High-flexibility temperature-resistant epoxy structural adhesive and preparation method thereof

Abstract

The invention discloses a high-flexibility temperature-resistant epoxy structural adhesive and a preparation method thereof, and the high-flexibility temperature-resistant epoxy structural adhesive comprises the following components in parts by mass: 50-60 parts of epoxy resin, 10-15 parts of temperature-resistant modified resin, 100-150 parts of acetone and 3-5 parts of a curing agent, the temperature-resistant modified resin is prepared by mixing boron nitride / MOF powder with styrene, unsaturated linear thermosetting resin and modified siloxane and reacting under the catalysis of potassium hydroxide; the prepared high-flexibility temperature-resistant epoxy structural adhesive has relatively high fluidity during coating, is suitable for uniform coating of a thin-layer epoxy structural adhesive in the field of circuit boards, and improves the high temperature resistance of the epoxy structural adhesive through the synergistic effect of the inorganic heat-resistant filler and the polysiloxane chain; and the adhesive can maintain good mechanical strength at high temperature, has high bonding strength, and has strong applicability in the field of circuit boards which are easy to generate high temperature.

Description

Technical Field

[0001] The present invention belongs to the technical field of epoxy adhesives, and particularly relates to a highly flexible heat-resistant epoxy structural adhesive and a preparation method thereof. Background Art

[0002] With the progress of electronic information technology, people have higher and higher requirements for various electronic products. More and more consumers like light, thin and flexible products. Compared with printed circuit boards, flexible printed circuit boards have the advantages of high wiring density, light weight, thin thickness, good bending resistance, etc., making them widely used in electronic products such as mobile phones and computers, as well as in fields such as aviation, aerospace and healthcare. Flexible copper clad laminates are composed of copper foil, polyimide film and adhesives. The adhesives can be polyester adhesives, acrylic adhesives, epoxy resin adhesives, etc. Among them, epoxy resin adhesives are widely used due to their good bonding performance. However, epoxy adhesives have the disadvantages of brittleness and poor high-temperature resistance, so toughening and high-temperature modification are required.

[0003] The Chinese patent application with the publication number CN114752333A discloses a room-temperature curing high-strength, high-toughness and high-temperature-resistant epoxy structural adhesive and a preparation method thereof. Using POSS-modified flexible amine curing agent as an internal toughening agent and polyurethane as an external toughening agent to improve the toughness of the adhesive, and using the high heat resistance of POSS and the increase in crosslinking density to improve the heat resistance of the epoxy structural adhesive; this solution improves the heat resistance of the epoxy structural adhesive by increasing the crosslinking density, but the increase in crosslinking density is not conducive to maintaining the fluidity of the epoxy structural adhesive before curing, and the flexibility is low. During coating, it cannot be evenly coated due to low fluidity and is not suitable for thin-layer coating of circuit boards. Moreover, after curing, the epoxy structural adhesive with a high crosslinking density will generate strong stress when the flexible copper clad laminate is bent, and it is easy to cause the aluminum foil to rupture due to strong stress during the use of flexible circuit boards.

[0004] The Chinese patent application with the publication number CN117487495A discloses a glue for flexible printed circuit boards and a preparation method thereof. Using epoxy resin as the base material, and forming a skeleton structure in the glue system with modified glass fibers to improve mechanical strength, adhesion and aging resistance, and having good flexibility after curing and molding; this solution uses inorganic fillers to improve the strength of the epoxy structural adhesive. The improvement of the strength by inorganic fillers is affected by the dispersibility, but the improvement of the heat resistance of the epoxy structural adhesive in this solution is small. In electronic components, long-term power-on use will generate high temperature, and the high temperature will affect the performance of the epoxy structural adhesive. During the use of flexible circuit boards, bending may cause the structural adhesive to crack.

[0005] The epoxy structural adhesive with high crosslinking density has poor fluidity after crosslinking, which is not conducive to coating; the epoxy structural adhesive with a high inorganic filler filling amount has good heat resistance, but the internal friction increases, affecting the fluidity; the epoxy structural adhesive with high fluidity has poor bonding performance and is not resistant to high temperature. When used at high temperature, the bonding performance of the epoxy structural adhesive is likely to decrease, which may lead to the phenomenon of bleeding. Summary of the Invention

[0006] The purpose of the present invention is to solve the problem of how to maintain high fluidity and have good bonding performance at high temperatures, and to provide a high-flexibility heat-resistant epoxy structural adhesive and its preparation method.

