JP2024102995A - Insulated Wire - Google Patents

Abstract

[Problem] To provide an insulated wire with excellent deformation resistance. [Solution] An insulated wire comprising a conductor and an insulating layer covering the conductor, the insulating layer containing a resin matrix mainly composed of polyimide and a plurality of pores, the porosity of the insulating layer being 25 volume % or more, the average thickness of the insulating layer being 45 μm or more, the average distance in the thickness direction between the plurality of pores in the cross section of the insulating layer being more than 0.2 μm, and the flatness of the plurality of pores being 1.5 or less. [Selected Figure] Figure 1

Description

This disclosure relates to insulated wire.

Patent Document 1 describes an insulating varnish containing a coating resin and a heat-decomposable resin that decomposes at a temperature lower than the baking temperature of the coating resin, and an insulated electric wire having a heat-cured film of the insulating varnish, in which pores are formed in the heat-cured film due to the heat decomposition of the heat-decomposable resin.

JP 2012-224714 A

The insulated wire according to one embodiment of the present disclosure includes a conductor and an insulating layer covering the conductor, the insulating layer containing a resin matrix mainly composed of polyimide and a plurality of pores, the porosity of the insulating layer is 25% by volume or more, the average thickness of the insulating layer is 45 μm or more, the average distance between the plurality of pores in the thickness direction in the cross section of the insulating layer is more than 0.2 μm, and the flatness of the plurality of pores is 1.5 or less.

FIG. 1 is a schematic cross-sectional view illustrating an insulated wire according to one embodiment of the present disclosure.

[Problem to be solved by this disclosure]
An object of the present disclosure is to provide an insulated wire having excellent deformation resistance.

[Effects of the present disclosure]
The insulated wire according to one embodiment of the present disclosure has excellent deformation resistance.

Description of the embodiments of the present disclosure
First, the embodiments of the present disclosure will be listed and described.
Item 1.
A conductor;
and an insulating layer covering the conductor.
the insulating layer contains a resin matrix mainly composed of polyimide and a plurality of pores;
The insulating layer has a porosity of 25 volume % or more,
The average thickness of the insulating layer is 45 μm or more,
an average distance in a thickness direction between the plurality of pores in a cross section of the insulating layer is greater than 0.2 μm;
The insulated wire, wherein the flatness of the plurality of pores is 1.5 or less.
Item 2.
2. The insulated wire according to item 1, wherein the average diameter of the pores is 0.1 μm or more and 10 μm or less.
Item 3.
3. The insulated wire according to item 1 or 2, wherein the pores have a flatness of 0.5 or more and 1.5 or less.
Item 4.
4. The insulated wire according to any one of items 1 to 3, wherein the porosity is 40 volume % or less.
Item 5.
5. The insulated wire according to any one of items 1 to 4, wherein the insulating layer has an average thickness of 45 μm or more and 200 μm or less.
Item 6.
6. The insulated wire according to any one of items 1 to 5, wherein the pores originate from heat-decomposable resin-containing particles.
Item 7.
7. The insulated wire according to any one of items 1 to 6, wherein the insulating layer has a thickness deformation rate of less than 10%.
Item 8.
8. The insulated wire according to any one of items 1 to 7, wherein the insulated wire is a magnet wire.

[Details of the embodiment of the present disclosure]
Hereinafter, an insulated wire according to one embodiment of the present disclosure will be described with reference to the drawings.

<Insulated wire>
1 includes a conductor 2 and an insulating layer 3 that covers the conductor 2. The insulating layer 3 contains a resin matrix mainly composed of polyimide and a plurality of pores 4.

The cross-sectional shape of the insulated electric wire 1 is not particularly limited, and examples thereof include a circle (round wire), an ellipse, a square (rectangular wire), and a rectangle (rectangular wire). It is preferable that the cross-sectional shape of the insulated electric wire 1 is a rectangle, in other words, a rectangular wire. In this case, the insulated electric wire 1 can be wound at high density during coil processing. It is also preferable that the cross-sectional shape of the insulated electric wire 1 and the cross-sectional shape of the conductor 2 described later are of the same type of shape.

The insulated wire 1 can be suitably used as a magnet wire.

〔conductor〕
Examples of the cross-sectional shape of the conductor 2 include a circular shape (round wire), an elliptical shape, a square shape, and a rectangular shape. When the insulated electric wire 1 is a rectangular wire, the cross-sectional shape of the conductor 2 is preferably a rectangular shape.

