High-thermal-conductivity low-dielectric-constant silica gel composition and preparation method thereof

Abstract

The invention belongs to the technical field of heat-conducting silica gel, and particularly relates to a silica gel composition with high heat conductivity and low dielectric constant and a preparation method thereof. The silica gel composition with high thermal conductivity and low dielectric constant provided by the invention is prepared from vinyl silicone oil, hydrogen-containing silicone oil, boron nitride, heat-conducting filler, a coupling agent, a catalyst and hollow spherical silicon carbide. A gel material and alpha-Al2O3 powder are adopted to form ceramic slurry, a pore forming agent is added to prepare reticular alumina ceramic microspheres, the reticular alumina ceramic microspheres are used for wrapping graphene powder to serve as a heat-conducting filler, a silane coupling agent is adopted for modifying the reticular alumina ceramic microspheres, and the reticular alumina ceramic microspheres are added into the silica gel composition, so that the heat-conducting property of the silica gel composition is effectively improved; phenolic resin is prepared on the surfaces of spherical silicon dioxide particles, mesoporous spherical silicon carbide particles are prepared through segmented calcination, and the dielectric constant of the silica gel composition is effectively reduced by adding the mesoporous spherical silicon carbide particles into the silica gel composition.

Description

Technical Field

[0001] This invention belongs to the field of thermally conductive silicone technology, specifically relating to a silicone combination with high thermal conductivity and low dielectric constant and its preparation method. Background Technology

[0002] High thermal conductivity and low dielectric constant silicone is a material with important applications in the electronics and semiconductor fields. It can quickly conduct heat, effectively reducing heat accumulation during the operation of electronic devices, thereby improving device stability and lifespan. The low dielectric constant can reduce signal attenuation and delay, ensuring stable transmission of high-frequency signals. With the rapid development of emerging industries such as 5G communication, artificial intelligence, and new energy vehicles, the demand for high thermal conductivity and low dielectric constant silicone will continue to grow.

[0003] Currently, in the preparation of silicone materials with low dielectric constant and high thermal conductivity, insufficient preparation processes can lead to poor thermal conductivity and excessively high dielectric constants. Existing preparation processes often result in the agglomeration and disordered distribution of thermally conductive fillers in the matrix, making it difficult to form continuous and efficient thermal conduction paths. Even with high-speed stirring or ultrasonic dispersion, the agglomeration problem can only be partially alleviated; the random distribution of fillers still limits the improvement of thermal conductivity. Furthermore, to improve the thermal conductivity of silicone materials, the filler ratio is usually increased. However, high filler content significantly increases the dielectric constant and dielectric loss, weakening its insulation performance in high-frequency environments. For example, Chinese patent application CN111378284A discloses a low dielectric constant thermally conductive silicone sheet, the formulation of which includes low dielectric constant thermally conductive powder.

[0004] The formulation contains 40%-90% vinyl silicone oil, 4%-59% hydrogen-containing silicone oil, 0.4%-1% silicone rubber reinforcing agent, 1%-4% platinum catalyst, 0.2%-1% inhibitor, 0.01%-0.03% silane coupling agent, and 0.1%-0.6%. This low-dielectric-constant thermally conductive silicone sheet formulation has a high proportion of thermally conductive powder, resulting in a maximum thermal conductivity of only 1.8 W / (m·K), indicating poor thermal conductivity. Furthermore, it only exhibits a low dielectric constant within the range of 8 GHz. Summary of the Invention

[0005] To address the technical problems of poor thermal conductivity, high dielectric loss, and filler agglomeration in the prior art, this invention provides a high thermal conductivity, low dielectric constant silicone composite and its preparation method.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A high thermal conductivity, low dielectric constant silicone composition comprising the following components in parts by weight:

[0008] The mixture comprises 20-30 parts vinyl silicone oil, 5-10 parts hydrogen-containing silicone oil, 15-30 parts boron nitride, 40-50 parts thermally conductive filler, 3-5 parts coupling agent, and 1-3 parts catalyst. The preparation method of the thermally conductive filler is as follows: graphene powder is added to deionized water, ultrasonically dispersed, and then network alumina ceramic microspheres are added. The mixture is stirred and ultrasonically sonicated for 3-4 hours, and the solid and liquid are separated. Then, the filler is added to an aqueous solution of silane coupling agent and ultrasonically reacted for 5-6 hours. The mixture is then filtered, washed, dried, and ground to obtain the thermally conductive filler.

[0009] Sheet graphene possesses high thermal conductivity and a large specific surface area, providing an excellent and broad thermal pathway for phonon heat transfer within polymers. However, its electrical conductivity increases the dielectric constant of the silicone composition. This invention employs a network of alumina ceramic microspheres encapsulating graphene powder, utilizing the porous structure of the microspheres to store some air, significantly reducing the increase in dielectric constant caused by the addition of graphene. However, alumina itself has a high dielectric constant, so there is still room for further reduction in the dielectric constant of the silicone composition. Simultaneously, alumina itself has high thermal conductivity (30 W / m·K), and after high-temperature sintering, alumina ceramics form a dense structure. This significantly reduces the contact area between ceramic particles and between ceramic particles and the polymer matrix, decreasing the scattering of phonons at the interface and increasing the mean free path of phonons. This effectively reduces interfacial thermal resistance and improves the thermal conductivity of the silicone composition.

[0010] Furthermore, this invention also uses a silane coupling agent to modify the thermally conductive filler, which effectively improves the dispersion performance of the thermally conductive filler in the silicone composition. The modified thermally conductive filler is covalently connected to the matrix, exhibiting strong interfacial interaction with almost no voids at the interface. This reduces the presence of low thermal conductivity air phase, lowers phonon scattering at defects and interfacial thermal resistance, and effectively improves the thermal conductivity of the silicone composition. At the same time, the strong interaction between the modified thermally conductive filler and the matrix can suppress the polarization and relaxation of dipoles at the interface, reducing dipole relaxation loss under an external electric field, thereby reducing the dielectric loss of the material.

