A swelling-resistant insulating silicone rubber, its preparation method and application

Abstract

This application belongs to the field of electrical insulation materials technology, and particularly relates to an anti-swelling insulating silicone rubber, its preparation method, and its application. The preparation method of the anti-swelling insulating silicone rubber provided in this application includes steps such as hydroxylation modification, isocyanate activation, chemical grafting modification, and silicone rubber molding. After the hydroxylation modification step, isocyanate activation and grafting with 1-dodecyl-2-imidazoline are performed. The hydroxylation modification step introduces additional hydroxyl groups into the silicone oil molecular chain, which can serve as active sites for grafting 1-dodecyl-2-imidazoline. This results in the chemically grafted silicone oil molecular chain forming a comb-like structure of main chain and side chains, fully utilizing the molecular structural barrier effect of the imidazoline heterocycle. This optimizes the anti-swelling properties, mechanical properties, and insulation properties of the insulating silicone rubber, solving the technical problem of low performance of existing anti-swelling silicone rubbers.

Description

Technical Field

[0001] This application belongs to the field of electrical insulation materials technology, and in particular relates to an anti-swelling insulating silicone rubber, its preparation method and application. Background Technology

[0002] Gas-insulated switchgear (GIS), as a core piece of equipment in the power system, boasts significant advantages such as small footprint, excellent insulation performance, high operational reliability, and long maintenance cycles. It is widely used in key power nodes such as power plants, substations, and ultra-high voltage transmission lines, undertaking the core functions of power transmission, distribution, and fault isolation. In the structural design of GIS, silicone rubber, due to its excellent electrical insulation properties, resistance to high and low temperatures, elastic sealing performance, and weather resistance, is widely used as a core material for key components such as insulating bushings, pot insulators, and sealing gaskets. Its performance stability directly determines the operational safety and service life of the GIS.

[0003] However, during the operation of gas-insulated switchgear, the insulating oil filling the internal components, such as 25# transformer oil and DB-45 synthetic ester oil, may come into contact with the silicone rubber components. Silicone rubber has a polydimethylsiloxane (PDMS) molecular chain structure, with weak intermolecular forces and a large free volume. Oil molecules can easily penetrate into the molecular chain network, causing the silicone rubber to swell. Swelled silicone rubber is prone to volume expansion, decreased tensile strength, reduced elongation at break, and deterioration of electrical insulation properties. In severe cases, this can lead to sealing failure, insulation breakdown, and malfunctions of the gas-insulated switchgear, even causing large-scale power outages. Therefore, solving the swelling problem of silicone rubber in the oil-immersed environment of gas-insulated switchgear is a key technical requirement for ensuring the safe and stable operation of the power system.

[0004] To address the swelling problem of silicone rubber in oil-immersed environments of gas-insulated switchgear, current mainstream research directions are divided into physical doping modification and chemical grafting modification. Physical doping modification involves mixing oil-resistant filler particles such as polytetrafluoroethylene (PTFE) with raw silicone rubber, crosslinking agents, and vulcanizing agents, followed by homogenization on a two-roll mill and vulcanization molding to produce physically doped, anti-swelling silicone rubber. However, compatibility issues easily arise between the oil-resistant filler particles and the silicone rubber matrix, leading to agglomeration during mixing. This results in discontinuous oleophobic layers in the physically doped, anti-swelling silicone rubber, unstable anti-swelling effects, and large fluctuations in the swelling rate. Furthermore, agglomerated particles form internal defects, increasing the dielectric loss factor and reducing insulation performance. To promote better dispersion of the oil-resistant filler particles, high-shear mixing is required, which can easily lead to molecular chain breakage in the silicone rubber. The mechanical properties of anti-swelling silicone rubber decrease. Furthermore, the oil-resistant filler particles in physically doped anti-swelling silicone rubber are physically doped and lack chemical bonding. Under long-term high-temperature and vibration conditions in gas-insulated switchgear, these filler particles are prone to detachment, resulting in unstable performance. Chemical grafting modification, on the other hand, involves grafting oleophobic groups such as perfluoroalkyl and phenyl groups onto the silicone rubber molecular chain through a chemical reaction. This utilizes the chemical oleophobic mechanism and the mechanism of restricting the movement of the siloxane backbone to produce chemically grafted modified silicone oil. This oil is then mixed with a crosslinking agent, vulcanizing agent, and filler, and after homogenization on a two-roll mill, it is vulcanized to produce anti-swelling silicone rubber, which exhibits superior anti-swelling stability compared to physically doped silicone rubber. However, current chemical grafting modification mainly focuses on introducing a single oleophobic group, resulting in a lack of variety and quantity of oleophobic groups on the silicone rubber molecular chain. This makes it difficult to effectively improve the performance of anti-swelling silicone rubber, leading to its currently low performance. Summary of the Invention

[0005] In view of this, this application provides an anti-swelling insulating silicone rubber, its preparation method, and its application, to solve the technical problem of low performance of anti-swelling silicone rubber in the prior art.

[0006] The first aspect of this application provides a method for preparing anti-swelling insulating silicone rubber, comprising the following steps:

[0007] The steps of hydroxylation modification are as follows: hydroxyl-terminated polydimethylsiloxane and a silane coupling agent having epoxy and alkoxy groups undergo an epoxy ring-opening addition reaction and a silane hydrolysis-condensation reaction to obtain a hydroxylated PDMS intermediate. The silane coupling agent has at least two alkoxy groups.

