Insulated metal wire

Abstract

To provide a coated metal wire that can withstand high voltages and has excellent processability. [Solution] A coated metal wire is provided, comprising a metal wire and a coating layer formed around the metal wire, wherein the coating layer contains polytetrafluoroethylene having functional groups, has a pull-out strength of 12 kgf / 76.2 mm or more, and has a partial discharge initiation voltage of 900 V / 35 μm or more.

Description

[Technical Field]

[0001] This disclosure relates to coated metal wires. [Background technology]

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

[0003] [Patent Document 1] International Publication No. 2011 / 024809 [Overview of the project] [Problems that the invention aims to solve]

[0004] The purpose of this disclosure is to provide a coated metal wire that can withstand high voltages and has excellent processability. [Means for solving the problem]

[0005] The present disclosure provides a coated metal wire comprising a metal wire and a coating layer formed around the metal wire, wherein the coating layer contains polytetrafluoroethylene having functional groups, the pull-out strength is 12 kgf / 76.2 mm or more, and the partial discharge initiation voltage is 900 V / 35 μm or more. [Effects of the Invention]

[0006] According to this disclosure, it is possible to provide a coated metal wire that can withstand high voltages and has excellent processability. [Modes for carrying out the invention]

[0007] The following describes specific embodiments of this disclosure in detail, but this disclosure is not limited to the embodiments described below.

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

[0009] 1. Metal wire Examples of metals used to 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, with copper being more preferred.

[0010] The metal wire may be round or rectangular. In one embodiment, the metal wire is round. 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 flat wire. The width of the cross-section of the rectangular flat wire may be 1 to 75 mm, and the thickness of the cross-section 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 ratio of width to thickness may be greater than 1 and 30 or less.

[0012] The surface roughness (Rzjis) of the metal wire is preferably 4.0 μm or more, more preferably 6.0 μm or more, and there is no particular upper limit, but it may be 100 μm or less, as this further improves the dielectric strength and processability.

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

[0014] The surface of the metal wire is preferably roughened. Methods for roughening the surface include surface treatments 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 the range described above.

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

[0016] 2.Coating layer The coated metal wire of this disclosure comprises a coating layer, the metal wire and the coating layer being directly bonded. The coating layer contains polytetrafluoroethylene having functional groups.

[0017] There is a demand for higher drive voltages for motors installed in automobiles, with the aim of increasing motor rotation speed and torque. Increasing the drive voltage of an inverter-driven motor also increases the surge voltage. The wires used in the motor need to withstand not only the drive voltage but also the surge voltage. In other words, to prevent dielectric breakdown of the insulated metal wire due to inverter surges, it is necessary to increase the partial discharge initiation voltage of the coating layer. Increasing the thickness of the coating layer increases the partial discharge initiation voltage, but this is undesirable because it increases the size of the motor.

[0018] By forming the insulating layer of a coated metal wire with polytetrafluoroethylene, the partial discharge initiation voltage of the coating layer can be increased without increasing the thickness of the coating layer, compared to cases where the insulating layer is formed with thermosetting resin or conventional fluororesin. However, the adhesion between the metal wire and the coating layer may not be sufficient, and problems such as the coating layer lifting off the metal wire during winding may occur. In addition, the coating layer may wear down or deform due to impact or friction during processing, which can lead to a decrease in insulation performance.

[0019] In this disclosure, since the coating layer is formed from polytetrafluoroethylene having functional groups, the metal wire and the coating layer can be firmly bonded, improving the winding properties of the coated metal wire. Furthermore, even if impact or friction occurs when processing the coated metal wire, the insulation properties are less likely to deteriorate. In other words, the processability of the coated metal wire is improved, so when the coated metal wire of this disclosure is used in a motor, the motor defect rate decreases and the motor productivity increases.

[0020] Furthermore, when using metal wires with a surface roughness (Rzjis) within the above-mentioned range, the pull-out strength is further increased and winding performance is further improved. In addition, due to the skin effect, surface current is less likely to flow, thus preventing the flow of high-voltage surge currents.

[0021] The pull-out strength of the coated metal wire in this disclosure is 12 kgf / 76.2 mm or more. The upper limit of the pull-out strength is not particularly limited and may be any 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 compliant with MIL C-17. In this disclosure, the pull-out strength is the maximum tensile force measured when the coating layer is pulled from the metal wire over a distance of 76.2 mm at a speed of 12.7 mm / min. Therefore, the pull-out strength represents the adhesive or bonding strength between the metal wire and the coating layer; the higher the pull-out strength, the higher the adhesive or bonding strength between the metal wire and the coating layer. If the pull-out strength exceeds 15 kgf / 76.2 mm, the coating layer will break or the metal wire will break during measurement.

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

[0024] The peel strength can be determined by preparing a test specimen by bonding polytetrafluoroethylene containing functional groups in the coating layer onto a copper foil using a hot press, and then measuring the peel strength of the obtained test specimen using the 90°C peel test method of JIS K6481-1996.

