Al2o3@siO2-kh560 double core-shell structure heat-conducting filler, heat-conducting insulating silicone rubber composite material and preparation method thereof

Abstract

This invention discloses an Al2O3@SiO2-KH560 dual-core-shell thermally conductive filler, a thermally conductive and insulating silicone rubber composite material, and their preparation methods. The core-shell thermally conductive filler comprises α-Al2O3 core particles, an amorphous SiO2 intermediate shell layer coating the surface of the core particles, and a KH560 organic outer layer grafted onto the surface of the SiO2 shell layer. The composite material uses addition-type liquid silicone rubber as the matrix and the aforementioned core-shell thermally conductive filler as the filler, with a total filler content of 50-80 wt%. The preparation method includes: coating the α-Al2O3 surface with a SiO2 shell layer using the TEOS sol-gel method and calcining to densify it; then obtaining the dual-modified core-shell filler through KH560 wet grafting; mixing the filler with vinyl silicone oil and other components, centrifuging to remove bubbles, and then curing under vacuum with stepped heating. The composite material achieves a thermal conductivity of 3.04 W / (m·K) and a volume resistivity of 3.5 × 10⁻⁶ at a 70 wt% filler content. 14 It has a strength of Ω·cm, a tensile strength of 0.53 MPa, an elongation at break of 73.9%, and combines high thermal conductivity, high insulation and good mechanical flexibility.

Description

Technical Field

[0001] This invention relates to the field of thermal interface materials and functional fillers, specifically to a thermally conductive filler with a multi-level core-shell structure, a thermally conductive and insulating silicone rubber composite material containing the filler, and a method for preparing the same. Background Technology

[0002] With the rapid development of 5G communication, artificial intelligence computing, and high-power-density electronic components, the local heat flux density inside equipment continues to rise, making thermal management a key bottleneck restricting the reliability and lifespan of electronic devices. Addition-cure liquid silicone rubber, due to its excellent weather resistance, low elastic modulus, and good thermal stress buffering capacity, is a widely used polymer matrix for thermal interface materials. However, pure silicone rubber has extremely low intrinsic thermal conductivity (typically only 0.1~0.3 W / (m·K)), necessitating the construction of a three-dimensional thermally conductive network through the extensive filling of highly thermally conductive inorganic particles.

[0003] Currently, existing technologies for improving the thermal conductivity of thermally conductive silicone rubber composites mainly include the following approaches: One approach is to achieve close packing by increasing the amount of inorganic filler or using multi-scale particle size distribution. For example, US Patent 6380301B2 discloses a thermally conductive silicone rubber composition that uses oligomeric siloxanes to treat the filler surface and proposes a binary compounding scheme of spherical alumina. Chinese Patent CN115627075A discloses a scheme for constructing a thermally conductive framework by physically blending spherical and angular alumina. However, in purely physically packed high-filler schemes, when the filler content approaches the close packing limit, the system viscosity increases sharply, making processing difficult. Furthermore, it traps a large number of micron-sized air bubbles, drastically worsening the interfacial contact thermal resistance and causing the material to exhibit brittle fracture.

[0004] Secondly, organic modification of the filler surface can be achieved using silane coupling agents. For example, Chinese patent CN112457673A discloses a scheme for surface modification of spherical alumina using silane coupling agents, and Chinese patent CN104231631A discloses a scheme for treating thermally conductive fillers with coupling agents. Monolayer modification with silane coupling agents improves particle surface wettability to some extent, but at high filling amounts, the monolayer thickness is extremely thin, failing to provide a sufficient insulating physical barrier, making it easy for charge carriers to undergo interfacial tunneling transitions. Simultaneously, the nanoscale organic layer cannot smoothly bridge the acoustic impedance difference between rigid ceramics and flexible elastomers on a spatial scale, resulting in persistently high interfacial thermal resistance.

