Corona-resistant enameled stranded wire and method for manufacturing the same

Abstract

This invention relates to the field of enameled stranded wire technology, specifically to a corona-resistant enameled stranded wire and its preparation method. A corona-resistant enameled stranded wire is made of enameled wire stranded together, wherein the enameled wire includes a conductor core and a composite primer and a composite topcoat sequentially coated on the surface of the conductor core. This invention utilizes potassium perfluorobutoxybutane sulfonate to electrostatically adsorb and exchange ions between layered double hydroxide nanosheets, grafting long-chain fluoroalkyl groups onto the surface and interlayer of the layered double hydroxide nanosheets. Then, nano-alumina is uniformly loaded onto the modified layered double hydroxide nanosheets to form a binary composite filler. Adding this to the composite primer not only achieves uniform dispersion of the binary composite filler but also effectively improves the corona resistance of the composite primer when uniformly dispersed in it.

Description

Technical Field

[0001] This invention relates to the field of enameled stranded wire technology, specifically to a corona-resistant enameled stranded wire and its preparation method. Background Technology

[0002] Enamelled stranded wire, a conductor made of multiple strands of fine enamelled wire, is widely used in high-frequency transformers, new energy vehicle drive motors, wind turbine generators, and aerospace vehicles due to its excellent flexibility and resistance to bending fatigue.

[0003] Polyimide, due to its excellent heat resistance and electrical insulation properties, has become the preferred material for high-end enameled wire insulation. However, enameled wires made from pure polyimide have poor corona resistance and are prone to corona erosion under prolonged high-voltage conditions, leading to insulation aging and cracking, and significantly shortening equipment lifespan. Currently, existing technologies mainly modify polyimide by adding inorganic fillers such as alumina and silica to improve its corona resistance. However, inorganic fillers have poor compatibility with the polyimide matrix and are prone to agglomeration, which not only reduces the density of the coating but also makes it difficult to effectively improve its corona resistance.

[0004] Furthermore, traditional polyimide materials have high molecular chain rigidity and strong surface chemical inertness, resulting in weak interfacial bonding with copper conductors. Under thermal stress or external force, the enamel film is prone to peeling off, directly affecting the processing yield and long-term service stability of stranded wires. In addition, its inherent high coefficient of friction leads to high wear rate, which seriously affects its service life as a moving part or protective coating. When used as an internal current-carrying component, if the enameled wire itself does not have flame retardancy, it can easily become an ignition source or accelerant. Once electrical breakdown or short circuit occurs, the fire will spread rapidly, causing safety hazards.

[0005] Therefore, there is a need to propose a wear-resistant, flame-retardant, and corona-resistant enameled stranded wire with strong coating adhesion and its preparation method, so as to extend its service life and reduce safety hazards. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a corona-resistant enameled stranded wire and its preparation method.

[0007] This invention provides a corona-resistant enameled stranded wire, which is made of enameled wire stranded together. The enameled wire includes a conductor core and a composite primer and a composite topcoat sequentially coated on the surface of the conductor core. The preparation steps of the composite primer are as follows: Step 1: Add benzotriazole to concentrated sulfuric acid at 1-3℃ at a ratio of 1g:(6-8)mL, stir thoroughly to dissolve, add fuming nitric acid, and continue stirring for 3-4 hours. Then pour into crushed ice to precipitate the precipitate, and then filter, wash until neutral and vacuum dry to obtain nitrated benzotriazole. Step 2: Under nitrogen protection, the above-mentioned nitrated benzotriazole was added to anhydrous ethanol at a ratio of 1g:(12-13)mL, ultrasonically dispersed for 20-30min, then Pd / C catalyst with a mass fraction of 5% was added, stirred and mixed evenly, then hydrazine hydrate aqueous solution with a mass fraction of 85% was added, and the mixture was heated and refluxed at 70-80℃ for 5-6h. The catalyst was then removed by filtration, and activated carbon was added to the filtrate for decolorization by reflux for 30-40min. After filtration, the solution was concentrated under reduced pressure to 1 / 3 of the original volume, allowed to stand for crystallization for 3-4h, and then filtered, washed and vacuum dried to obtain the benzotriazole-based modifier. Step 3: Add 4,4′-diaminodiphenyl ether and the above-mentioned benzotriazole modifier to N,N-dimethylacetamide at a ratio of (9.8-10.2) g: 1 g: (170-180) mL, stir thoroughly to dissolve, then add the mixed dianhydride in 3-4 batches at 15-20℃, with an interval of 10-15 min between each batch, and then stir the reaction for 4-6 h to obtain the modified polyimide solution; Step 4: Add the binary composite filler to the above modified polyimide solution at a mass ratio of 1:(13-15), stir and mix thoroughly, and then degas under vacuum for 20-30 minutes to obtain the composite primer.

[0008] Furthermore, the amount of fuming nitric acid added is 18-20% of the volume of concentrated sulfuric acid.

[0009] Furthermore, the amount of Pd / C catalyst added is 3% of the mass of nitrated benzotriazole, and the molar ratio of hydrazine hydrate to nitrated benzotriazole is (2.8-3.2):1.

[0010] Furthermore, the mixed dianhydride is prepared by mixing pyromellitic dianhydride and diphenyl ether tetracarboxylic dianhydride at a mass ratio of 1:(2.3-2.5), and the ratio of the total molar amount of the mixed dianhydride to 4,4′-diaminodiphenyl ether and benzotriazole modifier is (0.98-1.02):1.

[0011] Furthermore, the preparation steps of the binary composite filler are as follows: Step 1: Add layered double hydroxide nanosheets to deionized water at a ratio of 1g:(80-90)mL, sonicate for 40-50min, then add 0.1mol / L dilute nitric acid to adjust the pH to 5-6 to obtain a layered double hydroxide nanosheet dispersion. Step 2: Add potassium perfluorobutoxybutane sulfonate at a ratio of 1g:(160-180)mL to a 50% ethanol solution and stir thoroughly until completely dissolved to obtain a potassium perfluorobutoxybutane sulfonate solution. Then add the potassium perfluorobutoxybutane sulfonate solution to the above layered double hydroxide nanosheet dispersion and stir for 3-4 hours to obtain a modified layered double hydroxide nanosheet dispersion. Step 3: Add nano-alumina to anhydrous ethanol at a ratio of 1g:(90-100)mL, and ultrasonically disperse for 30-40min to obtain a nano-alumina dispersion. Then add the nano-alumina dispersion to the above modified layered double hydroxide nanosheet dispersion, and heat and stir at 50-60℃ for 3-4h. After cooling, centrifuge, wash and vacuum dry to obtain the binary composite filler.

