Cord heaters and surface heaters

Abstract

To provide a cord-shaped heater improved in terminal workability and a planar heater employing the same.SOLUTION: The present invention relates to a cord-shaped heater 10 comprising one or more conductor strands 5a covered by an insulation coating 5b. The insulation coating 5b consists of at least an inner layer formed on the conductor strands 5a and an outer layer formed outside of the inner layer. A thermal decomposition temperature of a material constituting the inner layer is lower than lower one of a fusing point and a thermal decomposition temperature of a material constituting the outer layer. A thickness of the inner layer is 2 μm or more and 5 μm or less or less than 2 / 3 of an entire thickness of the insulation coating 5b. A thickness of the outer layer is 1 μm or more and 5 μm or less or less than 3 / 4 of the entire thickness of the insulation coating 5b. In the cord-shaped heater 10, the material constituting the inner layer is a polyurethane resin and the material constituting the outer layer is a polyamide-imide resin. The present invention also relates to a planar heater in which the cord-shaped heater is disposed in a substrate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a cord-shaped heater that is suitable for use in electric blankets, electric carpets, car seat heaters, steering wheel heaters, etc., and has high flexibility and improved processability, and also to a plane heater that uses this cord-shaped heater. [Background technology]

[0002] Cord heaters are used in electric blankets, electric carpets, car seat heaters, etc. Commonly known cord heaters are formed by first spirally winding a heater wire around a core wire, and then covering the core wire with an insulating layer. The heater wire is formed by either pulling together a plurality of conductor wires such as copper wires or nickel-chromium alloy wires, or twisting together a plurality of such conductor wires. A heat-sealing member is formed around the heater wire, and the heater wire is bonded to a substrate made of, for example, nonwoven fabric or aluminum foil by this heat-sealing member (see, for example, Patent Document 1).

[0003] When a conductor wire is pulled or bent, a portion of the conductor wire may break. In conventional cord-shaped heaters, the conductor wires are in contact with each other, so if a portion of a conductor wire breaks, the diameter of the heater wire narrows at the broken portion. The portion of the heater wire with a narrower diameter increases the amount of current per unit cross-sectional area, so this portion may generate more heat than usual. As another example, if a heater wire is formed by individually coating each conductor wire with an insulating coating, the conductor wires form a parallel circuit. In this heater wire, if a portion of a conductor wire breaks, part of the parallel circuit will break. This heater wire can prevent excessive heat generation (see, for example, Patent Document 2 and Patent Document 3).

[0004] Furthermore, the applicant has filed patent documents 4 and 5 as technologies related to the present invention. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2003-174952 A: Kurabe [Patent Document 2] Japanese Patent Publication No. 61-47087: Matsushita Electric Industrial Co., Ltd. [Patent Document 3] Patent Publication No. 2008-311111: Kurabe [Patent Document 4] Patent Publication No. 2010-15691: Kurabe [Patent Document 5] International Publication WO2011 / 001953: Kurabe DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0006] Here, the above-mentioned Patent Documents 2 and 3 describe several materials for the insulating coating of conductor wires. The most commonly used conductor wires are so-called enameled wires, and the insulating coating of enameled wires is typically made of polyurethane resin. Polyurethane resin has low heat resistance and insufficient flame retardancy. When heat resistance and flame retardancy are required for the insulating coating, hard materials such as silicone resin and polyimide resin, which have excellent heat resistance and flame retardancy, are used as the insulating coating material. It is difficult to process the terminals of conductor wires made of silicone resin or polyimide resin. Silicone resin and polyimide resin have high heat resistance and excellent flame retardancy. For example, when connecting a conductor wire to a lead wire by soldering, the insulating coating made of silicone resin or polyimide resin cannot be removed because it does not melt at the melting temperature of solder. When connecting a conductor wire to a lead wire by crimping a terminal, the hardness of silicone resin and polyimide resin prevents the insulating coating from being destroyed by the pressure of the crimping, resulting in no electrical continuity between the conductor wire and the lead wire. Therefore, it is necessary to remove the insulating coating of silicone resin or polyimide resin in a polishing process separate from the connection process. However, the conductor wires used in cord-shaped heaters are extremely thin, with an outer diameter of 0.1 mm or less. The polishing process requires careful attention to prevent wire breakage, which results in poor productivity.

[0007] The present invention has been made to solve the problems of the prior art, and its purpose is to provide a cord-shaped heater with improved terminal workability and a surface heater using the same. [Means for solving the problem]

[0008] In order to achieve the above object, the cord-shaped heater according to the present invention is a cord-shaped heater having one or more conductor wires covered with an insulating coating, wherein the insulating coating comprises at least an inner layer formed on the conductor wires and an outer layer formed outside the inner layer, the thermal decomposition temperature of the material constituting the inner layer is lower than the lower of the melting point and the thermal decomposition temperature of the material constituting the outer layer, the thickness of the inner layer is 2 μm or more and is 5 μm or less or is less than two-thirds of the total thickness of the insulating coating, and the thickness of the outer layer is 1 μm or more and is 5 μm or less or is less than three-quarters of the total thickness of the insulating coating. It is also conceivable that the material constituting the inner layer is a polyurethane resin or a polyester resin, and the material constituting the outer layer is any one of a polyimide resin, a polyamide-imide resin, and a silicone resin. The planar heater according to the present invention is obtained by disposing the cord-shaped heater described above on a substrate. The thermal decomposition temperature is the temperature at which weight loss begins when the temperature is gradually increased, and is measured in accordance with JIS-K7120-1997 Thermogravimetric Measurement Method for Plastics (or ISO7111-1997). [Effects of the Invention]

