Epoxy structural adhesive, preparation method and application thereof

Abstract

This invention belongs to the field of epoxy adhesive technology, and specifically relates to an epoxy structural adhesive, its preparation method, and its application. The epoxy structural adhesive of this invention comprises epoxy resin, liquid crystal epoxy resin, modified boron nitride nanotubes, and a curing agent; the liquid crystal epoxy resin includes 4,4'-biphenyl diglycidyl ether; the modified boron nitride nanotubes are obtained by modifying silanized boron nitride nanotubes with liquid crystal epoxy resin. This invention, by modifying silanized boron nitride nanotubes with liquid crystal epoxy resin and grafting thermotropic liquid crystal epoxy resin onto the surface of the boron nitride nanotubes (BNNT), combined with the liquid crystal epoxy resin, can obtain an epoxy structural adhesive with low viscosity, high thermal conductivity, high adhesion, high heat resistance, and a low coefficient of linear expansion.

Description

Technical Field

[0001] This invention belongs to the field of epoxy adhesive technology, and specifically relates to an epoxy structural adhesive, its preparation method, and its application. Background Technology

[0002] High-voltage insulated-gate bipolar transistors (IGBTs) and other power devices are widely used in ultra-high voltage (UHV) flexible power grids and new energy vehicles. With the continuous development of DC transmission technology and new energy vehicles, and the emergence of new-generation silicon carbide (SiC) and gallium nitride (GaN) IGBT devices, power electronic devices such as IGBTs are continuously upgrading towards higher voltage and higher power. This continuous high-voltage, high-power operating environment, along with the market's mandatory standards for product stability, places higher demands on existing adhesives used for IGBT packaging.

[0003] When an IGBT module operates in a cyclical state of on / off for an extended period, it generates a significant amount of heat, causing the internal temperature of the encapsulation structure to rise. How to dissipate this heat is a crucial factor affecting the device's operational status. Furthermore, the high-temperature environment caused by this intense heat can soften and age the internal polymer materials, especially the epoxy structural adhesive with bonding properties, leading to a significant decrease in its adhesive strength and insulation performance. The encapsulation structure may also experience interface cracking or fatigue damage due to thermal stress. Although adding highly thermally conductive inorganic particles to the polymer matrix can effectively improve the polymer's thermal conductivity, excessive filling with thermally conductive fillers (≥70%) significantly reduces the adhesive strength of the adhesive. This often results in a sharp increase in the viscosity of the adhesive product, a severe decline in adhesive performance, and the adhesive becoming susceptible to cracking and other damage due to internal stress, failing to meet the bonding performance requirements of IGBTs. Moreover, a high content of thermally conductive particles can cause significant electric field distortion within the epoxy structural adhesive, reducing the breakdown field strength and insulation resistance, increasing the dielectric constant and losses, which is detrimental to the safe operation of ultra-high frequency microelectronics and high-voltage power equipment. In addition, conventional epoxy resins used in traditional epoxy adhesives have insufficient structural rigidity and generally have a high coefficient of linear expansion after curing. This can cause the adhesive to expand excessively when heated, leading to deformation of the substrate at the bonding site and resulting in device failure.

[0004] One study provides a high thermal conductivity, flame retardancy, and moisture resistance epoxy structural adhesive for power batteries and its preparation method, which meets the performance requirements of power batteries for thermal conductivity, flame retardancy, and moisture resistance. However, this technology fails to meet the requirements of IGBTs for epoxy adhesives with high thermal conductivity, high temperature resistance, and low linear expansion rate (as consistent as possible with the substrate).

[0005] One study provides an intrinsic liquid crystal epoxy material for potting high-voltage, high-power IGBTs, which resolves the contradiction between the traditional thermal conductivity λ and breakdown field strength Eb. However, this material is not used as a structural adhesive and does not address its improvement effects on bonding strength, etc.

[0006] Therefore, it is of great significance to provide an epoxy structural adhesive with high thermal conductivity, high adhesive strength and low linear expansion coefficient. Summary of the Invention

[0007] The present invention aims to solve one or more technical problems existing in the prior art, and at least provide a beneficial solution. Specifically, the present invention provides an epoxy structural adhesive with high thermal conductivity, high adhesive strength and low linear expansion coefficient, which can significantly improve the stability and reliability of IGBT modules in high-temperature environments, and is suitable for the encapsulation needs of high-performance power electronic equipment such as ultra-high voltage (UHV) flexible power grids and new energy vehicles.

