Conductive polyimide film and sandwich composite material and preparation method thereof

Abstract

The application provides a conductive polyimide film and a sandwich composite material and a preparation method thereof, and belongs to the technical field of composite materials. The polyimide film is prepared, a fiber reinforced fabric is embedded into the polyamide acid film, and then the fiber reinforced polyimide film is formed by solidification. The fiber reinforced polyimide film is combined with the fabric / resin through RTM forming to form the sandwich composite material. The sandwich composite material prepared by the application has few forming defects and high interlayer bonding strength, and can be applied to the aerospace field to prepare structure-function integrated composite materials and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of composite materials, and particularly relates to a conductive polyimide film and a sandwich composite material and a preparation method thereof. BACKGROUND

[0002] With the iteration of aerospace technology, composite materials are rapidly developing in the direction of functionalization and integration. The sandwich composite material with special electromagnetic function is a kind of structural and functional integrated composite material. It is usually composed of three parts, namely resin matrix, reinforcing body and electromagnetic functional film. The resin matrix and the reinforcing body constitute the main body of the composite material, and the electromagnetic functional film is embedded in the composite material to form a sandwich structure.

[0003] The electromagnetic functional film generally uses a polyimide film as a carrier film. Polyimide has excellent mechanical properties, heat resistance, thermal stability, insulation and other properties, and is therefore widely used as a base material in the fields of aerospace, electronics and electrical appliances, and is the mainstream material for functional film formation. The polyimide film is generally formed by casting or coating polyamide acid resin to form a polyamide acid film, and then removing the solvent and imidizing at high temperature to form a polyimide film.

[0004] There are still two problems in the actual forming of sandwich composite material components. Firstly, an interface is formed between the resin matrix and the functional film, and the surface energy of the polyimide film is low, which reduces the interlaminar shear strength of the composite material. Therefore, the polyimide film generally needs to be surface treated before the formation of the sandwich composite material to increase the surface activity and improve the interfacial bonding strength of the composite material. Common treatment methods include physical methods such as plasma treatment, flame treatment and irradiation treatment, and chemical methods such as alkali treatment. However, simple surface activation treatment still cannot well improve the interfacial strength of the composite material and the film, and defects such as delamination and bulging are easily caused by solidification shrinkage and internal stress during the forming process.

[0005] Therefore, it is one of the research focuses in the field to develop a new functional film preparation method based on polyimide and solve the problem of forming defects of functional sandwich composite materials. SUMMARY

[0006] The purpose of the present application is to provide a conductive polyimide film and a sandwich composite material and a preparation method thereof. By embedding a fiber fabric in the manufacturing process of the film, the defects such as misalignment, wrinkles, delamination and bulging of the prepared composite material are overcome, and the comprehensive mechanical properties of the composite material are provided.

[0007] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0008] A method for preparing a conductive polyimide film, comprising the following steps:

[0009] 1) preparing a polyamide acid solution;

[0010] 2) coating the polyamide acid solution on the surface of a glass substrate using a coating device, performing a pre-baking treatment to remove the solvent, forming a polyamide acid film on the surface of the substrate, obtaining a substrate containing a polyamide acid film, and then placing the substrate containing the polyamide acid film in a high-temperature oven for pre-curing;

[0011] 3) cooling the substrate containing the polyamide acid film after pre-curing in step 2) to room temperature, and then printing a periodic array structure onto the surface of the substrate containing the polyamide acid film by using a silk-screen printing method to form a conductive functional layer;

[0012] 4) performing a defoaming treatment on the polyamide acid solution, and then coating the polyamide acid solution onto the surface of the substrate on which the periodic array structure is printed in step 3) for pre-baking treatment in an oven;

[0013] 5) placing an inorganic fiber mesh cloth on the surface of the substrate coated with the polyamide acid after the pre-baking treatment in step 4), and then performing a pre-baking treatment in a drying oven to remove the solvent, and placing the substrate in a high-temperature oven for pre-curing;

