Gradient interface modified aluminum oxide-aluminum nitride two-component heat-conducting filler and preparation method thereof

Abstract

The invention belongs to the field of heat conduction materials, and particularly relates to gradient interface modified aluminum oxide-aluminum nitride bi-component heat conduction filler and a preparation method thereof, and the gradient interface modified aluminum oxide-aluminum nitride bi-component heat conduction filler comprises spherical aluminum oxide, flaky aluminum nitride and double gradient modified layers coating the surfaces of the spherical aluminum oxide and the flaky aluminum nitride; the D50 of the spherical aluminum oxide is 2-5 microns, and the sphericity is greater than or equal to 0.85; the sheet-shaped aluminum nitride is in a hexagonal sheet shape, the average particle size is 8-12 microns, the thickness is 200-500 nanometers, and the radius-thickness ratio is 20-50; the mass ratio of the spherical aluminum oxide to the flaky aluminum nitride is (40-70): (30-60); the double-layer gradient modification layer comprises an inner-layer hydrophobic silane layer and an outer-layer reactive silane layer, the inner-layer hydrophobic silane layer is formed by grafting alkyl trialkoxy silane with the carbon chain length of 8-16, the outer-layer reactive silane layer is formed by grafting a silane coupling agent containing an epoxy group or an amino group, and morphological complementary optimization of a filler network is achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of heat-conducting materials, and particularly relates to a gradient interface modified alumina-aluminum nitride dual-component heat-conducting filler and a preparation method thereof, and is particularly suitable for the preparation of electronic device thermal interface materials. BACKGROUND

[0002] With the development of electronic devices towards high power density and miniaturization, thermal management has become a key factor restricting the performance and reliability of electronic products. As a key medium connecting heat-generating components and heat dissipation devices, the thermal conductivity of thermal interface materials directly affects the efficiency of the entire thermal management system. Traditional thermal interface materials mainly use silicone rubber or epoxy resin as the matrix, and add heat-conducting fillers to improve the thermal conductivity. Commonly used heat-conducting fillers include ceramic materials such as alumina, boron nitride and aluminum nitride. Among them, alumina is widely used due to its low price and easy processing, but its intrinsic thermal conductivity is only 30 to 40 watts per meter kelvin, limiting the space for improving the thermal conductivity of the composite material.

[0003] Chinese Patent Application Publication No. CN115678105A discloses a heat-conducting filler and a thermal interface material and a preparation method thereof. The patent uses dopamine-modified fumed alumina and micron-sized alumina to reduce viscosity and improve thermal conductivity through particle size grading optimization. In this patent, the specific surface area of the fumed alumina is 20 to 150 square meters per gram, the average particle size is 20 to 800 nanometers, the D50 of the micron-sized alumina is 1 to 1000 micrometers, and the mass ratio of the two is 1 to 0.3 to 10. The preparation method is to disperse the fumed alumina and micron-sized alumina in water to obtain a suspension, add dopamine hydrochloride and a tris-hydroxymethyl aminomethane buffer solution to adjust the system to be alkaline, and react under ultrasonic oscillation for 48 to 96 hours. The thermal conductivity of the obtained thermal interface material is 1.49 watts per meter kelvin when the filling amount is 400 parts, and the viscosity is 13000 centipoise.

[0004] However, the above technical solution still has the following deficiencies. First, the single alumina filler system used in this solution improves the dispersibility and fluidity through particle size grading optimization, but the thermal conductivity of alumina itself is low, which limits the improvement of the thermal conductivity of the composite material. Second, the single-layer interface structure formed by dopamine modification improves the compatibility of the filler and the matrix, but it fails to achieve deep regulation of the interface thermal resistance, and there is still a lot of interface phonon scattering at high filling amounts. Third, this solution does not consider the long-term stability of the filler, which may cause performance degradation in high temperature and high humidity environments. Finally, the single-morphology spherical filler fails to fully utilize the morphology synergy effect to construct an efficient heat-conducting network.

[0005] Aluminum nitride, as a high-performance thermal conductive ceramic, has an intrinsic thermal conductivity of 200 to 320 W / mK, which is much higher than that of aluminum oxide, and also has good electrical insulation performance. However, the surface of aluminum nitride is prone to hydrolysis reaction with water to generate aluminum hydroxide and ammonia gas, resulting in a decrease in thermal conductivity and the generation of corrosive gas, which seriously limits its application in thermal interface materials. Therefore, how to effectively utilize the high thermal conductivity of aluminum nitride while overcoming the problem of hydrolysis failure is a technical problem that needs to be solved in the field.

[0006] In addition, the surface modification of fillers in the prior art often uses a single modifier or a single layer of modification structure, and the multiple interface regulation requirements between fillers and fillers, and between fillers and matrix are not fully considered. Theoretical research on interface engineering shows that by constructing a gradient functional interface, a continuous transition from hydrophobic to hydrophilic and from physical isolation to chemical bonding can be achieved, thereby reducing filler aggregation while strengthening interface heat conduction. However, the systematic application of this theory in the preparation of thermal conductive fillers has not been reported. SUMMARY

[0007] The purpose of the present application is to overcome the shortcomings of the prior art and provide a gradient interface modified aluminum oxide-aluminum nitride dual-component thermal conductive filler and a preparation method thereof. The filler, through the systematic integration of the morphology synergy of spherical aluminum oxide and flaky aluminum nitride, double-layer gradient silanization modification, and aluminum nitride hydrolysis protection, significantly improves the processing performance and long-term stability while maintaining excellent thermal conductivity, providing an innovative technical solution for high-performance thermal interface materials.

[0008] To achieve the above-mentioned purposes, the present application adopts the following technical solutions. The present application provides a gradient interface modified aluminum oxide-aluminum nitride dual-component thermal conductive filler, which includes spherical aluminum oxide, flaky aluminum nitride, and a double-layer gradient modification layer coated on the surface of the spherical aluminum oxide and the flaky aluminum nitride. The D50 of the spherical aluminum oxide is 2 to 5 microns, and the sphericity is greater than or equal to 0.85. The flaky aluminum nitride is in the form of a hexagonal flake, with an average particle size of 8 to 12 microns, a thickness of 200 to 500 nanometers, and a diameter-to-thickness ratio of 20 to 50. The mass ratio of the spherical aluminum oxide to the flaky aluminum nitride is 40 to 70 to 30 to 60. The double-layer gradient modification layer includes an inner hydrophobic silane layer and an outer reactive silane layer. The inner hydrophobic silane layer is formed by grafting alkyl trialkoxysilane with a carbon chain length of 8 to 16, and the outer reactive silane layer is formed by grafting silane coupling agents containing epoxy or amino groups. The surface of the flaky aluminum nitride is also coated with a hydrolysis protection layer below the double-layer gradient modification layer, which is a polyimide layer or a liquid metal layer.

