Insulated electric wire and method for manufacturing the same

Abstract

An insulated electric wire includes a conductor and an insulating layer covering the conductor, wherein the insulating layer contains a resin and a first filler, the resin contains a polyimide, the first filler exists in the form of primary particles or secondary particles formed by aggregation of a plurality of the primary particles, the primary particles are silica or alumina, a particle diameter of the secondary particles is 0.03 μm or more and 5 μm or less, and in a cross section of the insulated electric wire, a proportion of a total value of areas of the secondary particles with respect to a sum of a total value of areas of the primary particles and the total value of areas of the secondary particles is 50% or more.

Description

Technical Field

[0001] This disclosure relates to insulated wires and methods for manufacturing the same. This application claims priority based on Japanese Patent Application No. 2021-036490, filed March 8, 2021. The entire contents of that Japanese patent application are incorporated herein by reference. Background Technology

[0002] In the past, insulated wires with conductors and insulation covering the conductors were used in motors, transformers and the like.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2008-251295

[0006] Patent Document 2: Japanese Patent Application Publication No. 2009-140878

[0007] Patent Document 3: Japanese Patent Application Publication No. 2010-040320 Summary of the Invention

[0008] The insulated wire disclosed herein comprises: a conductor; and an insulating layer covering the conductor, wherein the insulating layer comprises a resin and a first filler, the resin comprising polyimide, the first filler being in the form of primary particles or secondary particles formed by an aggregation of multiple primary particles, the primary particles being silicon dioxide or aluminum oxide, the secondary particles having a particle size of 0.03 μm or more and 5 μm or less, and in the cross-section of the insulated wire, the ratio of the total area of ​​the secondary particles to the sum of the total area of ​​the primary particles and the total area of ​​the secondary particles being 50% or more. Attached Figure Description

[0009] Figure 1 The image shown is a microscopic photograph of a cross-section of one embodiment of the insulated wire of this disclosure.

[0010] Figure 2 This is a schematic cross-sectional view illustrating one embodiment of the insulated wire of this disclosure.

[0011] Figure 3 This is a schematic cross-sectional view illustrating one embodiment of the insulated wire of this disclosure.

[0012] Figure 4 yes Figure 3 A schematic enlarged view of region IV. Detailed Implementation

[0013] [The problem this disclosure aims to solve]

[0014] If a voltage is applied rapidly to insulated wires, a small discharge (surge) occurs between the insulated wires. This surge can accelerate insulation breakdown. Therefore, insulated wires require improved properties to suppress insulation breakdown caused by surges (hereinafter referred to as "surge resistance").

[0015] Japanese Patent Application Publication No. 2008-251295 (Patent Document 1) discloses the following: In an insulated wire having at least two insulating layers on a conductor, the surge resistance of the insulated wire can be improved by making at least one layer (insulating layer A) contain inorganic compound particles and making the thickness of insulating layer A within a specific range.

[0016] Japanese Patent Application Publication No. 2009-140878 (Patent Document 2) discloses a varnish containing hollow silica particles with nanoscale dimensions. It describes how using the aforementioned varnish to manufacture insulated wires improves the surge resistance of the insulated wires.

[0017] Japanese Patent Application Publication No. 2010-040320 (Patent Document 3) discloses a varnish containing a specific amount of phenyltrialkoxysilane. It describes how using the aforementioned varnish to manufacture insulated wires can improve the surge resistance of the insulated wires.

[0018] However, recently, there has been a demand for further improvements in surge resistance.

[0019] Therefore, the purpose of this disclosure is to provide insulated wires with excellent surge resistance.

[0020] [The Effects of This Disclosure]

[0021] According to this disclosure, insulated wires with excellent surge resistance can be provided.

[0022] [Description of embodiments of this disclosure]

[0023] First, embodiments of this disclosure will be described.

[0024] [1] The insulated wire disclosed herein comprises: a conductor; and an insulating layer covering the conductor, wherein the insulating layer comprises a resin and a first filler, the resin comprising polyimide, the first filler being present in the form of primary particles or secondary particles formed by an aggregation of a plurality of primary particles, the primary particles being silicon dioxide or aluminum oxide, the secondary particles having a particle size of 0.03 μm or more and 5 μm or less, and in the cross-section of the insulated wire, the ratio of the total area of ​​the secondary particles to the sum of the total area of ​​the primary particles and the total area of ​​the secondary particles being 50% or more.

[0025] Previously, if an insulated wire overheats due to surges, the resin contained in the insulation layer can decompose thermally and volatilize to the outside of the insulation layer. Consequently, repeated surges can erode the insulation layer, sometimes leading to insulation breakdown. The insulated wire of this disclosure physically suppresses resin volatilization by setting the particle size of the secondary particles (first filler) in the insulation layer within a specific range and setting the area ratio of the secondary particles (first filler) in the cross-section of the insulated wire within a specific range. As a result, surge-induced insulation breakdown can be suppressed. That is, according to this disclosure, an insulated wire with excellent surge resistance can be provided.

[0026] Furthermore, polyimide exhibits excellent toughness. Therefore, the insulated wire of this disclosure contains polyimide in the resin, thus resulting in excellent toughness.

[0027] [2] Preferably, in the above-mentioned cross-section, the total area of ​​the secondary particles with a particle size of 0.2 μm or more and 1 μm or less is 30% or more relative to the total area of ​​the secondary particles. This further improves the surge resistance of the insulated wire.

