Method for manufacturing insulated electric wire, and insulated electric wire

Abstract

This method for manufacturing an insulated electric wire includes: a step for preparing a conducting body; a step for annealing the conducting body; a step for applying a varnish around the conducting body, wherein the varnish contains a polyamide-imide resin or a polyimide resin and further contains a carbodiimide compound or organified clay containing a quaternary ammonium salt; and a step for baking the varnish applied to the conducting body to form an insulation film. In the insulation film, the organified clay or the carbodiimide compound is blended in an amount of 1 mass% or more and less than 10 mass%.

Description

Insulated wire manufacturing method and insulated wire

[0001] The present invention relates to a method for manufacturing an insulated wire and an insulated wire.

[0002] Conventionally, motors mounted on battery-powered electric vehicles, hybrid vehicles, and the like are often used in oils such as automatic transmission fluid (ATF) and gear oil to improve efficiency. Since the ATF and gear oil reach high temperatures during use, motors require oil resistance and heat resistance. Highly heat-resistant polyamideimide and polyimide are used for insulating coatings of motor windings (see, for example, Patent Document 1).

[0003] Patent Document 1 describes an insulated wire having a conductor and an insulating coating with a three-layer structure, in which the insulating coating has a first layer made of a first polyamide-imide containing an adhesion improver, a second layer made of a highly flexible second polyamide-imide, and a third layer made of a polyimide.

[0004] Japanese Patent Application Laid-Open No. 2015-135766

[0005] In the near future, it is expected that oils with lower molecular weights than those currently on the market will be used to reduce the viscosity of oils around motors. When using low-molecular-weight oils, insulating coatings made of polyamide-imide or polyimide, as described in Patent Document 1, cannot prevent the penetration of low-molecular-weight oils. However, by blending insulating coatings with crystalline polymers (thermoplastic resins) such as polyether ether ketone (PEEK) or polyphenylene sulfide (PPS), the penetration of low-molecular-weight oils can be prevented. However, insulating coatings containing these materials cannot be used for motor windings because they deform in high-temperature environments.

[0006] Furthermore, insulated wires (enameled wires) such as those used in motor windings, residual stress occurs in the insulating coating after molding, which can cause cracks when the insulating coating comes into contact with polar solvents or oil. Even if cracks do not occur, hydrolysis due to the moisture in the oil or oxidation of additives contained in the oil in high-temperature environments can accelerate deterioration of the insulating coating.

[0007] SUMMARY OF THE INVENTION It is therefore a primary object of the present invention to provide an insulated wire having oil resistance and heat resistance, and a method for manufacturing the same.

[0008] In order to solve the above-mentioned problems, one aspect of the present invention provides a method for producing an insulated wire having a conductor and an insulating coating covering the conductor, the method comprising the steps of: preparing the conductor; annealing the conductor; applying a varnish containing a polyamide-imide resin or a polyimide resin and an organized clay containing a quaternary ammonium salt around the conductor; and baking the varnish applied to the conductor to form the insulating coating, wherein the insulating coating contains 1% by mass or more and less than 10% by mass of the organized clay.

[0009] According to another aspect of the present invention, there is provided a method for producing an insulated wire having a conductor and an insulating coating covering the conductor, the method comprising the steps of: preparing the conductor; annealing the conductor; applying a varnish containing a polyamide-imide resin or a polyimide resin and a carbodiimide compound around the conductor; and baking the varnish applied to the conductor to form the insulating coating, wherein the carbodiimide compound is blended in an amount of 1% by mass or more and less than 10% by mass in the insulating coating.

[0010] According to another aspect of the present invention, there is provided an insulated wire having a conductor and an insulating coating covering the conductor, wherein the insulating coating contains a polyamide-imide resin or a polyimide resin, and an organized clay containing a quaternary ammonium salt, and the amount of the organized clay in the insulating coating is 1% by mass or more and less than 10% by mass.