[0009] Preferably, the D50 of the spherical alumina is 3 to 4 microns, the specific surface area is 8 to 15 square meters per gram, and the average particle size of the flaky aluminum nitride is 9 to 11 microns. Further preferably, the mass ratio of the spherical alumina to the flaky aluminum nitride is 55 to 60 to 40 to 45, which can achieve the best balance between the packing effect and the construction of the heat conduction network.

[0010] In an embodiment of the present application, the inner layer of the hydrophobic silane layer is formed by grafting hexadecyltrimethoxysilane or isobutyltrimethoxysilane, and the grafting amount is 0.3% to 1.2% of the total mass of the filler. The outer layer of the reactive silane layer is formed by grafting γ-glycidoxypropyltrimethoxysilane or γ-aminopropyltriethoxysilane, and the grafting amount is 0.8% to 2.5% of the total mass of the filler. When the anti-hydrolysis protective layer is a polyimide layer, the thickness is 5 to 15 nanometers, and the content is 1.5% to 5.0% of the mass of the flaky aluminum nitride. When the anti-hydrolysis protective layer is a liquid metal layer, the liquid metal is a gallium-indium-tin alloy, and the content is 0.5% to 2.0% of the mass of the flaky aluminum nitride.

[0011] The present application also provides a preparation method of the gradient interface modified alumina-aluminum nitride dual-component heat-conducting filler, which comprises the following steps. Step one is to perform anti-hydrolysis pretreatment on the flaky aluminum nitride. The flaky aluminum nitride is dried under vacuum at 120 degrees Celsius for 8 to 12 hours, then subjected to surface hydroxylation treatment to obtain hydroxylated aluminum nitride, mixed with a polyamide acid solution or a gallium-indium-tin liquid metal, and subjected to spray drying or ball milling, and then heat-treated under nitrogen protection to obtain pretreated aluminum nitride with a surface coated with an anti-hydrolysis protective layer. Step two is to perform inner layer hydrophobic silane modification. The mixture of spherical alumina and pretreated aluminum nitride is dispersed in an alcohol solution of alkyltrialkoxysilane with a carbon chain length of 8 to 16, the alcohol solution is adjusted to a pH value of 4.0 to 4.5 with glacial acetic acid, and the reaction is carried out at 50 to 70 degrees Celsius for 4 to 6 hours. After filtration, drying is performed at 100 to 120 degrees Celsius, and then heat treatment is performed at 150 degrees Celsius for 2 hours to obtain the inner layer modified filler. Step three is to perform outer layer reactive silane modification. The inner layer modified filler is dispersed in an alcohol solution of silane coupling agent containing an epoxy group or an amino group, the alcohol solution is adjusted to a pH value of 4.5 to 5.0 with glacial acetic acid, and the reaction is carried out at 60 to 80 degrees Celsius for 5 to 8 hours. After filtration, drying is performed at 110 degrees Celsius for 4 hours, and then heat treatment is sequentially performed at 150 degrees Celsius for 2 hours and at 180 degrees Celsius for 2 hours under nitrogen protection to obtain the gradient interface modified alumina-aluminum nitride dual-component heat-conducting filler.

[0012] In a specific implementation, the surface hydroxylation treatment is performed as follows. The dried flaky aluminum nitride is dispersed in deionized water to form a suspension with a solid content of 15% to 25%, a sodium hydroxide solution is added to adjust the pH value to 9.5 to 10.5, and the reaction is stirred at 60 to 80 degrees Celsius for 2 to 4 hours. After filtration, the product is washed with deionized water until neutral, and dried at 80 degrees Celsius. When the hydrolysis-resistant protective layer is a polyimide layer, the hydroxylated aluminum nitride is mixed with a polyamide acid N-methyl pyrrolidone solution with a solid content of 8% to 12% at a mass ratio of 100 to 2.5 to 3.5, ultrasonic dispersion is performed for 30 minutes, mechanical stirring is performed for 2 hours, and then spray drying or rotary evaporation is performed to remove the solvent. Under nitrogen protection, heat treatment is sequentially performed at 80 degrees Celsius for 1 hour, at 150 degrees Celsius for 1 hour, at 250 degrees Celsius for 2 hours, and at 350 degrees Celsius for 1 hour to complete imidization. When the hydrolysis-resistant protective layer is a liquid metal layer, the dried flaky aluminum nitride is mixed with a gallium-indium-tin liquid metal at a mass ratio of 100 to 0.8 to 1.2, mechanical ball milling is performed at a ball-to-material ratio of 5 to 1, a rotation speed of 300 to 400 revolutions per minute, and a ball milling time of 3 to 6 hours.

[0013] Further, in step two, the alkyl trialkoxysilane with a carbon chain length of 8 to 16 is hexadecyl trimethoxysilane or isobutyl trimethoxysilane, the concentration in the alcohol solution is 2% to 5%, the mass ratio of alcohol to water is 90 to 10 to 95 to 5, and the solid-to-liquid ratio is 1 to 8 to 1 to 12. In step three, the silane coupling agent containing an epoxy group or an amino group is γ-glycidoxypropyltrimethoxysilane or γ-aminopropyltriethoxysilane, the concentration in the alcohol solution is 3% to 6%, the mass ratio of alcohol to water is 85 to 15 to 90 to 10, and the solid-to-liquid ratio is 1 to 10 to 1 to 15.

[0014] The beneficial effects of the present application are as follows. First, through the dual-component synergistic design of spherical alumina and flaky aluminum nitride, the morphology of the filler network is optimized. Spherical alumina provides a three-dimensional isotropic filling skeleton, maintaining a low viscosity at a high filler loading, while flaky aluminum nitride forms a lapped heat conduction path in the gap between spherical particles, building a high-efficiency heterogeneous heat conduction network. This morphology synergy makes the thermal conductivity of the filler 3 to 4 times higher than that of a single alumina system at the same filler loading, while the viscosity is reduced by more than 30%. Second, the dual-layer gradient silanization modification builds a continuous transition interface from hydrophobic to hydrophilic, from physical isolation to chemical bonding. The inner layer of hydrophobic silane reduces the surface energy of the filler through long-chain alkyl groups, reducing the van der Waals attraction and agglomeration tendency between fillers, and the flexible alkyl chain partially matches the phonon density of states mismatch between inorganic fillers and organic matrix as a phonon buffer layer. The epoxy or amino group of the outer layer of reactive silane chemically bonds with the silicone rubber matrix, eliminating the physical interface gap, allowing phonons to be transmitted through covalent bond bridges, and the interface thermal conductivity is increased by 3 to 5 times. This gradient interface design maintains good dispersion while deeply regulating the interface thermal resistance. Third, to address the problem of hydrolysis failure of aluminum nitride, a double protection mechanism is built through polyimide coating or liquid metal coating. Polyimide forms a chemical bond with the surface of aluminum nitride, and its dense imide ring structure and low free volume fraction effectively block water penetration. After 1000 hours of aging at 85 degrees Celsius and 85% relative humidity, the ammonia release is less than 50 ppm, and the thermal conductivity retention rate is more than 95%, while untreated aluminum nitride releases more than 5000 ppm of ammonia after 168 hours and its thermal conductivity decreases by more than 30%. Fourth, the preparation method of the present application is simple and controllable, and through the step-by-step modification strategy, the structure and performance of each functional layer are accurately controlled, suitable for industrial scale production. Fifth, compared with the use of high-end thermal conductive fillers such as boron nitride alone, the present application reduces the raw material cost by 35% to 45% while maintaining high thermal conductivity through the reasonable ratio of alumina and aluminum nitride, with a significant economic advantage. DETAILED DESCRIPTION

[0015] The present application will be further described in conjunction with specific embodiments. It should be noted that the following examples are used to illustrate the present application but not to limit the scope of protection of the present application.

