ELECTRICALLY CONDUCTIVE FLAT BRAIDE

Description

[0001] The invention relates to an electrically conductive textile material, in particular a braid for dissipating static charge, consisting of plastic and metal threads, wherein the textile material is designed as a flat braid in which the plastic threads are integrally connected to one another at connecting points.

[0002] A textile material designed as a round braid is known from DE 91 04 795 U1. This describes a round braid made of plastic and metal threads that is intended for the dissipation of static charges, particularly in work shoes, and is considered advantageous over previously used woven straps. It is true that such a round braid exhibits considerably greater flexibility than a relatively stiff fabric. However, tests with such a round braid have shown that it has a certain surface roughness that tends to chafe when used in a shoe, which can be uncomfortable for the wearer. Furthermore, it has been found that the conductivity of the round braid can reach its limits even during the production of a new shoe, resulting in an increased scrap rate in shoe production.To avoid these disadvantages, the applicant's earlier application DE 10 2006 051 001 A1 proposes forming the textile material as a flat braid, in which the plastic threads are firmly bonded to one another at the connecting points. This flat braid is subject to a certain degree of longitudinal stretching under tensile load. However, in certain applications, it is advantageous if such stretching does not occur.

[0003] US 2,257,649 A (D1) concerns a braid with plastic and metallic threads. The braid forms a reinforcement element for articles made of rubber or plastic material.

[0004] US 5 899 134 A (D3) relates to a hollow cylindrical braid. The braid comprises two sets of yarns arranged diagonally across each other and held together by longitudinal yarns.

[0005] In the book: "Knitting and knitting, nets and filet knitting, machine braiding and machine bobbin lace making, braiding and bobbin lace making machines, velvet, plush, artificial furs, the manufacture of carpets, knitting machines" by the authors: Walter Krumme, H. Sautter, Carl Aberle, H. Glafey, R. Glafey, with the publication date: November 21, 2013 (2013-11-21), ISBN: 978-3-662-29465-9, pages 319-320, braids with center-end threads are described.

[0006] EP 0 742 195 B1 relates to a fiber-reinforced ceramic matrix composite material comprising a ceramic matrix and a fiber preform integrally incorporated into the matrix. The fiber preform comprises a braided fabric obtainable by braiding a yarn, and the yarn is composed of multiple fiber bundles formed from multiple bundled monofilaments. The braided fabric has a fiber volume fraction (Vt) of 10 to 40 vol.%, based on the total volume of the ceramic matrix composite material, and contains center-end yarns arranged at a bend-free portion where the fiber bundles intersect each other.

[0007] Based on this, the invention is based on the object of further developing an electrically conductive flat braid of the type mentioned at the beginning in such a way that no significant longitudinal stretching occurs under tensile load.

[0008] To solve this problem, the combination of features specified in claim 1 is proposed. Advantageous embodiments and further developments of the invention are set out in the dependent claims. A method for producing the flat braid according to the invention is set out in claims 6 to 11.

[0009] The textile material is designed as a flat braid, in which the plastic threads are bonded to one another at connection points, at least in sections. According to the invention, it is proposed that, to create fabric-like stability, additional center-end threads are provided that braid the plastic and metal threads of the flat braid. The flat braid remains flexible, but the threads are supported against one another, preventing the braid from fanning out under compressive loads. The steel threads are subjected to less stress, thus reducing their risk of breakage. Furthermore, the surface roughness of the flat braid is reduced, which improves the preferred use of the flat braid as a grounding conductor for static electrical charges in safety clothing, particularly safety shoes and boots.The center-end threads reduce the extensibility of the flat braid without diminishing its advantage over previously used fabrics. According to the invention, the connection points of the plastic threads are created by a chemical and / or thermomechanical treatment of the flat braid. The connection points between the plastic threads can be point-shaped or linear, but should not be so extensive that they would cause the threads to clump together. The plastic threads are preferably made of polyester and the metal threads of stainless steel. The ratio of plastic to metal threads can be in the range of 80:20 to 50:50 and is preferably approximately 60:40. To ensure sufficient flexibility of the flat braid, the fineness of the threads is advantageously in the range of Nm 50 / 2. The plastic and metal threads are preferably spun into a yarn, from which the flat braid is then braided.A flat braid with the above properties has an electrical resistance in the range of 500 to 3,000 Ω / m. In a further preferred embodiment of the invention, the flat braid has a width in the range of 5 to 15 mm and is designed as a double braid. The number of braids can advantageously be in the range of 50 to 70 per 10 cm of length. According to the invention, a number of 82 threads is provided, of which 66 threads on 33 spools form the already known flat braid, and 16 additional center-end threads stabilize the braid and reduce its extensibility.

[0010] To prevent moisture absorption, in a further embodiment of the invention, the flat braid is advantageously treated with a hydrophobic agent, preferably a paraffin-containing agent. The treatment is advantageously carried out using a discontinuous extraction process at a temperature of less than 80°C and a residence time of up to 60 minutes at the final temperature. Additional treatment components can be acetic acid or citric acid.

