A corona-resistant insulating paint for enameled wire and its preparation method

Abstract

The present invention discloses a corona-resistant insulating paint for enameled wire and its preparation method, belonging to the technical field of insulating paint preparation. The raw material composition by weight comprises: 70-80 parts of hybrid polyimide, 10-15 parts of composite nanoparticles, 30-36 parts of composite solvent, and 6-8 parts of auxiliary additives. A chain extender with a siloxane chain segment as the chain segment structure is prepared through telomerization reaction. After the polyamic acid chain segment containing a large number of fluorine groups and directly chain segment nanometer titanium dioxide particles is chain-extended, hybrid polyimide is obtained through hot pressing amidation. And a silicon-aluminum-boron composite nanoparticle is prepared, and perfluoro groups and double bonds are modified on its surface. The composite nanoparticle is cross-linked with the hybrid polyimide through a free radical reaction, and finally a corona-resistant insulating paint is prepared by mixing with auxiliary materials.

Description

Technical Field

[0001] The present invention relates to the technical field of insulating paint preparation, and particularly relates to a corona-resistant insulating paint for enameled wire and a preparation method thereof. Background Art

[0002] The development of corona-resistant insulating paint has gone through multiple stages from improving electrical insulation to enhancing corona resistance. Initially, the focus of the paint was on improving electrical insulation. With the increasing demand for high-voltage equipment, corona resistance has gradually become the research focus. In the 1980s, materials such as polyurethane and epoxy resin were used to enhance the corona resistance of the paint film, and flame retardants were added to cope with high temperatures. In the 21st century, research has focused on strengthening flame retardant properties, using phosphorus-based and nitrogen-based flame retardants. At the same time, nanotechnology has been used to improve the electrical and thermal stability of the paint film. Nowadays, modern paint not only has excellent corona resistance, but also has flame retardancy and high-temperature resistance, thus meeting the requirements of high-voltage electrical equipment.

[0003] For example, the prior art CN105219233B discloses a corona-resistant enameled wire paint and a preparation method thereof. Under the condition of stirring with a toothed disk disperser, inorganic oxide raw materials are added to an organic solvent, the linear velocity of the toothed disk disperser is controlled to be 10 - 22 m / s, and the shear dispersion time is 0.5 - 2 h. Then, grinding is carried out using a grinder, the linear velocity of the grinder is controlled to be 15 - 25 m / s, and the grinding time is 3 - 6 h to prepare an inorganic oxide pre-dispersion with D50 < 150 nm and a solid content of 50 - 70%. A coupling agent is added to the inorganic oxide pre-dispersion to form a corona-resistant modifier, and the corona-resistant modifier and the paint body are stirred at 70 - 100 °C to obtain the corona-resistant enameled wire paint.

[0004] However, the above invention modifies metal oxides with a coupling agent to obtain a corona-resistant modifier, and thus obtains a corona-resistant enameled wire paint. However, the metal oxides modified by the silane coupling agent only have improved compatibility with the paint body, but do not form a cross-linked structure with the organic segments of the paint body, resulting in the need to further improve the dispersion of the corona-resistant modifier in the paint, causing agglomeration of the corona-resistant modifier in the paint, and thus the corona resistance and wear resistance of the material need to be further improved. Summary of the Invention

[0005] The purpose of the present invention is to provide a corona-resistant insulating paint for enameled wire and a preparation method thereof, aiming to solve the technical problem that the corona resistance and flame retardancy of the insulating paint in the prior art need to be further improved.

[0006] The purpose of the present invention can be achieved by the following technical solutions: A corona-resistant insulating paint for enameled wire comprises the following raw materials by weight: 70 - 80 parts of hybrid polyimide, 10 - 15 parts of composite nano-particles, 30 - 36 parts of composite solvent, and 13 - 19 parts of auxiliary additives;

[0007] The preparation method of the hybrid polyimide comprises the following steps:

[0008] A1. Add the hybrid polyamic acid and N,N-dimethylformamide into a reaction kettle, stir at room temperature for 10 - 15 min, then dropwise add the modification liquid into the reaction kettle. After the dropping is completed, continue to stir for 3 - 5 min, let it stand for 20 - 30 min, and perform post-treatment to obtain the composite polyamic acid;

[0009] A2. Perform thermal imidization on the composite polyamic acid to obtain the hybrid polyimide.

[0010] Furthermore, the composite solvent includes: butyl acetate, toluene and isopropanol; the auxiliary additives include: ultraviolet absorber, thickener, leveling agent, initiator and hardener;

[0011] Furthermore, the dosage ratio of butyl acetate, toluene and isopropanol is 180 - 200 g: 80 - 100 g: 40 - 60 g; the dosage ratio of the ultraviolet absorber, thickener, leveling agent, initiator and hardener is 2 - 3 g: 3 - 5 g: 1 - 2 g: 2 - 3 g: 5 - 6 g;

[0012] Furthermore, the ultraviolet absorber is one or two of 2-hydroxy-4-octyloxybenzophenone and bis(2,2,6,6-tetramethylpiperidyl) sebacate; the thickener is one or more of sodium carboxymethyl cellulose, polyvinyl alcohol and sodium polyacrylate; the leveling agent is one or more of dimethyl silicone oil, ethoxylated silicone oil and polyether modified silicone oil; the initiator is one or two of potassium persulfate and azobisisobutyronitrile; the hardener is one or more of maleic anhydride, diaminodiphenylmethane and diaminodiphenyl ether.

[0013] The reaction principle for preparing the hybrid polyimide is as follows: tetraethyl titanate hydrolyzes in deionized water to produce a titanium hydroxide structure, and the titanium hydroxide and the hybrid polyamic acid form a hydrogen bond structure, so that the titanium hydroxide is uniformly dispersed on the surface of the hybrid polyamic acid chain segments. Finally, with the progress of thermal imidization, the titanium hydroxide continuously dehydrates to form a titanium dioxide structure, and finally the hybrid polyimide is prepared.

[0014] Furthermore, in step A1, the dosage ratio of the hybrid polyamic acid, N,N-dimethylformamide and the modification liquid is 8 - 10 g: 40 - 50 mL: 10 mL, wherein the modification liquid is obtained by mixing and stirring tetraethyl titanate and deionized water according to the dosage ratio of 1 - 2 g: 10 mL. The post-treatment includes: after the reaction is completed, when the temperature of the reaction kettle drops to room temperature, transfer the reaction solution to a rotary evaporator, raise the temperature of the rotary evaporator to 60 - 80 °C, and perform vacuum distillation until no liquid is collected, then obtain the modified polyamic acid;

[0015] Further, in step A2, the preparation method of the hybrid polyimide is as follows: transfer the composite polyamic acid into an electrothermal constant temperature oven, after introducing nitrogen for protection, heat the electrothermal constant temperature oven to 100 °C, keep it warm for 60 - 80 min, then continue to raise the temperature of the electrothermal constant temperature oven to 200 °C, keep it warm for 1 h, then raise the temperature of the electrothermal constant temperature oven to 300 °C again, keep it warm for 1 h, and then naturally cool it to room temperature to obtain the hybrid polyimide.