[0012] Furthermore, the mass ratio of layered double hydroxide nanosheets to potassium perfluorobutoxybutanesulfonate is 1:(0.2-0.3), and the mass ratio of modified layered double hydroxide nanosheets to nano-alumina is 1:(0.3-0.5).

[0013] Furthermore, the preparation steps of the composite topcoat are as follows: Step 1: Add toluene diisocyanate to anhydrous N,N-dimethylformamide at a ratio of 1g:(8-10)mL, stir thoroughly to dissolve, and obtain a toluene diisocyanate solution. Then add 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide to anhydrous N,N-dimethylformamide at a ratio of 1g:(3-5)mL, stir thoroughly to dissolve, and obtain a 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide solution. Step 2: Add the above 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide solution to the above toluene diisocyanate solution, then add dibutyltin dilaurate, heat and stir at 40-50℃ for 3-4 hours, cool, dropwise add petroleum ether for precipitation, then filter and vacuum dry to obtain the flame retardant modifier; Step 3: Add hexagonal boron nitride powder to a 30% hydrogen peroxide solution at a ratio of 1g:(180-200)mL, disperse ultrasonically for 30-40min, then hydrothermally react at 80-100℃ for 24-28h. After cooling, separate by centrifugation, wash and dry to obtain hydroxylated boron nitride powder. Step 4: Add the above hydroxylated boron nitride powder to a sodium hydroxide solution with a pH of 10-12 at a ratio of 1g:(150-160)mL, sonicate for 30-40min, stir for 1-2h, centrifuge at 2000-3000rpm for 9-10min, collect the supernatant, centrifuge at 9000-10000rpm for 4-6min, collect the precipitate and dry it to obtain hydroxylated boron nitride nanosheets; Step 5: Add the above hydroxylated boron nitride nanosheets to anhydrous N,N-dimethylformamide at a ratio of 1g:(60-70)mL, and ultrasonically disperse at 1-3℃ for 1-2h. Then, under nitrogen protection, add the above flame retardant modifier while stirring. After complete dissolution, add dibutyltin dilaurate and heat and stir at 40-50℃ for 6-8h. After cooling, centrifuge, wash 2-3 times with anhydrous ethanol, wash 2-3 times with acetone, and vacuum dry to obtain modified boron nitride nanosheets. Step 6: Add polyimide to N,N-dimethylacetamide at a ratio of 1g:(6-8)mL, heat and stir at 130-140℃, cool, add the above modified boron nitride nanosheets at 7.6-8.2g / L, stir and mix evenly, and degas under vacuum to obtain the composite topcoat.

[0014] Further, in step two, the molar ratio of 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide to toluene diisocyanate is 1:(2-2.2), and the amount of dibutyltin dilaurate added is 0.4-0.6% of the mass of 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide.

[0015] Furthermore, in step five, the mass ratio of the flame retardant modifier to the hydroxylated boron nitride nanosheets is (0.9-1.1):1, and the amount of dibutyltin dilaurate added is 0.5-0.6% of the mass of the hydroxylated boron nitride nanosheets.

[0016] Furthermore, a method for preparing a corona-resistant enameled stranded wire includes the following steps: Step 1: Apply the composite primer evenly to the surface of the conductor core material, cure it, then apply the composite topcoat evenly, and cure it again to obtain the enameled wire; Step 2: Twist the above enameled wires together, then coat the outer surface with a composite topcoat. After curing, you will get enameled stranded wire.

[0017] The present invention has the following advantages: 1. In this invention, a flame retardant modifier is generated by first reacting the isocyanate group of toluene diisocyanate with the phenolic hydroxyl group of 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide. Then, the isocyanate group at the end of the flame retardant modifier reacts with the hydroxyl groups on the surface of hydroxylated boron nitride nanosheets to graft the flame retardant modifier onto the boron nitride nanosheets, resulting in modified boron nitride nanosheets. These modified nanosheets are then added to polyimide to form a composite topcoat. Since the flame retardant modifier is an organophosphorus-nitrogen type prepolymer, it is grafted onto the boron nitride nanosheets via a reaction. After surface treatment, boron nitride nanosheets can be encapsulated by a layer of organic molecules, thereby achieving a high degree of matching between the surface properties of the modified boron nitride nanosheets and polyimide. This improves the dispersibility of boron nitride nanosheets in the polyimide matrix. The uniformly dispersed boron nitride nanosheets can form a wear-resistant skeleton in the composite topcoat, reducing the coefficient of friction and reducing paint film wear, thus improving the wear resistance of the enameled stranded wire. In addition, since the flame retardant modifier is grafted onto the surface of the boron nitride nanosheets, it can firmly lock the flame retardant units onto the boron nitride nanosheets, reducing their migration or precipitation, thereby improving the long-lasting flame retardancy of the composite topcoat.

[0018] 2. In this invention, long-chain fluoroalkyl groups are grafted onto the surface and interlayer of layered double hydroxide nanosheets by electrostatic adsorption and interlayer ion exchange using potassium perfluorobutoxybutane sulfonate, achieving a transformation from hydrophilic inorganic to hydrophobic organic modification. Then, strong hydrogen bonds and electrostatic interactions are formed with nano-alumina to uniformly load the modified layered double hydroxide nanosheets, forming a binary composite filler. After being added to a composite primer and organically modified with fluoroalkyl groups, the compatibility between the layered double hydroxide nanosheets and polyimide is effectively improved. Simultaneously, the nano-alumina is loaded onto the layered double hydroxide nanosheets... The above can prevent the stacking of layered double hydroxide nanosheets and the agglomeration of nano-alumina particles, thereby achieving uniform dispersion of binary composite fillers. When the binary composite fillers are uniformly dispersed in the composite primer, the layered double hydroxides can uniformly disperse the local concentrated electric field, block the extension of electric tree caused by corona discharge, and delay the breakdown of the paint film. Nano-alumina can adjust the dielectric constant of the primer, reduce the dielectric difference with the conductor core material, reduce electric field distortion, and reduce the corona arc initiation point from the source. Fluorine atoms can reduce the surface conductivity of the paint film, inhibit partial discharge and arc corrosion, and improve the corona resistance and arc resistance life, thereby effectively improving the corona resistance performance of the composite primer.

