High-thermal-conductivity flame-retardant pouring sealant mixed and filled with epoxy resin

Abstract

The invention discloses a high-thermal-conductivity flame-retardant pouring sealant mixed and filled with epoxy resin. The high-thermal-conductivity flame-retardant pouring sealant comprises a component A and a component B, the component A comprises epoxy resin and aluminum hydroxide with nano-diamond adsorbed on the surface; the component B comprises a curing agent and boron nitride; the aluminum hydroxide with the nano-diamond adsorbed on the surface is prepared from nano-diamond powder modified by polydopamine and aluminum hydroxide micro-powder through a wet nano-composite process. The epoxy resin pouring sealant is filled with aluminum hydroxide to endow the product with flame retardance, and the thermal conductivity of the aluminum hydroxide filler is improved by adsorbing the nano-diamond on the surface; the aluminum hydroxide with the nano-diamond adsorbed on the surface is tightly connected with the boron nitride through electrostatic attraction, so that the contact thermal resistance is reduced, and the thermal conductivity is further improved; the epoxy resin pouring sealant filled with the two fillers in a mixed manner has the dual characteristics of high thermal conductivity and flame retardance, and meets the requirements of high-thermal-conductivity flame-retardant potting of high-power electronic devices.

Description

Technical Field

[0001] The present invention relates to the technical field of potting adhesives for electronic devices, and particularly relates to a hybrid-filled epoxy resin high thermal conductivity and flame retardant potting adhesive. Background Art

[0002] Potting adhesive is a liquid active composite composed of a resin matrix, a curing agent (or crosslinking agent), fillers, etc. It has fluidity before curing and can be poured into and penetrate the voids inside electronic devices. It cures into a thermosetting composite material under certain conditions, playing roles such as bonding and fixing, waterproofing and moisture-proofing, dust-proofing, corrosion-proofing, insulation, flame retardancy, shock-proofing, explosion-proofing, and anti-vibration and impact. Epoxy resin potting adhesive has high bonding strength, good sealing stability, chemical resistance, weather and aging resistance, waterproofing and moisture-proofing, and excellent comprehensive mechanical and electrical properties. It is one of the most widely used potting adhesives for electronic devices. Modern electronic devices are increasingly tending to develop towards high power, high density, high frequency, integration, and miniaturization. The direct consequence of this trend is that more heat is generated in a limited volume. If this heat cannot be dissipated in time, it will seriously affect the stability, reliability, and safety of the device operation. Using high thermal conductivity potting adhesive is the most effective way to solve the heat dissipation problem of the electronic device structure. However, the epoxy resin material itself has a low thermal conductivity (about 0.2 W·m -1 ·K -1 ), and it is becoming increasingly difficult to meet the timely and efficient heat dissipation requirements of modern electronic devices. Epoxy resin high thermal conductivity potting adhesives can be divided into two categories according to the heat conduction mechanism: intrinsic type and filled type. The preparation process of intrinsic high thermal conductivity epoxy resin is complex, the product has a high melting point and high viscosity, and requires special molding and processing equipment, which is difficult to meet the process performance requirements of electronic device potting and casting. There is still a long way to go before industrial application. For industrial scale applications, the thermal conductivity of potting adhesive is improved by filling high thermal conductivity insulating fillers. Commonly used thermal conductivity insulating fillers include: alumina (Al2O3), magnesia (MgO), boron nitride (BN), aluminum nitride (AlN), diamond, etc. The thermal conductivities and costs of various insulating fillers vary greatly. For example, the thermal conductivity of diamond is 2000 W·m -1 ·K -1 , the thermal conductivities of BN and AlN are 280 - 300 W·m -1 ·K -1 , but they are expensive; Al2O3 and MgO are cheap, but their thermal conductivities are relatively low, only 30 - 35 W·m -1 ·K -1。For filled epoxy resin potting adhesives, when the filler dosage is low, it is similar to the "sea-island" structure of the polymer blend system. The fillers, as the dispersed phase, are surrounded by the epoxy resin matrix and are not connected to each other, resulting in only a small increase in thermal conductivity. When the filler dosage increases to a certain critical value, the particles start to contact and interact with each other, and the thermal conductivity begins to increase significantly. However, at the same time, due to the relatively weak intermolecular forces between the fillers, the contact between the fillers is loose, and there are inevitably air gaps, resulting in a large contact thermal resistance, which limits the increase in thermal conductivity. Therefore, how to make the fillers tightly connected to each other, reduce the contact thermal resistance, and form an effective thermal conduction path is one of the key technologies in the development and application of filled high thermal conductivity epoxy resin potting adhesives.

