Nano silicone rubber composite material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of low-dielectric heat-conducting functional materials, in particular to a nano silicone rubber composite material as well as a preparation method and application thereof. According to the preparation method, a modified vinyl silsesquioxane coupling agent is taken as a bridge, and boron nitride nanosheets, silicon carbide nanowires and the modified vinyl silsesquioxane coupling agent are covalently connected through hydrolysis reaction, so that a heterostructure is constructed, and the nano heat-conducting filler is obtained; the preparation method comprises the following steps: dispersing a nano heat-conducting filler in vinyl silicone oil, and constructing a covalent cross-linked network through addition cross-linking reaction and curing treatment to obtain the nano composite silicone rubber material. According to the processing method, the filling amount, the dielectric constant and the dielectric loss can be reduced, meanwhile, the heat conduction capacity is improved, and the problems that in the prior art, the dielectric constant and the dielectric loss are low due to simple mixing of the boron nitride nanosheets and the silicon carbide nanowires are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of low dielectric thermal conductive functional materials, and in particular to a nano silicone rubber composite material and a preparation method and application thereof. Background Art

[0002] With the rapid development of modern electronic technology, especially the rapid progress in integrated circuits, high-voltage transmission equipment, energy storage systems, and high-power LEDs, more stringent requirements have been placed on dielectric materials. These applications require not only excellent insulation properties, but also excellent thermal conductivity and low dielectric constant to ensure efficient operation and long-term stability of the equipment.

[0003] Polymer materials have been widely used in many fields due to their low cost, easy processing, light weight and good insulation properties. However, traditional polymer materials often have unsatisfactory thermal conductivity and dielectric constant, which makes it difficult to meet the needs of modern electronic technology for efficient heat dissipation and high-performance media. Therefore, the development of polymer composites with high thermal conductivity and low dielectric constant has become a hot topic in current research.

[0004] Methods for improving the thermal conductivity of polymers mainly include preparing polymer matrix materials with high intrinsic thermal conductivity and adding thermal conductivity. For example, the thermal conductivity can be improved by changing the orientation of polymer material links and constructing liquid crystal structures, but this method is technically difficult and has limited effects. In contrast, adding thermally conductive fillers such as metal oxides such as Al2O3, ZnO and MgO, metal particles such as Cu, Zn and Ag, aluminum nitride, boron nitride, silicon carbide, graphene and carbon nanotubes is a simpler and more effective method. However, when a single nanofiller is used for filling, an extremely high filling amount is often required to obtain ideal thermal conductivity, but a high filling amount of thermally conductive fillers will damage the processability and mechanical properties of the polymer material.

[0005] In order to reduce the filling amount of thermally conductive fillers, researchers have adopted the doping of multiple thermally conductive fillers. The synergistic effect of multiple thermally conductive fillers can bring greater thermal conductivity improvement with a smaller filling amount. However, the simple blending of multiple thermally conductive fillers will increase the interface between the thermally conductive fillers, resulting in higher interface thermal resistance, which hinders the increase of thermal conductivity of thermally conductive polymer composites. Therefore, high interface thermal resistance is also a key factor restricting the performance of high thermal conductive polymer composites.

[0006] For example, boron nitride nanosheets have a two-dimensional structure similar to graphene, with high thermal conductivity and high aspect ratio, as well as excellent electrical insulation properties, making them a promising thermal conductive filler for polymer composites. Silicon carbide nanowires, as a commonly used one-dimensional nano thermal conductive material, can form a good synergistic effect with boron nitride nanosheets, showing excellent thermal management and electromagnetic wave absorption capabilities; however, the higher dielectric constant and dielectric loss limit the application of silicon carbide. Summary of the invention

[0007] In order to solve the problem in the prior art that a simple mixture of boron nitride nanosheets and silicon carbide nanowires leads to a higher dielectric constant and dielectric loss, the present invention aims to provide a nano-silicone rubber composite material with high thermal conductivity, low dielectric constant and low dielectric loss, and a preparation method and application thereof.

[0008] Reducing the polarizability and introducing pores can effectively reduce the dielectric constant and dielectric loss of the material. The cage structure of polyhedral oligomeric silsesquioxane, referred to as POSS, is a high-temperature resistant inorganic rigid skeleton that can reduce the dielectric constant of composite materials; therefore, it is often used in the preparation of low-dielectric materials. In addition, the active groups on the surface of POSS can reduce the interfacial thermal resistance between nanofillers and silicone rubber and improve thermal conductivity.

[0009] Based on this, the present invention uses the synergistic effect of boron nitride nanosheets and silicon carbide nanowires and uses a modified vinyl silsesquioxane coupling agent for surface treatment to form a nano thermally conductive filler with a heterogeneous structure, thereby reducing the filling amount, dielectric constant and dielectric loss while improving thermal conductivity, solving the problem of high dielectric constant and dielectric loss caused by simple mixing of boron nitride nanosheets and silicon carbide nanowires in the prior art.

[0010] To achieve the above objectives, the technical solution of the present invention is as follows.

[0011] The first aspect of the present invention provides a method for preparing a nanocomposite silicone rubber material, comprising the following steps:

[0012] In a first alcohol-water solvent system, a modified vinyl silsesquioxane coupling agent, boron nitride nanosheets and silicon carbide nanowires are subjected to a reflux reaction; during the reflux reaction, the methoxy group of the modified vinyl silsesquioxane coupling agent is hydrolyzed to generate silanol groups, and then the hydrolyzed modified vinyl silsesquioxane coupling agent is used as an intermediate bridge to react with the surface hydroxyl groups of the boron nitride nanosheets and the silicon carbide nanowires respectively, and at the same time, the boron nitride nanosheets and the silicon carbide nanowires are covalently connected to construct a heterostructure to obtain a nano thermal conductive filler.

[0013] The nano thermal conductive filler is uniformly dispersed in the vinyl silicone oil to obtain a mixture.

[0014] With hydrogen-containing silicone oil as a crosslinking agent, under the action of a first catalyst and an inhibitor, the vinyl silicone oil in the mixture undergoes an addition crosslinking reaction with the hydrogen-containing silicone oil to form an addition-type liquid silicone rubber.

[0015] Addition liquid silicone rubber is used as the matrix, and a curing treatment is performed after vacuum degassing, so that the residual vinyl in the nano thermal conductive filler reacts with the silicon-hydrogen bond in the matrix, so that the nano thermal conductive filler constructs a covalent cross-linking network in the matrix to obtain a nano composite silicone rubber material.