[0016] Further, the preparation method of the hybrid polyamic acid includes the following steps:

[0017] B1. Add (E)-but-2-ene-1,4-diamine and N,N-dimethylformamide into a reaction kettle at a temperature of 0 - 5 °C, keep stirring until all the reactants are dissolved, then add 4,4'-(hexafluoroisopropylidene)diphthalic anhydride into the reaction kettle in three portions. After the addition is completed, steadily raise the temperature of the reaction kettle to 30 - 50 °C, keep the reaction at this temperature for 2 - 4 h, and then perform post-treatment to obtain the modified polyamic acid;

[0018] B2. Add the modified polyamic acid, modified chain extender, benzoic acid and N,N-dimethylformamide into the reaction kettle and stir. Raise the temperature of the reaction kettle to 60 - 80 °C, keep stirring for 60 - 80 min, and then perform post-treatment to obtain the hybrid polyamic acid.

[0019] Further, in step B1, the dosage ratio of (E)-but-2-ene-1,4-diamine, N,N-dimethylformamide and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride is 2.0 - 2.4 g: 80 - 100 mL: 10.7 - 11.2 g. The post-treatment includes: after the reaction is completed, wait for the temperature of the reaction kettle to drop to room temperature, transfer the reaction solution to a rotary evaporator, raise the temperature of the rotary evaporator to 60 - 80 °C, and perform vacuum distillation until no liquid is collected to obtain the modified polyamic acid;

[0020] Further, in step B2, the dosage ratio of the modified polyamic acid, modified chain extender, benzoic acid and N,N-dimethylformamide is 8 - 10 g: 2 - 3 g: 0.3 - 0.5 g: 40 - 50 mL. The post-treatment includes: after the reaction is completed, wait for the temperature of the reaction kettle to drop to room temperature, transfer the reaction solution to a rotary evaporator, raise the temperature of the rotary evaporator to 60 - 80 °C, and perform vacuum distillation until no liquid is collected to obtain the hybrid polyamic acid.

[0021] Further, the preparation method of the modified chain extender includes the following steps:

[0022] C1. Add 2,4,6-trivinyl-2,4,6-trimethylcyclotrisiloxane, 1,3-dimethyl-1,1,3,3-tetravinyldisiloxane and diethyl ether into a reaction kettle and stir. During stirring, add 98 wt% concentrated sulfuric acid. After stirring at room temperature for 8 - 10 h, add sodium bicarbonate powder into the reaction kettle, adjust the pH of the system to 8 - 9, and obtain the modified silicone oil through post-treatment;

[0023] C2. Add the modified silicone oil, benzoic acid, aluminum chloride and dimethyl sulfoxide into a reaction kettle and stir. Lower the temperature of the reaction kettle to 0 - 5 °C, and dropwise add saturated hydrogen peroxide solution into the reaction kettle under the state of heat preservation and stirring. The dropping operation lasts for 3 - 4 h. After the dropping is completed, stir for 1 h under heat preservation, and obtain the modified chain extender through post-treatment.

[0024] Further, in step C1, the dosage ratio of 2,4,6-trivinyl-2,4,6-trimethylcyclotrisiloxane, 1,3-dimethyl-1,1,3,3-tetravinyldisiloxane, diethyl ether and 98 wt% concentrated sulfuric acid is 7 - 9 g: 2 - 3 g: 50 - 80 mL: 10 - 12 mL. The post-treatment includes: after the reaction is completed, wait for the temperature of the reaction kettle to drop to room temperature, transfer the reaction solution to a rotary evaporator, raise the temperature of the rotary evaporator to 60 - 80 °C, and perform vacuum distillation until no liquid is collected, then obtain the modified silicone oil;

[0025] Further, in step C2, the dosage ratio of the modified silicone oil, benzoic acid, aluminum chloride, dimethyl sulfoxide and saturated hydrogen peroxide solution is 12 - 16 g: 3 - 5 g: 0.5 - 0.8 g: 60 - 80 mL: 10 - 12 mL. The post-treatment includes: after the reaction is completed, wait for the temperature of the reaction kettle to drop to room temperature, transfer the reaction solution to a rotary evaporator, raise the temperature of the rotary evaporator to 60 - 80 °C, and perform vacuum distillation until no liquid is collected, then obtain the modified chain extender.

[0026] The reaction equation for preparing the modified chain extender is:

[0027]

[0028] The reaction principle for preparing the modified chain extender is: under the catalysis of concentrated sulfuric acid, 2,4,6-trivinyl-2,4,6-trimethylcyclotrisiloxane and 1,3-dimethyl-1,1,3,3-tetravinyldisiloxane undergo telomerization reaction to form a modified silicone oil with a large number of double bond structures, and further oxidize the double bonds into epoxy groups through peroxyacid oxidation, and finally obtain the modified chain extender.

[0029] Further, the preparation method of the composite nanoparticles includes the following steps:

[0030] D1. Methyl orthosilicate, tributyl borate, and deionized water were slowly added to a three-necked flask equipped with a thermometer, a stirrer, and a cooling reflux device in sequence. Under stirring conditions, the three-necked flask was heated to reflux, and after holding the temperature and stirring for 4 - 5 h, the cooling reflux device was removed and replaced with a distillation device. Then, aluminum isopropoxide was added to the reaction kettle. After heating the temperature of the three-necked flask to 115 - 120 °C, it was held at this temperature for 10 - 20 min, and then post-treatment was carried out to obtain modified nanoparticles.

[0031] D2. The modified nanoparticles, toluene, a composite modifier, and deionized water were added to the reaction kettle. The pH of the system was adjusted to 8 - 10 using saturated sodium hydroxide solution. Then, the temperature of the reaction kettle was raised to 30 - 40 °C, and it was held at this temperature and stirred for 30 - 40 min. After post-treatment, composite nanoparticles were obtained.

[0032] The reaction principle for preparing the composite nanoparticles is as follows: Under reflux conditions, methyl orthosilicate and tributyl borate hydrolyze to produce a cross-linked structure, and under the conditions of heating and distillation, aluminum isopropoxide continues to hydrolyze to form a supplementary structure. Finally, after calcination, modified nanoparticles are prepared. Finally, through the modification of the composite modifier, perfluorinated groups and double bond structures are introduced onto the surface of the modified nanoparticles, and finally, composite nanoparticles are prepared.