[0011] Furthermore, the preparation method of the reticulated alumina ceramic microspheres is as follows: (1) Carboxymethyl cellulose and sucrose are added to deionized water, heated, stirred until completely dissolved, α-Al2O3 powder and dispersant are added, stirred thoroughly and evenly, and allowed to stand to remove gas to obtain a mixture A; (2) The mixture A obtained in step (1) is added dropwise to aluminum sulfate solution, soaked for 20-24 hours, and filtered after solidification to obtain alumina microspheres with a diameter of 2-3 mm; (3) The alumina microspheres obtained in step (2) are placed in a sintering furnace for calcination to obtain reticulated alumina ceramic microspheres.

[0012] This invention utilizes the characteristic that the carboxyl groups in carboxymethyl cellulose can react with trivalent aluminum ions to form a gel with a three-dimensional network structure. α-Al₂O₃ powder is added to an aqueous solution of carboxymethyl cellulose to form a ceramic slurry, and sucrose is added as a pore-forming agent. Through the reaction and cross-linking curing of aluminum ions with carboxymethyl cellulose, the ceramic slurry can maintain a spherical structure for a certain period. As the immersion time in aluminum sulfate solution increases, aluminum ions gradually penetrate into the interior of the microspheres through permeation, continuing the cross-linking curing reaction. This causes the ceramic slurry droplets to solidify in the aluminum sulfate solution, forming alumina microspheres. The sucrose and carboxymethyl cellulose in the alumina microspheres are then removed by calcination, yielding alumina ceramic microspheres with a network structure.

[0013] Furthermore, in the preparation method of the reticulated alumina ceramic microspheres, step (1) states that the mass percentage of carboxymethyl cellulose in the mixture A is 1.3%-1.5%, the mass percentage of sucrose is 13%-15%, the mass percentage of α-Al2O3 powder is 15%-20%, and the dispersant is an anionic surfactant, with the amount of dispersant being 15%-20% of the mass of α-Al2O3 powder.

[0014] In this invention, the pore structure and pore volume of the prepared reticulated alumina ceramic microspheres are controlled by adjusting the mass percentages of carboxymethyl cellulose, sucrose, and α-Al2O3 powder in the ceramic slurry. Studies have shown that excessive carboxymethyl cellulose increases the viscosity of the ceramic slurry, leading to a higher carboxymethyl cellulose content on the surface of the alumina microspheres. This results in a thicker outer shell formed after the reaction with aluminum ions, affecting the cross-linking and curing within the microspheres and reducing the pore volume of the alumina ceramic microspheres. Increasing the amount of sucrose can effectively increase the pore volume of the alumina ceramic microspheres, but the larger pore volume reduces the compressive strength, which is detrimental to their application in silica gel compositions.

[0015] Furthermore, the concentration of the aluminum sulfate solution in step (2) of the preparation method of the reticulated alumina ceramic microspheres is 3-5 mol / L.

[0016] Furthermore, the specific calcination process described in step (3) of the preparation method of the reticulated alumina ceramic microspheres is as follows: heat up to 700-800℃ at a rate of 3-5℃ / min, hold for sintering for 20-30min, then heat up to 1400-1500℃ at a rate of 5-10℃ / min, hold for sintering for 1.5-2h, and then cool.

[0017] Furthermore, the mass ratio of the reticulated alumina ceramic microspheres to graphene powder is 12-15:3-7.

[0018] Furthermore, the silane coupling agent in the aqueous solution has a mass percentage of 1-3%, and the amount of silane coupling agent used is 20%-25% of the mass of the network alumina ceramic microspheres; the silane coupling agent is one of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β(aminoethyl)-γ-aminopropyltrimethoxysilane, N-β(aminoethyl)-γ-aminopropylmethyldimethoxysilane, N-β(aminoethyl)-γ-aminopropyltriethoxysilane, and N-β(aminoethyl)-γ-aminopropylmethyldiethoxysilane.

[0019] Furthermore, the high thermal conductivity and low dielectric constant silicone composition further includes 13-17 parts by weight of hollow spherical silicon carbide.

[0020] Furthermore, the method for preparing the hollow spherical silicon carbide is as follows: (1) Tetraethyl silicate is added to a mixed solution of ethanol aqueous solution and ammonia water, and the mixture is stirred for 1-1.5 h. Then phenol and formaldehyde are added, and the mixture is stirred for 24-26 h. After centrifugation, the lower precipitate is removed, washed, and dried to obtain particle I; (2) Particle I obtained in step (1) is calcined once under inert gas protection, and then heated for a second calcination. After cooling, hollow spherical silicon carbide is obtained.

[0021] In this invention, when ammonia is used as a catalyst, tetraethyl silicate undergoes a hydrolysis-condensation reaction in an ethanol-water solution to form spherical silica particles, thus preparing spherical silica. Phenol and formaldehyde are then added, and under stirring, phenol and formaldehyde form a layer of phenolic resin on the surface of the spherical silica. The mixture is then subjected to staged calcination in an oxygen-free environment, causing the phenolic resin to carbonize. At high temperatures, this carbonized resin reacts with elemental silicon generated from the decomposition of silica to form silicon carbide. When the amount of silica is small, all the phenolic resin-coated silica reacts, forming hollow spherical silicon carbide particles. Because of the hollow structure within these spherical silicon carbide particles, this invention effectively reduces the dielectric constant of the silica composition by incorporating these porous spherical silicon carbide particles into the silica gel composition.

