Conductive wire heater element

Abstract

The present invention provides a conductive wire heater element including a core made of synthetic fiber and a plurality of heater wires wound around the core. The core is twisted in a predetermined direction X, and the plurality of heater wires are wound in a predetermined direction Y. The predetermined direction X is different from the predetermined direction Y. A predetermined number of the heater wires are individually coated with a non-conductive material.

Description

[Technical Field]

[0001] explanation Technical Field The present invention relates to the field of flexible heating elements, including electric heating cables, for example vehicle (automotive) seat heating elements. [Background technology]

[0002] Background technology Electric heater cables containing metal filaments (e.g., 15 to 150 metal filaments) are known and are used in seat heaters in automobiles. Each of the metal filaments may have a diameter of approximately 50 μm. An automobile seat heater can be realized by attaching an electric heater cable, for example in the form of one or more loops, within the seat to form an automobile seat heater element. In an automobile seat heater element, such a heater cable is connected to a power supply unit that delivers an electric current, thereby heating the element to a suitable temperature.

[0003] Among the requirements for an automobile seat heater system is a long lifespan for proper and reliable operation of the automobile seat heater system.

[0004] In an automobile seat heater element or system, an electric heater cable is subjected to dynamic bending forces. Therefore, flex failure life (resistance to dynamic bending) is an important parameter for the durability and lifespan of the heater cable, and therefore of the automobile seat heater element or system. One way to increase the flex failure life or flex durability of the heater cable, and therefore of the automobile seat heater element, to a required level is to use smaller diameter metal filaments in the heater cable. However, as the diameter of the metal filament decreases, the manufacturing costs of the heater cable and automobile seat heater element increase exponentially.

[0005] Damage or breakage of individual metal filaments in the heater cable of an automobile seat heater element can lead to localized changes in electrical properties along the entire length of the heater cable. So-called hot spots can occur at the location of the broken filament, where heat generation is higher than in other parts of the heater cable along its length. Hot spots should be avoided because they pose a safety hazard. WO 01 / 058315, relating to a device for heating components in an automotive environment, describes a method for eliminating the formation of hot spots that occur at the point of interruption (break) of some of the metal filaments of the heater cable. This solution provides a heater cable consisting of multiple strands, a predetermined number of which are individually electrically insulated by an insulating lacquer layer.

[0006] Although individual insulation of the strands or metal filaments by lacquering is an effective method for eliminating hot spot formation, individual lacquering or individual coating of the strands or metal filaments of a heater cable has the significant drawback that it is technically very difficult to apply the lacquer uniformly and effectively to thin metal filaments or strands. If the lacquer layer is not applied uniformly or is not properly dried and cured, flexing of the heater cable during use can damage the lacquer layer, resulting in a shorter lifespan of the heater cable or inadequate protection against hot spots.

[0007] To protect the metal filaments from corrosion (especially galvanic corrosion) and to extend the flex failure life of the heater cable to the level required for car seat heaters, the heater cable of a car seat heater element can be provided with a polymer sheath. To obtain the best flex failure life figures, a high-grade polymer coating is required. Such high-grade polymer coatings (e.g., perfluoroalkoxy polymers, PFA) have the disadvantage that they are expensive and difficult to apply. Summary of the Invention [Problem to be solved by the invention]

[0008] Disclosure of the Invention It is an object of the present invention to provide an easily manufactured conductive wire heater element that is particularly useful for automotive interior heating applications, such as automobile seat heaters, heater panel armrests and headrests, and that functions properly and reliably, has a long lifespan (including having excellent flex failure lifespan and effective hot spot prevention). [Means for solving the problem]

[0009] According to the present invention, there is provided a conductive linear heater element including a core made of synthetic fiber and a plurality of heater conductive wires surrounding the core. The core is twisted in a predetermined direction X, and the plurality of heater conductive wires are wound in a predetermined direction Y. The predetermined direction X is different from the predetermined direction Y. A predetermined number of the heater conductive wires are individually coated with a non-conductive material. For example, the predetermined direction X is the S direction, and the predetermined direction Y is the Z direction. As another example, the predetermined direction X is the Z direction, and the predetermined direction Y is the S direction. In this way, the "S" and "Z" torques of the conductive linear heater element are balanced, and therefore the conductive linear heater element does not rotate.

