Laminated body of conductor and insulating coating, coil, rotary electric machine, and insulating paint

Abstract

Provided is a laminated body including a conductor and an insulating coating containing a metal hydroxide hydrate, the laminated body having an enhanced partial discharge inception voltage (PDIV) while having an effect of suppressing erosion with respect to partial discharge.　The laminated body comprises at least a conductor and an insulating coating. The insulating coating includes a first insulating coating and a second insulating coating. The second insulating coating is formed from a resin composition containing a resin and a metal oxide hydrate. The content of the metal oxide hydrate in the resin composition is 18-40 parts by mass relative to 100 parts by mass of the total of the resin and the metal oxide hydrate.

Description

Laminates of conductors and insulating coatings, coils, rotating electrical machines, and insulating paints

[0001] The present invention relates to a laminate of a conductor and an insulating coating, a coil, a rotating electric machine, and an insulating coating.

[0002] Electric wires used in electrical equipment such as motors have an insulating layer formed by applying an insulating coating made by dissolving a resin such as polyimide or polyamideimide, or a resin precursor, in an organic solvent to the surface of the conductor and baking it.

[0003] In electrical equipment with high operating voltages, such as motors operated at high voltages, high voltages are applied to the insulated wires that make up the coils. If there are minute gaps between adjacent insulated wires or in the insulating coating, an electric field may concentrate in those areas, causing partial discharges. Such partial discharges can cause deterioration of the insulating layer, leading to early breakdown of the coil and damage to the electrical equipment.

[0004] In recent years, in systems that drive motors and other devices using inverters for energy conservation or variable speed, even in devices classified as low-voltage drives, sudden overvoltages (so-called inverter surges) have repeatedly occurred in the drive voltage over a very short period of time, often causing dielectric breakdown. This dielectric breakdown is caused by partial discharges triggered by the repeated overvoltages caused by inverter surges.

[0005] As a countermeasure against partial discharge, a method has been disclosed in which the voltage at which partial discharge occurs, i.e., the partial discharge inception voltage (PDIV), is increased to prevent partial discharge (Patent Document 1). However, because the partial discharge inception voltage varies depending on the external environment, such as temperature and dirt, it is difficult to completely suppress the occurrence of partial discharge with the conventional method, and there has also been a problem that the resistance of the electric wire when partial discharge occurs is very low, similar to that of an ordinary electric wire.

[0006] On the other hand, as a method for improving the voltage life against partial discharge, a method has been disclosed in which metal oxides or metal oxide hydrates are filled into the insulating coating to effectively suppress erosion due to partial discharge (Patent Documents 2 and 3).

[0007] Patent No. 5972244 Patent No. 3496636 Patent No. 6567797

[0008] The methods disclosed in Patent Documents 2 and 3, in which a filler such as a metal oxide is filled into an insulating coating, have a problem in that the dielectric constant of the filler to be filled is high, which increases the dielectric constant of the insulating coating, thereby decreasing the partial discharge inception voltage (PDIV) and making partial discharges more likely to occur.

[0009] The present invention aims to provide a laminate including a conductor and an insulating coating containing a metal hydroxide hydrate, which laminate has an improved partial discharge inception voltage (PDIV) while having an effect of suppressing corrosion due to partial discharge. The present invention also aims to provide a coil and a rotating electrical machine that use the laminate as an insulated wire, as well as an insulating coating and a film for forming the laminate.

[0010] The present inventors conducted extensive research to solve the above-mentioned problems. As a result, they unexpectedly discovered that a laminate including at least a conductor and an insulating coating, the insulating coating including a first insulating coating and a second insulating coating, the second insulating coating being formed from a resin composition containing a resin and a metal oxide hydrate, and that when the content of the metal oxide hydrate in the resin composition is set within a specific range, the partial discharge inception voltage (PDIV) is improved while maintaining the effect of suppressing erosion due to partial discharge. The present invention was completed based on this discovery and through further research.

