Flexible polyimide composite film for spaceflight and preparation method of flexible polyimide composite film

Abstract

The invention particularly relates to a polyimide flexible composite film for spaceflight and a preparation method of the polyimide flexible composite film. The polyimide flexible composite film for spaceflight comprises an optical function layer, a supporting layer, a bonding layer and a reinforcing layer which are sequentially stacked. According to the invention, through the design and preparation process of the four-layer structure composite film, the product weight reduction is realized, the weight is reduced compared with the existing product, and the launch cost of a spacecraft can be reduced; the heat control performance is good, the solar absorption ratio of an aluminized surface is low, the hemispherical emissivity is low, the alpha s / epsilon h ratio is small, and the heat control characteristic is superior to that of a traditional aluminized film; an ultra-thin structure design is adopted, and the thickness is smaller than that of existing similar products; by introducing the silicon dioxide protective layer, the tolerance of the aluminum layer to atomic oxygen is improved, the service life of the material in a space environment is prolonged, the optical performance change is small after a thermal cycle test, and the material has good environmental adaptability; meanwhile, certain electromagnetic shielding capability is achieved, and the aerospace application requirement can be met.

Description

Technical Field

[0001] This invention relates to a flexible polyimide composite film for aerospace applications and its preparation method, belonging to the field of aerospace materials technology. Background Technology

[0002] In spacecraft thermal control systems, flexible thermal control thin film materials are widely used for critical functions such as surface thermal protection, infrared radiation modulation, and atomic oxygen shielding. These materials need to maintain stable optical and mechanical properties over long periods under extreme space environments (such as high vacuum, strong ultraviolet radiation, atomic oxygen corrosion, and significant temperature fluctuations). Currently, polyimide (PI)-based thin films have become one of the mainstream flexible substrates in the aerospace field due to their excellent temperature resistance, low outgassing rate, and good mechanical properties. Furthermore, by depositing an aluminum layer on the surface of the PI film, its solar reflectivity and infrared emissivity can be significantly improved, thereby achieving highly efficient thermal control functions.

[0003] While existing technologies have improved the adhesion between the metal layer and the substrate to some extent, the following prominent problems still exist: The existing aluminum-coated PI films are mostly two- or three-layer structures (such as substrate / aluminum layer / protective layer), lacking a systematic design for lightweight, high durability, and multi-faceted functional control. Especially in deep space exploration missions, spacecraft have extremely stringent requirements for material areal density, and existing technologies have failed to effectively resolve the contradiction between high reflectivity and low areal density.

[0004] Insufficient tolerance to atomic oxygen: The low Earth orbit (LEO) environment is rich in highly reactive atomic oxygen, which has a strong corrosive effect on organic materials (such as polyimide). Although existing aluminized thin films have protective layers such as silica to slow down oxidation, they still suffer from problems such as mass loss and delamination and cracking under long-term exposure.

[0005] Thermal control performance of non-aluminized surfaces has been neglected: Existing technologies mainly focus on the optical properties of aluminized working surfaces (such as low solar absorptivity αs and high hemispherical emissivity εh), while lacking means to control the thermal radiation characteristics of non-aluminized surfaces. This makes it difficult for spacecraft to achieve precise thermal balance control in complex thermal environments, limiting their application in high-precision detection missions.

[0006] Poor compatibility between the reinforcing structure and functional layers: To improve mechanical strength, some technologies use PI woven fabric as a reinforcing layer. However, its surface roughness and chemical inertness result in insufficient bonding with the adhesive layer and functional layers, making it prone to delamination defects during thermal cycling. Existing technologies have not proposed effective interface modification solutions.

[0007] Therefore, existing technologies in the field of aluminized polyimide films for aerospace applications still suffer from key technical bottlenecks such as unreasonable structural design, poor atomic oxygen durability, lack of thermal control functions on non-working surfaces, and weak interfacial bonding of the reinforcing layer. How to achieve lightweight, high durability, and multi-functional integration while ensuring high optical performance has become a pressing technical challenge in this field. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a flexible polyimide composite film for aerospace applications and its preparation method.

[0009] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a flexible polyimide composite film for aerospace applications, the flexible polyimide composite film for aerospace applications comprising an optical functional layer, a support layer, an adhesive layer and a reinforcing layer stacked sequentially; This invention, through a multi-layered integrated design, effectively solves the problems of unreasonable structural design, poor atomic oxygen resistance, lack of thermal control function on non-working surfaces, and weak interfacial bonding of reinforcing layers in existing technologies, achieving lightweight, high durability, and multi-faceted functional control. Specifically, the optical functional layer includes an aluminum coating and a silica protective layer on its surface. The aluminum coating provides high reflectivity, while the silica protective layer protects the aluminum coating from atomic oxygen corrosion, thereby enhancing atomic oxygen resistance. The support layer uses a polyimide film of a specific thickness to provide basic mechanical strength and flexible support. The adhesive layer uses a polyimide adhesive of a specific thickness to ensure a firm bond between the support layer and the reinforcing layer, preventing delamination. The reinforcing layer uses a polyimide woven fabric of a specific thickness to enhance overall mechanical properties, and its surface is coated with a polyimide coating containing titanium dioxide nanoparticles. This coating controls the thermal radiation characteristics of the non-working surface by controlling the particle size, concentration, and thickness of the nanoparticles, solving the problem of lack of thermal control function on the non-working surface. The total thickness, areal density, and optical performance parameters of the overall composite film ensure a balance between lightweight and high optical performance.

