Stranded wire

Abstract

A stranded wire (10) according to the present invention is obtained by twisting together a plurality of insulated electrical wires (11), each having a conductor (12) and a coating layer (13) that coats the conductor (12), wherein the coating layer (13) includes a polyimide resin, the proportion of benzene rings in the polyimide resin is 60.5 mass% or more, and the thickness of the coating layer (13) is in the range of 0.005-0.020 mm.

Description

twisted wire

[0001] The present invention relates to a stranded wire.

[0002] Conventionally, insulated wires (enameled wires) have been used as windings for motors and coils. Recently, to reduce eddy current loss caused by magnetic flux linkages in a conductor, stranded wires, in which multiple insulated wires are twisted together, have been used as windings. An insulated wire has a conductor and an insulating layer that coats the conductor. Known insulated wires are those in which polyimide is primarily used as the material for the insulating layer (see, for example, Patent Document 1).

[0003] Patent Document 1 describes an insulated wire having a conductor and an insulating layer coating the conductor. The insulating layer of the insulated wire described in Patent Document 1 is formed by applying a polyimide resin varnish to the conductor and baking it. The polyimide resin varnish contains an aromatic tetracarboxylic acid dihydrate, an aromatic diamine, and an end-capping agent. The insulated wire described in Patent Document 1 is produced by adjusting the content of the end-capping agent in the polyimide resin varnish to shorten the synthesis reaction time.

[0004] JP 2013-28695 A

[0005] When a stranded wire made by twisting together the insulated wires described in Patent Document 1 is used as a motor winding, the thinner the insulating layer covering the conductor, the higher the space factor of the insulated wire, which is advantageous in terms of improving motor performance. Because a stranded wire has multiple insulated wires (element wires) compared to a solid wire, reducing the thickness of the insulating layer has a significant effect on improving the space factor. On the other hand, reducing the thickness of the insulating layer reduces the long-term heat resistance of the insulated wire (stranded wire).

[0006] An object of the present invention is to provide a stranded wire that can ensure a high space factor and high heat resistance.

[0007] In order to solve the above-mentioned problems, according to one aspect of the present invention, there is provided a twisted wire obtained by twisting together a plurality of insulated wires, each of which has a conductor and a coating layer coating the conductor, wherein the coating layer contains a polyimide resin, the proportion of benzene rings in the polyimide resin is 60.5 mass % or more, and the thickness of the coating layer is within a range of 0.005 to 0.020 mm.

[0008] According to the present invention, a stranded wire that can ensure a high space factor and high heat resistance can be provided.

[0009] 1A to 1C are schematic cross-sectional views of a stranded wire and an insulated wire, and FIGS. 2A and 2B are diagrams showing examples of the structure of polyimide resin.

[0010] A stranded wire according to one embodiment of the present invention will be described below. The stranded wire is a winding that can be used for coils in electromagnetic circuits, various motors, reactors, etc. In this specification, when a numerical range is indicated by "to", the lower limit and upper limit are included in the numerical range.

[0011] (Stranded Wire Structure) FIG. 1A is a schematic diagram of a cross section of a stranded wire, FIG. 1B is a schematic diagram of a cross section of an insulated wire having a circular cross section, and FIG. 1C is a schematic diagram of a cross section of an insulated wire having a rectangular cross section.

[0012] 1A, the stranded wire 10 has a plurality of insulated wires 11 each having a conductor 12 coated with a coating layer 13. The stranded wire 10 has a plurality of insulated wires 11 twisted in one direction.

[0013] The insulated wire 11 has a conductor 12 and a coating layer 13 that coats the conductor 12 .

[0014] The conductor 12 is similar to the conductor in a conventional insulated wire and is made of a metal with high electrical conductivity. Examples of the metal include copper, aluminum, copper alloys, and aluminum alloys. In the present embodiment, the conductor 12 is a copper wire. The copper in the copper wire may be a tough pitch material, but low-oxygen copper with an oxygen content of 30 ppm or less is preferred, low-oxygen copper or oxygen-free copper (MiDIP (registered trademark)) with an oxygen content of 20 ppm or less is more preferred, and oxygen-free copper with an oxygen content of 10 ppm or less is even more preferred. If the copper is low-oxygen copper or oxygen-free copper, voids that cause electrical resistance are less likely to occur when the conductors 12 of multiple insulated wires 11 are welded together. Furthermore, when a high current value is required for the insulated wire 11, the conductor 12 is preferably made of pure aluminum with a high purity (e.g., 99.00% or higher).

