Insulated wire and method for producing same, coil, motor, and thermoplastic polyimide resin composition

Abstract

Provided are: an insulated electric wire comprising a conductor and a coating including a thermoplastic polyimide resin, the surface roughness Ra of the being 0.50-4.00 μm; an insulated electric wire comprising a conductor and a coating that is made of a resin composition containing a thermoplastic polyimide resin, the coating further including at least one selected from the group consisting of high-melting point resins different from the thermoplastic polyimide resin and having a melting point of 260°C or more, and inorganic particles; a method for producing these; a coil and a motor that use the insulated electric wire; and a thermoplastic polyimide resin composition used to form the coating on the insulated electric wire.

Description

Insulated electric wire and its manufacturing method, coil, motor, and thermoplastic polyimide resin composition

[0001] This disclosure relates to insulated wires and methods for manufacturing the same, coils, motors, and thermoplastic polyimide resin compositions.

[0002] Magnet wire is used in the coils of industrial motors and home appliance motors. In recent years, magnet wire has also been used in electric motors of electric vehicles (EVs), and in this field, there is a focus on increasing the power density of drive motors from the viewpoint of improving power performance and fuel efficiency, such as increasing power output and miniaturization. Materials with high heat resistance, excellent moldability, mechanical properties and chemical resistance are used as insulating films for the wires, and mainly materials called super engineering plastics are used, and are widely used as materials for various parts in industrial materials, automobiles, electrical and electronic and industrial applications. Polyimide resin compositions, in particular, have the best heat resistance.

[0003] Patent Document 1 discloses an insulated wire in which an insulating film is formed by extruding a thermoplastic polyimide onto the outer circumference of a conductor.

[0004] Patent Document 1: International Publication No. 2014 / 084063

[0005] As a result of diligent research by the inventors, conventional insulated wires using thermoplastic polyimide resin have the problem that when inserting hairpin wires into the stator slots, they get caught on the slot walls or insulating paper, causing resistance during insertion and resulting in poor productivity.

[0006] One of the problems that one embodiment of this disclosure aims to solve is to provide an insulated wire with excellent surface slipperiness, a method for manufacturing the same, and a coil and a motor using the insulated wire. Another problem that one embodiment of this disclosure aims to solve is to provide a thermoplastic polyimide resin composition used for forming a coating on an insulated wire with excellent surface slipperiness.

[0007] The means for solving the above problems include the following embodiments: <1> An insulated wire comprising a conductor and a coating containing a thermoplastic polyimide resin, wherein the surface roughness Ra is 0.50 μm or more and 4.00 μm or less. <2> An insulated wire comprising a conductor and a coating containing a thermoplastic polyimide resin, wherein the coating further comprises at least one selected from the group consisting of a high-melting-point resin having a melting point of 260°C or higher, different from the thermoplastic polyimide resin, and inorganic particles. <3> The insulated wire according to <2>, wherein the high-melting-point resin is at least one resin selected from the group consisting of polyetheretherketone resin, polyphenylene sulfide resin, syndiotactic polystyrene resin, polyamide resin, polyimidoamide resin, and modified versions thereof. <4> The insulated wire according to any one of <1> to <3>, wherein the thermoplastic polyimide resin includes a structural unit represented by the following formula (1).

[0008] In equation (1) above, X is a direct bond, -SO ２ -, -CO-, -C(CH ３ ) ２ -, -C(CF ３ ) ２ The group is - or S-, and 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 the bond position, and the hydrogen atom of the aromatic ring may be substituted. Also, the position of the bond group whose bond position has not been determined in formula (1) is either the para or meta position relative to the position to which the oxygen atom is bonded.

[0009]

[0010] <5> An insulated wire according to any one of <1> to <4>, wherein the static friction coefficient of the surface of the coating is lower than 0.35. <6> An insulated wire according to any one of <1> to <5>, wherein the conductor is a rectangular conductor. <7> An insulated wire according to <6>, wherein the value of the length of the long side of the rectangular cross-section of the rectangular conductor / the length of the short side of the rectangular cross-section of the rectangular conductor is 1 or more and 4 or less. <8> An insulated wire according to any one of <1> to <7>, for inserting a status rod. <9> A coil comprising an insulated wire according to any one of <1> to <8>. <10> A motor comprising an insulated wire according to any one of <1> to <8>. <11> A method for manufacturing an insulated wire comprising a conductor and a coating made of a resin composition containing a thermoplastic polyimide resin, comprising the step of extruding the conductor with the resin composition, wherein the surface roughness Ra of the coating is 0.50 μm or more and 4.00 μm or less. <12> A method for manufacturing an insulated electric wire comprising a conductor and a coating made of a resin composition containing a thermoplastic polyimide resin, comprising the step of extruding the conductor with the resin composition, wherein the coating further comprises at least one selected from the group consisting of a high-melting-point resin having a melting point of 260°C or higher and different from the thermoplastic polyimide resin, and inorganic particles. <13> A thermoplastic polyimide resin composition comprising a thermoplastic polyimide resin and at least one selected from the group consisting of a high-melting-point resin having a melting point of 260°C or higher and different from the thermoplastic polyimide resin, and inorganic particles.

[0011] According to one embodiment of the present disclosure, an insulated wire having excellent surface slipperiness and a method for manufacturing the same, as well as a coil and a motor using the insulated wire, are provided. Furthermore, according to another embodiment of the present disclosure, a thermoplastic polyimide resin composition is provided that allows for easy acquisition of an insulated wire having excellent surface slipperiness.

[0012] This is a cross-sectional view of an example of an insulated electric wire related to this disclosure.

[0013] The embodiments of this disclosure are described below. The description is illustrative and does not limit the scope of this disclosure. The description refers to the drawings as appropriate.

[0014] In this specification, numerical ranges indicated using "~" represent a range that includes the numbers listed before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages within this embodiment, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in numerical ranges described within this embodiment, the upper or lower limit of that numerical range may be replaced with the values ​​shown in the examples.

[0015] In this specification, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, provided that their intended purpose is achieved.

[0016] In this specification, when embodiments are described with reference to the drawings, the configuration of the embodiments is not limited to the configuration shown in the drawings. Furthermore, the sizes of the members in each figure are conceptual, and the relative relationships between the sizes of the members are not limited thereto.

[0017] In this specification, each component may contain multiple of the corresponding substances. When referring to the amount of each component in a composition in this specification, if there are multiple substances corresponding to each component in the composition, it means the total amount of those multiple substances present in the composition unless otherwise specified.

[0018] In this specification, the term "(meth)acrylic" means either "acrylic" or "methacrylic."

[0019] (Insulated wire) A first embodiment of the insulated wire according to the present disclosure comprises a conductor and a coating containing a thermoplastic polyimide resin, wherein the surface roughness Ra is 0.50 μm or more and 4.00 μm or less.

[0020] A second embodiment of the insulated wire according to the present disclosure comprises a conductor and a coating containing a thermoplastic polyimide resin, wherein the coating further comprises at least one selected from the group consisting of a high-melting-point resin having a melting point of 260°C or higher, different from the thermoplastic polyimide resin, and inorganic particles.

[0021] In this specification, unless otherwise specified, the term "insulated wire according to this disclosure" refers to all of the first and second embodiments. Also, unless otherwise specified, the term "thermoplastic polyimide resin, etc." refers to all of the thermoplastic polyimide resins, etc. of the first and second embodiments.