[0010] The core element is preferably a rope made of synthetic yarn, for example, aromatic polyester fibers. The core according to the present invention has a twisted configuration. The core can be a strand made of synthetic fiber yarn. Synthetic yarns that can be used as the core according to the present invention include all yarns known for use in fully synthetic ropes. Such yarns can include yarns made of polypropylene, nylon, and polyester fibers. Preferably, yarns of highly elastic fibers are used, for example, yarns of fibers of liquid crystal polymers (LCP), aramids such as poly(p-phenylene terephthalamide) (known as Kevlar®), high molecular weight polyethylene (HMwPE), ultra-high molecular weight polyethylene (UHMwPE) such as Dyneema®, PBO (poly(p-phenylene-2,6-benzobisoxazole), and aromatic polyesters (known as Vectran®). For the core, monofilaments, multifilaments, or spun yarns of inorganic fibers such as glass fibers or organic fibers such as polyester fibers (e.g., polyethylene terephthalate), fatty acid polyamide fibers, aromatic polyamide fibers, and wholly aromatic polyester fibers can be used. Additionally, combinations of the above-mentioned fibers can also be used.

[0011] The core is twisted, preferably with a pitch length of 2 to 25 mm, preferably 2 to 20 mm, more preferably 2 to 15 mm, and most preferably 5 to 15 mm. If the pitch length is too long, a substantial gap will be created in the center if the core is not completely covered by the heater wire when one core strand is pressed. If the pitch length is too short, the strands will be packed together, leaving no room for a gap in the center, but the core strand will become stiff and its flexibility will be reduced, which is undesirable for a flexible heater element.

[0012] Conventionally known materials can be used for the heater conductive wire. For example, copper wire, copper alloy wire, nickel wire, iron wire, aluminum wire, nickel-chromium alloy wire, and iron-chromium alloy wire can be used. If a heater element with higher resistance is required, stainless steel wire or copper-clad steel wire can be applied. Examples of copper alloy wire that can be used include tin-copper alloy wire, copper-nickel alloy wire, and silver-containing copper alloy wire. Among the materials listed above, copper wire and copper alloy wire are preferred in terms of the balance between cost and properties. For copper wire and copper alloy wire, both soft and hard materials can be used, with semi-hard materials being more desirable than soft and hard materials in terms of bending resistance.

[0013] The heater wires are wound helically around the core. When the heater wires are wound parallel to each other or twisted together around the core, the parallel winding is preferable to the twisted winding because it reduces the diameter of the heater element and creates a smoother surface. In addition to the parallel and twisted windings, the wires can also be braided around the core material. The number of heater wires and the length of the turns or twists depend on the desired resistance. Preferably, the heater wires cover at least 25% of the core surface. More preferably, the heater wires cover at least 50% of the core surface. For example, the heater wires cover 100% of the core surface. In this case, the heater element provides maximum conductivity. On the other hand, the twisted core is well protected and gaps in the core are avoided.

[0014] According to the present invention, the heater wires are individually coated with a non-conductive material. The non-conductive coating can be produced by applying varnish and allowing it to dry. A predetermined number of the heater wires can be individually coated with resin. Alternatively, and preferably, the predetermined number of the heater wires are individually wrapped with one or more non-conductive filaments, individually wrapped with non-conductive fibers, or individually wrapped with one or more non-conductive tapes. While essentially any non-conductive filament, fiber, or tape can be used to wrap the metal filaments, preferred examples of filaments include polyester, polyurethane, polyamide, fiberglass, polybenzobisoxazole (PBO), aramid, polypropylene, polyethylene, fused yarn, bicomponent fiber, bicomponent filament (preferably a type with a lower melting point sheath), or polytetrafluoroethylene (PTFE). High-tenacity polyester filaments are more preferred because their higher tensile strength results in a significantly longer flex-failure life of the heater cable. The wrapping filament preferably has a diameter of 12 to 70 micrometers. Individual lengths of fibers can also be used to wrap the metal filaments, examples of which are natural fibers (e.g., cotton) or synthetic fibers (polyester, polyamide, polypropylene, polyethylene, etc.). In this regard, reference is made to EP 2761977 B1 for wrapping materials and methods, the contents of which are expressly incorporated into the disclosure of the present invention.

