Method for manufacturing insulated wire, insulated wire, coil, and motor

Abstract

Provided are: a method for manufacturing an insulated wire including a conductor and a coating which is composed of a thermoplastic resin having a melting point of 340°C or higher or a glass transition temperature of 200°C or higher, or a resin composition containing the thermoplastic resin, the method comprising a step for preheating the conductor to a temperature higher than 250°C but not higher than 400°C, and a step for extrusion-coating the preheated conductor with the thermoplastic resin or the resin composition containing the thermoplastic resin; an insulated wire; a coil; and a motor.

Description

Insulated wire manufacturing method, insulated wire, coil, and motor

[0001] The present disclosure relates to a method for manufacturing an insulated wire, an insulated wire, a coil, and a motor.

[0002] Insulated electric wires are used for coils in industrial motors and motors for home appliances. In recent years, insulated electric wires have also been used in electric motors for electric vehicles (EVs). In these fields, there is a trend toward improving the power density of drive motors from the viewpoint of improving power performance and fuel efficiency, such as by increasing output and downsizing.

[0003] On the other hand, with the increase in power density, higher voltages are being applied to insulated wires than ever before. This can lead to partial discharges on the surface of the insulated wire, which can lead to dielectric breakdown. Insulated wires are now required to have higher heat resistance and lower dielectric constant than ever before in order to suppress partial discharges.

[0004] Patent Document 1 discloses an insulated wire in which an insulating film is formed by extrusion coating a thermoplastic polyimide on the outer periphery of a conductor.

[0005] Patent Document 1: International Publication No. 2014 / 084063

[0006] As a result of extensive research, the present inventors have found that there is room for improvement in the adhesion between a conductor and an insulating coating formed on a conductor by extrusion coating, the insulating coating containing a thermoplastic resin with a high melting point or a high glass transition point, such as a thermoplastic polyimide. If the adhesion between the conductor and the coating is poor, gaps may form between the conductor and the coating, which may result in a deterioration in the insulating properties of the insulated wire.

[0007] An object of one embodiment of the present disclosure is to provide an insulated wire manufacturing method, an insulated wire, a coil, and a motor that can improve the adhesion between a conductor and a coating made of a thermoplastic resin having a melting point of 340°C or higher or a glass transition temperature of 200°C or higher, or a resin composition containing the thermoplastic resin, and can improve the insulation properties of the insulated wire.

[0008] Means for solving the above problems include the following aspects. <1> A method for manufacturing an insulated wire including a conductor and a coating made of a thermoplastic resin having a melting point of 340°C or higher or a glass transition temperature of 200°C or higher, or a resin composition containing the thermoplastic resin, the method comprising the steps of preheating the conductor to a temperature of more than 250°C and not more than 400°C, and extrusion coating the preheated conductor with the thermoplastic resin or the resin composition containing the thermoplastic resin. <2> The method for manufacturing an insulated wire according to <1>, in which the thermoplastic resin is a thermoplastic polyimide resin. <3> The method for manufacturing an insulated wire according to <1> or <2>, in which the conductor has a plated surface. <4> The method for manufacturing an insulated wire according to any one of <1> to <3>, in which the extrusion coating step is a step of extrusion coating the preheated conductor with the thermoplastic resin or the resin composition containing the thermoplastic resin using a pressure die. <5> The method for producing an insulated wire according to any one of <1> to <4>, wherein the thermoplastic resin has a melting point of 340°C or higher, and the preheating step is a step of preheating the conductor to a temperature higher than 250°C but lower than the melting point of the thermoplastic resin. <6> The method for producing an insulated wire according to any one of <1> to <4>, wherein the preheating step is a step of preheating the conductor to a temperature higher than 350°C but lower than 400°C. <7> The method for producing an insulated wire according to any one of <2> to <6>, wherein the thermoplastic polyimide resin contains a structural unit represented by the following formula (1):

[0009]

[0010] In the formula (1), X is a direct bond, —SO ２ -, -CO-, -C(CH ３ ) ２ -, -C(CF ３ ) ２- or -S-, R1, R2, R3, and R4 each independently represent a hydrogen atom, an alkyl group, an alkoxy group, a halogenated alkyl group, a halogenated alkoxy group, or a halogen atom, and Y is a group selected from the group consisting of four groups represented by any of the following formulas (2-1) to (2-4): In the following formulas (2-1) to (2-4), * represents a bonding position, and the hydrogen atom on the aromatic ring may be substituted. In addition, the position of a bonding group whose bonding position in the formula (1) is not determined is the para-position or meta-position relative to the position to which the oxygen atom is bonded.

[0011] <8> The method for producing an insulated wire according to any one of <2> to <7>, wherein the thermoplastic polyimide resin contains a structural unit represented by the following formula (3):

[0012] <9> The method for producing an insulated wire according to any one of <2> to <8>, wherein the thermoplastic polyimide resin contains a structural unit represented by the following formula (6) and a structural unit represented by the following formula (7):

[0013]

[0014] In the formulas (6) and (7), p / q is 0.01 to 100.

[0015] <10> The method for producing an insulated wire according to any one of <2> to <9>, wherein the thermoplastic polyimide resin has a weight-average molecular weight Mw of 25,000 to 30,000. <11> An insulated wire comprising a conductor and a coating made of a thermoplastic resin having a melting point of 340°C or higher or a glass transition temperature of 200°C or higher, or a resin composition containing the thermoplastic resin, wherein the conductor and the coating are in direct contact with each other, and wherein, in a cross section perpendicular to the longitudinal direction of the insulated wire, the ratio of the length of a portion where the conductor and the coating are in close contact with each other to the total circumference of the conductor is 80% or more. <12> The insulated wire according to <11>, wherein the thermoplastic resin is a thermoplastic polyimide resin. <13> The insulated wire according to <11> or <12>, wherein, in a cross section perpendicular to the longitudinal direction of the insulated wire, the ratio of the length of a portion where the conductor and the coating are in close contact with each other to the total circumference of the conductor is 90% or more. <14> The insulated wire according to <12> or <13>, wherein the thermoplastic polyimide resin contains a structural unit represented by the following formula (1):

[0016]

[0017] In the formula (1), X is a direct bond, —SO ２ -, -CO-, -C(CH ３ ) ２ -, -C(CF ３ ) ２ - or -S-, R1, R2, R3, and R4 each independently represent a hydrogen atom, an alkyl group, an alkoxy group, a halogenated alkyl group, a halogenated alkoxy group, or a halogen atom, and Y is a group selected from the group consisting of four groups represented by any of the following formulas (2-1) to (2-4): In the following formulas (2-1) to (2-4), * represents a bonding position, and the hydrogen atom on the aromatic ring may be substituted. In addition, the position of a bonding group whose bonding position in the formula (1) is not determined is the para-position or meta-position relative to the position to which the oxygen atom is bonded.

[0018] <15> A coil comprising the insulated wire according to any one of <11> to <14>. <16> A motor comprising the insulated wire according to any one of <11> to <14>.

[0019] According to one embodiment of the present disclosure, there are provided a method for producing an insulated wire, an insulated wire, a coil, and a motor, which can improve the adhesion between a conductor and a coating made of a thermoplastic resin having a melting point of 340°C or higher or a glass transition temperature of 200°C or higher or a resin composition containing the thermoplastic resin, and can improve the insulation properties of the insulated wire.

[0020] Fig. 1 is a schematic diagram showing an example of an apparatus used in the manufacturing method of the present disclosure. Fig. 2A is a schematic diagram showing an example of a die structure in an extrusion coating unit of the apparatus used in the manufacturing method of the present disclosure. Fig. 2B is a schematic diagram showing an example of a die structure in an extrusion coating unit of the apparatus used in the manufacturing method of the present disclosure.

[0021] Hereinafter, embodiments of the present disclosure will be described. The description is for illustrating the embodiments and is not intended to limit the scope of the present disclosure. The description will be made with appropriate reference to the drawings.

[0022] In this specification, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this embodiment, the upper limit or lower limit described in one numerical range may be replaced with the upper limit or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in this embodiment, the upper limit or lower limit of that numerical range may be replaced with a value shown in an example.

[0023] In this specification, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0024] In this specification, when an embodiment is described with reference to drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. Furthermore, the sizes of components in each drawing are conceptual, and the relative size relationships between components are not limited to these.

[0025] In this specification, each component may contain a plurality of corresponding substances. When referring to the amount of each component in a composition in this specification, if a plurality of substances corresponding to each component are present in the composition, the amount refers to the total amount of the plurality of substances present in the composition, unless otherwise specified.

