Insulated wire

Abstract

To provide an electric insulated wire which easily maintains adhesion in an insulation film.SOLUTION: Provided are a conductor 20 with a long shape, formed of a conductive material, and an insulation film 30 with at least a plurality of isolation layers covering the periphery of the conductor 20, formed of an insulating material. The insulating material makes a value of a storage elastic modulus in a dynamic viscoelasticity at a temperature higher than 100°C to be decreased by one digit or more in the storage elastic modulus in the dynamic viscoelasticity at a temperature of 30°C. Since the value of the storage elastic modulus of the insulating material to form the insulation film 30 is decreased by one digit or more with an increase in temperature, an anchor effect on the surface of the conductor 20 from the isolation layers and an anchor effect between isolation layers adjacent to each other, and adhesion in the insulation film 30 are easily maintained. The insulation film 30 can hardly peel off when an electric insulated wire is bent or extended.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to insulated wires. [Background technology]

[0002] Conventionally, enameled wires using polyimide (hereinafter also referred to as "PI") as the material for the multiple coating layers surrounding the conductor are known. Widely used PI (hereinafter also referred to as "general-purpose PI") include Kapton® and Upilex® (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2012-153848 [Overview of the project] [Problems that the invention aims to solve]

[0004] It is known that general-purpose PI (polyinfiltrate) does not have good adhesion to the conductor of the enameled wire or to the adjacent coating layer. Therefore, when the enameled wire is bent or stretched during manufacturing, there is a problem in that the coating layer peels off.

[0005] Furthermore, general-purpose PI (polyethylene ion) exhibits little change in elastic modulus with temperature, making it difficult for the coating layer to soften during the manufacturing of enameled wire. In other words, it is difficult to obtain an anchoring effect from the coating layer to the conductor surface, or between adjacent coating layers. As a result, there was a problem in obtaining good adhesion between the coating layer and the conductor, and between adjacent coating layers.

[0006] The present invention was made to solve the above problems and aims to provide an insulated wire that facilitates the maintenance of adhesion in the insulating coating. [Means for solving the problem]

[0007] To achieve the above objective, the present invention provides the following means. The insulated wire of the present invention comprises a conductor formed from a conductive material and having a long shape, and an insulating coating formed from an insulating material and having at least a plurality of insulating layers covering the conductor, wherein the storage modulus of dynamic viscoelasticity at temperatures higher than 100°C is at least one order of magnitude lower than the storage modulus of dynamic viscoelasticity at a temperature of 30°C.

[0008] According to the insulated wire of the present invention, the storage modulus of the insulating material forming the insulating coating at temperatures higher than 100°C is more than an order of magnitude lower than the storage modulus in dynamic viscoelasticity at a temperature of 30°C. Therefore, anchoring effects from the insulating layer to the surface of the conductor and between adjacent insulating layers are easily obtained. In other words, adhesion between the insulating layer and the conductor, and adhesion between adjacent insulating layers are easily obtained. Furthermore, the insulating coating is less likely to peel off when the enameled wire is bent or stretched. [Effects of the Invention]

[0009] According to the insulated wire of the present invention, the storage modulus of the insulating material forming the insulating coating decreases by more than an order of magnitude as the temperature rises, thus making it easier to maintain adhesion in the insulating coating. [Brief explanation of the drawing]

[0010] [Figure 1] This is a cross-sectional view illustrating the configuration of an insulated wire according to the first embodiment. [Figure 2] This table compares the evaluation results of the insulated wires in each embodiment with the evaluation results of each comparative example. [Figure 3] This graph shows the temperature dependence of the storage modulus in the dynamic viscoelasticity of each material forming the insulating coating. [Figure 4] This is a schematic diagram illustrating the testing apparatus used in the peel test. [Figure 5] This is a cross-sectional view illustrating the sample used in the peel test. [Figure 6] It is a cross-sectional view for explaining the configuration of the insulated wire according to the second embodiment. [Figure 7] It is a schematic diagram for explaining the configuration of the first insulating layer and the second insulating layer in FIG. 6. [Figure 8] It is a flowchart for explaining the manufacturing method of the insulated wire in FIG. 6. [Figure 9] It is a schematic diagram for explaining a method of preparing an insulating film used for longitudinal section observation. [Figure 10] It is a schematic diagram for explaining a method of preparing an insulating film used for longitudinal section observation. [Figure 11] It is a SEM image for explaining the interface adjacent to the conductor in the first insulating layer. [Figure 12] It is a SEM image for explaining the interface adjacent to the first insulating layer in the second insulating layer.

Embodiments for Carrying Out the Invention

[0011] 〔First Embodiment〕 Hereinafter, the insulated wire 10 according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 5. In this embodiment, the insulated wire 10 is an enameled wire, specifically, an example of an enameled wire used for the winding of a motor will be described. More specifically, an example of an enameled wire used for the winding of a drive motor of an electric vehicle such as a hybrid electric vehicle (HEV), an electric vehicle (EV), or a plug-in hybrid electric vehicle (PHEV) will be described.

[0012] FIG. 1 is a cross-sectional view for explaining the configuration of the insulated wire 10 of this embodiment. As shown in FIG. 1, the insulated wire 10 is provided with a conductor 20 and an insulating coating 30. The conductor 20 is a member that extends in a long length and has a circular cross-sectional shape. In this embodiment, the explanation applies to an example where the conductor 20 is a round copper wire with a diameter of 0.8 mm. Note that the cross-sectional shape of the conductor 20 may be circular or rectangular, and is not limited to a specific shape.

