Insulated wire, coil, rotating electrical machine, and electrical / electronic device

Abstract

An insulated wire having a conductor and an insulating coating film formed by repeating coating / baking of a resin varnish on the outer periphery of the conductor, the insulating coating film comprising an inner layer and an outer layer, the inner layer comprising one or more insulating layers having a thickness of less than 5 [mu] m, the outer layer comprising one or more insulating layers having a thickness of less than 5 [mu] m, and the outer layer comprising one or more insulating layers having a thickness of less than 5 [mu] m. The outer layer is further outside than the inner layer and is composed of a plurality of insulating layers, among the insulating layers constituting the outer layer, the thickness of the insulating layer in contact with the inner layer is 5 [mu] m or more, and the average thickness of the insulating layers constituting the outer layer is 5 [mu] m or more.

Description

Technical Field

[0001] The present invention relates to an insulated electric wire, a coil, a rotating electric machine, and an electric / electronic device. Background Art

[0002] In the coils for electrical / electronic equipment such as high-speed switching elements, inverter motors, and transformers, an insulated wire having a resin insulating film on the outer peripheral surface of a linear metal conductor is used as a magnetic conductor. The insulating film of the insulated wire is formed by coating / baking a thermosetting resin, extruding a thermoplastic resin, or a combination thereof.

[0003] Such insulated wires are required to have properties such as not to break the insulating film and not to peel off the conductor when subjected to bending, stretching, etc., in addition to high insulation properties provided by the insulating film. For example, Patent Document 1 discloses an insulated wire characterized in that a bonding layer having a total formula weight content of imide structures in a polyimide resin skeleton of 27% to 33% is directly in contact with the conductor, and an insulating layer composed of a polyimide resin having a total formula weight content of the imide structures in the polyimide resin skeleton of more than 27% and less than 37% is provided on the bonding layer, and the obtained insulated wire is described as having excellent conductor adhesion and interlayer adhesion.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2017-107701 Summary of the invention

[0007] Problems to be solved by the invention

[0008] The winding process (coil process) of insulated wires is increasing year by year, and the insulated wires are bent in a complicated manner with a small bending radius. Such insulated wires are required to have a conductor adhesion that makes it difficult for the insulating film to be peeled off from the conductor even through a higher degree of bending, and a high degree of flexibility that does not cause cracks in the insulating film.

[0009] An object of the present invention is to provide an insulated wire having excellent adhesion between an insulating layer and a conductor and excellent flexibility, and a coil, a rotating electrical machine, and an electric / electronic device using the insulated wire.

[0010] Means for solving problems

[0011] The present inventors have conducted research to solve the above-mentioned problems and have found that when an insulating film is formed by repeatedly applying and baking a resin varnish around a conductor, an inner layer is formed by providing one or more insulating layers (I) having a thickness of less than 5 μm from the conductor side, an insulating layer (II) having a thickness of 5 μm or more is formed in contact with the inner layer, and a plurality of insulating layers (III) are formed on the periphery of the insulating layer (II). In this case, by making the average thickness of the insulating layer of the outer layer composed of the insulating layer (II) and the insulating layer (III) 5 μm or more, the insulating film of the obtained insulated wire has excellent adhesion to the conductor and excellent flexibility. The present invention was completed by further repeated research based on these findings.

[0012] That is, the above-mentioned problems of the present invention are solved by the following means. [1]

[0014] An insulated wire comprises a conductor and an insulating coating formed by repeatedly applying and baking a resin varnish on the outer periphery of the conductor, wherein:

[0015] The insulating film is composed of an inner layer and an outer layer, the inner layer is composed of one or more insulating layers having a thickness of less than 5 μm, and the outer layer is located outside the inner layer and is composed of a plurality of insulating layers.

[0016] Among the insulating layers constituting the outer layer, the insulating layer in contact with the inner layer has a thickness of 5 μm or more, and the average thickness of the insulating layers constituting the outer layer is 5 μm or more. [2]

[0018] The insulated wire as described in the above [1], wherein, among the insulating layers constituting the inner layer, the maximum thickness and the minimum thickness of the insulating layer in contact with the conductor satisfy [maximum thickness / minimum thickness] ≤ 2.5. [3]

[0020] The insulated wire according to the above [1] or [2], wherein the thickness of the insulating film is 60 μm or more and 350 μm or less. [4]

[0022] The insulated wire as described in any one of [1] to [3] above, wherein the insulating coating includes polyamide-imide and / or polyimide. [5]

[0024] A coil using the insulated wire according to any one of [1] to [4] above. [6]

[0026] A rotating electrical machine or an electrical / electronic device comprising the coil described in [5] above.

[0027] In the present invention or in this specification, when simply referred to as "insulating layer", it refers to a layer formed by applying / baking a resin varnish once. In the present invention, an insulating layer formed by repeatedly applying / baking the same resin varnish multiple times is referred to as a multi-layer insulating layer. That is, regardless of whether the resin varnishes are the same or different, a layer formed by applying / baking once is counted as one insulating layer. In other words, when applying / baking is repeated, an insulating film is formed by laminating the same number of insulating layers as the number of repeated times. It should be noted that the number of layers can be confirmed using an optical microscope or a microscope after etching the cross section of the insulating layer.