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

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

[0027] As for the functional groups that polytetrafluoroethylene possesses, cyano groups (-CN) can further increase the tensile strength. General formula (1): [ka] (R 1 and R 2 Each is independently a hydrogen atom, a halogen atom, and -OR 3 , -N(R 3 )2, -R 3 And R 3 (1) is a functional group (which may contain fluorine or hydrogen atoms having 1 to 10 carbon atoms), and General formula (2): [ka] (R1 is a hydrogen atom, a halogen atom, -OR 3 , -N(R 3 )2, -R 3 where R 3 is an alkyl group which may contain fluorine and has 1 to 10 carbon atoms or a hydrogen atom), and the functional group (2) represented by at least one selected from the group consisting of is preferable.

[0028] As the functional group possessed by polytetrafluoroethylene, among these, since the pull-out strength can be further increased, the functional group represented by the general formula (2) is preferable, and -COOR 3 (R 3 is an alkyl group which may contain fluorine and has 1 to 10 carbon atoms or a hydrogen atom) is more preferable, and at least one selected from the group consisting of -COOH and -COOCH3 is even more preferable.

[0029] Since the content of the functional group in polytetrafluoroethylene can further increase the pull-out strength, it is preferably 0.0001 to 2 mol% with respect to all monomer units constituting polytetrafluoroethylene, 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 even more preferably 0.30 mol% or less, and particularly preferably 0.20 mol% or less.

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

[0031] Since the number of functional groups in polytetrafluoroethylene can further increase the pull-out strength, the main chain carbon atoms are 1×10 6Preferably, there is one or more functional groups per unit, more preferably three or more, and even more preferably five or more. There is no particular upper limit, but it may be 12,000 or less, 6,000 or less, or 3,000 or less. The above number of functional groups includes the number of functional groups present at the ends of the side chains in addition to the number of functional groups present at the ends of the main chain of polytetrafluoroethylene.

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

[0033] In one embodiment, a coating layer is formed using non-melt-processable polytetrafluoroethylene. This further improves dielectric strength and processability. Non-melt-processability means that, in accordance with ASTM D 1238 and D 2116, the melt flow rate cannot be measured at temperatures higher than the crystallization melting point. In other words, non-melt-processable polytetrafluoroethylene does not flow substantially 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, preferably 350°C or lower, and more preferably 348°C or lower.

[0035] The melting point of polytetrafluoroethylene can be measured by differential thermogravimetric analysis.

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

[0037] The standard specific gravity (SSG) of polytetrafluoroethylene can be measured using a sample prepared in accordance with ASTM D 4895-89 and the water displacement method in accordance with ASTM D 792.

[0038] The functional groups described above can be introduced into polytetrafluoroethylene by using a polymerization initiator or chain transfer agent that can introduce the functional groups described above to the molecular chain ends of polytetrafluoroethylene in a polymerization reaction for producing polytetrafluoroethylene. For example, when a persulfate such as ammonium persulfate is used as a polymerization initiator in a polymerization reaction, -COOH, -COOCH3, etc., can be introduced to the molecular chain ends of polytetrafluoroethylene. 3 (R 3 A functional group represented by (which may contain fluorine or hydrogen atoms with 1 to 10 carbon atoms) can be introduced. Also, -COOR 3 By treating polytetrafluoroethylene having the functional group shown by with ammonia, -COOR 3 The functional group shown can be converted to -CONH2. In this way, for example, the functional group (1) or functional group (2) described above can be introduced to the molecular chain end of polytetrafluoroethylene.

[0039] Furthermore, the functional groups described above can be introduced into polytetrafluoroethylene by copolymerization of tetrafluoroethylene with a monomer having a functional group.

[0040] Examples of monomers having functional groups include monomers 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 can further increase the draw strength, so it 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 the total monomer units constituting polytetrafluoroethylene.

[0042] The content of units based on monomers with functional groups in polytetrafluoroethylene can be measured by NMR spectroscopy.

[0043] A monomer having a functional group is the general formula (3): CY 1 Y 2 =CY 3 (O) m (R 8 ) n -Z 1 (3) (In the formula, Y 1 ~Y 3 Each of these is independently a hydrogen atom, a halogen atom, -CH3, or -CF3, and R 8 is a divalent organic group, n is 0 or 1, m is 0 if n is 0, and 0 or 1 if n is 1, Z 1 A monomer represented by a cyano group (-CN), a functional group (1) represented by general formula (1), and a functional group (2) represented by general formula (2) is preferred.

[0044] Y 1 and Y 2 As such, fluorine atoms are preferred. Also, Y 3 Fluorine atoms or -CF3 are preferred as the element.

