High ignition point high thermal conductivity mineral insulating oil and preparation method thereof

Abstract

The application discloses a high-ignition-point high-thermal-conductivity mineral insulating oil and a preparation method thereof, and belongs to the technical field of insulating oil preparation, and is used for solving the technical problem that the ignition point and the thermal conductivity of the mineral insulating oil in the prior art need to be further improved, and specifically comprises the following raw material components in parts by weight: 80-90 parts of modified mineral base oil and 5-6 parts of an insulating thermal conductor, in the application, a flame-retardant modifier is first synthesized, then free radical initiation is adopted to graft glycidyl methacrylate and the flame-retardant modifier to liquid paraffin to prepare modified mineral base oil containing an epoxy group; subsequently, modified nitrogenized modified graphene oxide is prepared by using the prepared modified nitrogenized modified graphene oxide, modified graphene is obtained, the modified graphene and epoxidized soybean oil are crosslinked under catalysis of triethylamine to generate modified soybean oil, and an insulating thermal conductor is prepared by introducing a perfluoro group, and finally, the modified mineral insulating oil is synthesized by reacting the components at high temperature.

Description

Technical Field

[0001] This invention relates to the field of insulating oil preparation technology, specifically to a high-ignition-point, high-thermal-conductivity mineral insulating oil and its preparation method. Background Technology

[0002] The development of high thermal conductivity and high flash point mineral insulating oil has followed an evolutionary path of "safety - performance - function". In the early days, mineral oil-based insulating oils mainly met the electrical insulation requirements, but their low thermal conductivity, flash point and ignition point limited their application in high-voltage and high-load equipment. As the power system develops towards high voltage and large capacity, higher requirements are placed on the thermal management and safety of insulating oils.

[0003] Therefore, research has gradually focused on improving thermal conductivity and flame retardancy: first, physical mixing methods were used to introduce nanoparticles such as alumina and boron nitride, and then surface modification technology was developed to improve the dispersion stability and interfacial thermal conductivity of nanofillers. At the same time, chemically modified mineral oils have also gradually emerged, improving the thermal stability and flash point of oils through structural design. In recent years, functional composite insulating oils have become a hot topic. For example, natural ester-based or mineral oil composite systems that combine environmental friendliness, renewability and high thermal conductivity are becoming an important direction for the next generation of insulating oils.

[0004] The prior art CN111808667B discloses a high flash point mineral insulating oil, which is composed of mineral insulating oil and a liquid flame retardant. The liquid flame retardant is toluene diphenyl phosphate, triisopropylphenyl phosphate, tris(1,3-dichloroisopropyl) phosphate, and chlorinated paraffin 42. The content of the liquid flame retardant accounts for 3.5-7% of the mass of the high flash point mineral insulating oil. The preparation method includes: adding toluene diphenyl phosphate, triisopropylphenyl phosphate, tris(1,3-dichloroisopropyl) phosphate, and chlorinated paraffin 42 to the mineral insulating oil and stirring until well mixed. This invention improves the flash point of the insulating oil by adding a suitable liquid flame retardant. The addition of the liquid flame retardant does not change the physicochemical and electrical properties of the mineral insulating oil, so that the insulating oil has both the excellent cooling and insulating properties of the mineral insulating oil.

[0005] However, the above invention only increases the ignition point of the insulating oil by adding a suitable liquid flame retardant to the mineral insulating oil. However, the chemical stability and compatibility of the above organic flame retardants at high temperatures are limited. During long-term use, precipitation, stratification or side reactions may occur, affecting the physical and chemical properties and electrical insulation performance of the oil and reducing the ignition point of the mineral insulating oil.

[0006] Moreover, while increasing the ignition point, the thermal conductivity of the oil was not optimized. Some organic flame retardants have high viscosity, which may adversely affect the overall heat dissipation capacity of the oil. Therefore, the ignition point and thermal conductivity of this mineral insulating oil need to be further improved. Summary of the Invention

[0007] The purpose of this invention is to provide a high-ignition-point, high-thermal-conductivity mineral insulating oil and its preparation method, in order to solve the technical problem that the ignition point and thermal conductivity of mineral insulating oils in the prior art need to be further improved.

[0008] The objective of this invention can be achieved through the following technical solution: a high-ignition-point, high-thermal-conductivity mineral insulating oil, comprising the following raw material components by weight: 80-90 parts modified mineral base oil and 5-6 parts insulating and thermally conductive agent;

[0009] The modified mineral-based oil is prepared by adding liquid paraffin, glycidyl methacrylate, flame retardant modifier, and o-xylene into a reaction vessel and stirring. After the temperature of the reaction vessel is raised to 70-80℃, azobisisobutyronitrile is added to the reaction vessel, and the mixture is kept warm and stirred for 2-4 hours. The modified mineral-based oil is then obtained through post-treatment. The ratio of liquid paraffin, glycidyl methacrylate, flame retardant modifier, o-xylene, and azobisisobutyronitrile is 8-10g:0.3-0.5g:1-2g:40-50mL:0.1g.

[0010] The reaction principle for preparing modified mineral-based oil is as follows: Azobisisobutyronitrile decomposes under heating to generate free radicals, which initiate the breaking of carbon-carbon double bonds in glycidyl methacrylate and flame retardant modifier molecules, and graft glycidyl methacrylate into liquid paraffin to introduce epoxy groups, thereby obtaining modified mineral-based oil.

[0011] Further post-processing includes: after the reaction is completed, wait for the temperature of the reactor to drop to room temperature, transfer the reaction liquid to a rotary evaporator at a temperature of 70-80℃, and distill under reduced pressure until no liquid is collected to obtain modified mineral-based oil.

[0012] Furthermore, the preparation method of the flame retardant modifier includes the following steps:

[0013] A1. N,N-dimethylformamide and 3-butenetriethoxysilane were added to a reaction vessel. After the temperature of the reaction vessel was raised to 60-80℃, aluminum chloride and a calculated amount of DOPO were added to the reaction vessel. The mixture was kept warm and stirred for 1-2 hours. The modified siloxane was obtained after post-treatment.

