Preparation method of a functional epoxy resin coating with heat conduction, corrosion resistance and self-repairing

Abstract

The application discloses a preparation method of a heat-conducting, corrosion-proof and self-repairing functional epoxy resin coating, and specifically comprises the following steps: firstly, preparing coaxial coated BN@SiC composite fibers and (HHPA / THPA)@PU self-repairing microspheres, and then synchronously modifying the two and adding them into an EP matrix for stirring to form a multifunctional boron nitride / epoxy resin-based composite coating with a rough surface. The multifunctional boron nitride / epoxy resin-based composite coating prepared by the method has the effects of corrosion-proof, high-temperature resistance and self-repairing, and the BN@SiC composite fibers are in a network fiber structure in the epoxy resin matrix to form a high-efficiency heat-conducting path. After the curing effect of the epoxy resin is regulated, the self-repairing microspheres protrude from the surface to obtain a rough surface with a hydrophobic effect, so that the obtained coating has a wide application prospect in the fields of buildings, industries, automobiles and household appliances.

Description

Technical Field

[0001] This invention belongs to the field of coating preparation technology and relates to a method for preparing a thermally conductive, corrosion-resistant, and self-healing functional epoxy resin coating. Background Technology

[0002] Epoxy resin (EP) coatings are popular coating resins due to their strong mechanical properties, corrosion resistance, and electrical insulation, and have significant potential value in energy pipelines, building material corrosion protection, and electronic component encapsulation. However, epoxy coatings have low thermal conductivity, requiring the addition of inorganic thermally conductive fillers to improve their thermal conductivity. Moreover, compared to traditional coatings, most coatings only focus on substrate protection and decoration, failing to simultaneously meet requirements for high temperature resistance, corrosion resistance, and superhydrophobicity. Therefore, developing a functional epoxy resin coating that is thermally conductive, corrosion-resistant, and self-healing, capable of meeting the diverse application needs of the substrate material, and whose excellent heat dissipation and self-healing effects can extend the service life of the material, has become one of the urgent technical problems to be solved in this field.

[0003] Zhang et al. (Zhang ZH, Wei M, Liu CQ, et al. Preparation and properties of hyperbranched modified boron nitride epoxy insulating coatings[J]. Plastics Science and Technology, 2022, 50(8):10-15.) obtained BN-HBP through hyperbranching modification. They then added BN-HBP to solvent-free epoxy coatings to prepare EP / BN-HBP composite coatings, which have good volume resistivity and corrosion resistance. However, the BN particles are prone to agglomeration, resulting in extremely limited enhanced thermal conductivity. Furthermore, they do not possess self-healing properties or superhydrophobicity.

[0004] Chinese patent "A Waterproof, Corrosion-Resistant, and Heat-Insulating Composite Coating for Polymer Metals and Its Preparation Method" (Application No.: CN202311326742.9, Publication No.: CN117106360A, Publication Date: 2023.10.13) discloses a waterproof, corrosion-resistant, and heat-insulating composite coating for polymer metals and its preparation method. The prepared waterproof, corrosion-resistant, and heat-insulating composite coating includes a pretreatment coating and an epoxy resin coating, which solves the problem of weak adhesion between the coating and the substrate and can obtain a composite coating with waterproof, corrosion-resistant, and heat-insulating effects. However, the coating obtained by this method has poor thermal conductivity and is not suitable for use on substrates with heat dissipation requirements. Furthermore, it cannot achieve self-repair after damage.

[0005] Chinese patent "A Self-Healing Superhydrophobic Composite Anti-corrosion Coating for Magnesium Alloy and Its Preparation Method" (Application No.: CN202311179011.6, Publication No.: CN117186775A, Publication Date: 2023.09.13) discloses a self-healing superhydrophobic composite anti-corrosion coating for magnesium alloy and its preparation method. This method achieves superhydrophobicity and anti-corrosion performance by sequentially depositing a micro-arc oxidation ceramic underlayer, a polyvinyl alcohol-tannic acid self-healing intermediate layer, and a ZnO-epoxy resin outer layer on the surface of the magnesium alloy, and also exhibits a certain degree of self-healing effect. However, the self-healing effect of this method is weak, the swelling size upon contact with water is difficult to control, stress is easily generated, and it is also unsuitable for use on substrates with heat dissipation requirements.