[0013] The conductor 20 is formed using a metal material commonly used for electric wires. Examples of metal materials used to form the conductor 20 include copper, copper alloys, aluminum, or aluminum alloys. In this embodiment, the explanation will be applied to an example in which the conductor 20 is formed using low-oxygen copper or oxygen-free copper with an oxygen content of 30 ppm or less.

[0014] The insulating coating 30 is a component that covers the circumferential surface of the conductor 20. The insulating coating 30 is formed using a material that has insulating and thermosetting properties (i.e., an insulating material). In this embodiment, the explanation will be applied to an example in which the insulating coating 30 is formed from all aromatic polyimide (hereinafter also simply referred to as polyimide).

[0015] Specifically, the explanation will apply to an insulated wire 10 in which the insulating coating 30 is formed from material 1 (hereinafter also referred to as Example 1) and an insulated wire 10 in which the insulating coating 30 is formed from material 3 (hereinafter also referred to as Example 2).

[0016] Material 1 is a material obtained by synthesizing polyamic acid by stirring in a solvent. Polyamic acid is a precursor of polyimide, which is an insulating material that constitutes the insulating film 30. In this embodiment, the explanation will be applied to an example in which the polyamic acid is obtained by polymerizing a diamine and a tetracarboxylic dianhydride.

[0017] Diamines include 4,4'-diaminodiphenyl ether (hereinafter also referred to as ODA). In addition to ODA, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, and 4,4'-bis(4-aminophenoxy)biphenyl may also be included in diamines.

[0018] Tetracarboxylic acid dianhydrides include pyromellitic acid dianhydride (hereinafter also referred to as PMDA). In addition to PMDA, 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic acid dianhydride, 4,4'-oxydiphthalic acid dianhydride, 4,4'-(2,2-hexafluoroisopropylidene)diphthalic acid anhydride, and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride may also be included in tetracarboxylic acid dianhydrides.

[0019] In this embodiment, the explanation applies to an example in which the polyamic acid is obtained by polymerizing the diamine and tetracarboxylic dianhydride described below. The diamine is composed of 4,4'-diaminodiphenyl ether and 4,4'-bis(4-aminophenoxy)biphenyl. The tetracarboxylic dianhydride is composed of pyromellitic dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride.

[0020] The polyamic acid may also be obtained by polymerizing the diamine and tetracarboxylic dianhydride described below. The diamine is composed of 4,4'-diaminodiphenyl ether. The tetracarboxylic dianhydride is composed of pyromellitic dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride.

[0021] Furthermore, the polyimide constituting the insulating coating 30, which is an imidized polyamic acid as described above, may have its polymer ends capped. As the material used for capping, a compound containing anhydride or a compound containing an amino group may be used.

[0022] Compounds containing anhydrides that can be used for capping include phthalic anhydrides, 4-methylphthalic anhydrides, 3-methylphthalic anhydrides, 1,2-naphthalic anhydrides, maleic anhydrides, 2,3-naphthalenedicarboxylic acid anhydrides, various fluorinated phthalic anhydrides, various brominated phthalic anhydrides, various chlorinated phthalic anhydrides, 2,3-anthracenedicarboxylic acid anhydrides, 4-ethynylphthalic anhydrides, and 4-phenylethynylphthalic anhydrides.

[0023] For capping, a compound containing one amino group may be used.

[0024] As solvents, NMP (N-methylpyrrolidone), DMAc (dimethylacetamide), etc., can be used. In this embodiment, the explanation will be applied to an example in which DMAc is used as the solvent.

[0025] Material 3 includes a material obtained by polymerizing a diamine or acid dianhydride, which is a silicone monomer in which at least a portion of the main chain consists of siloxane bonds (-Si-O-Si-). The molecular weight of the silicone monomer used in material 3 is less than 1,000. In this embodiment, the example will be described using a case where the molecular weight of the silicone monomer is 260. DMAc can be used as an example of a solvent in material 3.

[0026] In this embodiment, the entire insulating coating 30 is composed of 15 insulating layers, and the description applies to an example where the thickness of the insulating coating 30 is approximately 42 μm. However, the thickness of the insulating coating 30 may be thicker or thinner than 42 μm. For example, the thickness of the insulating coating 30 may be between 10 μm and 200 μm. Furthermore, the number of insulating layers constituting the insulating coating 30 may be more or less than 15.

[0027] One insulating layer is formed by applying and baking (curing by heating) either material 1 or material 3 as described above. The formation of the insulating layer is repeated until the thickness of the insulating film 30 reaches the desired thickness. In this embodiment, the formation of the insulating layer is repeated 15 times.

[0028] Next, we will explain the comparison of the evaluation results of the insulated wire 10 according to the above-described Examples 1 and 2 with each comparative example, referring to Figures 2 and 3. First, we will explain Comparative Examples 1 and 2, which will be used for comparison.

[0029] The insulated wire in Comparative Example 1 is provided with a conductor and a single-coat insulating film. The conductor in Comparative Example 1 is the same as the conductor 20 in the first embodiment. The insulating film in Comparative Example 1 is a component that covers the circumferential surface of the conductor and is formed using Kapton® (hereinafter also referred to as general-purpose PI).

[0030] DMAc is an example of a solvent used in general-purpose PIs. Specifically, the single-coat insulating film in Comparative Example 1 is constructed by laminating 15 insulating layers formed using general-purpose PI. Each insulating layer has a thickness of approximately 3 μm. The entire insulating film in Comparative Example 1 has a thickness of approximately 42 μm.

[0031] The insulated wire in Comparative Example 2 is provided with a conductor and a single-coat insulating coating. The conductor in Comparative Example 2 is the same as the conductor 20 in the first embodiment. The insulating coating in Comparative Example 2 is a component that covers the circumferential surface of the conductor and is formed using material 2.

