Insulating paint, insulating film, and insulated wire

Abstract

To provide an insulating coating material or the like capable of forming an insulating film excellent in interlayer adhesion.SOLUTION: The insulating coating material contains a polyimide resin, a nanofiller and a dispersant. The dispersant may be blended at a ratio of 0.1 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the polyimide-based resin.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an insulating varnish, an insulating film, and an insulated wire. [Background technology]

[0002] BACKGROUND ART Insulated wires used as coil windings for motors and the like require an insulating coating that covers a conductor, with excellent insulating properties, adhesion to the conductor, heat resistance, mechanical strength, and the like.

[0003] Insulated wire coatings are obtained by applying an insulating varnish to a conductor, baking the varnish to form an insulating layer, and then repeating the application and baking of insulating varnish to form an insulating film having multiple insulating layers. However, when a polyimide resin such as polyamic acid is used as the resin contained in the insulating varnish, the adhesion between the insulating layers in the insulating film for the insulated wire coating is poor, and improvement is particularly desired.

[0004] Non-Patent Document 1 below discloses an insulating film obtained by applying and baking a varnish containing polyamic acid to the surface of an insulating layer (first insulating layer) containing polyimide imidized by baking polyamic acid, thereby forming an insulating layer (second insulating layer).The document discloses that in this insulating film, the surface of the first insulating layer is stable and does not allow the polymer in the first insulating layer and the polymer in the varnish applied later to penetrate between the first and second insulating layers, so that no adhesion can be obtained between adjacent insulating layers. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] SFTead et al, “Interdiffusion at polyimide interfaces”, Polymer, 1992, Volume 33, Number 16, p.3382-3387 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide an insulating coating material capable of forming an insulating film having excellent interlayer adhesion. A further object of the present invention is to provide an insulating film that exhibits excellent interlayer adhesion and an insulated wire using the insulating film. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above-mentioned problems. As a result, they have made the unexpected discovery that by incorporating a material with specific properties into an insulating varnish containing a polyimide resin, which is an insulating resin, and a nanofiller, excellent adhesion can be achieved between the insulating layers in the coating of an insulated electric wire. Based on this discovery, the present inventors have conducted further research and have completed this invention.

[0008] The present invention provides the following insulating varnish, insulating film, and insulated wire. Item 1. An insulating paint containing a polyimide resin, a nanofiller, and a dispersant. Item 2. The insulating varnish according to Item 1, wherein the dispersant is blended in an amount of 0.1 to 5 parts by mass per 100 parts by mass of the polyimide resin. Item 3. The insulating varnish according to Item 1 or 2, wherein the nanofiller is blended in an amount of 1 part by mass or more and 30 parts by mass or less per 100 parts by mass of the polyimide resin. Item 4. An insulating film having a plurality of insulating layers formed from the insulating coating material according to any one of items 1 to 3. Item 5. An insulated wire comprising a conductor and an insulating coating covering the conductor, the insulating coating having the insulating film according to Item 4. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an insulating coating material capable of forming an insulating film having excellent interlayer adhesion. Furthermore, according to the present invention, it is also possible to provide an insulating film having excellent interlayer adhesion, and an insulated wire using the insulating film. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic cross-sectional view showing an example of an insulated wire according to an embodiment of the present invention. [Figure 2] FIG. 4 is a schematic cross-sectional view showing another example of an insulated wire according to an embodiment of the present invention. [Figure 3] FIG. 4 is a schematic cross-sectional view showing another example of an insulated wire according to an embodiment of the present invention. [Figure 4] FIG. 4 is a schematic cross-sectional view showing another example of an insulated wire according to an embodiment of the present invention. [Figure 5] FIG. 4 is a schematic cross-sectional view showing another example of an insulated wire according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Several embodiments of an insulating veneer, an insulating film, and an insulated wire according to one aspect of the present invention are 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 limits and multiple upper limits are listed separately, any lower limit and upper limit can be selected and connected with "~".

[0012] <Insulating paint> The insulating coating material of the present invention contains a polyimide resin, a nanofiller, and a dispersant. The insulating coating material of the present invention can form an insulating film having excellent interlayer adhesion.

[0013] (Polyimide resin) The polyimide resin is preferably a polyimide resin or a polyimide resin precursor. The polyimide resin and the polyimide resin precursor are preferably compounds containing an aromatic group from the viewpoints of heat resistance and insulating properties.

[0014] The polyimide resin is preferably a polymer having an imide structure. The polyimide resin precursor is a polymer having an imide structure by imidization, and is preferably formed from a diamine or a derivative thereof and an acid anhydride or a derivative thereof.

[0015] A more preferred polyimide resin is a compound having the repeating structure of the following formula (1). It is more preferred that the polyimide resin precursor (polyamic acid) is also a precursor that becomes a compound (polyimide resin) having the repeating structure of the following formula (1) upon imidization. In the following formula (1), n ​​is the number of repeating structures and is a positive integer. The polyimide resin may have one type of repeating structure of the following formula (1), or two or more types.

[0016] [ka]

[0017] In the formula (1), R 1 is a tetravalent group and is an organic group having one or two benzene rings. 1 is preferably at least one of the structures exemplified in the following formula (2). 1 The copolymer may be a homopolymer having only one of the structures represented by the following formula (2), or a copolymer having two or more of the structures.