[0005] Thirdly, Xu et al. (Applied Physics Letters, 2020) reported a composite material filled with epoxy resin using an Al@Al2O3@SiO2 dual core-shell structure filler. This composite material uses metallic Al nanoparticles as the core, and a SiO2 layer is coated onto the Al2O3 self-passivation layer via the TEOS sol-gel method. However, this approach, using metallic Al as the core, lacks electrical insulation properties and does not involve organic secondary grafting or multi-level interface design for silicone rubber matrices under high-filling conditions.

[0006] In summary, the core problem facing existing technologies in the field of high-filler thermally conductive silicone rubber is how to simultaneously achieve high thermal conductivity, high insulation, and high mechanical flexibility at the limit of filler content. Summary of the Invention

[0007] I. Technical problems to be solved The present invention aims to solve the following technical problems existing in the current high-filler thermally conductive silicone rubber composite materials: poor compatibility between inorganic fillers and organic matrix interfaces, high processing viscosity and easy generation of micropores; severe acoustic impedance mismatch at heterogeneous interfaces and high interfacial thermal resistance; single-layer organic modification layer cannot provide sufficient insulating physical barrier under high filling; brittle interfacial peeling fracture of composite materials under high filling due to weak interfacial bonding force.

[0008] II. Technical Solution The first aspect of this invention provides a core-shell structured thermally conductive filler, comprising: α-Alumina (α-Al2O3) core particles; An amorphous silica (SiO2) intermediate shell layer covering the surface of the α-alumina core particles; And an organic outer layer of γ-glycidyl etheroxypropyltrimethoxysilane (KH560) grafted onto the surface of the silica intermediate shell.

[0009] This core-shell thermally conductive filler forms a three-tiered, multi-level interface structure: an α-Al₂O₃ core, an amorphous SiO₂ intermediate shell, and a KH₅60 organic outer layer. The amorphous SiO₂ intermediate shell creates an acoustic impedance gradient transition between the rigid alumina core and the flexible silicone rubber matrix, reducing the backscattering probability of high-frequency phonons at the heterogeneous interface. Simultaneously, it acts as a wide-bandgap insulator, constructing an insulating barrier between adjacent filler particles and cutting off the cross-interface tunneling pathway for charge carriers. The silanol groups enriched on the SiO₂ shell surface provide abundant chemical reaction sites for the high-density grafting of KH₅60. The KH₅60 organic outer layer transforms the inorganic filler surface into a hydrophobic surface, and its epoxy groups and flexible aliphatic long chains can penetrate deep into the silicone rubber crosslinking network, forming physical entanglement and chemical anchoring. The nanoscale surface roughness imparted by the SiO₂ shell provides a mechanically interlocking physical effect, which, combined with the high-density chemical anchoring network of KH₅60, transforms the tensile fracture mode of the composite material from interfacial delamination to in-matrix cohesive failure.

[0010] The α-alumina core particles are preferably spherical or near-spherical particles.

[0011] The α-alumina core particles preferably comprise a first component and a second component, wherein the average particle size of the first component is 25-35 μm, and the average particle size of the second component is 0.8-3 μm; the mass ratio of the first component to the second component is 6.5:3.5 to 7.5:2.5. More preferably, the average particle size of the first component is 30 μm, the average particle size of the second component is 1 μm, and the mass ratio is 7:3.

[0012] The amorphous silica intermediate shell is formed by coating tetraethyl orthosilicate (TEOS) using a sol-gel method, with the amount of TEOS being 0.3~0.5 mL / g α-alumina core particles.

[0013] The grafting amount of the KH560 organic outer layer is 1.0~2.0 wt% of the total mass of the core-shell structure thermally conductive filler.

[0014] The second aspect of the present invention provides a thermally conductive and insulating silicone rubber composite material, comprising: a matrix (addition-cured liquid silicone rubber) and a filler (the above-mentioned core-shell structure thermally conductive filler), wherein the total filler content is 50~80 wt%.

