insulated wire

Abstract

This insulated wire comprises a linear conductor and an insulating layer that coats the outer peripheral surface of the conductor. The insulating layer contains, as residual solvents, a first solvent having a dielectric constant of at least 15 and a second solvent having a dielectric constant of less than 15. A first ratio, which is the ratio of the content of the second solvent to the total content of the first solvent and second solvent contained in the insulating layer, is at least 50 mass%. A second ratio, which is the ratio of the content of the second solvent to the total content of the first solvent and second solvent contained in the insulating layer after the insulated wire has been heat-treated by heating for 1 minute at 350°C, is higher than the first ratio.

Description

[Technical Field]

[0001] The present disclosure relates to an insulated electric wire. This application claims priority to Japanese Patent Application No. 2021-136332, filed on August 24, 2021, the entire contents of which are incorporated herein by reference. [Background technology]

[0002] Insulated wires have been known in the art, each comprising a linear conductor and an insulating layer covering the outer surface of the conductor. These insulated wires are suitable for use as coils in motors, transformers, and the like. Japanese Patent Application Laid-Open Publication No. 2004-269770 (Patent Document 1) discloses a polyurethane-based insulated wire coating material that can produce an insulated wire with excellent insulating properties by significantly reducing the amount of residual solvent in the insulating coating. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-269770 Summary of the Invention

[0004] The insulated wire of the present disclosure is an insulated wire including a linear conductor and an insulating layer covering an outer peripheral surface of the conductor, wherein the insulating layer includes, as residual solvents, a first solvent having a relative dielectric constant of 15 or more and a second solvent having a relative dielectric constant of less than 15, a first ratio which is a ratio of the content of the second solvent to the total content of the first solvent and the second solvent contained in the insulating layer is 50 mass% or more, and a second ratio which is a ratio of the content of the second solvent to the total content of the first solvent and the second solvent contained in the insulating layer after a heat treatment in which the insulated wire is heated at 350°C for 1 minute is higher than the first ratio. DETAILED DESCRIPTION OF THE INVENTION

[0005] [Problem to be solved by this disclosure] From the viewpoint of reducing manufacturing costs, there is a demand for coating the outer peripheral surface of a conductor with an insulating layer by drying an insulating varnish applied and baked on the outer peripheral surface of the conductor for a short time at a low temperature. In this case, polar solvents derived from the insulating varnish tend to remain in the insulating layer, which increases the dielectric constant of the insulating layer and tends to impair the insulating properties. On the other hand, from the viewpoint of the storage stability of the resin, etc., it is necessary to contain a predetermined amount of polar solvent in the insulating varnish. Therefore, there is a strong demand for the development of an insulated wire in which an insulating layer is formed by drying an insulating varnish for a short time at a low temperature, and which contains a predetermined amount of polar solvent, thereby reducing the dielectric constant of the insulating layer and thereby improving the insulating properties while maintaining the storage stability of the insulating varnish.

[0006] In view of the above circumstances, an object of the present disclosure is to provide an insulated wire having an insulating layer with a reduced dielectric constant.

[0007] [Effects of this disclosure] According to the present disclosure, it is possible to provide an insulated wire having an insulating layer with a reduced dielectric constant.

[0008] [Description of the embodiments of the present disclosure] The present inventors have conducted extensive research to solve the above problems and have completed the present disclosure. Specifically, they focused on reducing the amount of high-dielectric-constant solvent remaining in an insulating layer by adding a low-dielectric-constant solvent together with a polar solvent (hereinafter also referred to as a "high-dielectric-constant solvent") to an insulating varnish used to form the insulating layer. As a result, they surprisingly found that when an insulating layer is formed on the outer surface of a conductor using an insulating varnish to which a low-dielectric-constant solvent having a boiling point higher than that of the high-dielectric-constant solvent has been added, the dielectric constant of the insulating layer can be reduced, thereby improving the insulating properties, and have arrived at the present disclosure.

[0009] First, embodiments of the present disclosure will be listed and described. [1] An insulated wire according to one embodiment of the present disclosure includes a linear conductor and an insulating layer covering an outer peripheral surface of the conductor, wherein the insulating layer contains, as residual solvents, a first solvent having a dielectric constant of 15 or more and a second solvent having a dielectric constant of less than 15, a first ratio, which is a ratio of the content of the second solvent to the total content of the first solvent and the second solvent contained in the insulating layer, is 50 mass% or more, and a second ratio, which is a ratio of the content of the second solvent to the total content of the first solvent and the second solvent contained in the insulating layer after a heat treatment in which the insulated wire is heated at 350°C for 1 minute, is higher than the first ratio. An insulated wire having such characteristics can reduce the dielectric constant of the insulating layer, thereby improving insulation properties.

[0010] [2] The insulating layer preferably contains one or more resins selected from the group consisting of polyimide resins, polyamide-imide resins, polyester-imide resins, and polyether-imide resins. This reduces the dielectric constant of an insulating layer containing a resin commonly used in insulated wires.

[0011] [3] The insulating layer preferably contains the first solvent and the second solvent in a total amount of 0.2% by mass to 10% by mass, which further reduces the dielectric constant of the insulating layer.

[0012] [4] Preferably, the insulating layer contains 5% by mass or less of the first solvent and 0.1% by mass or more and 5% by mass or less of the second solvent, thereby further reducing the dielectric constant of the insulating layer.

[0013] [5] The insulating layer contains a curing agent, and the curing agent is selected from the group consisting of alicyclic acid anhydrides, aliphatic acid anhydrides, and aromatic acid anhydrides. 、 It is preferable that the insulating varnish contains one or more selected from the group consisting of imidazole, triethylamine, titanium compounds, isocyanate compounds, blocked isocyanates, urea, melamine, melamine compounds, and acetylene derivatives, which can promote the formation of an insulating layer having the above-mentioned characteristics from the insulating varnish.

