Nano-composite heat-conducting coating and preparation method thereof

Abstract

The invention relates to the technical field of polymer composite materials, and discloses a nano composite heat-conducting coating and a preparation method thereof, the coating comprises the following components by mass: 20-40 parts of bisphenol A epoxy resin; 6.3 to 12.6 parts of polyether amine; 15 to 35 parts of vinyl-terminated polydimethylsiloxane; 5.6 to 13.1 parts of hydrogen-containing silicone oil; 0.03 to 0.08 part of a platinum catalyst; 25 to 45 parts of spherical aluminum oxide subjected to surface modification; 15 to 35 parts of flaky boron nitride subjected to surface modification; and 0.5 to 3.0 parts of a bridging nano filler. The preparation method comprises the following steps: respectively placing polyether amine of an amine curing agent and a platinum catalyst serving as a hydrosilylation catalyst in two premixes, mixing the two premixes before coating, heating and curing to form an epoxy organic silicon interpenetrating network structure in situ, and constructing a three-dimensional heat conduction path through filler compounding modification. The coating prepared by the invention has high heat conductivity coefficient, high mechanical strength and excellent flexibility.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high polymer composite materials, in particular to a nano-composite heat-conducting coating and a preparation method thereof. BACKGROUND

[0002] With the increasing integration and power density of electronic devices, efficient thermal management has become the key to ensuring the stable operation of the devices. Heat-conducting polymer composites, especially heat-conducting coatings, are widely used as thermal interface materials because they have the processability, flexibility of polymer matrix and the heat conductivity of heat-conducting fillers.

[0003] The matrix of the heat-conducting coating mainly includes epoxy resin or silicone resin. The epoxy resin-based coating has excellent substrate adhesion and mechanical strength, but its crosslinked network is rigid, resulting in large brittleness and insufficient flexibility of the coating, which is prone to cracking under thermal cycle impact. The silicone-based coating has excellent flexibility and high and low temperature resistance, but its mechanical strength is low and is prone to tearing.

[0004] In order to improve the thermal conductivity, it is usually necessary to add a high filling amount of heat-conducting fillers to the matrix. Although the high filling amount improves the thermal conductivity, it also causes the viscosity of the composite material to rise sharply, the processability to become poor, and the mechanical properties of the cured coating to further decrease. In addition, the poor interfacial compatibility between the fillers and the polymer matrix results in high interfacial thermal resistance, which limits the further improvement of the heat-conducting efficiency. SUMMARY

[0005] The purpose of the present application is to provide a nano-composite heat-conducting coating and a preparation method thereof, which solves the problem that the existing heat-conducting coating is difficult to balance the mechanical properties, electrical insulation and the reaction deactivation of the curing agent and catalyst in the epoxy-silicone hybrid system while achieving high thermal conductivity.

[0006] To achieve the above purpose, the present application is implemented by the following technical scheme: a nano-composite heat-conducting coating, by mass parts, comprising the following components: 20-40 parts of bisphenol A type epoxy resin; 6.3-12.6 parts of polyether amine; 15-35 parts of vinyl-terminated polydimethylsiloxane; 5.6-13.1 parts of hydrogen-containing silicone oil; 0.03-0.08 parts of platinum gold catalyst; 25-45 parts of spherical alumina modified by surface modification; 15-35 parts of flaky boron nitride modified by surface modification; 0.5-3.0 parts of bridged nano filler.

[0007] Further, the present application constructs a dual curing system, in which two independent crosslinking reactions occur simultaneously during the curing process.

[0008] Epoxy network curing: the epoxy groups of bisphenol A type epoxy resin and the amine groups of polyether amine undergo ring-opening addition reaction to form an epoxy resin crosslinking network.

[0009] Silicone network curing: the vinyl groups of end-vinyl polydimethylsiloxane and the silicon-hydrogen bonds of hydrogen-containing silicone oil undergo silicon-hydrogen addition reaction under the action of platinum catalyst to form a silicone crosslinking network.

[0010] The two curing reactions occur in situ to form an epoxy-silicone interpenetrating network structure that is structurally interpenetrated and topologically intertwined. This structure combines the high strength, high substrate adhesion, and heat resistance of the epoxy network, as well as the flexibility, toughness, and low stress properties of the silicone network, making the final coating have high tensile strength and elongation at break, overcoming the mechanical performance defects of a single matrix.

[0011] At the same time, the two different forms of thermally conductive fillers, spherical alumina and flaky boron nitride, form a high-density packing in the matrix, constructing a basic heat-conducting skeleton; and the bridging nano-filler acts as a heat-conducting bridge in the high-filled system, connecting isolated basic filler particles to construct a three-dimensional efficient heat-conducting path, significantly reducing the interfacial thermal resistance.

[0012] Preferably, the bridging nano-filler is at least one of graphene oxide or carboxylated carbon nanotube.

[0013] Further, the surfaces of graphene oxide and carboxylated carbon nanotube are rich in oxygen-containing functional groups. These functional groups improve the dispersibility of the nano-filler in the resin matrix on the one hand, and can react with epoxy groups or amine groups on the other hand, enhancing the interfacial bonding between the filler and the matrix, providing a bridging heat-conducting path while further reducing the interfacial thermal resistance and improving the macroscopic mechanical properties of the coating.

