Silica gel composite heat-conducting material and preparation process thereof

Abstract

This invention relates to the field of silicone technology, specifically to a silicone composite thermally conductive material and its preparation process. The preparation process of a silicone composite thermally conductive material includes: pretreatment of graphene filler, preparation of modified graphene filler, preparation and modification of heterogeneous filler, and preparation of the silicone composite thermally conductive material. This invention utilizes modified graphene and the construction of a boron nitride-silica heterogeneous filler to form a multi-level thermally conductive network. Combined with electric field-induced ordered arrangement of fillers and pretreatment of graphene with chemically reduced gel and directional ice template, multiple methods are used synergistically to reduce interfacial thermal resistance and phonon scattering, constructing continuous thermally conductive channels. Simultaneously, it improves the structural uniformity, thermal conductivity stability, and mechanical properties of the composite material, effectively solving problems such as filler agglomeration and migration, and significantly improving the thermal conductivity of the silicone composite material.

Description

Technical Field

[0001] This invention relates to the field of silicone technology, specifically to a silicone composite thermally conductive material and its preparation process. Background Technology

[0002] With the rapid development of modern electronic information, new energy vehicles, 5G communications, aerospace and other fields, electronic devices are rapidly iterating towards miniaturization, integration and high power density. If the large amount of heat generated during the operation of the equipment cannot be dissipated in time, it will significantly reduce the working stability and service life of electronic components, and even cause equipment failure. Therefore, high-efficiency thermal management materials have become one of the core key materials that restrict technological breakthroughs in related fields.

[0003] Silicone, with its excellent flexibility, resistance to high and low temperatures, chemical stability, electrical insulation, and good interfacial compatibility, can tightly adhere to the surfaces of complex-shaped electronic components, filling tiny gaps at the interface. It has been widely used in thermal management and is an ideal matrix material for preparing composite thermally conductive materials. However, pure silicone has extremely low thermal conductivity, which cannot meet the heat dissipation requirements of high-power devices. Therefore, it must be modified by adding highly thermally conductive fillers to construct effective thermal conduction pathways and improve its thermal conductivity, thereby achieving rapid heat conduction and dissipation.

[0004] Currently, the industry commonly uses the method of adding high thermal conductivity fillers to a silicone matrix to prepare silicone composite thermal conductive materials. Commonly used thermal conductive fillers mainly include metal powders (copper powder, silver powder, aluminum powder, etc.) and inorganic non-metallic fillers (alumina, boron nitride, graphene, silicon dioxide, etc.). Among them, metal powders have high thermal conductivity, but they have defects such as high density, easy oxidation, and poor insulation, which limit their application in electronic devices with high insulation requirements. Inorganic non-metallic fillers combine high thermal conductivity, insulation, and chemical stability, and have moderate density and controllable cost, making them the mainstream filler choice for current silicone composite thermal conductive materials.

[0005] However, inorganic fillers exhibit strong hydrophobic inertness on their surfaces, resulting in poor compatibility with the silicone matrix. This leads to uneven dispersion of the filler within the silicone matrix, preventing the formation of continuous, interconnected thermal conductive pathways. This not only hinders the utilization of the filler's inherent high thermal conductivity but may also cause a decline in the mechanical properties of the composite material due to uneven dispersion, leading to delamination and cracking. Furthermore, existing technologies often employ simple physical mixing or modification with a single silane coupling agent to improve the compatibility between the filler and the matrix. However, this modification method only forms simple physical adsorption or weak chemical bonds on the filler surface, failing to effectively eliminate the interfacial thermal resistance between the filler and the silicone matrix. Phonons are easily scattered at the interface, significantly reducing heat transfer efficiency. This results in limited improvement in the thermal conductivity of the composite material, and after long-term use or thermal cycling, the filler is prone to migration and interfacial debonding, exhibiting extremely poor thermal stability. Therefore, current silicone composite thermal conductive materials generally suffer from technical problems during preparation, such as poor filler dispersion, high interfacial thermal resistance, discontinuous thermal conductive network, insufficient thermal conductivity stability, and difficulty in simultaneously improving mechanical and thermal conductivity properties. These problems fail to meet the requirements of modern high-power electronic devices for efficient, stable, and long-lasting thermal management materials.

[0006] Therefore, developing a silicone composite thermally conductive material and its preparation process that can solve the above-mentioned technical bottlenecks, achieve uniform dispersion of fillers, tight interfacial bonding, continuous and stable thermal conductive network, and simultaneously improve thermal conductivity, mechanical properties and thermal stability, has important practical significance and industrial application value. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a silicone composite thermally conductive material and its preparation process.

[0008] This invention provides a process for preparing a silicone composite thermally conductive material, comprising: S1: Pretreatment of graphene filler; Graphene oxide was dispersed in deionized water and rotary evaporated, then VC was added and mixed. The mixture was subjected to directional freezing-thawing-pre-reduction, followed by freezing treatment and gradient heating reaction. After washing and drying, the pretreated graphene filler was obtained by air heating, high-temperature treatment in a quartz tube furnace and high-temperature treatment in a graphitization furnace. S2: Preparation of modified graphene filler; Aminated graphene was reacted with 4,4'-diaminodiphenylmethane and maleic anhydride in N,N-dimethylformamide. After adding a catalyst and xylene, the mixture was refluxed to remove water, washed and dried to obtain grafted modified graphene. The grafted modified graphene was then reacted with 2,2'-diallylbisphenol A and triallyl isocyanurate to obtain modified graphene filler. S3: Preparation and modification of heterogeneous fillers; KH550 modified boron nitride and KH560 modified silica were added to anhydrous ethanol, and after reflux reaction, washed and dried to obtain heterogeneous filler; it was then mixed with 1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt and toluene, and refluxed in an oil bath, and after washing and drying, modified heterogeneous filler was obtained. S4: Preparation of silicone composite thermally conductive material; Liquid silicone rubber, vinyl silicone oil, hydrogen-containing silicone oil and inhibitor are mixed to obtain silicone base material. Then, modified graphene filler and modified heterogeneous filler are added. After vacuum kneading, platinum catalyst is added and vacuum stirring is continued to obtain composite silicone slurry. Then, a specific electric field is applied before calendering, and then the material is baked and cooled in a gradient to obtain silicone composite thermal conductive material.

[0009] As a preferred aspect, S1: The preparation of the functional anti-corrosion filler specifically includes the following steps: S1: Pretreatment of graphene filler, specifically including the following steps: S1.1: Add 3-5 parts by weight of graphene oxide to 200-230 parts by weight of deionized water, stir and disperse for 20-30 min, then rotary evaporate at 60-65℃ to obtain a graphene oxide dispersion with a concentration of 25-28 mg / mL. Then add vitamin C to the graphene oxide dispersion, with a mass ratio of graphene oxide dispersion to vitamin C of 20-22:1. Then stir and mix at 200-300 rpm for 20-30 min to obtain a mixture. S1.2: Place the mixture into a directional freezing mold consisting of an aluminum base and four walls of silicone, and let it stand at room temperature for 1-2 hours. Then, suspend the directional freezing mold in an alcohol bath of liquid nitrogen for directional freezing for 25-30 minutes. After freezing, thaw the mixture to room temperature, seal it, and place it in an oven at 60-62℃ for pre-reduction for 2-3 hours. Then, cool it to 25-30℃ and perform a second directional freezing. After freezing, thaw it to room temperature and then continue the reaction in an oven at 60-62℃ for 4-6 hours to obtain the chemically reduced hydrogel. S1.3: The chemically reduced hydrogel was frozen at -22°C for 4-5 hours to completely solidify it. Then it was thawed to room temperature and reacted in an oven at 60-62°C for 5-6 hours and then in an oven at 80-82°C for 3-4 hours. The reaction product was washed with deionized water 3-5 times and then air-dried at room temperature to obtain reduced graphene oxide dry gel. S1.4: The reduced graphene oxide dry gel is heated to 200-230℃ in air, then placed in a quartz tube furnace and heated to 1150-1200℃ at a heating rate of 10-12℃ / min under an argon atmosphere, and held at that temperature for 2-3 hours. Then it is placed in a graphitization furnace and heated to 2850-2900℃ under vacuum for 3-5 hours. After cooling to room temperature, the pretreated graphene filler is obtained.

