A water-based polyimide / SiO2 nanocomposite coating and its preparation method

Abstract

This invention relates to an aqueous polyimide / SiO₂ nanocomposite coating and its preparation method. The preparation method of the aqueous polyimide / SiO₂ nanocomposite coating includes: dissolving an aromatic diamine monomer in a system composed of water and an organic base; adding an aromatic dianhydride monomer in batches to react and prepare an aqueous polyamic acid salt solution; adding a silane coupling agent to the aqueous polyamic acid salt solution to react and then adding an orthosilicate ester for in-situ hydrolysis and condensation to prepare an aqueous polyamic acid / SiO₂ nanocomposite coating; coating the aqueous polyamic acid / SiO₂ nanocomposite coating onto a substrate surface, followed by drying and imidization treatment to obtain the aqueous polyimide / SiO₂ nanocomposite coating. The aqueous polyimide / SiO₂ nanocomposite coating of this invention has excellent heat resistance and adhesion properties, and can be widely used in high-temperature protective coatings and electronic packaging fields.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to an aqueous polyimide / SiO2 nanocomposite coating and its preparation method, which can be used in high-temperature resistant protective coatings and electronic packaging. Background Technology

[0002] In the field of polymer materials, polyimide, as a high-performance functional polymer, possesses outstanding high-temperature resistance, low-temperature stability, and excellent mechanical and chemical stability due to the presence of rigid aromatic and imide ring structures in its molecular backbone. It has been widely used in electronic packaging, flexible displays, aerospace insulation materials, and high-temperature protective coatings. Because of its outstanding comprehensive performance, polyimide materials are often referred to as "materials at the top of the polymer pyramid."

[0003] Currently, the main methods for synthesizing polyimides include dianhydride condensation polymerization and aromatic nucleophilic substitution. Among these, dianhydride condensation polymerization is the most widely used method due to its mature technology and relatively mild reaction conditions. This method typically uses aromatic diamines and aromatic tetracarboxylic dianhydrides as raw materials, reacting them in a polar organic solvent to generate a polyamic acid precursor, which is then subjected to a thermal imidization reaction to obtain the polyimide material.

[0004] However, the aforementioned traditional synthesis methods typically rely on high-boiling-point polar organic solvents such as N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc). These solvents are not only highly toxic, posing potential hazards to the environment and operators, but also require removal under heating or vacuum conditions during subsequent processing, increasing process complexity and energy consumption.

[0005] To overcome the aforementioned problems, aqueous polyimide systems have gradually attracted attention in recent years. Based on different synthesis routes, aqueous polyimides mainly fall into two categories: organic phase synthesis and aqueous phase synthesis. Organic phase synthesis can be further divided into homogeneous salt formation and heterogeneous salt formation, while aqueous phase synthesis directly uses water as the reaction medium to prepare polyamates. For example, patent: [A waterborne polyimide nanocomposite film and its preparation method and application, publication number: CN115353662 A]. Compared with traditional organic solvent systems, using water as the reaction medium has significant advantages: on the one hand, it eliminates the need for large amounts of organic solvents during the synthesis stage, effectively reducing toxicity and environmental pollution; on the other hand, in the subsequent thermal imidization process, the absence of high-boiling-point organic solvents in the system avoids defects such as bubbles and pores caused by solvent evaporation, and also eliminates the need for vacuum treatment, thus simplifying the process.

[0006] Since heating is required to evaporate the solvent and complete the dehydration and cyclization reaction during thermal imidization, regardless of whether water or organic solvents are used, the basic molecular structure of the resulting polyimide materials is essentially the same, and their operating temperature range remains largely consistent. This indicates that while changing the solvent system can significantly improve the environmental friendliness of the synthesis process, it has limited effect on improving the intrinsic properties of the material. Furthermore, some applications require materials with higher heat resistance. Existing waterborne polyimide coatings, after curing and imidization, are prone to microcracks and even localized peeling when subjected to thermal shock, mechanical bending, or external forces, affecting the long-term service life of the coating. Therefore, some technologies improve the heat resistance and mechanical properties of waterborne polyimide systems by adding inorganic fillers, such as patent: [A high-temperature resistant waterborne dispersion coating of polyimide and its preparation method and application, publication number CN 101139501 B]. However, when using direct physical blending, problems such as nanoparticle agglomeration, uneven dispersion, and poor interfacial compatibility often arise. This not only makes it difficult to fully utilize the reinforcing effect of nanomaterials but may also reduce the continuity and stability of the coating, such as patent: [A waterborne polyimide / POSS-GO composite coating and its preparation method and application, publication number CN 121249261 A].