[0022] As described above, the insulated wire according to this disclosure comprises a conductor and a coating containing a thermoplastic polyimide resin, wherein the surface roughness Ra is 0.50 μm or more and 4.00 μm or less, or the coating further comprises at least one selected from the group consisting of a high-melting-point resin different from the thermoplastic polyimide resin having a melting point of 260°C or higher, and inorganic particles.

[0023] If the surface roughness Ra of the insulated wire, i.e., the surface roughness Ra of the coating, is between 0.50 μm and 4.00 μm, the appropriate surface irregularities reduce the contact area between the insulated wire and another component when the wire is brought into contact with that component. This lowers the static friction coefficient and improves the sliding properties.

[0024] Furthermore, by further including at least one selected from the group consisting of a high-melting-point resin different from the thermoplastic polyimide resin having a melting point of 260°C or higher, and inorganic particles, the surface of the insulated wire is given appropriate irregularities, which reduces the contact area with another component when the insulated wire is brought into contact with that other component, thereby lowering the static friction coefficient and improving the sliding properties.

[0025] Furthermore, the insulated wires relating to this disclosure have excellent surface slipperiness, resulting in superior slot insertion capabilities for status rods and the like.

[0026] The insulated wire according to this disclosure is preferably used as a winding (magnet wire) for forming a coil in a motor or the like. Since the insulated wire according to this embodiment has excellent insulation properties, using the insulated wire according to this disclosure as a magnet wire can further increase the output of the motor.

[0027] Figure 1 shows a cross-sectional view of an example of an insulated wire according to this disclosure. As shown in Figure 1, the insulated wire 10 comprises a conductor 11 and a coating 12. The coating 12 directly covers the conductor 11. The coating 12 also has irregularities (not shown) on its surface.

[0028] [Surface Roughness] In the first embodiment of the insulated wire according to the present disclosure, the surface roughness Ra (arithmetic mean roughness) is 0.50 μm or more and 4.00 μm or less, preferably 0.60 μm or more and 3.50 μm or less, more preferably 0.70 μm or more and 3.00 μm or less, and particularly preferably 0.80 μm or more and 2.50 μm or less from the viewpoint of slipperiness.

[0029] In the second embodiment of the insulated wire according to the present disclosure, the surface roughness Ra is preferably 0.50 μm or more and 4.00 μm or less, more preferably 0.60 μm or more and 3.50 μm or less, even more preferably 0.70 μm or more and 3.00 μm or less, and particularly preferably 0.80 μm or more and 2.50 μm or less, from the viewpoint of slipperiness.

[0030] Furthermore, it is preferable that the insulated wire according to this disclosure has a surface roughness Ra in the width direction (TD) that is greater than the surface roughness Ra in the longitudinal direction (MD).

[0031] The insulated wire according to this disclosure preferably has a surface roughness Rz (maximum height roughness) of 2.00 μm or more and 15.00 μm or less, more preferably 3.00 μm or more and 14.00 μm or less, even more preferably 3.50 μm or more and 13.00 μm or less, and particularly preferably 4.00 μm or more and 12.00 μm or less, from the viewpoint of slipperiness.

[0032] Furthermore, it is preferable that the insulated wire according to this disclosure has a surface roughness Rz in the width direction (TD) that is greater than the surface roughness Rz in the longitudinal direction (MD).

[0033] The insulating wire according to the present disclosure preferably has a surface roughness Sm (average length of roughness curve elements) of 0.05 μm or more and 1.00 μm or less, more preferably 0.10 μm or more and 0.50 μm or less, still more preferably 0.12 μm or more and 0.40 μm or less, and particularly preferably 0.15 μm or more and 0.35 μm or less, from the viewpoint of slipperiness.

[0034] In addition, for the insulating wire according to the present disclosure, it is preferable that the surface roughness Sm in the width direction (TD) is greater than the surface roughness Sm in the longitudinal direction (MD).

[0035] The surface roughness Ra, Rz, and Sm of the insulating wire according to the present disclosure are average values of the surface roughness in the longitudinal direction (MD) of the insulating wire and the surface roughness in the width direction (TD) of the insulating wire.

[0036] The measuring method of the surface roughness Ra, Rz, and Sm in the present disclosure is as follows: using a surface roughness measuring machine (Surftest SV-3200, manufactured by Mitutoyo Corporation), in accordance with JIS B0601:1994, with a cut-off value of 0.8 mm and an evaluation length of 4.0 mm for the longitudinal direction (MD) and 2.4 mm for the width direction (TD). Also, the surface roughness Ra is measured for both the longitudinal direction (MD) and the width direction (TD) of the insulating wire, and the surface roughness Ra of the insulating wire is calculated as the average value thereof.

[0037] The method for imparting irregularities to the surface of the insulating wire is not particularly limited, but preferably includes a method of physically imparting irregularities, a method of adding a high melting point resin to the resin composition for forming the coating, a method of adding inorganic particles to the resin composition for forming the coating, and the like. The high melting point resin and inorganic particles to be used will be described later.

[0038] The method of physically imparting irregularities is not particularly limited, and known methods can be used. For example, a method of forming irregularities on the surface by a surface treatment method such as sandblasting, a method of passing through a roller having irregularities to impart irregularities, a method of pressing a member having irregularities to impart irregularities, and the like can be mentioned.

[0039] [Coating] <High melting point resin different from the thermoplastic polyimide resin having a melting point of 260°C or higher> In the second embodiment of the insulated wire according to the present disclosure, the coating further includes at least one selected from the group consisting of a high melting point resin (also simply referred to as "high melting point resin") different from the thermoplastic polyimide resin having a melting point of 260°C or higher, and inorganic particles. In the first embodiment of the insulated wire according to the present disclosure, it is preferable that the coating further includes at least one selected from the group consisting of a high melting point resin different from the thermoplastic polyimide resin having a melting point of 260°C or higher, and inorganic particles.

[0040] Also, from the viewpoint of ease of forming irregularities, the coating preferably contains a high melting point resin. By mixing the high melting point resin and the thermoplastic polyimide resin to form the coating, fine irregularities are formed on the surface due to differences in the viscosity and thermal shrinkage of both. Further, from the viewpoint of ease of forming irregularities, the high melting point resin is preferably incompatible with the thermoplastic polyimide resin.

[0041] The high melting point resin preferably has a melting point of 280°C or higher, more preferably 300°C or higher and 400°C or lower.

[0042] The melting point measurement method in the present disclosure can be measured using a differential scanning calorimeter (DSC220C type, manufactured by Seiko Instruments Inc.). Specifically, about 5 mg of the material is sealed in a measurement aluminum pan and set in the differential scanning calorimeter. Then, it is heated from room temperature to 450°C at 10°C / min. To completely melt the substance to be measured, it is held at 450°C for 5 minutes, then cooled to 30°C at 10°C / min. After leaving it at 30°C for 5 minutes, the second heating is performed from 30°C to 450°C at 10°C / min. The melting peak corresponding to the melting point is confirmed, and its apex is taken as the melting point.

