Anti-tearing polyimide film for aerospace and preparation method thereof

Abstract

The invention relates to the technical field of aerospace coating materials, and particularly discloses an anti-tearing polyimide film for aerospace and a preparation method thereof. The invention discloses an anti-tearing polyimide film for aerospace. The anti-tearing polyimide film is formed by bonding and compounding a base material layer and a reinforcing layer by adopting a hot melt adhesive, the base material layer is a modified polyimide film layer, and the modified polyimide film layer is prepared by the following steps: mixing 4, 4 '-diaminodiphenyl ether and N, N-dimethylacetamide, then adding silicon oxide sol and aluminum oxide sol, stirring and mixing, then adding pyromellitic dianhydride in batches under the condition of ice-water bath, stirring, and drying to obtain the modified polyimide film layer. After stirring is completed, film laying is conducted, then heating is conducted, thermal imidization is conducted, and then cooling is conducted. The anti-tear polyimide film for aerospace can maintain relatively stable tear resistance under frequent and violent temperature change, and the overall anti-tear polyimide film has relatively long service life.

Description

Technical Field

[0001] This application relates to the field of aerospace coating materials technology, and more specifically, it relates to a tear-resistant polyimide film for aerospace applications and a method for preparing the same. Background Technology

[0002] Tear-resistant films used in aerospace are primarily designed to prevent accidental damage to the surface of parts. They were initially used to protect metal and glass products, and with the development of the aerospace industry, they have rapidly expanded to the surface protection of aircraft windows, cockpit canopies, fuselages, and other critical components. Due to their excellent tear resistance, they are not easily damaged even under large external forces and can effectively meet the needs of aircraft under different climatic conditions.

[0003] Tear-resistant films used in aviation include Hutchinson's neoprene film composite polyester mesh, used in the aerospace industry to wrap glass wool, polyimide foam, and other insulation materials, serving a wrapping function to prevent damage to the insulation materials and to prevent static electricity and sparking. There are also elastic polyurethane film and polyester mesh composites, used in the aerospace industry to wrap glass wool, polyurethane, polyimide foam, and other insulation materials, serving a wrapping function to prevent damage to the insulation materials and to prevent static electricity and sparking. PEEK film composite fiber mesh, currently the mainstream practice for Boeing and Airbus, is also used to wrap glass wool or other insulation materials, serving a wrapping function to prevent damage to the insulation materials and to prevent static electricity and sparking. Additionally, there are polyimide film composite high-strength square meshes, used in the aerospace industry to wrap glass wool, polyurethane, polyimide foam, and other insulation materials, serving a wrapping function. These are used for insulation coverings of aerospace water pipes, air pipes, oil pipes, and fuselages, and are widely used due to their excellent flame-retardant properties, mechanical strength, and strong adaptability to high-altitude radiation environments.

[0004] Regarding the aforementioned technologies, the inventors believe that in practical applications in the aerospace field, frequent and drastic temperature changes are unavoidable. As a result, the movement of polyimide molecular chain segments is accelerated, resulting in localized stress concentration, irreversible deformation or breakage, which damages the integrity of the overall structure, significantly reduces tear resistance, and consequently greatly shortens the service life.

[0005] Therefore, there is an urgent need to propose a solution to address the aforementioned technical problems. Summary of the Invention

[0006] In order to improve the stability of the tear resistance of polyimide film structure under frequent and drastic temperature changes, and thus extend its service life, this application provides a tear-resistant polyimide film for aerospace and its preparation method.