[0011] According to another aspect of the present invention, there is provided an insulated wire having a conductor and an insulating coating covering the conductor, wherein the insulating coating contains a polyamide-imide resin or a polyimide resin and a carbodiimide compound, and the amount of the carbodiimide compound in the insulating coating is 1% by mass or more and less than 10% by mass.

[0012] According to the present invention, an insulated wire having oil resistance and heat resistance is provided.

[0013] 1A and 1B are cross-sectional views of an insulated wire according to an embodiment of the present invention, and Fig. 2 is a flowchart of a method for manufacturing an insulated wire according to an embodiment of the present invention.

[0014] An insulated wire and a method for manufacturing an insulated wire according to an embodiment of the present invention will now be described with reference to the accompanying drawings. The insulated wire manufactured by the method for manufacturing an insulated wire according to the embodiment of the present invention can be used, for example, as a winding for an in-vehicle motor.

[0015] First Embodiment (Configuration of Insulated Wire) FIGS. 1A and 1B are schematic diagrams showing the configuration of an insulated wire.

[0016] As shown in FIGS. 1A and 1B , the insulated wire 1 has a conductor 3 and an insulating coating 5. The conductor 3 is the same as that in conventional insulated wires, and is preferably a copper wire. The copper in the copper wire may be a tough pitch material, but low-oxygen copper with an oxygen content of 30 ppm or less is preferred, low-oxygen copper or oxygen-free copper with an oxygen content of 20 ppm or less is more preferred, and oxygen-free copper with an oxygen content of 10 ppm or less (MiDIP (registered trademark); SWCC Corporation) is particularly preferred. When the copper is low-oxygen copper or oxygen-free copper, voids that cause electrical resistance are less likely to occur when the conductors 3 of multiple insulated wires 1 are welded together. The conductor 3 may be an aluminum wire or an aluminum alloy wire. When a high current value is required for the insulated wire 1, the conductor 3 is preferably made of pure aluminum with a purity of, for example, 99.00% or higher.

[0017] The cross-sectional shape of the conductor 3 is not particularly limited and is selected appropriately depending on the application. As shown in FIG. 1A, the cross-section of the conductor 3 may be circular, or as shown in FIG. 1B, the cross-section of the conductor 3 may be rectangular. The cross-sectional shape of the conductor 3 may also be other shapes, such as a hexagon. If the cross-section is rectangular, it is preferable that the corners are chamfered. The cross-sectional size of the conductor 3 is selected appropriately depending on the application. If the cross-section is circular, its diameter is typically within the range of 0.3 mm to 3 mm. If the cross-section is rectangular, its long side is typically within the range of 1 mm to 10 mm, and its short side is typically within the range of 0.4 mm to 5 mm.

[0018] The insulating coating 5 is a layer that covers the conductor 3. In this embodiment, the insulating coating 5 contains a polyamide-imide resin or a polyimide resin and an organoclay containing a quaternary ammonium salt. The insulating coating 5 is a film formed by applying and baking a varnish, which will be described in the manufacturing method described below, i.e., a cured varnish film. The structure of the polyamide-imide resin is not particularly limited, but a polyamide-imide resin obtained from trimellitic anhydride and a diisocyanate is preferred. The structure of the polyimide resin is also not particularly limited, but a polyimide resin obtained from pyromellitic dianhydride and oxydiphenylamine is preferred. In this embodiment, the resin contained in the varnish is preferably a polyamide-imide resin rather than a polyimide resin, because it is resistant to abrasion and is less likely to be scratched during coil winding, and therefore is less likely to become a starting point for cracks when it comes into contact with oil, etc.

