Heat-conducting silica gel sheet and preparation process thereof

Abstract

The invention relates to the technical field of heat-conducting materials, in particular to a heat-conducting silica gel sheet and a preparation process thereof, and the heat-conducting silica gel sheet is prepared from the following components in parts by weight: 100 parts of organic silicon rubber; 300-500 parts of a heat conducting filler; 3-8 parts of a curing agent; 1-3 parts of a catalyst; according to the invention, a composite system of silicon carbide particles with a specific crystal structure, surface-modified graphene sheets and nano-diamond particles is used as a heat-conducting filler, and the filler is subjected to accurate proportioning and surface treatment, so that not only is the heat-conducting efficiency greatly improved, but also the internal binding force and heat stability of the material are effectively enhanced; compared with a traditional heat-conducting silica gel sheet, the heat-conducting silica gel sheet can more effectively transfer heat and reduce thermal resistance under the same condition, so that the heat dissipation performance and operation reliability of electronic equipment are improved, and in addition, the heat-conducting silica gel sheet has good mechanical performance and machinability and is easy to adapt to various complex application scenes.

Description

Technical Field

[0001] The invention relates to the technical field of heat-conducting materials, in particular to a heat-conducting silicone sheet and a preparation process thereof. Background Art

[0002] In the prior art, thermally conductive silicone sheets are key materials for heat dissipation of electronic equipment, and their performance is directly related to the stability and service life of the product. Traditional thermally conductive silicone sheets usually use a single thermally conductive filler, such as silicon carbide or graphite. Although these fillers have certain thermal conductivity, it is difficult to simultaneously meet the requirements of high thermal conductivity, good processability and mechanical strength. Therefore, the market is in urgent need of a new type of thermally conductive silicone sheet that can ensure excellent thermal conductivity while taking into account good processability and mechanical properties.

[0003] In order to solve the above problems, researchers began to try to combine different types of thermally conductive fillers in the hope of obtaining better overall performance. However, simply mixing different thermally conductive fillers together is often difficult to achieve the desired effect, because factors such as the compatibility, dispersibility and mutual synergy between different fillers will have an important impact on the performance of the final product. Therefore, how to scientifically and rationally select and combine thermally conductive fillers, and how to achieve synergy between components by optimizing the preparation process, have become technical problems that need to be urgently solved in the field of thermally conductive silicone sheets. Summary of the invention

[0004] Technical issues solved

[0005] In view of the above-mentioned shortcomings of the prior art, the present invention provides a thermally conductive silicone sheet and a preparation process thereof. The present invention adopts a composite system of silicon carbide particles with a specific crystal structure, surface-modified graphene flakes and nano-diamond particles as thermally conductive fillers. These fillers are precisely proportioned and surface-treated, which not only greatly improves the thermal conductivity efficiency, but also effectively enhances the internal bonding force and thermal stability of the material. Compared with traditional thermally conductive silicone sheets, the present invention can transfer heat more effectively and reduce thermal resistance under the same conditions, thereby improving the heat dissipation performance and operating reliability of electronic equipment. In addition, the thermally conductive silicone sheet also has good mechanical properties and processability, and is easy to adapt to various complex application scenarios.

[0006] Technical Solution

[0007] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0008] In one aspect, a thermally conductive silicone sheet is provided, wherein the thermally conductive silicone sheet is composed of the following components in parts by weight:

[0009] 100 parts of silicone rubber;

[0010] 300-500 parts of a thermally conductive filler, wherein the thermally conductive filler is a composite system of silicon carbide particles of a specific crystal structure, surface-modified graphene flakes and nano-diamond particles, wherein the mass ratio of the silicon carbide particles of a specific crystal structure, the surface-modified graphene flakes and the nano-diamond particles is 2-3:1:0.5-1, the silicon carbide particles of a specific crystal structure are hexagonal α-SiC, the average particle size of which is within the range of 5-20 μm, and the sphericity of the particles is between 0.8-0.95, the surface-modified graphene flakes are modified by grafting organic functional groups on the graphene surface, the grafting rate is between 10%-30%, the organic functional groups are organic molecular chains containing one or more of amino, epoxy or vinyl groups, the average thickness of the graphene flakes is between 3-10 nm, the average sheet diameter is between 10-50 μm, and the average particle size of the nano-diamond particles is between 5-50 nm;

[0011] 3-8 parts of curing agent;

[0012] 1-3 parts of catalyst;

[0013] 2-5 parts of a coupling agent, wherein the coupling agent is a silane coupling agent, and the molecular structure of the coupling agent contains one or more of an amino group, an epoxy group or a mercapto group.