[0010] The optical functional layer includes an aluminum coating and a silicon dioxide protective layer located on the surface of the aluminum coating; The support layer is a polyimide film with a thickness of 20-30 μm; The specific values ​​of 20-30 can be 20, 21, 22, 23, 24, 25, 26.5, 27, 28.9, 30, etc.

[0011] The adhesive layer is a polyimide adhesive with a thickness of 5-10 μm; the specific value of 5-10 can be 5, 6, 7, 8, 8.5, 9, 9.2, 9.8, 10, etc., and any specific value within the above range can be selected.

[0012] The reinforcing layer is a polyimide woven fabric with a thickness of 20-30 μm, and the surface of the reinforcing layer is provided with a polyimide coating containing titanium dioxide nanoparticles. The titanium dioxide nanoparticles have a particle size of 10-30 nm, a concentration of 3-8 wt%, and a coating thickness of 0.5-2 μm. The specific values ​​of 20-30 can be 20, 22, 24, 25, 26, 27.5, 28, 29, 30, etc.; The specific values ​​of 10-30 can be 10, 12, 15, 18, 20, 22, 25, 28, 30, etc. The specific values ​​of 3-8 can be 3, 4, 5, 5.5, 6, 6.8, 7, 7.5, 8, etc.; The specific value of 0.5-2 can be 0.5, 0.8, 1.0, 1.2, 1.5, 1.8, 2.0, etc., and any specific value within the above range can be selected.

[0013] The composite film has a total thickness of 45-70 μm and an areal density of ≤110 g / m³. 2 The aluminized surface has a solar absorptivity of ≤0.05 and a hemispherical emissivity of ≤0.06.

[0014] The specific values ​​of 45-70 can be 45, 46, 47, 48, 48.5, 49, 50, 51, 52, 53, 54, 55, 60, 65, 70, etc., and any specific point value within the above range can be selected.

[0015] Preferably, the thickness of the aluminum coating is 0.8-1.2 μm, and the thickness of the silicon dioxide protective layer is 40-60 nm. The specific values ​​for 0.8-1.2 can be 0.8, 0.9, 0.95, 1.0, 1.05, 1.1, 1.2, etc.; the specific values ​​for 40-60 can be 40, 45, 48, 50, 52, 55, 58, 60, etc., and any specific value within the above range can be selected.

[0016] Preferably, the polyimide adhesive is prepared by mixing thermoplastic polyimide resin and solvent in a mass ratio of 25-35:65-75. The specific values ​​of 25-35:65-75 can be 25:75, 28:72, 30:70, 32:68, 35:65, etc., and any specific ratio within the above range can be selected.

[0017] The composite film has an aluminized polyimide side hemispherical emissivity of 0.05-0.1, a polyimide woven fabric side solar absorptivity of 0.30-0.35, and a hemispherical emissivity of 0.75-0.80.

[0018] The specific values ​​of 0.05-0.1 can be 0.05, 0.063, 0.07, 0.08, 0.09, 0.1, etc.; The specific values ​​of 0.30-0.35 can be 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, etc.; The specific values ​​of 0.75-0.80 can be 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, etc., and any specific point value within the above range can be selected.

[0019] Preferably, the polyimide woven fabric in the reinforcing layer is subjected to hot pressing treatment at a temperature of 120-200°C.

[0020] The specific values ​​of 120-200 can be 120, 130, 140, 150, 160, 170, 180, 190, 200, etc., and any specific point value within the above range can be selected.

[0021] In a second aspect, the present invention provides a method for preparing the composite thin film described in the first aspect, the method comprising the following steps: (1) Provide a polyimide film as a support layer; (2) An aluminum coating and a silicon dioxide protective layer are deposited on the surface of the support layer to form an optical functional layer; (3) Coat the other surface of the support layer with polyimide adhesive as an adhesive layer; (4) Polyimide woven fabric is used as a reinforcing layer and is composited with the support layer through the adhesive layer; (5) Coating the surface of the reinforcing layer with a polyimide coating containing titanium dioxide nanoparticles.

[0022] The preparation method of this invention systematically solves the core problems that have long existed in the prior art, such as weak interfacial bonding, unstable deposition quality, and lack of thermal control on the non-working surface, through a series of closely related process steps, thereby significantly improving the overall performance and on-orbit reliability of the composite film. Specifically, this is reflected in: This invention selects polyimide film as the support layer, and utilizes its excellent mechanical properties and thermal stability to provide a high-quality substrate for the precise and stable deposition of subsequent multilayer structures.