[0028] In the present invention, as described above, the insulating coating in the insulated wire has a specific feature that it is formed by repeatedly applying and baking the resin varnish, but this only indicates the state of the insulating coating (i.e., indicates that the insulating coating is an enamel layer), thereby clarifying the structure or characteristics of the insulating coating.

[0029] In the present invention or in this specification, the cross-sectional shape of the insulated wire orthogonal to the longitudinal direction and the shape of the insulated wire including the conductor and the insulating film is sometimes referred to as simply the cross-sectional shape. The cross-sectional shape in the present invention does not mean that only the cut surface has a specific shape, but that the cross-sectional shape is continuously connected in the longitudinal direction of the entire insulated wire. Unless otherwise specified, the cross-sectional shape orthogonal to the longitudinal direction of the insulated wire is substantially the same for any part of the insulated wire.

[0030] In the present invention or this specification, a numerical range expressed using "to" means a range including the numerical values ​​described before and after the "to" as the lower limit and the upper limit.

[0031] In the present invention or this specification, "ppm" described as a unit of concentration is a mass standard.

[0032] Effects of the Invention

[0033] The insulated wire of the present invention has high adhesion between the insulating layer and the conductor and is also excellent in flexibility. In addition, the present invention provides a coil, a rotating electrical machine, and an electric / electronic device using the insulated wire having such excellent properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic cross-sectional view showing one embodiment of the insulated wire of the present invention.

[0035] Figure 2 This is a schematic cross-sectional view showing a method for measuring the thickness of the insulating layer of the insulated wire of the present invention.

[0036] Figure 3It is a schematic cross-sectional view showing a method for measuring the maximum thickness and the minimum thickness in the innermost layer of the insulated wire of the present invention.

[0037] Figure 4 This is a schematic exploded perspective view showing a preferred embodiment of a stator used in the electric / electronic device of the present invention.

[0038] Figure 5 This is a schematic perspective view showing a preferred embodiment of a stator used in the electric / electronic device of the present invention. DETAILED DESCRIPTION

[0039] Preferred embodiments of the present invention will be described, but the present invention is not limited to the following embodiments except as specified in the present invention.

[0040] [Insulated wire]

[0041] The insulated wire of the present invention comprises a conductor and an insulating film covering the outer periphery of the conductor. The insulating film is a so-called enamel layer (multi-layer enamel layer) formed by repeatedly applying and baking a resin varnish. The resin used in each insulating layer constituting the insulating film may be a thermosetting resin or a thermoplastic resin, and is usually a thermosetting resin.

[0042] The insulating layer is classified into an inner layer and an outer layer according to the thickness of the insulating layer, and the inner layer and the outer layer are combined together and are referred to as an insulating film in the present invention.

[0043] Figure 1 2 shows a cross-sectional view of an embodiment of the insulated wire of the present invention. The insulated wire 1 includes a conductor 11, an inner layer 12 formed on the outer peripheral surface of the conductor 11, and an outer layer 13 formed on the outer peripheral surface of the inner layer 12. Figure 1 In the insulated wire shown, both the inner layer 12 and the outer layer 13 are laminated insulating layers (multi-layer insulating layers) in which a plurality of insulating layers are laminated.

[0044] The insulating layer in the inner layer 12 that is in contact with the conductor and arranged on the outer peripheral surface of the conductor is the inner innermost layer 14. The insulating layer in the outer layer 13 that is in contact with the outermost insulating layer of the inner layer (inner outermost layer) and arranged on the outer peripheral surface of the inner outermost layer is the outer innermost layer 15.

[0045] The cross-sectional shape of the insulated wire of the present invention is preferably similar to that of the conductor, and it is particularly preferred that the shape of the entire insulating film, that is, the cross-sectional shape of the outermost surface of the insulating film on the opposite side of the conductor is similar to that of the conductor. It should be noted that the similar shape is not limited to a completely similar shape, as long as it is a substantially similar shape.

[0046] <Conductor>

[0047] As the conductor used in the present invention, the conductor used in the insulated wire in the past can be used, and metal conductors such as copper wire and aluminum wire can be mentioned. In the present invention, copper conductors are preferred, and the copper used is preferably low-oxygen copper with an oxygen content of 30 ppm or less, and more preferably low-oxygen copper or oxygen-free copper with an oxygen content of 20 ppm or less. If the oxygen content is 30 ppm or less, when the conductor is melted by heat for welding, voids caused by the contained oxygen will not be generated in the welded portion, and the resistance of the welded portion can be prevented from deteriorating, and the strength of the welded portion can be maintained.

[0048] It should be noted that when the conductor is aluminum, various aluminum alloys can be used according to the application in consideration of the required mechanical strength. For example, for applications such as rotating electrical machines, pure aluminum with a purity of 99.00% or more that can provide a high current value is preferably used.