[0014] [Details of the embodiments of the present disclosure] Hereinafter, embodiments of the present disclosure (hereinafter also referred to as "present embodiments") will be described in more detail. Herein, the notation "A to B" in the present specification means the upper and lower limits of a range (i.e., greater than or equal to A and less than or equal to B). When no unit is specified for A and only a unit is specified for B, the unit of A and the unit of B are the same. Furthermore, in this specification, the terms "dielectric constant" and "relative dielectric constant" are both used in the same context as indicators of the conductivity of a medium. In this specification, "high dielectric constant" means a relative dielectric constant of 15 or more, and "low dielectric constant" means a relative dielectric constant of less than 15. Furthermore, in this specification, "solvent" refers to a substance used to dissolve other substances. Therefore, in this specification, the category of "solvent" includes materials that are liquid at room temperature as well as solid materials, as long as they are materials used to dissolve other substances.

[0015] [Insulated wire] The insulated wire according to the present embodiment is an insulated wire including a linear conductor and an insulating layer covering the outer peripheral surface of the conductor. The insulating layer includes, as residual solvents, a first solvent having a relative dielectric constant of 15 or more and a second solvent having a relative dielectric constant of less than 15. A first ratio, which is the ratio of the content of the second solvent to the total content of the first solvent and the second solvent contained in the insulating layer, is 50 mass% or more. Furthermore, after a heat treatment in which the insulated wire is heated at 350°C for 1 minute, a second ratio, which is the ratio of the content of the second solvent to the total content of the first solvent and the second solvent contained in the insulating layer, is higher than the first ratio. An insulated wire having these characteristics can reduce the dielectric constant of the insulating layer, thereby improving insulation properties.

[0016] The reason why the insulated wire can reduce the dielectric constant of the insulating layer and thereby improve the insulating properties is unknown, but is presumed to be as follows.

[0017] That is, the insulated wire according to this embodiment contains, as residual solvents in the insulating layer, not only a first solvent having a dielectric constant of 15 or more, but also a second solvent having a dielectric constant of less than 15. Furthermore, a first ratio, which is the ratio of the content of the second solvent to the total content of the first solvent and the second solvent contained in the insulating layer, is 50 mass% or more. Since the first solvent has a dielectric constant of 15 or more, it is a high-dielectric-constant solvent, and the second solvent has a dielectric constant of less than 15, it is a low-dielectric-constant solvent. Therefore, an insulating layer in which more than half of the residual solvent is the second solvent is thought to have a low dielectric constant.

[0018] Furthermore, in this embodiment, when the insulated wire is subjected to a heat treatment in which the insulated wire is heated at 350°C for 1 minute, the ratio of the content of the second solvent to the total content of the first solvent and the second solvent contained in the insulating layer (second ratio) is higher than the first ratio. The fact that the second ratio is higher than the first ratio means that the first solvent volatilizes more actively from the insulating layer than the second solvent during the heat treatment. Here, since the heat treatment simulates a part of the drying process performed in the insulated wire manufacturing process, it is understood that the second solvent remains in the insulating layer in preference to the first solvent during the insulated wire manufacturing process. This means that by reducing the content of the second solvent in the insulating varnish and ensuring a sufficient content of the first solvent, it is possible to maintain the storage stability of the resin while making more than half of the residual solvent in the insulating layer of the insulated wire the second solvent, thereby enabling the dielectric constant of the insulating layer to be reduced as described above. From the above, it is presumed that the insulated wire according to the present embodiment can reduce the dielectric constant of the insulating layer while maintaining the storage stability of the insulating varnish, thereby improving the insulating properties.

[0019] <conductor> The insulated wire according to the present embodiment includes a linear conductor as described above. The conductor is an electrical conductor. The material of the conductor is preferably a metal with high electrical conductivity and high mechanical strength. Specific examples include copper, copper alloy, aluminum, aluminum alloy, nickel, silver, soft iron, steel, and stainless steel. The conductor may be a wire formed from any of these metals, a coated wire in which the surface of a wire is coated with another metal, or a twisted wire in which multiple wires are twisted together. Examples of the coated wire include, but are not limited to, nickel-coated copper wire, silver-coated copper wire, silver-coated aluminum wire, and copper-coated steel wire.

[0020] The shape of the conductor is not particularly limited, and a round wire, a rectangular wire, or the like can be selected as appropriate depending on the intended use and electrical characteristics of the insulated wire. That is, in a cross section obtained by cutting the insulated wire along a plane perpendicular to its longitudinal direction, the cross-sectional shape of the conductor may be circular or rectangular. The diameter or outer periphery of the conductor is not particularly limited, and can be selected as appropriate depending on the intended use and electrical characteristics of the insulated wire.

[0021] In this specification, "flat square," which is one of the cross-sectional shapes of a conductor, includes rectangles and squares, and also shapes in which the four corners of these rectangles and squares are chamfered, as well as shapes with a radius (R shape).

[0022] The minimum cross-sectional area of ​​the conductor is 0.01 mm 2 is preferable, and 0.1 mm 2 is more preferable, and the upper limit is 20 mm 2 is preferable, and 10 mm 2 It is more preferable that the cross-sectional area of ​​the conductor is 0.01 mm 2 If the cross-sectional area of ​​the conductor is less than 20 mm, the ratio of the volume of the insulating layer to the conductor becomes large, and the volume efficiency of a coil formed using the insulated wire may decrease. 2 If the thickness exceeds 1000 Ω / s, it becomes necessary to thicken the insulating layer in order to sufficiently improve the insulation properties of the insulated wire, which results in an increase in the diameter of the insulated wire, and tends to make it difficult to wind the insulated wire around the core at a high density.