[0033] Further, in step D1, the dosage ratio of methyl orthosilicate, tributyl borate, deionized water, and aluminum isopropoxide is 6 - 8 g : 2 - 3 g : 60 - 80 mL : 5 - 6 g. The post-treatment is as follows: The material was transferred to a tube furnace, and nitrogen was introduced for protection. The tube heating furnace was heated to 500 - 600 °C at a rate of 5 - 6 °C / min, held at this temperature for 5 - 6 h, then naturally cooled to 200 - 300 °C, the nitrogen was disconnected, and water vapor was introduced at a rate of 100 - 120 sccm, held at this temperature for 2 - 3 h, and then naturally cooled to obtain modified nanoparticles.

[0034] Further, in step D2, the dosage ratio of the modified nanoparticles, absolute ethanol, the composite modifier, and deionized water is 6 - 8 g : 20 - 25 mL : 10 - 15 mL : 10 - 15 mL. Among them, the composite modifier is obtained by mixing perfluorooctyltrimethoxysilane, 3-(methacryloyloxy)propyltrimethoxysilane, and absolute ethanol in a dosage ratio of 1 - 2 g : 1 - 2 g : 10 - 15 mL. The post-treatment includes: After the reaction is completed, when the temperature of the reaction kettle drops to room temperature, the reaction solution is filtered by suction to collect the filter cake. The filter cake is washed 3 - 5 times with absolute ethanol and deionized water, and then the filter cake is transferred to a drying oven at 60 °C and vacuum dried to constant weight to obtain composite nanoparticles.

[0035] The present invention also provides a method for preparing a corona-resistant insulating paint for enameled wires: adding hybrid polyimide, composite nanoparticles and a composite solvent into a reaction kettle and stirring. After the temperature of the reaction kettle rises to 60-80 °C, an initiator is added, and after heat preservation and stirring for 40-60 min, an ultraviolet absorber, a thickener, a leveling agent and a hardener are added to the reaction kettle, and after heat preservation and stirring for 10-15 min, it is naturally cooled to room temperature to obtain the corona-resistant insulating paint.

[0036] The reaction principle for preparing the corona-resistant insulating paint is as follows: under the catalysis of heating and an initiator, the double bonds on the hybrid polyimide and the double bonds modified on the surface of the composite nanoparticles undergo a free radical addition reaction to form a cross-linked structure, enabling the composite nanoparticles to be uniformly dispersed inside the matrix, and adding auxiliary materials to finally prepare the corona-resistant insulating paint.

[0037] The present invention has the following beneficial effects:

[0038] 1. In the present invention, a rigid-flexible polyimide main chain is constructed by introducing a polysiloxane chain extender. The flexible polysiloxane chain segment is combined with the rigid aromatic ring through hydrogen bonds, which improves the interfacial compatibility and mechanical toughness while maintaining the high-temperature resistance of the material, and inhibits the partial discharge caused by microcracks. Secondly, the nano-titanium dioxide particles and the silicon-aluminum-boron composite particles modified with fluorine groups act synergistically. Titanium dioxide evenly disperses the electric field through its high dielectric property, and the fluorine group captures free electrons with its strong electronegativity and forms a hydrophobic barrier to block the penetration of moisture and the erosion of reactive oxygen. Further, a three-dimensional cross-linked network is constructed through a free radical reaction, and the double bond on the surface of the silicon-aluminum-boron particles forms a dynamic bond with the polyimide main chain, and energy dissipation is achieved through the molecular chain slip under the electric field stress to avoid breakdown caused by charge concentration, thereby significantly improving the corona resistance, insulation and solvent resistance of the insulating paint.

[0039] 2. The polysiloxane chain extender prepared in the present invention forms a rigid-flexible structure with the rigid polyimide main chain through flexible chain segments, which not only maintains the high-strength characteristics of the material, but also disperses mechanical stress through molecular chain slip. Combined with the hard support and uniform dispersion of the nano-titanium dioxide particles, physical cross-linking points are formed to resist friction and wear and inhibit the propagation of surface cracks. Moreover, during the combustion process, the fluorine-containing free radicals generated by the high-temperature decomposition of the fluorine group interrupt the combustion chain reaction, and a dense oxide layer is formed on the surface of the silicon-aluminum-boron particles when heated, isolating the transfer of oxygen and heat, and boron elements catalyze the rapid formation of a carbonized layer to further block the spread of the flame; the strong binding between the fluorine-group modified nanoparticles and the polymer interface inhibits the crack propagation, and the rigid support of the cross-linked network and the flexible buffer of the polysiloxane chain form a complement, thereby significantly improving the flame retardancy and wear resistance of the insulating paint.

[0040] 3. In the insulating paint prepared by the present invention, a large number of fluorine groups absorb ultraviolet light energy through strong electronegativity and release it as heat energy. Their chemical inertness forms a dense barrier to block the direct damage of ultraviolet rays to the polymer main chain. At the same time, the hydrophobic property inhibits the synergistic photo-oxidation reaction of water vapor. The nano-titanium dioxide particles reflect and scatter ultraviolet rays by virtue of their high refractive index characteristics, reducing its penetration depth. The uniformly dispersed particles are chemically bonded to the polymer chain to synergistically inhibit the molecular chain breakage. The perfluorinated groups modified on the surface of the silicon-aluminum-boron composite nanoparticles crosslink with the polyimide chain segments through free radical reaction via double bonds to form a spatial crosslinking network, fixing the particle positions to enhance the coating density and reduce the propagation of microcracks induced by ultraviolet rays. The high thermal conductivity aids in the diffusion of heat energy to avoid local temperature rise and accelerate aging, thus significantly improving the ultraviolet resistance of the insulating paint. Detailed Embodiment

[0041] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work fall within the scope of protection of the present invention.

[0042] Example 1

[0043] This example provides a preparation method of a modified chain extender for the preparation of a corona-resistant insulating paint for enameled wires, including the following steps:

[0044] Step ①, prepare modified silicone oil

[0045] Weigh: 700.0 g of 2,4,6-trivinyl-2,4,6-trimethylcyclotrisiloxane, 200.0 g of 1,3-dimethyl-1,1,3,3-tetravinyldisiloxane and 5000.0 mL of ether are added to the reaction kettle and stirred. During the stirring process, 1000.0 mL of 98 wt% concentrated sulfuric acid is added. After stirring at room temperature for 8 h, sodium bicarbonate powder is added to the reaction kettle to adjust the system pH = 8. After the reaction is completed, when the temperature of the reaction kettle drops to room temperature, the reaction solution is transferred to a rotary evaporator. The temperature of the rotary evaporator is raised to 60 °C, and vacuum distillation is carried out until no liquid is collected, and then the modified silicone oil is obtained.