[0014] Preferably, the graphene oxide is prepared by oxidizing natural flake graphite with concentrated sulfuric acid, sodium nitrate, and potassium permanganate, and then ultrasonically exfoliating; and the carboxylated carbon nanotube is prepared by refluxing raw multi-walled carbon nanotubes with a mixture of concentrated sulfuric acid and concentrated nitric acid.

[0015] Preferably, the surface-modified spherical alumina is modified with epoxy silane; and the surface-modified flaky boron nitride is modified with long-chain alkyl silane.

[0016] Further, a differential filler surface treatment strategy is adopted. The epoxy group of epoxy silane can participate in the curing reaction of epoxy resin, so that spherical alumina is preferentially anchored in the epoxy network. Long-chain alkyl silane has hydrophobicity and good compatibility with the silicone network, so that flaky boron nitride is preferentially anchored in the silicone network. This partitioned anchoring design makes the two fillers respectively tightly combined with the polymer matrix with the best compatibility, maximally reduces the interfacial thermal resistance, and enhances the overall mechanical properties of the composite material.

[0017] Preferably, the epoxy silane is γ-glycidoxypropyltrimethoxysilane; the long-chain alkyl silane is n-octyltriethoxysilane.

[0018] A preparation method of a nanocomposite thermal conductive coating, comprising the following steps: S1, pretreatment of the thermal conductive filler; S2, preparation of a first premix: mixing and high-speed shearing and dispersing bisphenol A type epoxy resin, surface modified spherical alumina and bridged nano filler, then adding hydrogen-containing silicone oil and platinum catalyst, and vacuum degassing to obtain the first premix; S3, preparation of a second premix: mixing and high-speed shearing and dispersing vinyl-terminated polydimethylsiloxane and surface modified flaky boron nitride, then adding polyether amine, and vacuum degassing to obtain the second premix; S4, mixing and application: uniformly mixing the first premix and the second premix in proportion, and applying on the surface of a substrate; S5, curing: heating and curing the applied substrate to construct a thermal conductive network in situ, and obtaining a nanocomposite thermal conductive coating.

[0019] Preferably, the step S1 of pretreatment of the thermal conductive filler comprises: mixing the spherical alumina with epoxy silane equivalent to 0.5%-2.0% of the mass of the spherical alumina for surface modification; mixing the flaky boron nitride with long-chain alkyl silane equivalent to 0.5%-2.0% of the mass of the flaky boron nitride for surface modification.

[0020] Preferably, the rotation speed of high-speed shearing and dispersing in the steps S2 and S3 is 1500-2500 rpm, and the dispersing time is 30-90 minutes; the vacuum degree of vacuum degassing is controlled between -0.08 MPa and -0.09 MPa, and the degassing time is 15-30 minutes.

[0021] Further, the high-speed shearing process provides shearing force to open the agglomerates of high specific surface area fillers, so that they are uniformly dispersed in the resin matrix, which is a prerequisite for constructing a continuous thermal conductive path. The subsequent vacuum degassing step removes the air bubbles introduced in the high-speed stirring process, prevents the formation of void defects in the final coating, and ensures the coating density, electrical insulation and thermal conductivity stability.

[0022] Preferably, the mass ratio of the first premix to the second premix in step S4 is 1.07:1 to 1.65:1.

[0023] Preferably, the temperature for heating and curing in step S5 is 80-150℃, and the curing time is 30-90 minutes.

[0024] Further, the curing process window ensures that the two curing reactions can proceed. This temperature range can activate the activity of the platinum catalyst and provide the energy required for the epoxy-amine ring-opening reaction. The time range ensures that both reactions can be completed at the corresponding temperature to form an interpenetrating network structure, while taking into account production efficiency and avoiding performance degradation of the material due to excessive curing time or temperature.

[0025] In summary, the present application includes at least one of the following beneficial technical effects: 1. The present application realizes physical isolation by placing the platinum catalyst and polyether amine in two premixes, avoiding the coordination deactivation of polyether amine to platinum catalyst, solving the problem of catalyst reaction deactivation in the epoxy-silicone hybrid system, ensuring that both the silicon-hydrogen addition reaction and the epoxy-amine reaction can proceed normally, thereby constructing an interpenetrating network structure.

[0026] 2. The epoxy-silicone interpenetrating network structure formed by the present application has high strength and high adhesion of the epoxy resin network, as well as flexibility and low stress characteristics of the silicone network. This makes the coating have high tensile strength and elongation at break, improves the mechanical performance limitations of single matrix material, and improves the reliability of the coating.

[0027] 3. The present application uses spherical alumina, flaky boron nitride, and bridging nano fillers. By differentiating the surface modification of alumina and boron nitride, they are preferentially anchored in the epoxy network and the silicone network, respectively, reducing the interfacial thermal resistance; at the same time, the bridging nano filler connects the basic thermal conductive filler, constructing a high-efficiency three-dimensional thermal conduction path, and improving the thermal conductivity of the composite coating. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a flowchart of the preparation method of the present application; Figure 2 is a comparative column chart of the thermal conductivity of the present application; Figure 3 is a comparative column chart of the mechanical properties of the present application. DETAILED DESCRIPTION

[0029] The following will be described in detail in combination with the accompanying Figure 1 - the accompanying Figure 3 , the present application will be further described in detail.