[0023] Addressing the challenges of deposition quality and durability: To address the technical pain point of unstable optical functional layer deposition, a precisely controlled magnetron sputtering process is employed. By strictly controlling vacuum level, substrate temperature, and deposition rate, the uniformity, density, and defect-free nature of the optical coating are ensured, fundamentally enhancing its resistance to atomic oxygen erosion.

[0024] This invention uses a specially formulated polyimide adhesive to form a bonding layer, solving the problem of insufficient bonding strength between different materials, especially with the surface of the reinforcement layer. This adhesive layer effectively wets and penetrates to the surface of the reinforcement layer, forming a strong chemical and physical bond, ensuring that the composite film maintains its structural integrity and does not delaminate under extreme high and low temperature cycling.

[0025] By introducing polyimide woven fabric as a reinforcing layer and combining it with the aforementioned high-efficiency adhesive layer, the tensile and tear resistance of the entire film material is improved, meeting the stringent requirements for high reliability in aerospace applications.

[0026] By coating the outer surface of the reinforcing layer with a special coating containing titanium dioxide nanoparticles, specific thermal radiation characteristics are creatively endowed to the non-working surface of the film, enabling precise thermal management of the spacecraft in all aspects and overcoming the major limitation of existing technologies that can only be controlled on one side.

[0027] Preferably, the surface of the support layer in step (1) is subjected to corona treatment with a treatment voltage of 5-10 kV. The specific value of 5-10 can be 5, 6, 7, 8, 9, 10, etc., and any specific point value within the above range can be selected.

[0028] Preferably, the optical functional layer in step (2) is prepared by magnetron sputtering; the silicon dioxide protective layer of the optical functional layer is prepared by electron beam evaporation; the parameters of the electron beam evaporation deposition process are: oxygen partial pressure 3 × 10⁻⁶. -3 Pa-8×10 -3 Pa, deposition rate 0.08-0.12 nm / s The 3×10 -3 Pa-8×10 -3 The specific value of Pa can be 3 × 10 -3 4×10 -3 5×10 -3 6×10 -3 7×10 -3 8×10 -3 All specific point values ​​within the above range can be selected.

[0029] Preferably, the specific parameters of the magnetron sputtering process in step (2) are: controlling the vacuum degree ≤ 1×10 -4 Pa, substrate temperature 80-120℃, deposition rate 0.04-0.06 μm / min; The specific values ​​of 80-120 can be 80, 90, 100, 110, 120, etc.; the specific values ​​of 0.04-0.06 can be 0.04, 0.045, 0.05, 0.055, 0.06, etc., and any specific point value within the above range can be selected.

[0030] Preferably, the titanium dioxide nanoparticles in step (5) are ground to D using a sand mill. 50 Use after <100nm.

[0031] Compared with the prior art, the present invention has the following beneficial effects: This invention achieves lightweighting through the design and controlled fabrication process of a four-layer composite thin film, reducing weight by more than 20% compared to existing products, thus helping to lower spacecraft launch costs. It also exhibits excellent thermal control performance, with low solar absorptivity on the aluminized surface, low hemispherical emissivity, and a small αs / εh ratio, demonstrating superior thermal control characteristics compared to traditional aluminized thin films. Furthermore, it employs an ultra-thin structural design, with a thickness less than existing similar products. The introduction of a silicon dioxide protective layer improves the aluminum layer's resistance to atomic oxygen, extending the material's lifespan in the space environment. After thermal cycling testing, its optical performance shows minimal change, demonstrating good environmental adaptability. Simultaneously, it possesses a certain level of electromagnetic shielding capability, meeting the requirements of aerospace applications. Detailed Implementation

[0032] The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0033] Example 1 This embodiment provides a flexible polyimide composite film for aerospace applications and its preparation method. The specific steps are as follows: (1) Corona treatment of polyimide film surface A 25 μm thick polyimide film was selected and fed into a corona treatment machine. The treatment parameters were set as follows: voltage 8 kV, electrode spacing 30 mm, and the bombardment current density was stabilized at 0.8 mA / cm² by adjusting the treatment speed. 2 The film surface was uniformly bombarded, and the surface roughness (Ra) of the film after treatment was measured to reach 0.32 μm, in order to improve surface energy and adhesion.

[0034] (2) Vacuum environment preparation The corona-treated polyimide film is loaded onto the reel of the vacuum-wound magnetron sputtering system, and the cavity is closed. The vacuum pump unit is started to evacuate the sputtering chamber until the vacuum level inside the chamber reaches ≤1×10⁻⁶. -4 Pa.

[0035] (3) Aluminum layer deposition In the aforementioned vacuum environment, an aluminum target with a purity of 99.99% is bombarded using electron beam evaporation technology, causing aluminum atoms to vaporize and be uniformly deposited in an ionic state on the surface of a polyimide film, forming a dense aluminum metal layer.