[0006] Huang Peng et al. (Huang Peng, Pei Kemei. Preparation and performance study of modified boron nitride / waterborne epoxy thermally conductive and insulating coating [J]. Chinese Adhesives, 2023, 32(10): 16-22.) prepared a series of BN nanosheets modified by hydroxylation and synergistic modification with silane coupling agent. They added these samples to waterborne epoxy coatings to prepare waterborne epoxy thermally conductive and insulating coatings. BN has good dispersion in epoxy matrix and good thermal conductivity and electrical insulation, but its corrosion resistance is weak and it does not have self-healing properties or superhydrophobicity. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing a thermally conductive, corrosion-resistant, and self-healing functional epoxy resin coating, which solves the problem that coatings obtained by existing technologies cannot simultaneously meet the performance requirements of high temperature resistance, high thermal conductivity, insulation, and superhydrophobicity.

[0008] The technical solution adopted in this invention is a method for preparing a thermally conductive, corrosion-resistant, and self-healing functional epoxy resin coating, which is implemented according to the following steps:

[0009] Step 1, Preparation of coaxially coated BN@SiC composite fibers:

[0010] Boron nitride fibers were treated with NaOH solution, then impregnated in impregnation solution under vacuum, dried and calcined in nitrogen atmosphere to obtain coaxially coated BN@SiC composite fibers.

[0011] Step 2, Preparation of (HHPA / THPA)@PU self-healing microspheres:

[0012] Hexahydrophthalic anhydride (HHPA) and tetrahydrophthalic anhydride (THPA) were dissolved in chloroform, then mixed and emulsified with polyurethane (PU) acetone solution. The temperature of the emulsion was gradually increased and then separated and dried to obtain (HHPA / THPA)@PU self-healing microspheres.

[0013] Step 3, construct the composite coating with a mesh fiber structure:

[0014] The composite fibers obtained in step 1 and the self-healing microspheres obtained in step 2 were modified with silane coupling agent, and then mixed and stirred with epoxy resin (EP), leveling agent and defoamer to obtain a mesh fiber structure BN@SiC composite fiber / EP composite coating containing (HHPA / THPA)@PU self-healing microspheres.

[0015] Step 4, prepare boron nitride / epoxy resin-based composite coating:

[0016] The BN@SiC composite fiber / EP composite coating with a mesh fiber structure obtained in step 3 is mixed with the compounded HHPA / THPA curing agent and curing accelerator, and after stirring for a certain period of time, it is coated on the surface of an aluminum plate to obtain a multifunctional boron nitride / epoxy resin-based composite coating.

[0017] The preferred solution is:

[0018] In step 1, the NaOH solution concentration is 4 mol / L, and the treatment time is 2 h. The impregnation solution is 25%–40% by mass of polycarbosilane dissolved in tetrahydrofuran, the impregnation time is 0.5–2 h, the impregnation temperature is 30–60℃, the drying temperature is 40–70℃, the drying time is 3–6 h, the calcination temperature is 800–1400℃, and the holding time is 2.5–4 h, to obtain coaxially coated BN@SiC composite fibers.

[0019] In step 2, the mass ratio of HHPA to THPA is 9:1, accounting for 20% of the chloroform mass fraction. The polyurethane (PU) acetone solution is a 25%–35% polyurethane dissolved in acetone. The stirring temperature is 40℃ for 1.5–3 hours. Then, the temperature is adjusted to 60℃ at a heating rate of 0.5–0.8℃ / min. After separation, the mixture is dried at 60℃ for 6 hours to obtain (HHPA / THPA)@PU self-healing microspheres.