[0030] The application provides a nanocomposite heat-conducting paint and a preparation method thereof.

[0031] The main raw materials and reagents used in the following examples and comparative examples are as follows, and the reagents not specifically described are commercially available analytical pure or higher grade products.

[0032] Bisphenol A type epoxy resin, CAS No. 25068-38-6, epoxy equivalent weight (EEW) 180-195 g / eq, viscosity 10,000-15,000 mPa·s (25℃).

[0033] Vinyl-terminated polydimethylsiloxane, CAS No. 68083-19-2, vinyl content 0.002-0.003 mol / g.

[0034] Polyether amine, CAS No. 9046-10-0, amine equivalent weight (AHEW) 110-120 g / eq, viscosity 80-100 mPa·s (25℃).

[0035] Hydrogen-containing silicone oil, CAS No. 63148-57-2, hydrogen content 0.007-0.009 mol / g.

[0036] Platinum gold catalyst, CAS No. 68478-92-2, active platinum content 0.2-0.3 wt%, Karstedt type platinum complex.

[0037] Spherical alumina (Al2O3), CAS No. 1344-28-1, average particle size D50 10-20 μm.

[0038] Epoxy silane, CAS No. 2530-83-8, chemical name γ-glycidoxypropyltrimethoxysilane.

[0039] Flaky boron nitride (h-BN), CAS No. 10043-11-5, average particle size D50 5-15 μm.

[0040] Long-chain alkyl silane, CAS No. 2943-75-1, chemical name n-octyltriethoxysilane.

[0041] Preparation Example; Preparation Example 1: Preparation of graphene oxide The present preparation example provides a method for preparing graphene oxide, comprising the following steps: 5-10 g of natural flake graphite was placed in an ice bath, and 200-250 mL of concentrated sulfuric acid was slowly added. Under magnetic stirring (300-500 rpm), 5-10 g of sodium nitrate and 25-35 g of potassium permanganate were slowly added in batches, and the reaction temperature was controlled at 0-8℃, and the process took 60-90 minutes.

[0042] Remove the ice bath and slowly warm the reaction system to 35-40°C with continued stirring for 30-60 minutes. Slowly add 400-500 mL of deionized water and, after the system temperature stabilizes, slowly add 50-80 mL of 30% hydrogen peroxide solution until the system color changes from dark brown to light yellow. Pour the reaction product into a centrifuge tube and centrifuge at 8,000-10,000 rpm for 10-15 minutes.

[0043] Discard the supernatant and wash the precipitate with 5% dilute hydrochloric acid solution 2-3 times and deionized water 4-6 times, each time centrifuging to separate the filtrate until the pH reaches 5.5-6.5. Disperse the washed graphene oxide precipitate in 500-800 mL of deionized water and use an ultrasonic processor (power 600-800 W) to ultrasonically exfoliate for 2-3 hours. The exfoliated dispersion is freeze-dried (-50°C, 24-48 hours) or vacuum oven dried (60°C, 12-24 hours) to obtain graphene oxide (GO) powder with an average flake diameter D50 of 3-7 μm and a layer number of 1-5 layers.

[0044] Preparation Example 2: Preparation of carboxylated carbon nanotubes (CNT-COOH) This preparation example provides a method for preparing carboxylated carbon nanotubes, comprising the following steps: Place 5-10 g of raw multi-walled carbon nanotubes (diameter 10-30 nm, length 1-10 μm) in a muffle furnace and calcine at 300-400°C for 30-60 minutes in an air atmosphere. Add the pretreated carbon nanotubes to a mixture of 200-250 mL of concentrated sulfuric acid and concentrated nitric acid (volume ratio 3:1).

[0045] Place the mixture in an oil bath and magnetically stir at reflux at 80-120°C for 2-6 hours. After the reaction is complete, cool the mixture to room temperature. Isolate the carbon nanotubes by vacuum suction filtration and repeatedly wash the filter cake with a large amount of deionized water 5-8 times until the filtrate pH reaches 6.0-7.0.

[0046] Dry the washed carboxylated carbon nanotubes in a vacuum oven at 60-80°C for 12-24 hours to obtain carboxylated carbon nanotube (CNT-COOH) powder with a diameter of 10-30 nm, a length of 3-8 μm, and a carboxyl content of 3.0%-4.0% (atomic percent) Examples 1-5; Example 1: Preparation of the first premix (epoxy-catalyst base): In a clean planetary mixer, 30 parts by mass of bisphenol A type epoxy resin (EEW 190 g / eq) was added; under stirring speed 800 rpm, 30 parts by mass of epoxy-silane pre-treated spherical alumina (pre-treatment: 1.0% KH-560 of the mass of alumina) and 1.5 parts by mass of graphene oxide (GO) prepared in Preparation Example 1 were slowly added; the stirring speed was raised to 2000 rpm, and high-speed shearing dispersion was carried out for 60 minutes; the speed was reduced to 600 rpm, and 9.4 parts by mass of hydrogen-containing silicone oil (H content 0.008 mol / g) and 0.05 parts by mass of platinum gold catalyst were sequentially added; the vacuum system was turned on, and the vacuum degree was maintained below -0.09 MPa; under stirring at 300-500 rpm, the mixture was degassed for 20 minutes to obtain the first premix.