[0018] [ka]

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

[0020] [ka]

[0021] In addition, in the formula (1), R 2 represents a divalent group derived from an aromatic hydrocarbon (a divalent aromatic hydrocarbon group). 2 When two or more of these are combined, they may be linked via at least one bonding group selected from the group consisting of -O-, -SO2-, -CO-, -CH2-, and -S-.

[0022] R 2 The aromatic hydrocarbon group represented by the formula (which may or may not have the above-mentioned bonding group) is, for example, at least one of the structures exemplified in the following formula (4).

[0023] [ka]

[0024] R represented by the formula (4) 2 Among these, at least one of the structures exemplified in the following formula (5) is preferred.

[0025] [ka]

[0026] When preparing the insulating coating material of the present invention, the polyimide resin may be used in a form dissolved or dispersed in a solvent (such as a resin varnish). It is preferable that the solvent contained in the insulating coating material of the present invention contains a solvent having a boiling point of 100°C or higher at 1 atmosphere (hereinafter referred to as "solvent A") in an amount of 90% by mass or more. Therefore, when the polyimide resin is used in a form dissolved or dispersed in a solvent, the solvent for dissolving or dispersing the polyimide resin is prepared or selected so that the solvent contained in the insulating coating material of the present invention contains solvent A in an amount of 90% by mass or more.

[0027] Examples of solvents for dissolving or dispersing polyimide resins include amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone (NMP); cyclic ester solvents such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, ε-caprolactone, and α-methyl-γ-butyrolactone; carbonate solvents such as ethylene carbonate and propylene carbonate; glycol solvents such as triethylene glycol; phenol solvents such as phenol, o-cresol, m-cresol, p-cresol, 3-chlorophenol, and 4-chlorophenol; acetophenone, 1,3-dimethyl-2-imidazolidinone, sulfolane, and dimethyl sulfoxide. Furthermore, other common organic solvents, such as butyl acetate, ethyl acetate, isobutyl acetate, propylene glycol monomethyl ether acetate, ethyl cellosolve, butyl cellosolve, 2-methyl cellosolve acetate, ethyl cellosolve acetate, butyl cellosolve acetate, tetrahydrofuran, dimethoxyethane, diethoxyethane, dibutyl ether, diethylene glycol dimethyl ether, methyl isobutyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, methyl ethyl ketone, acetone, butanol, ethanol, xylene, toluene, chlorobenzene, benzyl alcohol, anisole, methoxypropanol, turpentine, mineral spirits, and petroleum naphtha-based solvents, can also be used. However, as mentioned above, from the viewpoint of ensuring that the ratio of solvent A in the solvents contained in the insulating coating material of the present invention is 90 mass % or more, the solvents for dissolving or dispersing the polyimide resin are preferably N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, γ-butyrolactone, sulfolane, dimethyl sulfoxide, and cyclohexanone.

[0028] (nanofiller) Nanofillers refer to nano-sized metal oxides and their hydrates.

[0029] An example of the nanofiller is alumina particles. The alumina particles are represented by, for example, the following general formula (1A). Al2O3·nH2O (1A)

[0030] In formula (1A), n is an integer of 0 to 3. When n is 0, general formula (1A) represents aluminum oxide. This aluminum oxide is α-alumina, γ-alumina, or alumina such as β, ρ, χ, ε, κ, κ', θ, η, δ, or λ. When n in formula (1A) is greater than 0, general formula (1A) represents a mixture of various aluminum hydroxides in the form of hydrated alumina.

[0031] Crystalline forms of aluminum hydroxide include the trihydroxide (Al(OH)3), which includes gibbsite, bayerite, and nordstrandite, and two modifications of aluminum oxide hydroxide (AlO(OH)). Two variants are boehmite (γ-aluminum oxide hydroxide) and diaspore (α-aluminum oxide hydroxide). The aluminum oxide hydroxide is represented by formula (1A) where n is 1, and the aluminum trihydroxide is represented by formula (1A) where n is 3. Among the above alumina particles, α-alumina, γ-alumina, and boehmite are preferred from the viewpoints of stability and ease of production.

[0032] The aspect ratio (major axis / minor axis) of the nanofiller is not particularly limited and may be, for example, 2 to 99, and is preferably 5 to 99, more preferably 10 to 99, from the viewpoint of partial discharge resistance.

[0033] In this specification, the aspect ratio refers to the ratio (major axis / minor axis) of the major axis to the minor axis of a particle (nanofiller) observed at 5000x magnification using a scanning electron microscope. In other words, in the case of a nanofiller having plate-like particles, the aspect ratio is the average particle diameter divided by the average plate thickness, and is the average particle diameter of at least 100 nanofiller plate-like particles divided by the average plate thickness. In other words, the "average particle diameter" is the "major axis" and the "plate thickness" is the "minor axis." The particle diameter of a plate-like particle here corresponds to the diameter of a circle having the same area as the area of ​​the main surface of the plate-like particle. In addition, in the case of columnar or acicular particles, the aspect ratio is the length of the column or needle divided by the diameter of the column or needle. In other words, the "length of the column or needle" is the "major axis," and the "diameter of the column or needle" is the "minor axis."