[0049] The cross-sectional shape of the conductor used in the present invention that is orthogonal to the longitudinal direction is not particularly limited. For example, conductors with circular or rectangular (square) cross-sectional shapes can be cited. In the present invention, conductors with rectangular cross-sectional shapes, i.e., square conductors, are preferred. Compared with circular conductors, conductors with rectangular cross-sectional shapes have a higher space factor relative to the slots of the stator core during winding. Therefore, it is preferred for applications in which multiple insulated wires are assembled in a certain narrow space. As a preferred example of the conductor used in the present invention, Figure 1 The case where the conductor has a rectangular cross section (square shape) is shown.

[0050] In terms of suppressing partial discharge from the corners (corners), the conductor having a rectangular cross-sectional shape is preferably as follows: Figure 1 The shape shown is provided with chamfers (curvature radius r) at four corners. The curvature radius r is preferably 0.6 mm or less, more preferably 0.2 to 0.4 mm.

[0051] The size of the conductor is not particularly limited. In the case of a square conductor, in a rectangular cross-sectional shape, the width (long side) is preferably 1.0 to 10.0 mm, more preferably 1.0 to 5.0 mm, and further preferably 1.4 to 4.0 mm, and the thickness (short side) is preferably 0.4 to 3.0 mm, and more preferably 0.5 to 2.5 mm. The ratio of the length of the width (long side) to the thickness (short side) (thickness: width) is preferably 1:1 to 1:20, and more preferably 1:1 to 1:4. On the other hand, in the case of a conductor with a circular cross-sectional shape, the diameter is preferably 0.3 to 3.0 mm, and preferably 0.4 to 2.7 mm.

[0052] <Insulation coating>

[0053] From the perspective of providing a higher partial discharge inception voltage to the insulated wire of the present invention, the thickness of the insulating film is preferably 60 μm to 350 μm, more preferably 80 μm to 300 μm, further preferably 90 μm to 250 μm, and further preferably 100 μm to 200 μm.

[0054] In addition, the number of repetitions of coating / baking for forming the insulating film is preferably 35 times or less, more preferably 10 times or more and 35 times or less, further preferably 12 times or more and 30 times or less, further preferably 15 times or more and 25 times or less. It should be noted that in the present invention, "the number of repetitions of coating / baking" has the same meaning as "the number of layers of the insulating layer constituting the insulating film". That is, the number of layers of the insulating layer constituting the above-mentioned insulating film is preferably 35 layers or less, more preferably 10 layers or more and 35 layers or less, further preferably 12 layers or more and 30 layers or less, further preferably 15 layers or more and 25 layers or less.

[0055] The insulating film in the insulated wire of the present invention is classified into an inner layer and an outer layer based on the thickness of each insulating layer.

[0056] In the present invention, the "inner layer" refers to the innermost layer and the region of the insulating layer whose thickness is continuously less than 5 μm among the insulating layers formed (laminated) from the innermost layer toward the outer side (opposite to the conductor). That is, the thickness of each insulating layer constituting the inner layer is less than 5 μm. In the present invention, when the inner layer is a single layer, the inner layer itself is the innermost layer.

[0057] In the present invention, the "outer layer" refers to a region formed by the outermost layer and the insulating layer formed from the outermost layer toward the outer side (opposite to the conductor side) among the insulating layers having a thickness of 5 μm or more. The outer layer may include an insulating layer having a thickness of less than 5 μm, but the average thickness of each insulating layer constituting the outer layer is 5 μm or more.

[0058] The thickness of each insulating layer can be measured, for example, by the method described in the examples. Specifically, when the conductor of the insulated wire is a square conductor, such as Figure 2 As shown in FIG. 1 , in cross-sectional observation of the insulated wire, the thickness of the two long sides and the two short sides corresponding to the plane of the insulating layer of the measuring object is measured at 5 points at equal intervals, a total of 20 points, and the average value of the thickness of the 20 points is taken as the thickness of the insulating layer. It should be noted that the above-mentioned "plane of the insulating layer" refers to the plane directly above the surface other than the chamfered portion of the conductor. In addition, when the cross-sectional shape of the conductor of the insulated wire is circular, in cross-sectional observation of the insulated wire, the thickness of the insulating layer of the measuring object is measured at 8 points at equal intervals, and the average value of the thickness of the 8 points is taken as the thickness of the insulating layer.

[0059] The thickness at each measurement point is the shortest distance between the inner boundary surface and the outer boundary surface of each insulating layer.

[0060] <Inner layer>

[0061] The insulating layers constituting the inner layer may be layers of the same material or layers of different materials, but are preferably layers of the same material.