The material of the conductor 2 is preferably a metal with high electrical conductivity and high mechanical strength. Examples of the above metals include copper, copper alloys, aluminum, nickel, silver, soft iron, steel, and stainless steel. The conductor 2 can be a material in which the above metals are formed into a wire shape, or a multilayer structure in which a wire-shaped material is further coated with another metal, such as a nickel-coated copper wire, a silver-coated copper wire, a copper-coated aluminum wire, or a copper-coated steel wire.

The lower limit of the average cross-sectional area of the conductor 2 may be 0.01 ^mm2 or 0.1 ^mm2 . In this case, the volume of the insulating layer 3 relative to the conductor 2 in the insulated wire can be made appropriate, and the volumetric efficiency of a coil or the like formed using the insulated wire can be improved. The upper limit of the average cross-sectional area of the conductor 2 may be ²⁰ mm2 or ¹⁰ mm2. In this case, the need to form the insulating layer 3 thick in order to sufficiently reduce the relative dielectric constant can be reduced, and unnecessary increase in the diameter of the insulated wire can be avoided.

[Insulating layer]
The insulating layer 3 is laminated on the outer peripheral surface of the conductor 2 so as to cover the conductor 2. The insulating layer 3 is composed of one or more layers. For example, when the insulating layer 3 is formed by a method described later (a method in which the application and baking of a resin varnish are repeated multiple times), insulating layers formed using the same type of resin varnish are considered to be the same insulating layer.

The insulating layer 3 contains a resin matrix whose main component is polyimide and a plurality of pores 4 scattered throughout the resin matrix.

The porosity of the insulating layer 3 is 25% by volume or more. The porosity of the insulating layer 3 is 25% by volume or more, so that the dielectric constant of the insulating layer can be reduced. The insulated wire has an average thickness of 45 μm or more, an average distance in the thickness direction between the multiple pores 4 in the cross section of the insulating layer 3 is 0.4 μm or more, and the flatness of the multiple pores 4 is 1.5 or less, as described below. This allows the insulating layer 3 to exhibit excellent deformation resistance even when the porosity of the insulating layer 3 is as high as 25% by volume or more. The lower limit of the porosity of the insulating layer 3 may be 30% by volume. The upper limit of the porosity of the insulating layer 3 may be 50% by volume or 40% by volume. When the porosity of the insulating layer 3 is 40% by volume or less, the toughness of the insulating layer can be maintained while improving the processability. The "porosity" means the percentage of the volume of the pores 4 relative to the volume of the insulating layer 3 including the resin matrix and the pores 4.

It is preferable that the thickness deformation rate of the insulating layer 3 is less than 10%. In this case, the insulated electric wire has excellent deformation resistance. "Thickness deformation rate" means the rate of reduction in the average thickness of the insulating layer after pressing relative to the average thickness before pressing.

The main component of the resin matrix is polyimide. The use of polyimide can improve the strength and heat resistance of the insulated wire. The resin matrix can contain synthetic resins other than polyimide.

The polyimide may be derived from a polyimide precursor, which is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine. The polyimide precursor is a compound also known as polyamic acid (polyamic acid). The polyimide precursor forms a cyclic imide by a dehydration cyclization reaction, becoming a polyimide.

The average thickness of the insulating layer 3 is 45 μm or more. The average thickness of the insulating layer 3 is 45 μm or more, the average distance in the thickness direction between the multiple pores 4 in the cross section of the insulating layer 3 described later is 0.4 μm or more, and the flatness of the multiple pores 4 described later is 1.5 or less, which are combined to provide excellent deformation resistance. Although not intended to be a restrictive interpretation, one of the reasons for the excellent deformation resistance is that the average thickness of the insulating layer 3 is 45 μm or more, which makes it easier to suppress stress concentration on the insulating layer 3. The lower limit of the average thickness of the insulating layer 3 may be 50 μm. The upper limit of the average thickness of the insulating layer 3 may be 200 μm, 150 μm, or 100 μm. In this case, the volume efficiency of a coil or the like formed using the insulated electric wire 1 can be improved.

The insulating layer 3 may contain other components in addition to the above components. The other components are not particularly limited as long as they are additives that are blended into the insulating layer of the insulated wire, and examples of such additives include fillers, antioxidants, leveling agents, curing agents, and adhesion aids.

