Composite heat-conducting filler, graphene in-situ modified heat-conducting gel, preparation and use

Abstract

Disclosed in the present invention is a composite heat-conducting filler, which is a graphene-oxide-coated aluminum oxide composite heat-conducting filler, wherein aluminum oxide grows in situ on the surface of graphene oxide, and a microsphere structure in which the graphene oxide is wrapped around the surface of the aluminum oxide is then formed by means of a special drying technique. Further disclosed in the present invention is a graphene in-situ modified heat-conducting gel, which comprises the composite heat-conducting filler. Further disclosed in the present invention are the preparation and use thereof. In a product prepared in the embodiments of the present invention, graphene is wrapped around the surface of aluminum oxide, and the two are overlapped with each other and cooperate with each other, thereby generating a two-dimensional and zero-dimensional spherical special compounding effect, constructing a three-dimensional wide heat-conducting network structure, and achieving a high heat-conductivity coefficient and a high extrusion rate under the condition of a relatively low filling amount.

Description

Composite thermal conductive filler, graphene in-situ modified thermal conductive gel, and its preparation and application Technical Field

[0001] The invention relates to a composite thermally conductive filler, a graphene in-situ modified thermally conductive gel, and preparation and application thereof. Background Art

[0002] During device heat dissipation, heat must be transferred from the inside of the device through the device packaging material and the heat sink interface, and then through the heat sink to the external environment. Because solid surfaces are rough and uneven at the microscopic scale, even when the contact pressure between two solid surfaces is as high as 10MPa, the actual contact area only accounts for 1-2% of the apparent contact area, and the rest is tiny pores filled with air. To reduce the interfacial thermal resistance, people have developed thermally conductive interface materials. Filling the interface thermal conductive material between the contact surfaces can remove the air in the contact interface pores, forming a continuous heat conduction channel across the entire contact interface, and improving heat dissipation efficiency.

[0003] Thermally conductive gel is a new type of thermal interface material. Conventional thermally conductive gel materials are typically composite materials made by directly mixing thermally conductive particles into organic polymer materials such as silicone oil. The addition of large amounts of thermally conductive fillers not only increases the cost and weight of the thermally conductive gel, but also reduces the material's interfacial wettability, increases viscosity, and increases hardness, while rarely significantly improving thermal conductivity.

[0004] Summary of the Invention

[0005] The present invention is made in order to further improve the thermal conductivity of the thermally conductive gel.

[0006] One aspect of the present invention relates to a composite thermally conductive filler comprising graphene oxide-coated aluminum oxide, wherein the aluminum oxide is in situ grown on the graphene surface. Generally speaking, during the implementation of the present invention, spherical aluminum oxide is first grown in situ on the two-dimensional graphene oxide surface. During this in-situ growth process, the aluminum oxide exhibits a biased tendency to grow on one side of the graphene, with less growth on the other side. Subsequently, during the spray drying process, the aluminum oxide curls up to form a graphene oxide-coated aluminum oxide morphology, typically in the form of microspheres. In the final product, the aluminum oxide is primarily located on the inner surface of the graphene.

[0007] Preferably, the microspheres have a diameter of 5 to 20 μm and a specific surface area of ​​1 to 5.1 m 2 / g (more preferably 1 to 5 m 2 / g).

[0008] Preferably, the graphene oxide is coupling agent-modified graphene. In a specific embodiment, the coupling agent is γ-aminopropyltriethoxysilane, a borate coupling agent, a titanate coupling agent, or an aluminate coupling agent.

[0009] As another aspect of the present invention, it relates to a graphene in-situ modified thermally conductive gel, which contains the above-mentioned graphene oxide-wrapped aluminum oxide composite thermally conductive filler.

[0010] As another aspect of the present invention, a method for preparing the above-mentioned graphene oxide-wrapped aluminum oxide composite thermally conductive filler comprises:

[0011] 1) Preparation of graphene oxide dispersion:

[0012] Dispersing graphite oxide in deionized water, adjusting the pH to between 4 and 7 (preferably 6 to 7) (by adding ammonia water), and preparing a graphite oxide suspension with a mass concentration of 1 to 20 g / L (preferably 5 to 10 g / L), exfoliating the graphite oxide suspension using a high-pressure homogenizer, and homogenizing (1 to 6 times) at a pressure of 30 to 80 MPa (preferably 40 to 60 MPa) to achieve monolayer exfoliation and a uniform and stable graphene oxide dispersion with a size of 5 to 20 μm;

[0013] 2) Preparation of graphene oxide-wrapped aluminum oxide composite thermal conductive filler:

[0014] Aluminum salt is dissolved in the graphene oxide dispersion, wherein the amount of the aluminum salt is 2 to 15 times the mass of the graphene oxide in terms of aluminum; the pH of the system is adjusted to between 8 and 12, and aluminum oxide particles are nucleated and in situ grown on the surface of the graphene oxide; spray drying is performed to obtain a graphene oxide with a size of 5 to 20 μm and a specific surface area of ​​1 to 5 m 2 / g of graphene oxide wrapped with aluminum oxide composite thermal conductive filler.

[0015] In a specific embodiment, in step 1), the pH is adjusted to between 6 and 7, and a graphite oxide suspension having a mass concentration of 5 to 10 g / L is prepared and homogenized under a pressure of 40 to 60 MPa.

[0016] In a specific embodiment, the aluminum salt is one of aluminum chloride, aluminum nitrate, aluminum sulfate, ammonium aluminum sulfate and sodium metaaluminate.

[0017] In a specific embodiment, in step 2), before spray drying, a coupling agent is added at a mass ratio of 1:5 to 1 to the graphene oxide, and the reaction is carried out at 40 to 100° C. for 0.5 to 10 hours. In a specific embodiment, the coupling agent is γ-aminopropyltriethoxysilane, a borate coupling agent, a titanate coupling agent, or an aluminate coupling agent.

[0018] In a specific embodiment, in step 2), the spray drying spray air pressure ranges from 2 to 20 MPa, and the outlet temperature ranges from 80 to 110°C.

[0019] As another aspect of the present invention, a method for preparing the above-mentioned graphene in-situ modified thermally conductive gel comprises:

[0020] A platinum catalyst is dispersed in a silicone oil matrix, with the mass percentage of the platinum catalyst to the silicone oil being 0.1 to 2.0%. A thermally conductive filler coated with aluminum oxide is dispersed in the silicone oil matrix (stirred at 1000 to 3000 rpm until uniformly mixed) in a mass ratio of the graphene oxide-coated aluminum oxide composite thermally conductive filler to the silicone oil matrix of 10 to 15:1. The graphene oxide is heated under vacuum conditions to vulcanize, crosslink, and reduce the graphene oxide while maintaining mechanical stirring.

[0021] As another aspect of the present invention, it relates to the use of the above-mentioned composite thermally conductive filler in the preparation of graphene in-situ modified thermally conductive gel.

[0022] As another aspect of the present invention, it relates to the application of the above-mentioned graphene in-situ modified thermal conductive gel in the preparation of electronic products (such as mobile phones, communication base stations, new energy battery vehicles, LED chips, IGBTs and other power modules, high-power semiconductors, aerospace, etc.).