[0010] As a preferred aspect, S2: the preparation of the modified graphene filler specifically includes the following steps: S2.1: Add 1-2 parts by weight of pretreated graphene filler to 50-60 parts by weight of N,N-dimethylformamide, and ultrasonically disperse for 30-40 min. Then add 12-15 parts by weight of silane coupling agent KH550, heat to 80-85℃ under nitrogen protection, and stir for 2-4 h. After the reaction is completed, centrifuge the dispersion at 8000 rpm for 10-12 min, discard the supernatant, wash the precipitate with anhydrous ethanol 3-5 times, and vacuum dry at 40-50℃ to obtain amino-based graphene. This step utilizes the silane coupling agent KH550 to aminate the graphene, anchoring the organosilane molecular layer with active amino ends to the surface of the graphene sheet, providing grafting active sites for the subsequent in-situ growth of BMI polymer chains. S2.2: Dissolve 20-23 parts by weight of 4,4'-diaminodiphenylmethane in 50-60 parts by weight of N,N-dimethylformamide, add 1-2 parts by weight of aminographene, and disperse at high speed of 2000-3000 rpm for 30 min at room temperature to obtain a uniform dispersion. Then add 20-22 parts by weight of maleic anhydride, stir at room temperature for 1-2 h, and then add 1-2 parts by weight of methanesulfonic acid catalyst and 172-175 parts by weight of xylene to the reaction system. Assemble an oil-water separator, heat to 136-138℃ and reflux under normal pressure to separate water until no more water is released. After the reaction is completed, cool to room temperature, pour the reaction solution into excess methanol to precipitate, filter, wash the filter cake with anhydrous ethanol 3-5 times, and dry under vacuum at 60℃ to obtain grafted modified graphene. This step first utilizes the suspended primary amine groups on the surface of aminated graphene as nucleophiles to attack the maleimide double bonds at the chain ends of the BMI prepolymer generated by the in-situ polycondensation of 4,4'-diaminodiphenylmethane and maleic anhydride, resulting in a Michael addition reaction to generate aspartic imide bridging bonds. This achieves covalent grafting of the BMI polymer chain onto the graphene surface. Simultaneously, free 4,4'-diaminodiphenylmethane and maleic anhydride in solution undergo an amidation-dehydration ring-closing tandem reaction to generate a linear BMI prepolymer with maleimide active end groups at both ends, which continues to grow under the initiation of the amino groups on the graphene surface. The reflux dehydration process promotes the complete ring closure of the amide acid intermediate, forming a stable five-membered maleimide ring structure. The resulting grafted and modified graphene product has a large number of suspended maleimide double bonds on its surface, providing sufficient reactive sites for further functionalization modification of the shell structure. S2.3: Add 3-5 parts by weight of grafted modified graphene and 0.5-0.8 parts by weight of 2,2'-diallylbisphenol A to 20-30 parts by weight of liquid paraffin, and ultrasonically disperse for 20-30 min. Then, under nitrogen protection, heat to 140-142℃ and stir for 20-30 min. Subsequently, add triallyl isocyanurate and continue stirring at 140-142℃ for 60-80 min. After the reaction is completed, cool to room temperature, add excess ethyl acetate for dilution and centrifuge. Wash the precipitate 3-5 times with acetone and vacuum dry at 60-70℃ to obtain the modified graphene filler.

[0011] At 140-142℃, the allyl group of the side chain of 2,2'-diallylbisphenol A undergoes an Alder-ene-coordinated pericyclic addition reaction with the maleimide double bond hanging on the surface of the grafted modified graphene to generate a substituted succinimide structure, thereby covalently grafting a flexible segment with a bisphenol A backbone onto the BMI backbone on the graphene surface. The introduction of this flexible spacer layer significantly improves the interfacial compatibility between graphene and the polymer matrix, and endows the grafted shell with a certain molecular chain mobility to dissipate impact energy. After adding the trifunctional crosslinking agent triallyl isocyanurate, the three allyl arms in its molecular structure react with the maleimide double bonds remaining on the surface of the grafted and modified graphene, forming a dense BMI-TAIC alternating copolymer crosslinking network on the graphene surface. Since the reaction is carried out in an inert liquid medium, the graphene particles are effectively isolated by the medium, avoiding interparticle bridging and agglomeration caused by TAIC, and ensuring that the final product is a monodisperse nanofiller powder.

[0012] As a preferred aspect, the amount of triallyl isocyanurate added in step S2.3 is 2-3 wt% of the total system mass.

[0013] As a preferred aspect, S3: the preparation and modification of heterogeneous fillers, specifically includes the following steps: S3.1: Add 2.5-3 parts by weight of silane coupling agent KH550 modified boron nitride and 2.5-3 parts by weight of silane coupling agent KH560 modified silica to 50-60 parts by weight of anhydrous ethanol, stir and mix at 300-500 rpm for 20-30 min, then reflux at 70-75℃ for 8-10 h. After the reaction is complete, filter and wash the precipitate 3-5 times with deionized water, then vacuum dry at 80-82℃ for 5-6 h to obtain heterogeneous filler; S3.2: Mix 5-8 parts by weight of heterogeneous filler, 2-3 parts by weight of 1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imine salt ionic liquid and 20-30 parts by weight of toluene solution, then stir and mix at 500-800 rpm for 20-30 min, then heat in an oil bath to 90-95℃ and reflux for 8-10 h. After the reaction is completed, cool to room temperature, filter, and wash the precipitate 3-5 times with dichloromethane and deionized water in sequence, then vacuum dry at 80-82℃ for 5-6 h to obtain the modified heterogeneous filler.

[0014] As a preferred aspect, the silane coupling agent KH550 modified boron nitride in step S3.1 is specifically as follows: hexagonal boron nitride is calcined in a muffle furnace at 800°C for 2 hours and then naturally cooled. After washing with water and drying, hydroxylated boron nitride is obtained. 10 parts by weight of hydroxylated boron nitride and 3 parts by weight of silane coupling agent KH550 are added to 20 parts by weight of 50wt% ethanol aqueous solution. After mixing, the mixture is subjected to reflux reaction at 80°C for 10 hours. After the reaction is completed, the reaction solution is filtered, the filter cake is washed three times with deionized water, and vacuum dried at 80°C for 10 hours to obtain silane coupling agent modified boron nitride. The process of modifying silica with silane coupling agent KH560 is as follows: 10 parts by weight of fumed silica and 3 parts by weight of silane coupling agent KH560 are added to 20 parts by weight of 50wt% ethanol aqueous solution. After mixing, the mixture is refluxed at 80℃ for 10h. After the reaction is completed, the reaction solution is filtered, the filter cake is washed 3 times with deionized water, and vacuum dried at 80℃ for 10h to obtain silica modified with silane coupling agent KH560.