[0016] Invention concept:

[0017] The present invention mainly utilizes a modified vinyl silsesquioxane coupling agent as an intermediate bridge, and through a reflux reaction, the methoxy group on the intermediate bridge is hydrolyzed to generate a silanol group, and the dehydration condensation reaction of the silanol group and the hydroxyl group is utilized to connect the boron nitride nanosheet and the silicon carbide nanowire, and at the same time, the boron nitride nanosheet and the silicon carbide nanowire are covalently connected to construct a heterogeneous structure, while reducing the carrier mobility, while improving the thermal conductivity. Moreover, when the nano thermal conductive filler is filled in the nano silicone rubber material, the filling amount can be reduced, and the dielectric constant and dielectric loss are lowered, which solves the problem of high dielectric constant and dielectric loss caused by simple mixing of the boron nitride nanosheet and the silicon carbide nanowire in the prior art.

[0018] The present invention performs a thermal alkali treatment on the silicon carbide nanowires, which can attach hydroxyl groups to the surface, and increase the surface roughness and oxidize the surface to form silicon oxide, thereby reducing the dielectric constant and dielectric loss.

[0019] The present invention disperses the nano thermally conductive filler in the vinyl silicone oil, which helps to disperse the nano thermally conductive filler in the addition-type liquid silicone rubber formed after the addition cross-linking reaction, and then in the subsequent thermal curing treatment, the nano thermally conductive filler can construct a covalent cross-linking network in the matrix, and the interface thermal resistance between the nano filler and the addition-type liquid silicone rubber is reduced by the constructed covalent cross-linking network, thereby improving the thermal conductivity, and thus the prepared nano composite silicone rubber material has excellent thermal conductivity and higher high temperature resistance, as well as lower dielectric constant and dielectric loss.

[0020] The present invention uses a modified vinyl silsesquioxane coupling agent as an intermediate bridge to connect boron nitride nanosheets and silicon carbide nanowires. At the same time, the boron nitride nanosheets and silicon carbide nanowires are covalently connected to construct a heterostructure, so that POSS can be introduced into a nano thermal conductive filler system. POSS has a large specific surface area and more active groups, and can adjust the interface compatibility and the trap distribution on the interface, thereby providing more scattering barriers and trap sites, and effectively reducing the carrier mobility.

[0021] Preferably, the mass ratio of the boron nitride nanosheets, the modified vinyl silsesquioxane coupling agent and the silicon carbide nanowires is 1:0.1-0.5:0.5-1.

[0022] Preferably, the first catalyst is a Custer catalyst; the inhibitor is ethynyl cyclohexanol; the doping amount of the nano thermal conductive filler accounts for 10% to 20% of the total mass of the liquid silicone rubber. For example, 10%, 15% and 20%. The molar ratio of the silicon-hydrogen bond in the hydrogen-containing silicone oil to the silicon-vinyl bond in the vinyl silicone oil is 1:1 to 1.5; the amount of the inhibitor is 1500ppm to 2000ppm of the total mass of the mixture and the hydrogen-containing silicone oil; the amount of the first catalyst is 4ppm to 10ppm of the mass of the addition-type liquid silicone rubber.

[0023] Preferably, during the preparation of the nano thermally conductive filler, the reflux reaction temperature is 60° C. to 80° C. and the time is 6 h to 10 h.

[0024] Preferably, the curing temperature is 90°C to 150°C, and the curing time is 1 hour to 3 hours. Specifically, the curing is first performed at 90°C for 1 hour, then the temperature is raised to 150°C, and the curing is performed at 150°C for 2 hours.

[0025] Preferably, the modified vinyl silsesquioxane coupling agent is prepared by the following method:

[0026] Under the action of the second catalyst, the vinyl groups in the vinyl silsesquioxane and the silicon-hydrogen bonds in the silane coupling agent undergo addition reaction in the second solvent system to obtain a modified vinyl silsesquioxane coupling agent.

[0027] The present invention uses a silane coupling agent to modify vinyl silsesquioxane to prepare a modified vinyl silsesquioxane coupling agent. The second catalyst is a Custer catalyst; and the silane coupling agent is trimethoxyhydrogen silane. Specifically, under the action of the Custer catalyst, vinyl silsesquioxane and trimethoxyhydrogen silane are subjected to silylation. The reaction is carried out in a toluene solvent, thereby preventing the decomposition of the silicon-hydrogen bond and allowing the methoxy group to be retained.

[0028] The boron nitride nanosheet is prepared by the following method: ultrasonically exfoliating hexagonal boron nitride in a third alcohol-water solvent, and introducing hydroxyl groups on the surface of the hexagonal boron nitride during the ultrasonic exfoliation process to obtain the boron nitride nanosheet.

[0029] The silicon carbide nanowire is prepared by the following method: silicon carbide is subjected to ultrasonic dispersion and surface hydroxylation reaction in an alkaline solution to obtain the silicon carbide nanowire.

[0030] The present invention performs hydroxylation modification on boron nitride nanosheets and silicon carbide nanowires, and the methoxy groups on the vinyl silsesquioxane coupling agent are hydrolyzed to form silanol groups, thereby utilizing the reaction between the silanol groups and the hydroxy groups on the surface of the nanofiller to attach POSS.

[0031] Preferably, the second catalyst is a Custer catalyst; the silane coupling agent is trimethoxyhydrogensilane; the particle size of hexagonal boron nitride is 5 μm to 10 μm; the molar ratio of vinyl silsesquioxane to the silane coupling agent is 1:5 to 30; and the amount of the second catalyst used is 1000 ppm to 2000 ppm of the mass of vinyl silsesquioxane.

[0032] Preferably, during the preparation of the modified vinyl silsesquioxane coupling agent, the temperature of the addition reaction is 60° C. to 80° C.; and the time of the addition reaction is 6 h to 10 h.

[0033] Preferably, during the preparation of silicon carbide nanowires, the temperature of the surface hydroxylation reaction is 80°C to 120°C; the alkaline solution is a sodium hydroxide solution; the concentration of the alkaline solution is 2mol / L to 4mol / L; the amount ratio of silicon carbide to the alkaline solution is 1g:50mL to 100mL. Preferably, the time of the surface hydroxylation reaction is 12h to 24h.

[0034] Preferably, the first alcohol-water solvent is an ethanol aqueous solution with a volume fraction of 50%; the second solvent is toluene; the usage ratio of vinyl silsesquioxane to the second solvent is 1g:50mL~100mL; the third alcohol-water solvent is an isopropanol aqueous solution with a volume fraction of 50%~80%; the usage ratio of hexagonal boron nitride to the second solvent is 1g:100mL~150mL.

[0035] Preferably, the ultrasonic stripping time is 6 h to 12 h.

[0036] The second aspect of the present invention provides a nano-composite silicone rubber material, which is prepared by the preparation method described in the first aspect.

[0037] The third aspect of the present invention provides an application of the nano-composite silicone rubber material described in the second aspect in the preparation of a low dielectric thermal conductive material.

[0038] Preferably, the low dielectric thermal conductivity material is a low dielectric thermal conductivity material used in heat dissipation of electronic devices.

