Insulated wire

Abstract

To provide an insulated wire with an insulating coating layer that contains a polyesterimide and has a low dielectric constant and excellent thermal stability, and a method for producing the same.SOLUTION: An insulated wire comprises a conductor, and an insulating coating layer covering the conductor. The insulating coating layer includes a polyesterimide having repeating units represented by the general formula (1) in the figure. (In the formula (1), X is at least one selected from the group consisting of a divalent group represented by the formula (X1) in the figure and a divalent group represented by the formula (X2) in the figure.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an insulated wire and a method for manufacturing the same.

Background Art

[0002] Motors are used in various applications such as industrial use and household use. Depending on the application, various motors such as high-power, small-sized, and lightweight motors have been developed and manufactured. Recently, with the spread of electric vehicles and the like, high-performance motors for transportation applications have also been developed. In such a situation, in recent years, high performance has also been required for the insulated wire constituting the motor coil. As the insulating layer (coating layer) of the insulated wire, polyimide resin, polyesterimide resin, polyamideimide resin, etc., which have excellent insulation and durability, are used. Further improvements have been made to the resins used for these insulating layers (coating layers). For example, in Patent Document 1, for the purpose of improving partial discharge resistance and processability at high temperatures, an acid component containing pyromellitic dianhydride and biphenyltetracarboxylic dianhydride in a specific molar ratio, and a diamine component such as diaminodiphenyl ether An insulated wire having a polyimide having a specific storage modulus obtained from is disclosed as an insulating layer. Further, as an example using a polyesterimide resin, Patent Document 2 discloses an ester bond component containing a phenol component composed of bisphenol having three or more aromatic rings for the purpose of increasing the partial discharge initiation voltage, and an imide dicarboxylic acid having an imide group in the molecular skeleton. An insulated wire having an insulating film formed by applying and baking an insulating paint containing a carboxylic acid component composed of is disclosed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

[0004] Polyesterimide is excellent as an insulating layer for insulated wires, but as mentioned above, in order to cope with the miniaturization and increased power output of motors in recent years, higher insulation and thermal stability are required. Therefore, there was a demand for insulated wires in which the conductor was covered with an insulating layer that had a particularly low dielectric constant and excellent thermal stability. This invention has been made in view of the above circumstances, and the object of this invention is to provide an insulated electric wire having an insulating coating layer that contains polyesterimide, has a low dielectric constant and excellent thermal stability, and a method for manufacturing the same. [Means for solving the problem]

[0005] The inventors have discovered that an insulated wire having an insulating coating layer containing a polyesterimide having a specific structure can solve the above problems, and have completed the invention.

[0006] In other words, the present invention relates to the following [1] to

[16] . [1] An insulated wire having a conductor and an insulating coating layer covering the conductor, An insulated wire comprising a polyesterimide having repeating units represented by the following general formula (1) in the insulating coating layer. [ka] (In formula (1), X is at least one selected from the group consisting of the divalent group represented by formula (X1) and the divalent group represented by formula (X2).) [2] The insulated wire according to [1] above, wherein the repeating unit represented by formula (1) is the repeating unit represented by formula (1-1) below. [ka] [3] An insulated wire as described in [1] or [2] above, wherein X contains a divalent group represented by formula (X2). [4] An insulated wire according to any one of [1] to [3] above, wherein X includes a divalent base represented by formula (X1) and a divalent base represented by formula (X2). [5] The insulated wire described in [4] above, wherein the molar ratio [(X1) / (X2)] of the base represented by formula (X1) to the base represented by formula (X2) is 30 / 70 to 95 / 5. [6] An insulated wire according to any one of [1] to [5] above, wherein the divalent base represented by formula (X1) is the divalent base represented by the following formula (X1-1). [ka] [7] An insulated wire according to any one of [1] to [6] above, wherein the divalent base represented by formula (X2) is the divalent base represented by formula (X2-1) below. [ka] [8] The insulated wire according to any one of [1] to [7] above, wherein the polyesterimide is substantially free of aliphatic hydrocarbon groups. [9] The insulated wire according to any one of [1] to [8] above, wherein the glass transition temperature of the polyesterimide is 220 to 280°C.

[10] The insulated wire according to any one of [1] to [9] above, wherein the 10% thermoweight loss temperature of the polyesterimide in air is 470°C or higher.

[11] The insulated wire according to any one of [1] to

[10] above, wherein the relative permittivity of the polyesterimide at 1 kHz is 3.1 or less.

[12] A method for manufacturing an insulated wire as described in any one of [1] to

[11] above, A method for manufacturing an insulated wire, comprising applying an insulating wire coating containing a polyesteramic acid having repeating units represented by the following general formula (2) and an organic solvent onto a conductor and baking it to form an insulating coating layer. [ka] (In formula (2), X is at least one selected from the group consisting of a divalent group represented by formula (X1) and a divalent group represented by formula (X2).)

[13] The method for manufacturing an insulated electric wire according to

[12] above, wherein the concentration of the polyester amic acid in the paint for insulated electric wire is 8 to 50% by mass.

[14] The method for manufacturing an insulated electric wire according to

[12] or

[13] above, wherein the viscosity of the paint for insulated electric wire at 25°C is 1 to 50 Pa·s.

[15] The method for manufacturing an insulated electric wire according to any one of

[12] to

[14] above, wherein the weight average molecular weight of the polyester amic acid is 5,000 to 1,000,000.

