Composite heat-conducting filler, preparation method thereof, heat-conducting silicone rubber, preparation method thereof and application of heat-conducting silicone rubber

Abstract

The application discloses a kind of composite heat-conducting filler and preparation method thereof, heat-conducting silicone rubber and preparation method thereof and application of heat-conducting silicone rubber, belong to heat-conducting material technical field, and its technical scheme main point is a kind of composite heat-conducting filler, the heat-conducting filler includes spherical boron nitride, flaky boron nitride, aluminium hydroxide and silane coupling agent, the mass ratio of spherical boron nitride, flaky boron nitride, aluminium hydroxide is (8-12) :(2-4) :(7-10), the addition amount of silane coupling agent is 0.8-3.2% of the total amount of spherical boron nitride, flaky boron nitride, aluminium hydroxide, reaches the filling amount of composite heat-conducting filler provided in the application, high heat-conducting coefficient, good flame-retardant effect, after the filler is applied in silicone rubber, so that silicone rubber has the excellent performance of high heat-conducting, low density, low viscosity, high flame-retardant grade, can quickly and effectively conduct heat generated by heat-dissipating component out, improve the service life of component.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat-conducting materials, in particular to a composite heat-conducting filler, a preparation method thereof, a heat-conducting silicone rubber, a preparation method thereof and application of the heat-conducting silicone rubber. BACKGROUND

[0002] In recent years, electronic products have developed rapidly towards miniaturization and high power, and thus higher requirements have been put forward for the performance of electronic products, especially the performance of heat dissipation, fire prevention and light weight. At present, the problem of heat accumulation exists in electronic products, and a large amount of heat will be generated in a short time during use, so the generated heat must be dissipated in time, otherwise the reliability and service life will be directly affected, and a fire may occur.

[0003] In order to improve the heat conductivity, a large amount of heat-conducting fillers such as aluminum oxide and zinc oxide are added to the traditional heat-conducting silicone rubber, and the fillers have low heat conductivity, poor flame retardant effect and large density, thereby causing the problems of low heat conductivity, low flame retardant grade, high density and high viscosity of the silicone rubber. SUMMARY

[0004] In order to solve the problems in the prior art, the present application provides a composite heat-conducting filler, a preparation method thereof, a heat-conducting silicone rubber, a preparation method thereof and application of the heat-conducting silicone rubber. The composite heat-conducting filler provided by the present application has high filling amount, high heat conductivity and good flame retardant effect. After the filler is applied in the silicone rubber, the silicone rubber has excellent performance of high heat conductivity, low density, low viscosity and high flame retardant grade, and can quickly and effectively conduct the heat generated by the heat dissipation components to improve the service life of the components.

[0005] The first aspect of the present application is to provide a composite heat-conducting filler. The following technical scheme is adopted:

[0006] The composite heat-conducting filler comprises spherical boron nitride, flaky boron nitride, aluminum hydroxide and a silane coupling agent. The mass ratio of the spherical boron nitride, the flaky boron nitride and the aluminum hydroxide is (8-12):(2-4):(7-10), and the addition amount of the silane coupling agent is 0.8-3.2% of the total amount of the spherical boron nitride, the flaky boron nitride and the aluminum hydroxide.

[0007] By adopting the technical scheme, the spherical boron nitride, the flaky boron nitride and the aluminum hydroxide contain hydroxyl groups on the surfaces and belong to hydrophilic substances. In the preparation of the silicone rubber, the compatibility between the fillers and the base rubber is poor, the oil absorption value is high, the filling amount of the fillers is low, the viscosity of the product is high, the thermal conductivity is low, and the like. After the fillers are modified by the silane coupling agent, the methoxy or ethoxy functional groups of the silane coupling agent can be hydrolyzed into hydroxyl groups, and the hydroxyl groups on the surfaces of the fillers can be reacted to make the fillers become hydrophobic substances with hydrophobicity. The modified fillers and the base rubber have good compatibility, the oil absorption value is low, the filling amount of the fillers can be significantly increased, the viscosity of the prepared silicone rubber is low, the thermal conductivity is high, the flame retardant grade is high, and the like.