[0028] [3] Preferably, the mass ratio of the first filler to the mass of the insulation layer is 5% or more and 30% or less. This further improves the surge resistance of the insulated wire.

[0029] [4] Preferably, the polyimide is a polymer of an acid dianhydride and a diamine compound. Thus, it can combine the excellent surge resistance of insulated wires with the excellent toughness of the insulation layer.

[0030] [5] Preferably, the acid dianhydride is either or both of pyromellitic dianhydride and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, and the diamine compound is 4,4'-oxodiphenylamine. Thus, it can combine the superior surge resistance of insulated wires with the superior toughness of the insulation layer.

[0031] [6] Preferably, the acid dianhydride is composed of the above-mentioned pyromellitic dianhydride and the above-mentioned 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, wherein the acid dianhydride contains more than 10 mol% and less than 50 mol% of the above-mentioned pyromellitic dianhydride, and contains more than 50 mol% and less than 90 mol% of the above-mentioned 3,3',4,4'-biphenyltetracarboxylic acid dianhydride.

[0032] Automatic Transmission Fluid (ATF) is used in vehicle transmissions and the like. Therefore, insulated wires used in vehicle motors and the like may come into contact with ATF. If conventional insulated wires come into contact with ATF, it promotes the hydrolysis of the resin contained in the insulation layer constituting the wire, sometimes causing cracks in the insulation layer. Generally, polyimide is easily hydrolyzed by moisture in ATF, thus exhibiting poor ATF resistance. However, the aforementioned acid dianhydride is composed of pyromellitic dianhydride and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, containing 10 mol% to 50 mol% of pyromellitic dianhydride and 50 mol% to 90 mol% of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride. This imparts hydrolysis resistance to the insulation layer, thus exhibiting excellent ATF resistance. It should be noted that in this specification, the property of inhibiting the hydrolysis of the insulation layer caused by contact between the insulated wire and ATF is defined as "ATF resistance."

[0033] [7] The method for manufacturing the insulated wire disclosed herein is the same as the method for manufacturing the insulated wire described above, comprising the following steps: a first step of preparing the conductor and an insulating varnish; a second step of coating the outer peripheral surface of the conductor with the insulating varnish; and a third step of baking the insulating varnish onto the conductor. The first step comprises: a step A of preparing the conductor; and a step B of preparing the insulating varnish. In step B, the insulating varnish is prepared by mixing a solvent, a first filler, and a resin or a resin precursor thereof. The solvent is N-methyl-2-pyrrolidone, N,N-dimethylacetamide, or a mixture thereof. In the first filler, the particle size of the primary particles is 0.01 μm or more and 0.1 μm or less. Therefore, it is possible to manufacture an insulated wire with excellent surge resistance.

[0034] [8] Preferably, the third step described above is performed at a temperature of 300°C or higher and 700°C or lower, for a duration of 0.1 minutes or higher and 5 minutes or lower. As a result, it is possible to manufacture insulated wires with superior surge resistance.

[0035] [9] Preferably, the concentration of the resin solids in the above-mentioned insulating varnish is 10% by mass or more and 40% by mass or less. As a result, it is possible to manufacture insulated wires with superior surge resistance.

[0036]

[10] Preferably, the mass ratio of the first filler in the above-mentioned insulating varnish to the mass ratio of the resin solids is 5% or more and 35% or less. As a result, it is possible to manufacture insulated wires with superior surge resistance.

[0037] [Details of the embodiments of this disclosure]

[0038] The following describes one embodiment of this disclosure (hereinafter referred to as "this embodiment"). However, this embodiment is not limited thereto. In this specification, the expression "A to B" refers to the upper and lower limits of the range (i.e., above A and below B). When no unit is specified in A but only in B, the unit of A is the same as the unit of B.

[0039] Insulated wires

[0040] Figure 2 This is a schematic cross-sectional view illustrating one embodiment of the insulated wire of this disclosure. The insulated wire 10 (hereinafter sometimes simply referred to as "insulated wire") of this disclosure includes a conductor 11 and an insulation layer 12 covering the conductor 11. Figure 2 Here, "covering" preferably refers to covering the entire surface of the conductor 11, but as long as the effects of this disclosure are achieved, it does not depart from the scope of this disclosure even if a portion of the surface of the conductor 11 is not covered by the insulation layer 12. In addition, the insulated wire of this disclosure may also include a base layer, a sealing layer, a protective layer, a surface layer, a lubricating layer, etc.

[0041] It should be noted that insulated wires are linear in shape. The cross-section of an insulated wire, as described later, refers to the cross-section obtained by cutting the wire in a plane perpendicular to its longitudinal direction. The cross-section of an insulated wire can be circular (including approximately circular) or flat.

[0042] <Conductor>

[0043] The insulated wire of this embodiment includes a conductor as described above. A conductor is a conductive material. Preferably, the conductor is a metal with high conductivity and high mechanical strength. Specifically, examples include copper, copper alloys, aluminum, aluminum alloys, nickel, silver, soft iron, steel, and stainless steel. The conductor can be a wire formed from these metals, a coated wire formed by coating the surface of the wire with another metal, or a stranded wire formed by twisting multiple wires together. Examples of coated wires include nickel-coated copper wire, silver-coated copper wire, silver-coated aluminum wire, and copper-coated steel wire, but the invention is not limited to these.

