Insulating coating material, insulating film, insulating coating, and insulated wire

Abstract

This insulating coating material is composed of a polyimide-based resin, a nanofiller, and a polyurethane resin. In the insulating coating material, the polyurethane resin is added at a ratio of 0.1 to 5 parts by mass, inclusive, per 100 parts by mass of the polyimide-based resin.

Description

Insulating paint, insulating film, insulating coating and insulated wire

[0001] The present invention relates to an insulating paint, an insulating film, an insulating coating, and an insulated wire.

[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, followed by baking the varnish to form insulating layers, which are then repeatedly formed into insulating layers consisting of multiple insulating varnish layers. However, when polyimide resins such as polyamic acid are used as the resin contained in the insulating varnish, the adhesion between the insulating varnish layers is poor, and improvement is particularly desired.

[0004] Non-Patent Document 1 discloses an insulating film obtained by forming an insulating layer (second insulating layer) containing polyimide imidized by applying and baking a varnish containing polyamic acid on the surface of an insulating layer (first insulating layer) containing polyimide imidized by applying and baking a varnish containing polyamic acid. The document discloses that in this insulating film, the surface of the first insulating layer is stable, and interpenetration between the polyimide in the first insulating layer and the polyamic acid in the varnish applied later does not occur between the first insulating layer and the second insulating layer, resulting in no adhesion between adjacent insulating layers.

[0005] SFTead et al, “Interdiffusion at polyimide interfaces”, Polymer, 1992, Volume 33, Number 16, p.3382-3387

[0006] An object of the present invention is to provide an insulating coating material capable of forming an insulating film or insulating layer including multiple insulating monolayers with excellent interlayer adhesion. Another object of the present invention is to provide an insulating film or insulating layer including multiple insulating monolayers with excellent interlayer adhesion, and an insulated wire including multiple insulating monolayers with excellent interlayer adhesion.

[0007] The present invention provides the following insulating varnish, insulating film, insulating coating, and insulated wire. Item 1. An insulating varnish comprising a polyimide resin, a nanofiller, and a polyurethane resin, wherein the polyurethane resin is blended in an amount of 0.1 to 5 parts by mass per 100 parts by mass of the polyimide resin. Item 2. The insulating varnish according to Item 1, wherein the nanofiller is blended in an amount of 1 to 30 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 polyimide resin contains a polyamic acid. Item 4. The insulating varnish according to Item 3, wherein the polyamic acid is imidized to form a resin having a repeating structure represented by the following formula (1): (In formula (1), R １ is a tetravalent group and is an organic group having one or two benzene rings. ２ represents a divalent aromatic hydrocarbon group, and n is a positive integer. Item 5. The insulating varnish according to any one of Items 1 to 4, wherein the nanofiller is represented by the following formula (1A): Al ２ O ３ ・mH ２ O (1A) (In formula (1A), m is 0 to 3.) Item 6. The insulating veneer according to Item 5, wherein the nanofiller is boehmite. Item 7. The insulating veneer according to any one of Items 1 to 6, wherein the nanofiller is a nanofiller that has been brought into contact with a surface treatment agent. Item 8. The insulating veneer according to Item 7, wherein the surface treatment agent is a phosphoric acid-based surface treatment agent. Item 9. The insulating veneer according to Item 7 or 8, wherein the amount of the surface treatment agent is 5 parts by mass or more per 100 parts by mass of the nanofiller. Item 10. The insulating veneer according to any one of Items 1 to 9, wherein the total content of the polyimide resin and the nanofiller is 10 to 30 mass%. Item 11. An insulating film having a plurality of insulating monolayers formed from the insulating veneer according to any one of Items 1 to 10. Item 12. An insulating coating comprising an insulating layer having a plurality of insulating monolayers formed from the insulating veneer according to any one of Items 1 to 10. Item 13. Item 13. An insulated wire comprising a conductor and an insulating coating covering the conductor, the insulating coating being the insulating coating according to Item 12.

[0008] According to the present invention, it is possible to provide an insulating coating material capable of forming an insulating film or insulating layer including a plurality of insulating monolayers with excellent interlayer adhesion, and also to provide an insulating film, insulating coating, and insulated wire including a plurality of insulating monolayers with excellent interlayer adhesion.