[0022] Furthermore, in the preparation method of hollow spherical silicon carbide, the mass percentages of each component are as follows: 30-35 parts tetraethyl silicate, 100-120 parts ethanol aqueous solution, 20-30 parts ammonia, 24-34 parts phenol, and 26-32 parts formaldehyde, with the ethanol aqueous solution containing 50%-60% by mass.

[0023] Furthermore, in step (2) of the method for preparing hollow spherical silicon carbide, the temperature of the first calcination is 700-750℃, the heating rate is 5-8℃ / min, and the calcination time is 4-5h; the temperature of the second calcination is 1500-1600℃, the heating rate is 5-10℃ / min, and the calcination time is 2.5-4h.

[0024] Furthermore, the vinyl silicone oil has a viscosity of 120 mPa·s and a vinyl content of 0.3 mmol / g; the hydrogen-containing silicone oil has a viscosity of 45 mPa·s and a hydrogen content of 1.0 mmol / L.

[0025] Furthermore, the coupling agent is dodecyltrimethoxysilane, and the catalyst is a platinum catalyst.

[0026] The present invention also provides a method for preparing the aforementioned high thermal conductivity and low dielectric constant silicone composition, specifically as follows:

[0027] S1: Mix vinyl silicone oil, hydrogen-containing silicone oil and coupling agent evenly, then add boron nitride and stir thoroughly to obtain mixture A;

[0028] S2: Add thermally conductive filler to mixture A obtained in step S1, stir thoroughly, add catalyst, stir evenly, and obtain mixture B;

[0029] S3: After degassing the mixture B obtained in step S2, calender it into shape and heat it to cure, thus obtaining a silicone composition with high thermal conductivity and low dielectric constant.

[0030] Compared with the prior art, the high thermal conductivity and low dielectric constant silicone composition and its preparation method provided by the present invention have the following technical advantages:

[0031] (1) In this invention, a ceramic slurry is formed by using gel material and α-Al2O3 powder, a pore-forming agent is added, and the gel material is cross-linked and cured with cationic material to form alumina microspheres. After calcination, a network alumina ceramic microspheres are obtained, and graphene powder is wrapped in them as a thermally conductive filler. A silane coupling agent is used to modify them, and they are added to the silicone composition to effectively improve the thermal conductivity of the silicone composition.

[0032] (2) The present invention utilizes the weak hydrogen bond connection between silica particles and phenolic resin to prepare phenolic resin on the surface of spherical silica particles, and obtains spherical silicon carbide particles with mesoporous structure by segmented calcination, which effectively reduces the dielectric constant of the silicone composition when added to the silicone composition.

[0033] (3) The thermal conductivity of the silicone composition provided by the present invention can reach 8.9w / mk and the dielectric constant can be reduced to below 3.0. When applied to electronic components, it can ensure the working stability of electronic components. Its low dielectric constant has little impact on signal transmission speed and signal delay when applied to 5G communication. Attached Figure Description

[0034] Figure 1 SEM image of the reticulated alumina ceramic microspheres prepared in Example 3;

[0035] Figure 2 SEM image of the hollow spherical silicon carbide prepared in Example 9;

[0036] Figure 3 The XRD pattern of the hollow spherical silicon carbide prepared in Example 9. Detailed Implementation

[0037] The principles and features of the present invention will be described below with reference to embodiments. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0038] The vinyl silicone oil described in this specific embodiment has a viscosity of 120 mPa·s and a vinyl content of 0.3 mmol / g; the hydrogen-containing silicone oil has a viscosity of 45 mPa·s and a hydrogen content of 1.0 mmol / L. Unless otherwise specified, all raw materials used in this embodiment are commercially available products.

[0039] Preparation Example 1

[0040] Preparation of reticulated alumina ceramic microspheres: (1) Add carboxymethyl cellulose and sucrose to deionized water, heat to 60°C, stir until completely dissolved, add α-Al2O3 powder and sodium fatty acid (15% of the mass of α-Al2O3 powder), stir thoroughly and let stand to degas, to obtain a mixture A with a mass percentage of 1.3% carboxymethyl cellulose, 13% sucrose, and 15% α-Al2O3 powder; (2) The mixture obtained in step (1) A was added dropwise to a 3 mol / L aluminum sulfate solution, soaked for 20 h, and then filtered after solidification to obtain alumina microspheres with a diameter of 2 mm; (3) The alumina microspheres obtained in step (2) were soaked in anhydrous ethanol for 24 h and then dried in a drying oven at 80 °C. Then they were placed in a pressureless sintering furnace and heated to 700 °C at a rate of 3 °C / min. They were then sintered at this temperature for 30 min, and then heated to 1400 °C at a rate of 5 °C / min. They were then sintered at this temperature for 2 h and then cooled to obtain network alumina ceramic microspheres.

[0041] Preparation Example 2

[0042] Preparation of reticulated alumina ceramic microspheres: (1) Add carboxymethyl cellulose and sucrose to deionized water, heat to 70°C, stir until completely dissolved, add α-Al2O3 powder and sodium di(2-ethylhexyl) succinate sulfonate (20% of the mass of α-Al2O3 powder), stir thoroughly and let stand to degas, to obtain a mixture A with a mass percentage of 1.5% carboxymethyl cellulose, 15% sucrose, and 20% α-Al2O3 powder; (2) The microspheres prepared in step (1) are... The mixture A was added dropwise to a 5 mol / L aluminum sulfate solution and soaked for 24 h. After solidification, it was filtered to obtain alumina microspheres with a diameter of 3 mm. (3) The alumina microspheres obtained in step (2) were soaked in anhydrous ethanol for 24 h and then dried in a drying oven at 80 °C. Then they were placed in a pressureless sintering furnace and heated to 800 °C at a rate of 5 °C / min. They were then sintered at this temperature for 20 min and then heated to 1500 °C at a rate of 10 °C / min. They were then sintered at this temperature for 1.5 h and then cooled to obtain network alumina ceramic microspheres.