[0007] In a first aspect, this application provides a tear-resistant polyimide film for aerospace applications, employing the following technical solution: A tear-resistant polyimide film for aerospace applications is composed of a substrate layer and a reinforcing layer bonded together with hot melt adhesive; the substrate layer is a modified polyimide film layer, which is prepared through the following steps: S1. Phenethyltriethoxysilane, deionized water and N,N-dimethylacetamide are heated and stirred together, and then cooled after heat treatment to obtain silica sol; Aluminum isopropoxide and toluene are heated and mixed, and then deionized water is added while stirring. After high-temperature reaction, the mixture is cooled to obtain alumina sol. S2. Mix 4,4'-diaminodiphenyl ether and N,N-dimethylacetamide, then add the silica sol and alumina sol obtained in step S1 and stir to mix. Then, under ice-water bath conditions, add pyromellitic dianhydride in batches and stir. After stirring, lay the film, then heat to perform thermal imidization, and finally cool to obtain the modified polyimide film layer.

[0008] By adopting the above technical solution, the substrate layer provides the foundation for temperature resistance and mechanical strength, the reinforcing layer enhances tensile and wind tear resistance, and the hot melt adhesive bonding ensures a balance between interlayer bonding strength and flexibility, thereby making it exhibit excellent tear resistance as a whole. In the preparation of modified polyimide film layers, silica sol imparts high heat resistance, reduces the thermal degradation of polyimide chains at high temperatures, and improves the flexibility of the film, providing elastic buffering through silicon-oxygen bonds. Alumina sol provides excellent thermal conductivity, accelerates heat diffusion, reduces local thermal stress, and strengthens local tear resistance points. The two work synergistically to optimize the matching of thermal expansion coefficients, prevent microcracks and delamination caused by sudden temperature changes, and form an interpenetrating network to disperse stress concentration points, significantly improving elongation and tear resistance. At the same time, the nanoparticles of silicon and aluminum oxides are embedded in the polyimide matrix to form a thermal barrier layer, which can also resist fatigue damage in thermal cycling. Therefore, in the preparation of modified polyimide film layers, the synergistic application of silica sol and alumina sol can significantly improve the stability of tear resistance under frequent and drastic temperature changes, enabling the final tear-resistant polyimide film for aerospace applications to maintain good stability during application and thus have a long service life.

[0009] Preferably, in step S1, phenethyltriethoxysilane, deionized water, and N,N-dimethylacetamide are heated to 60-70°C and stirred to mix in a weight ratio of 1:(0.4-0.8):(8-15). After heat treatment, the mixture is cooled to obtain silica sol. The heat treatment operation is as follows: first, stabilize at 80-90°C for 2.5-3.5 hours, then stabilize at 110-115°C for 35-45 minutes, and finally cool down to 60-70°C.

[0010] By employing the above technical solution, the specified ratio of phenylethyltriethoxysilane to water ensures that the silane is partially hydrolyzed but not completely polycondensed. Excessive water content accelerates gelation, leading to decreased sol stability; insufficient water content results in incomplete hydrolysis, affecting subsequent compatibility with the polyimide matrix. N,N-dimethylacetamide, as a polar solvent, ensures sufficient dispersion medium, preventing nanoparticle aggregation and guaranteeing sol uniformity at the specified ratio. Simultaneously, during heat treatment, stabilization at 80-90℃ for 2.5-3.5 hours promotes complete hydrolysis of the silane to generate active silanols and initiates controlled polycondensation, forming a linear / branched prepolymer framework, avoiding sol brittleness caused by excessive cross-linking at high temperatures. Further stabilization at 110-115℃ for 35-45 minutes accelerates polycondensation to complete the three-dimensional network structure, strengthening the sol's mechanical strength. This ensures the sol's dispersibility and interfacial bonding within the polyimide matrix.

[0011] Preferably, in step S1, aluminum isopropoxide and toluene are heated to 60-70°C and mixed, and then deionized water is added during stirring. After reacting at a high temperature of 250-280°C for 5-6 hours, the mixture is cooled to obtain alumina sol. The weight ratio of aluminum isopropoxide, toluene and deionized water used is 1: (5-10): (0.3-0.5).