[0003] Generally speaking, electronic devices need to have a certain flame retardant rating (e.g., UL94-V0) to ensure safety. Epoxy resin belongs to flammable materials and will produce a large amount of toxic gases when burning, which severely restricts its application in the field of electronic potting. Flame retardant epoxy resin refers to a type of epoxy resin that has the function of inhibiting flame combustion after the whole system is potted and cured by chemically treating or synthesizing the resin backbone or curing agent, or adding substances with flame retardant functions. Flame retardant epoxy resins can be divided into three categories according to the preparation process: intrinsic type, reactive type and filled type. The intrinsic type introduces flame retardant elements (such as Cl, Br, N, P, Si, S, etc.) during the synthesis of epoxy resin. Since halogens will produce toxic and corrosive hydrogen halide gases during combustion, which will damage the environment and human health, they have been banned in countries such as the European Union. Therefore, currently, mainly elements such as P, N and Si are introduced to prepare halogen-free intrinsic flame retardant epoxy resins. The reactive type is to design and synthesize a curing agent or flame retardant containing flame retardant elements, and carry out cross-linking polymerization reaction with epoxy functional groups to introduce flame retardant elements into the epoxy resin system. As an electronic potting material, epoxy resin must be used in combination with a curing agent. By introducing flame retardant elements into the curing agent, or synthesizing a flame retardant containing active groups (such as epoxy groups, amino groups, etc.), and making it participate in the curing reaction of epoxy, good flame retardancy can be imparted to the epoxy resin system. Intrinsic and reactive flame retardant epoxy resins have good compatibility with the matrix, are evenly dispersed, have little impact on the comprehensive properties of epoxy resin, and have excellent properties after curing, but the preparation process is complex and the difficulty of industrial application is large. The filled type is to add a flame retardant to a conventional epoxy resin system. Flame retardants can be further divided into inorganic flame retardants, organic flame retardants, and inorganic / organic synergistic flame retardants according to their types. Inorganic flame retardants are the earliest discovered flame retardants, mainly some simple substances or inorganic salts containing non-combustible or difficult-to-combust elements, such as red phosphorus, ammonium polyphosphate, ammonium chloride, aluminum oxalate, aluminum hydroxide, magnesium hydroxide, etc. Inorganic flame retardants usually need to be added in large amounts to achieve satisfactory flame retardant effects. Organic flame retardants are mainly some organic compounds with flame retardant functions, such as 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), aromatic polyphosphates, polysiloxanes, etc. Filled flame retardant epoxy resins are widely used due to the variety of flame retardants, simple process, low cost, etc., but they also have disadvantages such as high addition amount, which easily leads to a decline in the mechanical, electrical and processing properties of epoxy resin.

[0004] With the continuous improvement of the environmental protection and safety requirements of electronic products, aluminum hydroxide (Al(OH)3) powder has become the most widely used halogen-free flame retardant in the field of electronic potting due to its multiple functions such as flame retardancy, smoke suppression, filling and modification. Adding ultrafine aluminum hydroxide to epoxy resin not only makes the product have flame retardant and smoke suppression effects, but also improves the properties such as anti-electric leakage, arc resistance, wear resistance, and heat conduction. However, the thermal conductivity of Al(OH)3 is relatively low, only 20 W·m -1 ·K-1 Generally, it is necessary to be compounded with other high - thermal - conductivity fillers to improve the thermal conductivity. Summary of the Invention

[0005] Existing epoxy resin high - thermal - conductivity flame - retardant potting adhesives have the following technical defects: the thermal conductivity of flame - retardant fillers is low, the intermolecular force between fillers is small, the contact thermal resistance is large, it is not easy to form an effective thermal - conduction path by closely connecting with each other, and the improvement of thermal conductivity is limited, etc. To solve the above - mentioned technical defects, the present invention provides a hybrid - filled epoxy resin high - thermal - conductivity flame - retardant potting adhesive.

[0006] The technical solution provided by the present invention is as follows: a hybrid - filled epoxy resin high - thermal - conductivity flame - retardant potting adhesive, which includes component A and component B; component A includes epoxy resin and aluminum hydroxide adsorbed with nanodiamond on the surface; component B includes a curing agent and boron nitride; the aluminum hydroxide adsorbed with nanodiamond on the surface is prepared by a wet - process nano - composite process from polydopamine - modified nanodiamond powder and aluminum hydroxide micropowder. Filling aluminum hydroxide in the epoxy resin potting adhesive endows the product with flame retardancy, and adsorbing nanodiamond on the surface can improve the disadvantage of the relatively low thermal conductivity of the aluminum hydroxide filler. Mixing boron nitride and aluminum hydroxide adsorbed with nanodiamond on the surface to fill the epoxy resin potting adhesive has the dual characteristics of high thermal conductivity and flame retardancy.