[0047] Preparation of the second premix (silicone-amine base): In another clean planetary mixer, 25 parts by mass of vinyl-terminated polydimethylsiloxane (vinyl content 0.0025 mol / g) was added; under stirring speed 800 rpm, 15 parts by mass of long-chain alkyl silane pre-treated flaky boron nitride (pre-treatment: 1.0% n-octyl triethoxysilane of the mass of boron nitride) was slowly added; the stirring speed was raised to 2000 rpm, and high-speed shearing dispersion was carried out for 60 minutes; the speed was reduced to 600 rpm, and 9.5 parts by mass of polyetheramine (AHEW 60 g / eq) was added; the vacuum system was turned on, and the vacuum degree was maintained below -0.09 MPa; under stirring at 300-500 rpm, the mixture was degassed for 20 minutes to obtain the second premix.

[0048] Final mixing and application of the coating: The first premix and the second premix were taken in a mass ratio of 1.43:1 (calculated based on the above-mentioned parts by mass) and uniformly mixed through a static mixer; the mixed coating was applied on the surface of an aluminum alloy substrate by means of blade coating, and the wet film thickness was controlled to be 300 μm.

[0049] Curing and in-situ construction of the heat conduction network: the aluminum alloy substrate coated with the coating was placed in an oven and heated and cured at 120°C for 60 minutes to obtain a nano-composite heat-conductive coating.

[0050] Example 2: Preparation of the first premix (epoxy-catalyst base): In a clean planetary mixer, 20 parts by mass of bisphenol A type epoxy resin (EEW 190 g / eq) was added; under stirring speed 800 rpm, 25 parts by mass of epoxy-silane pre-treated spherical alumina (pre-treatment: 0.5% KH-560 of the mass of alumina) and 0.5 parts by mass of carboxylated carbon nanotubes (CNT-COOH) prepared in Preparation Example 2 were slowly added; the stirring speed was raised to 1500 rpm, and high-speed shearing dispersion was carried out for 30 minutes; the speed was reduced to 600 rpm, and 5.6 parts by mass of hydrogen-containing silicone oil (H content 0.008 mol / g) and 0.03 parts by mass of platinum gold catalyst were sequentially added; the vacuum system was turned on, the vacuum degree was maintained below -0.08 MPa, and degassing was carried out under stirring at 300-500 rpm for 30 minutes, to obtain the first premix.

[0051] Preparation of the second premix (silicone-amine base): In another clean planetary mixer, 15 parts by mass of vinyl-terminated polydimethylsiloxane (vinyl content 0.0025 mol / g) was added; under stirring speed 800 rpm, 15 parts by mass of long-chain alkyl silane pre-treated flaky boron nitride (pre-treatment: 0.5% n-octyl triethoxysilane of the mass of boron nitride) was slowly added; the stirring speed was raised to 1500 rpm, and high-speed shearing dispersion was carried out for 30 minutes; the speed was reduced to 600 rpm, and 6.3 parts by mass of polyetheramine (AHEW 60 g / eq) was added; the vacuum system was turned on, the vacuum degree was maintained below -0.08 MPa, and degassing was carried out under stirring at 300-500 rpm for 30 minutes, to obtain the second premix.

[0052] Final mixing and application of the coating: the first premix and the second premix were taken in a mass ratio of 1.41:1, and uniform mixing was carried out through a static mixer; the mixed coating was applied on the surface of the substrate by automatic dispensing, and the wet film thickness was controlled to be 100 μm.

[0053] Curing and in-situ construction of the heat-conducting network: the substrate coated with the coating was placed in an oven, and heated and cured at 80°C for 90 minutes, to obtain a nanocomposite heat-conducting coating.

[0054] Example 3: Preparation of the first premix (epoxy-catalyst base): In a clean planetary mixer, 40 parts by mass of bisphenol A type epoxy resin (EEW 190 g / eq) was added; 45 parts by mass of epoxy-silane pre-treated spherical alumina (pre-treatment: 2.0% KH-560 of the mass of alumina) and 3.0 parts by mass of graphene oxide (GO) prepared in Preparation Example 1 were slowly added at a stirring speed of 800 rpm; the stirring speed was increased to 2500 rpm and high-speed shearing was performed for 90 minutes; the stirring speed was decreased to 600 rpm, and 13.1 parts by mass of hydrogen-containing silicone oil (H content: 0.008 mol / g) and 0.08 parts by mass of platinum gold catalyst were sequentially added; a vacuum system was turned on, the vacuum degree was maintained below -0.09 MPa, and degassing was performed at 300-500 rpm for 15 minutes to obtain the first premix.