[0023] As another aspect of the present invention, it relates to an electronic product, which includes the graphene in-situ modified thermal conductive gel according to claim 13.

[0024] In the product prepared by the embodiment of the present invention, graphene and aluminum oxide balls are tightly coated. The present invention realizes the in-situ growth of aluminum oxide on the surface of graphene oxide by reacting aluminum salt with ammonia water in a graphene oxide dispersion, and also effectively inhibits the agglomeration of graphene oxide. In the drying stage, the preparation of spherical composite thermal conductive filler with graphene oxide wrapped in aluminum oxide is realized by spray drying, and the optimal spray droplet size is obtained by precisely controlling the pressure and outlet temperature range of the spray air. Under a smaller spray pressure, the droplet size is too large, resulting in a final composite thermal conductive filler size exceeding 20μm, and it is difficult for graphene to completely wrap aluminum oxide. The thermal conductivity of the thermal conductive gel obtained by this filler is low and the hardness is high; under a larger spray pressure, aluminum oxide will separate from the surface of graphene oxide, resulting in uneven composite of graphene and aluminum oxide in the obtained composite filler. The special spherical graphene structure can effectively reduce the specific surface area of ​​graphene (1 to 5m 2 / g), inhibiting large specific surface area graphene (theoretical specific capacity ~ 2600m 2 / g) The problem of large adsorption capacity of silicone oil matrix.

[0025] In the present invention, the principle of in-situ growth of aluminum oxide on the surface of graphene oxide is that aluminum salt is in the form of ionic Al in aqueous solution. 3+ The graphene oxide has a negative charge on its surface in the aqueous dispersion, so Al3+ It is adsorbed on the surface of graphene oxide sheets through the interaction of positive and negative charges; then, by adjusting the pH of the solution system to between 8 and 12, Al 3+ With OH - Reactive crystallization nucleates and grows in situ on the graphene oxide surface.

[0026] In the product prepared by the embodiment of the present invention, graphene is wrapped on the surface of alumina, and the two overlap and cooperate with each other to form a special compound effect of two-dimensional and zero-dimensional spheres, constructing a three-dimensional, extensive thermal conductive network structure, and achieving high thermal conductivity and high extrusion rate at a lower filling amount.

[0027] The thermal conductivity of the products produced in the embodiments of the present invention can reach 8 to 12 W / (m·K), or even higher, with extrusion rates often exceeding 60 g / min. The present process is simple and easy to implement, suitable for industrial large-scale production, and overcomes the technical drawback of existing graphene thermally conductive gels, which, despite complex preparation steps, still have a thermal conductivity of less than 8 W / (m·K). DETAILED DESCRIPTION

[0028] The inventors prepared heat dissipation gels based on several prior art documents, including CN 108148558 A, CN 110003438 A, CN 105754350 A, and CN 111471305 A. However, the thermal conductivity of the products produced could not exceed 8 W / (m·K), which did not meet the inventors' expectations. Further research and development led to the present invention, which develops a simple, industrially feasible large-scale production process to produce high-performance graphene thermally conductive gels with a thermal conductivity of 8 to 12 W / (m·K).

[0029] The inventors attempted to mechanically mix graphene powder and aluminum oxide powder based on existing technology. However, due to the huge difference between the density of graphene powder (0.003 g / mL) and the density of aluminum oxide (3.96 g / mL), graphene and aluminum oxide are difficult to mix evenly, graphene easily agglomerates, and it is difficult for graphene to form an effective path in the thermal conductive gel.

[0030] Based on the above, the inventors made the present invention after further research and development.

[0031] Source of raw materials or equipment:

[0032] Graphite oxide: The graphite oxide paste used has a solid content of 43±5wt%, a pH value of 1.8-2.3, a size ≤100μm, a carbon content of 51±5wt%, and a sulfur content ≤2wt%. It is SE2430W-N, a product of Changzhou Sixth Element Materials Technology Co., Ltd.

[0033] Evaluation and analysis methods: Test equipment—DRL thermal conductivity meter, test method—ASTM D5470 thermal impedance thermal conductivity test standard.

[0034] Example 1:

[0035] 1) Preparation of graphene oxide slurry

[0036] Graphite oxide was dispersed in deionized water to prepare 1 L of graphite oxide suspension with a mass concentration of 10 g / L. A certain amount of ammonia solution was added, the pH was adjusted to 5, and the mixture was stirred evenly to obtain a graphite oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 80 MPa to achieve monolayer exfoliation to obtain a uniform and stable graphene oxide dispersion. The size of the graphene oxide in the dispersion was 5 μm.

[0037] 2) Preparation of graphene oxide-wrapped aluminum oxide composite thermal conductive filler:

[0038] First, 100g of aluminum chloride was weighed and dissolved in 1L of graphene oxide dispersion with a mass concentration of 10g / L, and mechanically stirred until completely dissolved; then, ammonia water was added to adjust the pH to 9, and aluminum ions combined with hydroxide to achieve the nucleation of aluminum oxide particles and in-situ growth on the surface of graphene oxide; then, 2g of γ-aminopropyltriethoxysilane was added and reacted at 50℃ for 5h to achieve the modification of aluminum oxide and graphene oxide; finally, the mixed system was dried by spray drying with a spray air pressure of 20MPa and an outlet temperature of 110℃ to obtain a particle size of 5μm and a specific surface area of ​​5.1m 2 / g coupling agent modified graphene oxide wrapped alumina composite thermal conductive filler.

[0039] 3) Preparation of thermal conductive gel:

[0040] First, 0.01g of platinum catalyst was dispersed in 1g of vinyl silicone oil and mechanically stirred until uniformly dispersed. Then, 10g of the graphene oxide-encapsulated aluminum oxide composite thermally conductive filler prepared in Step 2 was dispersed in the vinyl silicone oil. Stirring was continued at 1000 rpm to uniformly disperse the thermally conductive filler throughout the vinyl silicone oil. Finally, the system was transferred to a planetary mixer, evacuated at 40 rpm, and heated to 120°C for 5 hours to produce a high-performance thermally conductive gel. Tests showed that the thermal conductivity of the thermally conductive gel was 8.3 W / (m·K) and the extrusion rate was 82 g / min.

[0041] Example 2:

[0042] 1) Preparation of graphene oxide slurry

[0043] Graphite oxide was dispersed in deionized water to prepare 1 L of graphite oxide suspension with a mass concentration of 10 g / L. A certain amount of ammonia solution was added, the pH was adjusted to 5, and the mixture was stirred evenly to obtain a graphite oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 80 MPa to achieve monolayer exfoliation to obtain a uniform and stable graphene oxide dispersion. The size of the graphene oxide in the dispersion was 5 μm.

[0044] 2) Preparation of graphene oxide-wrapped aluminum oxide composite thermal conductive filler:

[0045] First, 100g of aluminum chloride was weighed and dissolved in 1L of graphene oxide dispersion with a mass concentration of 10g / L, and mechanically stirred until completely dissolved; then, ammonia water was added to adjust the pH to 9, and aluminum ions combined with hydroxide to achieve the nucleation of aluminum oxide particles and in-situ growth on the surface of graphene oxide; then, 2g of γ-aminopropyltriethoxysilane was added and reacted at 50℃ for 5h to achieve the modification of aluminum oxide and graphene oxide; finally, the mixed system was dried by spray drying with a spray air pressure of 20MPa and an outlet temperature of 110℃ to obtain a particle size of 5μm and a specific surface area of ​​5.1m 2 / g coupling agent modified graphene oxide wrapped alumina composite thermal conductive filler.