[0007] Therefore, further structural modification of polyimides based on aqueous systems to improve performance has become an important research direction. Introducing siloxane segments or silicon-based structures into the polyimide molecule is an effective modification method. Siloxane structures possess high bond energy and high segmental flexibility; introducing them into the polyimide main chain or side chains can not only improve the material's heat resistance but also reduce intermolecular forces, improving flexibility and processability, thereby broadening its operating temperature range. Furthermore, this type of modification can significantly improve the adhesion of polyimide materials to substrates such as metals and glass, enhancing coating stability. In practical applications, the impact resistance, moisture resistance, and surface properties of polyimide materials can also be improved to varying degrees by the introduction of siloxane structures.

[0008] In summary, developing a water-based polyimide material combined with organosilicon modification is of great significance for achieving environmentally friendly preparation and synergistic performance improvement. Therefore, it is necessary to further optimize the synthesis method of water-based polyimides based on existing technologies and introduce inorganic or organosilicon components to construct an organic-inorganic hybrid system in situ to obtain polyimide materials with superior overall performance. Summary of the Invention

[0009] The purpose of this invention is to provide an aqueous polyimide / SiO2 nanocomposite coating and its preparation method. By introducing siloxane into the polyimide molecular backbone through the reaction between functional groups in the polyamic acid stage, and further introducing orthosilicate ester in situ hydrolysis to generate nano-SiO2, an organic-inorganic hybrid structure is achieved, thereby improving the adhesion, heat resistance and mechanical properties of the coating.

[0010] The present invention discloses an aqueous polyimide / SiO2 nanocomposite coating, characterized in that the coating is composed of an aqueous polyimide matrix and nano-SiO2 dispersed therein.

[0011] The present invention discloses an aqueous polyimide / SiO2 nanocomposite coating, characterized in that the nano-SiO2 is generated by in-situ hydrolysis and condensation of tetraethyl orthosilicate, propyl orthosilicate or isopropyl orthosilicate, and its particle size is 10-100 nm.

[0012] The present invention discloses an aqueous polyimide / SiO2 nanocomposite coating, characterized in that the coating thickness is 10-100 μm.

[0013] The present invention discloses a method for preparing an aqueous polyimide / SiO2 nanocomposite coating, characterized by comprising the following steps: (1) The diamine monomer is dissolved in a system composed of water and 1,2-dimethylimidazole at 20-30℃, and the dianhydride monomer is added in three batches. The reaction is carried out at 60-90℃ for 3-8h to prepare an aqueous polyamic acid salt solution. (2) Add γ-aminopropyltriethoxysilane to the aqueous polyamic acid solution and react at 60-90℃ for 0.5-3h to obtain an organosilicon-modified polyamic acid system; (3) Add orthosilicate to the system obtained in step (2) and carry out hydrolysis reaction at 50-60℃ and alkaline conditions for 1-4 hours to prepare waterborne polyamic acid / SiO2 nanocomposite coating. (4) The composite coating is applied to the surface of the substrate, and after drying and imidization treatment, an aqueous polyimide / SiO2 nanocomposite coating is obtained.

[0014] The present invention discloses a method for preparing an aqueous polyimide / SiO2 nanocomposite coating, characterized in that, in step (1), the diamine monomer includes at least one of 4,4'-diaminodiphenyl ether (ODA), p-phenylenediamine (PDA), m-phenylenediamine (m-PDA), 3,4'-diaminodiphenyl ether, and 4,4'-diaminobenzophenone, and the dianhydride monomer includes at least one of 4,4'-oxophthalic anhydride (ODPA), pyromellitic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA), and 1,2,4,5-phenyltetracarboxylic acid dianhydride, and the molar ratio of dianhydride to diamine is 1 to 1.05:1.

[0015] The present invention discloses a method for preparing an aqueous polyimide / SiO2 nanocomposite coating, characterized in that the amount of γ-aminopropyltriethoxysilane added in step (2) is 5% to 30% of the molar amount of diamine.

[0016] The present invention discloses a method for preparing an aqueous polyimide / SiO2 nanocomposite coating, characterized in that the amount of orthosilicate added in step (3) is 5% to 25% of the total mass of the system.