[0015] In addition, an insulating jacket layer can be formed around the heater wire. The insulating jacket layer is preferably formed on the outer periphery of the conductor wire. If the heater wire accidentally breaks, the power supply for other components is insulated by the insulating jacket layer. Furthermore, even if a spark occurs, the high temperature heat generated is insulated. The method for forming the insulating jacket layer is not particularly limited. Preferably, extrusion molding is used. When the insulating jacket layer is formed by extrusion molding, the position of the heater wire is fixed. This prevents friction and bending caused by displacement of the copper wire, thereby improving bending resistance. Materials for forming the insulating jacket layer include polyolefin resins, polyester resins, polyurethane resins, aromatic polyamide resins, fatty acid polyamide resins, vinyl chloride resins, modified Noryl resin (polyphenylene oxide resin), nylon resins, polystyrene resins, fluororesins, synthetic rubber, fluororubber, ethylene-based thermoplastic elastomers, urethane-based thermoplastic elastomers, ethylene-based thermoplastic elastomers, and polyester-based thermoplastic elastomers. In particular, a flame-retardant polymer composition is preferably used. Regarding flame-retardant materials, metal hydrates such as magnesium hydroxide and aluminum hydroxide, antimony oxide, melamine compositions, phosphorus compositions, chlorine-based flame retardants, and bromine-based flame retardants can be used. For example, PFA coatings are available in different grades, with more temperature-stable grades contributing more to a longer flex-failure life, but at the expense of higher material and coating application costs. A perfluoroalkoxy (PFA) grade with a temperature stability of 260°C is much more expensive than a PFA grade with a temperature stability of 225°C and requires higher temperatures during the application process. Due to the presence of individually insulated conductive wires, the polymer coating can be a lower-grade or less expensive coating (e.g., polyamide 12 or TPE), and while a higher-grade coating contributes to the flex-failure life of the heater cable, this contribution is less or not required at all in the heater cable according to the present invention, since the twisted synthetic core itself determines the flex-failure life of the conductive linear heater element.

[0016] A predetermined number of the heater wires are individually coated with a non-conductive material. Preferably, all of the heater wires are individually coated with a non-conductive material. Alternatively, the heater wires can be formed by alternating conductive wires coated with an insulating layer and conductive wires not coated with an insulating layer.

[0017] The conductive wire heater element of the present invention may have an electrical resistance of 0.2 to 1000 ohms / meter. In certain cases, the conductive wire heater element may have an electrical resistance of 0.2 to 3 ohms / meter. The present invention is particularly advantageous for automobile seat heater elements including heater cables having a resistance of less than 1 ohm / meter (measured at 20°C) and heater cables having a resistance of less than 0.75 ohms / meter (measured at 20°C).

[0018] The diameter of the conductive linear heater element is in the range of 0.1 to 1 mm, preferably 0.3 to 1 mm, and more preferably 0.5 to 0.8 mm. When referring to diameter, it means the equivalent diameter, which in the case of a non-circular cross section, is the diameter of a circle having the same surface as the non-circular cross section.

[0019] According to a second aspect of the present invention, there is provided a method for manufacturing a conductive wire heater element, the method comprising the steps of: (a) twisting a core made of synthetic fiber in a predetermined direction X, wherein the pitch length of the pre-twisted core is in the range of 2 to 25 mm; and (b) winding a plurality of conductive heater wires around the pre-twisted core in a predetermined direction Y, preferably at a pitch of 0.1 to 10 mm. The predetermined direction X is different from the predetermined direction Y. For example, the predetermined direction X is the S direction, and the predetermined direction Y is the Z direction. As another example, the predetermined direction X is the Z direction, and the predetermined direction Y is the Z direction. A predetermined number of the conductive heater wires are individually coated with a non-conductive material. Preferably, the plurality of conductive heater wires are parallel to each other.

[0020] The flexible conductive wire heater element of the present invention for automotive interior heating applications, such as seat heaters, heater panel armrests, and headrests, can be provided with a long lifespan during which it functions properly and reliably due to the combined effects of preventing hot spots and increasing flex fatigue resistance. Hot spot formation is effectively prevented by the insulation of the heater wire. On the other hand, surprisingly, the twisted fiber core significantly increases flex fatigue resistance, resulting in a longer lifespan during which the flexible heater element functions properly. [Brief explanation of the drawings]

[0021] Brief description of the figures in the drawing [Figure 1] 1 shows an example of a cross section of a conductive wire heater element according to the present invention. [Figure 2] 1 shows an example of a lengthwise view of a conductive wire heater element according to the present invention. [Figure 3] 10 shows another example of a longitudinal view of a heating cable according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] Modes for carrying out the present invention FIG. 1 shows a cross section of a conductive wire heater element 10, which can be used as a heater cable in a vehicle seat heater.

[0023] The construction of the conductive wire heater element is shown in Figure 1. A core strand 12 formed from a multifilament bundle of fibers with an outer diameter of 0.15 mm is provided. The core material is an aromatic polyester produced by polycondensation of 4-hydroxybenzoic acid and 6-hydroxynaphthalene-2-carboxylic acid, such as the commercially available Vectran®. The parallel, untwisted core is first pretwisted 300 turns / m in the S direction. Ten conductive wires 14, each with a diameter of 0.12 mm and made of tin-containing copper alloy wire, are wound helically around the periphery of the core strand 12 at 200 turns / m in the Z direction, parallel to each other. The conductive wires 14 are individually lacquered with a non-conductive material, such as silicone resin, by applying an alkyd silicone varnish to a thickness of approximately 8 μm and allowing it to dry. The conductive wire heater element 10 is formed by winding the conductive wires 14 around the core 12 with a gap 16 between adjacent turns. For example, the size of the gap is approximately the same as the diameter of the conductive wire. Then, a 0.25 mm thick extrusion covering of polyamide 12 resin is formed around the wound conductive wire 14 as an insulating jacket layer 18. The cross-sectional area of ​​the conductive wire heater element 10 upon completion is 0.12 mm. 2 and the electrical resistance is about 0.5 ohms / meter.