[0008] The isocyanate activation step involves reacting the hydroxylated PDMS intermediate and diisocyanate with an isocyanate-hydroxy addition reaction to obtain the isocyanate-activated PDMS intermediate.

[0009] The steps of chemical grafting modification are as follows: isocyanate-activated PDMS intermediate and 1-dodecyl-2-imidazoline undergo a nucleophilic addition reaction under the catalysis of a catalyst to obtain chemically grafted modified silicone oil;

[0010] The molding steps of silicone rubber are as follows: chemically grafted modified silicone oil, crosslinking agent, antioxidant, and surface oleophilic nanofiller are mixed and vulcanized to obtain anti-swelling insulating silicone rubber.

[0011] Preferably, in the hydroxylation modification step, the temperature of the epoxy ring-opening addition reaction and the silane hydrolysis condensation reaction are 80~90℃, and the time is 2~3h.

[0012] Preferably, in the hydroxylation modification step, the hydroxyl content of the terminal hydroxyl polydimethylsiloxane is 0.04~0.08 mmol / g, and the moisture content is ≤0.1%; the silane coupling agent having epoxy and alkoxy groups is selected from at least one of γ-glycidoxypropyltrimethoxysilane (KH-560), (3-epoxypropoxypropyl)triethoxysilane (KBE-403), and 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane (KBE-303).

[0013] Preferably, in the isocyanate activation step, the isocyanate-hydroxy addition reaction is carried out at a temperature of 60-65°C for 1-2 hours.

[0014] Preferably, in the isocyanate activation step, the diisocyanate is selected from at least one of toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate.

[0015] Preferably, in the chemical grafting modification step, the nucleophilic addition reaction is carried out at a temperature of 60-70°C for 4-6 hours.

[0016] Preferably, the catalyst is at least one of organotin catalysts, organobismuth catalysts, organozinc catalysts, and tertiary amine catalysts.

[0017] Preferably, in the molding step of silicone rubber, the mixing temperature is 50~60℃ and the time is 10~20min;

[0018] The vulcanization temperature is 120~150℃, the time is 1~2h, and the pressure is 5~8MPa.

[0019] Preferably, in the molding step of silicone rubber, the mold used for vulcanization is at least one of an insulating sleeve mold, a basin-type insulator mold, and a sealing gasket mold.

[0020] Preferably, the crosslinking agent is selected from at least one of methyltriacetoxysilane, tetraethoxysilane, and tetramethoxysilane.

[0021] The antioxidant is selected from at least one of antioxidant 1010, 2,6-di-tert-butyl-4-methylphenol, and antioxidant 1790.

[0022] The surface-oil-loving nanofiller is selected from at least one of silane coupling agent-treated fumed nano silica, precipitated nano silica, and nano alumina.

[0023] Preferably, the mass ratio of the hydroxyl-terminated polydimethylsiloxane, the silane coupling agent having epoxy and alkoxy groups, the diisocyanate, the 1-dodecyl-2-imidazoline, the catalyst, the crosslinking agent, the antioxidant, and the surface-lipophilic nanofiller is 100:5~8:3~5:8~12:0.1~0.3:2~3:0.5~1:5~10.

[0024] Preferably, in the chemical grafting modification step, the post-treatment steps of the nucleophilic addition reaction include: sequentially performing toluene dilution and vacuum distillation.

[0025] Preferably, after mixing and before vulcanization, the process further includes the steps of sheeting and cutting in sequence;

[0026] After vulcanization, the process also includes the steps of cooling and demolding, and removing flash.

[0027] The second aspect of this application provides an anti-swelling insulating silicone rubber, which is prepared by the method for preparing an anti-swelling insulating silicone rubber described in the first aspect.

[0028] The third aspect of this application provides the application of the anti-swelling insulating silicone rubber described in the second aspect in electrical equipment.

[0029] The fourth aspect of this application provides an electrical device comprising the anti-swelling insulating silicone rubber described in the second aspect.

[0030] Preferably, the electrical equipment described in the third or fourth aspect is selected from oil-immersed electrical equipment or dry-type electrical equipment.

[0031] Preferably, the electrical equipment described in the third or fourth aspect is selected from gas-insulated switchgear or transformers.

[0032] Compared with the prior art, the method for preparing anti-swelling insulating silicone rubber provided in this application has at least the following beneficial effects:

[0033] Compared to conventional insulating silicone rubber, which has weak intermolecular forces and a large free volume due to the polydimethylsiloxane molecular chains, allowing oil molecules to easily penetrate into the molecular chain network, the method for preparing an anti-swelling insulating silicone rubber provided in this application improves the anti-swelling performance of the insulating silicone rubber by introducing 1-dodecyl-2-imidazoline for chemical grafting modification. Furthermore, isocyanate activation and grafting of 1-dodecyl-2-imidazoline occur only after the hydroxylation modification step. The hydroxylation modification step introduces additional hydroxyl groups into the hydroxyl polydimethylsiloxane molecular chain, allowing hydroxyl groups to be distributed at multiple positions, including the ends and middle of the molecular chain. These hydroxyl groups act as active sites, enabling isocyanate activation and grafting of 1-dodecyl-2-imidazoline. This results in a comb-like structure of main chain-branched chains in the chemically grafted modified silicone oil molecular chain, fully utilizing the molecular structural barrier effect of the imidazoline heterocycle. Consequently, the anti-swelling performance, mechanical properties, and insulation properties of the insulating silicone rubber are all optimized, resulting in an anti-swelling insulating silicone rubber with excellent comprehensive performance. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0035] Figure 1 This is a schematic flowchart of a method for preparing an anti-swelling insulating silicone rubber as submitted in Embodiment 1 of this application. Detailed Implementation