[0009] Fig. 1 is a schematic cross-sectional view showing an example of an insulated wire according to an embodiment of the present invention. Fig. 2 is a schematic cross-sectional view showing another example of an insulated wire according to an embodiment of the present invention. Fig. 3 is a schematic cross-sectional view showing another example of an insulated wire according to an embodiment of the present invention. Fig. 4 is a schematic cross-sectional view showing another example of an insulated wire according to an embodiment of the present invention.

[0010] Several embodiments of the insulating varnish, insulating film, insulating coating, and insulated wire according to one aspect of the present invention are described in detail below. In this specification, a numerical value connected with "to" means a numerical range that includes the numerical values ​​before and after "to" as the lower and upper limits. When multiple lower limit values ​​and multiple upper limit values ​​are listed separately, any lower limit value and any upper limit value can be selected and connected with "to."

[0011] <Insulating varnish> The insulating varnish of the present invention contains a polyimide resin, a nanofiller, and a polyurethane resin. Here, the polyurethane resin is blended in a ratio of 0.1 to 5 parts by mass per 100 parts by mass of the polyimide resin. That is, the content of the polyurethane resin is 0.1 to 5 parts by mass per 100 parts by mass of the polyimide resin. The insulating varnish of the present invention makes it possible to form an insulating film or insulating layer including multiple insulating monolayers with excellent interlayer adhesion.

[0012] (Polyimide Resin) The polyimide resin is a polyimide resin or a polyimide resin precursor. The polyimide resin may be a mixture of a polyimide resin and a polyimide resin precursor. In addition, the polyimide resin and the polyimide resin precursor are preferably resins having an aromatic group from the viewpoints of heat resistance and insulating properties.

[0013] 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.

[0014] A more preferred polyimide resin is a resin having a repeating structure of the following formula (1). The polyimide resin precursor is also preferably a precursor (polyamic acid) that becomes a resin (polyimide resin) having a 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. In the polyimide resin, the repeating structure of the following formula (1) may be of one type or of two or more types.

[0015]

[0016] 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 any one of the structures shown in the following formula (2) alone, or a copolymer having two or more kinds of the structures.

[0017]

[0018] In the formula (1), more preferred R １ is at least one of the structures exemplified in the following formula (3).

[0019]

[0020] In addition, in the formula (1), R ２ represents a divalent group derived from an aromatic hydrocarbon (a divalent aromatic hydrocarbon group). ２ When contains a plurality of divalent aromatic hydrocarbon groups (including a combination of two or more types), these are -O-, -SO ２ -, -CO-, -CH ２They may be linked via at least one bonding group selected from the group consisting of - and S-.

[0021] R ２ The aromatic hydrocarbon group represented by the formula (1) (an aromatic hydrocarbon group having or not having the above-mentioned bonding group) is, for example, at least one of the structures exemplified in the following formula (4).

[0022]

[0023] R represented by the formula (4) ２ Among these, at least one of the structures exemplified in the following formula (5) is preferred.

[0024]

[0025] 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). The solvent contained in the insulating coating material of the present invention is preferably a solvent having a boiling point of 100°C or higher at 1 atmosphere (hereinafter referred to as "solvent A"), and the proportion of solvent A is preferably 90% by mass or higher. Therefore, when the polyimide resin is used in a form dissolved or dispersed in a solvent, it is preferable to prepare or select a solvent for dissolving or dispersing the polyimide resin so that the proportion of solvent A in the solvent contained in the insulating coating material of the present invention is 90% by mass or higher.

[0026] 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 can also be used as solvents for dissolving or dispersing polyimide resins. Common organic solvents include 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, petroleum naphtha-based solvents, etc. The above solvents may be used alone or in combination. However, as mentioned above, from the viewpoint of ensuring that the proportion of solvent A in the solvent contained in the insulating coating material of the present invention is 90 mass % or more, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, γ-butyrolactone, sulfolane, dimethyl sulfoxide, or cyclohexanone are preferably used as solvents for dissolving or dispersing polyimide resins.

[0027] (Nanofiller) The nanofiller is a nano-sized filler, and is preferably at least one of a nano-sized metal oxide and a hydrate thereof.

[0028] The nanofiller is, for example, represented by the following formula (1A): Al ２ O ３ ・mH ２ O (1A)

[0029] In formula (1A), m is an integer of 0 to 3. When m is 0, formula (1A) represents aluminum oxide (alumina particles). This aluminum oxide is an alumina such as α-alumina, γ-alumina or β-alumina, ρ-alumina, χ-alumina, ε-alumina, κ-alumina, κ'-alumina, θ-alumina, η-alumina, δ-alumina, or λ-alumina. When m is greater than 0 in formula (1A), formula (1A) represents an alumina hydrate in which alumina is hydrated, and represents, for example, a mixture of various aluminum hydroxides.