[16] The method for manufacturing an insulated electric wire according to any one of

[12] to

[15] above, wherein the organic solvent contains N,N-dimethylacetamide. <0********>[Advantages of the Invention]

[0007] According to the present invention, there can be provided an insulated electric wire having an insulating coating layer containing polyester imide, having a low dielectric constant, and excellent in thermal stability, and a method for manufacturing the same. [Embodiments for Carrying Out the Invention]

[0008] [Insulated Electric Wire] The insulated electric wire of the present invention is an insulated electric wire having a conductor and an insulating coating layer covering the conductor, wherein the insulating coating layer contains a polyester imide having a repeating unit represented by the following general formula (1). [Chemical Formula] (In formula (1), X is at least one selected from the group consisting of the divalent group represented by the above formula (X1) and the divalent group represented by the above formula (X2).)

[0009] The reason why the insulated electric wire of the present invention has an insulating coating layer having a low dielectric constant and excellent in thermal stability is not clear, but it is considered as follows. The insulated wire of the present invention contains a polyesterimide having repeating units represented by formula (1) in its insulating coating layer. Since this polyesterimide has a low proportion of highly polarizable imide groups as linking groups and instead contains ester groups with low polarizability, the resulting insulating coating layer is expected to have a low dielectric constant. Furthermore, because it contains rigid biphenylene groups, it is expected to have excellent thermal stability.

[0010] <Insulating coating layer> The insulating coating layer of the insulated wire of the present invention covers the conductor and contains polyesterimide having repeating units represented by the following general formula (1). [ka] (In formula (1), X is at least one selected from the group consisting of the divalent group represented by formula (X1) and the divalent group represented by formula (X2).)

[0011] (Polyesterimide having repeating units represented by general formula (1)) As described above, the insulating coating layer contains a polyesterimide having repeating units represented by the general formula (1). In formula (1), X is at least one selected from the group consisting of a divalent group represented by formula (X1) and a divalent group represented by formula (X2), preferably including a divalent group represented by formula (X2), more preferably including a divalent group represented by formula (X1) and a divalent group represented by formula (X2), and even more preferably including a divalent group represented by formula (X1) and a divalent group represented by formula (X2).

[0012] When X includes a divalent group represented by formula (X1) and a divalent group represented by formula (X2), the molar ratio of the group represented by formula (X1) to the group represented by formula (X2) [(X1) / (X2)] is preferably 30 / 70 to 95 / 5, more preferably 30 / 70 to 85 / 15, and even more preferably 40 / 60 to 85 / 15.

[0013] The repeating unit represented by formula (1) is preferably the repeating unit represented by the following formula (1-1) from the viewpoint of raw material availability and thermal stability. [ka] (In formula (1-1), X is at least one selected from the group consisting of the divalent group represented by formula (X1) and the divalent group represented by formula (X2).)

[0014] The divalent group represented by the above formula (X1) is preferably a divalent group represented by the following formula (X1-1) from the viewpoint of raw material availability and thermal stability. [ka]

[0015] The divalent group represented by the above formula (X2) is, from the viewpoint of raw material availability and thermal stability, the divalent group represented by the following formula (X2-1). [ka]

[0016] The polyesterimide has repeating units represented by the general formula (1), wherein the content of the repeating units represented by formula (1) is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 90 mol% or more, even more preferably 95 mol% or more, and 100 mol% or less, relative to the total repeating units constituting the polyesterimide. It is even more preferable that the polyesterimide consists only of repeating units represented by the general formula (1). Here, the repeating units that make up polyesterimide refer to units in which one tetracarboxylic dianhydride and one diamine are bonded via an imide structure.

[0017] The polyesterimide is preferably substantially free of aliphatic hydrocarbon groups. Here, "substantially free of aliphatic hydrocarbon groups" means that the content of aliphatic hydrocarbon groups in the polyesterimide is such that it does not affect the effects of the present invention, or that the polyesterimide contains no aliphatic hydrocarbon groups. Specifically, the content of aliphatic hydrocarbon groups in the polyesterimide is preferably 5% by mass or less, more preferably 1% by mass or less, even more preferably 0.5% by mass or less, and even more preferably 0% by mass. It is even more preferable that the polyesterimide does not contain aliphatic hydrocarbon groups. The aliphatic hydrocarbon groups mentioned above are saturated aliphatic hydrocarbon groups, unsaturated aliphatic hydrocarbon groups, and alicyclic hydrocarbon groups present in the main chain or side chain of the polyesterimide. Specifically, these include alkyl groups, alkylene groups, alkylidene groups, alkenyl groups, alkynyl groups, cycloalkyl groups, and the like.

[0018] The glass transition temperature of the polyesterimide is preferably 200 to 300°C, more preferably 220 to 285°C, even more preferably 220 to 280°C, and even more preferably 250 to 270°C. When the glass transition temperature of the polyesterimide is within this range, it exhibits excellent heat resistance and good thermal stability of the insulating coating layer. The glass transition temperature of the polyesterimide can be determined by measuring the temperature dependence of the loss tangent (tanδ) in the tensile mode on a film-like sample of polyesterimide using a dynamic viscoelasticity analyzer (DMA), and finding the temperature at which tanδ peaks. Specifically, it can be measured by the method described in the examples.

[0019] The relative permittivity of the polyesterimide at 1 kHz is preferably 3.1 or less, more preferably 3.0 or less, and even more preferably 2.9 or less. There is no lower limit, but it is generally 2.0 or higher. When the relative permittivity of the polyesterimide at 1 kHz is within the above range, the dielectric constant of the insulating coating layer is low, resulting in excellent insulating properties. The relative permittivity of the polyesterimide can be measured by the automatic equilibrium bridge method in accordance with JIS C 2138. Specifically, it can be measured by the method described in the examples.