[0026] In this specification, the term "(meth)acrylic" means either "acrylic" or "methacrylic".

[0027] <Method for manufacturing insulated wire> One embodiment of the present disclosure is a method for manufacturing an insulated wire including a conductor and a coating made of a thermoplastic resin having a melting point of 340°C or higher or a glass transition temperature of 200°C or higher (hereinafter also referred to as a "high heat resistant thermoplastic resin") or a resin composition containing the high heat resistant thermoplastic resin, the method including: a step of preheating the conductor to a temperature of more than 250°C and not more than 400°C (hereinafter also referred to as a "preheating step"); and a step of extrusion coating the preheated conductor with the high heat resistant thermoplastic resin or a resin composition containing the high heat resistant thermoplastic resin (hereinafter also referred to as an "extrusion coating step"). By including the above steps, adhesion between the conductor and the coating made of the high heat resistant thermoplastic resin or the resin composition containing the high heat resistant thermoplastic resin is improved.

[0028] As described above, the insulated wire according to the present embodiment includes a conductor and a coating made of a high heat-resistant thermoplastic resin or a resin composition containing a high heat-resistant thermoplastic resin. The coating is provided to cover the periphery of the conductor so as to be in direct contact with the surface of the conductor, and functions as an insulating coating for the conductor.

[0029] The insulated wire according to the present embodiment is preferably used as a winding wire (magnet wire) for forming a coil of a motor, etc. Because the insulated wire according to the present embodiment has excellent insulation properties, using the insulated wire according to the present embodiment as a magnet wire can further increase the output of the motor.

[0030] Fig. 1 is a schematic diagram showing an example of an apparatus used in the insulated wire manufacturing method of the present disclosure. As shown in Fig. 1, the apparatus 100 includes a feeding unit 30 for feeding out a conductor 20, a preheating unit 40 for preheating the conductor 20 fed from the feeding unit 30, an extrusion coating unit 50 for extrusion coating the preheated conductor 20 with a high heat-resistant thermoplastic resin or a resin composition containing a high heat-resistant thermoplastic resin to form an insulated wire 10, a cooling unit 60 for cooling the formed insulated wire 10, and a winding unit 70 for winding up the cooled insulated wire 10.

[0031] Hereinafter, each step of the method for producing an insulated wire according to the present disclosure will be described in detail.

[0032] - Preheating step - In the preheating step, the conductor is preheated. Preheating is performed in the preheating section (see Figure 1). In the preheating section, the conductor unwound from the unwinding section is preheated.

[0033] (Conductor) From the viewpoint of increasing the allowable current of the insulated wire, the conductor is preferably a copper wire or a wire made of a copper alloy, which has excellent electrical conductivity. When the conductor is a copper wire, a copper wire made from low-oxygen copper or oxygen-free copper is preferred because of its excellent electrical conductivity. The conductor may be a solid wire or a twisted wire.

[0034] The conductor preferably has a rectangular cross section from the viewpoint of improving the space factor of the conductor in the coil formed by winding the insulated wire. In other words, the conductor is preferably a rectangular wire.

[0035] When the cross section of the conductor perpendicular to the longitudinal direction is rectangular, the wire diameter of the conductor is preferably 1.0 mm to 5.0 mm, more preferably 1.4 mm to 4.0 mm, and may be, for example, 2.99 mm. The length of the short side is preferably 0.4 mm to 3.0 mm, more preferably 0.5 mm to 2.5 mm, and may be, for example, 1.54 mm. In this case, the ratio of the length of the long side of the rectangular conductor to the length of the short side of the rectangular conductor (length of the long side of the rectangular conductor / length of the short side of the rectangular conductor) is preferably 1 to 4.

[0036] In order to improve adhesion between the conductor and a coating made of a high-heat-resistant thermoplastic resin or a resin composition containing a high-heat-resistant thermoplastic resin, it is preferable that the paraffin used during production is degreased with alcohol. It is also preferable that the surface of the conductor is plated or the like to prevent the formation of an oxide film.

[0037] The conductor may be surface-modified to improve adhesion to a coating made of a high-heat-resistant thermoplastic resin or a resin composition containing a high-heat-resistant thermoplastic resin. Examples of surface-modification treatments include mechanical treatments such as blasting, polishing, and embossing, physical treatments such as laser treatment, corona treatment, plasma treatment, and dry etching, electrochemical treatments such as plating and anodizing, and chemical treatments such as chemical etching (wet etching) and surface coating.

[0038] In blasting, particulate or finely powdered media is sprayed onto a conductor and collided with it, creating irregularities on the conductor surface. The irregularities increase the surface roughness of the conductor surface, making it easier for the coating to adhere due to frictional resistance (anchor effect). This can improve adhesion between the conductor and the coating. Blasting is also advantageous because it can remove oxide coatings formed on the conductor surface, further improving adhesion with the coating. Examples of media that can be used include metal particles, carbon particles, oxide particles, carbide particles, and nitride particles. The conductor surface may be roughened by machining it to the shape of a die during conductor manufacturing.

[0039] Corona treatment involves modifying (hydrophilizing) the conductor surface by corona discharge treatment, which can improve adhesion between the conductor and the coating through chemical interaction.

[0040] In the plating process, the conductor is coated with a plating material. From the viewpoints of cost and productivity, wet plating is preferred. Electrolytic plating is more preferred. Examples of plating materials include nickel plating and silver plating. The plating thickness is preferably 0.1 to 10 μm, more preferably 0.5 to 5 μm.

[0041] In surface coating, a coating agent is applied or sprayed onto the conductor. Coating prevents surface oxidation of the conductor and also improves adhesion between the conductor and the coating layer through chemical interaction. A silane coupling agent can be used as the coating agent.

[0042] Examples of silane coupling agents include vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, N-2-(aminoethyl)- 3-aminopropylmethyldimethoxysilane, N-2(aminoethyl)3-aminopropyltrimethoxysilane, N-2(aminoethyl)3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, hexamethyldisilazane, 3-(2-aminoethylaminopropyl)dimethoxymethylsilane, 3-(2-aminoethylaminopropyl)trimethoxysilane, 2-(2-aminoethylthioethyl)diethoxymethylsilane, 2-(2-aminoethylthioethyl)triethoxysilane, 3-[2-(2-aminoethylaminoethylamino)propyl]trimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane hydrochloride, 3-ureidopropyltriethoxysilane, 3-chloropropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, bis(triethoxysilylpropyl)tetrasulfide, imidazolylalkyl-trialkoxysilane, diphenyldimethoxysilane, hexyltrimethoxysilane, decyltrimethoxysilane, trifluoropropyltrimethoxysilane, tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethyltriethoxysilane, phenyltriethoxysilane, 3-trimethoxysilylpropylsuccinic anhydride, and the like can be used. Among the above silane coupling agents, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, etc. are preferred. Commercially available silane coupling agents can be used, such as KBE-903, KBM-602, KBM-603, KBM903, KBE-402, KBE-403, KBM-303, KBM402, and KBM-403 (all manufactured by Shin-Etsu Chemical Co., Ltd.).

[0043] (Preheating) Preheating is performed so that the conductor reaches a temperature of more than 250°C and less than 400°C. Preheating is preferably performed so that the conductor reaches a temperature of more than 250°C and less than the melting point of the high-heat-resistant thermoplastic resin, and more preferably so that the conductor reaches a temperature of more than 250°C and less than the melting point of the high-heat-resistant thermoplastic resin. Specifically, preheating is preferably performed so that the conductor reaches a temperature of more than 250°C and less than 388°C, and more preferably so that the conductor reaches a temperature of more than 250°C and less than 388°C. By preheating the conductor within this temperature range, the temperature difference between the conductor and the molten high-heat-resistant thermoplastic resin or the resin composition containing the high-heat-resistant thermoplastic resin is reduced when the extrusion coating process is performed, thereby alleviating stress-strain and improving adhesion between the conductor and the coating. Furthermore, the small temperature difference allows the molten high-heat-resistant thermoplastic resin or the resin composition containing the high-heat-resistant thermoplastic resin to remain in contact with the surface of the conductor for a longer period of time. As a result, the fine irregularities formed on the surface of the conductor can be impregnated with the high-heat-resistant thermoplastic resin or a resin composition containing the high-heat-resistant thermoplastic resin, improving adhesion between the conductor and the coating. Also, by preheating the conductor to a temperature below the melting point of the high-heat-resistant thermoplastic resin, the fluidity of the high-heat-resistant thermoplastic resin or a resin composition containing the high-heat-resistant thermoplastic resin extrusion coated on the conductor in the extrusion coating process can be appropriately reduced, improving adhesion and improving the thickness uniformity of the coating.