[0007] Preferably, the preparation steps of the aluminum hydroxide adsorbed with nanodiamond on the surface are as follows: Step 1, disperse the nanodiamond powder in deionized water, then add hydrochloric acid dopamine, and raise the temperature to 50 °C and react for 2 hours to obtain a first suspension; Step 2, centrifuge and dry the first suspension obtained in Step 1 to obtain polydopamine - modified nanodiamond powder; Step 3, disperse the aluminum hydroxide micropowder in a pH buffer solution, then add the polydopamine - modified nanodiamond powder obtained in Step 2, and react at room temperature for 4 hours to obtain a second suspension; Step 4, filter, rinse, and dry the second suspension obtained in Step 3 to obtain the aluminum hydroxide powder adsorbed with nanodiamond on the surface. After the nanodiamond is modified with polydopamine, its surface is positively charged, which is conducive to adsorbing on the negatively charged surface of aluminum hydroxide, and makes the surface of the aluminum hydroxide adsorbed with nanodiamond on the surface positively charged, while the surface of boron nitride is negatively charged. The electrostatic attraction between the two fillers is conducive to the tight connection between the fillers, further reducing the contact thermal resistance and improving the thermal conductivity.

[0008] Preferably, the average particle size of the nanodiamond powder in Step 1 is 50 - 100 nanometers. If the particle size of the nanodiamond powder is too high, it is not easy to be adsorbed on the surface of aluminum hydroxide; if it is too low, the cost is high.

[0009] Preferably, the average particle size of the aluminum hydroxide micropowder in step three is 8 - 15 microns. If the particle size of the aluminum hydroxide micropowder is too high, it is prone to sedimentation, resulting in layering of the potting product. If it is too low, the thermal conductivity is poor. The reason is that filling fillers with smaller sizes will cause many filler / matrix and filler / filler interfaces inside the composite material. The more interfaces there are, the more intense the phonon scattering will be, the greater the thermal resistance, and the lower the thermal conductivity.

[0010] Preferably, the mass ratio of aluminum hydroxide to polydopamine-modified nanodiamond powder in step three is 100:2 - 5. The thermal conductivity of diamond (about 2000 W·m -1 ·K -1 ) is much greater than that of aluminum hydroxide. If the amount of polydopamine-modified nanodiamond powder used is small, it cannot completely cover the surface of the aluminum hydroxide powder, and the improvement of the thermal conductivity of the filler is less. If the amount used is too much, some polydopamine-modified nanodiamond powder cannot be adsorbed on the surface of aluminum hydroxide and is lost during the filtration in step four. Taking spherical fillers with an aluminum hydroxide particle size of 10 microns and a density of 2.4 g / cm 3 , and a nanodiamond particle size of 80 nanometers and a density of 3.5 g / cm 3 as an example, the specific surface area of aluminum hydroxide is about 2.5×10 3 cm 2 / g, and the specific surface area of nanodiamond is about 2.1×10 5 cm 2 / g. 1.2 grams of nanodiamond adsorbed on the surface of 100 grams of aluminum hydroxide can be completely covered. Considering that aluminum hydroxide is generally layered and nanodiamond is generally an irregular polyhedron, therefore, the mass ratio of aluminum hydroxide powder to polydopamine-modified nanodiamond powder is preferably 100:2 - 5 to ensure full coverage of nanodiamond on the surface of aluminum hydroxide and reduce losses during the filtration in step four.

[0011] Preferably, the pH value of the pH buffer solution in step three is 8.5 - 9.5. The isoelectric point on the surface of the aluminum hydroxide micropowder is pH = 8.1. When the pH value of the solution is greater than the isoelectric point, the surface of the aluminum hydroxide powder is negatively charged, which is conducive to adsorbing the positively charged polydopamine-modified nanodiamond powder.

[0012] Preferably, the mass ratio of component A to component B is 100:21. Mix component A and component B evenly according to the preferred ratio, and after vacuum degassing, it can be used for potting electronic devices. The thermal conductivity of the cured potting adhesive can reach 1.14 W·m -1 ·K -1 and above, and the flame retardant grade is UL94-V1 or UL94-V0.

[0013] Preferably, the component A includes: 100 parts of epoxy resin; 100 - 120 parts of aluminum hydroxide adsorbed with nanodiamond on its surface. In the component A, if the filling amount of the aluminum hydroxide adsorbed with nanodiamond on its surface is less than 100 parts, the flame retardancy of the product cannot reach the UL94 - V1 level; if it is greater than 120 parts, the viscosity of the system is high, and the processing and potting process performance is poor.

[0014] Preferably, the component B includes: 100 parts of curing agent; 40 - 50 parts of boron nitride. In the component B, if the filling amount of boron nitride is small, the thermal conductivity of the product is low; if the filling amount is large, the viscosity of the system is high, and the processing and potting process performance is poor.

