Preparation and application of double-sided aluminized polyimide film for ultra-low temperature multi-layer vacuum insulation

Abstract

The application discloses a kind of ultra-low temperature multilayer vacuum insulation with double-sided aluminum-plated polyimide film preparation and application, it is related to polyimide film preparation technical field.A kind of ultra-low temperature multilayer vacuum insulation with double-sided aluminum-plated polyimide film is formed by polyimide base film and the aluminum plating layer formed on its two surfaces by vacuum evaporation method;The polyimide base film is made of the raw materials comprising the following mass parts formula: phthalic anhydride 100 parts, 4,4'-diamino diphenyl ether, low-temperature modifier 5-15 parts, nano-silica filler 3-8 parts, leveling agent 0.5-2 parts, anti-aging agent 0.5-1.5 parts, silane coupling agent 3-6 parts, polyvinyl chloride 5-15 parts.The specific structure anti-aging agent of the application, its phenolic hydroxyl and benzotriazole structure synergistic effect, can capture free radical, absorb ultraviolet rays, and with polyimide matrix good compatibility, avoid low-temperature precipitation, solve traditional anti-aging agent low-temperature dispersion, easy failure problem, prolong the service life of film.

Description

Technical Field

[0001] This invention relates to the field of polyimide film preparation technology, specifically to the preparation and application of a double-sided aluminized polyimide film for ultra-low temperature multilayer vacuum insulation. Background Technology

[0002] In the field of ultra-low temperature multilayer vacuum insulation, such as LNG storage and transportation and superconducting equipment insulation, insulation materials must simultaneously possess excellent ultra-low temperature resistance, aging resistance, and mechanical toughness. Double-sided aluminized polyimide film, due to its combination of high barrier properties and mechanical strength, has become one of the core substrates in this field. However, polyimide films prepared by existing technologies still have significant shortcomings in practical applications and are difficult to meet the requirements of harsh operating conditions.

[0003] From the perspective of anti-aging performance, ultra-low temperature insulation environments are often accompanied by temperature fluctuations, residual oxygen, and trace amounts of ultraviolet radiation. Traditional polyimide films are prone to molecular chain degradation or oxidative cross-linking, leading to increased film brittleness and decreased barrier properties. Currently used anti-aging agents, such as hindered phenols and phosphites, have poor dispersibility at ultra-low temperatures and insufficient compatibility with the polyimide matrix. They are prone to precipitation after long-term use, failing to maintain their anti-aging effect, thus shortening the service life of the insulation system and increasing maintenance costs.

[0004] In terms of mechanical toughness (toughening), pure polyimide materials have relatively rigid molecular chains, which can easily become brittle in ultra-low temperature environments (below -196℃) due to restricted molecular movement. They are prone to cracking under external impact or vibration, leading to damage to the aluminum coating and failure of the vacuum insulation structure. Current toughening modification methods often involve adding rubber elastomers or flexible polymer segments. However, these modifiers have weak interfacial bonding with the polyimide matrix and are prone to phase separation at low temperatures. This not only fails to effectively improve toughness but also reduces the tensile strength and dimensional stability of the film, making it difficult to balance the requirements of toughness and mechanical properties.

[0005] Furthermore, while the introduction of nanofillers (such as nano-silica) can improve the mechanical properties of films to some extent, nanoparticles tend to agglomerate in traditional processes and cannot be uniformly dispersed in the polyimide matrix. This results in stress concentration points, further exacerbating the risk of brittle fracture at low temperatures. Therefore, developing a double-sided aluminized polyimide film that combines high-efficiency anti-aging properties with excellent low-temperature toughness has become a key direction for overcoming the material bottleneck in the field of ultra-low temperature multilayer vacuum insulation. Summary of the Invention