[0019] The organized clay contains a quaternary ammonium salt. Examples of the organized clay include organized montmorillonite and organized bentonite. Examples of the quaternary ammonium salt include dimethyldialkylammonium salt and dimethylalkylbenzylammonium salt. The number of carbon atoms in the alkyl group in the quaternary ammonium is preferably in the range of 1 to 20. The amount of organized clay in the insulating coating 5 is preferably in the range of 1% by mass or more but less than 10% by mass, more preferably in the range of 2% by mass or more but less than 4% by mass, and even more preferably in the range of 3% by mass or more but less than 4% by mass. When the amount of organized clay in the insulating coating 5 is less than 1% by mass, the oil resistance and hydrolysis resistance are reduced. On the other hand, when the amount of organized clay in the insulating coating 5 is 10% by mass or more, the flexibility is reduced. The organized clay is thought to adsorb substances that cause deterioration of the insulating coating 5. Examples of substances that cause deterioration of the insulating coating include adipic acid, carboxylic acid, and hot water. Because the organized clay adsorbs substances that cause deterioration, deterioration of the insulating coating 5 can be suppressed.

[0020] Examples of other components of the insulating coating 5 include pigments, dyes, and various additives. The thickness of the insulating coating 5 is selected appropriately depending on the application of the insulated wire 1, but is typically within the range of 10 μm to 60 μm. The insulating coating 5 may have a single-layer structure, a two-layer structure, a three-layer structure, or a structure with more layers. When the insulating coating 5 has a multilayer structure, it is sufficient that one of the layers has the above-described configuration.

[0021] The insulating coating 5 may further contain an antioxidant. The antioxidant may be a hindered phenol-based antioxidant, a hindered amine-based antioxidant, or a phosphite-based antioxidant. The antioxidant is preferably an antioxidant present in an amount of 1 mass % or more selected from compounds containing a tert-butyl group and an amide bond, and compounds containing two or more structures represented by the following general formula: An example of the compound containing a tert-butyl group and an amide bond includes Irganox (registered trademark) 1098 (BASF Japan Ltd.). An example of the compound containing two or more structures represented by the following general formula includes a compound containing an isocyanurate ring (Irganox 3114 (BASF Japan Ltd.)).

[0022] In the above formula, R １ , R ２ and R ３ is an alkyl group, an aryl group, or the like.

[0023] As mentioned above, examples of commercially available antioxidants that satisfy the above conditions include Irganox 1098 and 3114 (both manufactured by BASF Japan Ltd.). The amount of antioxidant in the insulating coating 5 is preferably in the range of 1% by mass to 4% by mass, more preferably in the range of 1% by mass to 2% by mass. When the insulating coating has a structure of two or more layers, the antioxidant is preferably contained in the outermost layer or in all layers.

[0024] (Method for Manufacturing Insulated Wire) Next, a method for manufacturing the insulated wire 1 will be described. FIG.

[0025] The method for manufacturing the insulated wire 1 includes a step of preparing the conductor 3 (S110), a step of annealing the conductor 3 (S120), a step of applying varnish (S130), and a step of baking the varnish (S140).

[0026] In the step (S110) of preparing the conductor 3, the above-described conductor 3 is prepared. The conductor 3 may be manufactured by any known method, and may be adjusted to a desired shape and size by wire drawing.

[0027] In the step of annealing the conductor 3 (S120), the conductor 3 obtained by wire drawing was annealed in a steam bright furnace at 500° C. for 10 to 30 seconds.

[0028] In the varnish application step (S130), the varnish is applied to the conductor 3. The varnish contains a polyamide-imide resin or polyimide resin, an organo-clay containing a quaternary ammonium salt, and a solvent. The varnish may also contain an antioxidant, if necessary. The resin, organo-clay, and antioxidant are as described above. Examples of the solvent include aprotic polar organic solvents such as N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and γ-butyrolactone. One or more solvents may be used. The method for preparing the varnish is not particularly limited. A resin-containing varnish containing a solvent and a resin is prepared, and a predetermined amount of organo-clay is added to the resin-containing varnish. In this case, after mixing the resin-containing varnish and the solvent, stirring or dispersion is preferably performed to ensure uniform dispersion of the solvent. The varnish can be applied using a known method. An example of a method for applying varnish includes inserting the conductor 3 into a die having an opening that is slightly larger than the cross section of the conductor 3 and has a shape that is approximately similar to the cross section of the conductor 3, and applying varnish within the die while moving the conductor 3 in one direction.