[0014] A2. Add modified siloxane, anhydrous ethanol and deionized water to the reactor. After the reactor temperature is raised to 40-60℃, adjust the pH of the reaction system to 4-5 with acetic acid. After stirring for 2-3 hours, add the end-capping agent to the reactor and keep it at the temperature for 20-30 minutes. The flame retardant modifier is then obtained after post-treatment.

[0015] The reaction equation for preparing the flame retardant modifier is:

[0016]

[0017] In the formula:

[0018] The reaction principle for preparing the flame retardant modifier is as follows: Under the catalysis of Lewis acid, DOPO undergoes a phosphorus hydroaddition reaction with part of 3-butenetriethoxysilane to prepare a two-component modified siloxane. Under acidic and heating conditions, the ethoxysilane structure on the modified siloxane undergoes hydrolysis to form an extended chain structure. Finally, through end-capping with perfluorobutanol, a flame retardant modifier with double bonds and flame retardant structure is finally prepared.

[0019] Further, in step A1, the ratio of N,N-dimethylformamide, 3-butenetriethoxysilane, and triethylamine is 20-24 mL: 3-4 g: 0.2-0.3 g, wherein the amount of DOPO is 0.3-0.4 times the molar amount of 3-butenetriethoxysilane. The post-treatment includes: after the reaction is completed, after the temperature of the reaction vessel is reduced to room temperature, the reaction solution is transferred to a rotary evaporator at a temperature of 70-80℃ and distilled under reduced pressure until no liquid is collected, thereby obtaining the modified siloxane;

[0020] Further, in step A2, the ratio of modified siloxane, anhydrous ethanol, deionized water, and end-capping agent is 4-5g:20-30mL:10-12mL:0.3-0.5g, wherein the end-capping agent is perfluorobutanol. The post-treatment includes: after the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, add sodium bicarbonate to the reaction vessel until the reaction system is neutral, transfer the reaction solution to a rotary evaporator at a temperature of 70-80℃, and distill under reduced pressure until no liquid is collected to obtain the flame retardant modifier.

[0021] Furthermore, the preparation method of the insulating and thermally conductive agent is as follows:

[0022] B1. Add epoxidized soybean oil and N,N-dimethylformamide to a reaction vessel and stir. After the temperature of the reaction vessel is raised to 60-80℃, add triethylamine and modified graphene to the reaction vessel, keep warm and stir for 2-4 hours, and then process to obtain modified soybean oil.

[0023] B2. Modified soybean oil and N,N-dimethylformamide are added to a reaction vessel. After the temperature of the reaction vessel is raised to 80-90℃, a calculated amount of 1H,1H-perfluorooctylamine is added to the reaction vessel. The reaction is kept at this temperature for 1-2 hours. The resulting insulating and thermally conductive agent is then obtained through post-treatment.

[0024] The reaction principle for preparing the insulating and thermally conductive agent is as follows: Under heating conditions and the catalysis of triethylamine, the epoxy groups in epoxidized soybean oil undergo ring-opening to generate free radicals, which then react with the active sites (such as hydroxyl and carboxyl groups) on modified graphene, thereby forming a cross-linked structure between the modified graphene and the epoxidized soybean oil, resulting in modified soybean oil. Under the promotion of heating conditions, the amino group on 1H,1H-perfluorooctylamine attacks the epoxy groups, and by controlling the amount of substance, the epoxy groups are completely consumed, and perfluorinated groups are introduced into the epoxidized soybean oil, thus obtaining the insulating and thermally conductive agent.

[0025] Furthermore, in step B1, the ratio of epoxidized soybean oil, N,N-dimethylformamide, triethylamine, and modified graphene is 4-5g:20-25mL:0.3-0.5g:1-2g. The post-processing includes: after the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, transfer the reaction solution to a rotary evaporator at a temperature of 70-80℃, and distill under reduced pressure until no liquid is collected to obtain modified soybean oil.

[0026] Furthermore, in step B2, the ratio of modified soybean oil to N,N-dimethylformamide is 1-2 g: 10-12 mL, wherein the amount of 1H,1H-perfluorooctylamine is 1.1-1.2 times the molar amount of epoxy groups in the modified soybean oil. The post-treatment includes: after the reaction is completed, after the temperature of the reaction vessel is reduced to room temperature, the reaction solution is transferred to a rotary evaporator at a temperature of 70-80℃ and distilled under reduced pressure until no liquid is collected, thus obtaining an insulating thermal conductive agent.

[0027] Furthermore, the preparation method of modified graphene includes the following steps:

[0028] C1. Add silicon nitride powder, anhydrous ethanol and deionized water to a reaction vessel and stir. Raise the reaction temperature to 40-60℃ and adjust the pH of the reaction system to 4-5 with acetic acid. Then add 3-aminopropyltrimethoxysilane to the reaction vessel, keep it warm and stir for 1-2 hours, and then process it to obtain modified silicon nitride.

[0029] C2. Graphene oxide, N,N-dimethylformamide and deionized water are added to a reaction vessel and stirred. After the temperature of the reaction vessel is raised to 70-80℃, modified silicon nitride is added to the reaction vessel and the reaction is maintained at this temperature for 2-4 hours. Modified graphene is then obtained through post-treatment.

[0030] The reaction principle for preparing modified graphene is as follows: under acidic and heating conditions, the methoxysilane on 3-aminopropyltrimethoxysilane hydrolyzes, thereby introducing an amino group onto silicon nitride to obtain modified silicon nitride; under stirring and heating conditions, the amino group on the modified silicon nitride reacts with the epoxy group on graphene oxide, thereby modifying and intercalating the surface of graphene oxide to obtain modified graphene.

[0031] Further, in step C1, the ratio of silicon nitride powder, anhydrous ethanol, deionized water, and 3-aminopropyltrimethoxysilane is 2-3g:20-25mL:10-12mL:0.1-0.2g. The post-treatment includes: after the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, add sodium bicarbonate to the reaction vessel until the reaction system is neutral, filter the reaction liquid to collect the filter cake, wash the filter cake 3-5 times with anhydrous ethanol and deionized water, and then transfer the filter cake to a drying oven at a temperature of 60-80℃ and vacuum dry it to constant weight to obtain modified silicon nitride.