[0008] Preferably, the particle size of the spherical boron nitride is 40-70 μm, the particle size of the flaky boron nitride is 0.8-3.2 μm, and the particle size of the aluminum hydroxide is 13-22 μm.

[0009] By adopting the technical scheme, the spherical boron nitride has a significant effect on improving the thermal conductivity of the fillers. However, due to the gaps between the fillers, the contact between the filler particles is not close enough, thereby reducing the thermal conduction effect. By adding the flaky boron nitride with a small particle size, the contact between the filler particles is more close, and the thermal conductivity can be significantly improved. The addition of the aluminum hydroxide can not only improve the flame retardant effect of the fillers, but also make the contact between the three fillers with different particle sizes more close and the viscosity lower, so that the overall addition amount of the fillers can be increased, and the thermal conductivity can be improved.

[0010] The second aspect of the application provides a preparation method of the composite thermal conductive filler, which comprises the following steps:

[0011] S1, the spherical boron nitride, the flaky boron nitride and the aluminum hydroxide are stirred and mixed to obtain a mixture;

[0012] S2, the silane coupling agent is added to the mixture obtained in step S1, and the mixture is stirred and reacted at a temperature of 90-130 ℃ for 50-120 min to obtain the composite thermal conductive filler.

[0013] By adopting the technical scheme, when the reaction temperature of the silane coupling agent and the fillers is too low, the reaction degree of the hydroxyl groups of the silane coupling agent and the hydroxyl groups on the surfaces of the fillers is not enough, and the modification effect is weakened. However, when the reaction temperature is too high, the silane coupling agent is easy to volatilize, which also leads to the weakening of the modification effect. Therefore, when the reaction temperature of the silane coupling agent and the fillers is limited to 90-130 ℃, the modification effect of the silane coupling agent on the fillers can be effectively improved.

[0014] The third aspect of the present application provides a heat-conducting silicone rubber, comprising, by weight parts, 100 parts of base glue, 10-50 parts of diluent, 0.3-3.2 parts of crosslinking agent, 0.3-3.2 parts of catalyst, and 800-1500 parts of the composite heat-conducting filler obtained by any one of claims 1-2.

[0015] Preferably, the base glue is one or both of alkoxysilicone oil and hydroxysilicone oil.

[0016] Preferably, the diluent is one or both of dimethyl silicone oil and MDT type silicone oil.

[0017] Preferably, the crosslinking agent is one or more of methyltrimethoxysilane, methyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, propyltrimethoxysilane, and propyltriethoxysilane.

[0018] Preferably, the catalyst is one or more of dibutyltin dilaurate, dibutyltin diacetate, diisopropyl titanate di(acetylacetate), tetrabutyl titanate, and di(acetylacetone)-1,3-propyldioxy titanium.

[0019] The fourth aspect of the present application provides a preparation method of heat-conducting silicone rubber, comprising the following steps:

[0020] S1, vacuum stirring the base glue, the diluent, and the composite heat-conducting filler at 90-130℃ for 40-130min to obtain a mixture; S2, adding the crosslinking agent and the catalyst to the mixture obtained in step S1 after cooling to room temperature, and stirring and mixing under vacuum for 50-130min to obtain the heat-conducting silicone rubber.

[0021] The fifth aspect of the present application provides an application of the heat-conducting silicone rubber in the field of electronic appliances and power adapters.