[0020] The 10% thermoweight loss temperature of the polyesterimide in air is preferably 470°C or higher, and more preferably 490°C or higher. There is no upper limit, but it is generally 800°C or lower. When the 10% thermoweight loss temperature of the polyesterimide in air is within the above range, it exhibits excellent heat resistance and good thermal stability of the insulating coating layer. The 10% thermoweight loss temperature of the polyesterimide in air can be measured by the TGA (thermogravimetric analysis) method. Specifically, it can be measured by the method described in the examples.

[0021] <Conductor> The conductor used in the insulated wire of the present invention is a linear material made of a substance with high electrical conductivity. The material used for the conductor is preferably a metal, more preferably at least one selected from the group consisting of copper and aluminum, and even more preferably copper. The conductor is preferably a wire, more preferably a metal wire, even more preferably at least one selected from the group consisting of copper wire and aluminum wire, and even more preferably a copper wire.

[0022] As described above, the insulated wire of the present invention has an insulating coating layer containing polyesterimide, which has a low dielectric constant and excellent thermal stability. For this reason, the insulated wire of the present invention is particularly suitable as an insulated wire for motor coils.

[0023] [Manufacturing method for insulated electric wires] The insulated wire of the present invention is not particularly limited as long as it is produced by the method described above, but it is preferably manufactured by the following method. In other words, a preferred method for manufacturing an insulated wire of the present invention is the above-mentioned method for manufacturing an insulated wire, This method involves applying an insulating wire coating containing a polyester amide acid having repeating units represented by the following general formula (2) and an organic solvent onto a conductor and baking it to form an insulating coating layer. [ka] (In equation (2), X is at least one selected from the group consisting of the divalent group represented by equation (X1) and the divalent group represented by equation (X2).)

[0024] <Insulated wire paint> The coating for insulating wires used in the above manufacturing method comprises a polyesteramic acid having repeating units represented by the general formula (2) and an organic solvent.

[0025] (Polyesteramide acid) As described above, the coating for insulating wires contains a polyesteramide acid having repeating units represented by the general formula (2). In formula (2), X is at least one selected from the group consisting of a divalent group represented by formula (X1) and a divalent group represented by formula (X2), preferably including a divalent group represented by formula (X2), more preferably including a divalent group represented by formula (X1) and a divalent group represented by formula (X2), and even more preferably including a divalent group represented by formula (X1) and a divalent group represented by formula (X2).

[0026] When X includes a divalent group represented by formula (X1) and a divalent group represented by formula (X2), the molar ratio of the group represented by formula (X1) to the group represented by formula (X2) [(X1) / (X2)] is preferably 30 / 70 to 95 / 5, more preferably 30 / 70 to 85 / 15, and even more preferably 40 / 60 to 85 / 15.

[0027] The repeating unit represented by formula (2) above is preferably the repeating unit represented by the following formula (2-1) from the viewpoint of raw material availability and the thermal stability of the polyesterimide (insulating coating layer) produced after baking. [ka] (In equation (2-1), X is at least one selected from the group consisting of the divalent group represented by equation (X1) and the divalent group represented by equation (X2).)

[0028] The divalent group represented by formula (X1) is preferably a divalent group represented by the following formula (X1-1), from the viewpoint of raw material availability and the thermal stability of the polyesterimide (insulating coating layer) formed after baking. [ka]

[0029] The divalent group represented by the above formula (X2) is the divalent group represented by the following formula (X2-1), from the viewpoint of raw material availability and the thermal stability of the polyesterimide (insulating coating layer) formed after baking. [ka]

[0030] The polyesteramic acid has repeating units represented by the general formula (2), wherein the content of the repeating units represented by formula (2) is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 90 mol% or more, even more preferably 95 mol% or more, and 100 mol% or less, relative to the total repeating units constituting the polyesteramic acid. It is even more preferable that the polyesteramic acid consists only of repeating units represented by the general formula (2). Here, the repeating unit that constitutes a polyesteramic acid refers to a unit in which one tetracarboxylic dianhydride and one diamine are bonded via an amide structure.

[0031] Furthermore, the polyesteramic acid preferably contains substantially no aliphatic hydrocarbon groups. Here, "substantially free of aliphatic hydrocarbon groups" means that the content of aliphatic hydrocarbon groups in the polyesteramic acid is such that it does not affect the effects of the present invention, or that the polyesteramic acid does not contain any aliphatic hydrocarbon groups. Specifically, the content of aliphatic hydrocarbon groups in the polyesteramic acid is preferably 5% by mass or less, more preferably 1% by mass or less, even more preferably 0.5% by mass or less, and even more preferably 0% by mass. It is even more preferable that the polyesteramic acid does not contain any aliphatic hydrocarbon groups. The aliphatic hydrocarbon groups mentioned above are saturated aliphatic hydrocarbon groups, unsaturated aliphatic hydrocarbon groups, and alicyclic hydrocarbon groups present in the main chain or side chain of the polyesteramic acid. Specifically, these include alkyl groups, alkylene groups, alkylidene groups, alkenyl groups, alkynyl groups, cycloalkyl groups, and the like.

[0032] The weight-average molecular weight of the polyesteramic acid is preferably 5,000 to 1,000,000, and more preferably 50,000 to 300,000. A weight-average molecular weight within this range is preferable because it allows the insulating wire coating to be adjusted to a concentration and viscosity suitable for the manufacture of insulating wires, and furthermore, the polyesterimide (insulating coating layer) produced by baking exhibits excellent mechanical properties such as elongation. The weight-average molecular weight of the polyesteramic acid can be determined, for example, by gel filtration chromatography to obtain a value equivalent to standard polystyrene (PS). Specifically, it can be measured by the method described in the examples.

