Insulated electric wire

Abstract

Provided is an insulated electric wire that suppresses the occurrence of partial discharge and the occurrence of film rupture even in the case of a coil of a motor for high-voltage drive or inverter drive. In an insulated electric wire having a conductor formed in a long strip shape and an insulating film configured by laminating one or more insulating layers that cover around the conductor, the insulating layer has a void region and a resin region. The void region is configured by resin and a plurality of voids. The resin region is configured by resin. The insulating layer is not provided with an interface between a first interface on the radially inner side and a second interface on the radially outer side, and is provided with the void region and the resin region in this order from the first interface along the second interface.

Description

Technical Field

[0001] This disclosure relates to insulated electrical wires. Background Technology

[0002] Insulated wires are known to have an insulating film disposed on the periphery of a conductor formed into an elongated strip (for example, see Patent Document 1).

[0003] This insulated wire is used, for example, as the coil of an industrial motor.

[0004] In industrial motors, high-voltage drive is used when high output is required. Additionally, inverter drive is employed, meaning that the motor speed is controlled using an inverter-driven AC power supply with variable voltage or frequency.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 9-106712 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] In inverter driving, inverter surges can occur, which are reflections that occur at points of impedance discontinuity caused by switching, resulting in a voltage of approximately twice the output voltage being applied.

[0010] Due to the high voltage applied to industrial motors for high-voltage drive and inverter surges occurring during inverter drive, partial discharge may occur in the insulation film of the insulated wires used in the motor coils. If partial discharge occurs, it can erode the insulation film, leading to insulation failure.

[0011] To address this issue, one approach is to increase the partial discharge initiation voltage and suppress partial discharge by using an insulating film with a low relative permittivity. To reduce the relative permittivity of the insulating film, multiple pores can be incorporated within it.

[0012] However, when multiple pores are provided within the insulating film, there is a possibility that these pores may connect and interlock (hereinafter also referred to as interconnected) along the thickness direction of the insulating film. If an insulated wire having such interconnected pore portions (hereinafter also referred to as connected portions) is bent and stretched in a spiral manner for manufacturing into a motor coil, the force applied in the stretching direction during bending and stretching may cause a rupture (hereinafter also referred to as film rupture) in the insulating film, originating from the connected portion, along the thickness direction. Furthermore, there is a possibility that the insulation performance of the insulating film may decrease due to the resulting film rupture.

[0013] The purpose of this disclosure is to provide an insulated wire that suppresses partial discharge and diaphragm rupture, even when used in the coils of a motor driven by a high voltage or inverter.

[0014] Methods for solving problems

[0015] One embodiment of this disclosure is an insulated wire having a conductor formed in the shape of an elongated strip and an insulating film formed by stacking one or more insulating layers covering the conductor. The insulating layer has a porous region and a resin region. The porous region is composed of resin and a plurality of pores. The resin region is composed of resin. No interface is provided between a first radially inner interface and a second radially outer interface of the insulating layer, and the porous region and the resin region are arranged sequentially along the second interface starting from the first interface.

[0016] With this configuration, the porous regions are formed within the insulating layer of the insulating film. Therefore, compared to insulating films without porous insulating layers, the relative permittivity can be reduced, and the partial discharge initiation voltage can be easily increased.

[0017] Furthermore, within the insulating layer, the resin region is arranged further outward along the radial direction than the void region. With this configuration, the resin region is positioned away from the conductor within the insulating layer, where it is easy to apply force in the tensile direction through bending and elongation, while the void region is positioned closer to the conductor, where it is difficult to apply force in the tensile direction through bending and elongation. Therefore, even when force is applied in the tensile direction through bending and elongation, the occurrence of film rupture originating from the connecting portion can be suppressed. Attached Figure Description

[0018] Figure 1 This is a schematic cross-sectional view showing a section orthogonal to the length direction of the insulated wire in this embodiment.

[0019] Figure 2 This is a schematic cross-sectional view showing the interior of an insulating layer in this embodiment.

[0020] Figure 3 This is a cross-sectional view schematically showing the laminated structure of the insulating layer of the insulating film in this embodiment.

[0021] Figure 4 This is a diagram showing a cross-sectional image of the insulating film taken using SEM.

[0022] Figure 5 This is a magnified image of a cross-section of an insulating film taken with a SEM.

[0023] Figure 6 This is a diagram schematically illustrating an example of the stacked structure of the insulating layer inside an insulating film in conventional technology.

[0024] Figure 7 It is a schematic diagram showing the connecting part formed by the connection of the hollow part and the rupture of the membrane.

[0025] Symbol Explanation

[0026] 1, 1x: Insulated wire; 3: Conductor; 5, 9: Insulating film; 51, 51a, 51b, 51c, 51x: Insulating layer; 511, 511a, 511b, 511c: Resin region; 513, 513a, 513b, 513c: Hole region; P1, P2, P3, P1x, P2x, P3x: Insulating coating; S: Connecting part; Va: Hole. Detailed Implementation

[0027] [1. Composition]

[0028] In this embodiment, the insulated wire 1 is, for example, an enameled wire used for coils in motors, etc., and will be described.

[0029] A rough cross-sectional diagram showing a section orthogonal to the length direction of the insulated wire 1 is shown in the figure. Figure 1 .

[0030] like Figure 1 As shown, the insulated wire 1 consists of a conductor 3 extending in a long strip shape and an insulating film 5 covering the periphery of the conductor 3. It should be noted that in this embodiment, the example in which the cross-sectional shape of the conductor 3 is formed as a circle is applied and described.

[0031] The example in which conductor 3 is used as a commonly used metallic wire is applied and explained. It should be noted that the metal used as conductor 3 can be, for example, copper, copper-containing alloys, aluminum, or aluminum-containing alloys. Additionally, as conductor 3, for example, low-oxygen copper with an oxygen content of 30 ppm or less, or oxygen-free copper, can be used.