[0032] Material 2 includes a material obtained by polymerizing a diamine or acid dianhydride, which is a silicone monomer in which at least a portion of the main chain is composed of siloxane bonds (-Si-O-Si-). The molecular weight of the silicone monomer used in Material 2 is 1,000 or more. In this embodiment, the explanation will be applied to an example in which the molecular weight of the silicone monomer is 1,340.

[0033] DMAc can be used as an example of a solvent in material 2. The insulating coating of Comparative Example 2 has 15 insulating layers formed on the outer circumference of the conductor using material 2. These insulating layers have a thickness of approximately 3 μm. The insulating coating of Comparative Example 2 has an overall thickness of approximately 42 μm.

[0034] Next, the evaluation results of the insulated wire 10 according to Examples 1 and 2 described above, and each comparative example will be explained. Figure 2 is a table illustrating the evaluation results of the insulated wire 10 according to Examples 1 and 2 described above, and each comparative example. Figure 3 is a graph illustrating the temperature change of the storage modulus in the dynamic viscoelasticity of each material used for the insulating coating.

[0035] The insulated wire 10 according to Example 1, the insulated wire 10 according to Example 2, the insulated wire according to Comparative Example 1, and the insulated wire according to Comparative Example 2 each have an insulating coating 30, an insulating coating according to Comparative Example 1, and an insulating coating according to Comparative Example 2, formed using one type of material, respectively.

[0036] The materials listed in Figure 2 are those used to form the insulating film. Material 1 is listed in the materials column for Example 1. Material 3 is listed in the materials column for Example 2. Note that both Material 1 and Material 3 have higher partial discharge initiation voltages (also known as PDIV) compared to general-purpose PI. General-purpose PI is listed in the materials column for Comparative Example 1. Material 2 is listed in the materials column for Comparative Example 2.

[0037] The column for the change in the order of magnitude of the storage modulus in Figure 2 shows the storage modulus (hereinafter also referred to as the storage modulus) in the dynamic viscoelasticity of the material forming the insulating film. Specifically, the change in the order of magnitude is shown in the temperature range of 300°C to 350°C.

[0038] The change in the order of magnitude of the storage modulus in Example 1, i.e., the change in the order of magnitude of the storage modulus of material 1, is 1 order of magnitude. The change in the order of magnitude of the storage modulus in Example 2, i.e., the change in the order of magnitude of the storage modulus of material 3, is 2 orders of magnitude. The change in the order of magnitude of the storage modulus in Comparative Example 1, i.e., general-purpose PI, is 0 orders of magnitude. The change in the order of magnitude of the storage modulus in Comparative Example 2, i.e., material 2, is 0 orders of magnitude.

[0039] Here, we will explain the measurement of the change in the order of magnitude of the storage modulus. The change in the order of magnitude of the storage modulus was evaluated by the storage modulus in the dynamic viscoelasticity of the PI film formed from the material that forms the insulating coating. The PI film was formed through the following process.

[0040] First, each material, polyamic acid varnish, is stretched onto a PEEK (polyether ether ketone) sheet using a bar coater with a 300 μm gap. Then, it is baked at 100°C, 200°C, and 300°C for 30 minutes each. This yields a PI film with a thickness of approximately 50 μm.

[0041] A test specimen is cut from the PI film formed through the process described above. The test specimen is 5 mm wide and 30 mm long. The distance between the chucks, which is the length used for the test, is 20 mm.

[0042] The aforementioned test specimens were evaluated in tensile mode using a dynamic viscoelasticity measuring device. The test conditions were a heating rate of 10°C / min, a frequency of 10Hz, a strain of 0.05%, and a data acquisition interval of 0.5°C.

[0043] Figure 3 is a graph showing the temperature dependence of the storage modulus E' in the dynamic viscoelasticity of each material forming the insulating film. As shown in Fig. 3, the storage elastic modulus E' of the general-purpose PI decreases in value as the temperature rises, and the rate of decrease in the temperature range of about 30°C or higher and about 390°C or lower is relatively small. Specifically, the change in the value of the storage elastic modulus E' of the general-purpose PI is within the range of 1×10 9 (Pa) or more and 1×10 10 (Pa) or less. The value of the storage elastic modulus E' of the general-purpose PI is 1×10 9 (Pa) or more at a temperature of 30°C.

[0044] In other words, the change in the value of the storage elastic modulus E' in the temperature range of about 30°C or higher and about 390°C or lower is within less than one digit (also expressed as 0 digits). In the temperature range of 300°C or higher and 350°C or lower, the change in the value of the storage elastic modulus E' of the general-purpose PI is also within less than one digit.

[0045] The storage elastic modulus E' of Material 1 decreases in value as the temperature rises, and the rate of decrease in the range of about 30°C or higher and about 390°C or lower is relatively large. Specifically, the change in the value of the storage elastic modulus E' in the range of about 30°C or higher and less than 300°C is within the range of 1×10 9 (Pa) or more and 1×10 10 (Pa) or less, and the change in value is less than one digit. The value of the storage elastic modulus E' of Material 1 is 1×10 9 (Pa) or more at a temperature of 30°C. On the other hand, the change in value in the range of 300°C (corresponding to the first predetermined threshold) or higher and 350°C or lower exceeds the range of 1×10 8 (Pa) or more and 1×10 9 (Pa) or less, and the change in value is one digit or more.