[0014] Furthermore, the organic silicone rubber is methyl vinyl silicone rubber, the vinyl content of which is between 0.05% and 0.2%, the molecular weight is between 400,000 and 800,000, and the Mooney viscosity at 25° C. is between 30 and 60.

[0015] Furthermore, the curing agent is an organic peroxide curing agent, including one or a mixture of two or more of dicumyl peroxide and benzoyl peroxide, and when it is a mixture, the mass ratio between the components is between 1:1-1:3.

[0016] Furthermore, the catalyst is a platinum catalyst, and its content in the thermally conductive silicone sheet is between 10-50 ppm in terms of platinum element. The platinum catalyst is one or more of chloroplatinic acid, platinum black, and platinum-vinylsiloxane complex.

[0017] Furthermore, the silane coupling agent is one or more of γ-aminopropyltriethoxysilane, γ-glycidyloxypropyltrimethoxysilane or γ-mercaptopropyltrimethoxysilane.

[0018] On the other hand, a process for preparing the thermally conductive silicone sheet according to any one of claims 1 to 5 comprises the following steps:

[0019] Firstly, the surface-modified graphene flakes, nano-diamond particles and part of the silicone rubber are pre-mixed in an internal mixer at a mixing temperature between 40 and 60° C., a mixing time of 5 to 10 minutes and a rotating speed of 30 to 50 rpm to obtain a premix;

[0020] Then, silicon carbide particles with a specific crystal structure are added to the premix, and a coupling agent is added simultaneously, and the mixing is continued for 10-20 minutes, and the mixing temperature is increased to 60-80°C;

[0021] Then, the remaining silicone rubber, curing agent and catalyst are added and mixed on a double-roll mill at a mixing temperature between 30 and 50° C. for 15 to 30 minutes to obtain a rubber compound;

[0022] Finally, the rubber material is placed in a mold and vulcanized on a flat vulcanizer. The vulcanization temperature is 160-190°C, the vulcanization pressure is 8-15MPa, and the vulcanization time is 15-30 minutes. After the vulcanization is completed, the mold is cooled and demolded to obtain a thermally conductive silicone sheet.

[0023] Furthermore, before pre-mixing the surface-modified graphene flakes, nano-diamond particles and part of the silicone rubber, the surface-modified graphene flakes and nano-diamond particles are first dried in a vacuum drying oven at a drying temperature of 80-120° C., a drying time of 2-4 hours, and a vacuum degree of between -0.08 MPa and -0.1 MPa.

[0024] Furthermore, when the silicon carbide particles with a specific crystal structure are added to the premix, a dispersant is added simultaneously. The dispersant is one or both of zinc stearate and calcium stearate, and the amount of the dispersant added is 0.5%-2% of the mass of the silicon carbide particles with a specific crystal structure.

[0025] Furthermore, the inner surface of the mold is polished, and the surface roughness is between Ra0.8-Ra1.6, and the material of the mold is stainless steel or aluminum alloy, and the thickness tolerance of the mold is between ±0.05-±0.2mm.

[0026] Furthermore, during the vulcanization molding process, a segmented vulcanization process is adopted, first vulcanizing at 160-170°C for 10-15 minutes, then heating to 180-190°C, and continuing to vulcanize for 5-15 minutes. During the vulcanization process, the mold is vacuumed, and the vacuum degree is between -0.05MPa and -0.09MPa.

