A silicone rubber material for composite insulators and its preparation method

Abstract

This application provides a silicone rubber material for composite insulators and its preparation method. The silicone rubber material comprises the following raw materials in parts by weight: 100 parts vinyl-terminated polydimethylsiloxane, 12-16 parts hydrophobically modified silica, 3-5 parts borate-modified silica, 5-7 parts hydroxyl-terminated polydimethylsiloxane, 8-12 parts polymethylhydrosiloxane, 0.001-0.005 parts platinum-based catalyst, and 0.1-1 parts light stabilizer. By introducing borate-modified silica and hydroxyl-terminated polydimethylsiloxane synergistically into the silicone rubber system, an organic-inorganic composite interface structure with reversible bonding characteristics can be constructed within the material. This allows the polydimethylsiloxane segments to achieve slow-release migration and dynamic compensation under complex service environments, thereby significantly improving the hydrophobicity retention and surface self-healing ability of the composite insulator silicone rubber.

Description

Technical Field

[0001] This application relates to the field of silicone rubber technology, specifically to a silicone rubber material for composite insulators and its preparation method. Background Technology

[0002] Composite insulators are high-performance insulation structures that use glass fiber reinforced epoxy resin core rods as load-bearing elements, silicone rubber sheds as outer insulation layers, and hardware as end connectors. They possess advantages such as light weight, pollution resistance, arc resistance, and good seismic performance, and are widely used in high-voltage power transmission lines. As the key outer sheath of composite insulators, the physicochemical properties of silicone rubber directly determine the insulator's hydrophobicity, aging resistance, and long-term electrical stability.

[0003] While traditional silicone rubber contains a small amount of low-molecular-weight polydimethylsiloxane (PDMS), which can migrate to the surface and form a hydrophobic film in a short period, thus keeping the surface dry, under complex environments such as long-term corona discharge, ultraviolet radiation, or acid and alkaline rain, the surface PDMS is easily oxidized, decomposed, or washed away, leading to a gradual decrease in hydrophobicity. Composite insulators often experience loss of hydrophobicity during service, requiring "self-recovery" through the migration of internal PDMS. However, the existing system has a limited reserve of migratable low-molecular-weight PDMS, and the migration rate is difficult to control, resulting in a slow or even incomplete recovery process. Especially in high-temperature and high-humidity environments, the siloxane segments are easily hydrolyzed or oxidized, further reducing the efficiency of hydrophobicity recovery.

[0004] Therefore, existing silicone rubber materials for composite insulators generally suffer from problems such as short retention time of hydrophobicity, low recovery efficiency, and susceptibility to environmental aging. How to achieve long-term hydrophobicity retention and rapid recovery of silicone rubber materials has become a pressing technical problem to be solved in this field. Summary of the Invention

[0005] This invention provides a silicone rubber material for composite insulators and its preparation method, aiming to solve the problem that existing silicone rubber materials for composite insulators have a short hydrophobicity retention time and slow recovery during long-term operation.

[0006] In a first aspect, this application provides a silicone rubber material for composite insulators, comprising the following raw materials in parts by weight: 100 parts vinyl-terminated polydimethylsiloxane, 12-16 parts hydrophobically modified silica, 3-5 parts borate-modified silica, 5-7 parts hydroxyl-terminated polydimethylsiloxane, 8-12 parts polymethylhydrosiloxane, 0.001-0.005 parts platinum-based catalyst, and 0.1-1 parts light stabilizer.

[0007] According to this application, by introducing borate-modified silica and hydroxyl-terminated polydimethylsiloxane into a silicone rubber system, an organic-inorganic composite interface structure with reversible bonding characteristics can be constructed within the material. This allows the polydimethylsiloxane segments to achieve slow-release migration and dynamic compensation under complex service environments, thereby significantly improving the hydrophobicity retention and surface self-healing ability of the composite insulator silicone rubber. Even after being subjected to high temperature and high humidity conditions, this material can still maintain a high contact angle, effectively extending the service life of the insulator's outer sheath.

[0008] Specifically, vinyl-terminated polydimethylsiloxane serves as the main chain matrix, endowing the material with excellent flexibility and weather resistance. Polymethylhydrosiloxane undergoes an addition crosslinking reaction with vinyl segments under the action of a platinum-based catalyst, forming a stable three-dimensional network structure that ensures good mechanical strength and structural integrity. Hydrophobically modified silica enhances the interfacial bonding between the filler and the silicon-oxygen main chain through a surface organic layer compatible with the matrix, while maintaining the low polarity of the material's surface, thereby improving the overall reinforcement effect and hydrophobic stability. Boronate-modified silica introduces boron-oxygen structures on the silica surface that can dynamically bond with hydroxyl-terminated polydimethylsiloxane. These structures can partially and reversibly break and recombine under high humidity or high temperature conditions, allowing for the controlled release and migration of low-molecular-weight siloxane segments within the system, forming a continuously replenished surface hydrophobic film, thus endowing the material with long-term hydrophobic retention properties. Hydroxyl-terminated polydimethylsiloxane, as a migrating and self-healing active component, can be gradually released and redistributed on the surface under the regulation of reversible interfacial bonds, maintaining long-term hydrophobicity. In addition, the introduction of light stabilizers effectively inhibits the breakage of the silicon-oxygen backbone and surface aging caused by ultraviolet radiation, and together with hydrophobically modified silica, improves the anti-aging performance of the material under long-term outdoor operation conditions.