[0016] The raw materials used in the examples and their sources are as follows. Spherical alumina, product model HA-301, purity 99.5% or more. Flaky aluminum nitride, product model AlN-F10, purity 99.0% or more. Hexadecyltrimethoxysilane, product model HDTMS-99, purity 99% or more. Isobutyltrimethoxysilane, product model iBTMS, purity 98% or more, purchased from Shanghai Aldrin Biochemical Technology Co., Ltd. Gamma-glycidoxypropyltrimethoxysilane, product model KH560, purity 99% or more. Gamma-aminopropyltriethoxysilane, product model KH550, purity 98% or more. Polyamic acid solution, product model PAA-15, solid content 15%, solvent N-methylpyrrolidone, molecular weight 40000. Galinstan, product model Galinstan, composition 68.5% gallium, 21.5% indium, 10% tin. Vinyl silicone oil, product model RH-401, viscosity 1000 centipoise, vinyl content 0.15 mole%. Hydrogen-containing silicone oil, product model RH-580, hydrogen content 0.5%. Platinum-gold catalyst, platinum content 2500 ppm. Ethynylcyclohexanol, purity 98%. Sodium hydroxide, glacial acetic acid, anhydrous ethanol, and deionized water are all analytical reagents.

[0017] Example 1 In the gradient interface modified alumina-aluminum nitride dual-component thermal conductive filler prepared in this example, the D50 of the spherical alumina is 2 microns, the average particle size of the flaky aluminum nitride is 8 microns, the mass ratio of the two is 40 to 30, and the hydrolysis-resistant protective layer is a polyimide layer. The specific preparation method includes the following steps.

[0018] First, the flaky aluminum nitride is pretreated to prevent hydrolysis. 300 grams of flaky aluminum nitride with an average particle size of 8 microns and a thickness of 200 nanometers is placed in a vacuum drying oven and dried at 120 degrees Celsius and a vacuum degree less than 10 Pa for 12 hours to ensure that the residual moisture is less than 0.05%. The dried aluminum nitride is immediately transferred to a three-necked flask equipped with a mechanical stirrer, 1500 milliliters of deionized water is added, and ultrasonic dispersion is performed for 20 minutes to form a suspension with a solid content of 20%. Under continuous stirring, 5 moles per liter of sodium hydroxide solution is slowly added, the pH is monitored and adjusted to 10.0 with a pH meter. The reaction system is heated to 70 degrees Celsius, the stirring speed is kept at 300 revolutions per minute, and the reaction is carried out for 3 hours, so that hydroxyl groups are generated on the surface of the aluminum nitride. After the reaction is completed, hot filtration is performed, and the filter is washed repeatedly with deionized water at 80 degrees Celsius until the pH of the filtrate is 7, and then dried in an 80 degrees Celsius oven for 8 hours to obtain hydroxylated aluminum nitride.

[0019] Next, the polyimide coating was performed. 300 grams of the above hydroxylated aluminum nitride was added to a four-necked flask equipped with a mechanical stirrer and a condenser. 750 grams of a 10% solid polyamide acid solution in N-methyl pyrrolidone was slowly added, with the polyamide acid amount being 2.5% of the aluminum nitride mass. An ultrasonic processor with a power of 400 watts was used for intermittent ultrasonic dispersion for 30 minutes, with 5 seconds of work and 2 seconds of pause to avoid excessive heating. Then, the mixture was mechanically stirred at 400 rpm for 2 hours at room temperature to ensure uniform adsorption of the polyamide acid on the aluminum nitride surface. The mixture was transferred to a spray dryer, with the inlet temperature set to 200 degrees Celsius and the outlet temperature set to 110 degrees Celsius for spray drying, obtaining a powder with good flowability. The powder was placed in a tube furnace, with high-purity nitrogen gas being introduced for protection, and was subjected to imidization treatment by being subjected to a segmented temperature increase according to the following procedure. First, the temperature was increased to 80 degrees Celsius at a rate of 5 degrees Celsius per minute for 1 hour for preheating, then the temperature was increased to 150 degrees Celsius for 1 hour to dehydrate the amide acid into imide, then the temperature was increased to 250 degrees Celsius for 2 hours for deep imidization, and finally the temperature was increased to 350 degrees Celsius for 1 hour for curing. The nitrogen flow rate was maintained at 200 milliliters per minute throughout the process. After cooling, pretreated aluminum nitride with a polyimide hydrolysis-resistant layer with a thickness of about 5 nanometers on the surface was obtained.

[0020] Then, the inner layer hydrophobic silane modification was performed. 400 grams of spherical alumina with a D50 of 2 microns and 300 grams of the above pretreated aluminum nitride were mixed uniformly. 4000 milliliters of anhydrous ethanol and 400 milliliters of deionized water were added to a three-necked flask equipped with a mechanical stirrer and a reflux condenser, with the mass ratio of alcohol to water being 90 to 10. 80 grams of hexadecyltrimethoxysilane was slowly added under stirring to form a 2% solution in the alcohol solution. The pH value was adjusted to 4.0 with glacial acetic acid, and the solution was pre-hydrolyzed at room temperature for 60 minutes to form a stable silanol solution. The above filler mixture was dispersed in the silanol solution, with the solid-liquid ratio being 1 to 8, and ultrasonic treatment was performed for 20 minutes to fully disperse the fillers. The reaction system was heated to 50 degrees Celsius, and the stirring speed was maintained at 350 rpm for 6 hours of reaction. During the reaction, the silanol groups reacted with the hydroxyl groups on the surface of the fillers to form a hydrophobic hexadecylsilane layer on the surface of the fillers. After the reaction, the mixture was hot-filtered and washed with anhydrous ethanol 3 times to remove unreacted silane, and was dried in an oven at 100 degrees Celsius for 4 hours, then was transferred to a tube furnace under nitrogen protection and was heated at 150 degrees Celsius for 2 hours to promote deep condensation of the siloxane bonds, obtaining the inner layer modified filler.