[0020] In step 3, the silane coupling agent is selected from any one of KH-550, KH-560, and KH-570. The proportion of epoxy resin composite fiber added is 4-10%, the proportion of self-healing microspheres added is 6-15%, the leveling agent is polydimethylsiloxane at a proportion of 1%, the defoamer is silicate defoamer at a proportion of 1%, the stirring time is 10 min, and the temperature is 70℃, to obtain a mesh fiber structure BN@SiC composite fiber / EP composite coating containing (HHPA / THPA)@PU self-healing microspheres.

[0021] In step 4, the mass ratio of the compounded HHPA / THPA curing agent is 9:1, the ratio of the composite coating to the compounded curing agent is 100:10 to 100:25, the curing accelerator is 2-methylimidazole with an addition amount of 3%, the stirring temperature is 70℃, the time is 8min, and the coating is applied to the substrate to obtain a multifunctional boron nitride / epoxy resin-based composite coating.

[0022] The beneficial effects of this invention are as follows: The thermally conductive, corrosion-resistant, and self-healing functional epoxy resin coating prepared by this invention uses coaxially coated boron nitride@silicon carbide composite fibers and (HHPA / THPA)@PU self-healing microspheres as the core. Through simultaneous modification of both, a coating with anti-corrosion, high-temperature resistance, and self-healing effects is obtained. Furthermore, the BN@SiC composite fibers form a network fiber structure in the epoxy resin matrix, creating a highly efficient thermally conductive pathway. After controlling the curing effect of the epoxy resin, the self-healing microspheres protrude from the surface, resulting in a rough surface with hydrophobic properties. Therefore, the obtained coating has broad application prospects in the fields of construction, industry, automobiles, and home appliances. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the boron nitride / epoxy resin-based composite coating prepared according to the present invention. Detailed Implementation

[0024] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0025] The technical solution adopted in this invention is a method for preparing a thermally conductive, corrosion-resistant, and self-healing functional epoxy resin coating, which is implemented according to the following steps:

[0026] Step 1, Preparation of coaxially coated BN@SiC composite fibers:

[0027] Boron nitride fibers were treated in a 4 mol / L NaOH solution for 2 hours, followed by vacuum impregnation in a tetrahydrofuran solution containing 25%–40% polycarbosilane for 0.5–2 hours at an impregnation temperature of 30–60°C. The fibers were then dried at 40–70°C for 3–6 hours. After drying, the fibers were placed in a furnace and calcined in a nitrogen atmosphere at 800–1400°C for 2.5–4 hours to obtain coaxially coated BN@SiC composite fibers.

[0028] Step 2, Preparation of (HHPA / THPA)@PU self-healing microspheres:

[0029] Hexahydrophthalic anhydride (HHPA) and tetrahydrophthalic anhydride (THPA) were dissolved in chloroform at a mass ratio of 9:1, accounting for 20% of the chloroform mass fraction. The mixture was then emulsified with an acetone solution containing 25%–35% polyurethane by mass. The emulsion temperature was then adjusted to 60°C at a heating rate of 0.5–0.8°C / min. After separation, the emulsion was dried at 60°C for 6 hours to obtain (HHPA / THPA)@PU self-healing microspheres.

[0030] Step 3, construct the composite coating with a mesh fiber structure:

[0031] The composite fibers obtained in step 1 and the self-healing microspheres obtained in step 2 are modified with a silane coupling agent (any one of KH-550, KH-560, and KH-570). 4-10% of the composite fibers and 6-15% of the self-healing microspheres are added to EP, followed by the addition of 1% of polydimethylsiloxane leveling agent and 1% of silicate defoamer. The mixture is stirred at 70°C for 10 minutes to obtain a mesh fiber structure BN@SiC composite fiber / EP composite coating containing (HHPA / THPA)@PU self-healing microspheres.