[0017] The present invention discloses a method for preparing an aqueous polyimide / SiO2 nanocomposite coating, characterized in that, in step (4), the imidization is carried out by a temperature increase in stages, with the temperatures being 100℃, 150℃, 200℃, and 250℃ respectively, and each temperature stage is maintained for 0.5 to 2 hours.

[0018] The beneficial effects of this invention are that the provided waterborne polyimide / SiO2 nanocomposite coating has excellent heat resistance and adhesion properties, as well as good mechanical properties and film-forming properties. Detailed Implementation

[0019] The invention will be further illustrated by the following examples. Example 1

[0020] 1.00 g of 4,4'-diaminodiphenyl ether (ODA) was added to a three-necked flask equipped with a mechanical stirrer, along with 26 mL of deionized water and 1.2002 g of 1,2-dimethylimidazole. The mixture was stirred at 25°C until completely dissolved. The temperature was then raised, and 1.5492 g of 4,4'-oxyphthalic anhydride (ODPA) was added in three batches. The reaction was continued at 60°C for 8 h to obtain a homogeneous and transparent aqueous polyamic acid salt solution.

[0021] Then, 0.30 g of γ-aminopropyltriethoxysilane was added, and the reaction was continued at 60 °C for 1 h. Next, 3.0 g of tetraethyl orthosilicate was added, the pH was adjusted to 9, and the mixture was stirred at 50 °C for 2 h to obtain the composite coating.

[0022] The obtained composite coating was applied to the surface of a glass substrate and allowed to stand at room temperature for 1 h before undergoing a staged heating imidization treatment at temperatures of 100 ℃, 150 ℃, 200 ℃, and 250 ℃, with each stage lasting for 0.5 h, to obtain an aqueous polyimide / SiO2 nanocomposite coating. Example 2

[0023] 1.00 g of 4,4'-diaminodiphenyl ether (ODA) was added to a three-necked flask equipped with a mechanical stirrer, along with 26 mL of deionized water and 1.2233 g of 1,2-dimethylimidazole. The mixture was stirred at 25°C until completely dissolved. The temperature was raised, and 1.5802 g of 4,4'-oxyphthalic anhydride (ODPA) was added in three batches. The reaction was continued at 70°C for 6 h to obtain a homogeneous and transparent aqueous polyamic acid salt solution.

[0024] Then, 0.30 g of γ-aminopropyltriethoxysilane was added, and the reaction was continued at 70°C for 1 h. Next, 3.0 g of tetraethyl orthosilicate was added, the pH was adjusted to 9, and the mixture was stirred at 50°C for 2 h to obtain the composite coating.

[0025] The obtained composite coating was applied to the surface of a glass substrate and allowed to stand at room temperature for 1 hour before undergoing a staged imidization treatment at temperatures of 100 ℃, 150 ℃, 200 ℃, and 250 ℃, with each stage lasting for 1 hour, to obtain an aqueous polyimide / SiO2 nanocomposite coating. Example 3

[0026] 1.00 g of 4,4'-diaminodiphenyl ether (ODA) was added to a three-necked flask equipped with a mechanical stirrer, along with 26 mL of deionized water and 1.2353 g of 1,2-dimethylimidazole. The mixture was stirred at 25°C until completely dissolved. The temperature was then raised, and 1.5957 g of 4,4'-oxyphthalic anhydride (ODPA) was added in three batches. The reaction was continued at 80°C for 5 h to obtain a homogeneous and transparent aqueous polyamic acid salt solution.

[0027] Then, 0.30 g of γ-aminopropyltriethoxysilane was added, and the reaction was continued at 50 °C for 1 h. Next, 2.0 g of propyl orthosilicate was added, the pH was adjusted to 8, and the mixture was stirred at 60 °C for 4 h to obtain the composite coating.

[0028] The obtained composite coating was applied to the surface of a glass substrate and allowed to stand at room temperature for 1 hour before undergoing a staged imidization treatment at temperatures of 100 ℃, 150 ℃, 200 ℃, and 250 ℃, with each stage lasting for 1.5 hours, to obtain an aqueous polyimide / SiO2 nanocomposite coating. Example 4

[0029] 1.00 g of 4,4'-diaminodiphenyl ether (ODA) was added to a three-necked flask equipped with a mechanical stirrer, along with 26 mL of deionized water and 1.2482 g of 1,2-dimethylimidazole. The mixture was stirred at 25°C until completely dissolved. The temperature was then raised, and 1.6112 g of 4,4'-oxyphthalic anhydride (ODPA) was added in three batches. The reaction was continued at 90°C for 3 h to obtain a homogeneous and transparent aqueous polyamic acid salt solution.