[0036] (4) Deposition of silica protective layer The single-sided aluminized polyimide film with the aluminum layer deposited is reverse-wound using a high-precision rewinding machine. During the rewinding process, the film surface undergoes online optical inspection to confirm the absence of scratches, pinholes, and particle defects. The film is then reloaded into the sputtering equipment. The target material is then replaced with a high-purity silica target, and the vacuuming process in step 2 and the deposition process in step 3 are repeated to deposit a silica protective layer on the aluminum layer surface, forming a three-layer composite film of polyimide / aluminum / silica.

[0037] (5) Preparation of titanium dioxide suspension Titanium dioxide nanoparticles with a particle size of 50 nm were weighed and added to an oily solvent at a mass ratio of TiO2:silicone oil = 1:7. A polymeric dispersant was then added at 5% of the titanium dioxide powder mass. After preliminary stirring to form a slurry, the mixture was transferred to a ceramic sand mill. Zirconia beads with a diameter of 0.2 mm were loaded as grinding media, and the mill was circulated and ground at 2000 rpm for 3 hours. Samples were taken periodically during the grinding process and monitored using a Brookfield viscometer until the viscosity of the suspension reached 3.2 Pa·s and the particle size distribution D was measured by a laser particle size analyzer. 50 When the particle size is less than 100 nm, stop grinding to obtain a stable and uniform titanium dioxide suspension.

[0038] (6) Functional layer coating Polyimide woven fabric was selected as the reinforcing substrate, and the prepared titanium dioxide suspension was uniformly coated onto the surface of the polyimide woven fabric using a high-precision slit extrusion coating machine.

[0039] (7) Preparation of polyimide adhesive Weigh 30% of TPI thermoplastic polyimide resin by mass percentage and add it to 70% of N-methylpyrrolidone organic solvent. Stir continuously for 4 hours in a water bath at 60°C until the resin is completely dissolved to obtain a polyimide adhesive solution with a viscosity of 12 Pa·s.

[0040] (8) Multilayer composite and thermosetting The three-layer film obtained in step (4), the reinforcing cloth processed in step (6), and the adhesive prepared in step 7 are fed together into a high-precision coating composite line with a clamshell oven structure.

[0041] Coating and lamination: The adhesive solution is coated onto the surface of the silica protective layer of the three-layer film, and then laminated with the reinforcing fabric.

[0042] Gradient drying: The composite membrane is sequentially passed through a three-stage gradient oven set at 150℃, 180℃, and 80℃ to remove the solvent.

[0043] High-temperature curing: Finally, bake at 280℃ for 10 minutes to fully imidize and cure the polyimide resin, forming a strong multilayer composite structure.

[0044] Example 2 This embodiment aims to provide a lightweight composite film with a thinner overall thickness and lower areal density. The specific preparation steps are as follows: (1) Corona treatment of polyimide film surface A 12.5 μm thick aerospace-grade polyimide film was selected and fed into a corona treatment machine. The treatment parameters were set the same as in Example 1: voltage 8 kV, electrode spacing 30 mm, and the bombardment current density was stabilized at 0.8 mA / cm² by adjusting the treatment speed. 2 The film surface was subjected to uniform bombardment treatment, and the surface roughness (Ra) of the film was measured to reach 0.30 μm after treatment to ensure that the surface energy and subsequent interlayer adhesion meet the requirements.

[0045] (2) Vacuum environment preparation The corona-treated polyimide film is loaded onto the reel of the vacuum-wound magnetron sputtering system, and the cavity is closed. The vacuum pump unit is started to evacuate the sputtering chamber until the vacuum level inside the chamber reaches 5 × 10⁻⁶. -5 Pa.

[0046] (3) Aluminum layer deposition In the aforementioned vacuum environment, an aluminum target with a purity of 99.99% is bombarded using electron beam evaporation technology, causing aluminum atoms to vaporize and be uniformly deposited in an ionic state on the surface of a polyimide film, forming a dense aluminum metal reflective layer with a thickness controlled at 90 nm.

[0047] (4) Deposition of silica protective layer The operating steps are basically the same as in Example 1: The single-sided aluminum-coated polyimide film with the aluminum layer deposited is reverse-wound using a high-precision rewinding machine. During the rewinding process, the film surface is subjected to online optical inspection. After confirming that there are no scratches, pinholes, or particle defects, the film is reloaded into the sputtering equipment. The target material is changed to a high-purity silica target, and the vacuuming process in step 2 and the deposition process in step 3 are repeated to deposit a silica protective layer on the aluminum layer surface. The thickness of the silica layer is controlled to be 70 nm, forming a polyimide / aluminum / silica three-layer composite film.

[0048] (5) Preparation of titanium dioxide suspension The operating steps, raw material ratios, and process parameters were completely consistent with those in Example 1: Titanium dioxide nanoparticles with a particle size of 50 nm were weighed and added to an oily solvent at a mass ratio of TiO2:silicone oil = 1:7; then, a polymeric dispersant was added at 5% of the mass of the titanium dioxide powder. After preliminary stirring to form a slurry, the mixture was transferred to a ceramic sand mill. Zirconia beads with a diameter of 0.2 mm were loaded as the grinding media, and the mixture was circulated and ground at 2000 rpm for 3 hours. Samples were taken periodically during the grinding process and monitored using a Brookfield viscometer until the viscosity of the suspension reached 3.2 Pa·s, and the particle size distribution D was measured by a laser particle size analyzer. 50 When the particle size is less than 100 nm, stop grinding to obtain a stable and uniform titanium dioxide suspension.