[0046] Step ②, prepare modified chain extender

[0047] Weigh: 1200.0 g of modified silicone oil, 300.0 g of benzoic acid, 50.0 g of aluminum chloride, and 6000.0 mL of dimethyl sulfoxide are added to a reaction kettle and stirred. The temperature of the reaction kettle is lowered to 5 °C. While maintaining the state of heat preservation and stirring, 1000.0 mL of saturated hydrogen peroxide solution is added dropwise to the reaction kettle. The dropping operation is maintained for 3 h. After the dropping is completed, it is stirred with heat preservation for 1 h. After the reaction is completed, when the temperature of the reaction kettle is lowered to room temperature, the reaction solution is transferred to a rotary evaporator. The temperature of the rotary evaporator is raised to 60 °C, and vacuum distillation is carried out until no liquid is produced, and then a modified chain extender is obtained.

[0048] Example 2

[0049] This example provides a preparation method of a modified chain extender for preparing a corona-resistant insulating paint for enameled wires, including the following steps:

[0050] Step ①, prepare modified silicone oil

[0051] Weigh: 900.0 g of 2,4,6-trivinyl-2,4,6-trimethylcyclotrisiloxane, 300.0 g of 1,3-dimethyl-1,1,3,3-tetravinyldisiloxane, and 8000.0 mL of diethyl ether are added to a reaction kettle and stirred. During the stirring process, 1200.0 mL of 98 wt% concentrated sulfuric acid is added. After stirring at room temperature for 10 h, sodium bicarbonate powder is added to the reaction kettle to adjust the system pH = 9. After the reaction is completed, when the temperature of the reaction kettle is lowered to room temperature, the reaction solution is transferred to a rotary evaporator. The temperature of the rotary evaporator is raised to 80 °C, and vacuum distillation is carried out until no liquid is produced, and then modified silicone oil is obtained.

[0052] Step ②, prepare modified chain extender

[0053] Weigh: 1600.0 g of modified silicone oil, 500.0 g of benzoic acid, 80.0 g of aluminum chloride, and 8000.0 mL of dimethyl sulfoxide are added to a reaction kettle and stirred. The temperature of the reaction kettle is lowered to 0 °C. While maintaining the state of heat preservation and stirring, 1200.0 mL of saturated hydrogen peroxide solution is added dropwise to the reaction kettle. The dropping operation is maintained for 4 h. After the dropping is completed, it is stirred with heat preservation for 1 h. After the reaction is completed, when the temperature of the reaction kettle is lowered to room temperature, the reaction solution is transferred to a rotary evaporator. The temperature of the rotary evaporator is raised to 80 °C, and vacuum distillation is carried out until no liquid is produced, and then a modified chain extender is obtained.

[0054] Example 3

[0055] This example provides a preparation method of a modified chain extender for preparing a corona-resistant insulating paint for enameled wires, including the following steps:

[0056] Step ①, prepare modified silicone oil

[0057] Weigh: 800.0 g of 2,4,6-trivinyl-2,4,6-trimethylcyclotrisiloxane, 240.0 g of 1,3-dimethyl-1,1,3,3-tetravinyldisiloxane and 7200.0 mL of diethyl ether were added to a reaction kettle and stirred. During the stirring process, 1200.0 mL of 98 wt% concentrated sulfuric acid was added. After stirring at room temperature for 9 h, sodium bicarbonate powder was added to the reaction kettle to adjust the pH of the system to 9. After the reaction was completed and the temperature of the reaction kettle was lowered to room temperature, the reaction solution was transferred to a rotary evaporator. The temperature of the rotary evaporator was raised to 70 °C, and vacuum distillation was carried out until no liquid was collected, and a modified silicone oil was obtained.

[0058] Step ②: Prepare a modified chain extender

[0059] Weigh: 1500.0 g of modified silicone oil, 400.0 g of benzoic acid, 72.0 g of aluminum chloride and 7200.0 mL of dimethyl sulfoxide were added to a reaction kettle and stirred. The temperature of the reaction kettle was lowered to 3 °C, and 1200.0 mL of saturated hydrogen peroxide solution was added dropwise to the reaction kettle under the condition of heat preservation and stirring. The dropping operation was maintained for 4 h. After the dropping was completed, stirring was continued for 1 h under heat preservation. After the reaction was completed and the temperature of the reaction kettle was lowered to room temperature, the reaction solution was transferred to a rotary evaporator. The temperature of the rotary evaporator was raised to 70 °C, and vacuum distillation was carried out until no liquid was collected, and a modified chain extender was obtained.

[0060] Example 4

[0061] This example provides a method for preparing a hybrid polyamic acid for a corona-resistant insulating paint for enameled wires, including the following steps:

[0062] Step ㈠: Prepare a modified polyamic acid

[0063] Weigh: 200.0 g of (E)-but-2-ene-1,4-diamine and 8000.0 mL of N,N-dimethylformamide were added to a reaction kettle at a temperature of 5 °C. After heat preservation and stirring until all the reactants were dissolved, 1075.0 g of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride was added to the reaction kettle in three portions. After the addition was completed, the temperature of the reaction kettle was steadily raised to 30 °C, and the reaction was carried out under heat preservation for 2 h. After the reaction was completed and the temperature of the reaction kettle was lowered to room temperature, the reaction solution was transferred to a rotary evaporator. The temperature of the rotary evaporator was raised to 60 °C, and vacuum distillation was carried out until no liquid was collected, and a modified polyamic acid was obtained.

[0064] Step ㈡: Prepare a hybrid polyamic acid

[0065] Weigh: 800.0 g of modified polyamic acid, 200.0 g of the modified chain extender prepared in Step 1, 30.0 g of benzoic acid, and 4000.0 mL of N,N-dimethylformamide and add them to a reaction kettle for stirring. Heat the temperature of the reaction kettle to 60 °C, keep stirring for 60 min, and perform post-treatment. After the reaction is completed, wait for the temperature of the reaction kettle to drop to room temperature, transfer the reaction solution to a rotary evaporator, raise the temperature of the rotary evaporator to 60 °C, and perform vacuum distillation until no liquid is collected, then obtain the hybrid polyamic acid.

[0066] Example 5

[0067] This example provides a preparation method of hybrid polyamic acid for preparing corona-resistant insulating paint for enameled wires, including the following steps:

[0068] Step (i), prepare modified polyamic acid

[0069] Weigh: 240.0 g of (E)-but-2-ene-1,4-diamine and 10000.0 mL of N,N-dimethylformamide and add them to a reaction kettle at 0 °C. Keep stirring until all the reactants are dissolved, then add 1120.0 g of 4,4'-(hexafluoroisopropylidene) diphthalic anhydride to the reaction kettle in three portions. After the addition is completed, steadily raise the temperature of the reaction kettle to 50 °C and keep reacting for 4 h. After the reaction is completed, wait for the temperature of the reaction kettle to drop to room temperature, transfer the reaction solution to a rotary evaporator, raise the temperature of the rotary evaporator to 80 °C, and perform vacuum distillation until no liquid is collected, then obtain the modified polyamic acid.