[0033] (Production of polyesteramic acid) The aforementioned polyesteramic acid can be produced by reacting a tetracarboxylic acid component and a diamine component having ester bonds, as described below.

[0034] Examples of tetracarboxylic acid components used in the production of polyesteramic acid include compounds represented by the following general formula (a1). Among the compounds represented by the following general formula (a1), the compound represented by the following formula (a11) is preferred. [ka] The compound represented by formula (a11) is p-biphenylenebis(trimellitate) dianhydride. By using p-biphenylenebis(trimellitate) dianhydride as the tetracarboxylic acid component, an insulating coating layer with low dielectric constant, excellent thermal stability, and excellent elongation can be formed.

[0035] The proportion of the compound represented by formula (a1) in the tetracarboxylic acid component is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 90 mol% or more, and also preferably 100 mol% or less. The tetracarboxylic acid component may consist only of the compound represented by formula (a1).

[0036] The tetracarboxylic acid component may include tetracarboxylic dianhydrides other than the compound represented by formula (a1). Such tetracarboxylic dianhydrides are not particularly limited, but include aromatic tetracarboxylic dianhydrides other than the compound represented by formula (a1), alicyclic tetracarboxylic dianhydrides, and aliphatic tetracarboxylic dianhydrides. However, in the present invention, it is preferable not to use alicyclic tetracarboxylic dianhydrides or aliphatic tetracarboxylic dianhydrides substantially, and it is more preferable to use only aromatic tetracarboxylic dianhydrides. The tetracarboxylic acid component may optionally contain one or more tetracarboxylic dianhydrides. The tetracarboxylic acid component is not limited to tetracarboxylic dianhydride, but may also be a derivative thereof. Examples of such derivatives include the tetracarboxylic acid corresponding to the tetracarboxylic dianhydride and the alkyl ester of the tetracarboxylic acid. Among these, tetracarboxylic dianhydride is preferred.

[0037] Examples of diamine components used in the production of polyesteramic acid include the compound represented by the following general formula (b1) and the compound represented by the following general formula (b2). The diamine component used in the production of polyesteramic acid includes at least one selected from the group consisting of the compound represented by formula (b1) and the compound represented by formula (b2), preferably including the compound represented by formula (b2), and more preferably including the compound represented by formula (b1) and the compound represented by formula (b2).

[0038] When the diamine component includes a compound represented by formula (b1) and a compound represented by formula (b2), the molar ratio of the compound represented by formula (b1) to the compound represented by formula (b2) [(b1) / (b2)] is preferably 30 / 70 to 95 / 5, more preferably 30 / 70 to 85 / 15, and even more preferably 40 / 60 to 85 / 15. Among the compounds represented by the following general formula (b1), the compound represented by formula (b11) is preferred. Furthermore, among the compounds represented by the following general formula (b2), the compound represented by formula (b21) is preferred. [ka] The compound represented by formula (b11) is 4,4'-diaminodiphenyl ether (ODA), and the compound represented by formula (b21) is 4,4'-bis(4-aminophenoxy)biphenyl (BAPB). By using ODA or BAPB as the diamine component, an insulating coating layer with low dielectric constant, excellent thermal stability, and excellent elongation can be formed.

[0039] The total ratio of the compound represented by formula (b1) and the compound represented by formula (b2) in the diamine component is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 90 mol% or more, and preferably 100 mol% or less. The diamine component may consist only of the compound represented by formula (b1), only of the compound represented by formula (b2), or both of the compounds represented by formula (b1) and (b2), or consist only of these.

[0040] The diamine component may include diamines other than the compound represented by formula (b1) or the compound represented by formula (b2). Such diamines are not particularly limited, but include aromatic diamines, alicyclic diamines, and aliphatic diamines other than the compound represented by formula (b1) or the compound represented by formula (b2). However, in the present invention, it is preferable not to use alicyclic diamines or aliphatic diamines substantially, and it is more preferable to use only aromatic diamines. The diamine component may consist of one type of diamine or two or more types. The diamine component is not limited to diamines, but may also be a derivative thereof. Examples of such derivatives include diisocyanates corresponding to diamines. Among these, diamines are preferred.

[0041] The polyesteramic acid produced using the above raw materials has constituent units derived from the tetracarboxylic dianhydride and constituent units derived from the diamine. Furthermore, the polyesterimide produced using the polyesteramic acid produced using the above raw materials as a precursor has constituent units derived from the tetracarboxylic dianhydride and constituent units derived from the diamine. In other words, the polyesteramic acid of the present invention preferably has constituent units derived from the tetracarboxylic dianhydride and constituent units derived from the diamine. Furthermore, the polyesterimide of the present invention preferably has constituent units derived from the tetracarboxylic dianhydride and constituent units derived from the diamine.

[0042] The polyesteramic acid can be produced by reacting a tetracarboxylic acid component containing the compound represented by formula (a1) with a diamine component containing the compound represented by formula (b1) or the compound represented by formula (b2). The amount of the diamine component relative to the tetracarboxylic acid component is preferably 0.9 to 1.1 moles.

[0043] There are no particular restrictions on the method used to react the tetracarboxylic acid component with the diamine component in this manufacturing method; known methods can be used. Specific reaction methods include charging the tetracarboxylic acid component, diamine component, solvent, and optionally an end-capturing agent into a reactor and stirring at 0 to 120°C, preferably 5 to 80°C, for 1 to 72 hours. When the reaction is carried out at temperatures below 80°C, the molecular weight of the polyesteramic acid does not fluctuate depending on the temperature history during polymerization, and the progression of thermal imidization can also be suppressed, thus enabling the stable production of polyesteramic acid.