[Porosity]
The pores 4 may be derived from pyrolyzable resin-containing particles. The pyrolyzable resin-containing particles are gasified by pyrolysis, and the pores 4 are formed in the portions of the insulating layer 3 where the pyrolyzable resin-containing particles were present. In this case, the fine particles can be uniformly distributed as islands in the sea phase of the resin matrix forming the insulating layer 3, and independent pores can be formed. Although not intended to be a restrictive interpretation, the insulating layer 3 contains a plurality of pores 4, and thus the insulated wire can have a reduced relative dielectric constant.

The average distance in the thickness direction between the multiple pores 4 in the cross section of the insulating layer 3 is more than 0.2 μm. As described above, the average distance in the thickness direction between the multiple pores 4 is more than 0.2 μm, and the average thickness of the insulating layer 3 is 45 μm or more, and the flatness of the multiple pores 4 described below is 1.5 or less, which combine to provide excellent deformation resistance. Although not intended to be interpreted in a restrictive manner, one of the reasons for the excellent deformation resistance is that the average distance in the thickness direction between the multiple pores 4 in the cross section of the insulating layer 3 is more than 0.2 μm, which makes it easier to suppress stress concentration between the multiple pores 4. The "average distance in the thickness direction between the multiple pores 4" means the average value of the distance between two adjacent pores 4 in the thickness direction in the cross section of the insulating layer 3.

If the lower limit of the average diameter of the pores 4 is 0.1 μm, the mechanical properties of the insulating layer 3 can be improved. If the upper limit of the average diameter of the pores 4 is 10 μm, the insulating properties of the insulating layer 3 can be improved. The average diameter of the pores 4 is a value obtained by measuring the cross section of the insulated electric wire 1 using a pore diameter distribution measuring device (for example, Porous Materials' "Porous Material Automated Pore Size Distribution Measuring System").

The flatness of the pores 4 is 1.5 or less. As described above, the flatness of the pores 4 is 1.5 or less, the average distance between the pores 4 in the thickness direction is more than 0.2 μm, and the average thickness of the insulating layer 3 is 45 μm or more, which combine to provide excellent deformation resistance. Although not limiting, one of the reasons for the excellent deformation resistance is that the flatness of the pores 4 is 1.5 or less, which makes it easier to suppress stress concentration between the pores 4. If the lower limit of the flatness of the pores 4 is 0.5, the mechanical properties of the insulating layer 3 can be improved. The flatness of the pores 4 means the ratio of the vertical length to the horizontal length in the cross section of the pores 4.

The thermally decomposable resin contained in the thermally decomposable resin-containing particles is preferably a resin that thermally decomposes at a temperature lower than the baking temperature of the polyimide, which is the main component of the resin matrix of the insulating layer 3. The baking temperature is set appropriately depending on the type of polyimide, but is usually about 200°C to 600°C. The lower limit of the thermal decomposition temperature of the thermally decomposable resin may be 200°C, and the upper limit may be 400°C. The "thermal decomposition temperature" means the temperature at which the mass reduction rate reaches 50% when the temperature is increased from room temperature at 10°C/min in an air atmosphere. The thermal decomposition temperature can be measured by measuring the thermogravimetry using a thermogravimetry-differential thermal analyzer ("TG/DTA" by SII NanoTechnology Co., Ltd.).

Examples of thermally decomposable resins include compounds such as polyethylene glycol and polypropylene glycol in which one or both ends or a part of the end is alkylated, (meth)acrylated, or epoxidized; polymers of (meth)acrylic esters having an alkyl group with 1 to 6 carbon atoms, such as polymethyl (meth)acrylate, polyethyl (meth)acrylate, polypropyl (meth)acrylate, and polybutyl (meth)acrylate; polymers of modified (meth)acrylates, such as urethane oligomers, urethane polymers, urethane (meth)acrylates, epoxy (meth)acrylates, and ε-caprolactone (meth)acrylates; poly(meth)acrylic acid; crosslinked products thereof; polystyrene; and crosslinked polystyrene. Polymers of (meth)acrylic esters having an alkyl group with 1 to 6 carbon atoms are easily thermally decomposed at the above baking temperature, and are easy to form pores 4 in the insulating layer 3. Examples of the polymers of (meth)acrylic esters include polymethyl methacrylate (PMMA). The term "(meth)acrylic acid" includes both "acrylic acid" and "methacrylic acid".

