JP7214625B2 - insulated wire - Google Patents

Description

The present invention relates to insulated wires. This application claims priority based on Japanese application No. 2017-069028 filed on March 30, 2017, and incorporates all the descriptions described in the Japanese application.

In electrical equipment with high applied voltage, such as motors used at high voltage, high voltage is applied to the insulated wires that constitute the electrical equipment, and partial discharge (corona discharge) is likely to occur on the surface of the insulation layer. If corona discharge causes a local rise in temperature, generation of ozone, generation of ions, etc., dielectric breakdown occurs early, shortening the life of the insulated wires and, by extension, electrical equipment. For this reason, insulated wires used in electrical equipment with high applied voltage are required to have improved corona discharge inception voltage in addition to excellent electrical insulation properties, mechanical strength, and the like.

As a device for increasing the corona discharge inception voltage, it is effective to lower the dielectric constant of the insulating layer, and one of the methods for lowering the dielectric constant is to form pores in the insulating layer.

As a method for forming pores in the insulating layer, a method using a foaming agent such as azobisisobutyronitrile or a thermally expandable microcapsule (see JP-A-5-20928 and JP-A-8-77849), and A method of using a mixed solvent of a solvent for a thermosetting resin, a solvent having a boiling point higher than that of the solvent, and an air bubble forming agent has been proposed.

JP-A-5-20928 JP-A-8-77849

An insulated wire according to one aspect of the present invention is an insulated wire including a linear conductor and an insulating layer covering an outer peripheral surface of the conductor, wherein the insulating layer includes a plurality of pores, and the insulating layer The porosity is 20% by volume or more and 65% by volume or less, and the film thickness of the insulating layer is measured at 8 points in each cross section at 30 cross sections at intervals of 50 cm in the longitudinal direction of the insulated wire. The variation ratio of the following formula (1) calculated from the measured values is 25% or less.
Variation rate (%)=(4σ/average film thickness)×100 (1)
(In the above formula (1), the average film thickness indicates the average value of each measured value, and σ indicates the standard deviation of each measured value.)

1 is a schematic cross-sectional view of an insulated wire according to an embodiment of the present invention; FIG. It is a figure for demonstrating the measuring method of the variation ratio in an Example. FIG. 3 is a schematic diagram for explaining a method of measuring a dielectric constant in Examples.

[Problems to be Solved by the Present Disclosure]
In general, the dielectric constant can be lowered by increasing the porosity of the insulating layer. However, in the insulating layer formed by the above-described conventional technique, it is difficult to control the foaming ratio of the foaming agent, or multiple solvents with different volatilization speeds are used. becomes non-uniform around the cross-section of the conductor. In addition, the thickness of the insulating layer greatly affects the insulating properties and strength of the insulated wire, and there is a possibility that the insulating properties and strength may be insufficient particularly in a portion where the insulating layer is thin. Furthermore, in recent years, rectangular conductors having a substantially rectangular cross section have been widely used because of their high space factor and the ability to reduce the size of various devices. However, when this rectangular conductor is used, the thickness of the insulating layer tends to become non-uniform, so that the insulating properties and strength of the insulated wire tend to deteriorate. In addition, if a rectangular conductor having an insulating layer with an uneven thickness is used, the electric wires do not contact each other in the winding state, creating an unnecessary space, which may reduce the space factor.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an insulated wire excellent in insulation and strength while achieving a low dielectric constant of an insulating layer.

[Effect of the present disclosure]

The insulated wire of the present invention is excellent in insulation and strength while achieving a low dielectric constant of the insulating layer.

[Description of the embodiment of the present invention]
An insulated wire according to one aspect of the present invention is an insulated wire including a linear conductor and an insulating layer covering an outer peripheral surface of the conductor, wherein the insulating layer includes a plurality of pores, and the insulating layer The porosity is 20% by volume or more and 65% by volume or less, and the film thickness of the insulating layer is measured at 8 points in each cross section at 30 cross sections at intervals of 50 cm in the longitudinal direction of the insulated wire. The variation ratio of the following formula (1) calculated from the measured values is 25% or less.
Variation rate (%)=(4σ/average film thickness)×100 (1)
(In the above formula (1), the average film thickness indicates the average value of each measured value, and σ indicates the standard deviation of each measured value.)

The insulated wire includes pores in the insulating layer, and by setting the porosity of the insulating layer within the above range, it is possible to achieve a low dielectric constant of the insulating layer. In addition, in the insulated wire, the variation ratio of the thickness of the insulating layer is set to the above value or less, and the uniformity of the thickness is improved, so that the minimum thickness can be reduced, and as a result, the corona discharge inception voltage is improved. It has excellent insulation and strength. Here, the "porosity" means the percentage of the volume of pores to the volume of the insulating layer including pores.