[0044] Monoamines or dicarboxylic acids are preferred as end-cap encapsulants. The amount of end-cap encapsulant to be introduced is preferably 0.0001 to 0.1 moles, and more preferably 0.001 to 0.06 moles, per mole of tetracarboxylic acid component. Examples of monoamine end-cap encapsulants include methylamine, ethylamine, propylamine, butylamine, benzylamine, 4-methylbenzylamine, 4-ethylbenzylamine, 4-dodecylbenzylamine, 3-methylbenzylamine, 3-ethylbenzylamine, aniline, 3-methylaniline, 4-methylaniline, 3-phenoxyaniline, 4-phenoxyaniline, m-anisidine, and p-anisidine. Of these, aniline, 4-phenoxyaniline, and p-anisidine are preferred. Dicarboxylic acids are preferred as end-cap encapsulants, and a portion of them may be ring-closed. Examples include phthalic acid, phthalic anhydride, 4-chlorophthalic acid, tetrafluorophthalic acid, 2,3-benzophenone dicarboxylic acid, 3,4-benzophenone dicarboxylic acid, cyclopentane-1,2-dicarboxylic acid, and 4-cyclohexene-1,2-dicarboxylic acid. Of these, phthalic acid and phthalic anhydride are more preferred.

[0045] The solvent used in the production of polyesteramic acid can be any solvent capable of dissolving the resulting polyesteramic acid. Examples include aprotic solvents, phenolic solvents, etheric solvents, carbonate solvents, aromatic hydrocarbon solvents, etc., with aprotic solvents being preferred.

[0046] Specific examples of aprotic solvents include amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-methylcaprolactam, 1,3-dimethylimidazolidinone, and tetramethylurea; lactone solvents such as γ-butyrolactone and γ-valerolactone; phosphorus-containing amide solvents such as hexamethylphosphoricamide and hexamethylphosphinetriamide; sulfur-containing solvents such as dimethylsulfone, dimethyl sulfoxide, and sulfolane; ketone solvents such as acetone, methyl ethyl ketone, cyclohexanone, and methylcyclohexanone; and ester solvents such as acetic acid (2-methoxy-1-methylethyl). Preferably, the solvent is an amide or lactone solvent, more preferably an amide solvent, and even more preferably N,N-dimethylacetamide.

[0047] Specific examples of phenolic solvents include phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, and 3,5-xylenol. Specific examples of ether-based solvents include 1,2-dimethoxyethane, bis(2-methoxyethyl) ether, 1,2-bis(2-methoxyethoxy)ethane, bis[2-(2-methoxyethoxy)ethyl] ether, tetrahydrofuran, and 1,4-dioxane. Specific examples of carbonate-based solvents include diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, and propylene carbonate. Among the above solvents, amide solvents or lactone solvents are preferred, amide solvents are more preferred, and N,N-dimethylacetamide is even more preferred. Specific examples of aromatic hydrocarbon solvents include toluene, xylene, and ethylbenzene. The above solvents may be used individually or in combination of two or more.

[0048] By the above method, a polyester amide acid solution dissolved in a solvent is obtained. The concentration of polyesteramide acid in the resulting solution is preferably 1 to 80% by mass, more preferably 5 to 50% by mass, and even more preferably 10 to 30% by mass.

[0049] (Manufacturing and characteristics of coatings for insulated wires) The insulating wire coating used in the manufacture of the insulating wire of the present invention contains the aforementioned polyesteramic acid and organic solvent, wherein the polyesteramic acid is dissolved in the organic solvent. The organic solvent contained in the coating for insulating wires can be any solvent that dissolves polyesteramic acid and is not particularly limited, but the compounds mentioned above are preferred as solvents used in the production of polyesteramic acid. Specifically, the organic solvent contained in the coating for insulating wires preferably contains the amide-based solvent or the lactone-based solvent, more preferably contains the amide-based solvent, and even more preferably contains N,N-dimethylacetamide. The above solvents may be used individually or in combination of two or more.

[0050] The aforementioned coating for insulating wires may further contain a dehydration catalyst. Examples of dehydration catalysts include acid anhydrides such as acetic anhydride, propionic anhydride, n-butyric anhydride, benzoic anhydride, and trifluoroacetic anhydride; and carbodiimide compounds such as dicyclohexylcarbodiimide. These may be used individually or in combination of two or more.

[0051] Since the polyesteramic acid contained in the aforementioned insulating wire coating is solvent-soluble, it can be used to create a highly concentrated coating that is stable at room temperature. The concentration of the polyesteramide acid in the coating for insulating wires is preferably 5 to 70% by mass, more preferably 8 to 50% by mass, and even more preferably 10 to 30% by mass. The concentration of polyesteramide acid in the coating for insulating wires may be adjusted by diluting the polyesteramide acid solution immediately after its manufacture with an organic solvent, or the polyesteramide acid solution may be used as is as a coating for insulating wires if the concentration of polyesteramide acid in the polyesteramide acid solution is within the above range and is suitable for the manufacture of insulating wires. The viscosity of the aforementioned insulating wire coating at 25°C is preferably 1 to 50 Pa·s, and more preferably 5 to 30 Pa·s. The viscosity of the coating can be measured, for example, using an E-type (cone-plate type) viscometer. Specifically, it can be measured by the method described in the examples.