[0046] The storage elastic modulus E' of Material 2 decreases in value as the temperature rises, and the rate of decrease in the range of about 30°C or higher and about 390°C or lower is relatively small. In other words, the change in the value of the storage elastic modulus E' in the range of about 30°C or higher and about 390°C or lower is within less than one digit. The value of the storage elastic modulus E' of Material 2 is 1×10 9It is above (Pa). Even in the temperature range of 300°C to 350°C, the change in the value of the storage modulus E' of material 2 is within one order of magnitude. The value of the storage modulus E' of material 2 is 1 × 10 in the temperature range of 300°C to 350°C. 8 (Pa) or higher.

[0047] The storage modulus E' of material 3 decreases with increasing temperature, and the decrease is relatively large in the range of approximately 30°C to approximately 390°C. Specifically, the change in the value of the storage modulus E' in the range of approximately 30°C to less than approximately 150°C is 1 × 10⁻⁶. 8 (Pa) or more 1×10 9 The value will fall within the range of (Pa) or less, and the change in value will be less than one order of magnitude.

[0048] On the other hand, in the range of approximately 150°C (corresponding to the second predetermined threshold) to less than approximately 300°C, the change in the value of the storage modulus E' is approximately 1 × 10⁻⁶. 7 (Pa) or more about 1×10 8 Beyond the range of (Pa), the change in value becomes an order of magnitude or more. Furthermore, the change in value in the range of approximately 300°C (corresponding to the first predetermined threshold) to approximately 350°C is approximately 3 × 10⁻⁶. 4 (Pa) or more about 3×10 6 The value exceeds the range below (Pa), and the change in value is two orders of magnitude or more.

[0049] The adhesion column in Figure 2 shows the results of the adhesion evaluation for the insulated wires 10 in Examples 1 and 2, and for the insulated wires in each comparative example. The adhesion was evaluated by the peel test described below.

[0050] In the peel test, the test apparatus 100 shown in Figure 4 is used. The test apparatus 100 is equipped with gripping parts 110A and 110B for gripping the insulated wire, which is the sample 10T. The gripping parts 110A and 110B are positioned so that the longitudinal length of the gripped sample 10T is 250 mm. The gripping part 110A is attached to a mechanism 120 that rotates the gripped sample 10T around its longitudinal axis. The gripping part 110B is positioned so that it cannot rotate, in other words, it is fixed.

[0051] The peel test evaluation is performed as described below. First, the sample 10T is fixed to the gripping parts 110A and 110B of the test apparatus 100. A portion of the insulating coating 30 of the fixed sample 10T is removed as shown in Figure 5. Specifically, the insulating coating 30 on two sides parallel to the longitudinal direction of the sample 10T is removed until the conductor 20 is reached.

[0052] In other words, in Figure 5, which shows a cross-sectional view of sample 10T, the opposing portions of the insulating coating 30 with the conductor 20 in between are removed until the conductor 20 is exposed. The area from which the insulating coating 30 is removed covers the entire longitudinal region of sample 10T (perpendicular to the plane of the paper in Figure 5).

[0053] After removing a portion of the insulating coating 30, rotate the gripping part 110A. Rotate the gripping part 110A until the insulating coating 30 of sample 10T lifts away from the conductor 20 (also described as peeling off from the conductor 20). Measure the number of rotations at the point when the insulating coating 30 of sample 10T lifts away from the conductor 20. In this embodiment, a rotation angle of 360° of the gripping part 110A is denoted as one rotation.

[0054] As shown in Figure 2, in the peel test, the number of times the insulating coating 30 lifted from the conductor 20 was 98 for Example 1 and 74 for Example 2. In contrast, Comparative Example 1 required 72 times, and Comparative Example 2 required 0 times. In other words, in the peel test, Example 1 was evaluated as having higher adhesion than Comparative Example 1 and Comparative Example 2. Example 2 was evaluated as having similar adhesion to Comparative Example 1 and higher adhesion than Comparative Example 2.

[0055] The flexibility column in Figure 2 shows the evaluation results of the flexibility of the insulated wire 10 according to Example 1 and Example 2, as well as the insulated wires according to each comparative example.

[0056] The evaluation will be carried out as described below. First, an insulated wire 10 with a length of 500 mm is prepared as sample 10T. The length of the prepared sample 10T is stretched by 30% using a wire stretcher. The stretched sample 10T is wrapped around the circumference of a cylindrical winding rod. The diameter of the winding rod is the same as the diameter of the prepared sample 10T.

[0057] When the stretched sample 10T is wrapped around the circumference of the winding rod, if no cracks appear in the insulating coating 30 and the insulating coating 30 does not peel off from the conductor 20, it is evaluated as a pass (also indicated by ○). If cracks appear in the insulating coating 30 or the insulating coating 30 peels off from the conductor 20, it is evaluated as a fail (also indicated by ×).

[0058] When the stretched samples 10T from Example 1 and Example 2 were wrapped around the circumference of a winding rod, no cracks occurred in the insulating coating 30, and the insulating coating 30 did not peel off from the conductor 20. In other words, Example 1 and Example 2 were evaluated as passing (〇).

[0059] When the stretched samples 10T from Comparative Example 1 and Comparative Example 2 were wrapped around the circumference of a winding rod, cracks appeared in the insulating coating 30, or the insulating coating 30 peeled off from the conductor 20. In other words, Comparative Example 1 and Comparative Example 2 were evaluated as unacceptable (×).