[0062] The inner layer is formed by a coating / baking process of applying a resin varnish and baking. In the present invention, even if the coating / baking of the same resin varnish is repeated, the layer formed by one coating / baking is counted as one layer. Therefore, the inner layer is a layer formed by laminating more than one insulating layer. From the perspective of further improving the adhesion of the conductor and improving the flexibility, the number of repetitions of coating / baking for forming the inner layer is preferably more than 1 time and less than 6 times, more preferably more than 2 times and less than 5 times, and further preferably 2 times or 3 times. That is, the number of layers of the insulating layer constituting the inner layer is preferably more than 1 layer and less than 6 layers, more preferably more than 2 layers and less than 5 layers, and further preferably 2 layers or 3 layers.

[0063] In the insulated wire of the present invention, from the perspective of further improving the conductor adhesion, preventing the conductor from being oxidized, and suppressing the generation of uneven spots, the average thickness of each insulating layer constituting the inner layer is preferably 1 μm or more and less than 5 μm, more preferably 2 μm or more and 4.5 μm or less, and even more preferably 2 μm or more and 4 μm or less. The average thickness of each insulating layer constituting the inner layer is the arithmetic average of the thickness of each insulating layer obtained by measuring the thickness of each insulating layer as described above. That is, the thickness of each insulating layer is measured as described above, and is calculated by dividing the total value of the thickness of each insulating layer constituting the inner layer by the number of insulating layers constituting the inner layer.

[0064] In addition, the thickness of each insulating layer constituting the inner layer is preferably within the range of ±50% of the average thickness of each insulating layer constituting the inner layer, and more preferably within the range of ±25% of the average thickness of each insulating layer constituting the inner layer. That is, it is preferred to satisfy [average thickness of each insulating layer constituting the inner layer × 0.5] ≤ thickness of each insulating layer constituting the inner layer ≤ [average thickness of each insulating layer constituting the inner layer × 1.5], and it is more preferred to satisfy [average thickness of each insulating layer constituting the inner layer × 0.75] ≤ thickness of each insulating layer constituting the inner layer ≤ [average thickness of each insulating layer constituting the inner layer × 1.25].

[0065] (resin varnish)

[0066] The resin varnish contains an organic solvent (organic solvent) and the like in order to convert the resin into a varnish. Examples of the organic solvent include amide solvents such as N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), and N,N-dimethylformamide (DMF); urea solvents such as N,N-dimethylethyleneurea, N,N-dimethylpropyleneurea, and tetramethylurea; lactone solvents such as γ-butyrolactone and γ-caprolactone; carbonate solvents such as propylene carbonate; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ester solvents such as ethyl acetate, n-butyl acetate, butyl cellosolve acetate, butyl carbitol acetate, ethyl cellosolve acetate, and ethyl carbitol acetate; glycol dimethyl ether solvents such as diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; hydrocarbon solvents such as toluene, xylene, and cyclohexane; phenol solvents such as cresol, phenol, and halogenated phenols; sulfone solvents such as cyclopentane; dimethyl sulfoxide (DMSO), and the like.

[0067] Among these, DMAc, NMP, DMF, N,N-dimethylethylene urea, N,N-dimethylpropylene urea, tetramethyl urea and DMSO are more preferred, and DMAc and NMP are even more preferred, because they do not have hydrogen atoms that tend to inhibit a crosslinking reaction by heating.

[0068] The above-mentioned organic solvents and the like may be used alone or in combination of two or more.

[0069] The above-mentioned resin varnish may contain various additives such as adhesion aids, foaming agents for bubble formation, antioxidants, antistatic agents, ultraviolet light inhibitors, light stabilizers, fluorescent brighteners, pigments, dyes, extenders, lubricants, reinforcing agents, flame retardants, crosslinking agents, crosslinking aids, plasticizers, thickeners, viscosity reducers and elastomers within a range that does not affect the properties.

[0070] The resin varnish may contain inorganic fine particles within a range that does not affect the properties. Examples of such inorganic fine particles include zinc oxide, titanium oxide, silicon dioxide, aluminum oxide, tin oxide, silicon carbide, and strontium titanate.

[0071] -Resin-

[0072] The resin of each insulating layer constituting the inner layer is not particularly limited, and examples thereof include thermosetting resins with imide bonds such as polyimide (PI), polyamide-imide (PAI) and polyester-imide (PEsI), or polyurethane (PU), thermosetting polyester (PEst), H-type polyester (HPE), polyimide-hydantoin-modified polyester, polyhydantoin, polybenzimidazole, melamine resin or epoxy resin, and these resins can be used alone or in combination. In addition, amorphous thermoplastic resins such as polyetherimide (PEI) can also be used. Among them, the above-mentioned resin preferably includes a thermosetting resin with an imide bond, and more preferably includes polyimide (PI), polyamide-imide (PAI) or a mixed resin thereof. The above-mentioned resin is preferably a thermosetting resin with an imide bond, and more preferably polyimide (PI), polyamide-imide (PAI) or a mixed resin thereof.

[0073] The type of the polyimide (PI) is not particularly limited, and common polyimides such as wholly aromatic polyimide or thermosetting aromatic polyimide can be used. In addition, the following polyimide can be used: by conventional methods, using a polyamic acid solution obtained by reacting an aromatic tetracarboxylic dianhydride and an aromatic diamine compound in a polar solvent, imidizing by heat treatment during baking, thereby obtaining a polyimide.