[0052] Furthermore, the coating for insulated wires may also contain various additives such as inorganic fillers, adhesion promoters, release agents, flame retardants, ultraviolet stabilizers, surfactants, leveling agents, defoamers, fluorescent whitening agents, crosslinking agents, polymerization initiators, and photosensitive agents, to the extent that they do not impair the required characteristics of the resulting insulated wires. The method for manufacturing the coating for insulating wires is not particularly limited, and known methods can be applied. For example, it can be obtained by adjusting the concentration of the polyesteramic acid solution obtained by the above manufacturing method by mixing in additional solvents as needed.

[0053] [Manufacturing method for insulated electric wires] The method for manufacturing the insulated wire of the present invention is not particularly limited, but it is preferable to manufacture it using the aforementioned coating for insulated wires. Specifically, the present invention relates to a method for manufacturing an insulated wire, comprising applying an insulating wire coating containing a polyesteramic acid having repeating units represented by the following general formula (2) and an organic solvent onto a conductor and baking it to form an insulating coating layer. [ka] (In equation (2), X is at least one selected from the group consisting of the divalent group represented by equation (X1) and the divalent group represented by equation (X2).)

[0054] The insulating coating layer of the insulated wire obtained in this way is obtained by imidizing the aforementioned polyester amide acid, and therefore contains polyimide containing repeating units represented by general formula (1).

[0055] According to this manufacturing method, the insulating wire coating is applied to a conductor and baked to form an insulating coating layer, thereby obtaining an insulated wire. By repeating the application and baking process, an insulating coating layer of appropriate thickness can be formed. The curing temperature is preferably 180 to 600°C, more preferably 200 to 600°C, and even more preferably 250 to 500°C. The curing time is preferably 1 minute to 10 hours, more preferably 5 minutes to 3 hours, and even more preferably 5 minutes to 1 hour. When the curing temperature is low, a longer curing time is preferable, and when the temperature is high, a shorter curing time is preferable. The baking process is performed to remove organic solvents contained in the insulated wire coating, imide the polyesteramic acid, and fix the insulating coating layer onto the conductor. However, if chemical imidation is used instead of thermal imidation for the imidation reaction, baking may be performed at a lower temperature. The insulated wire of the present invention obtained as described above has an insulating coating layer containing polyesterimide, which has a low dielectric constant and excellent thermal stability. For this reason, the insulated wire of the present invention is particularly suitable as an insulated wire for motor coils. [Examples]

[0056] The present invention will be specifically described below with reference to examples. However, the present invention is not limited in any way by these examples.

[0057] [Physical property measurement and evaluation] The physical properties of the insulating wire coatings and polyesteramidic acid obtained in the manufacturing examples and comparative manufacturing examples, as well as the polyesterimide films obtained in the test examples and comparative test examples, were measured and evaluated by the methods described below.

[0058] (1) Weight-average molecular weight of polyesteramic acid The weight-average molecular weight of the polyesteramic acid obtained in the production example and comparative production example was measured as follows. The varnish containing the aforementioned polyesteramic acid was diluted with the mobile phase solvent shown below to obtain a measurement solution with a polyesteramic acid concentration of 0.2% by mass. Using the measurement solution, gel filtration chromatography was performed under the following conditions to determine the weight-average molecular weight of the polyesteramic acid in terms of polystyrene equivalent. Equipment: CBM-20A, SIL-10ADvp, LC-10ADvp, DGU-12A, SPD-10Avp, CTO-10Avp, RID-10A, FRC-10A (all manufactured by Shimadzu Corporation) Column: Shodex GPC K-804 Column temperature: 50℃ Mobile phase: N-methylpyrrolidone (LiBr (30mM), H3PO4 (30mM)) Mobile phase flow rate: 0.7mL / min Molecular weight standard material: Polystyrene (Shodex M-6.8,63,955)

[0059] (2) Viscosity of paint for insulating wires The viscosity of the insulating wire coatings obtained in the manufacturing example and comparative manufacturing example was measured using the following viscometer under the following conditions. Equipment: Type E (cone plate type) viscometer HAAKE RheoStress 6000 (manufactured by Thermo Scientific) Measurement temperature: 25℃ Shear rate: 3s -1

[0060] (3) Glass transition temperature (Tg) The films obtained in the test example and comparative test example were dried under vacuum at 100°C for 16 hours, cut into strips 10 mm wide and 30 mm long, and used as measurement samples. Using the aforementioned sample, the glass transition temperature (Tg) was measured under the following conditions using a dynamic viscoelasticity analyzer DMA7100 (manufactured by Hitachi High-Tech Science Corporation). Tg is the temperature at the peak top of the loss tangent (tanδ). Measurement mode: Tensile mode Heating conditions: Heat from 30°C to 320°C at a rate of 10°C / min, hold for 5 minutes. Frequency: 1Hz Amplitude: 10μm

[0061] (4) Permittivity (relative permittivity) The films obtained in the test example and comparative test example were cut into 60 mm x 60 mm sections, dried under vacuum at 100°C for 18 hours, and prepared as test specimens. Using the aforementioned test specimen, the dielectric constant (relative permittivity) was measured using a precision LCR meter E4980A (manufactured by Agilent Technologies) under the following conditions. The measurement frequency was 1 kHz. Measurement environment: 23℃±2℃, 50%RH±5%RH Electrode dimensions: Main electrode φ36mm, annular electrode inner diameter φ38mm Electrode material: Conductive silver paste