[0015] The addition-type liquid silicone rubber comprises vinyl silicone oil, hydrogen-containing silicone oil, a platinum catalyst, and an inhibitor. Preferably, the inhibitor is 1-ethynyl-1-cyclohexanol.

[0016] At a filler content of 70 wt%, the volume resistivity of the composite material is ≥1.0×10⁻⁶. 14 Ω·cm, thermal conductivity ≥2.5 W / (m·K).

[0017] A third aspect of the present invention provides a method for preparing the above-mentioned core-shell structured thermally conductive filler, comprising the following steps: (a) The α-alumina core particles were pre-dried at 110~130℃ for 3~5 h and dispersed in a mixed solvent of anhydrous ethanol and deionized water to obtain a suspension; (b) Adjust the pH of the suspension to 9.0~10.0, and add TEOS ethanol solution dropwise at a rate of 0.4~0.6 mL / min under constant temperature conditions of 35~45℃. After the addition is completed, stir the reaction at constant temperature for 6~12 h. (c) After centrifugation, washing and drying, the product is heated to 380-420℃ at a heating rate of 4-6℃ / min and calcined for 1.5-2.5 h to obtain α-Al2O3@SiO2 core-shell intermediate; (d) The α-Al2O3@SiO2 core-shell intermediate was added to a hydrolysate containing KH560 and refluxed at 70~80℃ for 5~7 h. After centrifugation, washing and drying, the core-shell structured thermally conductive filler was obtained.

[0018] Preferably, in step (a), the pre-drying temperature is 120℃ and the time is 4 h. In step (b), the alcohol-to-water ratio of the mixed solvent is 3.5~4.5:1, the isothermal temperature is 40℃, and the TEOS dropping rate is 0.5 mL / min. In step (c), the calcination heating rate is 5℃ / min, the calcination temperature is 400℃, and the holding time is 2 h. In step (d), the KH560 hydrolysate is prepared by adding KH560 to a mixed solvent with an alcohol-to-water ratio of 8.5~9.5:1, adjusting the pH to 4.0~4.5, and hydrolyzing and activating at room temperature for 0.5~2 h; the reflux reaction temperature is 80℃ and the time is 6 h.

[0019] A fourth aspect of this invention provides a method for preparing the above-mentioned thermally conductive and insulating silicone rubber composite material, comprising: preparing a core-shell structured thermally conductive filler according to the above method; adding the filler in batches to vinyl silicone oil and stirring to obtain component A; mixing hydrogen-containing silicone oil, inhibitor, and platinum catalyst to obtain component B; mixing components A and B at a mass ratio of 0.9~1.1:1, centrifuging to remove bubbles (speed 2000~2500 rpm, time 1.5~3 min), and then performing vacuum step-curing: holding at a vacuum degree ≤-0.095MPa and 58~62℃ for 0.8~1.5 h (first stage), followed by heating to 118~122℃ and holding for 1.5~2.5 h (second stage). Preferably, the first stage is 60℃ / 1 h, and the second stage is 120℃ / 2 h.

[0020] III. Beneficial Effects Compared with the prior art, the present invention has the following beneficial effects: (1) Significantly improved thermal conductivity. The amorphous SiO2 intermediate shell forms an acoustic impedance gradient buffer between the rigid alumina core and the flexible silicone rubber matrix, reducing the probability of backscattering of high-frequency phonons at the heterogeneous interface. The silanol groups enriched on the surface of the SiO2 shell provide reaction sites for the high-density grafting of KH560, further eliminating interfacial micro-gaps. At a filling amount of 70 wt%, the thermal conductivity of Example 1 reached 3.04 W / (m·K), which is about 23% higher than that of the KH560 single-modified system (2.47 W / (m·K)) and about 63% higher than that of the unmodified system (1.86 W / (m·K)).

