Imide resin solution, insulation coating film, electrical wire, and rotating electrical machine

Abstract

Provided is an imide resin solution that has excellent shelf life. Using this solution as a starting material for an insulation coating film enables the insulation coating film to have excellent mechanical properties and insulation performance.

Description

Imide resin solution, insulating film, electric wire, and rotating electrical machine

[0001] The present invention relates to an imide resin solution, an insulating coating, an electric wire, and a rotating electric machine.

[0002] BACKGROUND ART Insulated wires used in electric devices such as motors have an insulating coating formed by applying a solution of an imide resin such as polyimide or polyamideimide dissolved in an organic solvent to the surface of a conductor and baking it.

[0003] Patent No. 6524229 Specification Patent No. 6567797 Specification

[0004] An object of the present invention is to provide an imide resin solution that has excellent storage stability and, when used as a raw material for an insulating film, can provide the insulating film with excellent mechanical properties and insulating performance.

[0005] The present disclosure includes the following aspects: [Item 1] An imide-based resin solution containing an imide-based resin and / or a precursor thereof, an inorganic filler, an organic solvent, and water, wherein the water content is 0.2 to 9.0 mass% based on the total mass of the solution. [Item 2] The imide-based resin solution according to Item 1, wherein the inorganic filler is at least one selected from the group consisting of metal oxides and metal oxide hydrates. [Item 3] The imide-based resin solution according to Item 2, wherein the metal oxide hydrate is alumina hydrate. [Item 4] The imide-based resin solution according to any one of Items 1 to 3, wherein the imide-based resin is polyimide and the precursor is polyamic acid. [Item 5] An insulating coating formed from the imide-based resin solution according to any one of Items 1 to 4. [Item 6] An electric wire including a conductor and an insulating coating having a single layer or multiple layers formed on the outer periphery of the conductor, wherein at least one layer of the insulating coating is the insulating coating according to Item 5. [Item 7] A rotating electric machine including the electric wire according to Item 6.

[0006] According to the present invention, it is possible to provide an imide resin solution that has excellent storage stability and, when used as a raw material for an insulating film, can provide the insulating film with excellent mechanical properties and insulating performance.

[0007] Fig. 1 is a schematic cross-sectional view showing an example of an electric wire of the present invention, and Fig. 2 is a schematic view showing a method for evaluating insulation performance in the present invention.

[0008] The imide resin solution of the present invention contains an imide resin and / or its precursor, an inorganic filler, an organic solvent, and water, and has a water content of 0.2 to 9.0% by mass based on the total mass of the solution.

[0009] (Imide-based resin) The imide-based resin solution of the present invention contains an imide-based resin and / or a precursor thereof. The type of imide-based resin and its precursor is not particularly limited, and may be any of various imide-based resins and their precursors that are used in known insulating films, etc.

[0010] Examples of imide-based resins include polyesterimide resins, polyetherimide resins, polyamideimide resins, and polyimide resins. Examples of precursors of imide-based resins include polyamic acid resins. Among these, polyesterimide resins, polyamideimide resins, polyimide resins, and polyamic acid resins are preferably used from the viewpoint of further improving heat resistance.

[0011] In particular, the imide resin and / or its precursor used in the present invention is preferably a polyimide resin or a polyamic acid resin.

[0012] A preferred polyesterimide resin is a resin having an ester bond and an imide bond in the molecule, and may be a resin obtained by subjecting, for example, an acid anhydride, a diamine, and a dialcohol to imidization, esterification, and / or transesterification.

[0013] A preferred polyetherimide resin is a resin having an ether bond and an imide bond in the molecule. The polyetherimide resin may be, for example, a resin obtained by subjecting an acid anhydride having an ether bond in the molecule and a diamine to a dehydration condensation polymerization and an intramolecular dehydration cyclization (imidization) reaction. The polyetherimide resin may be, for example, a dehydration condensation polymer of phenylenediamine and 2,2'-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride.

[0014] A preferred polyimide resin is a compound having the repeating structure of the following formula (1). It is more preferred that the polyamic acid resin is a resin that becomes a polyimide resin having the repeating structure of the following formula (1) through an intramolecular dehydration condensation reaction between the amino group and the carboxy group in each repeating structure. The repeating unit in the repeating structure of the following formula (1) of the polyimide resin may be of one type or two or more types.

[0015] [wherein: n is the number of repeating units and is a positive integer; R １ are each independently a tetravalent organic group having one or two benzene rings, ２ are each independently a divalent group derived from an aromatic hydrocarbon.

[0016] In the above formula (1), n ​​is the number of repeating units and is a positive integer. n is preferably 50 or more, more preferably 100 or more, even more preferably 120 or more, and even more preferably 150 or more. n may be 500 or less, more preferably 400 or less.