[0022] In summary, the present application has the following beneficial effects:

[0023] 1. This application simultaneously adds spherical boron nitride with a particle size of 40-70 μm, flake boron nitride with a particle size of 0.8-3.2 μm, and aluminum hydroxide with a particle size of 13-22 μm. This allows the spherical fillers to make point-to-point contact with each other, and the flake fillers to make surface and point contact with the spherical fillers. Furthermore, when the mass ratio of spherical boron nitride, flake boron nitride, and aluminum hydroxide is limited to the range of (8-12):(2-4):(7-10), more contact points are generated between the fillers, resulting in a higher filler content and effectively improving the thermal conductivity of the filler. At the same time, the large difference in particle size between spherical boron nitride and flake boron nitride, along with the addition of aluminum hydroxide with a suitable particle size, can make the contact between the filler particles even tighter. Under the combined effect of the three, the viscosity is lower, thereby increasing the overall filler content and thus improving the thermal conductivity.

[0024] 2. In this application, spherical boron nitride, plate boron nitride, and aluminum hydroxide are modified with silane coupling agents, resulting in hydrophobicity and low oil absorption. Simultaneously, the modified fillers exhibit good compatibility with the base rubber in silicone rubber, leading to low viscosity after mixing. This reduces the amount of crosslinking agent and catalyst required, while increasing the overall filler content. Consequently, the prepared silicone rubber exhibits excellent properties such as high thermal conductivity, low density, low viscosity, and high flame retardancy, improving the service life and operating efficiency of components. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to the embodiments.

[0026] All raw materials used in this application are commercially available.

[0027] Example 1

[0028] A method for preparing a composite thermally conductive filler includes the following steps:

[0029] S1. Spherical boron nitride with a particle size of 40 μm, flake boron nitride with a particle size of 0.8 μm, and aluminum hydroxide with a particle size of 13 μm are added to a high-speed mixer in a weight ratio of 8:2:7 and stirred for 20 min at a stirring speed of 110 r / min to obtain a mixture.

[0030] S2. Add 0.8% of decyltrimethoxysilane, which accounts for the total weight of spherical boron nitride, plate boron nitride and aluminum hydroxide, to the mixture obtained in step S1, and stir the mixture at 500 r / min for 120 min at a temperature of 90℃ to obtain a composite thermally conductive filler.

[0031] Example 2

[0032] A preparation method of a composite heat-conducting filler, comprising the following steps:

[0033] S1, spherical boron nitride with a particle size of 40 μm, flaky boron nitride with a particle size of 0.8 μm, and aluminum hydroxide with a particle size of 13 μm are added into a high-speed mixer at a weight ratio of 10:3:8, and stirred and mixed at a stirring speed of 100 r / min for 15 min to obtain a mixture;

[0034] S2, 1.5% of propyl triethoxysilane based on the total weight of the spherical boron nitride, the flaky boron nitride, and the aluminum hydroxide is added into the mixture obtained in step S1, and stirred and reacted at a speed of 500 r / min at a temperature of 110°C for 90 min to obtain the composite heat-conducting filler.

[0035] Example 3

[0036] A preparation method of a composite heat-conducting filler, comprising the following steps:

[0037] S1, spherical boron nitride with a particle size of 40 μm, flaky boron nitride with a particle size of 0.8 μm, and aluminum hydroxide with a particle size of 13 μm are added into a high-speed mixer at a weight ratio of 10:3:8, and stirred and mixed at a stirring speed of 100 r / min for 15 min to obtain a mixture;

[0038] S2, 1.5% of propyl triethoxysilane based on the total weight of the spherical boron nitride, the flaky boron nitride, and the aluminum hydroxide is added into the mixture obtained in step S1, and stirred and reacted at a speed of 500 r / min at a temperature of 110°C for 90 min to obtain the composite heat-conducting filler.

[0039] Example 4

[0040] A preparation method of a composite heat-conducting filler, which is different from that of example 2 in that the particle sizes of the fillers are different, specifically, the particle size of the spherical boron nitride is 50 μm, the particle size of the flaky boron nitride is 2.5 μm, and the particle size of the aluminum hydroxide is 18 μm, and the others are the same as those of example 2.

