiber roving, the tapes or tows of essentially parallel non-metallic fibers. Possibly, additional bundles of fiber roving, the tapes or tows of essentially parallel non-metallic fibers may be linearly mixed with the metal cords, which mix is then crosswise bonded to the bundles of fiber roving, the tapes or tows of essentially parallel non-metallic fibers of the layer or layers of non-metallic fibers.  
      As an example, the metal cords my be provided as warp and/or weft inlay in a warp knitted textile fabric, being the textile product as subject of the invention.  
      The non-metallic fiber layer may be provided as essentially parallel bundles of fiber roving or tapes or tows of essentially parallel non-metallic fibers, provided as inlay in the direction perpendicular to the metal cords in this warp knitted fabric.  
      When a semifinished sheet as subject of the invention is used to provide a polymer article comprising such textile product, the metal cords are held in place during the press molding process. The don&#39;t tend to distort or migrate along with the molten polymer material. Further, the mechanical and chemical anchoring of the polymer matrix of the semifinished sheet, the metal cords and the non metallic fibers may be tuned more easily during production of the semifinished sheet as compared to the direct use of a textile product as subject of the invention in the same press molding process. The combination with other oriented or random layers in the semifinished sheet allows the production of a tailored sheet to meet the requirements of the final molded part. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention will now be described into more detail with reference to the accompanying drawings wherein  
       FIG. 1   a  and  FIG. 1   b  show schematically a textile fabric as subject of the invention.  
       FIG. 2   a  and  FIG. 2   b  show schematically an alternative textile fabric as subject of the invention.  
       FIG. 3   a  and  FIG. 3   b  show schematically an alternative textile fabric as subject of the invention.  
       FIG. 4 ,  FIG. 5 ,  FIG. 6  and  FIG. 7  show schematically a method to provide a semifinished sheet as subject of the invention.  
       FIG. 8  and  FIG. 9  show schematically a semifinished sheet as subject of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION  
      A first embodiment of a textile product  100  according to the present invention is schematically shown in  FIG. 1   a  and  FIG. 1   b,  being a side view ( FIG. 1   a ) and a top view ( FIG. 1   b ) of the textile product  100 .  
      A layer of non metallic fibers  101  is a woven textile fabric out of 1200 to 2400 tex glass fiber rovings, having a filament diameter of 15 to 20 μm and a weight between 200 and 2000 g/m 2 . A PP-compatible sizing may used. As an alternative, the fiber rovings or yarns comprise PET- or aramide fibers, next to the glass fibers of the woven textile fabric. Such combination of different fibers may be provided using commingled fiber rovings, or fiber rovings used separately one from the other in the woven fabric.  
      The textile product  100  further comprises metal cords  102 , being a compact cord of type 0.20+18×0.175. this is to be understood as a cord comprising a core wire of diameter 0.2 mm, around which  18  wires of diameter 0.175 mm are twisted in the most compact way, as shown in  FIG. 1 .  
      The non metallic fiber layer  101  and the metal cords  102  are bond to each other by means of stitches  103 , provided by sewing operation, using a sewing thread  104  being a glass fiber yarn or a PET- or aramide-fiber yarns having a fineness of 40 to 100 tex, preferably 60 to 80 tex.  
      The stitch length  105  may be chosen over a large range, but is preferably in the range of 2 mm to 10 mm, such as 4 mm.  
      The metal cords  102  are positioned in the textile product  100  in essentially parallel arrangement. The distance between adjacent metal cords may vary in a large range, according to the required properties of the textile product  100 . The distance between adjacent cords may all be identical, or may vary over the surface of the textile product  100 .  
      As shown in  FIG. 1   a  and  FIG. 1   b , all metal cords  102  are positioned at the same side of the non metallic fiber layer  101 . As an alternative, not shown in  FIG. 1   a  and  FIG. 1   b , some metal cords may be located at one side of the non metallic fiber layer, whereas the other metal cords are located at the opposite side of the non metallic fiber layer.  
      An alternative textile product as subject of the invention is shown schematically in  FIG. 2   a  and  FIG. 2   b , being a view of the face side ( FIG. 2   a ) and of the technical back side ( FIG. 2   b ) of a warp knitted textile product  200  or a textile product obtained by an “arachne-” or “malimo-”process.  
      The textile product  200  comprises metal cords  201 , present in the production direction or so-called warp direction of the textile product  200 . In the direction perpendicular to the warp direction, glass fiber rovings  202  are present. All rovings together provide a non metallic fiber layer to the textile product  200 . The stitches  203 , which bond the metal cords  201  to the non metallic fiber layer are made using a stitching yarn  204  being a glass fiber yarn or a PET- or aramide-fiber yarns having a fineness of 40 to 100 tex, preferably 60 to 80 tex. It is clear that the orientation of the metal cords differs 90° from the direction of the fiber rovings  202 .  