[0049] (6) Functional layer coating A surface density of 25 g / m³ was selected. 2 Using polyimide fiber woven fabric as the reinforcing substrate, the prepared titanium dioxide suspension was uniformly coated onto the surface of the polyimide woven fabric using a high-precision slit extrusion coating machine. According to the lightweight requirements, the coating thickness was adjusted to 80% of that in Example 1 to ensure that the coating was uniform, without any missed coatings or drips.

[0050] (7) Preparation of polyimide adhesive Weigh 30% of TPI thermoplastic polyimide resin by mass percentage and add it to 70% of N-methylpyrrolidone organic solvent. Stir continuously for 4 hours in a water bath at 60°C until the resin is completely dissolved to obtain a polyimide adhesive solution with a viscosity of 12 Pa·s.

[0051] (8) Multilayer composite and thermosetting The three-layer film obtained in step (4), the reinforcing cloth processed in step (6), and the adhesive prepared in step 7 are fed together into a high-precision coating composite line with a clamshell oven structure.

[0052] Coating and lamination: The adhesive solution is coated on the surface of the silica protective layer of the three-layer film. The thickness of the adhesive coating is adjusted to 75% of that in Example 1 according to the requirements of lightweighting. Then, it is precisely bonded to the reinforcing fabric to ensure no bubbles and no misalignment.

[0053] Gradient drying: The composite film is sequentially passed through a three-stage gradient oven set at 150°C, 180°C, and 80°C to remove the solvent. The drying time is the same as in Example 1.

[0054] High-temperature curing: Finally, bake at 280℃ for 10 minutes to fully imidize and cure the polyimide resin, forming a strong multilayer composite structure.

[0055] Example 3 (1) Corona treatment of polyimide film surface A 25 μm thick polyimide film was selected and fed into a corona treatment machine. The treatment parameters were set as follows: voltage 8 kV, electrode spacing 30 mm, and the bombardment current density was stabilized at 0.8 mA / cm² by adjusting the treatment speed. 2 The film surface was uniformly bombarded, and the surface roughness (Ra) of the film after treatment was measured to reach 0.32 μm, in order to improve surface energy and adhesion.

[0056] (2) Vacuum environment preparation The corona-treated polyimide film is loaded onto the reel of the vacuum-wound magnetron sputtering system, and the cavity is closed. The vacuum pump unit is started to evacuate the sputtering chamber until the vacuum level inside the chamber reaches 8 × 10⁻⁶. -5 Pa.

[0057] (3) Aluminum layer deposition In the aforementioned vacuum environment, an aluminum target with a purity of 99.99% is bombarded using electron beam evaporation technology, causing aluminum atoms to vaporize and be uniformly deposited in an ionic state on the surface of a polyimide film, forming a dense aluminum metal layer.

[0058] (4) Deposition of silica protective layer The single-sided aluminum-coated polyimide film with the aluminum layer deposited is reverse-wound using a high-precision rewinding machine. During the rewinding process, the film surface is subjected to online optical inspection. After confirming that there are no scratches, pinholes, or particle defects, the film is reloaded into the sputtering equipment. The target material is changed to a high-purity silica target, and the vacuuming process in step (2) and the deposition process in step (3) are repeated to deposit a silica protective layer on the aluminum layer surface, forming a polyimide / aluminum / silica three-layer composite film.

[0059] (5) Preparation of titanium dioxide suspension Titanium dioxide nanoparticles with a particle size of 50 nm were weighed and added to an oily solvent at a mass ratio of TiO2:silicone oil = 1:7. A polymeric dispersant was then added at 5% of the titanium dioxide powder mass, adjusting the mass fraction of titanium dioxide powder in the suspension to 25% to enhance the thermal radiation performance of the subsequent functional layer. After initial stirring to form a slurry, the mixture was transferred to a ceramic sand mill. Zirconia beads with a diameter of 0.2 mm were loaded as the grinding media, and the mill was circulated and ground at 2000 rpm for 3 hours. Samples were taken periodically during the grinding process and monitored using a Brookfield viscometer until the suspension viscosity reached 3.5 Pa·s and the particle size distribution D was measured by a laser particle size analyzer. 50 When the particle size is less than 100 nm, stop grinding to obtain a stable and uniform high-concentration titanium dioxide suspension.

[0060] (6) Functional layer coating A polyimide woven fabric with the same specifications as in Example 1 was selected as the reinforcing substrate. The high-concentration titanium dioxide suspension prepared above was uniformly coated onto the surface of the polyimide woven fabric using a high-precision slit extrusion coating machine. The coating thickness was consistent with that in Example 1 to ensure that the coating was uniform, dense, and free of defects.