[0070] Step (ii), prepare hybrid polyamic acid

[0071] Weigh: 1000.0 g of modified polyamic acid, 300.0 g of the modified chain extender prepared in Step 2, 50.0 g of benzoic acid, and 5000.0 mL of N,N-dimethylformamide and add them to a reaction kettle for stirring. Heat the temperature of the reaction kettle to 80 °C, keep stirring for 80 min, and perform post-treatment. After the reaction is completed, wait for the temperature of the reaction kettle to drop to room temperature, transfer the reaction solution to a rotary evaporator, raise the temperature of the rotary evaporator to 80 °C, and perform vacuum distillation until no liquid is collected, then obtain the hybrid polyamic acid.

[0072] Example 6

[0073] This example provides a preparation method of hybrid polyamic acid for preparing corona-resistant insulating paint for enameled wires, including the following steps:

[0074] Step (i), prepare modified polyamic acid

[0075] Weigh: 210.0 g of (E)-but-2-ene-1,4-diamine and 9000.0 mL of N,N-dimethylformamide are added to a reaction kettle at a temperature of 3 °C. After keeping warm and stirring until all the reactants are dissolved, 1100.0 g of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride is added to the reaction kettle in three portions. After the addition is completed, the temperature of the reaction kettle is steadily raised to 40 °C, and the reaction is carried out under heat preservation for 3 h. After the reaction is completed, when the temperature of the reaction kettle is lowered to room temperature, the reaction solution is transferred to a rotary evaporator. The temperature of the rotary evaporator is raised to 70 °C, and under reduced pressure distillation until no liquid is collected, a modified polyamic acid is obtained.

[0076] Step (ii), preparing a hybrid polyamic acid

[0077] Weigh: 900.0 g of the modified polyamic acid, 240.0 g of the modified chain extender prepared in Step 3, 40.0 g of benzoic acid, and 4800.0 mL of N,N-dimethylformamide are added to a reaction kettle and stirred. The temperature of the reaction kettle is raised to 70 °C, and stirring is carried out under heat preservation for 70 min. After post-treatment, when the temperature of the reaction kettle is lowered to room temperature, the reaction solution is transferred to a rotary evaporator. The temperature of the rotary evaporator is raised to 70 °C, and under reduced pressure distillation until no liquid is collected, a hybrid polyamic acid is obtained.

[0078] Example 7

[0079] This example provides a preparation method of a hybrid polyimide for a corona-resistant insulating paint for enameled wires, including the following steps:

[0080] Step (i), preparing a composite polyamic acid

[0081] Weigh: 100.0 g of tetraethyl titanate and 1000.0 mL of deionized water are mixed and stirred to obtain a modifier solution;

[0082] Weigh: 800.0 g of the hybrid polyamic acid prepared in Example 4 and 4000.0 mL of N,N-dimethylformamide are added to a reaction kettle. After stirring at room temperature for 10 min, 1000.0 mL of the modifier solution is added dropwise to the reaction kettle. After the addition is completed, stirring is continued for 3 min, and then it is left standing for 20 min. After post-treatment, a composite polyamic acid is obtained.

[0083] Step (ii), preparing a hybrid polyimide

[0084] Transfer 500.0 g of the composite polyamic acid to an electrothermal constant temperature oven. After purging with nitrogen for protection, the electrothermal constant temperature oven is heated to 100 °C, and after heat preservation treatment for 60 min, the electrothermal constant temperature oven is further heated to 200 °C, and after heat preservation for 1 h, the electrothermal constant temperature oven is heated to 300 °C again, and after heat preservation for 1 h, it is naturally cooled to room temperature to obtain a hybrid polyimide.

[0085] Example 8

[0086] This embodiment provides a preparation method of hybrid polyimide for preparing corona-resistant insulating paint for enameled wire, including the following steps:

[0087] Step (1), preparing composite polyamic acid

[0088] Weigh: 200.0 g of tetraethyl titanate and 1000.0 mL of deionized water, mix and stir to obtain a modification solution;

[0089] Weigh: 1000.0 g of the hybrid polyamic acid prepared in Example 5 and 5000.0 mL of N,N-dimethylformamide, add them to a reaction kettle, stir at room temperature for 15 min, then add 1000.0 mL of the modification solution dropwise to the reaction kettle. After the addition is complete, continue to stir for 5 min, stand for 30 min, and perform post-treatment to obtain the composite polyamic acid.

[0090] Step (2), preparing hybrid polyimide

[0091] Transfer 500.0 g of the composite polyamic acid to an electrothermal constant temperature oven. After introducing nitrogen protection, heat the electrothermal constant temperature oven to 100 °C, keep it warm for 80 min, then continue to heat the electrothermal constant temperature oven to 200 °C, keep it warm for 1 h, then heat the electrothermal constant temperature oven to 300 °C again, keep it warm for 1 h, and then naturally cool to room temperature to obtain the hybrid polyimide.

[0092] Example 9

[0093] This embodiment provides a preparation method of hybrid polyimide for preparing corona-resistant insulating paint for enameled wire, including the following steps:

[0094] Step (1), preparing composite polyamic acid

[0095] Weigh: 160.0 g of tetraethyl titanate and 1000.0 mL of deionized water, mix and stir to obtain a modification solution;

[0096] Weigh: 900.0 g of the hybrid polyamic acid prepared in Example 6 and 4800.0 mL of N,N-dimethylformamide, add them to a reaction kettle, stir at room temperature for 15 min, then add 1000.0 mL of the modification solution dropwise to the reaction kettle. After the addition is complete, continue to stir for 4 min, stand for 25 min, and perform post-treatment to obtain the composite polyamic acid.

[0097] Step (2), preparing hybrid polyimide

[0098] Transfer 500.0 g of the composite polyamic acid to an electrothermal constant temperature oven. After introducing nitrogen protection, heat the electrothermal constant temperature oven to 100 °C, keep it warm for 70 min, then continue to heat the electrothermal constant temperature oven to 200 °C, keep it warm for 1 h, then heat the electrothermal constant temperature oven to 300 °C again, keep it warm for 1 h, and then naturally cool to room temperature to obtain the hybrid polyimide.

[0099] Example 10

[0100] This example provides a preparation method of composite nanoparticles for preparing corona-resistant insulating paint for enameled wires, including the following steps:

[0101] Step I. Prepare modified nanoparticles

[0102] Weigh: 600.0 g of methyl orthosilicate, 200.0 g of tributyl borate and 6000.0 mL of deionized water are slowly added to a three-necked flask equipped with a thermometer, a stirrer and a cooling reflux device in sequence. Under stirring conditions, the three-necked flask is heated to reflux, and after heat preservation and stirring for 4 h, the cooling reflux device is removed and replaced with a rectification device. Then, 500.0 g of aluminum isopropoxide is added to the reaction kettle. After heating the temperature of the three-necked flask to 115 °C, heat preservation is carried out for 10 min. The materials are transferred to a tubular furnace, and nitrogen protection is introduced. The tubular heating furnace is heated to 500 °C at a rate of 5 °C / min, and after heat preservation for 5 h, it is naturally cooled to 200 °C, then nitrogen is disconnected, and water vapor is introduced at a rate of 100 ccm. After heat preservation for 2 h, it is naturally cooled to obtain modified nanoparticles.