[0009] Through the synergistic effect of the above components, the silicone rubber material of this application can maintain a high hydrophobicity level over a long service life and spontaneously recover in a short time after the hydrophobicity is damaged, exhibiting good hydrophobicity retention and rapid recovery performance, and is suitable for the outer sheath material of composite insulators.

[0010] In some embodiments, the borate-modified silica is obtained by transesterification of trialkylborates with silanols on the surface of silica.

[0011] In some of the above embodiments, trialkylboronic acid esters undergo transesterification with the silanol groups (Si-OH) on the surface of silica to generate surface Si-OB(OR)2 bonds and release the corresponding alcohols, transforming the silica surface from strongly hydrophilic silanol sites to low-polar boron-oxygen bond sites. During the mixing process, the B(OR)2 bonds further react with the terminal hydroxyl polydimethylsiloxane in the system, grafting the terminal hydroxyl polydimethylsiloxane onto the silica surface. In the humid and hot environment of service, the boron-oxygen bonds can undergo limited and reversible nucleophilic breakage and recombination, thereby forming a dynamically linked / released interface relationship with the terminal hydroxyl polydimethylsiloxane in the system: when the surface hydrophobicity decreases, the boron-oxygen bonds at the interface can gradually release a small amount of polydimethylsiloxane segments to replenish the surface organic phase, promoting the recovery of hydrophobicity in a short time; while in the absence of external disturbances, the interface structure remains stable, reducing hydrophilic sites and moisture absorption channels. Through the above mechanism, on the one hand, the effective silanol density and hygroscopic tendency on the filler surface are reduced, mitigating the continuous impact of water film formation on hydrophobicity; on the other hand, a controlled supply source is provided for polydimethylsiloxane segments, enabling the material to maintain a high hydrophobicity level and have a fast hydrophobicity recovery rate even after long-term humid or corona conditions.

[0012] In some embodiments, the borate-modified silica is prepared by the following method:

[0013] 100 parts of silica and 2-4 parts of trialkylboronic acid ester were dispersed in 20-40 parts of toluene and refluxed at 60-70°C for 30-60 min to obtain borate-grafted silica, which was used as borate-modified silica.

[0014] In some of the above embodiments, the reaction conditions enable transesterification between the trialkylboronic ester and the silanol groups on the surface of silica at a relatively mild temperature, resulting in a uniformly distributed Si-OB bond on the surface and reducing the self-condensation of the borate ester or the cross-linking and aggregation between silica particles. The resulting modified silica has a stable surface structure and good dispersibility, and can form a uniform and dynamically adjustable interface layer when subsequently compounded with a silicone rubber matrix, thereby achieving the slow release of low-molecular-weight siloxane segments and the continuous recovery of surface hydrophobicity.

[0015] In some embodiments, the trialkylboronic ester comprises trimethylboronic ester and triisopropylboronic ester, wherein the mass ratio of trimethylboronic ester to triisopropylboronic ester is 1:1 to 1.5.

[0016] In some of the above embodiments, the inventors found that when trimethylborate and triisopropylborate are used together in the above ratio for the modification of silica, the resulting silicone rubber can better balance the effects of rapid hydrophobicity recovery and long hydrophobicity retention. The reason may be that, due to steric hindrance, during the mixing process, the borate-modified silica mainly forms a Si-OB(OR)(OPDMS) structure with hydroxyl-terminated polydimethylsiloxane (PDMS-OH). The Si-OB(OMe)(OPDMS) and Si-OB(OiPr)(OPDMS) formed on the silica surface have significantly different hydrolytic activities. Si-OB(OMe)(OPDMS) has stronger polarity and relatively smaller steric hindrance, making it more susceptible to moisture attack and preferentially broken down. This allows it to withstand external moisture or damage to the surface hydrophobic layer. Rapid reversible hydrolysis promotes the release and migration of hydroxyl-terminated polydimethylsiloxane segments, thereby achieving short-term hydrophobicity recovery. In contrast, Si-OB(OiPr)(OPDMS) has greater steric hindrance and a slower hydrolysis rate, which can maintain the stability of the modified structure. In a long-term humid and hot environment, as Si-OB(OMe)(OPDMS) breaks down and is released, the hydrophilicity of the silica surface gradually increases, thus Si-OB(OiPr)(OPDMS) slowly releases the remaining polydimethylsiloxane segments, maintaining the continuous replenishment of the surface hydrophobic film.

[0017] Therefore, when the ratio of trimethylboronic acid ester to triisopropylboronic acid ester is controlled within the range of 1:1 to 1.5, a balance can be formed between rapid response and long-term sustained release, so that the silicone rubber material can still recover quickly and maintain its hydrophobic properties for a long time after being damaged by rain, corona or scrubbing.