[0074] Examples of commercially available polyimide (PI) include Uimide, a product manufactured by Unitika, U-varnish, a product manufactured by Ube Industries, Ltd., and #3000, a product manufactured by DuPont-Toray.

[0075] The polyamideimide (PAI) has a lower thermal conductivity than other resins, a higher dielectric breakdown voltage, and can be cured by baking. The types of polyamideimide that can be used in the present invention are not particularly limited, and examples thereof include polyamideimide obtained by directly reacting tricarboxylic anhydride with a diisocyanate compound in a polar solvent; or polyamideimide obtained by first reacting tricarboxylic anhydride with a diamine compound in a polar solvent, first introducing an imide bond, and then amidating the tricarboxylic anhydride with a diamine compound.

[0076] Examples of commercially available polyamideimide (PAI) include HI406, a product of Hitachi Chemical Co., Ltd., and the like.

[0077] When the inner layer is a laminated insulating layer in which a plurality of insulating layers are laminated, the thickness of the innermost layer is preferably thinner than the average thickness of the insulating layers constituting the inner layer.

[0078] From the perspective of improving the adhesion of the conductor and improving the flexibility, the relationship between the maximum thickness and the minimum thickness of the innermost layer preferably satisfies [maximum thickness / minimum thickness] ≤ 2.5, more preferably satisfies [maximum thickness / minimum thickness] ≤ 2.3, and further preferably satisfies [maximum thickness / minimum thickness] ≤ 2.1.

[0079] The maximum thickness of the innermost layer and the minimum thickness of the innermost layer can be measured, for example, by the method described in the Examples. Figure 3 For the square-shaped insulated wire shown in the figure, in cross-sectional observation of the insulated wire, the thickness of the innermost layer in the vertical direction is measured from the two long sides and the two short sides corresponding to the flat portion of the outer periphery of the conductor, and the maximum value of the obtained thickness is taken as the "maximum thickness", and the minimum value of the obtained thickness is taken as the "minimum thickness". It should be noted that the determination of the minimum thickness and the maximum thickness does not take into account the thickness of the chamfered portions of the four corners of the conductor.

[0080] In addition, when the cross-sectional shape of the conductor of the insulated wire is circular, when observing the cross section of the insulated wire, the thickness in the perpendicular direction is measured from the tangent line of the conductor surface, and the maximum value of the thickness obtained is taken as the "maximum thickness", and the minimum value of the thickness obtained is taken as the "minimum thickness".

[0081] <Outer Layer>

[0082] The insulating layers constituting the outer layer may be layers of the same material or layers of different materials, but are preferably layers of the same material.

[0083] The outer layer is also formed by a coating / baking process of coating a resin varnish and baking it in the same manner as the inner layer. From the perspective of achieving appropriate baking conditions, maintaining the adhesion with the conductor and mechanical properties, the number of repetitions of coating / baking for forming the outer layer is preferably 9 to 30 times, more preferably 10 to 25 times, and further preferably 13 to 22 times. That is, the number of layers of the insulating layer constituting the outer layer is preferably 9 to 30 layers, more preferably 10 to 25 layers, and further preferably 13 to 22 layers.

[0084] From the perspective of improving flexibility and suppressing the generation of small concave-convex spots associated with solvent volatilization, the thickness of each insulating layer constituting the outer layer is preferably 4 μm or more, more preferably 4.5 μm or more, and further preferably 5 μm or more. In addition, the thickness is preferably 15 μm or less, and more preferably 10 μm or less.

[0085] In addition, the average thickness of each insulating layer constituting the outer layer is 5 μm or more, and from the aspect of improving flexibility and suppressing the generation of concavo-convex small spots, it is preferably 5 μm or more and 15 μm or less, and more preferably 5 μm or more and 10 μm or less. The average thickness of each insulating layer constituting the outer layer is calculated by measuring the thickness of each insulating layer as described above (measured in the same manner as the thickness of each insulating layer constituting the inner layer), and dividing the total value of the thickness of each insulating layer constituting the outer layer by the number of insulating layers constituting the outer layer.

[0086] In addition, the thickness of each insulating layer constituting the outer layer is preferably within the range of ±50% of the average thickness of each insulating layer constituting the outer layer, and is preferably within the range of ±25% of the average thickness of each insulating layer constituting the outer layer. That is, it is preferred to satisfy [average thickness of each insulating layer constituting the outer layer × 0.5] ≤ thickness of each insulating layer constituting the outer layer ≤ [average thickness of each insulating layer constituting the outer layer × 1.5], and it is more preferred to satisfy [average thickness of each insulating layer constituting the outer layer × 0.75] ≤ thickness of each insulating layer constituting the outer layer ≤ [average thickness of each insulating layer constituting the outer layer × 1.25].

