Coated metal wire

Abstract

The present invention provides a coated metal wire comprising a metal wire and a coating layer formed around the metal wire. The coating layer contains polytetrafluoroethylene having a functional group, and has a drawing strength of 12 kgf／76.2 mm or more, and a partial discharge start voltage of 900 V / 35 m or more.

Description

coated metal wire

[0001] The present disclosure relates to coated metal wire.

[0002] Patent Document 1 describes an electric wire having a conductor and a first insulating layer formed on the outer periphery of the conductor, the first insulating layer being made of a thermosetting resin and a fluororesin, with the mass ratio of the thermosetting resin to the fluororesin being 90:10 to 10:90, and being formed by mixing a thermosetting resin solution with a fluororesin organosol, applying the resulting mixture onto the conductor, and baking it.

[0003] International Publication No. 2011 / 024809

[0004] An object of the present disclosure is to provide a coated metal wire that can withstand high voltage and has excellent processability.

[0005] According to the present disclosure, there is provided a coated metal wire comprising a metal wire and a coating layer formed around the metal wire, wherein the coating layer contains polytetrafluoroethylene having a functional group, and the coated metal wire has a pull-out strength of 12 kgf / 76.2 mm or more and a partial discharge inception voltage of 900 V / 35 μm or more.

[0006] According to the present disclosure, it is possible to provide a coated metal wire that can withstand high voltage and has excellent processability.

[0007] Specific embodiments of the present disclosure will be described in detail below, but the present disclosure is not limited to the following embodiments.

[0008] The coated metal wire of the present disclosure includes a metal wire and a coating layer formed around the metal wire.

[0009] 1. Metal Wire Examples of metals that form the metal wire include copper, stainless steel, aluminum, iron, and alloys thereof. Among these, at least one selected from the group consisting of copper and aluminum is preferred, and copper is more preferred.

[0010] The metal wire may be a round wire or a rectangular wire. In one embodiment, the metal wire is a round wire. The diameter of the metal wire is preferably 0.03 to 2.0 mm, more preferably 0.5 mm or more, and more preferably 1.5 mm or less.

[0011] In one embodiment, the metal wire is a rectangular wire. The cross-sectional width of the rectangular wire may be 1 to 75 mm, and the cross-sectional thickness of the conductor may be 0.1 to 30 mm. The outer diameter of the conductor may be 6.5 mm or more and 200 mm or less. The width-to-thickness ratio may be greater than 1 and less than 30.

[0012] The surface roughness (Rzjis) of the metal wire is preferably 4.0 μm or more, more preferably 6.0 μm or more, since this further improves the withstand voltage and processability. The upper limit is not particularly limited, but may be 100 μm or less.

[0013] The surface roughness (Rzjis) of the metal wire can be measured by observing the surface of the metal wire using a laser microscope.

[0014] The surface of the metal wire is preferably roughened. Examples of the roughening method include surface treatment methods such as etching, blasting, and laser treatment. By roughening the surface of the metal wire, the surface roughness (Rzjis) of the metal wire can be easily adjusted to fall within the above-mentioned range.

[0015] The surface of the metal wire may be subjected to a coupling treatment. The coupling treatment is preferably a silane coupling treatment. A silane coupling agent having a reactive functional group can be used for the silane coupling treatment. The reactive functional group is preferably at least one selected from an amino group, an alkoxy group, a (meth)acrylic group, a mercapto group, and an epoxy group.

[0016] 2. Covering Layer The covered metal wire of the present disclosure includes a covering layer, and the metal wire and the covering layer are directly bonded to each other. The covering layer contains polytetrafluoroethylene having functional groups.

[0017] There is a demand for higher drive voltages for motors installed in automobiles in order to increase the motor's rotational speed and torque. Increasing the drive voltage of inverter-driven motors also increases surge voltage. Electric wires used in motors must withstand not only the drive voltage but also surge voltage. That is, to prevent insulation breakdown of coated metal wires due to inverter surges, it is necessary to increase the partial discharge inception voltage of the coating layer. Increasing the thickness of the coating layer increases the partial discharge inception voltage, but this is undesirable because it increases the size of the motor.

[0018] By forming the insulating layer of a coated metal wire from polytetrafluoroethylene, the partial discharge inception voltage of the coating layer can be increased without increasing the thickness of the coating layer compared to when the insulating layer is formed from a thermosetting resin or a conventional fluororesin. However, the adhesion between the metal wire and the coating layer is insufficient, which can cause problems such as the coating layer lifting off the metal wire during winding. Furthermore, impacts and friction during processing can cause the coating layer to wear or deform, resulting in a decrease in insulation properties.

[0019] In the present disclosure, the coating layer is formed from polytetrafluoroethylene having functional groups, which allows for strong adhesion between the metal wire and the coating layer, improving the windability of the coated metal wire and making it less susceptible to deterioration in insulation even when impacts or friction occur during processing of the coated metal wire. In other words, the improved processability of the coated metal wire means that when the coated metal wire of the present disclosure is used in a motor, the motor's defect rate decreases and motor productivity increases.

[0020] Furthermore, when a metal wire having a surface roughness (Rzjis) within the above range is used, the pull-out strength is further increased, and the windability is further improved. Also, the skin effect makes it difficult for surface current to flow, thereby preventing the flow of high-voltage surge current.

[0021] The pull-out strength of the coated metal wire of the present disclosure is 12 kgf / 76.2 mm or more. The upper limit of the pull-out strength is not particularly limited, and may be a strength at which the coating layer breaks or the metal wire breaks during measurement.

[0022] The pull-out strength can be measured by a method conforming to MIL C-17. In the present disclosure, the pull-out strength is the tensile force (maximum value) measured when the coating layer is pulled from the metal wire at a speed of 12.7 mm / min over a distance of 76.2 mm. Therefore, the pull-out strength represents the adhesive strength or adhesion strength between the metal wire and the coating layer, and the higher the pull-out strength, the stronger the adhesive strength or adhesion strength between the metal wire and the coating layer. If the pull-out strength exceeds 15 kgf / 76.2 mm, the coating layer breaks or the metal wire breaks during measurement.

[0023] The polytetrafluoroethylene having functional groups contained in the coating layer can firmly adhere to the copper foil. The peel strength between the sheet made of polytetrafluoroethylene having functional groups and the copper foil is preferably 3 N / cm or more, more preferably 7 N / cm or more, and although there is no particular upper limit, it may be 20 N / cm or less.