[0014] 6) cooling the substrate to room temperature after pre-curing, and then immersing the substrate in water, and peeling the generated polyimide film from the surface of the substrate; and fixing the smooth surface of the peeled polyimide film on the surface of a flat tooling device;

[0015] 7) immersing the inorganic fiber mesh cloth in a polyamide acid solution in advance, and then placing the inorganic fiber mesh cloth on the smooth surface of the peeled polyimide film in step 6), performing a pre-baking treatment in a drying oven to remove the solvent, and placing the film together with the flat tooling device in a high-temperature oven for curing to obtain a conductive polyimide film.

[0016] Preferably, the polyamide acid solution in step 1) can be prepared by using an existing preparation method, including: mixing an aromatic diamine monomer and a solvent at a temperature of -5-15°C for primary stirring, and then adding an aromatic dianhydride in batches for secondary stirring at a temperature of -5-15°C, and then reacting to obtain a polyamide acid solution; the molar ratio of the aromatic diamine to the aromatic dianhydride can be 1:(0.9-1.1), but is not limited to this; the mass ratio of the aromatic diamine to the aromatic dianhydride in the polyamide acid solution can be 5%-35%, but is not limited to this.

[0017] Preferably, the aromatic diamine is at least one of 4,4-diaminodiphenyl ether, m-phenylenediamine, 4,4'-diaminodiphenyl methane, 4,4-diaminobiphenyl, p-phenylenediamine, 3,4-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,3'-diaminodiphenyl sulfone, 3,3'-dimethyl-4,4-diaminobiphenyl, 3,3'-diamino-benzophenone, 4,4'-diamino-benzophenone, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 4,4'-diaminobenzanilide, 2,2'-bis(4-aminophenyl)hexafluoropropane, 1,3-bis(4-aminophenoxy)benzene, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 1,4-bis(2-trifluoromethyl 4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, and 2,2-bis[4-(4-aminophenoxy)phenyl]propane.

[0018] Preferably, the aromatic dianhydride is at least one of 3,3',4,4'-benzophenonetetracarboxylic dianhydride, pyromellitic dianhydride, 3,3',4,4'-oxydiphthalic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4-hexafluoroisopropyl phthalic anhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-oxydiphthalic dianhydride, and 4,4'-(4,4'-isopropyl diphenyloxy) bis(phthalic anhydride).

[0019] Preferably, the time for the defoaming treatment of the polyamic acid solution in step 4) is 20-40 min.

[0020] Preferably, the coating method in steps 2) and 4) is wire bar coating.

[0021] Preferably, the pre-baking treatment in step 4) in the oven is not more than 1 h.

[0022] Preferably, the material of the inorganic fiber mesh in steps 5) and 7) is selected from one of glass fiber and quartz fiber.

[0023] Preferably, the pre-baking treatment in steps 5) and 7) in the drying oven is at a temperature of 35-80 °C for 6-24 h.

[0024] Preferably, the pre-curing in step 5) is thermal curing, and the temperature is raised at a rate of 3-5 °C / min from room temperature, and then held at 110-130 °C for 5-15 min, 190-210 °C for 5-15 min, and 290-360 °C for 5-20 min, respectively.

[0025] Preferably, the solidification in step 7) is heat solidification, and the temperature is raised by the following procedure: starting from room temperature, the temperature is raised to 110-130℃ at a rate of 3-5℃ / min, and then kept for 5-15min, then raised to 190-210℃ and kept for 5-15min, then raised to 290-310℃ and kept for 5-20min, and then raised to 350-380℃ and kept for 5-30min.

[0026] Preferably, after the solidification in step 7), the inorganic fiber mesh fabric is perforated in the mesh gap, and the distance between the holes is 1-10cm.