[0044] The preheating method is not particularly limited, and may be a contact heating method in which a heat source or flame heated to a high temperature is brought into direct contact with the conductor, or a non-contact heating method using microwaves, high frequency waves, etc. When preheating by a non-contact heating method, induction heating using high frequency waves is preferred from the viewpoint of preheating at a high temperature. The preheating section may be provided integrally with the unwinding section. Alternatively, the winding core (bobbin) of the unwinding section around which the conductor is wound may be heated.

[0045] When the conductor is a copper wire and the high frequency induction heating device is used, the preheating time is preferably 0.1 seconds to 5 minutes, more preferably 0.1 seconds to 1 minute.

[0046] Moreover, the preheating is preferably carried out in an inert gas atmosphere such as nitrogen or argon in order to prevent the conductor surface from being oxidized by high temperatures and forming an oxide film on the conductor surface.

[0047] After preheating, it is desirable to proceed to the extrusion coating process as soon as possible so as not to impair the effect of this process. The preheating process and the extrusion coating process may be carried out consistently in an inert gas atmosphere to prevent the preheated conductor from coming into contact with air.

[0048] - Extrusion coating process - In the extrusion coating process, a preheated conductor is extrusion coated with a high heat resistant thermoplastic resin or a resin composition containing a high heat resistant thermoplastic resin. Extrusion coating is performed in the extrusion coating section (see Figure 1). In the extrusion coating section, a preheated conductor delivered from the preheating section is extrusion coated with a high heat resistant thermoplastic resin or a resin composition containing a high heat resistant thermoplastic resin, which has been melted at a predetermined temperature. The thickness of the coating may be, for example, 40 to 250 μm.

[0049] The resin composition is not particularly limited as long as it contains a high heat-resistant thermoplastic resin. The resin composition may contain components other than the high heat-resistant thermoplastic resin, such as additives. Furthermore, the resin composition may contain multiple types of high heat-resistant thermoplastic resins.

[0050] (High Heat Resistant Thermoplastic Resin) Examples of thermoplastic resins (high heat resistant thermoplastic resins) having a melting point of 340°C or higher or a glass transition temperature of 200°C or higher include thermoplastic polyimide resins and polyether ether ketone resins (PEEK resins). The melting point of the high heat resistant thermoplastic resin is preferably 350°C or higher, more preferably 360°C or higher, even more preferably 370°C or higher, and particularly preferably 380°C or higher. The upper limit of the melting point of the high heat resistant thermoplastic resin is not particularly limited, but is preferably 400°C or lower, more preferably 390°C or lower. The glass transition temperature of the high heat resistant thermoplastic resin is preferably 210°C or higher, more preferably 220°C or higher, and even more preferably 230°C or higher. The upper limit of the glass transition temperature of the high heat resistant thermoplastic resin is not particularly limited, but is preferably 300°C or lower, more preferably 290°C or lower, even more preferably 280°C or lower, and particularly preferably 260°C or lower. From the viewpoint of producing an insulated wire, the highly heat-resistant thermoplastic resin is more preferably a thermoplastic polyimide resin. The melting point and glass transition temperature (glass transition point) are measured by the same methods as those described in the Examples.

[0051] (Thermoplastic Polyimide Resin) Examples of the thermoplastic polyimide resin include a thermoplastic polyimide resin (a1) having a structural unit represented by the following chemical formula (1), a thermoplastic polyimide resin (a1)' having a structural unit represented by the following chemical formula (1)', a thermoplastic polyimide resin (a2) having a structural unit represented by the following chemical formula (3), a thermoplastic polyimide copolymer resin (a3) ​​having structural units represented by the following chemical formula (4) and the following chemical formula (5), a thermoplastic polyimide resin (a4) having a structural unit represented by the following chemical formula (6), and a thermoplastic polyimide copolymer resin (a5) having a structural unit represented by the following chemical formula (6) and a structural unit represented by the following chemical formula (7).

[0052]

[0053] In the chemical formula (1), X is a direct bond, —SO ２ -, -CO-, -C(CH３ ) ２ -, -C(CF ３ ) ２ - or -S-, and R1, R2, R3, and R4 each independently represent a hydrogen atom, an alkyl group, an alkoxy group, a halogenated alkyl group, a halogenated alkoxy group, or a halogen atom, and Y represents a tetravalent aromatic group selected from the following linking group groups (2-1) to (2-4). In addition, the position of the linking group whose bonding position is not determined in the formula (1) is the para-position or meta-position relative to the bonding position of the oxygen atom.

[0054]

[0055] In the formula (1), the position of the bonding group whose bonding position is not determined is preferably the meta position relative to the bonding position of the oxygen atom. That is, the formula (1) is preferably the following formula (1)', and the thermoplastic polyimide preferably contains a structural unit represented by the following formula (1)'.

[0056]

[0057] From the viewpoint of suppressing a decrease in breakdown voltage, Y is preferably a group represented by formula (2-1) or formula (2-3), and more preferably a group represented by formula (2-1).

[0058] The substituent that the aromatic ring in formula (2-1) to formula (2-4) may have is preferably an alkyl group that may have a substituent, an alkoxy group that may have a substituent, a halogenated alkyl group that may have a substituent, a halogenated alkoxy group that may have a substituent, or a halogen atom. When the aromatic ring in formula (2-1) to formula (2-4) has multiple substituents, the substituents may be the same or different.

[0059]

[0060]

[0061] Here, n in chemical formula (4) and m in chemical formula (5) represent the copolymerization ratio of the polyimide copolymer, and n / m is in the range of 4 to 99 (mol % / mol %), and n / m is more preferably 5 to 50, further preferably 6 to 20, particularly preferably 7 to 15, and most preferably 9.

[0062]

[0063] Here, p in the above formula (6) and q in the formula (7) represent the copolymerization ratio of the thermoplastic polyimide copolymer, and p / q (mol % / mol %) is preferably 0.01 to 100, more preferably 0.1 to 50, even more preferably 0.3 to 10, particularly preferably 0.5 to 3, and most preferably 1.

[0064] Each of the thermoplastic polyimide resins (a1) to (a5) can be produced by reacting an aromatic diamine compound and an aromatic tetracarboxylic dianhydride, which form the structural units represented by the respective chemical formulas, with or without an organic solvent, and imidizing the resulting polyamic acid. For production, conditions for known polyimide production methods can be utilized. At least one of the aromatic diamine compound and the aromatic tetracarboxylic dianhydride may be a biomass-derived compound, at least a portion of which is derived from biomass. That is, the thermoplastic polyimide may be a biomass-derived thermoplastic polyimide.

[0065] To explain the thermoplastic polyimide resin (a1)' having a structural unit represented by chemical formula (1)' more specifically as an example, an aromatic diamine compound represented by the following chemical formula (8) and an aromatic tetracarboxylic dianhydride represented by the following chemical formula (9) are used as raw materials.

[0066]

[0067] In the chemical formula (8), X and R1 to R4 are the same as X and R1 to R4 in the chemical formula (1)'.

[0068]

[0069] In the chemical formula (9), Y is the same as Y in the chemical formula (1)′.

[0070] In chemical formulas (1), (1)′, and (8), specific examples of R1, R2, R3, and R4 include a hydrogen atom, an alkyl group such as a methyl group or an ethyl group; an alkoxy group such as a methoxy group or an ethoxy group; a halogenated alkyl group such as a fluoromethyl group or a trifluoromethyl group; a halogenated alkoxy group such as a fluoromethoxy group; and a halogen atom such as a chlorine atom or a fluorine atom; and is preferably a hydrogen atom.

[0071] In the chemical formulas (1), (1)', and (9), Y is a tetravalent aromatic group selected from the above-mentioned linking group (2-1) to (2-4), preferably a benzene ring. In this case, the aromatic tetracarboxylic acid dianhydride of the chemical formula (9) is pyromellitic dianhydride.

[0072] The thermoplastic polyimide resin is preferably a thermoplastic polyimide resin (a1), a thermoplastic polyimide resin (a1)', a thermoplastic polyimide resin (a2), a thermoplastic polyimide copolymer resin (a3), a thermoplastic polyimide resin (a4), or a thermoplastic polyimide copolymer resin (a5).