[0045] R 8 Preferably, the alkylene group may contain ether bonds with 1 to 100 carbon atoms. More preferably, the number of carbon atoms is 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 such, fluorine-containing alkylene groups, which may contain ether bonds having 1 to 10 carbon atoms, are particularly preferred.

[0046] Furthermore, based on the above configuration, the following compounds can be given as examples. CH2=CH-(CF2)n -Z 2 (4) (In the formula, n is an integer between 2 and 8) CY 4 2 = CY 4 (CF2) n -Z 2 (5) (In the formula, Y 4 (where n is a hydrogen atom or a fluorine atom, and n is an integer between 1 and 8) CF2 = CFCF2R f 4 -Z 2 (6) (In the formula, R f 4 ha-(OCF2) n -or-(OCF(CF3)) n - where n is an integer between 0 and 5) CF2 = CFCF2(OCF(CF3)CF2) m (OCH2CF2CF2) n OCH2CF2-Z 2 (7) (In the formula, m is an integer between 0 and 5, and n is an integer between 0 and 5.) CF2 = CFCF2(OCH2CF2CF2) m (OCF(CF3)CF2) n OCF(CF3)-Z 2 (8) (In the formula, m is an integer between 0 and 5, and n is an integer between 0 and 5.) CF2 = CF(OCF2CF(CF3)) m O(CF2) n -Z 2 (9) (In the formula, m is an integer between 0 and 5, and n is an integer between 1 and 8.) CF2 = CF(OCF2CF(CF3)) m -Z 2 (10) (In the formula, m is an integer between 1 and 5) CF2 = CFOCF2(CF(CF3)OCF2) n CF(-Z 2 )CF3(11) (In the formula, n is an integer between 1 and 4.) CF2 = CFO(CF2)n OCF(CF3)-Z 2 (12) (In the formula, n is an integer between 2 and 5.) CF2 = CFO(CF2) n -(C6H4)-Z 2 (13) (In the formula, n is an integer between 1 and 6.) CF2 = CF(OCF2CF(CF3)) n OCF2CF(CF3)-Z 2 (14) (In the formula, n is an integer between 1 and 2.) CH2=CFCF2O(CF(CF3)CF2O) n CF(CF3)-Z 2 (15) (In the formula, n is an integer between 0 and 5.) CF2 = CFO(CF2CF(CF3)O) m (CF2) n -Z 2 (16) (In the formula, m is an integer between 0 and 5, and n is an integer between 1 and 3.) CH2 = CFCF2OCF(CF3)OCF(CF3) - Z 2 (17) CH2=CFCF2OCH2CF2-Z 2 (18) CF2 = CFO(CF2CF(CF3)O) m CF2CF(CF3)-Z 2 (19) (In the formula, m is a non-negative integer.) CF2 = CFOCF(CF3)CF2O(CF2) n -Z 2 (20) (In the formula, n is an integer greater than or equal to 1.) CF2 = CFOCF2OCF2CF(CF3)OCF2 - Z 2 (twenty one) CF2 = CF - (CF2C(CF3)F) n -Z 2 (twenty two) (In the formula, n is an integer between 1 and 5.) CF2 = CFO - (CFY 5 ) n-Z 2 (23) (where Y 5 is F or -CF3, and n is an integer from 1 to 10) CF2=CFO-(CF2CFY 6 O) m -(CF2) n -Z 2 (24) (where Y 6 is F or -CF3, m is an integer from 1 to 10, and n is an integer from 1 to 3) CH2=CFCF2O-(CF(CF3)CF2O) n -CF(CF3)-Z 2 (25) (where n is an integer from 0 to 10) CF2=CFCF2O-(CF(CF3)CF2O) n -CF(CF3)-Z 2 (26) (where n is an integer from 1 to 10) CF2=C(CF3)-(CF2) n -Z 2 (27) (where n is an integer from 0 to 8) (In general formulas (4) to (27), Z 2 is any of the above functional groups)

[0047] Specific examples of the monomer represented by general formula (5) include CF2=CF-CF2-CN, CF2=CF-CF2CF2-CN, CF2=CFCF2-C(=NH)-OR, CF2=CFCF2CF2-C(=NH)-OR, CF2=CF-CF2-COOH, CF2=CF-CF2CF2-COOH, CF2=CF-CF2-COOCH3, CF2=CF-CF2CF2-COOCH3, etc.

[0048] Specific examples of the monomer represented by general formula (22) include CF2=CFCF2C(CF3)FCN, CF2=CF(CF2C(CF3)F)2CN, CF2=CFCF2C(CF3)FC(=NH)-OR, CF2=CF(CF2C(CF3)F)2-C(=NH)-OR, CF Examples include 2=CFCF2C(CF3)FCOOH, CF2=CF(CF2C(CF3)F)2COOH, CF2=CFCF2C(CF3)FCOOCH3, CF2=CF(CF2C(CF3)F)2COOCH3.