[0023] <Insulating layer> The insulated wire according to the present embodiment includes an insulating layer covering the outer surface of the conductor as described above. The insulating layer may include any of the conventionally known resins that are used to form insulating layers in this type of insulated wire.

[0024] Specifically, examples of resins contained in the insulating layer include thermosetting resins such as polyvinyl formal resin, polyurethane resin, alkyl resin, epoxy resin, phenoxy resin, polyester resin, polyesterimide resin, polyesteramideimide resin, polyamideimide resin, and polyimide resin, and thermoplastic resins such as polyetherimide resin, polyetheretherketone resin, polyethersulfone resin, and polyimide resin. These resins may be contained either alone or in combination of two or more.

[0025] In particular, the insulating layer preferably contains one or more resins selected from the group consisting of polyimide resin, polyamide-imide resin, polyester-imide resin, and polyether-imide resin. This allows the dielectric constant to be reduced in an insulating layer containing a resin commonly used in insulated wires. From the viewpoint of improving strength and heat resistance, the insulating layer more preferably contains a thermosetting polyimide resin.

[0026] Furthermore, when the insulating layer contains a polyimide resin, the polyimide resin preferably contains a small amount of a monomer other than polyimide, or is a polyimide resin into which a functional group has been introduced.

[0027] The lower limit of the thickness of the insulating layer is preferably 5 μm, and the upper limit is preferably 200 μm. If the thickness of the insulating layer is less than 5 μm, the insulating layer tends to be easily torn, which may result in insufficient insulation of the conductor. If the thickness of the insulating layer exceeds 200 μm, the volume efficiency of a coil or the like formed using the insulated wire tends to be low.

[0028] When the cross section of the conductor is rectangular, the thickness of the insulating layer refers to the average thickness of the insulating layer covering two pairs of opposing surfaces (top, bottom, left, and right) of the outer periphery of the conductor in a cross section obtained by cutting the insulated wire along a plane perpendicular to its longitudinal direction. Specifically, the cross section obtained by cutting the insulated wire along a plane perpendicular to its longitudinal direction is polished to prepare a measurement surface. Next, the measurement surface is photographed using a VHX-7000 digital microscope (manufactured by Keyence Corporation) to obtain an image. Finally, the thickness of the insulating layer covering the two pairs of opposing surfaces of the outer periphery of the conductor in the image is determined by, for example, selecting one location each from the top, bottom, left, and right sides of the conductor, measuring the thickness of the insulating layer at these four locations, and calculating the average value from the measured values. When the cross-sectional shape of the conductor is circular, the thickness of the insulating layer can be determined by selecting four equally spaced measurement points on the annular insulating layer in the image of the surface to be measured taken with the digital microscope, measuring the thickness of the insulating layer at the four measurement points, and calculating the average value of the thicknesses.

[0029] (residual solvent) The insulating layer contains, as residual solvents, a first solvent having a dielectric constant of 15 or more and a second solvent having a dielectric constant of less than 15. In this specification, "residual solvent" refers to a solvent component contained in an insulating varnish applied to the outer periphery of a conductor during the manufacturing process of an insulated electric wire, that remains in the insulating layer even after the insulating varnish is baked onto the conductor to form an insulating layer. The insulating varnish may be prepared by diluting the above-mentioned resin or its resin precursor with an organic solvent containing at least the first solvent and the second solvent. The organic solvent may consist of the above-mentioned first solvent and the second solvent.

[0030] 1) First solvent The first solvent is a high-dielectric-constant solvent having a dielectric constant of 15 or more. As long as the first solvent is a high-dielectric-constant solvent having a dielectric constant of 15 or more, any conventionally known organic solvent or a material that becomes solid at room temperature can be used. Specific examples of the first solvent include polar organic solvents such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide, dimethyl sulfoxide, tetramethylurea, hexaethylphosphoric triamide, and γ-butyrolactone, and ketone-based organic solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. As the first solvent, these organic solvents can be used alone or in combination of two or more.

[0031] 2) Second Solvent The second solvent is a low-dielectric-constant solvent with a dielectric constant of less than 15. Any conventionally known organic solvent or material that is solid at room temperature can be used as the second solvent, as long as it is a low-dielectric-constant solvent with a dielectric constant of less than 15 and satisfies the conditions described below in relation to the first solvent. Specific examples of the second solvent include ester-based organic solvents such as methyl acetate, ethyl acetate, butyl acetate, and diethyl oxalate; ether-based organic solvents such as diethyl ether, ethylene glycol dimethyl ether, diethylene glycol monomethyl ether, ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol dimethyl ether, and tetrahydrofuran; hydrocarbon-based organic solvents such as hexane, heptane, benzene, toluene, xylene, and naphtha; halogen-based organic solvents such as dichloromethane and chlorobenzene; phenol-based organic solvents such as cresol and chlorophenol; and amine-based organic solvents such as pyridine. An example of a material that is solid at room temperature for the second solvent is paraffin wax. These organic solvents and materials that are solid at room temperature can be used alone or in combination.

[0032] In this specification, when the second solvent is naphtha or paraffin wax, the "boiling point" of the second solvent means the boiling point (so-called "dry point") of the compound contained in the second solvent that has the highest boiling point.

[0033] A low-dielectric-constant solvent that can be used as the second solvent satisfies the following two conditions in relation to the first solvent (high-dielectric-constant solvent): The first condition is that a first ratio, which is the ratio of the content of the second solvent to the total content of the first solvent and the second solvent contained in the insulating layer of the insulated electric wire, is 50 mass % or more. Therefore, the second solvent has a relationship in which the amount of residual solvent contained in the insulating layer is equal to or greater than the amount of the first solvent in mass terms.