[0008] The inventive concept of this invention is as follows: The epoxy structural adhesive of this invention comprises epoxy resin, liquid crystal epoxy resin, modified boron nitride nanotubes, and a curing agent; the liquid crystal epoxy resin comprises 4,4'-biphenyl diglycidyl ether; the modified boron nitride nanotubes are obtained by modifying silanized boron nitride nanotubes with liquid crystal epoxy resin.

[0009] This invention modifies boron nitride silanized nanotubes (BNNTs) with a liquid crystal epoxy resin, grafting a thermotropic liquid crystal epoxy resin onto the BNNT surface. This results in better dispersibility and interaction within the liquid crystal epoxy resin. The modified BNNTs combined with the liquid crystal epoxy resin form an ordered liquid crystal state. During the curing process of the epoxy structural adhesive, the ordered arrangement of the liquid crystal molecules drives the orientation distribution of the BNNTs, resulting in an ordered thermally conductive network. This significantly improves the thermal conductivity of the material, ensures the high adhesion of the epoxy structural adhesive, and effectively transfers the enormous heat generated by the IGBT chip, ensuring effective temperature control within the encapsulation structure and guaranteeing encapsulation reliability. Simultaneously, the ordered arrangement of the liquid crystal epoxy resin and the oriented arrangement of the BNNTs provide excellent high-temperature resistance, capable of withstanding temperatures exceeding 150°C. Even at high temperatures, it exhibits an extremely low coefficient of linear expansion, reducing stress generated during thermal cycling and improving the reliability of the encapsulation structure.

[0010] Therefore, a first aspect of the present invention provides an epoxy structural adhesive.

[0011] Specifically, the raw materials for preparing the epoxy structural adhesive include epoxy resin, liquid crystal epoxy resin, modified boron nitride nanotubes, and curing agent;

[0012] The liquid crystal epoxy resin includes 4,4'-biphenyl diglycidyl ether; The modified boron nitride nanotubes were obtained by modifying silanized boron nitride nanotubes with liquid crystal epoxy resin.

[0013] Preferably, the liquid crystal epoxy resin is 4,4'-biphenyl diglycidyl ether.

[0014] Specifically, the liquid crystal epoxy resin is a thermotropic liquid crystal epoxy resin, which forms an ordered liquid crystal texture through the arrangement of its own structure during the heating process. This structure has a higher intrinsic thermal conductivity than other non-liquid crystal epoxy resins.

[0015] Preferably, by weight, the epoxy structural adhesive comprises 10-30 parts epoxy resin, 30-70 parts liquid crystal epoxy resin, 1-5 parts modified boron nitride nanotubes, and 1-10 parts curing agent.

[0016] Preferably, the epoxy structural adhesive further includes at least one of a diluent, a toughening agent, a defoamer, and a thixotropic agent.

[0017] Preferably, the epoxy structural adhesive further includes a diluent, a toughening agent, a defoamer, and a thixotropic agent; and by weight, the epoxy structural adhesive comprises 10-30 parts epoxy resin, 30-70 parts liquid crystal epoxy resin, 1-5 parts modified boron nitride nanotubes, 1-10 parts curing agent, 5-10 parts diluent, 5-10 parts toughening agent, 0.5-2 parts defoamer, and 1-5 parts thixotropic agent.

[0018] Preferably, the epoxy resin includes at least one of bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, and bisphenol S diglycidyl ether.

[0019] Preferably, the diluent includes at least one of benzyl glycidyl ether, C12-C14 glycidyl ether, ethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and glycidyl tert-carbonate.

[0020] Preferably, the toughening agent comprises at least one of the following: carboxyl-terminated butadiene-acrylonitrile rubber modified epoxy resin, amino-terminated butadiene-acrylonitrile rubber modified epoxy resin, acrylic-rubber core-shell toughening agent, silicone rubber, and butyl rubber.