[0087] The type of resin constituting the outer layer can preferably use the resin described as the resin constituting the inner layer. In addition, a resin of the same material as the resin constituting the inner layer can be used, or a resin of a different material can be used. Wherein, the outer layer preferably comprises polyimide (PI), polyamide-imide (PAI), or a mixed resin thereof, and is more preferably formed by polyimide (PI), polyamide-imide (PAI), or a mixed resin thereof. In addition, the type of organic solvent used to varnish the resin can also preferably use the organic solvent described as the organic solvent used in the resin of the inner layer.

[0088] The insulated wire of the present invention may also have a reinforced insulating layer on the outer periphery of the outer layer. By providing the reinforced insulating layer, the ATF resistance of the insulated wire of the present invention can be further improved. The reinforced insulating layer is preferably an extruded coating layer composed of a thermoplastic resin layer. As the thermoplastic resin constituting the thermoplastic resin layer, a thermoplastic resin commonly used in an insulating film can be applied.

[0089] [Manufacturing method of insulated electric wire]

[0090] The insulated wire of the present invention can be obtained by forming an insulating layer by repeating a coating / baking process of coating the same or different resin varnishes on the outer periphery of a conductor and baking the varnishes a plurality of times.

[0091] The method of coating the resin varnish on the conductor can be a conventional method, for example, a method using a varnish coating mold with a shape similar to the conductor shape; or when the conductor cross-section shape is rectangular, a mold formed in a tic-tac-toe shape called a "universal die" can be used.

[0092] As the resin varnish, a commercially available product may be used as described above. In this case, the resin varnish contains an organic solvent because the resin varnish is dissolved in the organic solvent.

[0093] The conductor coated with these resin varnishes is baked in a baking oven according to a conventional method. The specific baking conditions depend on the shape of the oven used, etc., but if it is a natural convection vertical oven of about 8m, it can be achieved by setting the temperature in the oven to 400-650°C and the passage time to 10-90 seconds. The amount of resin varnish applied can be appropriately set to achieve the target thickness of each insulating layer.

[0094] [Coils, rotating electrical machines, and electrical / electronic equipment]

[0095] The insulated wire of the present invention can be used as a coil in fields requiring electrical properties (voltage resistance) and heat resistance, such as rotating electrical machines and various electrical / electronic equipment. For example, the insulated wire of the present invention is used in motors, transformers, etc., and can constitute high-performance rotating electrical machines and electrical / electronic equipment. It is particularly suitable for use as a winding for a drive motor of a hybrid vehicle (HV) or an electric vehicle (EV).

[0096] Examples of the coil of the present invention include a coil formed by subjecting the insulated wire of the present invention to coil processing, and a coil formed by subjecting the insulated wire of the present invention to bending processing and then electrically connecting predetermined portions.

[0097] The coil formed by coiling the insulated wire of the present invention is not particularly limited, and a coil formed by winding a long insulated wire into a spiral shape can be cited. In such a coil, the number of windings of the insulated wire is not particularly limited. Usually, an iron core is used when winding the insulated wire.

[0098] As a coil formed by bending the insulated wire of the present invention and electrically connecting predetermined portions, a coil used in a stator of a rotating electric machine or the like can be cited. Figure 4 As shown, such a coil may be produced by cutting the insulated wire of the present invention into a predetermined length and bending it into a U-shape to produce a plurality of wire segments 34, and connecting two open ends (terminal ends) 34a of the U-shape of each wire segment 34 to each other to produce a coil 33 (see Figure 4 , Figure 5 ).

[0099] There is no particular limitation on the electrical / electronic device using the coil. A preferred embodiment of such an electrical / electronic device is a transformer. Figure 4 , Figure 5 The stator 30 shown is a rotating electric machine (particularly a driving motor for HVs and EVs). The rotating electric machine can have the same configuration as a conventional rotating electric machine except that the stator 30 is provided.

[0100] The stator 30 can be configured similarly to a conventional stator except that the wire segment 34 is formed of the insulated wire of the present invention. That is, the stator 30 includes a stator core 31 and a coil 33. The coil 33 is configured as follows. Figure 4 As shown in the figure, the wire segment 34 composed of the insulated wire of the present invention is assembled into the slot 32 of the stator core 31, and the open end 34a is electrically connected. The coil 33 is in a state where the adjacent heat-adhesive layers are adhered to each other or the heat-adhesive layer and the slot 32 are adhered and fixed. Here, the wire segment 34 can be assembled into the slot 32 alone, but it is preferably as follows Figure 4 As shown, two wires are assembled as a set. The stator 30 has a coil 33 accommodated in a slot 32 of a stator core 31, and the coil 33 is formed by connecting the two ends, i.e., the open ends 34a of the wire segment 34 that have been bent as described above, to each other. At this time, the open ends 34a of the wire segment 34 may be connected and then accommodated in the slot 32, or the open ends 34a of the wire segment 34 may be bent and connected after the insulating segment 34 is accommodated in the slot 32.

[0101] Example

[0102] Hereinafter, the present invention will be described in more detail based on Examples, but the present invention is not limited to these embodiments. In the following Examples, "ppm" is a mass standard.