[0044] There are no particular restrictions on the shape of the conductor; round or square wires can be selected appropriately based on the intended use and electrical characteristics of the insulated wire. That is, the cross-sectional shape of the conductor in the insulated wire can be circular (including approximately circular) or flat. Furthermore, there are no particular restrictions on the conductor's diameter or outer circumference length; these can also be selected appropriately based on the intended use and electrical characteristics of the insulated wire.

[0045] The lower limit of the cross-sectional area of ​​the conductor portion in the cross-section of an insulated wire is preferably 0.01 mm². 2 The above, more preferably 0.1mm2 The upper limit is preferably 40mm. 2 The following is more preferably 20mm 2 The following applies: The cross-sectional area of ​​the conductor portion in the cross-section of the insulated wire is less than 0.01 mm². 2 In such cases, the volume ratio of the insulation layer to the conductor increases; for example, the volumetric efficiency of coils formed using insulated wires may decrease. The cross-sectional area of ​​the conductor portion in the insulated wire exceeds 40 mm². 2 In such cases, the copper losses caused by eddy currents increase, and the output efficiency of the coil may decrease.

[0046] <Insulation layer>

[0047] Figure 3 This is a schematic cross-sectional view illustrating one embodiment of the insulated wire of this disclosure. The insulation layer 12 comprises resin 1 and a first filler ( Figure 3 In addition, the insulating layer may also contain curing agents, other additives, and a second filler.

[0048] The aforementioned curing agents have the function of curing resins. Specifically, examples include: imidazole, triethylamine, titanium compounds, isocyanate compounds, terminal isocyanates, urea, melamine compounds, acetylene derivatives, alicyclic anhydrides such as methyltetrahydrophthalic anhydride, aliphatic anhydrides, and aromatic anhydrides. Examples of titanium compounds include tetrapropyl titanate, tetraisopropyl titanate, tetramethyl titanate, tetrabutyl titanate, and tetrahexyl titanate. Examples of the aforementioned isocyanate compounds include: aromatic diisocyanates such as toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), terephthalic diisocyanate, and naphthalene diisocyanate; aliphatic diisocyanates with 3 to 12 carbon atoms such as hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexane diisocyanate, and lysine diisocyanate; and 1,4-cyclohexane diisocyanate (CDI), isophorone diisocyanate (IPDI), and 4,4'-dicyclohexylmethane diisocyanate (hydrogenated MDI). Alicyclic isocyanates with 5 to 18 carbon atoms, such as methylcyclohexane diisocyanate, isopropylidene dicyclohexyl-4,4'-diisocyanate, 1,3-diisocyanate-methylcyclohexane (hydrogenated XDI), hydrogenated TDI, 2,5-bis(isocyanate-methyl)-bicyclo[2,2,1]heptane, and 2,6-bis(isocyanate-methyl)-bicyclo[2,2,1]heptane; aliphatic diisocyanates with aromatic rings, such as phenyl dimethyl diisocyanate (XDI) and tetramethylphenyl dimethyl diisocyanate (TMXDI); and their modified forms. Examples of the aforementioned end-capped isocyanates include diphenylmethane-4,4'-diisocyanate (MDI), diphenylmethane-3,3'-diisocyanate, diphenylmethane-3,4'-diisocyanate, diphenyl ether-4,4'-diisocyanate, benzophenone-4,4'-diisocyanate, diphenyl sulfone-4,4'-diisocyanate, toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, naphthalene-1,5-diisocyanate, isophthalic diisocyanate, and terephthalic diisocyanate. Examples of the aforementioned melamine compounds include methylated melamine, butylated melamine, hydroxymethylated melamine, and hydroxybutylated melamine. Examples of the aforementioned acetylene derivatives include acetylenyl aniline and acetylenyl phthalic anhydride. As curing agents, nitrogen-containing compounds such as melamine compounds are preferred. This is because these curing agents have a high curing-promoting effect.

[0049] Other additives mentioned above include antioxidants, UV stabilizers, and surface lubricants.

[0050] The aforementioned second packing refers to packing other than the aforementioned first packing, and may include one or more such packings.

[0051] The thickness of the insulation layer is preferably 5 μm or more, and more preferably 200 μm or less. If the thickness of the insulation layer is less than 5 μm, the insulation layer is prone to damage, and the insulation of the conductor may become insufficient. If the thickness of the insulation layer exceeds 200 μm, the volumetric efficiency of coils and the like formed using insulated wires tends to decrease.

[0052] The thickness of the insulation layer refers to the average thickness of the insulation layer across the cross-section of the insulated wire. Specifically, for any five points along the length of the wire, a flat cross-section is created by grinding, and the insulation layer thickness is measured using a microscope. The average value obtained at each point is then calculated and taken as the insulation layer thickness.

[0053] (resin)

[0054] The aforementioned resin contains polyimide. Polyimide is a polymer having imide bonds (-CONCO-) in its main chain. Polyimide is known to have excellent heat resistance. Furthermore, polyimide has high toughness, thus preventing breakage of the insulation layer even if it contains secondary particles described later. The polyimide is preferably a polymer of an acid dianhydride and a diamine compound. In other words, the polyimide is preferably a polymer having a structure formed by the repeated bonding of structural units derived from the acid dianhydride and structural units derived from the diamine compound. Here, "acid dianhydride" refers to a compound with a structure in which two water molecules detach from four carboxylic acid groups present in its molecule (a structure in which two sets of carboxylic acid group pairs consisting of two adjacent carboxylic acid groups exist in one molecule, and one water molecule detaches from each carboxylic acid group pair). Furthermore, "containing polyimide" means that the resin may also contain other resins besides polyimide. Other resins include thermosetting resins such as polyvinyl alcohol formaldehyde resin, polyurethane resin, alkyl resin, epoxy resin, phenoxy resin, polyester resin, polyesterimide resin, polyesteramideimide resin, and polyamideimide resin, as well as thermoplastic resins such as polyetherimide resin, polyetheretherketone resin, and polyethersulfone resin.