[0034] Furthermore, the second condition is that a second ratio, which is the ratio of the content of the second solvent to the total content of the first solvent and the second solvent in the insulating layer after heating the insulated electric wire at 350°C for 1 minute, is higher than the first ratio. In this case, in the insulating layer of the insulated electric wire according to the present embodiment, the first solvent volatilizes more actively than the second solvent during the heating treatment, and therefore the second solvent has a higher boiling point than the first solvent. That is, the second solvent, as a residual solvent in the insulating layer, preferably has a higher boiling point than the first solvent. By satisfying the first and second conditions described above, the insulated electric wire according to the present embodiment can maintain the storage stability of the resin by reducing the content of the second solvent and ensuring a sufficient content of the first solvent in the insulating varnish, while at the same time, by using the second solvent to account for half or more of the residual solvent in the insulating layer of the insulated electric wire, thereby reducing the dielectric constant of the insulating layer.

[0035] With regard to the first ratio, from the viewpoint of further reducing the dielectric constant of the insulating layer, the value thereof is preferably 70 mass % or more, and more preferably 80 mass % or more. 1st ratioThe upper limit of the second ratio is 99.99% by mass, taking into consideration that the second ratio can be 100% by mass. The value of the second ratio is not particularly limited as long as it is higher than the value of the first ratio. From the viewpoint of further reducing the dielectric constant of the insulating layer, the difference between the value of the second ratio and the value of the first ratio (second ratio - first ratio) is preferably 5 or more, and more preferably 10 or more. The upper limit of the second ratio is also 100% by mass, which is an ideal value.

[0036] 3) The respective contents and total contents of the first and second solvents in the insulating layer of the insulated wire The insulating layer preferably contains the first solvent and the second solvent in a total amount of 0.2% by mass to 10% by mass, thereby further reducing the dielectric constant of the insulating layer.

[0037] If the total content of the first solvent and the second solvent in the insulating layer is less than 0.2% by mass, the dielectric constant reduction effect due to the inclusion of the second solvent may not be sufficiently confirmed. If the total content of the first solvent and the second solvent in the insulating layer exceeds 10% by mass, there may be concerns about an increase in the dielectric constant due to the first solvent and a decrease in the strength of the insulating layer. The insulating layer more preferably contains the first solvent and the second solvent in a total amount of 0.5% by mass to 5% by mass, and even more preferably 1% by mass to 4% by mass.

[0038] Furthermore, it is preferable that the insulating layer contains 5% by mass or less of the first solvent and 0.1% by mass or more and 5% by mass or less of the second solvent, which also makes it possible to further reduce the dielectric constant of the insulating layer.

[0039] If the content of the first solvent in the insulating layer exceeds 5% by mass, there is a possibility that the dielectric constant of the insulating layer may increase due to the first solvent. On the other hand, the lower limit of the content of the first solvent in the insulating layer may be 0.02% by mass. If the content of the second solvent in the insulating layer before the heat treatment is less than 0.1% by mass, the effect of reducing the dielectric constant due to the second solvent may be insufficient. If the content of the second solvent in the insulating layer before the heat treatment exceeds 5% by mass, there is a possibility that the strength of the insulating layer may be impaired. The insulating layer before the heat treatment more preferably contains 3% by mass or less of the first solvent, and even more preferably contains 1.5% by mass or less. The insulating layer more preferably contains 0.5% by mass to 4.5% by mass, and even more preferably contains 1.5% by mass to 4% by mass of the second solvent.

[0040] (Measurement method) The contents of the first solvent and the second solvent in the insulating layer of the insulated wire can be determined, for example, using a pyrolysis gas chromatography mass spectrometer (Py-GC / MS, product name: "6890N / 5973Network", manufactured by Agilent Technologies). In this case, the atmosphere is He gas, and the flow rate is 1 mL / min. Furthermore, the pyrolysis temperature is 500°C x 1 min, which is sufficient to volatilize all residual solvent.

[0041] The detailed conditions for measuring the contents of the first solvent and the second solvent in the insulating layer using the Py-GC / MS are shown below. Pyrolysis equipment: Double Shot Pyrolyzer (product name: PY-2020iD, manufactured by Frontier Labs) and Microjet CryoTracker P( Product name: MJT-1030E, manufactured by Frontier Labs Column: UA-5 (inner diameter 0.25 mm x length 30 m, film thickness 0.25 μm, manufactured by Frontier Labs) Thermal decomposition (temperature x time): 500℃ x 1min. Inlet: 300°C, split ratio 100:1 Trap: -150℃ Oven: 50℃ → (25℃ / min.) → 320℃ (5 min.) Ionization method: Electron Ionization (EI) MS temperature: 230℃ (ion source), 150℃ (quadrupole) Mass range: 33-550 a.mu.

[0042] Furthermore, the contents (remaining amounts) of the first solvent and the second solvent remaining in the insulating layer after a heat treatment in which an insulated wire is heated at 350°C for 1 minute can be determined using the pyrolysis gas chromatography mass spectrometer in a He gas atmosphere (flow rate 1 mL / min), similar to the method for measuring the contents of the first solvent and the second solvent in the insulating layer of an insulated wire described above. That is, the remaining amounts after the heat treatment can be determined by subtracting the amounts of solvent generated when measuring under the above-described measurement conditions, except that the pyrolysis temperature is changed to 350°C for 1 minute, from the contents of the first solvent and the second solvent remaining in the insulating layer.