[0043] The high-melting-point resin is preferably at least one resin selected from the group consisting of polyetheretherketone resin (PEEK resin), polyetherketone resin (PEK resin), polyetherketone ketone resin (PEKK resin), polyetheretherketone ketone resin (PEEKK resin), polyetherketone etherketone ketone resin (PEKEKK resin), polyphenylene sulfide resin (PPS resin), syndiotactic polystyrene resin, polyamide resin, polyimidoamide resin, and modified versions thereof, more preferably at least one resin selected from the group consisting of polyetheretherketone resin, polyphenylene sulfide resin, syndiotactic polystyrene resin, polyamide resin, polyimidoamide resin, and modified versions thereof, even more preferably at least one resin selected from the group consisting of polyetheretherketone resin and modified versions thereof, and particularly preferably polyetheretherketone resin.

[0044] From the viewpoint of lubricity, the content of the high-melting-point resin in the coating is preferably 5% to 50% by mass, more preferably 10% to 40% by mass, and particularly preferably 15% to 30% by mass, based on the total mass of the coating.

[0045] <Inorganic Particles> The coating preferably contains inorganic particles from the viewpoint of facilitating the formation of irregularities. When the inorganic particles and thermoplastic polyimide resin are mixed to form a coating, fine irregularities are formed on the surface of the coating, corresponding to the shape of the inorganic particles present on the surface and inside the coating.

[0046] Examples of materials for the inorganic particles include titanium dioxide, silica, talc, glass, alumina, calcium carbonate, zirconium silicate, calcium silicate, silicon nitride, aluminum nitride, boron nitride, beryllia, zirconia, zircon, fossterite, steatite, spinel, mullite, clay, mica, aluminum hydroxide, magnesium hydroxide, zinc borate, mica, wollastonite, molybdenum disulfide, diatomaceous earth, shirasu balloons, carbon nanotubes, calcium carbonate, hydrotalcite, and graphite. Among these, at least one inorganic particle selected from the group consisting of titanium dioxide, silica, and talc is preferred.

[0047] The shape of the inorganic particles is not particularly limited and may be spherical, ellipsoidal, plate-shaped, needle-shaped, or of any irregular shape.

[0048] The volume-average particle size of the inorganic particles is preferably 0.05 μm or more and 100 μm or less, more preferably 0.1 μm or more and 50 μm or less, even more preferably 0.15 μm or more and 20 μm or less, and particularly preferably 0.2 μm or more and 10 μm or less.

[0049] The volume-average particle size of inorganic particles is the particle size that accounts for 50% of the cumulative size distribution from the smallest diameter in a volume-based particle size distribution. The particle size distribution of inorganic particles is measured using a laser diffraction / scattering particle size distribution analyzer.

[0050] From the viewpoint of lubricity, the content of the inorganic particles in the coating is preferably 1% to 50% by mass, more preferably 5% to 40% by mass, and particularly preferably 10% to 30% by mass, based on the total mass of the coating.

[0051] <Thermoplastic Polyimide Resin> The insulated wire according to this disclosure is provided with a coating made of a resin composition containing a thermoplastic polyimide resin. The resin composition is not particularly limited as long as it contains a thermoplastic polyimide resin. Furthermore, the resin composition may or may not contain components other than the thermoplastic polyimide resin, such as additives. In other words, the resin composition may consist of a thermoplastic polyimide resin.

[0052] 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 a structural unit represented by the following chemical formula (4) and a structural unit represented by the following chemical formula (5), a thermoplastic polyimide resin (a4) having a structural unit represented by the following chemical formula (6), 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), and the like.

[0053]

[0054] In the chemical 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 tetravalent aromatic group selected from any of the following linking group groups (2-1) to (2-4). Also, the position of the bonding group whose bonding position is not determined in the formula (1) is the para position or the meta position with respect to the position where the oxygen atom is bonded.

[0055]

[0056] In the formula (1), it is preferable that the position of the bonding group whose bonding position is not determined is the meta position with respect to the position where the oxygen atom is bonded. 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)'.

[0057]

[0058] From the viewpoint of suppressing a decrease in dielectric 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).

[0059] The substituents that the aromatic ring in formulas (2-1) to (2-4) may have are preferably an optionally substituted alkyl group, an optionally substituted alkoxy group, an optionally substituted halogenated alkyl group, an optionally substituted halogenated alkoxy group, or a halogen atom. If the aromatic ring in formulas (2-1) to (2-4) has multiple substituents, the substituents may be the same or different from each other.

[0060]

[0061]

[0062] However, n in chemical formula (4) and m in chemical formula (5) represent the copolymerization ratio of the polyimide copolymer, where n / m = 4 to 99 (mol% / mol%), more preferably 5 to 50, even more preferably 6 to 20, particularly preferably 7 to 15, and most preferably 9.

[0063]

[0064] However, p in formula (6) and q in formula (7) represent the copolymerization ratio of the thermoplastic polyimide copolymer, where 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.

[0065] Each of the above-mentioned 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 shown in each chemical formula, as raw materials, in the presence or absence of an organic solvent, and imidizing the resulting polyamic acid. Known methods for producing polyimides can be used for production. At least one of the aromatic diamine compound and the aromatic tetracarboxylic dianhydride may be a biomass-derived compound, in which at least a portion of the raw materials are derived from biomass. In other words, the thermoplastic polyimide may be a biomass-derived thermoplastic polyimide.

[0066] To give a more specific example, a thermoplastic polyimide resin (a1)' having a structural unit represented by chemical formula (1)' is used, and 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.

[0067]

[0068] In chemical formula (8), X and R1 to R4 are the same as X and R1 to R4 in chemical formula (1)'.

[0069]

[0070] In chemical formula (9), Y is the same as Y in chemical formula (1)'.

[0071] In chemical formulas (1), (1)', and (8), specific examples of R1, R2, R3, and R4 include a hydrogen atom, alkyl groups such as a methyl group and an ethyl group; alkoxy groups such as a methoxy group and an ethoxy group; halogenated alkyl groups such as a fluoromethyl group and a trifluoromethyl group; halogenated alkoxy groups such as a fluoromethoxy group; and halogen atoms such as a chlorine atom and a fluorine atom; preferably, a hydrogen atom.

[0072] In chemical formulas (1), (1)', and (9), Y is a tetravalent aromatic group selected from the aforementioned linking group (2-1) to (2-4), and is preferably a benzene ring. In that case, the aromatic tetracarboxylic dianhydride of chemical formula (9) is a pyromellitic dianhydride.

[0073] The thermoplastic polyimide resin is preferably thermoplastic polyimide resin (a1), thermoplastic polyimide resin (a1)', thermoplastic polyimide resin (a2), thermoplastic polyimide copolymer resin (a3), thermoplastic polyimide resin (a4), or thermoplastic polyimide copolymer resin (a5).

[0074] The thermoplastic polyimide preferably contains the structural unit represented by the chemical formula (1), and more preferably consists of the structural unit represented by the chemical formula (1). By containing the structural unit represented by the chemical formula (1), the electrical properties and heat resistance of a coating composed of a resin composition containing the thermoplastic polyimide resin are superior.

[0075] The thermoplastic polyimide more preferably contains the structural unit represented by the chemical formula (1)', and even more preferably consists of the structural unit represented by the chemical formula (1)'. By containing the structural unit represented by the chemical formula (1)', the electrical properties and heat resistance of the coating composed of the resin composition containing the thermoplastic polyimide resin are improved.