[0055] Examples of the aforementioned dianhydrides include: pyromellitic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,2',3,3'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 4,4'-oxophthalic anhydride, and 2,2-bis(3,4-dicarboxyphenyl)propane dihydride. Anhydrides, 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, bis(3,4-dicarboxyphenyl)ether dianhydride, 1,2,5,6-naphthalenetetracarboxylic acid dianhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, etc.

[0056] Examples of the diamine compounds mentioned above include: 4,4'-oxydianiline (ODA), m-phenylenediamine, silicone diamine, bis(3-aminopropyl) ether ethane, 3,3'-diamino-4,4'-dihydroxydiphenyl sulfone (SO2-HOAB), 4,4'-diamino-3,3'-dihydroxybiphenyl (HOAB), 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HOCF3AB), siloxane diamine, bis(3-aminopropyl) ether ethane, N,N-bis(3-aminopropyl) ether, 1,4-Bis(3-aminopropyl)piperazine, isophorone diamine, 1,3'-bis(aminomethyl)cyclohexane, 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane, 4,4'-methylenebis(cyclohexylamine), 4,4'-diaminodiphenyl ether (DDE), 3,4'-diaminodiphenyl ether (m-DDE), 3,3'-diaminodiphenyl ether, 4,4'-diamino-diphenyl sulfone (p-DDS), 3,4'-diamino-diphenyl sulfone, 3,3'-diamino-diphenyl sulfone, 2,4'-diaminodiphenyl ether, 1,3-bis(4- Aminophenoxy)benzene (m-TPE), 1,3-bis(3-aminophenoxy)benzene (APB), 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HF-BAPP), bis[4-(4-aminophenoxy)phenyl]sulfone (p-BAPS), bis[4-(3-aminophenoxy)phenyl]sulfone (m-BAPS), 4,4'-bis(4-aminophenoxy)biphenyl (BAPB), 1,4-bis(4-aminophenoxy)benzene (p-TPE), 4 4'-Diaminodiphenyl sulfide (ASD), 3,4'-Diaminodiphenyl sulfide, 3,3'-Diaminodiphenyl sulfide, 3,3'-Diamino-4,4'-Dihydroxydiphenyl sulfone, 2,4-Diaminotoluene (DAT), 2,5-Diaminotoluene, 3,5-Diaminobenzoic acid (DABz), 2,6-Diaminopyridine (DAPy), 4,4'-Diamino-3,3'-Dimethoxybiphenyl (CH3OAB), 4,4'-Diamino-3,3'-Dimethylbiphenyl (CH3AB), 9,9'-Bis(4-aminophenyl)fluorene (FDA), etc.

[0057] Preferably, the aforementioned acid dianhydride is either or both of pyromellitic dianhydride and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, and the aforementioned diamine compound is 4,4'-oxodiphenylamine. Thus, the intermolecular interactions of the polyimide molecules function more strongly, thereby achieving both exceptionally excellent surge resistance and exceptionally excellent toughness of the insulation layer.

[0058] Preferably, the aforementioned acid dianhydride is composed of pyromellitic dianhydride and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, wherein the acid dianhydride contains 10 mol% to 50 mol% of pyromellitic dianhydride and 50 mol% to 90 mol% of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride. This improves hydrolysis resistance and thus provides particularly excellent ATF resistance.

[0059] The aforementioned acid dianhydride is composed of pyromellitic dianhydride and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride. The acid dianhydride contains 10 mol% to 50 mol% of pyromellitic dianhydride and 50 mol% to 90 mol% of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, obtained by alkaline hydrolysis of the coating component, using... 1 It is determined by analysis using H NMR (proton nuclear magnetic resonance).

[0060] The aforementioned diamine compound is preferably composed of 4,4'-oxodiphenylamine. This improves hydrolysis resistance and thus provides particularly excellent resistance to ATF.

[0061] (First packing material)

[0062] Figure 3 This is a schematic cross-sectional view illustrating one embodiment of the insulated wire of this disclosure. Figure 4 yes Figure 3 A schematic enlarged view of region IV. The aforementioned first filler exists in the form of primary particles 2, or secondary particles 3 composed of multiple primary particles. Figure 3 Here, "aggregate" refers to a state in which multiple primary particles 2 condense, for example, into a beaded shape, forming particles larger than primary particles 2. Figure 4 In this case, the contact state between the primary particles in the secondary particle 3 can be either purely visual contact or accompanied by interactions such as van der Waals forces and physical / chemical bonds; the contact state is not particularly limited. Therefore, when observing the cross-section of an insulated wire using a scanning electron microscope (SEM), if two or more primary particles 2 are observed in contact in the field of view, they are considered as secondary particles 3. Figure 1 These are microscope images of the cross-section of an insulated wire. (By...) Figure 1 It can be seen that in the insulating layer, the first filler exists in the form of primary particles 2 or secondary particles 3 composed of multiple primary particles.

[0063] It should be noted that, in this context, "contact" refers to a distance of less than 0.02 μm between adjacent primary particles. Furthermore, "distance between adjacent primary particles" refers to the length of the shortest line segment (straight line) connecting a point on the outer contour line of one primary particle to a point on the outer contour line of the other, relating to two adjacent primary particles.