[0043] Preparation Example 3

[0044] Preparation of reticulated alumina ceramic microspheres: (1) Add carboxymethyl cellulose and sucrose to deionized water, heat to 65°C, stir until completely dissolved, add α-Al2O3 powder and acesulfame potassium (18% of the mass of α-Al2O3 powder), stir thoroughly and let stand to remove gas, to obtain a mixture A with a mass percentage of 1.5% carboxymethyl cellulose, 14% sucrose, and 18% α-Al2O3 powder; (2) Add the mixture A obtained in step (1) Add the solution to a 3.8 mol / L aluminum sulfate solution, soak for 22 h, and filter after solidification to obtain alumina microspheres with a diameter of 2 mm; (3) Soak the alumina microspheres obtained in step (2) in anhydrous ethanol for 24 h and dry them in a drying oven at 80 °C. Then put them in a pressureless sintering furnace, heat them to 780 °C at a rate of 4 °C / min, hold for sintering for 25 min, then heat them to 1450 °C at a rate of 8 °C / min, hold for sintering for 1.7 h, and cool to obtain network alumina ceramic microspheres.

[0045] Preparation Example 4

[0046] Preparation of thermally conductive filler: Graphene powder was added to deionized water, and the ultrasonic frequency was set to 25 kHz and the ultrasonic power to 300 W. After ultrasonic dispersion for 30 min, reticulated alumina ceramic microspheres (mass ratio of reticulated alumina ceramic microspheres to graphene powder was 12:3) were added. The mixture was stirred and ultrasonically sonicated for another 3 h. Solid-liquid separation was then achieved. The mixture was then added to an aqueous solution of 1% γ-aminopropyltriethoxysilane, with the amount of silane coupling agent being 20% ​​of the mass of the reticulated alumina ceramic microspheres. Glacial acetic acid was added to adjust the pH of the solution to 4.8. The mixture was ultrasonically stirred at 15 kHz and 70 °C for 6 h. After filtration, the mixture was washed three times with deionized water until the pH of the washing solution was 7. The mixture was then dried in a vacuum drying oven at 60 °C and ground to obtain the thermally conductive filler.

[0047] The reticulated alumina ceramic microspheres in this preparation example were obtained in Preparation Example 1.

[0048] Preparation Example 5

[0049] Preparation of thermally conductive filler: Graphene powder was added to deionized water, and the ultrasonic frequency was set to 25 kHz and the ultrasonic power to 300 W. After ultrasonic dispersion for 30 min, reticulated alumina ceramic microspheres (mass ratio of reticulated alumina ceramic microspheres to graphene powder was 15:7) were added. The mixture was stirred and ultrasonically sonicated for 4 h, and the solid and liquid were separated. Then, it was added to an aqueous solution of N-β(aminoethyl)-γ-aminopropyltrimethoxysilane with a mass percentage of 3%. The amount of silane coupling agent was 25% of the mass of the reticulated alumina ceramic microspheres. Glacial acetic acid was added to adjust the pH of the solution to 5.2. The mixture was ultrasonically stirred at 18 kHz and 80 °C for 5 h. After filtration, the solution was washed 5 times with deionized water until the pH of the washing solution was 7. The solution was then dried in a vacuum drying oven at 70 °C and ground to obtain the thermally conductive filler.

[0050] The reticulated alumina ceramic microspheres in this preparation example were obtained in Preparation Example 2.

[0051] Preparation Example 6

[0052] Preparation of thermally conductive filler: Graphene powder was added to deionized water, and the ultrasonic frequency was set to 25 kHz with an ultrasonic power of 300 W. After ultrasonic dispersion for 30 min, reticulated alumina ceramic microspheres (mass ratio of reticulated alumina ceramic microspheres to graphene powder was 14:5) were added. The mixture was stirred and ultrasonically sonicated for another 3.5 h. Solid-liquid separation was then performed, and the mixture was added to an aqueous solution of N-β(aminoethyl)-γ-aminopropylmethyldiethoxysilane at a mass percentage of 2%. The amount of silane coupling agent was 23% of the mass of the reticulated alumina ceramic microspheres. Glacial acetic acid was added to adjust the pH of the solution to 5.1. The mixture was ultrasonically stirred at 17 kHz and 75 °C for 5.6 h. After filtration, the mixture was washed four times with deionized water until the pH of the washing solution was 7. The mixture was then dried in a vacuum drying oven at 65 °C and ground to obtain the thermally conductive filler.

[0053] The reticulated alumina ceramic microspheres in this preparation example were obtained in Preparation Example 3.

[0054] Preparation Example 7

[0055] Preparation of hollow spherical silicon carbide: (1) Add 30g of tetraethyl silicate to a mixed solution of 100g of 50% ethanol aqueous solution and 20g of ammonia water, stir and react for 1h, then add 24g of phenol and 26g of formaldehyde, continue stirring and react for 24h, centrifuge, take the lower precipitate and wash it with deionized water and ethanol, dry it at 80℃ for 12h to obtain particle I; (2) Heat the particle I obtained in step (1) to 700℃ at a heating rate of 5℃ / min under nitrogen protection, keep it heated and calcined for 5h, then heat it to 1500℃ at a heating rate of 5℃ / min, keep it heated and calcined for 4h, cool it to obtain hollow spherical silicon carbide.