[0103] Step II. Prepare composite nanoparticles

[0104] Weigh: 100.0 g of perfluorooctyltrimethoxysilane, 100.0 g of 3-(methacryloyloxy)propyltrimethoxysilane and 1000.0 mL of absolute ethanol are mixed to obtain a composite modifier;

[0105] Weigh: 600.0 g of modified nanoparticles, 2000.0 mL of toluene, 1000.0 mL of the composite modifier and 1000.0 mL of deionized water are added to the reaction kettle. The pH of the system is adjusted to 8 using saturated sodium hydroxide solution. Then, the temperature of the reaction kettle is raised to 30 °C, and heat preservation and stirring are carried out for 30 min. After the reaction is completed, when the temperature of the reaction kettle is lowered to room temperature, the reaction solution is filtered by suction to collect the filter cake. The filter cake is washed 3 times with absolute ethanol and deionized water, and then the filter cake is transferred to a drying oven at 60 °C and vacuum dried to constant weight to obtain composite nanoparticles.

[0106] Example 11

[0107] This example provides a preparation method of composite nanoparticles for preparing corona-resistant insulating paint for enameled wires, including the following steps:

[0108] Step I. Prepare modified nanoparticles

[0109] Weigh: 800.0 g of methyl orthosilicate, 300.0 g of tributyl borate and 8000.0 mL of deionized water were slowly added to a three-necked flask equipped with a thermometer, a stirrer and a cooling reflux device in sequence. Under stirring conditions, the three-necked flask was heated to reflux, and after heat preservation and stirring for 5 h, the cooling reflux device was removed and replaced with a rectification device. Then, 600.0 g of aluminum isopropoxide was added to the reaction kettle. After heating the temperature of the three-necked flask to 120 °C, it was kept warm for 20 min. The materials were transferred to a tube furnace, and nitrogen protection was introduced. The tube furnace was heated to 500 °C at a rate of 5 °C / min, and after heat preservation for 5 h, it was naturally cooled to 300 °C, then the nitrogen was disconnected, and steam was introduced at a rate of 120 sccm. After heat preservation for 3 h, it was naturally cooled to obtain modified nanoparticles.

[0110] Step II. Preparation of composite nanoparticles

[0111] Weigh: 200.0 g of perfluorooctyltrimethoxysilane, 200.0 g of 3-(methacryloyloxy)propyltrimethoxysilane and 1500.0 mL of absolute ethanol were mixed to obtain a composite modifier;

[0112] Weigh: 800.0 g of modified nanoparticles, 2500.0 mL of toluene, 1500.0 mL of composite modifier and 1500.0 mL of deionized water were added to the reaction kettle. The pH of the system was adjusted to 10 using saturated sodium hydroxide solution. Then, the temperature of the reaction kettle was raised to 40 °C, and it was kept warm and stirred for 40 min. After the reaction was completed, when the temperature of the reaction kettle decreased to room temperature, the reaction solution was filtered by suction to collect the filter cake. The filter cake was washed 5 times with absolute ethanol and deionized water, and then the filter cake was transferred to a drying oven at 60 °C and vacuum dried to constant weight to obtain composite nanoparticles.

[0113] Example 12

[0114] This example provides a preparation method of composite nanoparticles for preparing corona-resistant insulating paint for enameled wires, including the following steps:

[0115] Step I. Preparation of modified nanoparticles

[0116] Weigh: 700.0 g of methyl orthosilicate, 240.0 g of tributyl borate and 7200.0 mL of deionized water were successively and slowly added into a three-necked flask equipped with a thermometer, a stirrer and a cooling reflux device. Under stirring conditions, the three-necked flask was heated to reflux, and after heat preservation and stirring for 5 h, the cooling reflux device was removed and replaced with a rectification device. Then, 540.0 g of aluminum isopropoxide was added to the reaction kettle. After heating the temperature of the three-necked flask to 120 °C, it was kept warm for 20 min. The materials were transferred to a tubular furnace, and nitrogen protection was introduced. The tubular heating furnace was heated to 600 °C at a rate of 5 °C / min, and after heat preservation for 6 h, it was naturally cooled to 250 °C, then nitrogen was disconnected, and steam was introduced at a rate of 110 sccm. After heat preservation for 3 h, it was naturally cooled to obtain modified nanoparticles.

[0117] Step II. Preparation of composite nanoparticles

[0118] Weigh: 160.0 g of perfluorooctyltrimethoxysilane, 160.0 g of 3-(methacryloyloxy)propyltrimethoxysilane and 1200.0 mL of absolute ethanol were mixed to obtain a composite modifier;

[0119] Weigh: 720.0 g of modified nanoparticles, 2100.0 mL of toluene, 1200.0 mL of composite modifier and 1200.0 mL of deionized water were added to the reaction kettle. The pH of the system was adjusted to 9 using saturated sodium hydroxide solution. Then, the temperature of the reaction kettle was raised to 36 °C, and after heat preservation and stirring for 36 min, after the reaction was completed, when the temperature of the reaction kettle dropped to room temperature, the reaction solution was filtered by suction to collect the filter cake. The filter cake was washed 4 times with absolute ethanol and deionized water, and then the filter cake was transferred to a drying oven at 60 °C and vacuum dried to constant weight to obtain composite nanoparticles.

[0120] Example 13

[0121] This example provides a preparation method of a corona-resistant insulating paint for enameled wires, which includes the following steps:

[0122] Weigh: 180.0 g of butyl acetate, 80.0 g of toluene and 40.0 g of isopropanol were mixed to obtain a composite solvent;

[0123] Weigh: 700.0 g of the hybrid polyimide prepared in Example 7, 100.0 g of the composite nanoparticles prepared in Example 10 and 300.0 g of the composite solvent were added to the reaction kettle and stirred. After the temperature of the reaction kettle was raised to 60 °C, 20.0 g of azobisisobutyronitrile was added, and after heat preservation and stirring for 40 min, 20.0 g of 2-hydroxy-4-octyloxybenzophenone, 30.0 g of sodium carboxymethylcellulose, 10.0 g of dimethyl silicone oil and 50.0 g of diaminodiphenyl ether were added to the reaction kettle. After heat preservation and stirring for 10 min, it was naturally cooled to room temperature to obtain the corona-resistant insulating paint.