[0073] The thermoplastic polyimide preferably contains a structural unit represented by the above chemical formula (1), and more preferably consists of the structural unit represented by the above chemical formula (1). When the thermoplastic polyimide contains the structural unit represented by the above chemical formula (1), the electrical properties and heat resistance of a coating formed from a thermoplastic polyimide resin or a resin composition containing a thermoplastic polyimide resin are more excellent.

[0074] The thermoplastic polyimide more preferably contains a structural unit represented by the above chemical formula (1)', and even more preferably consists of the structural unit represented by the above chemical formula (1)'. When the thermoplastic polyimide contains the structural unit represented by the above chemical formula (1)', the electrical properties and heat resistance of a coating formed from a thermoplastic polyimide resin or a resin composition containing a thermoplastic polyimide resin become more excellent.

[0075] The thermoplastic polyimide more preferably contains a structural unit represented by the above chemical formula (3), and even more preferably consists of the structural unit represented by the above chemical formula (3). When the thermoplastic polyimide contains the structural unit represented by the above chemical formula (3), the electrical properties and heat resistance of a coating formed from a thermoplastic polyimide resin or a resin composition containing a thermoplastic polyimide resin are more excellent. When the thermoplastic polyimide contains the structural unit represented by the above chemical formula (3), the adhesion between a conductor and a coating formed from a thermoplastic polyimide resin or a resin composition containing a thermoplastic polyimide resin is more excellent.

[0076] It is even more preferable that the thermoplastic polyimide further contains a structural unit represented by the above chemical formula (7), and it is particularly preferable that the thermoplastic polyimide further contains a structural unit represented by the above chemical formula (1)' and a structural unit represented by the above chemical formula (7). By further containing the structural unit represented by the above chemical formula (7), the thermoplastic polyimide has particularly excellent adhesion between the conductor and a coating made of a thermoplastic polyimide resin or a resin composition containing a thermoplastic polyimide resin.

[0077] When producing a thermoplastic polyimide resin, other aromatic diamine compounds or aromatic tetracarboxylic dianhydrides as raw materials can be copolymerized singly or in combination, as long as the object of the present disclosure is not impaired.

[0078] The thermoplastic polyimide resins preferably used in the present disclosure may be blended with each other or with other polyimide resins as long as the objectives of the present disclosure are not impaired.

[0079] The weight average molecular weight (Mw) of the thermoplastic polyimide is preferably 20,000 or more from the viewpoint of heat resistance. The weight average molecular weight (Mw) of the thermoplastic polyimide is preferably 35,000 or less from the viewpoint of adhesion. The weight average molecular weight (Mw) of the thermoplastic polyimide is preferably 20,000 to 40,000, more preferably 22,000 to 35,000, and even more preferably 25,000 to 30,000.

[0080] In the present disclosure, the weight average molecular weight (Mw) of a thermoplastic polyimide refers to a value measured using gel permeation chromatography (GPC), and the measurement method is the same as that described in the Examples. When two or more types of thermoplastic polyimides are used in combination, the weight average molecular weight (Mw) of the thermoplastic polyimide refers to the value of the mixture of two or more types of thermoplastic polyimides.

[0081] The MFR (melt flow rate) of the thermoplastic polyimide resin, measured in accordance with JIS K7210-1:2014 at 400°C under a load of 1.05 kg, is not particularly limited, but is preferably 2 g / 10 min to 30 g / 10 min, more preferably 4 g / 10 min to 20 g / 10 min. When two or more types of thermoplastic polyimides are used in combination, the MFR of the thermoplastic polyimide is the value of the mixture of the two or more types of thermoplastic polyimides contained in the coating. The MFR of the thermoplastic polyimide resin is not particularly limited, but can be measured using a melt indexer (manufactured by Toyo Seiki Seisakusho, Ltd., model number: A-371401705).

[0082] The logarithmic viscosity of the thermoplastic polyimide resin is not particularly limited, but is preferably 0.1 dl / g to 3.0 dl / g, more preferably 0.2 dl / g to 2.0 dl / g, even more preferably 0.3 dl / g to 1.5 dl / g, and particularly preferably 0.4 dl / g to 1.0 dl / g. A logarithmic viscosity of 0.1 dl / g to 3.0 dl / g indicates that the molecular weight of the thermoplastic polyimide resin is appropriate. Therefore, the mechanical strength of a coating made of the thermoplastic polyimide resin or a resin composition containing the thermoplastic polyimide resin is excellent, and the flowability of the thermoplastic polyimide resin for producing a coating made of the thermoplastic polyimide resin or a resin composition containing the thermoplastic polyimide resin by injection molding or extrusion molding is excellent. When two or more types of thermoplastic polyimides are used in combination, the logarithmic viscosity of the thermoplastic polyimide is the value of the mixture of two or more types of thermoplastic polyimides contained in the coating.

[0083] The inherent viscosity is measured by heating a solution in a mixed solvent of parachlorophenol / phenol (90 / 10 weight ratio) at a concentration of 0.5 g / 100 ml to 200° C. and then cooling it to 35° C. The definition of inherent viscosity is given in the 1995 first edition of "Polymer Handbook," published by Asakura Shoten and published by the Japan Society for Analytical Chemistry, p. 58.

[0084] The glass transition temperature Tg of the thermoplastic polyimide resin is not particularly limited, and from the viewpoint of heat resistance, it is preferably 200° C. or higher, more preferably 210° C. or higher, even more preferably 220° C. or higher, and particularly preferably 230° C. or higher. The glass transition temperature Tg of the thermoplastic polyimide resin is not particularly limited, and is preferably 300° C. or lower, more preferably 290° C. or lower, even more preferably 280° C. or lower, and particularly preferably 260° C. or lower.

[0085] The glass transition temperature Tg can be determined by using a differential scanning calorimeter (DSC220C, manufactured by Seiko Instruments Inc.) to seal about 5 mg of the material in a measurement aluminum pan, set it in the differential scanning calorimeter, heat it from room temperature to 450°C at 10°C / min, hold it at 450°C for 5 minutes to completely melt the resin, then cool it to 30°C at 10°C / min, leave it at 30°C for 5 minutes, and heat it a second time to 450°C at 10°C / min; the inflection point corresponding to the glass transition is taken as the glass transition temperature (Tg).

[0086] The melting point of the thermoplastic polyimide resin is not particularly limited, and from the viewpoint of heat resistance, it is preferably 340° C. or higher, more preferably 350° C. or higher, even more preferably 360° C. or higher, still more preferably 370° C. or higher, and particularly preferably 380° C. or higher. The melting point of the thermoplastic polyimide resin is not particularly limited, and from the viewpoint of moldability, it is preferably 420° C. or lower, more preferably 410° C. or lower, even more preferably 400° C. or lower, and particularly preferably 390° C. or lower. The method for measuring the melting point is the same as that described in the examples.

[0087] A commercially available thermoplastic polyimide resin having the repeating structural unit of the above chemical formula (1)' is AURUM (registered trademark, manufactured by Mitsui Chemicals, Inc., glass transition temperature 250°C, melting point 388°C).

[0088] Although the above-mentioned commercially available thermoplastic polyimide resin may be used, the thermoplastic polyimide resin can also be synthesized by the following method: Specifically, a diamine represented by the following formula (10) and a tetracarboxylic dianhydride represented by the following formula (11) are subjected to dehydration co-condensation to obtain a thermoplastic polyimide resin.

[0089]

[0090]

[0091] A known imidization reaction can be applied to the production of a thermoplastic polyimide resin. The amount of raw material compound used is typically 0.90 to 0.99 equivalents of tetracarboxylic dianhydride per equivalent of diamine. The amount of raw material compound used is preferably 0.93 to 0.985 equivalents, more preferably 0.95 to 0.98 equivalents. When the amount of raw material compound used is 0.90 to 0.99 equivalents, the molecular weight of the thermoplastic polyimide resin is sufficiently high, so that the mechanical properties of a coating formed from the thermoplastic polyimide resin or a resin composition containing the thermoplastic polyimide resin are excellent, and the flowability of the thermoplastic polyimide resin is also excellent.

[0092] In synthesizing a thermoplastic polyimide resin, it is preferable to cap the reactive terminals of the molecule with phthalic anhydride, etc. By capping the reactive terminals, the thermal stability of the thermoplastic polyimide resin is significantly improved.