[0015] The cross-sectional shape and size of the conductor 12 are appropriately selected depending on the application. The cross-sectional shape of the conductor 12 may be circular (see FIG. 1B), rectangular (see FIG. 1C), or other polygonal shapes. Furthermore, when the cross-sectional shape of the conductor 12 is circular, the diameter is typically about 0.3 mm or more and 3.0 mm or less. When the cross-sectional shape of the conductor 12 is rectangular, the long side is about 0.2 mm or more and 5.0 mm or less, and the short side is about 0.1 mm or more and 3.0 mm or less. When the cross-section is rectangular, the corners may or may not be chamfered.

[0016] The coating layer 13 coats the conductors 12 and insulates the conductors 12 from each other. The coating layer 13 contains a polyimide resin. In this embodiment, the polyimide resin is a resin obtained by polycondensation of an aromatic tetracarboxylic acid contained in the varnish with an aromatic diamine. That is, the coating layer 13 is preferably made of an aromatic polyimide resin. The coating layer 13 may have a single-layer structure or a multi-layer structure. In this embodiment, the coating layer 13 has a single-layer structure. Note that when the coating layer 13 has a multi-layer structure, the polyimide resin may be contained in the inner coating, the outer coating, or both the inner and outer coatings.

[0017] The proportion of benzene rings in the polyimide resin is 60.5% by mass or more, preferably 64.0% by mass or less, and more preferably in the range of 61.0 to 63.5% by mass. If the proportion of benzene rings is less than 60.5% by mass, sufficient heat resistance cannot be ensured. If the proportion of benzene rings is more than 64.0% by mass, the coating layer 13 becomes rigid and easily oriented, which may cause crazing.

[0018] The proportion of components other than benzene rings and imide groups in the polyimide resin is preferably 6% by mass or less. The lower limit of the proportion of components other than benzene rings and imide groups in the polyimide resin is not particularly limited, but is, for example, 3.7% by mass or more. Components other than benzene rings and imide groups in the polyimide resin include alkyl groups, ketone groups, and ether groups. If the proportion of components other than benzene rings and imide groups in the polyimide resin exceeds 6% by mass, solvents and the like may easily penetrate into microvoids formed between molecules in the coating layer 13, which may result in crazing. In particular, if the proportion of polar groups such as ketone groups as components other than benzene rings and imide groups in the polyimide resin increases, crazing may become more likely to occur.

[0019] The proportion of benzene rings in a polyimide resin and the proportion of components other than benzene rings and imide groups in a polyimide resin can be measured by a known method. For example, a sample (polyimide resin) is heated together with an organic alkali (solvent), and then each monomer of the alkali-hydrolyzed components is identified using a gas chromatograph mass spectrometer (GC-MS). Note that instead of GC-MS, proton nuclear magnetic resonance ( １ H-NMR), carbon nuclear magnetic resonance ( １３ Next, the sample is subjected to Fourier transform infrared spectrophotometric measurement using a tablet method using KBr or an attenuated total reflectance (ATR) method, and the ratio of each monomer is identified and calculated from the peak ratio of the measurement results. For example, in the case of PMDA and BPDA, the peak ratio at 720 cm －１ and 740 cm －１ The ratio is calculated from the peak ratio. The ratio of each composition of aromatic tetracarboxylic acid (PMDA) and diamine (BPDA) is calculated, and the mass is calculated using atomic weights of C: 12, H: 1, O: 16, and N: 14. The mass ratio of each functional group is calculated from the total mass, and this is taken as the mass % of the functional group. The molar ratio of aromatic tetracarboxylic acid to diamine is 1:1.

[0020] FIG. 2A shows the structure of a portion of a polyimide resin obtained by reacting pyromellitic dianhydride with 2,2-bis[4-(4-aminophenoxy)phenyl]propane, and FIG. 2B shows the structure of a portion of a polyimide resin obtained by reacting 3,3',4,4'-benzophenonetetracarboxylic dianhydride with 4,4'-diaminodiphenyl ether.

[0021] The benzene ring in the polyimide resin is region A surrounded by a dotted line in Figures 2A and 2B. The imide group in the polyimide resin is region B surrounded by a dotted line in Figures 2A and 2B. The alkyl group in the polyimide resin is region C surrounded by a dotted line in Figures 2A and 2B. The ketone group in the polyimide resin is region D surrounded by a dotted line in Figures 2A and 2B. The ether group in the polyimide resin is region E surrounded by a dotted line in Figures 2A and 2B.

[0022] The coating layer 13 is a cured film obtained by applying and baking a varnish, which will be described later in the manufacturing method. The varnish contains an aromatic tetracarboxylic acid and a diamine.