[0032] Further, in step C2, the ratio of graphene oxide, N,N-dimethylformamide, deionized water, and modified silicon nitride is 3-4g:10-12mL:10-12mL:1-2g. The post-treatment includes: after the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, filter the reaction solution to collect the filter cake, wash the filter cake 3-5 times with anhydrous ethanol and deionized water, and then transfer the filter cake to a drying oven at a temperature of 60-80℃ and vacuum dry it to constant weight to obtain modified graphene.

[0033] The present invention also discloses a method for preparing a high-ignition-point, high-thermal-conductivity mineral insulating oil, wherein modified mineral base oil and insulating thermal conductive agent are added to a stirring vessel, the temperature of the stirring vessel is raised to 100-120°C, and the mixture is stirred at this temperature for 10-15 minutes. After stirring, the mixture is passed through an 80-100 mesh sieve and stored in the dark to obtain the modified mineral insulating oil.

[0034] The reaction principle for preparing modified mineral insulating oil is as follows: under the promotion of high temperature, the trace epoxy groups on the modified mineral base oil react with the active sites on the modified graphene and silicon nitride components on the insulating and thermally conductive agent, thereby preparing the modified mineral insulating oil.

[0035] The present invention has the following beneficial effects:

[0036] 1. This invention introduces perfluorinated groups into modified mineral insulating oil. Due to their high electronegativity and low polarizability, these groups significantly reduce the oil's polarity and conductivity, decreasing ion migration and leakage losses. This enhances insulation under strong electric fields and suppresses energy loss. Their hydrophobic properties effectively prevent moisture adsorption, further maintaining insulation stability. Modified silicon nitride introduces amino groups through 3-aminopropyltrimethoxysilane, forming a high-dielectric, low-conductivity structure. This structure, synergistically with graphene, constructs a uniform electric field barrier, reducing dielectric loss. Simultaneously, epoxidized soybean oil, through cross-linking with modified graphene, forms a dense molecular network, reducing the ionization tendency of microbubbles and impurities in the oil and strengthening insulation performance. By reducing system polarity, optimizing electric field distribution, and enhancing structural stability, each component synergistically improves the electrical properties of the insulating oil, ensuring its stability and low-loss performance under high-voltage environments, providing reliable insulation protection for transformers and other equipment.

[0037] 2. This invention introduces modified graphene into modified mineral insulating oil. Due to its excellent thermal conductivity, graphene serves as the main thermally conductive component. Through a cross-linking reaction with epoxidized soybean oil, it is uniformly dispersed in the oil matrix, forming a highly efficient thermally conductive network and improving thermal conductivity. Modified silicon nitride, through surface amylation, enhances its compatibility with the oil matrix and synergistically constructs multi-scale thermal conductive pathways with graphene, further strengthening thermal conductivity. The cross-linked structure of epoxidized soybean oil not only improves filler dispersion and reduces interfacial thermal resistance but also stabilizes the thermally conductive network through chemical bonding, enhancing heat transfer efficiency. Simultaneously, perfluorinated groups reduce intermolecular forces, optimize fluidity, and assist in the stability of the thermally conductive network. Through the uniform dispersion of highly thermally conductive fillers and the strengthening of the cross-linked structure, all components synergistically improve the thermal conductivity of the insulating oil, providing excellent heat dissipation capabilities for transformers and other equipment, ensuring efficient thermal management during operation.

[0038] 3. This invention introduces DOPO as a phosphorus-containing flame retardant into modified mineral insulating oil. At high temperatures, DOPO decomposes to generate phosphoric acid derivatives, promoting the formation of a carbonized layer, isolating oxygen and heat, and effectively inhibiting combustion reactions. The perfluorinated groups, due to their high thermal stability and low flammability, synergistically form a chemical flame retardant mechanism with DOPO, reducing the tendency to burn and enhancing flame resistance. Simultaneously, the carbonized structure of modified graphene acts as a physical barrier, slowing heat transfer and oxygen diffusion, further improving the flame retardant effect. Epoxidized soybean oil, through a cross-linking reaction with modified graphene, forms a dense organic network, strengthening structural stability at high temperatures and enhancing flame retardant performance. Through the synergistic mechanism of chemical flame retardancy, physical barriers, and structural stability, the components significantly increase the ignition point of the insulating oil, ensuring its safety under high temperature or spark conditions, and providing reliable flame-retardant protection for equipment such as transformers. Detailed Implementation

[0039] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] The liquid paraffin used in this invention was purchased from Shanghai Yuanye Biotechnology Co., Ltd., item number S68179; the silicon nitride powder was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., item number S817703; the graphene oxide was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., item number G768901; and the DOPO was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., item number D742470, CAS number 35948-25-5.

[0041] Example 1

[0042] This embodiment provides a method for preparing an insulating and thermally conductive agent for high-ignition-point, high-thermal-conductivity mineral insulating oil, comprising the following steps:

[0043] Step I: Preparation of modified silicon nitride

[0044] Weigh 20.0g of silicon nitride powder, 200.0mL of anhydrous ethanol and 100.0mL of deionized water and add them to the reaction vessel. Stir the mixture and raise the reaction temperature to 40℃. Adjust the pH of the reaction system to 5 with acetic acid. Then add 1.0g of 3-aminopropyltrimethoxysilane to the reaction vessel and stir for 1 hour. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature. Add sodium bicarbonate to the reaction vessel until the reaction system is neutral. Filter the reaction liquid and collect the filter cake. Wash the filter cake three times with anhydrous ethanol and deionized water. Transfer the filter cake to a drying oven at 60℃ and vacuum dry it to constant weight to obtain modified silicon nitride.