[0024] The peel strength can be determined by preparing a test piece by bonding polytetrafluoroethylene having a functional group contained in the coating layer onto copper foil by hot pressing, and measuring the peel strength of the obtained test piece using the 90°C peel test method of JIS K6481-1996.

[0025] The partial discharge inception voltage of the coated metal wire of the present disclosure is 900 V / 35 μm or more, preferably 950 V / 35 μm or more, more preferably 1000 V / 35 μm or more, and even more preferably 1100 V / 35 μm or more. The upper limit is not particularly limited, but is 2000 V / 35 μm or less.

[0026] In the present disclosure, the partial discharge inception voltage (V / 35 μm) is a converted value obtained by converting an actual measurement value into a value assuming that the thickness of the coating layer is 35 μm. The partial discharge inception voltage (actual measurement value) used for the conversion can be measured by the method described in the Examples. The partial discharge inception voltage can be adjusted to fall within the above range by appropriately selecting the type of polytetrafluoroethylene used for the coating layer, the thickness of the coating layer, the method for forming the coating layer, etc.

[0027] The functional groups contained in polytetrafluoroethylene are preferably a cyano group (—CN), a group represented by the general formula (1): (R １ and R ２ are each independently a hydrogen atom, a halogen atom, or —OR ３ , -N(R ３ ) ２ , -R ３ and R ３ is a C1 to C10 alkyl group which may contain fluorine or a hydrogen atom), and a functional group (1) represented by general formula (2): (R １ is a hydrogen atom, a halogen atom, -OR ３ , -N(R ３ ) ２ , -R ３ and R ３ is a C1-10 alkyl group which may contain fluorine or a hydrogen atom),

[0028] Among these, the functional group of polytetrafluoroethylene is preferably the functional group represented by the general formula (2) because it can further increase the pull-out strength, and is -COOR ３ (R ３ is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms which may contain fluorine), and —COOH and —COOCH ３ More preferably, at least one selected from the group consisting of:

[0029] The content of functional groups in polytetrafluoroethylene is preferably 0.0001 to 2 mol%, more preferably 0.001 mol% or more, even more preferably 0.003 mol% or more, more preferably 1 mol% or less, even more preferably 0.50 mol% or less, still more preferably 0.30 mol% or less, and particularly preferably 0.20 mol% or less, relative to all monomer units constituting polytetrafluoroethylene, because this can further increase the pull-out strength.

[0030] The content of functional groups in polytetrafluoroethylene can be measured by NMR measurement.

[0031] The number of functional groups in polytetrafluoroethylene is 1×10 main chain carbon atoms, which can further increase the pull-out strength. ６ The number of functional groups per unit is preferably 1 or more, more preferably 3 or more, and even more preferably 5 or more, and the upper limit is not particularly limited, but may be 12,000 or less, 6,000 or less, or 3,000 or less. The number of functional groups includes the number of functional groups present at the terminals of the main chain of polytetrafluoroethylene as well as the number of functional groups present at the terminals of the side chains.

[0032] The number of functional groups in polytetrafluoroethylene can be measured by Fourier transform infrared spectroscopy.

[0033] In one embodiment, the coating layer is formed of non-melt-processible polytetrafluoroethylene. This further improves the withstand voltage and processability. "Non-melt-processible" means that the melt flow rate cannot be measured at a temperature higher than the crystallization melting point in accordance with ASTM D 1238 and D 2116. In other words, non-melt-processible polytetrafluoroethylene does not substantially flow even when heated above its melting point.

[0034] The melting point of polytetrafluoroethylene is preferably 321° C. or higher, more preferably 325° C. or higher, and preferably 350° C. or lower, more preferably 348° C. or lower.

[0035] The melting point of polytetrafluoroethylene can be measured by simultaneous differential scanning calorimetry and thermogravimetry.

[0036] The standard specific gravity (SSG) of polytetrafluoroethylene is preferably 2.130 or more, more preferably 2.150 or more, and preferably 2.280 or less, more preferably 2.210 or less.

[0037] The standard specific gravity (SSG) of polytetrafluoroethylene can be measured by the water displacement method according to ASTM D 792 using a sample molded according to ASTM D 4895-89.

[0038] The above-mentioned functional groups can be introduced into polytetrafluoroethylene by using a polymerization initiator or chain transfer agent capable of introducing the above-mentioned functional groups into the molecular chain terminals of polytetrafluoroethylene in the polymerization reaction for producing polytetrafluoroethylene. For example, when a persulfate such as ammonium persulfate is used as the polymerization initiator in the polymerization reaction, -COOH, -COOCH ３ -COOR etc. ３ (R ３ is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms which may contain fluorine. ３ By treating polytetrafluoroethylene having a functional group represented by -COOR with ammonia, ３ The functional group represented by -CONH ２ In this way, for example, the above-mentioned functional group (1) or functional group (2) can be introduced into the molecular chain terminal of polytetrafluoroethylene.

[0039] The above-mentioned functional groups can also be introduced into polytetrafluoroethylene by copolymerizing tetrafluoroethylene with a monomer having a functional group.

[0040] Examples of the monomer having a functional group include a monomer having an ethylenically unsaturated bond and at least one selected from the group consisting of a cyano group (—CN), a functional group (1) represented by general formula (1), and a functional group (2) represented by general formula (2).

[0041] The content of units based on monomers having functional groups in polytetrafluoroethylene is preferably 0.0001 to 2 mol%, more preferably 0.001 mol% or more, even more preferably 0.003 mol% or more, more preferably 1 mol% or less, even more preferably 0.50 mol% or less, still more preferably 0.30 mol% or less, and particularly preferably 0.20 mol% or less, relative to all monomer units constituting polytetrafluoroethylene, because this can further increase the pull-out strength.

[0042] The content of units based on a monomer having a functional group in polytetrafluoroethylene can be measured by NMR measurement.

[0043] The monomer having a functional group includes a monomer represented by the general formula (3): CY １ Y ２ =CY ３ (O) ｍ (R ８ ) ｎ -Z １ (3) (wherein, Y １ ~Y ３ are each independently a hydrogen atom, a halogen atom, or —CH ３ , or -CF ３ and R ８ is a divalent organic group, n is 0 or 1, m is 0 when n is 0, and 0 or 1 when n is 1, Z １ is at least one selected from the group consisting of a cyano group (—CN), a functional group (1) represented by general formula (1), and a functional group (2) represented by general formula (2).