[0006] The purpose of this invention is to address the problems in the existing technology of poor anti-aging properties (insufficient low-temperature dispersibility and compatibility of traditional anti-aging agents, and easy precipitation), weak low-temperature toughness (pure films or traditionally modified films are prone to brittleness and difficult to balance mechanical properties), and easy agglomeration of nanofillers. The invention provides a method for preparing and applying a double-sided aluminized polyimide film for ultra-low temperature multilayer vacuum insulation that combines excellent anti-aging properties, good ultra-low temperature toughness and stable mechanical properties, and is suitable for ultra-low temperature insulation scenarios.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a double-sided aluminized polyimide film for ultra-low temperature multilayer vacuum insulation, characterized in that it is composed of a polyimide base film and an aluminized layer formed on its two surfaces by vacuum evaporation. The polyimide-based film is made from raw materials comprising the following parts by weight: 100 parts pyromellitic dianhydride, 4,4'-diaminodiphenyl ether, 5-15 parts low-temperature modifier, 3-8 parts nano-silica filler, 0.5-2 parts leveling agent, 0.5-1.5 parts anti-aging agent, 3-6 parts silane coupling agent, and 5-15 parts polyvinyl chloride; The molar ratio of 4,4'-diaminodiphenyl ether to pyromellitic dianhydride is 1:1; The anti-aging agent is a compound represented by chemical formula 1; The structure of chemical formula 1 is as follows: ; R1 in chemical formula 1 is a substituent, and R1 is selected from: methyl, phenyl, ... , Any of the following, where * in the substituent is the linking site.

[0008] Furthermore, the low-temperature resistant modifier is hydroxyl silicone oil with a hydroxyl content of 0.5-3%.

[0009] Furthermore, the particle size of the nano-silica filler is 10-50 nm.

[0010] Furthermore, the leveling agent is at least one of diacetone alcohol, polydimethylsiloxane, polymethylalkylsiloxane, organically modified polysiloxane, acrylic resin, urea-formaldehyde resin, melamine-formaldehyde resin, fluorinated acrylate, and fluorocarbon compound.

[0011] Furthermore, the silane coupling agent is selected from at least one of KH550 and KH560.

[0012] Furthermore, the anti-aging agent is any one of the compounds shown in the following structures: ; .

[0013] A method for preparing a double-sided aluminized polyimide film for ultra-low temperature multilayer vacuum insulation includes the following steps: a. Polyamic acid resin synthesis: Under inert gas protection, the 4,4'-diaminodiphenyl ether is dissolved in a polar aprotic solvent and stirred evenly. Then, the pyromellitic dianhydride is added in batches, and the reaction temperature is controlled at 0-10℃. The reaction is carried out for 4-8 hours to obtain a polyamic acid resin solution. b. Formulation mixing: The low-temperature resistant modifier, nano silica filler, leveling agent, anti-aging agent, silane coupling agent and polyvinyl chloride are added sequentially to the polyamic acid resin solution. The mixture is stirred continuously for 2-4 hours to ensure thorough and uniform mixing. The solution is then degassed under vacuum to obtain the casting solution. c. Casting and imidization: The casting solution is cast onto a clean steel strip or release paper and cured by gradient heating to form a polyimide-based film; d. Double-sided aluminum plating: The polyimide-based film is placed in a high-vacuum coating apparatus, with a vacuum degree better than 3.0 × 10⁻⁶. -3 Under the condition of Pa, an electron beam evaporation source is used to deposit aluminum layers on the two surfaces of the base film to form the aforementioned double-sided aluminum-plated polyimide film for ultra-low temperature multilayer vacuum insulation. The gradient heating program is as follows: first, maintain the temperature at 80-120℃ for 30-60 minutes, then gradually increase the temperature to 200-250℃ and maintain it for 30 minutes, and finally increase the temperature to 300-350℃ and maintain it for 10-20 minutes.

[0014] Furthermore, the polar aprotic solvent is one of N,N-dimethylacetamide, N-methylpyrrolidone, or dimethyl sulfoxide, and the solid content is controlled at 15%-25%.