[0011] That is, the present invention provides the following configurations. Item 1. A laminate including at least a conductor and an insulating coating, wherein the insulating coating includes a first insulating coating and a second insulating coating, and the second insulating coating is formed from a resin composition containing a resin and a metal oxide hydrate, and the content of the metal oxide hydrate in the resin composition is 18 parts by mass or more and 40 parts by mass or less, relative to 100 parts by mass of the total of the resin and the metal oxide hydrate. Item 2. The laminate according to Item 1, wherein the insulating coating has a ratio of the relative dielectric constants of the first insulating coating and the second insulating coating at 25°C and 1 kHz of 1.5<(relative dielectric constant of the second insulating coating) / (relative dielectric constant of the first insulating coating)<1.8. Item 3. The laminate according to Item 1 or 2, wherein the insulating coating is an insulating coating that forms an inorganic insulating layer when the laminate is exposed to partial discharge due to an inverter surge. Item 4. The laminate according to any one of Items 1 to 3, wherein the thickness of the second insulating coating is 1 μm or more. Item 5. The laminate according to any one of Items 1 to 4, wherein the thickness of the second insulating coating accounts for less than 75% of the total thickness of the insulating coating. Item 6. The laminate according to any one of Items 1 to 5, wherein the first insulating coating is formed from a resin composition that does not contain a filler. Item 7. The laminate according to any one of Items 1 to 6, wherein the second insulating coating is not in contact with the conductor. Item 8. The laminate according to any one of Items 1 to 7, wherein the metal oxide hydrate is alumina hydrate. Item 9. The laminate according to any one of Items 1 to 8, wherein the resin constituting the first insulating coating and / or the second insulating coating is at least one selected from the group consisting of formal resin, polyurethane, epoxy resin, polyester, polyesterimide, polyetherimide, polyamideimide, polyimide, and precursors thereof. Item 10. Item 11. The laminate according to any one of items 1 to 9, in the form of an insulated wire or a film. Item 11. A coil comprising the insulated wire according to item 10. Item 12. A rotating electric machine comprising the insulated wire according to item 10. Item 13. An insulating coating material for producing the laminate according to any one of items 1 to 3, the insulating coating material comprising a resin composition containing a metal oxide hydrate.

[0012] According to the present invention, it is possible to provide a laminate including a conductor and an insulating coating containing a metal hydroxide hydrate, which laminate has an improved partial discharge inception voltage (PDIV) while maintaining an effect of suppressing erosion against partial discharge. Furthermore, according to the present invention, it is also possible to provide a coil and a rotating electrical machine that use the laminate as an insulated wire, and an insulating paint for forming the laminate.

[0013] 1 is a schematic cross-sectional view showing an example of a laminate (insulated wire) according to an embodiment of the present invention; 2 is a schematic cross-sectional view showing another example of a laminate (insulated wire) according to an embodiment of the present invention; 3 is a schematic cross-sectional view showing another example of a laminate (insulated wire) according to an embodiment of the present invention;

[0014] The laminate, coil, rotating electrical machine, and insulating coating of the present invention will be described in detail below. In this specification, a numerical value connected with "~" means a numerical range that includes the numerical values ​​before and after "~" as the lower and upper limits. When multiple lower limit values ​​and multiple upper limit values ​​are listed separately, any lower limit value and upper limit value can be selected and connected with "~".

[0015] The laminate of the present invention includes at least a conductor and an insulating coating formed on the conductor. In the laminate of the present invention, the insulating coating is composed of at least two layers. That is, the insulating coating includes a first insulating coating and a second insulating coating. The second insulating coating is composed of a resin composition containing a resin and a metal oxide hydrate. Furthermore, the content of the metal oxide hydrate in the resin composition is 18 parts by mass or more and 40 parts by mass or less, relative to 100 parts by mass of the total of the resin and the metal oxide hydrate. By having these configurations, the laminate of the present invention exhibits the excellent effect of improving the partial discharge inception voltage (PDIV) while maintaining the erosion suppression effect of the laminate against partial discharge.

[0016] More specifically, for example, a laminate including a conductor and an insulating coating formed thereon exhibits a higher partial discharge inception voltage (PDIV) than a laminate including an insulating coating formed only from the resin forming the second insulating coating (assuming the insulating coating has the same thickness). This is because the partial discharge inception voltage A of the insulating coating formed from the first insulating coating and the second insulating coating is higher than the partial discharge inception voltage B of a coating formed only from the resin of the second insulating coating and having the same thickness as the insulating coating. The higher the partial discharge inception voltage (PDIV), the higher the voltage until partial discharge starts, and therefore the more effectively partial discharge can be suppressed. The laminate of the present invention will be described in detail below with reference to FIGS. 1 to 3.

[0017] In this invention, "inverter surge" refers to a steep overvoltage that occurs due to inverter switching and is superimposed on the drive voltage. Since the switching frequency of an inverter ranges from a relatively slow 1 kHz to a high 100 kHz, the frequency of inverter surges also ranges from about 1 kHz to 100 kHz, which is extremely high. The voltage ranges from about 1.1 kVp when superimposed on the 400 V drive voltage of an industrial inverter motor to about 3 kVp when superimposed on the operating voltage of a high-voltage inverter motor.

[0018] The laminate 10 of the present invention may be in the form of an insulated wire having a conductor 1 in the center and an insulating coating 2 formed around the conductor 1, as shown in Figures 1 to 3, for example. When the laminate 10 of the present invention is in the form of an insulated wire, the cross-sectional shape may be circular, elliptical, polygonal (it may be rectangular or irregular), or the like. Figures 1 and 2 show an insulated wire having a circular cross section. Figure 3 shows an insulated wire having a substantially rectangular cross section.