[0007] In the present invention, boron nitride with heat-resistant properties and Zn-MOF are compounded to form an inorganic heat-resistant filler, which is mixed with an unsaturated linear thermosetting resin to improve the compatibility between the inorganic heat-resistant filler and the epoxy resin. The flexible ester chain formed by the esterification reaction of the unsaturated linear thermosetting resin and styrene is used to improve the fluidity of the epoxy structural adhesive.

[0008] The purpose of the present invention can be achieved by the following technical solutions: A high-flexibility heat-resistant epoxy structural adhesive, by mass, comprises the following components: 50 - 60 parts of epoxy resin, 10 - 15 parts of heat-resistant modified resin, 100 - 150 parts of acetone, and 3 - 5 parts of curing agent.

[0009] The heat-resistant modified resin is prepared by the following steps: Disperse boron nitride / MOF powder in styrene in a reaction kettle, add an unsaturated linear thermosetting resin and a modified siloxane, stir and mix for 1 - 2 h, dropwise add 1 M potassium hydroxide solution, raise the temperature to 80 - 90 °C, stir and react for 5 - 6 h, cool, filter to collect the precipitate, wash the precipitate, and vacuum dry to obtain the heat-resistant modified resin.

[0010] The curing agent is 4,4'-sulfonyldianiline.

[0011] Furthermore, the dosage ratio of boron nitride / MOF powder, styrene, unsaturated linear thermosetting resin, modified siloxane, and potassium hydroxide solution is 1 - 2 g: 100 - 150 mL: 10 - 15 g: 1 - 1.2 g: 1 - 1.5 mL.

[0012] Furthermore, the boron nitride / MOF powder is prepared by the following steps: Ultrasonically disperse hydroxyboron nitride in deionized water in a reaction kettle, add zinc nitrate hexahydrate, (5-amino-1H-tetrazol-1-yl)acetic acid, and tetramethylammonium bromide, raise the temperature to 150 - 160 °C, react for 70 - 72 h, cool, centrifuge to collect the precipitate, wash the precipitate, and vacuum dry to obtain the boron nitride / MOF powder.

[0013] Further, the dosage ratio of boron nitride hydroxide, deionized water, zinc nitrate hexahydrate, (5-amino-1H-tetrazol-1-yl)acetic acid, and tetramethylammonium bromide is 1-2 g: 500-700 mL: 3-5 g: 3-5 g: 1.5-2 g.

[0014] Further, the boron nitride hydroxide is prepared by the following steps: In a reaction kettle, 1-2 g of boron nitride powder and 0.2-0.3 g of sodium hydroxide are ground in agate for 4-5 h to obtain boron nitride hydroxide.

[0015] Further, the mass ratio of boron nitride powder to sodium hydroxide is 1-2:0.2-0.3.

[0016] Further, the modified silicone is prepared by the following steps In a reaction kettle, γ-methacryloxypropyltrimethoxysilane and deionized water are mixed, hydrochloric acid is added dropwise to adjust the pH to 1-2, the temperature is raised to 50-60 °C and stirred for reaction for 60-70 min. Benzyl alcohol, stannous chloride, and hydroquinone are added to the reaction kettle, the temperature is raised to 150-160 °C and sealed for reaction for 5-6 h, and the solvent is removed by rotary evaporation to obtain the modified silicone.

[0017] Further, the dosage ratio of γ-methacryloxypropyltrimethoxysilane, deionized water, benzyl alcohol, stannous chloride, and hydroquinone is 15-20 g: 10-20 mL: 5-8 g: 0.1-0.2 g: 0.15-0.2 g.

[0018] A preparation method of a highly flexible high-temperature resistant epoxy structural adhesive includes the following steps: In a reaction kettle, epoxy resin and high-temperature resistant modified resin are mixed, heated to 150-170 °C and stirred for mixing for 2-3 h, then acetone and 4,4'-sulfonyldianiline are added, and stirring is continued until acetone is removed to obtain the highly flexible high-temperature resistant epoxy structural adhesive.

[0019] The beneficial effects of the present invention: The highly flexible high-temperature resistant epoxy structural adhesive prepared by the present invention has high fluidity during coating, is suitable for uniform coating of thin-layer epoxy structural adhesives in the field of circuit boards. Through the synergistic effect of inorganic heat-resistant fillers and polysiloxane chains, the high-temperature resistance of the epoxy structural adhesive is improved, and good mechanical strength can also be maintained at high temperatures, with high bonding strength and strong applicability in the field of circuit boards where high temperatures are likely to occur.