[0032] Step 4, prepare boron nitride / epoxy resin-based composite coating:

[0033] The BN@SiC composite fiber / EP composite coating with a mesh fiber structure obtained in step 3 is mixed with HHPA / THPA curing agent at a ratio of 9:1, with a mixing ratio of 100:10 to 100:25. At the same time, 3% of 2-methylimidazole is added, and the mixture is stirred at 70°C for 8 minutes. The mixture is then coated onto the substrate to obtain a multifunctional boron nitride / epoxy resin-based composite coating.

[0034] This invention employs coaxial coating technology to adjust the surface state of boron nitride fibers and controls the concentration and impregnation of polycarbosilane to obtain coaxially coated boron nitride@silicon carbide composite fibers. These fibers not only possess excellent high-temperature resistance and corrosion resistance but also form a thermally conductive network, exhibiting superior thermal conductivity. The invention utilizes an emulsification-curing method to regulate the structure of an oil-in-water (O / W) emulsion and synthesize self-healing microspheres to promote the damage repair effect of the coating material. Simultaneous modification of the composite fibers and self-healing microspheres, controlling their uniform dispersion in the coating and their bonding with epoxy resin, not only yields a coating with thermal conductivity, corrosion resistance, high-temperature resistance, and self-healing effects but also, by controlling the curing effect, allows the self-healing microspheres to protrude from the coating surface, resulting in a multifunctional composite coating with a rough surface and hydrophobic properties.

[0035] The thermally conductive, corrosion-resistant, and self-healing functional epoxy resin coating prepared by this invention uses coaxially coated boron nitride@silicon carbide composite fibers and (HHPA / THPA)@PU self-healing microspheres as the core. Through simultaneous modification of both, a coating with anti-corrosion, high-temperature resistance, and self-healing effects is obtained. Furthermore, the BN@SiC composite fibers form a network fiber structure in the epoxy resin matrix, creating a highly efficient thermally conductive pathway. After controlling the curing effect of the epoxy resin, the self-healing microspheres protrude from the surface, resulting in a rough surface with hydrophobic properties. Therefore, the obtained coating has broad application prospects in the fields of construction, industry, automobiles, and home appliances.

[0036] Example 1

[0037] Preparation of boron nitride / epoxy resin-based composite coating:

[0038] First, boron nitride fibers were treated in a 4 mol / L NaOH solution for 2 hours, then vacuum impregnated in a tetrahydrofuran solution containing 40% polycarbosilane for 2 hours at an impregnation temperature of 60°C, followed by drying at 70°C for 6 hours. After drying, the fibers were placed in a heating furnace and calcined in a nitrogen atmosphere at a temperature of 1400°C for 4 hours to obtain coaxially coated BN@SiC composite fibers.

[0039] HHPA and THPA were dissolved in chloroform at a mass ratio of 9:1, accounting for 20% of the chloroform mass fraction. The mixture was then emulsified with an acetone solution containing 25% polyurethane by mass. The emulsion temperature was then adjusted to 60°C at a heating rate of 0.8°C / min. After separation, the emulsion was dried at 60°C for 6 hours to obtain (HHPA / THPA)@PU self-healing microspheres.

[0040] The composite fibers and self-healing microspheres were modified with silane coupling agent KH-550. Then, 10% of the modified composite fibers and 15% of the self-healing microspheres were added to EP, followed by 1% of polydimethylsiloxane leveling agent and 1% of silicate defoamer. The mixture was stirred at 70°C for 10 min to obtain a mesh fiber structure BN@SiC composite fiber / EP composite coating containing (HHPA / THPA)@PU self-healing microspheres.

[0041] The composite coating was mixed with HHPA / THPA curing agent in a ratio of 9:1 at 100:25, and 3% 2-methylimidazole was added. The mixture was stirred at 70°C for 8 minutes and then coated onto the substrate to obtain a multifunctional boron nitride / epoxy resin-based composite coating.