[0046] 3) Preparation of thermal conductive gel:

[0047] First, 0.02g of platinum catalyst was dispersed in 1g of dimethyl silicone oil and mechanically stirred until uniformly dispersed. Then, 12g of the graphene oxide-encapsulated aluminum oxide composite thermally conductive filler prepared in Step 2 was dispersed in the dimethyl silicone oil. Stirring was carried out at 2000 rpm to uniformly disperse the thermally conductive filler throughout the dimethyl silicone oil. Finally, the system was transferred to a planetary mixer, evacuated at 80 rpm, and heated to 200°C for 0.5 h to produce a high-performance thermally conductive gel. Tests showed that the thermal conductivity of the gel was 9.5 W / (m·K) and the extrusion rate was 72 g / min.

[0048] Example 3:

[0049] 1) Preparation of graphene oxide slurry

[0050] Graphite oxide was dispersed in deionized water to prepare 1 L of graphite oxide suspension with a mass concentration of 10 g / L. A certain amount of ammonia solution was added, the pH was adjusted to 5, and the mixture was stirred evenly to obtain a graphite oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 80 MPa to achieve monolayer exfoliation to obtain a uniform and stable graphene oxide dispersion. The size of the graphene oxide in the dispersion was 5 μm.

[0051] 2) Preparation of graphene oxide-wrapped aluminum oxide composite thermal conductive filler:

[0052] First, 100g of aluminum chloride was weighed and dissolved in 1L of graphene oxide dispersion with a mass concentration of 10g / L, and mechanically stirred until completely dissolved; then, ammonia water was added to adjust the pH to 9, and aluminum ions combined with hydroxide to achieve the nucleation of aluminum oxide particles and in-situ growth on the surface of graphene oxide; then, 2g of γ-aminopropyltriethoxysilane was added and reacted at 50℃ for 5h to achieve the modification of aluminum oxide and graphene oxide; finally, the mixed system was dried by spray drying with a spray air pressure of 20MPa and an outlet temperature of 110℃ to obtain a particle size of 5μm and a specific surface area of ​​5.1m 2 / g coupling agent modified graphene oxide wrapped alumina composite thermal conductive filler.

[0053] 3) Preparation of thermal conductive gel:

[0054] First, 0.01g of platinum catalyst was dispersed in 1g of methylphenyl silicone oil and mechanically stirred until uniformly dispersed. Then, 13g of the graphene oxide-encapsulated aluminum oxide composite thermally conductive filler prepared in Step 2 was dispersed in the methylphenyl silicone oil. Stirring was carried out at 3000 rpm to uniformly disperse the thermally conductive filler throughout the methylphenyl silicone oil. Finally, the system was transferred to a planetary mixer, evacuated at 60 rpm, and heated to 160°C for 2 hours to produce a high-performance thermally conductive gel. Tests showed that the thermal conductivity of the thermally conductive gel was 10.6 W / (m·K) and the extrusion rate was 69 g / min.

[0055] Example 4:

[0056] 1) Preparation of graphene oxide slurry

[0057] Graphite oxide was dispersed in deionized water to prepare 1 L of graphite oxide suspension with a mass concentration of 10 g / L. A certain amount of ammonia solution was added, the pH was adjusted to 5, and the mixture was stirred evenly to obtain a graphite oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 80 MPa to achieve monolayer exfoliation to obtain a uniform and stable graphene oxide dispersion. The size of the graphene oxide in the dispersion was 5 μm.

[0058] 2) Preparation of graphene oxide-wrapped aluminum oxide composite thermal conductive filler:

[0059] First, 100g of aluminum chloride was weighed and dissolved in 1L of graphene oxide dispersion with a mass concentration of 10g / L, and mechanically stirred until completely dissolved; then, ammonia water was added to adjust the pH to 9, and aluminum ions combined with hydroxide to achieve the nucleation of aluminum oxide particles and in-situ growth on the surface of graphene oxide; then, 2g of γ-aminopropyltriethoxysilane was added and reacted at 50℃ for 5h to achieve the modification of aluminum oxide and graphene oxide; finally, the mixed system was dried by spray drying with a spray air pressure of 20MPa and an outlet temperature of 110℃ to obtain a particle size of 5μm and a specific surface area of ​​5.1m 2 / g coupling agent modified graphene oxide wrapped alumina composite thermal conductive filler.

[0060] 3) Preparation of thermal conductive gel:

[0061] First, 0.02g of platinum catalyst was dispersed in 1g of methylchlorophenyl silicone oil and mechanically stirred until uniformly dispersed. Then, 15g of the graphene oxide-encapsulated aluminum oxide composite thermally conductive filler prepared in Step 2 was dispersed in the methylchlorophenyl silicone oil. Stirring was carried out at 2000 rpm to uniformly disperse the thermally conductive filler throughout the methylchlorophenyl silicone oil. Finally, the system was transferred to a planetary mixer, evacuated at 80 rpm, and heated to 200°C for 1 hour to produce a high-performance thermally conductive gel. Tests showed that the thermal conductivity of the thermally conductive gel was 12.1 W / (m·K) and the extrusion rate was 63 g / min.

[0062] Example 5:

[0063] 1) Preparation of graphene oxide slurry

[0064] Graphite oxide was dispersed in deionized water to prepare 1 L of graphite oxide suspension with a mass concentration of 10 g / L. A certain amount of ammonia solution was added, the pH was adjusted to 5, and the mixture was stirred evenly to obtain a graphite oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 80 MPa to achieve monolayer exfoliation to obtain a uniform and stable graphene oxide dispersion. The size of the graphene oxide in the dispersion was 5 μm.

[0065] 2) Preparation of graphene oxide-wrapped aluminum oxide composite thermal conductive filler:

[0066] First, 100g of aluminum chloride was weighed and dissolved in 1L of graphene oxide dispersion with a mass concentration of 10g / L, and mechanically stirred until completely dissolved; then, ammonia water was added to adjust the pH to 9, and aluminum ions combined with hydroxide to achieve the nucleation of aluminum oxide particles and in-situ growth on the surface of graphene oxide; then, 2g of γ-aminopropyltriethoxysilane was added and reacted at 50℃ for 5h to achieve the modification of aluminum oxide and graphene oxide; finally, the mixed system was dried by spray drying with a spray air pressure of 20MPa and an outlet temperature of 110℃ to obtain a particle size of 5μm and a specific surface area of ​​5.1m 2 / g coupling agent modified graphene oxide wrapped alumina composite thermal conductive filler.

[0067] 3) Preparation of thermal conductive gel:

[0068] First, 0.001g of platinum catalyst was dispersed in 1g of vinyl silicone oil and mechanically stirred until uniformly dispersed. Then, 15g of the graphene oxide-encapsulated aluminum oxide composite thermally conductive filler prepared in Step 2 was dispersed in the vinyl silicone oil. Stirring was performed at 2000 rpm to uniformly disperse the thermally conductive filler. Finally, the system was transferred to a planetary mixer, evacuated at 10 rpm, and heated to 200°C for 2 hours to produce a high-performance thermally conductive gel. Tests showed that the thermal conductivity of the thermally conductive gel was 12.3 W / (m·K) and the extrusion rate was 68 g / min.