[0019] The first insulating coating 21 and the second insulating coating 22 are different coatings (layers) from each other. Details of the first insulating coating 21 and the second insulating coating 22 will be described later, but it is preferable that the first insulating coating 21 and the second insulating coating 22 are made of different materials.

[0020] To more effectively achieve the effects of the present invention, the ratio of the dielectric constants of the first insulating coating 21 and the second insulating coating 22 at 25°C and 1 kHz is preferably in the range of 1.5 < (dielectric constant of the second insulating coating) / (dielectric constant of the first insulating coating) < 1.8. The dielectric constant of the insulating coating is determined by the type and content of the resin, metal oxide hydrate, etc. that constitutes the insulating coating. Therefore, even if the resin or metal oxide hydrate is of the same type, the dielectric constant ratio can be adjusted to the above range by adjusting the structure and content.

[0021] The first insulating coating 21 and the second insulating coating 22 may be stacked in the order shown, for example, starting from the conductor 1 side, followed by the first insulating coating 21 and the second insulating coating 22, or the second insulating coating 22 and the first insulating coating 21, starting from the conductor 1 side. From the viewpoint of more effectively achieving the effects of the present invention, it is preferable that the first insulating coating 21 and the second insulating coating 22 are stacked in the order shown, starting from the conductor 1 side. From the same viewpoint, it is also preferable that the first insulating coating 21 and the second insulating coating 22 are adjacent to each other. From the same viewpoint, it is also preferable that the second insulating coating 22 is not in contact with the conductor 1.

[0022] The insulating coating 2 may be composed of only the first insulating coating 21 and the second insulating coating 22 (i.e., a two-layer configuration), or may further include one or more other insulating coating layers (i.e., a three-layer or more configuration). The other insulating coatings may be any coatings that have insulating properties that do not impair the effects of the present invention, such as the first insulating coating 21, the second insulating coating 22, or the insulating layers 3 and 4 described below.

[0023] Other layers that may be included in the laminate 10 of the present invention include, for example, insulating layers 3 and 4. For example, Fig. 2 shows a laminate 10 (insulated wire) including a conductor 1, an insulating layer 3 formed around the conductor 1, and an insulating coating 2 further formed around the conductor 1. Fig. 3 shows a laminate 10 (insulated wire) including a conductor 1, an insulating layer 3 formed around the conductor 1, an insulating coating 2 formed around the conductor 1, and an insulating layer 4 further formed around the insulating layer 3. Examples of materials that may be used to form the insulating layers 3 and 4 include heat-resistant resins, which will be described later.

[0024] The insulating layers 3 and 4 may be made of the same resin as the first insulating coating 21 or the second insulating coating 22, respectively, or may be made of a different insulating material. The insulating layers 3 and 4 may be made of the same resin or may be made of a different insulating material. The insulating layers 3 and 4 may be provided below the insulating coating 2 (i.e., on the conductor 1 side) or above the insulating coating 2 (i.e., on the opposite side from the conductor 1 side).

[0025] As another layer, a plating layer made of a metal different from that of the conductor 1 and formed between the surface of the conductor 1 and the insulating coating 2 may be provided.

[0026] The material constituting the conductor 1 is not particularly limited as long as it is a conductive material, and examples thereof include copper (such as low-oxygen copper, oxygen-free copper, and copper alloys), as well as metals such as aluminum, silver, nickel, and iron. The material constituting the conductor 1 can be appropriately selected depending on the application of the present invention.

[0027] The size (thickness, diameter, etc.) of the conductor 1 is adjusted appropriately depending on the application of the laminate 10. For example, if the laminate 10 is an insulated wire, the diameter is, for example, 0.02 to 3.2 mm.

[0028] The first insulating coating 21 is preferably made of a resin. The resin may be a resin with excellent heat resistance (heat-resistant resin), and may be, for example, a resin used in known insulated wires. Specific examples of resins include formal resin, polyurethane, epoxy resin, polyester, polyamide, polyesterimide, polyetherimide, polyamideimide, polyimide, and precursors thereof. Among these, imide-based resins such as polyesterimide, polyamideimide, and polyimide are preferably used from the viewpoint of further improving heat resistance. The resin constituting the first insulating coating 21 may be one type or two or more types.