[0019] 3. In this invention, benzotriazole is used as a raw material to prepare a benzotriazole-based modifier through nitration and reduction reactions. Then, it is reacted with 4,4′-diaminodiphenyl ether, pyromellitic dianhydride, and diphenyl ether tetracarboxylic dianhydride to prepare a modified polyimide. Since the benzotriazole ring is rich in nitrogen atoms, it can form stable coordination bonds with metal ions on the conductor surface, forming a chemical adsorption layer at the metal interface. Moreover, the benzotriazole heterocycle has a rigid structure, which can improve the molecular cohesion of the polyimide without damaging the toughness of the coating film, thereby effectively improving the adhesion of the composite primer to the conductor core material surface. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating the preparation method of the corona-resistant enameled stranded wire used in an embodiment of the present invention. Detailed Implementation

[0021] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this invention.

[0022] Example 1: A method for preparing corona-resistant enameled stranded wire, such as... Figure 1 As shown, it includes the following steps: (1) Preparation of binary composite fillers: Step 1: Add zinc-aluminum layered double hydroxide nanosheets to deionized water at a ratio of 1g:80mL, sonicate for 40min, then add 0.1mol / L dilute nitric acid to adjust the pH to 5 to obtain a layered double hydroxide nanosheet dispersion. Step 2: Add potassium perfluorobutoxybutane sulfonate to a 50% ethanol solution at a ratio of 1g:160mL, and stir thoroughly until completely dissolved to obtain a potassium perfluorobutoxybutane sulfonate solution. Then, add the potassium perfluorobutoxybutane sulfonate solution to the above layered double hydroxide nanosheet dispersion and stir for 3 hours to obtain a modified layered double hydroxide nanosheet dispersion. The mass ratio of layered double hydroxide nanosheets to potassium perfluorobutoxybutane sulfonate is 1:0.2. Step 3: Add nano-alumina to anhydrous ethanol at a ratio of 1g:90mL, and ultrasonically disperse for 30min to obtain a nano-alumina dispersion. Then add the nano-alumina dispersion to the above modified layered double hydroxide nanosheet dispersion, heat and stir at 50℃ for 3h, cool, and centrifuge. Wash the precipitate with deionized water until neutral and free perfluorobutoxybutanesulfonate potassium residue is removed, then wash twice with anhydrous ethanol and vacuum dry to obtain a binary composite filler, wherein the mass ratio of modified layered double hydroxide nanosheets to nano-alumina is 1:0.3. (2) Preparation of composite primer: Step 1: Add benzotriazole to concentrated sulfuric acid at 1°C at a ratio of 1g:6mL, stir thoroughly to dissolve, add fuming nitric acid, and continue stirring for 3 hours. Then pour into crushed ice to precipitate the precipitate, filter, wash until neutral, and dry under vacuum to obtain nitrated benzotriazole. The amount of fuming nitric acid added is 18% of the volume of concentrated sulfuric acid. Step 2: Under nitrogen protection, the above-mentioned nitrated benzotriazole was added to anhydrous ethanol at a ratio of 1g:12mL, and ultrasonically dispersed for 20min. Then, a Pd / C catalyst with a Pd mass fraction of 5% was added, and the mixture was stirred and mixed evenly. Then, an aqueous solution of hydrazine hydrate with a mass fraction of 85% was added, and the mixture was heated and refluxed at 70℃ for 5h. The catalyst was then removed by filtration, and activated carbon was added to the filtrate for decolorization by reflux for 30min. The mixture was then filtered, concentrated under reduced pressure to 1 / 3 of the original volume, and allowed to stand for crystallization for 3h. After filtration, washing, and vacuum drying, the benzotriazole-based modifier was obtained. The amount of Pd / C catalyst added was 3% of the mass of nitrated benzotriazole, and the molar ratio of hydrazine hydrate to nitrated benzotriazole was 2.8:1. Step 3: Add 4,4′-diaminodiphenyl ether and the above-mentioned benzotriazole modifier to N,N-dimethylacetamide at a ratio of 9.8g:1g:170mL, stir thoroughly to dissolve, and then add the mixed dianhydride in 3 batches at 15℃, with an interval of 10min between each batch. Stir and react for 4h to obtain a modified polyimide solution. The mixed dianhydride is prepared by mixing pyromellitic dianhydride and diphenyl ether tetracarboxylic dianhydride at a mass ratio of 1:2.3, and the molar ratio of the mixed dianhydride to the total molar amount of 4,4′-diaminodiphenyl ether and benzotriazole modifier is 0.98:1. Step 4: Add the binary composite filler to the above modified polyimide solution at a mass ratio of 1:13, stir and mix thoroughly, and then degas under vacuum for 20 minutes to obtain the composite primer; (3) Preparation of composite topcoat: Step 1: Add toluene diisocyanate to anhydrous N,N-dimethylformamide at a ratio of 1g:8mL, stir thoroughly to dissolve, and obtain a toluene diisocyanate solution. Then add 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide to anhydrous N,N-dimethylformamide at a ratio of 1g:3mL, stir thoroughly to dissolve, and obtain a 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide solution. Step 2: The above solution of 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide was added to the above solution of toluene diisocyanate, and then dibutyltin dilaurate was added. The mixture was heated and stirred at 40°C for 3 hours. After cooling, petroleum ether was added dropwise for precipitation. After filtration and vacuum drying, the flame retardant modifier was obtained. The molar ratio of 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide to toluene diisocyanate was 1:2, and the amount of dibutyltin dilaurate added was 0.4% of the mass of 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide. Step 3: Add hexagonal boron nitride powder to a 30% hydrogen peroxide solution at a ratio of 1g:180mL, disperse ultrasonically for 30min, then hydrothermally react at 80℃ for 24h. After cooling, centrifuge, wash and dry to obtain hydroxylated boron nitride powder. Step 4: Add the above hydroxylated boron nitride powder to a sodium hydroxide solution with a pH of 10 at a ratio of 1g:150mL, sonicate for 30min, stir for 1h, centrifuge at 2000rpm for 9min, collect the supernatant, centrifuge at 9000rpm for 4min, collect the precipitate and dry it to obtain hydroxylated boron nitride nanosheets. Step 5: Add the above-mentioned hydroxylated boron nitride nanosheets to anhydrous N,N-dimethylformamide at a ratio of 1g:60mL, and ultrasonically disperse at 1℃ for 1h. Then, under nitrogen protection, add the above-mentioned flame retardant modifier while stirring. After complete dissolution, add dibutyltin dilaurate and heat and stir at 40℃ for 6h. After cooling, centrifuge, wash twice with anhydrous ethanol, wash twice with acetone, and vacuum dry to obtain modified boron nitride nanosheets. The mass ratio of flame retardant modifier to hydroxylated boron nitride nanosheets is 0.9:1, and the amount of dibutyltin dilaurate added is 0.5% of the mass of hydroxylated boron nitride nanosheets. Step 6: Add polyimide to N,N-dimethylacetamide at a ratio of 1g:6mL, heat and stir at 130℃, cool, add the above modified boron nitride nanosheets at 7.6g / L, stir and mix evenly, and degas under vacuum to obtain the composite topcoat; (4) Preparation of enameled stranded wire: Step 1: Apply the composite primer evenly to the surface of the conductor core material, cure it, then apply the composite topcoat evenly, and cure it again to obtain the enameled wire; Step 2: Twist the above enameled wires together, then coat the outer surface with a composite topcoat. After curing, you will get enameled stranded wire.