[0021] Preferably, the curing agent includes at least one of dicyandiamide (DICY), 3,3'-diaminodiphenyl sulfone (DDS), and p-diaminodiphenylmethane (DDM).

[0022] A second aspect of the present invention provides a method for preparing the epoxy structural adhesive described in the first aspect of the present invention.

[0023] Specifically, the preparation method of the epoxy structural adhesive includes the following steps: The raw material components are mixed to obtain the product.

[0024] Preferably, the preparation method of the epoxy structural adhesive includes the following steps: Epoxy resin and liquid crystal epoxy resin are mixed, heated, and cooled to room temperature; then diluent, defoamer, toughening agent, modified BNNT, curing agent, thixotropic agent are added, and vacuum is applied to obtain the epoxy structural adhesive.

[0025] Preferably, the temperature after heating is 165-175℃.

[0026] Preferably, the heating time is 15-30 minutes, and stirring is performed during the heating process.

[0027] Preferably, after adding diluent, defoamer, and toughening agent, stir for 15-30 minutes, then add modified BNNT, disperse by high-speed shearing, cool to room temperature, add curing agent, disperse, and finally add thixotropic agent, disperse, and vacuum to obtain the epoxy structural adhesive.

[0028] Preferably, the high-speed shear dispersion time is 20-90 min.

[0029] Preferably, the dispersion time after adding the curing agent is 30-60 minutes.

[0030] Preferably, the dispersion time after adding the thixotropic agent is 30-60 minutes.

[0031] Preferably, the method for preparing the modified boron nitride nanotubes includes the following steps: The boron nitride nanotubes were mixed with a solvent, and then a liquid crystal epoxy resin was added and reacted to obtain the final product.

[0032] Preferably, the solvent comprises N-methylpyrrolidone.

[0033] Preferably, the mixing is carried out by ultrasonic dispersion for 1-3 hours.

[0034] Preferably, the mass ratio of the silanized boron nitride nanotubes to the liquid crystal epoxy resin is 1:(2-4).

[0035] Preferably, the reaction temperature is 75-85°C and the reaction time is 8-24 hours.

[0036] Preferably, the reaction is carried out under stirring.

[0037] Preferably, the reaction further includes processes of cooling, filtering, washing, and drying.

[0038] Preferably, the drying temperature is 75-85℃ and the drying time is 12-24h.

[0039] Preferably, the method for preparing the silanized boron nitride nanotubes includes the following steps: mixing hydroxylated boron nitride nanotubes, a silane coupling agent, and a solvent, and then refluxing the mixture to obtain the nanotubes.

[0040] Preferably, the mass ratio of the hydroxylated boron nitride nanotubes to the silane coupling agent is 1:(5-10).

[0041] Preferably, the silane coupling agent comprises γ-aminopropyltriethoxysilane.

[0042] Preferably, in the preparation process of the silanized boron nitride nanotubes, the solvent includes anhydrous ethanol.

[0043] Preferably, the reflux temperature is 75-85℃, and the reflux time is 8-16h.

[0044] Preferably, the preparation process of the silanized boron nitride nanotubes further includes cooling, filtering, washing, and drying after reflux.

[0045] Preferably, the drying temperature is 75-85℃ and the drying time is 12-24h.

[0046] Preferably, the method for preparing the hydroxylated boron nitride nanotubes includes the following steps: mixing boron nitride nanotubes and an oxidant, and then performing a hydrothermal reaction to obtain the nanotubes.

[0047] Preferably, the oxidant includes at least one of concentrated nitric acid, concentrated sulfuric acid, and hydrogen peroxide.

[0048] Preferably, the weight ratio of the boron nitride nanotubes to the oxidant is 1:(30-50).

[0049] Preferably, the boron nitride nanotubes and oxidant are mixed at room temperature using magnetic stirring.

[0050] Preferably, the magnetic stirring time is 16-32 hours.

[0051] Preferably, the hydrothermal reaction temperature is 110-140℃, and the hydrothermal reaction time is 16-32h.

[0052] Preferably, the preparation process of the hydroxylated boron nitride nanotubes further includes cooling, filtering, washing, and drying processes after the reaction.

[0053] Preferably, the drying temperature is 75-85℃ and the drying time is 12-24h.