[0069] Example 6:

[0070] 1) Preparation of graphene oxide slurry

[0071] Graphite oxide was dispersed in deionized water to prepare 1 L of graphite oxide suspension with a mass concentration of 10 g / L. A certain amount of ammonia solution was added, the pH was adjusted to 5, and the mixture was stirred evenly to obtain a graphite oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 80 MPa to achieve monolayer exfoliation to obtain a uniform and stable graphene oxide dispersion. The size of the graphene oxide in the dispersion was 5 μm.

[0072] 2) Preparation of graphene oxide-wrapped aluminum oxide composite thermal conductive filler:

[0073] First, 100g of aluminum chloride was weighed and dissolved in 1L of graphene oxide dispersion with a mass concentration of 10g / L, and mechanically stirred until completely dissolved; then, ammonia water was added to adjust the pH to 9, and aluminum ions combined with hydroxide to achieve the nucleation of aluminum oxide particles and in-situ growth on the surface of graphene oxide; then, 2g of γ-aminopropyltriethoxysilane was added and reacted at 50℃ for 5h to achieve the modification of aluminum oxide and graphene oxide; finally, the mixed system was dried by spray drying with a spray air pressure of 20MPa and an outlet temperature of 110℃ to obtain a particle size of 5μm and a specific surface area of ​​5.1m 2 / g coupling agent modified graphene oxide wrapped alumina composite thermal conductive filler.

[0074] 3) Preparation of thermal conductive gel:

[0075] First, 0.02g of platinum catalyst was dispersed in 1g of vinyl silicone oil and mechanically stirred until uniformly dispersed. Then, 15g of the graphene oxide-encapsulated aluminum oxide composite thermally conductive filler prepared in Step 2 was dispersed in the vinyl silicone oil. Stirring was performed at 2000 rpm to uniformly disperse the thermally conductive filler. Finally, the system was transferred to a planetary mixer, evacuated at 10 rpm, and heated to 200°C for 2 hours to produce a high-performance thermally conductive gel. Tests showed that the thermal conductivity of the thermally conductive gel was 12.1 W / (m·K) and the extrusion rate was 65g / min.

[0076] Example 7:

[0077] 1) Preparation of graphene oxide slurry

[0078] Graphite oxide was dispersed in deionized water to prepare 1 L of graphite oxide suspension with a mass concentration of 10 g / L. A certain amount of ammonia solution was added, the pH was adjusted to 5, and the mixture was stirred evenly to obtain a graphite oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 80 MPa to achieve monolayer exfoliation to obtain a uniform and stable graphene oxide dispersion. The size of the graphene oxide in the dispersion was 5 μm.

[0079] 2) Preparation of graphene oxide-wrapped aluminum oxide composite thermal conductive filler:

[0080] First, 100g of aluminum chloride was weighed and dissolved in 1L of graphene oxide dispersion with a mass concentration of 10g / L, and mechanically stirred until completely dissolved; then, ammonia water was added to adjust the pH to 9, and aluminum ions combined with hydroxide to achieve the nucleation of aluminum oxide particles and in-situ growth on the surface of graphene oxide; then, 2g of γ-aminopropyltriethoxysilane was added and reacted at 50℃ for 5h to achieve the modification of aluminum oxide and graphene oxide; finally, the mixed system was dried by spray drying with a spray air pressure of 20MPa and an outlet temperature of 110℃ to obtain a particle size of 5μm and a specific surface area of ​​5.1m 2 / g coupling agent modified graphene oxide wrapped alumina composite thermal conductive filler.

[0081] 3) Preparation of thermal conductive gel:

[0082] First, 0.003g of platinum catalyst was dispersed in 1g of vinyl silicone oil and mechanically stirred until uniformly dispersed. Then, 15g of the graphene oxide-encapsulated aluminum oxide composite thermally conductive filler prepared in Step 2 was dispersed in the vinyl silicone oil. Stirring was performed at 2000 rpm to uniformly disperse the thermally conductive filler. Finally, the system was transferred to a planetary mixer, evacuated at 10 rpm, and heated to 200°C for 2 hours to produce a high-performance thermally conductive gel. Tests showed that the thermal conductivity of the thermally conductive gel was 12.2 W / (m·K) and the extrusion rate was 58 g / min.

[0083] Example 8:

[0084] 1) Preparation of graphene oxide slurry

[0085] Graphite oxide was dispersed in deionized water to prepare 1 L of graphite oxide suspension with a mass concentration of 10 g / L. A certain amount of ammonia solution was added, the pH was adjusted to 5, and the mixture was stirred evenly to obtain a graphite oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 80 MPa to achieve monolayer exfoliation to obtain a uniform and stable graphene oxide dispersion. The size of the graphene oxide in the dispersion was 5 μm.

[0086] 2) Preparation of graphene oxide-wrapped aluminum oxide composite thermal conductive filler:

[0087] First, 100g of aluminum chloride was weighed and dissolved in 1L of graphene oxide dispersion with a mass concentration of 10g / L, and mechanically stirred until completely dissolved; then, ammonia water was added to adjust the pH to 9, and aluminum ions combined with hydroxide to achieve the nucleation of aluminum oxide particles and in-situ growth on the surface of graphene oxide; then, 2g of γ-aminopropyltriethoxysilane was added and reacted at 50℃ for 5h to achieve the modification of aluminum oxide and graphene oxide; finally, the mixed system was dried by spray drying with a spray air pressure of 20MPa and an outlet temperature of 110℃ to obtain a particle size of 5μm and a specific surface area of ​​5.1m 2 / g coupling agent modified graphene oxide wrapped alumina composite thermal conductive filler.

[0088] 3) Preparation of thermal conductive gel:

[0089] First, 0.005g of platinum catalyst was dispersed in 1g of vinyl silicone oil and mechanically stirred until uniformly dispersed. Then, 15g of the graphene oxide-encapsulated aluminum oxide composite thermally conductive filler prepared in Step 2 was dispersed in the vinyl silicone oil. Stirring was carried out at 2000 rpm to uniformly disperse the thermally conductive filler. Finally, the system was transferred to a planetary mixer, evacuated at 10 rpm, and heated to 200°C for 2 hours to produce a high-performance thermally conductive gel. Tests showed that the thermal conductivity of the thermally conductive gel was 12.1 W / (m·K) and the extrusion rate was 55g / min.

[0090] Example 9:

[0091] 1) Preparation of graphene oxide slurry

[0092] Graphite oxide was dispersed in deionized water to prepare 5 L of graphite oxide suspension with a mass concentration of 1 g / L. A certain amount of ammonia solution was added, the pH was adjusted to 7, and the solution was stirred evenly to obtain a graphene oxide dispersion. The graphene oxide dispersion was homogenized three times under a pressure of 30 MPa to achieve monolayer exfoliation to obtain a uniform and stable graphite oxide dispersion. The size of the graphene oxide in the dispersion was 10 μm.