[0015] Furthermore, the thickness of the aluminum plating layer is controlled at 30-50 nanometers.

[0016] Furthermore, step b is performed under a nitrogen atmosphere.

[0017] Furthermore, in the aforementioned ultra-low temperature multilayer vacuum insulation double-sided aluminized polyimide film, the aluminized layer serves as a reflective screen, and the polyimide base film acts as an insulation layer. The aluminized layer is prepared using a vapor deposition process, resulting in a dense, low-porosity vapor-deposited layer with high light reflectivity. The polyimide base film layer exhibits low water absorption and a low dielectric constant. The entire film structure possesses excellent high-temperature resistance, and its internal structure is not easily damaged during long-term use, resulting in a longer service life.

[0018] An ultra-low temperature multilayer vacuum insulation structure is composed of multiple layers of ultra-low temperature multilayer vacuum insulation double-sided aluminized polyimide film alternately stacked with a reflective screen material. The layers of film are separated by spacers with low thermal conductivity and are encapsulated in a high vacuum environment.

[0019] Application of an ultra-low temperature multilayer vacuum insulation structure in ultra-low temperature components of liquid hydrogen and liquid nitrogen storage and transportation equipment, space probes, or superconducting magnet insulation systems.

[0020] In the anti-aging agent molecule used in this invention, the phenolic hydroxyl group and the benzotriazole structure work synergistically to form a highly efficient anti-aging mechanism: the phenolic hydroxyl group, as a free radical scavenger, can provide active hydrogen to combine with free radicals generated by temperature cycling and trace ultraviolet radiation in the ultra-low temperature environment, thereby terminating the molecular chain degradation reaction initiated by free radicals and avoiding the problem of increased brittleness of the polyimide matrix due to oxidative crosslinking; at the same time, the benzotriazole structure can selectively absorb ultraviolet light, reducing the damage of ultraviolet light to the polyimide molecular chain, and its molecular structure has excellent compatibility with the polyimide matrix. Combined with the stabilizing effect of the phenolic hydroxyl group, it can prevent the anti-aging agent from precipitating at ultra-low temperatures.

[0021] This invention overcomes three core problems in existing technologies—poor anti-aging properties, weak low-temperature toughness, and easy agglomeration of nanofillers—through the synergistic formulation of various raw materials. Regarding the poor anti-aging properties, the anti-aging agent with a specific structure can capture free radicals generated by temperature cycling and ultraviolet radiation in ultra-low temperature environments, and also absorb ultraviolet radiation. Furthermore, its molecular structure exhibits excellent compatibility with the polyimide matrix and silane coupling agent, avoiding the defects of poor low-temperature dispersion and easy precipitation of traditional anti-aging agents, thus achieving long-lasting anti-aging effects. Regarding the weak low-temperature toughness, the low-temperature resistant modifier hydroxyl silicone oil works synergistically with polyvinyl chloride, and the two can form a tight bond with the polyimide matrix. The tight interface bonding avoids the phase separation problem of traditional rubber elastomer modification, while improving the low-temperature ductility of the film and balancing toughness, tensile strength, and dimensional stability. To address the problem of easy agglomeration of nanofillers, nano-silica, under the action of silane coupling agent, can form stable chemical bonds with the polyimide matrix and other components, achieving uniform dispersion, avoiding stress concentration, and helping to enhance mechanical properties. In addition, leveling agent ensures the uniformity of film formation in the casting solution, and combined with gradient temperature imidization process, ensures that the synergistic effect of each component is fully exerted, ultimately making the double-sided aluminized polyimide film suitable for ultra-low temperature multilayer vacuum insulation scenarios.

[0022] Compared with the prior art, the beneficial effects of the present invention are: 1. Superior anti-aging performance: The anti-aging agent with a specific structure works synergistically with the phenolic hydroxyl group and benzotriazole structure to capture free radicals and absorb ultraviolet rays. It also has good compatibility with the polyimide matrix, avoiding precipitation at low temperatures. This solves the problems of poor low-temperature dispersion and easy failure of traditional anti-aging agents, thus extending the service life of the film.