[0064] The primary particles mentioned above are silicon dioxide or aluminum oxide. Therefore, the secondary particles can be composed of either silicon dioxide or aluminum oxide alone, or they can be composed of both silicon dioxide and aluminum oxide.

[0065] The shape of the primary particles is not particularly limited. For example, they can be irregular, roughly spherical, rugby ball-shaped, polygonal, or any other shape. The particle size of the primary particles is the distance between the two furthest points on the outer contour line of a primary particle in the cross-section of the insulated wire. Furthermore, the particle size of the primary particles refers to the average particle size. It should be noted that the particle size of the primary particles is determined as follows: by observing the cross-section of the insulated wire using a scanning electron microscope (SEM), measuring the particle size of any 50 primary particles on the SEM image, and then calculating the average particle size of these 50 primary particles (average particle size).

[0066] The particle size of the aforementioned primary particles is not particularly limited, but is preferably 0.01 μm or more and 0.1 μm or less.

[0067] The aforementioned secondary particles may consist solely of the aforementioned primary particles, or they may contain other components.

[0068] The shape of the aforementioned secondary particles is not particularly limited. For example, they can be any shape, such as irregular, roughly spherical, rugby ball-shaped, or polygonal. The particle size of the aforementioned secondary particle 3 is the distance D1 between the two furthest points on the outer contour line of a secondary particle 3 in the cross-section of the insulated wire. Figure 4 Furthermore, the particle size of secondary particles refers to the average particle size. It should be noted that the particle size of secondary particles is determined as follows: by observing the cross-section of the insulated wire using a scanning electron microscope (SEM), measuring the particle size of any 50 secondary particles on the SEM image, and then calculating the average particle size (average particle size) obtained by averaging the sizes of these 50 secondary particles.

[0069] The secondary particles have a particle size of 0.03 μm or more and 5 μm or less. This physically suppresses resin volatilization, thus providing excellent surge resistance and appropriate toughness. The particle size of the secondary particles is preferably 0.1 μm or more, more preferably 0.15 μm or more, and even more preferably 0.2 μm or more. Furthermore, the particle size of the secondary particles is preferably 3.0 μm or less, more preferably 1.5 μm or less, and even more preferably 1.0 μm or less. Additionally, the particle size of the aforementioned secondary particles is preferably 0.1 μm or more and 3.0 μm or less, more preferably 0.15 μm or more and 1.5 μm or less, and even more preferably 0.2 μm or more and 1.0 μm or less.

[0070] Ideally, in the cross-section of the aforementioned insulated wire, the ratio of the total area of ​​secondary particles to the sum of the total area of ​​primary particles and the total area of ​​secondary particles (hereinafter also referred to as "secondary particle area percentage (%)") is 50% or more. Here, "primary particle area" refers to the area of ​​primary particles other than the primary particles constituting the secondary particles. As a result, resin volatilization is physically suppressed by the secondary particles, thus preventing insulation breakdown caused by resin erosion and providing excellent surge resistance. The secondary particle area percentage (%) is preferably 50% or more, more preferably 55% or more, and even more preferably 60% or more. Furthermore, the secondary particle area percentage (%) is preferably 90% or less. This prevents the particle size from exceeding 5 μm due to excessive agglomeration between particles, avoiding a decrease in the toughness of the insulation layer caused by increased particle size, and thus enabling the insulated wire to possess appropriate toughness. The secondary particle area percentage (%) is more preferably 80% or less, and even more preferably 75% or less. The secondary particle area occupancy rate (%) is preferably 50% or more and 90% or less, more preferably 55% or more and 80% or less, and even more preferably 60% or more and 75% or less. It should be noted that the secondary particle area occupancy rate (%) is determined by observing the cross-section of the insulated wire using a scanning electron microscope (SEM) and calculating the total area of ​​primary particles and the total area of ​​secondary particles in the specified area using image processing software (Winroof, manufactured by Mitani Corporation).

[0071] In the cross-section of the aforementioned insulated wire, the ratio of the total area of ​​secondary particles with a particle size of 0.2 μm or more and 1 μm or less to the total area of ​​all secondary particles (hereinafter also referred to as "the area percentage of secondary particles with a particle size of 0.2 to 1 μm") is preferably 30% or more. This allows for the physical suppression of resin volatilization by the secondary particles, resulting in particularly excellent surge resistance. The area percentage of secondary particles with a particle size of 0.2 to 1 μm is preferably 50% or more, more preferably 55% or more, and even more preferably 60% or more. Furthermore, the area percentage of secondary particles with a particle size of 0.2 to 1 μm is preferably 90% or less. This prevents the particle size from exceeding 5 μm due to excessive agglomeration between particles, avoids a decrease in the toughness of the insulation layer caused by increased particle size, and thus enables the insulated wire to possess appropriate toughness. Here, the area percentage of secondary particles with a particle size of 0.2 to 1 μm is more preferably 80% or less, and even more preferably 75% or less. The area percentage (%) of secondary particles with a particle size of 0.2 to 1 μm is preferably 50% or more and 90% or less, more preferably 55% or more and 80% or less, and even more preferably 60% or more and 75% or less. Furthermore, the area percentage (%) of secondary particles with a particle size of 0.2 to 1 μm is determined by observing the cross-section of the insulated wire using a scanning electron microscope (SEM) and calculating, using image processing software (Winroof, manufactured by Mitani Corporation), the total area of ​​secondary particles occupying a specified area and the total area of ​​secondary particles with a particle size of 0.2 μm or more and 1 μm or less.