[0020] The preparation method of the present invention forms an inorganic heat-resistant filler by compounding boron nitride with heat-resistant properties and Zn-MOF. The functional groups in the Zn-MOF ligand are used to uniformly disperse the boron nitride / MOF powder in the heat-resistant modified resin. By virtue of the compatibility between the heat-resistant modified resin and epoxy resin, the boron nitride / MOF powder is uniformly dispersed in the epoxy structural adhesive, reducing the influence of the inorganic filler on the fluidity of the epoxy structural adhesive. Through the esterification reaction between the unsaturated linear thermosetting resin and styrene under the catalysis, a flexible ester chain is formed. The flexible ester chain can not only improve the heat resistance of the epoxy structural adhesive but also avoid the influence of high crosslinking density on fluidity and enable the uniform distribution of the inorganic filler, thereby enhancing the fluidity of the epoxy resin. Detailed Embodiment

[0021] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0022] Embodiment 1: A preparation method of a highly flexible heat-resistant epoxy structural adhesive, comprising the following steps: S1. Grind 1 g of boron nitride powder and 0.2 g of sodium hydroxide in an agate mortar in a reaction kettle for 4 h to obtain hydroxyboron nitride.

[0023] S2. Ultrasonically disperse 1 g of hydroxyboron nitride in 500 mL of deionized water in a reaction kettle, add 3 g of zinc nitrate hexahydrate, 3 g of (5-amino-1H-tetrazol-1-yl)acetic acid, and 1.5 g of tetramethylammonium bromide, heat up to 150 °C and react for 70 h. After cooling, centrifuge to collect the precipitate, wash the precipitate with deionized water and ethanol, and vacuum dry at 60 °C for 10 h to obtain boron nitride / MOF powder.

[0024] S3. Mix 15 g of γ-methacryloxypropyltrimethoxysilane and 10 mL of deionized water in a reaction kettle, add hydrochloric acid dropwise to adjust the pH to 1, heat up to 50 °C and stir for 60 min. Add 5 g of benzyl alcohol, 0.1 g of stannous chloride, and 0.15 g of hydroquinone to the reaction kettle, heat up to 150 °C and react in a closed system for 5 h. Rotate and evaporate to remove the solvent to obtain modified siloxane.

[0025] S4. Disperse 1 g of boron nitride / MOF powder in 100 mL of styrene in a reaction kettle, add 10 g of unsaturated linear thermosetting resin and 1 g of modified siloxane, stir and mix for 1 h, add 1 mL of 1 M potassium hydroxide solution dropwise, heat up to 80 °C and stir for 5 h. After cooling, filter to collect the precipitate, wash with styrene, ethanol, and deionized water, and vacuum dry at 70 °C to obtain heat-resistant modified resin.

[0026] S5. Mix 5 g of epoxy resin and 10 g of temperature-resistant modified resin in a reaction kettle, heat to 150 °C and stir for 2 h, then add 100 g of acetone and 3 g of 4,4'-sulfonyldianiline, and continue stirring until acetone is removed to obtain a high-flexibility temperature-resistant epoxy structural adhesive.

[0027] Example 2: A preparation method of a high-flexibility temperature-resistant epoxy structural adhesive, comprising the following steps: S1. Grind 1.5 g of boron nitride powder and 0.25 g of sodium hydroxide in an agate mortar for 4.5 h to obtain hydroxyboron nitride.

[0028] S2. Ultrasonically disperse 1.5 g of hydroxyboron nitride in 600 mL of deionized water in a reaction kettle, add 4 g of zinc nitrate hexahydrate, 4 g of (5-amino-1H-tetrazol-1-yl)acetic acid and 1.75 g of tetramethylammonium bromide, heat to 155 °C and react for 71 h, cool and centrifuge to collect the precipitate, wash the precipitate with deionized water and ethanol, and vacuum dry at 65 °C for 11 h to obtain boron nitride / MOF powder.

[0029] S3. Mix 17.5 g of γ-methacryloxypropyltrimethoxysilane and 15 mL of deionized water in a reaction kettle, adjust the pH to 1.5 by dropping hydrochloric acid, heat to 55 °C and stir for 65 min, add 6.5 g of benzyl alcohol, 0.15 g of stannous chloride and 0.17 g of hydroquinone to the reaction kettle, heat to 155 °C and react in a closed system for 5.5 h, rotary evaporate to remove the solvent to obtain modified siloxane.