[0029] Examples of the imide-based resin include aromatic polyimides obtained by dehydration condensation of diamines such as 4,4'-diaminodiphenyl ether (ODA) with acid anhydrides such as pyromellitic dianhydride (PMDA) and biphenyltetracarboxylic dianhydride (BPDA). Specific examples include aromatic polyimides obtained by dehydration condensation of ODA and PMDA, and aromatic polyimides obtained by dehydration condensation of ODA and BPDA. The imide-based resin may have a structure in which the main chain terminals of the polyimide are capped with a capping agent, or a structure in which the main chain terminals are not capped. The capping agent may be any monofunctional compound reactive with the main chain terminals, such as monocarboxylic acids, monoamines, acid anhydrides, monoisocyanates, monoacid halides, monoesters, and monoalcohols. The capping agent may be added by any method, such as adding the capping agent beforehand during polymerization, adding it during polymerization, adding it at the end of polymerization, adding it during a melt-kneading or molding process, or adding it to a commercially available product.

[0030] The imide-based resin may be a commercially available product, such as Pyer ML RC-5019 (manufactured by IST Corporation), Torenice #3000 (manufactured by Toray Industries, Inc.), UPIA (registered trademark)-AT, UPIA (registered trademark)-ST (manufactured by Ube Industries, Ltd.), Meirejicoat 26 (manufactured by Nagoya Chemical Industry Co., Ltd.), PIQ (manufactured by Hitachi Chemical Co., Ltd.), SPI-200N, SPI-300N (manufactured by Nippon Steel Chemical Co., Ltd.), Rikacoat SN-20 (manufactured by New Japan Chemical Co., Ltd.), Neoheat 8600 (manufactured by Totoku Toryo Co., Ltd.), or HPC-5012 (manufactured by Showa Denko Material K.K.). These may be used alone or in combination of two or more. An example of a combination of two resins is a combination of Pyer ML RC-5019 and UPIA-AT.

[0031] The first insulating coating 21 may contain inorganic or organic fillers or bubbles as a third component, as long as the third component does not impair the performance of the first insulating coating 21. Examples of the inorganic or organic fillers include metal oxides, metal hydroxides, metal carbonates, and polymeric fine particles. Examples of the bubbles include air. From the viewpoints of electrical properties, physical properties, and cost, it is preferable that the first insulating coating 21 does not contain inorganic or organic fillers.

[0032] The first insulating coating 21 and the second insulating coating 22 may each contain the same resin. From the viewpoint of improving the adhesion between the first insulating coating 21 and the second insulating coating 22, the resins contained in the first insulating coating 21 and the second insulating coating 22 are preferably the same type of resin. That is, if the resin contained in the resin composition that makes up the second insulating coating 22 is an imide-based resin, the resin that makes up the first insulating coating 21 is also preferably an imide-based resin. If the adhesion between the first insulating coating 21 and the second insulating coating 22 is low, gaps may form between them, which could cause peeling between the coatings.

[0033] The thickness of the first insulating coating 21 is preferably 2 to 150 μm, more preferably 10 to 100 μm, and even more preferably 15 to 80 μm.

[0034] The first insulating coating 21 can be formed, for example, by applying and baking an insulating varnish in which the aforementioned resin is dissolved or dispersed in a solvent. Suitable solvents for dissolving or dispersing the aforementioned resin include cresol-based phenols, aromatic alcohols, NMP (N-methyl-2-pyrrolidone), DMAC (N,N-dimethylacetamide), DMF (N,N-dimethylformamide), DMI (1,3-dimethyl-2-imidazolidinone), carbonate-based solvents, lactone-based solvents, and glycol ether-based solvents, primarily high-boiling-point solvents. The insulating varnish may contain trace amounts of acid or alkaline components to stabilize the dispersion. Similarly, it may contain water, low-boiling-point alcohol, or a low-viscosity solvent that contributes to reducing the viscosity of the insulating varnish. If necessary, dispersants or surface treatment agents may be added to the insulating varnish to impart hydrophobicity or improve dispersibility.

[0035] The second insulating coating 22 is composed of a resin composition containing at least a resin and a metal oxide hydrate. The resin may be a resin with excellent heat resistance (heat-resistant resin), and known resins used in known insulated wires, etc., may be used. Specific examples of heat-resistant resins include the same resins as those exemplified for the first insulating coating 21. The second insulating coating 22 may contain one type of heat-resistant resin, or two or more types.

[0036] Furthermore, when preparing the insulating coating material for forming the second insulating coating 22, the resin may be used in a form dissolved or dispersed in a solvent (such as a resin varnish). As will be described later, it is preferable to further disperse a metal oxide hydrate in the insulating coating material before use in forming the second insulating coating 22.

[0037] The resin content (%) in the second insulating coating 22 is preferably 60% by mass at the lower limit, more preferably 75% by mass, and even more preferably 80% by mass at the upper limit, and is preferably 82% by mass, and more preferably 80% by mass at the upper limit.