[0072] The mass ratio of the first filler to the insulation layer is preferably 5% or more and 30% or less. This allows for a good balance between excellent surge resistance and appropriate toughness. When the mass ratio of the first filler to the insulation layer is less than 5%, there is a tendency to achieve sufficient surge resistance. Furthermore, when the mass ratio of the first filler to the insulation layer exceeds 30%, there is a tendency for the flexibility of the insulation layer to deteriorate. The mass ratio of the first filler to the insulation layer is preferably 5% or more, more preferably 10% or more, and even more preferably 15% or more. Furthermore, the mass ratio of the first filler to the insulation layer is preferably 30% or less, more preferably 26% or less, and even more preferably 23% or less. It should be noted that the mass ratio of the first filler to the insulation layer can be determined by measuring the remaining portion of the insulation layer after heating (considered as the filler weight) using thermogravimetric analysis.

[0073] The insulated wire of this disclosure described above has excellent surge resistance, thus electrical equipment using it can suppress insulation breakdown caused by surges even when used under high voltage. Examples of such electrical equipment include motors and transformers.

[0074] Manufacturing Method of Insulated Wires

[0075] From the viewpoint of achieving a high yield rate, the insulated wire of this disclosure can be manufactured, for example, by the following method for manufacturing insulated wires. Specifically, the method for manufacturing the insulated wire of this embodiment sequentially includes: a step of preparing the conductor and insulating varnish (first step); a step of coating the outer peripheral surface of the conductor with insulating varnish (second step); and a step of baking the insulating varnish onto the conductor (third step). Furthermore, the step of preparing the conductor and insulating varnish (first step) includes: a step of preparing the conductor (step A); and a step of preparing the insulating varnish (step B).

[0076] Here, the step of preparing the insulating varnish (step B) is characterized in that the insulating varnish is prepared by mixing a solvent, the first filler, and the resin or its resin precursor, wherein the solvent is N-methyl-2-pyrrolidone, N,N-dimethylacetamide, or a mixture thereof. Furthermore, the first filler is characterized in that the particle size of the primary particles is 0.01 μm or more and 0.1 μm or less. Furthermore, in step B, the insulating varnish is preferably prepared by mixing the solvent, the first filler, and the resin or its resin precursor under conditions of a stirring time of 30 minutes or more and 180 minutes or less, and a stirring speed of 20 rpm or more and 500 rpm or less. Furthermore, the insulating varnish preferably does not contain a silane coupling agent. Furthermore, the step of baking the insulating varnish onto the conductor (third step) is preferably performed under conditions of 300°C or more and 700°C or less, and 0.1 minutes or more and 5 minutes or less.

[0077] The insulated wire obtained by performing steps B and the third step, which possess these characteristics, has the configuration described above, and therefore exhibits excellent surge resistance. Hereinafter, each step included in the manufacturing method of the insulated wire according to this embodiment will be described in detail.

[0078] <First Process>

[0079] (Process A)

[0080] The aforementioned process for preparing the conductor (Process A) can be performed, for example, by obtaining a commercially available product. Alternatively, this process can be performed by casting, stretching, drawing into wire, and further softening the aforementioned metal, which serves as the conductor material.

[0081] (Process B)

[0082] The above-mentioned process for preparing insulating varnish (process B) can be performed as follows: a resin solution is obtained by dissolving the above-mentioned resin, or its resin precursor, which is the material of the insulating layer, in N-methyl-2-pyrrolidone, N,N-dimethylacetamide, or a mixture thereof (solvent), and a first filler with a primary particle size of 0.01 μm or more and 0.1 μm or less is dispersed in the resin solution.

[0083] Polyimide precursors can be cited as examples of resin precursors.

[0084] The concentration of resin solids in the insulating varnish is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more. Furthermore, the concentration of resin solids in the insulating varnish is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less. Additionally, the concentration of resin solids in the insulating varnish is preferably 10% by mass or more and 40% by mass or less, more preferably 15% by mass or more and 35% by mass or less, and even more preferably 20% by mass or more and 30% by mass or less. Here, "resin solids concentration" refers to the concentration of the resin itself when the insulating varnish contains only the resin and its resin precursor; the concentration of the resin precursor when the insulating varnish contains only the resin and its resin precursor; and the total concentration of both when the insulating varnish contains both the resin and its resin precursor.

[0085] The mass ratio of the first filler in the insulating varnish to the solid resin component is preferably 5% or more, more preferably 10% or more, and even more preferably 15% or more. Furthermore, the mass ratio of the first filler in the insulating varnish to the solid resin component is preferably 35% or less, more preferably 30% or less, and even more preferably 25% or less. Additionally, the mass ratio of the first filler in the insulating varnish to the solid resin component is preferably 5% or more and 35% or less, more preferably 10% or more and 30% or less, and even more preferably 15% or more and 25% or less. Here, regarding the "mass of the solid resin component," when the insulating varnish contains only the resin and its resin precursor, it refers to the mass of the resin; when the insulating varnish contains only the resin precursor, it refers to the mass of the resin precursor; and when the insulating varnish contains both the resin and its resin precursor, it refers to the total mass of both.

[0086] In this context, the insulating varnish may contain other solvents, the curing agent, other additives, and the second filler, in addition to N-methyl-2-pyrrolidone, N,N-dimethylacetamide, or mixtures thereof (solvents), resin or resin precursor thereof, and the first filler. However, the insulating varnish preferably does not contain silane coupling agents.