[0015] The present invention has the following beneficial effects: 1. Dual properties of high thermal conductivity and flame retardancy: Through the electrostatic attraction between negatively charged boron nitride and positively charged aluminum hydroxide adsorbed with nanodiamond on its surface, a tightly connected thermal conductivity network is constructed, significantly reducing the contact thermal resistance between fillers, and increasing the thermal conductivity of the potting adhesive to 1.14 - 1.75 W·m⁻¹·K⁻¹, meeting the high - efficiency heat dissipation requirements of high - power electronic devices; Aluminum hydroxide, as the main flame retardant, combined with the nanodiamond adsorbed on its surface, enables the potting adhesive to reach the UL94 - V0 / V1 level of flame retardancy standard; 2. Synergistic optimization of fillers: By modifying nanodiamond with polydopamine to endow it with positive charge, ensuring the stable adsorption of nanodiamond on the surface of aluminum hydroxide, forming a "core - shell" structure with aluminum hydroxide as the core and nanodiamond as the shell, which not only retains the flame retardancy of aluminum hydroxide but also makes up for its short board in thermal conductivity by highly thermally conductive nanodiamond; 3. Precise control of particle size and ratio: The particle size of nanodiamond is 50 - 100 nanometers, and the particle size of aluminum hydroxide is 8 - 12 micrometers, balancing the specific surface area and dispersibility, reducing the interface thermal resistance; The mass ratio of aluminum hydroxide to nanodiamond is 100:2 - 5, ensuring the full coverage of the surface of aluminum hydroxide by nanodiamond and avoiding excessive loss at the same time; 4. Process stability and advantages for industrial application: Defining the conditions of pH buffer solution, reaction temperature and time, and the mixing ratio of component A / component B, ensuring the uniform dispersion of fillers, avoiding agglomeration or sedimentation, and controlling the viscosity of the potting adhesive within 6000 - 11000 cP, meeting the requirements of the casting process; 5. Enhanced mechanical properties: The electrostatic interaction between boron nitride and modified aluminum hydroxide improves the interaction force between fillers, and the tensile strength after curing reaches 51.7 - 56.6 MPa, significantly superior to the traditional filler system; 6. Environmental protection and economic benefits: Completely relying on aluminum hydroxide to achieve flame retardancy, avoiding the high toxicity and environmental hazards of halogen - based flame retardants, meeting the requirements of environmental protection regulations; By optimizing the dosage of nanodiamond and industrial - feasible processes, reducing the cost pressure of highly thermally conductive fillers and at the same time reducing raw material waste; 7. Wide applicability: It is applicable to fields with strict requirements for heat dissipation and safety, such as high-power LEDs, new energy vehicle electronic control systems, 5G communication devices, etc., improving the stability and lifespan of electronic devices during long-term operation. Detailed implementation manners

[0016] The present invention will be further described below in conjunction with Examples (a total of 6 examples) and Comparative Examples (a total of 3 examples).

[0017] Example 1 A high thermal conductivity and flame retardant epoxy resin potting adhesive filled with a mixture of boron nitride and aluminum hydroxide adsorbed with nanodiamonds on the surface, comprising component A and component B; Component A contains the following parts by mass of preparation raw materials: 100 parts of YDF-170 bisphenol F epoxy resin (Guodu Chemical Co., Ltd.), 100 parts of aluminum hydroxide adsorbed with nanodiamonds on the surface; Component B contains the following parts by mass of preparation raw materials: 100 parts of 593 curing agent (Baleng Petrochemical), 40 parts of boron nitride (Suzhou Napu Materials Technology Co., Ltd.).

[0018] In component A, the aluminum hydroxide adsorbed with nanodiamonds on the surface is prepared by a method including the following steps: Step 1, by mass, add 10 parts of nanodiamond powder (average particle size 50 nm, Shanghai Xiangtian Nano Materials Co., Ltd.) to 500 parts of deionized water, disperse it by ultrasonic wave for 30 minutes, then add 1 part of dopamine hydrochloride (Shanghai Macklin Biochemical Co., Ltd.), stir and heat up to 50 °C for reaction for 2 hours; Step 2, centrifuge and dry the suspension obtained in step 1 to obtain polydopamine-modified nanodiamond powder; Step 3, by mass, disperse 100 parts of aluminum hydroxide powder (average particle size 8 µm, Hefei Wuran New Materials Technology Co., Ltd.) in 1000 parts of buffer solution with pH = 8.5 - 9.5, then add 2 parts of the polydopamine-modified nanodiamond powder obtained in step 2, and react at room temperature for 4 hours; Step 4, filter, rinse and dry the suspension obtained in step 3 to obtain aluminum hydroxide powder adsorbed with nanodiamonds on the surface.

[0019] Weigh the YDF-170 bisphenol F epoxy resin and aluminum hydroxide adsorbed with nanodiamonds on the surface of component A according to the formula, add them to a dispersion mixer, disperse and stir at 100 °C and 1000 rpm for 1 hour, then turn on the vacuum, and continue to disperse and stir at 0.01 MPa for 1 hour to obtain component A. Weigh the 593 curing agent and boron nitride of component B according to the formula, add them to a dispersion mixer, disperse and stir at 100 °C and 1000 rpm for 1 hour, then turn on the vacuum, and continue to disperse and stir at 0.01 MPa for 1 hour to obtain component B.