The average film thickness of the insulating layer is preferably 60 μm or more. Thus, by setting the average film thickness of the insulating layer to the above value or more, the insulated wire can further improve the insulating properties and strength.

The conductor is preferably a rectangular conductor having a rectangular cross section. Even in the case of a rectangular conductor in which it is generally difficult to make the film thickness of the insulating layer uniform, it is possible to achieve a low dielectric constant of the insulating layer and to obtain an insulated wire having excellent insulating properties and strength.

[Details of the embodiment of the present invention]
Hereinafter, an insulated wire and a method for manufacturing an insulated wire according to an embodiment of the present invention will be described with reference to the drawings.

[Insulated wire]
The insulated wire shown in FIG. 1 includes a linear conductor 1 and an insulating layer 2 covering the outer peripheral surface of the conductor 1 . This insulating layer 2 contains a plurality of pores 3 .

<Conductor>
Examples of the cross-sectional shape of the conductor 1 include polygonal shapes such as circular, elliptical, racetrack, hexagonal, triangular, square, and rectangular shapes. As the conductor 1, among these, a square conductor with a square cross section or a rectangular conductor with a rectangular cross section is preferable.
Also, the conductor 1 may be a twisted wire obtained by twisting a plurality of strands.

As a material for the conductor 1, a metal having high electrical conductivity and high mechanical strength is preferable. Examples of such metals include copper, copper alloys, aluminum, nickel, silver, soft iron, steel, and stainless steel. As the conductor 1, a material in which these metals are formed into a linear shape, or a multi-layered structure in which such a linear material is further coated with another metal, such as nickel-coated copper wire, silver-coated copper wire, copper-coated aluminum wire, copper-coated steel wire, or the like can be used.

The lower limit of the average cross-sectional area of the conductor 1 is preferably 0.01 mm ² , more preferably 0.1 mm ² . On the other hand, the upper limit of the average cross-sectional area of the conductor 1 is preferably 20 mm ² , more preferably 5 mm ² . If the average cross-sectional area of the conductor 1 is less than the above lower limit, the volume of the insulating layer 2 with respect to the conductor 1 increases, and the volume efficiency of a coil or the like formed using the insulated wire may decrease. Conversely, if the average cross-sectional area of the conductor 1 exceeds the above upper limit, the insulating layer 2 must be formed thick enough to sufficiently lower the dielectric constant, and the insulated wire may unnecessarily increase in diameter. be.

<Insulating layer>
The insulating layer 2 includes a plurality of pores 3, as shown in FIG.

The lower limit of the porosity of the insulating layer 2 is 20% by volume, preferably 25% by volume, and more preferably 30% by volume. On the other hand, the upper limit of the porosity of the insulating layer 2 is 65% by volume, preferably 60% by volume, and more preferably 55% by volume. If the porosity of the insulating layer 2 is less than the above lower limit, the dielectric constant of the insulating layer 2 may not sufficiently decrease, and the corona discharge inception voltage may not be sufficiently improved. Conversely, if the porosity of the insulating layer 2 exceeds the above upper limit, the strength of the insulated wire may not be ensured. The porosity (% by volume) of the insulating layer 2 is calculated by multiplying the apparent volume V1 calculated from the outer shape of the insulating layer 2 by the density ρ1 of the material of the insulating layer 2 and the mass W1 when there are no pores, and the insulating It is a value obtained from the actual mass W2 of the layer 2 by the formula (W1−W2)×100/W1.

The lower limit of the average film thickness of the insulating layer 2 is preferably 10 μm, more preferably 60 μm, still more preferably 80 μm, and particularly preferably 100 μm. On the other hand, the upper limit of the average film thickness of the insulating layer 2 is preferably 300 μm, more preferably 200 μm. If the average film thickness of the insulating layer 2 is less than the above lower limit, the insulating layer 2 may break, and the insulation of the conductor 1 may become insufficient. Conversely, if the average film thickness of the insulating layer 2 exceeds the above upper limit, there is a risk that the volumetric efficiency of a coil or the like formed using the insulated wire will be low.

The upper limit of the variation ratio of the film thickness of the insulating layer 2 is 25%, preferably 20%, more preferably 15%, even more preferably 12%, and particularly preferably 10%. On the other hand, the lower limit of the variation ratio of the film thickness of the insulating layer 2 is preferably 1%, more preferably 5%. If the variation ratio of the thickness of the insulating layer 2 exceeds the above upper limit, the insulating properties and strength of the insulated wire may become insufficient.