[0018] It should be noted that when fumed silica is modified with trimethylborate and triisopropylborate respectively and then blended, the fumed silica modified with trimethylborate and triisopropylborate respectively play their roles. As Si-OB(OMe)(OPDMS) hydrolyzes and breaks down, its impact on the stability of fumed silica modified with triisopropylborate is small. In the later stage, it cannot effectively release polydimethylsiloxane segments, which leads to the inability to effectively improve the long-term hydrophobic retention performance. The modification in this application further optimizes the hydrophobic performance.

[0019] In some of the above embodiments, the method further includes: dispersing 100 parts of borate-grafted silica and 0.5 to 1 part of hexamethyldisilazane in 10 to 30 parts of toluene, and refluxing at 70 to 80°C for 20 to 40 minutes to obtain passivated borate-grafted silica, which is used as borate-modified silica.

[0020] In some of the above embodiments, the inventors found that when hexamethyldisilazane (HMDS) was further introduced for passivation after the borate ester grafting reaction, the resulting modified silica exhibited superior hydrophobicity retention and faster hydrophobicity recovery in silicone rubber systems. This may be because, on the one hand, HMDS can undergo a silicon-nitrogen exchange reaction with residual silanol groups on the surface to generate a hydrophobic Si-O-Si(CH3)3 structure, thereby reducing surface polarity and hygroscopicity and preventing the silica from agglomerating due to hydrogen bonding. On the other hand, the unpassivated silica surface contains a large number of polar Si-OH groups, which easily form stable hydrogen bond complexes with water, causing water to be adsorbed or bound by these hydroxyl groups, making it difficult for water to further act on the borate ester bonds. This results in the terminal hydroxyl polydimethylsiloxane segments not being able to quickly release and restore the hydrophobic layer, while excessive water adsorbed by too many hydroxyl groups on the surface leads to interfacial structural instability. After HMDS passivation, the hydroxyl groups are partially replaced by hydrophobic Si-O-Si(CH3)3 structures, which significantly reduces the water adsorption capacity on the surface of silica. This makes it easier for trace amounts of water that have penetrated into the system to act directly on the reversible Si-OB bonds, thereby promoting the directional hydrolysis of borate esters and the effective release of hydroxyl-terminated polydimethylsiloxane segments, which helps to quickly restore the hydrophobic layer.

[0021] By introducing HMDS passivation after borosilicate esterification, some residual hydroxyl groups and highly reactive sites can be selectively blocked, giving the surface of silica both a stable hydrophobic region and a reversible borosilicate ester region. The hydrophobic region can maintain the interfacial stability and moisture-proof performance of the system under normal conditions; the reversible borosilicate ester region preferentially hydrolyzes when exposed to moisture, releasing the terminal hydroxyl polydimethylsiloxane segments that migrate to the surface and restore hydrophobicity. If silica is completely borosilicate esterified, it may lead to excessively rapid hydrolysis when exposed to moisture, resulting in high hydrophilicity of silica and reduced compatibility with the system, which in turn makes it prone to cracking and accelerates the aging of silicone rubber.

[0022] Therefore, HMDS passivation can work synergistically with borate esterification to establish a "partially stable-partially reversible" interface structure by regulating the reaction density and interface distribution. This allows water to preferentially attack reversible Si-OB bonds rather than be adsorbed by hydroxyl groups under humid conditions, thereby achieving a hydrophobic retention mechanism that enables controlled slow release, rapid recovery, and long-term stable coexistence.

[0023] In some embodiments, the hydrophobically modified silica is obtained by modifying silica with a vinylsilane coupling agent.

[0024] In some of the above embodiments, when fumed silica is surface-modified using a vinyl silane coupling agent, the resulting hydrophobically modified fumed silica significantly improves the compatibility between the filler and the matrix in the silicone rubber system, and enhances the mixing uniformity and interfacial bonding stability. The vinyl silane coupling agent can undergo a hydrolytic condensation reaction with the silanol groups (Si-OH) on the surface of fumed silica to form stable Si-O-Si bonds, thus retaining the vinyl functional groups on the fumed silica surface. During the subsequent addition crosslinking process of silicone rubber, this vinyl structure can form chemical bonds with vinyl-terminated polydimethylsiloxane or polymethylhydrosiloxane through an addition reaction, thereby constructing a covalently bridging structure between the inorganic filler and the organic matrix.

[0025] This chemical bonding significantly reduces the tendency of fillers to debond at the interface under stress, avoids the propagation of microcracks under corona or mechanical aging conditions, and helps maintain the compactness and long-term hydrophobic properties of the silicone rubber outer layer. At the same time, due to the improved surface hydrophobicity brought about by vinylsilane modification, the filler is easier to disperse in the system and form a uniform network structure, reducing the electric field distortion in the aggregation areas and making the overall hydrophobic film distribution of the material more uniform.

[0026] Therefore, surface modification of silica using vinylsilane coupling agents not only enhances the dispersibility and interfacial bonding strength of the filler, but also introduces synergistic bonding points during the crosslinking and curing process, enabling the system to maintain stable hydrophobicity and excellent electrical insulation properties under long-term service conditions.

[0027] In some embodiments, the hydrophobically modified silica is prepared by the following method:

[0028] 100 parts of silica and 3-5 parts of vinylsilane coupling agent are dispersed in 20-50 parts of an alcohol-water solution and refluxed at 60-80°C for 1-3 hours to obtain hydrophobically modified silica.