[0039] Beneficial effects of the present invention:

[0040] 1. The present invention mainly utilizes a modified vinyl silsesquioxane coupling agent as an intermediate bridge, and through a hydrolysis reaction, hydrolyzes the methoxy group on the intermediate bridge to generate a silanol group, and utilizes the dehydration condensation reaction of the silanol group and the hydroxyl group to connect the boron nitride nanosheets and the silicon carbide nanowires. At the same time, the boron nitride nanosheets and the silicon carbide nanowires are covalently connected to construct a heterogeneous structure, which reduces the carrier mobility and improves the thermal conductivity. Moreover, when the nano thermal conductive filler is filled in the nano silicone rubber material, the filling amount can be reduced, and the dielectric constant and dielectric loss are lowered, which solves the problem of high dielectric constant and dielectric loss caused by the simple mixing of boron nitride nanosheets and silicon carbide nanowires in the prior art.

[0041] 2. The present invention disperses the nano-thermal conductive filler in the vinyl silicone oil, so that the nano-thermal conductive filler can be dispersed in the addition-type liquid silicone rubber formed after the addition cross-linking reaction, and then in the subsequent thermal curing treatment, the nano-thermal conductive filler can construct a covalent cross-linking network in the matrix, so that the prepared nano-composite silicone rubber material has excellent thermal conductivity and higher high temperature resistance, as well as lower dielectric constant and dielectric loss.

[0042] 3. The present invention uses a modified vinyl silsesquioxane coupling agent as an intermediate bridge to connect boron nitride nanosheets and silicon carbide nanowires. At the same time, the boron nitride nanosheets and silicon carbide nanowires are covalently connected to construct a heterostructure, so that POSS can be introduced into the nano thermal conductive filler system. POSS has a large specific surface area and more active groups, which can adjust the interface compatibility and the trap distribution on the interface, thereby providing more scattering barriers and trap sites, and effectively reducing the carrier mobility.

[0043] 4. The present invention adjusts the performance of the nano thermal conductive filler by coordinating boron nitride nanosheets, silicon carbide nanowires and vinyl silsesquioxane coupling agent intermediates to make it have lower dielectric properties and higher thermal conductivity. The prepared nano silicone rubber composite material has strong stability and good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is an electron microscope photograph of the boron nitride nanosheets obtained in Example 1.

[0045] Figure 2 This is the Fourier transform infrared spectrum of the boron nitride nanosheets obtained in Example 1.

[0046] Figure 3 This is an electron microscope photograph of the silicon carbide nanowires obtained after hot alkali treatment in Example 1.

[0047] Figure 4 This is the Fourier infrared spectrum of the thermal alkali treated silicon carbide nanowires obtained in Example 1.

[0048] Figure 5 This is a physical photo of the modified vinyl silsesquioxane coupling agent obtained in Example 1.

[0049] Figure 6 This is the Fourier infrared spectrum of the modified vinyl silsesquioxane coupling agent obtained in Example 1.

[0050] Figure 7 This is the hydrogen nuclear magnetic resonance spectrum of the modified vinyl silsesquioxane coupling agent obtained in Example 1.

[0051] Figure 8 This is an electron microscope photograph of the nano thermally conductive filler obtained in Example 1.

[0052] Fig. 9 This is the Fourier infrared spectrum of the nano thermal conductive filler obtained in Example 1.

[0053] Fig.10 This is a comparison chart of the thermal conductivity of the nano-silicone rubber composite materials obtained in Examples 1 to 10.

[0054] Fig.11 This is a data comparison chart of the dielectric constants of the nano-silicone rubber composite material prepared by doping silicone rubber with nano-thermal conductive filler in Example 1, the nano-silicone rubber composite material prepared by doping silicone rubber with pure SICNW-OH in Example 8, and the nano-silicone rubber composite material prepared by doping silicone rubber with pure SICNW in Comparative Example 1.

[0055] Fig.12 This is a data comparison chart of dielectric loss of the nano-silicone rubber composite material prepared by doping silicone rubber with nano-thermal conductive filler in Example 1, the nano-silicone rubber composite material prepared by doping silicone rubber with pure SICNW-OH in Example 8, and the nano-silicone rubber composite material prepared by doping silicone rubber with pure SICNW in Comparative Example 1. DETAILED DESCRIPTION

[0056] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0057] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making any creative work shall fall within the scope of protection of the present invention.

[0058] The present invention provides a method for preparing a nano-silicone rubber composite material, comprising the following steps:

[0059] Step 1, preparing a modified vinyl silsesquioxane coupling agent:

[0060] Under the action of the second catalyst, the vinyl groups in the vinyl silsesquioxane and the silicon-hydrogen bonds in the silane coupling agent undergo addition reaction in the second solvent system to obtain a modified vinyl silsesquioxane coupling agent.

[0061] The second catalyst is a Custer catalyst; the silane coupling agent is trimethoxyhydrogensilane; the molar ratio of vinyl silsesquioxane to the silane coupling agent is 1:5-30; the amount of the second catalyst is 1000ppm-2000ppm of the mass of the vinyl silsesquioxane. The second solvent is toluene; the amount ratio of vinyl silsesquioxane to the second solvent is 1g:50mL-100mL. The addition reaction is carried out under reflux conditions. The temperature of the addition reaction is 60℃-80℃; the time of the addition reaction is 6h-10h.

[0062] In step 1, the second catalyst reduces the activation energy of the reaction, making the addition reaction between the vinyl functional group and the silicon-hydrogen bond relatively easier, and a new silicon-carbon bond is generated after the addition reaction, thereby obtaining a modified vinyl silsesquioxane coupling agent. The present invention uses a silane coupling agent to modify vinyl silsesquioxane to prepare a modified vinyl silsesquioxane coupling agent. Specifically, vinyl silsesquioxane and trimethoxyhydrosilane are subjected to silicon hydrogen addition under the action of a Custer catalyst. The reaction is carried out in a toluene solvent to prevent the decomposition of the silicon-hydrogen bond and to retain the methoxy group.

[0063] Step 2, preparation of boron nitride nanosheets:

[0064] The hexagonal boron nitride is subjected to ultrasonic exfoliation in a third alcohol-water solvent, and hydroxyl groups are introduced onto the surface of the hexagonal boron nitride during the ultrasonic exfoliation process to obtain boron nitride nanosheets.

[0065] The particle size of hexagonal boron nitride is 5 μm to 10 μm; the third alcohol-water solvent is an isopropanol aqueous solution with a volume fraction of 50% to 80%; the dosage ratio of hexagonal boron nitride to the second solvent is 1 g: 100 mL to 150 mL; and the ultrasonic peeling time is 6 h to 12 h.

[0066] In step 2, an isopropanol aqueous solution is used as the third alcohol-water solvent, which has good solubility and dispersibility, and is conducive to the dispersion and hydroxylation modification of hexagonal boron nitride; ultrasonic oscillation is used to peel off the hexagonal boron nitride layer to form smaller boron nitride nanosheets. At the same time, during the ultrasonic oscillation process, hydroxyl functional groups are introduced on the surface of the boron nitride nanosheet to obtain a boron nitride nanosheet with hydroxyl groups on the surface. After the ultrasonic peeling, the present invention allows the boron nitride nanosheet to settle and stratify by standing still, thereby facilitating the separation of the boron nitride nanosheets in the solution.