[0021] Finally, the outer layer of reactive silane was modified. The inner layer modified filler 700 grams was placed in a three-neck flask equipped with a mechanical stirrer and reflux condenser. The outer layer silane solution was prepared in another flask. 6000 ml of absolute ethanol and 1000 ml of deionized water were added, with a mass ratio of alcohol to water of 85 to 15. 210 grams of γ-glycidoxypropyltrimethoxysilane was added under stirring, with a concentration of 3% in the alcohol solution. The pH value was adjusted to 4.5 with glacial acetic acid, and pre-hydrolysis was carried out at room temperature for 90 minutes. The inner layer modified filler was dispersed in the solution with a solid-liquid ratio of 1 to 10, and ultrasonic treatment was carried out for 15 minutes. The temperature was raised to 60 degrees Celsius, and the stirring speed was maintained at 350 revolutions per minute for 8 hours of reaction. The epoxy silane was grafted onto the surface of the filler to form an outer layer of reactive silane, with the epoxy group facing outward to facilitate subsequent reaction with the silicone rubber matrix. After the reaction was completed, the product was filtered and washed with absolute ethanol three times, and dried at 110 degrees Celsius for 4 hours. It was then transferred to a tube furnace under nitrogen protection for gradient heat treatment, first at 150 degrees Celsius for 2 hours of preliminary condensation, and then at 180 degrees Celsius for 2 hours of deep condensation, with a nitrogen flow rate of 200 ml per minute. After cooling, the gradient interface modified alumina-aluminum nitride two-component thermal conductive filler of this example was obtained. The amount of inner layer hydrophobic silane grafting in the filler was 0.3% of the total mass of the filler, and the amount of outer layer reactive silane grafting was 0.8% of the total mass of the filler.

[0022] Example 2 In the filler prepared in this example, the D50 of the spherical alumina was 3 microns, the average particle size of the flaky aluminum nitride was 10 microns, and the mass ratio of the two was 55 to 45, and the hydrolysis-resistant protective layer was a polyimide layer. Step one of the preparation method was similar to that of Example 1, except that 450 grams of flaky aluminum nitride with an average particle size of 10 microns and a thickness of 350 nanometers was used, the pH value was adjusted to 9.5 during hydroxylation treatment, the reaction temperature was 60 degrees Celsius, and the reaction time was 4 hours. A polyimide acid solution with a solid content of 12% was used for polyimide coating, with a polyimide acid dosage of 3.5% of the mass of the aluminum nitride. The spray drying inlet temperature was 220 degrees Celsius and the outlet temperature was 120 degrees Celsius, and the imidization program was the same, resulting in pre-treated aluminum nitride coated with a polyimide layer with a thickness of about 10 nanometers.

[0023] Step two, inner layer hydrophobic silane modification, 550 grams of spherical alumina with D50 of 3 microns and 450 grams of the pretreated aluminum nitride above were mixed. 125 grams of hexadecyltrimethoxysilane was added to a mixture of 5000 milliliters of absolute ethanol and 278 milliliters of deionized water, with an alcohol to water mass ratio of 92 to 8, a silane concentration of 2.5%, and the pH was adjusted to 4.2 with glacial acetic acid. The pre-hydrolysis was performed for 45 minutes. The solid to liquid ratio was 1 to 10 after the filler was dispersed, the reaction temperature was 60 degrees Celsius, and the reaction time was 5 hours. After washing and drying, the inner layer modified filler was dried at 110 degrees Celsius for 4 hours and heat treated at 150 degrees Celsius for 2 hours, resulting in an inner layer silane grafting amount of 0.5% of the total mass of the filler.

[0024] Step three, outer layer reactive silane modification, 1000 grams of the inner layer modified filler was dispersed in a mixture of 7500 milliliters of absolute ethanol and 882 milliliters of deionized water, with an alcohol to water mass ratio of 87 to 13. 300 grams of gamma-aminopropyltriethoxysilane was added, with a concentration of 4%, and the pH was adjusted to 4.8 with glacial acetic acid. The pre-hydrolysis was performed for 60 minutes. The solid to liquid ratio was 1 to 12, the reaction temperature was 70 degrees Celsius, and the reaction time was 6 hours. After washing and drying, the outer layer silane grafting amount was 1.5% of the total mass of the filler, and the gradient interface modified filler of this example was obtained by gradient heat treatment at 150 degrees Celsius for 2 hours and then at 180 degrees Celsius for 2 hours.

[0025] Example 3 In the filler prepared in this example, the D50 of the spherical alumina was 4 microns, the average particle size of the flaky aluminum nitride was 11 microns, and the mass ratio of the two was 60 to 40. The hydrolysis-resistant protective layer was a liquid metal layer. In step one of the preparation method, 400 grams of flaky aluminum nitride with an average particle size of 11 microns and a thickness of 400 nanometers was dried at 120 degrees Celsius for 8 hours in a vacuum. The liquid metal coating was performed using a mechanical ball milling method. 400 grams of the dried aluminum nitride and 4.8 grams of gallium-indium-tin liquid metal were mixed in a mass ratio of 100 to 1.2, and were placed in a planetary ball mill. Zirconium oxide grinding balls were used, with a ball to material ratio of 5 to 1 and a rotation speed of 350 revolutions per minute. The ball milling was performed for 5 hours. During the ball milling process, the liquid metal was uniformly spread and covered on the surface of the aluminum nitride under the action of mechanical force, and a gallium oxide protective layer with a thickness of about 3 nanometers was spontaneously formed on the surface, together with the internal liquid metal forming a double-layer protective structure, resulting in the pretreated aluminum nitride.

[0026] Step two, inner layer modification, 600 grams of spherical alumina with D50 of 4 microns and 400 grams of pretreated aluminum nitride were mixed. 220 grams of isobutyl trimethoxysilane was added into 6000 milliliters of anhydrous ethanol and 300 milliliters of deionized water mixture, the alcohol to water mass ratio was 95 to 5, the silane concentration was 3.5%, the pH was adjusted to 4.3, and the pre-hydrolysis was performed for 40 minutes. The solid to liquid ratio was 1 to 9, the reaction temperature was 65 degrees Celsius, and the reaction time was 4.5 hours. After treatment, the inner layer modified filler was obtained, and the inner layer silane grafting amount was 0.8% of the total mass of the filler.

[0027] Step three, outer layer modification, 1000 grams of inner layer modified filler was dispersed in 8000 milliliters of anhydrous ethanol and 1000 milliliters of deionized water mixture, the alcohol to water mass ratio was 88 to 12. 450 grams of γ-glycidoxypropyltrimethoxysilane was added, the concentration was 5%, the pH was adjusted to 5.0, and the pre-hydrolysis was performed for 50 minutes. The solid to liquid ratio was 1 to 13, the reaction temperature was 75 degrees Celsius, and the reaction time was 7 hours. Gradient heat treatment was the same as in Example 2, and the gradient interface modified filler of this example was obtained, and the outer layer silane grafting amount was 2.0% of the total mass of the filler.

[0028] Example 4 In the filler prepared in this example, the D50 of the spherical alumina was 5 microns, the average particle size of the flaky aluminum nitride was 12 microns, and the mass ratio of the two was 70 to 60. The hydrolysis-resistant protective layer was a polyimide layer. In step one of the preparation method, 600 grams of flaky aluminum nitride with an average particle size of 12 microns and a thickness of 500 nanometers was used, and the pH was adjusted to 10.5 during hydroxylation treatment. The reaction temperature was 80 degrees Celsius, and the reaction time was 2 hours. 375 grams of polyamide acid solution with a solid content of 8% was used for polyimide coating, and the polyamide acid dosage was 5.0% of the mass of the aluminum nitride. The pretreated aluminum nitride with a polyimide layer with a coating thickness of about 15 nanometers was obtained.