[0034] The nanofiller may be formed in any of the known shapes, such as plate-like, fibrous, spindle-like, needle-like, cylindrical, or columnar particles, with anisotropic shapes such as plate-like or columnar being preferred because they provide the insulating coating of the present invention with superior partial discharge resistance. Furthermore, the nanofiller may exist as flat particles in which columnar particles are arranged, or as hollow particles. When hollow particles are used as the nanofiller, they can reduce the dielectric constant of the insulating coating and suppress the occurrence of partial discharge, thereby contributing to improved durability of the insulating coating.

[0035] The nanofiller has an average particle size of about 1 nm to 1000 nm. Furthermore, when the alumina particles have a plate-like structure, the nanofiller also includes particles with a plate thickness (minor axis) of about 1 nm to 1000 nm.

[0036] The average particle size of the alumina particles is preferably 1 nm to 1000 nm, more preferably 5 nm to 500 nm, from the viewpoint of improving partial discharge resistance. The average particle size is the particle size at 50% of the cumulative value in the particle size distribution obtained by measurement using a laser diffraction scattering particle size measuring device (Microtrac).

[0037] When preparing the insulating coating material of the present invention, the nanofiller can be used as a dispersion obtained by dispersing the nanofiller in a solvent or as a dispersion obtained by a sol-gel method. Commercially available nanofiller dispersions may be used. Examples of commercially available nanofiller dispersions include "Aluminasol 15A," "Aluminasol 10A," and "Aluminasol 10D" manufactured by Kawaken Fine Chemicals Co., Ltd., and "AS-520" manufactured by Nissan Chemical Industries, Ltd.

[0038] The nanofiller is preferably surface-treated. Examples of the surface treatment method include a method using a surface treatment agent, specifically a method of treating with a silane coupling agent (such as an epoxy-based silane coupling agent or a methacrylic-based silane coupling agent), a method of treating with a titanate coupling agent, a method of treating with an aluminate-based surface treatment agent, a method of treating with a phosphoric acid-based surface treatment agent, or a method of treating with a carboxylic acid anhydride such as phthalic anhydride. Among these, metal oxide hydrates surface-treated with a silane coupling agent and metal oxide hydrates surface-treated with a phosphoric acid-based surface treatment agent are preferred, and metal oxide hydrates surface-treated with a phosphoric acid-based surface treatment agent are more preferred. Examples of phosphoric acid surface treatment agents include phosphonic acid derivative surface treatment agents such as phenylphosphonic acid, octadecylphosphonic acid, 11-{2-[2-(2-methoxyethoxy)ethoxy]ethoxy}undecylphosphonic acid, 1H,1H,2H,2H-perfluoro-n-decylphosphonic acid, 1H,1H,2H,2H-perfluoro-n-hexylphosphonic acid, 11-hydroxyundecylphosphonic acid, 10-carboxydecylphosphonic acid, and 11-aminoundecylphosphonic acid.

[0039] The method of surface treatment is not particularly limited. When the nanofiller is a powder, a method of spraying a solution in which a surface treatment agent is dissolved in a solvent onto the powder using a spray or the like, followed by drying at 20 to 60°C, or when a metal oxide hydrate sol is used, a method of adding and dissolving a surface treatment agent, followed by stirring at 20 to 60°C for 1 to 24 hours, etc., can be used. When treating the nanofiller with a surface treatment agent, the amount of the surface treatment agent used per 100 parts by mass of the nanofiller is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and preferably 70 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 40 parts by mass or less.

[0040] In the insulating coating material of the present invention, the content of the nanofiller is not particularly limited, but is preferably 1 part by mass or more and 30 parts by mass or less per 100 parts by mass of the polyimide resin. From the viewpoint of partial discharge resistance, the lower limit of the content of the nanofiller is preferably 1 part by mass, more preferably 2 parts by mass, even more preferably 3 parts by mass, and particularly preferably 15 parts by mass. From the viewpoint of flexibility of the insulating film formed from the insulating coating material, the upper limit of the content of the nanofiller is preferably 25 parts by mass.

[0041] In the insulating coating material of the present invention, the total content of the polyimide resin (solid content) and the nanofiller (solid content) is 10 to 30 mass %, and from the viewpoint of more suitably forming an insulating film having excellent nanofiller dispersibility, industrially suitable viscosity, and excellent interlayer adhesion, it is preferably 12 to 30 mass %, more preferably 12 to 25 mass %.

[0042] The nanofiller dispersion contains a solvent (dispersion medium) for dispersing the nanofiller. As mentioned above, the proportion of solvent A, which has a boiling point of 100°C or higher at 1 atmosphere, in the solvent contained in the insulating coating of the present invention is preferably 90% by mass or more. Therefore, it is preferable to prepare or select the dispersion medium for the nanofiller dispersion so that the proportion of solvent A in the solvent contained in the insulating coating of the present invention is 90% by mass or more. The dispersion medium of the nanofiller dispersion and the solvent for dissolving or dispersing the polyimide resin may be the same or different, but it is preferable that they are the same.