[0067] Step 3, preparing silicon carbide nanowires:

[0068] Silicon carbide is subjected to ultrasonic dispersion and surface hydroxylation reaction in an alkaline solution to obtain silicon carbide nanowires. The concentration of the alkaline solution is 2 mol / L to 4 mol / L; the amount ratio of silicon carbide to the alkaline solution is 1 g: 50 mL to 100 mL. The temperature of the surface hydroxylation reaction is 80°C to 120°C; and the time is 12h to 24h.

[0069] In step 3, the cavitation effect of ultrasound is used to disperse the silicon carbide in the alkaline solution to increase the contact area between the dispersed silicon carbide nanowires and the alkaline solution; then, at a certain temperature, the alkaline solution is used as an alkaline catalyst to promote the hydroxylation of the silicon carbide surface. Specifically, the surface hydroxylation reaction is a reaction between the silicon atoms on the surface of the silicon carbide and the OH in the alkaline solution. - The -OH functional group is introduced into the SiC surface. At the same time, the oxidation of the hot alkali increases the surface roughness of the SiC nanowires and forms silicon oxide, which reduces the dielectric constant and dielectric loss of the SiC nanowires.

[0070] In step 2 and step 3, the present invention performs hydroxylation modification on boron nitride nanosheets and silicon carbide nanowires, and the methoxy groups on the vinyl silsesquioxane coupling agent are hydrolyzed to form silanol groups, which react with hydroxyl groups on the surface of the nanofiller to allow POSS to attach.

[0071] Step 4, preparing nano thermal conductive filler:

[0072] In the first alcohol-water solvent system, a modified vinyl silsesquioxane coupling agent, a boron nitride nanosheet and a silicon carbide nanowire are subjected to a reflux reaction; during the reflux reaction, the modified vinyl silsesquioxane coupling agent is used as an intermediate bridge, and the methoxy group on the intermediate bridge is hydrolyzed to generate silanol groups, and the boron nitride nanosheet and the silicon carbide nanowire are connected by a dehydration condensation reaction of the silanol groups and the hydroxy groups, and the boron nitride nanosheet and the silicon carbide nanowire are covalently connected to construct a heterostructure to obtain a nano thermal conductive filler.

[0073] The mass ratio of boron nitride nanosheets, modified vinyl silsesquioxane coupling agent and silicon carbide nanowires is 1: 0.1-0.5: 0.5-1. The first alcohol-water solvent is an ethanol aqueous solution with a volume fraction of 50%; the temperature of the reflux reaction is 60° C.-80° C., and the time is 6h-10h.

[0074] In step 4, modified vinyl silsesquioxane is used as an intermediate bridge to connect BNNS and SiCNW to construct a heterostructure, so that POSS can be introduced into the nano thermal conductive filler system. POSS has a large specific surface area and more active groups, which can adjust the interface compatibility and the trap distribution on the interface, thereby providing more scattering barriers and trap sites, effectively reducing the carrier mobility.

[0075] The present invention introduces -OH functional groups on the SiC surface by processing silicon carbide nanowires, thereby significantly reducing the dielectric constant and dielectric loss of the silicon carbide nanowires, and can enhance thermal conductivity through the heterostructure formed by boron nitride nanosheets and silicon carbide nanowires.

[0076] Step 5, preparing nano-silicone rubber composite material:

[0077] The nano thermal conductive filler is uniformly dispersed in the vinyl silicone oil to obtain a mixture.

[0078] With hydrogen-containing silicone oil as a crosslinking agent, under the action of a first catalyst and an inhibitor, the vinyl silicone oil in the mixture undergoes an addition crosslinking reaction with the hydrogen-containing silicone oil to form an addition-type liquid silicone rubber.

[0079] Addition liquid silicone rubber is used as the matrix, and a curing treatment is performed after vacuum degassing, so that the residual vinyl in the nano thermal conductive filler reacts with the silicon-hydrogen bond in the matrix, so that the nano thermal conductive filler constructs a covalent cross-linking network in the matrix to obtain a nano composite silicone rubber material.

[0080] The first catalyst is a Custer catalyst; the inhibitor is ethynyl cyclohexanol; the doping amount of the nano thermal conductive filler accounts for 10% to 20% of the total mass of the liquid silicone rubber. The molar ratio of the silicon-hydrogen bond in the hydrogen-containing silicone oil to the silicon-vinyl bond in the vinyl silicone oil is 1:1 to 1.5; the amount of the inhibitor is 1500ppm to 2000ppm of the total mass of the mixture and the hydrogen-containing silicone oil; the amount of the first catalyst is 4ppm to 10ppm of the mass of the addition-type liquid silicone rubber.

[0081] The curing temperature is 90°C to 150°C, and the curing time is 1h to 3h. Specifically, the curing is performed at 90°C for 1h, then the temperature is raised to 150°C, and the curing is performed at 150°C for 2h.

[0082] In step 5, the present invention disperses the nano-thermal conductive filler in the vinyl silicone oil, which helps to disperse the nano-thermal conductive filler in the addition-type liquid silicone rubber formed after the addition cross-linking reaction, and then in the subsequent thermal curing treatment, the nano-thermal conductive filler can construct a covalent cross-linking network in the matrix. The constructed covalent cross-linking network reduces the interfacial thermal resistance between the nano-filler and the silicone rubber, thereby improving the thermal conductivity, and the prepared nano-composite silicone rubber material has excellent thermal conductivity and higher high temperature resistance.

[0083] The technical solution of the present invention is further described below through specific embodiments.

[0084] In the following examples, the methods described are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0085] In the following embodiments, silicon carbide nanowires have a diameter of 100 nm to 600 nm and a length of 50 nm to 100 nm, and are from Shanghai Dibai Biotechnology Co., Ltd.

[0086] Hexagonal boron nitride, denoted as h-BN, 5μm~10μm, Shanghai Adamas Reagent Co., Ltd. BNNS is boron nitride nanosheets; SiCNW is silicon carbide nanowires. Hexagonal boron nitride.

[0087] Vinyl silsesquioxane, referred to as vinyl POSS, is called PSS-Octavinyl substituted in English; its Chinese name is octavinyl octasilsesquioxane, and its molecular formula is C 16 H 24 O 12 Si8. Vinyl POSS has a unique cage-like framework structure, which is an inorganic core composed of a silicon-oxygen skeleton alternately connected by Si-O. It is shaped like a "cage" with a three-dimensional size between 1nm and 3nm. This structure gives vinyl POSS good dielectric, optical properties and thermal stability.