[0021] (2) Significantly improved insulation performance. Amorphous SiO2 is a wide-bandgap insulator, forming an insulating passivation layer between adjacent filler particles, cutting off the interfacial tunneling transition path of charge carriers, and simultaneously filling lattice defects on the alumina surface and introducing deep trap energy levels to capture injected charge carriers. In Example 1, the volume resistivity reached 3.5 × 10⁻⁶ at a filler content of 70 wt%. 14 Ω·cm, compared to the unmodified system (3.2×10⁻⁶). 13 The Ω·cm (Ω·cm) is increased by about an order of magnitude, which is better than the KH560 single-modified system (1.2×10). 14 Ω·cm).

[0022] (3) Synergistic enhancement of mechanical toughness and strength. The nanoscale surface roughness imparted by the SiO2 shell allows the silicone rubber macromolecular chains to penetrate deep into the micropores of the shell to form mechanical engagement. Combined with the high-density chemical anchoring network of KH560, the fracture mode is changed from interfacial peeling to cohesive failure within the matrix. In Example 1, the tensile strength reached 0.53 MPa and the elongation at break reached 73.9% with a filler content of 70 wt%, both of which were significantly better than the KH560 single-modified system (0.33 MPa / 55.5%) and the unmodified system (0.20 MPa / 43.6%).

[0023] (4) Low porosity. The vacuum stepped temperature curing process first allows the slurry to fully eliminate internal air bubbles at a low temperature of 60°C, and then completes deep curing at 120°C. The apparent porosity of the composite material in Example 1 is less than 0.6%.

[0024] (5) Synergistic effect of SiO2 intermediate shell and KH560 organic outer layer. Comparative Example 1 (only KH560, no SiO2 shell) showed improvements in thermal conductivity, tensile strength and volume resistivity compared to the unmodified system (Comparative Example 2), indicating the independent contribution of KH560 single modification; while the further significant improvement of Example 1 (dual core-shell structure) compared to Comparative Example 1 proved the incremental contribution of SiO2 intermediate shell alone. More importantly, the improvement of Example 1 compared to Comparative Example 2 (thermal conductivity +63%, tensile strength +165%, volume resistivity +10×) is significantly greater than the simple sum of the improvement of Comparative Example 1 compared to Comparative Example 2 (thermal conductivity +33%, tensile strength +65%, volume resistivity +3.8×) and the improvement of Example 1 compared to Comparative Example 1 (thermal conductivity +23%, tensile strength +61%, volume resistivity +2.9×). This indicates a significant synergistic effect between the SiO2 shell and the KH560 organic layer. The silanols enriched on the surface of the SiO2 shell provide KH560 with far more chemical reaction sites than the bare Al2O3 surface, resulting in a qualitative improvement in the grafting density and interface coverage of KH560. Meanwhile, the nano-roughness and acoustic impedance gradient buffering provided by the inorganic shell are functions that a single layer of organic molecules cannot achieve alone. The two form a synergistic relationship in terms of structure and function, which is mutually dependent and amplifies each other. Attached Figure Description

[0025] Figure 1 This is a comparison chart of the thermal conductivity of the composite materials of Example 1, Comparative Example 1, and Comparative Example 2.

[0026] Figure 2 This is a comparison chart of the tensile strength of the composite materials of Example 1, Comparative Example 1, and Comparative Example 2.

[0027] Figure 3 This is a comparison chart of the elongation at break of the composite materials of Example 1, Comparative Example 1, and Comparative Example 2.

[0028] Figure 4 This is a comparison graph of the volume resistivity of the composite materials of Example 1, Comparative Example 1, and Comparative Example 2.

[0029] Figure 5 The image shows a cross-sectional SEM comparison of the composite materials of Example 1, Comparative Example 1, and Comparative Example 2. Detailed Implementation

[0030] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The following embodiments are based on the technical solution of the present invention and provide detailed implementation methods and operating procedures; however, the scope of protection of the present invention is not limited to the following embodiments.