[0012] By adopting the above technical solution, the specific ratio of aluminum isopropoxide and toluene avoids rapid hydrolysis and gelation caused by excessive water, ensuring that aluminum isopropoxide partially hydrolyzes to form boehmite precursors while retaining an appropriate amount of alkoxy groups to maintain sol fluidity and controllability of subsequent polycondensation. The aforementioned amount of toluene provides an inert reaction environment, suppresses side reactions, ensures solvent stability for subsequent high-temperature reactions, and prevents particle agglomeration, ensuring uniform dispersion of nanoparticles. Furthermore, the high-temperature reaction at 250-280℃ for 5-6 hours accelerates the alkoxy group de-alcoholization polycondensation, promoting the transition of amorphous aluminum hydroxide to a crystalline state, improving the thermal stability of the sol while ensuring complete polycondensation and forming a three-dimensional network structure. This enhances its dispersibility and interfacial bonding within the polyimide matrix.

[0013] Preferably, in step S2, the weight ratio of silica sol to alumina sol is (3-5):1.

[0014] By adopting the above technical solution, the silica sol and alumina sol in the above proportion can form a better toughness-rigidity balance control mechanism and crack propagation inhibition mechanism after application, thereby enabling the modified polyimide film layer to maintain tear resistance stability under extreme temperature alternation, and the overall application brings better corresponding effects.

[0015] Preferably, in step S2, a functional additive is also used, which is added and mixed together with the silica sol and alumina sol. The functional additive accounts for 5-8% of the total weight of the silica sol and alumina sol, and the functional additive is composed of carbon nitride and boron nitride, with a weight ratio of carbon nitride to boron nitride of 1:(4-6).

[0016] By adopting the above technical solution, the layered structure of boron nitride is stacked parallel between the polyimide molecular chains, forming physical cross-linking points with the imide rings through van der Waals forces, which can significantly improve the interfacial bonding performance. The nitrogen-containing groups of carbon nitride form a hydrogen bond network with the carbonyl groups of polyimide, enhancing the chemical bonding strength and also improving the interfacial shear strength. When carbon nitride and boron nitride are used as functional additives in appropriate proportions, they can form a CTE transition layer from the polyimide matrix to the inorganic filler. This gradient CTE transition layer can significantly reduce the thermal stress concentration, thereby inhibiting the initiation of microcracks in the film under frequent and rapid temperature changes. This significantly improves the tear resistance stability of the modified polyimide film layer, ultimately resulting in a tear-resistant polyimide film with better application quality for aerospace applications.

[0017] Preferably, the weight ratio of carbon nitride to boron nitride is 1:5.

[0018] By adopting the above technical solution, when carbon nitride and boron nitride in the above proportion are used as functional additives, the synergistic effect between the two is better, and the tear resistance stability of the modified polyimide film layer is also better improved.

[0019] Preferably, both carbon nitride and boron nitride have a layered nanosheet structure with a diameter of 1-3 μm, a thickness of 3-5 nm, and a specific surface area of ​​200-300 m². 2 / g.

[0020] By adopting the above technical solution, both carbon nitride and boron nitride are layered nanosheet structures, which can absorb energy through interlayer slip under temperature stress, reducing the risk of matrix molecular chain breakage. The aforementioned diameter and thickness of carbon nitride and boron nitride can overlap in the matrix to form a continuous thermally conductive network and fill the gaps between large-sized layers, suppressing crack penetration paths. At the same time, the high specific surface area can increase the contact area with the matrix, disperse local stress throughout the filler network, reduce the crack density under frequent and rapid temperature changes, and thus obtain a modified polyimide film layer with better tear resistance and stability.

[0021] Preferably, the reinforcing layer is any one of a square fiberglass mesh, a nylon mesh, and a polyester mesh.

[0022] By adopting the above technical solutions, the above-mentioned types of reinforcing layers are all suitable for the preparation of tear-resistant polyimide films for aerospace applications.