[0036] This application provides an anti-swelling insulating silicone rubber, its preparation method, and its application, which addresses the technical problem of low performance of anti-swelling silicone rubber in the prior art.

[0037] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0038] Example 1

[0039] This embodiment provides a method for preparing anti-swelling insulating silicone rubber, the process diagram of which is shown below. Figure 1 As shown; including the steps of raw material preparation, hydroxylation modification, isocyanate activation, chemical grafting modification, and silicone rubber molding.

[0040] The steps for preparing raw materials include:

[0041] Weigh the following components according to a mass ratio of 100:6.5:4:10:0.2:2.5:0.75:7.5:0.5: hydroxyl-terminated polydimethylsiloxane (viscosity at 25℃ is 5000-10000 mPa·s), γ-glycidyl etheroxypropyltrimethoxysilane, toluene diisocyanate, 1-dodecyl-2-imidazoline, dibutyltin dilaurate, methyltriacetoxysilane, antioxidant 1010, fumed silica nanoparticles (particle size approximately 15~20 nm) and γ-aminopropyltriethoxysilane.

[0042] The steps of hydroxylation modification include:

[0043] The weighed hydroxyl-terminated polydimethylsiloxane was added to a vacuum drying oven for pre-treatment. The pre-treatment process was as follows: the drying temperature was set to 105℃, the vacuum degree to -0.085MPa, and drying was continued for 2 hours. During this period, the mixture was stirred once every 30 minutes at a stirring rate of 100r / min to ensure that the internal moisture was fully evaporated. After drying, the moisture content of the hydroxyl-terminated polydimethylsiloxane was measured to be ≤0.1% using a Karl Fischer moisture analyzer.

[0044] Add the pre-treated hydroxyl-terminated polydimethylsiloxane to a four-necked flask equipped with a stirrer, thermometer, and nitrogen inlet tube. Start stirring at an initial speed of 300 r / min and simultaneously introduce nitrogen at a flow rate of 75 mL / min to purge air from the flask. Maintain nitrogen protection throughout the process to prevent moisture and oxygen in the air from interfering with the reaction.

[0045] The temperature inside the four-necked flask was raised to 85°C. After the temperature stabilized, the weighed γ-glycidoxypropyltrimethoxysilane was slowly added through a constant pressure dropping funnel. The dropping rate was controlled at 1.5 mL / min to avoid excessive local concentration that could lead to the self-polymerization of γ-glycidoxypropyltrimethoxysilane.

[0046] After the addition was complete, the temperature was maintained at 85℃ and the stirring rate at 350r / min for 2.5 hours to obtain hydroxylated PDMS intermediate, which is a transparent viscous liquid with a viscosity of 8000~12000mPa·s at 25℃.

[0047] In the hydroxylation modification step, this embodiment used hydroxyl-terminated polydimethylsiloxane and γ-glycidoxypropyltrimethoxysilane as raw materials. γ-glycidoxypropyltrimethoxysilane has two independent highly active reaction sites: an epoxy group and a trimethoxysilyl group. Under nitrogen protection and with the activation energy provided by heating at 85°C, the hydroxyl group at the end of the hydroxyl-terminated polydimethylsiloxane molecular chain acts as a nucleophile, attacking the high-strain epoxy three-membered ring in the γ-glycidoxypropyltrimethoxysilane molecule to undergo ring-opening addition. This reaction consumes one of the original hydroxyl-terminated polydimethylsiloxane but simultaneously generates one new secondary hydroxyl group. At this point, the number of hydroxyl groups temporarily remains equal, and the hydroxyl-terminated polydimethylsiloxane contains ≤0.1% residual trace moisture, which initiates γ-... The stepwise hydrolysis of the trimethoxysilane molecule in glycidyl etheroxypropyltrimethoxysilane generates three highly active silanol groups. One of these silanol groups undergoes a dehydration condensation reaction with another terminal hydroxyl group of an adjacent terminal hydroxyl polydimethylsiloxane molecule, consuming one terminal hydroxyl group of the terminal hydroxyl polydimethylsiloxane. The remaining two silanol groups remain stably retained on the molecular chain. Simultaneously, the hydrolyzed silanol groups further promote epoxy ring-opening, forming a mild autocatalytic effect, sufficient to ensure that the reaction reaches the target hydroxyl content in about 2 hours. Thus, through the dual synergistic reaction of epoxy ring-opening addition and silane hydrolysis condensation, additional hydroxyl groups are introduced, increasing the active sites for chemical grafting modification. Furthermore, no additional acid or base catalysts are added, avoiding the formation of gel-like impurities due to the self-polymerization side reaction of γ-glycidyl etheroxypropyltrimethoxysilane caused by acid and base catalysis, as well as the breakage and degradation of the terminal hydroxyl polydimethylsiloxane molecular chain. This process simplifies the steps and reduces raw material costs.