[0103] <Manufacturing method>

[0104] [Example 1]

[0105] An insulated electric wire composed of a conductor and an insulating film (inner layer and outer layer) was produced by the following method.

[0106] As the conductor, a square conductor (copper with an oxygen content of 15 ppm) having a square cross section (length 3.5 mm×width 2.0 mm, four corners chamfered with a curvature radius r=0.3 mm) was used.

[0107] A polyimide (PI) varnish (trade name: Uimide, solvent: DMAc, manufactured by Unitika) was applied to the surface of the conductor using a mold in which the cross-sectional shape of the innermost thermosetting resin layer in contact with the conductor was similar to the cross-sectional shape of the conductor. The varnish was passed through a baking furnace set at 600° C. and having a length of 8 m at a speed of 20 seconds. The coating and baking were repeated a total of 2 times to form a thermosetting resin layer (inner layer) consisting of two layers in a manner to achieve the thickness described in Table 1 below.

[0108] Next, using a mold whose cross-sectional shape is similar to the conductor cross-sectional shape, the above-mentioned PI varnish is applied to the surface of the above-mentioned thermosetting resin layer (inner layer), and it is passed through a baking furnace set at 600°C and with a furnace length of 8m at a speed of 20 seconds. The coating and baking are repeated a total of 20 times to form a thermosetting resin layer (outer layer) consisting of 20 layers in a manner to achieve the thickness described in the following Table 1.

[0109] In this manner, an insulated wire of Example 1 having an inner layer and an outer layer as an insulating film was obtained.

[0110] The measurement of the thickness of the insulating layer in this example will be described.

[0111] In cross-sectional observation of the insulated wire, the thickness of the two long sides and two short sides corresponding to the plane of the insulation layer to be measured was measured at five points at equal intervals, for a total of 20 points, using a digital microscope (trade name: VHX-7000, manufactured by KEYENCE Corporation). The average of the measured values ​​was taken as the thickness of each insulation layer.

[0112] The thickness of each insulating layer constituting the inner layer was summed up to calculate the total thickness (μm) of each insulating layer belonging to the inner layer, and the total thickness was divided by the number of inner layers, and the obtained value was used as the "average thickness (μm) of the insulating layer" in the inner layer. In addition, the thickness of each insulating layer belonging to the outer layer was summed up to calculate the total thickness (μm) of each insulating layer belonging to the outer layer, and the total thickness was divided by the number of outer layers, and the obtained value was used as the "average thickness (μm) of the insulating layer" in the outer layer. The measurement results are shown in Table 1.

[0113] In addition, the maximum thickness and minimum thickness of the innermost layer of the inner layer were measured, and the "maximum thickness / minimum thickness" of the innermost layer was calculated. The results are also shown in Table 1.

[0114] [Examples 2 to 10]

[0115] Insulated wires of Examples 2 to 10 were obtained in the same manner as in Example 1 except that the thicknesses of the insulating layers constituting the inner layer and the outer layer were set to the thicknesses described in Table 1 below.

[0116] [Example 11]

[0117] An insulated wire of Example 11 was obtained in the same manner as in Example 1 except that the resin was polyamideimide (PAI) varnish (trade name: HI406, solvent: DMAc, manufactured by Hitachi Chemical Co., Ltd.) and the varnish was applied and baked so that the insulating layer had a thickness as shown in Table 1 below.

[0118] [Comparative Example 1]

[0119] An insulated wire of Comparative Example 1 was obtained in the same manner as in Example 1 except that the inner layer was not formed and the thickness of the insulating layer constituting the outer layer was set to the thickness described in Table 1 below.

[0120] [Comparative Example 2]

[0121] An insulated electric wire of Comparative Example 2 was obtained in the same manner as in Example 1 except that the outer layer was not formed and the thickness of the insulating layer constituting the inner layer was set to the thickness described in Table 1 below.

[0122] It should be noted that, for the insulated wires of Examples 1 to 11 and Comparative Example 2, the thickness of the insulating layer constituting the inner layer is less than 5 μm (1 to 4.5 μm). In addition, for the insulated wires of Examples 1 to 11 and Comparative Example 1, the thickness of the outermost layer (for the insulated wires of Examples 1 to 11, the adhesion layer with the inner layer in the outer layer, and for the insulated wire of Comparative Example 1, the adhesion layer with the conductor in the outer layer) is 5 μm or more (5 to 15 μm).

[0123] The thickness of each insulating layer constituting the inner layer is within the range of ±50% of the average thickness of each insulating layer constituting the inner layer, and the thickness of each insulating layer constituting the outer layer is within the range of ±25% of the average thickness of each insulating layer constituting the outer layer.

[0124] The conductor adhesion and flexibility of each of the insulated wires produced above were evaluated as follows. The obtained results are summarized in Table 1 below.