[0029] In some of the above embodiments, the alcohol-water solution in the reaction system promotes the hydrolysis of the vinylsilane coupling agent to generate silanol intermediates, which then undergo a condensation reaction with the silanol groups on the surface of silica to form stable Si-O-Si bonds. Controlling the reaction temperature at 60-80℃ helps promote the coupling reaction while avoiding side reactions or polymerization of vinyl groups at high temperatures, making the modification process mild and controllable. The hydrophobically modified silica prepared by this process has a uniform distribution of vinyl groups on its surface and a moderate degree of reaction. It can form a chemical bond with the matrix during subsequent silicone rubber crosslinking while maintaining appropriate surface activity to ensure filler dispersibility. The resulting organosilicon layer has a dense and stable structure, which can significantly reduce the polarity of the filler surface and improve the overall hydrophobicity and interfacial uniformity of the system, thereby enhancing the hydrophobic retention performance and long-term electrical stability of the composite silicone rubber material.

[0030] In some embodiments, the specific surface area of ​​silica is 150~300m². 2 / g.

[0031] In some embodiments, the vinyl-terminated polydimethylsiloxane has a viscosity of 200-400 Pa·s at 25°C and a vinyl content of 0.08 wt%-0.12 wt%. Based on the above embodiments, the vinyl-terminated polydimethylsiloxane within this range has a suitable molecular weight and crosslinking reactivity, which can form a uniform three-dimensional network structure during the curing process while maintaining the fluidity and processability of the system.

[0032] In some embodiments, the hydroxyl-terminated polydimethylsiloxane has a viscosity of 0.3~1.5 Pa·s at 25°C and a hydroxyl content of 0.8wt%~1.2wt%. Based on the above embodiments, the hydroxyl-terminated polydimethylsiloxane within this range is a low-viscosity active silicone oil, which can act as a "dynamic reservoir" of low molecular weight chain segments in the system, gradually releasing them to the material surface under ambient humidity or corona treatment. Its moderate hydroxyl content ensures both reversible bonding with the Si-OB bonds on the surface of borate-modified silica and selective hydrolysis under humid conditions, achieving rapid restoration of hydrophobicity.

[0033] In some embodiments, the viscosity of the polymethylhydrosiloxane at 25°C is 0.015~0.03 Pa·s. Based on the above embodiments, this low-viscosity polymethylhydrosiloxane has high fluidity and reactivity, and can fully add with vinyl-terminated polydimethylsiloxane during vulcanization to form a dense cross-linked network. At the same time, it forms a hydrophobic barrier structure with Si-H as reaction sites on the surface, thereby improving the waterproof and electrolytic corrosion resistance of the material.

[0034] In some embodiments, the platinum-based catalyst includes a Karstedt catalyst. Based on the above embodiments, the Karstedt catalyst can efficiently catalyze the Si-H and C=C addition reaction at lower temperatures, with fewer reaction byproducts and uniform crosslinking. Using this catalyst can effectively shorten the sulfidation time and avoid premature decomposition of the borate ester structure caused by excessively high temperatures, thereby ensuring the integrity of the reversible Si-OB bond and subsequent slow-release function, achieving a balance between dense crosslinking and hydrophobic retention properties of the material.

[0035] In some embodiments, the light stabilizer includes at least one of light stabilizer 770 and light stabilizer 400. Based on the above embodiments, light stabilizer 770 can efficiently scavenge free radicals induced by ultraviolet radiation and slow down the photo-oxidative degradation of polysiloxane segments; light stabilizer 400 can absorb ultraviolet light and inhibit the photolysis reaction of borate ester bonds and organosilicon segments.

[0036] Secondly, this application provides a method for preparing a silicone rubber material for composite insulators, comprising:

[0037] Provide raw materials for the silicone rubber material according to any embodiment of the first aspect.

[0038] The raw materials are mixed and then hot-pressed and vulcanized to obtain a silicone rubber material for composite insulators.

[0039] According to this application, this method can achieve uniform dispersion and structural synergy of different modified silicas in a silicone rubber matrix by rationally controlling the mixing and vulcanization processes. This results in a material that maintains excellent mechanical properties while exhibiting more durable hydrophobicity retention and faster self-healing ability. Specifically, hydrophobic modified silica can form a stable network framework with vinyl polysiloxane through addition crosslinking, providing interfacial anchoring and deformation stability. Boronate-modified silica, after hot-press vulcanization, is distributed within the matrix, forming an energy-storing and slow-release structure that dynamically responds to humidity changes. The hot-press vulcanization process allows for sufficient addition reactions of Si-H and C=C bonds within the system under lower stress, ensuring a dense and uniform crosslinked structure and preventing premature hydrolysis of boron-oxygen bonds due to localized thermal accumulation. Simultaneously, the hot-pressing process helps eliminate air bubbles and volatiles in the system, forming a smooth, continuous rubber body, thereby further improving the uniformity of hydrophobic film formation and electrical insulation properties.

[0040] Therefore, the silicone rubber obtained by the method of this application has good hydrophobicity retention and surface self-healing ability. Even after being subjected to conditions such as humidity and salt spray, this material can still maintain a high contact angle, effectively extending the service life of the insulator's outer sheath.