[0027] Beneficial Effects

[0028] Compared with the known public technology, the technical solution provided by the present invention has the following advantages:

[0029] Beneficial effects:

[0030] 1. The present invention significantly improves thermal conductivity by carefully selecting and combining silicon carbide particles with a specific crystal structure, surface-modified graphene flakes and nano-diamond particles as thermal conductive fillers. The hexagonal α-SiC has excellent thermal conductivity and stability. Its specific particle size and sphericity ensure the uniform distribution of the filler in the silica gel matrix, effectively reducing obstacles on the heat conduction path. At the same time, the surface-modified graphene flakes not only enhance the compatibility with the silica gel matrix by grafting organic functional groups, but also greatly improve the thermal conduction efficiency. The nano-diamond particles further strengthen the thermal conduction network with their extremely high thermal conductivity and unique nanoscale effect. In addition, with the optimized curing agent, catalyst and coupling agent system, the present invention successfully achieves the synergistic effect between the components, so that the thermal conductive silicone sheet shows excellent thermal conductivity and thermal stability while maintaining good processing performance, which is of great significance for improving the heat dissipation efficiency and extending the service life of electronic products.

[0031] 2. The present invention realizes uniform dispersion of thermally conductive fillers and sufficient cross-linking of the silica gel matrix through the steps of pre-mixing, adding thermally conductive fillers and coupling agents, re-mixing and vulcanization molding, thereby preparing a thermally conductive silica gel sheet with excellent thermal conductivity and mechanical properties. In particular, in the preparation process, vacuum drying treatment, segmented vulcanization process and polishing treatment of the inner surface of the mold are adopted to effectively eliminate defects and bubbles inside the material and improve the density and flatness of the product. In addition, the present invention further improves the comprehensive performance of the thermally conductive silica gel sheet by strictly controlling the quality and ratio of raw materials and optimizing the performance parameters of production equipment. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] The present invention will be further described below in conjunction with the embodiments.

[0034] Embodiment 1:

[0035] Raw materials preparation:

[0036] Silicone rubber: Methyl vinyl silicone rubber is selected, with a vinyl content of 0.1%, a molecular weight of 600,000, and a Mooney viscosity of 45 at 25°C.

[0037] Thermally conductive filler:

[0038] Silicon carbide particles with a specific crystal structure: hexagonal α-SiC is selected, the average particle size is 12 μm, the sphericity of the particles is 0.9, and the mass is 360 parts.

[0039] Surface-modified graphene flakes: Graphene surfaces are modified by grafting organic molecular chains containing amino groups and epoxy groups, with a grafting rate of 20%, an average thickness of 6 nm, an average flake diameter of 30 μm, and a mass of 120 parts.

[0040] Nano diamond particles: average particle size is 25 nm, mass is 60 parts.

[0041] Curing agent: A mixture of dicumyl peroxide and benzoyl peroxide is used, with a mass ratio of 1:2 and a total mass of 5 parts.

[0042] Catalyst: Chloroplatinic acid was selected, and its content in the thermally conductive silicone sheet was 30 ppm based on the platinum element, with a mass of 2 parts.

[0043] Coupling agent: a mixture of γ-aminopropyltriethoxysilane and γ-glycidyloxypropyltrimethoxysilane, with a mass ratio of 1:1 and a total mass of 3 parts.

[0044] Preparation process:

[0045] The surface-modified graphene flakes and nano-diamond particles were dried in a vacuum drying oven at a drying temperature of 100° C., a drying time of 3 hours, and a vacuum degree of -0.09 MPa.

[0046] The dried surface-modified graphene flakes and 60 parts of silicone rubber were premixed in an internal mixer at a mixing temperature of 50° C., a mixing time of 8 minutes, and a rotation speed of 40 rpm to obtain a premix.

[0047] Add silicon carbide particles with a specific crystal structure to the premix, add a coupling agent simultaneously, and add zinc stearate as a dispersant in an amount of 1% of the mass of the silicon carbide particles with a specific crystal structure. Continue kneading for 15 minutes, and raise the kneading temperature to 70°C.

[0048] The remaining 40 parts of silicone rubber, curing agent and catalyst were added and mixed on a double-roll mill at a mixing temperature of 40° C. for 20 minutes to obtain a rubber compound.

[0049] The rubber material is placed in a mold with a polished inner surface (surface roughness is Ra1.2), made of stainless steel and with a thickness tolerance of ±0.1mm, and vulcanized on a flat vulcanizer. A segmented vulcanization process is adopted. It is first vulcanized at 165°C for 12 minutes, then heated to 185°C and continued to vulcanize for 8 minutes. During the vulcanization process, the mold is vacuumed with a vacuum degree of -0.07MPa, a vulcanization pressure of 12MPa, and a vulcanization time of 20 minutes. After the vulcanization is completed, it is cooled and demolded to obtain a thermally conductive silicone sheet.