[0093] 2) Preparation of graphene oxide-wrapped aluminum oxide composite thermal conductive filler:

[0094] First, 140 g of aluminum sulfate was weighed and dissolved in 5 L of graphene oxide dispersion with a mass concentration of 1 g / L, and mechanically stirred until completely dissolved; then, ammonia water was added to adjust the pH to 12, and aluminum ions combined with hydroxide to achieve the nucleation of aluminum oxide particles and in-situ growth on the surface of graphene oxide; then, 5 g of borate coupling agent was added and the reaction was carried out at 90 ° C for 0.5 h to achieve the modification of aluminum oxide and graphene oxide; finally, the mixed system was dried by spray drying method with a spray air pressure of 20 MPa and an outlet temperature of 100 ° C to obtain a particle size of 5 μm and a specific surface area of ​​4.9 m 2 / g coupling agent modified graphene oxide wrapped alumina composite thermal conductive filler.

[0095] 3) Preparation of thermal conductive gel:

[0096] First, 0.01g of platinum catalyst was dispersed in 1g of vinyl silicone oil and mechanically stirred until uniformly dispersed. Then, 15g of the graphene oxide-encapsulated aluminum oxide composite thermally conductive filler prepared in Step 2 was dispersed in the vinyl silicone oil. Stirring was performed at 2000 rpm to uniformly disperse the thermally conductive filler. Finally, the system was transferred to a planetary mixer, evacuated at 10 rpm, and heated to 200°C for 2 hours to produce a high-performance thermally conductive gel. Tests showed that the thermal conductivity of the thermally conductive gel was 11.6 W / (m·K) and the extrusion rate was 65 g / min.

[0097] Example 10:

[0098] 1) Preparation of graphene oxide slurry

[0099] Graphite oxide was dispersed in deionized water to prepare 5 L of graphite oxide suspension with a mass concentration of 2 g / L. A certain amount of ammonia solution was added, the pH was adjusted to 6, and the mixture was stirred evenly to obtain a graphite oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 60 MPa to achieve monolayer exfoliation to obtain a uniform and stable graphite oxide dispersion. The size of the graphene oxide in the dispersion was 15 μm.

[0100] 2) Preparation of graphene oxide-wrapped aluminum oxide composite thermal conductive filler:

[0101] First, 300g of aluminum nitrate was weighed and dissolved in 5L of graphene oxide dispersion with a mass concentration of 2g / L, and mechanically stirred until completely dissolved; then, ammonia water was added to adjust the pH to 11, and aluminum ions combined with hydroxide to achieve the nucleation of aluminum oxide particles and in-situ growth on the surface of graphene oxide; then, 5g of titanate coupling agent was added and reacted at 80℃ for 1h to achieve the modification of aluminum oxide and graphene oxide; finally, the mixed system was dried by spray drying method with a spray air pressure of 12MPa and an outlet temperature of 100℃ to obtain a particle size of 10μm and a specific surface area of ​​2.3m 2 / g coupling agent modified graphene oxide wrapped alumina composite thermal conductive filler.

[0102] 3) Preparation of thermal conductive gel:

[0103] First, 0.01g of platinum catalyst was dispersed in 1g of vinyl silicone oil and mechanically stirred until uniformly dispersed. Then, 15g of the graphene oxide-encapsulated aluminum oxide composite thermally conductive filler prepared in Step 2 was dispersed in the vinyl silicone oil. Stirring was performed at 2000 rpm to uniformly disperse the thermally conductive filler. Finally, the system was transferred to a planetary mixer, evacuated at 10 rpm, and heated to 200°C for 2 hours to produce a high-performance thermally conductive gel. Tests showed that the thermal conductivity of the thermally conductive gel was 11.7 W / (m·K) and the extrusion rate was 61 g / min.

[0104] Example 11:

[0105] 1) Preparation of graphene oxide slurry

[0106] Graphite oxide was dispersed in deionized water to prepare 5 L of graphite oxide suspension with a mass concentration of 4 g / L. A certain amount of ammonia solution was added, the pH was adjusted to 7, and the solution was stirred evenly to obtain a graphene oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 50 MPa to achieve monolayer exfoliation to obtain a uniform and stable graphite oxide dispersion. The size of the graphene oxide in the dispersion was 20 μm.

[0107] 2) Preparation of graphene oxide-wrapped aluminum oxide composite thermal conductive filler:

[0108] First, 400 g of ammonium aluminum sulfate was weighed and dissolved in 5 L of graphene oxide dispersion with a mass concentration of 4 g / L, and mechanically stirred until completely dissolved; then, ammonia water was added to adjust the pH to 10, and aluminum ions combined with hydroxide to achieve the nucleation of aluminum oxide particles and in-situ growth on the surface of graphene oxide; then, 5 g of aluminate coupling agent was added and reacted at 60 ° C for 5 h to achieve the modification of aluminum oxide and graphene oxide; finally, the mixed system was dried by spray drying method with a spray air pressure of 2 MPa and an outlet temperature of 80 ° C to obtain a particle size of 20 μm and a specific surface area of ​​1 m 2 / g coupling agent modified graphene oxide wrapped alumina composite thermal conductive filler.

[0109] 3) Preparation of thermal conductive gel:

[0110] First, 0.01g of platinum catalyst was dispersed in 1g of vinyl silicone oil and mechanically stirred until uniformly dispersed. Then, 15g of the graphene oxide-encapsulated aluminum oxide composite thermally conductive filler prepared in Step 2 was dispersed in the vinyl silicone oil. Stirring was performed at 2000 rpm to uniformly disperse the thermally conductive filler. Finally, the system was transferred to a planetary mixer, evacuated at 10 rpm, and heated to 200°C for 2 hours to produce a high-performance thermally conductive gel. Tests showed that the thermal conductivity of the thermally conductive gel was 11.9 W / (m·K) and the extrusion rate was 63 g / min.

[0111] Example 12:

[0112] 1) Preparation of graphene oxide slurry

[0113] Graphite oxide was dispersed in deionized water to prepare 2L of graphite oxide suspension with a mass concentration of 5g / L. A certain amount of ammonia solution was added, the pH was adjusted to 7, and the solution was stirred evenly to obtain a graphene oxide dispersion. The graphene oxide dispersion was homogenized twice under a pressure of 30MPa to achieve monolayer exfoliation to obtain a uniform and stable graphite oxide dispersion. The size of the graphene oxide in the dispersion was 12μm.

[0114] 2) Preparation of graphene oxide-wrapped aluminum oxide composite thermal conductive filler:

[0115] First, 300g of sodium aluminate was weighed and dissolved in 2L of graphene oxide dispersion with a mass concentration of 5g / L, and mechanically stirred until completely dissolved; then, ammonia water was added to adjust the pH to 12, and aluminum ions combined with hydroxide to achieve the nucleation of aluminum oxide particles and in-situ growth on the surface of graphene oxide; then, 5g of aluminate coupling agent was added and the reaction was carried out at 50℃ for 5h to achieve the modification of aluminum oxide and graphene oxide; finally, the mixed system was dried by spray drying method with the spray air pressure range of 12MPa and the outlet temperature of 90℃ to obtain a particle size of 10μm and a specific surface area of ​​3.2m 2 / g coupling agent modified graphene oxide wrapped alumina composite thermal conductive filler.