[0061] (7) Preparation of polyimide adhesive Weigh 30% of TPI thermoplastic polyimide resin by mass percentage and add it to 70% of N-methylpyrrolidone organic solvent. Stir continuously for 4 hours in a water bath at 60°C until the resin is completely dissolved to obtain a polyimide adhesive solution with a viscosity of 12 Pa·s.

[0062] (8) Multilayer composite and thermosetting The three-layer film obtained in step (4), the reinforcing cloth processed in step (6), and the adhesive prepared in step 7 are fed together into a high-precision coating composite line with a clamshell oven structure.

[0063] Coating and lamination: The adhesive solution is coated onto the surface of the silica protective layer of the three-layer film, and then laminated with the reinforcing fabric. The operation steps are the same as in Example 1.

[0064] Gradient drying: The composite film is sequentially passed through a three-stage gradient oven set at 150°C, 180°C and 80°C to remove the solvent. The operation steps are the same as in Example 1.

[0065] High-temperature curing: Finally, bake at 250℃ for 12 minutes to fully imidize and cure the polyimide resin, while ensuring that the titanium dioxide functional layer is firmly bonded to the reinforcing fabric, forming a multi-layer composite structure with excellent thermal control performance.

[0066] Comparative Example 1 The specific preparation steps are as follows: (1) Corona treatment of polyimide film surface A 25 μm thick polyimide film was selected and fed into a corona treatment machine. The treatment parameters were set as follows: voltage 8 kV, electrode spacing 30 mm, and the bombardment current density was stabilized at 0.8 mA / cm² by adjusting the treatment speed. 2 The film surface was uniformly bombarded, and the surface roughness (Ra) of the film after treatment was measured to reach 0.32 μm, in order to improve surface energy and adhesion.

[0067] (2) Vacuum environment preparation The corona-treated polyimide film is loaded onto the reel of the vacuum-wound magnetron sputtering system, and the cavity is closed. The vacuum pump unit is started to evacuate the sputtering chamber until the vacuum level inside the chamber reaches 5 × 10⁻⁶. -4 Pa.

[0068] (3) Aluminum layer deposition In the aforementioned vacuum environment, an aluminum target with a purity of 99.99% is bombarded using electron beam evaporation technology, causing aluminum atoms to vaporize and be uniformly deposited in an ionic state on the surface of a polyimide film, forming a dense aluminum metal layer.

[0069] (4) Deposition of silica protective layer The single-sided aluminized polyimide film with the aluminum layer deposited is reverse-wound using a high-precision rewinding machine. During the rewinding process, the film surface undergoes online optical inspection to confirm the absence of scratches, pinholes, and particle defects. The film is then reloaded into the sputtering equipment. The target material is then replaced with a high-purity silica target, and the vacuuming process in step 2 and the deposition process in step 3 are repeated to deposit a silica protective layer on the aluminum layer surface, forming a three-layer composite film of polyimide / aluminum / silica.

[0070] (5) Preparation of polyimide adhesive Weigh 30% of TPI thermoplastic polyimide resin by mass percentage and add it to 70% of N-methylpyrrolidone organic solvent. Stir continuously for 4 hours in a water bath at 60°C until the resin is completely dissolved to obtain a polyimide adhesive solution with a viscosity of 12 Pa·s.

[0071] (6) Multilayer composite and thermosetting The three-layer film obtained in step (4), the polyimide woven fabric (reinforcing substrate) without functional layer coating, and the adhesive prepared in step (5) are fed together into a high-precision coating composite line with a clamshell oven structure.

[0072] Coating and lamination: An adhesive solution is coated onto the surface of the silica protective layer of the three-layer film, and then directly bonded to an untreated polyimide woven fabric.

[0073] Gradient drying: The composite membrane is sequentially passed through a three-stage gradient oven set at 150℃, 180℃, and 80℃ to remove the solvent.

[0074] High-temperature curing: Finally, bake at 280℃ for 10 minutes to fully imidize and cure the polyimide resin to form a composite film. The exposed side of the reinforcing layer is the original polyimide woven fabric surface without any thermal control coating.

[0075] Comparative Example 2 (1) Corona treatment of polyimide film surface A 25 μm thick polyimide film was selected and fed into a corona treatment machine. The treatment parameters were set as follows: voltage 8 kV, electrode spacing 30 mm, and the bombardment current density was stabilized at 0.8 mA / cm² by adjusting the treatment speed. 2The film surface was uniformly bombarded, and the surface roughness (Ra) of the film after treatment was measured to reach 0.32 μm, in order to improve surface energy and adhesion.

[0076] (2) Vacuum environment preparation The corona-treated polyimide film is loaded onto the reel of the vacuum-wound magnetron sputtering system, and the cavity is closed. The vacuum pump unit is started to evacuate the sputtering chamber until the vacuum level inside the chamber reaches 5 × 10⁻⁶. -4 Pa.

[0077] (3) Aluminum layer deposition In the aforementioned vacuum environment, an aluminum target with a purity of 99.99% is bombarded using electron beam evaporation technology, causing aluminum atoms to vaporize and be uniformly deposited in an ionic state on the surface of a polyimide film, forming a dense aluminum metal layer.