[0011] According to the invention, the plastic and metal threads, as well as the center-end threads, are each subjected to tension by springs in the bobbins of a braiding machine during the production of the flat braid. The tension of the center-end threads is 40% to 60% greater than the tension of the plastic and metal threads, in particular approximately 50% greater. The tension of the plastic and metal threads can be approximately 80 g, and the tension of the center-end threads approximately 120 g. The tensile forces acting on the threads slow them down during braiding.

[0012] To avoid material waste and machine downtime during braiding, it is essential that the braiding body is properly adjusted. It is very important that the appropriate tension is applied via a spring. The rocker arm clapper is a single-action clapper.

[0013] The center-end threads, also known as warp threads or stay threads, are specifically used to reinforce the braid in the axial direction. This increases its strength in the axial (longitudinal) direction. The warp threads are embedded in the braiding ribs and are fed through the center of a flywheel of the braiding machine (drilled wheel pillars) and tied or covered with yarn from both sides (top and bottom of the heddle) by the bobbins. This gives the heddle braid the following properties: Precisely shaped in the width of the strand. Less stretching of the strand as the warp threads are stressed.

[0014] The tension springs for the sheath braid advantageously have a wire thickness of 0.6 mm and a tensile force of approximately 80 g, while the tension springs for the incoming middle-end threads or warp threads have a wire thickness of 0.63 mm and a tensile force of approximately 120 g. The tension springs in the bobbin ensure consistent tension for the interwoven yarn. The different spring thicknesses allow the braid to be produced with the following properties: Lower tension means the braid is less tightly bound around the core / warp thread, making the braid more flexible. Higher tension means the braid is more tightly bound around the core / warp thread, making the braid stiffer. Failure to observe the developed parameters will result in the braid not being bound evenly, and the following unfavorable characteristics or defects may occur: Loops in the braid; Zigzags in the braid; Thick / thin patches in the braid; One- or two-sided distortion of the braid; Thread breakage due to unevenness.

[0015] The process for producing a flat braid of the type described above provides that, after braiding, the flat braid is chemically and / or thermomechanically treated to create cohesive connections between the plastic threads. In principle, the desired properties can also be achieved solely through thermomechanical treatment; however, it has been found that chemical pretreatment allows the use of lower temperatures during the thermomechanical treatment. Preferably, the flat braid is first passed through a liquid bath consisting of water and acetone in a mixture ratio of approximately 10:1 before being passed through a pair of heated rollers. The roller temperature should be in the range of 30 to 60°C and is preferably 35 to 40°C for wet chemical pretreatment.

[0016] According to the invention, the plastic and metal threads, as well as the center-end threads, are each subjected to tension by springs in the bobbins of a braiding machine during the production of the flat braid. The tension of the center-end threads is 40% to 60% greater than the tension of the plastic and metal threads, in particular approximately 50% greater. The tension of the plastic and metal threads can be approximately 80 g, and the tension of the center-end threads approximately 120 g.

[0017] The invention is explained in more detail below using an exemplary embodiment schematically illustrated in the drawing. It shows: Fig. 1 shows a production line for the manufacture of a flat braid according to the invention; Fig. 2 shows a detailed view of the flat braid after heat-setting; and Fig. 3 shows a detailed view of the flat braid with a plurality of center end threads.

[0018] The production line schematically shown in the drawing essentially consists of a conventional braiding machine 10, in which yarn 14 stored on a plurality of spools 12 is braided into a flat braid 16, a liquid bath 18, and a heated pair of rollers 20. The yarn 14 consists of approximately 60% polyester and approximately 40% stainless steel fibers with a maximum cross-section of 12 micrometers. The yarn count is Nm 50 / 2, and the flat braid 16 is two-braided with a width of approximately 10 mm and a braid count of 62 per 10 cm with a thread count of 66. Furthermore, the threads 14 of the flat braid 16 are braided with center end threads 24, which are fed from spools 26 arranged below the level of the spools 12 via guide tubes 28.

[0019] After braiding, the braid 16 is passed through the liquid bath 18, which consists of a mixture of water and acetone in a ratio of approximately 10:1. This dissolves the polyester material of the yarn 14, allowing the subsequent heat-setting process in the heated roller pair 20 to operate at relatively low temperatures in the range of 35-40°C. The heat-setting process creates a cohesive bond between adjacent threads in places, so that the braid 16 retains its high flexibility on the one hand, but on the other hand becomes resistant to thread breakage under repeated compression loads, since the yarn threads are mutually supported.

[0020] Fig. 2 shows a short section of the flat braid 16 in an enlarged view. In a conventional braid (not shown) at this scale, clear gaps between the braided fiber bundles are visible. Here, the fibers 14 are firmly bonded to one another at many points 22 by heat setting, resulting in a dense, yet highly flexible flat braid. Even if the flat braid 16 is compressed, the fibers 14 remain in the illustrated composite, reducing the stress on individual fibers or yarns 14 and preventing breakage of the steel fibers contained therein, or at least less frequently than before. The firmly bonded connection of the fibers at many connection points prevents relative movement and thus chafing of the fibers against one another. The center-end threads 24 braid the threads of the yarn 14 and reduce the extensibility of the flat braid 16.