[0020] By mass, 100 parts of the above-prepared component A and 21 parts of the above-prepared component B are respectively added into the A barrel and B barrel of a two-component glue filling machine. After degassing for 30 minutes under the conditions of 50 °C and 0.01 MPa vacuum, they are mixed and extruded into an electronic device. Then the potted electronic device is placed in an oven and can be completely cured at 80 °C for 4 hours. Using the same method, the potting adhesive is poured into a mold for curing, and is used for testing the thermal conductivity, flame retardancy and tensile properties of the product.

[0021] Examples 2 - 6 The differences between Examples 2 to 6 and Example 1 are as follows: (1) the dosage of aluminum hydroxide with surface-adsorbed nanodiamond in component A; (2) the dosage of boron nitride in component B; (3) the average particle size of nanodiamond in Step 1 of preparing aluminum hydroxide with surface-adsorbed nanodiamond; (4) the average particle size of aluminum hydroxide in Step 3 of preparing aluminum hydroxide with surface-adsorbed nanodiamond; (5) the dosage of polydopamine-modified nanodiamond in Step 3 of preparing aluminum hydroxide with surface-adsorbed nanodiamond.

[0022] Except for the above differences, Examples 2 to 6 are the same as Example 1. For easy comparison and analysis, Table 1 lists the comparison of the formulations and preparation processes of Examples 1 to 6.

[0023] Table 1 Comparison of the Formulations and Preparation Processes of Examples 1 to 6

[0024] Comparative Example 1 According to the ratio of Example 2, a nanodiamond and aluminum hydroxide mixed filler is used to replace aluminum hydroxide with surface-adsorbed nanodiamond to prepare an epoxy resin potting adhesive, which includes component A and component B.

[0025] Component A contains the following raw materials in parts by mass: 104 parts of YDF-170 bisphenol F type epoxy resin, 4 parts of nanodiamond, and 100 parts of aluminum hydroxide.

[0026] Description: In Example 2, Component A includes 100 parts of YDF-170 bisphenol F type epoxy resin and 100 parts of aluminum hydroxide adsorbed with nanodiamond on its surface, that is, the mass ratio of bisphenol F type epoxy resin to aluminum hydroxide adsorbed with nanodiamond on its surface is 1:1. According to this ratio, if the YDF-170 bisphenol F type epoxy resin in Component A is 104 parts, then the aluminum hydroxide adsorbed with nanodiamond on its surface is also 104 parts. According to Step 3 of the preparation of aluminum hydroxide adsorbed with nanodiamond on its surface in Example 2, the dosage ratio of aluminum hydroxide to nanodiamond powder modified with polydopamine is 100:4. Therefore, in 104 parts of aluminum hydroxide adsorbed with nanodiamond on its surface, there are 100 parts of aluminum hydroxide and 4 parts of nanodiamond powder modified with polydopamine. Therefore, in Comparative Example 1, the ratio of epoxy resin, nanodiamond, and aluminum hydroxide is the same as that of epoxy resin, nanodiamond modified with polydopamine, and aluminum hydroxide in Example 2, which is 104:4:100.

[0027] The composition of Component B is the same as that in Example 2.

[0028] The preparation process, mixing ratio, mixing, and curing process of Component A and Component B are the same as those in Example 2.

[0029] Comparative Example 2 According to the ratio in Example 6, using a mixture of nanodiamond and aluminum hydroxide as a filler to replace aluminum hydroxide adsorbed with nanodiamond on its surface, an epoxy resin potting adhesive is prepared, which includes Component A and Component B.

[0030] Component A contains the following raw materials in parts by mass: 105 parts of YDF-170 bisphenol F type epoxy resin, 6 parts of nanodiamond, and 120 parts of aluminum hydroxide.

[0031] Description: In Example 6, Component A includes 100 parts of YDF-170 bisphenol F type epoxy resin and 120 parts of aluminum hydroxide adsorbed with nanodiamond on its surface, that is, the mass ratio of bisphenol F type epoxy resin to aluminum hydroxide adsorbed with nanodiamond on its surface is 1:1.2. According to this ratio, if the YDF-170 bisphenol F type epoxy resin in Component A is 105 parts, then the aluminum hydroxide adsorbed with nanodiamond on its surface is 126 parts. According to Step 3 of the preparation of aluminum hydroxide adsorbed with nanodiamond on its surface in Example 6, the dosage ratio of aluminum hydroxide to nanodiamond powder modified with polydopamine is 100:5. Therefore, in 126 parts of aluminum hydroxide adsorbed with nanodiamond on its surface, there are 120 parts of aluminum hydroxide and 6 parts of nanodiamond powder modified with polydopamine. Therefore, in Comparative Example 2, the ratio of epoxy resin, nanodiamond, and aluminum hydroxide is the same as that of epoxy resin, nanodiamond modified with polydopamine, and aluminum hydroxide in Example 6, which is 105:6:120.