[0050] Embodiment 2:

[0051] Raw materials preparation:

[0052] Silicone rubber: methyl vinyl silicone rubber, vinyl content is 0.08%, molecular weight is 500,000, Mooney viscosity is 40 at 25°C.

[0053] Thermally conductive filler:

[0054] Silicon carbide particles with a specific crystal structure: hexagonal α-SiC, with an average particle size of 8 μm, a sphericity of 0.85, and a mass of 320 parts.

[0055] Surface-modified graphene flakes: modified by grafting organic molecular chains containing vinyl groups, with a grafting rate of 15%, an average thickness of 4 nm, an average flake diameter of 20 μm, and a mass of 100 parts.

[0056] Nano diamond particles: average particle size is 15 nm, mass is 50 parts.

[0057] Curing agent: benzoyl peroxide, mass 4 parts.

[0058] Catalyst: platinum-vinylsiloxane complex, calculated as platinum element, content of 20 ppm, mass of 1.5 parts.

[0059] Coupling agent: γ-mercaptopropyltrimethoxysilane, 2.5 parts by weight.

[0060] Preparation process:

[0061] The surface-modified graphene flakes and nano-diamond particles were dried in a vacuum drying oven at a temperature of 90° C. for 3.5 hours and a vacuum degree of −0.085 MPa.

[0062] The dried surface-modified graphene flakes and 50 parts of silicone rubber were premixed in an internal mixer at a mixing temperature of 45° C., a mixing time of 9 minutes, and a rotation speed of 35 rpm to obtain a premix.

[0063] Silicon carbide particles with a specific crystal structure are added to the premix, and a coupling agent and calcium stearate (the amount added is 1.2% of the mass of the silicon carbide particles) are added simultaneously, and kneaded for 18 minutes, and the temperature is raised to 75°C.

[0064] The remaining 50 parts of the organosilicon rubber, curing agent and catalyst were added and mixed on a double-roll mill at a temperature of 35° C. for 25 minutes to obtain a rubber compound.

[0065] The rubber material was placed in a polished (surface roughness Ra1.0) aluminum alloy mold (thickness tolerance ±0.15mm) and vulcanized on a flat vulcanizer. It was first vulcanized at 160°C for 13 minutes, then heated to 180°C for 10 minutes, with a vacuum degree of -0.06MPa, a pressure of 10MPa, a vulcanization time of 25 minutes, and cooled and demolded to obtain a thermally conductive silicone sheet.

[0066] Embodiment three:

[0067] Raw materials preparation:

[0068] Silicone rubber: methyl vinyl silicone rubber, vinyl content is 0.15%, molecular weight is 700,000, Mooney viscosity is 50 at 25°C.

[0069] Thermally conductive filler:

[0070] Silicon carbide particles with a specific crystal structure: hexagonal α-SiC, with an average particle size of 15 μm, a sphericity of 0.92, and a mass of 400 parts.

[0071] Surface-modified graphene flakes: modified by grafting organic molecular chains containing amino groups and epoxy groups, with a grafting rate of 25%, an average thickness of 8 nm, an average flake diameter of 40 μm, and a mass of 130 parts.

[0072] Nano diamond particles: average particle size is 35nm, mass is 70 parts.

[0073] Curing agent: mixture of dicumyl peroxide and benzoyl peroxide (mass ratio 1:1.5), mass 6 parts.

[0074] Catalyst: mixture of platinum black and chloroplatinic acid (mass ratio 1:1), with a content of 35 ppm and a mass of 2.5 parts based on the platinum element.

[0075] Coupling agent: a mixture of γ-aminopropyltriethoxysilane and γ-glycidyloxypropyltrimethoxysilane (mass ratio 2:1), with a mass of 4 parts.

[0076] Preparation process:

[0077] The surface-modified graphene flakes and nano-diamond particles were vacuum dried at a temperature of 110° C. for 2.5 hours and a vacuum degree of -0.095 MPa.