[0045] Step II: Preparation of modified graphene

[0046] Weigh out 30.0 g of graphene oxide, 100.0 mL of N,N-dimethylformamide and 100.0 mL of deionized water and add them to the reaction vessel. Stir the mixture and raise the temperature of the reaction vessel to 70°C. Then add 10.0 g of modified silicon nitride to the reaction vessel and keep it at this temperature for 2 hours. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature. Filter the reaction liquid and collect the filter cake. Wash the filter cake three times with anhydrous ethanol and deionized water. Transfer the filter cake to a drying oven at 60°C and vacuum dry it to constant weight to obtain modified graphene.

[0047] Step III: Preparation of modified soybean oil

[0048] Weigh out 40.0g of epoxidized soybean oil and 200.0mL of N,N-dimethylformamide and add them to the reaction vessel. Stir the mixture. After the temperature of the reaction vessel is raised to 60℃, add 3.0g of triethylamine and 10.0g of modified graphene to the reaction vessel. Keep the mixture warm and stir for 2 hours. After the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature. Transfer the reaction solution to a rotary evaporator at 70℃ and distill under reduced pressure until no liquid is collected to obtain modified soybean oil.

[0049] Step VI: Preparation of insulating and thermally conductive agent

[0050] Weigh out 10.0g of modified soybean oil and 100.0mL of N,N-dimethylformamide and add them to the reactor. After the reactor temperature is raised to 80℃, add 1H,1H-perfluorooctylamine, which is 1.1 times the molar amount of epoxy groups in the modified soybean oil, to the reactor. Keep the reactor at this temperature for 1 hour. After the reaction is complete, wait for the reactor temperature to drop to room temperature, then transfer the reaction solution to a rotary evaporator at 70℃ and distill under reduced pressure until no liquid is collected to obtain the insulating thermal conductive agent.

[0051] Example 2

[0052] This embodiment provides a method for preparing an insulating and thermally conductive agent for high-ignition-point, high-thermal-conductivity mineral insulating oil, comprising the following steps:

[0053] Step I: Preparation of modified silicon nitride

[0054] Weigh out 30.0 g of silicon nitride powder, 250.0 mL of anhydrous ethanol and 120.0 mL of deionized water and add them to the reaction vessel. Stir the mixture and raise the reaction temperature to 60 °C. Adjust the pH of the reaction system to 4 with acetic acid. Then add 2.0 g of 3-aminopropyltrimethoxysilane to the reaction vessel and stir for 2 h. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature. Add sodium bicarbonate to the reaction vessel until the reaction system is neutral. Filter the reaction liquid and collect the filter cake. Wash the filter cake 5 times with anhydrous ethanol and deionized water. Transfer the filter cake to a drying oven at 80 °C and vacuum dry it to constant weight to obtain modified silicon nitride.

[0055] Step II: Preparation of modified graphene

[0056] Weigh out 40.0 g of graphene oxide, 120.0 mL of N,N-dimethylformamide and 120.0 mL of deionized water and add them to the reaction vessel. Stir the mixture and raise the temperature of the reaction vessel to 80°C. Then add 20.0 g of modified silicon nitride to the reaction vessel and keep it at this temperature for 4 hours. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature. Filter the reaction liquid and collect the filter cake. Wash the filter cake 5 times with anhydrous ethanol and deionized water. Transfer the filter cake to a drying oven at 80°C and vacuum dry it to constant weight to obtain modified graphene.

[0057] Step III: Preparation of modified soybean oil

[0058] Weigh out 50.0g of epoxidized soybean oil and 250.0mL of N,N-dimethylformamide and add them to the reaction vessel. Stir the mixture. After the temperature of the reaction vessel is raised to 80℃, add 5.0g of triethylamine and 20.0g of modified graphene to the reaction vessel. Keep the mixture warm and stir for 4 hours. After the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature. Transfer the reaction solution to a rotary evaporator at 80℃ and distill under reduced pressure until no liquid is collected to obtain modified soybean oil.

[0059] Step VI: Preparation of insulating and thermally conductive agent

[0060] Weigh 20.0g of modified soybean oil and 120.0mL of N,N-dimethylformamide and add them to the reactor. After the reactor temperature is raised to 90℃, add 1H,1H-perfluorooctylamine, which is 1.2 times the molar amount of epoxy groups in the modified soybean oil, to the reactor. Keep the reactor at this temperature for 2 hours. After the reaction is complete, wait for the reactor temperature to drop to room temperature, then transfer the reaction solution to a rotary evaporator at 80℃ and distill under reduced pressure until no liquid is collected to obtain the insulating thermal conductive agent.

[0061] Example 3

[0062] This embodiment provides a method for preparing an insulating and thermally conductive agent for high-ignition-point, high-thermal-conductivity mineral insulating oil, comprising the following steps:

[0063] Step I: Preparation of modified silicon nitride

[0064] Weigh out 24.0 g of silicon nitride powder, 240.0 mL of anhydrous ethanol and 120.0 mL of deionized water and add them to the reaction vessel. Stir the mixture and raise the reaction temperature to 50 °C. Adjust the pH of the reaction system to 4 with acetic acid. Then add 1.6 g of 3-aminopropyltrimethoxysilane to the reaction vessel and stir for 3 h. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature. Add sodium bicarbonate to the reaction vessel until the reaction system is neutral. Filter the reaction liquid and collect the filter cake. Wash the filter cake 4 times with anhydrous ethanol and deionized water. Transfer the filter cake to a drying oven at 70 °C and vacuum dry it to constant weight to obtain modified silicon nitride.

[0065] Step II: Preparation of modified graphene

[0066] Weigh out 36.0 g of graphene oxide, 120.0 mL of N,N-dimethylformamide and 120.0 mL of deionized water and add them to the reaction vessel. Stir the mixture and raise the temperature of the reaction vessel to 75°C. Then add 16.0 g of modified silicon nitride to the reaction vessel and keep it at this temperature for 3 hours. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature. Filter the reaction liquid and collect the filter cake. Wash the filter cake four times with anhydrous ethanol and deionized water. Transfer the filter cake to a drying oven at 70°C and vacuum dry it to constant weight to obtain modified graphene.