[0029] Step two, inner layer modification, 600 grams of spherical alumina with D50 of 4 microns and 400 grams of pretreated aluminum nitride were mixed. 220 grams of isobutyl trimethoxysilane was added into 6000 milliliters of anhydrous ethanol and 300 milliliters of deionized water mixture, the alcohol to water mass ratio was 95 to 5, the silane concentration was 3.5%, the pH was adjusted to 4.3, and the pre-hydrolysis was performed for 40 minutes. The solid to liquid ratio was 1 to 9, the reaction temperature was 65 degrees Celsius, and the reaction time was 4.5 hours. After treatment, the inner layer modified filler was obtained, and the inner layer silane grafting amount was 0.8% of the total mass of the filler.

[0030] Step three, outer layer modification, 1300 grams of the inner layer modified filler was dispersed in 15600 milliliters of absolute ethanol and 1950 milliliters of deionized water, with a ratio of 88:12 of alcohol to water. 936 grams of gamma-glycidoxypropyltrimethoxysilane was added, with a concentration of 6%, and the pH was adjusted to 5.0. The pre-hydrolysis was performed for 45 minutes. The solid to liquid ratio was 1:15, the reaction temperature was 80 degrees Celsius, and the reaction time was 5 hours. The outer layer silane grafting amount was 2.5% of the total mass of the filler. The gradient heat treatment included a 2 hour hold at 150 degrees Celsius, a 2 hour hold at 180 degrees Celsius, and a 1 hour hold at 220 degrees Celsius for the enhanced bonding step.

[0031] Comparative Example 1 This comparative example used a single spherical alumina filler without the aluminum nitride component to verify the necessity of the dual component synergy. 1000 grams of spherical alumina with a D50 of 3 microns was weighed out without the hydrolysis protection pretreatment. The double layer silane modification was performed directly. The inner layer modification used 125 grams of hexadecyltrimethoxysilane, with the same reaction conditions as Example 2, and the grafting amount was 0.5% of the mass of the filler. The outer layer modification used 300 grams of gamma-aminopropyltriethoxysilane, with the same reaction conditions as Example 2, and the grafting amount was 1.5% of the mass of the filler. The double layer modified spherical alumina filler was obtained.

[0032] Comparative Example 2 This comparative example used a single flaky aluminum nitride filler without the spherical alumina component to verify the importance of the morphology synergy. 1000 grams of flaky aluminum nitride with an average particle size of 10 microns was weighed out. The hydroxylation and polyimide coating treatment were performed according to the method of Example 2, with a polyamic acid dosage of 3.5% of the mass of the aluminum nitride. Then the double layer silane modification was performed. The inner layer modification used 125 grams of hexadecyltrimethoxysilane, with a grafting amount of 0.5% of the mass of the filler. The outer layer modification used 300 grams of gamma-aminopropyltriethoxysilane, with a grafting amount of 1.5% of the mass of the filler. The reaction conditions were the same as those of Example 2.

[0033] Comparative Example 3 This comparative example used a dual component system of spherical alumina and flaky aluminum nitride with the same ratio as Example 2, but the aluminum nitride was not pretreated for hydrolysis protection, to verify the role of the hydrolysis protection layer. 550 grams of spherical alumina with a D50 of 3 microns and 450 grams of flaky aluminum nitride with an average particle size of 10 microns were weighed out and mixed directly before double layer silane modification. The inner layer modification used 125 grams of hexadecyltrimethoxysilane, and the outer layer modification used 300 grams of gamma-aminopropyltriethoxysilane, with the same reaction conditions as Example 2. The grafting amounts were 0.5% and 1.5% of the total mass of the filler, respectively.

[0034] Comparative Example 4 This comparative example uses the two-component ratio and hydrolysis-resistant pretreatment of Example 2, but only performs single-layer silane modification to verify the necessity of the gradient interface. The pretreated aluminum nitride is prepared according to the method of Example 2, and is mixed with spherical alumina at a mass ratio of 55 to 45. Only the outer layer of reactive silane modification is performed, using 425 grams of γ-aminopropyl triethoxysilane to achieve a total grafting amount of 2.0% of the mass of the filler, and the reaction conditions are the same as those of Step Three of Example 2, and the inner layer of hydrophobic silane modification step is omitted.

[0035] Comparative Example 5 This comparative example refers to the technical solution of Chinese Patent CN115678105A, and uses dopamine-modified fumed alumina compounded with micron-sized alumina. 120 grams of fumed alumina with a specific surface area of 60 square meters per gram and an average particle size of 60 nanometers and 680 grams of micron-sized alumina with a D50 of 10 microns are weighed and dispersed in 1 liter of deionized water to obtain a suspension. 1.2 grams of dopamine hydrochloride and a tris-hydroxymethyl aminomethane buffer solution are added to adjust the pH value to 8, and the reaction is carried out under ultrasonic oscillation conditions for 72 hours. After the reaction is completed, filtration is performed, and the sample is washed with an ethanol aqueous solution and dried to obtain the thermal conductive filler of Comparative Example 5.

[0036] Thermal Interface Material Preparation and Performance Testing The fillers prepared in each example and comparative example are applied to a silicone rubber-based thermal interface material. The basic formula is 100 parts of vinyl silicone oil, 5 parts of hydrogen-containing silicone oil, 600 parts of filler, 0.2 parts of platinum catalyst, and 0.5 parts of ethynylcyclohexanol. The specific preparation process is as follows. The vinyl silicone oil and hydrogen-containing silicone oil are pre-mixed in a planetary mixer, and the vacuum degree is controlled below 50 Pa. The filler is added in three batches, 200 parts each time, and after each batch is mixed, vacuum degassing is performed for 15 minutes. After all the fillers are added, high-speed mixing is performed under vacuum for 45 minutes at a speed of 1000 revolutions per minute. The catalyst and inhibitor are added, and low-speed mixing is performed for 10 minutes. The mixture is cured at 120 degrees Celsius for 1 hour to obtain a thermal interface material sample.

[0037] The performance test methods are as follows. The thermal conductivity is tested according to the ASTM D5470 standard using the steady-state heat flow method, with a test temperature of 25 degrees Celsius and a pressure of 50 pounds per square inch. The viscosity is tested using a rotational rheometer at a temperature of 25 degrees Celsius and a shear rate of 6 millimeters per second. The tensile strength and elongation at break are tested according to the GB / T 528 standard, with a tensile rate of 500 millimeters per minute. The thickness of the bonding wire is measured using a micrometer to measure the thickness of the cured sample. The hydrolysis stability test is performed in a constant temperature and humidity chamber at 85 degrees Celsius and 85% relative humidity, and the ammonia release amount and thermal conductivity change are tested periodically. The ammonia release amount is determined using acid-base titration. The test results are shown in Table 1.