[0029] In the step of baking the varnish (S140), the varnish is applied and then baked. Baking the varnish can be performed by a known method, and heating may be performed in a vertical furnace or a horizontal furnace. The baking temperature is selected appropriately depending on the resin in the varnish, and may be a temperature that can remove the solvent in the varnish. The baking time is selected appropriately depending on the type of resin and the amount of solvent in the varnish. The thickness of the film formed by applying and baking the varnish once is preferably in the range of 1 μm to 6 μm, and it is preferable to form the insulating coating 5 by applying and baking the varnish multiple times (e.g., 8 or more times) until the desired thickness is achieved.

[0030] (Effects) As described above, the insulated wire of the present embodiment contains polyamide-imide resin or polyimide resin and a predetermined amount of organized clay, and therefore has excellent oil resistance and heat resistance.

[0031] Second Embodiment (Configuration of Insulated Wire) The insulated wire 1 has a conductor 3 and an insulating coating 5. The conductor 3 is the same as in the first embodiment.

[0032] The insulating coating 5 contains a polyamide-imide resin or a polyimide resin and a carbodiimide compound. The structure of the polyamide-imide resin is not particularly limited, but a polyamide-imide resin obtained from trimellitic anhydride and diisocyanate is preferred. The structure of the polyimide resin is also not particularly limited, but a polyimide resin obtained from pyromellitic dianhydride and oxydiphenylamine is preferred. In this embodiment, the resin contained in the varnish is preferably a polyamide-imide resin rather than a polyimide resin, because it is resistant to abrasion and is less likely to be scratched during coil winding, and therefore is less likely to become a starting point for cracks when it comes into contact with oil, etc.

[0033] The carbodiimide compound has a carbodiimide group. Examples of carbodiimide compounds include monomers having a carbodiimide group, such as N,N'-bis(2,6-diisopropylphenyl)carbodiimide, N,N'-isopropylphenyl)carbodiimide, 1,3-diisopropylcarbodiimide, and N,N'-dicyclohexylcarbodiimide, as well as oligomers in which a small number of the above-mentioned monomers are bonded, and polymers in which a large number of the above-mentioned monomers are bonded. Examples of commercially available carbodiimide compounds include Stabaxol (registered trademark) I (Hiraizumi Yoko Co., Ltd.), Carbodilite V-05, and V-09 (all manufactured by Nisshinbo Chemical Inc.). The amount of the carbodiimide compound in the insulating coating 5 is preferably in the range of 1% by mass or more but less than 10% by mass, more preferably in the range of 1% by mass or more but less than 4% by mass, and even more preferably in the range of 1% by mass or more but less than 2% by mass. If the amount of the carbodiimide compound in the insulating coating 5 is less than 1% by mass, the oil resistance and hydrolysis resistance are reduced. On the other hand, when the carbodiimide compound in the insulating coating 5 is 10 mass % or more, flexibility decreases. It is believed that the carbodiimide compound adsorbs substances that cause deterioration of the insulating coating 5. Examples of substances that cause deterioration of the insulating coating include adipic acid, carboxylic acid, and high-temperature water. Because the carbodiimide compound adsorbs the substances that cause deterioration, deterioration of the insulating coating 5 can be suppressed.

[0034] The insulating coating 5 may further contain the above-mentioned antioxidant. The antioxidant is preferably one or more antioxidants selected from compounds containing a tert-butyl group and an amide bond, and compounds containing two or more structures represented by the following general formula: Irganox 1098 (BASF Japan Ltd.) An example of a compound containing two or more structures represented by the following general formula: Irganox 3114 (BASF Japan Ltd.) A compound containing an isocyanurate ring is included.

[0035] In the above formula, R １ , R ２ and R ３ is an alkyl group, an aryl group, or the like.