[0093] The reaction is particularly preferably carried out in an organic solvent. Examples of the organic solvent include N,N-dimethylformamide, N,N-diethylacetamide, N,N-dimethoxyacetamide, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, N-methylcaprolactam, 1,2-dimethoxyethane, bis(2-methoxyethyl)ether, 1,2-bis(2-methoxyethoxy)ethane, bis[2-(2-methoxyethoxy)ethyl]ether, tetrahydrofuran, 1,3-dioxane, 1,4-dioxane, pyrroline, picoline, dimethyl sulfoxide, dimethyl sulfone, tetramethylurea hexamethylphosphoramide, phenol, o-cresol, m-cresol, p-cresol, p-chlorophenol, anisole, benzene, toluene, and xylene. The organic solvent may be used alone or in combination.

[0094] The reaction temperature is usually room temperature to 250°C, preferably 140°C to 200°C. The reaction pressure is not particularly limited, and normal pressure is sufficient. The reaction time varies depending on the type of solvent and the reaction temperature, but is usually 4 to 24 hours. As for the imidization method, the precursor polyamic acid is heated to 100°C to 300°C to be imidized, or chemically imidized using an imidizing agent such as acetic anhydride to obtain the desired polyimide resin.

[0095] The additive may contain at least one kind selected from the group consisting of carbon fiber, glass fiber, potassium titanate fiber, aluminum borate fiber, metal fiber, ceramic fiber, boron fiber, silicon carbide fiber, asbestos fiber, rock wool fiber, and aramid fiber, within a range that does not impair the properties of the high heat resistant thermoplastic resin.

[0096] The additives may contain, as needed, at least one of fillers such as mica, synthetic mica, wollastonite, talc, silicone oil, fluorine-based oil, glass beads, molybdenum disulfide, clay, silica, alumina, diatomaceous earth, hydrated alumina, shirasu balloons, carbon nanotubes, calcium carbonate, hydrotalcite, fluorine, graphite (e.g., artificial graphite, natural graphite (e.g., flake graphite, flaky graphite, earthy graphite)), lubricants, release agents, stabilizers, colorants, crystal nucleating agents, and the like, within the range that does not impair the properties of the high heat-resistant thermoplastic resin.

[0097] The additive may contain, as needed, at least one of various liquid crystal polymers, a thermoplastic resin different from the high heat resistant thermoplastic resin (e.g., fluororesin, polyetherimide, polyethernitrile, polyetherketone, polyetherketoneketone, polyetherketoneetherketoneketone, polyamideimide, polyethersulfone, polysulfone, polyarylate and / or polyphenylene sulfide), or a thermosetting resin (e.g., epoxy resin, polybenzimidazole resin, polyimide resin, etc.), within a range that does not impair the properties of the high heat resistant thermoplastic resin.

[0098] When the resin composition contains an additive, the contents of the additive and the highly heat-resistant thermoplastic resin are not particularly limited and are selected appropriately depending on the type of additive, etc., and are preferably within the following ranges. The content of the additive is preferably 0% by mass to 40% by mass relative to the total amount of the resin composition. The content of the highly heat-resistant thermoplastic resin is preferably 60% by mass to 100% by mass relative to the total amount of the resin composition.

[0099] The highly heat-resistant thermoplastic resin or a resin composition containing a highly heat-resistant thermoplastic resin is preferably in the form of pellets.

[0100] (Extrusion Coating) Extrusion coating is carried out using an extruder, such as a single-screw extruder, a twin-screw extruder, or an L-shaped extruder.

[0101] The extruder is equipped with a hopper for supplying the high heat resistant thermoplastic resin or a resin composition containing the high heat resistant thermoplastic resin, a screw for melt-kneading the high heat resistant thermoplastic resin or the resin composition containing the high heat resistant thermoplastic resin, a cylinder for extruding the high heat resistant thermoplastic resin or the resin composition containing the high heat resistant thermoplastic resin, and a die for molding the high heat resistant thermoplastic resin or the resin composition containing the high heat resistant thermoplastic resin to produce an insulated electric wire, and also equipped with a heater for heating the cylinder and a filter for removing foreign matter.

[0102] From the viewpoint of suppressing the generation of carbides on the screw and cylinder, the hopper is preferably purged with an inert gas such as nitrogen or argon or evacuated to a vacuum, but is not limited thereto.

[0103] The shape of the screw is not particularly limited and may be appropriately selected from, for example, a full flight shape, a rapid compression shape, a gentle compression shape, a barrier flight shape, a mixing flight shape, and the like.

[0104] The effective screw length L is, for example, 625 mm.

[0105] The screw diameter D is, for example, φ25 mm.

[0106] The ratio (L / D) of the effective screw length L to the screw diameter D is, for example, 25.

[0107] The compression ratio of the screw (the ratio of the flight groove depths of the cylinder portions C-1 and C-3) is, for example, 3.0.

[0108] The rotation speed of the screw is, for example, 3.0 rpm.

[0109] The heating temperature of the extruder is, for example, 390°C to 400°C in the cylinder section C-1; 410°C to 420°C in the cylinder section C-2; 420°C to 430°C in the cylinder section C-3; 420°C to 430°C in the neck section; 420°C to 430°C in the head section; and 410°C to 420°C in the die section.

[0110] The die is preferably a crosshead die. The die diameter may be, for example, 7.2 mm. The die tip may have a diameter of 6.0 mm and a length of 9.0 mm.

[0111] In addition, suitable die structures include a die structure in which a sleeve (sheath-core) is provided around the conductor as shown in FIG. 2A and a pressure die structure as shown in FIG. 2B. The pressure die structure shown in FIG. 2B is more preferable than the die structure in which a sleeve (sheath-core) is provided around the conductor as shown in FIG. 2A. The die shown in FIG. 2B has a conductor outlet path for feeding the conductor and a resin extrusion flow path, and is provided with a contact path 22 that brings the resin into contact with the conductor periphery upstream from the tip (extrusion port) Q of the extrusion section of the die. By using the pressure die structure shown in FIG. 2B, the molten resin is compressed by the internal clearance and contacts the conductor under increased static pressure, improving adhesion between the conductor and the coating.

[0112] In addition, the land length of the die is preferably long from the viewpoint of allowing the molten high heat resistant thermoplastic resin or the resin composition containing the high heat resistant thermoplastic resin to flow smoothly and increasing the back pressure to improve the adhesion between the conductor and the coating.

[0113] From the viewpoint of reducing the resin pressure, the mesh of the filter is preferably less than 200 mesh, for example, 30 mesh to 100 mesh. A plurality of meshes may be combined.

[0114] The conductor payout rate into the extruder may be from 1 mm / min to 300 mm / min.

[0115] The extrusion coating may be performed by increasing the degree of vacuum inside the cylinder. Increasing the degree of vacuum makes it difficult for an oxide film to form on the conductor surface, improving compatibility between the conductor and the coating, and therefore improving adhesion.

[0116] According to the method of one embodiment of the present disclosure described above, an insulated wire is produced. In the insulated wire, the adhesion between the conductor and the coating is improved. The produced insulated wire is then wound on a winding unit (see FIG. 1 ). The method may further include the following steps.

[0117] In addition to the above steps, the method of the present disclosure may further include a step of cooling the coated conductor (i.e., the insulated wire) (hereinafter also referred to as a "cooling step").

[0118] In the cooling step, the insulated wire is cooled in a cooling section (see FIG. 1). The cooling may be air-cooling or water-cooling.

[0119] Furthermore, the method of the present disclosure may further include, after the extrusion coating step and before the cooling step, a step of maintaining a temperature of the extrusion coating part (e.g., die part) at a temperature of −10° C. to a heating temperature of the extrusion coating part +10° C. (hereinafter also referred to as a “temperature maintaining step”). The inclusion of the temperature maintaining step improves compatibility between the conductor and the coating, thereby improving adhesion between the conductor and the coating.

[0120] The method of the present disclosure may further include a post-heating step after the extrusion coating step and before the cooling step. The additional heating step after the extrusion coating improves compatibility between the conductor and the coating, thereby improving adhesion between the conductor and the coating.

[0121] The method of the present disclosure may further include a rolling step after the extrusion coating step and before the cooling step. By rolling the manufactured insulated wire at a predetermined pressure, adhesion between the conductor and the coating is improved. The rolling can be performed by, for example, a roll press, cold isostatic pressing (CIP), or the like.