[0054] Specifically, boron nitride nanotubes (BNNTs) possess excellent thermal conductivity and insulation properties. By treating BNNTs with a strong oxidizing agent at high temperatures, boron hydroxyl and amino groups are generated on their surface. These functional groups react with epoxy groups to graft thermotropic liquid crystal epoxy resin molecules onto the BNNT surface, resulting in better dispersibility and good interaction within the liquid crystal epoxy resin. Furthermore, a one-component epoxy structural adhesive is prepared using the liquid crystal epoxy resin as the matrix and the modified BNNTs as fillers. During the curing process, the ordered arrangement of liquid crystal molecules drives the orientation distribution of BNNTs, forming an ordered thermally conductive network. With a small amount of filler, extremely high thermal conductivity can be achieved, while also ensuring high adhesion. In addition, the high heat resistance and low linear expansion coefficient of the liquid crystal epoxy resin and BNNTs themselves, along with the formed cross-linked network system, ensure that the adhesive maintains an extremely low linear expansion coefficient even at high temperatures.

[0055] A third aspect of the present invention provides the application of the epoxy structural adhesive described in the first aspect of the present invention in the packaging of a high-voltage insulated gate bipolar transistor.

[0056] Compared with the prior art, the beneficial effects of the technical solution provided by the present invention are as follows: The epoxy structural adhesive of this invention ensures high bonding strength between the IGBT chip and the substrate (DBC ceramic copper-clad laminate) or heat sink, and withstands the huge heat generated during efficient operation (up to 150°C or above). At the same time, it also has an extremely low coefficient of linear expansion. This overcomes the inability of traditional thermally conductive adhesives to simultaneously meet the requirements of high thermal conductivity, high bonding strength and low coefficient of linear expansion, thereby significantly improving the stability and reliability of IGBT modules in high-temperature environments. It is suitable for the packaging needs of high-performance power electronic equipment such as ultra-high voltage (UHV) flexible power grids and new energy vehicles.

[0057] (1) High thermal conductivity and high adhesion: By modifying and grafting thermotropic liquid crystal epoxy resin onto the surface of BNNT and mixing it with liquid crystal epoxy resin, an ordered liquid crystal state is formed, which allows the BNNT to be oriented during the curing process. This significantly improves the thermal conductivity of the material with a small amount of filler, while also ensuring high adhesion of the epoxy structural adhesive. Experimental results show that the thermal conductivity of this epoxy structural adhesive is significantly higher than that of traditional epoxy resin, which can effectively transfer the huge heat generated by the IGBT chip, ensuring that the internal temperature of the encapsulation structure is effectively controlled, and it also has good adhesion, which can ensure the reliability of the encapsulation.

[0058] (2) High heat resistance: Through the ordered arrangement of liquid crystal epoxy resin and the directional arrangement of BNNT, the epoxy structural adhesive has excellent high temperature resistance and can withstand high temperature environments of up to 150°C or higher. Under long-term high-temperature working conditions, the adhesive maintains good insulation performance and mechanical strength, thereby extending the service life of IGBT modules.

[0059] (3) High strength performance: By introducing a toughening system, the overall mechanical strength is enhanced, which can effectively resist the thermal and mechanical stress generated under high temperature and high frequency working environment, and prevent interface cracking or fatigue damage inside the encapsulation structure. Experimental results show that the tensile strength and shear strength of the epoxy structural adhesive of the present invention are significantly better than those of traditional epoxy resin, thus improving the reliability of the encapsulation structure.

[0060] (4) Low coefficient of linear expansion: Through the ordered arrangement of liquid crystal epoxy resin and the directional arrangement of BNNT, the adhesive has a low coefficient of linear expansion, which can reduce the stress generated in the encapsulation structure during thermal cycling and further improve the reliability of the encapsulation structure. Experimental results show that the coefficient of linear expansion of the epoxy structural adhesive of the present invention is much lower than that of traditional epoxy resin, effectively reducing the thermal stress of the encapsulation structure. Detailed Implementation

[0061] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0062] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.