      The fiber rovings used for this embodiment are 1200 to 2400 tex glass fiber rovings, having a filament diameter of 15 to 20 μm. A PP-compatible sizing may used. As an alternative, the fiber rovings or yarns comprise PET- or aramide fibers, next to the glass fibers of the non metallic fiber layer  101 . Such combination of different fibers may be provided using commingled fiber rovings, or fiber rovings used separately one from the other.  
      The metal cords for this embodiment were a yellow brass coated steel cord of type 0.2+18×0.175 compacted cord.  
      It is understood hat the election of the fiber roving and metal cords may differ, so providing alternative embodiments of textile products as subject of the invention, having other mechanical and physical properties.  
      Alternatively, non metallic fiber rovings or yarns may be provided in the direction of the metal cords, by replacing some of the metal cords by such non metallic fiber rovings, or by adding additional fiber rovings to the metal cords.  
      Shown schematically in  FIG. 3   a  and  FIG. 3   b , two sides of a textile product  300  as subject of the invention are provided. To an identical combination of non metallic fiber layer and metal cord as in  FIG. 1   a  and  FIG. 1   b , additional metal cords are provided at the second side of the textile product. The metal cords  301  present on the first side of the textile product and the metal cords  302  present on the second side of the textile product are inclined to each other over an angle θ. All metal cords are stitches to the layer of non metallic fibers  303  using an identical yarn as shown in  FIG. 1   a  and  FIG. 1   b.    
      A process for providing a semifinished sheet  400  as subject of the invention is shown in  FIG. 4 .  
      A polymer matrix  403  is provided on one or both (as shown) sides of the textile product  401  by extrusion of the polymer matrix material. This combination is provided to the double belt press  402 . During pressing, the polymer matrix  403  is forces to impregnate in the textile product  401 . For this purpose, the polymer matrix and textile product may be heated (indicated  404 ) in the first part of the process. In order to solidify the polymer matrix, the textile product impregnated with polymer matrix is cooled (indicated  405 ). Pressure is applied using rollers  406  and a belt  407  on both sides of the polymer matrix and textile product during operation of the double belt press. At the end of the double belt process, a semifinished sheet  400  as subject of the invention is obtained, which may be rolled on a coil or (as shown) cut into desired lengths by means of an appropriate cutting device  408 .  
      As shown in  FIG. 5 , the polymer matrix is provided to the textile product  400  as polymer tapes  501 , in stead of by an extrusion operation. All other steps apply as described in  FIG. 4 .  
      As an alternative, shown in  FIG. 6 , between the textile product  401  as subject of the invention, and the polymer tapes  501 , additional layers of unidirectional layers, random orientated layers or additional woven, knitted or nonwoven layers of non metallic fibers may be provided (layers indicated  601 ). All other steps apply as described in  FIG. 4 . It is understood that these additional layers  601  may also be provided in case the polymer matrix is provided by extrusion as shown in  FIG. 4 .  
      As a further alternative, a textile product  701  as subject of the invention comprising metal cords, non metallic fiber layer to which the metal cords are bond, and polymer matrix fibers is used to be subjected to a double pelt process  704 . It is understood that additional layers of fibers ( 702 ,  703 ), being non metallic fibers possibly commingled with polymer matrix fibers, may be provided to the textile product  701  as subject of the invention, prior to applying the double belt pressing operation.  
      The semifinished sheet ( 800 ,  900 ) as subject of the invention, which may be obtained by the methods as described above, is schematically shown in  FIG. 8  and  FIG. 9 .  
      In  FIG. 8 , a transversal cut of a semifinished sheet is shown, which comprises a textile product  801  as subject of the invention, being embedded in a layer of polymer matrix  802 . The polymer matrix is preferably polypropelyne (PP), but may alternatively be polyolefins, polyamides, linear polyesters, polycarbonates, polyacetals, polysulfones, polyether ketones, polyimides or polyether imides. The thickness  803  of the semifinished sheet is preferably in the range of 1 mm to 6 mm, such as 3 mm.  
      In  FIG. 9 , a transversal cut of a semifinished sheet is shown, which comprises two textile products  901  as subject of the invention, being embedded in a layer of polymer matrix  902 . Preferably the two textile products  901  are provided in such a way that similar the surfaces on which the metal cords are present, face one to the other. The polymer matrix is preferably polypropelyne (PP), but may alternatively be polyolefins, polyamides, linear polyesters, polycarbonates, polyacetals, polysulfones, polyether ketones, polyimides or polyether imides.  
      Additional to the textile product  901  as subject of the invention, the semifinished sheet  900  comprises additional layers of non metallic fibers  903  and  904 , which have properties being chosen according to the needs of the semifinished sheet  900 . As an example, such additional layers  903  and  904  are layers of unidirectional fibers, random oriented fiber mats, or a combination of layers of unidirectional fiber and random oriented fiber mats. Such layers may have a total fiber weight of 900 g/m 2 , where the ratio of unidirectional fiber to random oriented fiber may vary from 300 g/m 2  unidirectional fiber and 600 g/m 2  random oriented fiber to 600 g/m 2  unidirectional fiber and 300 g/m 2  random oriented fiber.