[0043] From the viewpoint of the appearance and uniformity of the resulting insulating film, the dispersion medium for the nanofiller dispersion is preferably a solvent (ie, solvent A) having a boiling point of 100° C. or higher under 1 atmosphere (normal pressure). Examples of the dispersion medium for the nanofiller dispersion include amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone (NMP); cyclic ester solvents such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, ε-caprolactone, and α-methyl-γ-butyrolactone; phenolic solvents such as phenol, o-cresol, m-cresol, p-cresol, 3-chlorophenol, and 4-chlorophenol; acetophenone, 1,3-dimethyl-2-imidazolidinone, sulfolane, and diisopropyl ether. Examples of the dispersion medium include methyl sulfoxide, other common organic solvents, butyl acetate, isobutyl acetate, propylene glycol methyl ether acetate, ethyl cellosolve, butyl cellosolve, 2-methyl cellosolve acetate, ethyl cellosolve acetate, butyl cellosolve acetate, diethoxyethane, dibutyl ether, methyl isobutyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, propanol, butanol, methoxypropanol, benzyl alcohol, xylene, toluene, chlorobenzene, anisole, etc. The dispersion medium for the nanofiller dispersion may be one type or a mixture of two or more types.

[0044] Among these, from the viewpoints of compatibility with the polyimide resin and dispersibility of the nanofiller, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, γ-butyrolactone, methyl isobutyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, methoxypropanol, and benzyl alcohol are preferred.

[0045] (dispersant) The dispersant is a material that improves the dispersibility of the nanofiller. Examples of dispersants include polyurethane resin, acrylic resin, and polyester resin. These can be used alone or in combination of two or more.

[0046] The polyurethane resin includes unmodified polyurethane resin, modified polyurethane resin, and mixtures thereof. Examples of modified polyurethane resins include amine-modified polyurethane resins, silicone-modified polyurethane resins, acrylic-modified polyurethane resins, polyether-based polyurethane resins, polyester-based polyurethane resins, and polycarbonate-based polyurethane resins. Examples of polyester resins include phosphate polyester resins. When preparing the insulating coating material of the present invention, the dispersant can be used as a dispersant-containing liquid containing the dispersant in a solvent. Commercially available dispersant-containing liquids may be used. Examples of commercially available dispersant-containing liquids include "DISPERBYK-162," "DISPERBYK-168," "DISPERBYK-184," "DISPERBYK-2019," and "DISPERBYK-111," all manufactured by BYK.

[0047] The blending ratio of the dispersant per 100 parts by mass of polyimide resin is not particularly limited, but is preferably 0.1 parts by mass or more from the viewpoint of forming an insulating film that exhibits excellent interlayer adhesion. The blending ratio of the dispersant per 100 parts by mass of polyimide resin is also not particularly limited, but is preferably 5 parts by mass or less. In this case, heat resistance can be further improved compared to when the blending ratio of the dispersant exceeds 5 parts by mass. The blending ratio of the dispersant per 100 parts by mass of polyimide resin is more preferably 0.1 parts by mass or more and 3.5 parts by mass or less.

[0048] The insulating coating material of the present invention may contain various additives such as lubricants and adhesion promoters, reactive low-molecular-weight compounds, compatibilizers, etc., as needed, within the scope of the present invention.

[0049] <Insulating film> The insulating film of the present invention has a plurality of insulating layers formed from the above-mentioned insulating coating material. When the polyimide resin contained in the insulating varnish is a polyimide resin, the insulating layer is formed by drying the insulating varnish to remove the solvent. When the polyimide resin contained in the insulating varnish is a polyimide resin precursor (polyamic acid), the insulating layer is formed by imidizing the insulating varnish and removing the solvent during the drying process.

[0050] The insulating layer contains a polyimide resin. The lower limit of the polyimide resin content in the insulating layer is not particularly limited, but is preferably 50 mass %, more preferably 60 mass %, and the upper limit of the polyimide resin content is preferably 97 mass %, more preferably 90 mass %, and even more preferably 85 mass %.

[0051] In the insulating layer, the lower limit of the nanofiller content is preferably 3 mass %, more preferably 10 mass %, and even more preferably 12 mass %, and the upper limit is preferably 50 mass %, more preferably 40 mass %.

[0052] In the insulating film, the blending ratio of the nanofiller to 100 parts by mass of the polyimide resin is preferably 1 to 30 parts by mass, more preferably 2 to 30 parts by mass, even more preferably 3 to 25 parts by mass, and even more preferably 15 to 25 parts by mass.

[0053] <Insulated wire> An insulated wire according to an embodiment of the present invention includes a conductor and an insulating coating covering the conductor. The insulating coating has the insulating film described above at least in part, and the insulating film has multiple insulating layers formed from the insulating varnish described above. By having such a configuration, the insulated wire according to the embodiment of the present invention has excellent adhesion between the insulating layers. An insulated wire according to an embodiment of the present invention will be described in detail below with reference to FIGS.

[0054] As described above, the insulated wire 10 only needs to have at least the conductor 1 and the insulating coating including the insulating film 2 (see FIGS. 1 and 2), and the insulating coating may further have other layers (FIGS. 3 to 5). As other layers, the insulating coating may further have, for example, an insulating layer 3 provided on the outer side of the insulating film 2 (FIGS. 3 and 4), or an insulating layer 4 provided on the inner side of the insulating film 2 (FIGS. 4 and 5).

[0055] The insulating layer 4 may be an adhesive layer provided between the conductor 1 and the insulating coating 2. The adhesive layer may contain the above-mentioned dispersant.

[0056] The adhesive layer may be made of a polyimide resin.