[0038] Table 1 Performance test results of examples and comparative examples Sample Thermal conductivity (W / (m·K)) Viscosity (Pa·s) Tensile strength (MPa) Elongation at break (%) Bonding wire thickness (μm) 1000h Ammonia gas release (ppm) 1000h Thermal conductivity retention rate (%) Example 1 5.52 18500 2.85 165 32 42 96.2 Example 2 6.25 22000 3.12 178 28 38 97.1 Example 3 6.08 20500 2.98 172 30 35 97.5 Example 4 5.88 24800 2.76 158 34 48 95.8 Comparative Example 1 1.62 15200 3.05 185 28 - - Comparative Example 2 4.38 38600 1.85 92 45 1280 72.5 Comparative Example 3 5.95 21800 2.88 170 29 4850 68.2 Comparative Example 4 5.58 28500 2.62 148 31 40 96.8 Comparative Example 5 1.49 13000 4.5 180 30 - - From the test results of Table 1, it can be seen that the embodiments of the present application exhibit significant comprehensive performance advantages compared to the comparative examples. Example 2, as the best embodiment, has a thermal conductivity of 6.25 watts per meter kelvin, which is 3.86 times that of the single alumina system of Comparative Example 1 and 4.19 times that of the dopamine modified alumina of Comparative Example 5, fully embodying the superiority of the dual-component synergistic design. By introducing high-thermal-conductivity flaky aluminum nitride, a high-efficiency thermal conduction network is constructed in the filling skeleton provided by the spherical alumina, achieving a leap in thermal conduction performance.

[0039] Although the thermal conductivity of Comparative Example 2 using single flaky aluminum nitride reaches 4.38 watts per meter kelvin, the viscosity is as high as 38,600 pascal seconds, 1.75 times that of Example 2, and the tensile strength is only 1.85 megapascals and the elongation at break is only 92%, with significant deterioration in processing performance and mechanical properties. This shows that although single flaky fillers are beneficial to the construction of thermal conduction paths, the high specific surface area and interlayer interaction of the flakes lead to serious agglomeration and viscosity increase problems. The embodiment, through the morphology synergy of spherical alumina and flaky aluminum nitride, the spherical particles play a supporting and spacing role between the flaky layers, effectively reducing the frictional resistance between the fillers, while maintaining high thermal conductivity performance, achieving good processing performance.

[0040] Comparative Example 3 does not perform hydrolysis prevention pretreatment on the aluminum nitride, although the initial thermal conductivity is close to that of Example 2, reaching 5.95 watts per meter kelvin, but after 1,000 hours of aging at 85 degrees Celsius and 85% relative humidity, the ammonia release amount is as high as 4,850 ppm and the thermal conductivity retention rate is only 68.2%. While Example 2 has an ammonia release amount of only 38 ppm and a thermal conductivity retention rate of 97.1% under the same conditions, with a significant improvement in long-term stability. This fully demonstrates the important role of the polyimide or liquid metal hydrolysis protection layer. The chemical bonding of polyimide to the surface of aluminum nitride forms a dense water barrier, and its low free volume and high glass transition temperature characteristics make the water diffusion coefficient 2 to 3 orders of magnitude lower than that of the silicone rubber matrix, effectively blocking the contact between water and aluminum nitride and inhibiting the hydrolysis reaction. Example 3 uses liquid metal coating, with an ammonia release amount of only 35 ppm and a thermal conductivity retention rate of 97.5%, because the high surface free energy of the liquid metal imparts hydrophobicity, and the surface oxide layer and the internal liquid metal together form a double protection, with more excellent hydrolysis prevention effect.

[0041] Comparative Example 4 only has a single layer of silane modification, although it has hydrolysis protection, the viscosity reaches 28500 Pa s, which is 29.5% higher than Example 2, and the elongation at break is only 148%, which is 16.9% lower than Example 2. This shows the necessity of gradient interface design. Although a single reactive silane can form a chemical bond with the matrix to reduce the interfacial thermal resistance, it cannot effectively solve the problem of filler aggregation. The double-layer gradient silane modification used in the examples reduces the surface energy of the filler through the long-chain alkyl group of the inner layer hydrophobic silane, reducing the van der Waals attraction, and the outer layer reactive silane provides chemical bonding with the matrix, achieving a functional gradient from anti-aggregation to strong interface, while reducing the viscosity and strengthening the interfacial thermal conductivity.

[0042] Comparative Example 5 uses the technical solution of Comparative Document CN115678105A, and its thermal conductivity is only 1.49 W / mK, although the viscosity is relatively low at 13000 Pa s, but the thermal conductivity performance cannot meet the heat dissipation requirements of high-power electronic devices. This is because the single aluminum oxide system used in this solution has a low intrinsic thermal conductivity, even if the dispersion is improved through particle size grading optimization and dopamine modification, but due to the thermal conductivity characteristics of the material itself, the performance improvement space is limited. The present application introduces aluminum nitride, a high-thermal-conductivity filler, in combination with morphology synergy and gradient interface design, to achieve a significant improvement in thermal conductivity while maintaining good processing performance.

[0043] Further analysis of the differences between the examples shows that Example 2 has the most excellent comprehensive performance. The mass ratio of spherical aluminum oxide to flaky aluminum nitride is 55 to 45, and the D50 is 3 microns and 10 microns respectively, this combination of ratio and particle size achieves the best balance between packing effect and thermal network construction. Example 1 uses smaller filler particle sizes, with spherical aluminum oxide D50 of 2 microns and flaky aluminum nitride average particle size of 8 microns, although it helps to reduce the bonding line thickness to 32 microns, but the smaller particle size leads to an increase in specific surface area, an increase in contact points between fillers, and an increase in phonon scattering, resulting in a slightly lower thermal conductivity of 5.52 W / mK. Example 4 uses larger filler particle sizes, with spherical aluminum oxide D50 of 5 microns and flaky aluminum nitride average particle size of 12 microns, and the ratio is 70 to 60, which is biased towards aluminum oxide. Although the viscosity is controlled within the acceptable range of 24800 Pa s, the high proportion of aluminum oxide weakens the efficient thermal conduction path constructed by aluminum nitride, resulting in a thermal conductivity of 5.88 W / mK. Example 3 uses liquid metal coating, which has the best anti-hydrolysis performance, but the metal properties of the liquid metal may pose a risk of forming a conductive path in some areas, so it should be used with caution in applications that require strict electrical insulation.