[0032] The composition of Component B is the same as that in Example 6.

[0033] The preparation processes, mixing ratios, mixing, and curing processes of Component A and Component B are the same as those in Example 6.

[0034] Comparative Example 3 Prepare an epoxy potting adhesive using only aluminum hydroxide as the filler in accordance with the total filler usage amount in Example 6 or Comparative Example 2, which includes Component A and Component B.

[0035] Component A contains the following raw materials for preparation in parts by mass: 100 parts of YDF-170 bisphenol F type epoxy resin and 120 parts of aluminum hydroxide.

[0036] Component B contains the following raw materials for preparation in parts by mass: 100 parts of 593 curing agent and 50 parts of aluminum hydroxide.

[0037] The preparation processes, mixing ratios, mixing, and curing processes of Component A and Component B are the same as those in Example 6.

[0038] Performance Detection Experiment Uniformly test and compare the properties of the epoxy resin high thermal conductivity and flame retardant potting adhesives in Examples 1 to 6 and Comparative Examples 1 to 3. The test methods are as follows: 1. The viscosities of Component A and Component B of the potting adhesive are tested in accordance with "GB / T 12007.4-1989 Determination Method for Viscosity of Epoxy Resins", and the test temperature is 50 °C. 2. The thermal conductivity is tested in accordance with "GB / T 10295-2008 Determination of Steady-State Thermal Resistance and Related Characteristics of Thermal Insulation Materials - Heat Flow Meter Method", and the test is carried out after the potting adhesive is cured. 3. The flame retardancy is tested in accordance with the UL94 vertical burning test standard, and the test is carried out after the potting adhesive is cured. 4. The tensile fracture strength is tested in accordance with "GB / T 1040.1-2018 Determination of Tensile Properties of Plastics", and the test is carried out after the potting adhesive is cured.

[0039] Result Analysis The performance test results of the epoxy resin high thermal conductivity and flame retardant potting adhesives in Examples 1 to 6 and Comparative Examples 1 to 3 are shown in Table 2.

[0040] Table 2 Performance Test Results of Examples 1 to 6 and Comparative Examples 1 to 2

[0041] Examples 1 to 3 and Comparative Example 1 have the same composition of Component B, so their viscosities are the same. The differences among Examples 1 to 3 are only in: the preparation of aluminum hydroxide adsorbed with nanodiamond on the surface, Step 3, and the different dosages of polydopamine-modified nanodiamond, which are 2, 4, and 5 grams respectively. The viscosity of Component A is mainly affected by the filling amount of aluminum hydroxide adsorbed with nanodiamond on the surface, and the flame retardancy of the potting adhesive is mainly affected by the dosage of aluminum hydroxide flame retardant. In Examples 1 to 3, the filling amount of aluminum hydroxide adsorbed with nanodiamond in Component A is the same. Therefore, the viscosities and flame retardancy grades of Component A in Examples 1 to 3 are basically the same. Although the dosages of polydopamine-modified nanodiamond in Examples 1 to 3 are different, their proportions are relatively low (2% - 5% of aluminum hydroxide), and the influence on viscosity and flame retardancy is very small.

[0042] The difference between Example 2 and Comparative Example 1 is that: in Example 2, the filler of Component A is aluminum hydroxide adsorbed with nanodiamond on the surface, while in Comparative Example 1, the filler of Component A is a simple mixture of nanodiamond and aluminum hydroxide. It can be seen from the table that the viscosities and flame retardancy grades of Component A in Example 2 and Comparative Example 1 are the same, which is because the total dosage of the fillers and the dosage of aluminum hydroxide in Component A of Example 2 and Comparative Example 1 are the same. However, the thermal conductivity of Example 2 (1.29 W·m -1 ·K -1 ) is significantly greater than that of Comparative Example 1 (0.67 W·m -1 ·K -1 ). This is because Example 2 uses aluminum hydroxide adsorbed with nanodiamond on the surface, which improves the disadvantage of the low thermal conductivity of the aluminum hydroxide filler. On the other hand, after the nanodiamond is modified with polydopamine, its surface is positively charged, which is beneficial to its adsorption on the surface of negatively charged aluminum hydroxide and makes the surface of the filler positively charged. When filling two fillers, boron nitride and the aluminum hydroxide adsorbed with nanodiamond on the surface, in the epoxy resin potting adhesive, the surface of boron nitride is negatively charged and the aluminum hydroxide adsorbed with nanodiamond on the surface is positively charged. The electrostatic attraction between the two fillers is beneficial to the tight connection between the fillers, reducing the contact thermal resistance and improving the thermal conductivity. While in Comparative Example 1, it is just a simple mixture of nanodiamond, aluminum hydroxide, and boron nitride, and the intermolecular force between the fillers is small, and they cannot be tightly connected to each other, resulting in a large contact thermal resistance.