[0032] The example of using a round copper wire with a diameter of 0.8 mm as conductor 3 in this embodiment is applicable and will be described.

[0033] The insulating film 5 covers the periphery of the conductor 3, suppressing conduction caused by contact between an object outside the insulating film 5 and the conductor 3 located inside the insulating film 5.

[0034] The term "outer side" here refers to the side of the insulating film 5 relative to the conductor 3 along the radial direction of the conductor 3 in a cross section orthogonal to the longitudinal direction of the conductor 3. The term "inner side" is the opposite of "outer side" and refers to the side of the conductor 3 relative to the insulating film 5 along the radial direction of the conductor 3 in a cross section orthogonal to the longitudinal direction of the conductor 3.

[0035] It should be noted that the example in which a thermosetting resin is used as the material for the insulating film 5 is applicable and explained. As a thermosetting resin, polyimide or polyamide-imide, etc., can be used.

[0036] In this embodiment, an example in which polyimide is used as the thermosetting resin in the insulating film 5 is applied and described.

[0037] Furthermore, regarding the insulating film 5, a coating layer is formed by applying an insulating coating containing a thermosetting resin once around the conductor 3, and an insulating layer 51 is formed by baking (curing) the coating layer once. Alternatively, the above-mentioned coating and baking of the insulating coating are repeated multiple times, forming a structure by stacking multiple insulating layers 51 containing the same insulating coating. The thickness of an insulating layer 51 is formed to be 1 μm or more and less than 10 μm (for example, around 3 μm). Through the stacking of multiple insulating layers 51, interfaces are formed on the inner and outer sides of the portions where adjacent insulating layers 51 contact each other. There are no interfaces of insulating layers 51 inside the insulating layers 51 (i.e., the inner surface of the insulating layer 51 in contact with the outer surface of the conductor 3). The interface of the insulating layer 51 referred to here means, for example, the surface that serves as the boundary between the insulating layer 51 and other layers. Specifically, it can be the boundary between radially adjacent insulating layers 51, or the boundary between the insulating layer 51 and a gas layer such as air. It should be noted that, in each of the plurality of insulating layers 51, the radially inner interface will be referred to as the first interface, and the radially outer interface will be referred to as the second interface.

[0038] Figure 2 This is a schematic cross-sectional view showing the interior of an insulating layer 51. Additionally, Figure 2 This is a cross-sectional view taken from a section orthogonal to the longitudinal direction of insulated wire 1. Additionally, in Figure 2 In this description, the upper side of the paper is used as the outer side of the insulated wire 1, and the lower side of the paper is used as the inner side of the insulated wire 1. It should be noted that... Figures 3-5 and Figures 6-7In the diagram, the upper side of the paper is shown as the outer side of the insulated wire 1, and the lower side as the inner side. Additionally, in... Figure 2 , Figure 3 , Figure 6 and Figure 7 For illustrative purposes, the upper and lower surfaces of the insulating layer 51 are described as planar, but the insulating layer 51 may also be curved along the circumference of the conductor 3.

[0039] like Figure 2 As shown, the insulating layer 51 has a plurality of pores Va inside. Hereinafter, in the insulating layer 51, the region formed of resin without pores Va will be referred to as resin region 511, and the region having resin and a plurality of pores Va will be referred to as pore region 513. That is, in this embodiment, resin region 511 is a pore-free region without pores Va. Furthermore, in this embodiment, the resin constituting pore region 513 is the same resin as that constituting resin region 511.

[0040] In this embodiment, the example in which the size of the pore Va contained in the pore region 513 is 0.1 μm or more and 2 μm or less is applied and described. In addition, the shape of the pore Va is formed, for example, an elliptical shape or a circular shape.

[0041] It should be noted that in the insulating layer 51, the resin region 511 is located near the outer side of the insulating layer 51, while the void region 513 is located near the inner side of the insulating layer 51. In other words, the resin region 511 is located in the region away from the conductor 3 in the thickness direction (i.e., radial direction) of the insulating layer 51, and the void region 513 is located in the region near the conductor 3 in the thickness direction of the insulating layer 51. The inner surface of the void region 513 is the first interface in the insulating layer 51, and the outer surface of the resin region 511 is the second interface in the insulating layer 51.

[0042] In addition, the thickness of the resin region 511 contained in an insulating layer 51 is more than 5% and less than 70% of the thickness of the insulating layer 51.

[0043] A cross-sectional diagram schematically representing the laminated structure of the insulating layer 51 in the insulating film 5 is shown in the figure. Figure 3 .

[0044] like Figure 3 As shown, in each of the plurality of insulating layers 51 forming the insulating film 5, the outer region of the insulating layer 51 is a resin region 511, and the inner region of the insulating layer 51 is a void region 513. That is, in the stacked plurality of insulating layers 51, the resin region 511 and the void region 513 are arranged in an alternating adjacent manner along the radial direction of the insulated wire 1. Specifically, as Figure 3As shown, this example applies to and is explained in the case where insulating layers 51a, 51b, and 51c are stacked sequentially from the inside of the insulating film 5. It should be noted that, hereinafter, the resin regions 511 of insulating layers 51a, 51b, and 51c will also be referred to as resin regions 511a, 511b, and 511c, respectively, and the void regions 513 of insulating layers 51a, 51b, and 51c will be referred to as void regions 513a, 513b, and 513c, respectively.

[0045] Between the inner insulating layer 51a and the adjacent insulating layer 51b, the resin region 511a of the insulating layer 51a is adjacent to the void region 513b of the insulating layer 51b. Similarly, between the adjacent insulating layer 51b and the adjacent insulating layer 51c, the resin region 511b is adjacent to the void region 513c.