[0042] Example 2

[0043] Preparation of boron nitride / epoxy resin-based composite coating:

[0044] First, boron nitride fibers were treated in a 4 mol / L NaOH solution for 2 hours, then vacuum impregnated in a tetrahydrofuran solution containing 35% polycarbosilane for 1.5 hours at an impregnation temperature of 50°C, followed by drying at 60°C for 5 hours. After drying, the fibers were placed in a heating furnace and calcined in a nitrogen atmosphere at a temperature of 1200°C for 3.5 hours to obtain coaxially coated BN@SiC composite fibers.

[0045] HHPA and THPA were dissolved in chloroform at a mass ratio of 9:1, accounting for 20% of the chloroform mass fraction. The mixture was then mixed and emulsified with an acetone solution containing 35% polyurethane by mass fraction. The emulsion temperature was then adjusted to 60℃ at a heating rate of 0.8℃ / min. After separation, the emulsion was dried at 60℃ for 6h to obtain (HHPA / THPA)@PU self-healing microspheres.

[0046] The composite fibers and self-healing microspheres were modified with silane coupling agent KH-560. Then, 8% of the modified composite fibers and 12% of the self-healing microspheres were added to EP, followed by 1% of polydimethylsiloxane leveling agent and 1% of silicate defoamer. The mixture was stirred at 70°C for 10 min to obtain a mesh fiber structure BN@SiC composite fiber / EP composite coating containing (HHPA / THPA)@PU self-healing microspheres.

[0047] The composite coating was mixed with HHPA / THPA curing agent at a ratio of 9:1 in a ratio of 100:20, and 3% 2-methylimidazole was added. The mixture was stirred at 70°C for 8 minutes and then coated onto the substrate to obtain a multifunctional boron nitride / epoxy resin-based composite coating.

[0048] Example 3

[0049] Preparation of boron nitride / epoxy resin-based composite coating:

[0050] First, boron nitride fibers were treated in a 4 mol / L NaOH solution for 2 hours, then vacuum impregnated in a tetrahydrofuran solution containing 30% polycarbosilane for 1 hour at an impregnation temperature of 40°C, followed by drying at 50°C for 4 hours. After drying, the fibers were placed in a heating furnace and calcined in a nitrogen atmosphere at a temperature of 1000°C for 3 hours to obtain coaxially coated BN@SiC composite fibers.

[0051] HHPA and THPA were dissolved in chloroform at a mass ratio of 9:1, accounting for 20% of the chloroform mass fraction. The mixture was then emulsified with an acetone solution containing 30% polyurethane by mass. The emulsion temperature was then adjusted to 60°C at a heating rate of 0.66°C / min. After separation, the emulsion was dried at 60°C for 6 hours to obtain (HHPA / THPA)@PU self-healing microspheres.

[0052] The composite fibers and self-healing microspheres were modified with silane coupling agent KH-570. Then, 6% of the modified composite fibers and 9% of the self-healing microspheres were added to EP, followed by 1% of polydimethylsiloxane leveling agent and 1% of silicate defoamer. The mixture was stirred at 70°C for 10 min to obtain a mesh fiber structure BN@SiC composite fiber / EP composite coating containing (HHPA / THPA)@PU self-healing microspheres.

[0053] The composite coating was mixed with HHPA / THPA curing agent at a ratio of 9:1 in a ratio of 100:15, and 3% of 2-methylimidazole was added. The mixture was stirred at 70°C for 8 minutes and then coated onto the substrate to obtain a multifunctional boron nitride / epoxy resin-based composite coating.