[0044] Y １ and Y ２ A fluorine atom is preferred as Y. ３ is a fluorine atom or —CF ３ is preferred.

[0045] R ８As R, an alkylene group having 1 to 100 carbon atoms which may contain an ether bond is preferred. The number of carbon atoms is more preferably 1 to 50, and even more preferably 1 to 20. In such an alkylene group, some or all of the hydrogen atoms may be substituted with halogen atoms, particularly fluorine atoms. ８ As the alkylene group, a fluorine-containing alkylene group having 1 to 10 carbon atoms which may contain an ether bond is particularly preferred.

[0046] In addition, from the above-mentioned structure, the following compound can be exemplified as an example: CH ２ =CH-(CF ２ ) ｎ -Z ２ (4) (wherein n is an integer of 2 to 8) CY ４ ２ =CY ４ (CF ２ ) ｎ -Z ２ (5) (wherein, Y ４ is a hydrogen atom or a fluorine atom, and n is an integer of 1 to 8) CF ２ =CFCF ２ R ｆ ４ -Z ２ (6) (wherein, R ｆ ４ Ha-(OCF ２ ) ｎ - or - (OCF (CF ３ )) ｎ -, and n is an integer from 0 to 5) CF ２ =CFCF ２ (OCF (CF ３ )CF ２ ) ｍ (OCH ２ CF ２ CF ２ ) ｎ OCH ２ CF ２ -Z ２ (7) (wherein m is an integer from 0 to 5, and n is an integer from 0 to 5) CF ２ =CFCF ２ (OCH ２ CF ２ CF ２ )ｍ (OCF (CF ３ )CF ２ ) ｎ OCF (CF ３ )-Z ２ (8) (wherein m is an integer of 0 to 5, and n is an integer of 0 to 5) CF ２ =CF(OCF ２ CF (CF ３ )) ｍ O (CF ２ ) ｎ -Z ２ (9) (wherein m is an integer of 0 to 5, and n is an integer of 1 to 8) CF ２ =CF(OCF ２ CF (CF ３ )) ｍ -Z ２ (10) CF (wherein m is an integer from 1 to 5) ２ = CFOCF ２ (CF (CF ３ ) OCF ２ ) ｎ CF(-Z ２ )CF ３ (11) CF (wherein n is an integer from 1 to 4) ２ = CFO (CF ２ ) ｎ OCF (CF ３ )-Z ２ (12) CF (wherein n is an integer from 2 to 5) ２ = CFO (CF ２ ) ｎ -(C ６ H ４ )-Z ２ (13) CF (wherein n is an integer from 1 to 6) ２ =CF(OCF ２ CF (CF ３ )) ｎ OCF ２ CF (CF ３ )-Z ２ (14) (wherein n is an integer of 1 to 2) CH ２ =CFCF ２ O(CF(CF ３ )CF ２ O) ｎ CF (CF３ )-Z ２ (15) (wherein n is an integer from 0 to 5), CF ２ = CFO (CF ２ CF (CF ３ ) O) ｍ (CF ２ ) ｎ -Z ２ (16) (wherein m is an integer of 0 to 5, and n is an integer of 1 to 3) CH ２ =CFCF ２ OCF (CF ３ ) OCF (CF ３ )-Z ２ (17) CH ２ =CFCF ２ OCH ２ CF ２ -Z ２ (18) CF ２ = CFO (CF ２ CF (CF ３ ) O) ｍ CF ２ CF (CF ３ )-Z ２ (19) (wherein m is an integer of 0 or more) CF ２ = CFOCF(CF ３ )CF ２ O (CF ２ ) ｎ -Z ２ (20) (wherein n is an integer of 1 or more) CF ２ = CFOCF ２ OCF ２ CF (CF ３ ) OCF ２ -Z ２ (21) CF ２ =CF-(CF ２ C (CF ３ ) F) ｎ -Z ２ (22) (wherein n is an integer from 1 to 5), CF ２ = CFO - (CFY ５ ) ｎ -Z ２ (23) (wherein, Y ５ is F or -CF ３and n is an integer from 1 to 10. ２ = CFO-(CF ２ CFY ６ O) ｍ -(CF ２ ) ｎ -Z ２ (24) (wherein, Y ６ is F or -CF ３ wherein m is an integer from 1 to 10, and n is an integer from 1 to 3. ２ =CFCF ２ O-(CF(CF ３ )CF ２ O) ｎ -CF (CF ３ )-Z ２ (25) (wherein n is an integer from 0 to 10) CF ２ =CFCF ２ O-(CF(CF ３ )CF ２ O) ｎ -CF (CF ３ )-Z ２ (26) CF (wherein n is an integer from 1 to 10) ２ = C(CF ３ )-(CF ２ ) ｎ -Z ２ (27) (wherein n is an integer of 0 to 8) (in the general formulas (4) to (27), Z ２ is any of the above functional groups)

[0047] Specific examples of the monomer represented by the general formula (5) include: ２ =CF-CF ２ -CN,CF ２ =CF-CF ２ CF ２ -CN,CF ２ =CFCF ２ -C(=NH)-OR, CF ２ =CFCF ２ CF ２ -C(=NH)-OR, CF ２ =CF-CF ２ -COOH, CF ２ =CF-CF ２ CF ２ -COOH, CF２ =CF-CF ２ -COOCH ３ , C.F. ２ =CF-CF ２ CF ２ -COOCH ３ Examples include:

[0048] Specific examples of the monomer represented by the general formula (22) include: ２ =CFCF ２ C (CF ３ ) FCN, CF ２ =CF(CF ２ C (CF ３ ) F) ２ C.N., C.F. ２ =CFCF ２ C (CF ３ )FC(=NH)-OR, CF ２ =CF(CF ２ C (CF ３ ) F) ２ -C(=NH)-OR, CF ２ =CFCF ２ C (CF ３ ) FCOOH, CF ２ =CF(CF ２ C (CF ３ ) F) ２ COOH, C.F. ２ =CFCF ２ C (CF ３ ) FCOOCH ３ , C.F. ２ =CF(CF ２ C (CF ３ ) F) ２ COOCH ３ Examples include:

[0049] Specific examples of the monomer represented by the general formula (23) include: ２ = CFOCF ２ CF ２ CF ２ C.N., C.F. ２ = CFOCF ２ CF ２ C.N., C.F. ２ = CFOCF ２ C.N., C.F. ２ = CFOCF ２ CF ２CF ２ -C(=NH)-OR, CF ２ = CFOCF ２ CF ２ -C(=NH)-OR, CF ２ = CFOCF ２ -C(=NH)-OR, CF ２ = CFOCF ２ CF ２ CF ２ COOH, C.F. ２ = CFOCF ２ CF ２ COOH, C.F. ２ = CFOCF ２ COOH, C.F. ２ = CFOCF ２ CF ２ CF ２ COOCH ３ , C.F. ２ = CFOCF ２ CF ２ COOCH ３ , C.F. ２ = CFOCF ２ COOCH ３ Examples include:

[0050] Specific examples of the monomer represented by the general formula (24) include: ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ C.N., C.F. ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ -C(=NH)-OR, CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ COOH, C.F. ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ COOCH ３ Examples include:

[0051] Specific examples of the monomer represented by the general formula (25) include:２ =CFCF ２ OCF(CF ３ )CN、CH ２ =CFCF ２ OCF(CF ３ )CF ２ OCF(CF ３ )CN、CH ２ =CFCF ２ O(CF(CF ３ )CF ２ O) ２ CF(CF ３ )CN、CH ２ =CFCF ２ OCF(CF ３ )-C(=NH)-OR、CH ２ =CFCF ２ OCF(CF ３ )CF ２ OCF(CF ３ )-C(=NH)-OR、CH ２ =CFCF ２ O(CF(CF ３ )CF ２ O) ２ CF(CF ３ )-C(=NH)-OR、CH ２ =CFCF ２ OCF(CF ３ )COOH、CH ２ =CFCF ２ OCF(CF ３ )CF ２ OCF(CF ３ )COOH、CH ２ =CFCF ２ O(CF(CF ３ )CF ２ O) ２ CF(CF ３ )COOH、CH ２ =CFCF ２ OCF(CF ３ )COOCH ３ 、CH ２ =CFCF ２ OCF(CF ３ )CF ２ OCF(CF ３ )COOCH ３ 、CH ２ =CFCF ２O(CF(CF ３ )CF ２ O) ２ CF (CF ３ ) COOCH ３ Examples include:

[0052] Specific examples of the monomer represented by the general formula (26) include: ２ =CFCF ２ OCF (CF ３ )CF ２ OCF (CF ３ ) CN, CF ２ =CFCF ２ OCF (CF ３ )CF ２ OCF (CF ３ )-C(=NH)-OR, CF ２ =CFCF ２ OCF (CF ３ )CF ２ OCF (CF ３ ) COOH, CF ２ =CFCF ２ OCF (CF ３ )CF ２ OCF (CF ３ ) COOCH ３ Examples include:

[0053] Specific examples of the monomer represented by the general formula (27) include: ２ = C(CF ３ )-CN, CF ２ = C(CF ３ )-CF ２ -CN,CF ２ = C(CF ３ )-CF ２ CF ２ -CN,CF ２ = C(CF ３ )-C(=NH)-OR, CF ２ = C(CF ３ )CF ２ -C(=NH)-OR, CF ２ = C(CF ３ )CF ２ CF ２ -C(=NH)-OR, CF ２ = C(CF ３ )-COOH, CF ２= C(CF ３ )-CF ２ -COOH, CF ２ = C(CF ３ )-CF ２ CF ２ -COOH, CF ２ = C(CF ３ )-COOCH ３ , C.F. ２ = C(CF ３ )-CF ２ -COOCH ３ , C.F. ２ = C(CF ３ )-CF ２ CF ２ -COOCH ３ Examples include:

[0054] Among the monomers having functional groups, CF is particularly preferred because it can further increase the pull-out strength. ２ = C(CF ３ ) COOCH ３ , C.F. ２ = CFOCF ２ CF ２ COOH and CF ２ = CFOCF ２ C (CF ３ ) FOCF ２ CF ２ COOCH ３ At least one selected from the group consisting of CF ２ = CFOCF ２ C (CF ３ ) FOCF ２ CF ２ COOCH ３ is more preferable.

[0055] Polytetrafluoroethylene may contain units based on a monomer other than tetrafluoroethylene and a monomer having a functional group. As the monomer other than the monomer having a functional group, a fluorine-containing monomer (excluding tetrafluoroethylene and a monomer having a functional group) is preferred.

[0056] Examples of the fluorine-containing monomer include hexafluoropropylene, chlorotrifluoroethylene, trifluoroethylene, perfluoro(alkyl vinyl ether), perfluoro(alkoxy vinyl ether), (perfluoroalkyl)ethylene, etc. Among these, at least one selected from the group consisting of hexafluoropropylene and perfluoro(alkyl vinyl ether) is preferred.

[0057] The perfluoro(alkyl vinyl ether) is preferably at least one selected from the group consisting of perfluoro(methyl vinyl ether) [PMVE], perfluoro(ethyl vinyl ether) [PEVE], perfluoro(propyl vinyl ether) [PPVE], and perfluoro(butyl vinyl ether).

[0058] The content of units based on other monomers is preferably 0 to 2 mol %, more preferably 0.01 mol % or more, even more preferably 0.03 mol % or more, more preferably 1 mol % or less, and even more preferably 0.50 mol % or less, based on the total monomer units constituting polytetrafluoroethylene.

[0059] The coating layer may contain only polytetrafluoroethylene having a functional group as a polymer, or may contain a polymer other than polytetrafluoroethylene having a functional group. The content of polytetrafluoroethylene having a functional group in the coating layer is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 99% by mass or more, still more preferably 99.9% by mass or more, and preferably 100% by mass or less, when the polymer contained in the coating layer is 100% by mass.

[0060] Polytetrafluoroethylene having a functional group can be produced, for example, by the method described in JP-A-2009-44018.

[0061] The coating layer may contain inorganic pigments, fillers, adhesion promoters, antioxidants, lubricants, dyes, etc. The inorganic pigments are preferably those that are stable during molding, and examples thereof include oxides of titanium and iron, and carbon powder.

[0062] The thickness of the coating layer is preferably 1 μm to 1 mm, more preferably 5 μm or more, even more preferably 10 μm or more, more preferably 300 μm or less, even more preferably 100 μm or less, and still more preferably 50 μm or less.