[0046] It should be noted that the outer surface of the outermost insulating layer 51 in the insulating film 5 is the surface of the resin region 511 (second interface).

[0047] Figure 4 A cross-sectional image of the insulating layer 51, taken using SEM, is shown. Additionally, Figure 5 An enlarged view of insulating layer 51 is shown. It should be noted that... Figure 4 The magnified image shown is taken with the SEM magnification set to 2000x. Here, SEM stands for Scanning Electron Microscope.

[0048] like Figure 4 and Figure 5 As shown, in the insulating layer 51 photographed by SEM, the boundary line between the resin region 511 and the void region 513 cannot be observed.

[0049] <Materials of Insulating Film>

[0050] The example in which the polyimide forming the insulating film 5 is manufactured by imidizing the polyamic acid obtained by polymerizing a diamine with a tetracarboxylic dianhydride is applicable and illustrated.

[0051] As a diamine, for example, 1,4-bis(4-aminophenoxy)benzene (TPE-Q), 1,3-bis(4-aminophenoxy)benzene (TPE-R), 1,3-bis(3-aminophenoxy)benzene (APB), 4,4'-bis(4-aminophenoxy)biphenyl (BODA), and 4,4'-diaminodiphenyl ether (ODA) can be used.

[0052] Examples of tetracarboxylic dianhydrides that can be used include 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride (DSDA), 4,4'-oxobisphthalic dianhydride (ODPA), 4,4'-(2,2-hexafluoroisopropylidene)diphthalic anhydride (6FDA), pyromellitic dianhydride (PMDA), and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA).

[0053] It should be noted that the polyimide used as the polymer material in the insulating film 5 can also be a polyimide whose end portions are capped.

[0054] As materials for end capping, compounds containing acid anhydrides or compounds containing amino groups can be used.

[0055] As compounds containing anhydrides used for end capping, phthalic anhydride, 4-methylphthalic anhydride, 3-methylphthalic anhydride, 1,2-naphthalenedicarboxylic anhydride, maleic anhydride, 2,3-naphthalenedicarboxylic anhydride, various fluorinated phthalic anhydrides, various brominated phthalic anhydrides, various chlorinated phthalic anhydrides, 2,3-anthracitelic anhydride, 4-ethynylphthalic anhydride, 4-phenylethynylphthalic anhydride, etc., can be used.

[0056] As an amino-containing compound for end-capping, a compound containing one amino group can be used.

[0057] The example of synthesizing the polyimide used for insulating film 5 in a state where the material is dissolved in a solvent is applicable and will be described. Additionally, the example of using polyimide dissolved in a solvent after synthesis as an insulating coating is applicable and will be described.

[0058] As solvents for the synthesis of polyimide used in insulating film 5 and for coatings, polar aprotic solvents such as N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), and N,N-dimethyl sulfoxide (DMF), as well as γ-butyrolactone, dimethylimidazolinone (DMI), cyclohexanone, methylcyclohexanone, and hydrocarbon solvents can be used. It should be noted that multiple solvents can be used in combination.

[0059] In this embodiment, an example in which the molar ratio of the anhydride component to the diamine component in the polyimide used for the insulating film 5 is 100:100 is applied and described. It should be noted that the molar ratio of the anhydride component to the diamine component is not limited to 100:100, and the ratio can be different without impairing the flexibility of the insulating film 5. For example, the diamine component may be added in excess relative to the anhydride component.

[0060] By using polyimide in such a molar ratio, the molecular weight can be reduced, and the viscosity of the coating can be decreased. As a result, the workability of the coating process for forming the insulating film 5, as described later, can be improved. For example, the molar ratio of the anhydride component to the diamine component can also be in the range of 100:100.1 or higher and 100:100.7 or lower.

[0061] Conversely, an anhydride component can be combined in excess relative to the diamine component.

[0062] The insulating coating forming the insulating film 5 is synthesized at a temperature that does not impair the properties of the polyamic acid. Specifically, the temperature can be, for example, from 0°C to 100°C. Alternatively, after synthesizing the insulating coating forming the insulating film 5, the viscosity of the insulating coating can be adjusted by stirring while heating it to, for example, a temperature from 50°C to 100°C.

[0063] In this embodiment, the pores Va in the pore region 513 of the insulating film 5 are formed by using a foaming agent.

[0064] [2. Function]

[0065] <Method for making insulated wires>

[0066] The manufacturing steps for insulated wire 1 are explained.

[0067] In this embodiment, an example using round copper wire with a diameter of 0.8 mm as conductor 3 is applied and described. An insulating coating is applied to conductor 3 using a mold with a gap of 25 μm or more and 30 μm or less, and then baked in an oven with a temperature gradient from 300°C to 400°C to form an insulating layer 51. The insulating layer 51 is repeatedly laminated so that the thickness of the insulating film 5 formed by applying and baking the insulating coating is 40 μm. It should be noted that in this embodiment, an example of forming an insulating layer 51 with a thickness of approximately 3 μm through a single coating and baking process is applied and described.

[0068] <Synthesis Method of Insulating Coating>

[0069] The synthesis of the insulating coating for the insulating film 5 of the insulated wire 1 is carried out according to the following steps. Insulated wires 1 manufactured under different conditions are described as Examples 1 to 3, and the manufacturing methods of the insulated wires manufactured for comparison with the insulated wires 1 manufactured by Examples 1 to 3 are described as Comparative Examples 1 to 6.

[0070] (Example 1)

[0071] Equal amounts of 4,4'-diaminodiphenyl ether and 1,3-bis(4-aminophenoxy)benzene, which are the raw materials for the diamine (hereinafter also referred to as diamine raw materials), were dissolved in DMAc. It should be noted that the dissolution in DMAc was at a molar ratio of 1.00 mol 1,3-bis(4-aminophenoxy)benzene to 1.00 mol 4,4'-diaminodiphenyl ether.