[0078] The dried surface-modified graphene flakes and 70 parts of silicone rubber were premixed in an internal mixer at a temperature of 55° C. for 7 minutes at a rotation speed of 45 rpm to obtain a premix.

[0079] Silicon carbide particles with a specific crystal structure are added to the premix, and a coupling agent and zinc stearate (the amount added is 0.8% of the mass of the silicon carbide particles) are added simultaneously, and the mixture is kneaded for 12 minutes, and the temperature is raised to 72°C.

[0080] The remaining 30 parts of the organosilicon rubber, curing agent and catalyst were added and mixed on a double-roll mill at a temperature of 45° C. for 18 minutes to obtain a rubber compound.

[0081] The rubber material was placed in a polished (surface roughness Ra1.4) stainless steel mold (thickness tolerance ±0.08mm) and vulcanized on a flat vulcanizer. It was first vulcanized at 168°C for 11 minutes, then heated to 188°C for 7 minutes, with a vacuum degree of -0.08MPa, a pressure of 13MPa, a vulcanization time of 18 minutes, and cooled and demolded to obtain a thermally conductive silicone sheet.

[0082] Comparative Example 1:

[0083] Raw materials preparation:

[0084] Silicone rubber: methyl vinyl silicone rubber, vinyl content is 0.1%, molecular weight is 600,000, Mooney viscosity is 45 at 25°C.

[0085] Thermally conductive filler:

[0086] Silicon carbide particles: Silicon carbide particles with a non-specific crystal structure were selected, with an average particle size of 12 μm and a mass of 360 parts.

[0087] Graphene flakes: no surface modification, average thickness of 6 nm, average flake diameter of 30 μm, mass of 120 parts.

[0088] Nano diamond particles: average particle size is 25 nm, mass is 60 parts.

[0089] Curing agent: a mixture of dicumyl peroxide and benzoyl peroxide, with a mass ratio of 1:2 and a total mass of 5 parts.

[0090] Catalyst: Chloroplatinic acid, calculated as platinum element, the content in the thermally conductive silicone sheet is 30 ppm, and the mass is 2 parts.

[0091] Coupling agent: a mixture of γ-aminopropyltriethoxysilane and γ-glycidyloxypropyltrimethoxysilane, with a mass ratio of 1:1 and a total mass of 3 parts.

[0092] Preparation process:

[0093] The graphene flakes and nano-diamond particles were dried in a vacuum drying oven at a drying temperature of 100° C., a drying time of 3 hours, and a vacuum degree of -0.09 MPa.

[0094] The dried graphene flakes and 60 parts of silicone rubber were premixed in an internal mixer at a mixing temperature of 50° C., a mixing time of 8 minutes, and a rotation speed of 40 rpm to obtain a premix.

[0095] Add silicon carbide particles to the premix, add a coupling agent simultaneously, and add zinc stearate as a dispersant in an amount of 1% of the mass of the silicon carbide particles. Continue kneading for 15 minutes, and raise the kneading temperature to 70°C.

[0096] The remaining 40 parts of silicone rubber, curing agent and catalyst were added and mixed on a double-roll mill at a mixing temperature of 40° C. for 20 minutes to obtain a rubber compound.

[0097] The rubber material is placed in a mold with a polished inner surface (surface roughness is Ra1.2), made of stainless steel and with a thickness tolerance of ±0.1mm, and vulcanized on a flat vulcanizer. A segmented vulcanization process is adopted. It is first vulcanized at 165°C for 12 minutes, then heated to 185°C and continued to vulcanize for 8 minutes. During the vulcanization process, the mold is vacuumed with a vacuum degree of -0.07MPa, a vulcanization pressure of 12MPa, and a vulcanization time of 20 minutes. After the vulcanization is completed, it is cooled and demolded to obtain a thermally conductive silicone sheet.

[0098] Comparative Example 2:

[0099] Raw materials preparation:

[0100] Silicone rubber: methyl vinyl silicone rubber, vinyl content is 0.1%, molecular weight is 600,000, Mooney viscosity is 45 at 25°C.

[0101] Thermally conductive filler:

[0102] Silicon carbide particles with a specific crystal structure: hexagonal α-SiC is selected, with an average particle size of 12 μm, a sphericity of 0.9, and a mass of 540 parts.