[0124] Example 14

[0125] This example provides a preparation method of corona-resistant insulating paint for enameled wire, including the following steps:

[0126] Weigh: 200.0 g of butyl acetate, 100.0 g of toluene and 60.0 g of isopropanol, and mix them to obtain a composite solvent;

[0127] Weigh: 800.0 g of the hybrid polyimide prepared in Example 8, 150.0 g of the composite nanoparticles prepared in Example 11 and 360.0 g of the composite solvent, add them to a reaction kettle and stir. After the temperature of the reaction kettle rises to 80 °C, add 30.0 g of azobisisobutyronitrile, keep stirring for 60 min, then add 30.0 g of 2-hydroxy-4-octyloxybenzophenone, 50.0 g of sodium carboxymethylcellulose, 20.0 g of dimethyl silicone oil and 60.0 g of diaminodiphenyl ether to the reaction kettle, keep stirring for 15 min, and cool naturally to room temperature to obtain the corona-resistant insulating paint.

[0128] Example 15

[0129] This example provides a preparation method of corona-resistant insulating paint for enameled wire, including the following steps:

[0130] Weigh: 180.0 g of butyl acetate, 100.0 g of toluene and 60.0 g of isopropanol, and mix them to obtain a composite solvent;

[0131] Weigh: 720.0 g of the hybrid polyimide prepared in Example 9, 120.0 g of the composite nanoparticles prepared in Example 12 and 340.0 g of the composite solvent, add them to a reaction kettle and stir. After the temperature of the reaction kettle rises to 80 °C, add 25.0 g of azobisisobutyronitrile, keep stirring for 50 min, then add 24.0 g of 2-hydroxy-4-octyloxybenzophenone, 36.0 g of sodium carboxymethylcellulose, 16.0 g of dimethyl silicone oil and 54.0 g of diaminodiphenyl ether to the reaction kettle, keep stirring for 12 min, and cool naturally to room temperature to obtain the corona-resistant insulating paint.

[0132] Comparative Example 1

[0133] The difference between this comparative example and Example 15 is that in the preparation of the hybrid polyimide used, step (1) is cancelled, and hybrid polyamic acid is used to replace composite polyamic acid in step (2).

[0134] Comparative Example 2

[0135] The difference between this comparative example and Example 15 is that in the preparation of the hybrid polyamic acid used in the preparation of the hybrid polyimide, step (ii) is cancelled.

[0136] Comparative Example 3

[0137] The difference between this comparative example and Example 15 is that the use of composite nanoparticles is cancelled.

[0138] Performance test:

[0139] Referring to the standard GB / T 24122-2009 "Paint for corona-resistant enamelled wire", the corona resistance life, scratch resistance and solvent resistance of the cured paint surface of the corona-resistant insulating paint prepared in Examples 13-15 and Comparative Examples 1-3 were measured;

[0140] Referring to the standard GB 28374-2012 "Cable fire retardant paint", the flame retardant performance of the cured paint surface of the corona-resistant insulating paint prepared in Examples 13-15 and Comparative Examples 1-3 was measured;

[0141] Referring to the standard GB / T 31838.2-2019 "Dielectric and resistive properties of solid insulating materials - Part 2: Resistive properties (DC method) - Volume resistance and volume resistivity", the volume resistivity of the cured paint surface of the corona-resistant insulating paint prepared in Examples 13-15 and Comparative Examples 1-3 was tested;

[0142] Referring to the standard GB / T 16422.3-2022 "Plastics - Methods of exposure to laboratory light sources - Part 3: Fluorescent UV lamps", the cured paint surfaces of the corona-resistant insulating paint prepared in Examples 13-15 and Comparative Examples 1-3 were subjected to ultraviolet aging test, and the scratch resistance pressure retention rate of the paint surface was measured referring to the standard GB / T 24122-2009. The specific data are shown in Table 1.

[0143] Table 1 - Performance test data table of each sample

[0144]

[0145]

[0146] Data analysis:

[0147] Comparing and analyzing the data in Table 1 above, the corona resistance performance of the cured paint surface of the corona-resistant insulating paint prepared by the present invention is 5 h, the scratch resistance pressure is 13.2 N, the hardness after solvent immersion is 3H, the carbonization height is 1.1 m, and the volume resistivity is 3.78×10 16 Ω·m, and the scratch resistance pressure retention rate after ultraviolet aging is 98.9%. All the data are better than those of the comparative examples;

[0148] The present invention constructs a polyimide main chain combining rigidity and flexibility through the introduction of a polysiloxane chain extender. The flexible silicone chain segments are combined with the rigid aromatic rings through hydrogen bonds, improving the interfacial compatibility and mechanical toughness while maintaining the high-temperature resistance of the material, and suppressing partial discharge caused by microcracks. Secondly, the nano-titanium dioxide particles and the silicon-aluminum-boron composite particles modified with fluorine groups act synergistically. Titanium dioxide evenly disperses the electric field through its high dielectric properties, while the fluorine groups capture free electrons with their strong electronegativity and form a hydrophobic barrier to block moisture penetration and active oxygen erosion. Furthermore, a three-dimensional crosslinked network is constructed through free radical reactions, and the double bonds on the surface of the silicon-aluminum-boron particles form dynamic bonding with the polyimide main chain, achieving energy dissipation through molecular chain slippage under electric field stress and avoiding breakdown caused by charge concentration, thus significantly improving the corona resistance, insulation and solvent resistance of the insulating paint;

[0149] The silicone chain extender prepared by the present invention forms a structure combining rigidity and flexibility with the rigid polyimide main chain through flexible chain segments. It not only maintains the high-strength characteristics of the material but also disperses mechanical stress through molecular chain slippage. Combining with the hard support and uniform dispersion of the nano-titanium dioxide particles, physical crosslinking points are formed to resist friction and wear and inhibit the propagation of surface cracks. During the combustion process, the fluorine-containing free radicals generated by the high-temperature decomposition of the fluorine groups interrupt the combustion chain reaction. When the silicon-aluminum-boron particles are heated, a dense oxide layer is formed on the surface to isolate the transfer of oxygen and heat, and the boron element catalyzes the rapid formation of a char layer to further block the spread of the flame; The strong binding between the fluorine-group modified nanoparticles and the polymer interface inhibits crack propagation, and the rigid support of the crosslinked network and the flexible buffer of the silicone chain complement each other, thus significantly improving the flame retardancy and wear resistance of the insulating paint;

[0150] A large number of fluorine groups in the insulating paint prepared by the present invention absorb ultraviolet light energy through their strong electronegativity and release it as heat. Their chemical inertness forms a dense barrier to block the direct damage of ultraviolet rays to the polymer main chain. At the same time, the hydrophobic property inhibits the photooxidation reaction synergistically with water vapor. The nano-titanium dioxide particles reflect and scatter ultraviolet rays with their high refractive index characteristics, reducing its penetration depth. The evenly dispersed particles are chemically bonded to the polymer chains, synergistically inhibiting the breakage of molecular chains. The perfluorinated groups modified on the surface of the silicon-aluminum-boron composite nanoparticles are crosslinked with the polyimide segments through double bonds through free radical reactions to form a spatial crosslinked network, fixing the particle positions to enhance the coating denseness and reducing the propagation of microcracks induced by ultraviolet rays. The high thermal conductivity aids in heat energy diffusion, avoiding local temperature rise and accelerating aging, thus significantly improving the ultraviolet resistance of the insulating paint.