The thermally decomposable resin-containing particles may be spherical. The lower limit of the average particle diameter of the thermally decomposable resin-containing particles may be 0.1 μm, 0.5 μm, or 1 μm. In this case, pores 4 are easily formed in the insulating layer 3. The upper limit of the average particle diameter of the thermally decomposable resin-containing particles may be 100 μm, 50 μm, 30 μm, or 10 μm. In this case, it is possible to suppress the occurrence of unevenness on the surface of the insulating layer 3. The "average particle diameter of the thermally decomposable resin-containing particles" means the particle size that shows the highest content in the particle size distribution measured by a laser diffraction particle size distribution measuring device.

The thermally decomposable resin-containing particles may be particles consisting of only the thermally decomposable resin, or may be particles having a core-shell structure with a core mainly composed of the thermally decomposable resin and a shell mainly composed of a resin having a thermal decomposition temperature higher than that of the thermally decomposable resin. When the thermally decomposable resin-containing particles are particles having the core-shell structure, the interconnection of the pores 4 can be suppressed, and the variation in size of the pores 4 can be reduced.

When the thermally decomposable resin-containing particles are particles with the core-shell structure, the pores 4 have an outer shell at their periphery that originates from the shell of the particles with the core-shell structure.

The main component of the shell is not particularly limited as long as it has a higher thermal decomposition temperature than the core, and is preferably a synthetic resin with a low dielectric constant and high heat resistance. Examples include polystyrene, silicone, fluororesin, polyimide, etc. Silicone is easy to increase elasticity, improve the dispersion of pores 4 in the insulating layer 3, and has excellent insulating properties and heat resistance. "Fluororesin" refers to a material in which at least one hydrogen atom bonded to a carbon atom constituting a repeating unit of a polymer chain is replaced with a fluorine atom or an organic group having a fluorine atom (hereinafter also referred to as a "fluorine atom-containing group"). The fluorine atom-containing group is a linear or branched organic group in which at least one hydrogen atom is replaced with a fluorine atom, and examples of the fluorine atom-containing group include a fluoroalkyl group, a fluoroalkoxy group, and a fluoropolyether group. The outer shell may contain a metal to the extent that it does not impair the insulating properties.

It is preferable that the outer shell has a defect penetrating from the inside to the outside. In the insulated electric wire 1, the gasified core is released to the outside through this defect, so that pores 4 can be formed in the outer shell. The shape of this defect varies depending on the material and shape of the shell, but from the viewpoint of enhancing the effect of the outer shell in preventing the pores 4 from communicating with each other, it is preferable that the defect be a crack, a crevice, or a hole. The insulating layer 3 may include an outer shell without a defect. Depending on the conditions for releasing the gasified core to the outside of the shell, a defect may not be formed in the shell.

The insulating layer 3 may have an outer shell around the periphery of all pores 4 in order to improve the dispersibility of the pores 4, or may include some pores 4 that are not covered by an outer shell. The lower limit of the ratio of the number of pores 4 with an outer shell to the total number of pores 4 in the insulating layer 3 is preferably 70%, more preferably 90%, and most preferably 100%. In this case, the dispersibility of the pores 4 in the insulating layer 3 can be improved, and the communication between multiple pores 4 can be suppressed.

The outer shell is composed of the hollow shell obtained by removing the core of the particle. In other words, the pores 4 originate from the core of the particle with the core-shell structure, and the outer shell originates from the shell of the particle with the core-shell structure.

The upper limit of the CV value of the thermally decomposable resin-containing particles may be 30% or 20%. In this case, it is possible to suppress a decrease in insulation due to charge concentration in the pores caused by differences in pore size, and a decrease in the strength of the insulating layer 3 due to concentration of processing stress. There is no particular limit to the lower limit of the CV value, and it can be, for example, 1%. "CV value" refers to the variable defined in JIS-Z8825 (2013).

<Method of manufacturing insulated wire>
The insulated wire 1 can be manufactured by a method including a step of applying a resin varnish containing thermally decomposable resin-containing particles to the outer peripheral side of the conductor 2 (a coating step), and a step of curing the resin varnish applied in the coating step (a curing step).

[Coating process]
In the coating process, a resin varnish, which will be described later, is applied to the outer periphery of the conductor 2. Examples of methods for applying the resin varnish include a method using a coating device equipped with a storage tank for storing the resin varnish and a coating die. With this coating device, the resin varnish adheres to the outer periphery of the conductor 2 as the conductor 2 passes through the storage tank, and the resin varnish is applied to a substantially uniform thickness as the conductor 2 passes through the coating die.