[0009] In the cord-shaped heater of the present invention, the inner layer undergoes thermal decomposition below the temperature at which the outer layer melts or thermally decomposes. Therefore, at temperatures above the thermal decomposition temperature of the inner layer and below the lower of the melting point or thermal decomposition temperature of the outer layer, only the inner layer thermally decomposes and disappears, creating a space between the conductor wire and the insulating coating. When the outer layer is formed by extrusion or tape-wound methods, the outer layer is stretched in the longitudinal direction. When the outer layer is formed by a coating-and-curing method, the outer layer experiences a shrinkage force during curing. Both outer layers have residual stress in the longitudinal direction, compressing them. Therefore, when a space is created between the outer layer of the insulating coating and the conductor wire, and when heat is applied to the outer layer, the outer layer of the insulating coating shrinks. As a result, for example, when the end of the conductor wire is heated to the aforementioned predetermined temperature (such as the melting temperature of solder), the insulating coating is removed, exposing the conductor wire. In particular, if the thicknesses of the inner layer and outer layer are within the above ranges, the shrinkage of the outer layer is more reliably achieved, which in turn more reliably removes the insulating coating and exposes the conductor wires. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing an embodiment of the present invention, and is a partially cutaway side view showing the configuration of a cord-shaped heater. [Figure 2] FIG. 1 is a diagram showing an embodiment of the present invention, and is a partially cutaway side view showing the configuration of a conductor wire on which an insulating coating is formed. [Figure 3] 1 is a diagram showing an embodiment of the present invention, illustrating the configuration of a hot press heater manufacturing apparatus. FIG. [Figure 4] FIG. 1 is a diagram showing an embodiment of the present invention, and is a partial perspective view showing how cord-shaped heaters are arranged in a predetermined pattern. [Figure 5] FIG. 1 is a diagram showing an embodiment of the present invention, and is a plan view showing the configuration of a planar heater. [Figure 6] FIG. 10 is a partially cutaway side view showing the configuration of a cord-shaped heater according to another embodiment of the present invention. [Figure 7]FIG. 10 is a partially cutaway side view showing the configuration of a cord-shaped heater according to another embodiment of the present invention. [Figure 8] FIG. 10 is a partially cutaway side view showing the configuration of a cord-shaped heater according to another embodiment of the present invention. [Figure 9] FIG. 10 is a partially cutaway side view showing the configuration of a cord-shaped heater according to another embodiment of the present invention. [Figure 10] FIG. 10 is a partially cutaway side view showing the configuration of a cord-shaped heater according to another embodiment of the present invention. [Figure 11] FIG. 10 is a partially cutaway side view showing the configuration of a cord-shaped heater according to another embodiment of the present invention. [Figure 12] 1 is a perspective view showing an embodiment of the present invention, with a portion cut away, illustrating a state in which a sheet heater is embedded in a vehicle seat. FIG. [Figure 13] 1 is a partially cutaway perspective view showing a planar heater according to the present invention embedded in a steering wheel. [Figure 14] FIG. 10 is a reference diagram for explaining a bending test method. BEST MODE FOR CARRYING OUT THE INVENTION

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the accompanying drawings. These embodiments are intended to illustrate examples in which the present invention is applied to a sheet heater as a vehicle seat heater.

[0012] First, the present embodiment will be described with reference to FIGS. 1 to 5. The configuration of a cord-shaped heater 10 in this embodiment will be described. The cord-shaped heater 10 in this embodiment has a configuration as shown in FIG. 1. The core wire 3 is formed of an aromatic polyamide fiber bundle having an outer diameter of approximately 0.2 mm. Five conductor wires 5a, which are hard tin-containing copper alloy wires having an element diameter of 0.08 mm, are wound helically around the core wire 3 at a pitch of approximately 1.0 mm. As shown in FIGS. 1 and 2, an insulating coating 5b is formed around the conductor wires 5a. The insulating coating 5b is formed of an inner layer 5c made of polyurethane resin and an outer layer 5d made of polyamide-imide resin. The inner layer 5c of the insulating coating 5b is formed by applying polyurethane varnish around the conductor wires 5a and drying it to form a layer with a thickness of 4 μm. Next, the outer layer 5d is formed by applying polyamide-imide varnish around the inner layer 5c and drying it to form a layer with a thickness of 4 μm. The heating wire 1 is formed by winding a conductor wire 5a around a core wire 3. The cord-shaped heater 10 is formed by covering the outer periphery of the heating wire 1 with an insulating layer 7. The insulating layer 7 is formed by extrusion coating the outer periphery of the heating wire 1 with polyethylene resin containing a flame retardant to a thickness of 0.2 mm. In this embodiment, the polyethylene resin of the insulating layer 7 functions as a thermal adhesive material. The finished outer diameter of the cord-shaped heater 10 is 0.8 mm. The core wire 3 is effective in that it has high flexibility and tensile strength. It is also possible to form the heating wire 1 by aligning or twisting multiple conductor wires together without using the core wire 3.

[0013] Next, the structure of the substrate 11 to which the cord-shaped heater 10 having the above-mentioned structure is adhered and fixed will be described. The substrate 11 in this embodiment is a nonwoven fabric (basis weight 100 g / m) made of a mixture of 10% heat-fusible fibers having a core-sheath structure with a low-melting-point polyester as the sheath component and 90% flame-retardant fibers made of flame-retardant polyester fibers. 2 The substrate 11 is formed into a desired shape by a known method such as die cutting.

[0014] Next, a configuration for arranging, adhering, and fixing the cord heater 10 on the substrate 11 in a predetermined pattern will be described. FIG. 3 shows the configuration of a hot-press heater manufacturing apparatus 13 for adhering and fixing the cord heater 10 on the substrate 11. First, the hot-press jig 15 will be described. A plurality of locking mechanisms 17 are arranged on the top surface of the hot-press jig 15. As shown in FIG. 4, the locking mechanisms 17 include pins 19, which are inserted upward into holes 21 drilled in the hot-press jig 15. A locking member 23 is attached to the top surface of the pin 19 so as to be movable in the axial direction of the pin 19, and the locking member 23 is constantly biased upward by a coil spring 25. As shown by the phantom lines in FIG. 4, the cord heater 10 is arranged in a predetermined pattern corresponding to the positions of the locking members 23 while being locked by the locking members 23 on the top surfaces of the plurality of locking mechanisms 17.

[0015] Returning to FIG. 3 , a press hot plate 27 is arranged above the multiple locking mechanisms 17 in a manner that allows it to be raised and lowered. First, the cord-shaped heater 10 is hooked onto the locking members 23 of the multiple locking mechanisms 17 and arranged to form a predetermined pattern. Next, the substrate 11 is placed on the cord-shaped heater 10. In this state, the press hot plate 27 descends to press the substrate 11 against the cord-shaped heater 10. At this time, the press hot plate 27 applies heat and pressure to the substrate 11 and cord-shaped heater 10 at 230°C for 5 seconds, for example. As a result, the heat-sealable portion 9 of the cord-shaped heater 10 and the heat-sealable fibers of the substrate 11 are both heated and pressurized and fused to each other. As a result, the cord-shaped heater 10 and the substrate 11 are bonded and fixed together. During the heating and pressurizing process, the press hot plate 27 moves downward against the biasing force of the coil springs 25 of the locking members 23 of the multiple locking mechanisms 17.