[0088] Custer catalyst, Chinese name is platinum (0)-1,3-diethylene-1,1,3,3-tetramethyldisiloxane, molecular formula is C8H 18 OPtSi2.

[0089] Vinyl silicone oil, purchased from Ambia Specialty Silicone, VS10000, is a colorless or light yellow transparent liquid, with a viscosity specification of 10000 cps measured at 25°C and a vinyl content of 0.05 mmol / g.

[0090] Hydrogen-containing silicone oil, purchased from Ambia Specialty Silicone, XL13, is a colorless or slightly yellow transparent liquid with a viscosity of 100 cst and a hydrogen content of 3.8 mmol / g.

[0091] Example 1

[0092] A method for preparing a nano-silicone rubber composite material comprises the following steps:

[0093] Step 1, preparing a modified vinyl silsesquioxane coupling agent:

[0094] Dissolve 5g of vinyl POSS in 250mL of toluene and stir thoroughly to make it evenly dissolved. Then add trimethylsilane equivalent to 10 times the molar amount of vinyl POSS and stir thoroughly. Then add 1000ppm of Custer catalyst equivalent to vinyl POSS and stir thoroughly. Then add it to a three-necked flask, condense and reflux, stir magnetically, and react at 70℃ for 8h.

[0095] After the reaction is completed, 1g of activated carbon is added and the reaction is continued for 2 hours; after the reaction is completed, the mixture is cooled to room temperature, centrifuged at 9000rpm for 10min, and the supernatant is taken. After repeating twice, a light yellow liquid is obtained. The light yellow liquid is subjected to vacuum conditions at 70°C to remove the solvent to obtain a light yellow oily substance, which is a modified vinyl POSS coupling agent. The obtained modified vinyl POSS coupling agent needs to be sealed and stored, and it will gradually solidify after contact with air, proving that the product is a modified vinyl POSS coupling agent.

[0096] Step 2, preparation of boron nitride nanosheets:

[0097] Isopropyl alcohol and deionized water were mixed in a volume ratio of 4:1 to obtain an isopropyl alcohol aqueous solution.

[0098] The 5μm to 10μm hexagonal boron nitride raw material purchased from the market was added to the isopropanol aqueous solution at a ratio of 10g / L, and ultrasonically vibrated for 12 hours, and then allowed to stand for 2 hours. The ultrasonic power was 600W and the frequency was 40KHZ. After the unpeeled h-BN settled to the bottom, the supernatant was filtered to obtain boron nitride nanosheets with hydroxyl groups on the surface, which were recorded as OH-BNNS. They were placed in an oven at 80°C and dried for 12 hours before use.

[0099] The unpeeled h-BN raw material was added to the isopropanol aqueous solution and stirred thoroughly, and then allowed to stand for 2 hours again, and the supernatant was filtered. After repeating three times, the remaining raw material was used for the next ultrasonic treatment.

[0100] Step 3, preparing silicon carbide nanowires:

[0101] 2g of purchased silicon carbide nanowires with a diameter of 100nm to 600nm and a length of 50nm to 100nm were dissolved in 200mL of 4mol / L sodium hydroxide aqueous solution, and magnetically stirred at 80℃ for 24h. After the reaction, the precipitate was centrifuged at 9000rpm. 1L of water was added, stirred for 30min to wash away the residual sodium hydroxide, and the washing was repeated three times and then filtered to obtain silicon carbide nanowires with hydroxyl groups on the surface, which were recorded as SiCNW-OH and dried at 80℃ for 12h.

[0102] Step 4, preparing nano thermal conductive filler:

[0103] Take 0.4g OH-BNNS, 0.2g SiCNW-OH and 0.2g modified vinyl POSS coupling agent. Dissolve 0.4g OH-BNNS in 20mL ethanol, 0.2g SiCNW-OH in 40mL deionized water, and 0.2g modified vinyl POSS coupling agent in 20mL ethanol, stir evenly and mix them together, pour them into a three-necked flask, and condense and reflux at 70℃ for 8h under magnetic stirring. After the reaction is completed, filter, wash with ethanol and deionized water, and dry at 80℃ for 12h to obtain a nano thermal conductive filler with a heterogeneous structure.

[0104] Step 5, preparing nano-silicone rubber composite material:

[0105] 0.2 g of nano thermal conductive filler was mixed with 2 g of vinyl silicone oil VS10000, 40 mL of n-pentane was added, ultrasonicated for 5 min, and stirred evenly. The n-pentane was removed by magnetic stirring at 50° C., and the mixture was cooled to room temperature to obtain a mixture.

[0106] Using hydrogen-containing silicone oil XL13 as a crosslinking agent and ethynyl cyclohexanol as an inhibitor, 0.04 g of hydrogen-containing silicone oil XL13 and the inhibitor were added to the mixture; wherein the molar ratio of the silicon-hydrogen bond in the hydrogen-containing silicone oil to the silicon-vinyl bond in the vinyl silicone oil was Si-H:Si-V=1.3; the amount of the inhibitor used was 1500 ppm of the total mass of the mixture and the hydrogen-containing silicone oil.

[0107] After sufficient stirring, add the Custer catalyst, the amount of which is 8 ppm of the total mass of the mixture and the hydrogen-containing silicone oil. Continue stirring the reaction to utilize the vinyl silicone oil in the mixture to undergo an addition crosslinking reaction with the hydrogen-containing silicone oil to form an addition-type liquid silicone rubber.

[0108] Addition type liquid silicone rubber is used as the matrix, and vacuum degassing is performed after sufficient stirring. After degassing, it is poured into a mold and placed in an oven. After drying at 90°C for 1 hour, the temperature is raised to 150°C and heated for 2 hours to allow the nano thermal conductive filler to construct a covalent cross-linked network in the matrix; after curing, a nano silicone rubber composite material is obtained.

[0109] Example 2

[0110] A method for preparing a nano-silicone rubber composite material, which differs from Example 1 in that, in step 5, the amount of the nano-thermal conductive filler added is 0.4 g, and the amount of the nano-thermal conductive filler added accounts for 20% of the mass fraction of the vinyl silicone oil; the specific preparation method comprises the following steps:

[0111] Steps 1 to 4 are carried out according to Example 1 to prepare a nano thermally conductive filler with a heterogeneous structure.

[0112] Step 5, preparing nano-silicone rubber composite material:

[0113] 0.4 g of nano thermal conductive filler was mixed with 2 g of vinyl silicone oil VS10000, 40 mL of n-pentane was added, ultrasonicated for 5 min, and stirred evenly. The n-pentane was removed by magnetic stirring at 50° C., and the mixture was cooled to room temperature to obtain a mixture.

[0114] Using hydrogen-containing silicone oil XL13 as a crosslinking agent and ethynyl cyclohexanol as an inhibitor, 0.04 g of hydrogen-containing silicone oil XL13 and the inhibitor were added to the mixture; wherein the molar ratio of the silicon-hydrogen bond in the hydrogen-containing silicone oil to the silicon-vinyl bond in the vinyl silicone oil was Si-H:Si-V=1.3; the amount of the inhibitor used was 1500 ppm of the total mass of the mixture and the hydrogen-containing silicone oil.