[0015] As a preferred aspect, S4: The preparation of the silicone composite thermal conductive material specifically includes the following steps: S4.1: Add 60-70 parts by weight of liquid silicone rubber, 100-120 parts by weight of vinyl silicone oil, 15-20 parts by weight of hydrogen-containing silicone oil, and 0.5-0.8 parts by weight of inhibitor 1-ethynyl-1-cyclohexanol to a planetary mixer and stir at 30-50 rpm for 15-20 min at room temperature to obtain silicone base material; S4.2: At 500-800 rpm, add 30-40 parts by weight of modified graphene filler and 15-20 parts by weight of modified heterogeneous filler to the silica base material in sequence. Then, evacuate to -0.09 to -0.1 MPa and perform vacuum kneading at a revolution speed of 80-120 rpm and a dispersion disk speed of 800-1200 rpm for 40-60 min. Then, add 0.8-1.2 parts by weight of platinum catalyst with a platinum content of 3000-5000 ppm and continue vacuum stirring for 10-15 min to obtain composite silica slurry. S4.3: Then, immediately after applying an electric field perpendicular to the calendering surface to the composite silicone slurry, calendering is performed. After calendering, the slurry is then heated to 120°C. Bake at 130℃ for 10-15 minutes, then bake at 150-160℃ for 30-40 minutes, and cool to room temperature to obtain silicone composite thermal conductive material.

[0016] As a preferred aspect, in step S4.1, the vinyl silicone oil has a vinyl content of 0.22-0.28 mmol / g, a viscosity of 500-1000 mPa•s, and the hydrogen content of the hydrogen-containing silicone oil is 0.18-0.25 wt%.

[0017] As a preferred aspect, in step S4.3, the electric field parameters are E=2kVpp / mm, f=2kHz, and t=8-10min.

[0018] The present invention also provides a silicone composite thermal conductive material, which is prepared by any of the preparation processes of the silicone composite thermal conductive material described in any one of the claims.

[0019] The present invention has the following advantages: 1. This invention utilizes BMI oligomer chains generated by the condensation polymerization of 4,4'-diaminodiphenylmethane and maleic anhydride. These chains, acting as a moderately rigid and highly polar polymer brush, provide significant steric hindrance and repulsion to graphene, inhibiting graphene sheet aggregation and ensuring uniform dispersion within a silica matrix. Furthermore, the modification introduces polar functional groups, significantly reducing the filler-matrix interface thermal resistance, decreasing phonon scattering, and improving thermal conductivity. Subsequent modification with 2,2'-diallylbisphenol A and triallyl isocyanurate introduces allyl active double bonds onto the graphene surface. During subsequent vulcanization, these double bonds can undergo hydrosilylation reactions with vinyl silicone oil and hydrogen-containing silicone oil under platinum catalysis, resulting in... The modified graphene forms a covalent network with the silicone matrix, eliminating the interfacial thermal resistance between the thermally conductive filler and the matrix, and significantly improving the interfacial bonding strength. The silicone composite material is less prone to problems such as filler migration, delamination, and interfacial debonding during thermal cycling and long-term use, thus improving its thermal conductivity and thermal stability simultaneously. Furthermore, the dense cross-linked shell of BMI-TAIC on the surface of the modified graphene filler has a certain rigidity, while the internal bisphenol A segments are flexible. When microcracks extend to the graphene interface, the flexible interfacial layer can dissipate strain energy through the viscoelastic movement of the molecular chains; while the rigid shell is strongly bonded to the graphene, which can force the cracks to deflect or pin, avoiding penetrating fracture. This allows the silicone composite thermally conductive material to maintain high thermal conductivity while significantly improving its mechanical properties.

[0020] 2. This invention utilizes boron nitride and silicon dioxide through an amino-epoxy ring-opening reaction to form a stable heterogeneous filler. The sheet-like boron nitride provides a high in-plane thermal conductivity main channel, while spherical silicon dioxide fills the gaps between the sheets and bridges adjacent boron nitride / graphene sheets, forming a multi-level thermally conductive network of "two-dimensional sheets + zero-dimensional particles." This avoids the thermal conductivity bottleneck of a single filler. The two fillers are covalently linked through the functional group reaction of a silane coupling agent, preventing phase separation and sedimentation in the silica matrix, thus improving the structural uniformity and long-term thermal conductivity stability of the composite material. Furthermore, 1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt is used to surface-treat the heterogeneous filler. Surface modification: 1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt is adsorbed onto the surface of heterogeneous fillers through the π-π stacking and electrostatic interaction of its imidazole cations, forming a nanoscale organic modification layer. The hydrophobic organic functional groups of the anions endow the filler surface with excellent hydrophobicity and organic compatibility, enhancing the dispersibility of heterogeneous fillers in the silica matrix. Furthermore, 1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt can form a "flexible interface layer" on the filler surface, which can buffer the thermal stress between the filler and the matrix, while reducing interfacial phonon scattering and reducing phonon scattering loss at the interface, further improving the thermal conductivity of the composite material.

[0021] 3. This invention applies an electric field before calendering, utilizing the polarization effect of the filler to drive the modified graphene and heterogeneous fillers to align in a highly ordered manner along the electric field direction, constructing a continuous and interconnected thermally conductive main channel. This significantly reduces phonon scattering and substantially improves the thermal conductivity of the material along the field direction. Applying an electric field before low-temperature pre-curing allows for filler orientation before the matrix solidifies. The electric field not only drives the orientation of the modified graphene backbone but also causes the sheet-like boron nitride to align in an ordered manner along the electric field direction, forming a three-dimensional ordered thermally conductive network of "graphene backbone + boron nitride bridging + silica filling". This eliminates the thermal bottleneck in the filler gaps. The synergistic effect of fillers with different morphologies and sizes further reduces the overall thermal resistance, improves thermal conductivity, and enhances the mechanical properties and structural stability of the material.

[0022] 4. This invention also combines chemical reduction gel technology and directional ice template technology to pretreat graphene fillers, giving them a layered, ordered, and uniformly oriented structure. This eliminates the need for prolonged freeze-drying, saving energy. An aluminum base and a silicone four-wall mold are used to achieve directional heat transfer and ice crystal growth in a liquid nitrogen-alcohol bath. The ice crystals act as directional templates, forcing the graphene oxide sheets to align perpendicularly along the ice crystal growth direction, forming a layered, ordered, and uniformly oriented microstructure. This makes it easier for graphene to form continuous thermal pathways within the matrix, significantly reducing phonon transport obstacles. Directional freezing induces the formation of an oriented layered structure in graphene oxide. After thawing, the graphene is gently reduced using VC to achieve chemical gelation while maintaining its orientation, thereby locking the orientation structure. Then, a freezing and step-heating reaction is carried out. The step-heating reaction avoids severe volume shrinkage of the gel structure, which would lead to structural collapse. This makes the pore structure more uniform and the pore walls more continuous, giving the graphene framework both high pore connectivity and structural strength. It is not easily deformed or broken during subsequent composite processes. The ordered structure provides a favorable basis for high-temperature lattice repair. The mean free path of phonons in highly crystalline graphene is significantly increased, giving the pretreated graphene a thermal conductivity much higher than that of conventional reduced graphene oxide, thereby significantly improving the thermal conductivity of the silicone composite material. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating the preparation process of the silicone composite thermally conductive material used in an embodiment of the present invention. Detailed Implementation

[0024] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this invention.