[0067] Step III: Preparation of modified soybean oil

[0068] Weigh out 45.0g of epoxidized soybean oil and 240.0mL of N,N-dimethylformamide and add them to the reaction vessel and stir. After the temperature of the reaction vessel is raised to 70℃, add 4.0g of triethylamine and 16.0g of modified graphene to the reaction vessel and keep it heated and stirred for 3h. After the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, transfer the reaction solution to a rotary evaporator at 75℃ and distill under reduced pressure until no liquid is collected to obtain modified soybean oil.

[0069] Step VI: Preparation of insulating and thermally conductive agent

[0070] Weigh out 16.0 g of modified soybean oil and 120.0 mL of N,N-dimethylformamide and add them to the reactor. After the reactor temperature is raised to 80°C, add 1H,1H-perfluorooctylamine, which is 1.2 times the molar amount of epoxy groups in the modified soybean oil, to the reactor. Keep the reactor at this temperature for 2 hours. After the reaction is complete, wait for the reactor temperature to drop to room temperature, then transfer the reaction solution to a rotary evaporator at 75°C and distill under reduced pressure until no liquid is collected to obtain the insulating thermal conductive agent.

[0071] Example 4

[0072] This embodiment provides a method for preparing a flame retardant modifier for high-ignition-point, high-thermal-conductivity mineral insulating oil, comprising the following steps:

[0073] Step ①: Preparation of modified siloxanes

[0074] Weigh out 200.0 mL of N,N-dimethylformamide and 30.0 g of 3-butenetriethoxysilane and add them to the reaction vessel. After the temperature of the reaction vessel is raised to 60°C, add 2.0 g of aluminum chloride and DOPO (0.3 times the molar amount of 3-butenetriethoxysilane) to the reaction vessel. Keep the mixture warm and stir for 1 h. After the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, and transfer the reaction solution to a rotary evaporator at 70°C. Distill under reduced pressure until no liquid is collected to obtain modified siloxane.

[0075] Step 2: Preparation of flame retardant modifier

[0076] Weigh out 40.0 g of modified siloxane, 200.0 mL of anhydrous ethanol and 100.0 mL of deionized water and add them to the reaction vessel. After the temperature of the reaction vessel is raised to 40℃, adjust the pH of the reaction system to 5 with acetic acid. After stirring for 2 hours, add 3.0 g of perfluorobutanol to the reaction vessel and keep it at the temperature for 20 minutes. After the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, add sodium bicarbonate to the reaction vessel until the reaction system is neutral, and then transfer the reaction solution to a rotary evaporator at 70℃. Distill under reduced pressure until no liquid is collected to obtain the flame retardant modifier.

[0077] Example 5

[0078] This embodiment provides a method for preparing a flame retardant modifier for high-ignition-point, high-thermal-conductivity mineral insulating oil, comprising the following steps:

[0079] Step ①: Preparation of modified siloxanes

[0080] Weigh out 240.0 mL of N,N-dimethylformamide and 40.0 g of 3-butenetriethoxysilane and add them to the reaction vessel. After the temperature of the reaction vessel is raised to 80°C, add 3.0 g of aluminum chloride and DOPO (0.4 times the molar amount of 3-butenetriethoxysilane) to the reaction vessel. Keep the mixture warm and stir for 2 h. After the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, and transfer the reaction solution to a rotary evaporator at 80°C. Distill under reduced pressure until no liquid is collected to obtain modified siloxane.

[0081] Step 2: Preparation of flame retardant modifier

[0082] Weigh out 50.0 g of modified siloxane, 300.0 mL of anhydrous ethanol and 120.0 mL of deionized water and add them to the reaction vessel. After the temperature of the reaction vessel is raised to 60℃, adjust the pH of the reaction system to 4 with acetic acid. After stirring for 3 h, add 4.0 g of perfluorobutanol to the reaction vessel and keep the reaction at the temperature for 30 min. After the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, add sodium bicarbonate to the reaction vessel until the reaction system is neutral, and then transfer the reaction solution to a rotary evaporator at 80℃. Distill under reduced pressure until no liquid is collected to obtain the flame retardant modifier.

[0083] Example 6

[0084] This embodiment provides a method for preparing a flame retardant modifier for high-ignition-point, high-thermal-conductivity mineral insulating oil, comprising the following steps:

[0085] Step ①: Preparation of modified siloxanes

[0086] Weigh 210.0 mL of N,N-dimethylformamide and 36.0 g of 3-butenetriethoxysilane and add them to the reaction vessel. After the temperature of the reaction vessel is raised to 70°C, add 2.5 g of aluminum chloride and DOPO (0.4 times the molar amount of 3-butenetriethoxysilane) to the reaction vessel. Keep the mixture warm and stir for 2 hours. After the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, and transfer the reaction solution to a rotary evaporator at 80°C. Distill under reduced pressure until no liquid is collected to obtain the modified siloxane.

[0087] Step 2: Preparation of flame retardant modifier

[0088] Weigh out 45.0 g of modified siloxane, 240.0 mL of anhydrous ethanol and 120.0 mL of deionized water and add them to the reaction vessel. After the temperature of the reaction vessel is raised to 50 °C, adjust the pH of the reaction system to 4 with acetic acid. After stirring for 3 h, add 4.0 g of perfluorobutanol to the reaction vessel and keep the reaction at the temperature for 25 min. After the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, add sodium bicarbonate to the reaction vessel until the reaction system is neutral, and then transfer the reaction solution to a rotary evaporator at 80 °C. Distill under reduced pressure until no liquid is collected to obtain the flame retardant modifier.

[0089] Example 7

[0090] This embodiment provides a method for preparing a high-ignition-point, high-thermal-conductivity mineral insulating oil, comprising the following steps:

[0091] Step 1: Preparation of modified mineral-based oil

[0092] Weigh out 80.0g of liquid paraffin, 3.0g of glycidyl methacrylate, 10.0g of the flame retardant modifier prepared in Example 4, and 400.0mL of o-xylene and add them to the reaction vessel. After the temperature of the reaction vessel is raised to 70°C, add 1.0g of azobisisobutyronitrile to the reaction vessel and keep it at the temperature and stir for 2 hours. After the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, transfer the reaction solution to a rotary evaporator at a temperature of 70°C, and distill under reduced pressure until no liquid is collected to obtain modified mineral oil.