The ratio of variation in the thickness of the insulating layer 2 is obtained by measuring the thickness of the insulating layer at 8 points in each cross section at 30 cross sections at intervals of 50 cm in the longitudinal direction of the insulated wire, and using these measured values, the following formula Calculated by (1).
Variation rate (%)=(4σ/average film thickness)×100 (1)
(In the above formula (1), the average film thickness indicates the average value of each measured value, and σ indicates the standard deviation of each measured value.)

The lower limit of the average diameter of the pores 3 is preferably 0.1 μm, more preferably 1 μm. On the other hand, the upper limit of the average diameter of the pores 3 is preferably 10 μm, more preferably 8 μm. If the average diameter of the pores 3 is less than the lower limit, the occurrence of corona discharge in the insulating layer 2 may not be sufficiently suppressed. Conversely, if the average diameter of the pores 3 exceeds the upper limit, it will be difficult to make the distribution of the pores 3 uniform, and there is a possibility that the distribution of the dielectric constant tends to be uneven.

The insulating layer 2 is formed of an insulating resin composition and pores 3 scattered in the resin composition. The insulating layer 2 is formed by coating and baking a varnish on the outer peripheral surface of the conductor 1, which will be described later.

The resin forming the insulating layer 2 is not particularly limited, but examples include polyvinyl formal, thermosetting polyurethane, thermosetting acrylic, epoxy, thermosetting polyester, thermosetting polyesterimide, thermosetting polyesteramideimide, aromatic polyamide, and thermosetting. Thermosetting resins such as polyamideimide and thermosetting polyimide, and thermoplastic resins such as polyetherimide, polyphenylene ether, polyethersulfone, and thermoplastic polyimide are main components. Here, the "main component" is the component with the largest content, for example, a component containing 50% by mass or more.

In addition, the resin composition forming the insulating layer 2 may contain a curing agent together with the resin.
Curing agents include titanium-based curing agents, isocyanate-based compounds, blocked isocyanates, urea and melamine compounds, amino resins, alicyclic acid anhydrides such as methyltetrahydrophthalic anhydride, aliphatic acid anhydrides, and aromatic acid anhydrides. etc. are exemplified. These curing agents are appropriately selected according to the type of resin contained in the resin composition used. For example, in the case of a polyamide-imide system, imidazole, triethylamine, etc. are preferably used as curing agents.

Examples of the titanium-based curing agent include tetrapropyl titanate, tetraisopropyl titanate, tetramethyl titanate, tetrabutyl titanate, tetrahexyl titanate, and the like. Examples of the isocyanate-based compounds include aromatic diisocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), p-phenylene diisocyanate and naphthalene diisocyanate, hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexane diisocyanate, Aliphatic diisocyanates having 3 to 12 carbon atoms such as lysine diisocyanate, 1,4-cyclohexane diisocyanate (CDI), isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane diisocyanate (hydrogenated MDI), methylcyclohexane diisocyanate, isopropylidene Dicyclohexyl-4,4′-diisocyanate, 1,3-diisocyanatomethylcyclohexane (hydrogenated XDI), hydrogenated TDI, 2,5-bis(isocyanatomethyl)-bicyclo[2.2.1]heptane, 2 , 6-bis(isocyanatomethyl)-bicyclo[2.2.1]heptane and other alicyclic isocyanates having 5 to 18 carbon atoms, xylylene diisocyanate (XDI), aromatics such as tetramethylxylylene diisocyanate (TMXDI) Aliphatic diisocyanates having a ring and modified products thereof are exemplified. Examples of the blocked isocyanate include diphenylmethane-4,4'-diisocyanate (MDI), diphenylmethane-3,3'-diisocyanate, diphenylmethane-3,4'-diisocyanate, diphenylether-4,4'-diisocyanate, benzophenone-4,4 '-diisocyanate, diphenylsulfone-4,4'-diisocyanate, tolylene-2,4-diisocyanate, tolylene-2,6-diisocyanate, naphthylene-1,5-diisocyanate, m-xylylene diisocyanate, p-xylylene diisocyanate, etc. A compound obtained by adding a blocking agent such as dimethylpyrazole to the isocyanate group of is exemplified. Examples of the melamine compound include methylated melamine, butylated melamine, methylolated melamine, and butyrolated melamine.

[Manufacturing method of insulated wire]
Next, a method for manufacturing the insulated wire will be described. In the method of manufacturing the insulated wire, the resin forming the insulating layer 2 and the particles containing the thermally decomposable resin that thermally decomposes at a temperature lower than the baking temperature of the resin (thermally decomposable resin-containing particles) are diluted to form a varnish. (varnish preparation step), the step of applying the varnish to the outer peripheral surface of the conductor 1 (varnish coating step), and the step of removing the thermally decomposable resin in the particles containing the thermally decomposable resin by heating (heating process).