[0025] In the embodiment, the silane coupling agent KH550 modified boron nitride is specifically as follows: hexagonal boron nitride is calcined in a muffle furnace at 800°C for 2 hours and then naturally cooled. After washing with water and drying, hydroxylated boron nitride is obtained. 10 parts by weight of hydroxylated boron nitride and 3 parts by weight of silane coupling agent KH550 are added to 20 parts by weight of 50wt% ethanol aqueous solution. After mixing, the mixture is subjected to reflux reaction at 80°C for 10 hours. After the reaction is completed, the reaction solution is filtered, the filter cake is washed 3 times with deionized water, and vacuum dried at 80°C for 10 hours to obtain silane coupling agent modified boron nitride with a hexagonal boron nitride sheet diameter of 200 nm and a thickness of 10 nm.

[0026] In the example, the silane coupling agent KH560 modified silica was specifically prepared as follows: 10 parts by weight of fumed silica and 3 parts by weight of silane coupling agent KH560 were added to 20 parts by weight of 50wt% ethanol aqueous solution. After mixing, the mixture was subjected to reflux reaction at 80°C for 10 hours. After the reaction was completed, the reaction solution was filtered, the filter cake was washed three times with deionized water, and vacuum dried at 80°C for 10 hours to obtain silane coupling agent KH560 modified silica with a silica particle size of 50nm.

[0027] Example 1: A preparation process for a silicone composite thermally conductive material, referring to... Figure 1 ,include: S1: Pretreatment of graphene filler S1.1: Add 3 parts by weight of graphene oxide to 200 parts by weight of deionized water, stir and disperse for 20 min, then evaporate at 60℃ to obtain a graphene oxide dispersion with a concentration of 25 mg / mL. Then add VC to the graphene oxide dispersion, with a mass ratio of graphene oxide dispersion to VC of 20:1. Then stir and mix at 200 rpm for 20 min to obtain a mixture. S1.2: The mixture was placed in a directional freezing mold consisting of an aluminum base and four walls of silicone, and left to stand at room temperature for 1 hour. Then, the directional freezing mold was suspended in an alcohol bath of liquid nitrogen for directional freezing for 25 minutes. After the frozen mixture was thawed to room temperature, it was sealed and placed in a 60°C oven for pre-reduction for 2 hours. After that, it was cooled to 25°C and subjected to a second directional freezing. After freezing, it was thawed to room temperature and then reacted in a 60°C oven for 4 hours to obtain the chemically reduced hydrogel. S1.3: The chemically reduced hydrogel was frozen at -22°C for 4 hours to completely solidify it. Then it was thawed to room temperature and reacted in an oven at 60°C for 5 hours and in an oven at 80°C for 3 hours. The reaction product was washed three times with deionized water and then air-dried at room temperature to obtain reduced graphene oxide dry gel. S1.4: The reduced graphene oxide dry gel was heated to 200°C in air, then placed in a quartz tube furnace and heated to 1150°C at a heating rate of 10°C / min under an argon atmosphere, held for 2 hours, and then placed in a graphitization furnace and heated to 2850°C under vacuum for 3 hours. After cooling to room temperature, the pretreated graphene filler was obtained. S2: Preparation of modified graphene fillers S2.1: 1 part by weight of pretreated graphene filler was added to 50 parts by weight of N,N-dimethylformamide and ultrasonically dispersed for 30 min. Then, 12 parts by weight of silane coupling agent KH550 was added. The mixture was heated to 80℃ under nitrogen protection and stirred for 2 h. After the reaction was completed, the dispersion was centrifuged at 8000 rpm for 10 min, the supernatant was discarded, the precipitate was washed 3 times with anhydrous ethanol and vacuum dried at 40℃ to obtain amino-based graphene. S2.2: Dissolve 20 parts by weight of 4,4'-diaminodiphenylmethane in 50 parts by weight of N,N-dimethylformamide, add 1 part by weight of aminographene, and disperse at room temperature at 2000 rpm for 30 min to obtain a uniform dispersion. Then add 20 parts by weight of maleic anhydride and stir at room temperature for 1 h. After that, add 1 part by weight of methanesulfonic acid catalyst and 172 parts by weight of xylene to the reaction system. Assemble an oil-water separator, heat to 136℃ and reflux under normal pressure to separate water until no more water is released. After the reaction is completed, cool to room temperature, pour the reaction solution into excess methanol to precipitate, filter, wash the filter cake three times with anhydrous ethanol, and dry under vacuum at 60℃ to obtain grafted modified graphene. S2.3: 3 parts by weight of grafted modified graphene and 0.5 parts by weight of 2,2'-diallylbisphenol A were added to 20 parts by weight of liquid paraffin and ultrasonically dispersed for 20 min. Then, under nitrogen protection, the temperature was raised to 140℃ and the reaction was stirred for 20 min. Subsequently, triallyl isocyanurate was added at an amount of 2 wt% of the total system mass, and the reaction was continued at 140℃ for 60 min. After the reaction was completed, the mixture was cooled to room temperature, diluted with excess ethyl acetate, and centrifuged. The precipitate was washed three times with acetone and dried under vacuum at 60℃ to obtain the modified graphene filler. S3: Preparation and Modification of Heterogeneous Fillers S3.1: 2.5 parts by weight of silane coupling agent KH550 modified boron nitride and 2.5 parts by weight of silane coupling agent KH560 modified silica were added to 50 parts by weight of anhydrous ethanol and stirred at 300 rpm for 20 min. Then, the mixture was refluxed at 70 °C for 8 h. After the reaction was completed, the mixture was filtered and the precipitate was washed three times with deionized water. Then, it was vacuum dried at 80 °C for 5 h to obtain heterogeneous filler. S3.2: Mix 5 parts by weight of heterogeneous filler, 2 parts by weight of 1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imine salt ionic liquid and 20 parts by weight of toluene solution, then stir at 500 rpm for 20 min, then heat in an oil bath to 90 °C and reflux for 8 h. After the reaction is completed, cool to room temperature, filter, and wash the precipitate three times with dichloromethane and deionized water in sequence, then vacuum dry at 80 °C for 5 h to obtain the modified heterogeneous filler; S4: Preparation of silicone composite thermal conductive materials S4.1: 60 parts by weight of RTV room temperature vulcanizing silicone rubber, 100 parts by weight of vinyl silicone oil with a vinyl content of 0.22 mmol / g and a viscosity of 500 mPa•s, 15 parts by weight of hydrogen-containing silicone oil with a hydrogen content of 0.18 wt%, and 0.5 parts by weight of 1-ethynyl-1-cyclohexanol were added to a planetary mixing vessel and stirred at 30 rpm for 15 min at room temperature to obtain silicone base material; S4.2: At 500 rpm, 30 parts by weight of modified graphene filler and 15 parts by weight of modified heterogeneous filler were added to the silica base material in sequence. Then, the vacuum was drawn to -0.09 MPa, and vacuum kneading was performed at a revolution speed of 80 rpm and a dispersion disk speed of 800 rpm for 40 min. Then, 0.8 parts by weight of platinum catalyst with a platinum content of 3000 ppm was added, and vacuum stirring was continued for 10 min to obtain composite silica slurry. S4.3: Then, after applying an electric field perpendicular to the calendering surface to the composite silicone slurry, calendering is performed immediately. The electric field parameters are E=2kVpp / mm, f=2kHz, and t=8min. After calendering, the material is baked at 120℃ for 10min, then at 150℃ for 30min, and cooled to room temperature to obtain the silicone composite thermal conductive material.