[0049] Specifically, the monomer represented by general formula (23) is: Examples include CF2=CFOCF2CF2CF2CN, CF2=CFOCF2CF2CN, CF2=CFOCF2CN, CF2=CFOCF2CF2CF2-C(=NH)-OR, CF2=CFOCF2CF2-C(=NH)-OR, CF2=CFOCF2-C(=NH)-OR, CF2=CFOCF2CF2CF2COOH, CF2=CFOCF2CF2COOH, CF2=CFOCF2COOH, CF2=CFOCF2CF2CF2COOCH3, CF2=CFOCF2CF2COOCH3, and CF2=CFOCF2COOCH3.

[0050] Specifically, the monomer represented by general formula (24) is: Examples include CF2=CFOCF2CF(CF3)OCF2CF2CN, CF2=CFOCF2CF(CF3)OCF2CF2-C(=NH)-OR, CF2=CFOCF2CF(CF3)OCF2CF2COOH, and CF2=CFOCF2CF(CF3)OCF2CF2COOCH3.

[0051] Specifically, the monomer represented by general formula (25) is: CH2=CFCF2OCF(CF3)CN, CH2=CFCF2OCF(CF3)CF2OCF(CF3)CN, CH2=CFCF2O(CF(CF3)CF2O)2CF(CF3)CN, CH2=CFCF2OCF (CF3)-C(=NH)-OR, CH2=CFCF2OCF(CF3)CF2OCF(CF3)-C(=NH)-OR, CH2=CFCF2O(CF(CF3)CF2O)2CF(CF3)-C(=NH)-OR, C Examples include H2=CFCF2OCF(CF3)COOH, CH2=CFCF2OCF(CF3)CF2OCF(CF3)COOH, CH2=CFCF2O(CF(CF3)CF2O)2CF(CF3)COOH, CH2=CFCF2OCF(CF3)COOCH3, CH2=CFCF2OCF(CF3)CF2OCF(CF3)COOCH3, and CH2=CFCF2O(CF(CF3)CF2O)2CF(CF3)COOCH3.

[0052] Specifically, the monomer represented by general formula (26) is: Examples include CF2=CFCF2OCF(CF3)CF2OCF(CF3)CN, CF2=CFCF2OCF(CF3)CF2OCF(CF3)-C(=NH)-OR, CF2=CFCF2OCF(CF3)CF2OCF(CF3)COOH, and CF2=CFCF2OCF(CF3)CF2OCF(CF3)COOCH3.

[0053] Specifically, the monomer represented by general formula (27) is: CF2=C(CF3)-CN, CF2=C(CF3)-CF2-CN, CF2=C(CF3)-CF2CF2-CN, CF2=C(CF3)-C(=NH)-OR, CF2=C(CF3)CF2-C(=NH)-OR, CF2=C(CF3)CF2CF2-C(=NH)-OR, CF2 =C(CF3)-COOH, CF2=C(CF3)-CF2-COOH, CF2=C(CF3)-CF2CF2-COOH, CF2=C(CF3)-COOCH3, CF2=C(CF3)-CF2-COOCH3, CF2=C(CF3)-CF2CF2-COOCH3 and the like.

[0054] Among the monomers having functional groups, at least one selected from the group consisting of CF2=C(CF3)COOCH3, CF2=CFOCF2CF2COOH, and CF2=CFOCF2C(CF3)FOCF2CF2COOCH3 is preferred, as it can further increase the tensile strength, and CF2=CFOCF2C(CF3)FOCF2CF2COOCH3 is even more preferred.

[0055] Polytetrafluoroethylene may contain units based on tetrafluoroethylene and monomers other than monomers having functional groups. Preferred monomers other than monomers having functional groups are fluorine-containing monomers (excluding tetrafluoroethylene and monomers having functional groups).

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

[0057] As the perfluoro(alkyl vinyl ether), 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) is preferred.

[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, relative to the total monomer units constituting polytetrafluoroethylene.

[0059] The coating layer may contain only polytetrafluoroethylene having functional groups as the polymer, or it may contain polymers other than polytetrafluoroethylene having functional groups. The content of polytetrafluoroethylene having functional groups 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, even more preferably 99.9% by mass or more, and preferably 100% by mass or less, when the total amount of polymer contained in the coating layer is taken as 100% by mass.

[0060] Polytetrafluoroethylene having functional groups can be produced, for example, by the method described in Japanese Patent Publication No. 2009-44018.

[0061] The coating layer may contain inorganic pigments, fillers, adhesion promoters, antioxidants, lubricants, dyes, etc. The inorganic pigments are preferably stable during molding, and examples include titanium, iron oxides, 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 relative permittivity of the coating layer is preferably 2.1 to 2.6. The relative permittivity of the coating layer is the relative permittivity of the coating layer alone. The relative permittivity of the coating layer can be measured by removing the metal wires constituting the coating metal wire, recovering only the coating layer, and measuring the recovered coating layer using the cavity resonator method at 6 GHz and 25 ± 3°C.