[0056] Preparation Example 8

[0057] Preparation of hollow spherical silicon carbide: (1) Add 35g of tetraethyl silicate to a mixed solution of 120g of 60% ethanol aqueous solution and 30g of ammonia water, stir and react for 1.5h, then add 34g of phenol and 32g of formaldehyde, continue stirring and react for 26h, centrifuge, take the lower precipitate and wash it with deionized water and ethanol, dry it at 80℃ for 12h to obtain particle I; (2) Heat the particle I obtained in step (1) to 750℃ at a heating rate of 8℃ / min under nitrogen protection, keep it heated for 4h, then heat it to 1600℃ at a heating rate of 10℃ / min, keep it heated for 2.5h, cool it to obtain hollow spherical silicon carbide.

[0058] Preparation Example 9

[0059] Preparation of hollow spherical silicon carbide: (1) Add 33g of tetraethyl silicate to a mixed solution of 115g of 57% ethanol aqueous solution and 25g of ammonia water, stir and react for 1.3h, then add 29g of phenol and 29g of formaldehyde, continue stirring and react for 25h, centrifuge, take the lower precipitate and wash it with deionized water and ethanol, dry it at 80℃ for 12h to obtain particle I; (2) Heat the particle I obtained in step (1) to 730℃ at a heating rate of 6℃ / min under nitrogen protection, keep it heated and calcined for 4.5h, then heat it to 1550℃ at a heating rate of 8℃ / min, keep it heated and calcined for 3.0h, cool it to obtain hollow spherical silicon carbide.

[0060] Example 1

[0061] A high thermal conductivity, low dielectric constant silicone composition comprising the following components in parts by weight:

[0062] 20g of vinyl silicone oil, 10g of hydrogen-containing silicone oil, 15g of boron nitride, 40g of thermally conductive filler, 3g of dodecyltrimethoxysilane, 1g of platinum catalyst, and 17g of hollow spherical silicon carbide; the thermally conductive filler was prepared in Preparation Example 4, and the hollow spherical silicon carbide was prepared in Preparation Example 7.

[0063] The preparation method of the high thermal conductivity and low dielectric constant silicone composition is as follows:

[0064] S1: After uniformly mixing vinyl silicone oil, hydrogen-containing silicone oil and dodecyltrimethoxysilane, add boron nitride and stir at 500 rpm for 40 min to obtain mixture A;

[0065] S2: Add thermally conductive filler to mixture A obtained in step S1, stir at 300 rpm for 40 min, add platinum catalyst, and continue stirring for 2 h to obtain mixture B.

[0066] S3: After the mixture B obtained in step S2 is allowed to stand for 1 hour, it is degassed using a vacuum degassing device with a vacuum degree of -0.1 MPa and a degassing time of 10 min. Then, 5 g of the degassed mixture B is calendered using a three-roll calender (the temperature of roll III is 60℃, the temperature of roll II is 50℃, the temperature of roll I is 35℃, the roller pressure is 0.2 MPa, the roller speed is 5 m / min, and the roller gap is 3 mm). Subsequently, it is cured in a two-stage curing manner (the temperature of the first stage of curing is 60℃ and the curing time is 90 min, and the temperature of the second stage of curing is 120℃ and the curing time is 60 min). After cooling, a high thermal conductivity and low dielectric constant silicone composition is obtained.

[0067] Example 2

[0068] A high thermal conductivity, low dielectric constant silicone composition comprising the following components in parts by weight:

[0069] 30g of vinyl silicone oil, 5g of hydrogen-containing silicone oil, 30g of boron nitride, 50g of thermally conductive filler, 5g of dodecyltrimethoxysilane, 3g of platinum catalyst, and 13g of hollow spherical silicon carbide; the thermally conductive filler was prepared in Preparation Example 5, and the hollow spherical silicon carbide was prepared in Preparation Example 8.

[0070] The preparation method of the high thermal conductivity and low dielectric constant silicone composition is as follows:

[0071] S1: After uniformly mixing vinyl silicone oil, hydrogen-containing silicone oil and dodecyltrimethoxysilane, add boron nitride and stir at 700 rpm for 30 min to obtain mixture A;

[0072] S2: Add thermally conductive filler to mixture A obtained in step S1, stir at 400 rpm for 30 min, add platinum catalyst, and continue stirring for 2.5 h to obtain mixture B;

[0073] S3: After the mixture B obtained in step S2 is allowed to stand for 1 hour, it is degassed using a vacuum degassing device with a vacuum degree of -0.1 MPa and a degassing time of 20 min. Then, 5 g of the degassed mixture B is calendered using a three-roll calender (the temperature of roll III is 70℃, the temperature of roll II is 60℃, the temperature of roll I is 45℃, the roller pressure is 0.5 MPa, the roller speed is 8 m / min, and the roller gap is 4 mm). Subsequently, it is cured in a two-stage curing manner (the temperature of the first stage of curing is 70℃ and the curing time is 60 min, and the temperature of the second stage of curing is 130℃ and the curing time is 30 min). After cooling, a high thermal conductivity and low dielectric constant silicone composition is obtained.

[0074] Example 3

[0075] A high thermal conductivity, low dielectric constant silicone composition comprising the following components in parts by weight:

[0076] 28g of vinyl silicone oil, 8g of hydrogen-containing silicone oil, 20g of boron nitride, 47g of thermally conductive filler, 4g of dodecyltrimethoxysilane, 2g of platinum catalyst, and 15g of hollow spherical silicon carbide; the thermally conductive filler was prepared in Preparation Example 6, and the hollow spherical silicon carbide was prepared in Preparation Example 9.