[Curing process]
In the curing step, the resin varnish applied in the coating step is heated. In the curing step, the resin varnish is baked onto the outer periphery of the conductor 2, thereby laminating the insulating layer 3 on the outer periphery of the conductor 2. The baking method is not particularly limited, but includes conventionally known methods such as hot air heating, infrared heating, high-frequency heating, and UV irradiation. The baking temperature is usually 200°C or higher and 600°C or lower.

The coating process and the curing process may be repeated multiple times. In other words, the insulating layer 3 may be configured as a laminate of multiple baked layers. When the insulating layer 3 is configured as a laminate of multiple baked layers, pores 4 are formed in each baked layer, so the dispersibility of the pores 4 can be improved. When the coating process and the curing process are repeated multiple times, the dispersibility of the pores 4 can be further improved by setting the coating thickness of the resin varnish in the coating process per coating process to a thickness smaller than the average diameter of the pores 4.

<Resin varnish>
The resin varnish contains a polyimide precursor, thermally decomposable resin-containing particles, and an organic solvent. The resin varnish may contain other components in addition to the above components.

The polyimide precursor is a component that forms polyimide, which is the main component of the resin matrix of the insulating layer 3. Polyimide is explained in the "Insulated Wire" section above.

Particles containing thermally decomposable resin are explained in the "Insulated wire" section above.

As the solvent, known organic solvents conventionally used as resin varnishes for forming insulating layers of insulated electric wires can be used. Specific examples include polar organic solvents such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, tetramethylurea, hexaethylphosphoric triamide, and γ-butyrolactone; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; esters such as methyl acetate, ethyl acetate, butyl acetate, and diethyl oxalate; ethers such as diethyl ether, ethylene glycol dimethyl ether, diethylene glycol monomethyl ether, ethylene glycol monobutyl ether (butyl cellosolve), 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; and tertiary amines such as pyridine. The organic solvents can be used alone or in combination of two or more.

The lower limit of the resin solids concentration of the resin varnish may be 15 mass%, 20 mass%, or 30 mass%. In this case, when forming an insulating layer using the resin varnish, the amount of resin varnish required in the entire manufacturing process to obtain an insulating layer of the desired thickness can be reduced, and the number of coating steps and heating steps can be reduced. The upper limit of the resin solids concentration of the resin varnish may be 50 mass% or 40 mass%. In this case, the viscosity of the resin varnish can be appropriately adjusted, and storage stability and coatability can be improved.

[Other embodiments]
The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present disclosure is not limited to the configurations of the above-described embodiments, but is indicated by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

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

In the insulated wire, an additional layer such as a primer-treated layer may be provided between the conductor and the insulating layer. The primer-treated layer is provided to increase adhesion between the layers, and can be formed, for example, from a known resin composition.

When a primer-treated layer is provided between the conductor and the insulating layer, the resin composition forming the primer-treated layer may contain one or more types of resin selected from the group consisting of polyimide, polyamideimide, polyesterimide, polyester, and phenoxy resin. The resin composition forming the primer-treated layer may also contain additives such as adhesion improvers. By forming a primer-treated 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, and as a result, it is possible to effectively improve the properties of the insulated wire, such as flexibility, abrasion resistance, scratch resistance, and processing resistance.

The resin composition forming the primer-treated layer may contain other resins, such as epoxy resins and melamine resins, in addition to the above resins. In addition, a commercially available liquid composition (insulating varnish) may be used as each resin contained in the resin composition forming the primer-treated layer.

The lower limit of the average thickness of the primer treatment layer may be 1 μm or 2 μm. The upper limit of the average thickness of the primer treatment layer may be 30 μm or 20 μm.

The present invention will be described in more detail below with reference to examples. The present invention is not limited to these examples.

<Preparation of Resin Varnish and Production of Insulated Wire>
[No. 1]
(Preparation of resin varnish)
A polyimide precursor as a synthetic resin was diluted with N-methyl-2-pyrrolidone as a solvent. Next, a thermally decomposable resin-containing particle was added in an amount such that the calculated porosity of the insulating layer was 30% by volume to 100 parts by mass of the polyimide precursor, to prepare resin varnish No. 1. As the polyimide precursor, a reaction product of pyromellitic dianhydride (PMDA) as an aromatic tetracarboxylic dianhydride and 4,4'-diaminodiphenyl ether (ODA) as an aromatic diamine (mixing ratio (molar ratio) of PMDA and ODA was 100:100) was used. As the thermally decomposable resin-containing particles, core-shell particles (average particle size: 3 μm, flatness: 1.0) in which the core is a polymethyl methacrylate particle and the shell is silicone were used.