[0057] 1 to 5, the laminated structure of the insulated wire 10 according to the embodiment of the present invention is an insulated wire including at least a conductor 1 and an insulating coating including an insulating film 2. Specifically, the insulated wire 10 according to the embodiment of the present invention may be in the form of a film including at least the conductor 1 and an insulating coating having the insulating film 2 laminated on the conductor 1, for example, as shown in FIG. Furthermore, the insulated wire 10 according to an embodiment of the present invention may be in the form of an insulated wire having a conductor 1 in the central portion and an insulating coating having an insulating film 2 formed on the outer periphery of the conductor 1, as shown in Figures 2 to 5, for example. The cross-sectional shape of the insulated wire 10 according to the embodiment of the present invention may be a circle, an ellipse, a polygon (it may be a rectangular shape or an irregular shape), or the like. An insulated wire with a circular cross section is shown in Figures 2 to 4. An insulated wire with a substantially rectangular cross section is shown in Figure 5. When the cross section of the conductor 1 is circular, the diameter of the insulated wire 10 is, for example, about 0.03 to 4.0 mm.

[0058] The insulating layer 3 and the insulating layer 4 may each be made of the same material as the insulating film 2, or may be made of another material (for example, an organic insulating layer). The organic insulating layer is preferably made of the above-mentioned polyimide resin. The insulating layer 3 and the insulating layer 4 may also be made of the same material, or may be made of different materials.

[0059] The conductor 1 may be composed of only a central conductor, or may be composed of a central conductor and a coating covering the central conductor, such as a plating layer made of a metal different from that of the central conductor.

[0060] The material constituting the conductor 1 may be any conductive material, and examples of the conductive material include metals such as copper (low-oxygen copper, oxygen-free copper, copper alloy, etc.), aluminum, silver, nickel, iron, etc. The material constituting the conductor 1 can be appropriately selected depending on the application of the present invention.

[0061] The total thickness of the insulating coating of the insulated wire 10 according to the embodiment of the present invention is not particularly limited, and is, for example, 3 μm or more, 5 μm or more, 10 μm or more, or 20 μm or more. The total thickness of the insulating coating may be 200 μm or less, 100 μm or less, or 50 μm or less.

[0062] An insulated wire 10 according to an embodiment of the present invention can be produced by covering a conductor 1 with an insulating coating having an insulating film 2. The insulated wire 10 can be produced, for example, by applying the insulating coating described above onto the conductor 1, drying it, and baking it as necessary, repeatedly multiple times to form the insulating film 2 that covers the conductor 1 and obtain the insulating coating.

[0063] Examples of methods for applying the insulating coating include coating with a coater, applying with a dip coater or die and repeatedly drying to obtain a coating of a predetermined thickness, and spray coating, but the method for applying the insulating coating is not particularly limited to these. Furthermore, baking of the polyimide resin can be carried out, for example, by heating at a high temperature (e.g., 300°C or higher) for a predetermined period of time. The insulating film 2 is formed by repeating a series of steps of application and heating multiple times until the insulating film 2 reaches a predetermined thickness.

[0064] For example, when the insulated wire 10 according to the embodiment of the present invention is in the form of an insulated wire, the insulated wire can be manufactured by applying an insulating varnish to the surface of the conductor 1 in the form of a wire and baking it as necessary. Specifically, the insulating film 2 can be formed by applying the insulating varnish to the conductor 1 in a predetermined thickness and heating it at a high temperature (e.g., 300 to 500°C) 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 the insulating film 2 reaches the predetermined thickness.

[0065] Furthermore, when preparing the insulating coating material for forming the insulating film 2, the polyimide resin and the nanofiller may be used in a form in which they are dissolved or dispersed in a solvent (such as a resin varnish).

[0066] When forming the insulating film 2, it is preferable to use an insulating paint in which a resin is dissolved or dispersed in a solvent and a nanofiller is dispersed, and to form the insulating film 2 by applying this insulating paint to the surface of the conductor 1 and baking it as necessary. Suitable solvents for dissolving or dispersing polyimide resins while also dispersing nanofillers 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, glycol ether-based solvents, and other high-boiling point solvents. Examples of methods for producing the insulating coating material include methods using commonly known mixing means such as a kneader, pressure kneader, kneading roll, Banbury mixer, twin-screw extruder, planetary mixer, homomixer, etc. The mixing temperature is usually 5 to 30°C.

[0067] The insulating coating material may contain an acid or alkali component to stabilize dispersion. Similarly, it may contain water, a low-boiling alcohol, or a low-viscosity solvent that contributes to reducing the viscosity of the insulating coating material. If necessary, other metal oxide hydrates or metal oxides may be mixed into the insulating coating material, and additives may be added to improve hydrophobicity or dispersibility. Suitable additives include fluorine-based and silicone-based additives, citric acid, ethylenediaminetetraacetic acid, and 8-quinolinol. [Example]

[0068] 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.

[0069] The polyimide resin solutions used in the examples and comparative examples are as follows:

[0070] [Polyimide resin solution] As the polyimide resin solution, "Meirejicoat" manufactured by Nagoya Chemical Industry Co., Ltd., which contains a polyimide precursor (polyamic acid), was used.

[0071] [Insulating paint] Insulating coating materials were prepared according to the procedures shown in the following Production Examples 1 to 12.