[0063] The dielectric constant of the coating layer is preferably 2.1 to 2.6. The dielectric constant of the coating layer is the dielectric constant of the coating layer alone. The dielectric constant of the coating layer can be measured by removing the metal wire constituting the coated metal wire and recovering only the coating layer, and then measuring the recovered coating layer by a cavity resonator method at 6 GHz and 25±3°C.

[0064] 3. Coated Metal Wire The coated metal wire of the present disclosure can be produced, for example, by a production method in which polytetrafluoroethylene having functional groups is coated and molded onto a metal wire.

[0065] Methods for covering and molding polytetrafluoroethylene having functional groups include dipping, wrapping, extrusion, etc. Among these, the dipping method is preferred because it allows for easy production of a covered metal wire having high pull-out strength and excellent windability (processability). By using the dipping method, it is possible to increase the pull-out strength even when the number of functional groups in the polytetrafluoroethylene is small.

[0066] When using the dipping method, an aqueous dispersion containing polytetrafluoroethylene having functional groups is prepared, and the metal wire is immersed in the aqueous dispersion and then pulled out, thereby forming a coating layer. The content of polytetrafluoroethylene in the aqueous dispersion may be, for example, 20 to 60 mass %. Furthermore, the operation of immersing the metal wire in the aqueous dispersion and then pulling it out may be repeated multiple times until the desired thickness is achieved. Furthermore, the metal wire may be dried or heat-treated each time it is pulled out of the aqueous dispersion.

[0067] When the wrapping method is used, the coating layer can be formed by paste-extrusion molding of polytetrafluoroethylene having functional groups to produce an extrudate, rolling the extrudate to produce a sheet, and wrapping the sheet around a metal wire.

[0068] When using the extrusion molding method, the coating layer can be formed by paste extrusion molding polytetrafluoroethylene having functional groups onto the metal wire.

[0069] In the above manufacturing method, after the coating layer is formed, the coating layer may be baked. The baking temperature may be equal to or higher than the melting point of polytetrafluoroethylene and equal to or lower than 420° C. The baking time may be equal to or higher than 10 seconds and equal to or lower than 60 minutes.

[0070] The coated metal wire of the present disclosure can be suitably used for coils used in various motors such as automobile motors and robot motors.

[0071] The coated metal wire of the present disclosure has a coating layer with a particularly high partial discharge inception voltage, and therefore can withstand not only drive voltage but also surge voltage. Therefore, the coated metal wire of the present disclosure is particularly suitable for use as a coil for a motor driven by a DC power inverter.

[0072] Although the embodiments have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the claims.

[0073] <1> According to a first aspect of the present disclosure, there is provided a coated metal wire comprising a metal wire and a coating layer formed around the metal wire, the coating layer containing polytetrafluoroethylene having a functional group, and having a pull-out strength of 12 kgf / 76.2 mm or more and a partial discharge inception voltage of 900 V / 35 μm or more. <2> According to a second aspect of the present disclosure, there is provided a coated metal wire according to the first aspect, in which the polytetrafluoroethylene is non-melt-processable. <3> According to a third aspect of the present disclosure, there is provided a coated metal wire in which the functional group is a cyano group (—CN), a fluorine-containing compound represented by general formula (1): (R １ and R ２are each independently a hydrogen atom, a halogen atom, or —OR ３ , -N(R ３ ) ２ , -R ３ and R ３ is a C1 to C10 alkyl group which may contain fluorine or a hydrogen atom), and a functional group (1) represented by general formula (2): (R １ is a hydrogen atom, a halogen atom, -OR ３ , -N(R ３ ) ２ , -R ３ and R ３ (2) where (C) is an alkyl group having 1 to 10 carbon atoms which may contain fluorine or a hydrogen atom). <4> According to a fourth aspect of the present disclosure, there is provided a covered metal wire according to any one of the first to third aspects, wherein the content of the functional group in the polytetrafluoroethylene is 0.0001 to 2 mol % based on the total monomer units constituting the polytetrafluoroethylene. <5> According to a fifth aspect of the present disclosure, there is provided a covered metal wire according to any one of the first to fourth aspects, wherein the metal wire has a surface roughness (Rzjis) of 4.0 μm or more. <6> According to a sixth aspect of the present disclosure, there is provided a coil including the covered metal wire according to any one of the first to fifth aspects. <7> According to a seventh aspect of the present disclosure, there is provided a motor including the coil according to the sixth aspect. <8> According to an eighth aspect of the present disclosure, there is provided a coil for a motor driven by a DC power supply inverter, including the covered metal wire according to any one of the first to fifth aspects. <9> According to a ninth aspect of the present disclosure, there is provided a DC power supply inverter-driven motor including the coil for a DC power supply inverter-driven motor according to the eighth aspect.

[0074] Next, embodiments of the present disclosure will be described with reference to examples, but the present disclosure is not limited to these examples.

[0075] 1. Preparation of Polytetrafluoroethylene (PTFE) The values ​​in the examples were measured by the following methods.

[0076] <Average primary particle diameter> A PTFE aqueous dispersion with a solid content adjusted to approximately 1.0% by mass was prepared, and the average primary particle diameter was measured at 25°C and 70 times cumulatively using an ELSZ-1000S (manufactured by Otsuka Electronics Co., Ltd.) The refractive index of the solvent (water) was 1.3328, and the viscosity was 0.8878 mPa s.

[0077] <Melting point> Approximately 10 mg of PTFE powder was weighed out and placed in a dedicated aluminum pan, and measured using a TG / DTA (thermogravimetric / differential thermal analyzer). The aluminum pan was heated in an air atmosphere from 25°C to 600°C at a rate of 10°C / min to obtain a differential thermal (DTA) curve, and the melting point (peak temperature) was determined as the temperature corresponding to the maximum value in the obtained differential thermal (DTA) curve.

[0078] <Standard Specific Gravity (SSG)> Using a sample molded in accordance with ASTM D 4895-89, the standard specific gravity was measured by the water displacement method in accordance with ASTM D 792.

[0079] <Modification amount (monomer content)> Solid １９ A peak derived from TFE and a peak derived from the modifier were detected by F-MAS NMR measurement (probe diameter: 4.0 mm, rotation speed: 30 KHz, measurement atmosphere: nitrogen, measurement temperature: 150°C), and the ratio was calculated from the area ratio of these peaks.