[0087] As other solvents mentioned above, well-known organic solvents can be used. Specifically, examples include: polar organic solvents such as N,N-dimethylformamide, dimethyl sulfoxide, tetramethylurea, hexaethylphosphoryltriamine, and γ-butyrolactone; ketone organic solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ester organic solvents such as methyl acetate, ethyl acetate, butyl acetate, and diethyl oxalate; ether organic solvents such as diethyl ether, ethylene glycol dimethyl ether, diethylene glycol monomethyl ether, ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol dimethyl ether, and tetrahydrofuran; hydrocarbon organic solvents such as hexane, heptane, benzene, toluene, and xylene; halogen organic solvents such as dichloromethane and chlorobenzene; phenolic organic solvents such as cresol and chlorophenol; and amine organic solvents such as pyridine. These organic solvents can be used individually or in combination of two or more.

[0088] When the solvent contains other solvents, the proportion of such solvents relative to N-methyl-2-pyrrolidone, N,N-dimethylacetamide, or mixtures thereof is preferably set to 10% by mass or more and 50% by mass or less.

[0089] The above-mentioned step B is preferably performed by mixing the above-mentioned components under the conditions of a stirring time of 30 minutes or more and 180 minutes or less, and a stirring speed of 20 rpm or more and 500 rpm or less.

[0090] <Second Process>

[0091] The aforementioned process of applying insulating varnish to the outer peripheral surface of the conductor (the second process) involves applying the prepared varnish to the outer peripheral surface of the conductor. The coating method is not particularly limited, and conventionally known coating methods can be used. For example, when using a coating mold with an opening, the varnish can be applied with a uniform thickness, and the surface of the applied varnish can be smooth.

[0092] <Third Process>

[0093] The aforementioned process of baking the insulating varnish onto the conductor (the third process) is a process of forming an insulating layer through baking. Specifically, the conductor coated with varnish is placed in a baking oven, and the varnish is baked. The process of baking the insulating varnish onto the conductor (the third process) is preferably performed under conditions of 300°C or higher and 700°C or lower, and for 0.1 minutes or higher and 5 minutes or lower.

[0094] The above method is used to manufacture an insulated wire having a conductor and an insulating layer covering the conductor. It should be noted that the second and third steps described above can be repeated until the insulating layer laminated onto the surface of the conductor reaches a specified thickness.

[0095] Example

[0096] The following description is based on specific embodiments of the present disclosure, but the present invention is not limited to the following embodiments.

[0097] Manufacturing of Insulated Wires

[0098] The insulated wires of Examples 1 to 7, Comparative Example 1, and Comparative Example 2 were manufactured in the following manner. First, a conductor with an average diameter of 1 mm (metal type: copper) was prepared (Step A). ​​Next, the acid dianhydride and diamine compound shown in Table 1 were dissolved in N-methyl-2-pyrrolidone, and the two were reacted to obtain a polyimide precursor solution (resin solution) with a concentration of 25 wt%. A first filler with a primary particle size of 0.03 μm and being silica was dispersed in the resin solution at 20 wt% relative to the polyimide precursor (resin solid component) to prepare an insulating varnish (Step B). Next, the insulating varnish was applied to the outer peripheral surface of the conductor using a coating mold, thereby manufacturing a conductor coated with insulating varnish (Step 2). Next, the conductor coated with insulating varnish was placed in a baking oven and baked at 450°C for 90 seconds (Step 3). By repeating the second and third steps a predetermined number of times, an insulating layer with the thickness (μm) of the insulating layer shown in Table 1 (measured by the method described above) was formed, and an insulated wire was manufactured. By performing the above steps, insulated wires of Examples 1 to 4, Example 7, Comparative Example 1, and Comparative Example 2 with the configuration shown in Table 1 were manufactured. Furthermore, in step B above, the insulated wire of Example 5 was manufactured by changing the mol% of the dianhydride as shown in Table 1 and dispersing the first filler in the resin solution at 10% by mass relative to the polyimide precursor (resin solid component), except that the same steps as in Example 3 were performed. Furthermore, in step B above, the insulated wire of Example 6 was manufactured by dispersing the first filler in the resin solution at 15% by mass relative to the polyimide precursor (resin solid component) and changing the thickness (μm) of the insulating layer (measured by the method described above) as shown in Table 1, except that the same steps as in Example 5 were performed.

[0099] Determination of the ratio of the mass of the first filler to the mass of the insulating layer

[0100] For the insulated wires of Examples 1 to 7, Comparative Examples 1 and 2, the ratio of the mass of the first filler to the mass of the insulation layer was determined by the method described above. The results are recorded in the "Ratio of the mass of the first filler to the mass of the insulation layer (%)" item of Table 1.

[0101] Determination of secondary particle area occupancy (%) and secondary particle area occupancy (%) with particle size of 0.2–1 μm

[0102] For the insulated wires of Examples 1 to 7, Comparative Examples 1 and 2, the secondary particle area occupancy (%) and the secondary particle area occupancy (%) with a particle size of 0.2 to 1 μm were determined by the above method. The results were recorded in the "Secondary Particle Area Occupancy (%)" item and the "Secondary Particle Area Occupancy (%) with a Particle Size of 0.2 to 1 μm" item of Table 1, respectively.