[0055] Preparation of the second premix (silicone-amine base): In another clean planetary mixer, 35 parts by mass of vinyl-terminated polydimethylsiloxane (vinyl content: 0.0025 mol / g) was added; 35 parts by mass of long-chain alkyl silane pre-treated flaky boron nitride (pre-treatment: 2.0% n-octyl triethoxysilane of the mass of boron nitride) was slowly added at a stirring speed of 800 rpm; the stirring speed was increased to 2500 rpm and high-speed shearing was performed for 90 minutes; the stirring speed was decreased to 600 rpm, and 12.6 parts by mass of polyetheramine (AHEW 60 g / eq) was added; a vacuum system was turned on, the vacuum degree was maintained below -0.09 MPa, and degassing was performed at 300-500 rpm for 15 minutes to obtain the second premix.

[0056] Final mixing and application of the coating: The first premix and the second premix were taken in a mass ratio of 1.22:1, uniformly mixed through a static mixer; the mixed coating was applied on the surface of the substrate by silk screen printing, and the wet film thickness was controlled to be 500 μm.

[0057] Curing and in-situ construction of the heat conduction network: the substrate coated with the coating was placed in an oven and heated and cured at 150°C for 30 minutes to obtain a nano-composite heat-conductive coating.

[0058] Example 4: Preparation of the first premix (epoxy-catalyst base): In a clean planetary mixer, 35 parts by mass of bisphenol A type epoxy resin (EEW 190 g / eq) was added; under stirring speed 800 rpm, 40 parts by mass of epoxy-silane pre-treated spherical alumina (pre-treatment: 1.5% KH-560 of the mass of alumina) and 2.0 parts by mass of carboxylated carbon nanotubes (CNT-COOH) prepared in Preparation Example 2 were slowly added; the stirring speed was raised to 2200 rpm, and high-speed shearing dispersion was carried out for 75 minutes; the speed was reduced to 600 rpm, and 7.5 parts by mass of hydrogen-containing silicone oil (H content 0.008 mol / g) and 0.04 parts by mass of platinum gold catalyst were sequentially added; the vacuum system was turned on, the vacuum degree was maintained below -0.09 MPa, and degassing was carried out under stirring at 300-500 rpm for 25 minutes to obtain the first premix.

[0059] Preparation of the second premix (silicone-amine base): In another clean planetary mixer, 20 parts by mass of vinyl-terminated polydimethylsiloxane (vinyl content 0.0025 mol / g) was added; under stirring speed 800 rpm, 20 parts by mass of long-chain alkyl silane pre-treated flaky boron nitride (pre-treatment: 1.5% n-octyl triethoxysilane of the mass of boron nitride) was slowly added; the stirring speed was raised to 2200 rpm, and high-speed shearing dispersion was carried out for 75 minutes; the speed was reduced to 600 rpm, and 11.1 parts by mass of polyetheramine (AHEW 60 g / eq) was added; the vacuum system was turned on, the vacuum degree was maintained below -0.09 MPa, and degassing was carried out under stirring at 300-500 rpm for 25 minutes to obtain the second premix.

[0060] Final mixing and application of the coating: The first premix and the second premix were taken in a mass ratio of first premix: second premix = 1.65:1, and uniform mixing was carried out through a static mixer; the mixed coating was applied on the surface of the substrate by means of blade coating, and the wet film thickness was controlled to be 250 μm.

[0061] Curing and in-situ construction of the heat-conducting network: the substrate coated with the coating was placed in an oven and heated and cured at 130°C for 45 minutes to obtain a nanocomposite heat-conducting coating.

[0062] Example 5: Preparation of the first premix (epoxy-catalyst base): In a clean planetary mixer, 25 parts by mass of bisphenol A type epoxy resin (EEW 190 g / eq) was added; 30 parts by mass of epoxy-silane pre-treated spherical alumina (pre-treatment: 1.0% KH-560 of the mass of alumina) and 1.0 part by mass of graphene oxide (GO) prepared in Preparation Example 1 were slowly added at a stirring speed of 800 rpm; the stirring speed was raised to 1800 rpm and high-speed shearing dispersion was performed for 45 minutes; the stirring speed was lowered to 600 rpm, and 11.3 parts by mass of hydrogen-containing silicone oil (H content: 0.008 mol / g) and 0.06 parts by mass of platinum gold catalyst were sequentially added; a vacuum system was turned on, the vacuum degree was maintained below -0.08 MPa, and defoaming was performed at 300-500 rpm for 25 minutes to obtain the first premix.

[0063] Preparation of the second premix (silicone-amine base): In another clean planetary mixer, 30 parts by mass of vinyl-terminated polydimethylsiloxane (vinyl content: 0.0025 mol / g) was added; 25 parts by mass of long-chain alkyl silane pre-treated flaky boron nitride (pre-treatment: 1.0% n-octyl triethoxysilane of the mass of boron nitride) was slowly added at a stirring speed of 800 rpm; the stirring speed was raised to 1800 rpm and high-speed shearing dispersion was performed for 45 minutes; the stirring speed was lowered to 600 rpm, and 7.9 parts by mass of polyetheramine (AHEW 60 g / eq) was added; a vacuum system was turned on, the vacuum degree was maintained below -0.08 MPa, and defoaming was performed at 300-500 rpm for 25 minutes to obtain the second premix.

[0064] Final mixing and application of the coating: the first premix and the second premix were taken in a mass ratio of 1.07:1, uniformly mixed through a static mixer; the mixed coating was applied on the surface of the substrate by means of blade coating, and the wet film thickness was controlled to be 400 μm.