[0023] Secondly, this application provides a method for preparing a tear-resistant polyimide film for aerospace applications, employing the following technical solution: A method for preparing a tear-resistant polyimide film for aerospace applications includes the following steps: (1) Prepare the raw materials for the substrate layer, the reinforcing layer and the hot melt adhesive; (2) The substrate layer and the reinforcing layer in step (1) are preheated, and then hot melt adhesive is applied between the substrate layer and the reinforcing layer. The film is then hot-pressed to obtain a tear-resistant polyimide film for aerospace applications.

[0024] By adopting the above technical solution, the above preparation method is simple to operate, suitable for large-scale industrial production, and can ensure that a structurally stable and excellent tear-resistant polyimide film for aerospace applications is obtained.

[0025] In summary, this application has the following beneficial effects: 1. In the preparation of the modified polyimide film layer, this application achieves a significant improvement in tear resistance stability under frequent and drastic temperature changes through the synergistic application of silica sol and alumina sol, so that the final tear-resistant polyimide film for aerospace applications maintains better stability during application and thus has a longer service life. 2. In the preparation of the modified polyimide film layer, this application uses functional additives mixed with silica sol and alumina sol. By utilizing the synergistic effect between carbon nitride and boron nitride in the functional additives, the tear resistance stability of the modified polyimide film layer can be significantly improved, thereby ultimately obtaining a tear-resistant polyimide film with better application quality for aerospace. Detailed Implementation

[0026] The present application will be further described in detail below with reference to preparation examples, embodiments and comparative examples.

[0027] Unless otherwise specified, all raw materials used in the preparation examples, embodiments and comparative examples of this application are commercially available.

[0028] The hot melt adhesive was purchased from Henkel TECHNOMELT PUR MC9350 polyurethane hot melt adhesive; The reinforcing layer is a square fiberglass mesh, purchased from Shanghai Jiebo Industrial Co., Ltd., with a mesh size of 5mm × 5mm and a basis weight of 15g / m². 2 .

[0029] Preparation examples of raw materials and / or intermediates Preparation Example 1 A modified polyimide film layer is prepared by the following steps: S1. Phenethyltriethoxysilane, deionized water and N,N-dimethylacetamide are heated and stirred together, and then cooled after heat treatment to obtain silica sol; Aluminum isopropoxide and toluene are heated and mixed, and then deionized water is added while stirring. After high-temperature reaction, the mixture is cooled to obtain alumina sol. S2. Mix 4,4'-diaminodiphenyl ether and N,N-dimethylacetamide, then add the silica sol and alumina sol obtained in step S1 and stir for 30 min. Then, under ice-water bath conditions, add pyromellitic dianhydride in six equal batches and stir for 6 h. After stirring, lay the film and then heat it to perform thermal imidization. The thermal imidization operation is to keep the film at 80℃, 120℃, 150℃, 250℃ and 300℃ in an oven for 0.5 h each, and then cool it to obtain the modified polyimide film layer.

[0030] Note: In step S1 above, phenethyltriethoxysilane, deionized water, and N,N-dimethylacetamide were heated to 65°C and stirred to obtain silica sol after heat treatment and cooling. The heat treatment process involved stabilizing at 85°C for 3 hours, stabilizing at 112.5°C for 40 minutes, and finally cooling to 65°C. Aluminum isopropoxide and toluene were heated to 65°C and mixed. Deionized water was then added during stirring, and the mixture was reacted at 265°C for 5.5 hours before cooling to obtain alumina sol. The weight ratio of aluminum isopropoxide, toluene, and deionized water was 1:7.5:0.4. In step S2, the weight ratio of silica sol to alumina sol is 4:1; the weight ratio of 4,4'-diaminodiphenyl ether, N,N-dimethylacetamide, and pyromellitic dianhydride is 1:5:1; and the total amount of silica sol and alumina sol is 13% of the mixed weight of 4,4'-diaminodiphenyl ether, N,N-dimethylacetamide, and pyromellitic dianhydride.