[0041] In some embodiments, the step of mixing and vulcanizing the raw materials to obtain the silicone rubber material for composite insulators includes:

[0042] The first component is obtained by mixing and degassing vinyl-terminated polydimethylsiloxane, hydrophobically modified silica, and light stabilizer;

[0043] The second component is obtained by mixing and degassing hydroxyl-terminated polydimethylsiloxane, borate-modified silica, and polymethylhydrosiloxane.

[0044] The first component, the second component, and the platinum-based catalyst are mixed and hot-pressed to obtain a silicone rubber material for composite insulators.

[0045] In some of the above embodiments, this two-step premixing process enables different modified silicas to form stable pre-dispersion systems with specific polysiloxanes, thereby improving the uniformity of filler dispersion and the controllability of interfacial reactions. The hydrophobic modified silica in the first component is treated with a vinyl silane coupling agent, and its surface vinyl structure has good compatibility with vinyl-terminated polydimethylsiloxane. The premixing stage allows for sufficient physical dispersion and wetting coating, providing a uniform reaction environment for subsequent addition crosslinking reactions. In the second component, the borate ester modified silica, during the mixing process with hydroxyl-terminated polydimethylsiloxane, allows its surface Si-OB-(OR) bonds to undergo reversible coordination or transesterification reactions with the hydroxyl groups of the polydimethylsiloxane, forming an interfacial pre-bonded structure. This improves the bonding efficiency and reversible sustained-release performance of the two phases during subsequent vulcanization.

[0046] After mixing the two components, a platinum-based catalyst is added for hot-press vulcanization, which allows vinyl-terminated polydimethylsiloxane, hydrophobically modified silica, and polymethylhydrosiloxane to form a dense three-dimensional cross-linked network through Si-H and C=C addition reactions. Simultaneously, the two types of modified silica dispersed in the system are immobilized. During this process, the reversible binding structure between borate-modified silica and hydroxyl-terminated polydimethylsiloxane is preserved, providing a controllable release pathway for subsequent materials under humid heat or corona treatment, thus achieving the self-healing function of the hydrophobic film.

[0047] Therefore, the two-step mixing and final co-vulcanization process design enables the hydrophobic modified silica to play a reinforcing and interfacial stabilizing role, while the borate ester modified silica provides a slow-release and self-recovery function. The two work synergistically in spatial distribution and reaction stage, giving the resulting silicone rubber material long-term stable hydrophobic retention properties and excellent environmental adaptability.

[0048] Compared with the prior art, the beneficial effects of this application are at least as follows:

[0049] By modifying silica with trialkyl borate and passivating it with hexamethyldisilazane, a stable and reversible Si-OB bond is formed in the silicone rubber system. When the hydrophobicity of the material decreases under moisture or corona conditions, the terminal hydroxyl polydimethylsiloxane segments can be slowly released to the surface to quickly restore the hydrophobic film, thus achieving long-term maintenance of hydrophobicity. At the same time, the vinyl silane coupling agent modifies silica, which improves the dispersibility and interfacial bonding of the filler, making the material structure more uniform and the interface more stable. This significantly improves the problem of rapid hydrophobicity decay and slow recovery in traditional composite insulator silicone rubber. Detailed Implementation

[0050] The various embodiments or implementation schemes in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments.

[0051] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0052] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0053] In this specification, unless otherwise specified, "parts" refers to "parts by weight".

[0054] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0055] Vinyl-terminated polydimethylsiloxane, viscosity 300 Pa·s (25℃), vinyl content 0.1 wt%;

[0056] Hydroxyl-terminated polydimethylsiloxane, viscosity 1.0 Pa·s (25 °C), hydroxyl content 1 wt%;

[0057] Polymethylhydrosiloxane, viscosity 0.025 Pa·s (25℃);

[0058] Silica, specific surface area 200 m² 2 / g, loss on drying <1.5%.

[0059] Preparation Example 1

[0060] Preparation of borate ester modified silica:

[0061] 100 parts of silica and 30 parts of toluene were added to a reaction vessel and dispersed under mechanical stirring for 20 min. 3 parts of a trialkylboronic acid ester mixture (in which the mass ratio of trimethylboronic acid ester to triisopropylboronic acid ester was 1:1.2) were added and stirring was continued for 10 min. The mixture was heated to 65 °C and refluxed for 45 min to allow the trialkylboronic acid ester to undergo ester exchange with the silanol groups on the surface of silica. After the reaction was completed, the solvent was removed and the silica was dried under vacuum at 60 °C for 12 h to obtain boronic acid ester-grafted silica.

[0062] Take 100 parts of borate-grafted silica, add 20 parts of anhydrous toluene and disperse evenly; add 0.8 parts of hexamethyldisilazane, reflux at 75℃ for 30 min; after reaction, filter, wash twice with toluene, and vacuum dry at 80℃ for 8 h to obtain passivated borate-modified silica, as borate-modified silica A.

[0063] Preparation Example 2

[0064] Preparation of borate ester modified silica:

[0065] 100 parts of silica and 30 parts of toluene were added to the reactor and dispersed under mechanical stirring for 20 min; 3 parts of trimethylboronic acid ester were added and stirring was continued for 10 min; the temperature was raised to 65℃ and refluxed for 45 min to allow the trimethylboronic acid ester to undergo ester exchange with the silanol groups on the surface of silica. After the reaction was completed, the solvent was removed and the silica was dried under vacuum at 60℃ for 12 h to obtain boronic acid ester-grafted silica.