[0031] raw material The raw materials used in the following examples and comparative examples are all commercially available: α-Spherical alumina powder: average particle size 30 μm and 1 μm, purity ≥99%; Tetraethyl orthosilicate (TEOS): analytical grade; γ-glycidyl etheroxypropyltrimethoxysilane (KH560): Industrial grade; Anhydrous ethanol and ammonia (25-28 wt%): analytical grade; Vinyl silicone oil: viscosity 500~2000 mPa·s; Hydrogen-containing silicone oil: hydrogen content 0.3~0.8 wt%; Platinum catalyst: Karstedt catalyst; Inhibitor: 1-ethynyl-1-cyclohexanol, purity ≥98%.

[0032] Test methods Thermal conductivity: Tested using laser flare method. The sample was a circular disc with a diameter of 12.7 mm and a thickness of 2~3 mm. The test temperature was 25℃.

[0033] Tensile properties: Tested using a universal testing machine according to GB / T 528 standard, with a tensile rate of 50 mm / min, and the sample is a dumbbell-shaped specimen.

[0034] Volume resistivity: Tested using a high resistivity meter according to GB / T 1410 standard, with a test voltage of 500 V and the sample being a disc with a diameter of 50 mm and a thickness of 2 mm.

[0035] Cross-sectional morphology: The cross-section of the composite material after liquid nitrogen embrittlement was observed using a scanning electron microscope.

[0036] Apparent porosity: The Archimedes displacement method was used for testing, with deionized water as the impregnation medium. The porosity was calculated according to the formula P = (1- ρ_b / ρ_t) × 100%, where ρ_b is the measured bulk density and ρ_t is the theoretical density (calculated by weighting the mass fraction and true density of each component). Three parallel samples were tested for each group of samples and the average value was taken.

[0037] Example Example 1: Preparation of Al2O3@SiO2-KH560 dual core-shell filler and composite material (1) Preparation of Al2O3@SiO2-KH560 dual-modified core-shell filler: Spherical α-Al₂O₃ powders with average particle sizes of 30 μm and 1 μm were mixed at a mass ratio of 7:3 and dried at 120 °C for 4 h. The dried mixed powder was dispersed in a mixture of anhydrous ethanol and deionized water at a volume ratio of 4:1 and ultrasonically dispersed until homogeneous. Ammonia was added dropwise to adjust the pH to 9.0–10.0, and the temperature was raised to 40 °C and kept constant. An ethanol solution of TEOS was slowly added dropwise at a rate of 0.5 mL / min at a ratio of 0.4 mL / 1 g Al₂O₃. After the addition was complete, the mixture was stirred at 40 °C for 6–12 h. After the reaction was completed, the mixture was centrifuged, and the precipitate was washed alternately with anhydrous ethanol and deionized water, and dried at 60–80 °C. The dried product was placed in a muffle furnace and calcined at a rate of 5 °C / min to 400 °C for 2 h, then naturally cooled to room temperature to obtain the Al₂O₃@SiO₂ core-shell intermediate.

[0038] KH560 was added to a mixed solvent of anhydrous ethanol and deionized water at a volume ratio of 9:1, and the pH was adjusted to 4.0–4.5 with dilute hydrochloric acid. The mixture was then hydrolyzed and activated at room temperature for 0.5–2 h to obtain the KH560 alcohol-water hydrolysate. The above Al2O3@SiO2 core-shell intermediate was redispersed in the KH560 hydrolysate (KH560 was used at 1.5 wt% of the total mass of alumina powder), and refluxed at 80 °C for 6 h. After the reaction was complete, the mixture was centrifuged, washed with anhydrous ethanol, and vacuum dried at 60 °C to obtain the Al2O3@SiO2-KH560 dual-modified core-shell filler.