[0031] Preparation Example 2 A modified polyimide film layer differs from Preparation Example 1 in that, in step S1, phenethyltriethoxysilane, deionized water, and N,N-dimethylacetamide are heated to 60°C and stirred to mix in a weight ratio of 1:0.4:8. After heat treatment, the mixture is cooled to obtain a silica sol. The heat treatment operation involves stabilizing at 80°C for 3.5 hours, stabilizing at 110°C for 45 minutes, and finally cooling to 60°C.

[0032] Preparation Example 3 A modified polyimide film layer differs from Preparation Example 1 in that, in step S1, phenethyltriethoxysilane, deionized water, and N,N-dimethylacetamide are heated to 70°C and stirred to mix in a weight ratio of 1:0.8:15. After heat treatment, the mixture is cooled to obtain a silica sol. The heat treatment operation involves stabilizing at 90°C for 2.5 hours, stabilizing at 115°C for 35 minutes, and finally cooling to 70°C.

[0033] Preparation Example 4 A modified polyimide film layer differs from Preparation Example 1 in that, in step S1, aluminum isopropoxide and toluene are heated to 60°C and mixed, and then deionized water is added during stirring. After reacting at 250°C for 6 hours, the mixture is cooled to obtain alumina sol. The weight ratio of aluminum isopropoxide, toluene and deionized water used is 1:5:0.3.

[0034] Preparation Example 5 A modified polyimide film layer differs from Preparation Example 1 in that, in step S1, aluminum isopropoxide and toluene are heated to 70°C and mixed, and then deionized water is added during stirring. After reacting at 280°C for 5 hours, the mixture is cooled to obtain alumina sol. The weight ratio of aluminum isopropoxide, toluene and deionized water used is 1:10:0.5.

[0035] Preparation Example 6 A modified polyimide film layer, which differs from the preparation example 1 in that, in step S2, the weight ratio of silica sol to alumina sol is 3:1.

[0036] Preparation Example 7 A modified polyimide film layer, which differs from the preparation example 1 in that, in step S2, the weight ratio of silica sol to alumina sol is 5:1.

[0037] Preparation Example 8 A modified polyimide thin film layer differs from Preparation Example 1 in that, in step S2, a functional additive is added and mixed with silica sol and alumina sol. The functional additive constitutes 6.5% of the total weight of the silica sol and alumina sol, and is composed of carbon nitride and boron nitride in a weight ratio of 1:5. Both carbon nitride and boron nitride have layered nanosheet structures with a diameter of 2 μm, a thickness of 4 nm, and a specific surface area of ​​250 m². 2 / g.

[0038] Preparation Example 9 A modified polyimide film layer, which differs from Preparation Example 8 in that the functional additive is 5% of the total weight of silica sol and alumina sol.

[0039] Preparation Example 10 A modified polyimide film layer, which differs from Preparation Example 8 in that the functional additive is 8% of the total weight of silica sol and alumina sol.

[0040] Preparation Example 11 A modified polyimide film layer, which differs from Preparation Example 8 in that the functional additives are composed of carbon nitride and boron nitride in a weight ratio of 1:4.

[0041] Preparation Example 12 A modified polyimide film layer, which differs from Preparation Example 8 in that the functional additives are composed of carbon nitride and boron nitride in a weight ratio of 1:6.

[0042] Preparation Example 13 A modified polyimide thin film layer, differing from Preparation Example 8, wherein the carbon nitride and boron nitride are both layered nanosheet structures with a diameter of 1 μm, a thickness of 3 nm, and a specific surface area of ​​200 m². 2 / g.

[0043] Preparation Example 14 A modified polyimide thin film layer, differing from Preparation Example 8, wherein the carbon nitride and boron nitride are both layered nanosheet structures with a diameter of 3 μm, a thickness of 5 nm, and a specific surface area of ​​300 m². 2 / g.

[0044] Preparation Example 15 A modified polyimide film layer, which differs from Preparation Example 8 in that carbon nitride, one of the functional additives, is not used.