(Preparation of insulated wire)
A round copper wire having an average diameter of 1 mm was used as the conductor. Resin varnish No. 1 was applied to the surface of the conductor, and the conductor coated with resin varnish No. 1 was heated in a heating furnace at a set temperature of 500° C. by repeatedly performing the steps, thereby forming an insulating layer having an average thickness of 150 μm, to produce insulated wire No. 1.

[No. 2 to No. 5, No. 7, No. 9 and No. 10]
Resin varnishes No. 2 to No. 5, No. 7, No. 9, and No. 10 were prepared in the same manner as No. 1, except that core-shell particles (average particle size: 3 μm) having the flatness shown in Table 1 below were used. Resin varnishes No. 2 to No. 5, No. 7, No. 9, and No. 10 were used to form insulating layers having average thicknesses shown in Table 1 below, and insulated wires No. 2 to No. 5, No. 7, No. 9, and No. 10 were produced.

[No. 6]
Resin varnish No. 6 was prepared in the same manner as No. 1, except that a reaction product of pyromellitic dianhydride (PMDA) and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) as aromatic tetracarboxylic dianhydride and 4,4'-diaminodiphenyl ether (ODA) as aromatic diamine (mixing ratio (molar ratio) of PMDA, BPDA, and ODA was 30:70:100) was used as the polyimide precursor. Insulated wire No. 6 was produced in the same manner as No. 1, except that an insulating layer having an average thickness shown in Table 1 below was formed using resin varnish No. 6.

[No. 8]
Resin varnish No. 8 was prepared in the same manner as No. 1, except that polytetrafluoroethylene (PTFE) was used as the matrix resin. Insulated wire No. 8 was produced in the same manner as No. 1, except that an insulating layer having an average thickness shown in Table 1 below was formed using resin varnish No. 8.

<Evaluation>
The pore distance and thickness deformation rate of the insulated electric wires No. 1 to No. 10 prepared above were measured according to the following method. The results are shown in Table 1 below.

[Measurement of pore distance]
The cross sections of the insulated electric wires No. 1 to No. 10 prepared above were observed with a scanning electron microscope, and the distance between pores in the thickness direction was measured. More specifically, the minimum distance between two adjacent pores in the thickness direction within 40 different fields of view was measured, and the average value was taken as the measured value.

[Measurement of thickness deformation rate]
The insulated electric wires No. 1 to No. 10 prepared above were pressed in the vertical direction with an indenter at 120 MPa. The average thickness of the insulated electric wires before and after pressing was measured, and the thickness deformation rate was calculated by the following formula. Those with a thickness deformation rate of less than 10% were evaluated as having excellent deformation resistance.
Thickness deformation rate (%) = (average thickness before pressing - average thickness after pressing) ÷ average thickness before pressing

From Table 1, it can be seen that insulated wires No. 1 to No. 6 have superior deformation resistance compared to insulated wires No. 7 to No. 10.

1 Insulated wire 2 Conductor 3 Insulating layer 4 Pore

Claims (8)

A conductor;
and an insulating layer covering the conductor.
the insulating layer contains a resin matrix mainly composed of polyimide and a plurality of pores;
The insulating layer has a porosity of 25 volume % or more,
The average thickness of the insulating layer is 45 μm or more,
an average distance in a thickness direction between the plurality of pores in a cross section of the insulating layer is greater than 0.2 μm;
The insulated wire, wherein the flatness of the plurality of pores is 1.5 or less. The insulated wire according to claim 1, wherein the average diameter of the pores is 0.1 μm or more and 10 μm or less. The insulated wire according to claim 1, wherein the flatness of the pores is 0.5 or more and 1.5 or less. The insulated wire according to claim 1, wherein the porosity is 40% by volume or less. The insulated wire according to claim 1, wherein the average thickness of the insulating layer is 45 μm or more and 200 μm or less. The insulated wire according to claim 1, wherein the pores are derived from particles containing a thermally decomposable resin. The insulated wire according to claim 1, wherein the thickness deformation rate of the insulating layer is less than 10%. 2. The insulated wire of claim 1, wherein the insulated wire is a magnet wire.

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