[0023] Examples of aromatic tetracarboxylic acids include 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 3,3',4,4'-biphenylethertetracarboxylic dianhydride (OPDA), 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride (DSDA), bicyclo(2,2,2)-oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BCD), 1,2,4,5-cyclohexenetetracarboxylic dianhydride (CCD ... Examples of suitable dianhydrides include hexanetetracarboxylic dianhydride (H-PMDA), pyromellitic dianhydride (PMDA), 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride (CP), 4,4'-[propane-2,2-diylbis(1,4-phenyleneoxy)]diphthalic dianhydride (BISDA), and 4,4'-oxydiphthalic anhydride (ODPA).

[0024] From the viewpoints of availability and safety, the aromatic tetracarboxylic acid is preferably PMDA, BPDA, or BTDA. One type of aromatic tetracarboxylic acid may be used alone, or two or more types may be used in combination.

[0025] Examples of diamines include p-phenylenediamine, m-phenylenediamine, silicone diamine, bis(3-aminopropyl)etherethane, 3,3'-diamino-4,4'-dihydroxydiphenyl sulfone (SO2-HOAB), 4,4'-diamino-3,3'-dihydroxybiphenyl (HOAB), 4,4'-diaminodiphenyl ether (ODA), 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HOCF3AB), siloxane diamine, bis(3-aminopropyl)etherethane, N,N- bis(3-aminopropyl)ether, 1,4-bis(3-aminopropyl)piperazine, isophoronediamine, 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,These include 3'-dimethoxybiphenyl (CH3OAB), 4,4'-diamino-3,3'-dimethylbiphenyl (CH3AB), and 9,9'-bis(4-aminophenyl)fluorene (FDA).

[0026] From the viewpoints of availability and safety, the diamine is preferably ODA or BAPP. One type of diamine may be used alone, or two or more types may be used in combination.

[0027] In addition to the components described above, the varnish may contain other components as long as the purpose and effects of the present embodiment are not impaired. Examples of other components include solvents, other resins, pigments, dyes, and various additives.

[0028] The solvent disperses the aromatic tetracarboxylic acid and the diamine uniformly. Examples of the solvent include aprotic polar organic solvents such as N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and γ-butyrolactone. One type of solvent may be used alone, or multiple types may be used in combination.

[0029] Examples of the other resins include polyvinyl formal resin, polyurethane resin, polyester resin, polyesterimide resin, and polyamideimide resin. One type of the other resins may be used alone, or two or more types may be used in combination.

[0030] The thickness of the coating layer 13 is appropriately selected depending on the application of the insulated wire 11, but is within the range of 0.005 mm to 0.020 mm, preferably 0.005 to 0.015 mm, and more preferably 0.007 to 0.013 mm. If the thickness of the coating layer 13 is less than 0.005 mm, heat resistance may be poor. If the thickness of the coating layer 13 exceeds 0.020 mm, the area of ​​the coating increases, resulting in a reduced space factor. Here, the thickness of the coating layer 13 refers to the minimum local coating thickness in any cross section as shown in Figures 1A and 1C, and is the shortest distance connecting the conductor 12 and the air in contact with each insulated wire 11.

[0031] The content ratio of aromatic tetracarboxylic acid to diamine in the varnish is not particularly limited as long as the proportion of benzene rings in the polyimide resin and the proportion of components other than benzene rings and imide groups in the polyimide resin are within the above-mentioned ranges, and is preferably within the range of 98:100 to 100:100, and more preferably 100:100. The proportion of benzene rings in the polyimide resin assumed to be formed by condensation polymerization of aromatic tetracarboxylic acid and diamine in the varnish is approximately the same as the proportion of benzene rings in the actual condensation-polymerized polyimide resin. Therefore, by adjusting the contents of aromatic tetracarboxylic acid and diamine in the varnish, the proportions of components such as benzene rings, alkyl groups, ketone groups, and ether groups in the polyimide resin can be easily adjusted.

[0032] The number of insulated wires 11 in the stranded wire 10 is not particularly limited as long as it is plural. The number of insulated wires 11 is, for example, in the range of 6 to 100, and preferably in the range of 6 to 16. If the number of insulated wires 11 is 5 or less, the cross-sectional area of ​​each insulated wire 11 becomes large to maintain the current amount, resulting in increased eddy current loss due to interlinkage magnetic flux. On the other hand, if the number of insulated wires 11 is 100 or more, workability decreases. Note that a number of 16 or less insulated wires 11 is preferable from the viewpoints of reduced AC resistance, a high space factor, and eddy current loss. In this embodiment, the number of insulated wires 11 is 10.