[0060] With the insulated wire 10 configured as described above, the storage modulus of the material 1 forming the insulating film 30 decreases by more than an order of magnitude as the temperature rises. In other words, with the insulated wire 10, the storage modulus of the insulating material forming the insulating film 30 in dynamic viscoelasticity at temperatures above 100°C decreases by more than an order of magnitude as the temperature rises to 30°C compared to the storage modulus in dynamic viscoelasticity. Therefore, an anchoring effect from the first insulating layer 31 to the surface of the conductor 20 and an anchoring effect between it and the adjacent second insulating layer 41 are easily obtained.

[0061] In other words, good adhesion between the first insulating layer 31 and the conductor 20, good adhesion between the first insulating layer 31 and the second insulating layer 41, and good adhesion between adjacent second insulating layers 41 are easily achieved.

[0062] By using material 1, in which the storage modulus E' decreases by more than an order of magnitude compared to the storage modulus E' in dynamic viscoelasticity at 30°C when the temperature rises in the temperature range of approximately 300°C to approximately 350°C, the storage modulus E' of the insulating film 30 can be made different in the low-temperature region below approximately 300°C and the high-temperature region above approximately 300°C. This makes it easier to give the insulating film 30 the desired properties.

[0063] By using material 1, which contains at least 4,4'-diaminodiphenyl ether and pyromellitic dianhydride as an insulating material, the storage modulus E' when the temperature rises in the temperature range of approximately 300°C to approximately 350°C can be reduced by more than an order of magnitude compared to the storage modulus E' in dynamic viscoelasticity at a temperature of 30°C.

[0064] Furthermore, compared to insulated wires using other methods for ensuring adhesion, as described below, the insulated wire 10 of this embodiment exhibits less deterioration in adhesion even after time has passed since its manufacture. Other methods include forming the insulating coating with polyethersulfone (hereinafter also referred to as PES) or introducing chemical bonds at the interface between the insulating coating and the conductor. It is known that these other methods result in a decrease in adhesion over time after the manufacture of the insulated wire.

[0065] Compared to these methods, the material 1 of this embodiment, which contains at least 4,4'-diaminodiphenyl ether and pyromellitic dianhydride, exhibits less deterioration in adhesion even after time has elapsed since the manufacture of the insulated wire 10.

[0066] Specifically, the following applies: In conventional methods using PES, the main chain of the molecular structure contains sulfonyl groups (-SO2-) which have poor heat resistance. Therefore, when exposed to high temperatures for extended periods (e.g., 100°C to 180°C), the main chain breaks, making it impossible to guarantee long-term adhesion.

[0067] In contrast, Material 1 of this embodiment has an imide bond in its molecular structure that has excellent heat resistance. Furthermore, Material 1's monomers, the diamine and acidic dianhydride, are composed only of ether bonds (-O-) and benzene rings, which have excellent long-term heat resistance. Therefore, the insulating film 30 formed using Material 1 is less susceptible to thermal decomposition and can provide adhesion to the conductor 20 through a physical anchoring effect. In other words, it is possible to reduce the decrease in adhesion after prolonged heating.

[0068] [Second Embodiment] Next, a second embodiment of the present invention will be described with reference to Figures 6 to 12. The basic configuration of the insulated wire in this embodiment is the same as in the first embodiment, but the insulating coating is different from that of the first embodiment. Therefore, in this embodiment, the parts of the insulating coating that differ from the first embodiment will be explained using Figures 6 to 12, and the explanation of the parts that are the same will be omitted.

[0069] Figure 6 is a cross-sectional view illustrating the configuration of the insulated wire 10A in this embodiment. As shown in Figure 6, the insulated wire 10A is provided with a conductor 20 and an insulating coating 30A. The insulating coating 30A is a component that covers the circumferential surface of the conductor 20.

[0070] The insulating coating 30A differs from the insulating coating 30 formed without a foaming agent in that it is formed using an insulating material (hereinafter also referred to as paint) that has insulating and thermosetting properties with a foaming agent added. Here, the explanation applies to an insulated wire 10A (hereinafter also referred to as Example 3) in which the insulating coating 30A is formed using material 1 with a foaming agent added. In the case of the insulated wire 10A, the explanation uses the insulating coating 30A formed using material 1 with a foaming agent added, but is not limited to this. In other words, the insulating coating 30A of the insulated wire 10A may also be formed using material 3 with a foaming agent added.

[0071] Figure 7 is a schematic diagram illustrating the configuration of the first insulating layer 31 and the second insulating layer 41. As shown in Figure 7, the insulating coating 30A is provided with one first insulating layer 31 and a plurality of second insulating layers 41. In this embodiment, the explanation will be applied to an example in which 14 second insulating layers 41 are provided. Note that the number of second insulating layers 41 may be more or less than 14.

[0072] As shown in Figure 7, the first insulating layer 31 is positioned adjacent to the outer surface of the conductor 20. The first insulating layer 31 is a layer formed to cover the periphery of the conductor 20 and has three regions, which will be described later.

[0073] The first insulating layer 31 has, in order from the inside out, a first inner region 32, a first central region 33, and a first outer region 34. Hereafter, in the thickness direction of the insulating film 30A, the side facing the conductor 20 will be referred to as the inside, and the side facing the circumferential surface will be referred to as the outside.

[0074] The first insulating layer 31 is a layer obtained by applying paint to the outer surface of the conductor and baking (curing by heating) it only once. The thickness of the first insulating layer 31 is, for example, 1 μm or more and 5 μm or less.

[0075] The first inner region 32 is a region in the first insulating layer 31 that is in contact with the conductor 20. In other words, it is a region in the first insulating layer 31 that is closer to the conductor 20 than the first central region 33 and is composed of an insulating resin such as polyimide. The first inner region 32 is also a region that does not include the first void 37, which will be described later (it is also referred to as the first inner void-free region).