[0062] (5) Thermogravimetric temperature (Td), evaluation of thermal stability The resin coating layers obtained in the examples, or the films obtained in the test examples and comparative test examples, were pulverized using a freeze-drying machine, dried under vacuum at 100°C for 16 hours, and used as samples for measurement. Using a sample for measurement, the 10% mass thermogravimetric loss temperature (Td10%) was measured by TGA (thermogravimetric analysis) under the following conditions using a differential thermogravimetric analyzer STA7200 (manufactured by Hitachi High-Tech Science Co., Ltd.). Td10% was defined as the temperature at which the mass of the sample for measurement decreased by 10% compared to the mass at the start of the measurement. A higher thermogravimetric loss temperature indicates superior thermal stability. Samples that did not reach a Td of 10% even after heating to 500°C were considered to have a measurement value exceeding the upper limit of 490°C and were marked as ">490" in Table 1. Heating conditions: Heat from 30°C to 500°C at a rate of 10°C / min, hold for 5 minutes. Measurement environment: Under an air atmosphere

[0063] [Raw materials] The raw materials and their abbreviations used in the manufacturing example and comparative manufacturing example are as follows. <Raw materials for polyesterimide and polyesteramic acid> TA-BP: p-biphenylene bis(trimellitate) dianhydride (BP-TME, manufactured by Honshu Chemical Industry Co., Ltd.; compound represented by formula (a11). Purity 98.6%. For the production of polyesteramic acid, a compound dried under vacuum at 100°C for approximately 2 hours was used.) TA-BPZ: p-(cyclohexylidenebisphenylene)bis(trimellitate) dianhydride (BPZ-TME, manufactured by Honshu Chemical Industry Co., Ltd.; compound represented by the following formula; purity 99.2%) [ka] TA-HMBP: p-(2,2',3,3',5,5'-hexamethylbiphenylene)-bis(trimellitate) dianhydride (manufactured by Honshu Chemical Industry Co., Ltd., TMPBP-TME; compound represented by the following formula; purity 99.5%) [ka] ODA: 4,4'-diaminodiphenyl ether (manufactured by Tokyo Chemical Industry Co., Ltd.; compound represented by formula (b11). Purity 99.4%) BAPB: 4,4'-Bis(4-aminophenoxy)biphenyl (manufactured by Tokyo Chemical Industry Co., Ltd.; compound represented by formula (b21); purity 100%) BAPP: 2,2-Bis[4-(4-aminophenoxy)phenyl]propane (manufactured by Tokyo Chemical Industry Co., Ltd.; compound represented by the following formula; purity 99.4%) [ka] In comparative test example 4 below, PMDA / ODA:poly(pyromellitic dianhydride-co-4,4'-diaminodiphenyl ether) (manufactured by Sigma-Aldrich, N-methylpyrrolidone solution, 15.7% by mass) was used. The raw materials were the above-mentioned ODA and PMDA (pyromellitic dianhydride).

[0064] <Solvent> DMAc: N,N-dimethylacetamide

[0065] [Manufacturing of coatings for insulating wires (polyesteramide acid)] Manufacturing Example 1 A 300 mL separable flask equipped with a mechanical stirrer featuring a nitrogen inlet tube, exhaust tube, and stirring blades was circulated with nitrogen to create a nitrogen atmosphere. Next, 2.0 g (10 mmol) of ODA was added to the separable flask. Then, DMAc was added to achieve a concentration of 12.5% ​​by mass of the resulting polyesteramic acid. Next, 5.4 g (10 mmol) of TA-BP was added. The reaction was carried out at 25°C with stirring, and after confirming the start of viscosity increase, DMAc was added to obtain a reaction mixture so that the concentration of the resulting polyesteramic acid was 10% by mass. The reaction mixture was further reacted at 25°C for 20 hours with stirring to obtain a polyesteramic acid solution (paint for insulating wires).

[0066] Manufacturing Example 2 and Comparative Manufacturing Examples 1-3 In Production Example 1, a polyester amide acid solution (insulating wire coating) was obtained in the same manner as in Production Example 1, except that TA-BP or ODA was replaced with the raw materials shown in Table 1.

[0067] Manufacturing Example 3 A 300 mL separable flask equipped with a mechanical stirrer featuring a nitrogen inlet tube, exhaust tube, and stirring blades was circulated with nitrogen to create a nitrogen atmosphere. Next, 1.8 g (5 mmol) of BAPB was added to the separable flask. Then, DMAc was added to achieve a concentration of 12.5% ​​by mass of the resulting polyesteramic acid. Next, 5.4 g (10 mmol) of TA-BP was added. The reaction was carried out at 25°C with stirring, and after confirming the start of viscosity increase, 1.0 g (5 mmol) of ODA was added. Then, DMAc was added to obtain a reaction mixture so that the concentration of the resulting polyesteramic acid was 10% by mass. The reaction mixture was further reacted at 25°C for 20 hours with stirring to obtain a polyesteramic acid solution (paint for insulating wires).