[0063] The sources of the raw material components of the epoxy structural adhesives in the embodiments and comparative examples of this invention are as follows: Epoxy resin: Nan Ya Kunshan NPEL-128G; Diluent: Anhui Xinyuan XY-692; Thixotropic agent: Tokuyama DM-20S hydrophobic fumed silica (Japan); Defoamer: BYK-530 (Germany); Toughening agent: Shenzhen Jiadida 86840; Dicyandiamide curing agent: Huntsman OMICURE DDA 10.

[0064] The raw material components and dosages of the epoxy structural adhesives in Examples 1-4 of this invention are shown in Table 1.

[0065] Table 1: Raw material components and dosage (parts by mass) of the epoxy structural adhesives in Examples 1-4 of the present invention

[0066] Example 1 This embodiment provides an epoxy structural adhesive, the raw material components and dosages of which are shown in Table 1.

[0067] This embodiment also provides a method for preparing epoxy structural adhesive, the specific steps of which are as follows: Epoxy resin and liquid crystal epoxy resin were mixed and heated and stirred at 170℃ for 20 min, then cooled to room temperature. Diluent, defoamer, and toughening agent were added and stirred for 20 min. Modified BNNT was added and dispersed at high speed of 1500 rpm for 20 min, then cooled to room temperature. Dicyandiamide curing agent was added and dispersed for 45 min. Thixotropic agent was added and dispersed for 45 min. Then, the mixture was stirred for 15 min under a relative vacuum of -0.098 MPa and discharged to obtain epoxy structural adhesive.

[0068] The preparation method of the liquid crystal epoxy resin 4,4'-biphenyl diglycidyl ether is as follows: (1) Add 4,4'-biphenyl (37.2g) and epichlorohydrin (370.1g) to a four-necked flask in sequence, and then heat to 50°C under N2 protection and mechanically stir until all the raw materials are dissolved. (2) Add sodium hydroxide (48g) and stir for 10 min; then add tetramethylammonium bromide (2.04g); heat the mixture to 65℃ and react for 6 h, then cool to room temperature and continue stirring for 3 h until a large amount of white precipitate appears and stop stirring. (3) After the above reactants were allowed to stand at room temperature for 2 hours, they were filtered by a sand core funnel. The filter cake was washed with deionized water until the filtrate was neutral. Then, the product was washed three times with toluene. Finally, the product was dried in a vacuum oven at 80°C for 12 hours to obtain a white powder of 4,4'-biphenyl diglycidyl ether.

[0069] The preparation method of modified BNNT is as follows: (1) Add BNNT and 30wt% hydrogen peroxide solution in a weight ratio of 1:40 to a stainless steel hydrothermal reactor. First, stir magnetically for 24h at room temperature, then hydrothermally react at 125℃ for 24h. Then cool to room temperature, filter with a 0.45-micron filter membrane, wash three times with deionized water, and dry at 80℃ for 18h to obtain hydroxylated BNNT powder. (2) The hydroxylated BNNT powder was added to a two-necked flask containing anhydrous ethanol and a reflux condenser, and then γ-aminopropyltriethoxysilane was added, wherein the mass ratio of hydroxylated BNNT to γ-aminopropyltriethoxysilane was 1:7.5. The mixture was refluxed at 80°C for 12 h, cooled to room temperature, filtered through a 0.45 μm filter membrane, washed three times with anhydrous ethanol, and dried at 80°C for 18 h to obtain silanized BNNT powder. (3) The silanized BNNT powder was added to a single-necked flask containing N-methylpyrrolidone and ultrasonically dispersed for 2 hours. Then it was transferred to a three-necked flask equipped with a mechanical stirrer and a reflux condenser, and 4,4'-biphenyl diglycidyl ether was added. The mass ratio of silanized BNNT powder to 4,4'-biphenyl diglycidyl ether was 1:3. The mixture was stirred at 80°C for 16 hours, cooled to room temperature, filtered through a 0.45-micron tetrafluoroethylene filter membrane, washed three times with anhydrous ethanol, and dried at 80°C for 18 hours to obtain the modified BNNT powder modified with liquid crystal epoxy resin.

[0070] Example 2 This embodiment provides an epoxy structural adhesive, the raw material components and dosages of which are shown in Table 1.

[0071] The preparation methods of epoxy structural adhesive, liquid crystal epoxy resin 4,4'-biphenyl diglycidyl ether, and modified BNNT in Example 2 are the same as in Example 1.