[0076] The first central region 33 is the central region of the first insulating layer 31. The first central region 33 is located adjacent to the first inner region 32 and the first outer region 34, and is a region (also referred to as the first void region) composed of an insulating resin such as polyimide and a plurality of first voids 37.

[0077] The first outer region 34 is the region of the first insulating layer 31 that is closer to the second insulating layer 41 than the first central region 33. The first outer region 34 is composed of an insulating resin such as polyimide and does not contain the first void 37 (also referred to as the first outer void-free region).

[0078] The first void 37 is a space containing gas. The gas includes air, gases generated from the decomposition of the pyrolytic polymer described later, etc. The void diameter of the first void 37 is 2 μm or less.

[0079] The void diameter is the diameter when the space is spherical, the diameter along the major axis when it is an ellipsoid obtained by rotating an ellipse around its axis, and the maximum length when it is any other solid shape.

[0080] The pore diameter is the diameter or length of an independent first pore 37. Spaces formed by multiple first pores 37 connected during the formation of the first insulating layer 31, or spaces formed by multiple first pores 37 connected after the formation of the first insulating layer 31, are not considered to have the pore diameter of the first pore 37.

[0081] The first inner region 32 and the first outer region 34 are preferably such that the thickness along the thickness direction of the insulating film 30A is greater than the diameter of the first void 37 contained in the first central region 33. This makes it less likely for voids to communicate, as described later, and also improves the adhesion at the interface between the conductor 20 and the first insulating layer 30.

[0082] An example of an independent first void 37 is one in which the inner wall has only a continuous curved shape that is convex outward, such as a sphere or a spheroid. An example of a connected group of first voids 37 is one in which the inner wall has shapes other than a curved shape that is convex outward.

[0083] The second insulating layer 41 is positioned on the outer periphery of the first insulating layer 31 and is a layer that covers the conductor 20 and the first insulating layer 31. The second insulating layer 41 has a second inner region 42 and a second outer region 44, in that order from the inside out.

[0084] The second inner region 42 is the region of the second insulating layer 41 on the side of the first insulating layer 31 and is composed of polyimide and a plurality of second vacancies 47 (also referred to as the second vacancy region). The second outer region 44 is located adjacent to the second inner region 42 and is the outer region on the opposite side from the first insulating layer 31 and is composed of polyimide (also referred to as the second outer vacancy-free region). The vacancy diameter of the second vacancies 47 is 2 μm or less.

[0085] The second outer region 44 is preferably such that the thickness along the thickness direction of the insulating film 30A is greater than the pore diameter of the second pore 47 contained in the second inner region 42. This makes it less likely for pores to communicate in the second insulating layer 41, as described later.

[0086] Next, the manufacturing method of the insulated wire 10A described above will be explained with reference to Figure 8. Specifically, the manufacturing method of the insulating coating 30A on the insulated wire 10A will be explained. Figure 8 is a flowchart illustrating the manufacturing method of the insulated wire 10A.

[0087] First, a step is taken to prepare material 1, which is made by adding a foaming agent to form an insulating coating 30A on an insulated wire 10A (S11). Specifically, a step is taken to obtain material 1 by stirring and synthesizing polyamic acid in a solvent. Next, a step is taken to obtain material 1 with the foaming agent added (in the case of Example 3) by adding a foaming agent made of a pyrolytic polymer to material 1 and stirring and mixing.

[0088] The foaming agent, consisting of a pyrolytic polymer, is added to the resin content of the paint before stirring synthesis in an amount of, for example, 10 parts by weight (phr: per hundred resin) to 60 parts by weight (corresponding to a predetermined amount by weight). In this embodiment, the explanation will be applied to an example in which 20 parts by weight of pyrolytic polymer are added to the resin content of the paint after stirring synthesis.

[0089] As a thermally decomposable polymer used as a blowing agent, for example, polypropylene glycol (also written as PPG) can be used. In this embodiment, the explanation will be applied to an example in which diol-type polypropylene glycol (also written as PPG400) with a molecular weight of 400 is used as the thermally decomposable polymer.

[0090] Next, a first coating step is performed in which the prepared paint is applied around the conductor 20 (S12). Specifically, the paint that forms the first insulating layer 31 is applied. The coating obtained by applying the paint once is formed on the circumferential surface of the conductor 20.

[0091] The paint is applied to a desired thickness such that the thickness of the first insulating layer 31 is, for example, about 3 μm after the subsequent first insulating layer formation step. In this embodiment, the example will be described in which a paint of a desired thickness is formed around the conductor 20 using a die.

[0092] The die described above has a through hole for inserting a conductor 20 with a coating formed inside it. After forming a coating made of material 1 with a foaming agent added that is thicker than the desired thickness of the first insulating layer 31 around the conductor 20, the conductor 20 is passed through the through hole of the die. The die removes a portion of the outer periphery of the coating, leaving a coating of a thickness corresponding to the outer diameter of the through hole around the conductor 20.

[0093] Furthermore, the method for applying the paint around the conductor 20 is not limited to the method described above, and other known application methods used in the manufacture of enameled wire can be used.

[0094] Next, a first insulating layer formation step is performed (S13) in which the conductor 20, which has been coated with paint once, is heated to form the first insulating layer 31. Specifically, the conductor 20, which has been coated with paint once, is placed in a furnace maintained at a temperature between 300°C and 500°C.

[0095] Inside the furnace, the solvent is removed from the paint due to the high temperature. Subsequently, with the pyrolytic polymer and polyamic acid in a phase-separated state, the imidation reaction of the polyamic acid contained in the paint proceeds, forming the first insulating layer 31. Simultaneously with the imidation reaction of the polyamic acid, the pyrolytic polymer, which is a foaming agent, is thermally decomposed, and the first void 37 is formed in the first insulating layer 31.