[0045] Preparation Example 16 A modified polyimide film layer, which differs from Preparation Example 8 in that boron nitride, one of the functional additives, is not used.

[0046] Preparation Example 17 A modified polyimide film layer, which differs from Preparation Example 1 in that it does not use silica sol.

[0047] Preparation Example 18 A modified polyimide film layer, which differs from Preparation Example 1 in that it does not use alumina sol.

[0048] Preparation Example 19 A modified polyimide film layer, which differs from Preparation Example 1 in that it does not use silica sol and alumina sol.

[0049] Preparation Example 20 A modified polyimide film layer, which differs from Preparation Example 8 in that it does not use silica sol and alumina sol.

[0050] Example Example 1 A tear-resistant polyimide film for aerospace applications is composed of a substrate layer and a reinforcing layer bonded together with hot melt adhesive, and the specific preparation steps are as follows: (1) Prepare the raw materials for the substrate layer, the reinforcing layer and the hot melt adhesive; (2) The substrate layer and the reinforcing layer in step (1) are preheated, and then hot melt adhesive is applied between the substrate layer and the reinforcing layer. The film is then hot-pressed to obtain a tear-resistant polyimide film for aerospace applications.

[0051] Note: The substrate layer in the above operation is a modified polyimide film layer, obtained from Preparation Example 1; the reinforcing layer is a square fiberglass mesh; and the substrate layer thickness is 0.01 mm, and the hot melt adhesive thickness is 0.02 mm.

[0052] Example 2 A tear-resistant polyimide film for aerospace applications, differing from Example 1 in that the modified polyimide film layer was obtained from Preparation Example 2.

[0053] Example 3 A tear-resistant polyimide film for aerospace applications, differing from Example 1 in that the modified polyimide film layer was obtained from Preparation Example 3.

[0054] Example 4 A tear-resistant polyimide film for aerospace applications, differing from Example 1 in that the modified polyimide film layer was obtained from Preparation Example 4.

[0055] Example 5 A tear-resistant polyimide film for aerospace applications, differing from Example 1 in that the modified polyimide film layer was obtained from Preparation Example 5.

[0056] Example 6 A tear-resistant polyimide film for aerospace applications, differing from Example 1 in that the modified polyimide film layer was obtained from Preparation Example 6.

[0057] Example 7 A tear-resistant polyimide film for aerospace applications, differing from Example 1 in that the modified polyimide film layer was obtained from Preparation Example 7.

[0058] Example 8 A tear-resistant polyimide film for aerospace applications, differing from Example 1 in that the modified polyimide film layer was obtained from Preparation Example 8.

[0059] Example 9 A tear-resistant polyimide film for aerospace applications, differing from Example 1 in that the modified polyimide film layer was obtained from Preparation Example 9.

[0060] Example 10 A tear-resistant polyimide film for aerospace applications, differing from Example 1 in that the modified polyimide film layer was obtained from Preparation Example 10.

[0061] Example 11 A tear-resistant polyimide film for aerospace applications, differing from Example 1 in that the modified polyimide film layer was obtained from Preparation Example 11.

[0062] Example 12 A tear-resistant polyimide film for aerospace applications, differing from Example 1 in that the modified polyimide film layer was obtained from Preparation Example 12.

[0063] Example 13 A tear-resistant polyimide film for aerospace applications, differing from Example 1 in that the modified polyimide film layer was obtained from Preparation Example 13.

[0064] Example 14 A tear-resistant polyimide film for aerospace applications, differing from Example 1 in that the modified polyimide film layer was obtained from Preparation Example 14.

[0065] Example 15 A tear-resistant polyimide film for aerospace applications differs from Example 1 in that the modified polyimide film layer was obtained from Preparation Example 15.

[0066] Example 16 A tear-resistant polyimide film for aerospace applications, differing from Example 1 in that the modified polyimide film layer was obtained from Preparation Example 16.