[0030] The crystalline form of aluminum hydroxide is trihydroxide (Al(OH) ３ ), and aluminum oxide hydroxide (AlO(OH)). The trihydroxides include gibbsite, bayerite, and nordstrandite. The aluminum oxide hydroxides include boehmite (γ-aluminum oxide hydroxide) and diaspore (α-aluminum oxide hydroxide). The aluminum oxide hydroxide is represented by the formula (1A) where m is 1, and the trihydroxide is represented by the formula (1A) where m is 3. From the viewpoints of stability and ease of production, α-alumina, γ-alumina, or boehmite is preferably used as the nanofiller.

[0031] The aspect ratio (major axis / minor axis) of the nanofiller is not particularly limited and may be, for example, 2 to 99. From the viewpoint of partial discharge resistance, it is preferably 5 to 99, and more preferably 10 to 99.

[0032] In this specification, the aspect ratio refers to the ratio of the major axis to the minor axis of a particle (nanofiller) (major axis / minor axis).

[0033] As the nanofiller, particles of known shapes such as plate-like, fibrous, spindle-like, needle-like, cylindrical, and columnar shapes are used, and anisotropic shapes such as plate-like and columnar shapes are preferred because they provide better partial discharge resistance to the insulating coating of the present invention. Furthermore, the nanofiller may exist as flat particles in which columnar particles are arranged, hollow particles, etc. If hollow particles are used as the nanofiller, the hollow particles can reduce the dielectric constant of the insulating coating and suppress the occurrence of partial discharge, thereby contributing to improving the durability of the insulating coating.

[0034] The nanofiller has an average particle size of about 1 nm to 1000 nm. In addition, when the nanofiller has a flat plate-like structure, the nanofiller also includes particles having a plate thickness (minor axis) of about 1 nm to 1000 nm.

[0035] The average particle diameter of the nanofiller represented by formula (1A) is preferably 1 nm to 1000 nm, more preferably 5 nm to 500 nm, even more preferably 10 nm to 100 nm, and particularly preferably 15 nm to 50 nm, from the viewpoint of improving partial discharge resistance. The average particle diameter is the average diameter obtained by particle diameter measurement using dynamic light scattering. For example, it is the average diameter calculated by the cumulant method in the analysis of the autocorrelation function.

[0036] 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.

[0037] The nanofiller is preferably surface-treated. Examples of surface treatment methods for nanofillers include methods 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, and a method of treating with a carboxylic acid anhydride such as phthalic anhydride. As the nanofiller, a metal oxide hydrate surface-treated with a silane coupling agent or a metal oxide hydrate surface-treated with a phosphoric acid-based surface treatment agent is preferred, and a metal oxide hydrate surface-treated with a phosphoric acid-based surface treatment agent is 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.

[0038] The surface treatment method is not particularly limited, and it is sufficient to contact the nanofiller with a surface treatment agent. For example, when the nanofiller is a powder, a method is used in which a solution of the surface treatment agent in a solvent is sprayed onto the powder using a spray or the like, and then dried at 20 to 60°C. Furthermore, when a metal oxide hydrate sol is used as the nanofiller, a method is used in which the surface treatment agent is added and dissolved in the sol, and then stirred at 20 to 60°C for 1 to 24 hours. 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, even more preferably 15 parts by mass or more, and particularly preferably 19 parts by mass or more. The amount of the surface treatment agent per 100 parts by mass of the nanofiller is preferably 70 parts by mass or less, more preferably 60 parts by mass or less, even more preferably 40 parts by mass or less, and particularly preferably 36 parts by mass or less.