[0080] <Solid content concentration (P)> 1 g of the aqueous PTFE dispersion (X) was placed in an aluminum cup having a diameter of 5 cm, dried at 100°C for 60 minutes, and further dried at 300°C for 60 minutes to obtain a heating residue (Z). Based on this, the solid content concentration (P) was determined by the formula: P = Z / X × 100 (%).

[0081] <Nonionic surfactant content (N)> 1 g of the aqueous PTFE dispersion (X) was placed in an aluminum cup having a diameter of 5 cm and heated at 100°C for 60 minutes to obtain a heating residue (Y). The heating residue (Y) thus obtained was then heated at 300°C for 60 minutes to obtain a heating residue (Z). From this, the nonionic surfactant content (N) was calculated from the formula: N=[(Y-Z) / Z]×100(%).

[0082] <Method for measuring the number of functional groups> PTFE powder is compression molded at 25°C to produce a film with a thickness of 0.25 to 0.5 mm. The obtained film is analyzed by Fourier transform infrared spectroscopy to obtain a difference spectrum between the infrared absorption spectrum of the fluororesin and the spectrum in which no functional groups are present. From the absorption peaks of specific functional groups that appear in this difference spectrum, the number of main chain carbon atoms in PTFE is calculated according to the following formula (A): ６ The number of functional groups per molecule, N, is calculated as follows: N = (I x K) / t (A), where I is absorbance, K is correction coefficient, and t is film thickness (mm).

[0083] The correction factor for the target terminal group is shown below. This correction factor is 1 x 10 ６ The functional group absorption frequency (cm) was determined from the infrared absorption spectrum of a model compound to calculate the functional group per unit area. －１ ) Correction coefficient -COOH (free) 1815 439 -COOH (associated) 1779 439 -COOCH ３ 1795 342 -CONH ２ 3436 460

[0084] (Synthesis Example 1) 3,560 g of deionized water, 104 g of paraffin wax, and 3.58 g of a white solid obtained by the method described in Synthesis Example 1 of WO 2021 / 045228 were placed in a 6 L stainless steel reactor equipped with a stirrer. The contents of the reactor were then heated to 70°C while being aspirated and simultaneously purged with TFE monomer to remove oxygen from the reactor. Thereafter, 10.0 g of perfluoro[3-(1-methyl-2-vinyloxy-ethoxy)methyl propionate] (CF ２ = CFOCF ２ C (CF ３ ) FOCF ２ CF ２ COOCH ３RVEE) was added to the reactor, and the contents were stirred at 280 rpm. TFE monomer was added to the reactor until the pressure reached 0.73 MPa. 0.036 g of ammonium persulfate (APS) initiator dissolved in 20 g of deionized water was injected into the reactor, and the reactor pressure was adjusted to 0.83 MPa. After the initiator injection, a drop in pressure occurred and the initiation of polymerization was observed. TFE monomer was added to the reactor to maintain the pressure, and polymerization was continued until approximately 1.5 kg of TFE monomer had reacted. Thereafter, the reactor was vented, and the contents were removed from the reactor and cooled. The supernatant paraffin wax was removed from the PTFE aqueous dispersion. The solids concentration of the resulting PTFE aqueous dispersion (1-1) was 29.2 mass %, and the average primary particle size was 217 nm.

[0085] The resulting PTFE aqueous dispersion (1-1) was diluted with deionized water to a solids concentration of approximately 15% by mass and coagulated under high-speed stirring conditions. The coagulated powder was dried at 150°C for 18 hours. The resulting PTFE powder had a melting point of 334.8°C, an SSG of 2.183, and a RVEE modification level of 0.122 mol%. The RVEE modification level was determined by detecting a TFE-derived peak (-150 to -90 ppm) and a RVEE-derived peak (-85 to -72 ppm) and calculating the area ratio of these peaks.

[0086] The resulting PTFE aqueous dispersion (1-1) was mixed with a nonionic surfactant RO(CH ２ CH ２ O) ｎH (R: tridecyl group) (product name: Noigen TDS-80, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was added to prepare an aqueous PTFE dispersion with a nonionic surfactant concentration of 10 parts by mass per 100 parts by mass of PTFE solids. Subsequently, a 20 mm diameter column was filled with 250 ml of OH-type anion exchange resin (trade name: Amberjet 4002, manufactured by Rohm and Haas Co.), and the aqueous PTFE dispersion was passed through at an SV of 1. Furthermore, a nonionic surfactant (Noigen TDS-80) was added to the aqueous PTFE dispersion obtained after passing through the column so that the concentration was 16 parts by mass per 100 parts by mass of PTFE solids, and the mixture was maintained at 65°C for 3 hours, allowing the dispersion to separate into a supernatant phase and a concentrated phase. The concentrated phase was recovered, yielding aqueous PTFE dispersion (1-2). The resulting PTFE aqueous dispersion (1-2) had a solids concentration of 65.2% by mass and an ionic surfactant content of 2.8% by mass relative to the PTFE solids. A nonionic surfactant (Noigen TDS-80) was added to the resulting PTFE aqueous dispersion (1-2) so that the content was 5.0% by mass relative to the PTFE solids, and deionized water and aqueous ammonia were further added to obtain a PTFE aqueous dispersion (1-3). The resulting PTFE aqueous dispersion (1-3) had a solids concentration of 60.0% by mass and a nonionic surfactant content of 5.0% by mass relative to the PTFE solids.

[0087] Synthesis Example 2 Polymerization was carried out in the same manner as in Synthesis Example 1, except that 10.0 g of RVEE was not added. The solid content concentration of the resulting PTFE aqueous dispersion (2-1) was 23.7% by mass, and the average primary particle diameter was 287 nm.

[0088] The PTFE aqueous dispersion (2-1) obtained in Synthesis Example 2 could be coagulated in the same manner as in Synthesis Example 1 to obtain a PTFE powder. The melting point of the obtained PTFE powder was 342.5°C, the SSG was 2.173, and the number of terminal functional groups was 1 x 10, the number of main chain carbon atoms. ６ There were eight per piece.