[0016] An adhesive layer may be formed or double-sided tape may be attached to the surface of the base material 11 on which the cord heater 10 is not to be disposed. These adhesive layers or double-sided tape are used to fix the sheet heater 31 to the seat.

[0017] By performing the above steps, a sheet heater 31 for a vehicle seat heater as shown in FIG. 5 can be obtained. Lead wires 40 are connected to both ends of the cord-shaped heater 10 in the sheet heater 31 and to a temperature control device 39 via connection terminals (not shown). The cord-shaped heater 10, the temperature control device 39, and the connector 35 are connected to one another by the lead wires 40. The connection of the cord-shaped heater 10 and the lead wires 40 via these connection terminals will be described in detail below. At the end of the cord-shaped heater 10, the insulating layer 7 of the heating wire 1 is removed using a stripping machine to expose the heating wire 1. At the end of the lead wire 40, the insulating layer of the lead wire 40 is also removed using a stripping machine to expose the conductor. The end of the cord-shaped heater 10 where the heating wire 1 is exposed and the end of the lead wire 40 where the conductor is exposed are soldered to connection terminals. This connects the cord-shaped heater 10, the lead wire 40, and the connection terminals to one another. The insulating coating 5b formed on the conductor wire 5a of the cord-shaped heater 10 is removed by the heat of soldering, electrically connecting the conductor wire 5a to the conductor of the lead wire 40. The mechanism of this action is described in detail below. The soldering temperature is approximately 360°C. This temperature is higher than the thermal decomposition temperature of the polyamide resin constituting the inner layer 5c, so the inner layer 5c thermally decomposes. On the other hand, this temperature of 360°C is below the melting point and thermal decomposition temperature of the polyamide-imide resin constituting the outer layer 5d. That is, when the conductor wire 5a is heated at the soldering temperature, the inner layer 5c of the insulating coating 5b thermally decomposes, forming a space between the outer layer 5d of the insulating coating 5b and the conductor wire 5a. Furthermore, since the outer layer 5d is applied around the inner layer 5c and then dried, the outer layer 5d is in a stretched state, and therefore compressive residual stress is generated in the outer layer 5d. When the outer layer 5d of the insulating coating 5b and the conductor wires 5a are no longer in close contact with each other at the end of the cord heater 10, the insulating coating 5b is heated and shrinks. Therefore, the end of the conductor wires 5a is naturally exposed. Because the end of the conductor wires 5a is naturally exposed as described above, there is no need to polish the end of the conductor wires 5a to remove the insulating coating 5b. This significantly improves the workability of the end of the conductor wires 5a. The cord heater 10 is connected to the vehicle's electrical system (not shown) via a connector 35.

[0018] The sheet heater 31 is then disposed in a state embedded in a vehicle seat 41 as shown in Fig. 12. That is, as described above, the sheet heater 31 is attached to the upholstery cover 43 or the seat pad 45 of the vehicle seat 41.

[0019] The present invention is not limited to the above embodiment. First, various conventionally known cord-shaped heaters can be used as the cord-shaped heater 10.

[0020] The heating wire 1 can have, for example, the following configuration. 1. As shown in FIG. 1, first, a plurality of conductor wires 5a covered with an insulating coating 5b are twisted or pulled together and wound around a core wire 3, and then an insulating coating 7 is applied to the outer periphery of the conductor wires 5a to form a heating wire 1. 2. As shown in FIG. 6, a heating wire 1 is formed by twisting together a plurality of conductor wires 5a covered with an insulating coating 5b. 3. As shown in FIG. 7, a heating wire 1 is formed by arranging a plurality of conductor wires 5a covered with an insulating coating 5b. 4. As shown in FIG. 8, a heating wire 1 is formed by alternately arranging conductor wires 5a covered with an insulating coating 5b and conductor wires 5a not covered with an insulating coating 5b. 5. As shown in FIG. 9, the number of conductor wires 5a covered with insulating coatings 5b is increased compared to that shown in FIG. 8, and the conductor wires 5a covered with insulating coatings 5b are arranged in a line to form a heating wire 1. In addition to these, various other configurations are conceivable for the heating wire 1. The heating wire 1 can also be formed by twisting together the core wire 3 and the conductor wires 5a.

[0021] Examples of the core wire 3 include monofilaments, multifilaments, and spun organic fibers such as inorganic fibers like glass fibers, polyester fibers like polyethylene terephthalate, aliphatic polyamide fibers, aromatic polyamide fibers, and wholly aromatic polyester fibers, or fibers having a core made of these fiber materials or an organic polymer material constituting these fiber materials and a thermoplastic organic polymer material covering the periphery. Furthermore, when a heat-shrinkable and heat-fusible core wire 3 is used, if a conductor wire 5a breaks and abnormal heating occurs, the core wire 3 melts and is cut, and also shrinks. When the core wire 3 shrinks, the conductor wires 5a wound around the core wire 3 follow the movement of the core wire 3, causing the ends of the broken conductor wire 5a to separate. This prevents the ends of the broken conductor wire 5a from repeatedly coming into contact and separating. Furthermore, the ends of the broken conductor wire 5a do not come into contact with each other over a small area, such as a point contact. This prevents abnormal heat generation. Furthermore, if the conductor wires 5a are insulated by the insulating coating 5b, the core wire 3 does not need to be made of an insulating material. For example, a stainless steel wire or a titanium alloy wire can be used as the core wire 3. However, since there is a possibility that the conductor wires 5a may break, it is preferable that the core wire 3 be made of an insulating material.