[0125] [Conductor tightness]

[0126] The adhesion between the conductor and the inner layer (innermost layer) (in the insulated wire of Comparative Example 1, the adhesion between the conductor and the outer layer (outermost layer)) was measured by a 180-degree peel test between the conductor and the insulating layer (JIS method) based on Japanese Industrial Standards: JIS Z 0237.

[0127] For each insulated wire manufactured in the embodiments and comparative examples, a fixture with a cutter connected to a micrometer is used to cut an incision of more than 50 mm in width in the length direction. It should be noted that the incision reaches the conductor. The insulating film is peeled off from the end of the insulated wire with the incision, and a tensile testing machine (manufactured by Shimadzu Corporation, device name "Autograph AGS-X") is used to perform a 180° peel test along the incision in the length direction at a speed of 4 mm / minute. The average value of the peel strength of 50 mm in length (average value of concave and convex) is used as the adhesion strength, and the conductor adhesion is evaluated based on the following evaluation criteria.

[0128] -Evaluation Criteria-

[0129] A+: 1.2N / mm or more

[0130] A: 0.8N / mm or more and less than 1.2N / mm

[0131] B: 0.5N / mm or more and less than 0.8N / mm

[0132] C: less than 0.5N / mm

[0133] [flexibility]

[0134] For each insulated wire manufactured in the embodiment and the comparative example, a straight test piece with a length of 300 mm was cut out, and after being stretched to 15% in the length direction, the straight test piece was bent into 180° (U-shape) in the edge (short side) surface direction of the conductor with an iron core of 4.0 mm in diameter as the axis. Investigate whether there are cracks in the film at the top of the bent portion. If no cracks are confirmed, the insulated wire is stretched to 20% and evaluated in the same way. In addition, if no cracks are confirmed even under the 20% condition, the insulated wire is stretched to 25% and evaluated in the same way. The results are evaluated for flexibility based on the following evaluation criteria. It should be noted that "15% elongation" means that the length of the straight test piece is stretched to 1.15 times the length before the test.

[0135] -Evaluation Criteria-

[0136] A+: No cracks occurred at 25% elongation.

[0137] A: No cracks occurred at 20% elongation, but cracks occurred at 25% elongation.

[0138] B: No cracks occurred at 15% elongation, but cracks occurred at 20% elongation.

[0139] C: Cracks occurred at 15% elongation.

[0140]

[0141] Since the insulated wire of Comparative Example 1 does not have an inner layer, the thickness of the insulating layer disposed in contact with the conductor is 5 μm or more, and thus the conductor adhesion of the insulating layer is poor. This is considered to be because the thickness of the insulating layer disposed in contact with the conductor is thick, resulting in small uneven spots, etc., which reduces the adhesion between the insulating layer and the conductor. In addition, since the insulated wire of Comparative Example 2 does not have an outer layer, the average thickness of the insulating layer constituting the inner layer is 4 μm, and therefore it is known that the mechanical properties of the insulating layer cannot be improved, and the bending processability is poor.

[0142] On the other hand, the insulated wires (Examples 1 to 11) satisfying all the requirements of the present invention have excellent conductor adhesion and excellent bending workability.

[0143] The present invention has been described in conjunction with its embodiments, but the applicant believes that, unless otherwise specified, the present invention is not limited to any details in the description and should be broadly interpreted without violating the spirit and scope of the invention as shown in the appended claims.

[0144] This application claims the priority based on Japanese Patent Application No. 2022-203729 filed in Japan on December 20, 2022, the contents of which are incorporated herein by reference as a part of the contents described in this specification.

[0145] Explanation of symbols

[0146] 1 Insulated wire

[0147] 11 Conductor

[0148] 12 Inner layer

[0149] 13 Outer layer

[0150] 14 Innermost layer

[0151] 15 Outermost layer

[0152] 30 Stator

[0153] 31 stator core

[0154] 32 slots

[0155] 33 Coil

[0156] 34 Wire Segment

[0157] 34a Open end

Claims

1. An insulated wire comprising a conductor and an insulating coating formed by repeatedly applying and baking a resin varnish on the outer periphery of the conductor, wherein: The insulating film is composed of an inner layer and an outer layer, wherein the inner layer is composed of one or more insulating layers having a thickness of less than 5 μm, and the outer layer is located outside the inner layer and is composed of a plurality of insulating layers. Among the insulating layers constituting the outer layer, the insulating layer in contact with the inner layer has a thickness of 5 μm or more, and the average thickness of the insulating layers constituting the outer layer is 5 μm or more.

2. The insulated wire according to claim 1, wherein In the insulating layer constituting the inner layer, the maximum thickness and the minimum thickness of the insulating layer in contact with the conductor satisfy [maximum thickness / minimum thickness] ≤ 2.

5.

3. The insulated wire according to claim 1 or 2, wherein: The thickness of the insulating film is not less than 60 μm and not more than 350 μm.

4. The insulated wire according to any one of claims 1 to 3, wherein The insulating film includes polyamide-imide and / or polyimide. 5 . A coil using the insulated wire according to claim 1 .

6. A rotating electrical machine or an electrical or electronic device comprising the coil according to claim 5.

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