[0036] Examples of commercially available antioxidants that satisfy the above conditions include Irganox (registered trademark) 1098 and 3114 (both manufactured by BASF Japan Ltd.). The amount of antioxidant in the insulating coating 5 is preferably in the range of 1% by mass to 4% by mass, more preferably in the range of 1% by mass to 2% by mass. When the insulating coating has a multilayer structure, the antioxidant is preferably contained in the outermost layer or in all layers.

[0037] (Method for Producing Insulated Wire) Next, a description will be given of a method for producing the insulated wire 1. The method for producing the insulated wire 1 in this embodiment differs from the method for producing the insulated wire 1 in the first embodiment in that the varnish contains a carbodiimide compound instead of an organized clay.

[0038] The method for manufacturing the insulated wire 1 includes a step of preparing the conductor 3 (S110), a step of annealing the conductor 3 (S120), a step of applying varnish (S130), and a step of baking the varnish (S140) (see FIG. 2).

[0039] In the step (S110) of preparing the conductor 3, the above-described conductor 3 is prepared. The conductor 3 may be manufactured by any known method, and may be adjusted to a desired shape and size by wire drawing.

[0040] In the step of annealing the conductor 3 (S120), the conductor 3 obtained by wire drawing was annealed in a steam bright furnace at 500° C. for 10 to 30 seconds.

[0041] In the varnish application step (S130), the varnish is applied to the conductor 3. The varnish contains a polyamide-imide resin or polyimide resin, a carbodiimide compound, and a solvent. The varnish may contain an antioxidant, if necessary. The resin, carbodiimide compound, and antioxidant are as described above. Examples of the solvent include aprotic polar organic solvents such as N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and γ-butyrolactone. One or more solvents may be used. The method for preparing the varnish is not particularly limited. A resin-containing varnish containing a solvent and a resin is prepared, and a predetermined amount of a carbodiimide compound is added to the resin-containing varnish. In this case, after mixing the resin-containing varnish and the solvent, stirring or dispersion is preferably performed to ensure uniform dispersion of the solvent. The varnish can be applied using a known method. An example of a method for applying varnish includes inserting the conductor 3 into a die having an opening that is slightly larger than the cross section of the conductor 3 and has a shape that is approximately similar to the cross section of the conductor 3, and applying varnish within the die while moving the conductor 3 in one direction.

[0042] In the step of baking the varnish (S140), the varnish is applied and then baked. Baking the varnish can be performed by a known method, and heating may be performed in a vertical furnace or a horizontal furnace. The baking temperature is selected appropriately depending on the resin in the varnish, and may be a temperature that can remove the solvent in the varnish. The baking time is selected appropriately depending on the type of resin and the amount of solvent in the varnish. The thickness of the film formed by applying and baking the varnish once is preferably in the range of 1 μm to 6 μm, and it is preferable to form the insulating coating 5 by applying and baking the varnish multiple times (e.g., 8 or more times) until the desired thickness is achieved.

[0043] (Effects) As described above, the insulated wire of the present embodiment contains polyamide-imide resin or polyimide resin and a predetermined amount of carbodiimide compound, and therefore has excellent oil resistance and heat resistance.

[0044] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited by these examples, and the embodiments can be modified without departing from the spirit of the present invention.

[0045] [Manufacturing of Insulated Wire] (Insulated Wire 1) A round wire conductor (oxygen-free copper, MiDIP®; SWCC Corporation) with a circular cross-sectional shape (diameter approximately 1.0 mm) was prepared as the conductor. A varnish composed of polyamide-imide resin, organo-clay (organo-montmorillonite, product name: SANZ (Hojun Co., Ltd.)), and solvents (NMP, xylene, ethylbenzene) was prepared. The amount of organo-clay (organo-montmorillonite) added was 4 mass% relative to the insulating coating (varnish solids: polyamide-imide resin and organo-clay). The conductor was inserted into a varnish-applying die, and while moving the conductor in one direction, the varnish was applied within the die and baked at 400°C. The varnish application and baking were repeated 8 to 13 times to obtain an insulated wire 1 having an insulating coating thickness of 35 μm (0.035 mm).