[0028] Example 2, a preparation process of a silicone composite thermally conductive material, see [link to example]. Figure 1 ,include: S1: Pretreatment of graphene filler S1.1: Add 5 parts by weight of graphene oxide to 230 parts by weight of deionized water, stir and disperse for 30 min, then evaporate at 65℃ to obtain a graphene oxide dispersion with a concentration of 28 mg / mL. Then add VC to the graphene oxide dispersion, with a mass ratio of graphene oxide dispersion to VC of 22:1. Then stir and mix at 300 rpm for 30 min to obtain a mixture. S1.2: The mixture was placed in a directional freezing mold consisting of an aluminum base and four walls of silicone, and left to stand at room temperature for 2 hours. Then, the directional freezing mold was suspended in an alcohol bath of liquid nitrogen for directional freezing for 30 minutes. After the frozen mixture was thawed to room temperature, it was sealed and placed in a 62°C oven for pre-reduction for 3 hours. After that, it was cooled to 30°C and subjected to a second directional freezing. After freezing, it was thawed to room temperature and then reacted in a 62°C oven for 6 hours to obtain the chemically reduced hydrogel. S1.3: The chemically reduced hydrogel was frozen at -22°C for 5 hours to completely solidify it. Then it was thawed to room temperature and reacted in an oven at 62°C for 6 hours and in an oven at 82°C for 4 hours. The reaction product was washed with deionized water 5 times and then air-dried at room temperature to obtain reduced graphene oxide dry gel. S1.4: The reduced graphene oxide dry gel was heated to 230°C in air, then placed in a quartz tube furnace and heated to 1200°C at a heating rate of 12°C / min under an argon atmosphere, and held for 3 hours. Then it was placed in a graphitization furnace and heated to 2900°C under vacuum for 5 hours. After cooling to room temperature, the pretreated graphene filler was obtained. S2: Preparation of modified graphene fillers S2.1: Add 2 parts by weight of pretreated graphene filler to 60 parts by weight of N,N-dimethylformamide and disperse ultrasonically for 40 min. Then add 15 parts by weight of silane coupling agent KH550. Under nitrogen protection, heat to 85℃ and stir for 4 h. After the reaction is completed, centrifuge the dispersion at 8000 rpm for 12 min, discard the supernatant, wash the precipitate 5 times with anhydrous ethanol, and dry it under vacuum at 50℃ to obtain amino-based graphene. S2.2: 23 parts by weight of 4,4'-diaminodiphenylmethane were dissolved in 60 parts by weight of N,N-dimethylformamide, and 2 parts by weight of aminographene were added. The mixture was dispersed at 3000 rpm for 30 min at room temperature to obtain a uniform dispersion. Then, 22 parts by weight of maleic anhydride were added, and the mixture was stirred at room temperature for 2 h. After that, 2 parts by weight of methanesulfonic acid catalyst and 175 parts by weight of xylene were added to the reaction system. An oil-water separator was assembled, and the mixture was heated to 138 °C and refluxed under normal pressure to separate water until no more water was released. After the reaction was completed, the mixture was cooled to room temperature, and the reaction solution was poured into excess methanol to precipitate. The mixture was filtered, and the filter cake was washed 5 times with anhydrous ethanol and dried under vacuum at 60 °C to obtain grafted modified graphene. S2.3: 5 parts by weight of grafted modified graphene and 0.8 parts by weight of 2,2'-diallylbisphenol A were added to 30 parts by weight of liquid paraffin and ultrasonically dispersed for 30 min. Then, under nitrogen protection, the temperature was raised to 142℃ and the reaction was stirred for 30 min. Subsequently, triallyl isocyanurate was added at an amount of 3 wt% of the total system mass, and the reaction was continued at 142℃ for 80 min. After the reaction was completed, the mixture was cooled to room temperature, diluted with excess ethyl acetate, and centrifuged. The precipitate was washed 5 times with acetone and dried under vacuum at 70℃ to obtain the modified graphene filler. S3: Preparation and Modification of Heterogeneous Fillers S3.1: 3 parts by weight of silane coupling agent KH550 modified boron nitride and 3 parts by weight of silane coupling agent KH560 modified silica were added to 60 parts by weight of anhydrous ethanol. The mixture was stirred at 500 rpm for 30 min, and then refluxed at 75 °C for 10 h. After the reaction was completed, the mixture was filtered and the precipitate was washed 5 times with deionized water. Then it was vacuum dried at 82 °C for 6 h to obtain heterogeneous filler. S3.2: 8 parts by weight of heterogeneous filler, 3 parts by weight of 1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imine salt ionic liquid and 30 parts by weight of toluene solution were mixed and stirred at 800 rpm for 30 min. Then, the mixture was heated to 95 °C in an oil bath and refluxed for 10 h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the precipitate was washed 5 times with dichloromethane and deionized water in sequence. Then, it was vacuum dried at 82 °C for 6 h to obtain the modified heterogeneous filler. S4: Preparation of silicone composite thermal conductive materials S4.1: 70 parts by weight of RTV room temperature vulcanizing silicone rubber, 120 parts by weight of vinyl silicone oil with a vinyl content of 0.28 mmol / g and a viscosity of 1000 mPa•s, 20 parts by weight of hydrogen-containing silicone oil with a hydrogen content of 0.25 wt%, and 0.8 parts by weight of 1-ethynyl-1-cyclohexanol were added to a planetary mixer and stirred at 50 rpm for 20 min at room temperature to obtain silicone base material; S4.2: At 800 rpm, 40 parts by weight of modified graphene filler and 20 parts by weight of modified heterogeneous filler were added to the silica base material in sequence. Then, the vacuum was evacuated to -0.1 MPa, and vacuum kneading was performed at a revolution speed of 120 rpm and a dispersion disk speed of 1200 rpm for 60 min. Then, 1.2 parts by weight of platinum catalyst with a platinum content of 5000 ppm was added, and vacuum stirring was continued for 15 min to obtain composite silica slurry. S4.3: Then, after applying an electric field perpendicular to the calendering surface to the composite silicone slurry, calendering is immediately performed. The electric field parameters are E=2kVpp / mm, f=2kHz, and t=10min. After calendering, the material is baked at 130℃ for 15min, then at 160℃ for 40min, and cooled to room temperature to obtain the silicone composite thermal conductive material.