[0048] The steps for isocyanate activation include:

[0049] After the hydroxylation modification reaction, the temperature of the four-necked flask was reduced to 62℃, the stirring speed was adjusted to 450 r / min, and the weighed toluene diisocyanate was slowly added dropwise through a constant pressure dropping funnel. The dropping rate was controlled at 1.5 mL / min to avoid the phenomenon that the -NCO group will aggregate and form cross-linking byproducts due to the excessively fast dropping rate.

[0050] After the addition was complete, the temperature was maintained at 62℃ and the stirring rate at 450 r / min, and the isocyanate-hydroxy addition reaction was continued for 1.5 hours. During this period, the reaction progress was monitored by Fourier transform infrared spectroscopy. When the characteristic absorption peak of the -NCO group in the infrared spectrum (2270 cm⁻¹) was reached... -1 When the strength is stable and the peak intensity changes by ≤5% within 30 minutes, it indicates that the activation reaction is complete, and the isocyanate-activated PDMS intermediate is obtained. It is a pale yellow viscous liquid with a viscosity of 10,000~15,000 mPa·s at 25℃.

[0051] The steps of chemical grafting modification include:

[0052] The temperature of the four-necked flask was controlled at 65℃ and the stirring speed was 450 r / min. The weighed dibutyltin dilaurate catalyst was added to the isocyanate-activated PDMS intermediate and stirred for 10 minutes to disperse it evenly. Then, the weighed 1-dodecyl-2-imidazoline was slowly added dropwise through a constant pressure dropping funnel at a dropping rate of 2.5 mL / min to ensure that the imino group in 1-dodecyl-2-imidazoline undergoes a full nucleophilic addition reaction with the isocyanate-activated PDMS intermediate.

[0053] After the addition was complete, the temperature was maintained at 65℃ and the stirring rate at 450 r / min for 5 hours, and then the reaction was stopped. The reaction product was cooled to room temperature and diluted with 30% toluene by mass of the product. Then, the product was distilled under reduced pressure at 80℃ and a vacuum of -0.09 MPa to remove unreacted toluene diisocyanate and 1-dodecyl-2-imidazoline, yielding chemically grafted modified silicone oil, which is a pale yellow transparent viscous liquid with a viscosity of 15000~20000 mPa·s at 25℃.

[0054] Commercially available conventional hydroxyl-terminated polydimethylsiloxanes have a low hydroxyl content, with two terminal hydroxyl groups distributed at both ends of the molecular chain. If they react directly with diisocyanates, introducing isocyanate and grafting 1-dodecyl-2-imidazoline onto the terminal groups cannot alter the flexibility and free volume of the middle segment of the hydroxyl-terminated polydimethylsiloxane molecular chain. Oil molecules can still easily penetrate into the molecular chain. Simultaneously, the two -NCO groups of the diisocyanate will react with the terminal hydroxyl groups of two different hydroxyl-terminated polydimethylsiloxane molecules. When the reaction exceeds 10%,... In the past, the system would rapidly form an insoluble and infusible gel, making subsequent grafting reactions and vulcanization impossible. In this embodiment, isocyanate activation and grafting of 1-dodecyl-2-imidazoline were carried out only after the hydroxylation modification step. The hydroxylation modification step introduced additional hydroxyl groups into the hydroxyl polydimethylsiloxane molecular chain, allowing hydroxyl groups to be distributed at multiple positions, such as at both ends and in the middle of the molecular chain. These hydroxyl groups serve as active sites, enabling isocyanate activation and grafting of 1-dodecyl-2-imidazoline. This allows the chemically grafted modified silicone oil molecular chain to form a comb-like structure of main chain and side chain, fully utilizing the molecular structural barrier effect of the imidazoline heterocycle while effectively avoiding the problem of excessive cross-linking.

[0055] The molding steps for silicone rubber include:

[0056] Weighed fumed nano-silica and γ-aminopropyltriethoxysilane were added to a high-speed mixer. The mixing temperature was set to 80℃ and the stirring speed to 800 r / min. The mixture was mixed for 30 minutes to allow the amino group of γ-aminopropyltriethoxysilane to react with the hydroxyl group of fumed nano-silica to form an organosilane layer, which reduced its polarity and improved its compatibility. This yielded oleophilic nano-silica with an activation index ≥95%, which was tested by the flotation method.

[0057] Chemically grafted modified silicone oil was added to a two-roll mill. The two-roll mill was set to a roll temperature of 55°C and a roll gap of 1.5 mm. The two-roll mill was started at a speed ratio of 1:1.2. The weighed crosslinking agent methyltriacetoxysilane, antioxidant 1010, and surface-oil-treated nano-silica were added in sequence. The mixture was mixed for 15 minutes, with the mixture turned over every 5 minutes to ensure that all additives were evenly dispersed. Observation under a polarizing microscope showed no obvious agglomerates, and the agglomerate particle size was ≤1 μm.