[0072] Next, relative to 1.00 mol of diamine raw material, 1.03 mol of the same amount of pyromellitic dianhydride and diphenyl-3,3',4,4'-tetracarboxylic acid dianhydride (s-BPDA) as raw materials for acid dianhydrides (hereinafter also referred to as acid dianhydride raw materials) were dissolved.

[0073] The polyimide coating is obtained by stirring in nitrogen at room temperature for 12 hours. Polyimide coating refers to an insulating coating made by dissolving or dispersing a polyimide precursor (polyamic acid) composed of diamine raw materials and acid dianhydride raw materials in a solvent.

[0074] The polyimide coating obtained by this method will also be referred to as insulating coating P1x (coating 1 shown in Table 1).

[0075] A compound with a boiling point above 210°C (a high-boiling-point solvent) dissolved in DMAc, which is the main solvent, is added as a foaming agent to the insulating coating P1x. The coating with this foaming agent added to insulating coating P1x is also referred to as insulating coating P1.

[0076] (Example 2)

[0077] The 4,4'-diaminodiphenyl ether of the diamine raw material was dissolved in DMAc. Next, 1.05 mol of pyromellitic dianhydride, used as the acid dianhydride raw material, was dissolved relative to 1.00 mol of the diamine raw material. The solution was then stirred under nitrogen at room temperature for 12 hours to obtain a polyimide coating.

[0078] The polyimide coating obtained by this method will also be referred to as insulating coating P2x below.

[0079] A compound with a boiling point above 210°C (a high-boiling-point solvent) dissolved in DMAc, which is the main solvent, is added as a foaming agent to the insulating coating P2x. Coatings to which this foaming agent is added (coating 2 shown in Table 1) is also recorded as insulating coating P2.

[0080] (Example 3)

[0081] Trimeric trioxide and 4,4'-diphenylmethane diisocyanate were dissolved in NMP. It should be noted that the dissolution ratio in NMP was 1.02 mol of 4,4'-diphenylmethane diisocyanate to 1.00 mol of trimellitic anhydride. The solution was then stirred at 160°C for 4 hours under nitrogen atmosphere to obtain a polyamide-imide coating. Polyamide-imide coatings refer to insulating coatings made by dissolving or dispersing polyamide-imide in a solvent.

[0082] The polyamide-imide coating obtained by this method will also be referred to below as insulating coating P3x (coating 3 shown in Table 1).

[0083] A compound with a boiling point above 210°C (a high-boiling-point solvent) dissolved in NMP, the main solvent, is added as a foaming agent to the insulating coating P3x. The coating with this foaming agent added to insulating coating P3x is also recorded as insulating coating P3.

[0084] (Comparative Example 1)

[0085] In Comparative Example 1, no foaming agent was added to the insulating coating P1x, and the insulating coating P1x was used as an insulating coating.

[0086] (Comparative Example 2)

[0087] In Comparative Example 2, insulating coating P1, in which decomposable polymer microparticles with a particle size of about 1.0 μm were added as a foaming agent, was used as an insulating coating.

[0088] (Comparative Example 3)

[0089] In Comparative Example 3, no foaming agent was added to the insulating coating P2x, and the insulating coating P2x was used as an insulating coating.

[0090] (Comparative Example 4)

[0091] In Comparative Example 4, insulating coating P2, in which decomposable polymer particles with a particle size of about 1.0 μm were added as a foaming agent, was used as an insulating coating.

[0092] (Comparative Example 5)

[0093] In Comparative Example 5, no foaming agent was added to the insulating coating P3x, and the insulating coating P3x was used as an insulating coating.

[0094] (Comparative Example 6)

[0095] In Comparative Example 6, insulating coating P3, in which decomposable polymer particles with a particle size of about 1.0 μm were added as a foaming agent, was used as an insulating coating.

[0096] <Method for calculating the thickness ratio of the resin region>

[0097] The thicknesses of the resin region 511 and the void region 513, and the ratio of the thicknesses of the resin region 511 and the void region 513 to the thickness of the insulation layer 51, are calculated based on an image of the cross-section of the insulated wire 1 taken by SEM.

[0098] Specifically, first, the insulating film 5 is cut along a direction orthogonal to the length of the enameled wire, and the cut surface is ground. Next, the ground cut surface is photographed using SEM, and the resulting SEM image is used to calculate...

[0099] When using SEM for shooting, the magnification should be adjusted appropriately within a range of, for example, 2000x to 5000x.

[0100] In this embodiment, the example in which the thickness ratio of the resin region 511 and the void region 513 is calculated by the ratio of the thickness of the resin region 511 and the void region 513 to the thickness of the insulating layer 51 is applied and explained.

[0101] The thickness of resin region 511 refers to the length along the thickness direction in an insulating layer 51 from the radially outer interface (second interface) of the insulating layer 51 to the outer boundary of the radially outermost void Va in the insulating layer 51. The thickness of void region 513 refers to the length along the thickness direction in an insulating layer 51 from the outer boundary of the radially outermost void Va to the radially inner interface (first interface) of the insulating layer 51.

[0102] By using this method to determine the thickness of the resin region 511 and the pore region 513, the thickness can be easily determined even in SEM images where the boundary between the resin region 511 and the pore region 513 is not observed.

[0103] It should be noted that the thickness ratio of the resin region 511 and the void region 513 is not limited to the ratios calculated separately from the resin region 511 and the void region 513 relative to the insulating layer 51. For example, if the thickness ratio of the resin region 511 relative to the insulating layer 51 is calculated, the thickness ratio of the remaining portion can also be used as the thickness ratio of the void region 513.

[0104] The thickness of the resin region 511 and the porous region 513 can be changed, for example, by adjusting the boiling point of the foaming agent or the amount of foaming agent added.