[0029] Example 3, a preparation process of a silicone composite thermally conductive material, see [link to example]. Figure 1 ,include: S1: Pretreatment of graphene filler S1.1: Add 4 parts by weight of graphene oxide to 215 parts by weight of deionized water, stir and disperse for 25 min, then rotary evaporate at 62.5℃ to obtain a graphene oxide dispersion with a concentration of 26.5 mg / mL. Then add VC to the graphene oxide dispersion, with a mass ratio of graphene oxide dispersion to VC of 21:1. Then stir and mix at 250 rpm for 25 min to obtain a mixture. S1.2: The mixture was placed in a directional freezing mold consisting of an aluminum base and four walls of silicone, and left to stand at room temperature for 1.5 hours. Then, the directional freezing mold was suspended in an alcohol bath of liquid nitrogen for directional freezing for 27 minutes. After freezing, the mixture was thawed to room temperature, sealed, and placed in a 61°C oven for pre-reduction for 2.5 hours. After cooling to 27°C, it was directionally frozen a second time. After freezing, it was thawed to room temperature and then reacted in a 61°C oven for 5 hours to obtain the chemically reduced hydrogel. S1.3: The chemically reduced hydrogel was frozen at -22°C for 4.5 h to completely solidify it. Then it was thawed to room temperature and reacted in an oven at 61°C for 5.5 h and then in an oven at 81°C for 3.5 h. The reaction product was washed with deionized water 4 times and then air-dried at room temperature to obtain reduced graphene oxide dry gel. S1.4: The reduced graphene oxide dry gel was heated to 215°C in air, then placed in a quartz tube furnace and heated to 1175°C at a heating rate of 11°C / min under an argon atmosphere, held for 2.5 h, and then placed in a graphitization furnace and heated to 2875°C under vacuum for 4 h. After cooling to room temperature, the pretreated graphene filler was obtained. S2: Preparation of modified graphene fillers S2.1: 1.5 parts by weight of pretreated graphene filler were added to 55 parts by weight of N,N-dimethylformamide and ultrasonically dispersed for 35 min. Then, 13.5 parts by weight of silane coupling agent KH550 were added. The mixture was heated to 82.5℃ under nitrogen protection and stirred for 3 h. After the reaction was completed, the dispersion was centrifuged at 8000 rpm for 11 min, the supernatant was discarded, the precipitate was washed 4 times with anhydrous ethanol and dried under vacuum at 45℃ to obtain amino-based graphene. S2.2: 21 parts by weight of 4,4'-diaminodiphenylmethane were dissolved in 55 parts by weight of N,N-dimethylformamide, and 1.5 parts by weight of aminographene were added. The mixture was dispersed at 2500 rpm for 30 min at room temperature to obtain a uniform dispersion. Then, 21 parts by weight of maleic anhydride were added, and the mixture was stirred at room temperature for 1.5 h. After that, 1.5 parts by weight of methanesulfonic acid catalyst and 173.5 parts by weight of xylene were added to the reaction system. An oil-water separator was assembled, and the mixture was heated to 137 °C and refluxed under normal pressure to separate water until no more water was released. After the reaction was completed, the mixture was cooled to room temperature, and the reaction solution was poured into excess methanol to precipitate. The mixture was filtered, and the filter cake was washed 4 times with anhydrous ethanol and dried under vacuum at 60 °C to obtain grafted modified graphene. S2.3: 4 parts by weight of grafted modified graphene and 0.65 parts by weight of 2,2'-diallylbisphenol A were added to 25 parts by weight of liquid paraffin and ultrasonically dispersed for 25 min. Then, under nitrogen protection, the temperature was raised to 141℃ and the reaction was stirred for 25 min. Subsequently, triallyl isocyanurate was added at an amount of 2.5 wt% of the total system mass, and the reaction was continued at 141℃ for 70 min. After the reaction was completed, the mixture was cooled to room temperature, diluted with excess ethyl acetate, and centrifuged. The precipitate was washed four times with acetone and dried under vacuum at 65℃ to obtain the modified graphene filler. S3: Preparation and Modification of Heterogeneous Fillers S3.1: 2.75 parts by weight of silane coupling agent KH550 modified boron nitride and 2.75 parts by weight of silane coupling agent KH560 modified silica were added to 55 parts by weight of anhydrous ethanol and stirred at 400 rpm for 25 min. Then, the mixture was refluxed at 72.5 °C for 9 h. After the reaction was completed, the mixture was filtered and the precipitate was washed 4 times with deionized water. Then, it was vacuum dried at 81 °C for 5.5 h to obtain heterogeneous filler. S3.2: 6.5 parts by weight of heterogeneous filler, 2.5 parts by weight of 1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imine salt ionic liquid and 25 parts by weight of toluene solution were mixed and stirred at 650 rpm for 25 min. Then, the mixture was heated to 92.5 °C in an oil bath and refluxed for 9 h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the precipitate was washed four times with dichloromethane and deionized water, respectively. Then, the mixture was vacuum dried at 81 °C for 5.5 h to obtain the modified heterogeneous filler. S4: Preparation of silicone composite thermal conductive materials S4.1: 65 parts by weight of RTV room temperature vulcanizing silicone rubber, 110 parts by weight of vinyl silicone oil with a vinyl content of 0.25 mmol / g and a viscosity of 750 mPa•s, 17.5 parts by weight of hydrogen-containing silicone oil with a hydrogen content of 0.21 wt%, and 0.65 parts by weight of 1-ethynyl-1-cyclohexanol were added to a planetary mixing vessel and stirred at 40 rpm for 17.5 min at room temperature to obtain silicone base material; S4.2: At 650 rpm, 35 parts by weight of modified graphene filler and 17.5 parts by weight of modified heterogeneous filler were added to the silica base material in sequence. Then, the vacuum was drawn to -0.095 MPa, and vacuum kneading was performed at a revolution speed of 100 rpm and a dispersion disk speed of 1000 rpm for 50 min. Then, 1 part by weight of platinum catalyst with a platinum content of 4000 ppm was added, and vacuum stirring was continued for 12.5 min to obtain composite silica slurry. S4.3: Then, after applying an electric field perpendicular to the calendering surface to the composite silicone slurry, calendering is performed immediately. The electric field parameters are E=2kVpp / mm, f=2kHz, and t=9min. After calendering, the material is baked at 125℃ for 12.5min, then at 155℃ for 35min, and cooled to room temperature to obtain the silicone composite thermal conductive material.

[0030] Comparative Example 1 differs from Example 1 in that step S2 is removed, and the modified graphene filler in step S4.2 is replaced with an equal amount of pretreated graphene filler, while the remaining steps remain unchanged to prepare the silicone composite thermal conductive material. This is referred to as Comparative Example 1.

[0031] Comparative Example 2 differs from Example 1 in that step S1 is removed, and the pretreated graphene filler in step S2.1 is replaced with an equal amount of graphene, while the remaining steps remain unchanged to prepare the silicone composite thermal conductive material. This is referred to as Comparative Example 2.

[0032] Comparative Example 3 differs from Example 1 in that the modified heterogeneous filler in steps S3 and S4.2 is removed, while the remaining steps remain unchanged to prepare the silicone composite thermal conductive material. This is referred to as Comparative Example 3.

[0033] Comparative Example 4 differs from Example 1 in that step S3.2 is removed, and the modified heterogeneous filler in step S4.2 is replaced with a heterogeneous filler, while the remaining steps remain unchanged to prepare the silicone composite thermal conductive material. This is referred to as Comparative Example 4.

[0034] Comparative Example 5 differs from Example 1 in that the electric field treatment in step S4.3 is removed in Comparative Example 5, while the remaining steps remain unchanged in preparing the silicone composite thermal conductive material.

[0035] Comparative Example 6 differs from Example 1 in that it uses a commercially available thermally conductive silicone sheet, and is referred to as Comparative Example 5.