[0066] Take 100 parts of borate-grafted silica, add 20 parts of anhydrous toluene and disperse evenly; add 0.8 parts of hexamethyldisilazane, reflux at 75℃ for 30 min; after reaction, filter, wash twice with toluene, and vacuum dry at 80℃ for 8 h to obtain passivated borate-modified silica, as borate-modified silica B.

[0067] Preparation Example 3

[0068] Preparation of borate ester modified silica:

[0069] 100 parts of silica and 30 parts of toluene were added to a reaction vessel and dispersed under mechanical stirring for 20 min. 3 parts of a trialkylboronic acid ester mixture (in which the mass ratio of trimethylboronic acid ester to triisopropylboronic acid ester was 1:0.5) were added and stirring was continued for 10 min. The mixture was heated to 65 °C and refluxed for 45 min to allow the trialkylboronic acid ester to undergo ester exchange with the silanol groups on the surface of silica. After the reaction was completed, the solvent was removed and the silica was dried under vacuum at 60 °C for 12 h to obtain boronic acid ester-grafted silica.

[0070] Take 100 parts of borate-grafted silica, add 20 parts of anhydrous toluene and disperse evenly; add 0.8 parts of hexamethyldisilazane, reflux at 75℃ for 30 min; after reaction, filter, wash twice with toluene, and dry under vacuum at 80℃ for 8 h to obtain passivated borate-modified silica, which is used as borate-modified silica C.

[0071] Preparation Example 4

[0072] Preparation of borate ester modified silica:

[0073] 100 parts of silica and 30 parts of toluene were added to a reaction vessel and dispersed under mechanical stirring for 20 min. 3 parts of a trialkylboronic acid ester mixture (in which the mass ratio of trimethylboronic acid ester to triisopropylboronic acid ester was 1:2) were added and stirring was continued for 10 min. The mixture was heated to 65 °C and refluxed for 45 min to allow the trialkylboronic acid ester to undergo ester exchange with the silanol groups on the surface of silica. After the reaction was completed, the solvent was removed and the silica was dried under vacuum at 60 °C for 12 h to obtain boronic acid ester-grafted silica.

[0074] Take 100 parts of borate-grafted silica, add 20 parts of anhydrous toluene and disperse evenly; add 0.8 parts of hexamethyldisilazane, reflux at 75℃ for 30 min; after reaction, filter, wash twice with toluene, and vacuum dry at 80℃ for 8 h to obtain passivated borate-modified silica, as borate-modified silica D.

[0075] Preparation Example 5

[0076] Preparation of borate ester modified silica:

[0077] 100 parts of silica and 30 parts of toluene were added to the reactor and dispersed under mechanical stirring for 20 min; 3 parts of triisopropylboronic acid ester were added and stirring was continued for 10 min; the temperature was raised to 65℃ and refluxed for 45 min to allow the triisopropylboronic acid ester to undergo ester exchange with the silanol groups on the surface of silica. After the reaction was completed, the solvent was removed and the silica was dried under vacuum at 60℃ for 12 h to obtain boronic acid ester grafted silica.

[0078] Take 100 parts of borate-grafted silica, add 20 parts of anhydrous toluene and disperse evenly; add 0.8 parts of hexamethyldisilazane, reflux at 75℃ for 30 min; after reaction, filter, wash twice with toluene, and vacuum dry at 80℃ for 8 h to obtain passivated borate-modified silica, as borate-modified silica E.

[0079] Preparation Example 6

[0080] Preparation of borate ester modified silica:

[0081] 100 parts of silica and 30 parts of toluene were added to the reactor and dispersed under mechanical stirring for 20 min. 3 parts of a trialkylboronic acid ester mixture (in which the mass ratio of trimethylboronic acid ester to triisopropylboronic acid ester was 1:1.2) were added and stirring was continued for 10 min. The mixture was heated to 65 °C and refluxed for 45 min to allow the trialkylboronic acid ester to undergo ester exchange with the silanol groups on the surface of silica. After the reaction was completed, the solvent was removed and the silica was dried under vacuum at 60 °C for 12 h to obtain borate-grafted silica, which was used as borate-modified silica F.

[0082] Preparation Example 7

[0083] Preparation of hydrophobically modified silica:

[0084] 100 parts of silica, 40 parts of ethanol and 10 parts of deionized water were added to the reactor and dispersed under mechanical stirring for 20 min. 4 parts of vinyltriethoxysilane were added and refluxed at 70 °C for 2 h. After the reaction was completed, the mixture was cooled, filtered, washed twice with ethanol, and dried at 100 °C for 12 h to obtain hydrophobically modified silica.

[0085] Example 1

[0086] Preparation of silicone rubber materials:

[0087] 100 parts of vinyl-terminated polydimethylsiloxane, 14 parts of hydrophobic modified silica prepared by the method of Preparation Example 7, and 0.5 parts of light stabilizer 770 were added to a mixer and mixed for 30 minutes. The mixture was then degassed under vacuum for 10 minutes to obtain the first component.