[0023] Example 2, a method for preparing corona-resistant enameled stranded wire, such as... Figure 1 As shown, it includes the following steps: (1) Preparation of binary composite fillers: Step 1: Add zinc-aluminum layered double hydroxide nanosheets to deionized water at a ratio of 1g:85mL, sonicate for 45min, then add 0.1mol / L dilute nitric acid to adjust the pH to 5.5 to obtain a layered double hydroxide nanosheet dispersion. Step 2: Add potassium perfluorobutoxybutane sulfonate to a 50% ethanol solution at a ratio of 1g:170mL, and stir thoroughly until completely dissolved to obtain a potassium perfluorobutoxybutane sulfonate solution. Then, add the potassium perfluorobutoxybutane sulfonate solution to the above layered double hydroxide nanosheet dispersion and stir for 3.5h to obtain a modified layered double hydroxide nanosheet dispersion. The mass ratio of layered double hydroxide nanosheets to potassium perfluorobutoxybutane sulfonate is 1:0.25. Step 3: Add nano-alumina to anhydrous ethanol at a ratio of 1g:95mL, and ultrasonically disperse for 35min to obtain a nano-alumina dispersion. Then add the nano-alumina dispersion to the above modified layered double hydroxide nanosheet dispersion, heat and stir at 55℃ for 3.5h, cool, and centrifuge. Wash the precipitate with deionized water until neutral and free perfluorobutoxybutanesulfonate potassium residue is removed, then wash twice with anhydrous ethanol and vacuum dry to obtain a binary composite filler, wherein the mass ratio of modified layered double hydroxide nanosheets to nano-alumina is 1:0.4. (2) Preparation of composite primer: Step 1: Add benzotriazole to concentrated sulfuric acid at 2℃ at a ratio of 1g:7mL, stir thoroughly to dissolve, add fuming nitric acid, and continue stirring for 3.5h. Then pour into crushed ice to precipitate the precipitate, filter, wash until neutral and vacuum dry to obtain nitrated benzotriazole. The amount of fuming nitric acid added is 19% of the volume of concentrated sulfuric acid. Step 2: Under nitrogen protection, the above-mentioned nitrated benzotriazole was added to anhydrous ethanol at a ratio of 1g:12.5mL, and ultrasonically dispersed for 25min. Then, a Pd / C catalyst with a Pd mass fraction of 5% was added, and the mixture was stirred and mixed evenly. Then, an aqueous solution of hydrazine hydrate with a mass fraction of 85% was added, and the mixture was heated and refluxed at 75℃ for 5.5h. The catalyst was then removed by filtration, and activated carbon was added to the filtrate for decolorization by reflux for 35min. The mixture was then filtered, concentrated under reduced pressure to 1 / 3 of the original volume, and allowed to stand for crystallization for 3.5h. After filtration, washing, and vacuum drying, the benzotriazole-based modifier was obtained. The amount of Pd / C catalyst added was 3% of the mass of nitrated benzotriazole, and the molar ratio of hydrazine hydrate to nitrated benzotriazole was 3:1. Step 3: Add 4,4′-diaminodiphenyl ether and the above-mentioned benzotriazole modifier to N,N-dimethylacetamide at a ratio of 10g:1g:175mL, stir thoroughly to dissolve, and then add the mixed dianhydride in 3 batches at 17℃, with an interval of 13min between each batch. Then stir and react for 5h to obtain a modified polyimide solution. The mixed dianhydride is prepared by mixing pyromellitic dianhydride and diphenyl ether tetracarboxylic dianhydride at a mass ratio of 1:2.4, and the molar ratio of the mixed dianhydride to the total molar amount of 4,4′-diaminodiphenyl ether and benzotriazole modifier is 1:1. Step 4: Add the binary composite filler to the above modified polyimide solution at a mass ratio of 1:14, stir and mix thoroughly, and then degas under vacuum for 25 minutes to obtain the composite primer; (3) Preparation of composite topcoat: Step 1: Add toluene diisocyanate to anhydrous N,N-dimethylformamide at a ratio of 1g:9mL, stir thoroughly to dissolve, and obtain a toluene diisocyanate solution. Then add 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide to anhydrous N,N-dimethylformamide at a ratio of 1g:4mL, stir thoroughly to dissolve, and obtain a 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide solution. Step 2: The above 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide solution was added to the above toluene diisocyanate solution, and then dibutyltin dilaurate was added. The mixture was heated and stirred at 45°C for 3.5 h. After cooling, petroleum ether was added dropwise for precipitation. After filtration and vacuum drying, the flame retardant modifier was obtained. The molar ratio of 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide to toluene diisocyanate was 1:2.1, and the amount of dibutyltin dilaurate added was 0.5% of the mass of 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide. Step 3: Add hexagonal boron nitride powder to a 30% hydrogen peroxide solution at a ratio of 1g:190mL, disperse ultrasonically for 35min, then react hydrothermally at 90℃ for 26h. After cooling, centrifuge, wash and dry to obtain hydroxylated boron nitride powder. Step 4: Add the above hydroxylated boron nitride powder to a sodium hydroxide solution with pH 11 at a ratio of 1g:155mL, sonicate for 35min, stir for 1.5h, centrifuge at 2500rpm for 9.5min, collect the supernatant, centrifuge at 9500rpm for 5min, collect the precipitate and dry it to obtain hydroxylated boron nitride nanosheets. Step 5: Add the above-mentioned hydroxylated boron nitride nanosheets to anhydrous N,N-dimethylformamide at a ratio of 1g:65mL, and ultrasonically disperse at 2℃ for 1.5h. Then, under nitrogen protection, add the above-mentioned flame retardant modifier while stirring. After complete dissolution, add dibutyltin dilaurate and heat and stir at 45℃ for 7h. After cooling, centrifuge, wash twice with anhydrous ethanol, wash twice with acetone, and vacuum dry to obtain modified boron nitride nanosheets. The mass ratio of flame retardant modifier to hydroxylated boron nitride nanosheets is 1:1, and the amount of dibutyltin dilaurate added is 0.55% of the mass of hydroxylated boron nitride nanosheets. Step 6: Add polyimide to N,N-dimethylacetamide at a ratio of 1g:7mL, heat and stir at 135℃, cool, add the above modified boron nitride nanosheets at 7.9g / L, stir and mix evenly, and degas under vacuum to obtain the composite topcoat; (4) Preparation of enameled stranded wire: Step 1: Apply the composite primer evenly to the surface of the conductor core material, cure it, then apply the composite topcoat evenly, and cure it again to obtain the enameled wire; Step 2: Twist the above enameled wires together, then coat the outer surface with a composite topcoat. After curing, you will get enameled stranded wire.