[0105] For example, when using a high-boiling-point blowing agent, the thickness proportion of the resin region 511 decreases. Specifically, when the boiling point of the blowing agent is approximately 290°C, the thickness proportion of the resin region 511 is between 10% and 20%. Conversely, when using a low-boiling-point blowing agent, the thickness of the resin region 511 increases. A preferred boiling point for the blowing agent used is, for example, a boiling point between 210°C and 350°C. If the amount of blowing agent added is reduced, the thickness of the resin region 511 increases; if the amount of blowing agent added is increased, the thickness of the resin region 511 decreases.

[0106] <Methods for determining porosity>

[0107] The porosity of the void regions 513 of the insulating film 5 of the insulated wire 1 is determined by a water displacement method. Specifically, for example, an insulated wire 1 of a predetermined length, such as 1 m, is placed in water, thereby displacing the air inside the voids Va. The specific gravity of the insulating film 5 before and after peeling is measured relative to that of the insulated wire 1 after the voids Va have been displaced by water. For an insulated wire 1x of the same length and made of the same material as the insulated wire 1, having an insulating layer 51x without voids Va, the specific gravity of the insulating layer 51x before and after peeling is measured. The porosity is determined by comparing the specific gravity of these insulated wires 1 with insulating films 5 containing voids Va before and after peeling with the specific gravity of insulated wires 1x with insulating layers 51x without voids Va before and after peeling.

[0108] The porosity is calculated using the formula: porosity (%) = (ρ1 - ρ2) / ρ1 × 100. Here, ρ1 refers to the overall density of the insulating film 5 without voids Va, and ρ2 refers to the overall density of the insulating film 5 containing voids Va.

[0109] In this embodiment, the example in which the porosity relative to the overall insulating film 5 is 2% or more and less than 25% is applicable and will be described.

[0110] <PDIV Measurement>

[0111] Using a twisted-pair cable made of insulated wire 1, a voltage of 50Hz is boosted within a range of 10V / s to 30V / s at 23°C and 50% humidity. The voltage at which a 50pC discharge occurs 50 times is taken as the partial discharge initiation voltage (PDIV).

[0112] It should be noted that the target value for PDIV is 950Vp when polyimide is used as the material of insulating film 5, and 830Vp when polyamide-imide is used as the material of insulating film 5.

[0113] <Flexibility Test>

[0114] Regarding the flexibility test, the flexibility of the insulated wire 1 was evaluated by simulating the fabrication of the insulated wire 1 into a coil.

[0115] In Examples 1, 2, and Comparative Example 1, where polyimide was used as the insulating film 5, the insulated wire 1 was stretched by 30% and then wound with 50 turns of self-diameter. Then, it was checked whether any film rupture occurred. The target for film rupture was set as no film rupture.

[0116] In Examples 1, 2, and Comparative Example 1, where polyamide-imide was used as the insulating film 5, the insulated wire 1 was stretched by 30% and then wound with 50 turns of self-diameter. Then, it was checked whether the film rupture occurred. The target for film rupture was defined as no film rupture. It should be noted that in Table 1, the case of no film rupture passing the flexibility test is marked as "0", and the case of film rupture is marked as "×".

[0117] <Insulation Breakdown Voltage (BDV) Measurement>

[0118] Using a twisted-pair cable made of insulated wire 1, the voltage is boosted from 0.0V to 20.0kV in air at 50Hz, and the voltage at which insulation breakdown occurs is taken as the insulation breakdown voltage.

[0119] <Results of measurements for the Examples and Comparative Examples>

[0120] The measurement results of the insulated wires 1 of Examples 1 to 3 and the insulated wires of Comparative Examples 1 to 6 are shown in Table 1.

[0121] [Table 1]

[0122]

[0123] As shown in Examples 1 and 2 of Table 1, when the overall porosity is above 20%, the target PDIV of 950Vp is met when polyimide is used as the material of the insulating film 5.

[0124] This can be interpreted as utilizing the void Va in the void region 513 to reduce the overall relative permittivity of the insulating film 5, which results in an easy increase in the partial discharge initiation voltage (PDIV) of the insulating film 5.

[0125] The PDIV (Polydimension Intensity Variability) meets the target PDIV. Furthermore, in Examples 1 and 2, the thickness of the resin region 511 relative to the thickness of the insulation layer 51 is 50% and 20%, respectively, resulting in good flexibility. The self-winding after the target 30% elongation when using polyimide as the insulating film 5 is good. Additionally, Examples 1 and 2 are insulated wires 1 having an insulating film 5 with a void region 513, but their insulation breakdown voltages (BDVs) are 16kV and 15kV, respectively. Furthermore, Comparative Examples 1 and 3, which are insulated wires having an insulating film 5 without voids Va formed from the same coating, have insulation breakdown voltages (BDVs) of 17kV and 16kV, respectively. That is, the insulated wires 1 of Examples 1 and 2 having an insulating film 5 containing a void region 513 can be evaluated as having an insulation breakdown voltage (BDV) of the same degree as that of insulated wires having an insulating film 5 without voids Va.

[0126] On the other hand, in Comparative Examples 2 and 4, which do not have the resin region 511, the membrane ruptured during the flexibility test. Furthermore, in Comparative Examples 2 and 4, which do not have the resin region 511, the insulation breakdown voltages were 6kV and 7kV, respectively, which are lower than those of the configuration with the resin region 511.

[0127] Regarding the insulated wire 1 of Example 3, the insulating film 5 uses polyamide-imide. In Example 3, the porosity is 20%. The PDIV of Example 3 is 850Vp, which meets the target value of 830Vp when the insulating film 5 uses polyamide-imide.