[0088] Six parts of hydroxyl-terminated polydimethylsiloxane, four parts of borate-modified silica A, and ten parts of polymethylhydrosiloxane were mixed for 30 minutes and then vacuum-degassed for 10 minutes to obtain the second component.

[0089] Mix the first component with the second component, add 0.002 parts of Karstedt catalyst, stir evenly, and then pour into a mold;

[0090] Hot-pressing and vulcanizing at 130℃ for 15 minutes, followed by demolding and post-vulcanization at 180℃ for 2 hours, yields silicone rubber material.

[0091] Example 2

[0092] Preparation of silicone rubber materials:

[0093] Similar to Example 1, except that borate-modified silica B is used instead of borate-modified silica A.

[0094] Example 3

[0095] Preparation of silicone rubber materials:

[0096] The method is largely the same as in Example 1, except that borate-modified silica C is used instead of borate-modified silica A.

[0097] Example 4

[0098] Preparation of silicone rubber materials:

[0099] Similar to Example 1, except that borate-modified silica D is used instead of borate-modified silica A.

[0100] Example 5

[0101] Preparation of silicone rubber materials:

[0102] Similar to Example 1, except that borate-modified silica E is used instead of borate-modified silica A.

[0103] Example 6

[0104] Preparation of silicone rubber materials:

[0105] Similar to Example 1, except that borate-modified silica B and borate-modified silica E in a mass ratio of 1:1.2 are used instead of borate-modified silica A.

[0106] Example 7

[0107] Preparation of silicone rubber materials:

[0108] The method is largely the same as in Example 1, except that borate-modified silica F is used instead of borate-modified silica A.

[0109] Comparative Example 1

[0110] Preparation of silicone rubber materials:

[0111] 100 parts of vinyl-terminated polydimethylsiloxane, 14 parts of hydrophobically modified silica and 0.5 parts of light stabilizer 770 were added to a mixer and mixed for 30 minutes. The mixture was then degassed under vacuum for 10 minutes to obtain the first component.

[0112] Six parts of hydroxyl-terminated polydimethylsiloxane, four parts of hydrophobically modified silica, and ten parts of polymethylhydrosiloxane were mixed for 30 minutes and then vacuum-degassed for 10 minutes to obtain the second component.

[0113] Mix the first component with the second component, add 0.002 parts of Karstedt catalyst, stir evenly, and then pour into a mold;

[0114] Hot-pressing and vulcanizing at 130℃ for 15 minutes, followed by demolding and post-vulcanization at 180℃ for 2 hours, yields silicone rubber material.

[0115] Test section

[0116] Hydrophobicity retention test: The silicone rubber materials obtained in each example and comparative example were prepared into sheets with specifications of 50mm×25mm×2mm as samples. The static water contact angle δ0 of the samples was tested at 25℃. Then, the samples were placed in an incubator at 85℃ and 85%RH for 1000h. After being taken out and conditioned at (25±2)℃ and (50±5)%RH for 24h, the static water contact angle δ1 of the samples was tested at 25℃.

[0117] Hydrophobic recovery performance test: The silicone rubber materials obtained in each example and comparative example were prepared into sheets with specifications of 50mm×25mm×2mm as samples. Degreased cotton soaked in anhydrous isopropanol was used to wipe the sample surface back and forth 10 times in the same direction. The samples were dried at room temperature for 30min. After drying, the samples were conditioned at (25±2)℃ and (50±5)%RH for 24h. The static water contact angle δ2 of the samples was then tested at 25℃.

[0118] The test results are shown in Table 1.

[0119] Table 1

[0120]

[0121] According to Table 1, the initial static water contact angle δ0 of the materials obtained in each embodiment and the comparative example is relatively similar. However, the hydrophobicity retention (δ1) and rapid recovery performance (δ2) of each embodiment are significantly improved compared with those of Comparative Example 1. This indicates that the silicone rubber material provided in this application can maintain high surface hydrophobicity under long-term humid heat aging conditions and quickly recover its hydrophobic state after being damaged on the surface. The possible reason is that borate-modified silica was not introduced in Comparative Example 1, and the system lacked a controllable reserve and slow-release mechanism of low molecular weight polydimethylsiloxane segments. After long-term aging, the surface hydrophobic groups were oxidized or migrated and depleted, resulting in a significant decrease in hydrophobicity. Moreover, since no borate bonds were introduced, the surface hydrophobic layer mainly relied on self-migration during the mixing process. Therefore, after wiping, the surface segments were removed, and there was a lack of rapidly replenishable segment sources. After wiping, there was a lack of internally migratable segments for surface reconstruction.