[0017] In the above formula (1), R １ R are each independently a tetravalent organic group having one or two benzene rings. １ is preferably at least one of the structures exemplified in the following formula (2): １ may be the same or different.

[0018]

[0019] In the formula (1), R １ is more preferably at least one of the structures exemplified in the following formula (3).

[0020]

[0021] In the formula (1), R ２ each independently represents a divalent group derived from an aromatic hydrocarbon. ２ When contains two or more aromatic groups, these aromatic groups may be -O-, -SO ２ -, -CO-, -CH ２ They may be linked via at least one bonding group selected from the group consisting of - and -S-.

[0022] R ２ is preferably at least one of the structures exemplified by the following formula (4).

[0023]

[0024] R ２ is more preferably at least one of the structures exemplified in the following formula (5).

[0025]

[0026] In addition to the above-mentioned polyimide resins, polyimide resins having excellent heat resistance and insulating properties can be used, such as those described in Japanese Patent No. 5281568 and Japanese Patent No. 5523456.

[0027] A preferred polyamide-imide resin is a resin having a repeating structure of the following formula (6). The polyamide-imide resin may be a resin produced by, for example, an isocyanate method or an amine method (such as an acid chloride method, a low-temperature solution polymerization method, or a room-temperature solution polymerization method). The polyamide-imide resin used in the present invention is preferably a resin produced by the isocyanate method. The repeating unit in the repeating structure of the following formula (6) may be of one type or of two or more types.

[0028] [wherein: m is the number of repeating units and is a positive integer; R ３ are each independently a trivalent organic group having one or two benzene rings, ４ are each independently a divalent group.

[0029] m is the number of repeating units and is a positive integer. m is preferably 50 or more, more preferably 100 or more, even more preferably 120 or more, and even more preferably 150 or more. m may be 500 or less, and more preferably 400 or less.

[0030] In the above formula (6), R ３ R are each independently a trivalent organic group having one or two benzene rings. ３ is preferably at least one of the structures exemplified in the following formula (7): ３ may be the same or different.

[0031]

[0032] R ３ More preferably, the structure is exemplified by the following formula (8).

[0033]

[0034] In the formula (6), R ４ are each independently a divalent group, preferably a divalent group derived from an aromatic hydrocarbon. ４ is preferably at least one of the structures exemplified in the following formula (9).

[0035]

[0036] R in each repeating unit of the above formula (6) ４ may be the same or different.

[0037] R ４ is more preferably at least one of the structures exemplified in the following formula (10).

[0038]

[0039] The imide resin solution of the present invention may contain only one type of these resins, or may contain two or more types.

[0040] Examples of polyesterimide resins that can be used include Neoheat 8600 manufactured by Totoku Toryo Co., Ltd. Examples of polyamideimide resins include resins obtained by reacting trimellitic anhydride with 4,4'-diphenylmethane diisocyanate, such as the HI-400, HI-405, and HI-406 series manufactured by Hitachi Chemical Co., Ltd. Examples of polyimide resins and their precursors, polyamic acid resins, include aromatic polyimides obtained by dehydration condensation of known diamines and acid anhydrides. Examples of known diamines include 4,4'-diaminodiphenyl ether, and examples of acid anhydrides include pyromellitic anhydride and biphenyltetracarboxylic dianhydride, such as Meirejicoat 26 manufactured by Nagoya Chemical Industry Co., Ltd.

[0041] The content of the imide resin and / or its precursor in the imide resin solution of the present invention is not particularly limited, but is preferably 3 to 40 mass %, more preferably 5 to 35 mass %, and even more preferably 10 to 30 mass %, based on the total mass of the solution. If the content is too low, a large amount of organic solvent must be removed during molding, which is uneconomical. On the other hand, if the content is too high, the viscosity of the solution may become too high, which may impair workability such as metering and transfer.

[0042] (Inorganic Filler) The imide resin solution of the present invention contains an inorganic filler. The type of inorganic filler is not particularly limited, and various inorganic fillers used in known insulating coatings and the like may be contained. Specific examples include silicon, metals such as iron, aluminum, magnesium, titanium, rhodium, tantalum, zirconium, silver, and copper, and compounds thereof (e.g., oxides, oxide hydrates, etc.).

[0043] In a preferred embodiment, the inorganic filler contained in the imide resin solution of the present invention is at least one selected from the group consisting of metal oxides and metal oxide hydrates, with metal oxide hydrates being more preferred.

[0044] The type of metal oxide is not particularly limited, but silica, titania, alumina, magnesia, etc. are preferred, and silica is more preferred. The metal oxide may be used alone or in combination of two or more. The type of metal oxide hydrate is not particularly limited, but alumina hydrate, rhodium oxide hydrate, tantalum oxide hydrate, zirconium oxide hydrate, etc. are preferred, and alumina hydrate is more preferred. The metal oxide and metal oxide hydrate may be used alone or in combination of two or more.