[0128] Furthermore, the flexibility test results of the insulated wire 1 of Example 3 can be evaluated as good. That is, the self-winding result after achieving a target elongation of 20% when using polyamide-imide in the insulating film 5 can be evaluated as good. Regarding the insulation breakdown voltage, when using the same material, the insulated wire of Comparative Example 5 without voids Va has an insulation breakdown voltage of 17 kV, while the insulation breakdown voltage of the insulated wire 1 of Example 3 is 15 kV. That is, it can be evaluated that the insulated wire 1 of Example 3 with voids Va is to the same degree as the insulated wire of Comparative Example 5 without voids Va.

[0129] Regarding Comparative Example 6, compared to Example 3, the porosity is low, the thickness of the resin region 511 is 2% of the thickness of the insulating film 5, and film rupture occurs during the flexibility test. Furthermore, the insulation breakdown voltage of the insulated wire 1 in Comparative Example 6 is also reduced.

[0130]

[0131] In the insulated wire 1 disclosed herein, a hypothetical mechanism for forming an insulating film 5 having a resin region 511 and a void region 513 on the peripheral surface of the conductor 3 is explained.

[0132] First, an insulating coating for forming the insulating film 5 is applied to the conductor 3. The film formed by applying the insulating coating is also referred to as the coating film. When the conductor 3, to which the coating film has been formed by the insulating coating, is first baked, the main solvent of the insulating coating evaporates. As the main solvent evaporates, the amount of the main solvent in the coating that forms the coating film decreases. In addition, as the main solvent evaporates, phase separation of the coating film and the foaming agent occurs.

[0133] Here, on the inner side of the coating film, phase separation occurs between the coating film and the foaming agent due to the reduction of the main solvent, resulting in the foaming agent being dispersed in the coating film. Furthermore, the foaming agent dispersed in the coating film evaporates through further baking, thereby forming pores Va. The portion of the coating film with these pores Va forms the pore region 513 of the insulating film 5.

[0134] On the other hand, on the outer side of the coating film, the foaming agent is easily released from the coating film before phase separation. Therefore, there is essentially no foaming agent separating from the coating film on the outer side of the coating film, and thus no voids Va are formed on the outer side of the coating film. This outer portion of the coating film without voids Va becomes the resin region 511 of the insulating film 5.

[0135] It should be noted that a foaming agent with a boiling point that readily evaporates before phase separation can also be selected for the outer side of the coating film. Alternatively, the phase separation state of the outer side of the coating film can be adjusted to facilitate evaporation before phase separation.

[0136] Each time the insulating coating is applied and baked as described above, an insulating layer 51 is formed with a resin region 511 on the outside and a void region 513 on the inside.

[0137] Furthermore, as for the coating method of the insulating coating, there is no particular limitation as long as the resin region 511 and the void region 513 can be formed on the single insulating layer 51, and conventional coating methods can be used. Specifically, the insulating coating is applied to the conductor 3 and baked in an oven at, for example, 350°C or higher and 500°C or lower for 1 to 2 minutes to form a single insulating layer 51. By repeating this coating and baking process, an insulating film 5 having multiple insulating layers 51 is formed on the peripheral surface of the conductor 3. In addition, the thickness of the insulating film 5 can be adjusted by changing the number of times the coating and baking are repeated.

[0138] The coating conditions can also be adjusted according to the type of foaming agent, the temperature of the heating furnace, and the coating speed.

[0139] The thickness ratio of the resin region 511 in the insulating layer 51 can also be adjusted according to the type of foaming agent and the coating conditions.

[0140] Multiple insulating layers 51 are stacked by repeatedly applying and baking the insulating coating.

[0141] With this configuration, since only one type of insulating coating is needed to form the insulating film 5 having multiple insulating layers 51, the insulating film 5 can be formed more easily compared to preparing multiple insulating coatings. Furthermore, since it is not necessary to change the coating apparatus or coating conditions by preparing multiple insulating coatings, the coating process can be simplified.

[0142] As foaming agents, ethylene glycol, propylene glycol, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, etc., can be used. It should be noted that triethylene glycol dimethyl ether is also called triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether is also called tetraethylene glycol dimethyl ether.

[0143] <Regarding its role in preventing membrane rupture>

[0144] In the insulating film 5 of the insulated wire 1 of this embodiment, among the multiple insulating layers 51 stacked together, the resin region 511 is the region further outward than the void region 513.

[0145] For comparison, Figure 6 and Figure 7 A schematic diagram is shown of an insulating film 9 having regions containing voids throughout the insulating layer.

[0146] like Figure 6 and Figure 7 As shown, as the number of pores Va inside the insulating layer increases, the pores Va become interconnected. Hereafter, the interconnected pores Va will also be referred to as the connecting portion S. Here, the connecting portion of pores Va is where multiple pores Va are connected to each other within the insulating layer, forming a common internal space.

[0147] In such Figure 7 In the insulation layer shown with the connecting part S, when force is applied to the insulated wire by bending or stretching, the film rupture Cr starting from the connecting part S is easily generated.

[0148] On the other hand, in the insulating film 5 of the insulated wire 1 of this embodiment, the outer region of the insulating layer 51, which is easily subjected to tensile force by bending and stretching, is a resin region 511 formed of resin. Therefore, in the resin region 511 formed of resin, it is not easy to generate a connecting portion with a void Va. As a result, it is not easy for the film to break at the starting point of the connecting portion.

[0149] <Measurement results regarding other embodiments>

[0150] Table 2 shows the measurement results of insulated wires 1 of Examples 4 to 6, which were manufactured using the same method as in Example 2 above, but with a different ratio of the thickness of the resin region 511 to the thickness of the insulation layer 51.

[0151] (Examples 4-6)

[0152] In Examples 4 to 6, insulating coatings were used in which a compound with a boiling point of 210°C or higher (a high-boiling-point solvent) dissolved in DMAc, which was used as the main solvent, was added as a foaming agent to the insulating coating P2x.