<Varnish preparation process>
In the varnish preparation step, the varnish is prepared by diluting the resin forming the insulating layer 2 and the particles containing the thermally decomposable resin with a solvent.

The thermally decomposable resin contained in the particles containing the thermally decomposable resin is not particularly limited as long as it has a thermal decomposition temperature lower than the baking temperature of the resin forming the insulating layer 2 . The baking temperature of the resin forming the insulating layer 2 is appropriately set according to the type of the resin, but is usually about 200° C. or higher and 350° C. or lower. Therefore, the lower limit of the thermal decomposition temperature of the thermally decomposable resin is preferably 200°C, and the upper limit is preferably 300°C. Here, the thermal decomposition temperature means the temperature at which the mass reduction rate becomes 50% when the temperature is raised from room temperature at a rate of 10° C./min in a nitrogen atmosphere. The thermal decomposition temperature can be determined by measuring thermogravimetry using, for example, a thermogravimetry-differential thermal analyzer ("TG/DTA" available from SII Nano Technology Co., Ltd.).

The above-mentioned thermally decomposable resin is not particularly limited, but for example polyethylene glycol, polypropylene glycol, etc., a compound obtained by alkylating, (meth)acrylating or epoxidizing one or both ends or a part thereof, poly(meth)acrylic acid C1-C6 alkyl ester polymers of (meth)acrylic acid such as methyl, poly(ethyl(meth)acrylate), poly(propyl(meth)acrylate), poly(meth)acrylate and poly(butyl)acrylate, urethane oligomers, urethane polymers , polymers of modified (meth)acrylates such as urethane (meth)acrylate, epoxy (meth)acrylate, ε-caprolactone (meth)acrylate, poly(meth)acrylic acid, crosslinked products thereof, polystyrene, crosslinked polystyrene, etc. be done.
Among these, crosslinked products of (meth)acrylic polymers are preferred, and crosslinked poly(meth)acrylates are more preferred. Moreover, it is preferable that the thermally decomposable resin can be evenly distributed as an island phase of fine particles in the sea phase of the resin forming the insulating layer 2 in that independent pores can be formed.
Therefore, the thermally decomposable resin is preferably a resin that has excellent compatibility with the resin forming the insulating layer 2 and can be formed into a spherical shape. Specifically, a crosslinked resin is preferable.

The crosslinked poly(meth)acrylic polymer can be obtained, for example, by polymerizing a (meth)acrylic monomer and a polyfunctional monomer by emulsion polymerization, suspension polymerization, solution polymerization, or the like.

Here, the (meth)acrylic monomers include acrylic acid, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, dodecyl acrylate, stearyl acrylate, and acrylic acid 2. -ethylhexyl, tetrahydrofurfuryl acrylate, diethylaminoethyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-octyl methacrylate , dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, diethylaminoethyl methacrylate and the like.

Examples of polyfunctional monomers include divinylbenzene, ethylene glycol di(meth)acrylate, trimethylolpropane triacrylate, and the like.

In addition to the (meth)acrylic monomer and the polyfunctional monomer, monomers other than the (meth)acrylic monomer and the polyfunctional monomer may be used as constituent monomers of the crosslinked poly(meth)acrylic polymer. Other monomers include glycol esters of (meth)acrylic acid such as ethylene glycol mono(meth)acrylate and polyethylene glycol mono(meth)acrylate, alkyl vinyl ethers such as methyl vinyl ether and ethyl vinyl ether, vinyl acetate and vinyl butyrate. vinyl esters, N-methylacrylamide, N-ethylacrylamide, N-methylmethacrylamide, N-alkyl-substituted (meth)acrylamides such as N-ethylmethacrylamide, acrylonitrile, nitriles such as methacrylonitrile, styrene, p -Styrenic monomers such as methylstyrene, p-chlorostyrene, chloromethylstyrene and α-methylstyrene.

It is preferable that the thermally decomposable resin-containing particles are spherical. The lower limit of the average particle size of the thermally decomposable resin-containing particles is preferably 0.1 μm, more preferably 0.5 μm, and even more preferably 1 μm. On the other hand, the upper limit of the average particle size of the thermally decomposable resin-containing particles is preferably 100 µm, more preferably 50 µm, still more preferably 30 µm, and particularly preferably 10 µm. The thermally decomposable resin-containing particles are thermally decomposed at the time of baking the resin forming the insulating layer 2 to form pores in the existing portions. Therefore, if the average particle size of the thermally decomposable resin-containing particles is less than the lower limit, formation of pores in the insulating layer 2 may be difficult. Conversely, if the average particle diameter of the thermally decomposable resin-containing particles exceeds the upper limit, the surface of the insulating layer 2 may become uneven. Here, the average particle size of the thermally decomposable resin-containing particles means the particle size showing the highest content in the particle size distribution measured with a laser diffraction particle size distribution analyzer.