[0151] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments only. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A corona-resistant insulating paint for enameled wire, characterized in that, Comprising the following raw material components by weight parts: 70 - 80 parts of hybrid polyimide, 10 - 15 parts of composite nanoparticles, 30 - 36 parts of composite solvent, and 6 - 8 parts of auxiliary additives, wherein the composite solvent includes: butyl acetate, toluene, and isopropanol; the auxiliary additives include: ultraviolet absorber, thickener, leveling agent, initiator, and hardener; The preparation method of the hybrid polyimide includes the following steps: A1. Add hybrid polyamic acid and N,N - dimethylformamide into a reaction kettle, stir at room temperature for 10 - 15 min, then add the modification liquid dropwise into the reaction kettle. After the dropping is completed, continue to stir for 3 - 5 min, let it stand for 20 - 30 min, and perform post - treatment to obtain composite polyamic acid, wherein the modification liquid is obtained by mixing and stirring tetraethyl titanate and deionized water according to the dosage ratio of 1 - 2 g:10 mL; A2. Perform thermal imidization on the composite polyamic acid to obtain hybrid polyimide; The preparation method of the hybrid polyamic acid includes the following steps: B1. Add (E) - but - 2 - ene - 1,4 - diamine and N,N - dimethylformamide into a reaction kettle at a temperature of 0 - 5 °C, keep warm and stir until all the reactants are dissolved, then add 4,4' - (hexafluoroisopropylidene) diphthalic anhydride into the reaction kettle in three portions. After the addition is completed, the temperature of the reaction kettle is steadily raised to 30 - 50 °C, keep warm and react for 2 - 4 h, and perform post - treatment to obtain modified polyamic acid; B2. Add the modified polyamic acid, modified chain extender, benzoic acid, and N,N - dimethylformamide into a reaction kettle and stir. The temperature of the reaction kettle is raised to 60 - 80 °C, keep warm and stir for 60 - 80 min, and perform post - treatment to obtain hybrid polyamic acid; The preparation method of the modified chain extender includes the following steps: C1. Add 2,4,6 - trivinyl - 2,4,6 - trimethylcyclotrisiloxane, 1,3 - dimethyl - 1,1,3,3 - tetraethenyldisiloxane, and diethyl ether into a reaction kettle and stir. During the stirring process, add 98 wt% concentrated sulfuric acid. After stirring at room temperature for 8 - 10 h, add sodium bicarbonate powder into the reaction kettle to adjust the system pH = 8 - 9, and perform post - treatment to obtain modified silicone oil; C2. Add the modified silicone oil, benzoic acid, aluminum chloride, and dimethyl sulfoxide into a reaction kettle and stir. The temperature of the reaction kettle is lowered to 0 - 5 °C, and saturated hydrogen peroxide solution is added dropwise into the reaction kettle under the condition of keeping warm and stirring. The dropping operation lasts for 3 - 4 h. After the dropping is completed, keep warm and stir for 1 h, and perform post - treatment to obtain the modified chain extender; The preparation method of the composite nanoparticles includes the following steps: D1. Slowly add methyl orthosilicate, tributyl borate, and deionized water into a three - necked flask equipped with a thermometer, stirrer, and cooling reflux device in sequence. Under the condition of stirring, heat the three - necked flask to reflux, then keep warm and stir for 4 - 5 h. Remove the cooling reflux device and replace it with a rectification device, then add aluminum isopropoxide into the reaction kettle. Heat the temperature of the three - necked flask to 115 - 120 °C, keep warm for 10 - 20 min, and perform post - treatment to obtain modified nanoparticles; D2. Add the modified nanoparticles, toluene, composite modifier and deionized water into a reaction kettle. After adjusting the pH of the system to 8 - 10 with saturated sodium hydroxide solution, raise the temperature of the reaction kettle to 30 - 40 °C, keep warm and stir for 30 - 40 min, and then conduct post-treatment to obtain composite nanoparticles. Among them, the composite modifier is obtained by mixing perfluorooctyltrimethoxysilane, 3-(methacryloyloxy)propyltrimethoxysilane and absolute ethanol in a dosage ratio of 1 - 2 g:1 - 2 g:10 - 15 mL.

2. The corona-resistant insulating paint for enameled wire according to claim 1, wherein In step A1, the dosage ratio of the hybrid polyamic acid, N,N-dimethylformamide and the modifier solution is 8 - 10 g:40 - 50 mL:10 mL; in step A2, the preparation method of the hybrid polyimide is as follows: transfer the composite polyamic acid to an electrothermal constant temperature oven, after introducing nitrogen protection, heat the electrothermal constant temperature oven to 100 °C, keep warm for 60 - 80 min, then continue to raise the temperature of the electrothermal constant temperature oven to 200 °C, keep warm for 1 h, then raise the temperature of the electrothermal constant temperature oven to 300 °C again, keep warm for 1 h, and then naturally cool to room temperature to obtain the composite polyimide.

3. An anti-corona insulating paint for enameled wire according to claim 1, characterized in that, In step C1, the dosage ratio of 2,4,6-trivinyl-2,4,6-trimethylcyclotrisiloxane, 1,3-dimethyl-1,1,3,3-tetravinyldisiloxane, diethyl ether and 98 wt% concentrated sulfuric acid is 7 - 9 g:2 - 3 g:50 - 80 mL:10 - 12 mL; in step C2, the dosage ratio of the modified silicone oil, benzoic acid, aluminum chloride, dimethyl sulfoxide and saturated hydrogen peroxide solution is 12 - 16 g:3 - 5 g:0.5 - 0.8 g:60 - 80 mL:10 - 12 mL.

4. A method for preparing a corona-resistant insulating varnish for enameled wire as described in any one of claims 1-3, characterized in that, Add the hybrid polyimide, composite nanoparticles and composite solvent into a reaction kettle and stir. After raising the temperature of the reaction kettle to 60 - 80 °C, add an initiator, keep warm and stir for 40 - 60 min, then add an ultraviolet absorber, a thickener, a leveling agent and a hardener into the reaction kettle, keep warm and stir for 10 - 15 min, and then naturally cool to room temperature to obtain the corona-resistant insulating paint.

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