[0030] S4. Disperse 1.5 g of boron nitride / MOF powder in 125 mL of styrene in a reaction kettle, add 12.5 g of unsaturated linear thermosetting resin and 1.1 g of modified siloxane, stir and mix for 1.5 h, dropwise add 1.25 mL of 1 M potassium hydroxide solution, heat to 85 °C and stir for 5.5 h, cool and filter to collect the precipitate, wash with styrene, ethanol and deionized water, and vacuum dry at 75 °C to obtain temperature-resistant modified resin.

[0031] S5. Mix 55 g of epoxy resin and 12.5 g of temperature-resistant modified resin in a reaction kettle, heat to 160 °C and stir for 2.5 h, then add 125 g of acetone and 4 g of 4,4'-sulfonyldianiline, and continue stirring until acetone is removed to obtain a high-flexibility temperature-resistant epoxy structural adhesive.

[0032] Example 3: A preparation method of a high-flexibility temperature-resistant epoxy structural adhesive, comprising the following steps: S1. Grind 2 g of boron nitride powder and 0.3 g of sodium hydroxide in an agate mortar for 5 h to obtain hydroxyboron nitride.

[0033] S2. Ultrasonically disperse 2 g of hydroxyboron nitride in 700 mL of deionized water in a reaction kettle, add 5 g of zinc nitrate hexahydrate, 5 g of (5-amino-1H-tetrazol-1-yl)acetic acid, and 2 g of tetramethylammonium bromide, heat up to 160 °C and react for 72 h. After cooling, centrifuge to collect the precipitate, wash the precipitate with deionized water and ethanol, and dry it in vacuum at 70 °C for 12 h to obtain boron nitride / MOF powder.

[0034] S3. Mix 20 g of γ-methacryloxypropyltrimethoxysilane and 20 mL of deionized water in a reaction kettle, adjust the pH to 2 by dropping hydrochloric acid, heat up to 60 °C and stir for 70 min. Add 8 g of benzyl alcohol, 0.2 g of stannous chloride, and 0.2 g of hydroquinone to the reaction kettle, heat up to 160 °C and react in a closed system for 6 h. Rotate and evaporate to remove the solvent to obtain modified siloxane.

[0035] S4. Disperse 2 g of boron nitride / MOF powder in 150 mL of styrene in a reaction kettle, add 15 g of unsaturated linear thermosetting resin and 1.2 g of modified siloxane, stir and mix for 2 h, dropwise add 1.5 mL of 1 M potassium hydroxide solution, heat up to 90 °C and stir for 6 h. After cooling, filter to collect the precipitate, wash it with styrene, ethanol, and deionized water, and dry it in vacuum at 80 °C to obtain temperature-resistant modified resin.

[0036] S5. Mix 60 g of epoxy resin and 15 g of temperature-resistant modified resin in a reaction kettle, heat up to 170 °C and stir for 3 h, then add 150 g of acetone and 5 g of 4,4'-sulfonyldianiline, and continue stirring until acetone is removed to obtain a highly flexible temperature-resistant epoxy structural adhesive.

[0037] Principle of the invention: By hydroxylating boron nitride, hydroxyl groups are grafted onto the surface of boron nitride. Utilize the reaction of hydroxyl groups with (5-amino-1H-tetrazol-1-yl)acetic acid to graft (5-amino-1H-tetrazol-1-yl)acetic acid onto the surface of hydroxyboron nitride, enabling the in-situ generation of Zn-MOF with temperature-resistant properties on the surface of hydroxyboron nitride, and making Zn-MOF and hydroxyboron nitride act synergistically to enhance the temperature-resistant performance.

[0038] By end-capping γ-methacryloxypropyltrimethoxysilane with benzyl alcohol, a modified silicone is obtained. The polysiloxane chain with a benzene ring has heat resistance. Mixing it with an unsaturated linear thermosetting resin can improve the heat resistance of the unsaturated linear thermosetting resin. The unsaturated linear thermosetting resin and styrene can undergo an esterification reaction under the catalysis to form a flexible ester chain. The flexible ester chain can not only improve the heat resistance of the epoxy structural adhesive but also avoid the influence of high crosslinking density on fluidity and make the inorganic filler evenly distributed, thereby improving the fluidity of the epoxy resin. By using the carboxyl group in the ligand (5-amino-1H-tetrazol-1-yl)acetic acid of MOF in boron nitride / MOF powder to combine with the chain segment formed by the esterification reaction, the flexible ester chain is grafted onto the surface of boron nitride / MOF powder, thereby improving the dispersibility of boron nitride / MOF powder in the temperature-resistant modified resin. Using the good compatibility between the temperature-resistant modified resin and the epoxy resin, the heat-resistant filler boron nitride / MOF powder is evenly dispersed in the epoxy resin to obtain a highly flexible temperature-resistant epoxy structural adhesive with good heat resistance and fluidity.