[0038] The insulating coating 2 is an insulating coating that forms an inorganic insulating layer when the laminate is exposed to partial discharge caused by an inverter surge. The metal oxide hydrate may be any metal oxide hydrate that forms an inorganic insulating layer (described below) in a portion of the area where the insulating coating 2 was formed after the insulating coating 2 of the laminate of the present invention is exposed to partial discharge. Alumina hydrate is preferred as the metal oxide hydrate because it forms a particularly strong inorganic insulating layer. Examples of alumina hydrate include trihydroxide (Al(OH)) and two variants of aluminum oxide hydroxide (AlO(OH)), boehmite (γ-aluminum oxide hydroxide) and diaspore (α-aluminum oxide hydroxide). Boehmite is classified into pseudocrystalline boehmite and microcrystalline boehmite, and either type can be used in the present invention.

[0039] The metal oxide hydrate is preferably contained in the insulating coating 2 in the form of fine particles, as long as it is uniformly dispersed throughout the insulating coating 2. The particle diameter is preferably 100 nm or less, and more preferably 50 nm or less. Regarding the shape of the metal oxide hydrate, since this facilitates the formation of an inorganic insulating layer, it is preferable that the metal oxide hydrate be in the form of flat fine particles with a large aspect ratio (side / thickness), and the aspect ratio is preferably 4 to 200, and more preferably 4 to 50.

[0040] The metal oxide hydrate is preferably uniformly dispersed in nano-sized particles in the insulating coating 2. The dispersed state can be observed using a TEM, and it is preferable that the dispersed particle diameter of the agglomerated particles is less than five times the particle diameter of the metal oxide hydrate, for example. If agglomerated particles are present, partial discharge may concentrate in the agglomerated areas, leading to dielectric breakdown in a short period of time. Here, nano-sized refers to a dispersed particle diameter of 500 nm or less.

[0041] The method of mixing the metal oxide hydrate with the resin is preferably a metal oxide hydrate sol, as long as the metal oxide hydrate is uniformly dispersed in the second insulating coating 22. The use of a metal oxide hydrate sol facilitates uniform dispersion of the metal oxide hydrate in the second insulating coating 22. If a metal oxide hydrate powder or gel is used, aggregates of the metal oxide hydrate may form in the second insulating coating 22, which may reduce the flexibility of the insulating coating 22.

[0042] The content of the metal oxide hydrate in the second insulating coating 22 is 18 parts by mass or more and 40 parts by mass or less, based on 100 parts by mass of the total of the resin and the metal oxide hydrate. The lower limit is preferably 20 parts by mass. The upper limit is preferably 35 parts by mass, more preferably 30 parts by mass, even more preferably 25 parts by mass, even more preferably 22 parts by mass, and still more preferably 20 parts by mass. If the content of the metal oxide hydrate is less than 18 parts by mass, the effect of improving the partial discharge inception voltage (PDIV) may not be exerted. If the content is more than 40 parts by mass, the flexibility of the insulating coating 2 may be lost, resulting in a decrease in flexibility, and the effect of increasing the partial discharge inception voltage (PDIV) may not be exerted.

[0043] When preparing the insulating coating for the second insulating coating 22, it is preferable to prepare an insulating coating in which a heat-resistant resin and a metal oxide hydrate are dissolved or dispersed in a solvent, and then apply and bake the insulating coating to form the insulating coating 2. Suitable solvents for dissolving or dispersing the heat-resistant resin and dispersing the metal oxide hydrate include cresol-based phenols, aromatic alcohols, NMP (N-methyl-2-pyrrolidone), DMAC (N,N-dimethylacetamide), DMF (N,N-dimethylformamide), DMI (1,3-dimethyl-2-imidazolidinone), carbonate solvents, lactone solvents, and glycol ether solvents. The insulating coating may contain trace amounts of acid or alkaline components to stabilize the dispersion. Similarly, the insulating coating may contain water, low-boiling alcohols, or low-viscosity solvents that contribute to reducing the viscosity of the insulating coating. If necessary, other metal oxide sols may be mixed into the insulating coating material, and a dispersant or surface treatment agent may be added to make the material hydrophobic or improve dispersibility.

[0044] The resins contained in typical insulating coatings have excellent electrical properties such as breakdown voltage and mechanical properties such as flexibility. However, when fillers such as metal oxides are mixed into the insulating layer, it is known that these properties deteriorate as the proportion of fillers increases.