[0054] Example 4

[0055] Preparation of boron nitride / epoxy resin-based composite coating:

[0056] First, boron nitride fibers were treated in a 4 mol / L NaOH solution for 2 hours, then vacuum impregnated in a tetrahydrofuran solution containing 25% polycarbosilane for 0.5 hours at an impregnation temperature of 30°C. Subsequently, they were dried at 40°C for 3 hours. After drying, they were placed in a heating furnace and calcined in a nitrogen atmosphere at a temperature of 800°C for 2.5 hours to obtain coaxially coated BN@SiC composite fibers.

[0057] HHPA and THPA were dissolved in chloroform at a mass ratio of 9:1, accounting for 20% of the chloroform mass fraction. The mixture was then emulsified with an acetone solution containing 28% polyurethane by mass. The emulsion temperature was then adjusted to 60°C at a heating rate of 0.55°C / min. After separation, the emulsion was dried at 60°C for 6 hours to obtain (HHPA / THPA)@PU self-healing microspheres.

[0058] The composite fibers and self-healing microspheres were modified with silane coupling agent KH-550. Then, 4% of the modified composite fibers and 6% of the self-healing microspheres were added to EP, followed by 1% of polydimethylsiloxane leveling agent and 1% of silicate defoamer. The mixture was stirred at 70°C for 10 min to obtain a mesh fiber structure BN@SiC composite fiber / EP composite coating containing (HHPA / THPA)@PU self-healing microspheres.

[0059] The composite coating was mixed with HHPA / THPA curing agent at a ratio of 9:1 in a ratio of 100:10, and 3% of 2-methylimidazole was added. The mixture was stirred at 70°C for 8 minutes and then coated onto the substrate to obtain a multifunctional boron nitride / epoxy resin-based composite coating.

[0060] Table 1 compares the thermal conductivity, 3.5% NaCl salt spray corrosion length, volume resistivity, water contact angle, and self-healing rate of boron nitride / epoxy resin-based composite coating, waterborne epoxy thermally conductive and insulating coating, and h-BN@PDA@APTES doped EP powder coating in Example 1.

[0061]

[0062]

[0063] As can be seen from Table 1, the boron nitride / epoxy resin-based composite coating in Example 1 has the highest thermal conductivity and the shortest salt spray corrosion length. This is because the coaxially coated BN@SiC composite fibers form a network fiber structure in the epoxy resin matrix, creating an efficient thermal conductivity pathway. Furthermore, BN and SiC are inorganic ceramic bodies, which synergistically enhance the corrosion resistance of the coating. The water contact angle and self-healing rate of the waterborne epoxy thermally conductive and insulating coating and the h-BN@PDA@APTES doped EP powder coating were not investigated. However, the water contact angle and self-healing rate of the boron nitride / epoxy resin-based composite coating in Example 1 were 159° and 80.1%, respectively. This is because there are self-healing microspheres inside the boron nitride / epoxy resin-based composite coating. After the epoxy resin cures and shrinks, the self-healing microspheres protrude from the surface, forming a rough surface with hydrophobic effect. Furthermore, when the coating is damaged, the self-healing microspheres rupture, and the compound epoxy resin curing agent in the core is released, which can play the role of a self-healing coating. The volume resistivity of the boron nitride / epoxy resin-based composite coating in Example 1 is also the highest. This is because the materials used in the composite coating have good electrical insulation properties, so it has excellent insulation performance. In addition, because a compound curing agent system is used, the curing time is also greatly shortened.

[0064] Figure 1 This is a schematic diagram of the boron nitride / epoxy resin-based composite coating prepared according to the present invention. From... Figure 1 It can be seen that the epoxy resin coating matrix contains self-healing microspheres, and the coaxially coated BN@SiC composite fibers form a network fiber structure in the coating matrix. After curing, the self-healing microspheres protrude from the coating to form a rough surface.