[0065] Curing and in-situ construction of the heat-conducting network: the substrate coated with the coating was placed in an oven and heated and cured at 100°C for 75 minutes to obtain a nanocomposite heat-conductive coating.

[0066] Comparative Examples 1-7; Comparative Example 1: Compared with Example 1, the difference lies in that the graphene oxide prepared in Preparation Example 1 was not added in the first premix, and the rest was the same.

[0067] Comparative Example 2: Compared with Example 2, the difference lies in that the carboxylated carbon nanotube (CNT-COOH) prepared in Preparation Example 2 was not added in the first premix, and the rest was the same.

[0068] Comparative Example 3: The difference compared with Example 1 is that this comparative example is a pure epoxy system without silicone component. Its formulation only contains: 30 parts by mass of bisphenol A type epoxy resin, 30 parts by mass of spherical alumina, 15 parts by mass of flaky boron nitride, 1.5 parts by mass of graphene oxide and 9.5 parts by mass of polyether amine.

[0069] Comparative Example 4: The difference compared with Example 1 is that this comparative example is a pure silicone system without epoxy component. Its formulation only contains: 25 parts by mass of vinyl-terminated polydimethylsiloxane, 9.4 parts by mass of hydrogen-containing silicone oil, 0.05 parts by mass of platinum gold catalyst, 30 parts by mass of spherical alumina, 15 parts by mass of flaky boron nitride and 1.5 parts by mass of graphene oxide.

[0070] Comparative Example 5: The difference compared with Example 3 is that neither the spherical alumina nor the flaky boron nitride used is pretreated with any silane coupling agent, and the rest is the same.

[0071] Comparative Example 6: The difference compared with Example 1 is that the 15 parts by mass of flaky boron nitride in the second premix is replaced by 15 parts by mass of spherical alumina pretreated with epoxy-based silane, and the rest is the same.

[0072] Comparative Example 7: The difference compared with Example 1 is that the 0.05 parts by mass of platinum gold catalyst in the first premix is transferred to the second premix and added together with the polyether amine, and the rest is the same.

[0073] Test Example 1: Basic Physical Properties and Thermal Conductivity Test of Thermal Conductive Coating This test example aims to evaluate the curing performance, hardness and thermal conductivity of the prepared thermal conductive coating to verify the feasibility and advantages of the present solution.

[0074] Experimental Steps: The curing time test will mix the two premixes prepared according to the examples or comparative examples in the specified mass ratio (such as 1.43:1 for the first premix:second premix in Example 1). Take about 10 mL of the mixed coating and place it in a clean glass test tube. Place the test tube in a 25°C constant temperature water bath. Use a glass rod to slowly stir the coating in the test tube at a constant speed (about 1 time per second). Record the time required from the start of mixing of the two premixes to the loss of flowability of the coating, the inability of the glass rod to rotate freely, and the formation of a gel state. Each sample is tested 3 times, and the average value is taken.

[0075] Shore hardness test The blocky coating samples with thickness of 6 mm were prepared according to the curing conditions of the examples or comparative examples. After the samples were cured at 25 °C for 7 days, the Shore D hardness tester was used for testing. When testing, the hardness tester indenter was vertically pressed on the surface of the sample, and the reading was recorded after the reading was stable. Each sample was tested at least 5 points at different positions, and the average value was taken.

[0076] Planar thermal conductivity test The self-supporting coating samples with thickness of 0.5-1.0 mm were prepared according to the curing conditions of the examples or comparative examples. The samples were cut into circular pieces with a diameter of 10 mm. The thermal diffusivity and specific heat capacity of the samples were measured at 25 °C using a laser flash instrument. The density of the sample was determined by the Archimedes drainage method. The planar thermal conductivity of the sample was calculated according to the formula: thermal conductivity = thermal diffusivity x specific heat capacity x density. Each sample was tested 3 times, and the average value was taken.

[0077] Vertical thermal conductivity test The self-supporting coating samples with thickness of 0.5-1.0 mm were prepared according to the curing conditions of the examples or comparative examples. The samples were cut into square pieces with a size of 10 mm x 10 mm. The vertical thermal conductivity of the samples was measured at 25 °C using a heat flow method thermal conductivity tester. The surface of the sample needs to be smoothed before testing to ensure good contact with the hot plate. Each sample was tested 3 times, and the average value was taken.

[0078] The experimental data is shown in Table 1; Table 1: Basic physical properties and thermal conductivity test results of thermal conductive coating Summary: Except for Comparative Example 7, all example and comparative sample samples can be normally cured, and show stable Shore D hardness. Comparative Example 7 failed to completely cure due to the pre-mixing of platinum catalyst and amine curing agent, resulting in catalyst deactivation. This result clearly confirms the necessity of separating the platinum catalyst and amine curing agent in different pre-mixes in the present application, which ensures the effective progress of the silicon hydrogen addition reaction, thereby realizing the formation of a double curing network.