[0023] 2. Enhanced low-temperature toughness: The low-temperature modifier hydroxyl silicone oil works synergistically with polyvinyl chloride to form a tight interfacial bond with the polyimide matrix, avoiding the phase separation problem of traditional modification, improving the ultra-low temperature ductility of the film, balancing toughness, tensile strength, and dimensional stability, and reducing the risk of low-temperature brittleness.

[0024] 3. More stable overall performance: Silane coupling agent helps nano-silica to be uniformly dispersed in the matrix, avoiding agglomeration and stress concentration. This not only enhances mechanical properties, but also, together with leveling agent and gradient heating process, ensures film uniformity. Ultimately, the film has excellent mechanical and thermal insulation properties in ultra-low temperature environments, making it suitable for ultra-low temperature multilayer vacuum insulation scenarios. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of a double-sided aluminized polyimide film for ultra-low temperature multilayer vacuum insulation according to the present invention; 1 is a polyimide-based film, and 2 is an aluminum-plated layer.

[0026] Figure 2 This is the NMR spectrum of the anti-aging agent 1 described in this invention.

[0027] Figure 3 This is the NMR spectrum of intermediate 1 described in this invention. Detailed Implementation

[0028] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Preparation Example 1: Preparation of anti-aging agent 1: ; ; CAS number of compound 1: 95-14-7; CAS number of compound 2: 115997-68-7; CAS number of compound 3: 40248-01-9; Intermediate 1 and anti-aging agent 1 are new compounds without CAS numbers.

[0030] Under a nitrogen atmosphere, 15.00 g of compound 1, 34.44 g of compound 2, 24.20 g of sodium tert-butoxide, and 200 ml of toluene were added sequentially to the reaction system. The mixture was stirred until homogeneous, then 4.37 g of tetrakis(triphenylphosphine)palladium was added. The temperature was raised to 120 °C and refluxed for 12 h. After the reaction was complete, the temperature was slightly lowered, and the mixture was filtered through silica gel. The filtrate was cooled to room temperature, washed three times with water, and the organic phase was retained. The aqueous phase was then extracted with toluene. The combined organic phases were dried over anhydrous magnesium sulfate, and the solvent was removed using a rotary evaporator. The solution was evaporated to dryness, and silica gel column chromatography was performed using a mixture of petroleum ether and ethyl acetate as eluent. The solution was evaporated to dryness again to give 31.24 g of intermediate 1. NMR results are shown below. Figure 3 .

[0031] Under a nitrogen atmosphere, 31.24 g of intermediate 1, 13.26 g of compound 3, 18.32 g of sodium tert-butoxide, and 350 mL of toluene were added sequentially to the reaction system. The mixture was stirred until homogeneous, then 3.30 g of tetrakis(triphenylphosphine)palladium was added. The mixture was heated to 120 °C and refluxed for 12 h. After the reaction was complete, the temperature was slightly lowered, and the mixture was filtered through silica gel. The filtrate was cooled to room temperature, washed three times with water, and the organic phase was retained. The aqueous phase was then extracted with toluene. The combined organic phases were dried over anhydrous magnesium sulfate, and the solvent was removed using a rotary evaporator. The mixture was evaporated to dryness, and silica gel column chromatography was performed using a mixture of petroleum ether and ethyl acetate as eluent. The resulting product was evaporated to dryness to obtain 29.38 g of anti-aging agent 1. The compound was analyzed by mass spectrometry (MS+H). + :415, see MRI Figure 2 .

[0032] Preparation Examples 2-4 In Preparation Examples 2-4, anti-aging agents 2-4 were prepared sequentially, following the preparation method of Preparation Example 1, except that compound 3 was replaced, and the rest remained the same as in Preparation Example 1. See Table 1 for details.