[0043] (hardening agent) The insulating layer preferably contains a curing agent. In this case, the curing agent is selected from the group consisting of alicyclic acid anhydrides, aliphatic acid anhydrides, and aromatic acid anhydrides. 、 It is preferable that the curing agent contains at least one selected from the group consisting of imidazole, triethylamine, titanium-based compounds, isocyanate-based compounds, blocked isocyanates, urea, melamine, melamine compounds, and acetylene derivatives. This can promote the formation of an insulating layer with a reduced dielectric constant from the insulating varnish. These curing agents are appropriately selected depending on the type of resin or resin precursor in the insulating varnish, and for example, imidazole, melamine, melamine compounds, etc. are preferably used.

[0044] [Method for manufacturing insulated wire] The insulated wire according to the present embodiment can be obtained by applying a conventionally known method for producing an insulated wire of this type, except for preparing a predetermined insulating varnish containing at least a first solvent and a second solvent. From the viewpoint of, for example, high production yield, the insulated wire according to the present embodiment is preferably obtained by the following method for producing an insulated wire.

[0045] That is, the method for producing an insulated wire according to this embodiment preferably includes a step of preparing a conductor and an insulating varnish (first step) and a step of coating the outer peripheral surface with an insulating layer (second step). Furthermore, the coating step (second step) preferably includes a step of applying an insulating varnish to the outer peripheral surface (step A) and a step of baking the insulating varnish onto the conductor (step B). Each step included in the method for producing an insulated wire according to this embodiment will be described below.

[0046] <1st process> The first step is to prepare a conductor and insulating varnish. The conductor can be prepared by, for example, purchasing a commercially available product. Alternatively, the conductor can be prepared by casting, drawing, and wire-drawing the metal mentioned above into a wire, followed by softening.

[0047] The insulating varnish can be prepared by diluting the resin or its resin precursor described above as the material for the insulating layer with an organic solvent containing at least the first and second solvents described above. The resin solids concentration in the insulating varnish is, for example, preferably 15% by mass as a lower limit, more preferably 20% by mass, and preferably 50% by mass as an upper limit, more preferably 30% by mass. When the insulating varnish contains a resin precursor, the resin solids concentration refers to the concentration of the resin precursor. Furthermore, the insulating varnish may contain a curing agent in addition to the first and second solvents and the resin or its resin precursor, and may also contain fillers, various additives, and the like. The insulating varnish may also contain a solvent other than the first and second solvents described above.

[0048] Here, with regard to the first and second solvents contained in the insulating varnish, redundant descriptions of the conditions (dielectric constant, boiling point, remaining amount before and after heat treatment, etc.) required for use as the first or second solvent, as well as the specific solvent names, etc., will not be repeated. Furthermore, redundant descriptions of the specific resin names of the resins or resin precursors contained in the insulating varnish will also not be repeated. The mass ratio of the first and second solvents contained in the insulating varnish is preferably first solvent:second solvent = 99.8:0.2 to 70:30. The content of the first solvent in the insulating varnish can be 55 to 97 mass%, and the content of the second solvent in the insulating varnish can be 0.1 to 30 mass%.

[0049] The curing agent that can be contained in the insulating varnish can be one that has the function of curing the resin or the function of promoting the polymerization of the resin precursor. Specifically, alicyclic acid anhydrides such as methyltetrahydrophthalic anhydride, aliphatic acid anhydrides, aromatic acid anhydrides, etc. 、 Examples of the curing agent include imidazole, triethylamine, titanium compounds, isocyanate compounds, blocked isocyanates, urea, melamine compounds, and acetylene derivatives. These curing agents are appropriately selected depending on the type of resin or resin precursor in the insulating varnish. For example, when the insulating varnish contains a thermosetting polyimide precursor, imidazole or the like is preferably used as the curing agent.

[0050] Examples of the titanium compounds include tetrapropyl titanate, tetraisopropyl titanate, tetramethyl titanate, tetrabutyl titanate, tetrahexyl titanate, etc. Examples of the isocyanate compounds include aromatic diisocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), p-phenylene diisocyanate, and naphthalene diisocyanate; aliphatic diisocyanates having 3 to 12 carbon atoms such as hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexane diisocyanate, and lysine diisocyanate; 1,4-cyclohexane diisocyanate (CDI), isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane diisocyanate (hydrogenated MDI), and methyl diisocyanates. Examples of the diisocyanates include alicyclic isocyanates having 5 to 18 carbon atoms such as methylcyclohexane diisocyanate, isopropylidenedicyclohexyl-4,4'-diisocyanate, 1,3-diisocyanatomethylcyclohexane (hydrogenated XDI), hydrogenated TDI, 2,5-bis(isocyanatomethyl)-bicyclo[2,2,1]heptane, and 2,6-bis(isocyanatomethyl)-bicyclo[2,2,1]heptane; aliphatic diisocyanates having an aromatic ring such as xylylene diisocyanate (XDI) and tetramethylxylylene diisocyanate (TMXDI); and modified products thereof.

[0051] Examples of the blocked isocyanate include diphenylmethane-4,4'-diisocyanate (MDI), diphenylmethane-3,3'-diisocyanate, diphenylmethane-3,4'-diisocyanate, diphenylether-4,4'-diisocyanate, benzophenone-4,4'-diisocyanate, diphenylsulfone-4,4'-diisocyanate, tolylene-2,4-diisocyanate, tolylene-2,6-diisocyanate, naphthylene-1,5-diisocyanate, m-xylylene diisocyanate, and p-xylylene diisocyanate. Examples of the melamine compound include melamine, methylated melamine, butylated melamine, methylolated melamine, and butyrolated melamine. Examples of the acetylene derivative include ethynylaniline and ethynylphthalic anhydride.