[0039] (2) Preparation of component A: Vinyl silicone oil was added to a high-speed stirrer, and the aforementioned dual-modified core-shell packing material (total packing mass fraction of 70 wt%) was added in portions at low speed (300~500 rpm). After the addition was complete, the stirring was switched to high speed mode (1500~2000 rpm) and continued for 15 min to ensure thorough dispersion of the packing material. Then, a measured amount of platinum catalyst solution was added at low speed (300~500 rpm), and the mixture was stirred at low speed for 5 min to ensure uniform dispersion of the catalyst. The resulting slurry of component A was transferred to a brown wide-mouth bottle, sealed with nitrogen gas, and stored away from light.

[0040] (3) Preparation of component B: The dispersion of vinyl silicone oil and dual-modified core-shell filler was performed in the same manner as in step (2). After dispersion, the slurry was allowed to stand and cool to below 40°C. Hydrogen-containing silicone oil and 1-ethynyl-1-cyclohexanol were added sequentially under low-speed stirring. The mixture was stirred at high speed for 10 minutes and then sealed to obtain component B.

[0041] (4) Curing and molding: Components A and B were premixed at a mass ratio of 1:1, centrifuged at 2200 rpm for 2 min to remove bubbles, and then poured into a mold. The mold was placed in a vacuum drying oven (vacuum degree ≤ -0.095 MPa), first kept at 60℃ for 1 h, then heated to 120℃ and maintained in a vacuum environment for another 2 h to cure. After natural cooling, the mixture was demolded to obtain the thermally conductive and insulating silicone rubber composite material.

[0042] Comparative Example Comparative Example 1: KH560 single-layer modification (without SiO2 intermediate shell) Compared with Example 1, the only difference is that the SiO2 shell coating step is omitted, and the alumina powder is directly modified by KH560 single silane coupling.

[0043] (1) Spherical α-Al2O3 powders with average particle sizes of 30 μm and 1 μm were mixed at a mass ratio of 7:3 and dried at 120℃ for 4 h. The dried mixed powder was directly dispersed in KH560 alcohol-water hydrolysate (the hydrolysate preparation conditions were the same as in Example 1, and the amount of KH560 was 1.5 wt% of the total mass of alumina powder), and refluxed at 60~80℃ for 6 h. After centrifugation, the mixture was washed with anhydrous ethanol and dried under vacuum at 60℃ to obtain KH560 single-component modified filler.

[0044] (2) Preparation of component A: The operation is the same as step (2) in Example 1, except that the packing is replaced with the above-mentioned KH560 single modified packing, and the total mass fraction of the packing is 70 wt%.

[0045] (3) Preparation of component B: The operation is the same as step (3) in Example 1, except that the filler is replaced with the above-mentioned KH560 single modified filler.

[0046] (4) Curing and molding: The operation is the same as step (4) in Example 1.

[0047] Comparative Example 2: Unmodified alumina The only difference from Example 1 is that the filler was not coated or chemically modified.

[0048] (1) Mix spherical α-Al2O3 powders with average particle sizes of 30 μm and 1 μm at a mass ratio of 7:3 and dry them at 120℃ for 4 h for later use.

[0049] (2) Preparation of component A: The operation is the same as step (2) in Example 1, except that the filler is replaced with the above-mentioned unmodified alumina powder, and the total mass fraction of the filler is 70 wt%.

[0050] (3) Preparation of component B: The operation is the same as step (3) in Example 1, except that the filler is replaced with the above-mentioned unmodified alumina powder.

[0051] (4) Curing and molding: The operation is the same as step (4) in Example 1.

[0052] Experimental results The composite materials prepared in Example 1 and Comparative Examples 1 and 2 were subjected to performance tests, and the results are shown in the table below: The results above show that: (1) Thermal conductivity: The thermal conductivity of Example 1 (3.04 W / (m·K)) is significantly higher than that of Comparative Example 1 (2.47 W / (m·K)) and Comparative Example 2 (1.86 W / (m·K)), indicating the buffering effect of the acoustic impedance gradient of the SiO2 intermediate shell and the synergistic effect of KH560 high-density grafting.