[0103] Curing agent: a mixture of dicumyl peroxide and benzoyl peroxide, with a mass ratio of 1:2 and a total mass of 5 parts.

[0104] Catalyst: Chloroplatinic acid, calculated as platinum element, the content in the thermally conductive silicone sheet is 30 ppm, and the mass is 2 parts.

[0105] Coupling agent: a mixture of γ-aminopropyltriethoxysilane and γ-glycidyloxypropyltrimethoxysilane, with a mass ratio of 1:1 and a total mass of 3 parts.

[0106] Preparation process:

[0107] The silicon carbide particles with a specific crystal structure were dried in a vacuum drying oven at a drying temperature of 100° C., a drying time of 3 hours, and a vacuum degree of -0.09 MPa.

[0108] 360 parts of dried silicon carbide particles with a specific crystal structure and 60 parts of silicone rubber were premixed in an internal mixer at a mixing temperature of 50° C., a mixing time of 8 minutes, and a rotation speed of 40 rpm to obtain a premix.

[0109] The remaining 180 parts of silicon carbide particles with a specific crystal structure are added to the premix, and a coupling agent is added simultaneously. Zinc stearate is added as a dispersant in an amount of 1% of the mass of the silicon carbide particles. The mixing is continued for 15 minutes, and the mixing temperature is increased to 70°C.

[0110] The remaining 40 parts of silicone rubber, curing agent and catalyst were added and mixed on a double-roll mill at a mixing temperature of 40° C. for 20 minutes to obtain a rubber compound.

[0111] The rubber material is placed in a mold with a polished inner surface (surface roughness is Ra1.2), made of stainless steel and with a thickness tolerance of ±0.1mm, and vulcanized on a flat vulcanizer. A segmented vulcanization process is adopted. It is first vulcanized at 165°C for 12 minutes, then heated to 185°C and continued to vulcanize for 8 minutes. During the vulcanization process, the mold is vacuumed with a vacuum degree of -0.07MPa, a vulcanization pressure of 12MPa, and a vulcanization time of 20 minutes. After the vulcanization is completed, it is cooled and demolded to obtain a thermally conductive silicone sheet.

[0112] Comparative Example 3:

[0113] Raw materials preparation:

[0114] Silicone rubber: methyl vinyl silicone rubber, vinyl content is 0.1%, molecular weight is 600,000, Mooney viscosity is 45 at 25°C.

[0115] Thermally conductive filler:

[0116] Silicon carbide particles with a specific crystal structure: hexagonal α-SiC is selected, with an average particle size of 12 μm, a sphericity of 0.9, and a mass of 360 parts.

[0117] Surface-modified graphene flakes: Graphene surfaces are modified by grafting organic molecular chains containing amino groups and epoxy groups, with a grafting rate of 20%, an average thickness of 6 nm, an average flake diameter of 30 μm, and a mass of 120 parts.

[0118] Nano diamond particles: average particle size is 25 nm, mass is 60 parts.

[0119] Curing agent: a mixture of dicumyl peroxide and benzoyl peroxide, with a mass ratio of 1:2 and a total mass of 5 parts.

[0120] Catalyst: Chloroplatinic acid, calculated as platinum element, the content in the thermally conductive silicone sheet is 30 ppm, and the mass is 2 parts.

[0121] Coupling agent: a mixture of γ-aminopropyltriethoxysilane and γ-glycidyloxypropyltrimethoxysilane, with a mass ratio of 1:1 and a total mass of 3 parts.

[0122] Preparation process:

[0123] The surface-modified graphene flakes, nano-diamond particles and silicon carbide particles with a specific crystal structure were dried in a vacuum drying oven at a drying temperature of 100° C., a drying time of 3 hours and a vacuum degree of -0.09 MPa.

[0124] The dried surface-modified graphene flakes, nano-diamond particles, silicon carbide particles with a specific crystal structure, and 60 parts of silicone rubber were pre-mixed in an internal mixer at a mixing temperature of 50° C., a mixing time of 8 minutes, and a rotation speed of 40 rpm to obtain a premix.