[0067] Comparative Example Comparative Example 1 A tear-resistant polyimide film for aerospace applications, differing from Example 1 in that the modified polyimide film layer was obtained from Preparation Example 17.

[0068] Comparative Example 2 A tear-resistant polyimide film for aerospace applications, differing from Example 1 in that the modified polyimide film layer was obtained from Preparation Example 18.

[0069] Comparative Example 3 A tear-resistant polyimide film for aerospace applications, differing from Example 1 in that the modified polyimide film layer was obtained from Preparation Example 19.

[0070] Comparative Example 4 A tear-resistant polyimide film for aerospace applications, differing from Example 1 in that the modified polyimide film layer was obtained from Preparation Example 20.

[0071] Performance testing Test samples: The tear-resistant polyimide film for aerospace obtained in Examples 1-16 was selected as test sample 1-16, and the tear-resistant polyimide film for aerospace obtained in Comparative Examples 1-4 was selected as control sample 1-4.

[0072] Test method: Take a tear-resistant polyimide film used in aerospace and test its tear resistance using a tear tester. The obtained tear resistance value is recorded as the initial value A. Then, the same type of tear-resistant polyimide film used in aerospace was placed in a high and low temperature alternating test chamber. The initial temperature was 25℃. The temperature was first increased to 400℃ at 5℃ / min and held for 30min. Then, the temperature was decreased to -70℃ at 3℃ / min and held for 15min. Then, the temperature was increased to 25℃ at 2℃ / min. This was recorded as 1 cycle. After 50 cycles, the above test was performed again in the same way. The resulting tear resistance value was recorded as test value B. Finally, the tear strength loss rate of the ripstop polyimide film used in aerospace was calculated under severe temperature change conditions. Tear strength loss rate = (AB) / A. The lower the tear strength loss rate, the better the skin feel stability of the ripstop polyimide film used in aerospace under severe temperature change conditions.

[0073] After performing the above tests on test samples 1-16 and control samples 1-4, the test results are recorded in Table 1.

[0074] Table 1. Test results of test samples 1-16 and control samples 1-4 sample Tear strength loss rate (%) Test sample 1 7.32 Test sample 2 7.43 Test sample 3 7.38 Test sample 4 7.39 Test sample 5 7.41 Test sample 6 7.36 Test sample 7 7.40 Test sample 8 4.17 Test sample 9 4.24 Test sample 10 4.21 Test sample 11 4.19 Test sample 12 4.23 Test sample 13 4.20 Test sample 14 4.22 Test sample 15 6.09 Test sample 16 5.96 Control sample 1 10.74 Control sample 2 10.65 Control sample 3 13.48 Control sample 4 10.52 As can be seen from Examples 1-7 and Comparative Examples 1-3, and Table 1, the synergistic application of silica sol and alumina sol in the preparation of modified polyimide film layers significantly improves tear resistance stability under frequent and drastic temperature changes. Consequently, the tear strength loss rate of the final aerospace-grade tear-resistant polyimide film is significantly reduced after the aforementioned tests. Furthermore, while using silica sol or alumina sol alone in the preparation of modified polyimide film layers can improve tear resistance stability, the improvement is limited, and the combined effect of their individual use is far less than the superior effect of their combined use. Therefore, the use of silica sol and alumina sol in the preparation of modified polyimide film layers ultimately yields a significant improvement effect greater than the sum of its parts (1+1>2).

[0075] Combining Examples 1 and 8-14 with Table 1, it can be seen that in the preparation of the modified polyimide film layer, by using functional additives mixed with silica sol and alumina sol, and utilizing the synergistic effect between carbon nitride and boron nitride in the functional additives, the tear strength loss rate of the final aerospace-grade tear-resistant polyimide film is further significantly reduced after the above tests. Furthermore, combining Examples 15-16 with Table 1, it can be seen that the combination of carbon nitride and boron nitride can bring about a compound improvement effect, while the improvement effect brought by using them alone is limited. Combined with Comparative Examples 3-4 and Table 1, it can be seen that if silica sol and alumina sol are not used in the preparation of the modified polyimide film layer, the corresponding improvement effect brought about by the application of functional additives will be significantly reduced. This shows that the interaction system formed by silica sol and alumina sol can complement and enhance the interaction system formed by carbon nitride and boron nitride, and ultimately obtain a tear-resistant polyimide film with better application quality for aerospace.