[0076] The thermoplastic polyimide is more preferably composed of the structural unit represented by the chemical formula (3), and even more preferably composed of the structural unit represented by the chemical formula (3). By including the structural unit represented by the chemical formula (3), the electrical properties and heat resistance of the coating made of the resin composition containing the thermoplastic polyimide resin are improved. By being composed of the structural unit represented by the chemical formula (3), the adhesion between the conductor and the coating made of the resin composition containing the thermoplastic polyimide resin is improved.

[0077] The thermoplastic polyimide is more preferably further comprising the structural unit represented by chemical formula (7), and is particularly preferably comprising the structural unit represented by chemical formula (1)' and the structural unit represented by chemical formula (7). By further comprising the structural unit represented by chemical formula (7), the thermoplastic polyimide exhibits particularly excellent adhesion between the conductor and the coating composed of a resin composition containing the thermoplastic polyimide resin.

[0078] In manufacturing thermoplastic polyimide resins, copolymerization can be carried out using one or more other aromatic diamine compounds or aromatic tetracarboxylic dianhydrides as raw materials, to the extent that the issues of this disclosure are not impaired.

[0079] The thermoplastic polyimide resins preferably used in this disclosure, or other polyimide resins, may be used in polymer blends as desired, provided that they do not impair the issues addressed in this disclosure.

[0080] The weight-average molecular weight (Mw) of thermoplastic polyimide is preferably 20,000 or more from the viewpoint of heat resistance. The weight-average molecular weight (Mw) of thermoplastic polyimide is preferably 35,000 or less from the viewpoint of adhesion. The weight-average molecular weight (Mw) of 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.

[0081] In this disclosure, the weight-average molecular weight (Mw) of a thermoplastic polyimide refers to the 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) value of the thermoplastic polyimide shall be the value of the mixture of the two or more types of thermoplastic polyimides.

[0082] The melt flow rate (MFR) of thermoplastic polyimide resin, measured under conditions of 400°C and a 1.05 kg load in accordance with JIS K7210-1:2014, is not particularly limited, but is preferably 2 g / 10 min to 30 g / 10 min, and more preferably 4 g / 10 min to 20 g / 10 min. When two or more types of thermoplastic polyimide are used in combination, the MFR of the thermoplastic polyimide shall be the value of the mixture of the two or more types of thermoplastic polyimide contained in the coating. The MFR of thermoplastic polyimide resin is not particularly limited, but can be measured using a melt indexer (manufactured by Toyo Seiki Seisakusho Co., Ltd., model number: A-371401705).

[0083] 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. When the logarithmic viscosity is 0.1 dl / g to 3.0 dl / g, the molecular weight of the thermoplastic polyimide resin is appropriate. Therefore, the coating made from the resin composition containing the thermoplastic polyimide resin has excellent mechanical strength, and the thermoplastic polyimide resin has excellent fluidity for manufacturing the coating made from the resin composition containing the thermoplastic polyimide resin by injection molding or extrusion molding. When two or more types of thermoplastic polyimide are used in combination, the logarithmic viscosity of the thermoplastic polyimide is the value of the mixture of the two or more types of thermoplastic polyimide contained in the coating.

[0084] Logarithmic viscosity is measured by heating a 0.5 g / 100 ml solution of parachlorophenol / phenol (90 / 10 mass ratio) to 200°C and then cooling it to 35°C. The definition of logarithmic viscosity is described on page 58 of the 1995 first edition of the 'Polymer Handbook', published by Asakura Shoten and edited by the Japan Society for Analytical Chemistry.

[0085] The glass transition temperature Tg of the thermoplastic polyimide resin is not particularly limited, but from the viewpoint of heat resistance, it is preferably 200°C or higher, more preferably 210°C or higher, and even more preferably 220°C or higher. The glass transition temperature Tg of the thermoplastic polyimide resin is not particularly limited, but is preferably 300°C or lower, more preferably 290°C or lower, and even more preferably 280°C or lower.

[0086] The glass transition temperature Tg can be determined using a differential scanning calorimeter (DSC220C model, manufactured by Seiko Instruments Inc.). Approximately 5 mg of the material is sealed in a measuring aluminum pan, placed in the differential scanning calorimeter, heated from room temperature to 450°C at a rate of 10°C / min, held at 450°C for 5 minutes to completely melt the resin, then cooled to 30°C at a rate of 10°C / min, left at 30°C for 5 minutes, and then heated a second time to 450°C at a rate of 10°C / min. The displacement point corresponding to the glass transition is then determined as the glass transition temperature (Tg).

[0087] The melting point of the thermoplastic polyimide resin is not particularly limited, but from the viewpoint of heat resistance, it is preferably 340°C or higher, more preferably 350°C or higher, and even more preferably 360°C or higher. The melting point of the thermoplastic polyimide resin is not particularly limited, but from the viewpoint of moldability, it is preferably 420°C or lower, more preferably 410°C or lower, and even more preferably 400°C or lower. The method for measuring the melting point is the same as in the example.

[0088] The imide group concentration of a thermoplastic polyimide resin is calculated as (molecular weight of the imide group portion) / (total molecular weight) × 100 (%) in the molecular structure of the thermoplastic polyimide resin. For example, in the case of a polyimide in which the content of the structural unit represented by formula (3) is 100%, the imide group concentration is ((molecular weight of the imide group portion) / (total molecular weight)) × 100 (%) = (70.03 × 2) / (550.53) = 25.44%.

[0089] A commercially available thermoplastic polyimide resin having the repeating structural unit of the chemical formula (1)' mentioned above is AURUM (registered trademark, manufactured by Mitsui Chemicals, Inc., glass transition temperature 250°C, melting point 388°C).

[0090] While commercially available thermoplastic polyimide resins may be used, thermoplastic polyimide resins can also be synthesized by the following method. Specifically, a thermoplastic polyimide resin is obtained by dehydration cocondensation of a diamine represented by formula (10) and a tetracarboxylic dianhydride represented by formula (11).

[0091]

[0092]

[0093] A known imidization reaction can be applied to the method for producing thermoplastic polyimide resin. The amount of raw material compound used is usually 0.90 to 0.99 equivalents of tetracarboxylic dianhydride per equivalent of diamine. Preferably, the amount of raw material compound used is 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 the mechanical properties of the coating composed of the resin composition containing the thermoplastic polyimide resin are excellent, and the fluidity of the thermoplastic polyimide resin is also excellent.

[0094] In the synthesis of thermoplastic polyimide resins, it is preferable to encapsulate the reaction ends of the molecules with phthalic anhydride or the like. By encapsulating the reaction ends, the thermal stability of the thermoplastic polyimide resin is significantly improved.

[0095] The reaction is particularly preferably carried out in an organic solvent. Examples of organic solvents 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, xylene, etc. Organic solvents may be used individually or in mixtures of two or more types.

[0096] The reaction temperature is usually room temperature to 250°C, preferably 140°C to 200°C. The reaction pressure is not particularly limited and can be carried out at atmospheric pressure. The reaction time varies depending on the type of solvent and the reaction temperature, but is usually 4 to 24 hours. As for the imidation method, the desired polyimide resin can be obtained by imidizing the precursor polyamic acid by heating it to 100°C to 300°C, or by chemical imidation using an imidizing agent such as acetic anhydride.

[0097] <Other Components> The coating may contain components other than thermoplastic polyimide resin, high melting point resin, and inorganic particles. Examples of other components include known additives.

[0098] The additive may contain at least one 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 thermoplastic polyimide resin.