[0072] <Production Example 1> To an NMP-dispersed boehmite sol [product name: Alumina NMP Sol A1-10 (containing 10% by mass of boehmite), average particle size of the boehmite: 15 to 50 nm, manufactured by Kawaken Fine Chemicals Co., Ltd.], 20 parts by mass of phenylphosphonic acid per 100 parts by mass of boehmite (equivalent to alumina) and 24 parts by mass of 8-quinolinol (manufactured by Tokyo Chemical Industry Co., Ltd.) per 100 parts by mass of boehmite (equivalent to alumina) were added, and the resulting liquid was stirred at room temperature for 1 hour to obtain an NMP-dispersed boehmite sol (first dispersion) containing boehmite surface-treated with phenylphosphonic acid. Next, the first dispersion was uniformly mixed and dispersed at room temperature using a planetary centrifugal mixer into the polyimide resin solution containing polyamic acid so that the amount of boehmite was 15 parts by mass, calculated as alumina, per 85 parts by mass of polyamic acid, thereby obtaining a second dispersion. Furthermore, a dispersant solution (product name "DISPERBYK-162", manufactured by BYK, amine value: 13 mg KOH / g) containing a polyurethane resin (modified polyurethane resin) as a dispersant was added to the second dispersion in a blend ratio of 2.34 parts by mass of dispersant per 100 parts by mass of polyamic acid, and the mixture was mixed and dispersed using a planetary centrifugal mixer. In this way, insulating paint 1 was obtained.

[0073] <Production Example 2> The dispersant solution was changed from "DISPERBYK-162" to "DISPERBYK-168 (product name, manufactured by BYK, amine value: 11 mg KOH / g)" which contains a polyurethane resin (modified polyurethane resin) as a dispersant, and the blending ratio of "DISPERBYK-168" to 100 parts by mass of polyamic acid was changed from "2.34 parts by mass" to "1.19 parts by mass." Insulating paint 2 was obtained in the same manner as in Production Example 1, except that the dispersant solution was changed from "DISPERBYK-162" to "DISPERBYK-168" which contains a polyurethane resin (modified polyurethane resin) as a dispersant, and the blending ratio of "DISPERBYK-168" to 100 parts by mass of polyamic acid was changed from "2.34 parts by mass" to "1.19 parts by mass."

[0074] <Production Example 3> The dispersant solution was changed from "DISPERBYK-162" to "DISPERBYK-184 (product name, manufactured by BYK, amine value: 15 mg KOH / g)" which contains a polyurethane resin (modified polyurethane resin) as a dispersant, and the blending ratio of "DISPERBYK-184" to 100 parts by mass of polyamic acid was changed from "2.34 parts by mass" to "3.19 parts by mass." Insulating paint 3 was obtained in the same manner as in Production Example 1, except that the dispersant solution was changed from "DISPERBYK-162" to "DISPERBYK-184 (product name, manufactured by BYK, amine value: 15 mg KOH / g)" which contains a polyurethane resin (modified polyurethane resin) as a dispersant, and the blending ratio of "DISPERBYK-184" to 100 parts by mass of polyamic acid was changed from "2.34 parts by mass" to "3.19 parts by mass."

[0075] <Production Example 4> Insulating paint 4 was obtained in the same manner as in Production Example 1, except that the dispersant solution was changed from "DISPERBYK-162" to "DISPERBYK-168" which contains a polyurethane resin (modified polyurethane resin) as a dispersant, the blending ratio of phenylphosphonic acid per 100 parts by mass of boehmite (equivalent to alumina) was changed from "20 parts by mass" to "35 parts by mass," and the blending ratio of dispersant in "DISPERBYK-168" per 100 parts by mass of polyamic acid was changed from "2.34 parts by mass" to "1.91 parts by mass."

[0076] <Production Example 5> Insulating paint 5 was obtained in the same manner as in Production Example 1, except that the dispersant solution was changed from "DISPERBYK-162" to "DISPERBYK-168" which contains a polyurethane resin (modified polyurethane resin) as a dispersant, the blending ratio of phenylphosphonic acid per 100 parts by mass of boehmite (equivalent to alumina) was changed from "20 parts by mass" to "35 parts by mass", and the blending ratio of dispersant in "DISPERBYK-168" per 100 parts by mass of polyamic acid was changed from "2.34 parts by mass" to "1.19 parts by mass".

[0077] <Production Example 6> Insulating paint 6 was obtained in the same manner as in Production Example 1, except that the dispersant solution was changed from "DISPERBYK-162" to "DISPERBYK-168" which contains a polyurethane resin (modified polyurethane resin) as a dispersant, the blending ratio of phenylphosphonic acid per 100 parts by mass of boehmite (equivalent to alumina) was changed from "20 parts by mass" to "35 parts by mass", and the blending ratio of dispersant in "DISPERBYK-168" per 100 parts by mass of polyamic acid was changed from "2.34 parts by mass" to "0.54 parts by mass".

[0078] <Production Example 7> Insulating paint 7 was obtained in the same manner as in Production Example 1, except that the dispersant solution was changed from "DISPERBYK-162" to "DISPERBYK-168" which contains a polyurethane resin (modified polyurethane resin) as a dispersant, the blending ratio of phenylphosphonic acid per 100 parts by mass of boehmite (equivalent to alumina) was changed from "20 parts by mass" to "35 parts by mass", and the blending ratio of dispersant in "DISPERBYK-168" per 100 parts by mass of polyamic acid was changed from "2.34 parts by mass" to "0.22 parts by mass".