[0046] (Insulated Wire 2) An insulated wire 2 was obtained in the same manner as in the production of the insulated wire 1, except that a carbodiimide compound (Stabaxol I (Heisen Yoko Co., Ltd.)) was added to the varnish instead of the organized clay (organically-modified montmorillonite), and the amount of the carbodiimide compound added was 2 mass % relative to the insulating coating (solid content of the varnish: polyamide-imide resin and carbodiimide compound).

[0047] (Insulated Wire 3) Insulated wire 3 was obtained in the same manner as in the production of insulated wire 1, except that a carbodiimide compound (Carbodilite V-05 (Nisshinbo Chemical Inc.)) was added to the varnish instead of the organized clay (organically-modified montmorillonite), and the amount of the carbodiimide compound added was 1 mass % relative to the insulating coating (solid content of the varnish: polyamideimide resin and carbodiimide compound).

[0048] (Insulated Wire 4) A first varnish consisting of polyamide-imide resin and solvents (NMP, xylene, and ethylbenzene) and a second varnish consisting of polyamide-imide resin, organo-clay (organo-montmorillonite), and solvents (NMP, xylene, and ethylbenzene) were prepared. The amount of organo-clay (organo-montmorillonite) added was 3 mass% of the total insulating coating (the total solid content of the first varnish and the second varnish). A conductor was inserted into a varnish-applying die, and while the conductor was moved in one direction, the first varnish was applied within the die and baked at 400°C to form a 17 μm-thick coating (first layer). The second varnish was then baked on the first layer at 400°C to form a 17 μm-thick coating (second layer). The application of the first varnish and the second varnish and the baking were repeated 8 to 13 times in total to obtain an insulated wire 4 having an insulating coating with a thickness of 34 μm (0.034 mm).

[0049] (Insulated Wire 5) A first varnish containing polyamide-imide resin, organo-clay (organo-montmorillonite), and solvents (NMP, xylene, and ethylbenzene) was prepared. A second varnish containing polyamide-imide resin and solvents (NMP, xylene, and ethylbenzene) was prepared. The amount of organo-clay (organo-montmorillonite) added was 4 mass% of the total insulating coating (the total solid content of the first varnish and the second varnish). A conductor was inserted into a die for applying the varnish. While the conductor was moved in one direction, the first varnish was applied to the die and baked at 400°C to form a 17 μm-thick coating (first layer). The second varnish was then baked on the first layer at 400°C to form an 18 μm-thick coating (second layer). The application of the first varnish and the second varnish and the baking were repeated 8 to 13 times in total to obtain an insulated wire 5 having an insulating coating with a thickness of 35 μm (0.035 mm).

[0050] (Insulated Wire 6) Insulated wire 6 was obtained in the same manner as insulated wire 1, except that a varnish containing polyamide-imide resin, organized clay (organically modified montmorillonite), antioxidant (Irganox 1098 (BASF Japan Ltd.)), and solvents (NMP, xylene, ethylbenzene) was used instead of the varnish used in producing insulated wire 1. In this case, the amount of the organized clay added was 3 mass % relative to the insulating coating (solid content of the varnish: polyamide-imide resin, organized clay, and antioxidant), and the amount of the antioxidant added was 2 mass % relative to the insulating coating (solid content of the varnish: polyamide-imide resin, organized clay, and antioxidant).

[0051] (Insulated Wire 7) Insulated wire 7 was obtained in the same manner as insulated wire 1, except that a varnish containing polyamide-imide resin, organized clay (organically modified montmorillonite), antioxidant (Irganox 3114 (BASF Japan Ltd.)), and solvents (NMP, xylene, ethylbenzene) was used instead of the varnish used in producing insulated wire 1. In this case, the amount of the organized clay added was 3 mass % relative to the insulating coating (solid contents of the varnish: polyamide-imide resin, organized clay, and antioxidant), and the amount of the antioxidant added was 2 mass % relative to the insulating coating (solid contents of the varnish: polyamide-imide resin, organized clay, and antioxidant).