[0058] After the mixture is evenly mixed, the gap between the rollers of the open mill is adjusted to 4mm, and a 4mm thick mixed rubber sheet is produced. According to the size requirements of the product, it is cut into blanks of the corresponding shape. The blanks are placed into the mold of the flat vulcanizing machine. The mold is preheated to 135℃, the vulcanizing pressure is set to 6MPa, and the vulcanizing time is 1 hour to obtain anti-swelling insulating silicone rubber.

[0059] After vulcanization is complete, turn off the heating device of the flat vulcanizing machine, keep the pressure constant, and allow it to cool naturally to room temperature. Then open the mold, take out the anti-swelling insulating silicone rubber product, remove the flash, and the product will be transparent and uniform in appearance. It is ready for use.

[0060] Comparative Example 1

[0061] To investigate the effect of the additional hydroxyl groups introduced by hydroxylation modification on the properties of insulating silicone rubber, this comparative example provides a method for preparing insulating silicone rubber, including the steps of raw material preparation, isocyanate activation, chemical grafting modification, and silicone rubber molding.

[0062] The steps for preparing raw materials include:

[0063] Weigh the following components according to a mass ratio of 100:4:10:0.2:2.5:0.7:7.5:0.5: hydroxyl-terminated polydimethylsiloxane (viscosity at 25℃ is 5000-10000 mPa·s), toluene diisocyanate, 1-dodecyl-2-imidazoline, dibutyltin dilaurate, methyltriacetoxysilane, antioxidant 1010, fumed silica nanoparticles (particle size approximately 15~20 nm), and γ-aminopropyltriethoxysilane.

[0064] The steps for isocyanate activation include:

[0065] The material was placed in a vacuum drying oven for pre-treatment. The pre-treatment process was as follows: the drying temperature was set to 105℃, the vacuum degree to -0.085MPa, and drying was continued for 2 hours. During this period, the material was stirred once every 30 minutes at a stirring rate of 100r / min to ensure that the internal moisture was fully evaporated. After drying, the moisture content of the hydroxyl-terminated polydimethylsiloxane was measured to be ≤0.1% using a Karl Fischer moisture analyzer.

[0066] The pre-treated hydroxyl-terminated polydimethylsiloxane was added to a four-necked flask equipped with a stirrer, thermometer, and nitrogen inlet tube. The temperature of the four-necked flask was controlled at 62°C and the stirring rate was 450 r / min. The weighed toluene diisocyanate was slowly added dropwise through a constant pressure dropping funnel at a dropping rate of 1.5 mL / min to avoid the phenomenon that the -NCO group agglomeration reaction and cross-linking byproducts would be caused by the dropping rate being too fast.

[0067] After the addition is complete, maintain the temperature at 62℃ and the stirring speed at 450r / min to continue the isocyanate-hydroxy addition reaction for 1.5 hours.

[0068] The steps of chemical grafting modification include:

[0069] The temperature of the four-necked flask was controlled at 65℃ and the stirring speed was 450 r / min. The weighed dibutyltin dilaurate catalyst was added to the isocyanate-activated PDMS intermediate and stirred for 10 minutes to disperse it evenly. Then, the weighed 1-dodecyl-2-imidazoline was slowly added dropwise through a constant pressure dropping funnel at a dropping rate of 2.5 mL / min to ensure that the imino group in 1-dodecyl-2-imidazoline undergoes a full nucleophilic addition reaction with the isocyanate-activated PDMS intermediate.

[0070] After the addition was complete, the temperature was maintained at 65℃ and the stirring rate at 450 r / min for 5 hours. The reaction was then stopped, and local gelation was observed. The reaction product was cooled to room temperature and diluted with 30% toluene by mass of the product. Then, it was distilled under reduced pressure at 80℃ and a vacuum of -0.09 MPa to remove unreacted toluene diisocyanate and 1-dodecyl-2-imidazoline, yielding chemically grafted modified silicone oil.

[0071] The molding steps for silicone rubber include:

[0072] Weighed fumed nano-silica and γ-aminopropyltriethoxysilane were added to a high-speed mixer. The mixing temperature was set to 80℃ and the stirring speed to 800 r / min. The mixture was mixed for 30 minutes to allow the amino group of γ-aminopropyltriethoxysilane to react with the hydroxyl group of fumed nano-silica to form an organosilane layer, which reduced its polarity and improved its compatibility. This yielded oleophilic nano-silica with an activation index ≥95%, which was tested by the flotation method.

[0073] Chemically grafted modified silicone oil was added to a two-roll mill. The two-roll mill was set to a roll temperature of 55°C and a roll gap of 1.5 mm. The two-roll mill was started at a speed ratio of 1:1.2. The weighed crosslinking agent methyltriacetoxysilane, antioxidant 1010, and surface-oil-treated nano-silica were added in sequence. The mixture was mixed for 15 minutes, with the mixture turned over every 5 minutes to ensure that all additives were evenly dispersed. Observation under a polarizing microscope showed no obvious agglomerates, and the agglomerate particle size was ≤1 μm.

[0074] After the mixture is evenly mixed, the gap between the rollers of the open mill is adjusted to 4mm, and a 4mm thick mixed rubber sheet is produced. According to the size requirements of the product, it is cut into blanks of the corresponding shape. The blanks are placed into the mold of the flat vulcanizing machine. The mold is preheated to 135℃, the vulcanizing pressure is set to 6MPa, and the vulcanizing time is 1 hour to obtain insulating silicone rubber.