[0022] The conductor wires 5a may be conventionally known, such as copper wire, copper alloy wire, nickel wire, iron wire, aluminum wire, nickel-chromium alloy wire, and iron-chromium alloy wire. Examples of copper alloy wires include tin-copper alloy wire, copper-nickel alloy wire, and silver-bearing copper alloy wire in which a copper solid solution and a copper-silver eutectic are fibrous. Among these, copper wire or copper alloy wire is preferred from the viewpoint of cost-performance balance. These copper wires and copper alloy wires are available in both soft and hard varieties. From the viewpoint of flex resistance, hard wires are particularly preferred over soft wires. Hard copper wires and hard copper alloy wires are formed by elongating individual metal crystal grains in the processing direction through cold processing such as wiredrawing, resulting in a fibrous structure. When such hard copper wires or hard copper alloy wires are heated above their recrystallization temperature, the processing strain generated within the metal crystals is eliminated, and crystal nuclei that serve as starting points for new metal crystals begin to appear. These crystal nuclei develop, and recrystallization occurs, successively replacing the old crystal grains, leading to further growth of the crystal grains. A soft copper wire or soft copper alloy wire is a wire in this state of crystal grain growth. Although these soft copper wires or soft copper alloy wires have higher elongation and electrical resistance than hard copper wires or hard copper alloy wires, they have lower tensile strength, and therefore lower bending resistance than hard copper wires or hard copper alloy wires. As such, hard copper wires or hard copper alloy wires become soft copper wires or soft copper alloy wires with low bending resistance through heat treatment, so it is preferable to carry out processing with as little thermal history as possible. Hard copper wires are defined in JIS-C3101 (1994), and soft copper wires are defined in JIS-C3102 (1984). Soft copper wires are defined as those with an elongation of 15% or more for an outer diameter of 0.10 to 0.26 mm, 20% or more for an outer diameter of 0.29 to 0.70 mm, 25% or more for an outer diameter of 0.80 to 1.8 mm, and 30% or more for an outer diameter of 2.0 to 7.0 mm. Tin-plated copper wires are also included. Tin-plated hard copper wires are defined in JIS-C3151 (1994), and tin-plated soft copper wires are defined in JIS-C3152 (1984). Various cross-sectional shapes can be used for the conductor wires 5a, and they are not limited to the commonly used circular cross-sections; so-called rectangular wires may also be used.

[0023] However, when winding the conductor wires 5a around the core wire 3, among the above-mentioned materials for the conductor wires 5a, those with a small amount of springback when wound are preferred, and those with a recovery rate of 200% or less are preferable. For example, a silver-copper alloy wire, in which a copper solid solution and a copper-silver eutectic are fibrous, has excellent tensile strength and bending strength, but is prone to springback when wound. Therefore, when winding the conductor wires 5a around the core wire 3, the conductor wires 5a are prone to lifting or breakage due to excessive winding tension, and are prone to twisting after processing, making this undesirable. In particular, when the conductor wires 5a are coated with an insulating coating 5b, the insulating coating 5b also exerts a recovery force. Therefore, it is important to select a conductor wire 5a with a small recovery rate to compensate for the recovery force of the insulating coating 5b.

[0024] The measurement of the recovery rate defined in the present invention will now be described in detail. First, while applying a constant load to the conductor wire, the conductor wire is wound three or more times around a cylindrical mandrel with a diameter 60 times the diameter of the conductor wire without overlapping. After 10 minutes, the load is removed, the conductor wire is removed from the mandrel, and the inner diameter of the shape restored by elasticity is measured. The rate of springback of the conductor wire is calculated using the following formula (I) and evaluated as the recovery rate. R=(d2 / d1)×100―――(I) Symbols: R: Recovery rate (%) d1: Mandrel diameter used in the winding test (mm) d2: Inner diameter (mm) of the conductor wire after it has been wound around the mandrel and the load is released and it has restored its original shape

[0025] The insulating coating 5b covering the conductor wires 5a may be formed of two layers, an inner layer 5c and an outer layer 5d, as in the above embodiment, or may be formed of three or more layers. However, the thermal decomposition temperature of the material constituting the inner layer must be lower than the lower of the melting point and thermal decomposition temperature of the material constituting the outer layer. Here, the inner layer refers to a layer formed on the conductor wires 5a. The outer layer may be any layer located outside the inner layer, so it is possible to form another outer layer outside the outer layer or another intermediate layer between the inner and outer layers.

[0026] Examples of materials for the insulating coating 5b include polyurethane resin, polyamide resin, polyimide resin, polyamideimide resin, polyesterimide resin, nylon resin, polyesternylon resin, polyethylene resin, polystyrene resin, polypropylene resin, polyester resin, polybenzimidazole resin, vinyl chloride resin, fluororesin, and silicone resin. These materials may be used in combination, or may contain various known additives such as flame retardants and antioxidants. By combining these resins, the thermal decomposition temperature of the material constituting the inner layer is lower than the lower of the melting point and thermal decomposition temperature of the material constituting the outer layer. Materials for the inner layer may include polyurethane resin, vinyl chloride resin, polyacetal resin, polystyrene resin, polypropylene resin, polyester resins such as polymethyl methacrylate and polyethylene terephthalate, and polyvinyl alcohol. It is particularly preferable that the material for the inner layer be a thermosetting resin and the material for the outer layer be a thermosetting resin. Here, thermosetting resins also include crosslinkable materials. From the viewpoints of heat generation characteristics as a cord-shaped heater and ease of terminal processing such as soldering, it is preferable that the material of the inner layer is polyurethane resin or polyester resin, and the material of the outer layer is either polyimide resin, polyamide-imide resin, or silicone resin. It is particularly preferable that the material of the inner layer is polyurethane resin and the material of the outer layer is polyamide-imide resin. This polyurethane resin may be variously modified or compounded, such as imide-containing polyurethane.

[0027] In the present invention, the inner layer undergoes thermal decomposition below the temperature at which the outer layer melts or thermally decomposes. Therefore, when the end of a conductor wire coated with an insulating coating is heated to a temperature above the thermal decomposition temperature of the inner layer and below the lower of the melting point or thermal decomposition temperature of the outer layer, only the inner layer thermally decomposes, creating a gap between the conductor wire and the insulating coating. On the other hand, when the outer layer is formed by an extrusion method or a tape horizontal winding method, it is stretched in the longitudinal direction. Furthermore, when the outer layer is formed by a coating and curing method, a shrinkage force occurs during curing. That is, the outer layer has residual stress in the longitudinal direction that compresses it. When the inner layer of a conductor wire coated with an insulating coating thermally decomposes, a gap is created between the insulating coating and the conductor wire. Furthermore, when heat is applied, the outer layer of the insulating coating shrinks. Due to this effect, for example, when the end of a conductor wire coated with an insulating coating is heated to a predetermined temperature, such as the melting temperature of solder, the insulating coating can be removed to expose the conductor wire. This improves terminal processability.