[0064] 3. Insulated metal wire The coated metal wire of this disclosure can be manufactured, for example, by a manufacturing method that involves coating a metal wire with polytetrafluoroethylene having functional groups.

[0065] Methods for coating polytetrafluoroethylene having functional groups include dipping, wrapping, and extrusion molding. Among these, the dipping method is preferred because it allows for the easy production of coated metal wires with high pull-out strength and excellent winding properties (processability). By using the dipping method, high pull-out strength can be achieved even when the number of functional groups in the polytetrafluoroethylene is small.

[0066] When using the dipping method, a coating layer can be formed by preparing an aqueous dispersion containing polytetrafluoroethylene having functional groups, immersing a metal wire in the aqueous dispersion, and then withdrawing it. The polytetrafluoroethylene content in the aqueous dispersion may be, for example, 20 to 60% by mass. The operation of immersing the metal wire in the aqueous dispersion and withdrawing it may be repeated multiple times until the desired thickness is achieved. Furthermore, drying or heat treatment may be performed each time the metal wire is withdrawn from the aqueous dispersion.

[0067] When using the wrapping method, a polytetrafluoroethylene having functional groups is paste-extruded to produce an extruded product, the extruded product is rolled to produce a sheet, and the sheet is wrapped around a metal wire to form a coating layer.

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

[0069] In the above manufacturing method, the coating layer may be fired after it has been formed. The firing temperature may be between the melting point of polytetrafluoroethylene and 420°C. The firing time may be between 10 seconds and 60 minutes.

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

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

[0072] Although embodiments have been described above, it should be understood that various modifications to the form and details are possible without departing from the spirit and scope of the claims.

[0073] <1> According to the first aspect of this disclosure, A coated metal wire is provided, comprising a metal wire and a coating layer formed around the metal wire, wherein the coating layer contains polytetrafluoroethylene having functional groups, has a pull-out strength of 12 kgf / 76.2 mm or more, and has a partial discharge initiation voltage of 900 V / 35 μm or more. <2> According to the second aspect of this disclosure, The polytetrafluoroethylene coating provides a metal wire that is non-melt processable according to a first aspect. <3> According to the third aspect of this disclosure, The aforementioned functional group is a cyano group (-CN), General formula (1): [ka] (R 1 and R 2 Each is independently a hydrogen atom, a halogen atom, and -OR 3 , -N(R 3 )2, -R 3 And R 3 (1) is a functional group (which may contain fluorine or hydrogen atoms having 1 to 10 carbon atoms), and General formula (2): [ka] (R 1 is a hydrogen atom, halogen atom, -OR 3 ,-N(R 3 )2,-R 3 And R3 (2) A functional group represented by an alkyl group or hydrogen atom having 1 to 10 carbon atoms, which may contain fluorine. A coated metal wire is provided, which is at least one selected from the group consisting of the following, in a first or second manner. <4> According to the fourth aspect of this disclosure, A coated metal wire is provided in which the content of the functional group in the polytetrafluoroethylene is 0.0001 to 2 mol% relative to the total monomer units constituting the polytetrafluoroethylene, according to any one of the first to third viewpoints. <5> According to the fifth aspect of this disclosure, A coated metal wire is provided, wherein the surface roughness (Rzjis) of the metal wire is 4.0 μm or greater, according to any of the first to fourth views. <6> According to the sixth aspect of this disclosure, A coil comprising coated metal wire according to any of the first to fifth aspects is provided. <7> According to the seventh aspect of this disclosure, A motor is provided that includes a coil according to a sixth perspective. <8> According to the eighth aspect of this disclosure, A coil for a DC power inverter-driven motor is provided, comprising insulated metal wire according to one of the first to fifth aspects. <9> According to the ninth aspect of this disclosure, A DC power inverter-driven motor is provided, equipped with a coil for a DC power inverter-driven motor according to the eighth aspect. [Examples]

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

[0075] 1. Preparation of polytetrafluoroethylene (PTFE) Each value in the examples was measured by the following method.

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

[0077] <Melting point> Approximately 10 mg of PTFE powder was accurately weighed and placed in a dedicated aluminum pan. The melting point was measured using a TG / DTA (Differential Thermogravimetric Analysis) device. The melting point (peak temperature) was determined by obtaining a differential thermal (DTA) curve by heating the aluminum pan in an atmospheric environment from 25°C to 600°C at a rate of 10°C / min, and the temperature corresponding to the maximum value in the obtained differential thermal (DTA) curve was used as the melting point.

[0078] <Standard specific gravity (SSG)> Samples were prepared according to ASTM D 4895-89 and measured using the water displacement method according to ASTM D 792.