[0125] The remaining 40 parts of silicone rubber, curing agent and catalyst were added and mixed on a double-roll mill at a mixing temperature of 40° C. for 20 minutes to obtain a rubber compound.

[0126] The rubber material is placed in a mold with a polished inner surface (surface roughness is Ra1.2), made of stainless steel and with a thickness tolerance of ±0.1mm, and vulcanized on a flat vulcanizer. A segmented vulcanization process is adopted. It is first vulcanized at 165°C for 12 minutes, then heated to 185°C and continued to vulcanize for 8 minutes. During the vulcanization process, the mold is vacuumed with a vacuum degree of -0.07MPa, a vulcanization pressure of 12MPa, and a vulcanization time of 20 minutes. After the vulcanization is completed, it is cooled and demolded to obtain a thermally conductive silicone sheet.

[0127] Performance Testing:

[0128] 1. Thermal conductivity test:

[0129] The thermal conductivity of the thermally conductive silicone sheets prepared in Example 1, Example 2, Example 3 and Comparative Example 1, Comparative Example 2, and Comparative Example 3 was tested using a thermal conductivity tester by using a laser flash method. The test results are shown in the following table:

[0130] Sample No. Thermal conductivity (W / m·K) Embodiment 1 3.5 Embodiment 2 3.2 Embodiment 3 3.6 Comparative Example 1 2.5 Comparative Example 2 2.8 Comparative Example 3 3.0

[0131] It can be seen from the test results that the thermal conductivity of the thermally conductive silicone sheets of Example 1, Example 2 and Example 3 is higher than that of Comparative Example 1, Comparative Example 2 and Comparative Example 3. This is because the present invention adopts a composite system of silicon carbide particles with a specific crystal structure, surface-modified graphene flakes and nano-diamond particles as a thermally conductive filler, and the components have a specific mass ratio. At the same time, through a specific preparation process, the thermally conductive filler is more evenly dispersed in the silicone rubber matrix, forming a more effective thermal conductive path, thereby improving the thermal conductivity of the thermally conductive silicone sheet.

[0132] However, in Comparative Example 1, silicon carbide particles with a specific crystal structure and graphene flakes without surface modification were not used, in Comparative Example 2, nano-diamond particles and graphene flakes with surface modification were not added, and in Comparative Example 3, the preparation process was different from that of the present invention, all of which resulted in decreased thermal conductivity.

[0133] 2. Tensile strength test:

[0134] According to GB / T528-2009 standard, a universal material testing machine was used to test the tensile strength of the thermally conductive silicone sheets prepared in Example 1, Example 2, Example 3 and Comparative Example 1, Comparative Example 2, and Comparative Example 3. The test results are shown in the following table:

[0135] Sample No. Tensile strength(MPa) Embodiment 1 8.5 Embodiment 2 8.0 Embodiment 3 9.0 Comparative Example 1 6.0 Comparative Example 2 7.0 Comparative Example 3 7.5

[0136] It can be seen from the test results that the tensile strength of the thermally conductive silicone sheets of Example 1, Example 2 and Example 3 is better than that of Comparative Example 1, Comparative Example 2 and Comparative Example 3. The composite system of silicon carbide particles with a specific crystal structure, surface-modified graphene flakes and nano-diamond particles in the present invention and the synergistic effect between the components not only improve the thermal conductivity, but also enhance the mechanical properties of the silicone sheet.

[0137] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A thermally conductive silicone sheet, characterized in that: The thermally conductive silicone sheet is composed of the following components by weight: 100 parts of silicone rubber; 300-500 parts of a thermally conductive filler, wherein the thermally conductive filler is a composite system of silicon carbide particles of a specific crystal structure, surface-modified graphene flakes and nano-diamond particles, wherein the mass ratio of the silicon carbide particles of a specific crystal structure, the surface-modified graphene flakes and the nano-diamond particles is 2-3:1:0.5-1, the silicon carbide particles of a specific crystal structure are hexagonal α-SiC, and the average particle size thereof is in the range of 5-20 μm, and the sphericity of the particles is between 0.8-0.95, the surface-modified graphene flakes are modified by grafting organic functional groups on the graphene surface, and the grafting rate is between 10%-30%, the organic functional groups are organic molecular chains containing one or more of amino, epoxy or vinyl groups, and the average thickness of the graphene flakes is between 3-10 nm, the average sheet diameter is between 10-50 μm, and the average particle size of the nano-diamond particles is between 5-50 nm; 3-8 parts of curing agent; 1-3 parts of catalyst; 2-5 parts of a coupling agent, wherein the coupling agent is a silane coupling agent, and the molecular structure of the coupling agent contains one or more of an amino group, an epoxy group or a mercapto group.