[0077] The preparation method of the high thermal conductivity and low dielectric constant silicone composition is as follows:

[0078] S1: After mixing vinyl silicone oil, hydrogen-containing silicone oil and dodecyltrimethoxysilane evenly, add boron nitride and stir at 600 rpm for 35 min to obtain mixture A;

[0079] S2: Add thermally conductive filler to mixture A obtained in step S1, stir at 350 rpm for 38 min, add platinum catalyst, and continue stirring for 2.2 h to obtain mixture B;

[0080] S3: After the mixture B obtained in step S2 is allowed to stand for 1 hour, it is degassed using a vacuum degassing device with a vacuum degree of -0.1 MPa and a degassing time of 17 min. Then, 5 g of the degassed mixture B is calendered using a three-roll calender (the temperature of roll III is 65℃, the temperature of roll II is 57℃, the temperature of roll I is 40℃, the roller pressure is 0.4 MPa, the roller speed is 7 m / min, and the roller gap is 3.5 mm). Subsequently, it is cured in a two-stage curing manner (the temperature of the first stage of curing is 65℃ and the curing time is 80 min, and the temperature of the second stage of curing is 125℃ and the curing time is 40 min). After cooling, a high thermal conductivity and low dielectric constant silicone composition is obtained.

[0081] Example 4

[0082] A high thermal conductivity, low dielectric constant silicone composition comprising the following components in parts by weight:

[0083] 28g of vinyl silicone oil, 8g of hydrogen-containing silicone oil, 20g of boron nitride, 47g of thermally conductive filler, 4g of dodecyltrimethoxysilane, 2g of platinum catalyst, and 15g of hollow spherical silicon carbide; the thermally conductive filler was prepared in Preparation Example 6, and the hollow spherical silicon carbide was prepared in Preparation Example 9.

[0084] The preparation method of the high thermal conductivity and low dielectric constant silicone composition is the same as that in Example 3.

[0085] Example 5

[0086] A high thermal conductivity, low dielectric constant silicone composition comprising the following components in parts by weight:

[0087] 28g of vinyl silicone oil, 8g of hydrogen-containing silicone oil, 18g of boron nitride, 43g of thermally conductive filler, 4g of dodecyltrimethoxysilane, 2g of platinum catalyst, and 16g of hollow spherical silicon carbide; the thermally conductive filler was prepared in Preparation Example 6, and the hollow spherical silicon carbide was prepared in Preparation Example 9.

[0088] The preparation method of the high thermal conductivity and low dielectric constant silicone composition is the same as that in Example 3.

[0089] Example 6

[0090] A high thermal conductivity, low dielectric constant silicone composition comprising the following components in parts by weight:

[0091] 28g of vinyl silicone oil, 8g of hydrogen-containing silicone oil, 23g of boron nitride, 46g of thermally conductive filler, 4g of dodecyltrimethoxysilane, 2g of platinum catalyst, and 14g of hollow spherical silicon carbide; the thermally conductive filler was prepared in Preparation Example 6, and the hollow spherical silicon carbide was prepared in Preparation Example 9.

[0092] The preparation method of the high thermal conductivity and low dielectric constant silicone composition is the same as that in Example 3.

[0093] Comparative Example 1

[0094] The silica gel composition described in this comparative example is similar to that in Example 4. The difference between this comparative example and Example 4 is as follows: The preparation method of the thermally conductive filler in this comparative example is as follows: Graphene powder is added to deionized water, the ultrasonic frequency is set to 25 kHz, the ultrasonic power is 300 W, and after ultrasonic dispersion for 30 min, mesoporous silica (the mass ratio of mesoporous silica to graphene powder is 14:5) is added, and the mixture is stirred and ultrasonically sonicated for another 3.5 h. After solid-liquid separation, the mixture is added to an aqueous solution of N-β(aminoethyl)-γ-aminopropylmethyldiethoxysilane at a mass percentage of 2%. The amount of silane coupling agent is 23% of the mass of mesoporous silica. Glacial acetic acid is added to adjust the pH of the solution to 5.1. The mixture is ultrasonically stirred at 17 kHz and 75 °C for 5.6 h, filtered, and washed four times with deionized water until the pH of the washing solution is 7. The solution is then dried in a vacuum drying oven at 65 °C and ground to obtain the thermally conductive filler. The particle size of the mesoporous silica is 500 μm, and the porosity is 60%.

[0095] Comparative Example 2

[0096] The silica gel composition described in this comparative example is similar to that in Example 4. The difference between this comparative example and Example 4 is as follows: The preparation method of the network alumina ceramic microspheres in this comparative example is as follows: (1) Carboxymethyl cellulose and sucrose are added to deionized water, heated to 65°C, stirred until completely dissolved, α-Al2O3 powder and acesulfame potassium (18% of the mass of α-Al2O3 powder) are added, stirred thoroughly and evenly, and allowed to stand to remove gas, to obtain a mass percentage of 2.5% carboxymethyl cellulose, 7% sucrose, and 18% α-Al2O3 powder. (1) Mixture A; (2) Add the mixture A obtained in step (1) to a 3.8 mol / L aluminum sulfate solution, soak for 22 h, and filter after solidification to obtain alumina microspheres with a diameter of 2 mm; (3) Soak the alumina microspheres obtained in step (2) in anhydrous ethanol for 24 h, dry them in a drying oven at 80 °C, and then put them in a pressureless sintering furnace, raise the temperature to 780 °C at a rate of 4 °C / min, hold for sintering for 25 min, raise the temperature to 1450 °C at a rate of 8 °C / min, hold for sintering for 1.7 h, cool, and obtain network alumina ceramic microspheres.

[0097] Comparative Example 3

[0098] The silicone composition described in this comparative example is similar to that in Example 5. The difference between this comparative example and Example 5 is that an equal amount of boron nitride is used instead of hollow spherical silicon carbide in this comparative example.