[0096] In this embodiment, the pyrolytic polymer used as a foaming agent has a relatively lower tendency to adhere to the conductor 20 (also referred to as wettability or affinity) than its tendency to adhere to the polyamic acid. Therefore, when comparing the portion corresponding to the first inner region 32 in the paint with the portions corresponding to the first central region 33 and the first outer region 34, it is considered that the proportion of the pyrolytic polymer, which is the foaming agent, is higher in the portions corresponding to the first central region 33 and the first outer region 34.

[0097] In other words, it is thought that the proportion of the pyrolytic polymer, which is a foaming agent, present in the portion corresponding to the first inner region 32 will be low. Therefore, the first inner region 32 of the first insulating layer 31 is composed of polyimide, which is an insulating resin, and does not contain the first void 37 described later.

[0098] As described above, the portion corresponding to the first outer region 34 in the paint coating has a high proportion of pyrolytic polymer, which is a foaming agent. On the other hand, it is thought that the pyrolytic polymer that is decomposed and vaporized by heating is released from the paint coating before the polyamic acid is imidized to become polyimide. Therefore, the first outer region 34 of the first insulating layer 31 is composed of polyimide, which is an insulating resin, and does not contain the first pores 37 described later.

[0099] In the portion corresponding to the first central region 33 in the paint coating, it is thought that the polyamic acid is imidized to polyimide before the vaporized pyrolytic polymer is released from the paint coating. Therefore, the first central region 33 of the first insulating layer 31 is composed of polyimide, which is an insulating resin, and a plurality of first pores 37.

[0100] Next, a second coating step is performed in which the prepared paint is applied around the first insulating layer 31 (S14). Specifically, the paint that will form the second insulating layer 41 is applied to the circumferential surface of the first insulating layer 31. A coating paint made of material 1 with a foaming agent added is formed around the first insulating layer 31.

[0101] The paint is applied to a desired thickness such that the thickness of the second insulating layer 41 is approximately 3 μm after the subsequent second insulating layer formation step. The thickness of the paint is adjusted using a die, similar to the first coating step S12. The die used here has a through hole corresponding to the outer diameter of the conductor 20 on which the first insulating layer 31 is formed.

[0102] Furthermore, the method for applying the paint around the first insulating layer 31 is not limited to the method described above, and other known application methods used in the manufacture of enameled wire can be used.

[0103] Next, a second insulating layer formation step is performed in which the paint is heated to form a second insulating layer 41 (S15). Specifically, similar to the first insulating layer formation step S13, the conductor 20 with the paint applied and the first insulating layer 31 are placed in a furnace maintained at a temperature between 300°C and 500°C.

[0104] Similar to the first insulating layer formation step S13, the solvent is removed from the coating material 1 by high temperature in the furnace. Subsequently, the polyamic acid and the pyrolytic polymer contained in the coating material undergo phase separation, and the imidation reaction of the polyamic acid proceeds, forming the second insulating layer 41. Simultaneously with the imidation reaction of the polyamic acid, the pyrolytic polymer, which is a foaming agent, is thermally decomposed, and the second void 47 is formed in the second insulating layer 41.

[0105] Unlike the first insulating layer formation step S13, the coating paint of material 1 formed on the circumferential surface of the first insulating layer 31 is in contact with the first insulating layer 31, not the conductor 20. Therefore, it is considered that the thermally decomposable polymer, which is a foaming agent, is relatively more uniformly present in the coating paint formed in the second coating step S14 compared to the coating paint formed in the first coating step S12.

[0106] In the portion corresponding to the second outer region 44 of the second insulating layer 41 in the paint coating, it is thought that the pyrodegradable polymer that is decomposed and vaporized by heating is released from the paint coating before the polyamic acid is imidized to form polyimide. Therefore, the second outer region 44 is composed of polyimide, which is an insulating resin, and does not contain the second void 47.

[0107] In the portion corresponding to the second inner region 42 in the paint coating, it is thought that the polyamic acid is imidized to polyimide before the vaporized pyrodegradable polymer is released from the paint coating. Therefore, the second inner region 42 is composed of polyimide, which is an insulating resin, and a plurality of second pores 47.

[0108] If 14 layers of the second insulating layer 41 have not been formed (in the case of NO in S16), the process returns to the second coating step S14 described above, and the process of forming the second insulating layer 41 is repeated. If 14 layers of the second insulating layer 41 have been formed (in the case of YES in S16), the process of forming the insulating film 30A around the conductor 20 is completed.

[0109] In other words, the combination of the second coating step S14 and the second insulating layer formation step S15 is performed 14 times to form 14 layers of the second insulating layer 41. In particular, in the second coating step S14 from the second time onward, material 1 is applied around the second insulating layer 41 to form a coating around the second insulating layer 41. Also, in the second insulating layer formation step S15 from the second time onward, the coating formed around the second insulating layer 14 is heated to form the second insulating layer 41 around the second insulating layer 41. This produces the insulating coating 30A for the insulated wire 10A. The insulating coating 30A as a whole consists of one layer of the first insulating layer 31 and 14 layers of the second insulating layer 41. An insulating coating 30A with a film thickness of approximately 42 μm is formed.

[0110] Next, the results of the longitudinal cross-sectional observation of the interface of the insulating coating 30A on the insulated wire 10A described above will be explained with reference to Figures 9 to 12. Figures 9 and 10 are schematic diagrams illustrating the preparation method of the insulating coating 30A used for longitudinal cross-sectional observation.