[0041] Example 5

[0042] A preparation method of a composite heat-conducting filler, which is different from that of example 2 in that the particle sizes of the fillers are different, specifically, the particle size of the spherical boron nitride is 70 μm, the particle size of the flaky boron nitride is 3.2 μm, and the particle size of the aluminum hydroxide is 22 μm, and the others are the same as those of example 2.

[0043] Example 6

[0044] A preparation method of the composite heat-conducting filler, different from example 2 is that the particle size of the filler is different, specifically: the particle size of the spherical boron nitride is 30 μm, the particle size of the flaky boron nitride is 0.5 μm, the particle size of the aluminum hydroxide is 10 μm, and the others are the same as example 2.

[0045] Example 7

[0046] A preparation method of the composite heat-conducting filler, different from example 2 is that the particle size of the filler is different, specifically: the particle size of the spherical boron nitride is 75 μm, the particle size of the flaky boron nitride is 3.5 μm, the particle size of the aluminum hydroxide is 25 μm, and the others are the same as example 2.

[0047] Comparative example 1

[0048] A preparation method of the composite heat-conducting filler, different from example 2 is that the particle size of the filler is different, specifically: the particle size of the spherical boron nitride is 75 μm, the particle size of the flaky boron nitride is 3.5 μm, the particle size of the aluminum hydroxide is 25 μm, and the others are the same as example 2.

[0049] Comparative example 2

[0050] A preparation method of the composite heat-conducting filler, different from example 2 is that the particle size of the filler is different, specifically: the particle size of the spherical boron nitride is 75 μm, the particle size of the flaky boron nitride is 3.5 μm, the particle size of the aluminum hydroxide is 25 μm, and the others are the same as example 2.

[0051] Comparative example 3

[0052] A preparation method of the composite heat-conducting filler, different from example 2 is that the particle size of the filler is different, specifically: the particle size of the spherical boron nitride is 75 μm, the particle size of the flaky boron nitride is 3.5 μm, the particle size of the aluminum hydroxide is 25 μm, and the others are the same as example 2.

[0053] Comparative example 4

[0054] A preparation method of the composite heat-conducting filler, different from example 2 is that the particle size of the filler is different, specifically: the particle size of the spherical boron nitride is 75 μm, the particle size of the flaky boron nitride is 3.5 μm, the particle size of the aluminum hydroxide is 25 μm, and the others are the same as example 2.

[0055] Comparative example 5

[0056] A preparation method of the composite heat-conducting filler, different from example 2 is that the particle size of the filler is different, specifically: the particle size of the spherical boron nitride is 75 μm, the particle size of the flaky boron nitride is 3.5 μm, the particle size of the aluminum hydroxide is 25 μm, and the others are the same as example 2.

[0057] Comparative example 6

[0058] A preparation method of the composite heat-conducting filler, different from example 2 is that the particle size of the filler is different, specifically: the particle size of the spherical boron nitride is 75 μm, the particle size of the flaky boron nitride is 3.5 μm, the particle size of the aluminum hydroxide is 25 μm, and the others are the same as example 2.

[0059] The composite heat-conductive filler obtained in the above Examples 1-7 and Comparative Examples 1-6 is applied to heat-conductive silicone rubber, wherein the crosslinking agent in the heat-conductive silicone rubber can be one or more of methyltrimethoxysilane, methyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, propyltrimethoxysilane, and propyltriethoxysilane, and the effects achieved are basically the same. In the application examples, methyltrimethoxysilane is used as an example;

[0060] The catalyst can be one or more of dibutyltin dilaurate, dibutyltin diacetate, diisopropyl titanate di(acetylacetate), tetrabutyl titanate, and diisopropyl titanate di(acetylacetone-1,3-propyldioxy), and the effects achieved are basically the same. In the application examples, diisopropyl titanate di(acetylacetate) is used as an example. Specifically as follows: Application Example 1

[0061] A preparation method of heat-conductive silicone rubber, comprising the following steps:

[0062] S1, 100 kg of alkoxy silicone oil, 10 kg of dimethyl silicone oil, and 800 kg of the composite heat-conductive filler obtained in Example 1 are added into a kneader, and vacuum stirring is performed at a vacuum degree of -0.1 MPa and a temperature of 90°C for 130 min to obtain a mixture;

[0063] S2, the mixture obtained in step S1 is cooled to room temperature, and then 0.3 kg of methyltrimethoxysilane and 0.3 kg of diisopropyl titanate di(acetylacetate) are added. Stirring and mixing are performed at a vacuum degree of -0.095 MPa, a stirring speed of 60 r / min, and a dispersing speed of 200 r / min for 130 min, and then the heat-conductive silicone rubber is discharged under the protection of inert gas.

[0064] Application Example 2

[0065] A preparation method of heat-conductive silicone rubber, comprising the following steps:

[0066] S1, 100 kg of alkoxy silicone oil, 10 kg of dimethyl silicone oil, and 800 kg of the composite heat-conductive filler obtained in Example 1 are added into a kneader, and vacuum stirring is performed at a vacuum degree of -0.1 MPa and a temperature of 90°C for 130 min to obtain a mixture;

[0067] S2, the mixture obtained in step S1 is cooled to room temperature, and then 0.3 kg of methyltrimethoxysilane and 0.3 kg of diisopropyl titanate di(acetylacetate) are added. Stirring and mixing are performed at a vacuum degree of -0.095 MPa, a stirring speed of 60 r / min, and a dispersing speed of 200 r / min for 130 min, and then the heat-conductive silicone rubber is discharged under the protection of inert gas.

[0068] Application Example 3

[0069] A preparation method of a heat conductive silicone rubber, comprising the following steps:

[0070] S1, 100 kg of alkoxysilicone oil, 50 kg of dimethyl silicone oil, and 1500 kg of the composite heat conductive filler obtained in Example 1 are added into a kneader, and vacuum stirring is performed at a vacuum degree of -0.1 MPa and a temperature of 130°C for 40 min to obtain a mixture;

[0071] S2, the mixture obtained in step S1 is cooled to room temperature, and 3.2 kg of methyltrimethoxysilane and 3.2 kg of titanium diisopropyl di(acetoacetate) ethyl ester are added, and stirring and mixing are performed at a vacuum degree of -0.095 MPa, a stirring speed of 60 r / min, and a dispersing speed of 230 r / min for 50 min, and then the product is discharged under the protection of inert gas to obtain the heat conductive silicone rubber.

[0072] Application Example 4

[0073] A preparation method of a heat conductive silicone rubber, which is different from that of Application Example 2 in that the composite heat conductive filler is the composite heat conductive filler obtained in Example 2, and the others are the same as those of Application Example 2.

[0074] Application Example 5

[0075] A preparation method of a heat conductive silicone rubber, which is different from that of Application Example 2 in that the composite heat conductive filler is the composite heat conductive filler obtained in Example 3, and the others are the same as those of Application Example 2.

[0076] Application Example 6

[0077] A preparation method of a heat conductive silicone rubber, which is different from that of Application Example 2 in that the composite heat conductive filler is the composite heat conductive filler obtained in Example 4, and the others are the same as those of Application Example 2.

[0078] Application Example 7

[0079] A preparation method of a heat conductive silicone rubber, which is different from that of Application Example 2 in that the composite heat conductive filler is the composite heat conductive filler obtained in Example 5, and the others are the same as those of Application Example 2.

[0080] Application Example 8

[0081] A preparation method of a heat conductive silicone rubber, which is different from that of Application Example 2 in that the composite heat conductive filler is the composite heat conductive filler obtained in Example 6, and the others are the same as those of Application Example 2.

[0082] Application Example 9

[0083] A preparation method of the heat conductive silicone rubber, wherein the difference from the application example 2 is that the composite heat conductive filler is the composite heat conductive filler obtained in the example 7, and the others are the same as the application example 2.