[0039] In the insulating varnish of the present invention, the content of the nanofiller is not particularly limited, but is preferably 1 part by mass or more per 100 parts by mass of polyimide-based resin. When the content of the nanofiller per 100 parts by mass of polyimide-based resin is 1 part by mass or more, partial discharge resistance is improved. From the viewpoint of partial discharge resistance, the lower limit of the content of the nanofiller is more preferably 2 parts by mass, even more preferably 3 parts by mass, even more preferably 5 parts by mass, still more preferably 10 parts by mass, and particularly preferably 15 parts by mass. The content of the nanofiller per 100 parts by mass of polyimide-based resin is preferably 30 parts by mass or less. When the content of the nanofiller per 100 parts by mass of polyimide-based resin is 30 parts by mass or less, the flexibility of the insulating film formed from the insulating varnish is improved. From the viewpoint of the flexibility of the insulating film formed from the insulating varnish, the upper limit of the content of the nanofiller is more preferably 25 parts by mass, and particularly preferably 20 parts by mass.

[0040] In the insulating varnish of the present invention, the total content of the polyimide resin (solid content) and the nanofiller (solid content) is preferably 10 to 30 mass %. In this case, the insulating varnish has excellent nanofiller dispersibility and an industrially suitable viscosity. Furthermore, from the viewpoint of more suitably forming an insulating film with excellent interlayer adhesion, the total content of the polyimide resin (solid content) and the nanofiller (solid content) in the insulating varnish of the present invention is more preferably 12 to 30 mass %, and even more preferably 12 to 25 mass %.

[0041] A nanofiller dispersion may be used when preparing the insulating coating of the present invention. The nanofiller dispersion contains a solvent (dispersion medium) for dispersing the nanofiller. As described above, it is preferable that the proportion of solvent A having a boiling point of 100°C or higher at 1 atmosphere in the solvent contained in the insulating coating of the present invention is 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 for the nanofiller dispersion and the solvent for dissolving or dispersing the polyimide resin may be the same or different, but are preferably the same.

[0042] From the viewpoint of the appearance and uniformity of the resulting insulating film, the dispersion medium for the nanofiller dispersion is preferably a solvent (i.e., solvent A) having a boiling point of 100°C or higher under 1 atmosphere (normal pressure). Examples of dispersion mediums 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 dimethyl sulfoxide. Other common organic solvents can also be used as the dispersion medium for the nanofiller dispersion. Common organic solvents include 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. Only one type of dispersion medium may be used for the nanofiller dispersion, or two or more types may be mixed and used.

[0043] 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.

[0044] (Polyurethane Resin) The insulating coating material of the present invention further contains a polyurethane resin in addition to the polyimide resin and the nanofiller.

[0045] In this embodiment, examples of the polyurethane resin include unmodified polyurethane resin, modified polyurethane resin, and mixtures thereof. Examples of modified polyurethane resin include amine-modified polyurethane resin, silicone-modified polyurethane resin, acrylic-modified polyurethane resin, polyether-based polyurethane resin, polyester-based polyurethane resin, and polycarbonate-based polyurethane resin. When preparing the insulating coating material of the present invention, the polyurethane resin can be used as a polyurethane resin-containing liquid containing the polyurethane resin in a solvent. Commercially available polyurethane resin-containing liquids may be used. Examples of commercially available polyurethane resin-containing liquids include "DISPERBYK-162," "DISPERBYK-168," and "DISPERBYK-184" manufactured by BYK.

[0046] The blending ratio of the polyurethane resin is 0.1 parts by mass or more per 100 parts by mass of polyimide-based resin, from the viewpoint of being able to form an insulating film or insulating layer including multiple insulating monolayers that exhibit excellent interlayer adhesion. The blending ratio of the polyurethane resin is preferably 5 parts by mass or less per 100 parts by mass of polyimide-based resin. In this case, heat resistance can be further improved compared to when the blending ratio of the polyurethane resin exceeds 5 parts by mass. The blending ratio of the polyurethane resin per 100 parts by mass of polyimide-based resin is more preferably 0.1 parts by mass or more but 3.5 parts by mass or less, even more preferably more than 0.2 parts by mass or more but 3.5 parts by mass or less, and particularly preferably 0.3 parts by mass or more but 3.3 parts by mass or less, or 1.1 parts by mass or more but 3.3 parts by mass or less.

[0047] The insulating veneer of the present invention may contain various additives such as lubricants and adhesion improvers, as well as reactive low-molecular-weight compounds, compatibilizers, etc., as necessary, within the scope of the present invention. The insulating veneer of the present invention may be an insulating veneer that does not contain boron nitride, or may be an insulating veneer that does not contain boron nitride and has a particle diameter (D90) of 1 to 20 μm. The insulating veneer of the present invention may be an insulating veneer that does not contain nanosilica, or may be an insulating veneer that does not contain nanosilica and has an average particle diameter of 1 to 200 nm. The insulating veneer of the present invention may be an insulating veneer that does not contain boron nitride and nanosilica, or may be an insulating veneer that does not contain boron nitride and has a particle diameter (D90) of 1 to 20 μm and nanosilica and has an average particle diameter of 1 to 200 nm.