[0122] The various conditions for each step of the above-described method for producing an insulated electric wire may be combined as appropriate. For example, a Ni-plated rectangular copper wire may be used as the conductor, and after degreasing with alcohol, the conductor may be preheated to 300°C to 400°C by high-frequency induction heating, and then extrusion coating may be performed using a pressure die. Furthermore, the atmosphere surrounding the conductor during preheating may be an inert gas atmosphere.

[0123] <Insulated wire> The insulated wire of the present disclosure includes a conductor and a coating made of a high-heat-resistant thermoplastic resin or a resin composition containing a high-heat-resistant thermoplastic resin, wherein the conductor and the coating are in direct contact with each other, and the length of a portion where the conductor and the coating are in close contact with each other (hereinafter simply referred to as the "closed portion") accounts for 80% or more of the total circumference of the conductor in a cross section perpendicular to the longitudinal direction of the insulated wire. In other words, the length of a portion where a gap exists between the conductor and the coating accounts for 20% or more of the total circumference of the conductor in a cross section perpendicular to the longitudinal direction of the insulated wire.

[0124] When the ratio of the length of the adhesive portion to the total circumference in a cross section perpendicular to the longitudinal direction of the insulated wire is 80% or more, the adhesion between the conductor and the coating is high, which makes it possible to suppress a deterioration in the insulation properties of the insulated wire. The ratio of the length of the adhesive portion to the total circumference in a cross section perpendicular to the longitudinal direction of the insulated wire can be measured by the method described in the Examples.

[0125] From the viewpoint of adhesion between the conductor and the coating, the ratio of the length of the adhesive portion to the total circumference of the conductor in a cross section perpendicular to the longitudinal direction of the insulated wire is preferably 90% or more, more preferably 95% or more, even more preferably 97% or more, and particularly preferably 98% or more.

[0126] Details of the conductor and the highly heat-resistant thermoplastic resin or the resin composition containing a highly heat-resistant thermoplastic resin are as described in the method for producing an insulated wire.

[0127] In the insulated wire of the present disclosure, the highly heat-resistant thermoplastic resin is preferably a thermoplastic polyimide resin, and the thermoplastic polyimide resin preferably contains a structural unit represented by the following formula (1):

[0128]

[0129] In the formula (1), X is a direct bond, —SO ２ -, -CO-, -C(CH ３ ) ２ -, -C(CF ３ ) ２- or -S-, R1, R2, R3, and R4 each independently represent a hydrogen atom, an alkyl group, an alkoxy group, a halogenated alkyl group, a halogenated alkoxy group, or a halogen atom, and Y is a group selected from the group consisting of four groups represented by any of the following formulas (2-1) to (2-4): In the following formulas (2-1) to (2-4), * represents a bonding position, and the hydrogen atom on the aromatic ring may be substituted. In addition, the position of a bonding group whose bonding position in the formula (1) is not determined is the para-position or meta-position relative to the position to which the oxygen atom is bonded.

[0130]

[0131] The insulated wire of the present disclosure can be produced by the above-described method for producing an insulated wire.

[0132] <Coil> The use of the insulated wire of the present disclosure is not particularly limited, but as described above, the insulated wire has excellent adhesion between the conductor and the coating and excellent insulation, and therefore can be suitably used for coils of motors and the like. The coil can be obtained by winding the insulated wire into a coil shape. The insulated wire of the present disclosure can be wound into a coil shape.

[0133] <Motor> The insulated wire according to the present disclosure may be formed into a coil and then combined with a stator to form a motor. In this case, from the viewpoint of forming a motor, the coil is preferably wound around a rotor.

[0134] Hereinafter, one embodiment of the present disclosure will be described in more detail with reference to examples, but the embodiment of the present disclosure is not limited to the following examples.

[0135] - Preparation - The following materials were prepared. Conductor (copper wire): Round wire A (diameter: 2 mm, no Ni plating) Round wire B (diameter: 2 mm, with Ni plating (2-3 μm)) Rectangular wire C (thickness x width: 1.54 mm x 2.99 mm, corner curvature radius: 6 mm, no Ni plating) Rectangular wire D (thickness x width: 1.54 mm x 2.99 mm, corner curvature radius: 6 mm, with Ni plating (2-3 μm)) High heat resistant thermoplastic resin or resin composition containing high heat resistant thermoplastic resin: TPI1 to TPI5

[0136] TPI1 to TPI5 were synthesized according to the following procedure.

[0137] Synthesis Example 1 Thermoplastic polyimide resin (molecular weight) TPI1 containing a structural unit represented by formula (3) was synthesized according to the following procedure. A vessel equipped with a stirrer, reflux condenser, water separator, and nitrogen inlet tube was prepared. 2.886 kg (7.8 mol) of 4,4'-bis(3-aminophenoxy)biphenyl, 1.604 kg (7.37 mol) of pyromellitic dianhydride, 0.148 kg (1.0 mol) of phthalic anhydride, and 21.53 kg of m-cresol were added to the vessel. The mixture was then heated to 200°C with stirring under a nitrogen atmosphere. During this time, approximately 350 ml of water was confirmed to be distilled off. The reaction was continued for another 6 hours at 200°C. The mixture was then cooled to room temperature, and 10.8 kg of toluene was added. This was followed by filtration to obtain a yellow polyimide powder. The polyimide powder was washed with toluene and then dried at 180°C for 24 hours to obtain 5.46 kg (98.5% yield) of polyimide powder (thermoplastic polyimide). The polyimide powder was extruded at 400°C using a Takayasu 25mm diameter extruder to obtain pellets. The melting point of the thermoplastic polyimide resin TPI1 was 388°C, the glass transition temperature was 245°C, and the imide group concentration was 25.5%. The melting point and glass transition temperature of the thermoplastic polyimide resin were measured using a differential scanning calorimeter (DSC) (DSC220C, manufactured by Seiko Instruments Inc.) (the same applies to the following synthesis examples). The weight-average molecular weight Mw of the thermoplastic polyimide resin TPI1 was 32,500.

[0138] The weight-average molecular weight Mw of the thermoplastic polyimide resin TPI1 was measured using gel permeation chromatography (GPC) as follows. The weight-average molecular weight Mw of the other thermoplastic polyimide resins in this example was also measured in the same manner. 1.5 mL of 4-chlorophenol was added to 5 mg of sample and gently stirred at 130°C to 140°C. The resulting solution was air-cooled to room temperature, and then 3.5 mL of chloroform was added. This was then filtered using a 0.2 μm filter to prepare a sample solution. Measurements were performed using the prepared sample solution under the following conditions. Detector: Differential refractive index detector RI (RI-8020, manufactured by Tosoh) Column: Two TSKgel GMHXL columns, one G2500HXL column (7.8 mm ID x 300 mm, manufactured by Tosoh) Column temperature: 23°C Solvent: 4-chlorophenol / chloroform (3 / 7) (volume / volume) Flow rate: 0.8 mL / min, sample concentration: 1 mg / mL, injection volume: 0.3 mL Standard sample: Monodisperse polystyrene manufactured by Tosoh

[0139] Synthesis Example 2: Thermoplastic polyimide resin (low molecular weight) TPI2 containing a structural unit represented by formula (3) was synthesized according to the following procedure. A vessel equipped with a stirrer, reflux condenser, water separator, and nitrogen inlet tube was prepared. 2.886 kg (7.8 mol) of 4,4'-bis(3-aminophenoxy)biphenyl, 1.582 kg (7.25 mol) of pyromellitic dianhydride, 0.148 kg (1.0 mol) of phthalic anhydride, and 21.53 kg of m-cresol were added to the vessel. The mixture was then heated to 200°C with stirring under a nitrogen atmosphere. During this time, approximately 350 ml of water was confirmed to be distilled off. The reaction was continued at 200°C for an additional 6 hours. The mixture was then cooled to room temperature, and 10.8 kg of toluene was added. This was followed by filtration to obtain a yellow polyimide powder. This polyimide powder was washed with toluene and then dried at 180°C for 24 hours to obtain 5.46 kg (yield 98.5%) of polyimide powder (thermoplastic polyimide powder). This polyimide powder was extruded at 400°C using a Takayasu 25mm diameter extruder to obtain pellets. The melting point of thermoplastic polyimide resin TPI2 was 386°C, the glass transition temperature was 240°C, and the imide group concentration was 25.5%. The weight average molecular weight Mw of thermoplastic polyimide resin TPI2 was 28,200. Mw was measured using the method described above.