[0084] Application Comparative Example 1

[0085] A preparation method of the heat conductive silicone rubber, wherein the difference from the application example 2 is that the composite heat conductive filler is the composite heat conductive filler obtained in the application comparative example 1, and the others are the same as the application example 2.

[0086] Application Comparative Example 2

[0087] A preparation method of the heat conductive silicone rubber, wherein the difference from the application example 2 is that the composite heat conductive filler is the composite heat conductive filler obtained in the application comparative example 2, and the others are the same as the application example 2.

[0088] Application Comparative Example 3

[0089] A preparation method of the heat conductive silicone rubber, wherein the difference from the application example 2 is that the composite heat conductive filler is the composite heat conductive filler obtained in the application comparative example 3, and the others are the same as the application example 2.

[0090] Application Comparative Example 4

[0091] A preparation method of the heat conductive silicone rubber, wherein the difference from the application example 2 is that the composite heat conductive filler is the composite heat conductive filler obtained in the application comparative example 4, and the others are the same as the application example 2.

[0092] Application Comparative Example 5

[0093] A preparation method of the heat conductive silicone rubber, wherein the difference from the application example 2 is that the composite heat conductive filler is the composite heat conductive filler obtained in the application comparative example 5, and the others are the same as the application example 2.

[0094] Application Comparative Example 6

[0095] A preparation method of the heat conductive silicone rubber, wherein the difference from the application example 2 is that the composite heat conductive filler is the composite heat conductive filler obtained in the application comparative example 6, and the others are the same as the application example 2.

[0096] Control Example

[0097] A preparation method of the heat conductive silicone rubber, wherein the difference from the application example 2 is that the composite heat conductive filler is composed of aluminum oxide and zinc oxide, and the weight ratio of the aluminum oxide to the zinc oxide is 1:1, and the others are the same as the application example 2.

[0098] Performance test:

[0099] The thermal conductive silicone rubber obtained from the above application examples and application comparative examples was tested for viscosity, density, thermal conductivity, tensile strength, flame retardant grade, and the test results are shown in Table 1, wherein the viscosity was tested according to GB / T2794-2013; the density was tested according to GB / T13354-1992; the thermal conductivity was tested according to ISO / DIS22007; the tensile strength was tested according to ASTM D412; and the flame retardant grade was tested according to UL94.

[0100] Table 1: Test results of silicone rubber

[0101]

[0102]

[0103] As can be seen from Table 1:

[0104] The viscosity of the silicone rubber obtained from the application examples is much lower than that of the silicone rubber in the comparative examples, and the thermal conductivity, tensile strength and flame retardant grade are much higher than those in the comparative examples, indicating that the application of the composite thermal conductive filler obtained in the application to the silicone rubber can effectively reduce the viscosity of the silicone rubber, and at the same time improve the thermal conductivity and flame retardant performance of the silicone rubber.

[0105] In the case where the composite thermal conductive filler is obtained from Example 1, the viscosity of the thermal conductive silicone rubber obtained from application examples 1-3 first decreases and then increases with the increase of the amount of the composite thermal conductive filler, and the thermal conductivity and tensile strength first increase and then decrease, which shows that when the amount of the composite thermal conductive filler is within the range defined in the application, the thermal conductivity and tensile strength of the silicone rubber can be effectively improved, and at the same time the silicone rubber can have a lower viscosity.

[0106] Compared with application example 2, when the particle size of spherical boron nitride, flaky boron nitride and aluminum hydroxide exceeds the range defined in the application, the viscosity of the silicone rubber obtained from application example 8 increases significantly, and the viscosity of the silicone rubber obtained from application example 9 decreases, but the thermal conductivity and tensile strength of the silicone rubber obtained from application examples 8-9 decrease, which shows that when the particle size of spherical boron nitride, flaky boron nitride and aluminum hydroxide is within the range defined in the application, not only can the silicone rubber have a lower viscosity, but also the thermal conductivity and tensile strength of the silicone rubber can be improved.