[0115] After sufficient stirring, add the Custer catalyst, the amount of which is 8 ppm of the total mass of the mixture and the hydrogen-containing silicone oil. Continue stirring the reaction to utilize the vinyl silicone oil in the mixture to react with the hydrogen-containing silicone oil to form an addition-type liquid silicone rubber.

[0116] Addition type liquid silicone rubber is used as the matrix, and vacuum degassing is performed after sufficient stirring. After degassing, it is poured into a mold and placed in an oven. After drying at 90°C for 1 hour, the temperature is raised to 150°C and heated for 2 hours to allow the nano thermal conductive filler to construct a covalent cross-linked network in the matrix; after curing, a nano silicone rubber composite material is obtained.

[0117] Example 3

[0118] A method for preparing a nano-silicone rubber composite material is different from Example 1 in that in step 5, the amount of the nano-thermal conductive filler added is 0.3 g, and the mass fraction of the nano-thermal conductive filler added to the vinyl silicone oil is 15%.

[0119] Example 4

[0120] A method for preparing a nano-silicone rubber composite material is different from Example 1 in that, in step 5, the amount of the nano-thermal conductive filler added is 0.1 g, and the mass fraction of the nano-thermal conductive filler added to the vinyl silicone oil is 5%.

[0121] Example 5

[0122] A method for preparing a nano-silicone rubber composite material comprises the following steps:

[0123] Step 1, preparing boron nitride nanosheets: According to step 2 of Example 1, boron nitride nanosheets with hydroxyl groups on the surface are prepared, which are denoted as OH-BNNS.

[0124] Step 2, preparing nano-silicone rubber composite material:

[0125] OH-BNNS was used as a nano-thermal conductive filler, the amount of OH-BNNS added was 0.2 g, and the mass fraction of OH-BNNS added to the vinyl silicone oil was 10%. Specifically, 0.2 g OH-BNNS was mixed with 2 g vinyl silicone oil VS10000, 40 mL of n-pentane was added, ultrasonicated for 5 minutes, and stirred evenly. At 50°C, n-pentane was removed by magnetic stirring, and the mixture was cooled to room temperature to obtain a mixture.

[0126] Using hydrogen-containing silicone oil XL13 as a crosslinking agent and ethynyl cyclohexanol as an inhibitor, 0.04 g of hydrogen-containing silicone oil XL13 and the inhibitor were added to the mixture; wherein the molar ratio of the silicon-hydrogen bond in the hydrogen-containing silicone oil to the silicon-vinyl bond in the vinyl silicone oil was Si-H:Si-V=1.3; the amount of the inhibitor used was 1500 ppm of the total mass of the mixture and the hydrogen-containing silicone oil.

[0127] After sufficient stirring, add the Custer catalyst, the amount of which is 8 ppm of the total mass of the mixture and the hydrogen-containing silicone oil. Continue stirring the reaction to utilize the vinyl silicone oil in the mixture to undergo an addition crosslinking reaction with the hydrogen-containing silicone oil to form an addition-type liquid silicone rubber.

[0128] Addition type liquid silicone rubber is used as the matrix, and vacuum degassing is performed after sufficient stirring. After degassing, it is poured into a mold and placed in an oven. After drying at 90°C for 1 hour, the temperature is raised to 150°C and heated for 2 hours to allow the nano thermal conductive filler to construct a covalent cross-linked network in the matrix; after curing, a nano silicone rubber composite material is obtained.

[0129] Example 6

[0130] A method for preparing a nano-silicone rubber composite material, which is different from Example 5 in that the amount of OH-BNNS added is 0.3 g, and the mass fraction of OH-BNNS added to the vinyl silicone oil is 15%.

[0131] Example 7

[0132] A method for preparing a nano-silicone rubber composite material, which is different from Example 5 in that the amount of OH-BNNS added is 0.4 g, and the mass fraction of OH-BNNS added to the vinyl silicone oil is 20%.

[0133] Example 8

[0134] A method for preparing a nano-silicone rubber composite material comprises the following steps:

[0135] Step 1, preparing silicon carbide nanowires: According to step 3 of Example 1, silicon carbide nanowires with hydroxyl groups on the surface are prepared, which are denoted as SiCNW-OH.

[0136] Step 2, preparing nano-silicone rubber composite material:

[0137] SiCNW-OH was used as a nano-thermal conductive filler, the amount of SiCNW-OH added was 0.2 g, and the mass fraction of SiCNW-OH added was 10% of the vinyl silicone oil. Specifically, 0.2 g of SICNW-OH was mixed with 2 g of vinyl silicone oil VS10000, 40 mL of n-pentane was added, ultrasonicated for 5 minutes, and stirred evenly. At 50°C, n-pentane was removed by magnetic stirring, and the mixture was cooled to room temperature to obtain a mixture.

[0138] Using hydrogen-containing silicone oil XL13 as a crosslinking agent and ethynyl cyclohexanol as an inhibitor, 0.04 g of hydrogen-containing silicone oil XL13 and the inhibitor were added to the mixture; wherein the molar ratio of the silicon-hydrogen bond in the hydrogen-containing silicone oil to the silicon-vinyl bond in the vinyl silicone oil was Si-H:Si-V=1.3; the amount of the inhibitor used was 1500 ppm of the total mass of the mixture and the hydrogen-containing silicone oil.

[0139] After sufficient stirring, add the Custer catalyst, the amount of which is 8 ppm of the total mass of the mixture and the hydrogen-containing silicone oil. Continue stirring the reaction to utilize the vinyl silicone oil in the mixture to undergo an addition crosslinking reaction with the hydrogen-containing silicone oil to form an addition-type liquid silicone rubber.

[0140] Addition type liquid silicone rubber is used as the matrix, and vacuum degassing is performed after sufficient stirring. After degassing, it is poured into a mold and placed in an oven. After drying at 90°C for 1 hour, the temperature is raised to 150°C and heated for 2 hours to allow the nano thermal conductive filler to construct a covalent cross-linked network in the matrix; after curing, a nano silicone rubber composite material is obtained.

[0141] Example 9

[0142] A method for preparing a nano-silicone rubber composite material, which is different from Example 8 in that the added amount of SiCNW-OH is 0.3 g, and the added amount of SiCNW-OH accounts for 15% of the mass fraction of the vinyl silicone oil.

[0143] Example 10

[0144] A method for preparing a nano-silicone rubber composite material, which is different from Example 8 in that the added amount of SiCNW-OH is 0.4 g, and the added amount of SiCNW-OH accounts for 20% of the mass fraction of the vinyl silicone oil.