[0078] (4) Deposition of silica protective layer The single-sided aluminized polyimide film with the aluminum layer deposited is reverse-wound using a high-precision rewinding machine. During the rewinding process, the film surface undergoes online optical inspection to confirm the absence of scratches, pinholes, and particle defects. The film is then reloaded into the sputtering equipment. The target material is then replaced with a high-purity silica target, and the vacuuming process in step 2 and the deposition process in step 3 are repeated to deposit a silica protective layer on the aluminum layer surface, forming a three-layer composite film of polyimide / aluminum / silica.

[0079] (5) Preparation of titanium dioxide suspension Titanium dioxide nanoparticles with a particle size of 50 nm were weighed and added to an oily solvent at a mass ratio of TiO2:silicone oil = 1:7. A polymeric dispersant was then added at 5% of the titanium dioxide powder mass. After preliminary stirring to form a slurry, the mixture was transferred to a ceramic sand mill. Zirconia beads with a diameter of 0.2 mm were loaded as the grinding media, and the mill was circulated and ground at 2000 rpm for 3 hours. Samples were taken periodically during the grinding process and measured using a Brookfield viscometer until the viscosity of the suspension reached 3.2 Pa·s and the particle size distribution D was measured by a laser particle size analyzer. 50 When the particle size is less than 100 nm, stop grinding to obtain a stable and uniform titanium dioxide suspension.

[0080] (6) Functional layer coating Polyimide woven fabric was selected as the reinforcing substrate, and the prepared titanium dioxide suspension was uniformly coated onto the surface of the polyimide woven fabric using a high-precision slit extrusion coating machine.

[0081] (7) Multilayer composite and thermosetting The three-layer film obtained in step (4), the reinforcing cloth processed in step (6), and the traditional acrylic pressure-sensitive adhesive are fed together into a high-precision coating composite line with a clamshell oven structure.

[0082] Coating and lamination: A 15μm thick acrylic pressure-sensitive adhesive film is uniformly bonded to the surface of the silica protective layer of the three-layer film through heat transfer, and then precisely bonded to the reinforcing fabric to ensure no bubbles and no misalignment.

[0083] Gradient drying: The composite film is sequentially passed through a three-stage gradient oven set at 120°C, 150°C, and 70°C to remove residual solvent from the pressure-sensitive adhesive. The drying time is the same as in Example 1.

[0084] High-temperature curing: Finally, bake at 180℃ for 8 minutes to complete the curing and shaping of the composite film.

[0085] Test case (1) The aerospace polyimide flexible composite films prepared in Examples 1-3 and Comparative Examples 1-2 were characterized and tested. The test methods are as follows.

[0086] Total thickness: Using an optical interferometer, nine points were selected on the sample surface for measurement and the average value was taken.

[0087] Areal density: Based on GB / T6673 standard, a 100mm×100mm sample was cut and weighed using an electronic balance to calculate the areal density.

[0088] Solar absorptivity α s The results were obtained by measuring the reflectance spectrum in the 250nm-2500nm band and performing a weighted integral of the solar spectrum, according to the GJB2502.2-2007 standard, using an ultraviolet-visible-near-infrared spectrophotometer (with integrating sphere).

[0089] hemispherical emissivity ε h Fourier transform infrared spectrometer was used to measure the reflectance spectrum in the 2.5μm-25μm band according to GJB 2502.3-2015 "Test Methods for Thermal Control Coatings of Spacecraft Part 3: Emissivity Test". The reflectance (R) in the infrared band was measured, and the emissivity was indirectly calculated according to Kirchhoff's law (ε=1-R for opaque objects).

[0090] (2) The surface environmental stability of the aerospace-grade polyimide flexible composite films prepared in Examples 1-3 and Comparative Examples 1-2 was tested. The test methods are as follows: Thermal cycling test: According to GJB 150.5A-2009, the temperature range was set to -196℃ to 300℃, and the cycle was 100 times to test the rate of change of optical performance; Peel strength after thermal cycling: The interlayer peel strength measured after the sample has been cycled 100 times in an environment of -150℃ to +150℃.

[0091] Proton irradiation test: Irradiate with a proton beam generated by an accelerator in a vacuum environment, with a total dose of 100 kGy, and test the retention rate of tensile strength; Changes in αs after atomic oxygen irradiation: The change in solar absorptivity of a sample after being irradiated with an equivalent dose of atomic oxygen for 10 years in a low Earth orbit (LEO) environment.

[0092] Atomic oxygen exposure test: According to T / CSTM01323-2024, the cumulative flux of atomic oxygen is controlled at 5×10⁻⁶. 20 atoms / cm², the mass loss rate is measured.

[0093] The test results are shown in Table 1.

[0094] Table 1. Test results of the examples and comparative samples.

[0095] 1. Peel strength after thermal cycling: The interlayer peel strength of the sample was measured after 100 cycles in an environment ranging from -150°C to 150°C, according to the standard GJB5278-2003.