[0045] The type of alumina hydrate is not particularly limited, but examples thereof include gibbsite, bayerite, nordstrandite, boehmite, diaspore, and tordite. One type of alumina hydrate may be used alone, or two or more types may be used in combination. Boehmite is particularly preferred from the viewpoint of improving the insulating properties, heat resistance, and the like of the insulating coating formed from the imide resin solution of the present invention.

[0046] The boehmite of the present invention is aluminum oxyhydroxide (AlO(OH)) or alumina hydrate (Al ２ O ３ ・H ２ O). Boehmite is broadly classified into pseudo-crystalline boehmite and microcrystalline boehmite based on differences in crystallinity, crystal size, and crystal structure, but either type can be used in the present invention without limitation. Pseudo-crystalline boehmite, also known as pseudo-boehmite or pseudo-boehmite, typically has a very large surface area, large pores and pore volume, a low specific gravity, a smaller crystal size than microcrystalline boehmite, and contains more hydrated water molecules per crystal. The form of boehmite is not particularly limited, and may be powder, liquid, or the like. However, boehmite sol dispersed in a solvent such as an organic solvent is preferred because it can be easily mixed uniformly with the imide-based resin solution of the present invention. Methods for producing these boehmite sols include, but are not limited to, a method of hydrolyzing aluminum isopropoxide followed by adding an acid to peptize the resulting solution, and a method of hydrolyzing aluminum dodexide to obtain an alumina slurry and then aging the resulting slurry.

[0047] Commercially available products may be used as the boehmite in the present invention. Examples of commercially available boehmite alumina applicable to the present invention include "Alumina Sol 15A," "Alumina Sol 10A," "Alumina Sol 10D," and "Alumina NMP Sol-A1-10" manufactured by Kawaken Fine Chemicals Co., Ltd., and "AS-520" manufactured by Nissan Chemical Industries, Ltd. From the viewpoint of the mechanical properties and insulating properties of the resulting insulating coating, the average particle diameter of the boehmite is preferably 1 nm to 5 μm, and more preferably 5 nm to 500 nm. The average particle diameter is the particle diameter at 50% of the cumulative value in the particle size distribution obtained by measurement using a laser diffraction particle size analyzer (manufactured by Shimadzu Corporation).

[0048] In the present invention, the aspect ratio (major axis / minor axis) of the boehmite is preferably 2 or more, more preferably 4 to 100, and even more preferably 5 to 100. When the aspect ratio of the boehmite is 2 or more, when exposed to partial discharge during current flow, the boehmite particles are regularly aligned in a direction opposite to the direction of erosion of the resin by partial discharge, which is presumed to further enhance the effect of partial discharge resistance and to exhibit good insulating performance.

[0049] The content of inorganic filler in the imide resin solution of the present invention is not particularly limited, but is, for example, 1 to 30% by mass, preferably 5 to 25% by mass, and more preferably 10 to 25% by mass, relative to the total solids content of the solution. By incorporating an inorganic filler into the polyimide resin solution of the present invention, the mechanical and electrical properties, particularly the insulating performance, of the resulting insulating film can be improved compared to a solution containing no inorganic filler. A low content results in poor effectiveness, while a high content undesirably reduces the flexibility of the insulating film. Hereinafter, the term "total solids content" refers to the total amount of nonvolatile matter remaining after all solvents in the solution have been dried and removed. Hereinafter, the content (mass%) of inorganic filler relative to the total solids content of the solution will also be referred to as the inorganic filler concentration (%).

[0050] (Organic Solvent) The imide resin solution of the present invention contains an organic solvent. The type of organic solvent is not particularly limited, and various organic solvents used in known insulating films and the like may be contained. Specific examples of organic solvents include amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone; alcohol solvents such as methanol, ethanol, propanol, butanol, methoxypropanol, and benzyl alcohol; polyhydric alcohol solvents such as ethylene glycol, diethylene glycol, triethylene glycol, glycerin, propylene glycol, dipropylene glycol, and methylpropanediol; ether solvents such as dimethyl ether, diethyl ether, dipropyl ether, dibutyl ether, tetrahydrofuran, diethylene glycol, diethylene glycol dimethyl ether, and triethylene glycol; butyl acetate, ethyl acetate, isobutyl acetate, propylene glycol methyl acetate, ethyl cellosolve, butyl cellosolve, and 2-methyl cellosolve acetate. ester-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, acetophenone, etc.; carbonate-based solvents such as diethyl carbonate and propylene carbonate; hydrocarbon-based solvents such as hexane, heptane, octane, benzene, toluene, and xylene; phenol-based solvents such as phenol, m-cresol, p-cresol, 3-chlorophenol, and 4-chlorophenol; 1,3-dimethyl-2-imidazolidinone, dimethyl sulfoxide, sulfolane, dimethyl starch, mineral spirits, and petroleum naphtha-based solvents. The organic solvents may be used alone or in combination of two or more.