[0107] Compared with application example 2, the viscosity of the silicone rubber obtained from application comparative examples 1-4 is obviously increased, and the thermal conductivity and tensile strength of the silicone rubber are decreased, when the spherical boron nitride, the flaky boron nitride, the aluminum hydroxide or the silane coupling agent is absent in the composite heat-conductive filler. It can be seen that the spherical boron nitride, the flaky boron nitride, the aluminum hydroxide and the silane coupling agent are used in combination in the present application, which effectively reduces the viscosity of the silicone rubber, and also improves the thermal conductivity and tensile strength of the silicone rubber.

[0108] Compared with application example 2, the viscosity of the silicone rubber obtained from application comparative examples 5-6 is high, the thermal conductivity is low, and the tensile strength is low, when the weight ratio of the spherical boron nitride, the flaky boron nitride and the aluminum hydroxide is not within the range defined in the present application. It can be further illustrated that the weight ratio of the spherical boron nitride, the flaky boron nitride and the aluminum hydroxide has a greater influence on the performance of the silicone rubber.

[0109] The embodiments of the specific implementation are the preferred embodiments of the present application, and do not limit the protection scope of the present application. Therefore, any equivalent changes made according to the structure, shape, principle of the present application should be covered within the protection scope of the present application.

Claims

1. A composite thermally conductive filler, characterized by: The heat-conducting filler comprises spherical boron nitride, flaky boron nitride, aluminum hydroxide and silane coupling agent, the mass ratio of the spherical boron nitride, the flaky boron nitride and the aluminum hydroxide is (8-12):(2-4):(7-10), and the addition amount of the silane coupling agent is 0.8-3.2% of the total amount of the spherical boron nitride, the flaky boron nitride and the aluminum hydroxide. The particle size of the spherical boron nitride is 40-70 μm, the particle size of the flaky boron nitride is 0.8-3.2 μm, and the particle size of the aluminum hydroxide is 13-22 μm.

2. A method of making the composite thermally conductive filler of claim 1, characterized by: The method comprises the following steps: S1, stirring and mixing spherical boron nitride, flaky boron nitride and aluminum hydroxide to obtain a mixture; S2, adding silane coupling agent to the mixture obtained in step S1, and stirring and reacting at a temperature of 90-130 ℃ for 50-120 min to obtain a composite heat-conducting filler.

3. A heat conductive silicone rubber, characterized by: The composite heat-conducting filler obtained in claim 1, 800-1500 parts by weight.

4. A heat conductive silicone rubber according to claim 3, characterized in that: The base glue is one or both of alkoxy silicone oil and hydroxyl silicone oil.

5. A heat conductive silicone rubber according to claim 3, wherein: The diluent is one or both of dimethyl silicone oil and MDT type silicone oil.

6. A heat conductive silicone rubber according to claim 3, wherein: The crosslinking agent is one or more of methyltrimethoxysilane, methyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, propyltrimethoxysilane and propyltriethoxysilane.

7. A heat conductive silicone rubber according to claim 3, wherein: The catalyst is one or more of dibutyltin dilaurate, dibutyltin diacetate, titanium diisopropylate di(acetylacetate), tetrabutyl titanate, titanium diisopropylate 1,3-propylenedioxydi(acetylacetate) and tetraisopropyl titanate.

8. A process for the preparation of a heat conductive silicone rubber according to any one of claims 3 to 7, characterized in that, The method comprises the following steps: S1, stirring and mixing base glue, diluent and composite heat-conducting filler under vacuum at a temperature of 90-130 ℃ for 40-130 min to obtain a mixture; S2, adding crosslinking agent and catalyst to the mixture obtained in step S1 after cooling to room temperature, and stirring and mixing under vacuum for 50-130 min to obtain heat-conducting silicone rubber.

9. Use of the heat-conducting silicone rubber according to any one of claims 3-7 in the field of electronic appliances.

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