[0027] A method for preparing a conductive polyimide film sandwich composite material, comprising the following steps:

[0028] Placing the conductive polyimide film prepared by the above method and two layers of inorganic fiber mesh fabric in the mold cavity of the RTM forming mold, with the conductive polyimide film between the two layers of inorganic fiber mesh fabric, and then adding resin, followed by closing the mold, solidification, and demolding to obtain a polyimide film sandwich composite material.

[0029] Preferably, the material of the inorganic fiber mesh fabric is selected from one of glass fiber and quartz fiber.

[0030] Preferably, the added resin is one of polyarylacetylene resin, cyanate ester resin, and phthalonitrile resin.

[0031] Preferably, the way of adding resin includes: injection after the upper and lower molds of the RTM forming mold are closed; or pre-impregnating the inorganic fiber mesh fabric with resin, and then placing the pre-impregnated two layers of inorganic fiber mesh fabric in the mold cavity of the RTM forming mold.

[0032] A conductive polyimide film sandwich composite material prepared by the above method.

[0033] Compared with the prior art, the present application has at least the following beneficial effects:

[0034] 1. In the preparation of the conductive polyimide film, two layers of inorganic fiber mesh fabric are embedded, which has the following effects:

[0035] (1) Enhancing the interfacial bonding strength: the embedded mesh fabric film forms a rough structure, which mechanically embeds with the matrix resin in the sandwich composite material, thereby improving the interfacial bonding strength between the film surface and the matrix of the composite material.

[0036] (2) Reducing wrinkle formation: the embedded mesh fabric film has increased thickness and rigidity, which can reduce the wrinkle phenomenon caused by stress during the forming process. The presence of the mesh fabric increases the rigidity of the film, making it more stable during extrusion, thereby reducing the wrinkles on the surface of the film.

[0037] (3) Improve material misregistration: After embedding the grid cloth, the rough structure on the surface of the film is beneficial to form an anchoring effect with the prepreg or fiber fabric of the composite material. This anchoring effect can prevent the film from misregistration during the molding process, keep the position of the film stable, and avoid position deviation or misregistration.

[0038] (4) Improve tear resistance: The tear resistance of polyimide film itself is poor, and small defects can easily cause tearing. However, when the film is embedded in the grid cloth, the grid cloth can hinder the propagation of cracks, thereby effectively improving the tear resistance of the film. As a reinforcing material, the grid cloth can absorb and disperse stress, prevent the continuous propagation of cracks, and thus improve the overall tear resistance.

[0039] In summary, the effects of embedding the grid cloth in the composite material molding process mainly include enhancing the interfacial bonding strength, reducing wrinkle formation, improving material misregistration, and improving tear resistance, which are achieved through mechanisms such as the rough structure of the grid cloth, increased film thickness and stiffness, anchoring effect, and crack hindering mechanism.

[0040] 2、The conductive polyimide film embedded with fabric prepared by the method can be applied to various resin-based sandwich composite materials, and the sandwich composite material prepared by the film is not prone to delamination, bulging, and other molding defects. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 is a flowchart of the preparation method of the conductive polyimide film sandwich composite material proposed by the present application.

[0042] Figure 2 is a schematic diagram of the structure of the polyimide functional film embedded with fabric. DETAILED DESCRIPTION

[0043] In order to make the technical features and advantages or technical effects of the above technical solutions of the present application more obvious and easy to understand, the following detailed description is given with reference to the accompanying drawings.

[0044] Figure 1 is a flowchart of the preparation method of the conductive polyimide film sandwich composite material proposed by the present application, which covers the preparation method of the conductive polyimide film. The fabric in the figure is inorganic fiber grid cloth, and the structure of the polyimide film sandwich composite material finally prepared is as shown in Figure 2 The following gives a specific example of the entire preparation process.

[0045] Example 1

[0046] 1) 90 g of 4,4-diaminodiphenyl ether monomer and 1070 g of N,N-dimethylacetamide were mixed and stirred to dissolve at a temperature of 5°C, and then 97 g of pyromellitic dianhydride was added and stirred at a temperature of 5°C to obtain a polyamic acid solution.