[0051] In one embodiment, the organic solvent contained in the imide resin solution of the present invention is N-methyl-2-pyrrolidone.

[0052] The content of the organic solvent in the imide resin solution of the present invention is not particularly limited, and may be, for example, 60% by mass or more, or 70% by mass or more, and may be, for example, 95% by mass or less, 90% by mass or less, or 80% by mass or less, relative to the total mass of the solution.

[0053] (Water) The imide resin solution of the present invention contains water, and the water content is 0.2 to 9.0% by mass based on the total mass of the solution. Any water source can be used, such as tap water, industrial water, pure water, or ion-exchanged water. One water source may be used alone, or two or more water sources may be used in combination.

[0054] In the imide-based resin solution of the present invention, by maintaining the water content at a predetermined concentration or higher, it is possible to suppress the generation of aggregates and prevent a decrease in the mechanical properties of an insulating coating formed from the solution. Therefore, the water content is 0.2% by mass or higher, preferably 0.3% by mass or higher, and more preferably 0.5% by mass or higher. Furthermore, maintaining the water content at a predetermined concentration or lower can suppress hydrolysis of the imide-based resin or its precursor during storage of the imide-based resin solution, thereby minimizing changes in the viscosity of the solution over time and improving the storage stability of the solution. Therefore, the water content is 9.0% by mass or lower, preferably 1.5% by mass or lower, and more preferably 1.0% by mass or lower. Furthermore, the water content of the imide-based resin solution of the present invention is 0.2 to 9.0% by mass, preferably 0.2 to 1.3% by mass or 0.3 to 1.5% by mass, and more preferably 0.5 to 1.0% by mass. If the water content is less than 0.2% by mass, aggregates are more likely to occur in the imide-based resin solution, potentially resulting in a decrease in insulating performance. If the water content exceeds 9.0% by mass, precipitates are likely to form during the adjustment of the water content, making it difficult to obtain a uniform solution. Even if a uniform solution is obtained, the storage stability of the imide-based resin solution deteriorates, making it difficult to use in practice. By keeping the water content within the above range, the insulating coating obtained from the imide-based resin solution of the present invention has good mechanical properties and insulating performance.

[0055] The water content in the present invention is not particularly limited, but can be obtained by a method based on the Karl Fischer titration method described in JIS-K-0113 (2005), and can be calculated by dividing the amount of water by the total mass of the imide resin solution.

[0056] (Other Components) The imide-based resin solution of the present invention may contain known additives, such as dispersion stabilizers and mechanical property improvers, as needed. Examples of such additives include tackifiers such as alkylphenol resins, alkylphenol-acetylene resins, xylene resins, coumarone-indene resins, terpene resins, and rosin; bromine-based flame retardants such as polybromodiphenyl oxide and tetrabromobisphenol A; chlorine-based flame retardants such as chlorinated paraffins and perchlorocyclodecane; phosphorus-based flame retardants such as phosphate esters, phosphonic acids, and halogen-containing phosphate esters; boron-based flame retardants; oxide-based flame retardants such as antimony trioxide; phenolic, phosphorus-based, and sulfur-based antioxidants; heat stabilizers, light stabilizers, UV absorbers, lubricants, pigments, crosslinking agents, crosslinking aids, silane coupling agents, and titanate coupling agents; and aromatic polyamide fibers. Furthermore, to enhance the storage stability of the imide-based resin solution, a stabilizer may be added to the imide-based resin solution as needed. Examples of stabilizers include organic phosphorus compounds, sulfonic acid compounds, amide acid compounds, and triazole compounds. The stabilizer may be added during the process of producing the imide resin solution, or may be added to the imide resin solution after production. These additives may be contained in the imide resin solution in an amount of, for example, 0.1 to 10% by mass.

[0057] <Method for Producing Imide Resin Solution> Next, a method for producing the imide resin solution of the present invention will be described.

[0058] The imide resin solution of the present invention can be produced by mixing the above-mentioned imide resin and / or its precursor, inorganic filler, organic solvent, water, and other components as needed by a generally known method. Heating may be performed during mixing, if necessary. Examples of the mixing method include methods using generally known mixing means such as a kneader, pressure kneader, kneading roll, Banbury mixer, twin-screw extruder, planetary mixer, or homomixer.

[0059] The inorganic filler may be pulverized in advance before being mixed with the imide-based resin, etc. Examples of the pulverization method include methods using commonly known pulverization means such as a ball mill, a rod mill, a mass colloider, a dry jet mill, a homogenizer, and a wet jet mill.