[0103] Surge Resistance Test

[0104] For the insulated wires of Examples 1 to 7, Comparative Examples 1 and 2, surge resistance tests were conducted according to the following procedure. Specifically, stranded wire samples, consisting of two insulated wires twisted together, were manufactured and evaluated according to the methods specified in JISC 3003 and IEC 60851-5. It should be noted that the detailed test conditions are as follows.

[0105] (Experimental conditions)

[0106] Waveform: Rectangular wave

[0107] • Frequency: 20kHz

[0108] Voltage: 1500V

[0109] • Atmosphere temperature: 155℃

[0110] Here, durability time refers to the time from insulation breakdown between the two stranded wires (insulated wires) to a short circuit during the durability test under the above test conditions. A longer durability time indicates better surge resistance of the insulated wire. Furthermore, in this test, insulated wires with a durability time of 45 hours or more are defined as having good surge resistance. The test results are shown in Table 1.

[0111] [Table 1]

[0112]

[0113] The abbreviations in Table 1 above are as follows.

[0114] PMDA: Pyromellitic dianhydride

[0115] BPDA: 3,3',4,4'-Biphenyltetracarboxylic dianhydride

[0116] ODA: 4,4'-Oxydianiline

[0117] As shown in Table 1, the insulated wires of Examples 1 to 7 exhibit superior surge resistance compared to the insulated wires of Comparative Examples 1 and 2. It should be noted that the filler used in the insulated wires of Examples 1 to 7, Comparative Examples 1 and 2 is only silica. However, since both alumina and silica are highly insulating particles, it is anticipated that the same effect will be achieved when silica is replaced with alumina, or when silica and alumina are combined.

[0118] ATF Resistance Test

[0119] For the insulated wires of Examples 1 to 7, Comparative Examples 1 and 2, an ATF resistance test was conducted according to the following procedure: The winding samples were immersed in ATF oil containing 0.5% by mass water in a sealed SUS container, heated at 150°C for 1000 hours in a sealed state, and then the winding samples were removed to evaluate whether cracks had formed in the coating. The results are shown in Table 1.

[0120] As can be seen from the results in Table 1, the insulated wires of Examples 2 to 6 have ATF resistance of the same excellent degree as those of Comparative Examples 1 and 2.

[0121] The embodiments and examples of the present invention have been described above, but it is initially intended that the above-described embodiments and examples be appropriately combined.

[0122] The embodiments and examples disclosed herein should be considered exemplary rather than limiting in all respects. The scope of the invention is not shown by the foregoing description but by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0123] Explanation of reference numerals in the attached figures

[0124] 1: Resin; 2: Primary particle (first filler); 3: Secondary particle (first filler); 10: Insulated wire; 11: Conductor; 12: Insulation layer; D1: Distance between the two furthest points on the outer contour of a secondary particle in the cross-section of the insulated wire.

Claims

1. An insulated wire comprising: a conductor; and an insulating layer covering the conductor, wherein, The insulating layer comprises resin and a first filler. The resin comprises a polyimide, which is a polymer of an acid dianhydride and a diamine compound, wherein the acid dianhydride is either or both of pyromellitic dianhydride and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, and the diamine compound is 4,4'-oxodiphenylamine. The first filler exists in the form of primary particles or secondary particles composed of a plurality of said primary particles. The primary particles are silicon dioxide or aluminum oxide. The secondary particles have a particle size of 0.03 μm or larger and 5 μm or smaller. In the cross-section of the insulated wire, the total area of ​​the secondary particles relative to the sum of the total area of ​​the primary particles and the total area of ​​the secondary particles is 50% or more.

2. The insulated wire according to claim 1, wherein, In the cross-section, the total area of ​​the secondary particles with a particle size of 0.2 μm or more and 1 μm or less is 30% or more of the total area of ​​the secondary particles.

3. The insulated wire according to claim 1 or 2, wherein, The mass ratio of the first filler to the mass of the insulating layer is more than 5% and less than 30%.

4. The insulated wire according to claim 1, wherein, The acid dianhydride is composed of the pyromellitic dianhydride and the 3,3',4,4'-biphenyltetracarboxylic acid dianhydride. The acid dianhydride contains more than 10 mol% and less than 50 mol% of the pyromellitic dianhydride. Furthermore, it contains 50 mol% to 90 mol% of the 3,3',4,4'-biphenyltetracarboxylic acid dianhydride.

5. A method for manufacturing an insulated wire, comprising the following steps as described in any one of claims 1 to 4: The first step is to prepare the conductor and insulating varnish; The second step is to coat the outer peripheral surface of the conductor with the insulating varnish. as well as The third step involves baking the insulating varnish onto the conductor. The first process includes: process A, preparing the conductor; and process B, preparing the insulating varnish. In step B, the insulating varnish is prepared by mixing a solvent, the first filler, and the resin or its resin precursor. The solvent is N-methyl-2-pyrrolidone, N,N-dimethylacetamide, or a mixture thereof. In the first filler, the particle size of the primary particles is greater than 0.01 μm and less than 0.1 μm.

6. The method for manufacturing an insulated wire according to claim 5, wherein, The third process is performed under conditions of above 300°C and below 700°C, and for more than 0.1 minutes and less than 5 minutes.

7. The method for manufacturing an insulated wire according to claim 5 or 6, wherein, The concentration of the resin solids in the insulating varnish is 10% by mass or more and 40% by mass or less.

8. The method for manufacturing an insulated wire according to claim 5 or 6, wherein, The mass ratio of the first filler in the insulating varnish to the mass of the resin solids is more than 5% and less than 35%.

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