[0044] The technical effect mechanism of the present application can be understood in the following aspects. First is the heat conduction network construction mechanism of the two-component morphology synergy. The heterogeneous filler system composed of spherical alumina and flaky aluminum nitride forms a complementary filling mode in space. The spherical particles are arranged in the most compact manner, and the theoretical packing density can reach 74%, providing a stable support skeleton for the filler network. Flaky aluminum nitride has a high aspect ratio characteristic, and is arranged in the gap between spherical particles, forming a lapping heat conduction path using its high heat conduction characteristics in the plane direction. This ball-plate hybrid structure significantly reduces the percolation threshold of the heat conduction network. According to the percolation theory, when the filler reaches the percolation threshold, the thermal conductivity will have a sharp jump. The percolation threshold of single spherical filler is usually 45% to 50% by volume, while the ball-plate hybrid system can reduce the percolation threshold to 35% to 40% by volume, which means that a more perfect heat conduction network can be formed under the same filling amount. At the same time, the high aspect ratio characteristic of the flaky particle makes it tend to arrange along the flow direction under the action of the shear field, and this micro-orientation is conducive to building a continuous heat conduction path in the thickness direction, improving the heat conduction efficiency in the vertical direction.

[0045] Second is the phonon transport regulation mechanism of the gradient interface. Phonon, as the main heat carrier in non-conductive materials, its transmission and scattering behavior at the heterogeneous interface directly determines the interface thermal conductivity. According to the acoustic mismatch theory, when phonons transfer from one material to another, due to the difference in acoustic velocity and density between the two sides, an interface thermal resistance will be generated. The Debye temperature of inorganic fillers is usually 600 to 900 Kelvin, while the Debye temperature of organic polymers is only 200 to 300 Kelvin. This huge phonon state density mismatch causes strong scattering of phonons at the filler-matrix interface, a large number of phonons are reflected back into the filler and cannot enter the matrix, forming a significant interface thermal resistance. The double-layer gradient silanization modification layer constructed in the present application effectively alleviates this problem. The long-chain alkyl group (C8 to C16) of the inner layer hydrophobic silane provides a flexible organic transition layer, whose phonon state density is between inorganic fillers and organic matrix, acting as a phonon buffer, partially matching the acoustic properties of the two sides. At the same time, the flexible motion mode of the long-chain alkyl group can couple the high-frequency phonons of the inorganic side and the low-frequency phonons of the organic side through low-frequency phonon modes, promoting the gradual transfer of phonon energy. The outer layer reactive silane forms a covalent bond with the silicone rubber matrix through the epoxy group or amino group, eliminating the Van der Waals gap of the physical interface. Without chemical bonding, there is a physical gap of 2 to 5 angstroms between the filler and the matrix, and the phonon needs to cross this gap through tunneling effect, with very low transmission probability. The formation of covalent bond establishes a continuous path at the atomic scale, and the phonon can be directly transmitted through the vibration mode of the chemical bond, and the interface phonon transmission coefficient is increased by 3 to 5 times.

[0046] Again, the double barrier mechanism of the hydrolysis protection layer. The reaction of aluminum nitride with water is a surface corrosion process, water molecules first adsorbed on the surface of aluminum nitride, and then with aluminum and nitrogen atoms react to generate aluminum hydroxide and ammonia. This process not only leads to the gradual consumption of aluminum nitride particles, the generated aluminum hydroxide thermal conductivity is only 1 to 2 watts per meter kelvin, far lower than aluminum nitride, resulting in a decrease in thermal conductivity. The generated ammonia gas is corrosive, will erode electronic components. The polyimide coating layer used in the invention forms a double barrier through chemical bonding and dense structure. The carboxyl group in the polyamide acid precursor and the aluminum hydroxyl group generated by the hydroxylation treatment of the surface of aluminum nitride undergoes dehydration condensation reaction to form a stable aluminum-oxygen-carbon covalent bond. This chemical bonding not only provides strong interfacial bonding, more importantly, it builds a passivation layer on the surface of aluminum nitride, occupies the active sites on the surface, and blocks the adsorption and reaction path of water molecules. After imidization, the rigid backbone and five-membered imide ring structure of polyimide make it have a very low free volume fraction, and the small molecule penetration diffusion coefficient is 2 to 3 orders of magnitude lower than that of conventional polymers. At a service temperature of 85 degrees Celsius, the polyimide is still in a glass state, and the chain segment movement is limited, and it cannot provide enough free volume for water molecules to diffuse, thereby effectively blocking the penetration of water to the surface of aluminum nitride. The liquid metal coating scheme takes advantage of the unique properties of gallium-indium-tin alloy, which is liquid at room temperature, with a surface free energy of 500 to 600 millijoules per square meter, and has strong hydrophobicity, with a water droplet contact angle on its surface of more than 130 degrees. More importantly, the liquid metal surface will spontaneously form a 2 to 5 nanometer thick gallium oxide layer, and this oxide layer is dense and stable, together with the internal liquid metal to form a double-layer structure of liquid core-solid shell, which not only provides a hydrophobic barrier, but also forms a chemically inert protection, the double mechanism ensures the long-term stability of aluminum nitride.

[0047] Finally, the synergistic mechanism of the gradient silanization was analyzed at the molecular level. The hexadecyltrimethoxysilane molecule contains a long hexadecyl chain and three methoxy groups. Under acidic conditions, the methoxy group hydrolyzes to form a silanol group, which further condenses with the hydroxyl group on the filler surface to form a siloxane bond, achieving silane grafting on the filler surface. The long hexadecyl chain is oriented outward, and the chains interact with each other through van der Waals forces to form an ordered and hydrophobic layer, significantly reducing the surface energy of the filler. According to the surface energy theory, the driving force for filler aggregation is proportional to the surface energy, and the reduction in surface energy reduces the attraction between fillers, making them more easily dispersed under shear. At the same time, the steric hindrance effect of the long-chain alkyl group prevents direct contact between fillers, further inhibiting aggregation. In the second layer modification, γ-glycidoxypropyltrimethoxysilane or γ-aminopropyltriethoxysilane is grafted onto the inner silanized surface through a similar silanol condensation mechanism. Since the inner layer has been grafted with hydrophobic silane, the grafting of the second layer silane mainly occurs in the areas not completely covered by the first layer or through condensation between silanols on the surface of the first layer, forming a gradient transition. The epoxy or amino groups of the outer layer silane have high reactivity, and during the curing process of the thermal interface material, the epoxy groups can undergo a silicon-hydrogen addition reaction with the hydrogen-containing siloxane in the silicone rubber matrix under platinum catalysis, and the amino groups can react with the epoxy groups or undergo condensation with the siloxane chain, thereby establishing covalent bond bridges between the filler and the matrix. This chemical bonding not only eliminates the physical interface gap, but more importantly, anchors the filler in the matrix network during curing, preventing filler migration and aggregation and maintaining uniform dispersion. The gradient combination of the inner layer hydrophobicity and the outer layer reactivity achieves a functional progression from reducing filler interaction to strengthening filler-matrix bonding, maintaining good dispersion while maximizing interfacial thermal conductivity efficiency.

[0048] In summary, the present application achieves comprehensive improvement in thermal conductivity, processing performance, and service stability through the synergistic effect of three major technical innovations: two-component morphology synergistic construction of high-efficiency thermal conduction network, gradient interface engineering for phonon transport regulation, and hydrolysis-resistant protective layer for long-term stability, providing an innovative technical path and theoretical guidance for the development of high-performance thermal interface materials.