[0099] Comparative Example 4

[0100] The silica gel composition in this comparative example is similar to that in Example 5. The difference between this comparative example and Example 5 is as follows: The preparation method of hollow spherical silicon carbide in this comparative example is as follows: (1) 66g of tetraethyl silicate is added to a mixed solution of 230g of 57% ethanol aqueous solution and 50g of ammonia water, and the mixture is stirred for 1.3h. Then 29g of phenol and 29g of formaldehyde are added, and the mixture is stirred for 25h. After centrifugation, the lower precipitate is taken out and washed with deionized water and ethanol. It is then dried at 80°C for 12h to obtain particle I. (2) Particle I obtained in step (1) is heated to 730°C at a heating rate of 6°C / min under nitrogen protection and calcined for 4.5h. Then it is heated to 1550°C at a heating rate of 8°C / min and calcined for 3.0h. After cooling, hollow spherical silicon carbide is obtained.

[0101] Test case

[0102] Pore ​​structure testing of reticulated alumina ceramic microspheres: The bulk density and porosity of the reticulated alumina ceramic microspheres prepared in Preparation Examples 1-3 and Comparative Example 2 were calculated using the Archimedes' displacement method. During testing, the regularly shaped reticulated alumina ceramic microsphere samples were suspended in deionized water without contact with the bottom or sides of the container. The density and porosity of the material were calculated based on the balance readings. The experimental results are shown in Table 1.

[0103] Dielectric constant test: The dielectric constant of the silicone compositions prepared in Examples 1-6 and Comparative Examples 1-4 was tested using a ZJD-C type dielectric constant tester (Beijing Zhonghang Times Instrument Equipment Co., Ltd.). The test frequency was 1MHz. The test results are shown in Table 2.

[0104] Thermal conductivity test: The thermal conductivity of the silicone compositions prepared in Examples 1-6 and Comparative Examples 1-4 were tested according to ISO22007-2.2. The test results are shown in Table 2.

[0105] Scanning electron microscopy (SEM): The reticulated alumina ceramic microspheres prepared in Example 3 and the hollow spherical silicon carbide prepared in Example 9 were tested using a SU8220 cold field emission scanning electron microscope. The test results are shown in [Figure number missing]. Figure 1 and Figure 2 .

[0106] X-ray diffraction analysis: The hollow spherical silicon carbide prepared in Example 9 was analyzed using a horizontal high-power X-ray powder diffractometer TTR-III. The test results are shown in […]. Figure 3 .

[0107] Table 1. Test results of the hole structure

[0108] Group <![CDATA[Apparent density / g·cm -3 > Apparent porosity / % Preparation Example 1 0.98 61.7 Preparation Example 2 0.94 64.0 Preparation Example 3 0.89 67.2 Comparative Example 2 1.67 36.8

[0109] As shown in Table 1, the reticulated alumina ceramic microspheres provided by this invention have a low bulk density and a high apparent porosity, which can effectively coat graphene powder and uniformly disperse it in the silica gel composition to achieve a three-dimensional network thermal conductivity pathway, effectively improving the thermal conductivity of the silica gel composition. In Comparative Example 2, the amounts of carboxymethyl cellulose and sucrose were changed, but the bulk density of the alumina ceramic microspheres increased and the apparent porosity decreased. This indicates that the amount of carboxymethyl cellulose affects the pore structure and pore volume of the alumina ceramic microspheres, while reducing the amount of sucrose as a pore-forming agent leads to a significant decrease in the apparent porosity of the alumina microspheres.

[0110] Table 2. Test results of dielectric and thermal conductivity properties

[0111] Group Dielectric constant Thermal conductivity / W / mK Example 1 2.9 7.8 Example 2 2.6 7.6 Example 3 2.8 8.1 Example 4 2.3 8.9 Example 5 2.1 8.6 Example 6 2.4 8.4 Comparative Example 1 2.2 2.5 Comparative Example 2 2.3 4.2 Comparative Example 3 5.8 8.3 Comparative Example 4 4.5 8.4

[0112] As shown in Table 2, the dielectric constant of the high thermal conductivity and low dielectric constant silicone composition provided by the present invention is 2.1-2.9, and the thermal conductivity is 7.6-8.9 W / mK. This indicates that the high thermal conductivity and low dielectric constant silicone composition provided by the present invention has good thermal conductivity and low dielectric properties, and its application in 5G communication has little impact on signal transmission speed and signal delay.

[0113] Compared to Example 4, Comparative Example 1 used mesoporous silica instead of reticulated alumina ceramic microspheres. However, the dielectric constant of the resulting silica composition was slightly reduced, and the thermal conductivity was significantly reduced. This indicates that although the porosity of the mesoporous silica was not much different from the apparent porosity of the reticulated alumina ceramic microspheres prepared in Example 4, the apparent porosity of the mesoporous silica was lower, resulting in reduced graphene coating. Furthermore, the lower thermal conductivity of silica caused a significant reduction in the thermal conductivity of the silica composition. Comparative Example 2 changed the amount of carboxymethyl cellulose and sucrose in the preparation method of the reticulated alumina ceramic microspheres, but the thermal conductivity of the resulting silica composition was reduced. This was due to the change in the amount of carboxymethyl cellulose and sucrose affecting the pore structure of the reticulated alumina ceramic microspheres.

[0114] Compared to Example 5, Comparative Example 3 did not add hollow spherical silicon carbide, but the dielectric constant of the resulting silicone composition increased significantly. This indicates that adding porous spherical silicon carbide particles to the silicone composition can effectively reduce the dielectric constant of the silicone composition. In Comparative Example 4, the amount of tetraethyl silicate, aqueous ethanol solution, and ammonia was increased in the preparation method of hollow spherical silicon carbide, but the dielectric constant of the resulting silicone composition increased significantly. This is because there is excess silicon dioxide in the preparation method of hollow spherical silicon carbide. After the silicon carbide microspheres are generated, there is still excess silicon dioxide in the center, resulting in the silicon carbide not having a hollow structure, thus increasing the dielectric constant of the silicone composition.