[0122] As shown in Examples 1-5, the ratio of trimethylboronic acid ester to triisopropylboronic acid ester has a significant impact on the reversible bond structure and chain segment release rate of the silica surface. When the ratio is 1:1.2 (Example 1), it can rapidly release some terminal hydroxyl polydimethylsiloxane segments after moisture absorption or surface damage to restore the surface hydrophobicity, and can also slowly release the remaining segments under long-term conditions to maintain the stable replenishment of the hydrophobic film. Therefore, both δ1 and δ2 remain at a high level. When the proportion of trimethylboronic acid ester is high (Examples 2 and 3), the proportion of Si-OB(OMe)(OPDMS) in the system increases, the activity of the outer layer bond is enhanced, the hydrolysis reaction is triggered earlier, and the terminal hydroxyl polydimethylsiloxane segments are released rapidly, resulting in a significant improvement in short-term recovery (δ2). However, the reversible structure is consumed quickly, leading to a slight decrease in hydrophobicity retention (δ1) after aging. When the proportion of triisopropylboronic acid ester is too high (Examples 4 and 5), although the Si-OB(OiPr)(OPDMS) bond is relatively stable and theoretically beneficial for long-term retention, its reactivity is too low, resulting in a significant reduction in the release and migration rate of low molecular weight polydimethylsiloxane segments under humid and hot conditions. Due to the slower recovery rate of the hydrophobic layer, the hydrophobic film on the surface of the silicone rubber cannot be replenished in time during long-term aging under high temperature and high humidity, resulting in excessive surface exposure time, enrichment of polar groups, further initiating oxidation and hydrolytic destruction of the microstructure, and ultimately causing a decrease in overall hydrophobicity retention. Therefore, although triisopropylboronic acid ester can improve the durability of the system, when the proportion is too high, its slow-release effect is excessively delayed, causing the surface hydrophobicity (δ1) of the material in a long-term humid and hot environment to be lower than that in Example 1 with the proportion balance.

[0123] As can be seen from Examples 1 and 6, when trimethylborate-modified silica and triisopropylborate-modified silica are blended and added to the system, although the short-term recovery effect is good, it cannot effectively improve the water-repellent retention after aging.

[0124] As shown in Examples 1 and 7, passivation with hexamethyldisilazane significantly affects the interfacial stability of silica. In the unpassivated sample, residual silanol groups readily adsorb moisture and competitively hydrolyze, weakening the controllable hydrolysis channels of the Si-OB bonds. This leads to instability of the modified filler surface structure, and a significant decrease in both hydrophobicity retention and recovery rate.

[0125] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. 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 silicone rubber material for composite insulators, characterized in that, Includes the following quantities of raw materials: 100 parts vinyl-terminated polydimethylsiloxane, 12-16 parts hydrophobically modified silica, 3-5 parts borate-modified silica, 5-7 parts hydroxyl-terminated polydimethylsiloxane, 8-12 parts polymethylhydrosiloxane, 0.001-0.005 parts platinum-based catalyst, 0.1-1 parts light stabilizer. The borate ester modified silica was prepared by the following method: 100 parts of silica and 2-4 parts of trialkylboronic acid ester are dispersed in 20-40 parts of toluene and refluxed at 60-70°C for 30-60 min to obtain boronic acid ester-grafted silica; wherein the trialkylboronic acid ester includes trimethylboronic acid ester and triisopropylboronic acid ester, and the mass ratio of trimethylboronic acid ester to triisopropylboronic acid ester is 1:1-1.

5. 100 parts of borate-grafted silica and 0.5-1 parts of hexamethyldisilazane were dispersed in 10-30 parts of toluene and refluxed at 70-80℃ for 20-40 min to obtain passivated borate-grafted silica, which was used as borate-modified silica.

2. The silicone rubber material according to claim 1, characterized in that, The hydrophobic modified silica was obtained by modifying silica with a vinylsilane coupling agent.

3. The silicone rubber material according to claim 1, characterized in that, The hydrophobically modified silica was prepared by the following method: 100 parts of silica and 3-5 parts of vinylsilane coupling agent are dispersed in 20-50 parts of an alcohol-water solution and refluxed at 60-80°C for 1-3 hours to obtain hydrophobically modified silica.

4. The silicone rubber material according to any one of claims 1 to 3, characterized in that, The raw materials meet at least one of the following conditions: 1) The vinyl-terminated polydimethylsiloxane has a viscosity of 200~400 Pa·s at 25°C and a vinyl content of 0.08wt%~0.12wt%. 2) The hydroxyl-terminated polydimethylsiloxane has a viscosity of 0.3~1.5 Pa·s at 25°C and a hydroxyl content of 0.8wt%~1.2wt%. 3) The viscosity of the polymethylhydrosiloxane at 25°C is 0.015~0.03 Pa·s; 4) The platinum-based catalyst includes a Karstedt catalyst; 5) The light stabilizer includes at least one of light stabilizer 770 and light stabilizer 400.

5. A method for preparing a silicone rubber material for composite insulators, characterized in that, include: Provide the raw material for the silicone rubber material according to any one of claims 1 to 4, The raw materials are mixed and then hot-pressed and vulcanized to obtain a silicone rubber material for composite insulators.

6. The method according to claim 5, characterized in that, The process of mixing and vulcanizing the raw materials to obtain the silicone rubber material for composite insulators includes: The first component is obtained by mixing and degassing vinyl-terminated polydimethylsiloxane, hydrophobically modified silica, and light stabilizer; The second component is obtained by mixing and degassing hydroxyl-terminated polydimethylsiloxane, borate-modified silica, and polymethylhydrosiloxane. The first component, the second component, and the platinum-based catalyst are mixed and hot-pressed to obtain a silicone rubber material for composite insulators.

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