[0060] As a method for mixing and compounding an inorganic filler with an imide-based resin and / or a precursor thereof and an organic solvent, the inorganic filler may be directly dispersed and mixed in a mixed solution of the imide-based resin and / or a precursor thereof and an organic solvent. However, it is preferable to prepare a sol dispersion by dispersing the inorganic filler in an organic solvent or water, and then disperse and mix the sol dispersion with the mixed solution.

[0061] By preparing the sol dispersion and then mixing it with the mixed solution, the inorganic filler can be more thoroughly dispersed in the imide resin solution to form a composite.

[0062] That is, the method for producing the imide-based resin solution of the present invention preferably includes the steps of: (1) preparing a sol dispersion of an inorganic filler; and (2) mixing the sol dispersion of the inorganic filler, an imide-based resin and / or a precursor thereof, and an organic solvent.

[0063] In the step (1), the sol dispersion of the inorganic filler can be prepared by dispersing the inorganic filler in an organic solvent or water. Alternatively, a sol prepared from the beginning as the sol of the inorganic filler may be used as the raw material.

[0064] Examples of organic solvents for dispersing inorganic fillers include polar solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, methanol, ethanol, and propanol, as well as mixed solvents in which water is added to these polar solvents.

[0065] When preparing a sol dispersion of an inorganic filler, it is preferable to add 1 to 100 parts by mass of inorganic filler to 100 parts by mass of an organic solvent, water, or a mixed solvent and disperse the filler. Dispersion can be carried out using a known stirring means such as a mixer. The stirring speed and other dispersion conditions are appropriately selected depending on the solvent.

[0066] Next, in step (2), the sol dispersion of the inorganic filler, the imide-based resin and / or its precursor, and the organic solvent are mixed. The above-mentioned generally known mixing means can be used to mix the sol dispersion of the inorganic filler and the imide-based resin and / or its precursor. It is preferable to degas the mixture during mixing. The mixing conditions are appropriately selected depending on the solvent.

[0067] Methods for achieving a desired water content in the imide-based resin solution of the present invention include, for example, using a mixed solvent containing a predetermined amount of water in step (1), adding a predetermined amount of water to the mixture of the sol dispersion of the inorganic filler, the imide-based resin / or its precursor, and the organic solvent obtained in step (2), dehydrating the sol dispersion of the inorganic filler or the imide-based resin solution with a desiccant, etc. The desiccant used in the present invention is not particularly limited as long as it does not affect the dispersion of the sol dispersion or the imide-based resin solution and absorbs and adsorbs water, but synthetic zeolite (molecular sieves) is preferably used because it has excellent resistance to organic solvents, provides good insulating properties to the resulting imide-based resin solution after handling, and is inexpensive and easy to handle.

[0068] The method for producing an imide-based resin solution of the present invention may further include a step of mixing other components with the mixture of the sol dispersion of the inorganic filler, the imide-based resin and / or its precursor, and the organic solvent obtained in step (2).

[0069] <Insulating Film> Next, the insulating film of the present invention will be described.

[0070] The insulating film of the present invention is produced by heating and drying the imide resin solution of the present invention, distilling off the organic solvent, and then baking the resulting product.

[0071] The insulating coating of the present invention may be composed of a single layer, or may have a substrate and an insulating coating on the substrate.

[0072] The insulating film consisting of one layer can be produced, for example, by applying the imide resin solution of the present invention to a substrate, heating, drying, baking, and then peeling it off from the substrate, or by repeatedly applying the solution to a substrate using a dip coater or a die and drying the solution to obtain a film of a predetermined thickness, but this method is not particularly limited.

[0073] The temperature at which the insulating film of the present invention is formed is not particularly limited as long as it does not affect the physical properties of the insulating film formed, but is usually preferably 100 to 500°C, and particularly preferably 300 to 400°C.

[0074] The temperature and time for drying and baking the imide resin solution may be appropriately changed depending on the types of imide resin, inorganic filler, and organic solvent.

[0075] The thickness of the insulating coating of the present invention is preferably 2 μm to 250 μm, more preferably 10 μm to 150 μm. If it is less than 2 μm, it is too thin and there is a risk of defects occurring during production. If it exceeds 250 μm, there is a risk of the insulating coating losing its flexibility.

[0076] <Electric Wire> Next, the electric wire of the present invention will be described.

[0077] The electric wire of the present invention includes a conductor and an insulating coating having one or more layers formed on the outer periphery of the conductor, at least one layer of which is the insulating coating of the present invention.

[0078] The material of the conductor is not particularly limited, but examples thereof include metal materials such as copper, aluminum, and silver.

[0079] The insulating coating has a single layer or multiple layers formed on the outer periphery of the conductor. In the electric wire of the present invention, at least one layer of the insulating coating is the insulating coating of the present invention. Examples of other layers in the insulating coating include layers containing a polyamide-imide resin or a polyester-imide resin.