[0052] <Second process> The second step is a step of coating the outer peripheral surface of the conductor with an insulating layer, and can include a step (step A) of applying an insulating varnish to the outer peripheral surface of the conductor and a step (step B) of baking the insulating varnish onto the conductor.

[0053] (Process A) Step A is a step of applying the insulating varnish prepared in Step 1 to the outer peripheral surface of the conductor. Specifically, Step A can be performed by passing the conductor coated with the insulating varnish through the opening of a die. In Step A, it is preferable to use a die with an opening so that the insulating varnish can be applied to the outer peripheral surface of the conductor with a uniform thickness.

[0054] (B process) Step B is a step of baking the insulating varnish onto the conductor. Specifically, Step B can be carried out by placing the conductor coated with the insulating varnish after Step A in a baking oven and baking the insulating varnish onto the conductor. This gasifies the solvent in the insulating varnish and solidifies the resin, thereby forming an insulating layer on the outer surface of the conductor.

[0055] The baking temperature and time of the insulating varnish in the baking oven can be appropriately selected from among the temperature and time conditions known for manufacturing this type of insulated electric wire, depending on the type of resin and organic solvent in the insulating varnish. Specifically, first, a heat quantity sufficient to form an insulating layer on the outer surface of the conductor and to reduce the residual solvent to a desired amount is determined based on the type of resin, and then the baking temperature and time are determined based on that heat quantity. The heat quantity can be determined by the product of the baking temperature and the time. If the baking temperature is high, the heat quantity can be adjusted by shortening the time, and if the baking temperature is low, the heat quantity can be adjusted by extending the time.

[0056] Furthermore, in the second step, it is preferable to repeatedly apply the insulating varnish and bake the insulating varnish to laminate one or more insulating layers to a predetermined thickness. Conventionally known methods can be used for applying and baking the insulating varnish. The insulating layer is then dried by a conventionally known method to obtain an insulated wire.

[0057] In this specification, an insulating layer obtained by applying an insulating varnish once and baking the insulating varnish is referred to as a "single layer" insulating layer, and an insulating layer obtained by applying an insulating varnish multiple times and baking the insulating varnish is referred to as a "multiple layer" insulating layer.

[0058] <Action and effect> In this manner, the insulated wire according to the present embodiment can be manufactured. The insulated wire manufactured by the above-described manufacturing method has a reduced dielectric constant of the insulating layer, and therefore can have improved insulating properties.

[0059] [Note] The above description includes the following additional embodiments.

[0060] <Appendix 1> An insulated wire including a linear conductor and an insulating layer covering an outer peripheral surface of the conductor, the insulating layer contains, as residual solvents, a first solvent having a relative dielectric constant of 15 or more and a second solvent having a relative dielectric constant of less than 15; a first ratio, which is a ratio of the content of the second solvent to the total content of the first solvent and the second solvent contained in the insulating layer, is 50 mass% or more; The insulated wire, wherein the boiling point of the second solvent is higher than the boiling point of the first solvent.

[0061] <Appendix 2> 2. The insulated wire according to claim 1, wherein the insulating layer contains one or more resins selected from the group consisting of polyimide resins, polyamideimide resins, polyesterimide resins, and polyetherimide resins.

[0062] <Appendix 3> 3. The insulated wire according to claim 1, wherein the insulating layer contains the first solvent and the second solvent in a total amount of 0.2% by mass to 10% by mass.

[0063] <Appendix 4> the insulating layer contains the first solvent in an amount of 5 mass % or less; 4. The insulated wire according to claim 1, wherein the insulating layer contains the second solvent in an amount of 0.1% by mass or more and 5% by mass or less. [Example]

[0064] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples. Insulated electric wires of Samples 2, 4, 6, 8, 10, and 12 described below are examples, and insulated electric wires of Samples 1, 3, 5, 7, 9, 11, 13, and 14 are comparative examples.

[0065] [Measurement and evaluation method] First, the evaluation items and measurement methods used in this example will be described.

[0066] <Insulating layer thickness> For each of the insulated wires of the examples and comparative examples, the thickness of the insulating layer (unit: μm) was determined using a digital microscope VHX-7000 (manufactured by Keyence Corporation) based on the measurement method described above.

[0067] <Contents of the first and second solvents in the insulating layer of the insulated wire, and the first ratio> For each of the insulated wires of the Examples and Comparative Examples, the contents (unit: ppm) of the first solvent and the second solvent in the insulating layer were determined using a pyrolysis gas chromatography mass spectrometer (Py-GC / MS, product name: "6890N / 5973Network", manufactured by Agilent Technologies) based on the above-mentioned measurement method. The content ratio of the second solvent (first ratio) was also calculated from the total of the respective contents.

[0068] <Contents of the first solvent and the second solvent remaining in the insulating layer after heat treatment, and the second ratio> Each insulated wire in the examples and comparative examples was subjected to a heat treatment using a pyrolysis gas chromatography mass spectrometer (Py-GC / MS, product name: "6890N / 5973Network", manufactured by Agilent Technologies) based on the measurement method described above, and the contents of the first solvent and the second solvent remaining in the insulating layer after the heat treatment (remaining amounts, units: ppm) were determined. Furthermore, the ratio of the content of the second solvent remaining in the insulating layer after the heat treatment (second ratio) was calculated from the sum of the respective contents. The conditions for the heat treatment were as described above: a heating temperature of 350°C, a heating time of 1 minute, a pressure of 1 atom, and a He atmosphere (flow rate: 1 mL / min).