[0093] Step 2: Preparation of modified mineral insulating oil

[0094] Weigh out 80 parts by weight of modified mineral base oil and 5 parts by weight of the insulating and thermally conductive agent prepared in Example 1 and add them to a stirring vessel. Raise the temperature of the stirring vessel to 100°C, keep it warm and stir for 10 minutes, then pass it through an 80-mesh sieve and store it in the dark to obtain modified mineral insulating oil.

[0095] Example 8

[0096] This embodiment provides a method for preparing a high-ignition-point, high-thermal-conductivity mineral insulating oil, comprising the following steps:

[0097] Step 1: Preparation of modified mineral-based oil

[0098] Weigh out 100.0g of liquid paraffin, 5.0g of glycidyl methacrylate, 20.0g of the flame retardant modifier prepared in Example 5, and 500.0mL of o-xylene and add them to the reaction vessel. After the temperature of the reaction vessel is raised to 80°C, add 1.0g of azobisisobutyronitrile to the reaction vessel and keep it at the temperature and stir for 4 hours. After the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, transfer the reaction solution to a rotary evaporator at a temperature of 80°C, and distill under reduced pressure until no liquid is collected to obtain modified mineral oil.

[0099] Step 2: Preparation of modified mineral insulating oil

[0100] By weight, 90 parts of modified mineral base oil and 6 parts of the insulating and thermally conductive agent prepared in Example 2 were weighed and added to a stirring vessel. The temperature of the stirring vessel was raised to 120°C, and the mixture was stirred for 15 minutes. After stirring, the mixture was passed through a 100-mesh sieve and stored away from light to obtain the modified mineral insulating oil.

[0101] Example 9

[0102] This embodiment provides a method for preparing a high-ignition-point, high-thermal-conductivity mineral insulating oil, comprising the following steps:

[0103] Step 1: Preparation of modified mineral-based oil

[0104] Weigh out 96.0g of liquid paraffin, 4.0g of glycidyl methacrylate, 18.0g of the flame retardant modifier prepared in Example 6, and 500.0mL of o-xylene and add them to the reaction vessel. After the temperature of the reaction vessel is raised to 80°C, add 1.0g of azobisisobutyronitrile to the reaction vessel and keep it at this temperature for 3 hours. After the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, and then transfer the reaction solution to a rotary evaporator at a temperature of 75°C. Distill under reduced pressure until no liquid is collected to obtain modified mineral oil.

[0105] Step 2: Preparation of modified mineral insulating oil

[0106] By weight, 88 parts of modified mineral base oil and 5 parts of the insulating and thermally conductive agent prepared in Example 3 were weighed and added to a stirring vessel. The temperature of the stirring vessel was raised to 120°C, and after stirring for 15 minutes, it was passed through a 90-mesh sieve and stored in the dark to obtain modified mineral insulating oil.

[0107] Comparative Example 1

[0108] The difference between this comparative example and Example 9 is that the flame retardant modifier used in step one and the insulating thermal conductive agent used in step two respectively omit the use of perfluorobutanol and 1H,1H-perfluorooctylamine during the preparation process.

[0109] Comparative Example 2

[0110] The difference between this comparative example and Example 9 is that steps I, II, and III are omitted during the preparation of the insulating and thermally conductive agent used in step two.

[0111] Comparative Example 3

[0112] The difference between this comparative example and Example 9 is that steps III and VI are omitted during the preparation of the insulating and thermally conductive agent used in step two.

[0113] Performance testing:

[0114] The breakdown voltage and dielectric loss factor of the modified mineral insulating oils prepared in Examples 7-9 and Comparative Examples 1-3 were determined in accordance with the standard DL / T 2411-2021 "Field Test Guidelines for Mineral Insulating Oils for Power Equipment".

[0115] The low-temperature kinematic viscosity of the modified mineral insulating oils prepared in Examples 7-9 and Comparative Examples 1-3 was determined in accordance with the standard NB / SH / T 0837-2010 "Determination of Kinematic Viscosity of Mineral Insulating Oils at Low Temperature".

[0116] The thermal conductivity of the modified mineral insulating oils prepared in Examples 7-9 and Comparative Examples 1-3 was determined in accordance with standard DB61 / T 1609-2022 "Determination of Thermal Conductivity of Lubricating Oils".

[0117] The flash point of the modified mineral insulating oils prepared in Examples 7-9 and Comparative Examples 1-3 was determined according to the standard GB 267-1988 "Determination of Flash Point and Ignition Point of Petroleum Products (Open Cup Method)". The specific data are shown in Table 1.

[0118] Table 1 - Performance Test Data for Each Sample

[0119]

[0120]

[0121] Data Analysis:

[0122] A comparative analysis of the data in Table 1 reveals that the modified mineral insulating oil prepared in this invention has a breakdown voltage of 84 kV, a dielectric loss factor of 0.01, and a low-temperature kinematic viscosity of 446 mm³. 2 ·s -1 With a thermal conductivity of 0.18 and an ignition point of 206℃, all data are superior to the comparative example. This indicates that...

[0123] In Comparative Example 1, the removal of the perfluorinated group during the preparation of modified mineral insulation resulted in the loss of the positive effects of the high electronegativity and low polarizability of the perfluorinated group on the polarity and conductivity of the oil. This led to increased ion migration and leakage losses, a decrease in breakdown voltage, and an increase in dielectric loss factor. Simultaneously, the loss of hydrophobicity increased moisture adsorption, further weakening insulation stability. Regarding thermal conductivity and flowability, the reduction of intermolecular forces by the perfluorinated group disappeared, leading to increased kinematic viscosity, reduced oil flowability, limited efficiency of the heat-conducting network, and decreased heat dissipation performance. Furthermore, the high thermal stability and low flammability of the perfluorinated group are crucial components of chemical flame retardancy; their removal increased the tendency to burn, weakened the insulating effect of the carbonized layer, lowered the ignition point, and reduced flame resistance.