[0079] <Amount of denaturation (monomer content)> solid 19 F-MAS NMR measurements (probe diameter: 4.0 mm, rotation speed: 30 kHz, measurement atmosphere: nitrogen, measurement temperature: 150 °C) were used to detect peaks originating from TFE and peaks originating from the denaturing agent, and the results were determined from the area ratio of these peaks.

[0080] <Solid concentration (P)> 1 g (X) of aqueous PTFE dispersion was placed in a 5 cm diameter aluminum cup, dried at 100°C for 60 minutes, and then dried again at 300°C for 60 minutes. The percentage of P was determined based on the heat residue (Z) using the formula: P = Z / X × 100 (%).

[0081] <Content of nonionic surfactant (N)> The percentage was calculated using the formula: N = [(YZ) / Z] × 100 (%) from the following: 1 g (X) of PTFE aqueous dispersion was placed in a 5 cm diameter aluminum cup and heated at 100°C for 60 minutes to obtain the residual (Y); and then the obtained residual (Y) was heated at 300°C for 60 minutes to obtain the residual (Z).

[0082] <Method for measuring the number of functional units> A film with a thickness of 0.25 to 0.5 mm is prepared by compression molding of PTFE powder at 25°C. 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 without functional groups. From the absorption peak of a specific functional group appearing in this difference spectrum, the main chain carbon atoms in PTFE (1 × 10⁶) are determined according to the following formula (A). 6 Calculate the number of functional units N per individual. N = (I × K) / t (A) I: Absorbance K: Correction coefficient t: Film thickness (mm)

[0083] The correction factor for the target terminal group is shown below. This correction factor is 1 × 10¹⁶ carbon atoms in the main chain terminal carbon. 6 The number of functional groups per compound was determined from the infrared absorption vector of the model compound. Functional group Absorption frequency (cm) -1 ) Correction factor -COOH (Free) 1815 439 -COOH (Meeting) 1779 439 -COOCH31795 342 -CONH23436 460

[0084] (Synthesis Example 1) 3560 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 International Publication No. 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 the reactor was purged with TFE monomer to remove oxygen. Subsequently, 10.0 g of perfluoro[3-(1-methyl-2-vinyloxyethoxy)propionate methyl] (CF2=CFOCF2C(CF3)FOCF2CF2COOCH3, hereinafter abbreviated as RVEE) 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 increased to 0.83 MPa. A pressure drop occurred after the injection of the initiator, and the start of polymerization was observed. TFE monomers were added to the reactor, and the pressure was maintained. Polymerization continued until approximately 1.5 kg of TFE monomers had reacted completely. After that, the reactor was evacuated, and the contents were removed from the reactor and cooled. The supernatant paraffin wax was removed from the PTFE aqueous dispersion. The solid content concentration of the obtained PTFE aqueous dispersion (1-1) was 29.2% by mass, and the average primary particle size was 217 nm.

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

[0086] The resulting aqueous PTFE dispersion (1-1) is mixed with a nonionic surfactant RO(CH2CH2O) nA PTFE aqueous dispersion was prepared by adding H(R: tridecyl group) (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name: Neugen TDS-80) to a nonionic surfactant concentration of 10 parts by mass per 100 parts by mass of PTFE solids. Subsequently, 250 ml of OH-type anion exchange resin (product name Amberjet 4002, manufactured by Rohm & Haas) was packed into a 20 mm diameter column, and the above PTFE aqueous dispersion was passed through it at SV=1. Furthermore, nonionic surfactant (Neugen TDS-80) was added to the obtained PTFE aqueous dispersion so that it was 16 parts by mass per 100 parts by mass of PTFE solids, and the mixture was held at 65°C for 3 hours to separate the supernatant phase and the concentrated phase. The concentrated phase was recovered to obtain PTFE aqueous dispersion (1-2). The obtained 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. To the obtained PTFE aqueous dispersion (1-2), a nonionic surfactant (Neugen TDS-80) was added to a concentration of 5.0% by mass relative to the PTFE solids, and then deionized water and ammonia water were added to obtain PTFE aqueous dispersion (1-3). The obtained PTFE aqueous dispersion (1-3) had a solids concentration of 60.0% by mass, and the nonionic surfactant content was 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 obtained PTFE aqueous dispersion (2-1) was 23.7% by mass, and the average primary particle size was 287 nm.

[0088] The aqueous PTFE dispersion (2-1) obtained in Synthesis Example 2 could be coagulated by the same method as in Synthesis Example 1 to obtain 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 × 10⁶ carbon atoms in the main chain. 6 There were 8 per unit.

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

[0090] 2. Fabrication of coated metal wire Each value in the examples was measured by the following method.

[0091] <Relative permittivity> The relative permittivity of the coating layer at 6 GHz was measured using an EM Labs cavity resonator, a Keysight P5007A network analyzer, 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, 20x objective lens). Measurements were taken at five points along the diameter of the metal wire sample, and the average value was calculated as the surface roughness Rzjis.