[0068] [Manufacturing of insulated wires] Example 1 The polyesteramic acid solution (insulating wire coating) obtained in Manufacturing Example 3 was applied to a 1.6 mm diameter copper wire (Waki Sangyo Co., Ltd.'s electrical soft copper wire HW-312) by immersion (dip method) so that the insulating coating layer thickness was 0.04 to 0.05 mm. The solvent was removed by heating in a hot air dryer at 100°C for 2 hours. Then, the wire was heated at 200°C for 1 hour, and further heated at 250°C for 30 minutes to bake it, thereby producing a wire coated with resin. The electrical conductivity of the resin coating layer of the wire was measured using a tester (multimeter) to confirm that the resulting wire was an insulated wire. Next, the resin coating layer (insulating coating layer) of the insulated wire was peeled off, pulverized using a freeze-drying machine, dried under vacuum at 100°C for 16 hours, and used as a sample for measuring the 10% mass thermogravimetric temperature (Td10%). When the 10% mass thermogravimetric temperature (Td10%) of the coating layer was measured using the method described above, it was found that even when the temperature was raised to 500°C, it did not reach Td10%, and Td10% was above 490°C. From this, it can be seen that the resin coating layer (insulating coating layer) of the insulated wire in the example undergoes dehydration and imidization of polyesteramic acid through baking, forming polyesterimide, and thus exhibits excellent thermal stability. Furthermore, it can be seen that the insulated wire of the present invention has an insulating coating layer with excellent thermal stability.

[0069] [Manufacturing of insulating coating layer (model experiment)] As a model experiment for the insulating coating layer of the insulated wire of the present invention, a film made of polyesterimide was prepared by the following method and the evaluation was performed. Test Examples 1-3 and Comparative Test Examples 1-3 (Manufacturing of polyesterimide film (insulating coating layer)) A glass plate was prepared, and the polyesteramic acid solution (insulating wire coating) was applied to the glass plate using a coating machine to a film thickness of 0.04 to 0.05 mm. The coated glass plate was placed on a hot plate and heated at 100°C for 2 hours to remove the solvent. Then, using a hot air dryer, it was heated at 200°C for 1 hour, and then at 250°C for 30 minutes to thermally imide the polyesteramic acid and obtain a polyesterimide film (insulating coating layer, thickness 0.04 to 0.05 mm).

[0070] Comparative Test Example 4 A glass plate was prepared, and a commercially available polyester amide acid solution PMDA / ODA (insulating wire coating) was applied to the glass plate using a coating machine to a film thickness of 0.04-0.05 mm. The coated glass plate was placed on a hot plate and heated at 100°C for 2 hours to remove the solvent. Then, using a hot air dryer, it was heated at 200°C for 1 hour, and then at 250°C for 30 minutes to thermally imide the polyester amide acid and obtain a polyester imide film (insulating coating layer, thickness 0.04-0.05 mm).

[0071] Table 1 shows the physical properties of the insulating wire coating (polyesteramido acid) obtained in the above manufacturing example and comparative manufacturing example, as well as the physical properties and evaluation results of the insulating coating layer (polyesterimide) obtained in the above test example and comparative test example.

[0072] [Table 1]

[0073] From the results in Table 1, it can be seen that the insulated wire of the present invention has an insulating coating layer with a low dielectric constant and excellent thermal stability, due to the inclusion of a specific polyesterimide in the insulating coating layer.

Claims

1. An insulated wire having a conductor and an insulating coating layer covering the conductor, The insulating coating layer contains a polyester imide having repeating units represented by the following general formula (1), The content of the repeating unit represented by the following general formula (1) in the polyesterimide is 50 mol% or more relative to the total repeating units constituting the polyesterimide. The temperature at which the polyesterimide loses 10% of its thermoweight in air is 470°C or higher. An insulated wire wherein the relative permittivity of the polyesterimide at 1 kHz is 3.1 or less. 【Chemistry 1】 (In formula (1), X is at least one selected from the group consisting of the divalent group represented by formula (X1) and the divalent group represented by formula (X2).)

2. The insulated wire according to claim 1, wherein the repeating unit represented by formula (1) is the repeating unit represented by formula (1-1) below. 【Chemistry 2】

3. An insulated wire according to claim 1 or 2, wherein X contains a divalent group represented by formula (X2).

4. An insulated wire according to any one of claims 1 to 3, wherein X includes a divalent group represented by formula (X1) and a divalent group represented by formula (X2).

5. The insulated wire according to claim 4, wherein the molar ratio [(X1) / (X2)] of the group represented by formula (X1) to the group represented by formula (X2) is 30 / 70 to 95 / 5.

6. The insulated wire according to any one of claims 1 to 5, wherein the divalent group represented by the above formula (X1) is a divalent group represented by the following formula (X1-1). 【Transformation 3】

7. An insulated wire according to any one of claims 1 to 6, wherein the divalent group represented by the above formula (X2) is a divalent group represented by the following formula (X2-1). 【Chemistry 4】

8. The insulated wire according to any one of claims 1 to 7, wherein the polyesterimide is substantially free of aliphatic hydrocarbon groups.

9. The insulated wire according to any one of claims 1 to 8, wherein the glass transition temperature of the polyesterimide is 220 to 280°C.

10. A method for manufacturing an insulated wire according to any one of claims 1 to 9, A method for manufacturing an insulated wire, comprising applying an insulating wire coating containing a polyesteramic acid having repeating units represented by the following general formula (2) and an organic solvent onto a conductor and baking it to form an insulating coating layer. 【Transformation 5】 (In formula (2), X is at least one selected from the group consisting of the divalent group represented by formula (X1) and the divalent group represented by formula (X2).)

11. The method for manufacturing an insulated wire according to claim 10, wherein the concentration of the polyesteramic acid in the coating for the insulated wire is 8 to 50% by mass.

12. The method for manufacturing an insulated wire according to claim 10 or 11, wherein the viscosity of the coating for the insulated wire at 25°C is 1 to 50 Pa·s.

13. A method for manufacturing an insulated wire according to any one of claims 10 to 12, wherein the weight-average molecular weight of the polyesteramic acid is 5,000 to 1,000,000.

14. A method for producing an insulated wire according to any one of claims 10 to 13, wherein the organic solvent comprises N,N-dimethylacetamide.

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