[0076] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A tear-resistant polyimide film for aerospace applications, characterized in that, It is composed of a substrate layer and a reinforcing layer bonded together with hot melt adhesive; the substrate layer is a modified polyimide film layer, which is prepared by the following steps: S1. Phenethyltriethoxysilane, deionized water and N,N-dimethylacetamide are heated and stirred together, and then cooled after heat treatment to obtain silica sol; Aluminum isopropoxide and toluene are heated and mixed, and then deionized water is added while stirring. After high-temperature reaction, the mixture is cooled to obtain alumina sol. S2. Mix 4,4'-diaminodiphenyl ether and N,N-dimethylacetamide, then add the silica sol and alumina sol obtained in step S1 and stir to mix. Then, under ice-water bath conditions, add pyromellitic dianhydride in batches and stir. After stirring, lay the film, then heat to perform thermal imidization, and finally cool to obtain the modified polyimide film layer.

2. The tear-resistant polyimide film for aerospace applications according to claim 1, characterized in that: In step S1, phenethyltriethoxysilane, deionized water, and N,N-dimethylacetamide are heated to 60-70°C and stirred to mix in a weight ratio of 1:(0.4-0.8):(8-15). After heat treatment, the mixture is cooled to obtain silica sol. The heat treatment operation is as follows: first, stabilize at 80-90°C for 2.5-3.5 hours, then stabilize at 110-115°C for 35-45 minutes, and finally cool down to 60-70°C.

3. The tear-resistant polyimide film for aerospace applications according to claim 1, characterized in that: In step S1, aluminum isopropoxide and toluene are heated to 60-70℃ and mixed. Then, deionized water is added while stirring. After reacting at 250-280℃ for 5-6 hours, the mixture is cooled to obtain alumina sol. The weight ratio of aluminum isopropoxide, toluene and deionized water used is 1: (5-10): (0.3-0.5).

4. The tear-resistant polyimide film for aerospace applications according to claim 1, characterized in that: In step S2, the weight ratio of silica sol to alumina sol is (3-5):

1.

5. The tear-resistant polyimide film for aerospace applications according to claim 1, characterized in that: In step S2, a functional additive is also added and mixed with silica sol and alumina sol. The functional additive accounts for 5-8% of the total weight of silica sol and alumina sol, and the functional additive is composed of carbon nitride and boron nitride, with a weight ratio of carbon nitride to boron nitride of 1:(4-6).

6. The tear-resistant polyimide film for aerospace applications according to claim 5, characterized in that: The weight ratio of carbon nitride to boron nitride is 1:

5.

7. The tear-resistant polyimide film for aerospace applications according to claim 5, characterized in that: Both the carbon nitride and boron nitride described herein have a layered nanosheet structure with a diameter of 1-3 μm, a thickness of 3-5 nm, and a specific surface area of ​​200-300 m². 2 / g.

8. The tear-resistant polyimide film for aerospace applications according to claim 1, characterized in that: The reinforcing layer is any one of a square fiberglass mesh, nylon mesh, and polyester mesh.

9. The method for preparing the tear-resistant polyimide film for aerospace applications according to claim 1, characterized in that: Includes the following steps: (1) Prepare the raw materials for the substrate layer, the reinforcing layer and the hot melt adhesive; (2) The substrate layer and the reinforcing layer in step (1) are preheated, and then hot melt adhesive is applied between the substrate layer and the reinforcing layer. The film is then hot-pressed to obtain a tear-resistant polyimide film for aerospace applications.