[0124] In Comparative Example 2, the introduction of modified graphene and modified silicon nitride was omitted. Without the high thermal conductivity of modified graphene and silicon nitride to construct an efficient heat-conducting network, the thermal conductivity decreased, the heat dissipation capacity of the oil weakened, and the thermal management efficiency declined. At the same time, in terms of insulation performance, modified graphene optimizes the electric field distribution and reduces partial discharge, while silicon nitride provides a high dielectric and low conductivity structure. After its removal, the electric field distribution became uneven, the tendency for partial discharge increased, the breakdown voltage decreased, and the dielectric loss factor increased. Furthermore, in terms of flame retardant performance, the carbon layer structure of graphene slows down the diffusion of heat and oxygen. After its removal, the physical barrier effect was lost, the combustion inhibition effect weakened, the ignition point decreased, and the flame resistance decreased.

[0125] In Comparative Example 3, the cross-linking reaction of epoxidized soybean oil was eliminated. The cross-linked structure of epoxidized soybean oil forms a dense network, reducing microbubbles and impurity ionization. After elimination, the structural stability of the oil decreased, microbubbles and ion migration increased, the breakdown voltage decreased, and the dielectric loss factor increased. At the same time, in terms of thermal conductivity and flowability, the cross-linked structure improves the dispersibility of graphene and silicon nitride. After elimination, the fillers are prone to agglomeration, the efficiency of the thermal network decreases, the thermal conductivity decreases, the kinematic viscosity fluctuates due to agglomeration, and heat dissipation and flowability are weakened. Furthermore, the cross-linked structure forms a dense carbonized network during combustion, enhancing high-temperature stability. After elimination, the strength of the carbonized layer decreases, the combustion inhibition effect weakens, the ignition point decreases, and the flame resistance decreases.

[0126] This invention improves breakdown voltage by reducing polarity with perfluorinated groups, optimizing electric field distribution with modified graphene and silicon nitride, and reducing microbubbles with cross-linked epoxidized soybean oil. Comparative Example 1, by removing perfluorinated groups, increased polarity, exacerbated moisture adsorption, and increased ion migration and leakage losses, resulting in a slightly lower breakdown voltage than the original scheme. However, the modified graphene, silicon nitride, and cross-linked structure still provided some support. Comparative Example 3, by removing cross-linked epoxidized soybean oil, decreased structural stability, increased microbubbles and ion migration, and further reduced breakdown voltage, but the perfluorinated groups and fillers still retained some insulation. Comparative Example 2, by removing modified graphene and silicon nitride, resulted in uneven electric field distribution, increased partial discharge tendency, and the lowest breakdown voltage. It is difficult to maintain high insulation performance solely with perfluorinated groups and cross-linked structures. Therefore, in terms of breakdown voltage, Example 9 > Comparative Example 1 > Comparative Example 3 > Comparative Example 2.

[0127] This invention reduces the dielectric loss factor by using perfluorinated groups to lower conductivity, modifying graphene and silicon nitride to form a low-conductivity barrier, and using cross-linked epoxidized soybean oil to reduce ion migration. Comparative Example 1, by removing the perfluorinated groups, increases polarity and conductivity, resulting in a slightly higher dielectric loss factor, but the modified graphene, silicon nitride, and cross-linked structure still maintain low losses. Comparative Example 3, by removing the cross-linked epoxidized soybean oil, has a looser structure, increased ion migration, and a higher dielectric loss factor than Comparative Example 1, but the perfluorinated groups and fillers provide some inhibition. Comparative Example 2, by removing the modified graphene and silicon nitride, lacks an electric field barrier, significantly increases conductivity, and has the highest dielectric loss factor. Therefore, in terms of resistance to dielectric loss, Example 9 > Comparative Example 1 > Comparative Example 3 > Comparative Example 2.

[0128] This invention constructs a highly efficient thermally conductive network using modified graphene and silicon nitride. Epoxidized soybean oil crosslinking improves filler dispersion and enhances thermal conductivity. Comparative Example 3, by eliminating epoxidized soybean oil crosslinking, suffers from decreased filler dispersion and reduced thermal network efficiency, resulting in a thermal conductivity lower than the original scheme. However, graphene and silicon nitride still provide high thermal conductivity. Comparative Example 1, by eliminating perfluorinated groups, has a relatively small impact on thermal conductivity, as it is mainly contributed by graphene and silicon nitride. However, its fluidity is slightly reduced, and its thermal conductivity is slightly lower than Comparative Example 3. Comparative Example 2, by eliminating modified graphene and silicon nitride, lacks high thermal conductivity fillers, resulting in the lowest thermal conductivity. Relying solely on the low thermal conductivity of the base oil, its heat dissipation capacity is significantly reduced. Therefore, in terms of thermal conductivity, Example 9 > Comparative Example 3 > Comparative Example 1 > Comparative Example 2.

[0129] This invention optimizes the kinematic viscosity by cross-linking epoxidized soybean oil and using perfluorinated groups, achieving a balance between flowability and thermal conductivity. Comparative Example 1, by removing the perfluorinated groups, increases intermolecular forces, resulting in a slightly higher kinematic viscosity than the original scheme, but the impact is limited and close to the original scheme's level. Comparative Example 3, by removing the cross-linking of epoxidized soybean oil, causes filler agglomeration, leading to fluctuations in kinematic viscosity due to agglomeration, decreased flowability, and a viscosity higher than Comparative Example 1. Comparative Example 2, by removing modified graphene and silicon nitride, exacerbates filler agglomeration, further increasing kinematic viscosity and resulting in the worst flowability. Due to the lack of stability from the cross-linked structure, the viscosity fluctuation is the greatest. Therefore, in terms of flowability, Example 9 > Comparative Example 1 > Comparative Example 3 > Comparative Example 2.