[0039] Comparative Example 1: The difference from Example 1 is that in S2, boron nitride of equal mass is used to replace hydroxyboron nitride to prepare a highly flexible temperature-resistant epoxy structural adhesive.

[0040] Comparative Example 2: The difference from Example 1 is that in S4, γ-methacryloxypropyltrimethoxysilane of equal mass is used to replace the modified silicone to prepare a highly flexible temperature-resistant epoxy structural adhesive.

[0041] Comparative Example 3: The difference from Example 1 is that in S5, the temperature-resistant modified resin is replaced with an unsaturated linear thermosetting resin, boron nitride / MOF powder, and modified silicone according to the ratio of S4 to prepare a highly flexible temperature-resistant epoxy structural adhesive.

[0042] Perform performance tests on the highly flexible temperature-resistant epoxy structural adhesives prepared in Examples 1 - 3 and Comparative Examples 1 - 3. Coat the highly flexible temperature-resistant epoxy structural adhesive on a copper foil with a coating thickness of 25 μm, attach a PI film, and dry and cure it at 70 °C to obtain a flexible circuit board. Cut the flexible circuit board into pieces of 8 * 8 mm size to obtain specimens, and test the tensile strength and bending strength of the specimens, and also test the tensile strength and bending strength of the specimens at 80 °C. Test the fluidity of the highly flexible temperature-resistant epoxy structural adhesive. The test method is as follows: Drop the high-flexibility and high-temperature-resistant epoxy structural adhesive onto the test plate. There is a starting line drawn on the test plate. After dropping the high-flexibility and high-temperature-resistant epoxy structural adhesive behind the starting line, make the edge of the high-flexibility and high-temperature-resistant epoxy structural adhesive lie on the starting line. Then tilt the test plate at an angle of 5°. The tilting time t = 10 s. Then restore the test plate to the horizontal position and measure the distance S that the high-flexibility and high-temperature-resistant epoxy structural adhesive extends beyond the starting line. Calculate the flow rate V = S / t, (mm / min). Use the flow rate to reflect the fluidity of the high-flexibility and high-temperature-resistant epoxy structural adhesive.

[0043] The results are shown in Table 1 as follows: Table 1: Performance Test Table of High-Flexibility and High-Temperature-Resistant Epoxy Structural Adhesive Project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Tensile strength (Mpa) 56.7 56.9 57.3 53.2 51.4 32.5 Flexural strength (Mpa) 152.5 153.1 153.4 147.3 143.2 103.4 Tensile strength at 80°C (Mpa) 42.5 42.8 43.1 37.4 39.6 15.2 Flexural strength at 80°C (Mpa) 128.3 128.7 129.2 121.4 114.8 70.7 Flow rate (mm / min) 7.3 7.5 7.6 6.8 6.2 2.1 As can be seen from Table 1, the high-flexibility and high-temperature-resistant epoxy structural adhesive prepared by the present invention has good tensile strength and bending strength, and still maintains strong tensile strength and bending strength at 80 °C, indicating that the high-flexibility and high-temperature-resistant epoxy structural adhesive prepared by the present invention has good mechanical properties and high-temperature resistance. Through the flow rate test, it can be seen that the fluidity of the present invention is better, which is suitable for coating thin-layer adhesive films and the coating is more uniform.

[0044] In Comparative Example 1, since boron nitride was not modified with hydroxyl groups, the composite strength of Zn-MOF and boron nitride was relatively low, and the dispersion of boron nitride in the epoxy resin was relatively low, which affected the high-temperature resistance and mechanical strength of the epoxy structural adhesive.

[0045] In Comparative Example 2, since γ-methacryloxypropyltrimethoxysilane was not modified, and the silane coupling agent with a benzene ring was not used to form a polysiloxane chain, there was no synergistic effect on the high-temperature resistance performance of the epoxy structural adhesive, and the improvement of the high-temperature resistance performance was relatively small.