[0072] Example 3 This embodiment provides an epoxy structural adhesive, the raw material components and dosages of which are shown in Table 1.

[0073] The preparation methods of epoxy structural adhesive, liquid crystal epoxy resin 4,4'-biphenyl diglycidyl ether, and modified BNNT in Example 3 are the same as those in Example 1.

[0074] Example 4 This embodiment provides an epoxy structural adhesive, the raw material components and dosages of which are shown in Table 1.

[0075] The preparation methods of epoxy structural adhesive, liquid crystal epoxy resin 4,4'-biphenyl diglycidyl ether, and modified BNNT in Example 4 are the same as those in Example 1.

[0076] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that Comparative Example 1 uses BNNT (i.e., unmodified BNNT, BNNT-50, Suzhou Beike Nano) to replace the modified BNNT in Example 1 in equal amounts; otherwise, they are the same as in Example 1.

[0077] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that Comparative Example 2 uses an equal amount of AFG-90 epoxy resin produced by Shanghai Huayi to replace the liquid crystal epoxy resin in Example 1; otherwise, they are the same as in Example 1.

[0078] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that Comparative Example 3 uses hydroxylated BNNT to replace the modified BNNT in Example 1 in equal amounts; otherwise, it is the same as Example 1.

[0079] The preparation process of hydroxylated BNNT is the same as step (1) in the preparation method of modified BNNT in Example 1.

[0080] Performance testing The epoxy structural adhesives of Examples 1-4 and Comparative Examples 1-3 were subjected to performance tests. The test items and methods are as follows: viscosity was tested before the adhesive cured, while thermal conductivity, shear strength, and coefficient of linear expansion were tested after the adhesive was fully cured. The curing temperature was 125°C and the curing time was 45 min. Viscosity / cps@25℃: Tested according to GB / T 10247-2208; Thermal conductivity / W / mK: Tested according to ASTM D5470; Shear strength / MPa (ceramics-copper): Tested according to GB / T 7124-2008; Linear expansion coefficient / ppm: Tested in accordance with GB / T 36800.2-2018.

[0081] The performance test results of the epoxy structural adhesives in Examples 1-4 and Comparative Examples 1-3 are shown in Table 2.

[0082] Table 2: Performance test results of epoxy structural adhesives in Examples 1-4 and Comparative Examples 1-3

[0083] As can be seen from Table 2, the epoxy structural adhesive of the present invention has a low mixing viscosity, good flowability, and is easy to pot. It also has good thermal conductivity, shear strength and low coefficient of linear expansion, which solves the contradiction between low viscosity, high thermal conductivity and strong adhesion of existing structural adhesives. At the same time, it solves the problem of high coefficient of linear expansion of current epoxy potting adhesives and reduces the deformation effect of adhesive on substrate under high temperature conditions.

[0084] Comparative Example 1 uses BNNT, resulting in a significantly higher viscosity of the epoxy structural adhesive compared to Example 1, which is unfavorable for potting; its thermal conductivity and shear strength are significantly lower than those of Example 1, while its coefficient of linear expansion is higher. Comparative Example 3 uses hydroxylated BNNT, resulting in a significantly higher viscosity of the epoxy structural adhesive compared to Example 1, which is unfavorable for potting; its thermal conductivity and shear strength are significantly lower than those of Example 1, while its coefficient of linear expansion is significantly higher. This demonstrates that only by using the modified BNNT of this invention can the epoxy structural adhesive achieve a lower mixed viscosity, good flowability, and ease of potting; it also possesses good thermal conductivity, shear strength, and a low coefficient of linear expansion.

[0085] Comparative Example 2 used AFG-90 epoxy resin produced by Shanghai Huayi, resulting in a epoxy structural adhesive in Comparative Example 2 with lower thermal conductivity and shear strength than that in Example 1, but a significantly higher coefficient of linear expansion than that in Example 1. This demonstrates that using the liquid crystal epoxy resin of the present invention allows the epoxy structural adhesive to possess good thermal conductivity, shear strength, and a low coefficient of linear expansion while having low viscosity.