[0099] The additive may, if necessary, contain at least one of the following, within limits that do not impair the properties of the thermoplastic polyimide resin: fillers such as mica, synthetic mica, wollastonite, talc, glass beads, molybdenum disulfide, clay, silica, alumina, diatoms, soil, hydrated alumina, shirasu balloons, carbon nanotubes, calcium carbonate, hydrotalcite, fluororesin, graphite (e.g., artificial graphite, natural graphite (e.g., flake graphite, scaly graphite, earthy graphite), etc.), silicone oil, fluorine-based oil, lubricants, release agents, stabilizers, colorants, crystal nucleating agents, etc.

[0100] The additive may, if necessary, contain at least one of various liquid crystal polymers, thermoplastic resins (e.g., fluororesins, polyetherimide, polyethernitrile, polyetherketone, polyetheretherketone, polyetherketoneketone, polyetherketoneetherketoneketone, polyamideimide, polyethersulfone, polysulfone, polyarylate and / or polyphenylene sulfide), and thermosetting resins (e.g., epoxy resins, polybenzimidazole resins, polyimide resins, etc.), within a range that does not impair the properties of the thermoplastic polyimide resin.

[0101] When the resin composition contains additives, the content of the additives and the content of the thermoplastic polyimide resin are not particularly limited and are appropriately selected according to the type of additive, etc., and are preferably within the following ranges. The content of the additives is preferably 0% to 40% by mass with respect to the total amount of the resin composition. The content of the thermoplastic polyimide resin is preferably 60% to 100% by mass with respect to the total amount of the resin composition.

[0102] The resin composition before forming the aforementioned coating is preferably in the form of pellets.

[0103] [Conductor] The insulated wire according to this disclosure comprises a conductor. From the viewpoint of increasing the allowable current of the insulated wire, the conductor is preferably made of copper wire or copper alloy, which has excellent electrical conductivity. When the conductor is copper wire, copper wire made from low-oxygen copper or oxygen-free copper is preferred because it has excellent electrical conductivity. The conductor may be a single wire or a stranded wire.

[0104] From the viewpoint of improving the space factor of the conductor in a coil formed by winding insulated wire, it is preferable for the conductor to have a rectangular cross-section. In other words, it is preferable for the conductor to be a rectangular conductor.

[0105] When the cross-section perpendicular to the longitudinal direction of the conductor is rectangular, the length of the long side is preferably 1.0 mm to 5.0 mm, more preferably 1.4 mm to 4.0 mm. For example, it may be 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. For example, it may be 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.

[0106] From the viewpoint of improving adhesion between the conductor and the coating, which is made of a resin composition containing thermoplastic polyimide resin, it is preferable that the paraffin used during manufacturing is degreased with alcohol. It is also preferable to prevent the formation of an oxide film on the surface of the conductor by plating or other treatments.

[0107] The conductor may be surface-modified to improve adhesion with a coating made of a resin composition containing thermoplastic polyimide 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.

[0108] In blasting, particulate or fine powder media is sprayed onto a conductor and impacted, creating irregularities on the conductor's surface. These irregularities increase the surface roughness of the conductor, making it easier for the coating to adhere due to frictional resistance (anchor effect). Therefore, the adhesion between the conductor and the coating can be improved. Furthermore, blasting can also remove oxide films formed on the conductor surface, which further contributes to improved adhesion, making it a suitable method. As media, for example, those consisting of metal particles, carbon particles, oxide particles, carbide particles, nitride particles, etc., can be used. The conductor surface may also have irregularities created during conductor manufacturing by processing it to match the die shape.

[0109] Corona treatment modifies (makes hydrophilic) the conductor surface through corona discharge. Chemical interactions can improve the adhesion between the conductor and the coating.

[0110] In the plating process, the conductor is coated with a plating material. From the viewpoint of cost and productivity, wet plating is preferred. Furthermore, 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, and more preferably 0.5 to 5 μm.

[0111] In surface coating, a coating agent is applied or sprayed onto the conductor. Coating prevents surface oxidation of the conductor, and chemical interactions improve the adhesion between the coated conductor and the coating film. Silane coupling agents can be used as the coating agent.

[0112] 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-isocyanatetopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, bis(triethoxysilylpropyl)tetrasulfide, imidazolylalkyl-trialkoxysilane, diphenyldimethoxysilane, hexyltrimethoxysilane, decyltrimethoxysilane, trifluoropropyltrimethoxysilane, tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethyltriethoxysilane, phenyltriethoxysilane, 3-trimethoxysilylpropyl succinic anhydride, etc. can be used. Among the silane coupling agents mentioned above, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, and 3-glycidoxypropyltrimethoxysilane are preferred. Commercially available silane coupling agents can be used, for example, KBE-903, KBM-602, KBM-603, KBM-903, KBE-402, KBE-403, KBM-303, KBM402, and KBM-403 (all manufactured by Shin-Etsu Chemical Co., Ltd.).

[0113] [Method for Manufacturing Insulated Wires] The method for manufacturing insulated wires according to this disclosure is not particularly limited, but it is preferable to include a step of extruding and coating the conductor with the resin composition (hereinafter also referred to as the "extrusion coating step").

[0114] - Extrusion Coating Process - In the extrusion coating process, a preheated conductor is extruded and coated with a resin composition containing thermoplastic polyimide resin. For example, in the extrusion coating process, a resin composition containing thermoplastic polyimide resin, melted at a predetermined temperature, is extruded onto a preheated conductor fed out from a preheating section. The thickness of the coating can be, for example, 40 μm to 250 μm.

[0115] Extrusion coating is performed using an extruder. Examples of extruders include single-screw extruders, twin-screw extruders, and L-shaped extruders.

[0116] The extruder comprises a hopper for supplying a resin composition containing thermoplastic polyimide resin, a screw for melting and kneading the resin composition, a cylinder for extruding the resin composition, and a die for molding the resin composition to manufacture insulated wires. It also includes a heater for heating the cylinder and a filter for removing foreign matter.

[0117] From the viewpoint of suppressing the generation of carbides on the screw and cylinder, it is preferable to purge the hopper with an inert gas such as nitrogen or argon, or to evacuate it. However, it is not limited to this.

[0118] The screw shape is not particularly limited. For example, it may be appropriately selected from full-flight shape, sharp-compression shape, gradual-compression shape, barrier-flight shape, mixing-flight shape, etc.

[0119] The effective screw length L is, for example, 625 mm.

[0120] The screw diameter D is, for example, φ25 mm.

[0121] The ratio of the effective screw length L to the screw diameter D (L / D) is, for example, 25.

[0122] The compression ratio of the screw (the ratio of the flight groove depths of cylinder sections C-1 and C-3) is, for example, 3.0.

[0123] The screw rotation speed is, for example, 3.0 rpm (revolutions per minute).

[0124] The heating temperature of the extruder is, for example, 390°C to 400°C in cylinder section C-1, 410°C to 420°C in cylinder section C-2, 420°C to 430°C in 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.

[0125] A crosshead die is preferred. The die diameter may be, for example, φ7.2 mm. The die tip may have a diameter of φ6.0 mm and a length of 9.0 mm.