[0153] [Table 2]

[0154]

[0155] Regarding the insulated wires 1 of Examples 4-6, as shown in Table 2, the thickness ratio of the resin region 511 in the insulation layer 511 is 6% to 25%, which satisfies the target PDIV of 950Vp when using polyimide as the material of the insulating film 5. This can be considered as in Examples 1-2, where the proportion of the void region 513 reduces the overall relative permittivity of the insulating film 5 through void Va, thus increasing the partial discharge initiation voltage (PDIV) of the insulating film 5. Furthermore, in the insulated wires 1 of Examples 4-6, no film rupture occurred during the flexibility test.

[0156] <ATF Resistance Test>

[0157] Regarding the ATF resistance test, the insulated wire 1 from Example 2 was used as sample 1, and the test was conducted using the following method. The results of this test are shown in Table 3.

[0158] Regarding the ATF resistance test, firstly, a sample 1, consisting of an insulated wire 1 with a length of 25 cm and a roughly circular cross-section, was immersed in ATF (Automatic Transmission Fluid) with a water content of 0.2 wt%. At this time, all parts of the sample 1 were immersed in the ATF. Next, the sample 1 in this state was placed in a constant temperature bath at 150°C for 1000 hours. After 1000 hours, the sample 1 was removed from the constant temperature bath, and the ATF adhering to the sample 1 was wiped off. The sample 1 with the ATF removed was observed using a microscope at 5x magnification to confirm whether any cracks had occurred on the surface of the insulating film. Furthermore, to determine the relative permittivity of the sample 1, electrodes were formed on the surface of the sample 1 after it was removed from the constant temperature bath. As a method for forming the electrodes, silver paste was coated onto an insulating film with a length of 100 mm, serving as the main electrode. Further, two protective electrodes were coated with a width of 10 mm at a distance of 10 mm from the main electrode in the direction of the end of the sample 1. It should be noted that the silver paste used is Dotite D-550 manufactured by Fujikura Chemicals, and a 10mm wide tape can be used for masking during application. The relative permittivity after ATF impregnation can be determined by capacitance between the silver paste and the conductor of sample 1. To reduce the influence of absorbed moisture on the relative permittivity, the sample was heated in a constant temperature bath at 150°C for 1 hour to evaporate the moisture before measuring the relative permittivity. The frequency used for measuring the relative permittivity was 1kHz. It should be noted that in Table 3, cases where no cracks were observed on the surface of the insulating film after the ATF resistance test and the relative permittivity did not change compared to before the ATF resistance test are marked as "0".

[0159] <Heat Resistance Test>

[0160] Regarding the heat resistance test, the insulated wires 1 from Examples 5 and 6 were used as samples 2 and 3, respectively, and the results were evaluated using the following method. The test results are shown in Table 3.

[0161] Regarding the heat resistance test, firstly, samples 2 and 3, each consisting of an insulated wire 1 with a length of 25 cm and a roughly circular cross-section, were immersed in ATF. At this time, all parts of sample 1 were immersed in the ATF. Next, samples 2 and 3 were immediately removed from the ATF, and the ATF adhering to them was wiped off. Samples 2 and 3 were then placed in a constant temperature bath at 200°C for 1000 hours. After 1000 hours, samples 2 and 3 were removed from the constant temperature bath. Samples 2 and 3 removed from the constant temperature bath were observed using a microscope with a magnification of 5x to confirm whether any cracks had occurred on the surface of the insulating film. Furthermore, to determine the relative permittivity of samples 2 and 3, electrodes were formed on the surface of samples 2 and 3 removed from the constant temperature bath. The method for forming the electrodes and the method for determining the relative permittivity were the same as those described in the ATF resistance test. It should be noted that in Table 3, cases in which no cracks are found on the surface of the insulating film after the heat resistance test and the relative permittivity does not change compared with that before the heat resistance test are marked as "0".

[0162] [Table 3]

[0163]

[0164] Regarding sample 1 using the insulated wire 1 of Example 2, as shown in Table 3, no cracks were found on the surface of the insulating film after the ATF resistance test, and the relative permittivity remained unchanged compared to before the ATF resistance test. Similarly, regarding samples 2 and 3 using the insulated wire 1 of Examples 5 and 6, as shown in Table 3, no cracks were found on the surface of the insulating film after the heat resistance test, and the relative permittivity remained unchanged compared to before the heat resistance test. This suggests that in the insulated wire 1 of this embodiment, the outermost surface of the insulating film 5 is a resin region 511 without pores Va. Since the surface of the insulating film 5 does not have pores, ATF will not penetrate into the interior of the insulating film 5, and an increase in the relative permittivity can also be prevented. In other words, it can be said that the insulated wire 1 of this embodiment also exhibits good resistance when immersed in ATF.

[0165] [3. Effect]

[0166] (1) The insulated wire 1 of the above embodiment has a conductor 3 formed in the shape of an elongated strip and an insulating film 5 formed by stacking one or more insulating layers 51 covering the conductor 3. The insulating layer 51 has a porous region 513 and a resin region 511. The porous region 513 is composed of resin and a plurality of pores Va contained within the resin. The resin region 511 is composed of resin. The insulating layer 51 has no interface between a first interface on the radially inner side and a second interface on the radially outer side, and the porous region 513 and the resin region 511 are arranged sequentially along the second interface starting from the first interface.

[0167] With this configuration, the insulating layer 51 contained in the insulating film 5 has a void region 513 with a void Va. Therefore, compared with the insulating film 5 which does not have an insulating layer 51 containing a void Va, the relative permittivity can be reduced and the partial discharge initiation voltage can be easily increased.