[0024] Example 3: A method for preparing corona-resistant enameled stranded wire, such as... Figure 1 As shown, it includes the following steps: (1) Preparation of binary composite fillers: Step 1: Add zinc-aluminum layered double hydroxide nanosheets to deionized water at a ratio of 1g:90mL, sonicate for 50min, then add 0.1mol / L dilute nitric acid to adjust the pH to 6 to obtain a layered double hydroxide nanosheet dispersion; Step 2: Add potassium perfluorobutoxybutane sulfonate to a 50% ethanol solution at a ratio of 1g:180mL, and stir thoroughly until completely dissolved to obtain a potassium perfluorobutoxybutane sulfonate solution. Then, add the potassium perfluorobutoxybutane sulfonate solution to the above layered double hydroxide nanosheet dispersion and stir for 4 hours to obtain a modified layered double hydroxide nanosheet dispersion. The mass ratio of layered double hydroxide nanosheets to potassium perfluorobutoxybutane sulfonate is 1:0.3. Step 3: Add nano-alumina to anhydrous ethanol at a ratio of 1g:100mL, and ultrasonically disperse for 40min to obtain a nano-alumina dispersion. Then add the nano-alumina dispersion to the above modified layered double hydroxide nanosheet dispersion, heat and stir at 60℃ for 4h, cool, and centrifuge. Wash the precipitate with deionized water until neutral and free perfluorobutoxybutanesulfonate potassium residue is removed, then wash twice with anhydrous ethanol and vacuum dry to obtain a binary composite filler. The mass ratio of modified layered double hydroxide nanosheets to nano-alumina is 1:0.5. (2) Preparation of composite primer: Step 1: Add benzotriazole to concentrated sulfuric acid at 3℃ at a ratio of 1g:8mL, stir thoroughly to dissolve, add fuming nitric acid, and continue stirring for 4 hours. Then pour into crushed ice to precipitate the precipitate, filter, wash until neutral and vacuum dry to obtain nitrated benzotriazole. The amount of fuming nitric acid added is 20% of the volume of concentrated sulfuric acid. Step 2: Under nitrogen protection, the above-mentioned nitrated benzotriazole was added to anhydrous ethanol at a ratio of 1g:13mL, and ultrasonically dispersed for 30min. Then, a Pd / C catalyst with a Pd mass fraction of 5% was added, and the mixture was stirred and mixed evenly. Then, an aqueous solution of hydrazine hydrate with a mass fraction of 85% was added, and the mixture was heated and refluxed at 80℃ for 6h. The catalyst was then removed by filtration, and activated carbon was added to the filtrate for decolorization by reflux for 40min. The mixture was then filtered, concentrated under reduced pressure to 1 / 3 of the original volume, and allowed to stand for crystallization for 4h. After filtration, washing, and vacuum drying, the benzotriazole-based modifier was obtained. The amount of Pd / C catalyst added was 3% of the mass of nitrated benzotriazole, and the molar ratio of hydrazine hydrate to nitrated benzotriazole was 3.2:1. Step 3: Add 4,4′-diaminodiphenyl ether and the above-mentioned benzotriazole modifier to N,N-dimethylacetamide at a ratio of 10.2g:1g:180mL, stir thoroughly to dissolve, and then add the mixed dianhydride in 4 batches at 20℃, with an interval of 15min between each batch. Stir and react for 6h to obtain a modified polyimide solution. The mixed dianhydride is prepared by mixing pyromellitic dianhydride and diphenyl ether tetracarboxylic dianhydride at a mass ratio of 1:2.5, and the molar ratio of the mixed dianhydride to the total molar amount of 4,4′-diaminodiphenyl ether and benzotriazole modifier is 1.02:1. Step 4: Add the binary composite filler to the above modified polyimide solution at a mass ratio of 1:15, stir and mix thoroughly, and then degas under vacuum for 30 minutes to obtain the composite primer; (3) Preparation of composite topcoat: Step 1: Add toluene diisocyanate to anhydrous N,N-dimethylformamide at a ratio of 1g:10mL, stir thoroughly to dissolve, and obtain a toluene diisocyanate solution. Then add 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide to anhydrous N,N-dimethylformamide at a ratio of 1g:5mL, stir thoroughly to dissolve, and obtain a 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide solution. Step 2: The above 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide solution was added to the above toluene diisocyanate solution, and then dibutyltin dilaurate was added. The mixture was heated and stirred at 50°C for 4 hours. After cooling, petroleum ether was added dropwise for precipitation. After filtration and vacuum drying, the flame retardant modifier was obtained. The molar ratio of 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide to toluene diisocyanate was 1:2.2, and the amount of dibutyltin dilaurate added was 0.6% of the mass of 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide. Step 3: Add hexagonal boron nitride powder to a 30% hydrogen peroxide solution at a ratio of 1g:200mL, disperse ultrasonically for 40min, then react hydrothermally at 100℃ for 28h. After cooling, separate by centrifugation, wash and dry to obtain hydroxylated boron nitride powder. Step 4: Add the above hydroxylated boron nitride powder to a sodium hydroxide solution with pH 12 at a ratio of 1g:160mL, sonicate for 40min, stir for 2h, centrifuge at 3000rpm for 10min, collect the supernatant, centrifuge at 10000rpm for 6min, collect the precipitate and dry it to obtain hydroxylated boron nitride nanosheets. Step 5: Add the above-mentioned hydroxylated boron nitride nanosheets to anhydrous N,N-dimethylformamide at a ratio of 1g:70mL, and ultrasonically disperse at 3℃ for 2h. Then, under nitrogen protection, add the above-mentioned flame retardant modifier while stirring. After complete dissolution, add dibutyltin dilaurate and heat and stir at 50℃ for 8h. After cooling, centrifuge, wash three times with anhydrous ethanol, wash three times with acetone, and vacuum dry to obtain modified boron nitride nanosheets. The mass ratio of flame retardant modifier to hydroxylated boron nitride nanosheets is 1.1:1, and the amount of dibutyltin dilaurate added is 0.6% of the mass of hydroxylated boron nitride nanosheets. Step 6: Add polyimide to N,N-dimethylacetamide at a ratio of 1g:8mL, heat and stir at 140℃, cool, add the above modified boron nitride nanosheets at a ratio of 8.2g / L, stir and mix evenly, and degas under vacuum to obtain the composite topcoat; (4) Preparation of enameled stranded wire: Step 1: Apply the composite primer evenly to the surface of the conductor core material, cure it, then apply the composite topcoat evenly, and cure it again to obtain the enameled wire; Step 2: Twist the above enameled wires together, then coat the outer surface with a composite topcoat. After curing, you will get enameled stranded wire.