[0048] <Insulating Film> The insulating film or insulating layer of the present invention has multiple insulating monolayers formed from the insulating varnish described above. When the polyimide resin contained in the insulating varnish is a polyimide resin, the insulating monolayers are formed by drying the insulating varnish and removing the solvent. That is, the insulating monolayers contain a polyimide resin, a polyurethane resin, and a nanofiller. When the polyimide resin contained in the insulating varnish is a polyimide resin precursor (polyamic acid), the insulating monolayers are formed by imidizing the insulating varnish and removing the solvent during the drying process. That is, the insulating monolayers contain an imidized product of the polyimide resin precursor (polyamic acid), a polyurethane resin, and a nanofiller. The imidized product of the polyimide resin precursor (polyamic acid) is a polyimide resin.

[0049] The insulating monolayer contains a polyimide resin. The lower limit of the polyimide resin content in the insulating monolayer is not particularly limited, but is preferably 50% by mass, more preferably 60% by mass. The upper limit of the polyimide resin content is preferably 97% by mass, more preferably 90% by mass, and even more preferably 85% by mass.

[0050] In the insulating single layer, the blending ratio of polyurethane resin to 100 parts by mass of polyimide resin is preferably 0.1 to 5 parts by mass, more preferably more than 0.2 parts by mass and not more than 3.5 parts by mass, even more preferably 0.3 to 3.3 parts by mass, and particularly preferably 1.1 to 3.3 parts by mass.

[0051] In the insulating single layer, 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, still more preferably 10 to 25 parts by mass, and particularly preferably 15 to 25 parts by mass.

[0052] The laminated structure of the insulated conductor according to the embodiment of the present invention includes at least a conductor 1 and an insulating coating including an insulating layer 2. Specifically, the insulated conductor 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 layer 2 laminated on the conductor 1, as shown in Fig. 1 , for example.

[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 above-described insulating layer at least in part, and the insulating layer has a plurality of insulating monolayers formed from the above-described insulating varnish. By having such a configuration, the insulated wire according to an embodiment of the present invention has excellent adhesion between the insulating monolayers. Hereinafter, the insulated wire according to an embodiment of the present invention will be described in detail with reference to FIGS. 1 to 5.

[0054] As described above, the insulated wire 10 has at least the conductor 1 and the insulating coating 11 including the insulating layer 2 formed from the insulating varnish of the present invention (see FIGS. 1 and 2), and the insulating coating 11 may further have other layers ( FIGS. 3 to 5). For example, the insulating coating 11 may further have an insulating layer 3 provided on the outside of the insulating layer 2 ( FIGS. 3, 4, and 5), or an insulating layer 4 provided on the inside of the insulating layer 2 ( FIGS. 4 and 5).

[0055] The insulating layer 4 may be an adhesive layer provided between the conductor 1 and the insulating layer 2. The adhesive layer may contain the polyurethane resin described above.

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

[0057] An 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 a central portion and an insulating coating 11 having an insulating layer 2 formed on the outer periphery of the conductor 1, as shown in Figures 2 to 5, for example. Examples of the cross-sectional shape of the insulated wire 10 according to an embodiment of the present invention include a circle, an ellipse, and a polygon (which may be a rectangular shape or an irregular shape). Figures 2 to 4 show an insulated wire having a circular cross-section. Figure 5 shows an insulated wire having a substantially rectangular cross-section. When the cross-sectional shape 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 layer 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 11 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 11 may be 200 μm or less, 100 μm or less, or 50 μm or less.

[0062] The insulated wire 10 according to the embodiment of the present invention can be produced by coating a conductor 1 with an insulating coating 11 having an insulating layer 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, multiple times to form the insulating layer 2 including multiple insulating monolayers, thereby obtaining the insulating coating 11.

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

[0064] For example, the insulated wire 10 according to the embodiment of the present invention can be manufactured by applying an insulating varnish to the surface of the wire-shaped conductor 1 and baking it as necessary. Specifically, the insulating varnish is applied to the conductor 1 to a predetermined thickness, and then heated 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 layer 2 reaches the predetermined thickness, thereby manufacturing the insulated wire 10.