[0126] Furthermore, suitable die structures include a die structure with a sleeve (sheath core) around the conductor and a pressure die structure. Of the die structures, the pressure die structure is preferable to the die structure with a sleeve (sheath core) around the conductor. For example, the die has a conductor dispensing passage for feeding out the conductor and a resin extrusion passage, and a contact passage is provided on the upstream side in the extrusion direction from the extrusion tip (extrusion port) Q of the die to bring the resin into contact with the conductor. Because the die structure is a pressure die structure, the molten resin is compressed in the internal clearance and comes into contact with the conductor under increased static pressure, thus improving the adhesion between the conductor and the coating.

[0127] Furthermore, a longer land length on the die is preferable from the viewpoint of allowing the molten resin composition to flow well and increasing back pressure to improve adhesion between the conductor and the coating.

[0128] From the viewpoint of reducing resin pressure, the filter mesh is preferably less than 200 mesh. For example, 30 mesh to 100 mesh. Multiple meshes may be combined.

[0129] The feed speed of the conductor into the extruder may be between 1 mm / min and 300 mm / min.

[0130] Extrusion coating may be performed by increasing the vacuum level inside the cylinder. Increasing the vacuum level makes it more difficult for an oxide film to form on the conductor surface, improving the compatibility between the conductor and the coating, and thus improving adhesion.

[0131] -Surface Processing Process- The method for manufacturing an insulated wire according to the present disclosure may include a process of processing the surface of the obtained insulated wire to form irregularities (also referred to as the "surface processing process"). There are no particular restrictions on the surface processing method in the surface processing process, but examples include surface processing methods such as sandblasting, a method of imparting irregularities using a roller with irregularities, and a method of imparting irregularities by pressing a member with irregularities against the surface.

[0132] - Preheating step - The method for manufacturing an insulated wire according to the present disclosure may include a step of preheating a conductor (also referred to as the "preheating step").

[0133] Preheating is performed so that the conductor reaches a temperature higher than 250°C and 400°C or lower. Preferably, preheating is performed so that the conductor reaches a temperature higher than 250°C and below the melting point of the thermoplastic polyimide resin, and more preferably so that the conductor reaches a temperature higher than 250°C and below the melting point of the thermoplastic polyimide resin. Specifically, preheating is performed so that the conductor reaches a temperature higher than 250°C and 388°C or lower, and more preferably so that the conductor reaches a temperature higher than 250°C and below 388°C. By preheating the conductor within the above temperature range, when the process moves to the extrusion coating step, the temperature difference between the conductor and the resin composition containing the molten thermoplastic polyimide resin becomes small, stress strain is relieved, and the adhesion between the conductor and the coating is improved. Furthermore, because the temperature difference is small, the time that the resin composition containing the molten thermoplastic polyimide resin remains in contact with the surface of the conductor in a molten state can be extended. As a result, the resin composition containing the thermoplastic polyimide resin can be impregnated into the fine irregularities formed on the surface of the conductor, improving the adhesion between the conductor and the coating. Furthermore, by preheating the conductor to a temperature below the melting point of the thermoplastic polyimide resin, the fluidity of the thermoplastic polyimide extruded onto the conductor during the extrusion coating process can be moderately reduced, thereby improving adhesion while also improving the uniformity of the coating thickness.

[0134] The preheating method is not particularly limited and may be performed by 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 by a non-contact heating method using microwaves, high frequencies, etc. When preheating by a non-contact heating method, induction heating using high frequencies is preferred from the viewpoint of preheating to a high temperature. The preheating section may be provided integrally with the dispensing section. Alternatively, the winding core (bobbin) of the dispensing section around which the conductor is wound may be heated.

[0135] When the conductor is a copper wire and it is a high-frequency induction heating device, the preheating time is preferably 0.1 seconds to 5 minutes, more preferably 0.1 seconds to 1 minute.

[0136] Furthermore, preheating is preferably performed under an inert gas atmosphere such as nitrogen or argon, from the viewpoint of preventing oxidation of the conductor surface due to high temperatures and the formation of an oxide film on the conductor surface.

[0137] After preheating, it is desirable to proceed quickly to the extrusion coating process so as not to impair the effectiveness of this process. The preheating and extrusion coating processes may be carried out consistently under an inert gas atmosphere to prevent the preheated conductor from coming into contact with air.

[0138] According to the method for manufacturing an insulated wire according to the present disclosure described above, the insulated wire according to the present disclosure can be easily manufactured. In addition to the above steps, the method for manufacturing an insulated wire according to the present disclosure may further include a step of cooling the covered conductor (i.e., the insulated wire) (hereinafter also referred to as the "cooling step").

[0139] In the cooling process, the insulated wires are cooled. Cooling is performed in the cooling unit (see Figure 1). Cooling can be done by air or water.

[0140] Furthermore, the method for manufacturing an insulated wire according to this disclosure may further include a step (hereinafter also referred to as the "temperature holding step") in which the extruded coating portion (e.g., the die portion) is held at a temperature between the heating temperature of the extruded coating portion and the heating temperature of the extruded coating portion plus 10°C, after the extrusion coating step and before the cooling step. Including the temperature holding step improves the compatibility between the conductor and the coating, and improves the adhesion between the conductor and the coating.

[0141] Furthermore, the method for manufacturing an insulated wire according to this disclosure may further include a post-heating step after the extrusion coating step and before the cooling step. Further heating after extrusion coating improves the compatibility between the conductor and the coating, and improves the adhesion between the conductor and the coating.

[0142] Furthermore, the method for manufacturing an insulated wire according to this 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, the adhesion between the conductor and the coating is improved. The rolling can be carried out, for example, by a roll press, a cold isostatic press (CIP), or the like.

[0143] The various conditions of each step in the manufacturing method of the insulated wire according to this disclosure may be combined as appropriate. For example, a flat rectangular copper wire with Ni plating 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 extrusion coating may be performed using a pressure die as the die. Furthermore, during preheating, the atmosphere around the conductor may be an inert gas atmosphere.

[0144] The insulated wires relating to this disclosure are not particularly limited in their use, but can be suitably used in coils, rotors, stators, motors using these components, etc. In particular, they can be suitably used as insulated wires for inserting stator rods.

[0145] (Thermoplastic Polyimide Resin Composition) The thermoplastic polyimide resin composition according to the present disclosure comprises a thermoplastic polyimide resin, a high-melting-point resin different from the thermoplastic polyimide resin having a melting point of 260°C or higher, and at least one selected from the group consisting of inorganic particles. The thermoplastic polyimide resin composition according to the present disclosure can be suitably used in a second embodiment of the insulated wire according to the present disclosure.

[0146] The thermoplastic polyimide resin, the high-melting-point resin having a melting point of 260°C or higher, and the inorganic particles in the thermoplastic polyimide resin composition according to this disclosure are the same as those in the coating described above, and the preferred embodiments are also the same. Furthermore, the preferred content of each component in the thermoplastic polyimide resin composition according to this disclosure is the same as the preferred content of each component in the coating described above. Moreover, by using the thermoplastic polyimide resin composition according to this disclosure as a coating for insulated wires, by including at least one selected from the group consisting of the high-melting-point resin having a melting point of 260°C or higher and the inorganic particles, an appropriate unevenness is created on the surface of the insulated wire, and the coating can reduce the contact area with another member when the insulated wire comes into contact with another member, thereby reducing the static friction coefficient and improving slipperiness. For this reason, the thermoplastic polyimide resin composition according to this disclosure is preferably for use as a coating for insulated wires, and in particular, is preferably for use as a coating for insulated wires for status rod insertion.