[0028] The factors that improve termination workability can be explained as follows: Conductor wires expand thermally when heated by contact with solder or other materials. Insulating coatings, which are primarily made of resin or rubber materials, have a higher thermal expansion coefficient than conductor wires, which are often primarily made of metal materials such as copper, copper alloy, or nickel. Therefore, the insulating coating thermally expands more than the conductor wire, exerting a force that tries to peel the insulating coating from the conductor wire, causing cracks in the insulating coating. Solder or other materials penetrate these cracks in the insulating coating and promote the thermal decomposition of the inner layer of the insulating coating. Furthermore, the thermal decomposition of the inner layer generates decomposing gases, which push the outer layer away from the conductor wire. Based on these considerations, insulating coating materials with a high thermal expansion coefficient are preferred. Furthermore, if the temperature at which the inner layer material thermally decomposes is below the glass transition point of the outer layer material, the outer layer will not become rubbery and will be more susceptible to cracking.

[0029] Another factor that improves termination workability can be explained as follows: When solder or other materials come into contact with the insulating coating and are heated, the inner layer of the insulating coating thermally decomposes. If the decomposition gas produced by the thermal decomposition is a reducing gas, such as hydrogen, carbon monoxide, aldehyde, or low-molecular-weight alkane, the reducing gas reduces the oxide coating on the surface of the conductor wire. The reduction of the oxide coating on the surface of the conductor wire increases its wettability with solder or other materials. Increased wettability of the conductor wire surface facilitates penetration of solder or other materials between the conductor wire and the insulating coating, promoting the thermal decomposition of the inner layer and the peeling of the insulating coating, while ensuring reliable bonding between the solder or other materials and the conductor wire. The urethane resin used as the material for the inner layer 5c in the above embodiment generates reducing gases upon thermal decomposition. Alternatively, materials that generate reducing gases upon thermal decomposition can be blended with various resins, rubbers, etc., and the inner layer 5c can be made of this blend. These factors are conjectured by the inventors and do not affect or limit the scope of the present invention or patent rights.

[0030] The thickness of the inner layer 5c is preferably 2 μm or more. If the thickness is less than 2 μm, even if the inner layer 5c is thermally decomposed, there may not be enough space between the conductor wires 5a and the outer layer 5d, making it difficult to remove the outer layer 5d. Furthermore, the thickness of the inner layer 5c is preferably 5 μm or less or less than two-thirds of the total thickness of the insulating coating 5b. If the thickness of the inner layer 5c exceeds 5 μm and is two-thirds or more of the total thickness of the insulating coating 5b, a large amount of gas is generated during thermal decomposition of the inner layer 5c. For example, if the generated gas is combustible, it may adversely affect flame retardancy, making the influence of the generated gas no longer negligible. The thickness of the outer layer 5d is preferably 1 μm or more. As described above, the inner layer 5c is thermally decomposed at a relatively low temperature. Therefore, if the outer layer 5d is not thick enough, the insulating performance may not be maintained, especially at high temperatures. The thickness of the outer layer 5d is preferably 5 μm or less or less than three-quarters of the total thickness of the insulating coating. If the thickness of the outer layer 5d exceeds 5 μm and is 3 / 4 or more of the total thickness of the insulating coating, the outer layer 5d will become too rigid, and even if the inner layer 5c is thermally decomposed, it may be difficult to remove the outer layer 5d.

[0031] When winding the conductor wires 5a around the core material 3, it is preferable to wind them in parallel rather than twist them together. This is because winding them in parallel reduces the diameter of the heating core 4 and also makes the surface smoother. In addition to winding them in parallel and twisting them together, the conductor wires 5a can also be braided around the core material 3.

[0032] The insulator layer 7 may be formed by extrusion molding or the like, or a pre-formed tubular insulator layer 7 may be used. The method for forming the insulator layer 7 is not particularly limited. When the insulator layer 7 is formed by extrusion molding, the conductor wires 5a are fixed in position, making it less likely for the insulator layer 7 and the conductor wires 5a to become misaligned. This is preferable because it prevents friction and bending of the conductor wires 5a and improves bending resistance. The material for the insulator layer 7 can be appropriately selected depending on the usage form and environment of the cord-shaped heater. Examples of suitable materials include polyolefin resins, polyester resins, polyurethane resins, aromatic polyamide resins, aliphatic polyamide resins, vinyl chloride resins, modified Noryl resins (polyphenylene oxide resins), nylon resins, polystyrene resins, fluororesins, synthetic rubber, fluororubber, ethylene-based thermoplastic elastomers, urethane-based thermoplastic elastomers, styrene-based thermoplastic elastomers, polyester-based thermoplastic elastomers, and polyamide-based thermoplastic elastomers. In particular, flame-retardant polymer compositions are preferably used. Here, a flame-retardant polymer composition refers to one having an oxygen index of 21 or more in the flammability test of JIS-K7201 (1999). An oxygen index of 26 or more is particularly preferred. To achieve such flame retardancy, a flame retardant or the like may be appropriately blended into the material constituting the insulator layer 7. Examples of flame retardants include metal hydrates such as magnesium hydroxide and aluminum hydroxide, antimony oxide, melamine compounds, phosphorus-based compounds, chlorine-based flame retardants, and bromine-based flame retardants. These flame retardants may be appropriately surface-treated by known methods.

[0033] Furthermore, by forming the insulating layer 7 from a heat-sealing material, the cord-shaped heater 10 can be heat-sealed to the substrate 11 by applying heat and pressure. In such cases, among the materials constituting the insulating layer 7, olefin-based resins are preferred because of their excellent adhesion to the substrate 11. Examples of olefin-based resins include high-density polyethylene, low-density polyethylene, very-low-density polyethylene, linear low-density polyethylene, polypropylene, polybutene, ethylene-α-olefin copolymer, and ethylene-unsaturated ester copolymer. Examples of ethylene-unsaturated ester copolymers include ethylene-vinyl acetate copolymer, ethylene-methyl (meth)acrylate copolymer, ethylene-ethyl (meth)acrylate copolymer, and ethylene-butyl (meth)acrylate copolymer. These may be used alone or in combination. Here, "(meth)acrylic acid" refers to both acrylic acid and methacrylic acid. While any material may be selected from these, it is preferable to use a material that melts at a temperature below the decomposition onset temperature or melting point of the material constituting the insulating coating 5b. Furthermore, polyester-based thermoplastic elastomers are examples of materials that have excellent adhesion to the substrate 11. Polyester-based thermoplastic elastomers include polyester-polyester and polyester-polyether types, with polyester-polyether types being preferred due to their high adhesive properties. When heat-sealing the cord-shaped heater 10 to the substrate 11, the adhesive strength between the cord-shaped heater 10 and the substrate 11 is extremely important. If this adhesive strength is insufficient, the substrate 11 and the cord-shaped heater 10 may peel off over use, causing the cord-shaped heater 10 to bend unexpectedly, increasing the likelihood of the conductor wire 5a breaking. Breaking the conductor wire 5a not only renders the heater ineffective, but can also lead to chattering and sparks. Furthermore, when the cord-shaped heater 10 is used at high temperatures, it is preferable to use a polyamide-based thermoplastic elastomer. Of course, the above-mentioned materials for the insulating layer 7 may be used in combination, or various known additives such as flame retardants and antioxidants may be added.