[0079] <Production Example 8> Insulating paint 8 was obtained in the same manner as in Production Example 1, except that the blending ratio of phenylphosphonic acid per 100 parts by mass of boehmite (equivalent to alumina) was changed from 20 parts by mass to 35 parts by mass, and the blending ratio of dispersant "DISPERBYK-162" per 100 parts by mass of polyamic acid was changed from 2.34 parts by mass to 1.19 parts by mass.

[0080] <Production Example 9> Insulating paint 9 was obtained in the same manner as in Production Example 1, except that the dispersant solution was changed from "DISPERBYK-162" to "DISPERBYK-2019 (product name, manufactured by BYK, amine value: 22 mg KOH / g)" which contains an acrylic resin as a dispersant, and the blending ratio of "DISPERBYK-2019" to 100 parts by mass of polyamic acid was changed from "2.34 parts by mass" to "3.19 parts by mass."

[0081] <Production Example 10> An insulating coating material 10 was obtained in the same manner as in Production Example 1, except that no dispersant solution was added.

[0082] <Production Example 11> Insulating coating material 11 was obtained in the same manner as in Production Example 1, except that the blending ratio of phenylphosphonic acid per 100 parts by mass of boehmite (equivalent to alumina) was changed from 20 parts by mass to 35 parts by mass, and no dispersant solution was added.

[0083] <Production Example 12> A dispersant solution (product name "DISPERBYK-162", manufactured by BYK) was added to the above polyimide resin solution containing polyamic acid as the polyimide resin so that the blending ratio of dispersant per 100 mass parts of polyamic acid was 0.90 mass parts, and the mixture was mixed using a three-one motor to obtain insulating coating material 12 for the adhesion layer.

[0084] [Laminated film manufacturing] Laminated films serving as insulating films were produced according to the procedures shown in Examples 1 to 8 and Comparative Examples 1 and 2 below.

[0085] Example 1 Using a blade coater, insulating paint 1 was applied to the surface of a PET film measuring 36.4 cm x 51.5 cm to a coating thickness of 350 μm. Insulating paint 1 was dried in a fan dryer at 90°C for 80 minutes to obtain a dried film, and then a dried film measuring 20 cm x 27 cm was peeled off from the PET film. The peeled dry film was fixed to a horizontally positioned pin tenter with the surface that had been in contact with the air during drying facing upward, and baked in a baking machine according to the program at 150°C for 10 minutes, 200°C for 10 minutes, and 350°C for 30 minutes to obtain a film for the first insulating layer. Next, the film of the first insulating layer was removed from the pin tenter and attached to a coating table with the upper surface facing upward. Then, a Kapton tape measuring 1 cm wide and 20 cm long was attached to the surface of the film of the first insulating layer at a position approximately 2 cm from one end (the end of the short side). Next, insulating paint 1 was applied to one end of the Kapton tape and the opposite side (an area of ​​5 mm width x 20 cm length) so as to overlap the area, to a thickness of 500 μm. Then, the insulating paint 1 was dried in an air dryer at 90°C for 40 minutes, and the portion of the insulating paint 1 that had been applied on top of the Kapton tape was repaired (re-applied) with the same insulating paint 1, and the insulating paint 1 was dried again at 90°C for 40 minutes. The film thus obtained was fixed with a pin tenter and baked in a baking machine according to the above program. In this manner, a laminated film consisting of the first insulating layer and the second insulating layer was obtained.

[0086] Example 2 A laminated film was obtained in the same manner as in Example 1, except that the insulating paint 1 was replaced with the insulating paint 2.

[0087] Example 3 A laminated film was obtained in the same manner as in Example 1, except that insulating paint 1 was replaced with insulating paint 3.

[0088] Example 4 A laminated film was obtained in the same manner as in Example 1, except that the insulating paint 1 was replaced with the insulating paint 4.

[0089] Example 5 A laminated film was obtained in the same manner as in Example 1, except that the insulating paint 1 was replaced with the insulating paint 5.

[0090] Example 6 A laminated film was obtained in the same manner as in Example 1, except that the insulating paint 1 was replaced with the insulating paint 6.

[0091] Example 7 A laminated film was obtained in the same manner as in Example 1, except that the insulating paint 1 was replaced with the insulating paint 7.

[0092] Example 8 A laminated film was obtained in the same manner as in Example 1, except that the insulating paint 1 was replaced with the insulating paint 8.

[0093] Example 9 A laminated film was obtained in the same manner as in Example 1, except that the insulating paint 1 was replaced with the insulating paint 9.

[0094] (Comparative Example 1) A laminated film was obtained in the same manner as in Example 1, except that the insulating paint 1 was replaced with the insulating paint 10.

[0095] (Comparative Example 2) A laminated film was obtained in the same manner as in Example 1, except that the insulating paint 1 was replaced with the insulating paint 11.

[0096] [Laminated film evaluation] The laminated films obtained in the examples and comparative examples were subjected to the following peel test.