The lower limit of the content of the thermally decomposable resin in the varnish is preferably 5 parts by mass, more preferably 10 parts by mass, and even more preferably 15 parts by mass with respect to 100 parts by mass of the resin forming the insulating layer 2 . On the other hand, the upper limit of the content of the thermally decomposable resin in the varnish is preferably 350 parts by mass, more preferably 150 parts by mass, and even more preferably 90 parts by mass with respect to 100 parts by mass of the resin forming the insulating layer 2. . If the content of the thermally decomposable resin is less than the lower limit, the dielectric constant of the insulating layer 2 may not be lowered sufficiently. Conversely, if the content of the thermally decomposable resin exceeds the upper limit, the insulated wire may not have sufficient strength.

As the solvent for dilution, a known organic solvent conventionally used for insulating varnish can be used. Specifically, polar organic solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, dimethylsulfoxide, tetramethylurea, hexaethylphosphoric acid triamide, γ-butyrolactone, etc. First, acetone, methyl ethyl ketone, methyl isobutyl ketone, ketones such as cyclohexanone, esters such as methyl acetate, ethyl acetate, butyl acetate, diethyl oxalate, diethyl ether, ethylene glycol dimethyl ether, diethylene glycol monomethyl ether, ethylene glycol monobutyl ether (butyl cellosolve ), ethers such as diethylene glycol dimethyl ether and tetrahydrofuran; hydrocarbons such as hexane, heptane, benzene, toluene, and xylene; halogenated hydrocarbons such as dichloromethane and chlorobenzene; phenols such as cresol and chlorophenol; Examples include tertiary amines and the like, and these organic solvents may be used alone or in combination of two or more.

The lower limit of the resin solid content concentration of the varnish prepared by diluting with these organic solvents is preferably 15% by mass, more preferably 22% by mass. On the other hand, the upper limit of the resin solid content concentration of the varnish is preferably 50% by mass, more preferably 28% by mass. If the resin solid content concentration of the varnish is less than the lower limit, the amount of varnish applied at one time is small, so the number of repetitions of the varnish application process for forming the insulating layer 2 with the desired thickness is increased. This may increase the time required for the varnishing process. Conversely, if the resin solid content concentration of the varnish exceeds the above upper limit, the varnish may increase in viscosity, resulting in deterioration in storage stability of the varnish and deterioration in adhesion during varnish application.

The thermally decomposable resin-containing particles may be particles composed only of the thermally decomposable resin. Core-shell particles having a shell based on a resin having a high thermal decomposition temperature are preferred.

A resin having a low dielectric constant and a high heat resistance is preferable as the resin which is the main component of the shell. Examples of the resin that is the main component of the shell include polystyrene, silicone, fluororesin, polyimide, and the like. Among these, silicone is preferable in terms of imparting elasticity to the shell and easily improving insulation and heat resistance. Here, the "fluororesin" means an organic group in which at least one of the hydrogen atoms bonded to the carbon atoms constituting the repeating unit of the polymer chain has a fluorine atom or a fluorine atom (hereinafter also referred to as "fluorine atom-containing group" ) is replaced with The fluorine atom-containing group is a linear or branched organic group in which at least one hydrogen atom is substituted with a fluorine atom, and examples thereof include fluoroalkyl groups, fluoroalkoxy groups, and fluoropolyether groups. can be done. The shell may contain metal as long as it does not impair the insulation.

The resin that is the main component of the shell may be the same type as the resin forming the insulating layer 2, or may be different. For example, even if the same kind of resin as the resin forming the insulating layer 2 is used as the main component resin of the shell, the thermal decomposition temperature is higher than that of the thermally decomposable resin, so even if the thermally decomposable resin gasifies, the shell still remains intact. Since the resin as the main component of is difficult to thermally decompose, the effect of suppressing the communication of the pores 3 can be obtained. In the insulated wire formed with such varnish, the existence of the shell may not be confirmed even when observed with an electron microscope. On the other hand, by using a resin different from the resin forming the insulating layer 2 as the main component of the shell, it is possible to make the shell difficult to integrate with the insulating layer 2. Compared to the case of using resin, the effect of suppressing the communication of the pores 3 can be easily obtained.