[0030] Then, 0.30 g of γ-aminopropyltriethoxysilane was added, and the reaction was continued at 90 °C for 1 h. Next, 2.0 g of propyl orthosilicate was added, the pH was adjusted to 8, and the mixture was stirred at 60 °C for 4 h to obtain the composite coating.

[0031] The obtained composite coating was applied to the surface of a glass substrate and allowed to stand at room temperature for 1 hour before undergoing a staged imidization treatment at temperatures of 100 ℃, 150 ℃, 200 ℃, and 250 ℃, with each stage lasting for 2 hours, to obtain an aqueous polyimide / SiO2 nanocomposite coating. Example 5

[0032] 1.00 g of 4,4'-diaminodiphenyl ether (ODA) was added to a three-necked flask equipped with a mechanical stirrer, along with 27 mL of deionized water and 1.2603 g of 1,2-dimethylimidazole. The mixture was stirred at 25°C until completely dissolved. The temperature was raised, and 1.6266 g of 4,4'-oxyphthalic anhydride (ODPA) was added in three batches. The reaction was continued at 80°C for 8 h to obtain a homogeneous and transparent aqueous polyamic acid salt solution.

[0033] Then, 0.30 g of γ-aminopropyltriethoxysilane was added, and the reaction was continued at 70°C for 2 h. Next, 2.0 g of isopropyl orthosilicate was added, the pH was adjusted to 7, and the mixture was stirred at 60°C for 3 h to obtain the composite coating.

[0034] The obtained composite coating was applied to the surface of a glass substrate and allowed to stand at room temperature for 1 h before undergoing a staged heating imidization treatment at temperatures of 100 ℃, 150 ℃, 200 ℃, and 250 ℃, with each stage lasting for 0.5 h, to obtain an aqueous polyimide / SiO2 nanocomposite coating. Example 6

[0035] 1.00 g of p-phenylenediamine (PDA) was added to a three-necked flask equipped with a mechanical stirrer, along with 27 mL of deionized water and 2.2220 g of 1,2-dimethylimidazole. The mixture was stirred at 25°C until completely dissolved. The temperature was then raised, and 2.0980 g of pyromellitic dianhydride (PMDA) was added in three batches. The reaction was continued at 70°C for 5 h to obtain a homogeneous and transparent aqueous polyamic acid salt solution.

[0036] Then, 0.30 g of γ-aminopropyltriethoxysilane was added, and the reaction was continued at 60°C for 3 h. Next, 1.5 g of tetraethyl orthosilicate was added, the pH was adjusted to 9, and the reaction was continued at 50°C with stirring for 2 h to obtain the composite coating.

[0037] The obtained composite coating was applied to the surface of a glass substrate and allowed to stand at room temperature for 1 hour before undergoing a staged imidization treatment at temperatures of 100 ℃, 150 ℃, 200 ℃, and 250 ℃, with each stage lasting for 1 hour, to obtain an aqueous polyimide / SiO2 nanocomposite coating. Example 7

[0038] 1.00 g of m-phenylenediamine (m-PDA) was added to a three-necked flask equipped with a mechanical stirrer, along with 27 mL of deionized water and 2.2220 g of 1,2-dimethylimidazole. The mixture was stirred at 25°C until completely dissolved. The temperature was raised, and 2.8290 g of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA) was added in three batches. The reaction was continued at 60°C for 4 h to obtain a homogeneous and transparent aqueous polyamic acid salt solution.

[0039] Then, 0.30 g of γ-aminopropyltriethoxysilane was added, and the reaction was continued at 50 °C for 1 h. Next, 1.5 g of propyl orthosilicate was added, the pH was adjusted to 9, and the reaction was continued at 60 °C with stirring for 2 h to obtain the composite coating.

[0040] The obtained composite coating was applied to the surface of a glass substrate and allowed to stand at room temperature for 1 hour before undergoing a staged imidization treatment at temperatures of 100 ℃, 150 ℃, 200 ℃, and 250 ℃, with each stage lasting for 1.5 hours, to obtain an aqueous polyimide / SiO2 nanocomposite coating. Example 8

[0041] 1.00 g of 4,4'-diaminodiphenyl ether (ODA) was added to a three-necked flask equipped with a mechanical stirrer, along with 27 mL of deionized water and 1.2010 g of 1,2-dimethylimidazole. The mixture was stirred at 25°C until completely dissolved. The temperature was raised, and 1.1380 g of pyromellitic dianhydride (PMDA) was added in three batches. The reaction was continued at 80°C for 3 h to obtain a homogeneous and transparent aqueous polyamic acid salt solution.