[0033] The twist pitch of the stranded wire 10 is not particularly limited. For example, the twist pitch of the stranded wire 10 is within a range of 10 to 39 times the maximum length in a cross section (transverse cross section) perpendicular to the extension direction of the multiple insulated wires 11. If the twist pitch of the stranded wire 10 is less than 10 times the maximum length, the twist will be too tight, which may result in breakage during the manufacture of the stranded wire 10. On the other hand, if the twist pitch of the stranded wire 10 is more than 30 times the maximum length, some insulated wires 11 may separate from the other insulated wires 11, causing the shape of the stranded wire 10 to become distorted.

[0034] (Method of Manufacturing Stranded Wire) First, prepare the above-described conductor 12. The conductor 12 may be manufactured by any known method, and may be adjusted to a desired shape and size by wire drawing.

[0035] On the other hand, a varnish containing an aromatic tetracarboxylic acid and an aromatic diamine is prepared, and the types and contents of the aromatic tetracarboxylic acid and the aromatic diamine contained in the varnish are appropriately set so that the proportion of benzene rings in the polyimide resin of the coating layer 13 is 60.5 mass% or more.

[0036] The method for preparing the varnish is not particularly limited. For example, an aromatic tetracarboxylic acid and an aromatic diamine may be mixed together, or a solvent may be added to the aromatic tetracarboxylic acid and the aromatic diamine, and the aromatic tetracarboxylic acid and the aromatic diamine may be uniformly dispersed in the solvent.

[0037] Next, varnish is applied around the conductor 12. The varnish can be applied by a known method. Examples of methods for applying varnish include a method in which the conductor 12 is inserted into a die having an opening that is slightly larger than the cross section of the conductor 12 and has a shape that is approximately similar to the cross section of the conductor 12, and the varnish is applied inside the die while the conductor 12 is moved in one direction.

[0038] Next, the varnish is baked onto the conductor 12. The method for baking the varnish is not particularly limited, and can be any known method. Examples of the method for baking the varnish include a method of heating in a vertical furnace and a method of heating in a horizontal furnace. The baking temperature and baking time are appropriately selected depending on the components in the varnish.

[0039] The thickness of the film formed by one application and baking of varnish is preferably 0.001 mm or more and 0.006 mm or less, and it is preferable to apply and bake the varnish multiple times until the desired thickness is achieved to form the coating layer 13. The insulated wire 11 is obtained by the above steps.

[0040] Finally, a plurality of the obtained insulated wires 11 are twisted together to obtain a twisted wire 10.

[0041] (Effects) As described above, according to the stranded wire of the present invention, the proportion of benzene rings in the polyimide resin of the coating layer 13 of the insulated wire 11 is 60.5 mass % or more, and the thickness of the coating layer of the insulated wire 11 is within the range of 0.05 mm to 0.020 mm, so that heat resistance can be ensured even if the insulating layer is thin.

[0042] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited by these examples, and the embodiments can be modified without departing from the spirit of the present invention.

[0043] [Preparation of Stranded Wire] (Example 1) The stranded wire of Example 1 was prepared as follows. First, a copper wire with a diameter of 0.4 mm was prepared. Next, 0.60 mol of BPDA and 0.40 mol of PMDA were added as acid components, and 1.01 mol of ODA as a diamine component. 400 parts of N-methyl-2-pyrrolidone was added as a solvent to 100 parts of the acid and diamine components combined, and the resulting mixture was reacted to obtain the varnish of Example 1. A conductor was inserted into a die for applying the varnish, and while moving the conductor in one direction, the varnish was applied within the die and baked at 400°C. The application and baking of the varnish were repeated four times to obtain an insulated wire having a coating layer with a thickness of 0.005 mm. Ten of the resulting insulated wires were twisted together to obtain a twisted wire, with the twist being 15 times the maximum length of the cross section (transverse cross section) perpendicular to the extension direction of the insulated wires.

[0044] (Examples 2 to 13, Comparative Examples 1 to 6) The stranded wires of Examples 2 to 13 and Comparative Examples 1 to 6 were produced in the same manner as the stranded wire of Example 1, except that the content ratios of PMDA, BPDA, BTDA, ODA, and BAPP were set as shown in Table 1, and the film thickness of the coating layer was set as shown in Table 2.

[0045] The contents of the components of the varnish are shown in Table 1.