The lower limit of the average thickness of the shell is not particularly limited, but is preferably 0.01 μm, more preferably 0.02 μm, for example. On the other hand, the upper limit of the average shell thickness is preferably 0.5 μm, more preferably 0.4 μm. If the average thickness of the shell is less than the above lower limit, the effect of suppressing the communication of the pores 3 may not be sufficiently obtained. Conversely, if the average thickness of the shell exceeds the above upper limit, the volume of the pores 3 becomes too small, and there is a risk that the porosity of the insulating layer 2 cannot be increased above a predetermined level. In addition, the shell may be formed of one layer, or may be formed of a plurality of layers. When the shell is formed of multiple layers, the average total thickness of the multiple layers may be within the above thickness range.

The upper limit of the CV value of the thermally decomposable resin-containing particles is preferably 30%, more preferably 20%. In this way, by using the thermally decomposable resin-containing particles whose CV value is equal to or less than the above upper limit, the strength of the insulating layer 2 is reduced due to the concentration of electric charge in the pore portion due to the difference in pore size, which causes the deterioration of the insulation property and the concentration of the processing stress. can be suppressed. The lower limit of the CV value of the thermally decomposable resin-containing particles is not particularly limited, but is, for example, 1%. Here, "CV value" means a variable variable defined in JIS-Z8825 (2013).

<Varnish application process>
In the varnish application step, after the varnish prepared in the varnish preparation step is applied to the outer peripheral surface of the conductor 1, the amount of varnish applied to the conductor 1 is adjusted and the applied varnish surface is smoothed using a coating die.

The coating die has an opening, and excess varnish is removed by passing the varnish-coated conductor 1 through this opening to adjust the amount of varnish applied. As a result, the thickness of the insulating layer 2 of the insulated wire becomes more uniform, and the insulation and strength of the insulated wire are further improved.

<Heating process>
Next, in the heating step, the conductor 1 coated with the varnish is passed through a baking furnace to bake the varnish, thereby forming the insulating layer 2 on the surface of the conductor 1 . During baking, the thermally decomposable resin in the particles containing the thermally decomposable resin contained in the varnish is gasified and removed by thermal decomposition. As a result, pores 3 derived from the thermally decomposable resin-containing particles are formed in the insulating layer 2 . Thus, the heating process also serves as the varnish baking process.

[advantage]
In the insulated wire, the insulating layer 2 contains the pores 3 and the porosity of the insulating layer 2 is within the above range, so that the dielectric constant of the insulating layer 2 can be lowered. In addition, the insulated wire has excellent film thickness uniformity with the variation ratio of the insulating layer film thickness being less than the above value, so that the minimum film thickness can be reduced, and as a result, the corona discharge inception voltage is improved. It has excellent insulation and strength.

[Other embodiments]
It should be considered that the embodiments disclosed this time are illustrative in all respects and not restrictive. The scope of the present invention is not limited to the configuration of the above-described embodiment, but is indicated by the scope of the claims, and is intended to include all modifications within the scope and meaning equivalent to the scope of the claims. be.

In the above embodiment, an insulated wire in which a single insulating layer is laminated on the outer peripheral surface of the conductor has been described, but an insulated wire in which a plurality of insulating layers are laminated on the outer peripheral surface of the conductor may be used. That is, one or more insulating layers may be laminated between the conductor 1 and the insulating layer 2 containing the pores 3 in FIG. A plurality of insulating layers may be laminated, or one or a plurality of insulating layers may be laminated on both the outer peripheral surface and the inner peripheral surface of the insulating layer 2 including the pores 3 in FIG.

Further layers, such as priming layers, may also be provided between the conductor and the insulating layer, for example in the insulated wire. The primer treatment layer is a layer provided to enhance adhesion between layers, and can be formed of, for example, a known resin composition.

When a primer treatment layer is provided between the conductor and the insulating layer, the resin composition forming the primer treatment layer is, for example, one or more resins selected from polyimide, polyamideimide, polyesterimide, polyester and phenoxy resin. should include Moreover, the resin composition forming the primer treatment layer may contain an additive such as an adhesion improver. By forming a primer treatment layer between the conductor and the insulating layer using such a resin composition, it is possible to improve the adhesion between the conductor and the insulating layer. Properties such as strength can be effectively enhanced.

The resin composition forming the primer treatment layer may contain other resins such as epoxy resin, phenoxy resin, melamine resin, etc. in addition to the above resins. Moreover, you may use a commercially available liquid composition (insulating varnish) as each resin contained in the resin composition which forms a primer treatment layer.

The lower limit of the average thickness of the primer-treated layer is preferably 1 μm, more preferably 2 μm. On the other hand, the upper limit of the average thickness of the primer treatment layer is preferably 30 µm, more preferably 20 µm. If the average thickness of the primer-treated layer is less than the above lower limit, there is a possibility that sufficient adhesion to the conductor cannot be exhibited. Conversely, if the average thickness of the primer treatment layer exceeds the above upper limit, the diameter of the insulated wire may unnecessarily increase.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these Examples.