[0075] After vulcanization is complete, turn off the heating device of the flat vulcanizing machine, keep the pressure constant, and allow it to cool naturally to room temperature. Then open the mold, take out the insulating silicone rubber product, remove the flash, and the appearance will contain a small amount of gel particles. Set aside for later use.

[0076] Comparative Example 2

[0077] To investigate the effects of different oleophobic groups on the properties of insulating silicone rubber, this comparative example provides a method for preparing insulating silicone rubber, including the steps of raw material preparation, hydroxylation modification, isocyanate activation, chemical grafting modification, and silicone rubber molding.

[0078] The steps for preparing raw materials include:

[0079] Weigh the following components according to a mass ratio of 100:6.5:4:10:0.2:2.5:0.75:7.5:0.5: hydroxyl-terminated polydimethylsiloxane (viscosity 5000-10000 mPa·s at 25℃), γ-glycidyl etheroxypropyltrimethoxysilane, toluene diisocyanate, and n-dodecylamine (CH3(CH2)). 11 NH2), dibutyltin dilaurate, methyltriacetoxysilane, antioxidant 1010, fumed nano silica (particle size about 15~20nm) and γ-aminopropyltriethoxysilane.

[0080] The steps of hydroxylation modification include:

[0081] The weighed hydroxyl-terminated polydimethylsiloxane was added to a vacuum drying oven for pre-treatment. The pre-treatment process was as follows: the drying temperature was set to 105℃, the vacuum degree to -0.085MPa, and drying was continued for 2 hours. During this period, the mixture was stirred once every 30 minutes at a stirring rate of 100r / min to ensure that the internal moisture was fully evaporated. After drying, the moisture content of the hydroxyl-terminated polydimethylsiloxane was measured to be ≤0.1% using a Karl Fischer moisture analyzer.

[0082] Add the pre-treated hydroxyl-terminated polydimethylsiloxane to a four-necked flask equipped with a stirrer, thermometer, and nitrogen inlet tube. Start stirring at an initial speed of 300 r / min and simultaneously introduce nitrogen at a flow rate of 75 mL / min to purge air from the flask. Maintain nitrogen protection throughout the process to prevent moisture and oxygen in the air from interfering with the reaction.

[0083] The temperature inside the four-necked flask was raised to 85°C. After the temperature stabilized, the weighed γ-glycidoxypropyltrimethoxysilane was slowly added through a constant pressure dropping funnel. The dropping rate was controlled at 1.5 mL / min to avoid excessive local concentration that could lead to the self-polymerization of γ-glycidoxypropyltrimethoxysilane.

[0084] After the addition was complete, the temperature was maintained at 85℃ and the stirring rate at 350r / min for 2.5 hours to obtain hydroxylated PDMS intermediate, which is a transparent viscous liquid with a viscosity of 8000~12000mPa·s at 25℃.

[0085] The steps for isocyanate activation include:

[0086] After the hydroxylation modification reaction, the temperature of the four-necked flask was reduced to 62℃, the stirring speed was adjusted to 450 r / min, and the weighed toluene diisocyanate was slowly added dropwise through a constant pressure dropping funnel. The dropping rate was controlled at 1.5 mL / min to avoid the phenomenon that the -NCO group will aggregate and form cross-linking byproducts due to the excessively fast dropping rate.

[0087] After the addition was complete, the temperature was maintained at 62℃ and the stirring rate at 450 r / min, and the isocyanate-hydroxy addition reaction was continued for 1.5 hours. During this period, the reaction progress was monitored by Fourier transform infrared spectroscopy. When the characteristic absorption peak of the -NCO group in the infrared spectrum (2270 cm⁻¹) was reached... -1 When the strength is stable and the peak intensity changes by ≤5% within 30 minutes, it indicates that the activation reaction is complete, and the isocyanate-activated PDMS intermediate is obtained. It is a pale yellow viscous liquid with a viscosity of 10,000~15,000 mPa·s at 25℃.

[0088] The steps of chemical grafting modification include:

[0089] The temperature of the four-necked flask was controlled at 65℃ and the stirring rate was 450 r / min. The weighed dibutyltin dilaurate catalyst was added to the isocyanate-activated PDMS intermediate. After stirring for 10 minutes to make it uniformly dispersed, the weighed n-dodecylamine was slowly added dropwise through a constant pressure dropping funnel at a dropping rate of 2.5 mL / min to ensure that the amino group in n-dodecylamine and the isocyanate-activated PDMS intermediate undergo a full nucleophilic addition reaction.

[0090] After the addition was complete, the temperature was maintained at 65℃ and the stirring rate at 450 r / min for 5 hours, and then the reaction was stopped. The reaction product was cooled to room temperature and diluted with 30% toluene by mass of the product. Then, the product was distilled under reduced pressure at 80℃ and a vacuum of -0.09 MPa to remove unreacted toluene diisocyanate and n-dodecylamine, yielding chemically grafted modified silicone oil, which is a pale yellow transparent viscous liquid with a viscosity of 15000~20000 mPa·s at 25℃.