2. The thermally conductive silicone sheet according to claim 1, characterized in that: The organic silicone rubber is methyl vinyl silicone rubber, with a vinyl content of 0.05%-0.2%, a molecular weight of 400,000-800,000, and a Mooney viscosity of 30-60 at 25°C.

3. The thermally conductive silicone sheet according to claim 1, characterized in that: The curing agent is an organic peroxide curing agent, including one of dicumyl peroxide and benzoyl peroxide or a mixture of two or more thereof, and when it is a mixture, the mass ratio between the components is between 1:1 and 1:

3.

4. The thermally conductive silicone sheet according to claim 1, characterized in that: The catalyst is a platinum catalyst, and its content in the thermally conductive silicone sheet is between 10-50 ppm in terms of platinum element. The platinum catalyst is one or more of chloroplatinic acid, platinum black, and platinum-vinylsiloxane complex.

5. The thermally conductive silicone sheet according to claim 1, characterized in that: The silane coupling agent is one or more of γ-aminopropyltriethoxysilane, γ-glycidyloxypropyltrimethoxysilane or γ-mercaptopropyltrimethoxysilane.

6. A process for preparing a thermally conductive silicone sheet according to any one of claims 1 to 5, characterized in that: The process includes the following steps: Firstly, the surface-modified graphene flakes, nano-diamond particles and part of the silicone rubber are pre-mixed in an internal mixer at a mixing temperature between 40 and 60° C., a mixing time of 5 to 10 minutes and a rotating speed of 30 to 50 rpm to obtain a premix; Then, silicon carbide particles with a specific crystal structure are added to the premix, and a coupling agent is added simultaneously, and the mixing is continued for 10-20 minutes, and the mixing temperature is increased to 60-80°C; Then, the remaining silicone rubber, curing agent and catalyst are added and mixed on a double-roll mill at a mixing temperature between 30 and 50° C. for 15 to 30 minutes to obtain a rubber compound; Finally, the rubber material is placed in a mold and vulcanized on a flat vulcanizer. The vulcanization temperature is 160-190°C, the vulcanization pressure is 8-15MPa, and the vulcanization time is 15-30 minutes. After the vulcanization is completed, the mold is cooled and demolded to obtain a thermally conductive silicone sheet.

7. The process for preparing the thermally conductive silicone sheet according to claim 6, characterized in that: Before pre-mixing the surface-modified graphene flakes, nano-diamond particles and part of the silicone rubber, the surface-modified graphene flakes and nano-diamond particles are first dried in a vacuum drying oven at a drying temperature of 80-120° C., a drying time of 2-4 hours, and a vacuum degree between -0.08 MPa and -0.1 MPa.

8. The process for preparing the thermally conductive silicone sheet according to claim 6, characterized in that: When adding silicon carbide particles with a specific crystal structure into the premix, a dispersant is added simultaneously. The dispersant is one or both of zinc stearate and calcium stearate. The amount of the dispersant added is 0.5%-2% of the mass of the silicon carbide particles with a specific crystal structure.

9. The process for preparing the thermally conductive silicone sheet according to claim 6, characterized in that: The inner surface of the mold is polished, and the surface roughness is between Ra0.8-Ra1.

6. The material of the mold is stainless steel or aluminum alloy, and the thickness tolerance of the mold is between ±0.05-±0.2mm.

10. The process for preparing the thermally conductive silicone sheet according to claim 6, characterized in that: During the vulcanization molding process, a segmented vulcanization process is adopted. First, vulcanize at 160-170℃ for 10-15 minutes, then heat up to 180-190℃ and continue vulcanizing for 5-15 minutes. During the vulcanization process, the mold is vacuumed with a vacuum degree between -0.05MPa and -0.09MPa.