[0140] Synthesis Example 3 Thermoplastic polyimide resin (high molecular weight) TPI3 containing a structural unit represented by formula (3) was synthesized according to the following procedure. A vessel equipped with a stirrer, reflux condenser, water separator, and nitrogen inlet tube was prepared. 2.873 kg (7.8 mol) of 4,4'-bis(3-aminophenoxy)biphenyl, 1.570 kg (7.46 mol) of pyromellitic dianhydride, 0.148 kg (1.0 mol) of phthalic anhydride, and 21.53 kg of m-cresol were added to the vessel. The mixture was then heated to 200°C with stirring under a nitrogen atmosphere. During this time, approximately 350 ml of water was confirmed to be distilled off. The reaction was continued for another 6 hours at 200°C. The mixture was then cooled to room temperature, and 10.8 kg of toluene was added. This was followed by filtration to obtain a yellow polyimide powder. This polyimide powder was washed with toluene and then dried at 180°C for 24 hours to obtain 5.46 kg (yield 98.5%) of polyimide powder (thermoplastic polyimide powder). This polyimide powder was extruded at 400°C using a Takayasu 25mm diameter extruder to obtain pellets. The melting point of thermoplastic polyimide resin TPI3 was 389°C, the glass transition temperature was 248°C, and the imide group concentration was 25.5%. The weight average molecular weight Mw of thermoplastic polyimide resin TPI3 was 36,900. Mw was measured using the method described above.

[0141] Synthesis Example 4 Thermoplastic polyimide resin TPI4 containing a structural unit represented by formula (4) and a structural unit represented by formula (5) was synthesized according to the following procedure. 3.312 kg (9.0 mol) of 4,4'-bis(3-aminophenoxy)biphenyl, 0.2 kg (1.0 mol) of 4,4'-diaminodiphenyl ether, 2.071 kg (9.5 mol) of pyromellitic dianhydride, 0.148 kg (1.0 mol) of phthalic anhydride, and 21.53 kg of cresylic acid were added to a vessel equipped with a stirrer, reflux condenser, water separator, and nitrogen inlet tube. The mixture was then heated to 145°C with stirring under a nitrogen atmosphere. During this time, approximately 350 ml of water was confirmed to be distilled off. The reaction was continued for another 4 hours at 145°C. The mixture was then cooled to room temperature, and 10.8 kg of methyl ethyl ketone was added. This was then filtered to obtain a yellow polyimide powder. This polyimide powder was washed with methyl ethyl ketone and then dried at 180°C for 24 hours to obtain 5.26 kg (98% yield) of polyimide powder (thermoplastic polyimide). This polyimide powder was extruded at 400°C using a Takayasu 25mm diameter extruder to obtain pellets. The pellets were obtained. The melting point of the thermoplastic polyimide resin TPI4 could not be confirmed, the glass transition temperature was 253°C, and the imide group concentration was 23.9%. In TPI4, the ratio of the structural unit represented by formula (4) to the structural unit represented by formula (5) was 9:1.

[0142] Synthesis Example 5 Thermoplastic polyimide resin TPI5 containing a structural unit represented by formula (6) and a structural unit represented by formula (7) was synthesized according to the following procedure. A vessel equipped with a stirrer, reflux condenser, water separator, and nitrogen inlet tube was prepared. 3.684 kg (10.0 mol) of 4,4'-bis(3-aminophenoxy)biphenyl, 1.081 kg (4.96 mol) of pyromellitic dianhydride, 1.459 kg (4.86 mol) of 3,3',4,4'-biphenyltetracarboxylic dianhydride, 0.148 kg (1.0 mol) of phthalic anhydride, and 21.53 kg of m-cresol were added to the vessel. The mixture was then heated to 200°C with stirring under a nitrogen atmosphere. During this time, approximately 350 ml of water was confirmed to be distilled off. The reaction was continued for another 6 hours at 200°C. The mixture was then cooled to room temperature, and 10.8 kg of methanol was added. The mixture was then filtered to obtain a yellow polyimide powder. The polyimide powder was washed with methanol and then dried at 180°C for 24 hours to obtain 5.46 kg (98.5% yield) of polyimide powder (thermoplastic polyimide powder). The polyimide powder was extruded at 400°C using a Takayasu 25mm diameter extruder to obtain pellets. The melting point of the thermoplastic polyimide resin TPI5 could not be confirmed, the glass transition temperature was 235°C, and the imide group concentration was 23.9%. In TPI5, the ratio of the structural unit represented by formula (6) to the structural unit represented by formula (7) was 1:1.

[0143] Example 1 An extruder equipped with a die (screw: 20 mm diameter, full flight, L / D = 24, compression ratio: 3.0) was prepared. The heating temperature in the cylinder of the extruder was controlled by dividing it into three zones, C1, C2, and C3, starting from the material input side. The heating temperatures were set to 380°C in the C1 zone, 410°C in the C2 and C3 zones, and 420°C in the head section behind the extruder cylinder and the die at the end of the head section. The shape of the die hole was similar to the cross-sectional shape of the conductor. A conductor wire (round wire A) was prepared as the conductor and heated to 260°C (preheating process). Pellets of thermoplastic polyimide resin TPI1 were introduced into the extruder, and the molten TPI1 pellets were directly coated on the outer periphery of a conductor (copper wire, round wire A) preheated to 260°C (extrusion coating process), followed by cooling. This produced an insulated electric wire of Example 1. The insulated wire includes a conductor and a coating that directly covers the conductor. The coating is made of thermoplastic polyimide resin TPI1. The cross-sectional shape of the insulated wire is similar to that of the conductor. The coating thickness is 120 μm. Preheating was performed using a preheater, and the temperature of the preheated copper wire was measured just before the crosshead. The preheating temperature was measured using a traveling thermometer (MW-33E-TC1ASP, manufactured by Anritsu Meter Co., Ltd.).

[0144] - Adhesion Test - In accordance with the "Adhesion Test" specified in JIS C 3216-3 5.5, a linear test piece of approximately 300 mm was stretched by 15% at a rate of 5±1 mm per second using a tensile tester (product name: Autograph AGS-J, manufactured by Shimadzu Corporation). Before stretching, a slit was made in the coating at approximately the center of the test piece, extending all the way around the circumference to the conductor. After stretching, one test piece was checked for peeling or lifting of the coating. If lifting of the coating was observed, the length of the lifted portion of the coating from the slit was measured. All four sides of the test piece were observed, and the maximum peel distance was evaluated. Evaluation was performed according to the following criteria. The results are shown in Table 1.

[0145] A: The maximum peel distance is 0 mm to 5 mm. B: The maximum peel distance is more than 5 mm and 10 mm or less. C: The maximum peel distance is more than 10 mm.

[0146] In terms of evaluation, "B" is the minimum target level that should be achieved, and "A" is an especially excellent level for a product.

[0147] Examples 2 to 34 and Comparative Examples 1 to 13 Conductors were extrusion coated and the adhesion between the conductor and the coating was evaluated in the same manner as in Example 1, except that the conductor (copper wire), coating material (high heat-resistant thermoplastic resin or resin composition containing high heat-resistant thermoplastic resin), conductor preheating temperature, die structure, etc. were changed to those shown in Tables 1 to 9. The results are shown in Tables 1 to 9.

[0148]

[0149]

[0150]

[0151]

[0152]

[0153]

[0154]

[0155]

[0156]

[0157] The results in Table 1 show that when the conductor is preheated to a temperature higher than 250°C and lower than 400°C, the peel distance is shorter and the adhesion between the conductor and the coating is improved compared to when it is not (Examples 1 to 3 vs. Comparative Examples 1 and 2). The higher the preheating temperature of the conductor, the more the adhesion improved (Examples 1 to 3).

[0158] Furthermore, as shown in Table 2 (and Table 1), when the die structure was changed to a pressure die, the peel distance was further reduced and the adhesion was further improved (Example 1 vs. 4, Example 2 vs. 5, Example 3 vs. 6).

[0159] As shown in Table 3 (and Table 1), when the conductor was plated, the peel distance was significantly shorter and adhesion was significantly improved compared to when the conductor was not plated. In particular, when the conductor was preheated to a preheat temperature of 350°C, the peel distance was significantly shorter and adhesion was significantly improved (Examples 3 vs. 9). No difference due to the coating thickness was confirmed (Examples 9 to 11).

[0160] As shown in Table 4 (and Table 3), when the die structure was changed to a pressure die, the peel distance became smaller and the adhesion was improved (Example 7 vs. 12, Example 8 vs. 13, Example 9 vs. 14, Example 10 vs. 15, Example 11 vs. 16). In this case, when comparing the cases with and without plating, the case with plating significantly reduced the peel distance and significantly improved the adhesion (Example 6 vs. 14, see Tables 4 and 2).