[0053] (2) Tensile strength: Example 1 (0.53 MPa) was significantly higher than Comparative Example 1 (0.33 MPa) and Comparative Example 2 (0.20 MPa), indicating that the dual interlocking mechanism of the nano-roughness of the SiO2 shell and the chemical anchoring of KH560 effectively enhanced the interfacial bonding.

[0054] (3) Elongation at break: Example 1 (73.9%) was significantly better than Comparative Example 1 (55.5%) and Comparative Example 2 (43.6%), indicating that the dual core-shell structure changed the fracture mode of the composite material from interfacial peeling to matrix cohesive failure.

[0055] (4) Volume resistivity: Example 1 (3.5×10 14 (Ω·cm) Comparison Example 2 (3.2×10) 13 The improvement in Ω·cm is approximately an order of magnitude, which is superior to Comparative Example 1 (1.2 × 10⁻⁶). 14 The SiO2 shell effectively cuts off the cross-interface migration channels for charge carriers (Ω·cm), indicating that the SiO2 shell effectively cuts off the cross-interface migration channels for charge carriers.

[0056] (5) Cross-sectional morphology: The SEM cross-section of Example 1 shows that the filler particles are fully covered by the matrix and the interface is tightly bonded; in Comparative Example 1, some interface debonding is visible; in Comparative Example 2, obvious filler exposure and interface pores are observed.

[0057] Industrial applicability The core-shell structured thermally conductive filler and thermally conductive and insulating silicone rubber composite material provided by this invention are made from conventional chemicals that are readily available in industrial applications. The preparation process is compatible with existing silicone rubber composite material processing equipment, requiring no special or expensive dedicated equipment, and exhibits good feasibility for industrial scale-up. This composite material can be widely used as a thermally conductive and insulating interface material for electronic devices.

Claims

1. A core-shell structured thermally conductive filler, characterized in that, include: α-Alumina (α-Al2O3) core particles; An amorphous silica (SiO2) intermediate shell layer covering the surface of the α-alumina core particles; And an organic outer layer of γ-glycidyl etheroxypropyltrimethoxysilane (KH560) grafted onto the surface of the silica intermediate shell.

2. The core-shell structure thermally conductive packing according to claim 1, characterized in that, The α-alumina core particles are spherical or near-spherical particles.

3. The core-shell structure thermally conductive packing according to claim 1, characterized in that, The α-alumina core particles comprise a first component and a second component, wherein the average particle size of the first component is 25-35 μm and the average particle size of the second component is 0.8-3 μm. The mass ratio of the first component to the second component is 6.5:3.5 to 7.5:2.

5.

4. The core-shell structure thermally conductive filler according to claim 3, characterized in that, The average particle size of the first component is 30 μm, and the average particle size of the second component is 1 μm; the mass ratio of the first component to the second component is 7:

3.

5. The core-shell structure thermally conductive packing according to claim 1, characterized in that, The amorphous silica intermediate shell is formed by coating tetraethyl orthosilicate (TEOS) using a sol-gel method.

6. The core-shell structured thermally conductive packing according to claim 5, characterized in that, The amount of TEOS used is 0.3~0.5 mL / g α-alumina core particles.

7. The core-shell structured thermally conductive packing according to claim 1, characterized in that, The grafting amount of the KH560 organic outer layer is 1.0~2.0 wt% of the total mass of the core-shell structure thermally conductive filler.

8. A thermally conductive and insulating silicone rubber composite material, characterized in that, Include: Matrix: Addition-cured liquid silicone rubber; Filler: The core-shell structured thermally conductive filler according to any one of claims 1 to 7; The total filling amount of the filler in the composite material is 50~80 wt%.

9. The thermally conductive and insulating silicone rubber composite material according to claim 8, characterized in that, With a total filling amount of 70 wt% for the core-shell thermally conductive filler, the volume resistivity of the composite material is ≥1.0×10⁻⁶. 14 Ω·cm, thermal conductivity ≥2.5 W / (m·K).