[0145] Comparative Example 1

[0146] A method for preparing a nano-silicone rubber composite material is different from Example 8 in that step 1 is not performed, and step 2 is performed directly using SiCNW as a nano-thermal conductive filler.

[0147] Table 1 Feeding conditions of different nano thermal conductive fillers

[0148]

[0149]

[0150] Note: 1-0.5-0.5 indicates that the nano thermally conductive filler is prepared by mixing OH-BNNS, modified vinyl POSS coupling agent and SiCNW-OH in a mass ratio of 1:0.5:0.5; the amount of nano thermally conductive filler added indicates the mass fraction of the nano thermally conductive filler added to the vinyl silicone oil.

[0151] The performance of the nano-silicone rubber composite material prepared in the above examples is verified below.

[0152] Test 1: Electron microscopy and Fourier transform infrared spectroscopy analysis of boron nitride nanosheets.

[0153] Figure 1 This is an electron microscope photo of the boron nitride nanosheets obtained in Example 1. Figure 1 It can be seen that after ultrasonic treatment, the diameter of hexagonal boron nitride is reduced and the thickness is reduced to less than 100 nanometers.

[0154] Figure 2 This is the Fourier infrared spectrum of the boron nitride nanosheets obtained in Example 1. Figure 2 It can be seen that a hydroxyl peak appears at position 3400 in Fourier infrared, indicating that the hydroxyl group is successfully attached.

[0155] Test 2: Electron microscopy and Fourier transform infrared spectroscopy analysis of silicon carbide nanowires.

[0156] Figure 3 This is an electron microscope photo of the silicon carbide nanowires obtained after hot alkali treatment in Example 1. Figure 3 It can be seen that the surface of SiC nanowires is rough and small fragments appear, which is a sign of successful hot alkaline oxidation.

[0157] Figure 4 This is the Fourier infrared spectrum of the hot alkali treated silicon carbide nanowires obtained in Example 1. Figure 4 It can be seen that the hydroxyl peak appears at 3400, and the various peaks around 1600 are characteristic peaks of Si-O bonds.

[0158] Test 3: Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy analysis of the modified vinyl silsesquioxane coupling agent.

[0159] Figure 5 This is a physical photo of the modified vinyl silsesquioxane coupling agent obtained in Example 1. Figure 5 It shows that the modified vinyl silsesquioxane coupling agent obtained in Example 1 is a light yellow oily liquid.

[0160] Figure 6 This is the Fourier infrared spectrum of the modified vinyl silsesquioxane coupling agent obtained in Example 1. Figure 6 It shows that the peak around 2840 is the characteristic peak of methoxy, and the peak around 1100 is the characteristic peak of Si-O-Si.

[0161] Figure 7 The hydrogen nuclear magnetic resonance spectrum of the modified vinyl silsesquioxane coupling agent obtained in Example 1 is shown in FIG. Figure 6 and Figure 7 The results showed that the modified vinyl silsesquioxane coupling agent was successfully obtained.

[0162] Test 4: Electron microscopy and Fourier transform infrared spectroscopy analysis of the nano thermal conductive filler.

[0163] Figure 8 This is an electron microscope photograph of the nano thermally conductive filler obtained in Example 1. Fig. 9 This is the Fourier infrared spectrum of the nano thermal conductive filler obtained in Example 1.

[0164] Depend on Figure 8 It can be seen that some boron nitride nanosheets are successfully attached to the silicon carbide nanowires. Figure 8 and Fig. 9 It can be seen that the nano thermal conductive filler was successfully prepared.

[0165] Test 5: Thermal conductivity, dielectric constant and dielectric loss analysis of nano-silicone rubber composites.

[0166] Fig.10 This is a comparison chart of the thermal conductivity of the nano-silicone rubber composite materials obtained in Examples 1 to 10.

[0167] Depend on Fig.10 It can be seen that in Examples 1 to 10, compared with the same nano-thermal conductive filler, as the amount of nano-thermal conductive filler added increases, the thermal conductivity of the nano-silicone rubber composite material also increases. Among them, in Examples 1 to 4, the thermal conductivity of the nano-silicone rubber composite material increases with the increase in the amount of nano-thermal conductive filler added. However, when the amount of nano-thermal conductive filler added exceeds 20%, the colloid viscosity of the nano-silicone rubber composite material is too high and cannot be leveled.

[0168] Compared with the nano-silicone rubber composite material prepared by using OH-BNNS or SiCNW-OH as the nano-thermal conductive filler at the same addition amount, the nano-thermal conductive filler prepared by using OH-BNNS, modified vinyl POSS coupling agent and SiCNW-OH in a mass ratio of 1:0.5:0.5 in the embodiment of the present invention can greatly improve the thermal conductivity of the obtained nano-silicone rubber composite material while maintaining low dielectric properties.

[0169] In summary, the hot alkali treatment can significantly reduce the dielectric constant, dielectric loss and thermal conductivity of silicon carbide nanowires, but the nano thermal conductive filler prepared by OH-BNNS, modified vinyl POSS coupling agent and SiCNW-OH in a mass ratio of 1:0.5:0.5 can significantly improve the thermal conductivity of the obtained nano silicone rubber composite while maintaining low dielectric properties. Among them, when the addition amount of nano thermal conductive filler accounts for 10% of the mass fraction of vinyl silicone oil, the thermal conductivity of the obtained nano silicone rubber composite is about 40% higher than that of the nano silicone rubber composite prepared by pure SICNW-OH or BNNS as nano thermal conductive filler.

[0170] Fig.11 The data comparison chart of the dielectric constants of the nano-silicone rubber composite material prepared by doping silicone rubber with nano-thermal conductive fillers in Example 1, the nano-silicone rubber composite material prepared by doping silicone rubber with pure SICNW-OH in Example 8, and the nano-silicone rubber composite material prepared by doping silicone rubber with pure SICNW in Comparative Example 1 is shown. Among them, the data corresponding to 1-0.5-0.5 represent the dielectric constant of the nano-silicone rubber composite material prepared by doping silicone rubber with nano-thermal conductive fillers in Example 1. The data corresponding to SICNW-OH represent the dielectric constant of the nano-silicone rubber composite material prepared by doping silicone rubber with pure SICNW-OH in Example 8. The data corresponding to SICNW represent the dielectric constant of the nano-silicone rubber composite material prepared by doping silicone rubber with pure SICNW in Comparative Example 1.

[0171] Fig.12 The data comparison chart of dielectric loss of nano silicone rubber composite material prepared by doping silicone rubber with nano thermal conductive filler in Example 1, nano silicone rubber composite material prepared by doping silicone rubber with pure SICNW-OH in Example 8, and nano silicone rubber composite material prepared by doping silicone rubber with pure SICNW in Comparative Example 1 is shown. Among them, the data corresponding to 1-0.5-0.5 represent the dielectric loss of nano silicone rubber composite material prepared by doping silicone rubber with nano thermal conductive filler in Example 1. The data corresponding to SICNW-OH represent the dielectric loss of nano silicone rubber composite material prepared by doping silicone rubber with pure SICNW-OH in Example 8. The data corresponding to SICNW represent the dielectric loss of nano silicone rubber composite material prepared by doping silicone rubber with pure SICNW-OH in Comparative Example 1.