[0147] An embodiment of this disclosure will be described in more detail below with reference to examples. An embodiment of this disclosure is not limited to the following examples.

[0148] - Preparation - The following materials were prepared: • Conductor: Flat copper wire (thickness x width: 1.54 mm x 2.99 mm, radius of curvature of corner: 6 mm, with Ni plating, plating thickness 2 μm) • Resin composition containing thermoplastic polyimide resin: TPI1: Synthesized according to the synthesis example below. TPI2: Synthesized according to the synthesis example below. TPI3: Synthesized according to the synthesis example below. TPI4: Synthesized according to the synthesis example below. PEEK: Polyether ether ketone resin, product name: "KT-851 NT", manufactured by Solvay Co., Ltd. Silica: Silica particles, brand name: SO-C2, manufactured by Admatex Co., Ltd.

[0149] TPI1 to TPI4 were synthesized using the following procedure.

[0150] (Synthesis Example 1) Thermoplastic polyimide resin (molecular weight) TPI1 containing the structural unit represented by formula (3) was synthesized by the following procedure. A container 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 this container. The mixture was then heated to 200°C while stirring under a nitrogen atmosphere. During this time, approximately 350 ml of water was observed to distillate. The reaction was further carried out at 200°C for 6 hours. After that, the mixture was cooled to room temperature and 10.8 kg of toluene was added. The mixture was then filtered to obtain a yellow polyimide powder. After washing the polyimide powder with toluene, it was dried at 180°C for 24 hours to obtain 5.46 kg (yield 98.5%) of polyimide powder (thermoplastic polyimide). Using a Takayasu 25 mmφ extruder, this polyimide powder was extruded at 400°C to obtain pellets. The glass transition temperature of the thermoplastic polyimide resin TPI1 was 245°C, and the imide group concentration was 25.44%. The weight-average molecular weight Mw of the thermoplastic polyimide TPI1 was 32,500.

[0151] The weight-average molecular weight Mw of the thermoplastic polyimide resin was measured using gel permeation chromatography (GPC) as follows. The weight-average molecular weight Mw of other thermoplastic polyimide resins in this example was measured similarly. 5 mg of the sample was added to 1.5 mL of 4-chlorophenol and gently stirred at 130°C to 140°C. After the resulting solution was air-cooled to room temperature, 3.5 mL of chloroform was added. The sample solution was then filtered using a 0.2 μm filter to prepare it. The prepared sample solution was measured under the following conditions. Detector: Differential refractive index detector RI (RI-8020, manufactured by Tosoh Corporation) Column: TSKgel GMHXL x 2, G2500HXL x 1 (7.8 mm I.D. x 300 mm, manufactured by Tosoh Corporation) Column temperature: 23°C Solvent: 4-chlorophenol / chloroform (3 / 7) (volt / volt) Flow rate: 0.8 mL / min, Sample concentration: 1 mg / ml, Injection volume: 0.3 mL Standard sample: Monodisperse polystyrene, manufactured by Tosoh Corporation

[0152] (Synthesis Example 2) A thermoplastic polyimide resin TPI2 containing structural units represented by formula (4) and structural units represented by formula (5) was synthesized using 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 cresolic acid were added to a container equipped with a stirrer, reflux condenser, water separator, and nitrogen inlet tube. The mixture was then heated to 145°C while stirring under a nitrogen atmosphere. During this time, approximately 350 ml of water was observed to distillate. The reaction was further carried out at 145°C for 4 hours. After that, the mixture was cooled to room temperature and 10.8 kg of methyl ethyl ketone was added. The mixture was then filtered to obtain a yellow polyimide powder. The polyimide powder was washed with methyl ethyl ketone and then dried at 180°C for 24 hours to obtain 5.26 kg (yield 98%) of polyimide powder (thermoplastic polyimide). Using a Takayasu 25 mmΦ extruder, the polyimide powder was extruded at 400°C to obtain pellets. The glass transition temperature of the thermoplastic polyimide TPI2 was 253°C, and the imide group concentration was 26.56%. In TPI2, the ratio of structural units represented by formula (4) to structural units represented by formula (5) was 9:1.

[0153] (Synthesis Example 3) Thermoplastic polyimide resin (high molecular weight) TPI3 containing the structural unit represented by formula (3) was synthesized by the following procedure. A container 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 this container. The mixture was then heated to 200°C while stirring under a nitrogen atmosphere. During this time, approximately 350 ml of water was observed to distillate. The reaction was further carried out at 200°C for 6 hours. After that, the mixture was cooled to room temperature and 10.8 kg of toluene was added. The mixture was then filtered to obtain a yellow polyimide powder. After washing the polyimide powder with toluene, it was dried at 180°C for 24 hours to obtain 5.46 kg (yield 98.5%) of polyimide powder (thermoplastic polyimide powder). Using a Takayasu 25 mmΦ extruder, this polyimide powder was extruded at 400°C to obtain pellets. The glass transition temperature of the thermoplastic polyimide was 248°C, and the imide group concentration was 25.44%. The weight-average molecular weight Mw of the thermoplastic polyimide TPI3 was 36,900.

[0154] (Synthesis Example 4) A thermoplastic polyimide resin TPI4 containing structural units represented by formula (6) and structural units represented by formula (7) was synthesized according to the following procedure. A container 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 acid dianhydride, 0.148 kg (1.0 mol) of phthalic anhydride, and 21.53 kg of m-cresol were added to this container. The mixture was then heated to 200°C while stirring under a nitrogen atmosphere. During this time, approximately 350 ml of water was observed to distill off. The reaction was then carried out at 200°C for 6 hours. After that, the mixture was cooled to room temperature and 10.8 kg of methanol was added. Subsequently, the mixture was filtered to obtain a yellow polyimide powder. This polyimide powder was washed with methanol and then dried at 180°C for 24 hours to obtain 5.46 kg (yield 98.5%) of polyimide powder (thermoplastic polyimide powder). Using a Takayasu 25 mmΦ extruder, this polyimide powder was extruded at 400°C to obtain pellets. The glass transition temperature of thermoplastic polyimide TPI4 was 235°C, and the imide group concentration was 23.90%. In TPI4, the ratio of structural units represented by formula (6) to structural units represented by formula (7) was 1:1.

[0155] <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 section of the extruder was controlled by dividing it into three zones, C1, C2, and C3, in order from the material input side. The heating temperatures were set to 380°C for zone C1, 410°C for zones C2 and C3, and 420°C for the head section behind the cylinder of the extruder and the die at the front of the head section. The shape of the die hole was similar to the cross-sectional shape of a conductor.

[0156] Pellets of thermoplastic polyimide resin TPI1 were fed into an extruder, and the molten TPI1 pellets were directly coated onto the outer circumference of a conductor (flat copper wire) preheated to 350°C, and then allowed to cool. This resulted in the production of an insulated wire.

[0157] The resulting insulated wire comprised a conductor and a coating that directly covered the conductor. The coating was made of thermoplastic polyimide resin TPI1. The cross-sectional shape of the insulated wire was similar to that of the conductor. The thickness of the coating was 100 μm.

[0158] Preheating was performed using a preheater, and the temperature of the preheated conductor was measured just before the crosshead. A traveling thermometer (MW-33E-TC1ASP, manufactured by Anritsu Instruments) was used to measure the preheating temperature.