[0033] Table 1

[0034] Example 1: Preparation of a double-sided aluminized polyimide film for ultra-low temperature multilayer vacuum insulation; 1. Raw material components: Pyromellitic dianhydride: 100 parts, purchased from: Hubei Xinjiecheng Chemical Technology Co., Ltd.; The molar ratio of 4,4'-diaminodiphenyl ether to pyromellitic dianhydride was 1:1, and it was purchased from Beijing Hailiyang Chemical Technology Co., Ltd. Low-temperature resistant modifier: hydroxyl silicone oil, 10 parts, hydroxyl content 0.5-3%, purchased from: Anhui Aiyota Silicone Oil Co., Ltd.; Nano silica filler: 5 parts, average particle size 15nm, purchased from: Suzhou Meibang Nanomaterials Co., Ltd. Leveling agent: polydimethylsiloxane, 1 part, purchased from: Shanghai Dingfen Chemical Technology Co., Ltd.; Anti-aging agent: 1 part of the anti-aging agent 1 obtained in Preparation Example 1; Silane coupling agent: KH550, 4 parts, purchased from: Shandong Bosheng Chemical Co., Ltd.; Polyvinyl chloride: 10 parts, purchased from: Ningxia Jinyuyuan Chemical Group Co., Ltd.; Polar aprotic solvent: N,N-dimethylacetamide, purchased from: Jinan Chuangshi Chemical Co., Ltd.

[0035] 2. Preparation method: a. Synthesis of polyamic acid resin: Under nitrogen protection, 100 parts of 4,4'-diaminodiphenyl ether were dissolved in N,N-dimethylacetamide to prepare a solution with a solid content of 20%, and stirred for 30 minutes until completely dissolved. The system temperature was controlled at 5°C, and pyromellitic dianhydride was added to the solution in batches. After the addition was complete, the temperature was maintained at 5°C, and the reaction was continued for 6 hours to obtain a homogeneous and transparent polyamic acid resin solution. b. Formulation mixing: Transfer the above polyamic acid resin solution to a nitrogen-protected stirred tank, and add 10 parts of hydroxyl silicone oil, 5 parts of nano silica filler, 1 part of polydimethylsiloxane, 1 part of anti-aging agent 1, 4 parts of KH550 and 10 parts of polyvinyl chloride in sequence. Start stirring and control the speed at 300 r / min. Continue stirring for 3 hours until all components are completely mixed and uniform. Then perform vacuum degassing treatment (vacuum degree -0.095MPa, time 30 minutes) to obtain a bubble-free, uniform and stable casting solution. c. Casting and Imidization: The casting solution is uniformly cast onto a clean stainless steel strip using a casting machine, with the casting thickness controlled at 0.1 mm. The cast wet film is then sent into a hot air oven for gradient temperature imidization: first, it is held at 100℃ for 45 minutes to remove the solvent; then, the temperature is gradually increased to 220℃ and held for 30 minutes for pre-imidization; finally, the temperature is increased to 320℃ and held for 15 minutes to complete the imidization. After cooling to room temperature, the film is peeled off from the steel strip to obtain a polyimide-based film. d. Double-sided aluminum plating: Place the above-mentioned polyimide-based film in a high-vacuum coating equipment and evacuate to a vacuum level of 3.0 × 10⁻⁶. -3 Pa; Using an electron beam evaporation source, high-purity aluminum wire (purity ≥99.99%) was heated and evaporated, and aluminum layers were deposited on both surfaces of the base film, with the thickness of the aluminum layer controlled at 30 nm. After evaporation, it was naturally cooled to room temperature to obtain a double-sided aluminum-coated polyimide film for ultra-low temperature multilayer vacuum insulation.

[0036] Examples 2-4 The preparation of a double-sided aluminized polyimide film for ultra-low temperature multilayer vacuum insulation is carried out by referring to the preparation method of Example 1, except that the anti-aging agent is replaced with anti-aging agent 2-anti-aging agent 4 in sequence, and the rest is the same as in Example 1.