[0089] The PTFE aqueous dispersion (2-1) obtained in Synthesis Example 2 could be concentrated by the same method as in Synthesis Example 1, and an aqueous PTFE dispersion (2-2) could be obtained. The resulting aqueous PTFE dispersion (2-2) had a solids concentration of 64.2 mass% and an ionic surfactant content of 4.2 mass% based on the PTFE solids. The concentration of the resulting aqueous PTFE dispersion (2-2) could be adjusted by the same method as in Synthesis Example 1. The resulting aqueous PTFE dispersion (2-3) had a solids concentration of 60.0 mass% and a nonionic surfactant content of 5.0 mass% based on the PTFE solids.

[0090] 2. Preparation of coated metal wires The values ​​of the examples were measured by the following methods.

[0091] <Relative permittivity> The relative permittivity of the coating layer at 6 GHz was measured using a cavity resonator manufactured by EM Lab, a network analyzer P5007A manufactured by Keysight, and calculation software. The temperature was 25±3°C.

[0092] <Surface roughness Rzjis> In accordance with JIS B0601-2001, the ten-point average roughness (Rzjis) was measured using a laser microscope (Keyence VK-X1000, objective lens 20x) at five points in the diameter direction of the metal wire sample. The average value was calculated and used as the surface roughness Rzjis.

[0093] <Peel Strength> A metal foil (here, CF-T9DA-SV (surface-chemically treated copper foil, Rzjis 0.11 μm (Rzjis = 0.14 μm in the catalog value of the company) manufactured by Fukuda Metal Foil & Powder Co., Ltd.) and a fluororesin sheet were bonded by hot pressing, cut to a width of 10 mm, and one end was bent into a T-shape and peeled off to prepare a test piece for a peel test. Based on the 90°C peel test method of JIS K6481-1996, an autograph testing machine manufactured by Shimadzu Corporation was used to measure at room temperature and a crosshead speed of 50 mm / min.

[0094] <Insertion Loss (S21)> A coaxial cable having an impedance of 50 Ω was produced by extruding the resin of the present invention onto a metal core wire having a roughened surface, attaching a metal outer layer, and jacketing it with a heat-shrinkable tube, and attaching connectors to both ends. The insertion loss (S21) of this coaxial cable was measured using an HP8510 network analyzer manufactured by HP.

[0095] <Pull-out strength> The pull-out strength was measured according to a method in accordance with MIL C-17. The pull-out strength is the tensile force (maximum value) measured when the coating layer is pulled from the metal wire at a speed of 12.7 mm / min over a distance of 76.2 mm. In the table, the notation ">15" indicates that the coating layer was broken or the metal wire was broken during the measurement.

[0096] <Abrasion Resistance Test> An abrasion resistance test (reciprocating abrasion resistance, load 150 g) in accordance with JIS C-3003 was carried out, and the number of times until the coating was worn down and the metal wire was exposed was measured.

[0097] <Partial Discharge Inception Voltage> The partial discharge inception voltage was measured for a twisted piece produced in accordance with JIS C3003 using a DAC-PD-7 manufactured by Soken Denki Co., Ltd. under the conditions of a temperature of 25°C, a frequency of 100 kHz, a voltage increase rate of 100 V / sec, a voltage decrease rate of 100 V / sec, and a voltage holding time of 0 sec. The voltage at which a discharge with a charge amount of 10 pC or more occurred was taken as the partial discharge inception voltage.

[0098] Example 1 The solid content concentration of PTFE aqueous dispersion (1-3) was adjusted to 45% by mass, and a 1.0 mm diameter copper wire (RzJIS: 0.92 μm) that had not been subjected to a surface roughening treatment was subjected to dipping. The water was dried at room temperature for 5 minutes and at 110°C for 5 minutes, and then heat-treated at 330°C for 5 minutes. This was repeated 7 times, and then baked at 360°C for 10 minutes. As a result, a 40 μm thick PTFE-coated copper wire was obtained. The partial discharge inception voltage was 1050 V / 35 μm. The pull-out strength was 15 kgf / 76.2 mm or more.

[0099] Example 2 The solid content concentration of the PTFE aqueous dispersion (1-3) was adjusted to 45% by mass, and a 1.0 mm diameter copper wire (RzJIS: 2.00 μm) with a surface treated with #2000 was subjected to dipping. The water was dried at room temperature for 5 minutes and at 110 ° C for 5 minutes, and then heat-treated at 330 ° C for 5 minutes. This was repeated 7 times, and then baked at 360 ° C for 10 minutes. As a result, a 37 μm thick PTFE-coated copper wire was obtained. The partial discharge inception voltage was 942 V / 35 μm. The pull-out strength was 15 kgf / 76.2 mm or more.

[0100] Example 3: The solid content of the PTFE aqueous dispersion (1-3) was adjusted to 45% by mass, and a 1.0 mm diameter copper wire (RzJIS: 8.04 μm) with a surface treated with #240 was subjected to dipping. The wire was dried at room temperature for 5 minutes and at 110 ° C for 5 minutes to remove moisture, and then heat-treated at 330 ° C for 5 minutes. This was repeated 7 times, and then baked at 360 ° C for 10 minutes. As a result, a 36.5 μm thick PTFE-coated copper wire was obtained. The partial discharge inception voltage was 1005 V / 35 μm. The pull-out strength was 15 kgf / 76.2 mm or more.

[0101] Example 4: The solid content concentration of PTFE aqueous dispersion (1-3) was adjusted to 45% by mass, and a 1.0 mm diameter copper wire (RzJIS: 8.04 μm) with a surface treated with #240 was subjected to dipping. The wire was dried at room temperature for 5 minutes and at 110 ° C for 5 minutes, and then heat-treated at 330 ° C for 5 minutes. The surface was dipped with PTFE aqueous dispersion (2-3) with a solid content concentration adjusted to 45% by mass. The dipping, drying, and heat treatment of this PTFE aqueous dispersion (2-3) were repeated six times, and then baked at 360 ° C for 10 minutes. As a result, a 36 μm thick PTFE-coated copper wire was obtained. The partial discharge inception voltage was 1137 V / 35 μm. The pull-out strength was 15 kgf / 76.2 mm or more.

[0102] Example 5: The solid content of the PTFE aqueous dispersion (2-3) was adjusted to 45% by mass, and a 1.0 mm diameter copper wire (RzJIS: 0.92 μm) that had not been surface-treated was subjected to dipping. The wire was dried at room temperature for 5 minutes and at 110°C for 5 minutes to remove moisture, and then heat-treated at 330°C for 5 minutes. This dipping, drying, and heat treatment were repeated 7 times, and then baked at 360°C for 10 minutes. As a result, a 35 μm thick PTFE-coated copper wire was obtained. The partial discharge inception voltage was 1038 V / 35 μm. The pull-out strength was 14 kgf / 76.2 mm.