[0086] In summary, this invention modifies boron nitride nanotubes (BNNTs) with liquid crystal epoxy resin, grafts thermotropic liquid crystal epoxy resin onto the surface of the BNNTs, and combines this with the liquid crystal epoxy resin to achieve high thermal conductivity, high adhesion, high heat resistance, and low coefficient of linear expansion. This overcomes the problem that traditional thermally conductive adhesives cannot simultaneously meet the requirements of high thermal conductivity, high adhesive strength, and low coefficient of linear expansion, thereby significantly improving the stability and reliability of IGBT modules in high-temperature environments. It is suitable for the packaging requirements of high-performance power electronic equipment such as ultra-high voltage (UHV) flexible power grids and new energy vehicles.

[0087] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. An epoxy structural adhesive, characterized in that, The epoxy structural adhesive includes epoxy resin, liquid crystal epoxy resin, modified boron nitride nanotubes, and curing agent; The liquid crystal epoxy resin includes 4,4'-biphenyl diglycidyl ether; The modified boron nitride nanotubes were obtained by modifying silanized boron nitride nanotubes with liquid crystal epoxy resin.

2. The epoxy structural adhesive according to claim 1, characterized in that, The epoxy structural adhesive comprises, by weight, 10-30 parts epoxy resin, 30-70 parts liquid crystal epoxy resin, 1-5 parts modified boron nitride nanotubes, and 1-10 parts curing agent.

3. The epoxy structural adhesive according to claim 1, characterized in that, The epoxy structural adhesive also includes at least one of a diluent, a toughening agent, a defoamer, and a thixotropic agent.

4. The epoxy structural adhesive according to claim 3, characterized in that, The epoxy structural adhesive further includes a diluent, a toughening agent, a defoamer, and a thixotropic agent; and by weight, the epoxy structural adhesive comprises 10-30 parts epoxy resin, 30-70 parts liquid crystal epoxy resin, 1-5 parts modified boron nitride nanotubes, 1-10 parts curing agent, 5-10 parts diluent, 5-10 parts toughening agent, 0.5-2 parts defoamer, and 1-5 parts thixotropic agent.

5. The epoxy structural adhesive according to claim 4, characterized in that, The epoxy resin includes at least one of bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, and bisphenol S diglycidyl ether. And / or, the diluent includes at least one of benzyl glycidyl ether, C12-C14 glycidyl ether, ethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and glycidyl tert-carbonate; And / or, the toughening agent includes at least one of the following: carboxyl-terminated butadiene-acrylonitrile rubber modified epoxy resin, amino-terminated butadiene-acrylonitrile rubber modified epoxy resin, acrylic-rubber core-shell toughening agent, silicone rubber, and butyl rubber. And / or, the curing agent includes at least one of dicyandiamide, 3,3'-diaminodiphenyl sulfone, and p-diaminodiphenylmethane.

6. The method for preparing the epoxy structural adhesive according to any one of claims 1-5, characterized in that, The preparation method includes the following steps: The raw material components are mixed to obtain the product.

7. The preparation method according to claim 6, characterized in that, The method for preparing the modified boron nitride nanotubes includes the following steps: The boron nitride nanotubes were mixed with a solvent, and then a liquid crystal epoxy resin was added and reacted to obtain the final product.

8. The preparation method according to claim 7, characterized in that, The mass ratio of the silanized boron nitride nanotubes to the liquid crystal epoxy resin is 1:(2-4). And / or, the reaction temperature is 75-85°C, and the reaction time is 8-24 hours; And / or, the method for preparing the silanized boron nitride nanotubes includes the following steps: mixing hydroxylated boron nitride nanotubes, a silane coupling agent, and a solvent, and refluxing to obtain the nanotubes.

9. The preparation method according to claim 8, characterized in that, The mass ratio of the hydroxylated boron nitride nanotubes to the silane coupling agent is 1:(5-10). And / or, the reflux temperature is 75-85°C, and the reflux time is 8-16 hours; And / or, the method for preparing the hydroxylated boron nitride nanotubes includes the following steps: mixing boron nitride nanotubes and an oxidant, and performing a hydrothermal reaction to obtain the nanotubes.

10. The application of the epoxy structural adhesive according to any one of claims 1-5 in the packaging of high-voltage insulated gate bipolar transistors.

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