[0052] (Insulated Wire 8) Insulated wire 8 was obtained in the same manner as insulated wire 1, except that a varnish composed of polyamideimide resin and solvents (NMP, xylene, ethylbenzene) was used instead of the varnish used in producing insulated wire 1.

[0053] (Insulated Wire 9) Insulated wire 9 was obtained in the same manner as insulated wire 1, except that a varnish containing polyamideimide resin, an antioxidant (MD1024 (BASF Japan Ltd.)), and a solvent (NMP, xylene, ethylbenzene) was used instead of the varnish used in producing insulated wire 1. In this case, the amount of antioxidant (Irganox MD1024 (BASF Japan Ltd.)) added was 1 mass % with respect to the insulating coating (solid content of varnish: polyamideimide resin and antioxidant).

[0054] (Insulated wire 10) An insulated wire 10 was obtained in the same manner as in the production of the insulated wire 1, except that a varnish containing a polyamide-imide resin, an antioxidant (Nocrac White (Ouchi Shinko Chemical Industry Co., Ltd.)), and a solvent (NMP, xylene, ethylbenzene) was used instead of the varnish used in the production of the insulated wire 1. In this case, the amount of the antioxidant (Nocrac White) added was 1 mass % relative to the insulating coating (solid content of the varnish: polyamide-imide resin and antioxidant).

[0055] (Insulated wire 11) An insulated wire 11 was obtained in the same manner as in the production of the insulated wire 1, except that a varnish containing polyamide-imide resin, silica, and solvents (NMP, xylene, ethylbenzene) was used instead of the varnish used in the production of the insulated wire 1. In this case, the amount of silica added was 5 mass % relative to the insulating coating (solid content of the varnish: polyamide-silica resin and antioxidant).

[0056] (Insulated wire 12) An insulated wire 12 was obtained in the same manner as in the production of the insulated wire 1, except that a varnish containing polyamide-imide resin, titanium oxide, and solvents (NMP, xylene, ethylbenzene) was used instead of the varnish used in the production of the insulated wire 1. In this case, the amount of titanium oxide added was 4 mass % relative to the insulating coating (solid content of the varnish: polyamide-imide resin and antioxidant).

[0057] (Insulated wire 13) An insulated wire 13 was obtained in the same manner as in the production of the insulated wire 1, except that the amount of the organized clay (organized montmorillonite) added was 10 mass % relative to the insulating coating (solid content of the varnish: polyamideimide resin and organized clay).

[0058] (Insulated wire 14) An insulated wire 14 was obtained in the same manner as in the production of the insulated wire 1, except that the amount of the organized clay (organized montmorillonite) added was set to 0.5 mass % relative to the insulating coating (solid content of the varnish: polyamideimide resin and organized clay).

[0059] (Insulated wire 15) Insulated wire 15 was obtained in the same manner as in the production of insulated wire 1, except that a carbodiimide compound (Stabaxol I) was added to the varnish instead of the organized clay (organically-modified montmorillonite), and the amount of the carbodiimide compound added was 10 mass % relative to the insulating coating (solid content of the varnish: polyamideimide resin and carbodiimide compound).

[0060] (Insulated wire 16) Insulated wire 16 was obtained in the same manner as in the production of insulated wire 1, except that a carbodiimide compound (Stabaxol I) was added to the varnish instead of the organized clay (organically-modified montmorillonite), and the amount of the carbodiimide compound added was 0.5 mass % relative to the insulating coating (solid content of the varnish: polyamideimide resin and carbodiimide compound).