[0079] In terms of thermal conductivity, the thermal conductivity of the example samples is generally better than that of the comparative examples. Graphene oxide or carboxylated carbon nanotubes as bridging thermal conductive components effectively build thermal conductive paths and improve the thermal conductivity efficiency of the composite material. The epoxy-silicone interpenetrating network structure of the present application exhibits thermal conductivity beyond that of a single resin matrix. The surface modification of the thermal conductive filler by the silane coupling agent effectively reduces the interfacial thermal resistance by improving the interfacial compatibility of the filler and the resin matrix, further improving the thermal conductivity of the material.

[0080] The mixed filler strategy of spherical alumina and flaky boron nitride, combined with the synergistic effect of bridging components, effectively builds a high-efficiency heat conduction network, which is superior to a single filler system. The test results verify that the nano-composite heat-conducting coating prepared by optimizing component distribution, introducing bridging heat-conducting components, constructing interpenetrating network structure, and modifying filler interface, etc. design has good curing performance and heat conduction performance.

[0081] Test Example 2: Electrical performance and adhesion of heat-conducting coating test; This test example evaluates the electrical insulation performance and adhesion performance of the heat-conducting coating to the substrate.

[0082] Experimental steps: According to the curing conditions of the examples or comparative examples, self-supporting coating samples with a thickness of 1.0 mm were prepared. The volume resistivity of the samples was measured at 25°C under a voltage of 500V using a high resistance meter according to ASTM D257 standard. Each sample was tested 3 times, and the average value was taken.

[0083] According to the curing conditions of the examples or comparative examples, self-supporting coating samples with a thickness of 1.0 mm were prepared. The dielectric constant and dielectric loss of the samples at 25°C were measured at a frequency of 1 MHz using a precision LCR tester 3. Each sample was tested 3 times, and the average value was taken.

[0084] The coating prepared according to the examples or comparative examples was applied to the surface of an aluminum alloy substrate and cured according to the specified conditions. A crosshatch tool was used to draw a specified number of squares (e.g., 6 parallel lines with an interval of 1 mm, and 6 vertical parallel lines to form 36 1mm x 1mm squares) on the surface of the cured coating, ensuring that the scratches penetrate the coating to the substrate. A standard pressure-sensitive tape (such as 3M 898) was firmly attached to the crosshatched area, and then quickly peeled off at a specific angle (such as 60 degrees). According to the ASTM D3359 standard, the area percentage of the square remaining on the coating surface after the tape was peeled off was observed and evaluated, and an adhesion grade (0B-5B, 5B being the best) was given. Each sample was tested at least 3 times at different locations, and the grade range was taken.

[0085] The experimental data is shown in Table 2; Table 2: Electrical performance and adhesion of heat-conducting coating test results Summary: In terms of electrical properties, all cured example samples exhibited high volume resistivity, low dielectric constant and low dielectric loss. This indicates that the coating can maintain good electrical insulation performance even with the introduction of graphene oxide or carboxylated carbon nanotubes, ensuring the insulation properties of the material and meeting the insulation requirements of electronic device packaging. Comparative Example 3 and Comparative Example 4, as single resin system controls, have similar electrical properties to the examples and still maintain insulation. Comparative Example 7 cannot be effectively measured as it was not cured.

[0086] In terms of adhesion, all example samples exhibited an adhesion rating of 5B on aluminum alloy substrates. The adhesion rating of Comparative Example 5 (filler not pre-treated with silane coupling agent) decreased significantly to 2B. This result confirms the importance of surface modification of the thermally conductive filler with silane coupling agent. The silane coupling agent enhances the adhesion of the coating to the substrate by improving the interfacial compatibility between the filler and the resin matrix. Good adhesion is a prerequisite for long-term service stability of the coating.

[0087] The nanocomposite thermally conductive coating prepared according to the present application exhibits substrate adhesion while maintaining electrical insulation. This is attributed to the synergistic effect of surface modification of the thermally conductive filler and the epoxy-silicone interpenetrating network structure on the overall performance of the composite, enabling it to meet the requirements of electrical safety and interfacial stability for high-performance thermal conduction applications.

[0088] Test Example 3: Glass transition temperature and tensile property test of thermally conductive coating This test example evaluates the thermal resistance and mechanical properties of the thermally conductive coating.

[0089] Experimental procedure: Coating samples were prepared according to the curing conditions of the examples or comparative examples. 5-10 mg of coating sample was placed in an aluminum crucible and scanned using a differential scanning calorimeter at a heating rate of 10°C / min. The glass transition temperature was recorded. Each sample was tested 3 times and the average value was taken.

[0090] Dumbbell-shaped coating samples were prepared according to the curing conditions of the examples or comparative examples. A universal material testing machine was used for tensile testing. The test speed was set to 5 mm / min. The tensile strength and elongation at break of the sample were recorded. Each sample was tested at least 5 times and the average value was taken.