[0042] Then, 0.30 g of γ-aminopropyltriethoxysilane was added, and the reaction was continued at 60°C for 2 h. Next, 1.5 g of isopropyl orthosilicate was added, the pH was adjusted to 9, and the reaction was continued at 50°C with stirring for 4 h to obtain the composite coating.

[0043] The obtained composite coating was applied to the surface of a glass substrate and allowed to stand at room temperature for 1 hour before undergoing a staged imidization treatment at temperatures of 100 ℃, 150 ℃, 200 ℃, and 250 ℃, with each stage lasting for 2 hours, to obtain an aqueous polyimide / SiO2 nanocomposite coating.

[0044] Comparative Example Comparative Example 1 1.00 g of 4,4'-diaminodiphenyl ether (ODA) was added to a three-necked flask equipped with a mechanical stirrer, along with 26 mL of deionized water and 1.2482 g of 1,2-dimethylimidazole. The mixture was stirred at 25°C until completely dissolved. The temperature was raised, and 1.6112 g of 4,4'-oxyphthalic anhydride (ODPA) was added in three batches. The reaction was continued at 70°C for 8 h to obtain a homogeneous and transparent aqueous polyamic acid salt solution.

[0045] The obtained aqueous polyamic acid salt solution was coated onto the surface of a glass substrate. After standing at room temperature for 1 h, a staged imidization treatment was performed at temperatures of 100 ℃, 150 ℃, 200 ℃, and 250 ℃, with each stage held for 0.5 h, to obtain an aqueous polyimide coating.

[0046] Comparative Example 2 1.00 g of 4,4'-diaminodiphenyl ether (ODA) was added to a three-necked flask equipped with a mechanical stirrer, along with 26 mL of deionized water and 1.2482 g of 1,2-dimethylimidazole. The mixture was stirred at 25°C until completely dissolved. The temperature was then raised, and 1.6112 g of 4,4'-oxyphthalic anhydride (ODPA) was added in three batches. The reaction was continued at 80°C for 6 h to obtain a homogeneous and transparent aqueous polyamic acid salt solution.

[0047] Then 2.0 g of propyl orthosilicate was added, the pH was adjusted to 8, and the reaction was continued at 60°C for 4 h with stirring to obtain the composite coating.

[0048] The obtained composite coating was applied to the surface of a glass substrate and allowed to stand at room temperature for 1 hour before undergoing a staged imidization treatment at temperatures of 100 ℃, 150 ℃, 200 ℃, and 250 ℃, with each stage lasting for 1 hour, to obtain an aqueous polyimide / SiO2 nanocomposite coating.

[0049] Comparative Example 3 1.00 g of 4,4'-diaminodiphenyl ether (ODA) was added to a three-necked flask equipped with a mechanical stirrer, along with 26 mL of deionized water and 1.2482 g of 1,2-dimethylimidazole. The mixture was stirred at 25°C until completely dissolved. The temperature was then raised, and 1.6112 g of 4,4'-oxyphthalic anhydride (ODPA) was added in three batches. The reaction was continued at 70°C for 3 h to obtain a homogeneous and transparent aqueous polyamic acid salt solution.

[0050] Then, 0.30 g of γ-aminopropyltriethoxysilane was added, and the reaction was continued at 80°C for 2 h. Next, 2.0 g of commercially available nano-SiO2 powder was added using mechanical dispersion, the pH was adjusted to 8, and the reaction was continued at 50°C with stirring for 3 h to obtain the composite coating.

[0051] The obtained composite coating was applied to the surface of a glass substrate and allowed to stand at room temperature for 1 hour before undergoing a staged imidization treatment at temperatures of 100 ℃, 150 ℃, 200 ℃, and 250 ℃, with each stage lasting for 2 hours, to obtain an aqueous polyimide / SiO2 nanocomposite coating.

[0052] Performance testing methods (1) Adhesion test: The cross-cut test was used and evaluated according to GB / T 9286 standard.

[0053] (2) SiO2 particle size test: The particle size and distribution of SiO2 in the composite system were determined by transmission electron microscopy (TEM) and dynamic light scattering (DLS).