[Manufacturing of insulated wires]
No. in Table 1. 1 was manufactured as follows. First, polyimide as a resin for forming an insulating layer was diluted with N-methyl-2-pyrrolidone as a solvent. Next, core-shell particles having an average particle diameter of 3 μm with a core of PMMA (polymethyl methacrylate resin) particles and a shell of silicone as thermally decomposable resin-containing particles are added to this, and the calculated porosity of the insulating layer is 30 volumes. % to prepare a varnish. Using this varnish, using a vertical coating equipment, a rectangular conductor with a cross section of 2 mm × 2 mm is immersed, then passed through a die having an opening similar in shape to the conductor at a speed of 6 m / min, and baked. It was passed through a furnace and baked at 350° C. for 1 minute to form an insulating coating. This varnish application, die passing, and baking were repeated 13 times to produce an insulated wire (No. 1) having a polyimide resin coating as an insulating layer.

No. in Table 1. 2 was manufactured as follows. First, polyimide as a resin for forming an insulating layer was diluted with N-methyl-2-pyrrolidone as a solvent. Next, core-shell particles having an average particle diameter of 3 μm, in which the core is PMMA particles and the shell is silicone, as thermally decomposable resin-containing particles are dispersed in an amount such that the calculated porosity of the insulating layer is 30% by volume. A varnish was prepared. Using this varnish, using a vertical coating equipment, a rectangular conductor with a cross section of 2 mm × 2 mm is immersed, then passed through a die having an opening similar in shape to the conductor at a speed of 6 m / min, and baked. It was passed through a furnace and baked at 350° C. for 1 minute to form an insulating coating. This varnish application, die passing, and baking were repeated 15 times to produce an insulated wire (No. 2) having a polyimide resin film as an insulating layer.

No. in Table 1. 3 was manufactured as follows. First, polyimide as a resin for forming an insulating layer was diluted with N-methyl-2-pyrrolidone as a solvent. Next, core-shell particles having an average particle diameter of 3 μm, in which the core is PMMA particles and the shell is silicone, as thermally decomposable resin-containing particles are dispersed in an amount such that the calculated porosity of the insulating layer is 30% by volume. A varnish was prepared. Using this varnish, using a vertical coating equipment, a rectangular conductor with a cross section of 2 mm × 2 mm is immersed, then passed through a die having an opening similar in shape to the conductor at a speed of 6 m / min, and baked. It was passed through a furnace and baked at 350° C. for 1 minute to form an insulating coating. This varnish application, die passing, and baking were repeated 30 times to produce an insulated wire (No. 3) having a polyimide resin coating as an insulating layer.

No. in Table 1. 4 was manufactured as follows. First, polyimide as a resin for forming an insulating layer was diluted with N-methyl-2-pyrrolidone as a solvent. Next, core-shell particles having an average particle diameter of 3 μm and having a core of PMMA particles and a shell of silicone as thermally decomposable resin-containing particles were dispersed in an amount such that the calculated porosity of the insulating layer was 55% by volume. A varnish was prepared. Using this varnish, using a vertical coating equipment, a rectangular conductor with a cross section of 2 mm × 2 mm is immersed, then passed through a die having an opening similar in shape to the conductor at a speed of 6 m / min, and baked. It was passed through a furnace and baked at 350° C. for 1 minute to form an insulating coating. This varnish application, die passing, and baking were repeated 30 times to produce an insulated wire (No. 4) having a polyimide resin coating as an insulating layer.

No. in Table 1. 5 was manufactured as follows. First, polyimide as a resin for forming an insulating layer was diluted with N-methyl-2-pyrrolidone as a solvent. Next, azo thermally expandable microcapsule particles as a pore-forming material were dispersed in this in such an amount that the calculated porosity of the insulating layer was 30% by volume, thereby preparing a varnish. Using this varnish, using a vertical coating equipment, a rectangular conductor with a cross section of 2 mm × 2 mm is immersed, then passed through a die having an opening similar in shape to the conductor at a speed of 6 m / min, and baked. It was passed through a furnace and baked at 350° C. for 1 minute to form an insulating coating. This varnish application, die passing, and baking were repeated 15 times to produce an insulated wire (No. 5) having a polyimide resin coating as an insulating layer.

[evaluation]
No. 1 to No. 5, the porosity of the insulating layer, the average thickness of the insulating layer, the standard deviation σ, the variation rate, the dielectric constant and the corona discharge inception voltage (PDIV) were evaluated according to the following methods. The evaluation results are also shown in Table 1.