[0036] The thermal conductivity of the silicone composite thermally conductive materials of Examples 1-3 and Comparative Examples 1-5 were cut into thermally conductive silicone sheets with a diameter of 5 cm and a thickness of 1 cm, and the commercially available thermally conductive silicone sheet of Comparative Example 6 (diameter of 5 cm and thickness of 1 cm) was measured. The thermal conductivity perpendicular to the calendering surface, i.e., the thickness direction, was tested according to the ASTM D5470 (steady-state heat flow method) standard. The test was performed three times and the average value was taken. The test results are shown in Table 1.

[0037] Table 1. Results of thermal conductivity measurements for Examples 1-3 and Comparative Examples 1-6

[0038] As can be seen from the data in Table 1, the silicone composite thermally conductive material prepared by this invention has superior thermal conductivity compared to commercially available thermally conductive silicone sheets. Comparative Example 1 shows that the addition of modified graphene filler significantly improves the thermal conductivity of the silicone composite material. Comparative Example 2 shows that the thermal conductivity is significantly improved after pretreatment of the graphene filler using a combination of chemical reduction gel technology and directional ice template technology. Comparative Examples 3-4 show that the thermal conductivity is greatly improved after the addition of heterogeneous fillers, because the addition of heterogeneous fillers can form a synergistic effect of fillers with different morphologies and sizes, thereby effectively improving thermal conductivity. Furthermore, the modified heterogeneous fillers can reduce interfacial phonon scattering, reducing phonon scattering loss at the interface and further improving the thermal conductivity of the composite material. Comparative Example 5 shows that the thermal conductivity of the silicone composite material is also improved after applying an electric field.

[0039] The silicone composite thermally conductive materials prepared in Examples 1-3 and Comparative Example 1 were cut into thermally conductive silicone sheets with a diameter of 5 cm and a thickness of 1 cm. The tensile strength (tensile strength was tested according to ASTM D412 standard) and the rate of change of thermal conductivity after 500 h of hot and cold cycles were measured. The measurements were taken three times and the average value was taken. The measurement results are shown in Table 2.

[0040] The thermally conductive silicone sheet was placed in a high and low temperature alternating test chamber with a temperature range of -20℃ to 125℃ and a heating / cooling rate of 10℃ / min. The high and low temperatures were maintained for 30 minutes each, and the cycle was repeated 500 times. The thermal conductivity was measured perpendicular to the calendering surface, i.e., in the thickness direction, according to the ASTM D5470 (steady-state heat flow method) standard. Three measurements were taken, and the average value was taken. The change rate of thermal conductivity (%) = [(thermal conductivity after 500 cycles of thermal shock - initial thermal conductivity before thermal cycling test) / initial thermal conductivity before thermal cycling test] × 100%.

[0041] Table 2. Results of Tensile Strength and Thermal Conductivity Change Rate Measurements in Examples 1-3 and Comparative Example 1

[0042] As can be seen from the data in Table 2, compared with the unmodified graphene filler, the change rate of thermal conductivity is smaller after the addition of modified graphene filler, indicating that the addition of modified graphene filler can effectively improve thermal conductivity stability. Furthermore, the tensile strength data shows that the addition of modified graphene filler can improve the mechanical properties of silicone composite materials.

[0043] The silicone composite thermally conductive material prepared in Comparative Example 3 was cut into thermally conductive silicone sheets with a diameter of 5 cm and a thickness of 1 cm. The tensile strength was measured (tensile strength was tested according to ASTM D412 standard). The test was performed three times and the average value was taken. The test results are shown in Table 3.

[0044] Table 3. Tensile strength test results of Examples 1-3 and Comparative Example 3

[0045] As can be seen from the data in Table 3, the tensile strength decreased without the addition of modified heterogeneous fillers because of the lack of synergistic effect of fillers with different morphologies and sizes. After adding modified heterogeneous fillers, the spherical silica can fill the gaps between the sheets and bridge adjacent boron nitride / graphene sheets, forming a multi-level structure of "two-dimensional sheets + zero-dimensional particles", thereby effectively improving the mechanical properties.

[0046] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims. Parts not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A preparation process for a silicone composite thermally conductive material, characterized in that, include: S1: Pretreatment of graphene filler; Graphene oxide was dispersed in deionized water and rotary evaporated, then VC was added and mixed. The mixture was subjected to directional freezing-thawing-pre-reduction, followed by freezing treatment and gradient heating reaction. After washing and drying, the pretreated graphene filler was obtained by air heating, high-temperature treatment in a quartz tube furnace and high-temperature treatment in a graphitization furnace. S2: Preparation of modified graphene filler; Aminated graphene was reacted with 4,4'-diaminodiphenylmethane and maleic anhydride in N,N-dimethylformamide. After adding a catalyst and xylene, the mixture was refluxed to remove water, washed and dried to obtain grafted modified graphene. The grafted modified graphene was then reacted with 2,2'-diallylbisphenol A and triallyl isocyanurate to obtain modified graphene filler. S3: Preparation and modification of heterogeneous fillers; KH550 modified boron nitride and KH560 modified silica were added to anhydrous ethanol, and after reflux reaction, washed and dried to obtain heterogeneous filler; it was then mixed with 1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt and toluene, and refluxed in an oil bath, and after washing and drying, modified heterogeneous filler was obtained. S4: Preparation of silicone composite thermally conductive material; Liquid silicone rubber, vinyl silicone oil, hydrogen-containing silicone oil and inhibitor are mixed to obtain silicone base material. Then, modified graphene filler and modified heterogeneous filler are added. After vacuum kneading, platinum catalyst is added and vacuum stirring is continued to obtain composite silicone slurry. Then, a specific electric field is applied before calendering, and then the material is baked and cooled in a gradient to obtain silicone composite thermal conductive material.

2. The preparation process of a silicone composite thermally conductive material according to claim 1, characterized in that, S1: Pretreatment of graphene filler, specifically including the following steps: S1.1: Add 3-5 parts by weight of graphene oxide to 200-230 parts by weight of deionized water, stir and disperse for 20-30 min, then rotary evaporate at 60-65℃ to obtain a graphene oxide dispersion with a concentration of 25-28 mg / mL. Then add vitamin C to the graphene oxide dispersion, with a mass ratio of graphene oxide dispersion to vitamin C of 20-22:

1. Then stir and mix at 200-300 rpm for 20-30 min to obtain a mixture. S1.2: Place the mixture into a directional freezing mold consisting of an aluminum base and four walls of silicone, and let it stand at room temperature for 1-2 hours. Then, suspend the directional freezing mold in an alcohol bath of liquid nitrogen for directional freezing for 25-30 minutes. After freezing, thaw the mixture to room temperature, seal it, and place it in an oven at 60-62℃ for pre-reduction for 2-3 hours. Then, cool it to 25-30℃ and perform a second directional freezing. After freezing, thaw it to room temperature and then continue the reaction in an oven at 60-62℃ for 4-6 hours to obtain the chemically reduced hydrogel. S1.3: The chemically reduced hydrogel was frozen at -22°C for 4-5 hours to completely solidify it. Then it was thawed to room temperature and reacted in an oven at 60-62°C for 5-6 hours and then in an oven at 80-82°C for 3-4 hours. The reaction product was washed with deionized water 3-5 times and then air-dried at room temperature to obtain reduced graphene oxide dry gel. S1.4: The reduced graphene oxide dry gel is heated to 200-230℃ in air, then placed in a quartz tube furnace and heated to 1150-1200℃ at a heating rate of 10-12℃ / min under an argon atmosphere, and held at that temperature for 2-3 hours. Then it is placed in a graphitization furnace and heated to 2850-2900℃ under vacuum for 3-5 hours. After cooling to room temperature, the pretreated graphene filler is obtained.