[0045] In contrast, in the present invention, when the insulating coating 2 is composed of the first insulating coating 21 and the second insulating coating 22, the partial discharge inception voltage (PDIV) is improved compared to when the entire insulating coating 2 is composed of the first insulating coating 21 or the second insulating coating 22. While the mechanism behind this improvement is unclear, it is believed to be due to the electrical conductivity of the metal oxide hydrate contained in the second insulating coating 22. Specifically, it is presumed that a slight increase in the electrical conductivity of the second insulating coating 22 reduces electric field concentration and suppresses the occurrence of partial discharges. The thickness of the second insulating coating 22 required to improve the partial discharge inception voltage (PDIV) while maintaining other electrical and mechanical performance is, for example, 1 μm or more, preferably 5 μm or more. Furthermore, to maintain electrical and mechanical performance, the thickness of the second insulating coating 22 should be less than 75% of the total thickness of the insulating coating 2, preferably 50% or less, and more preferably 25% or less. Specifically, for example, if the overall thickness of the insulating coating 2 is 37 μm or less, the thickness of the second insulating coating 22 is preferably 28 μm or less, more preferably 20 μm or less, and even more preferably 15 μm or less.

[0046] Furthermore, metal oxide hydrates are more expensive than resins, and an operation for uniformly mixing the metal oxide hydrate and resin is also required, so that the cost of forming second insulating coating 22 generally tends to be higher than the cost of forming first insulating coating 21. For these reasons, by setting the thickness of second insulating coating 22 to, for example, 1 μm or more and setting the thickness of second insulating coating 22 to account for less than 75% of the overall thickness of insulating coating 2, an insulating coating 2 that is excellent in terms of dielectric breakdown resistance and cost can be obtained.

[0047] Furthermore, fillers are generally more expensive than resins, and because fillers must be mixed into resins, the cost of resin compositions containing fillers is high. Therefore, from the viewpoint of cost, first insulating coating 21 is preferably made of a resin that does not contain fillers.

[0048] The laminate 10 of the present invention can be manufactured by laminating at least a first insulating coating 21 and a second insulating coating 22 on a conductor 1. The first insulating coating 21 can be formed by applying an insulating varnish containing the aforementioned resin and baking it. The second insulating coating 22 can be formed by applying an insulating varnish containing a resin and a metal oxide hydrate and baking it. For example, when laminating the first insulating coating 21 and the second insulating coating 22 on the surface of the conductor 1, the insulating varnish can be applied to the surface of the conductor 1 and baked, and then the insulating varnish can be applied to the surface of the conductor 1 and baked, and then the insulating varnish can be applied to the surface of the conductor 1 and baked. Note that the insulating coating formed by laminating the first insulating coating 21 and the second insulating coating 22 can be determined by observation with an optical microscope, for example.

[0049] The insulating coating can be applied by any method, including, but not limited to, using a coater, applying and drying repeatedly using a dip coater or die to obtain a coating of a predetermined thickness, or spraying. Baking can be performed, for example, by heating at a high temperature (e.g., 300°C or higher) for a predetermined period of time. The first insulating coating 21 and the second insulating coating 22 can be formed by repeating a series of application and heating steps multiple times until each coating reaches the predetermined thickness. The baking temperature and time for forming the second insulating coating 22 are determined depending on the type of metal oxide hydrate, so that the metal oxide hydrate is not thermally transformed into another metal oxide hydrate or metal oxide.

[0050] For example, when the laminate 10 of the present invention is in the form of an insulated wire, the insulated wire can be manufactured by repeatedly applying and baking an insulating coating 2 onto the outer periphery of the conductor 1 or onto another layer that covers the outer periphery of the conductor 1. As described above, the first insulating coating 21 and the second insulating coating 22 can be formed by applying an insulating coating to the conductor 1 in a predetermined thickness and then heating the coating at a high temperature (e.g., 300 to 500°C or higher) for a predetermined time (e.g., 1 to 2 minutes) (application and heating), and repeating this series of operations multiple times (e.g., 10 to 20 times) until a coating of the predetermined thickness is obtained.

[0051] The coil of the present invention can be formed by winding the insulated wire around a core. The rotating electric machine of the present invention is a motor or the like that uses the coil of the present invention. That is, the rotating electric machine of the present invention may be a rotating electric machine that uses the insulated electric wire of the present invention, or may be a rotating electric machine that is formed using the conductor 1 and then an insulating coating 2 is formed on the surface of the conductor 1 to form an electric wire.

[0052] Examples of rotating electrical machines include motors and generators.

[0053] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0054] (Polyimide paint) Pyer ML RC-5019 manufactured by IST Corporation was used.

[0055] <Insulating Varnish> Insulating varnishes 1 to 5 were produced so as to have the compositions shown in Table 1 below.