[0130] This invention demonstrates that DOPO promotes carbonization, perfluorinated groups enhance chemical stability, modified graphene provides a physical barrier, and epoxidized soybean oil crosslinks form a dense carbonized network, resulting in the highest ignition point. Comparative Example 3, by eliminating the crosslinking of epoxidized soybean oil, reduces the strength of the carbonized network and slightly lowers the ignition point than the original scheme, but DOPO, perfluorinated groups, and graphene still provide strong flame retardancy. Comparative Example 1, by eliminating perfluorinated groups, weakens the chemical flame retardant effect and lowers the ignition point than Comparative Example 3, but the carbonization effect of DOPO and graphene still maintains a certain flame-retardant effect. Comparative Example 2, by eliminating modified graphene and silicon nitride, lacks a physical barrier and has the lowest ignition point, relying solely on the chemical flame retardancy of DOPO, resulting in a significant decrease in flame-retardant performance. Ultimately, this demonstrates that in terms of flame resistance, Example 9 > Comparative Example 3 > Comparative Example 1 > Comparative Example 2.

[0131] Ultimately, this invention demonstrates that through the synergistic effect of multiple functional materials such as perfluorinated groups, modified silicon nitride, modified graphene, epoxidized soybean oil, and DOPO, it systematically improves the electrical, thermal conductivity, and flame retardant properties of mineral insulating oil. Specifically, perfluorinated groups reduce polarity and conductivity, ensuring basic insulation; modified silicon nitride and graphene construct a uniform electric field and thermal conductivity network; epoxidized soybean oil enhances structural stability through cross-linking; and DOPO and graphene jointly provide chemical and physical flame retardant barriers. The coordinated action of these components forms a complementary and synergistic mechanism at the molecular level, providing a highly efficient, safe, and reliable insulating medium solution for high-voltage equipment.

[0132] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A high-ignition-point, high-thermal-conductivity mineral insulating oil, characterized in that, It comprises the following raw materials in parts by weight: 80-90 parts modified mineral oil and 5-6 parts insulating and thermally conductive agent; The modified mineral-based oil is prepared by adding liquid paraffin, glycidyl methacrylate, flame retardant modifier, and o-xylene into a reaction vessel and stirring. After the temperature of the reaction vessel is raised to 70-80℃, azobisisobutyronitrile is added to the reaction vessel and stirred for 2-4 hours. The modified mineral-based oil is then obtained through post-treatment. The ratio of liquid paraffin, glycidyl methacrylate, flame retardant modifier, o-xylene, and azobisisobutyronitrile is 8-10g:0.3-0.5g:1-2g:40-50mL:0.1g. The preparation method of the flame retardant modifier includes the following steps: A1. N,N-dimethylformamide and 3-butenetriethoxysilane were added to a reaction vessel. After the temperature of the reaction vessel was raised to 60-80℃, aluminum chloride and a calculated amount of DOPO were added to the reaction vessel. The mixture was kept warm and stirred for 1-2 hours. The modified siloxane was obtained after post-treatment. A2. Add modified siloxane, anhydrous ethanol and deionized water to the reaction vessel. After the temperature of the reaction vessel is raised to 40-60℃, adjust the pH of the reaction system to 4-5 with acetic acid. After stirring for 2-3 hours, add the end-capping agent perfluorobutanol to the reaction vessel and keep it at the temperature for 20-30 minutes. The flame retardant modifier is obtained after post-treatment. The method for preparing the insulating and thermally conductive agent is as follows: B1. Add epoxidized soybean oil and N,N-dimethylformamide to a reaction vessel and stir. After the temperature of the reaction vessel is raised to 60-80℃, add triethylamine and modified graphene to the reaction vessel, keep warm and stir for 2-4 hours, and then process to obtain modified soybean oil. B2. Modified soybean oil and N,N-dimethylformamide are added to a reaction vessel. After the temperature of the reaction vessel is raised to 80-90℃, a calculated amount of 1H,1H-perfluorooctylamine is added to the reaction vessel. The reaction is kept at the temperature for 1-2 hours. The post-treatment yields an insulating and thermally conductive agent. The method for preparing the modified graphene includes the following steps: C1. Add silicon nitride powder, anhydrous ethanol and deionized water to a reaction vessel and stir. Raise the reaction temperature to 40-60℃ and adjust the pH of the reaction system to 4-5 with acetic acid. Then add 3-aminopropyltrimethoxysilane to the reaction vessel, keep it warm and stir for 1-2 hours, and then perform post-treatment to obtain modified silicon nitride. C2. Graphene oxide, N,N-dimethylformamide and deionized water are added to a reaction vessel and stirred. After the temperature of the reaction vessel is raised to 70-80℃, modified silicon nitride is added to the reaction vessel and the reaction is maintained at this temperature for 2-4 hours. Modified graphene is then obtained through post-treatment.

2. The high-ignition-point, high-thermal-conductivity mineral insulating oil according to claim 1, characterized in that, In step B1, the ratio of epoxidized soybean oil, N,N-dimethylformamide, triethylamine, and modified graphene is 4-5g:20-25mL:0.3-0.5g:1-2g; in step B2, the ratio of modified soybean oil and N,N-dimethylformamide is 1-2g:10-12mL, wherein the amount of 1H,1H-perfluorooctylamine is 1.1-1.2 times the molar amount of epoxy groups in the modified soybean oil.

3. The high-ignition-point, high-thermal-conductivity mineral insulating oil according to claim 1, characterized in that, In step C1, the ratio of silicon nitride powder, anhydrous ethanol, deionized water, and 3-aminopropyltrimethoxysilane is 2-3g:20-25mL:10-12mL:0.1-0.2g; in step C2, the ratio of graphene oxide, N,N-dimethylformamide, deionized water, and modified silicon nitride is 3-4g:10-12mL:10-12mL:1-2g.

4. A method for preparing a high-ignition-point, high-thermal-conductivity mineral insulating oil as described in any one of claims 1-3, characterized in that, Modified mineral-based oil and insulating thermal conductive agent are added to a stirring vessel. The temperature of the stirring vessel is raised to 100-120℃, and the mixture is stirred for 10-15 minutes. After stirring, the mixture is passed through an 80-100 mesh sieve and stored away from light to obtain mineral insulating oil.

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