[0091] The molding steps for silicone rubber include:

[0092] Weighed fumed nano-silica and γ-aminopropyltriethoxysilane were added to a high-speed mixer. The mixing temperature was set to 80℃ and the stirring speed to 800 r / min. The mixture was mixed for 30 minutes to allow the amino group of γ-aminopropyltriethoxysilane to react with the hydroxyl group of fumed nano-silica to form an organosilane layer, which reduced its polarity and improved its compatibility. This yielded oleophilic nano-silica with an activation index ≥95%, which was tested by the flotation method.

[0093] Chemically grafted modified silicone oil was added to a two-roll mill. The two-roll mill was set to a roll temperature of 55°C and a roll gap of 1.5 mm. The two-roll mill was started at a speed ratio of 1:1.2. The weighed crosslinking agent methyltriacetoxysilane, antioxidant 1010, and surface-oil-treated nano-silica were added in sequence. The mixture was mixed for 15 minutes, with the mixture turned over every 5 minutes to ensure that all additives were evenly dispersed. Observation under a polarizing microscope showed no obvious agglomerates, and the agglomerate particle size was ≤1 μm.

[0094] After the mixture is evenly mixed, the gap between the rollers of the open mill is adjusted to 4mm, and a 4mm thick mixed rubber sheet is produced. According to the size requirements of the product, it is cut into blanks of the corresponding shape. The blanks are placed into the mold of the flat vulcanizing machine. The mold is preheated to 135℃, the vulcanizing pressure is set to 6MPa, and the vulcanizing time is 1 hour to obtain insulating silicone rubber.

[0095] After vulcanization is complete, turn off the heating device of the flat vulcanizing machine, keep the pressure constant, and allow it to cool naturally to room temperature. Then open the mold, take out the insulating silicone rubber product, remove the flash, and the product will be transparent and uniform in appearance. It is ready for use.

[0096] Comparative Example 3

[0097] To investigate the effect of oleophobic group grafting modification on the properties of insulating silicone rubber, this comparative example provides a method for preparing insulating silicone rubber, including raw material preparation steps and silicone rubber molding steps.

[0098] The steps for preparing raw materials include:

[0099] Weigh the following components according to a mass ratio of 100:2.5:0.75:7.5:0.5: hydroxyl-terminated polydimethylsiloxane (viscosity of 5000-10000 mPa·s at 25℃), methyltriacetoxysilane, antioxidant 1010, fumed nano silica (particle size of about 15~20 nm) and γ-aminopropyltriethoxysilane.

[0100] The molding steps for silicone rubber include:

[0101] Weighed fumed nano-silica and γ-aminopropyltriethoxysilane were added to a high-speed mixer. The mixing temperature was set to 80℃ and the stirring speed to 800 r / min. The mixture was mixed for 30 minutes to allow the amino group of γ-aminopropyltriethoxysilane to react with the hydroxyl group of fumed nano-silica to form an organosilane layer, which reduced its polarity and improved its compatibility. This yielded oleophilic nano-silica with an activation index ≥95%, which was tested by the flotation method.

[0102] Chemically grafted modified silicone oil was added to a two-roll mill. The two-roll mill was set to a roll temperature of 55°C and a roll gap of 1.5 mm. The two-roll mill was started at a speed ratio of 1:1.2. The weighed crosslinking agent methyltriacetoxysilane, antioxidant 1010, and surface-oil-treated nano-silica were added in sequence. The mixture was mixed for 15 minutes, with the mixture turned over every 5 minutes to ensure that all additives were evenly dispersed. Observation under a polarizing microscope showed no obvious agglomerates, and the agglomerate particle size was ≤1 μm.

[0103] After the mixture is evenly mixed, the gap between the rollers of the open mill is adjusted to 4mm, and a 4mm thick mixed rubber sheet is produced. According to the size requirements of the product, it is cut into blanks of the corresponding shape. The blanks are placed into the mold of the flat vulcanizing machine. The mold is preheated to 135℃, the vulcanizing pressure is set to 6MPa, and the vulcanizing time is 1 hour to obtain insulating silicone rubber.

[0104] After vulcanization is complete, turn off the heating device of the flat vulcanizing machine, keep the pressure constant, and allow it to cool naturally to room temperature. Then open the mold, take out the insulating silicone rubber product, remove the flash, and the product will be transparent and uniform in appearance. It is ready for use.

[0105] Experimental Example 1

[0106] This experiment tested the performance of the insulating silicone rubber provided in Example 1 and Comparative Examples 1-3. The performance tests included anti-swelling performance tests, mechanical and insulation performance tests, and the results are shown in Tables 1 and 2.

[0107] As can be seen from Table 1, the insulating silicone rubber provided in Comparative Example 3, due to its polydimethylsiloxane molecular chain structure, has weaker intermolecular forces and a larger free volume, allowing oil molecules to easily penetrate into the molecular chain network. This results in significant swelling in insulating oils such as 25# transformer oil and DB-45 synthetic ester oil.