[0172] Depend on Fig.11 It can be seen that the dielectric constant of the nano-silicone rubber composite material prepared by doping silicone rubber with 10% mass fraction SICNW-OH in Example 8 is reduced by 50% compared with the dielectric constant of the nano-silicone rubber composite material prepared by doping silicone rubber with 10% mass fraction SICNW in Comparative Example 1.

[0173] The dielectric constant of the nano-silicone rubber composite material prepared by doping silicone rubber with nano-thermal conductive fillers in Example 1 is slightly higher than that of the nano-silicone rubber composite material in Example 8. Fig.10 The results show that the thermal conductivity of the nano-silicone rubber composite material of Example 8 is much lower than the thermal conductivity of the nano-silicone rubber composite material of Example 1.

[0174] Depend on Fig.12 It can be seen that the dielectric loss of the nano-silicone rubber composite material of Comparative Example 1 is significantly higher than the dielectric loss of the nano-silicone rubber composite material of Example 8; while the dielectric loss of the nano-silicone rubber composite material of Example 1 is not much different from the dielectric loss of the nano-silicone rubber composite material of Example 8.

[0175] From the above analysis, it can be seen that the nano-silicone rubber composite material prepared by doping the nano-thermal conductive filler prepared by OH-BNNS, modified vinyl POSS coupling agent and SiCNW-OH in a mass ratio of 1:0.5:0.5 in Example 1 of the present invention greatly reduces the dielectric constant while ensuring that the dielectric loss is not increased, and can maintain a high thermal conductivity.

[0176] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a nanocomposite silicone rubber material, characterized in that: The following steps are involved: In a first alcohol-water solvent system, a modified vinyl silsesquioxane coupling agent, a boron nitride nanosheet and a silicon carbide nanowire are subjected to a reflux reaction; during the reflux reaction, the methoxy group of the modified vinyl silsesquioxane coupling agent is hydrolyzed to generate a silanol group, and then the hydrolyzed modified vinyl silsesquioxane coupling agent is used as an intermediate bridge to react with the surface hydroxyl groups of the boron nitride nanosheet and the silicon carbide nanowire respectively, and the boron nitride nanosheet and the silicon carbide nanowire are covalently connected to construct a heterogeneous structure to obtain a nano thermal conductive filler; uniformly dispersing the nano thermal conductive filler in the vinyl silicone oil to obtain a mixture; Using hydrogen-containing silicone oil as a crosslinking agent, under the action of a first catalyst and an inhibitor, the vinyl silicone oil in the mixture and the hydrogen-containing silicone oil undergo an addition crosslinking reaction to form an addition-type liquid silicone rubber; Addition liquid silicone rubber is used as the matrix, and a curing treatment is performed after vacuum degassing, so that the residual vinyl in the nano thermal conductive filler reacts with the silicon-hydrogen bond in the matrix, so that the nano thermal conductive filler constructs a covalent cross-linking network in the matrix to obtain a nano composite silicone rubber material.

2. The method for preparing the nanocomposite silicone rubber material according to claim 1, characterized in that: The mass ratio of the boron nitride nanosheets, the modified vinyl silsesquioxane coupling agent and the silicon carbide nanowires is 1:0.1-0.5:0.5-1.

3. The method for preparing the nanocomposite silicone rubber material according to claim 1, characterized in that: The first catalyst is a Custer catalyst; the inhibitor is ethynyl cyclohexanol; The doping amount of the nano thermal conductive filler accounts for 10% to 20% of the total mass of the liquid silicone rubber; The molar ratio of silicon-hydrogen bonds in hydrogen-containing silicone oil to silicon-ethylene bonds in vinyl silicone oil is 1:1 to 1.5; The dosage of the inhibitor is 1500ppm to 2000ppm of the total mass of the mixture and the hydrogen-containing silicone oil; The amount of the first catalyst used is 4 ppm to 10 ppm of the total mass of the mixture and the hydrogen-containing silicone oil.

4. The method for preparing the nanocomposite silicone rubber material according to claim 1, characterized in that: The modified vinyl silsesquioxane coupling agent is prepared by the following method: Under the action of the second catalyst, the vinyl groups in the vinyl silsesquioxane and the silicon-hydrogen bonds in the silane coupling agent undergo an addition reaction in the second solvent system to obtain a modified vinyl silsesquioxane coupling agent; The boron nitride nanosheets are prepared by the following method: Ultrasonic exfoliation of hexagonal boron nitride in a third alcohol-water solvent, and introducing hydroxyl groups on the surface of the hexagonal boron nitride during the ultrasonic exfoliation process to obtain boron nitride nanosheets; The silicon carbide nanowires are prepared by the following method: Silicon carbide is subjected to ultrasonic dispersion and surface hydroxylation reaction in an alkaline solution to obtain silicon carbide nanowires.

5. The method for preparing the nanocomposite silicone rubber material according to claim 4, characterized in that: The second catalyst is a Custer catalyst; the silane coupling agent is trimethoxyhydrogensilane; the particle size of hexagonal boron nitride is 5 μm to 10 μm; The molar ratio of vinyl silsesquioxane to silane coupling agent is 1:5-30; the dosage of the second catalyst is 1000ppm-2000ppm of the mass of vinyl silsesquioxane.

6. The method for preparing the nanocomposite silicone rubber material according to claim 4, characterized in that: The temperature of the surface hydroxylation reaction is 80°C to 120°C; The alkaline solution is a sodium hydroxide solution; the concentration of the alkaline solution is 2 mol / L to 4 mol / L; the dosage ratio of silicon carbide to the alkaline solution is 1 g: 50 mL to 100 mL.

7. The method for preparing the nanocomposite silicone rubber material according to claim 4, characterized in that: The first alcohol-water solvent is an ethanol-water solution with a volume fraction of 50%; The second solvent is toluene; the usage ratio of vinyl silsesquioxane to the second solvent is 1g:50mL-100mL; The third alcohol-water solvent is an isopropanol aqueous solution with a volume fraction of 50% to 80%; the dosage ratio of hexagonal boron nitride to the second solvent is 1g: 100mL to 150mL.

8. A nanocomposite silicone rubber material, characterized in that: The invention is prepared by the preparation method described in any one of claims 1 to 7.

9. Use of the nanocomposite silicone rubber material according to claim 8 in preparing low dielectric thermal conductive materials.

10. The use of the nanocomposite silicone rubber material according to claim 9 in the preparation of low dielectric thermal conductive materials, characterized in that: The low dielectric thermal conductive material is a low dielectric thermal conductive material used in heat dissipation of electronic devices.

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