[0049] The above only describes the preferred embodiments of the present application and is not intended to limit the protection scope of the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A gradient interface-modified alumina-alumina nitride two-component thermally conductive filler, characterized in that, It includes spherical alumina, sheet-like aluminum nitride, and a double-layer gradient modification layer covering the surfaces of the spherical alumina and the sheet-like aluminum nitride; The spherical alumina has a D50 of 2 to 5 micrometers and a sphericity greater than or equal to 0.

85. The aluminum nitride flakes are hexagonal flakes with an average particle size of 8 to 12 micrometers, a thickness of 200 to 500 nanometers, and an aspect ratio of 20 to 50. The mass ratio of the spherical alumina to the lamellar aluminum nitride is 40 to 70 to 30 to 60. The bilayer gradient modified layer includes an inner hydrophobic silane layer and an outer reactive silane layer. The inner hydrophobic silane layer is formed by grafting alkyltrialkoxysilanes with a carbon chain length of 8 to 16, and the outer reactive silane layer is formed by grafting silane coupling agents containing epoxy groups or amino groups. The surface of the sheet-like aluminum nitride is further covered with a hydrolytically resistant layer beneath the double-layer gradient modification layer. The hydrolytically resistant layer is a polyimide layer or a liquid metal layer.

2. The gradient interface modified alumina-alumina nitride bicomponent thermally conductive filler according to claim 1, characterized in that, The spherical alumina has a D50 of 3 to 4 micrometers and a specific surface area of ​​8 to 15 square meters per gram; the flake-shaped aluminum nitride has an average particle size of 9 to 11 micrometers.

3. The gradient interface modified alumina-alumina nitride bicomponent thermally conductive filler according to claim 1, characterized in that, The mass ratio of the spherical alumina to the lamellar aluminum nitride is 55 to 60 to 40 to 45.

4. The gradient interface modified alumina-alumina nitride bicomponent thermally conductive filler according to claim 1, characterized in that, The inner hydrophobic silane layer is formed by grafting hexadecyltrimethoxysilane or isobutyltrimethoxysilane, with the grafting amount accounting for 0.3% to 1.2% of the total mass of the filler; the outer reactive silane layer is formed by grafting γ-glycidoxypropyltrimethoxysilane or γ-aminopropyltriethoxysilane, with the grafting amount accounting for 0.8% to 2.5% of the total mass of the filler.

5. The gradient interface modified alumina-alumina nitride bicomponent thermally conductive filler according to claim 1, characterized in that, When the hydrolytic protection layer is a polyimide layer, the thickness of the polyimide layer is 5 to 15 nanometers, and its content accounts for 1.5% to 5.0% of the mass of the sheet aluminum nitride; when the hydrolytic protection layer is a liquid metal layer, the liquid metal is a gallium indium tin alloy, and its content accounts for 0.5% to 2.0% of the mass of the sheet aluminum nitride.

6. The method for preparing the gradient interface modified alumina-alumina nitride two-component thermally conductive filler according to any one of claims 1 to 5, characterized in that, Includes the following steps: Step 1: Pre-treatment of sheet aluminum nitride to prevent hydrolysis: After drying sheet aluminum nitride under vacuum at 120 degrees Celsius for 8 to 12 hours, surface hydroxylation treatment is performed to obtain hydroxylated aluminum nitride; The hydroxylated aluminum nitride is mixed with polyamic acid solution or gallium indium tin liquid metal, and after spray drying or ball milling, it is heat-treated under nitrogen protection to obtain pre-treated aluminum nitride with a surface coated with a hydrolysis protective layer; Step 2, inner layer hydrophobic silane modification: The mixture of spherical alumina and the pretreated aluminum nitride is dispersed in an alcohol solution of alkyltrialkoxysilane with a carbon chain length of 8 to 16. The pH of the alcohol solution is adjusted to 4.0 to 4.5 with glacial acetic acid. The reaction is carried out at 50 to 70 degrees Celsius for 4 to 6 hours. After filtration, it is dried at 100 to 120 degrees Celsius and then heat-treated at 150 degrees Celsius for 2 hours to obtain the inner layer modified filler. Step 3: Modify the outer layer with reactive silane: Disperse the inner layer modified filler in an alcohol solution containing an epoxy or amino silane coupling agent. Adjust the pH of the alcohol solution to 4.5 to 5.0 with glacial acetic acid. React at 60 to 80 degrees Celsius for 5 to 8 hours. After filtration, dry at 110 degrees Celsius for 4 hours. Then, under nitrogen protection, heat treat sequentially at 150 degrees Celsius for 2 hours and at 180 degrees Celsius for 2 hours to obtain the gradient interface modified alumina-alumina nitride bicomponent thermally conductive filler.

7. The preparation method according to claim 6, characterized in that, The specific steps of the surface hydroxylation treatment are as follows: the dried flake aluminum nitride is dispersed in deionized water to form a suspension with a solid content of 15% to 25%, sodium hydroxide solution is added to adjust the pH value to 9.5 to 10.5, the mixture is stirred and reacted at 60 to 80 degrees Celsius for 2 to 4 hours, filtered, washed with deionized water until neutral, and dried at 80 degrees Celsius.

8. The preparation method according to claim 6, characterized in that, When the hydrolytic protective layer is a polyimide layer, the hydroxylated aluminum nitride is mixed with a polyamic acid N-methylpyrrolidone solution with a solid content of 8% to 12% at a mass ratio of 100:2.5 to 3.

5. After ultrasonic dispersion for 30 minutes, the mixture is mechanically stirred for 2 hours. Then, the solvent is removed by spray drying or rotary evaporation. Under nitrogen protection, the mixture is then sequentially heat-treated at 80 degrees Celsius for 1 hour, 150 degrees Celsius for 1 hour, 250 degrees Celsius for 2 hours, and 350 degrees Celsius for 1 hour to complete the imidization.

9. The preparation method according to claim 6, characterized in that, When the hydrolytic protective layer is a liquid metal layer, the dried sheet aluminum nitride and gallium indium tin liquid metal are mixed at a mass ratio of 100:0.8 to 1.2, and then mechanically ball-milled at a ball-to-material ratio of 5:1, at a speed of 300 to 400 revolutions per minute, for a ball-milling time of 3 to 6 hours.

10. The preparation method according to claim 6, characterized in that, In step two, the alkyltrialkoxysilane with a carbon chain length of 8 to 16 is hexadecyltrimethoxysilane or isobutyltrimethoxysilane, with a concentration of 2% to 5% in the alcohol solution, an alcohol-to-water mass ratio of 90:10 to 95:5, and a solid-liquid ratio of 1:8 to 1:12; in step three, the silane coupling agent containing epoxy or amino groups is γ-glycidoxypropyltrimethoxysilane or γ-aminopropyltriethoxysilane, with a concentration of 3% to 6% in the alcohol solution, an alcohol-to-water mass ratio of 85:15 to 90:10, and a solid-liquid ratio of 1:10 to 1:15.