[0024] In this embodiment, the core 22 of the conductive wire heater element 20 is not completely coated, as shown in Figure 2. The conductive wire 24 covers approximately 90% of the surface of the core. In a bending durability test, the conductive wire heater element 20 of this embodiment has a flex failure life of approximately 40,000.

[0025] A similar sample was fabricated for comparison, having the same construction except that the core was made of parallel multifilaments but was not twisted. The flex failure life of the conductive wire heater element with a parallel, untwisted fiber core is approximately 22,000.

[0026] In a second embodiment, the core (not visible in FIG. 3) is fully coated. As shown in FIG. 3, the conductive wire 34 completely coats the surface of the core. There were eleven conductive wires 34 wound in parallel around the core with no distance between two adjacent turns. The flex failure life of this conductive wire heater element 30 in this second embodiment is comparable to the first embodiment, but the conductivity of the conductive wire heater element is higher when the conductive wire is fully coated.

[0027] The conductive wire elements of the present invention have significantly increased flex failure life, achieving a 45% increase in flex failure life over comparable conductive wire elements that are twisted but do not have a parallel synthetic fiber core. A longer flex failure life is advantageous for applications with high motion, such as automobile seat heaters. Experimental results show that automobile seat heaters incorporating the above-described conductive wire heater elements have efficient hot spot prevention and excellent flex failure life.

[0028] Combinations of elements and features from different embodiments and examples are within the spirit and scope of the present invention.

Claims

1. A conductive wire heater element, a core made of synthetic fibers twisted in a predetermined direction X; a plurality of heater conductive wires wound around the core in a predetermined direction Y; the predetermined direction X is different from the predetermined direction Y, and a predetermined number of the heater conductive wires are individually coated with a non-conductive material; A conductive wire heater element, wherein the pitch length of the twisted core is in the range of 2 to 25 mm.

2. 2. The conductive wire heater element according to claim 1, wherein the predetermined direction X is the S direction, and the predetermined direction Y is the Z direction.

3. 2. The conductive wire heater element according to claim 1, wherein the predetermined direction X is a Z direction and the predetermined direction Y is an S direction.

4. The conductive wire heater element according to any one of claims 1 to 3, wherein the pitch length of the twisted core is in the range of 2 to 20 mm, preferably 2 to 15 mm, more preferably 5 to 15 mm.

5. 5. The conductive wire heater element according to claim 1, wherein the plurality of heater conductive wires are made of copper or a copper alloy.

6. 6. The heater element according to claim 1, wherein the heater conductive wires are parallel to each other.

7. 7. The conductive wire heater element according to claim 1, wherein the plurality of heater conductive wires cover at least 50% of the surface of the core.

8. 7. The conductive wire heater element according to claim 1, wherein the plurality of heater conductive wires cover 100% of the surface of the core.

9. The conductive wire heater element according to any one of claims 1 to 8, wherein the predetermined number of the heater conductive wires are individually lacquered with resin.

10. 9. The conductive line heater element according to claim 1, wherein the predetermined number of the heater conductive wires are individually wrapped with one or more non-conductive filaments, individually wrapped with non-conductive fibers, or individually wrapped with one or more non-conductive tapes.

11. 11. The conductive wire heater element according to claim 1, wherein an insulating jacket layer is formed around the outer periphery of the heater conductive wire.

12. The conductive wire heater element of any one of claims 1 to 11, wherein the conductive wire heater element has an electrical resistance in the range of 0.2 to 1000 ohms per meter.

13. The conductive wire heater element of any one of claims 1 to 12, wherein the diameter of the conductive wire heater element is in the range of 0.1 to 1 millimeter.

14. A method for manufacturing a conductive wire heater element, comprising: (a) pre-twisting a core made of synthetic fibers in a predetermined direction X, the pitch length of the pre-twisted core being in the range of 2 to 25 mm; (b) winding a plurality of heater wires around the pre-twisted core in a predetermined direction Y, preferably with a pitch of 0.1 to 10 mm; the predetermined direction X is different from the predetermined direction Y, and a predetermined number of the heater conductive wires are individually coated with a non-conductive material.

15. The method for manufacturing a conductive linear heater element according to claim 14, wherein the plurality of heater conductive wires are parallel to each other.

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