[0116] 3) Preparation of thermal conductive gel:

[0117] First, 0.01g of platinum catalyst was dispersed in 1g of vinyl silicone oil and mechanically stirred until uniformly dispersed. Then, 15g of the graphene oxide-encapsulated aluminum oxide composite thermally conductive filler prepared in Step 2 was dispersed in the vinyl silicone oil. Stirring was performed at 2000 rpm to uniformly disperse the thermally conductive filler. Finally, the system was transferred to a planetary mixer, evacuated at 10 rpm, and heated to 200°C for 2 hours to produce a high-performance thermally conductive gel. Tests showed that the thermal conductivity of the thermally conductive gel was 11.7 W / (m·K) and the extrusion rate was 65g / min.

[0118] Comparative Example 1

[0119] 3g intercalated graphene powder, 400g spherical alumina filler with an average particle size of 50μm, 50g spherical alumina filler with an average particle size of 3μm, 100g viscosity of 6000mm 2 / s dimethyl silicone oil was placed in a ball mill and stirred at 100 rpm for 10 minutes. 200g of zirconium oxide balls were added to the mill. The mixture was ball milled at 500 rpm for 20 hours. After ball milling, the mixture was removed to obtain a thermally conductive gel composite containing graphene. Tests showed that the thermal conductivity of the thermally conductive gel was 5 W / (m·K). The extrusion rate was not measured.

[0120] Comparative Example 2

[0121] 1) Preparation of graphene oxide slurry:

[0122] Graphite oxide was dispersed in deionized water to prepare 5 L of graphite oxide suspension with a mass concentration of 4 g / L. A certain amount of ammonia solution was added, the pH was adjusted to 7, and the solution was stirred evenly to obtain a graphene oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 50 MPa to achieve monolayer exfoliation to obtain a uniform and stable graphite oxide dispersion. The size of the graphene oxide in the dispersion was 20 μm.

[0123] 2) Preparation of graphene oxide-wrapped aluminum oxide composite thermal conductive filler:

[0124] First, 400 g of ammonium aluminum sulfate was weighed and dissolved in 5 L of 4 g / L graphene oxide dispersion, and mechanically stirred until completely dissolved. Then, ammonia water was added to adjust the pH to 10, and aluminum ions combined with hydroxide to achieve the nucleation of aluminum oxide particles and in-situ growth on the graphene oxide surface. Then, 5 g of aluminate coupling agent was added and reacted at 60 ° C for 5 h to achieve the modification of aluminum oxide and graphene oxide. Finally, the mixed system was dried by freeze drying to obtain a specific surface area of ​​155 m 2 / g of aluminum oxide loaded on graphene oxide lamellar composite thermal conductive filler.

[0125] 3) Preparation of thermal conductive gel:

[0126] First, 0.02g of platinum catalyst was dispersed in 1g of methylchlorophenyl silicone oil and mechanically stirred until uniformly dispersed. Then, 15g of the alumina-supported graphene oxide lamellar composite thermally conductive filler prepared in Step 2 was dispersed in the methylphenyl silicone oil. Stirring was continued at 2000 rpm until the filler was uniformly dispersed throughout the methylchlorophenyl silicone oil. Finally, the system was transferred to a planetary mixer, evacuated at 80 rpm, and heated to 200°C for 1 hour to produce a thermally conductive gel. Tests showed that the thermal conductivity of the gel was 6 W / (m·K) and the extrusion rate was 5g / min.

[0127] Comparative Example 3

[0128] 1) Preparation of graphene oxide slurry:

[0129] Graphite oxide was dispersed in deionized water to prepare 5 L of graphite oxide suspension with a mass concentration of 4 g / L. A certain amount of ammonia solution was added, the pH was adjusted to 7, and the solution was stirred evenly to obtain a graphene oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 50 MPa to achieve monolayer exfoliation to obtain a uniform and stable graphite oxide dispersion. The size of the graphene oxide in the dispersion was 20 μm.

[0130] 2) Preparation of graphene oxide-wrapped aluminum oxide composite thermal conductive filler:

[0131] First, 400 g of commercial aluminum oxide spherical particles with a size of 5 μm were weighed and dispersed in 5 L of graphene oxide dispersion with a mass concentration of 4 g / L, and mechanically stirred until uniformly dispersed; then, 5 g of aluminate coupling agent was added and reacted at 60 ° C for 5 h to achieve the modification of aluminum oxide and graphene oxide; finally, the mixed system was dried by spray drying method with a spray air pressure of 2 MPa and an outlet temperature of 80 ° C to obtain a spherical particle with a size of 20 μm and a specific surface area of ​​63 m 2 / g coupling agent modified graphene oxide wrapped alumina composite thermal conductive filler.

[0132] 3) Preparation of thermal conductive gel:

[0133] First, 0.02g of platinum catalyst was dispersed in 1g of methylchlorophenyl silicone oil and mechanically stirred until uniformly dispersed. Then, 15g of the graphene oxide-encapsulated aluminum oxide composite thermally conductive filler prepared in Step 2 was dispersed in the methylchlorophenyl silicone oil. Stirring was carried out at 2000 rpm to uniformly disperse the thermally conductive filler throughout the methylchlorophenyl silicone oil. Finally, the system was transferred to a planetary mixer, evacuated at 80 rpm, and heated to 200°C for 1 hour to produce a thermally conductive gel. Tests showed that the thermal conductivity of the thermally conductive gel was 7 W / (m·K) and the extrusion rate was 13 g / min.

[0134] Comparative Example 4

[0135] 1) Preparation of graphene oxide slurry:

[0136] Graphite oxide was dispersed in deionized water to prepare 5 L of graphite oxide suspension with a mass concentration of 4 g / L. A certain amount of ammonia solution was added, the pH was adjusted to 7, and the solution was stirred evenly to obtain a graphene oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 50 MPa to achieve monolayer exfoliation to obtain a uniform and stable graphite oxide dispersion. The size of the graphene oxide in the dispersion was 20 μm.

[0137] 2) Preparation of graphene oxide-wrapped aluminum oxide composite thermal conductive filler:

[0138] First, 400 g of ammonium aluminum sulfate was weighed and dissolved in 5 L of graphene oxide dispersion with a mass concentration of 4 g / L, and mechanically stirred until completely dissolved; then, ammonia water was added to adjust the pH to 10, and aluminum ions combined with hydroxide to achieve the nucleation of aluminum oxide particles and in-situ growth on the graphene oxide surface; finally, the mixed system was dried by spray drying method with a spray air pressure of 2 MPa and an outlet temperature of 80 ° C to obtain a particle size of 20 μm and a specific surface area of ​​1.2 m 2 / g of graphene oxide wrapped with aluminum oxide composite thermal conductive filler.