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

[0066] When forming the insulating layer 2, it is preferable to use an insulating coating material in which a resin is dissolved or dispersed in a solvent and a nanofiller is dispersed. This insulating coating material is applied to the surface of the conductor 1 and baked as necessary to form the insulating layer 2. Suitable solvents for dissolving or dispersing polyimide resins and polyurethane 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 solvents, lactone solvents, and glycol ether solvents, primarily 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, and homomixer. The mixing temperature is typically 5 to 30°C.

[0067] The insulating paint may contain an acid component or an alkali component to stabilize dispersion. The insulating paint may contain water, a low-boiling alcohol, or a low-viscosity solvent that contributes to reducing the viscosity of the insulating paint. If necessary, other metal oxide hydrates or metal oxides may be mixed into the insulating paint, and additives may be added to impart hydrophobicity or improve dispersibility. As the additive, fluorine-based additives, silicone-based additives, citric acid, ethylenediaminetetraacetic acid, or 8-quinolinol are preferably used.

[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] The polyimide resin solution used was "Meirejicoat" manufactured by Nagoya Chemical Industry Co., Ltd., which contains a polyimide resin precursor (polyamic acid). The polyamic acid is a polyamic acid obtained by polymerizing pyromellitic dianhydride and diaminodiphenyl ether.

[0071] [Insulating Varnish] Insulating varnishes were prepared according to the procedures shown in the following Production Examples 1 to 11.

[0072] Production Example 1: To an NMP-dispersed boehmite sol [product name: Alumina NMP Sol A1-10 (containing 10% by weight of boehmite), average boehmite particle size: 15 nm × 50 nm (minor axis × major axis), manufactured by Kawaken Fine Chemicals Co., Ltd.], 20 parts by weight of phenylphosphonic acid per 100 parts by weight of boehmite (equivalent to alumina) and 24 parts by weight of 8-quinolinol (manufactured by Tokyo Chemical Industry Co., Ltd.) per 100 parts by weight of boehmite (equivalent to alumina) were added, and the resulting solution was stirred at room temperature for 1 hour to obtain an NMP-dispersed boehmite sol (first dispersion) containing phenylphosphonic acid surface-treated boehmite. Next, the first dispersion was added at room temperature to the above polyimide resin solution containing polyamic acid so that the boehmite was present in an alumina equivalent amount of 15 parts by weight per 85 parts by weight of polyamic acid, and the mixture was uniformly mixed and dispersed using a planetary centrifugal mixer to obtain a second dispersion. Furthermore, a polyurethane resin solution (product name "DISPERBYK-162", manufactured by BYK, amine value: 13 mgKOH / g) serving as a polyurethane resin-containing liquid was added to the second dispersion in a ratio of 2.34 parts by mass of polyurethane resin (modified polyurethane resin) 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. In insulating paint 1, the total content of polyamic acid and boehmite was 18% by mass.

[0073] <Production Example 2> Insulating coating material 2 was obtained in the same manner as in Production Example 1, except that the polyurethane resin solution was changed from "DISPERBYK-162" to "DISPERBYK-168 (product name, manufactured by BYK Corporation, amine value: 11 mgKOH / g)" and the blending ratio of the polyurethane resin per 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> Insulating coating material 3 was obtained in the same manner as in Production Example 1, except that the polyurethane resin solution was changed from "DISPERBYK-162" to "DISPERBYK-184 (product name, manufactured by BYK Corporation, amine value: 15 mg KOH / g)" and the blending ratio of the polyurethane resin per 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 coating material 4 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", the polyurethane resin solution was changed from "DISPERBYK-162" to "DISPERBYK-168", and the blending ratio of polyurethane resin 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 coating material 5 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", the polyurethane resin solution was changed from "DISPERBYK-162" to "DISPERBYK-168", and the blending ratio of polyurethane resin 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 coating material 6 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", the polyurethane resin solution was changed from "DISPERBYK-162" to "DISPERBYK-168", and the blending ratio of polyurethane resin 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 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", the polyurethane resin solution was changed from "DISPERBYK-162" to "DISPERBYK-168", and the blending ratio of polyurethane resin 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 coating material 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 polyurethane resin 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 polyurethane resin solution was not added.

[0081] <Production Example 10> Insulating coating material 10 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 polyurethane resin solution was added.