[0034] The insulator layer 7 may be formed in one or more layers. For example, a fluororesin layer may be formed around the conductor wires 5a, followed by a polyethylene resin layer as a thermal adhesive around the fluororesin layer, and these two layers may form the insulator layer 7. Of course, three or more layers may also be used. Furthermore, the insulator layer 7 is not limited to being formed continuously along the length. For example, it may be formed in a linear or spiral pattern along the length of the cord-shaped heater 10, in a dotted pattern, or intermittently. In this case, it is preferable that the thermal adhesive material is not continuous along the length of the cord-shaped heater, because even if a portion of the thermal adhesive material ignites, the combustion does not spread. Furthermore, if the volume of the thermal adhesive material is sufficiently small, even if the thermal adhesive material is flammable, the combustion will quickly disappear and the fire will be extinguished, and no drips (burning droplets) will be generated. Therefore, it is preferable to keep the volume of the thermal adhesive material to the minimum necessary to maintain adhesion to the substrate 11.

[0035] Furthermore, the cord-shaped heater 10 obtained as described above is preferably able to be bent 20,000 times or more before at least one of the conductor wires breaks in a bending test in which the cord-shaped heater 10 is bent 90 degrees at a radius of curvature six times its own diameter.

[0036] Furthermore, when processing the ends of the cord-shaped heater 10, soldering may be performed as in the above embodiment, or other methods may be used. For example, by bringing a heat source of a predetermined temperature close to the end where the heating wire 1 is exposed or by blowing hot air of a predetermined temperature onto the end, the inner layer 5c will thermally decompose and the insulating coating 5b (outer layer 5d) will shrink, exposing the end of the conductor wire 5a. Note that the predetermined temperature here refers to a temperature equal to or higher than the thermal decomposition temperature of the inner layer 5c.

[0037] In addition to the nonwoven fabric described in the above embodiment, various materials can be used for the substrate 11, such as woven fabric, paper, aluminum foil, mica plate, resin sheet, foamed resin sheet, rubber sheet, foamed rubber sheet, and expanded porous material. However, materials having flame retardancy that passes the FMVSS-No. 302 combustion test for automotive interior materials are preferred. Here, FMVSS stands for Federal Motor Vehicle Safety Standard, and No. 302 specifies the combustion test for automotive interior materials. Among these, nonwoven fabrics are preferred, particularly for use in car seat heaters, due to their pleasant texture and flexibility. Furthermore, even when using nonwoven fabric, in the above embodiment, the heat-fusible fibers constituting the nonwoven fabric have a sheath-core structure with a low-melting-point polyester as the sheath component. However, other materials, such as fibers with a sheath-core structure with a low-melting-point polypropylene as the sheath component or fibers with a sheath-core structure with a polyethylene as the sheath component, can also be used. By using such a heat-fusible fiber, the sheath of the heat-fusible fiber and the heat-fusible portion 9 are fused together and integrated while surrounding the core of the heat-fusible fiber, resulting in very strong adhesion between the cord-shaped heater 1 and the nonwoven fabric. Furthermore, as the flame-retardant fiber, various flame-retardant fibers may be used in addition to the flame-retardant polyester. Here, flame-retardant fiber refers to a fiber that meets JIS-L1091 (1999). The use of such a flame-retardant fiber imparts excellent flame retardancy to the substrate.

[0038] The blending ratio of the heat-fusible fiber is preferably 5% or more, and preferably 20% or less. If the blending ratio of the heat-fusible fiber is less than 5%, sufficient adhesion cannot be obtained. If the blending ratio of the heat-fusible fiber exceeds 20%, the nonwoven fabric becomes hard, which may cause discomfort to the seat occupant, and conversely, may reduce adhesion to the cord-shaped heater. Furthermore, the heat generated during heat fusion may cause the substrate to shrink, making it impossible to achieve the intended dimensions in the design. The blending ratio of the flame-retardant fiber is 70% or more, preferably 70% to 95%. If the blending ratio of the flame-retardant fiber is less than 70%, sufficient flame retardancy cannot be obtained. If the blending ratio of the flame-retardant fiber exceeds 95%, the blending ratio of the heat-fusible fiber becomes relatively insufficient, and sufficient adhesion cannot be obtained. The mixing ratio of the heat-fusible fiber and the mixing ratio of the flame-retardant fiber do not need to add up to 100%, and other fibers may be appropriately mixed in. Even if the heat-fusible fiber is not mixed in, for example, by using the same type of material for the heat-fusible portion and the fiber material constituting the base material, necessary and sufficient adhesiveness may be obtained, so it is entirely possible that the heat-fusible fiber may not be mixed in.

[0039] The size and thickness of the nonwoven fabric may be varied as appropriate depending on the intended use, but the thickness (measured when dry) is preferably about 0.6 mm to 1.4 mm, for example. If a nonwoven fabric of this thickness is used, when the cord-shaped heater and the nonwoven fabric are bonded and fixed together by heat and pressure, the nonwoven fabric will be well bonded to at least 30%, and preferably at least 50%, of the outer periphery of the cord-shaped heater, thereby achieving a strong bond.