[0046]

[0047] [Evaluation of heat resistance] The evaluation was performed in accordance with the two-piece method described in Appendix JA.1.2 b) of JIS C 3216-5-2019. As a pretreatment, each stranded wire was left in a thermostatic chamber at 300°C for a specified number of days. The number of days for leaving the wire in the thermostatic chamber was one day if the film thickness was 0.005 mm or less, four days if the film thickness was 0.01 mm or less, and seven days if the film thickness was 0.011 mm or more. Heat resistance was evaluated according to the following criteria: ◯: 1 kV or more; ×: Less than 1 kV.

[0048] [Evaluation of Crazing Resistance] To evaluate crazing resistance, first, each stranded wire with a length of 350 mm was prepared and elongated by 3% using a tensile tester. Next, each elongated stranded wire was immersed in ethanol for 10 seconds. Finally, whether or not crazing occurred was visually inspected using a 15x magnifying glass. Crazing resistance was evaluated according to the following criteria: ∘: No crazing occurred. ×: Crazing occurred.

[0049] [Calculation of space factor] The cross-sectional area of ​​the conductor in the cross section of the produced stranded wire was measured using a microscope (Keyence Corporation). The cross-sectional area of ​​the conductor in the cross section of the stranded wire was taken as the average value when measurements were taken at three locations. The finished cross-sectional area of ​​the stranded wire in the cross section was calculated by approximating it to a circle based on the finished dimensions of the stranded wire. The space factor was calculated using the following formula: Space factor (%) = (total cross-sectional area of ​​conductor) / (cross-sectional area of ​​stranded wire) x 100 The calculation results of the space factor were evaluated according to the following criteria: ◎: 65% or more. ◯: 60% or more but less than 65%. ×: Less than 60%.

[0050] The proportions of benzene rings, imide groups, and other groups in the polyimide resin contained in the coating layer of each stranded wire, the thickness of the coating layer, and the evaluation results are shown in Table 2. The proportions of benzene rings, imide groups, and other groups in the polyimide resin are values ​​calculated from the content in the varnish. The percentages of each component are rounded off, so they do not necessarily add up to 100%.

[0051]

[0052] As shown in Tables 1 and 2, the stranded wires of Examples 1 to 13, in which the proportion of benzene rings in the polyimide resin was 60.5% by mass or more and the thickness of the insulated wire coating layer was within the range of 0.005 to 0.020 mm, exhibited good heat resistance and space factor. In particular, the stranded wires of Examples 1 to 8, in which the proportion of benzene rings in the polyimide resin was 64.0% by mass or less and the proportion of components other than benzene rings and imide groups in the polyimide resin was 6% by mass or less, also exhibited good crazing resistance.

[0053] On the other hand, as shown in Tables 1 and 2, the stranded wires of Comparative Examples 1, 3, and 4, in which the proportion of benzene rings in the polyimide resin was less than 60.5% by mass, exhibited poor heat resistance. This is thought to be because the proportion of benzene rings was low, making the bonds in the polyimide resin more susceptible to breaking. Furthermore, Comparative Examples 2 and 5, in which the coating layer thickness was outside the range of 0.005 to 0.020 mm, exhibited low space factors. Furthermore, Comparative Example 6, in which the coating layer thickness was less than 0.005 mm, exhibited poor heat resistance.

[0054] The stranded wire according to the present invention is useful, for example, as a winding used in an electromagnetic circuit or a motor.

[0055] 10 stranded wire 11 insulated wire 12 conductor 13 coating layer

Claims

1. A twisted wire formed by twisting together a plurality of insulated wires, each having a conductor and a coating layer coating the conductor, wherein the coating layer contains a polyimide resin, the proportion of benzene rings in the polyimide resin is 60.5 mass% or more, and the thickness of the coating layer is within the range of 0.005 mm to 0.020 mm.

2. A stranded wire according to claim 1, characterized in that the proportion of benzene rings in the polyimide resin is 64.0 mass % or less.

3. A stranded wire according to claim 1, characterized in that the proportion of components other than the benzene rings and imide groups in the polyimide resin is 6 mass % or less.

4. A stranded wire according to claim 1, characterized in that the thickness of the coating layer is within the range of 0.005 to 0.015 mm.

5. A stranded wire according to claim 3, characterized in that the components other than the benzene ring and the imide group include an alkyl group, a ketone group, or an ether group.

6. A stranded wire according to claim 1, characterized in that the coating layer is made of polyimide resin.

7. A stranded wire according to claim 3, characterized in that the proportion of components other than the benzene rings and the imide groups in the polyimide resin is 3.7 mass % or more.

8. A stranded wire according to claim 1, characterized in that the number of the plurality of insulated wires is within the range of 6 to 16.

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