[0037] Comparative Example 1 The preparation of a double-sided aluminized polyimide film for ultra-low temperature multilayer vacuum insulation is carried out by referring to the preparation method of Example 1, except that the anti-aging agent is replaced with the antioxidant MDA, and the rest is the same as in Example 1.

[0038] Comparative Example 2 The preparation of a double-sided aluminized polyimide film for ultra-low temperature multilayer vacuum insulation is carried out by referring to the preparation method of Example 1, except that the anti-aging agent is replaced with the antioxidant MMB, and the rest is the same as in Example 1.

[0039] Comparative Example 3 The preparation of a double-sided aluminized polyimide film for ultra-low temperature multilayer vacuum insulation is carried out by referring to the preparation method of Example 1, except that the anti-aging agent is replaced with anti-aging agent DNP, and the rest is the same as in Example 1.

[0040] Comparative Example 4 The preparation of a double-sided aluminized polyimide film for ultra-low temperature multilayer vacuum insulation is carried out according to the preparation method of Example 1, except that the anti-aging agent is not added, and the rest is the same as in Example 1.

[0041] Comparative Example 5 The preparation of a double-sided aluminized polyimide film for ultra-low temperature multilayer vacuum insulation is carried out according to the preparation method of Example 1, except that the low temperature resistant modifier is not added, and the rest is the same as in Example 1.

[0042] Comparative Example 6 The preparation of a double-sided aluminized polyimide film for ultra-low temperature multilayer vacuum insulation is carried out according to the preparation method of Example 1, wherein the thickness of the aluminized layer is 20 nm, and the rest is the same as in Example 1.

[0043] Performance testing: Test sample: A double-sided aluminized polyimide film for ultra-low temperature multilayer vacuum insulation prepared in the examples and comparative examples.

[0044] 1. Tensile property test: The tensile strength of the sample was tested according to the test method of GB / T 1040.3-2006. The data are shown in Table 2.

[0045] 2. Freeze-thaw aging stability test: The test sample was stored in a liquid nitrogen environment at -196℃ for 5 hours, then heated to 80℃ and stored for 5 hours. This process was repeated 150 times. The tensile strength was then measured again, and the tensile strength retention rate was calculated. The data are shown in Table 2.

[0046] 3. UV stability test: The test sample was placed in a UV aging chamber with a UV wavelength of 340nm and an irradiation intensity of 0.68W / m². 2 The temperature was 60℃, the humidity was 50%, and the aging time was 3000h. The tensile strength was retested, and the tensile strength retention rate was calculated. The data are shown in Table 2.

[0047] 4. Vacuum insulation performance test: Refer to the test method of GB / T 10294-2008. Test conditions: vacuum degree ≤ 3.0 × 10⁻⁶. -3 Pa, cold end temperature -196℃, hot end temperature -23℃, 10 layers of thin film, the laminated insulation structure was placed in a vacuum insulation test device, and the thermal conductivity was measured after stabilization for 24 hours. The data are shown in Table 2.

[0048] Table 2

[0049] The tensile properties of the embodiments remained stable overall, and they exhibited better performance retention in both freeze-thaw aging and UV aging tests, with more outstanding vacuum insulation performance. The comparative examples with traditional anti-aging agents replaced or not added showed a significant decrease in UV aging resistance and freeze-thaw aging performance compared to the embodiments. The comparative examples lacking low-temperature modifiers showed a significant decline in freeze-thaw aging performance and were also affected by vacuum insulation performance. The comparative examples with reduced aluminum plating thickness showed a significant decrease in both tensile properties and vacuum insulation performance, with only the aging performance retention being similar to some embodiments.