[0139] 3) Preparation of thermal conductive gel:

[0140] First, 0.02g of platinum catalyst was dispersed in 1g of methylchlorophenyl silicone oil and mechanically stirred until uniformly dispersed. Then, 15g of the graphene oxide-encapsulated aluminum oxide composite thermally conductive filler prepared in Step 2 was dispersed in the methylchlorophenyl silicone oil. Stirring was performed at 2000 rpm to uniformly disperse the thermally conductive filler throughout the methylchlorophenyl silicone oil. Finally, the system was transferred to a planetary mixer, evacuated at 80 rpm, and heated to 200°C for 1 hour to produce a thermally conductive gel. Tests showed that the thermal conductivity of the thermally conductive gel was 3 W / (m·K) and the extrusion rate was 11 g / min.

[0141] Comparative Example 5

[0142] 1) Preparation of graphene oxide slurry:

[0143] Graphite oxide was dispersed in deionized water to prepare 5 L of graphite oxide suspension with a mass concentration of 4 g / L. A certain amount of ammonia solution was added, the pH was adjusted to 7, and the solution was stirred evenly to obtain a graphene oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 50 MPa to achieve monolayer exfoliation to obtain a uniform and stable graphite oxide dispersion. The size of the graphene oxide in the dispersion was 20 μm.

[0144] 2) Preparation of graphene oxide-wrapped aluminum oxide composite thermal conductive filler:

[0145] First, 400 g of ammonium aluminum sulfate was weighed and dissolved in 5 L of graphene oxide dispersion with a mass concentration of 4 g / L, and mechanically stirred until completely dissolved; then, ammonia water was added to adjust the pH to 10, and aluminum ions combined with hydroxide to achieve the nucleation of aluminum oxide particles and in-situ growth on the graphene oxide surface; finally, the mixed system was dried by spray drying method with a spray air pressure of 2 MPa and an outlet temperature of 80 ° C to obtain a particle size of 20 μm and a specific surface area of ​​1.2 m 2 / g of graphene oxide wrapped with aluminum oxide composite thermal conductive filler.

[0146] 3) Preparation of thermal conductive gel:

[0147] First, 0.02g of platinum catalyst was dispersed in 1g of methylchlorophenyl silicone oil and mechanically stirred until uniformly dispersed. Then, 5g of aluminate coupling agent was added, and 15g of the graphene oxide-encapsulated aluminum oxide composite thermally conductive filler prepared in Step 2 was dispersed in the methylchlorophenyl silicone oil. Stirring was continued at 2000 rpm to uniformly disperse the thermally conductive filler in the methylchlorophenyl silicone oil. Finally, the system was transferred to a planetary mixer, evacuated at 80 rpm, and heated to 200°C for 1 hour to produce a thermally conductive gel. Tests showed that the thermal conductivity of the thermally conductive gel was 4.1 W / (m·K) and the extrusion rate was 26 g / min.

[0148] Comparative Example 6

[0149] 1) Preparation of graphene oxide slurry:

[0150] Graphite oxide was dispersed in deionized water to prepare 5 L of a graphite oxide suspension with a mass concentration of 4 g / L. A certain amount of ammonia solution was added, the pH was adjusted to 7, and the mixture was stirred evenly to obtain a graphene oxide dispersion. The graphene oxide dispersion was homogenized once under a pressure of 50 MPa to achieve monolayer exfoliation to obtain a uniform and stable graphite oxide dispersion. The size of the graphene oxide in the dispersion was 20 μm.

[0151] 2) Preparation of graphene oxide-wrapped aluminum oxide composite thermal conductive filler:

[0152] First, 400g of ammonium aluminum sulfate was weighed and dissolved in 5L of graphene oxide dispersion with a mass concentration of 4g / L, and mechanically stirred until completely dissolved; then, 5g of aluminate coupling agent was added and stirred until dissolved; then, ammonia water was added to adjust the pH to 10, and aluminum ions combined with hydroxide to achieve the nucleation of aluminum oxide particles and in-situ growth on the graphene oxide surface; finally, the mixed system was dried by spray drying method with a spray air pressure of 2MPa and an outlet temperature of 80℃ to obtain a particle size of 20μm and a specific surface area of ​​1.2m 2 / g coupling agent modified graphene oxide wrapped alumina composite thermal conductive filler.

[0153] 3) Preparation of thermal conductive gel:

[0154] First, 0.02g of platinum catalyst was dispersed in 1g of methylchlorophenyl silicone oil and mechanically stirred until uniformly dispersed. Then, 15g of the graphene oxide-encapsulated aluminum oxide composite thermally conductive filler prepared in Step 2 was dispersed in the methylphenyl silicone oil. Stirring was carried out at 2000 rpm to uniformly disperse the thermally conductive filler throughout the methylchlorophenyl silicone oil. Finally, the system was transferred to a planetary mixer, evacuated at 80 rpm, and heated to 200°C for 1 hour to produce a thermally conductive gel. Tests showed that the thermal conductivity of the thermally conductive gel was 3.5 W / (m·K) and the extrusion rate was 13 g / min.

[0155] The properties of the graphene thermally conductive gels prepared in Examples 1 to 12 were compared with those prepared in Comparative Example 1. The thermal conductivity of the thermally conductive gel prepared in Example 4 reached 12 W / (m·K), significantly higher than the 5 W / (m·K) in Comparative Example 1. Furthermore, the extrusion rates of most examples exceeded 60 g / min, with the highest reaching 82 g / min.

[0156] The properties of the graphene thermal conductive gels prepared in Examples 1 to 12 were compared with those prepared in Comparative Example 2. The thermal conductivity of the thermal conductive gel prepared in Example 4 can reach 12W / (m·K), which is much higher than the 6W / (m·K) of Comparative Example 2. At the same time, the extrusion rate exceeds 60g / min, which is much higher than the 5g / min of Comparative Example 2. The main difference between Comparative Example 2 and the embodiment is that freeze drying is used instead of spray drying. The freeze drying method is to freeze the system into a solid, and then the sublimation principle of ice under low pressure is used to perfectly retain the two-dimensional layer structure of graphene. Therefore, the specific surface area of ​​the alumina-loaded graphene oxide composite filler obtained in Comparative Example 2 is as high as 155m 2 / g, much higher than 5.1m / g in Example 4 2 / g, such a high specific surface area is dispersed in methylphenyl silicone oil, and the methylphenyl silicone oil will quickly adsorb on the large area of ​​graphene surface, making it difficult for the silicone oil to evenly wet all the fillers and form a uniform and highly extrudable thermal conductive gel.

[0157] The properties of the graphene thermal conductive gels prepared in Examples 1 to 12 were compared with those prepared in Comparative Example 3. The thermal conductivity of the thermal conductive gel prepared in Example 4 can reach 12W / (m·K), which is much higher than the 7W / (m·K) of Comparative Example 3. At the same time, the extrusion rate exceeds 60g / min, which is much higher than the 13g / min of Comparative Example 3. The main difference between Comparative Example 3 and the embodiment is that commercial micron alumina is used. The density of alumina is as high as 3.96g / mL. It is difficult to evenly disperse it in the dispersion of graphene oxide by mechanical stirring, so it is difficult to evenly disperse it on the surface of graphene oxide. In the composite filler obtained by spray drying, most of the alumina particles are not compounded with graphene. Graphene oxide is wrapped and dried into a sphere alone. Alumina is dried into a powder in its initial state. Therefore, the specific surface area of ​​the composite filler is still as high as 63m 2 / g, which makes it difficult for silicone oil to evenly wet all the fillers and form a uniform and highly extrudable thermal conductive gel.