[0043] Since the dosage of polydopamine-modified nanodiamond in Example 2 is greater than that in Example 1, the thermal conductivity of Example 2 (1.29 W·m -1 ·K -1 ) is greater than that of Example 1 (1.14 W·m -1 ·K -1 ). Compared with Example 2, Example 3 increases the dosage of polydopamine-modified nanodiamond, but the thermal conductivity only increases by 0.03W·m -1 ·K-1 This is because if the amount of polydopamine-modified nanodiamond used is excessive, some of the polydopamine-modified nanodiamond powder may not be adsorbed on the surface of aluminum hydroxide and will be lost during the filtration in Step 4. The tensile strengths of Examples 1 to 3 are basically close (51.7 - 53.1 MPa), but are significantly greater than the tensile strength of Comparative Example 1 (42.3 MPa). This is due to the electrostatic attraction between the two fillers, i.e., aluminum hydroxide with surface-adsorbed nanodiamond and boron nitride, in Examples 1 to 3.

[0044] Examples 4 to 6 have the same composition of Component B as Comparative Examples 2 to 3, so their viscosities are the same. The differences in Examples 4 to 6 only lie in: the preparation of aluminum hydroxide with surface-adsorbed nanodiamond, in Step 3, the amount of polydopamine-modified nanodiamond used is different. The viscosity of Component A is mainly affected by the filling amount of aluminum hydroxide with surface-adsorbed nanodiamond, and the flame retardancy of the potting adhesive is mainly affected by the amount of aluminum hydroxide flame retardant used. In Examples 4 to 6, the filling amount of aluminum hydroxide with surface-adsorbed nanodiamond in Component A is the same. Therefore, the viscosities and flame retardancy grades of Component A in Examples 4 to 6 are basically the same. Although the amounts of polydopamine-modified nanodiamond used in Examples 4 to 6 are different, their proportions are relatively low (2% - 5% of aluminum hydroxide), and the influence on viscosity and flame retardancy is very small.

[0045] The difference between Example 6 and Comparative Example 2 is that: in Example 6, the filler of Component A is aluminum hydroxide with surface-adsorbed nanodiamond, while in Comparative Example 2, the filler of Component A is a simple mixture of nanodiamond and aluminum hydroxide. As can be seen from the table, the viscosities and flame retardancy grades of Component A in Example 6 and Comparative Example 2 are the same, which is because the total amount of fillers and the amount of aluminum hydroxide in Component A of Example 6 and Comparative Example 2 are the same. However, the thermal conductivity of Example 6 (1.75 W·m -1 ·K -1 ) is significantly greater than that of Comparative Example 2 (0.79 W·m -1 ·K -1 ). This is because Example 6 uses aluminum hydroxide with surface-adsorbed nanodiamond, which improves the disadvantage of the relatively low thermal conductivity of the aluminum hydroxide filler. On the other hand, after the nanodiamond is modified with polydopamine, its surface is positively charged, which is conducive to its adsorption on the negatively charged surface of aluminum hydroxide and makes the surface of the filler positively charged. When filling two fillers, boron nitride and the aluminum hydroxide with surface-adsorbed nanodiamond, in the epoxy resin potting adhesive, the surface of boron nitride is negatively charged and the aluminum hydroxide with surface-adsorbed nanodiamond is positively charged. The electrostatic attraction between the two fillers is conducive to the tight connection between the fillers, reducing the contact thermal resistance and improving the thermal conductivity. While in Comparative Example 2, it is just a simple mixture of nanodiamond, aluminum hydroxide, and boron nitride, and the intermolecular force between the fillers is small, they cannot be tightly connected to each other, and the contact thermal resistance is large.

[0046] Since the dosage of polydopamine-modified nanodiamond in Example 5 is greater than that in Example 4, the thermal conductivity of Example 5 (1.71 W·m -1 ·K -1 -1) is greater than that of Example 4 (1.58 W·m -1 ·K -1 -1). Compared with Example 5, the dosage of polydopamine-modified nanodiamond in Example 6 is increased, but the thermal conductivity only increases by 0.04 W·m -1 ·K -1 -1. This is because if the dosage of polydopamine-modified nanodiamond is too large, some of the polydopamine-modified nanodiamond powder may not be adsorbed on the surface of aluminum hydroxide and is lost during the filtration in Step 4. The tensile strengths of Examples 4 to 6 are basically close (55.5 to 56.6 MPa), but are significantly greater than the tensile strength of Comparative Example 2 (38.9 MPa). This is due to the electrostatic attraction between the aluminum hydroxide with surface-adsorbed nanodiamond and the two fillers of boron nitride in Examples 4 to 6.