[0080] The electric wire of the present invention can be produced, for example, by applying the imide resin solution of the present invention onto the surface of a conductor or onto another layer covering the conductor, and then forming an insulating coating by baking or the like.

[0081] The electric wire of the present invention includes a conductor and an insulating coating having one or more layers formed on the outer periphery of the conductor. By using the insulating coating of the present invention as at least one layer, an electric wire with excellent insulating performance can be obtained.

[0082] The electric wire of the present invention can be manufactured, for example, by applying an imide resin solution to the surface of a conductor or to another layer covering the conductor, followed by heating, drying, and baking, and then forming an insulating coating. A schematic cross-sectional view of an example of the electric wire of the present invention is shown in FIG. 1. The insulating coating 11 is formed by applying the imide resin solution of the present invention to a predetermined thickness on the conductor 12, and then heating at a high temperature (e.g., 300 to 500°C) for a predetermined time (e.g., 1 to 2 minutes). This series of operations (application and heating) is repeated multiple times (e.g., 10 to 20 times) until the insulating coating 11 reaches the predetermined thickness. The thickness of the insulating coating 11 is optimally selected depending on the application.

[0083] The conductor 12 may be, for example, a copper wire or copper alloy wire made of low-oxygen copper or oxygen-free copper, or another metal wire such as aluminum, silver, or nickel. While FIG. 1 shows the conductor 12 having a round cross section, the present invention is not limited to this and may also have a rectangular cross section. Furthermore, a twisted wire formed by twisting together multiple conductive wires may also be used as the conductor 12. The conductor diameter of the conductor 12 is not particularly limited, and an optimal value may be selected as appropriate depending on the application.

[0084] <Rotating Electric Machine> Next, a rotating electric machine according to the present invention will be described.

[0085] The rotating electric machine of the present invention is a rotating electric machine including the electric wire of the present invention. Examples of the rotating electric machine include a motor and a generator.

[0086] The present invention will now be described in more detail with reference to examples.

[0087] Example 1 (1-1. Preparation of boehmite sol dispersion) 200 g of a plate-shaped boehmite sol aqueous dispersion ("Aluminum Sol-10A" manufactured by Kawaken Fine Chemicals, 10.0 mass % boehmite, 2 mass % IPA (isopropyl alcohol)) and 187.2 g of NMP (N-methyl-2-pyrrolidone) were added to a 1 L four-neck flask equipped with a stirrer and a thermometer, and the IPA and water were distilled off while stirring under conditions of a reduced pressure of 100 to 10 torr and a temperature of 60 to 30°C, yielding 200 g of a plate-shaped boehmite sol NMP dispersion (10.0 mass % boehmite, water content 2.0%). 59.04 g of this was placed in a container, and 0.89 g of ethyl phosphate and 0.16 g of NMP for dilution were added, followed by stirring with a stirrer for 30 minutes to obtain a boehmite sol dispersion.

[0088] (1-2. Preparation of polyimide resin precursor (polyamic acid resin) solution) 72.6 g of 4,4'-diaminodiphenyl ether and 480 g of NMP were placed in a 1 L four-neck flask equipped with a stirrer and a thermometer, and the mixture was heated to 50°C with stirring to dissolve. Next, 78.3 g of pyromellitic anhydride was gradually added to the solution. After the addition was completed, the mixture was stirred for 1 hour to obtain a polyamic acid resin solution in which an aromatic polyamic acid represented by the following formula was dissolved in NMP at a concentration of 23.91% by mass. The same operation was repeated several times to prepare a polyamic acid resin solution.

[0089] (1-3. Production of imide-based resin solution) 139.92 g of the polyamic acid resin solution (solid content concentration 23.91% by mass) obtained in (1-2) and the above boehmite sol dispersion were added to a vessel, followed by addition of 23.58 g of NMP, and stirring for 3 minutes with a planetary centrifugal mixer to obtain an imide-based resin solution (boehmite concentration 15%). When the obtained imide-based resin solution was measured with a Karl Fischer moisture meter (Hiranuma Sangyo Co., Ltd., "AQV-2200"), the moisture content was found to be 0.5% by mass.

[0090] Example 2 (2-1. Preparation of boehmite sol dispersion) In (1-1), the boehmite content and water content were adjusted while adding NMP during vacuum distillation to obtain 200 g of a plate-like boehmite sol NMP dispersion (boehmite 7.0 mass%, water content 1.0%). 64.91 g of this was placed in a container, and the same procedure as in (1-1) was repeated except that 0.68 g of ethyl phosphate was added to obtain a boehmite sol dispersion.

[0091] (2-2. Production of imide-based resin solution) An imide-based resin solution (boehmite concentration 11%) was obtained in the same manner as in (1-3), except that 153.76 g of the polyamic acid resin solution (solid content concentration 23.91% by mass) obtained in (1-2) and the above boehmite sol dispersion were added to a vessel, and then 13.92 g of NMP was added. The water content of the obtained imide-based resin solution was 0.3% by mass.