[0040] Among the above substrates, those having voids are preferred, and it is particularly preferred that the surface on which the cord-shaped heater is disposed (hereinafter referred to as the "disposition surface") has more voids than the surface on which the cord-shaped heater is not disposed (hereinafter referred to as the "non-disposition surface"). A state with many voids refers, for example, to a state in which the basis weight, i.e., the fiber weight per unit volume, is low in the case of fabric bodies such as woven fabrics and nonwoven fabrics, or a state in which the porosity is high in the case of porous bodies such as foamed resin sheets and foamed rubber sheets. Specific embodiments of the substrate according to the present invention include, for example, woven fabrics or nonwoven fabrics that have been calendered to different strengths on only one side or both sides by adjusting the temperature or pressure, nonwoven fabrics that have been needle-punched from only one side, fabric bodies with pile formation or nap formation on one side, foamed resin sheets or foamed rubber sheets that have been foam-controlled so that the porosity gradients in the thickness direction, and laminated materials with different void counts. Furthermore, it is particularly preferred that the voids in the substrate are continuous. This is because the molten heat-sealing layer penetrates into the continuous voids, increasing the anchoring effect and improving the adhesive strength. Examples of materials with continuous voids include fabrics such as woven fabrics and nonwoven fabrics that are aggregates of fibers, and foamed resin sheets and foamed rubber sheets with continuous pores. Note that the non-applied surface may not have voids.

[0041] Furthermore, when the cord-shaped heater 10 is disposed on the substrate 11, the cord-shaped heater 10 may be fixed to the substrate 11 in a manner other than by bonding and fixing by fusion bonding using heat and pressure. For example, various manners are possible, such as a manner in which the insulating layer 7 made of a thermal adhesive material is melted by hot air to bond and fix the cord-shaped heater 10, a manner in which the insulating layer 7 made of a thermal adhesive material is melted by the heat generated by passing electricity through the conductor wires 5a to bond and fix the cord-shaped heater 10, and a manner in which the cord-shaped heater 10 is sandwiched and fixed between a pair of substrates 11 while being heated.

[0042] Also, configurations that do not use a heat-sealing material are conceivable, such as arranging the cord-shaped heater 10 on the base material 11 by sewing, or clamping and fixing the cord-shaped heater 10 between a pair of base materials 11. In such cases, it is conceivable to not form the insulating layer 7, as shown in Figures 10 and 11.

[0043] Furthermore, in terms of the flexibility of the substrate 11 and maintaining a good texture, it is preferable to form an adhesive layer for fixing the sheet heater 31 to the seat by forming an adhesive layer consisting only of an adhesive on a release sheet or the like and transferring the adhesive layer from the release sheet to the surface of the substrate 11. This adhesive layer is preferably flame-retardant, and preferably has flame retardancy sufficient to pass the FMVSS-No. 302 automotive interior material combustion test by itself. For example, a polymeric acrylic adhesive may be used. The adhesive layer may be formed on either the surface to be mounted or the surface not to be mounted of the substrate.

[0044] The planar heater 31 having the above configuration may also be installed on a steering wheel 71 in the state shown in Fig. 13. This steering wheel 71 comprises a wheel portion 72, spoke portions 73, and a boss portion 74, and the planar heater 31 is installed between a wheel core material 77 and a covering material 78 of the wheel portion 72. [Example]

[0045] The cord-shaped heater 10 (see FIG. 1) obtained by the above embodiment was used as Example 1, and a processability test (continuity check with connection terminals), an insulation test (dielectric breakdown voltage test), and a flammability test (horizontal flame retardancy test) were performed.

[0046] The workability test was performed by checking the electrical continuity after terminal processing. First, the cord-shaped heater 10 was cut so that the conductor wire 5a had an effective length of 90 mm, and the insulator layer 7 was stripped off over 8 mm of the end. Similarly, the lead wire was cut so that the conductor (1.73 mm diameter) had an effective length of 90 mm, and the insulator was stripped off over 8 mm of the end. The cord-shaped heater 10 and the lead wire were aligned, and connection terminals (commercially available splice terminals) were attached to the ends. The cord-shaped heater 10 and the lead wire were connected by soldering using flux-cored solder (melting point 340°C). The resistance between the cord-shaped heater 10 and the lead wire was then measured. The average value was calculated for 20 samples (excluding samples with resistance values ​​so high that they were unmeasurable). Samples with an average value of less than 1 Ω and no unmeasurable samples were considered to have passed the test. Samples with an average value of 1 Ω or more or with any unmeasurable samples were considered to have failed the test. The results are shown in Table 1, with passing marks indicated as "O" and failing marks indicated as "X".

[0047] The insulation test involved testing the breakdown voltage of the insulating coating 5b. AC 1.5 kV was applied to the conductor wire 5a, and samples that did not experience breakdown were rated as passing, while samples that did experience breakdown were rated as failing. The results are shown in Table 1, with passing samples marked with "O" and failing samples marked with "X."

[0048] The flammability test was carried out based on the UL1581 horizontal burning test (2008, 4th edition), and the burning distance (width affected by the flame) was measured. A burning distance of 30 mm or less was deemed a pass, and a burning distance of more than 30 mm was deemed a fail. The results are shown in Table 1, with a pass indicated by "O" and a fail indicated by "X".

[0049] Comparative Examples 1 to 3 were prepared by varying the material of the insulating coating 5b of the cord-shaped heater 10 according to Example 1 (the above embodiment). Comparative Example 1 employed a single layer of polyamide-imide resin for the insulating coating 5b. Comparative Example 2 employed a single layer of polyurethane resin for the insulating coating 5b. Comparative Example 3 employed an inner layer 5c of the insulating coating 5b made of imide-containing urethane resin and an outer layer 5d of acrylic resin. Furthermore, Examples 2 to 8 and Comparative Examples 4 to 11 were prepared by varying the thicknesses of the inner layer 5c and outer layer 5d of the insulating coating 5b of the cord-shaped heater 10 according to Example 1 (the above embodiment). The materials and thicknesses of the inner layer 5c and outer layer 5d of Examples 1 to 8 are shown in Table 1. The materials and thicknesses of the inner layer 5c and outer layer 5d of Comparative Examples 1 to 11 are shown in Table 2. Tests were also conducted on these samples in the same manner as in Example 1. The test results for the examples are shown in Table 1, and the test results for the comparative examples are shown in Table 2.

[0050] [Table 1]

[0051] [Table 2]

[0052] In all of the cord-shaped heaters in Examples 1 to 8, the thermal decomposition temperature of the material constituting the inner layer is lower than the lower of the melting point or thermal decomposition temperature of the material constituting the outer layer. On the other hand, in the cord-shaped heater in Comparative Example 3, the thermal decomposition temperature of the material constituting the inner layer is higher than the melting point of the material constituting the outer layer. These thermal decomposition temperatures were measured in accordance with JIS-K7120-1997, a method for thermogravimetric measurement of plastics (or ISO7111-1997). Furthermore, the melting points were measured in accordance with JIS-K7121-1987, a method for measuring transition temperatures of plastics.