[0096] 2. Changes in αs after atomic oxygen irradiation: The sample was subjected to a 10-year equivalent dose in a low Earth orbit (LEO) environment (total flux > 1 × 10⁻⁶). 21 atoms / cm 2 The change in solar absorptivity after irradiation with atomic oxygen.

[0097] Comparative examples and contrastive examples show that although conventional thin films are thin and light, they perform extremely poorly in simulated space environment tests. Specifically, their performance degrades after atomic oxygen irradiation, and they lack reinforced structures and double-sided thermal control functions. In contrast, the optical performance of the examples is superior to that of the contrastive examples. Through composite structures and functional coatings, they simultaneously achieve high strength, resistance to atomic oxygen, resistance to high and low temperature cycling, and double-sided thermal control.

[0098] The difference between Comparative Example 1 and Example 1 lies in whether or not they possess a reinforcing layer functional coating. Data shows that the hemispherical emissivity of Comparative Example 1 is only 0.45, far below the >0.8 required for aerospace thermal control, and completely fails to meet industry standards. Example 1, on the other hand, has an emissivity of ≥0.85, significantly higher than Comparative Example 1.

[0099] Comparative Example 2 used a conventional acrylic pressure-sensitive adhesive instead of the specially formulated adhesive layer of this invention, and its initial peel strength at room temperature was acceptable (≥6.0 N / m). After 100 cycles of high and low temperatures, its peel strength after thermal cycling decreased to <0.5 N / m. In contrast, Example 1 maintained a peel strength of ≥8.2 N / m after testing. This demonstrates the excellent performance of the specially formulated polyimide adhesive of this invention. Data from Example 2 shows that, while fully retaining the core technical features of this invention, the areal density can be successfully controlled at 78 g / m² by adjusting the specifications of the substrate and reinforcing layer. 2 This achieves the requirement for lightweight design and saves on space launch costs.

[0100] 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 flexible polyimide composite film for aerospace applications, characterized in that, It includes an optical functional layer, a support layer, an adhesive layer, and a reinforcement layer stacked sequentially. The optical functional layer includes an aluminum coating and a silicon dioxide protective layer located on the surface of the aluminum coating; The support layer is a polyimide film with a thickness of 20-30 μm; The adhesive layer is a polyimide adhesive with a thickness of 5-10 μm; The reinforcing layer is a polyimide woven fabric with a thickness of 20-30 μm, and the surface of the reinforcing layer is provided with a polyimide coating containing titanium dioxide nanoparticles. The titanium dioxide nanoparticles have a particle size of 10-30 nm, a concentration of 3-8 wt%, and a coating thickness of 0.5-2 μm. The total thickness of the composite film is 45-70 μm.

2. The composite film according to claim 1, characterized in that, The thickness of the aluminum coating is 0.8-1.2 μm, and the thickness of the silicon dioxide protective layer is 40-60 nm.

3. The composite film according to claim 1, characterized in that, The polyimide adhesive is prepared by mixing thermoplastic polyimide resin and solvent in a mass ratio of 25-35:65-75.

4. The composite film according to claim 1, characterized in that, The composite film has an aluminized polyimide side hemispherical emissivity of 0.05-0.1, a polyimide woven fabric side solar absorptivity of 0.30-0.35, and a hemispherical emissivity of 0.75-0.

80.

5. The composite film according to claim 1, characterized in that, The polyimide woven fabric is subjected to hot pressing treatment at a temperature of 120-200℃.

6. A method for preparing a composite thin film according to any one of claims 1-5, characterized in that, Includes the following steps: (1) Provide a polyimide film as a support layer; (2) An aluminum coating and a silicon dioxide protective layer are deposited on the surface of the support layer to form an optical functional layer; (3) Coat the other surface of the support layer with polyimide adhesive as an adhesive layer; (4) Polyimide woven fabric is used as a reinforcing layer and is composited with the support layer through the adhesive layer; (5) Coating the surface of the reinforcing layer with a polyimide coating containing titanium dioxide nanoparticles.

7. The preparation method according to claim 6, characterized in that, The surface of the support layer in step (1) is subjected to corona treatment with a treatment voltage of 5-10kV.

8. The preparation method according to claim 6, characterized in that, The optical functional layer in step (2) is prepared by magnetron sputtering; the silicon dioxide protective layer of the optical functional layer is prepared by electron beam evaporation; the parameters for electron beam evaporation are: oxygen partial pressure 3 × 10⁻⁶. -3 Pa-8×10 -3 Pa, deposition rate 0.08-0.12 nm / s.

9. The preparation method according to claim 6, characterized in that, The specific parameters for the magnetron sputtering process in step (2) are to control the vacuum level to ≤1×10⁻⁶. -4 Pa, substrate temperature 80-120℃, deposition rate 0.04-0.06μm / min.

10. The preparation method according to claim 6, characterized in that, The titanium dioxide nanoparticles described in step (5) are ground to D using a sand mill. 50 Use after <100nm.

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