[0092] Example 3 (3-1. Preparation of boehmite sol dispersion) In (1-1), DMF (N,N-dimethylformamide) was used instead of NMP. Distillation under reduced pressure was repeatedly performed to obtain a plate-like boehmite sol DMF dispersion (20.0 mass%, water content 0%). 17.16 g of this was placed in a container, and the procedure was repeated in the same manner as in (1-1), except that 0.51 g of ethyl phosphate, 0.39 g of water, and 17.25 g of DMF for dilution were added to obtain a boehmite sol dispersion.

[0093] (3-2. Production of imide-based resin solution) An imide-based resin solution (boehmite concentration 8%) was obtained in the same manner as in (1-3), except that 165.07 g of the polyamic acid resin solution (solid content concentration 23.91%) obtained in (1-2) and the above boehmite sol dispersion were added to a vessel, and then 41.2 g of DMF was added. The water content of the obtained imide-based resin solution was 0.2 mass%.

[0094] Example 4 An imide-based resin solution (boehmite concentration 15%) was obtained in the same manner as in Example 1, except that water was added to the imide-based resin solution obtained in Example 1 to adjust the water content to 0.8 mass%.

[0095] Example 5 An imide-based resin solution (boehmite concentration 15%) was obtained in the same manner as in Example 1, except that water was added to the imide-based resin solution obtained in Example 1 to adjust the water content to 1.0 mass%.

[0096] Example 6 An imide-based resin solution (boehmite concentration 15%) was obtained in the same manner as in Example 1, except that water was added to the imide-based resin solution obtained in Example 1 to adjust the water content to 1.3 mass%.

[0097] Example 7 An imide-based resin solution (boehmite concentration 15%) was obtained in the same manner as in Example 1, except that water was added to the imide-based resin solution obtained in Example 1 to adjust the water content to 1.5 mass%.

[0098] Comparative Example 1 An imide-based resin solution (boehmite concentration 15%) was obtained in the same manner as in Example 1, except that synthetic zeolite (molecular sieves) was added to the imide-based resin solution obtained in Example 1 and the water content was adjusted to 0.1 mass%.

[0099] Comparative Example 2 Water was added to the imide-based resin solution obtained in Example 1, and the same procedure as in Example 1 was carried out to adjust the water content to 10.0 mass %, but white precipitates were generated and a uniform imide-based resin solution (boehmite concentration 15%) could not be obtained.

[0100] <Evaluation of Storage Stability of Imide-Based Resin Solutions> The viscosities of the imide-based resin solutions obtained in Examples 1 to 7 and Comparative Example 1 were measured using an E-type viscometer (30°C, TVE-25 model viscometer manufactured by Toki Sangyo Co., Ltd.) to determine the viscosities of the imide-based resin solutions immediately after production.

[0101] Next, after storing the imide resin solutions in a thermostatic chamber set at 25°C for 30 days, the viscosity of each of the stored imide resin solutions was measured using an E-type rotational viscometer in the same manner, and the viscosity of the imide resin solutions 30 days after production was determined.

[0102] The evaluation criteria for the storage stability of the imide resin solution are as follows.

[0103] The viscosity of the imide resin solution immediately after production was set to 100, and the viscosity of the polyimide resin solution 30 days after production was calculated relative to this, and the storage stability was evaluated according to the following criteria. [Criteria for evaluation of storage stability] Excellent: 80 or more and 125 or less Good: 60 or more and 140 or less (excluding those rated "excellent") Unstable: less than 60 or more than 140

[0104] (1-3. Film Preparation) The imide resin solutions obtained in Examples 1 to 7 and Comparative Example 1 were applied to a 300 μm thick polyethylene terephthalate sheet in an area of ​​approximately A3 size using a multi-coater (Matsuo Sangyo, "K303"), and then placed in a hot air dryer pre-set to 90°C and dried by heating for 1 hour and 30 minutes to obtain a pre-baked imide resin film. Next, the obtained pre-baked imide resin film was peeled off from the polyethylene terephthalate sheet and attached to a pin tenter plate to prevent shrinkage after heating and baking. Then, the film was baked in a baking machine under the following conditions: Conditions: The temperature was raised to 150°C in 10 minutes, heat-treated at 150°C for 10 minutes, then heated to 200°C in 10 minutes, heat-treated at 200°C for 10 minutes, then heated to 300°C in 60 minutes, heat-treated at 300°C for 30 minutes, and then cooled to room temperature. The film was then taken out of the baking machine and removed from the pin tenter plates, and the edges were cut off to obtain a polyimide film having an average thickness of 35 μm.