[0082] <Production Example 11> A polyurethane resin solution (product name "DISPERBYK-162", manufactured by BYK Corporation) was added to the above polyimide resin solution containing polyamic acid as a polyimide resin so that the blending ratio of the polyurethane resin to 100 parts by mass of polyamic acid was 0.90 parts by mass, and the mixture was mixed using a three-one motor to obtain insulating coating material 11 for an adhesion layer.

[0083] [Production of Laminated Films] 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.

[0084] Example 1: Using a blade coater, insulating paint 1 was applied to the surface of a 36.4 cm x 51.5 cm PET film to a coating thickness of 350 μm. The insulating paint 1 was dried in a fan dryer at 90°C for 80 minutes to obtain a dried film, and then a 20 cm x 27 cm dried film was peeled off from the PET film. The peeled dried film was fixed to a horizontally positioned pin tenter with the side that had been in contact with the air during drying facing up, and baked in a baking oven at 150°C for 10 minutes, 200°C for 10 minutes, and 350°C for 30 minutes to obtain a first insulating layer film. Next, the first insulating layer film was removed from the pin tenter and attached to a coating table with the top side facing up. A 1 cm wide x 20 cm long Kapton tape was then attached to the surface of the first insulating layer film approximately 2 cm from one end (the end of the short side). Next, insulating varnish 1 was applied to the upper surface of the film of the first insulating layer to a thickness of 500 μm. However, the insulating varnish 1 was not applied to the area from one end to approximately half the width of the Kapton tape, so that the Kapton tape could be peeled back later to easily separate the first insulating layer from the second insulating layer. The insulating varnish 1 applied to the first insulating layer was then dried in a fan dryer at 90°C for 40 minutes. Because the insulating varnish 1 does not adhere well to the Kapton tape, another coating of insulating varnish 1 was applied to the Kapton tape and dried again at 90°C for 40 minutes. The resulting film was fixed with a pin tenter and baked in a baking machine at 150°C for 10 minutes, 200°C for 10 minutes, and 350°C for 30 minutes to form a second insulating layer on the first insulating layer. In this manner, a laminated film consisting of a first insulating layer and a second insulating layer was obtained.

[0085] 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.

[0086] Example 3 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 3.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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 9.

[0093] 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 10.

[0094] [Evaluation of Laminated Film] The laminated films obtained in the Examples and Comparative Examples were subjected to the following peel test.

[0095] [Preparation of Peel Test Samples] For the laminate films obtained in the Examples and Comparative Examples, a portion (peeled portion) of the laminated portion between the first insulating layer and the second insulating layer was carefully peeled off, starting 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 laminate 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. A 7.5 cm piece of double-sided tape was attached to the surface of the first insulating layer (the surface opposite the second insulating layer), and the laminate film was attached to a 3 cm x 12 cm x 1 mm thick aluminum plate with the double-sided tape to prepare a peel test sample.

[0096] [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. A handle made of cellophane tape was attached to the upper chuck. The upper chuck was set to move at a speed of 50 mm / min, and a 90° peel test was performed with a chuck movement distance of 15 mm to 50 mm. The average value of the peel test force 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" (see Table 1), which indicates that the peel strength was extremely high.

[0097]

[0098] [Production of Insulated Wires] Insulated wires were produced according to the procedures shown in the following Examples 9 and 10 and Comparative Examples 3 and 4. Table 2 shows the insulating coatings used to form the adhesive layer and insulating film constituting each insulated wire.

[0099] Example 9: An insulating coating 11 for the adhesion layer was applied to a copper conductor (copper wire with a diameter of 0.994 mm). The wire was then baked by passing it through a heating furnace set to continuously increase the temperature from 350°C to 430°C over one minute. This process was repeated seven times. Next, an insulating coating 8 was applied to the wire. The wire was then baked by passing it through a heating furnace set to continuously increase the temperature from 350°C to 430°C over one minute. This process was repeated ten times to form an insulating layer consisting of ten single insulating layers. In this way, an insulated wire was produced having an insulating coating formed by forming an adhesion layer and an insulating layer on the copper conductor in this order. The total thickness of the adhesion layer and insulating layer (thickness of the insulating coating) was 37 μm.