[0046] In Comparative Example 3, since the inorganic filler boron nitride / MOF powder was not compounded with the unsaturated linear thermosetting resin and the esterification reaction was not carried out, the agglomeration of the inorganic filler and the lack of flexible ester chains caused the mechanical properties and high-temperature resistance performance of Comparative Example 3 to decline, and the flow rate decreased significantly and the fluidity was poor.

[0047] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirits of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A highly flexible, heat-resistant epoxy structural adhesive, characterized in that: By mass, it contains the following components: 50-60 parts of epoxy resin, 10-15 parts of heat-resistant modified resin, 100-150 parts of acetone and 3-5 parts of curing agent; The temperature-resistant modified resin is prepared by the following steps: In a reaction kettle, the boron nitride / MOF powder is dispersed in styrene, an unsaturated linear thermosetting resin and a modified siloxane are added, the mixture is stirred for 1-2 hours, a 1M potassium hydroxide solution is added dropwise, the temperature is raised to 80-90° C., the mixture is stirred for reaction for 5-6 hours, the precipitate is collected by filtration after cooling, the precipitate is washed, and the precipitate is vacuum dried to obtain a temperature-resistant modified resin; The curing agent is 4,4'-sulfonyl diphenylamine.

2. The high-flexibility, heat-resistant epoxy structural adhesive according to claim 1, characterized in that: The amount ratio of the boron nitride / MOF powder, styrene, unsaturated linear thermosetting resin, modified siloxane and potassium hydroxide solution is 1-2g: 100-150mL: 10-15g: 1-1.2g: 1-1.5mL.

3. A highly flexible heat-resistant epoxy structural adhesive according to claim 2, characterized in that: The boron nitride / MOF powder is prepared by the following steps: Hydroxyboron nitride was ultrasonically dispersed in deionized water in a reaction kettle, and zinc nitrate hexahydrate, (5-amino-1H-tetrazol-1-yl)acetic acid and tetramethylammonium bromide were added. The temperature was raised to 150-160° C. and reacted for 70-72 hours. After cooling, the precipitate was collected by centrifugation, washed, and vacuum dried to obtain boron nitride / MOF powder.

4. The high-flexibility, heat-resistant epoxy structural adhesive according to claim 3, characterized in that: The dosage ratio of the hydroxyboron nitride, deionized water, zinc nitrate hexahydrate, (5-amino-1H-tetrazol-1-yl)acetic acid and tetramethylammonium bromide is 1-2 g: 500-700 mL: 3-5 g: 3-5 g: 1.5-2 g.

5. The high-flexibility, heat-resistant epoxy structural adhesive according to claim 4, characterized in that: The hydroxy boron nitride is prepared by the following steps: In a reaction kettle, 1-2 g of boron nitride powder and 0.2-0.3 g of sodium hydroxide are ground in agate for 4-5 hours to obtain hydroxyboron nitride.

6. The high-flexibility, heat-resistant epoxy structural adhesive according to claim 5, characterized in that: The mass ratio of the boron nitride powder to sodium hydroxide is 1-2:0.2-0.

3.

7. The high-flexibility, heat-resistant epoxy structural adhesive according to claim 2, characterized in that: The modified siloxane is prepared by the following steps: Mix γ-methacryloxypropyltrimethoxysilane and deionized water in a reaction kettle, add hydrochloric acid dropwise to adjust the pH to 1-2, heat to 50-60° C. and stir to react for 60-70 minutes, add benzyl alcohol, stannous chloride and hydroquinone to the reaction kettle, heat to 150-160° C. and seal to react for 5-6 hours, and remove the solvent by rotary evaporation to obtain modified siloxane.

8. The high-flexibility, heat-resistant epoxy structural adhesive according to claim 7, characterized in that: The usage ratio of the γ-methacryloxypropyltrimethoxysilane, deionized water, benzyl alcohol, stannous chloride and hydroquinone is 15-20 g: 10-20 mL: 5-8 g: 0.1-0.2 g: 0.15-0.2 g.

9. The method for preparing a highly flexible heat-resistant epoxy structural adhesive according to claim 1, characterized in that: The steps include: The epoxy resin and the heat-resistant modified resin are mixed in a reaction kettle, heated to 150-170° C. and stirred for 2-3 hours, and then acetone and 4,4'-sulfonyl diphenylamine are added, and stirring is continued until the acetone is removed to obtain a highly flexible heat-resistant epoxy structural adhesive.