[0025] Comparative Example 1 differs from Example 1 in that the modified boron nitride nanosheets in step six of (3) are replaced with an equal amount of hydroxylated boron nitride nanosheets.

[0026] Comparative Example 2 differs from Example 1 in that the modified boron nitride nanosheets in step six of (3) are replaced with directly added boron nitride nanosheets and flame retardant modifier, wherein the mass ratio of flame retardant modifier to boron nitride nanosheets is 1.3:1.

[0027] Comparative Example 3 differs from Example 1 in that the binary composite filler in step four of (2) is removed.

[0028] Comparative Example 4 differs from Example 1 in that: the potassium perfluorobutoxybutane sulfonate solution in step two of (1) is removed to obtain a layered double hydroxide nanosheet-nano alumina mixture, and the binary composite filler in step four is replaced with an equal amount of the layered double hydroxide nanosheet-nano alumina mixture.

[0029] Comparative Example 5 differs from Example 1 in that the binary composite filler in step four of (2) is replaced with an equal amount of modified layered double hydroxide nanosheets. The modified layered double hydroxide nanosheets are obtained by centrifugation of the modified layered double hydroxide nanosheet dispersion prepared in step two of (1), collecting the precipitate, washing the precipitate with deionized water until it is neutral and free of fluoride ions, washing it twice with anhydrous ethanol, and then vacuum drying.

[0030] Comparative Example 6 differs from Example 1 in that the benzotriazole modifier in step 3 of (2) is replaced with an equimolar amount of 4,4′-diaminodiphenyl ether, i.e., no benzotriazole modifier is added.

[0031] Test example: Test 1: The friction coefficients of the enameled wires prepared in Examples 1-3 and Comparative Examples 1-2 were tested using a reciprocating friction and wear tester. Each test was repeated 3 times, and the average value of the results was taken, as shown in Table 1.

[0032] Table 1: Test Results of Friction Coefficient of Enamelled Wire coefficient of friction Example 1 0.22 Example 2 0.21 Example 3 0.19 Comparative Example 1 0.33 Comparative Example 2 0.30 As shown in Table 1, in Comparative Example 1, after replacing the modified boron nitride nanosheets in the composite topcoat with hydroxylated boron nitride nanosheets, the resulting enameled wire had a higher coefficient of friction than in Example 1. Similarly, in Comparative Example 2, after replacing the modified boron nitride nanosheets in the composite topcoat with directly added boron nitride nanosheets and a flame retardant modifier, the resulting enameled wire also had a higher coefficient of friction than in Example 1. This demonstrates that by first utilizing the isocyanate group of toluene diisocyanate and 10-(2,5-dihydroxyphenyl)-1... The phenolic hydroxyl groups of 0-hydro-9-oxa-10-phosphaphenanthrene-10-oxide undergo an addition reaction to generate a flame retardant modifier. Then, the isocyanate group at the end of the flame retardant modifier reacts with the hydroxyl groups on the surface of hydroxylated boron nitride nanosheets to graft the flame retardant modifier onto the boron nitride nanosheets, resulting in modified boron nitride nanosheets. When these modified boron nitride nanosheets are added to polyimide to form a composite topcoat, the dispersibility of boron nitride nanosheets in the polyimide matrix is ​​improved, thereby improving the abrasion resistance of enameled stranded wire.