[0093] <Peel strength> Metal foil (here, CF-T9DA-SV manufactured by Fukuda Metal Foil & Powder Co., Ltd. (surface chemically treated copper foil, Rzjis 0.11 μm (the company's catalog value is Rzjis = 0.14 μm))) and a fluororesin sheet were bonded together 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 the peel test. Based on the 90°C peel test method of JIS K6481-1996, measurements were taken using an Autograph test machine manufactured by Shimadzu Corporation at room temperature with a crosshead speed of 50 mm / min.

[0094] <Insertion loss (S21)> A coaxial cable with an impedance of 50Ω was created by extruding the resin of the present invention onto a metal core wire with a roughened surface, attaching a metal outer layer, adding a jacket with heat-shrink tubing, and attaching connectors to both ends. Furthermore, the insertion loss (S21) of this coaxial cable was measured using an HP 8510 network analyzer manufactured by HP Corporation.

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

[0096] <Abrasion resistance test> A wear resistance test (reciprocating wear resistance, 150g load) was conducted in accordance with JISC-3003, and the number of cycles until the coating wore down and the metal wire was exposed was measured.

[0097] <Partial discharge initiation voltage> Twisted sections prepared in accordance with JIS C3003 were measured using a DAC-PD-7 manufactured by Soken Electric Co., Ltd. under the conditions of a temperature of 25°C, a frequency of 100kHz, a boost rate of 100V / sec, a buck rate of 100V / sec, and a voltage holding time of 0sec. The voltage at which a discharge of 10pC or more of charge occurred was defined as the partial discharge start voltage.

[0098] Example 1 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: 0.92 μm) that had not undergone surface roughening treatment was dipped in the dispersion. After drying the moisture at room temperature for 5 minutes and then at 110°C for 5 minutes, it was heat-treated at 330°C for 5 minutes. This was repeated 7 times, and then fired at 360°C for 10 minutes. As a result, a PTFE-coated copper wire with a thickness of 40 μm was obtained. The partial discharge initiation 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 dipped in the dispersion. After drying the moisture at room temperature for 5 minutes and then at 110°C for 5 minutes, it was heat-treated at 330°C for 5 minutes. This was repeated 7 times, and then fired at 360°C for 10 minutes. As a result, a PTFE-coated copper wire with a thickness of 37 μm was obtained. The partial discharge initiation voltage was 942 V / 35 μm. The pull-out strength was 15 kgf / 76.2 mm or more.

[0100] Example 3 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: 8.04 μm) with a surface treated with #240 was dipped in the dispersion. After drying the moisture at room temperature for 5 minutes and then at 110°C for 5 minutes, it was heat-treated at 330°C for 5 minutes. This was repeated 7 times, and then fired at 360°C for 10 minutes. As a result, a PTFE-coated copper wire with a thickness of 36.5 μm was obtained. The partial discharge initiation voltage was 1005 V / 35 μm. The pull-out strength was 15 kgf / 76.2 mm or more.

[0101] Example 4 A PTFE aqueous dispersion (1-3) was prepared with a solid content concentration of 45% by mass, and 1.0 mm diameter copper wire (Rzjis: 8.04 μm) with a surface treated with #240 was dipped in the dispersion. After drying the moisture at room temperature for 5 minutes and then at 110°C for 5 minutes, the wire was heat-treated at 330°C for 5 minutes. The surface was then dipped with PTFE aqueous dispersion (2-3) prepared with a solid content concentration of 45% by mass. This dipping, drying, and heat-treatment process was repeated six times, and the wire was further fired at 360°C for 10 minutes. As a result, a PTFE-coated copper wire with a thickness of 36 μm was obtained. The partial discharge initiation voltage was 1137 V / 35 μm. The pull-out strength was 15 kgf / 76.2 mm or more.

[0102] Example 5 The solid content concentration 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 undergone surface treatment was dipped in the dispersion. After drying the moisture at room temperature for 5 minutes and then at 110°C for 5 minutes, the wire was heat-treated at 330°C for 5 minutes. This dipping, drying, and heat-treatment process was repeated 7 times, and then the wire was fired at 360°C for 10 minutes. As a result, a PTFE-coated copper wire with a thickness of 35 μm was obtained. The partial discharge initiation voltage was 1038 V / 35 μm. The pull-out strength was 14 kgf / 76.2 mm.