[0056]

[0057] (Insulating Coating 1) 20 parts by mass of alumina hydrate boehmite (rectangular, flat particles with a particle size of approximately 10 nm × 50 nm, a thickness of approximately 1 to 5 nm, and an aspect ratio (long side / thickness) of 10 to 50) was mixed with 80 parts by mass of the polyimide coating resin, and uniformly dispersed to obtain Insulating Coating 1. When mixing, a sol of boehmite dispersed in NMP was used. Furthermore, to prevent gelation, 6 parts by mass of ethyl phosphate (ethyl acid phosphate (mono- and di-ester mixture), manufactured by Tokyo Chemical Industry Co., Ltd., monoester content 35.0 to 47.0%, diester content 53.0 to 67.0%)) was added to the boehmite sol per 100 parts by mass of boehmite.

[0058] (Insulating Varnish 2) Polyimide varnish was used as insulating varnish 2.

[0059] (Insulating paint 3) Insulating paint 3 was obtained in the same manner as insulating paint 1, except that 18 parts by mass of boehmite was mixed with 82 parts by mass of the resin content of the polyimide paint.

[0060] (Insulating paint 4) Insulating paint 4 was obtained in the same manner as insulating paint 1, except that 25 parts by mass of boehmite was mixed with 75 parts by mass of the resin content of the polyimide paint.

[0061] (Insulating paint 5) Insulating paint 5 was obtained in the same manner as insulating paint 1, except that 15 parts by mass of boehmite was mixed with 85 parts by mass of the resin content of the polyimide paint.

[0062] <Manufacturing of Electric Wire Having Conductor and Insulating Film Laminated> (Example 1) An insulated wire was fabricated using insulating varnish 1 and insulating varnish 2 to have a 37 μm-thick insulating coating on the surface of a conductor (copper wire with a diameter of approximately 1 mm) so as to have the configuration shown in Table 2. Specifically, insulating varnish 2 for forming a first insulating coating was applied to a copper conductor (with a diameter of approximately 1 mm), and the process of baking was performed for approximately 1 minute while continuously increasing the temperature from 350°C at the entrance to 420°C at the exit. This process was repeated until the first insulating coating reached the thickness shown in Table 2. Next, insulating varnish 1 for forming a second insulating coating was applied and baked in the same manner, and this process was repeated until the second insulating coating reached the thickness shown in Table 2. This produced an insulated wire having a 37 μm-thick insulating coating on the surface of the conductor (including a first insulating coating composed only of polyimide and a second insulating coating composed of a polyimide resin composition containing 20% ​​by mass of alumina hydrate).

[0063] Example 2 Insulated wires having the thicknesses shown in Table 2 were prepared in the same manner as in Example 1.

[0064] Example 3 Insulated wires having the thicknesses shown in Table 2 were prepared in the same manner as in Example 1.

[0065] Example 4 An insulated wire having the thickness shown in Table 2 was produced in the same manner as in Example 1, except that insulating paint 3 was used instead of insulating paint 1.

[0066] Example 5 An insulated wire having the thickness shown in Table 2 was produced in the same manner as in Example 1, except that insulating paint 4 was used instead of insulating paint 1.

[0067] Example 6 Insulated wires having the thicknesses shown in Table 2 were prepared in the same manner as in Example 5.

[0068] Example 7 Insulated wires having the thicknesses shown in Table 2 were prepared in the same manner as in Example 5.

[0069] (Comparative Example 1) Insulating paint 1 was applied to a conductor (a copper wire with a diameter of approximately 1 mm), and the process of baking was repeated for approximately 1 minute while continuously increasing the temperature from 350°C at the inlet to 420°C at the outlet, to produce an insulated wire having an insulating coating (including a second insulating coating composed of a polyimide resin composition containing 20% ​​by mass of alumina hydrate) with a thickness of 37 μm on the surface of the conductor.

[0070] (Comparative Example 2) An insulated wire having an insulating coating (including a first insulating coating composed only of polyimide) with a thickness of 37 μm on the surface of the conductor was produced in the same manner as in Comparative Example 1, except that insulating coating 2 was used instead of insulating coating 1.

[0071] (Comparative Example 3) An insulated wire having an insulating coating (including a second insulating coating composed of a polyimide resin composition containing 25% by mass of alumina hydrate) with a thickness of 37 μm on the surface of the conductor was produced in the same manner as in Comparative Example 1, except that insulating coating 4 was used instead of insulating coating 1.

[0072] Comparative Example 4 An insulated wire having the thickness shown in Table 2 was produced in the same manner as in Example 1, except that insulating paint 5 was used instead of insulating paint 1.

[0073] [Evaluation] <Flexibility Evaluation> The flexibility of each of the electric wires obtained above was evaluated by the following method. The results are shown in Table 2. The electric wires were tested in accordance with the JIS C3216-5-1 winding test.