[0053] As shown in Tables 1 and 2, the cord-shaped heater 10 according to this example was confirmed to have excellent terminal workability. The cord-shaped heaters according to Comparative Examples 1 and 3 were unmeasurable, meaning that more than half of the samples had no insulating coating removed, resulting in poor product yields. Furthermore, the cord-shaped heater 10 according to this example also passed the flammability test, with the cord-shaped heater according to Example 2 being particularly excellent in flammability. The flammability range of the cord-shaped heaters according to Comparative Examples 2 and 3 far exceeded the acceptable range, resulting in poor flammability.

[0054] In addition, the cord-shaped heaters 10 according to Examples 1 to 6 have an inner layer 5c with a thickness of 2 μm or more and 5 μm or less, and an outer layer 5d with a thickness of 1 μm or more and 5 μm or less. In the cord-shaped heater 10 according to Example 5, the inner layer 5c has a thickness of 2 μm or more and less than two-thirds the thickness of the insulating coating 5b, and the outer layer 5d has a thickness of 1 μm or more and 5 μm or less. In the cord-shaped heaters 10 according to Examples 7 and 8, the inner layer 5c has a thickness of 2 μm or more and 5 μm or less, and the outer layer 5d has a thickness of 1 μm or more and less than three-quarters the thickness of the insulating coating 5b. Therefore, excellent results were obtained in the processability test, the voltage resistance test, and the flammability test. On the other hand, in Comparative Example 4, the inner layer 5c had a thickness of less than 2 μm, and therefore the outer layer 5d could not be reliably removed, resulting in a failed processability test. In Comparative Examples 5 to 7, the thickness of the inner layer 5c exceeded 5 μm and was more than two-thirds the thickness of the insulating coating 5b, so the flammable range far exceeded the acceptable line, resulting in poor flammability. In Comparative Example 8, the thickness of the outer layer 5d was less than 1 μm, so there were areas of dielectric breakdown and the insulation was poor. In Comparative Examples 9 to 11, the thickness of the outer layer 5d exceeded 5 μm and was more than three-quarters the thickness of the insulating coating 5b, so the outer layer 5d could not be reliably removed, resulting in unacceptable processability.

[0055] The cord-shaped heater 10 according to Example 1 was disposed in a linear shape on the substrate 11, and was adhered and fixed to the substrate 11 using the hot press heater manufacturing apparatus 13 as described above. The cord-shaped heater 10 adhered and fixed to the substrate 11 was also subjected to a bending test in the same manner as described above. The cord-shaped heater 10 according to Example 1 was also disposed in a linear shape on the substrate 11, and was adhered and fixed to the substrate 11 using an adhesive tape. The cord-shaped heater 10 adhered and fixed to the substrate 11 was also subjected to a bending test in the same manner as described above. In all cases, sufficient bending resistance values ​​were observed, confirming that the cord-shaped heater 10 according to this example had sufficient bending resistance even when adhered and fixed to the substrate 11. [Industrial Applicability]

[0056] As described above, the present invention provides a cord-shaped heater with improved processability. This cord-shaped heater is formed into a predetermined shape, such as a serpentine shape, on a substrate such as aluminum foil, foamed resin, or nonwoven fabric to form a surface heater, which can be suitably used in electric blankets, electric carpets, car seat heaters, steering wheel heaters, heated toilet seats, heaters for anti-fog mirrors, anti-freeze heaters for cameras, cooking appliances, and the like. The cord-shaped heater can also be used alone, for example, by wrapping and adhering it around a pipe or a tank, or by placing it inside a pipe. Specific applications include anti-freeze heaters for pipes and freezer pipe drains, heat-retention heaters for air conditioners and dehumidifiers, defrosting heaters for refrigerators and freezers, drying heaters, and floor heating heaters. Furthermore, for the electric blankets, electric carpets, car seat heaters, steering wheel heaters, heated toilet seats, heaters for anti-fog mirrors, heating cookware, floor heating and the like, which are examples of uses for the above-mentioned surface heaters, the cord-shaped heater of the present invention can be directly attached to or wrapped around the object to be heated. [Explanation of symbols]

[0057] 1 heating wire 3 Core material 5a Conductor wire 5b Insulation coating 5c Inner layer 5d outer layer 7. Insulator layer 10 Cord heater 11 Base material 31 Planar heater 41 Vehicle seats

Claims

1. A cord-shaped heater having one or more conductor wires covered with an insulating coating, the insulating coating comprises at least an inner layer formed on the conductor wire and an outer layer formed outside the inner layer, the thermal decomposition temperature of the material constituting the inner layer is lower than the melting point or the thermal decomposition temperature of the material constituting the outer layer, whichever is lower; The thickness of the inner layer is 2 μm or more, the thickness of the inner layer is 5 μm or less or is less than two-thirds of the total thickness of the insulating coating; The thickness of the outer layer is 1 μm or more, the thickness of the outer layer is 5 μm or less or is less than 3 / 4 of the total thickness of the insulating coating; A cord-shaped heater characterized in that the material constituting the inner layer is a polyurethane resin or a polyester resin, and the material constituting the outer layer is any one of a polyimide resin, a polyamide-imide resin, and a silicone resin.

2. A cord-shaped heater having one or more conductor wires covered with an insulating coating, the insulating coating comprises at least an inner layer formed on the conductor wire and an outer layer formed outside the inner layer, the thermal decomposition temperature of the material constituting the inner layer is lower than the melting point or the thermal decomposition temperature of the material constituting the outer layer, whichever is lower; The thickness of the inner layer is 2 μm or more, the thickness of the inner layer is 5 μm or less or is less than two-thirds of the total thickness of the insulating coating; The thickness of the outer layer is 1 μm or more, the thickness of the outer layer is 5 μm or less or is less than 3 / 4 of the total thickness of the insulating coating; A cord heater characterized in that the material constituting the inner layer is a polyurethane resin, and the material constituting the outer layer is a polyamide-imide resin.

3. 3. A sheet heater comprising the cord heater according to claim 1 or 2 disposed on a substrate.

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