[0033] Test 2: The initial limiting oxygen index and the limiting oxygen index after hot air aging at 150°C for 168 hours were tested for the enameled wires prepared in Examples 1-3 and Comparative Example 2, respectively. The flame retardant retention rate was calculated using the following formula: Flame retardant retention rate = Limiting oxygen index after aging in hot air at 150℃ for 168 hours / Initial limiting oxygen index × 100%. Each test was repeated 3 times, and the average value of the results was taken, as shown in Table 2.

[0034] Table 2: Test Results of Flame Retardancy Retention Rate of Enamelled Wire Flame retardant retention rate (%) Example 1 92.6 Example 2 92.8 Example 3 93.1 Comparative Example 2 81.3 As shown in Table 2, the flame retardant retention rate of the enameled wire prepared in Comparative Example 2 after aging in hot air at 150°C for 168 hours was lower than that in Example 1. This indicates that grafting the flame retardant modifier onto the surface of boron nitride nanosheets can firmly lock the flame retardant units onto the boron nitride nanosheets, reducing their migration or precipitation, thereby improving the long-lasting flame retardancy of the composite topcoat.

[0035] Test 3: A high-frequency pulse voltage tester was used to test the corona resistance of the composite primers prepared in Examples 1-3 and Comparative Examples 3-5 after curing. Test conditions: pulse frequency 20kHz, pulse duty cycle 50%, pulse voltage peak-to-peak value 2.5kV. Each test was repeated 3 times, and the average value was taken. The results are shown in Table 3.

[0036] Table 3: Test results of corona resistance of composite primer Corona resistance lifetime (h) Example 1 92.4 Example 2 93.1 Example 3 95.3 Comparative Example 3 34.8 Comparative Example 4 57.2 Comparative Example 5 76.5 As shown in Table 3, in Comparative Example 3, without the addition of binary composite filler, the corona resistance life of the prepared composite primer was much lower than that of Example 1. In Comparative Example 4, when layered double hydroxide nanosheets and nano-alumina were directly added, the corona resistance life of the prepared composite primer was higher than that of Comparative Example 3, but still lower than that of Example 1. In Comparative Example 5, when only modified layered double hydroxide nanosheets were added, the corona resistance life of the prepared composite primer was still lower than that of Example 1. It can be seen that by first using potassium perfluorobutoxybutane sulfonate to undergo electrostatic adsorption and interlayer ion exchange with layered double hydroxide nanosheets to graft long-chain fluoroalkyl groups onto the surface and interlayer of layered double hydroxide nanosheets, and then uniformly loading nano-alumina onto the modified layered double hydroxide nanosheets to form a binary composite filler, the uniform dispersion of the binary composite filler can be achieved after adding it to the composite primer, thereby effectively improving the corona resistance performance of the composite primer.

[0037] Test 4: The composite primers prepared in Examples 1-3 and Comparative Example 6 were applied to the surface of the copper plate, dried and cured to obtain sample coatings. The adhesion strength of the sample coatings was then tested according to GB / T 5210-2006. Each test was repeated 3 times and the average value was taken. The results are shown in Table 4.

[0038] Table 4: Adhesion strength test results of composite primer Adhesion strength (MPa) Example 1 3.8 Example 2 3.9 Example 3 4.1 Comparative Example 6 1.2 As shown in Table 4, the adhesion strength of the composite primer to the copper plate in Comparative Example 6 without the addition of benzotriazole modifier was significantly lower than that in Example 1. This shows that by using benzotriazole as a raw material, preparing a benzotriazole modifier through nitration and reduction reactions, and then reacting it with 4,4′-diaminodiphenyl ether, pyromellitic dianhydride and diphenyl ether tetracarboxylic dianhydride to prepare a modified polyimide, the adhesion of the composite primer to the conductor core material can be effectively improved.

[0039] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims. Parts not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A corona-resistant enameled stranded wire, characterized in that, It is made of enameled wire stranded together, wherein the enameled wire includes a conductor core and a composite primer and a composite topcoat sequentially coated on the surface of the conductor core; The preparation steps of the composite primer are as follows: Step 1: Add benzotriazole to concentrated sulfuric acid at 1-3℃ at a ratio of 1g:(6-8)mL, stir thoroughly to dissolve, add fuming nitric acid, and continue stirring for 3-4 hours. Then pour into crushed ice to precipitate the precipitate, and then filter, wash until neutral and vacuum dry to obtain nitrated benzotriazole. Step 2: Under nitrogen protection, the above-mentioned nitrated benzotriazole was added to anhydrous ethanol at a ratio of 1g:(12-13)mL, ultrasonically dispersed for 20-30min, then Pd / C catalyst with a mass fraction of 5% was added, stirred and mixed evenly, then hydrazine hydrate aqueous solution with a mass fraction of 85% was added, and the mixture was heated and refluxed at 70-80℃ for 5-6h. The catalyst was then removed by filtration, and activated carbon was added to the filtrate for decolorization by reflux for 30-40min. After filtration, the solution was concentrated under reduced pressure to 1 / 3 of the original volume, allowed to stand for crystallization for 3-4h, and then filtered, washed and vacuum dried to obtain the benzotriazole-based modifier. Step 3: Add 4,4′-diaminodiphenyl ether and the above-mentioned benzotriazole modifier to N,N-dimethylacetamide at a ratio of (9.8-10.2) g: 1 g: (170-180) mL, stir thoroughly to dissolve, then add the mixed dianhydride in 3-4 batches at 15-20℃, with an interval of 10-15 min between each batch, and then stir the reaction for 4-6 h to obtain the modified polyimide solution; Step 4: Add the binary composite filler to the above modified polyimide solution at a mass ratio of 1:(13-15), stir and mix thoroughly, and then degas under vacuum for 20-30 minutes to obtain the composite primer.