[0021] Fig. 3shows a detailed view of the flat braid 16 with the center-end threads 24, which run in the longitudinal direction of the flat braid 16, and the plastic and metal threads 14 that braid the former. For better visibility, the flat braid 16 is shown quite loosely, although it is actually quite tight. When subjected to tensile stress, the center-end threads 24 are axially loaded in the direction of the longitudinal extension of the flat braid 16 and stabilize the flat braid 16 such that it does not stretch or only stretches slightly and remains dimensionally stable. The center-end threads 24 also stabilize the flat braid 16 in the transverse direction to the longitudinal extension. This prevents cyclical stresses, particularly on the metal threads, thus improving the longevity and functional reliability of the flat braid 16.The preferred use of the flat braid is to incorporate it into the side of the upper leather inside a safety shoe, extending approximately 5 cm above an assumed insole into the foot area. It can be sewn directly to the upper leather in the front part of the shoe. Because the flat braid is flexible, it adapts to any shoe shape. The flat braid is then pulled through a slit in the (non-conductive) insole and attached to the underside of the insole. This section of the flat braid should be approximately 5 cm long.

[0022] Finally, an electrically conductive rubber sole is glued to the underside of the insole using electrically conductive adhesive.

[0023] In summary, the following can be stated: The invention relates to an electrically conductive textile material, in particular a braid for dissipating static charge, consisting of plastic and metal threads 14. The textile material is designed as a flat braid 16, in which the plastic threads 14 are integrally connected to one another at least in sections at connection points. To reduce the extensibility of the flat braid, the invention proposes that center end threads be provided that braid the plastic and metal threads of the flat braid.

Claims

1. An electrically conductive textile material, in the form of a braid for dissipating static charge, consisting of plastic and metal threads (14), the textile material being designed as a flat braid (16), in which the plastic threads are connected to one another at connection points (22), the connection points (22) of the plastic threads being created by a chemical and / or thermomechanical treatment of the flat braid, wherein the connecting points (22) between the plastic threads are formed in the shape of points or lines, characterised by central end threads (24) braiding around the plastic and metal threads of the flat braid (16), and the number of threads is 82, provided by 33 bobbins (12) each with 2 threads and additionally 16 central end threads (24).

2. A textile material according to claim 1, characterised in that the plastic threads consist of polyester and the metal threads consist of stainless steel and that the ratio of plastic to metal threads is in the range from 80:20 to 50:50 and in particular is approximately 60:40, wherein the plastic and metal threads (14) have a fineness in the range of Nm 50 / 2.

3. A textile material according to one of claims 1 or 2, characterised in that the plastic and metal threads are spun into a yarn (14) from which the flat braid (16) is braided and in that the flat braid (16) has an electrical resistance of 500 to 3,000 Ω / m.

4. A textile material according to one of claims 1 to 3, characterised in that the flat braid (16) has a width of 5 to 15 mm.

5. A textile material according to any one of claims 1 to 4, characterised in that the flat braid (16) is formed in two braids and has a number of braids of 50 to 70 per 10 cm length.

6. A method for producing a flat braid according to one of claims 1 to 5, wherein the flat braid (16) is treated chemically and / or thermomechanically after braiding to produce materially bonding joints (22) between the plastic threads, characterised in that central end threads (24) are fed to the plastic and metal threads of the flat braid (16) via guide tubes (28), which central end threads are entrained by the plastic and metal threads and braid around them, and in that the plastic and metal threads (14) and the centre end threads (24) are each placed under tension by springs in bobbins of a braiding machine (10) during the production of the flat braid (16), the tension of the centre end threads (24) being 40% to 60% greater than the tension of the plastic and metal threads (14), and the number of threads being 82, provided by 33 bobbins (12) each having 2 threads and additionally 16 centre end threads (24).

7. A method according to claim 6, characterised in that the flat braid (16) is passed through a liquid bath (18) consisting of water and acetone, the mixing ratio of water and acetone being in the range from 5:1 to 20:1.

8. A method according to one of claims 6 or 7, characterised in that the flat braid (16) is passed through a pair of heated rollers (20), the roller temperature being in the range from 30 to 60 °C.

9. A method according to one of the claims 6 to 8, characterised in that the flat braid (16) is produced from a total of 82 threads, wherein 33 bobbins (12) with 2 threads each and 16 centre end threads (24) are used.

10. A method according to one of claims 6 to 9, characterised in that the flat braid (16) is treated with a hydrophobic, preferably a paraffin-containing agent, at a temperature of less than 80 °C and for a duration of up to 60 min at the maximum treatment temperature.

11. A method according to one of claims 6 to 10, characterised in that the tensile stress of the plastic and metal threads is about 80 g (= 8.26 N / m2) and the tensile stress of the middle-end threads is about 120 g (= 12.39 N / m2).