[0097] [Preparation of peel test samples] For the laminated films obtained in the Examples and Comparative Examples, the Kapton tape was removed, and a portion (the peeled portion) of the second insulating layer was carefully peeled from the Kapton tape. Then, using a trimming cutter (manufactured by WISTA Co., Ltd.), three strips measuring 15 mm x 80 mm were punched out along the longitudinal direction of the laminated film so that the length of the peeled portion was approximately 5 mm. Cellophane tape was then attached to the peeled portion to create a handle, and a 7.5 cm double-sided tape was attached to the surface of the first insulating layer. The laminated film was then attached to a 3 cm x 12 cm x 1 mm thick aluminum plate to prepare a peel test sample.

[0098] [Peel test] A jig for sliding the sample was attached to the bottom of a bench-top precision universal testing machine (Shimadzu Corporation, Autograph AGS-X5kN), and the sample was then placed on it, with the cellophane tape handle attached to the upper chuck. The upper chuck movement speed was set to 50 mm / min, and the average value of the peel test force over a chuck movement distance of 15 mm to 50 mm was taken as the peel strength. The results are shown in Table 1. A load cell with a full scale of 20 N was used. The peel strength of Example 1 was "fracture without peeling," which indicates that the peel strength was extremely high.

[0099] [Table 1]

[0100] [Insulated wire manufacturing] Insulated wires were produced according to the procedures shown in the following Examples 10 and 11 and Comparative Examples 3 and 4. Table 2 shows the insulating coating materials used to form the adhesive layer and insulating film that constitute each insulated wire.

[0101] Example 10 After applying insulating paint 12 for the adhesion layer onto a copper conductor (copper wire with a diameter of 0.994 mm), the wire was passed through a heating furnace set to continuously increase the temperature from 350°C to 430°C from the entrance to the exit, and the baking process was repeated seven times for one minute. Next, after applying insulating paint 8, the product was passed through a heating furnace set so that the temperature continuously increased from 350°C to 430°C from the entrance to the exit, and the baking process was repeated 10 times for 1 minute, forming an insulating film consisting of 10 insulating layers. In this way, an insulated wire having an insulating coating was produced by forming an adhesive layer and an insulating film in this order on a copper conductor. At this time, the total thickness of the adhesive layer and the insulating film (thickness of the insulating coating) was 37 μm.

[0102] Example 11 After applying insulating paint 2 onto a copper conductor (copper wire with a diameter of 0.995 mm), the conductor was passed through a heating furnace set to continuously increase the temperature from 350°C to 430°C from the entrance to the exit, and the baking process was repeated 17 times for one minute to form an insulating film consisting of 17 insulating layers. In this way, an insulating film was formed on the copper conductor to produce an insulated wire. At this time, the thickness of the insulating film (insulating film) (total thickness of the insulating layer) was 38 μm.

[0103] (Comparative Example 3) After applying insulating paint 10 onto a copper conductor (copper wire with a diameter of 0.997 mm), the conductor was passed through a heating furnace set to continuously increase the temperature from 350°C to 430°C from the inlet to the outlet, and the baking process was repeated 17 times for one minute to form an insulating film consisting of 17 insulating layers. In this way, an insulating film was formed on the copper conductor to produce an insulated wire. At this time, the thickness of the insulating film (insulating film) (total thickness of the insulating layers) was 37 μm.

[0104] Comparative Example 4 After applying insulating paint 11 onto a copper conductor (copper wire with a diameter of 0.991 mm), the conductor was passed through a heating furnace set to continuously increase the temperature from 350°C to 430°C from the inlet to the outlet, and the baking process was repeated 17 times for one minute to form an insulating film consisting of 17 insulating layers. In this way, an insulating film was formed on the copper conductor to produce an insulated wire. At this time, the thickness of the insulating film (insulating film) (total thickness of the insulating layers) was 37 μm.

[0105] [Evaluation of insulated wire characteristics] The insulated wires obtained in Examples 10 and 11 and Comparative Examples 3 and 4 were subjected to the following characteristic evaluations.

[0106] <Insulation film floating length> The length of the insulation film lift was measured in accordance with the method specified in "5.5 Adhesion Test" of JISC3216-3 (Winding Test Methods - Part 3: Mechanical Properties). The results are shown in Table 2. The lift of the insulation film is an indicator of peeling between adjacent insulation layers inside the insulation film. [Table 2]

[0107] In the evaluation of the laminated film, the peel strengths of Examples 1 to 9 were sufficiently greater than those of Comparative Examples 1 and 2, indicating good interlayer adhesion. Furthermore, the insulated wires of Examples 10 and 11 showed a lifting length of the insulating coating of 0 mm in the cut extension test, indicating no lifting of the insulating coating and good adhesion. [Explanation of symbols]

[0108] 10 Insulated wire 1 conductor 2. Insulating film 3. Insulation layer 4. Insulation layer

Claims

1. An insulating paint comprising a polyimide resin, a nanofiller and a dispersant.

2. 2. The insulating varnish according to claim 1, wherein the dispersant is blended in a proportion of 0.1 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the polyimide resin.

3. The insulating varnish according to claim 1 or 2, wherein the nanofiller is blended in an amount of 1 part by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the polyimide resin.

4. An insulating film having a plurality of insulating layers formed from the insulating paint according to claim 1 or 2.

5. A conductor; an insulating coating that covers the conductor; An insulated wire, wherein the insulating coating comprises the insulating film according to claim 4.

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