[0108] The insulating silicone rubber provided in Comparative Example 2 was chemically modified using dodecylamine. However, although the initial swelling rate of the dodecyl-grafted insulating silicone rubber was reduced, the swelling rate changed by more than 3% after 1000 hours of aging, indicating insufficient long-term stability and failure to meet the long-term operation requirements of electrical equipment. Although the insulating silicone rubber provided in Comparative Example 1 was also chemically modified using 1-dodecyl-2-imidazoline, the improvement in anti-swelling performance was not significant. By analyzing the chemically grafted modified silicone oils prepared by the preparation methods provided in Example 1 and Comparative Example 1 using ¹H-NMR spectroscopy, and using the peak area of ​​characteristic hydrogen atoms on the imidazoline heterocycle as the quantitative basis, it was found that the characteristic peak intensity was lower. This indicates that the grafting rate of the chemically grafted modified silicone oil prepared by the preparation method provided in Comparative Example 1 was lower than that in Example 1, resulting in a deterioration in the anti-swelling performance of the insulating silicone rubber provided in Comparative Example 1.

[0109] Compared to the insulating silicone rubbers provided in Comparative Examples 1-3, the preparation method provided in Example 1 involves isocyanate activation and grafting of 1-dodecyl-2-imidazoline only after the hydroxylation modification step. This allows the imidazoline heterocycle to achieve "structural barrier" at the molecular scale. By introducing rigid imidazoline heterocyclic groups onto the silicone rubber molecular chain, a physical barrier effect is generated based on the structural characteristics of the molecular chain itself. On the one hand, the imidazoline heterocycle is a five-membered nitrogen-containing heterocyclic structure with planar rigidity and significant steric hindrance, which restricts the free rotation and mutual slippage of adjacent siloxane backbones, making the molecular chain arrangement more compact and increasing the overall packing density. On the other hand... On the one hand, the tight packing of molecular chains directly leads to a significant reduction in the free volume inside the polymer, making it difficult for oil molecules to enter the gaps between the molecular chains. On the other hand, the presence of rigid heterocycles hinders the stretching and expansion of silicone rubber molecular chains in the oil medium, fundamentally inhibiting the swelling process. This molecular-scale structural barrier is fundamentally different from the macroscopic path barrier of oil-resistant filler particles such as polytetrafluoroethylene particles. It is achieved by changing the molecular structure of the polymer itself, and there are no problems such as particle agglomeration and poor interfacial bonding. Its stability is much higher than that of macroscopic doping. As a result, the anti-swelling performance, mechanical and insulation properties are all optimized, making it an anti-swelling insulating silicone rubber with excellent comprehensive performance.

[0110] Table 1: Results of Anti-swelling Performance Test

[0111]

[0112] Table 2: Results of Mechanical and Insulation Performance Tests

[0113]

[0114] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit it. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing an anti-swelling insulating silicone rubber, characterized in that, Includes the following steps: Hydroxy-terminated polydimethylsiloxane and a silane coupling agent having epoxy and alkoxy groups are subjected to an epoxy ring-opening addition reaction and a silane hydrolysis-condensation reaction to obtain a hydroxylated PDMS intermediate. The silane coupling agent has at least two alkoxy groups. The hydroxylated PDMS intermediate and diisocyanate were subjected to an isocyanate-hydroxy addition reaction to obtain an isocyanate-activated PDMS intermediate. A chemically grafted modified silicone oil was obtained by nucleophilic addition reaction of isocyanate-activated PDMS intermediate and 1-dodecyl-2-imidazoline under the catalysis of a catalyst. Chemically grafted modified silicone oil, crosslinking agent, antioxidant, and surface-oil-affinity treated nanofiller are mixed and vulcanized to obtain anti-swelling insulating silicone rubber.

2. The method for preparing an anti-swelling insulating silicone rubber according to claim 1, characterized in that, The epoxy ring-opening addition reaction and the silane hydrolysis condensation reaction are carried out at a temperature of 80~90℃ for 2~3h.

3. The method for preparing an anti-swelling insulating silicone rubber according to claim 1, characterized in that, The isocyanate-hydroxy addition reaction is carried out at a temperature of 60-65°C for 1-2 hours.

4. The method for preparing an anti-swelling insulating silicone rubber according to claim 1, characterized in that, The nucleophilic addition reaction is carried out at a temperature of 60-70°C for 4-6 hours.

5. The method for preparing an anti-swelling insulating silicone rubber according to claim 1, characterized in that, The mixing temperature is 50~60℃, and the time is 10~20min; The vulcanization temperature is 120~150℃, the time is 1~2h, and the pressure is 5~8MPa.

6. The method for preparing an anti-swelling insulating silicone rubber according to claim 1, characterized in that, The mold used for vulcanization is at least one of the following: insulating sleeve mold, basin insulator mold, and sealing gasket mold.

7. The method for preparing an anti-swelling insulating silicone rubber according to claim 1, characterized in that, The mass ratio of the hydroxyl-terminated polydimethylsiloxane, the silane coupling agent having epoxy and alkoxy groups, the diisocyanate, the 1-dodecyl-2-imidazoline, the catalyst, the crosslinking agent, the antioxidant, and the surface-lipophilic nanofiller is 100:5~8:3~5:8~12:0.1~0.3:2~3:0.5~1:5~10.

8. A swelling-resistant insulating silicone rubber, characterized in that, It is prepared by the method for preparing an anti-swelling insulating silicone rubber according to any one of claims 1-7.

9. The application of the anti-swelling insulating silicone rubber according to claim 8 in electrical equipment.

10. An electrical device, characterized in that, Including the anti-swelling insulating silicone rubber as described in claim 8.

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