[0074] <Partial Discharge Inception Voltage Test> Twisted pair samples were prepared using each electric wire in accordance with JIS C 3216, and the voltage applied between the two wires was gradually increased to measure the voltage at which partial discharge occurred (partial discharge inception voltage A). The measurement was carried out by an impulse voltage test in which a bipolar impulse voltage was applied with a rise time of 100 ns, a pulse width of 5 μs, a repetition frequency of 1 kHz, and a voltage increase rate of 75 V / s. Partial discharge was detected in accordance with JEC-0401-1990, using a method in which discharge light emission was detected using a photomultiplier tube in the impulse voltage test. The results are shown in Table 2.

[0075] Table 2 also shows the difference in partial discharge inception voltage between the electric wire prepared in Comparative Example 2 (electric wire having an insulating coating formed only of polyimide paint) and each of the electric wires of Examples 1 to 7 and Comparative Example 1.

[0076] <Partial Discharge Exposure Test and Vt Characteristic Evaluation> A partial discharge exposure test and a Vt characteristic evaluation (voltage-partial discharge life time characteristic test) were performed on each of the electric wires obtained above by the following methods. A twisted pair sample was prepared using each electric wire in accordance with JIS C 3216, and a voltage was applied between the two wires. The voltage was applied by generating a bipolar square wave with a pulse width of 5 μs and a frequency of 10 kHz using an inverter pulse generator PG-W03KP-A manufactured by Nissin Pulse Electronics Co., Ltd. In the Vt characteristic test, a voltage of 2.5 kVp was applied, and the time until the sample experienced dielectric breakdown was measured. The results are shown in Table 3.

[0077] <Breakdown Voltage Test> Twisted pair samples were prepared using the electric wires of Examples 1 to 3 and Comparative Example 2 in accordance with JIS C 3216, and the voltage at which the electric wires broke down was measured by gradually increasing the voltage applied between the two wires. The measurement device used was a breakdown voltage tester (manufactured by Yasuda Seiki Seisakusho). The results are shown in Table 3.

[0078]

[0079]

[0080] Each of the electric wires of Examples 1 to 7 is a laminate including at least a conductor and an insulating coating, the insulating coating including a first insulating coating and a second insulating coating, the second insulating coating being formed from a resin composition including a resin and a metal oxide hydrate, and the content of the metal oxide hydrate in the resin composition is 18 parts by mass or more and 40 parts by mass or less per 100 parts by mass of the total of the resin and the metal oxide hydrate. From the results shown in Table 2, it can be seen that the partial discharge inception voltage A of each of the electric wires of Examples 1 to 7 is higher (i.e., the voltage at which partial discharge is initiated is higher) than the partial discharge inception voltage B of the electric wire of Comparative Example 2 including an insulating coating formed only from polyimide paint (the thickness of the insulating coating is the same as that of Examples 1 to 7).

[0081] REFERENCE SIGNS LIST 1 conductor 2 insulating coating 21 first insulating coating 22 second insulating coating 3 insulating layer 4 insulating layer 10 laminate

Claims

1. A laminate comprising at least a conductor and an insulating coating, wherein the insulating coating includes a first insulating coating and a second insulating coating, and the second insulating coating is formed from a resin composition containing a resin and a metal oxide hydrate, and the content of the metal oxide hydrate in the resin composition is 18 parts by mass or more and 40 parts by mass or less per 100 parts by mass of the total of the resin and the metal oxide hydrate.

2. The laminate according to claim 1, wherein the ratio of the dielectric constants of the first insulating coating and the second insulating coating at 25°C and 1 kHz satisfies 1.5<(dielectric constant of the second insulating coating) / (dielectric constant of the first insulating coating)<1.

8.

3. The laminate according to claim 1 or 2, wherein the insulating coating is an insulating coating that forms an inorganic insulating layer when the laminate is exposed to partial discharge caused by an inverter surge.

4. The laminate according to claim 1 or 2, wherein the thickness of the second insulating coating is 1 μm or more.

5. A laminate according to claim 1 or 2, wherein the thickness of the second insulating coating is less than 75% of the total thickness of the insulating coating.

6. The laminate according to claim 1 or 2, wherein the first insulating coating is formed from a resin composition that does not contain a filler.

7. The laminate according to claim 1 or 2, wherein the second insulating coating is not in contact with the conductor.

8. The laminate according to claim 1 or 2, wherein the metal oxide hydrate is alumina hydrate.

9. The laminate according to claim 1 or 2, wherein the resin constituting the first insulating coating and / or the second insulating coating is at least one selected from the group consisting of formal resin, polyurethane, epoxy resin, polyester, polyesterimide, polyetherimide, polyamideimide, polyimide, and precursors thereof.

10. The laminate of claim 1 or 2 in the form of an insulated wire or film.

11. A coil comprising the insulated wire of claim 10.

12. A rotating electric machine comprising the insulated electric wire according to claim 10.

13. An insulating paint for producing the laminate according to claim 1 or 2, comprising a resin composition containing a metal oxide hydrate.

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