[0050] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A double-sided aluminized polyimide film for ultra-low temperature multilayer vacuum insulation, characterized in that, It consists of a polyimide-based film (1) and an aluminum-plated layer (2) formed on both of its surfaces by vacuum evaporation. The polyimide-based film (1) is made from raw materials comprising the following parts by weight: 100 parts pyromellitic dianhydride, 4,4'-diaminodiphenyl ether, 5-15 parts low-temperature modifier, 3-8 parts nano-silica filler, 0.5-2 parts leveling agent, 0.5-1.5 parts anti-aging agent, 3-6 parts silane coupling agent, and 5-15 parts polyvinyl chloride; The molar ratio of 4,4'-diaminodiphenyl ether to pyromellitic dianhydride is 1:1; The anti-aging agent is a compound represented by chemical formula 1; The structure of chemical formula 1 is as follows: ; R1 in chemical formula 1 is a substituent, and R1 is selected from: methyl, phenyl, ... , Any of the following, where the * in the substituent is the linking site; The low-temperature resistant modifier is hydroxyl silicone oil with a hydroxyl content of 0.5-3%. The thickness of the aluminum plating layer is controlled at 30-50 nanometers.

2. The ultra-low temperature multilayer vacuum insulation double-sided aluminized polyimide film according to claim 1, characterized in that, The particle size of the nano-silica filler is 10-50 nm.

3. The ultra-low temperature multilayer vacuum insulation double-sided aluminized polyimide film according to claim 1, characterized in that, The leveling agent is at least one of diacetone alcohol, polymethylalkylsiloxane, organic modified polysiloxane, acrylic resin, urea-formaldehyde resin, melamine-formaldehyde resin, fluorinated modified acrylate, and fluorocarbon compound.

4. The ultra-low temperature multilayer vacuum insulation double-sided aluminized polyimide film according to claim 1, characterized in that, The silane coupling agent is selected from at least one of KH550 and KH560.

5. A method for preparing a double-sided aluminized polyimide film for ultra-low temperature multilayer vacuum insulation as described in any one of claims 1-4, characterized in that, Includes the following steps: a. Polyamic acid resin synthesis: Under inert gas protection, the 4,4'-diaminodiphenyl ether is dissolved in a polar aprotic solvent and stirred evenly. Then, the pyromellitic dianhydride is added in batches, and the reaction temperature is controlled at 0-10℃. The reaction is carried out for 4-8 hours to obtain a polyamic acid resin solution. b. Formulation mixing: The low-temperature resistant modifier, nano silica filler, leveling agent, anti-aging agent, silane coupling agent and polyvinyl chloride are added sequentially to the polyamic acid resin solution. The mixture is stirred continuously for 2-4 hours to ensure thorough and uniform mixing. The solution is then degassed under vacuum to obtain the casting solution. c. Casting and imidization: The casting solution is cast onto a clean steel strip or release paper and cured by gradient heating to form a polyimide-based film; d. Double-sided aluminum plating: The polyimide-based film is placed in a high-vacuum coating apparatus, with a vacuum degree better than 3.0 × 10⁻⁶. -3 Under the condition of Pa, an electron beam evaporation source is used to deposit aluminum layers on the two surfaces of the base film to form the aforementioned double-sided aluminum-plated polyimide film for ultra-low temperature multilayer vacuum insulation. The gradient heating program is as follows: first, maintain the temperature at 80-120℃ for 30-60 minutes, then gradually increase the temperature to 200-250℃ and maintain it for 30 minutes, and finally increase the temperature to 300-350℃ and maintain it for 10-20 minutes.

6. The method for preparing a double-sided aluminized polyimide film for ultra-low temperature multilayer vacuum insulation according to claim 5, characterized in that, The polar aprotic solvent is one of N,N-dimethylacetamide, N-methylpyrrolidone, or dimethyl sulfoxide, and the solid content is controlled at 15%-25%.

7. The method for preparing a double-sided aluminized polyimide film for ultra-low temperature multilayer vacuum insulation according to claim 5, characterized in that, Step b is performed under a nitrogen atmosphere.

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