[0159] Next, the surface of the obtained insulated wire was sandblasted to adjust its surface roughness. This resulted in the insulated wire of Example 1.

[0160] <Examples 2 and 4, Comparative Examples 1 and 2> Insulated wires were obtained in the same manner as in Example 1, except that the conditions for sandblasting the surface of the insulated wire were changed.

[0161] <Example 3> An insulated wire was obtained in the same manner as in Example 1, except that instead of TPI1 pellets, pellets made by mixing 80% by mass of TPI1 and 20% by mass of PEEK were used, and no surface irregularities were formed.

[0162] <Example 5> An insulated wire was obtained in the same manner as in Example 1, except that TPI2 pellets were used instead of TPI1 pellets.

[0163] <Example 6, Comparative Examples 3 and 4> Insulated wires were obtained in the same manner as in Example 5, except that the conditions for sandblasting the surface of the insulated wire were changed.

[0164] <Example 7> An insulated wire was obtained in the same manner as in Example 1, except that a pellet made by mixing 95% by mass of TPI1 and 5% by mass of silica (brand name: SO-C2, manufactured by Admatex Co., Ltd.) was used, and no surface irregularities were formed.

[0165] <Example 8> An insulated wire was obtained in the same manner as in Example 1, except that TPI3 pellets were used instead of TPI1 pellets.

[0166] <Example 9> An insulated wire was obtained in the same manner as in Example 1, except that TPI4 pellets were used instead of TPI1 pellets.

[0167] <Method for measuring the sliding angle> A SUS plate (SUS304, Ra = 0.8 μm) with a width of 20 mm and a length of 100 mm was fixed to the sample stage, and an insulated wire cut to 50 mm was placed on the SUS plate. The sample stage was tilted at a speed of 1° / second, and the angle of the sample stage when it began to slide was measured and defined as the sliding angle. Ten measurements were taken, and the average value was adopted.

[0168] <Method for measuring the static friction coefficient> The static friction coefficient was determined from the sliding angle θ described above (static friction coefficient = tanθ).

[0169] <Method for Measuring Partial Discharge Inception Voltage (PDIV)> A partial discharge tester (manufactured by Kikusui Electronics Co., Ltd., product name: "KPD 2050") was used to measure the partial discharge inception voltage of an insulated wire. A sample was prepared by tightly attaching two insulated wires. In the sample, the flat surfaces of the outer periphery of the two insulated wires were in close contact with each other over a length of 150 mm without any gaps. A "flat surface" refers to the surface formed by the long side of the longitudinal cross-section of a rectangular insulated wire, which is continuous in the axial direction. Electrodes were connected between the two conductors of this sample, and the voltage was continuously increased while applying a 50 Hz AC voltage at a measurement temperature of 25°C. The voltage at the point when a partial discharge of 10 pC occurred was read as the peak voltage (Vp). The read peak voltage (Vp) was defined as the partial discharge inception voltage (25°C) (hereinafter also referred to as "Vp (25°C)"). The acceptable Vp (25°C) is 1,000 Vp or higher.

[0170] (Partial discharge initiation voltage (200°C)) Except for changing the measurement temperature to 200°C, the voltage at the time of partial discharge initiation (25°C) was read as the peak voltage (Vp), except that the measurement temperature was changed to 200°C. The read peak voltage (Vp) was defined as the partial discharge initiation voltage (200°C) (hereinafter also referred to as "Vp (200°C)"). The acceptable Vp (200°C) is 1,000Vp or higher.

[0171] <Method for Evaluating Heat Resistance> The heat resistance of insulated wires was quantitatively evaluated using the reduction rate of the partial discharge initiation voltage. The reduction rate of the partial discharge initiation voltage is expressed by the following formula (A). A reduction rate of 3% or less was considered to indicate excellent heat resistance.

[0172] Equation (A): Reduction rate of partial discharge initiation voltage = ((Vp(25°C) - Vp(200°C)) / Vp(25°C)) × 100

[0173]

[0174] In Table 1, MD represents the longitudinal direction (wire direction) of the insulated wire, and TD represents the width direction (direction perpendicular to the longitudinal direction) of the insulated wire.

[0175] As is clear from Table 1, the insulated wire of the example has a smaller sliding angle and a lower static friction coefficient compared to the insulated wire of the comparative example, resulting in superior surface slipperiness. Furthermore, because the insulated wire of the example has superior surface slipperiness, it also exhibits superior slot insertion properties.

[0176] The disclosure of Japanese Patent Application No. 2024-164305, filed on September 20, 2024, is incorporated herein by reference in its 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 were specifically and individually noted to be incorporated by reference.

[0177] 10: Insulated wire 11: Conductor 12: Coating

Claims

1. An insulated wire comprising a conductor and a coating containing a thermoplastic polyimide resin, wherein the surface roughness Ra is 0.50 μm or more and 4.00 μm or less.

2. An insulated wire comprising a conductor and a coating containing a thermoplastic polyimide resin, wherein the coating further comprises at least one selected from the group consisting of a high-melting-point resin having a melting point of 260°C or higher, different from the thermoplastic polyimide resin, and inorganic particles.

3. The insulated wire according to claim 2, wherein the high-melting-point resin is at least one resin selected from the group consisting of polyetheretherketone resin, polyphenylene sulfide resin, syndiotactic polystyrene resin, polyamide resin, polyimidoamide resin, and modified versions thereof.

4. The insulated wire according to claim 1 or claim 2, wherein the thermoplastic polyimide resin includes a structural unit represented by the following formula (1). In equation (1) above, X is a direct bond, -SO ２ -, -CO-, -C(CH ３ ) ２ -, -C (CF ３ ) ２ The group is - or S-, and 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 the bond position, and the hydrogen atom of the aromatic ring may be substituted. Also, the position of the bond group whose bond position has not been determined in formula (1) is either the para or meta position relative to the position to which the oxygen atom is bonded.

5. The insulated wire according to claim 1 or claim 2, wherein the static friction coefficient of the surface of the coating is lower than 0.

35.

6. The insulated wire according to claim 1 or claim 2, wherein the conductor is a rectangular conductor.

7. The insulated wire according to claim 6, wherein the ratio of the length of the long side of the rectangular cross-section of the rectangular conductor to the length of the short side of the rectangular cross-section of the rectangular conductor is 1 or more and 4 or less.

8. An insulated wire according to claim 1 or claim 2, for inserting a status rod.

9. A coil comprising an insulated wire as described in claim 1 or claim 2.

10. A motor comprising an insulated wire as described in claim 1 or claim 2.

11. A method for manufacturing an insulated electric wire comprising a conductor and a coating made of a resin composition containing a thermoplastic polyimide resin, the method comprising the step of extruding the conductor with the resin composition, wherein the surface roughness Ra of the coating is 0.50 μm or more and 4.00 μm or less.

12. A method for manufacturing an insulated electric wire comprising a conductor and a coating made of a resin composition containing a thermoplastic polyimide resin, comprising the step of extruding the conductor with the resin composition, wherein the coating further comprises at least one selected from the group consisting of a high-melting-point resin having a melting point of 260°C or higher and inorganic particles.

13. A thermoplastic polyimide resin composition comprising a thermoplastic polyimide resin, a high-melting-point resin different from the thermoplastic polyimide resin having a melting point of 260°C or higher, and at least one selected from the group consisting of inorganic particles.

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