(Porosity of insulating layer)
In the obtained insulated wire, the insulating layer was peeled off from the conductor into a cylindrical shape, and the mass W2 of this cylindrical insulating layer was measured. Also, the apparent volume V1 was obtained from the outer shape of the cylindrical insulating layer, and this V1 was multiplied by the density ρ1 of the material of the insulating layer to calculate the mass W1 in the absence of pores. From these W1 and W2 values, the porosity was calculated by the following formula.
Porosity = (W1-W2) x 100/W1 (% by volume)

(Average film thickness of insulating layer)
Regarding the cross section of the obtained insulated wire, the film thickness was measured at eight points indicated by circled numbers in FIG. The film thickness was measured for N=30 cross sections at intervals of 50 cm, and the average value (arithmetic mean) of the measured film thicknesses for 8 points×30=240 points was obtained and taken as the average film thickness. Also, the standard deviation σ of the measured values was obtained. Even if the average film thickness is approximately the same, a large value of 4σ means a large variation.

(percentage of variation)
Using the values of the average film thickness and the standard deviation σ obtained above, the variation ratio of the film thickness of the insulating layer was obtained by the following formula.
Variation rate = (4σ/average film thickness) x 100 (%)
If the variation rate exceeds 25%, the uniformity of the film thickness is low, and it can be said that a so-called dog-bone-shaped insulating layer is likely to be formed.

(permittivity)
No. 1 to No. For the insulated wire No. 5, the dielectric constant ε of the insulating layer 2 was measured. FIG. 3 is a schematic diagram for explaining the method of measuring the dielectric constant. First, silver paste P was applied to the surface of the insulated wire at three locations, and the insulating layer 2 on one end side of the insulated wire was peeled off to expose the conductor 1 to prepare a sample for measurement. Here, the application lengths of the silver paste P applied to the surface of the insulated wire at three locations in the longitudinal direction of the insulated wire were set to 10 mm, 100 mm, and 10 mm in order along the longitudinal direction. Two silver pastes P applied with a length of 10 mm are grounded, and the capacitance between the exposed conductor 1 and the silver paste P with a length of 100 mm applied between these two silver pastes is measured. Measured with an LCR meter M. The dielectric constant ε of the insulating layer 2 was calculated from the measured capacitance and the average film thickness of the insulating layer 2 . The dielectric constant ε was measured at n=3 after heating at 105° C. for 1 hour, and the average value was obtained.

(Measurement of corona discharge inception voltage)
It was measured using a partial discharge tester (“KPD2050S” manufactured by Kikusui Denshi Kogyo Co., Ltd.). The surfaces of the two insulated wires were brought into close contact with each other over a length of 100 mm without any gap, and an electrode was connected between the two conductors. At 25° C., the voltage was increased at a frequency of 60 Hz, and the voltage was read when a partial discharge of 100 pC or more occurred. It implemented by n=5 and evaluated by the average value.

From the results of Table 1, it can be seen that the porosity and variation ratio of the insulating layer are in the above range. 1 to No. The insulated wire of No. 4 has a low dielectric constant, a high corona discharge inception voltage, promotes a low dielectric constant of the insulating layer, and is excellent in insulating properties. On the other hand, No. The insulated wire No. 5 has a variation rate outside the above range, and the film thickness is similar to No. 5 insulated wire. The corona discharge starting voltage was lower than that of No. 2. These differences are thought to be due to the fact that core-shell particles are less likely to expand and foam, but the use of a pore-forming material (such as a foaming material) increases the variation in film thickness due to pore expansion within the coating.

1 conductor 2 insulating layer 3 pores M LCR meter P silver paste

Claims (3)

An insulated wire comprising a linear conductor and an insulating layer covering the outer peripheral surface of the conductor,
The insulating layer includes a plurality of pores,
The insulating layer has a porosity of 20% by volume or more and 65% by volume or less,
The film thickness of the insulating layer is measured at 8 points in each cross section at 30 cross sections at intervals of 50 cm in the longitudinal direction of the insulated wire, and the variation ratio of the following formula (1) calculated from these measured values is 25% or less,
The plurality of pores are derived from the thermally decomposable resin-containing particles,
The CV value of the thermally decomposable resin-containing particles is 30% or less ,
The thermally decomposable resin contained in the thermally decomposable resin-containing particles is a crosslinked product of a (meth)acrylic polymer,
The insulated wire, wherein the plurality of pores have an average diameter of 0.1 μm or more and 10 μm or less .
Variation rate (%)=(4σ/average film thickness)×100 (1)
(In the above formula (1), the average film thickness indicates the average value of each measured value, and σ indicates the standard deviation of each measured value.) 2. The insulated wire according to claim 1, wherein the insulating layer has an average film thickness of 60 [mu]m or more. 3. The insulated wire according to claim 1, wherein the conductor is a rectangular conductor having a rectangular cross section.

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