[0168] (2) In addition, within the insulating layer 51, the resin region 511 is arranged in a manner that is further outward along the radial direction than the pore region 513.

[0169] With this configuration, within the insulating layer 51, the resin region 511 is located in a region away from the conductor 3 where force can be easily applied in the tensile direction through bending and elongation, while the pore region 513 is located in a region close to the conductor 3 where force is difficult to apply in the tensile direction through bending and elongation. Therefore, even if force is applied in the tensile direction through bending and elongation, the generation of film rupture Cr originating from the connecting portion S can be suppressed.

[0170] (3) In this embodiment, polyimide is used as the thermosetting resin used as the material for the insulating film 5.

[0171] Based on this composition, the insulating film 5 has the mechanical properties of polyimide, a low relative permittivity, and heat resistance.

[0172] (4) In this embodiment, the outermost layer of the insulating film 5 is composed of a resin region 511 without multiple pores, and the surface of the insulating film 5 does not have pores.

[0173] With this configuration, even when the porous insulating film 5 comes into contact with ATF (Automatic Transmission Fluid), ATF can be prevented from penetrating into the interior of the insulating film 5. Therefore, in the insulated wire 1 according to this embodiment, even when the insulating film 5 comes into contact with ATF, the relative permittivity of the insulating film 5 is not easily increased. In addition, it is difficult for the insulating film 5 to break (film rupture) caused by ATF to occur.

[0174] [4. Other Implementation Methods]

[0175] (1) In the insulated wire 1 of the above embodiment, the thickness ratio of the resin region 511 is 5% or more and 70% or less of the overall thickness of the insulating film 5.

[0176] Here, the thickness ratio of the resin region 511 can also be more than 20% of the overall thickness of the insulating film 5.

[0177] If the thickness ratio is like this, then since the proportion of resin region 511 is greater than the proportion of porous region 513 with pores Va, it is suitable for suppressing film rupture.

[0178] (2) In addition, the thickness ratio of the resin region 511 can also be less than 50% of the overall thickness of the insulating film 5.

[0179] With this thickness ratio, the proportion of multiple voids Va in the void region 513 within the insulating film 5 as a whole is easily increased, which easily reduces the relative permittivity of the insulating film 5. Therefore, the partial discharge initiation voltage (PDIV) of the insulating film 5 is easily increased. Thus, the occurrence of partial discharge in the insulated wire 1 is easily suppressed.

[0180] (3) In the above embodiment, the thickness ratio of the resin region 511 to the insulating layer 51 is 5% or more and 70% or less. In addition, the thickness ratio of the void region 513 to the insulating layer 51 is 30% or more and 95% or less.

[0181] However, the thickness ratio of the resin region 511 and the thickness ratio of the porous region 513 are not limited to the ratio based on the insulating layer 51. For example, the thickness of the insulating film 5 as a whole can also be used as a reference. Specifically, based on the insulating film 5, the total thickness of the resin region 511 contained in each of the multiple insulating layers 51 contained in the insulating film 5 can be more than 5% and less than 70%, and the total thickness of the porous region 513 contained in each of the multiple insulating layers 51 contained in the insulating film 5 can be more than 30% and less than 95%.

[0182] (4) It should be noted that the insulating film 5 is not limited to an insulating film formed by stacking multiple insulating layers 51 made of the same material. For example, the insulating film 5 may also include an insulating film 5 formed of other insulating coatings. In this case, the insulating film 5 can be formed according to each insulating coating using different coating equipment and coating conditions.

[0183] (5) Alternatively, an adhesive layer may be provided between the conductor 3 and the insulating film 5. The adhesive layer may be made of a material that improves the adhesion between the conductor 3 and the insulating film 5. The thickness of the adhesive layer is not particularly limited, but is preferably a thickness that does not impair the flexibility of the insulated wire 1. Furthermore, the thickness of the adhesive layer is preferably a thickness that does not reduce the partial discharge initiation voltage. For example, the thickness of the adhesive layer is preferably 1 to 10 μm.

[0184] (6) Additives may be further added to the insulating film 5 and the insulating coating used to form the insulating film 5. The type of additive is not particularly limited; for example, additives added to improve the strength of the insulating film 5, improve the surface smoothness of the insulating film 5, improve the wear resistance of the insulating film 5, improve elongation characteristics, reduce the relative permittivity, or semiconduct the film may be used. Additionally, antioxidants may also be used as additives.

[0185] (7) In the above embodiment, the cross-sectional shape of the insulated wire 1, which includes the conductor 3 and the insulating film 5, is set to be circular, but the shape of each is not limited to circular, and can also be rectangular or polygonal.

Claims

1. An insulated wire comprising a conductor formed in the shape of an elongated strip and an insulating film formed by stacking one or more insulating layers covering the conductor. The insulating layer has: a porous region composed of resin and a plurality of pores, and a resin region composed of the resin. The insulating layer has no interface between the first interface on the radially inner side and the second interface on the radially outer side, and the porous region and the resin region are arranged sequentially along the second interface starting from the first interface.

2. The insulated wire according to claim 1, The plurality of pores are contained within the resin.

3. The insulated wire according to claim 1 or 2, In the insulating layer, the surface of the pore region is disposed on the first interface, and the surface of the resin region is disposed on the second interface.

4. The insulated wire according to claim 1 or 2, The thickness of the resin region contained in the insulating layer is more than 5% and less than 70% of the thickness of the insulating layer.

5. The insulated wire according to claim 4, The thickness of the resin region contained in the insulating layer is 20% or more relative to the thickness of the insulating layer.

6. The insulated wire according to claim 1 or 2, The thickness of the resin region contained in the insulating layer is less than 50% of the thickness of the insulating film.

7. The insulated wire according to claim 1 or 2, The insulating film is made of thermosetting resin, and the insulated wire is enameled wire.

Images