[0158] The properties of the graphene thermally conductive gels prepared in Examples 1 to 12 were compared with those prepared in Comparative Example 4. The thermal conductivity of the thermally conductive gel prepared in Example 4 reached 12 W / (m·K), significantly higher than the 3 W / (m·K) of Comparative Example 4. Furthermore, the extrusion rate exceeded 60 g / min, significantly higher than the 11 g / min of Comparative Example 4. The main difference between Comparative Example 4 and the examples is that the composite thermally conductive filler was not modified with a coupling agent. As a result, during the preparation of the thermally conductive gel, the graphene-encapsulated alumina thermally conductive filler had poor compatibility with the silicone oil, making it difficult to evenly disperse in the silicone oil. Consequently, it was difficult to form a thermally conductive network structure, resulting in lower thermal conductivity and extrusion rate.

[0159] The properties of the graphene thermal conductive gels prepared in Examples 1 to 12 were compared with those prepared in Comparative Example 5. The thermal conductivity of the thermal conductive gel prepared in Example 4 can reach 12W / (m·K), which is much higher than the 4.1W / (m·K) of Comparative Example 5. At the same time, the extrusion rate exceeds 60g / min, which is much higher than the 26g / min of Comparative Example 5. The main difference between Comparative Example 5 and the embodiment is that the silane coupling agent is added during the preparation of the thermal conductive gel and is added to the silicone oil matrix at the same time as the thermal conductive filler, without the thermal conductive filler being specifically modified beforehand. The coupling agent modification requires a certain temperature to react, while the mixing process of the thermal conductive filler and the silicone oil is carried out at room temperature. Therefore, it is difficult for the coupling agent to be effectively grafted onto the surface of the thermal conductive filler, resulting in poor compatibility between the thermal conductive filler and the silicone oil, making it difficult to evenly disperse in the silicone oil. Therefore, it is difficult to form a thermal conductive network structure, the thermal conductivity is low, and the extrusion rate is also low.

[0160] The properties of the graphene thermal conductive gels prepared in Examples 1 to 12 were compared with those prepared in Comparative Example 6. The thermal conductivity of the thermal conductive gel prepared in Example 4 can reach 12W / (m·K), which is much higher than the 3.5W / (m·K) of Comparative Example 6. At the same time, the extrusion rate exceeds 60g / min, which is much higher than the 13g / min of Comparative Example 6. The main difference between Comparative Example 6 and the embodiment is that the silane coupling agent is added before the formation of alumina. The modification of the coupling agent requires a certain temperature to react. The subsequent preparation of aluminum oxide and graphene wrapping process does not involve a high-temperature process. Moreover, in the subsequent drying process, the coupling agent is partially adsorbed on the surface of alumina, but not completely adsorbed on the surface of graphene. Therefore, it is difficult for the coupling agent to be effectively grafted onto the surface of graphene, resulting in poor compatibility between the thermal conductive filler and silicone oil, making it difficult to evenly disperse in the silicone oil. Therefore, it is difficult to form a thermal conductive network structure, the thermal conductivity is low, and the extrusion rate is also low.

Claims

1. A composite thermally conductive filler, characterized in that: The composite thermal conductive filler is a composite thermal conductive filler of aluminum oxide wrapped in graphene oxide, wherein aluminum oxide is in-situ grown on the surface of graphene oxide, and the composite thermal conductive filler is microspheres of the composite thermal conductive filler of aluminum oxide wrapped in graphene oxide.

2. The composite thermally conductive filler according to claim 1, characterized in that: The aluminum oxide is in-situ grown on the inner surface of the graphene oxide.

3. The composite thermally conductive filler according to claim 1, characterized in that: The microspheres have a diameter of 5 to 20 μm and a specific surface area of ​​1 to 5.1 m 2 / g.

4. The composite thermally conductive filler according to any one of claims 1 to 3, characterized in that: The graphene oxide is coupling agent modified graphene.

5. The composite thermally conductive filler according to claim 4, characterized in that: The coupling agent is γ-aminopropyltriethoxysilane, a borate coupling agent, a titanate coupling agent or an aluminate coupling agent.

6. A method for preparing the composite thermally conductive filler according to any one of claims 1 to 5, characterized in that: include: 1) Preparation of graphene oxide dispersion: The graphite oxide is dispersed in deionized water, and the pH is adjusted to between 4 and 7 to prepare a graphite oxide suspension with a mass concentration of 1 to 20 g / L. The graphite oxide suspension is exfoliated by a high-pressure homogenizer, and homogenized at a pressure of 30 to 80 MPa to achieve monolayer exfoliation and a uniform and stable graphene oxide dispersion with a size of 5 to 20 μm. 2) Preparation of graphene oxide wrapped aluminum oxide composite thermal conductive filler: The aluminum salt is dissolved in the graphene oxide dispersion, wherein the amount of the aluminum salt is 2 to 15 times the mass of the graphene oxide in terms of aluminum; the pH of the system is adjusted to between 8 and 12, and aluminum oxide particles are nucleated and in situ grown on the surface of the graphene oxide; spray drying is performed to obtain a graphene oxide dispersion having a size of 5 to 20 μm and a specific surface area of ​​1 to 5 m 2 / g of graphene oxide wrapped with aluminum oxide composite thermal conductive filler.

7. The method of claim 6, characterized in that In step 1), the pH is adjusted to between 6 and 7, and a graphite oxide suspension having a mass concentration of 5 to 10 g / L is prepared and homogenized under a pressure of 40 to 60 MPa.

8. The method of claim 6, characterized in that The aluminum salt is one of aluminum chloride, aluminum nitrate, aluminum sulfate, ammonium aluminum sulfate and sodium metaaluminate.

9. The method of claim 6, characterized in that In step 2), before spray drying, a coupling agent is added according to a mass ratio of the coupling agent to the graphene oxide of 1:5 to 1, and the reaction is carried out at 40 to 100° C. for 0.5 to 10 hours.

10. The method according to claim 9, characterized in that The coupling agent is γ-aminopropyltriethoxysilane, a borate coupling agent, a titanate coupling agent or an aluminate coupling agent.

11. The method of claim 6, characterized in that In step 2), the spray drying spray air pressure ranges from 2 to 20 MPa, and the outlet temperature ranges from 80 to 110°C.

12. A graphene in-situ modified thermally conductive gel, characterized in that: Contains the composite thermally conductive filler according to any one of claims 1 to 5.

13. A method for preparing the graphene in-situ modified thermally conductive gel according to claim 12, comprising: The platinum catalyst is dispersed in the silicone oil matrix, and the thermal conductive filler is dispersed in the silicone oil matrix according to a mass ratio of the composite thermal conductive filler to the silicone oil matrix of 10 to 15:1; While maintaining mechanical stirring, the graphene oxide is heated, sulfurized, cross-linked and reduced under vacuum conditions.

14. The method of claim 13, characterized in that The mass percentage of the platinum catalyst and the silicone oil is 0.1-2.0%.

15. An electronic product, characterized in that: The electronic product comprises the graphene in-situ modified thermally conductive gel according to claim 12.