2. The corona-resistant enameled stranded wire according to claim 1, characterized in that, The amount of fuming nitric acid added is 18-20% of the volume of concentrated sulfuric acid.

3. The corona-resistant enameled stranded wire according to claim 1, characterized in that, The amount of Pd / C catalyst added is 3% of the mass of nitrated benzotriazole, and the molar ratio of hydrazine hydrate to nitrated benzotriazole is (2.8-3.2):

1.

4. The corona-resistant enameled stranded wire according to claim 1, characterized in that, The mixed dianhydride is prepared by mixing pyromellitic dianhydride and diphenyl ether tetracarboxylic dianhydride in a mass ratio of 1:(2.3-2.5), and the total molar ratio of the mixed dianhydride to 4,4′-diaminodiphenyl ether and benzotriazole modifier is (0.98-1.02):

1.

5. The corona-resistant enameled stranded wire according to claim 1, characterized in that, The preparation steps of binary composite fillers are as follows: Step 1: Add layered double hydroxide nanosheets to deionized water at a ratio of 1g:(80-90)mL, sonicate for 40-50min, then add 0.1mol / L dilute nitric acid to adjust the pH to 5-6 to obtain a layered double hydroxide nanosheet dispersion. Step 2: Add potassium perfluorobutoxybutane sulfonate at a ratio of 1g:(160-180)mL to a 50% ethanol solution and stir thoroughly until completely dissolved to obtain a potassium perfluorobutoxybutane sulfonate solution. Then add the potassium perfluorobutoxybutane sulfonate solution to the above layered double hydroxide nanosheet dispersion and stir for 3-4 hours to obtain a modified layered double hydroxide nanosheet dispersion. Step 3: Add nano-alumina to anhydrous ethanol at a ratio of 1g:(90-100)mL, and ultrasonically disperse for 30-40min to obtain a nano-alumina dispersion. Then add the nano-alumina dispersion to the above modified layered double hydroxide nanosheet dispersion, and heat and stir at 50-60℃ for 3-4h. After cooling, centrifuge, wash and vacuum dry to obtain the binary composite filler.

6. The corona-resistant enameled stranded wire according to claim 4, characterized in that, The mass ratio of layered double hydroxide nanosheets to potassium perfluorobutoxybutane sulfonate is 1:(0.2-0.3), and the mass ratio of modified layered double hydroxide nanosheets to nano-alumina is 1:(0.3-0.5).

7. The corona-resistant enameled stranded wire according to claim 1, characterized in that, The preparation steps of the composite topcoat are as follows: Step 1: Add toluene diisocyanate to anhydrous N,N-dimethylformamide at a ratio of 1g:(8-10)mL, stir thoroughly to dissolve, and obtain a toluene diisocyanate solution. Then add 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide to anhydrous N,N-dimethylformamide at a ratio of 1g:(3-5)mL, stir thoroughly to dissolve, and obtain a 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide solution. Step 2: Add the above 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide solution to the above toluene diisocyanate solution, then add dibutyltin dilaurate, heat and stir at 40-50℃ for 3-4 hours, cool, dropwise add petroleum ether for precipitation, then filter and vacuum dry to obtain the flame retardant modifier; Step 3: Add hexagonal boron nitride powder to a 30% hydrogen peroxide solution at a ratio of 1g:(180-200)mL, disperse ultrasonically for 30-40min, then hydrothermally react at 80-100℃ for 24-28h. After cooling, separate by centrifugation, wash and dry to obtain hydroxylated boron nitride powder. Step 4: Add the above hydroxylated boron nitride powder to a sodium hydroxide solution with a pH of 10-12 at a ratio of 1g:(150-160)mL, sonicate for 30-40min, stir for 1-2h, centrifuge at 2000-3000rpm for 9-10min, collect the supernatant, centrifuge at 9000-10000rpm for 4-6min, collect the precipitate and dry it to obtain hydroxylated boron nitride nanosheets; Step 5: Add the above hydroxylated boron nitride nanosheets to anhydrous N,N-dimethylformamide at a ratio of 1g:(60-70)mL, and ultrasonically disperse at 1-3℃ for 1-2h. Then, under nitrogen protection, add the above flame retardant modifier while stirring. After complete dissolution, add dibutyltin dilaurate and heat and stir at 40-50℃ for 6-8h. After cooling, centrifuge, wash 2-3 times with anhydrous ethanol, wash 2-3 times with acetone, and vacuum dry to obtain modified boron nitride nanosheets. Step 6: Add polyimide to N,N-dimethylacetamide at a ratio of 1g:(6-8)mL, heat and stir at 130-140℃, cool, add the above modified boron nitride nanosheets at 7.6-8.2g / L, stir and mix evenly, and degas under vacuum to obtain the composite topcoat.

8. The corona-resistant enameled stranded wire according to claim 7, characterized in that, In step two of the preparation of the composite topcoat, the molar ratio of 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide to toluene diisocyanate is 1:(2-2.2), and the amount of dibutyltin dilaurate added is 0.4-0.6% of the mass of 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide.

9. The corona-resistant enameled stranded wire according to claim 7, characterized in that, In step five of the preparation of the composite topcoat, the mass ratio of the flame retardant modifier to the hydroxylated boron nitride nanosheets is (0.9-1.1):1, and the amount of dibutyltin dilaurate added is 0.5-0.6% of the mass of the hydroxylated boron nitride nanosheets.

10. A method for preparing a corona-resistant enameled stranded wire as described in any one of claims 1-9, characterized in that, Includes the following steps: Step 1: Apply the composite primer evenly to the surface of the conductor core material, cure it, then apply the composite topcoat evenly, and cure it again to obtain the enameled wire; Step 2: Twist the above enameled wires together, then coat the outer surface with a composite topcoat. After curing, you will get enameled stranded wire.

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