3. The preparation process of a silicone composite thermally conductive material according to claim 1, characterized in that, S2: the preparation of modified graphene filler specifically includes the following steps: S2.1: Add 1-2 parts by weight of pretreated graphene filler to 50-60 parts by weight of N,N-dimethylformamide, and ultrasonically disperse for 30-40 min. Then add 12-15 parts by weight of silane coupling agent KH550, heat to 80-85℃ under nitrogen protection, and stir for 2-4 h. After the reaction is completed, centrifuge the dispersion at 8000 rpm for 10-12 min, discard the supernatant, wash the precipitate with anhydrous ethanol 3-5 times, and vacuum dry at 40-50℃ to obtain amino-based graphene. S2.2: Dissolve 20-23 parts by weight of 4,4'-diaminodiphenylmethane in 50-60 parts by weight of N,N-dimethylformamide, add 1-2 parts by weight of aminographene, and disperse at high speed of 2000-3000 rpm for 30 min at room temperature to obtain a uniform dispersion. Then add 20-22 parts by weight of maleic anhydride, stir at room temperature for 1-2 h, and then add 1-2 parts by weight of methanesulfonic acid catalyst and 172-175 parts by weight of xylene to the reaction system. Assemble an oil-water separator, heat to 136-138℃ and reflux under normal pressure to separate water until no more water is released. After the reaction is completed, cool to room temperature, pour the reaction solution into excess methanol to precipitate, filter, wash the filter cake with anhydrous ethanol 3-5 times, and dry under vacuum at 60℃ to obtain grafted modified graphene. S2.3: Add 3-5 parts by weight of grafted modified graphene and 0.5-0.8 parts by weight of 2,2'-diallylbisphenol A to 20-30 parts by weight of liquid paraffin, and ultrasonically disperse for 20-30 min. Then, under nitrogen protection, heat to 140-142℃ and stir for 20-30 min. Subsequently, add triallyl isocyanurate and continue stirring at 140-142℃ for 60-80 min. After the reaction is completed, cool to room temperature, add excess ethyl acetate for dilution and centrifuge. Wash the precipitate 3-5 times with acetone and vacuum dry at 60-70℃ to obtain the modified graphene filler.

4. The preparation process of a silicone composite thermally conductive material according to claim 3, characterized in that, In step S2.3, the amount of triallyl isocyanurate added is 2-3 wt% of the total system mass.

5. The preparation process of a silicone composite thermally conductive material according to claim 1, characterized in that, S3: Preparation and modification of heterogeneous fillers, specifically including the following steps: S3.1: Add 2.5-3 parts by weight of silane coupling agent KH550 modified boron nitride and 2.5-3 parts by weight of silane coupling agent KH560 modified silica to 50-60 parts by weight of anhydrous ethanol, stir and mix at 300-500 rpm for 20-30 min, then reflux at 70-75℃ for 8-10 h. After the reaction is complete, filter and wash the precipitate 3-5 times with deionized water, then vacuum dry at 80-82℃ for 5-6 h to obtain heterogeneous filler; S3.2: Mix 5-8 parts by weight of heterogeneous filler, 2-3 parts by weight of 1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imine salt ionic liquid and 20-30 parts by weight of toluene solution, then stir and mix at 500-800 rpm for 20-30 min, then heat in an oil bath to 90-95℃ and reflux for 8-10 h. After the reaction is completed, cool to room temperature, filter, and wash the precipitate 3-5 times with dichloromethane and deionized water in sequence, then vacuum dry at 80-82℃ for 5-6 h to obtain the modified heterogeneous filler.

6. The preparation process of a silicone composite thermally conductive material according to claim 5, characterized in that, The specific steps of modifying boron nitride with silane coupling agent KH550 in step S3.1 are as follows: Hexagonal boron nitride is calcined in a muffle furnace at 800°C for 2 hours and then naturally cooled. After washing with water and drying, hydroxylated boron nitride is obtained. 10 parts by weight of hydroxylated boron nitride and 3 parts by weight of silane coupling agent KH550 are added to 20 parts by weight of 50wt% ethanol aqueous solution. After mixing, the mixture is subjected to reflux reaction at 80°C for 10 hours. After the reaction is completed, the reaction solution is filtered, the filter cake is washed 3 times with deionized water, and vacuum dried at 80°C for 10 hours to obtain silane coupling agent modified boron nitride. The process of modifying silica with silane coupling agent KH560 is as follows: 10 parts by weight of fumed silica and 3 parts by weight of silane coupling agent KH560 are added to 20 parts by weight of 50wt% ethanol aqueous solution. After mixing, the mixture is refluxed at 80℃ for 10h. After the reaction is completed, the reaction solution is filtered, the filter cake is washed 3 times with deionized water, and vacuum dried at 80℃ for 10h to obtain silica modified with silane coupling agent KH560.

7. The preparation process of a silicone composite thermally conductive material according to claim 1, characterized in that, S4: Preparation of silicone composite thermally conductive material, specifically including the following steps: S4.1: Add 60-70 parts by weight of liquid silicone rubber, 100-120 parts by weight of vinyl silicone oil, 15-20 parts by weight of hydrogen-containing silicone oil, and 0.5-0.8 parts by weight of inhibitor 1-ethynyl-1-cyclohexanol to a planetary mixer and stir at 30-50 rpm for 15-20 min at room temperature to obtain silicone base material; S4.2: At 500-800 rpm, add 30-40 parts by weight of modified graphene filler and 15-20 parts by weight of modified heterogeneous filler to the silica base material in sequence. Then, evacuate to -0.09 to -0.1 MPa and perform vacuum kneading at a revolution speed of 80-120 rpm and a dispersion disk speed of 800-1200 rpm for 40-60 min. Then, add 0.8-1.2 parts by weight of platinum catalyst with a platinum content of 3000-5000 ppm and continue vacuum stirring for 10-15 min to obtain composite silica slurry. S4.3: Then, immediately after applying an electric field perpendicular to the calendering surface to the composite silicone slurry, calendering is performed. After calendering, the slurry is then heated to 120°C. Bake at 130℃ for 10-15 minutes, then bake at 150-160℃ for 30-40 minutes, and cool to room temperature to obtain silicone composite thermal conductive material.

8. The preparation process of a silicone composite thermally conductive material according to claim 7, characterized in that, In step S4.1, the vinyl content of the vinyl silicone oil is 0.22-0.28 mmol / g, the viscosity is 500-1000 mPa•s, and the hydrogen content of the hydrogen-containing silicone oil is 0.18-0.25 wt%.

9. The preparation process of a silicone composite thermally conductive material according to claim 7, characterized in that, In step S4.3, the electric field parameters are E=2kVpp / mm, f=2kHz, and t=8-10min.

10. A silicone composite thermally conductive material, characterized in that, It is prepared by the preparation process of a silicone composite thermally conductive material as described in any one of claims 1-9.

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