[0091] The experimental data is shown in Table 3; Table 3: Glass transition temperature and tensile property test results of thermally conductive coating Sample Tg (°C) Tensile strength (MPa) Elongation at break (%) Example 1 138.5 35.2 12.8 Example 2 125.1 30.1 14.5 Example 3 145.8 38.7 10.2 Example 4 132.7 33.5 11.6 Example 5 118.9 28.9 15.3 Comparative Example 1 137.0 32.5 11.0 Comparative Example 2 124.0 27.8 13.0 Comparative Example 3 128.0 45.0 5.5 Comparative Example 4 105.0 18.0 30.0 Comparative Example 5 130.2 25.0 8.0 Comparative Example 6 135.0 31.0 10.5 Comparative Example 7 Not cured Not measured Not measured Summary: The Tg values of the example samples are in the middle-high level, indicating that the coating has cross-linking degree and heat resistance. Compared with Comparative Example 3 (pure epoxy system) and Comparative Example 4 (pure silicone system), the Tg values of the examples are between the two or have improved, showing the comprehensive heat resistance performance under the synergistic effect of the dual-curing system.

[0092] In terms of tensile properties, the example samples show balance in tensile strength and elongation at break. The interpenetrating network structure of the present application combines the strength of epoxy resin and the flexibility of silicone, which is better than the single performance of Comparative Example 3 (pure epoxy) and Comparative Example 4 (pure silicone). The mechanical properties of Comparative Example 5 (filler unmodified) are lower than the corresponding examples, indicating that the modification of the silane coupling agent enhances the combination of the filler and the matrix, and improves the macroscopic mechanical properties of the composite material.

[0093] The introduction of graphene oxide or carboxylated carbon nanotubes also enhances or synergizes the mechanical properties of the coating. Test results show that the nanocomposite thermal conductive coating prepared by the present application through multi-component synergy, construction of interpenetrating network and optimization of filler interface has comprehensive heat resistance and mechanical properties.

Claims

1. A nanocomposite thermally conductive coating, characterized by, By mass parts, including the following components; Bisphenol A type epoxy resin 20-40 parts; Polyether amine 6.3-12.6 parts; Vinyl-terminated polydimethylsiloxane 15-35 parts; Hydrogen-containing silicone oil 5.6-13.1 parts; Platinum gold catalyst 0.03-0.08 parts; Surface modified spherical alumina 25-45 parts; Surface modified flaky boron nitride 15-35 parts; Bridge nano filler 0.5-3.0 parts.

2. The nanocomposite thermally conductive paint according to claim 1, characterized in that, The bridge nano filler is at least one of graphene oxide or carboxylated carbon nanotube.

3. The nanocomposite thermally conductive paint according to claim 2, characterized in that, The graphene oxide is prepared by natural flake graphite, concentrated sulfuric acid, sodium nitrate and potassium permanganate oxidation, and then ultrasonic peeling; the carboxylated carbon nanotube is prepared by original multi-walled carbon nanotube, mixed acid refluxing reaction of concentrated sulfuric acid and concentrated nitric acid.

4. The nanocomposite thermally conductive paint according to claim 1, characterized in that, The surface modified spherical alumina is modified with epoxy silane; the surface modified flaky boron nitride is modified with long chain alkyl silane.

5. The nanocomposite thermally conductive paint according to claim 4, wherein the carbon nanotubes are multi-walled carbon nanotubes. The epoxy silane is γ-glycidyl ether propyl trimethoxysilane; the long chain alkyl silane is n-octyl triethoxysilane.

6. A method for preparing a nanocomposite thermal conductive coating according to any one of claims 1 to 5, characterized in that, Including the following steps; S1, pretreatment of the thermal conductive filler; S2, preparation of the first premix: mixing bisphenol A type epoxy resin, surface modified spherical alumina and bridge nano filler and high speed shearing dispersion, then adding hydrogen-containing silicone oil and platinum gold catalyst, vacuum degassing to obtain the first premix; S3, preparation of the second premix: mixing vinyl-terminated polydimethylsiloxane and surface modified flaky boron nitride and high speed shearing dispersion, then adding polyether amine, vacuum degassing to obtain the second premix; S4, mixing and application: uniformly mixing the first premix and the second premix in proportion, and applying on the surface of the substrate; S5, curing: heating and curing the applied substrate to construct a thermal conductive network in situ, and obtaining a nano-composite thermal conductive coating.

7. The method according to claim 6, wherein the method is characterized by, The step S1 of pretreatment of the thermal conductive filler includes: Mixing spherical alumina with epoxy silane equivalent to 0.5%-2.0% of its mass for surface modification; Mixing flaky boron nitride with long chain alkyl silane equivalent to 0.5%-2.0% of its mass for surface modification.

8. The method according to claim 6, wherein the method is characterized by, The rotation speed of high speed shearing dispersion in steps S2 and S3 is 1500-2500 rpm, and the dispersion time is 30-90 minutes; the vacuum degree of vacuum degassing is controlled between-0.08 MPa and-0.09 MPa, and the degassing time is 15-30 minutes.

9. The method of claim 6, wherein the nanocomposite thermal conductive paint is prepared by mixing the metal oxide nanoparticles and the metal powder in a weight ratio of 1: 1 to 1:

10. The mass ratio of the first premix to the second premix in step S4 is 1.07:1 to 1.65:

1.

10. The method of claim 6, wherein the nanocomposite thermal conductive paint is prepared by mixing the metal oxide nanoparticles and the metal powder in a weight ratio of 1: 1 to 1:

10. In step S5, the temperature of heating and curing is 80-150℃, and the curing time is 30-90 minutes.

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