[0054] (3) Thermal stability test: Thermogravimetric analyzer was used to test the temperature at a rate of 10 °C / min under nitrogen atmosphere. The 5% weight loss temperature (Td5) and the initial decomposition temperature were recorded.

[0055] (4) Mechanical property testing: Tensile strength and elongation at break were tested using a universal testing machine.

[0056] (5) Observation of coating morphology: The cross-sectional structure of the coating and the dispersion state of the inorganic phase were observed using a scanning electron microscope.

[0057] Table 1 Performance test results of different embodiments and comparative examples serial number Monomer system <![CDATA[SiO2 content / %]]> <![CDATA[SiO2 particle size / nm]]> Adhesion rating Initial decomposition temperature / °C Example 1 ODA / ODPA 18.5 43 Level 0 521 Example 2 ODA / ODPA 18.4 39 Level 0 532 Example 3 ODA / ODPA 14.2 34 Level 0 547 Example 4 ODA / ODPA 14.0 29 Level 0 559 Example 5 ODA / ODPA 13.8 36 Level 0 541 Example 6 PDA / PMDA 10.6 32 Level 0 576 Example 7 m-PDA / BPDA 10.2 28 Level 0 589 Example 8 ODA / PMDA 10.5 31 Level 0 568 Comparative Example 1 ODA / ODPA 0 - Level 2 482 Comparative Example 2 ODA / ODPA 13.7 91 Level 2 509 Comparative Example 3 ODA / ODPA 13.9 134 Level 2 503 The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A water-based polyimide / SiO2 nanocomposite coating, characterized in that, The coating consists of an aqueous polyimide matrix and nano-SiO2 dispersed therein.

2. The waterborne polyimide / SiO2 nanocomposite coating according to claim 1, characterized in that, The nano-SiO2 is SiO2 particles generated by in-situ hydrolysis and condensation of tetraethyl orthosilicate, propyl orthosilicate or isopropyl orthosilicate, with a particle size of 10-100 nm.

3. The waterborne polyimide / SiO2 nanocomposite coating according to claim 1, characterized in that, The coating thickness is 10-100 μm.

4. A method for preparing an aqueous polyimide / SiO2 nanocomposite coating, characterized in that, Includes the following steps: (1) The diamine monomer is dissolved in a system composed of water and 1,2-dimethylimidazole at 20-30℃. After heating, the dianhydride monomer is added in three batches and reacted at 60-90℃ for 3-8h to prepare an aqueous polyamic acid salt solution. (2) Add γ-aminopropyltriethoxysilane to the aqueous polyamic acid solution and react at 60-90℃ for 0.5-3h to obtain an organosilicon-modified polyamic acid system; (3) Add orthosilicate to the system obtained in step (2) and carry out hydrolysis reaction at 50-60℃ and alkaline conditions for 1-4 hours to prepare waterborne polyamic acid / SiO2 nanocomposite coating. (4) The composite coating is applied to the surface of the substrate, and after drying and imidization treatment, an aqueous polyimide / SiO2 nanocomposite coating is obtained.

5. The method for preparing an aqueous polyimide / SiO2 nanocomposite coating according to claim 4, characterized in that, The diamine monomer in step (1) is an aromatic diamine monomer, including at least one of 4,4'-diaminodiphenyl ether (ODA), p-phenylenediamine (PDA), m-phenylenediamine (m-PDA), 3,4'-diaminodiphenyl ether, and 4,4'-diaminobenzophenone; the dianhydride monomer in step (1) is an aromatic dianhydride monomer, including at least one of 4,4'-oxophthalic anhydride (ODPA), pyromellitic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA), and 1,2,4,5-phenyltetracarboxylic acid dianhydride; and the molar ratio of dianhydride to diamine is 1 to 1.05:

1.

6. The method for preparing an aqueous polyimide / SiO2 nanocomposite coating according to claim 4, characterized in that, In step (2), the amount of γ-aminopropyltriethoxysilane added is 5%-30% of the molar amount of the diamine monomer.

7. The method for preparing an aqueous polyimide / SiO2 nanocomposite coating according to claim 4, characterized in that, In step (3), the amount of orthosilicate added is 5%-25% of the total mass of the system, and the pH of the hydrolysis reaction is 7-10.

8. The method for preparing an aqueous polyimide / SiO2 nanocomposite coating according to claim 4, characterized in that, In step (4), imidization is carried out in stages with temperature increments of 100℃, 150℃, 200℃ and 250℃, and each temperature increment is maintained for 0.5 to 2 hours.