[0069] <Measurement of dielectric constant> The dielectric constant of the insulating layer of each of the insulated wires of the examples and comparative examples was determined using an impedance analyzer (product name (model number): "ZA5405", manufactured by NF Corporation). Furthermore, the difference in dielectric constant of the insulating layer between samples was also calculated in each test described below.

[0070] [First Exam] <Sample preparation> (Sample 1) 1) 1st process It is made of copper alloy and has a rectangular cross section (cross section area: 5 mm 2 ) commercially available linear conductors The following was prepared. Furthermore, tetracarboxylic dianhydride and diamine were dissolved in an equimolar ratio in a first solvent consisting of N-methyl-2-pyrrolidone (NMP, relative dielectric constant: 32.2, boiling point: 204°C), and then a condensation polymerization reaction was promoted to prepare polyamic acid (polyamide precursor) as an insulating varnish. Pyromellitic dianhydride was used as the tetracarboxylic dianhydride, and 4,4'-diaminodiphenyl ether was used as the diamine. This insulating varnish did not contain a second solvent.

[0071] 2) Second process The conductor prepared in Step 1 was immersed in the insulating varnish prepared in Step 1, thereby coating the outer peripheral surface of the conductor with the insulating varnish. Next, the conductor coated with the insulating varnish was passed through the opening of a coating die having a shape similar to the cross-sectional shape of the conductor (Step A). ​​The conductor, which had been uniformly coated with the insulating varnish after passing through Step A, was then baked in a baking oven to cover the outer peripheral surface of the conductor with an insulating layer (Step B). In the baking process, a predetermined amount of heat (+++) sufficient to form an insulating layer was calculated, and the baking temperature and time at which the amount of heat (+++) could be applied were determined.

[0072] Next, the insulating layer formed in the second step was repeatedly coated with the insulating varnish and baked, thereby obtaining an insulated wire of Sample 1 having a plurality of insulating layers.

[0073] (Sample 2) An insulated electric wire of Sample 2 was obtained in the same manner as Sample 1, except that in the first step, an insulating varnish was prepared by adding naphtha (relative dielectric constant: 1.8, boiling point: 247°C) as a second solvent to the first solvent so that the mass ratio of the first solvent to the second solvent was first solvent:second solvent = 9:1.

[0074] <Evaluation of insulated wires> For each of the insulated wires of Sample 1 and Sample 2, the material and thickness of the insulating layer, the dielectric constant of the insulating layer, the ratio of the content of the second solvent based on the total content of the first and second solvents in the insulating layer of the insulated wire (first ratio), the remaining amounts of the first and second solvents remaining in the insulating layer after heat treatment, and the ratio of the remaining amount of the second solvent based on the above remaining amounts (second ratio) were determined. The results are shown in Table 1. Table 1 also shows the dielectric constant and boiling point of NMP used as the first solvent and naphtha used as the second solvent.

[0075] [Second Exam] <Sample preparation> (Sample 3) In step B of the second step, the amount of heat used to carry out the baking treatment was set to two-thirds of that used in sample 1 (++), and the insulated wire of sample 3 was obtained in the same manner as sample 1.

[0076] (Sample 4) An insulated electric wire of Sample 4 was obtained in the same manner as Sample 3, except that in the first step, an insulating varnish was prepared by adding naphtha (relative dielectric constant: 1.8, boiling point: 247°C) as a second solvent to the first solvent so that the mass ratio of the first solvent to the second solvent was first solvent:second solvent = 9:1.

[0077] <Evaluation of insulated wires> The insulated wires of Samples 3 and 4 were subjected to various measurements for the same evaluation items as in the first test described above. The results are shown in Table 1.

[0078] [Third Exam] <Sample preparation> (Sample 5) In step B of the second step, the insulated wire of sample 5 was obtained in the same manner as sample 1, except that the amount of heat used to carry out the baking treatment was one-third of that of sample 1 (+).

[0079] (Sample 6) An insulated electric wire of Sample 6 was obtained in the same manner as Sample 5, except that in the first step, an insulating varnish was prepared by adding naphtha (relative dielectric constant: 1.8, boiling point: 247°C) as a second solvent to the first solvent so that the mass ratio of the first solvent to the second solvent was first solvent:second solvent = 9:1.

[0080] <Evaluation of insulated wires> The insulated wires of Samples 5 and 6 were subjected to various measurements for the same evaluation items as in the first test described above. The results are shown in Table 1.

[0081] [Fourth Exam] <Sample preparation> (Sample 7) An insulated wire of Sample 7 was obtained in the same manner as Sample 5, except that in the first step, the insulating varnish was prepared using a first solvent made of N,N-dimethylacetamide (DMAc, relative dielectric constant: 37.8, boiling point: 165°C) instead of NMP. The insulating varnish did not contain a second solvent.

[0082] (Sample 8) An insulated electric wire of Sample 8 was obtained in the same manner as Sample 7, except that in the first step, an insulating varnish was prepared by adding naphtha (relative dielectric constant: 1.8, boiling point: 247°C) as a second solvent to the first solvent so that the mass ratio of the first solvent to the second solvent was first solvent:second solvent = 9:1.

[0083] <Evaluation of insulated wires> The insulated wires of Samples 7 and 8 were subjected to various measurements for the same evaluation items as in the first test described above. The results are shown in Table 2. Table 2 also shows the dielectric constants and boiling points of DMAc and NMP used as the first solvent, as well as the dielectric constant and boiling point of naphtha used as the second solvent.

[0084] [5th ​​Exam] <Sample preparation> (Sample 9) An insulated wire of Sample 9 was obtained by preparing an insulated wire identical to Sample 5.