[0103] Comparative Example 1 A 35 μm thick coated copper wire was fabricated by coating a 1.0 mm diameter copper wire (Rzjis: 0.14 μm) that had not undergone surface roughening treatment with polyetherimide / polyamideimide. The partial discharge initiation 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. [Table 1]

[0105] Example 6 PTFE powder obtained from an aqueous PTFE dispersion (1-1) was mixed with 21% by mass of an extrusion aid (product name: Isopar G, manufactured by ExxonMobil), pre-formed, and then paste-extruded at a diameter of φ12 mm. This extruded material was rolled to a thickness of 100 μm using a rolling mill and cut into 5 mm wide strips. These sheets were wrapped around an untreated copper wire in a double layer. This unfired tape-coated copper wire was fired at 360°C for 3 minutes. The partial discharge initiation 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 an aqueous PTFE dispersion (1-1) was mixed with 21% by mass of an extrusion aid (product name: Isopar G, manufactured by ExxonMobil), pre-formed, and then paste-extruded at a diameter of φ12 mm. This extruded material was rolled to a thickness of 100 μm using a rolling mill and cut into 5 mm wide strips. These sheets were wrapped in a double layer around copper wire that had been surface-treated with #240 grit sandpaper. This unfired tape-coated copper wire was fired at 360°C for 3 minutes. The partial discharge initiation 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 an aqueous PTFE dispersion (2-1) was mixed with 21% by mass of an extrusion aid (product name: Isopar G, manufactured by ExxonMobil), pre-formed, and then paste-extruded at a diameter of φ12 mm. This extruded material was rolled to a thickness of 100 μm using a rolling mill and cut into 5 mm wide strips. These sheets were wrapped in a double layer around a copper wire (Rzjis 8.04 μm) that had been surface-treated with #240 grit. This unfired tape-coated copper wire was fired at 360°C for 3 minutes. The partial discharge initiation 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. [Table 2]

[0109] Experimental Example 1 A 1mm diameter copper wire was roughened using 240-grit sandpaper. The Rzjis value was measured to be 8.04 μm. A paste was prepared by mixing PTFE powder obtained from the PTFE aqueous dispersion (1-1) with 21% by mass of an extrusion aid (product name: Isopar G, manufactured by ExxonMobil). The prepared paste was extruded onto the obtained copper wire, coated by drying with an auxiliary agent and firing, and then covered with a shielding braided wire and secured with heat-shrink tubing to create a coaxial cable. The pull-out strength was 15 kgf / 76.2 mm or more. The insertion loss at 20 GHz was measured with a network analyzer and was -18.9 dB / 900 mm.

[0110] Experimental Example 2 Experimental Example 1 involved changing the sandpaper grit to 2000. The Rzjis was measured to be 2.00 μm. The rest of the setup was the same, and when measured, the pull-out strength was 15 kgf / 76.2 mm or higher. The insertion loss was -14.8 dB / 900 mm.

[0111] Experimental Example 3 A 1mm diameter copper wire was used as is. The Rzjis was measured to be 0.92 μm. Other measurements were performed using the same method, and the pull-out strength was 15 kgf / 76.2 mm or higher. The insertion loss was -12.4 dB / 900 mm.

[0112] Generally, automotive DC inverters generate a surge voltage that is 2 to 3 times the motor drive voltage at output. Considering the rise time of the surge voltage, when converted to frequency, it corresponds to tens of MHz to tens of GHz.

[0113] Among the coaxial cables fabricated in Experimental Examples 1-3, the coaxial cable equipped with metal wires with high surface roughness showed lower insertion loss. Therefore, it can be seen that by using metal wires with high surface roughness, surface current is made less likely to flow due to the skin effect, thereby preventing the flow of high-voltage surge currents.

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 functional groups, has a pull-out strength of 12 kgf / 76.2 mm or more, and has a partial discharge initiation voltage of 900 V / 35 μm or more.

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

3. The aforementioned functional group is a cyano group (-CN), General formula (1): 【Transformation 5】 (R １ and R ２ Each is independently a hydrogen atom, a halogen atom, and -OR ３ , -N(R ３ ) ２ , -R ３ And R ３ (1) is a functional group (which may contain fluorine or hydrogen atoms having 1 to 10 carbon atoms), and General formula (2): 【Transformation 6】 (R １ is a hydrogen atom, a halogen atom, -OR ３ , -N(R ３ ), -R ２ , and R ３ is an alkyl group optionally containing fluorine having 1 to 10 carbon atoms or a hydrogen atom), and the functional group (2) represented by ３ ​ The coated metal wire according to claim 1 or 2, which is at least one selected from the group consisting of the following.

4. The coated metal wire according to claim 1 or 2, wherein the content of the functional group in the polytetrafluoroethylene is 0.0001 to 2 mol% with respect to the total monomer units constituting the polytetrafluoroethylene.

5. The coated metal wire according to claim 1 or 2, wherein the surface roughness (Rzjis) of the metal wire is 4.0 μm or more.

6. A coil comprising a coated metal wire as described in claim 1 or 2.

7. A motor comprising the coil described in claim 6.

8. A coil for a DC power inverter-driven motor, comprising a coated metal wire as described in claim 1 or 2.

9. A DC power inverter-driven motor comprising a coil for a DC power inverter-driven motor as described in claim 8.

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