[0115] Depend on Figure 1 and Figure 2 It can be seen that the reticulated alumina ceramic microspheres prepared by the present invention have a good spherical structure and the surface pores are evenly distributed; the hollow spherical silicon carbide has a hollow spherical structure, but the phenomenon of mutual adhesion occurs, which is due to the high reaction temperature and violent exothermic process during the high-temperature carbothermic reduction process.

[0116] Depend on Figure 3 It can be seen that the XRD pattern of the hollow spherical silicon carbide shows the (111), (200), (220), and (311) crystal planes of silicon carbide, which indicates that the main component of the hollow spherical silicon carbide prepared by the present invention is silicon carbide.

[0117] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be within the protection scope of the present invention.

Claims

1. A silicone composition with high thermal conductivity and low dielectric constant, characterized in that, The components include the following parts by mass: The mixture comprises 20-30 parts vinyl silicone oil, 5-10 parts hydrogen-containing silicone oil, 15-30 parts boron nitride, 40-50 parts thermally conductive filler, 3-5 parts coupling agent, and 1-3 parts catalyst. The preparation method of the thermally conductive filler is as follows: graphene powder is added to deionized water, ultrasonically dispersed, and then network alumina ceramic microspheres are added. The mixture is stirred and ultrasonically sonicated for 3-4 hours, and the solid and liquid are separated. Then, the filler is added to an aqueous solution of silane coupling agent and ultrasonically reacted for 5-6 hours. The mixture is then filtered, washed, dried, and ground to obtain the thermally conductive filler.

2. The high thermal conductivity and low dielectric constant silicone composition according to claim 1, characterized in that, The preparation method of the network alumina ceramic microspheres is as follows: (1) Carboxymethyl cellulose and sucrose are added to deionized water, heated and stirred until completely dissolved, α-Al2O3 powder and dispersant are added, stirred thoroughly and evenly, and allowed to stand to remove gas to obtain a mixture A; (2) The mixture A obtained in step (1) is added dropwise to aluminum sulfate solution, soaked for 20-24 hours, and filtered after solidification to obtain alumina microspheres with a diameter of 2-3 mm; (3) The alumina microspheres obtained in step (2) are placed in a sintering furnace for calcination to obtain network alumina ceramic microspheres.

3. The high thermal conductivity and low dielectric constant silicone composition according to claim 2, characterized in that, In step (1), the mass percentage of carboxymethyl cellulose in the mixture A is 1.3%-1.5%, the mass percentage of sucrose is 13%-15%, the mass percentage of α-Al2O3 powder is 15%-20%, and the dispersant is an anionic surfactant, with the amount of dispersant being 15%-20% of the mass of α-Al2O3 powder.

4. The high thermal conductivity and low dielectric constant silicone composition according to claim 2, characterized in that, The concentration of the aluminum sulfate solution in step (2) is 3-5 mol / L; the specific calcination process in step (3) is as follows: heat up to 700-800℃ at a rate of 3-5℃ / min, hold for sintering for 20-30 min, then heat up to 1400-1500℃ at a rate of 5-10℃ / min, hold for sintering for 1.5-2 h, and then cool.

5. The high thermal conductivity and low dielectric constant silicone composition according to claim 1, characterized in that, The mass ratio of the reticulated alumina ceramic microspheres to graphene powder is 12-15:3-7; the mass percentage of the silane coupling agent in the aqueous solution is 1-3%.

6. The high thermal conductivity and low dielectric constant silicone composition according to claim 1, characterized in that, The high thermal conductivity and low dielectric constant silicone composition further includes 13-17 parts by weight of hollow spherical silicon carbide.

7. The high thermal conductivity, low dielectric constant silicone composition according to claim 6, characterized in that, The method for preparing hollow spherical silicon carbide is as follows: (1) Tetraethyl silicate is added to a mixed solution of ethanol aqueous solution and ammonia water, and the mixture is stirred for 1-1.5 h. Then phenol and formaldehyde are added, and the mixture is stirred for 24-26 h. After centrifugation, the lower precipitate is taken out, washed, and dried to obtain particle I; (2) Particle I obtained in step (1) is calcined once under inert gas protection, and then heated for a second calcination. After cooling, hollow spherical silicon carbide is obtained.

8. The high thermal conductivity and low dielectric constant silicone composition according to claim 7, characterized in that, The mass fractions of each component in the preparation method of hollow spherical silicon carbide are as follows: 30-35 parts tetraethyl silicate, 100-120 parts aqueous ethanol solution, 20-30 parts ammonia, 24-34 parts phenol, and 26-32 parts formaldehyde. The mass percentage of ethanol in the aqueous ethanol solution is 50%-60%.

9. The high thermal conductivity, low dielectric constant silicone composition according to claim 7, characterized in that, The temperature of the first roasting in step (2) is 700-750℃, the heating rate is 5-8℃ / min, and the roasting time is 4-5h; the roasting temperature of the second roasting is 1500-1600℃, the heating rate is 5-10℃ / min, and the roasting time is 2.5-4h.

10. The method for preparing the high thermal conductivity and low dielectric constant silicone composition according to any one of claims 1-9, characterized in that, Specifically: S1: Mix vinyl silicone oil, hydrogen-containing silicone oil and coupling agent evenly, then add boron nitride and stir thoroughly to obtain mixture A; S2: Add thermally conductive filler to mixture A obtained in step S1, stir thoroughly, add catalyst, stir evenly, and obtain mixture B; S3: After degassing the mixture B obtained in step S2, calender it into shape and heat it to cure, thus obtaining a silicone composition with high thermal conductivity and low dielectric constant.

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