10. The thermally conductive and insulating silicone rubber composite material according to claim 8, characterized in that, The addition-type liquid silicone rubber comprises vinyl silicone oil, hydrogen-containing silicone oil, platinum catalyst, and inhibitor.

11. The thermally conductive and insulating silicone rubber composite material according to claim 10, characterized in that, The inhibitor is 1-ethynyl-1-cyclohexanol.

12. A method for preparing a core-shell structured thermally conductive filler according to any one of claims 1 to 7, characterized in that, Includes the following steps: (a) The α-alumina core particles were pre-dried at 110~130℃ for 3~5 h and dispersed in a mixed solvent of anhydrous ethanol and deionized water to obtain a suspension; (b) Adjust the pH of the suspension to 9.0~10.0, and add an ethanol solution of tetraethyl orthosilicate (TEOS) dropwise at a rate of 0.4~0.6 mL / min under constant temperature conditions of 35~45℃. After the addition is complete, stir the mixture at a constant temperature for 6~12 h. (c) After centrifugation, washing and drying, the product obtained in step (b) is heated to 380-420℃ at a heating rate of 4-6℃ / min and calcined for 1.5-2.5 h to obtain α-Al2O3@SiO2 core-shell intermediate; (d) The α-Al2O3@SiO2 core-shell intermediate was added to a hydrolysate containing KH560 and refluxed at 70~80℃ for 5~7 h. After centrifugation, washing and drying, the core-shell structured thermally conductive filler was obtained.

13. The preparation method according to claim 12, characterized in that, In step (a), the pre-drying temperature is 120°C and the time is 4 h.

14. The preparation method according to claim 12, characterized in that, In step (b), the volume ratio of anhydrous ethanol to deionized water in the mixed solvent is 3.5:1 to 4.5:

1.

15. The preparation method according to claim 12, characterized in that, In step (b), the constant temperature is 40°C and the dropping rate of TEOS is 0.5 mL / min.

16. The preparation method according to claim 12, characterized in that, In step (c), the heating rate of calcination is 5℃ / min, the calcination temperature is 400℃, and the holding time is 2 h.

17. The preparation method according to claim 12, characterized in that, In step (d), the hydrolysate containing KH560 is prepared by adding KH560 to a mixed solvent of anhydrous ethanol and deionized water in a volume ratio of 8.5 to 9.5:1, adjusting the pH to 4.0 to 4.5, and activating by hydrolysis at room temperature for 0.5 to 2 h.

18. The preparation method according to claim 12, characterized in that, In step (d), the reflux reaction temperature is 80°C and the reaction time is 6 h.

19. A method for preparing a thermally conductive and insulating silicone rubber composite material according to any one of claims 8 to 11, characterized in that, Includes the following steps: The core-shell structured thermally conductive filler is prepared according to any one of claims 12 to 18; The core-shell structured thermally conductive filler was added to vinyl silicone oil in batches and mixed by stirring to obtain component A. Component B is obtained by mixing hydrogen-containing silicone oil, inhibitor, and platinum catalyst; Component A and component B are mixed, degassed, and then vacuum-cured to obtain the thermally conductive and insulating silicone rubber composite material.

20. The preparation method according to claim 19, characterized in that, The mixing mass ratio of component A to component B is 0.9~1.1:1, preferably 1:

1.

21. The preparation method according to claim 19, characterized in that, The degassing process is centrifugal degassing at a speed of 2000~2500 rpm for 1.5~3 min.

22. The preparation method according to claim 19, characterized in that, The vacuum step curing includes: First stage: Under conditions of vacuum degree ≤ -0.095 MPa and temperature 58~62℃, keep warm for 0.8~1.5 h; Second stage: Maintain vacuum, raise the temperature to 118~122℃, and hold for 1.5~2.5 hours.

23. The preparation method according to claim 22, characterized in that, The temperature of the first stage is 60℃ and the holding time is 1 hour; the temperature of the second stage is 120℃ and the holding time is 2 hours.

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