[0111] When observing the longitudinal section, first, an insulated wire 10A of a predetermined length is prepared as the object of observation. Next, as shown in Figure 9, the conductor 20 of the insulated wire 10A is removed to obtain a cylindrical insulating coating 30A. Electrolysis can be used to remove the conductor 20. Alternatively, the conductor 20 may be removed using methods other than electrolysis.

[0112] Next, the cylindrical insulating film 30A is processed to become a rectangular insulating film 30A. Specifically, a single cut Ct extending in the longitudinal direction is made in the cylindrical insulating film 30A. The longitudinal direction is perpendicular to the plane of the paper in Figure 9. The cylindrical insulating film 30A is opened at the cut Ct to become a rectangular insulating film 30A as shown in Figure 10.

[0113] Figure 11 is an SEM image illustrating the interface between the conductor 20 and the adjacent interface in the first insulating layer 31. As shown in Figure 11, no voids are observed at the interface 31f adjacent to the conductor 20 in the first insulating layer 31. In Figure 11, the white lines formed in a linear fashion extending in the longitudinal direction of the first insulating layer 31 are traces Wd of the surface irregularities of the conductor 20 transferred to the first insulating layer 31.

[0114] Figure 12 is an SEM image illustrating the interface between the second insulating layer 41 and the first insulating layer 31. As shown in Figure 12, a second void 47 is observed at the interface 41f adjacent to the first insulating layer 31 in the second insulating layer 41. The circular or elliptical white outlines in Figure 12 represent the second void 47 that appeared at the interface 41f. The interface 41f is, for example, the surface where the first insulating layer 31 is peeled off from the rectangular insulating film 30A to expose the second insulating layer 41.

[0115] In this embodiment, the interface 41f adjacent to the first insulating layer 31 in the second insulating layer 41 was observed, but the interface 41ff adjacent to the inner second insulating layer 41 in the outer second insulating layer 41 of two adjacent second insulating layers 41 may also be observed.

[0116] Next, we will explain the comparison of the evaluation results of the insulated wire 10A according to the above-described Example 3 with those of each comparative example, with reference to Figure 2.

[0117] In Figure 2, the "Materials" column for Example 3 lists Material 1 (also referred to as Material 1 + Foaming Agent), which has a foaming agent added to it. Note that the insulated wire 10A in Example 3 has an insulating coating 30A formed using only one type of material.

[0118] The "Adhesion" column in Figure 2 shows the evaluation results of the adhesion of the insulated wire 10A in Example 3, specifically the evaluation results from the peel test. In the peel test of Example 3, it took 98 passes for the insulating coating 30A to separate from the conductor 20.

[0119] In other words, in the peel test, Example 3 was evaluated as having higher adhesion than Comparative Example 1 (72 times) and Comparative Example 2 (0 times). Furthermore, the adhesion evaluation of Example 3 was equivalent to that of Example 1.

[0120] The flexibility column in Figure 2 shows the evaluation results for the flexibility of the insulated wire 10A according to Example 3 and the insulated wires according to each comparative example. When the stretched sample 10T according to Example 3 was wrapped around the circumference of a winding rod, no cracks occurred in the insulating coating 30A, and the insulating coating 30A did not peel off from the conductor 20. In other words, Example 3 was evaluated as passing (〇), similar to Examples 1 and 2.

[0121] It should be noted that the technical scope of the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention. For example, the present invention is not limited to those applied to the embodiments described above, but may also be applied to embodiments that combine these embodiments as appropriate, and is not particularly limited. [Explanation of Symbols]

[0122] 10, 10A…Insulated wire, 20…Conductor, 30, 30A…Insulating coating, 31…First insulating layer, 41…Second insulating layer

Claims

1. A conductor formed from a conductive material and having an elongated shape, An insulating coating formed from an insulating material and having at least a plurality of insulating layers covering the conductor, A system was established, The insulating material is a polyimide material obtained by polymerizing a diamine containing 4,4'-diaminodiphenyl ether and a tetracarboxylic dianhydride containing pyromellitic acid, and then synthesizing the resulting polyamic acid in a solvent while stirring. The insulating material satisfies at least one of the following conditions A and B: The insulating material is an insulated wire in which the storage modulus of dynamic viscoelasticity at 350°C is more than an order of magnitude lower than the storage modulus of dynamic viscoelasticity at a temperature of 30°C. (Condition A) The diamine, in addition to the 4,4'-diaminodiphenyl ether, includes any of 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, and 4,4'-bis(4-aminophenoxy)biphenyl. (Condition B) The tetracarboxylic dianhydride, in addition to the pyromellitic dianhydride, includes any of the following: 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 4,4'-oxydiphthalic acid dianhydride, 4,4'-(2,2-hexafluoroisopropylidene)diphthalic acid anhydride, and 3,3',4,4'-biphenyltetracarboxylic dianhydride.

2. A conductor formed from a conductive material and having an elongated shape, An insulating coating is provided, which is formed from an insulating material and has at least a plurality of insulating layers covering the periphery of the conductor. The aforementioned insulating material is a polyimide material obtained by polymerizing a diamine, which is a silicone monomer in which part of the main chain is composed of siloxane bonds and has a molecular weight of less than 1000, with an acidic dianhydride, and then synthesizing the resulting polyamic acid in a solvent while stirring. The insulating material is an insulated wire in which the storage modulus of dynamic viscoelasticity at 350°C is more than an order of magnitude lower than the storage modulus of dynamic viscoelasticity at a temperature of 30°C.

3. The insulating coating comprises voids, as described in claim 1 or 2.

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