[0085] (Sample 10) An insulated electric wire of Sample 10 was obtained in the same manner as Sample 9, except that an insulating varnish was prepared by adding naphtha (relative dielectric constant: 1.8, boiling point: 247°C) as a second solvent to the first solvent so that the mass ratio of the first solvent to the second solvent was first solvent:second solvent = 8.5:1.5.

[0086] <Evaluation of insulated wires> The insulated wires of Samples 9 and 10 were subjected to various measurements for the same evaluation items as in the first test described above. The results are shown in Table 2.

[0087] [Exam 6] <Sample preparation> (Sample 11) In the first step, pyromellitic dianhydride and 3,3',4,4'-biphenyltetracarboxylic acid are used as tetracarboxylic dianhydrides, which are raw materials for polyamic acid. dianhydride An insulated wire of Sample 11 was obtained in the same manner as Sample 3, except that an insulating varnish was prepared by using the above in a molar ratio of 3:7. The insulating varnish did not contain a second solvent.

[0088] (Sample 12) An insulated electric wire of Sample 12 was obtained in the same manner as Sample 11, except that in the first step, an insulating varnish was prepared by adding naphtha (relative dielectric constant: 1.8, boiling point: 247°C) as a second solvent to the first solvent so that the mass ratio of the first solvent to the second solvent was first solvent:second solvent = 9:1.

[0089] <Evaluation of insulated wires> The insulated wires of Samples 11 and 12 were subjected to various measurements for the same evaluation items as in the first test described above. The results are shown in Table 2.

[0090] [Exam 7] <Sample preparation> (Sample 13) An insulated wire of Sample 13 was obtained by preparing the same insulated wire as Sample 5.

[0091] (Sample 14) An insulated electric wire of Sample 14 was obtained in the same manner as Sample 13, except that in the first step, an insulating varnish was prepared by adding naphtha (relative dielectric constant: 1.8, boiling point: 175°C) as a second solvent to the first solvent so that the mass ratio of the first solvent to the second solvent was first solvent:second solvent = 8:2.

[0092] <Evaluation of insulated wires> The insulated wires of Samples 13 and 14 were subjected to various measurements for the same evaluation items as in the first test described above. The results are shown in Table 2.

[0093] [Table 1]

[0094] [Table 2]

[0095] <Consideration> According to Table 1, when an insulating layer contains a first solvent and a second solvent as residual solvents, the first ratio, which is the ratio of the content of the second solvent to the total content of the first and second solvents in the insulating layer, is 50 mass% or more, and the second ratio, which is the ratio of the remaining amount of the second solvent to the total amount of the first and second solvents remaining in the insulating layer after heating the insulated wire at 350°C for 1 minute, is higher than the first ratio, the effect of reducing the dielectric constant was confirmed. That is, in the first test, the dielectric constant of the insulating layer of Sample 2 was lower than that of Sample 1. In the second test, the dielectric constant of the insulating layer of Sample 4 was lower than that of Sample 3. In the third test, the dielectric constant of the insulating layer of Sample 6 was lower than that of Sample 5. Similarly, in the fourth test, the dielectric constant of the insulating layer of Sample 8 was lower than that of Sample 7. In the fifth test, the dielectric constant of the insulating layer of Sample 10 was lower than that of Sample 9. In the sixth test, the dielectric constant of the insulating layer of Sample 12 was lower than that of Sample 11.

[0096] On the other hand, in the seventh test, the boiling point of naphtha used as the second solvent in Sample 14 was 175°C, which was lower than the boiling point (204°C) of NMP used as the first solvent, and a larger amount of naphtha (second solvent) evaporated compared to NMP (first solvent) in the second step. As a result, the insulated wire of Sample 14 had a first ratio of less than 50 mass% and a second ratio lower than the first ratio, and therefore the dielectric constant was not reduced compared to Sample 13. From the above, it can be understood that the insulated wires of Samples 2, 4, 6, 8, 10, and 12 have reduced dielectric constants of the insulating layers, thereby enabling improved insulation properties.

[0097] Although the embodiments and examples of the present disclosure have been described above, it is also planned from the beginning that the configurations of the above-described embodiments and examples may be appropriately combined.

[0098] The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the embodiments and examples described above, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

Claims

1. An insulated wire including a linear conductor and an insulating layer covering an outer peripheral surface of the conductor, the insulating layer contains, as residual solvents, a first solvent having a relative dielectric constant of 15 or more and a second solvent having a relative dielectric constant of less than 15; a first ratio, which is a ratio of a content of the second solvent to a total content of the first solvent and the second solvent contained in the insulating layer, is 50 mass% or more; an insulated electric wire, wherein a second ratio, which is a ratio of a content of the second solvent to a total content of the first solvent and the second solvent contained in the insulating layer after a heat treatment in which the insulated electric wire is heated at 350°C for 1 minute, is higher than the first ratio.

2. 2. The insulated wire according to claim 1, wherein the insulating layer contains one or more resins selected from the group consisting of polyimide resins, polyamide-imide resins, polyester-imide resins, and polyether-imide resins.

3. The insulated wire according to claim 1 or 2, wherein the insulating layer contains the first solvent and the second solvent in a total amount of 0.2 mass % to 10 mass %.

4. the insulating layer contains the first solvent in an amount of 5 mass % or less; The insulated wire according to claim 1 or 2, wherein the insulating layer contains the second solvent in an amount of 0.1% by mass or more and 5% by mass or less.

5. the insulating layer contains a curing agent; 3. The insulated wire according to claim 1, wherein the curing agent comprises at least one selected from the group consisting of alicyclic acid anhydrides, aliphatic acid anhydrides, aromatic acid anhydrides, imidazole, triethylamine, titanium-based compounds, isocyanate-based compounds, blocked isocyanates, urea, melamine, melamine compounds, and acetylene derivatives.

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