[0061] (Insulated Wire 17) Insulated wire 17 was obtained in the same manner as in the production of insulated wire 1, except that a varnish containing polyamideimide resin, an antioxidant (Irganox 1098), and a solvent (NMP, xylene, ethylbenzene) was used instead of the varnish used in the production of insulated wire 1. In this case, the amount of antioxidant (Irganox 1098) added was 1 mass % relative to the insulating coating (solid content of varnish: polyamideimide resin and antioxidant).

[0062] [Evaluation] (Evaluation of oil resistance and heat resistance) Evaluation of oil resistance and heat resistance was carried out in accordance with JIS C 3216-3 JA. 5.1.1. Here, test specimens were prepared, with winding diameters of 1d (d = own diameter) and 2d, and the number of turns was 100. After winding, the test specimens were immersed in ATF (Toyota Auto Fluid WS) containing 0.5 wt% water at 150°C for a predetermined period of time, and the crack occurrence rate was examined (number of samples n = 15). The evaluation criteria for oil resistance and heat resistance are as follows. Evaluation criteria for oil resistance and heat resistance: ◯: No cracks occurred in all 15 samples; ×: Cracks occurred in at least one of the 15 samples.

[0063] Table 1 shows the insulated wire number, the various components of the insulating coating, the various sizes of the insulated wire, and the evaluation results.

[0064]

[0065] As shown in Table 1, the insulated wires 1 to 7, whose insulating coatings included a polyamideimide resin and an organo clay or a carbodiimide compound containing a predetermined amount of a quaternary ammonium salt, had good oil resistance and heat resistance.

[0066] On the other hand, as shown in Table 1, insulated wire No. 8, which did not contain any organo-clay or carbodiimide compound or antioxidant, had poor oil resistance and heat resistance. Insulated wires Nos. 13 to 16, in which the organo-clay (or carbodiimide compound) content was not within the specified range, had low oil resistance and heat resistance. Insulated wires Nos. 9 to 12 and 17, which did not contain any organo-clay or carbodiimide compound but contained an antioxidant or inorganic compound, had good oil resistance and heat resistance at 150°C for 250 hours, but poor oil resistance and heat resistance at 150°C for 500 hours.

[0067] The insulated wire obtained by the present invention is useful, for example, as a winding for an on-vehicle motor.

[0068] 1 insulated wire 3 conductor 5 insulating coating

Claims

1. A method for producing an insulated wire having a conductor and an insulating coating covering the conductor, comprising the steps of: preparing the conductor; annealing the conductor; applying a varnish containing a polyamide-imide resin or a polyimide resin and an organo-clay containing a quaternary ammonium salt around the conductor; and baking the varnish applied to the conductor to form the insulating coating, wherein the organo-clay is blended in an amount of 1% by mass or more and less than 10% by mass in the insulating coating.

2. A method for producing an insulated wire having a conductor and an insulating coating covering the conductor, comprising the steps of: preparing the conductor; annealing the conductor; applying a varnish containing a polyamide-imide resin or a polyimide resin and a carbodiimide compound around the conductor; and baking the varnish applied to the conductor to form the insulating coating, wherein the carbodiimide compound is blended in an amount of 1% by mass or more and less than 10% by mass in the insulating coating.

3. The method for producing an insulated electric wire according to claim 1 or 2, wherein the varnish further contains 1 mass % or more of an antioxidant.

4. An insulated wire having a conductor and an insulating coating covering the conductor, wherein the insulating coating contains a polyamide-imide resin or a polyimide resin, and an organo-clay containing a quaternary ammonium salt, and the amount of the organo-clay in the insulating coating is 1 mass % or more and less than 10 mass %.

5. An insulated wire having a conductor and an insulating coating covering the conductor, wherein the insulating coating contains a polyamide-imide resin or a polyimide resin, and a carbodiimide compound, and the amount of the carbodiimide compound in the insulating coating is 1 mass % or more and less than 10 mass %.

6. The insulated wire according to claim 4 or 5, wherein the insulating coating further contains 1 mass % or more of an antioxidant.

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