Claims

1. A method for preparing a thermally conductive, corrosion-resistant, and self-healing functional epoxy resin coating, characterized in that, The specific steps are as follows: Step 1: Preparation of coaxially coated BN@SiC composite fibers Boron nitride fibers were treated with NaOH solution, then impregnated in impregnation solution under vacuum, dried and calcined in nitrogen atmosphere to obtain coaxially coated BN@SiC composite fibers. The impregnation solution solvent is tetrahydrofuran, the mass of polycarbosilane accounts for 25% to 40% of the solvent system, the impregnation time is 0.5 to 2 hours, the impregnation temperature is 30 to 60°C, the drying temperature is 40 to 70°C, and the drying time is 3 to 6 hours. Step 2, Preparation of (HHPA / THPA)@PU self-healing microspheres Hexahydrophthalic anhydride (HHPA) and tetrahydrophthalic anhydride (THPA) were dissolved in chloroform, then mixed and emulsified with polyurethane (PU) acetone solution. The temperature of the emulsion was gradually increased and then separated and dried to obtain (HHPA / THPA)@PU self-healing microspheres. Step 3: Construct a composite coating with a mesh fiber structure The composite fibers obtained in step 1 and the self-healing microspheres obtained in step 2 were modified with silane coupling agent, and then mixed and stirred with epoxy resin (EP), leveling agent and defoamer to obtain a mesh fiber structure BN@SiC composite fiber / EP composite coating containing (HHPA / THPA)@PU self-healing microspheres. Step 4: Prepare boron nitride / epoxy resin-based composite coating The BN@SiC composite fiber / EP composite coating with a mesh fiber structure obtained in step 3 is mixed with the compounded HHPA / THPA curing agent and curing accelerator, and after stirring for a certain period of time, it is coated on the surface of an aluminum plate to obtain a multifunctional boron nitride / epoxy resin-based composite coating.

2. The preparation method according to claim 1, characterized in that, In step 1, the concentration of NaOH solution is 4 mol / L, and the treatment time is 2 hours.

3. The preparation method according to claim 1, characterized in that, The calcination process in step 1 is as follows: the obtained boron nitride fibers with polycarbosilane coating on the surface are placed in a heating furnace and calcined at 800-1400℃ for 2.5-4 hours to obtain coaxially coated BN@SiC composite fibers.

4. The preparation method according to claim 1, characterized in that, In step 2, the mass ratio of hexahydrophthalic anhydride to tetrahydrophthalic anhydride is 9:1, accounting for 20% of the chloroform mass fraction. The polyurethane (PU) acetone solution is a 25% to 35% polyurethane dissolved in acetone. The stirring temperature is 40°C, and the stirring time is 1.5 to 3 hours.

5. The preparation method according to claim 4, characterized in that, In step 2, the emulsion temperature was adjusted to 60°C at a heating rate of 0.5–0.8°C / min. After separation, the emulsion was dried at 60°C for 6 hours to obtain (HHPA / THPA)@PU self-healing microspheres.

6. The preparation method according to claim 1, characterized in that, In step 3, the silane coupling agent is selected from any one of KH-550, KH-560, and KH-570. The proportion of epoxy resin composite fiber added is 4-10%, the proportion of self-healing microspheres added is 6-15%, the leveling agent is polydimethylsiloxane at a proportion of 1%, and the defoamer is silicate defoamer at a proportion of 1%.

7. The preparation method according to claim 1, characterized in that, In step 3, the stirring time is 10 minutes and the temperature is 70°C, resulting in a BN@SiC composite fiber / EP composite coating with a mesh fiber structure containing (HHPA / THPA)@PU self-healing microspheres.

8. The preparation method according to claim 1, characterized in that, In step 4, the mass ratio of HHPA / THPA is 9:1, the mixing ratio of the composite coating and the compound curing agent is 100:10 to 100:25, and the curing accelerator is 2-methylimidazole, with an addition amount of 3%.

9. The preparation method according to claim 1, characterized in that, The stirring temperature in step 4 is 70°C and the time is 8 minutes. The resulting coating on the substrate is a multifunctional boron nitride / epoxy resin-based composite coating.

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