[0103] Comparative Example 1: A 1.0 mm diameter copper wire (RzJIS: 0.14 μm) that had not been subjected to a surface roughening treatment was coated with polyetherimide / polyamideimide to produce a 35 μm thick coated copper wire. The partial discharge inception voltage was 660 V / 35 μm. The pull-out strength was 15 kgf / 76.2 mm or more.

[0104] The results are shown in Table 1.

[0105] Example 6: PTFE powder obtained from the PTFE aqueous dispersion (1-1) was mixed with 21% by mass of an extrusion aid (trade name: Isopar G, manufactured by ExxonMobil Corporation), and the mixture was preformed and paste-extruded at a diameter of 12 mm. The extrudate was rolled to a thickness of 100 μm using a rolling mill and cut to a width of 5 mm. This sheet was wrapped around a copper wire that had not been surface-treated in two layers. This unsintered tape-coated copper wire was sintered at 360°C for 3 minutes. The partial discharge inception voltage was 1065 V / 35 μm. The pull-out strength was 15 kgf / 76.2 mm or more.

[0106] Example 7 PTFE powder obtained from the PTFE aqueous dispersion (1-1) was mixed with 21% by mass of an extrusion aid (trade name: Isopar G, manufactured by ExxonMobil Corporation), and the mixture was preformed and paste-extruded at a diameter of 12 mm. The extrudate was rolled to a thickness of 100 μm using a rolling mill and cut to a width of 5 mm. This sheet was wrapped around a copper wire that had been surface-treated with #240 so as to form a double layer. This unsintered tape-coated copper wire was sintered at 360°C for 3 minutes. The partial discharge inception voltage was 1020 V / 35 μm. The pull-out strength was 15 kgf / 76.2 mm or more.

[0107] Comparative Example 2: PTFE powder obtained from the PTFE aqueous dispersion (2-1) was mixed with 21% by mass of an extrusion aid (trade name: Isopar G, manufactured by ExxonMobil Corporation), and the mixture was preformed and paste-extruded at a diameter of 12 mm. The extrudate was rolled to a thickness of 100 μm using a rolling mill and cut to a width of 5 mm. This sheet was double-wrapped around a copper wire (RzJIS 8.04 μm) that had been surface-treated with #240. This unsintered tape-coated copper wire was sintered at 360 °C for 3 minutes. The partial discharge inception voltage was 1075 V / 35 μm. The pull-out strength was 0.9 kgf / 76.2 mm.

[0108] The results are shown in Table 2.

[0109] Experimental Example 1: A copper wire with a diameter of 1 mm was roughened using 240-grit sandpaper. The Rzjis was measured to be 8.04 μm. 21% by mass of an extrusion aid (trade name: Isopar G, manufactured by ExxonMobil Corporation) was mixed with PTFE powder obtained from the PTFE aqueous dispersion (1-1) to prepare a paste. The prepared paste was extruded onto the obtained copper wire, and the extrusion aid was dried and baked to form a coating. A shielding braided wire was placed on the outside and held in place with a heat-shrinkable tube to prepare a coaxial cable. The pull-out strength was 15 kgf / 76.2 mm or more. The insertion loss at 20 GHz was measured using a network analyzer and found to be -18.9 dB / 900 mm.

[0110] Experimental Example 2: In Experimental Example 1, the sandpaper roughness was changed to 2000. The Rzjis was measured and found to be 2.00 μm. The other conditions were the same as in Experimental Example 1, and the pull-out strength was 15 kgf / 76.2 mm or more. The insertion loss was -14.8 dB / 900 mm.

[0111] Experimental Example 3: A copper wire with a diameter of 1 mm was used as is. The Rzjis was measured and found to be 0.92 μm. Other than that, measurements were carried out in the same manner, and the pull-out strength was found to be 15 kgf / 76.2 mm or more. The insertion loss was found to be -12.4 dB / 900 mm.

[0112] Generally, DC inverters for automobiles generate a surge voltage two to three times the motor drive voltage during output. Taking into account the rise time of the surge voltage, the surge voltage can be converted into a frequency ranging from several tens of megahertz to several tens of gigahertz.

[0113] Among the coaxial cables fabricated in Experimental Examples 1 to 3, the coaxial cable with the metal wire having the high surface roughness exhibited a lower insertion loss. Therefore, it is clear that by using a metal wire with a high surface roughness, the skin effect makes it difficult for surface current to flow, thereby preventing the flow of high-voltage surge current.

Claims

1. A coated metal wire comprising a metal wire and a coating layer formed around the metal wire, wherein the coating layer contains polytetrafluoroethylene having a functional group, and has a pull-out strength of 12 kgf / 76.2 mm or more and a partial discharge inception voltage of 900 V / 35 μm or more.

2. The coated metal wire according to claim 1, wherein said polytetrafluoroethylene is non-melt processable.

3. The functional group is a cyano group (—CN), a compound represented by the general formula (1): (R １ and R ２ are each independently a hydrogen atom, a halogen atom, or —OR ３ , -N(R ３ ) ２ , -R ３ and R ３ is a C1 to C10 alkyl group which may contain fluorine or a hydrogen atom), and a functional group (1) represented by general formula (2): (R １ is a hydrogen atom, a halogen atom, -OR ３ , -N(R ３ ) ２ , -R ３ and R ３ (2) wherein the functional group is at least one selected from the group consisting of a C1 to C10 alkyl group which may contain fluorine or a hydrogen atom.

4. A coated metal wire according to any one of claims 1 to 3, wherein the content of said functional groups in said polytetrafluoroethylene is 0.0001 to 2 mol % based on the total monomer units constituting said polytetrafluoroethylene.

5. The coated metal wire according to any one of claims 1 to 4, wherein the surface roughness (Rzjis) of the metal wire is 4.0 µm or more.

6. A coil comprising the coated metal wire according to any one of claims 1 to 5.

7. A motor comprising the coil according to claim 6.

8. A coil for a DC power inverter-driven motor, comprising the coated metal wire according to any one of claims 1 to 5.

9. A DC power inverter-driven motor comprising the coil for a DC power inverter-driven motor according to claim 8.

Images