[0100] (Example 10) After applying insulating varnish 2 to a copper conductor (copper wire with a diameter of 0.995 mm), the wire was baked by passing it through a heating furnace set to continuously increase the temperature from 350°C to 430°C from the inlet to the outlet over one minute. This process was repeated 17 times to form an insulating layer consisting of 17 insulating single layers. In this way, an insulating coating consisting of insulating layers was formed on the copper conductor, and an insulated wire was produced. The thickness of the insulating layer (insulating coating) (total thickness of the 17 insulating single layers) was 38 μm.

[0101] (Comparative Example 3) After applying insulating varnish 9 to a copper conductor (copper wire with a diameter of 0.997 mm), the wire was baked by passing it through a heating furnace set to continuously increase the temperature from 350°C to 430°C from the inlet to the outlet over one minute. This process was repeated 17 times to form an insulating layer consisting of 17 insulating single layers. In this way, an insulating coating consisting of insulating layers was formed on the copper conductor, and an insulated wire was produced. At this time, the thickness of the insulating layer (insulating coating) (total thickness of the 17 insulating single layers) was 37 μm.

[0102] (Comparative Example 4) After applying the insulating varnish 10 to a copper conductor (copper wire with a diameter of 0.991 mm), the wire was baked by passing it through a heating furnace set to continuously increase the temperature from 350°C to 430°C from the inlet to the outlet over one minute. This process was repeated 17 times to form an insulating layer consisting of 17 insulating single layers. In this way, an insulating coating consisting of insulating layers was formed on the copper conductor, and an insulated wire was produced. At this time, the thickness of the insulating layer (insulating coating) (total thickness of the 17 insulating single layers) was 37 μm.

[0103] [Evaluation of Characteristics of Insulated Wire] The insulated wires obtained in Examples 9 and 10 and Comparative Examples 3 and 4 were evaluated for the following characteristics.

[0104] <Length of lifted insulation film> The length of lifted insulation film was measured in accordance with the method specified in "5.5.1 Enamelled rectangular wire" of JIS C3216-3 (Winding test methods - Part 3: Mechanical properties). The results are shown in Table 2. The lifted insulation film is a raised portion on the surface of the insulation film, and serves as a measure of peeling between adjacent insulating layers inside the insulation film.

[0105] In the evaluation of the laminated film, the peel strength of Examples 1 to 8 was significantly greater than that of Comparative Examples 1 and 2, indicating good interlayer adhesion. Furthermore, the insulated wires of Examples 9 and 10 had a length of 0 mm of insulation film lift in the winding test, indicating no lift of the insulation film and good adhesion.

[0106] REFERENCE SIGNS LIST 1 Conductor 2 Insulating layer formed from the insulating coating material of the present invention 3 Insulating layer 4 Insulating layer 10 Insulated wire 11 Insulating coating

Claims

1. An insulating paint comprising a polyimide resin, a nanofiller, and a polyurethane resin, wherein the polyurethane resin is blended in a ratio of 0.1 to 5 parts by mass per 100 parts by mass of the polyimide resin.

2. The insulating varnish according to claim 1, 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.

3. The insulating varnish according to claim 1 or 2, wherein the polyimide resin contains polyamic acid.

4. The insulating varnish according to claim 3, wherein the polyamic acid is imidized to form a resin having a repeating structure represented by the following formula (1): (In formula (1), R １ is a tetravalent group and is an organic group having one or two benzene rings. ２ represents a divalent aromatic hydrocarbon group, and n is a positive integer.

5. The insulating varnish according to claim 1 or 2, wherein the nanofiller is represented by the following general formula (1A): Al ２ O ３ ・mH ２ O (1A) (In formula (1A), m is 0 to 3.) 6. The insulating paint according to claim 5, wherein the nanofiller is boehmite.

7. The insulating paint according to claim 1 or 2, wherein the nanofiller is a nanofiller that has been contacted with a surface treatment agent.

8. The insulating paint according to claim 7, wherein the surface treatment agent is a phosphoric acid-based surface treatment agent.

9. The insulating coating according to claim 7, wherein the amount of the surface treatment agent is 5 parts by mass or more per 100 parts by mass of the nanofiller.

10. The insulating varnish according to claim 1 or 2, wherein the total content of the polyimide resin and the nanofiller is 10 to 30 mass %.

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

12. An insulating coating comprising an insulating layer having a plurality of insulating monolayers formed from the insulating paint according to claim 1 or 2.

13. An insulated wire comprising: a conductor; and an insulating coating covering the conductor, wherein the insulating coating is the insulating coating according to claim 12.

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