[0105] <Film Elongation> The obtained polyimide film was punched out using a dumbbell cutter (SDK-500D, manufactured by Dumbbell Co., Ltd.), and the breaking elongation of the film was measured at a tensile speed of 100 mm / min using an autograph (Shimadzu Corporation, trade name "AGS-X") (in accordance with JIS K7161). A film with an elongation of 10% or more was judged to have excellent flexibility.

[0106] <Flexibility (Cylindrical Mandrel Method)> The imide resin solutions obtained in Examples 1 to 7 and Comparative Example 1 were applied to copper plates to form polyimide films. Specifically, the solution was uniformly applied to the surface of a copper plate (300 μm thick) as a conductor using a multi-coater (Matsuo Sangyo Co., Ltd., "K303") and baked at 300°C for 1 hour to form a film (50 μm thick) on the surface of the copper plate. The resulting polyimide film applied to the copper plate was bent using a cylindrical mandrel in accordance with JIS K5600-5-1, and the occurrence of cracks on the surface was observed using a microscope (50x magnification, Keyence Corporation, "VK-X150"). This observation was performed at several points while changing the diameter of the mandrel rod. Based on the results, when a mandrel rod with a diameter of 2 mm (elongation of approximately 5%) was used, the flexibility was judged to be good if no changes in the surface condition, such as cracks or wrinkles, were observed.

[0107] <Insulating Performance (Breakdown Voltage)> The polyimide film obtained in (1-3) was evaluated for breakdown voltage using a breakdown voltage tester (Yasuda Seiki Seisakusho No. 175). To eliminate the effects of moisture absorption, the polyimide film was placed in a hot air dryer set to 125°C for 30 minutes immediately before the test, and then removed. As shown in Figure 2, the weight was adjusted so that the load during the test was 500 g, and the center of the polyimide film was sandwiched between a spherical upper electrode and a cylindrical lower electrode, and measurements were performed. The measurement conditions were a voltage rise rate of 0.5 kV / sec, a maximum voltage of 30 kV, and a breakdown voltage of 10 mA. The breakdown voltage per unit thickness was calculated from the test voltage at breakdown and the thickness of the polyimide film described above. In addition, the CV value (coefficient of variation, standard deviation / average value) was calculated from the average and standard deviation of the breakdown voltages of 12 polyimide films. Here, the evaluation criteria for the insulating performance of a polyimide film were that if the average value of the breakdown voltage per unit thickness was 120 kV / mm or more and the CV value was less than 0.15, the film was judged to have good insulating performance with little variation in the breakdown voltage.

[0108] (1-4. Preparation of Electric Wire Samples) The polyimide resin solutions obtained in Examples 1 to 7 and Comparative Example 1 were applied to copper conductors, and the copper conductors were passed through a furnace in which the temperature was continuously raised from 350°C at the entrance to 420°C at the exit over a period of about 1 minute, and the baking process was repeated to prepare electric wires having an insulating coating of 38 μm thick on the surface of the copper conductor (diameter 1 mm).

[0109] <Flexibility of Electric Wire> The electric wire obtained in (1-4) was cut to a length of 60 cm and elongated by 30% at an elongation rate of 1000 mm / min using an autograph (Shimadzu Corporation, trade name "AGS-X"), and then tested in accordance with JIS C3216-3. First, the wire was wound around a round bar (diameter 1 mm), and the surface was observed using a magnifying glass (magnification 15x) to confirm the absence of cracks or wrinkles (denoted as "1d good"). If cracks or wrinkles were found, the wire was wound around a round bar with a larger diameter, and the evaluation was continued until no cracks or wrinkles occurred. Here, the smaller the diameter of the round bar, the better the flexibility of the electric wire; "2d good" or better was considered good.

[0110] The compositions of the prepared solutions and the evaluation results are shown in Table 1 below.

[0111] The imide resin solution, insulating film, electric wire, and rotating electric machine of the present invention can be suitably used in a wide variety of applications.

[0112] 11 insulating film 12 conductor

Claims

1. An imide-based resin solution containing an imide-based resin and / or its precursor, an inorganic filler, an organic solvent, and water, the water content of which is 0.2 to 9.0 mass % relative to the total mass of the solution.

2. The imide resin solution according to claim 1, wherein the inorganic filler is at least one selected from the group consisting of metal oxides and metal oxide hydrates.

3. The imide resin solution according to claim 2, wherein the metal oxide hydrate is alumina hydrate.

4. The imide resin solution according to claim 1, wherein the imide resin is a polyimide and the precursor is a polyamic acid.

5. An insulating film formed from the imide resin solution according to any one of claims 1 to 4.

6. An electric wire comprising a conductor and an insulating coating having one or more layers formed on the outer periphery of the conductor, at least one layer of the insulating coating being the insulating coating described in claim 5.

7. A rotating electric machine including the electric wire according to claim 6.

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