[0161] Furthermore, as shown in Table 5, even when the shape of the conductor (copper wire) was changed, the adhesion between the conductor and the coating improved when the conductor was preheated to a temperature higher than 250°C and not higher than 400°C. The higher the preheating temperature of the conductor, the more the adhesion improved (Examples 17 to 19).

[0162] Even in this case, as shown in Table 6 (and Table 5), when the die structure was changed to a pressure die, the peel distance was further reduced and the adhesion was further improved (Examples 19 vs. 22). The adhesion was equivalent when the conductor preheating temperature was 350°C and when it was 380°C.

[0163] On the other hand, as shown in Table 7 (and Table 5), when the conductor was plated, the peel distance was significantly reduced and the adhesion was significantly improved (Examples 26 vs. 19).

[0164] Furthermore, as shown in Table 8 (and Table 7), when the die structure was changed to a pressure die, the peel distance was further reduced and the adhesion was further improved (Examples 26 and 29). In this case, when comparing the cases with and without plating, the case with plating significantly reduced the peel distance and significantly improved the adhesion (Examples 22 and 29, Examples 23 and 30, see Tables 8 and 6). When the conductor preheating temperature was 350°C and when it was 380°C, the adhesion was equivalent (Examples 29 and 30). In these two cases, the adhesion was better than when the conductor preheating temperature was lower.

[0165] Furthermore, as shown in Table 9, when the conductor preheating temperature was 380°C, the die structure was a pressure die, and plating was performed, the coating material was changed, and it was found that TPI5 containing a structural unit represented by formula (6) and a structural unit represented by formula (7) exhibited the best adhesion (Example 34), and TPI2 (low molecular weight) containing a structural unit represented by formula (3) exhibited the next best adhesion (Example 31).

[0166] For Examples 29 and 30 and Comparative Examples 12 and 13, the ratio of the length of the tightly contacted portion to the total circumference of the conductor in the cross section of the insulated wire was also determined.

[0167] - Ratio of the length of the adhesive portion to the total circumference in the cross section - The ratio of the length of the portion where the conductor and the coating are in close contact with each other (the adhesive portion) to the total circumference of the conductor was measured using the following procedure. Each insulated wire prepared in Examples 29 and 30 and Comparative Examples 12 and 13 was cut along a cross section perpendicular to the longitudinal direction of the insulated wire, embedded in epoxy resin, and mechanically polished to expose the cross section. The cross section was then observed at 500x magnification using a Keyence microscope (VHX-X1), and a microscopic image was obtained. The obtained microscopic image was analyzed using image processing software to measure the total circumference of the conductor (L1), the length of the portion where a gap exists between the conductor and the coating (L2), and the length of the portion where there is no gap between the conductor and the coating and where the conductor and the coating are in close contact with each other (the adhesive portion) (L3). From the measurement results, the ratio of the length of the adhesive portion to the total circumference was calculated (L3 / L1 × 100%). Measurements were taken of three cross sections of each insulated wire, and the ratio was calculated, and the average value was taken as the ratio of the length of the contacted portion to the total circumference. The results are shown in Table 10.

[0168]

[0169] As shown in Table 10, insulated wires obtained by preheating the conductor to a temperature of more than 250°C and not more than 400°C not only had a good peel distance but also had a high adhesion ratio of 98% or more to the total circumference of the conductor in the cross section of the insulated wire, demonstrating extremely good adhesion between the conductor and the coating.

[0170] The disclosures of Japanese Patent Application No. 2023-187207, filed October 31, 2023, and Japanese Patent Application No. 2024-152738, filed September 4, 2024, are incorporated herein by reference in their entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference. [Explanation of Symbols]

[0171] REFERENCE SIGNS LIST 100 Insulated wire manufacturing apparatus 10 Insulated wire 20 Conductor 22 Contact path 30 Payout section 40 Preheating section 50 Extrusion coating section 60 Cooling section 70 Winding section 200 Die (crosshead die) Q Tip of extrusion section (extrusion port) R Resin

Claims

1. A method for producing an insulated electric wire comprising a conductor and a coating made of a thermoplastic resin having a melting point of 340°C or higher or a glass transition temperature of 200°C or higher, or a resin composition containing said thermoplastic resin, comprising the steps of: preheating the conductor to a temperature of more than 250°C and not exceeding 400°C; and extrusion coating the preheated conductor with said thermoplastic resin or the resin composition containing said thermoplastic resin.

2. The method for manufacturing an insulated electric wire according to claim 1, wherein the thermoplastic resin is a thermoplastic polyimide resin.

3. The method for producing an insulated wire according to claim 1, wherein the conductor has a plated surface.

4. The method for producing an insulated wire according to claim 1, wherein the extrusion coating step is a step of extrusion coating the preheated conductor with the thermoplastic resin or a resin composition containing the thermoplastic resin using a pressure die.

5. The method for manufacturing an insulated wire according to claim 1, wherein the thermoplastic resin has a melting point of 340°C or higher, and the preheating step is a step of preheating the conductor to a temperature higher than 250°C and lower than the melting point of the thermoplastic resin.

6. The method for producing an insulated wire according to claim 1, wherein the preheating step is a step of preheating the conductor to a temperature higher than 350°C and lower than 400°C.

7. The method for producing an insulated wire according to claim 2, wherein the thermoplastic polyimide resin contains a structural unit represented by the following formula (1): In the formula (1), X is a direct bond, -SO ２ -, -CO-, -C(CH ３ ) ２ -, -C(CF ３ ) ２ - or -S-, R1, R2, R3, and R4 are each independently a hydrogen atom, an alkyl group, an alkoxy group, a halogenated alkyl group, a halogenated alkoxy group, or a halogen atom, and Y is a group selected from the group consisting of four groups represented by any of the following formulas (2-1) to (2-4). In the following formulas (2-1) to (2-4), * represents a bonding position, and the hydrogen atom of the aromatic ring may be substituted. In addition, the position of the bonding group in formula (1) whose bonding position is not determined is the para position or meta position with respect to the bonding position of the oxygen atom.

8. The method for producing an insulated wire according to claim 7, wherein the thermoplastic polyimide resin contains a structural unit represented by the following formula (3):

9. The method for producing an insulated wire according to claim 7, wherein the thermoplastic polyimide resin contains a structural unit represented by the following formula (6) and a structural unit represented by the following formula (7). In the formulas (6) and (7), p / q is 0.01 to 100.

10. The method for producing an insulated wire according to claim 7, wherein the weight average molecular weight Mw of the thermoplastic polyimide resin is 25,000 to 30,000.

11. An insulated wire comprising a conductor and a coating made of a thermoplastic resin having a melting point of 340°C or higher or a glass transition temperature of 200°C or higher, or a resin composition containing said thermoplastic resin, wherein the conductor and the coating are in direct contact with each other, and in a cross section perpendicular to the longitudinal direction of the insulated wire, the ratio of the length of the part where the conductor and the coating are in close contact with each other to the total circumference of the conductor is 80% or more.

12. The insulated wire according to claim 11, wherein the thermoplastic resin is a thermoplastic polyimide resin.

13. The insulated wire according to claim 11, wherein in a cross section perpendicular to the longitudinal direction of the insulated wire, the ratio of the length of the portion where the conductor and the coating are in close contact with each other to the total circumference of the conductor is 90% or more.

14. The insulated wire according to claim 12, wherein the thermoplastic polyimide resin contains a structural unit represented by the following formula (1): In the formula (1), X is a direct bond, -SO ２ -, -CO-, -C(CH ３ ) ２ -, -C(CF ３ ) ２ - or -S-, R1, R2, R3, and R4 are each independently a hydrogen atom, an alkyl group, an alkoxy group, a halogenated alkyl group, a halogenated alkoxy group, or a halogen atom, and Y is a group selected from the group consisting of four groups represented by any of the following formulas (2-1) to (2-4). In the following formulas (2-1) to (2-4), * represents a bonding position, and the hydrogen atom of the aromatic ring may be substituted. In addition, the position of the bonding group in formula (1) whose bonding position is not determined is the para position or meta position with respect to the bonding position of the oxygen atom.

15. A coil comprising an insulated wire according to any one of claims 11 to 14.

16. A motor comprising an insulated wire according to any one of claims 11 to 14.