[0047] Comparative Example 3 and Comparative Example 2 have the same total dosage of fillers. The difference is that Comparative Example 3 only uses a single filler of aluminum hydroxide, while Comparative Example 2 uses three fillers of aluminum hydroxide, nanodiamond, and boron nitride. The thermal conductivity of Comparative Example 3 is 0.72 W·m -1 ·K -1 -1. Since Comparative Example 2 adds nanodiamond and boron nitride with better thermal conductivity, its thermal conductivity increases to 0.79 W·m -1 ·K -1 -1, but the increase is not significant. This is because the dosages of nanodiamond and boron nitride are small and are surrounded by aluminum hydroxide with a lower thermal conductivity. If the dosages of diamond and boron nitride are increased, it is possible to increase the thermal conductivity, but at the same time, the viscosity of the system will also increase, making it difficult for potting and casting. If the dosage of aluminum hydroxide is reduced while increasing the dosages of diamond and boron nitride to ensure an appropriate viscosity, the flame retardancy will decrease.

[0048] Based on the above analysis, it can be seen that: for the high thermal conductivity and flame retardant epoxy resin potting adhesive filled with boron nitride and aluminum hydroxide adsorbed with nanodiamonds on the surface provided by the present invention, aluminum hydroxide endows the product with flame retardancy, and the nanodiamonds adsorbed on the surface can improve the disadvantage of the relatively low thermal conductivity of the aluminum hydroxide filler. By filling two kinds of fillers, boron nitride and aluminum hydroxide adsorbed with nanodiamonds on the surface, in the epoxy resin potting adhesive, the surface of boron nitride is negatively charged and the aluminum hydroxide adsorbed with nanodiamonds on the surface is positively charged. The electrostatic attraction between the two fillers is conducive to the tight connection between the fillers, reducing the contact thermal resistance and improving the thermal conductivity. The high thermal conductivity and flame retardant epoxy resin potting adhesive filled with boron nitride and aluminum hydroxide adsorbed with nanodiamonds on the surface provided by the present invention has high thermal conductivity and flame retardancy (UL94-V1 or UL94-V0 level flame retardancy), and is suitable for the requirements of high-power electronic devices for high thermal conductivity and flame retardant potting.

[0049] The above embodiments are only explanations of the present invention, and they do not limit the present invention. After reading this specification, those skilled in the art can make modifications to the embodiments without creative contributions according to needs, but as long as they are within the scope of the claims of this application, they are protected by the patent law.

Claims

1. A mixed filled epoxy resin high thermal conductivity flame retardant potting glue, characterized in that: The invention comprises component A and component B; component A comprises epoxy resin and aluminum hydroxide with nano-diamonds adsorbed on the surface; component B comprises curing agent and boron nitride; the aluminum hydroxide with nano-diamonds adsorbed on the surface is prepared from nano-diamond powder modified by polydopamine and aluminum hydroxide micro-powder through a wet nano-composite process.

2. The mixed filled epoxy resin high thermal conductivity flame retardant potting adhesive according to claim 1, characterized in that: The preparation steps of aluminum hydroxide with nano-diamond adsorbed on the surface are as follows: Step 1, dispersing nano diamond powder in deionized water, then adding dopamine hydrochloride, heating and reacting to obtain a first suspension; Step 2, centrifuging and drying the first suspension obtained in step 1 to obtain polydopamine-modified nano-diamond powder; Step 3, dispersing aluminum hydroxide powder in a pH buffer solution, then adding the polydopamine-modified nanodiamond powder obtained in step 2, reacting at room temperature to obtain a second suspension; Step 4: Filter, rinse and dry the second suspension obtained in step 3 to obtain aluminum hydroxide powder with nano-diamonds adsorbed on the surface.

3. The mixed filled epoxy resin high thermal conductivity flame retardant potting glue according to claim 2, characterized in that: The average particle size of the nano-diamond powder in step 1 is 50-100 nanometers.

4. The mixed filled epoxy resin high thermal conductivity flame retardant potting glue according to claim 2, characterized in that: The average particle size of the aluminum hydroxide powder in step three is 8 to 15 microns.

5. The mixed filled epoxy resin high thermal conductivity flame retardant potting glue according to claim 2, characterized in that: In step 3, the mass ratio of aluminum hydroxide to polydopamine-modified nano-diamond powder is 100:2~5.

6. The mixed filled epoxy resin high thermal conductivity flame retardant potting glue according to claim 2, characterized in that: The pH value of the pH buffer solution in step 3 is 8.5-9.

5.

7. The mixed filled epoxy resin high thermal conductivity flame retardant potting adhesive according to claim 1, characterized in that: The mass ratio of component A to component B is 100:

21.

8. The mixed filled epoxy resin high thermal conductivity flame retardant potting adhesive according to claim 1 or 7, characterized in that: Component A includes: 100 parts of epoxy resin; 100-120 parts of aluminum hydroxide with nano-diamonds adsorbed on the surface.

9. The mixed filled epoxy resin high thermal conductivity flame retardant potting adhesive according to claim 1 or 7, characterized in that: Component B includes: 100 parts of curing agent; 40-50 parts of boron nitride.

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