[0047] 2) The polyamic acid solution was coated on the surface of a glass plate using a wire bar coater using a coating device, and pre-baking was performed to remove the solvent to obtain a substrate having a polyamic acid film, and the substrate having the polyamic acid film was placed in a high-temperature oven for pre-curing.

[0048] 3) The substrate having the polyamic acid film after pre-curing was cooled to room temperature, and a conductive silver paste was printed on the surface of the substrate having the polyamic acid film after pre-curing by screen printing to form a conductive functional layer.

[0049] 4) The polyamic acid solution after defoaming was coated on the surface of the substrate having the polyamic acid film on which the conductive functional layer was printed using a wire bar coater, and pre-baking was performed in an oven for 50 min.

[0050] 5) A 5*5 mm / 80 g·m -2 A quartz fiber mesh was laid on the surface of the substrate coated with the polyamic acid resin, pre-baking was performed (drying treatment in a drying oven at 35°C for 24 h) to remove the solvent, and the substrate was placed in a high-temperature oven for pre-curing. The pre-curing conditions were as follows: temperature increase was performed using the following program, i.e., temperature increase was started at room temperature at a rate of 4°C / min, and then the temperature was increased to 120°C, 200°C, and 320°C, respectively, and maintained for 10 min each time.

[0051] 6) After curing, after the substrate was cooled to room temperature, the substrate was immersed in water, and the polyimide film was peeled off from the surface of the glass substrate, and the peeled polyimide film was fixed on the surface of a flat tool with the smooth surface facing upward.

[0052] 7) A 5*5 mm / 80 g·m -2 The quartz fiber mesh was previously impregnated with a polyamic acid resin, and then laid on the smooth surface of the peeled polyimide film, pre-baking was performed to remove the solvent, and the film was cured together with the flat tool in a high-temperature oven. The curing conditions were as follows: temperature increase was performed using the following program, i.e., temperature increase was started at room temperature at a rate of 4°C / min, and then the temperature was increased to 120°C, 200°C, 300°C, and 370°C, respectively, and maintained for 10 min each time. Then, a puncher was used to punch holes in the mesh gap, and the hole pitch was 5 cm.

[0053] 8) In the mold cavity of the RTM forming mold, place the quartz fiber mesh cloth, the polyimide functional interlayer, and the quartz fiber cloth in sequence, then assemble the upper and lower molds of the RTM forming mold, and inject the polyarylacetylene resin into the mold, so that the interlayer quartz fiber composite plate is cured and demolded to form.

[0054] Example 2

[0055] The polyamic acid solution preparation, substrate preparation containing polyamic acid film, and conductive functional layer printing of Example 2 are basically the same as those of Example 1, except that:

[0056] 5) 5*5mm / 80g·m -2 The glass mesh cloth is laid on the surface of the substrate coated with polyamic acid resin, and the substrate is pre-cured in a high-temperature oven after pre-drying treatment (drying treatment in a drying oven at 60°C for 12h). The pre-curing conditions are as follows: the temperature is raised by the following program, i.e. the temperature is raised at a speed of 3°C / min at room temperature, and the temperature is kept at 110°C for 15min, 190°C for 15min, and 290°C for 20min, respectively.

[0057] 6) After curing, the substrate is immersed in water after cooling to room temperature, and the polyimide film is peeled off from the surface of the glass substrate, and the smooth surface of the peeled polyimide film is fixed on the surface of the flat tooling.

[0058] 7) 5*5mm / 80g·m -2 The glass mesh cloth is pre-impregnated with polyamic acid resin, and then laid on the smooth surface of the peeled polyimide film, and the film is cured together with the flat tooling after pre-drying treatment to remove the solvent. The curing conditions are as follows: the temperature is raised by the following program, i.e. the temperature is raised at a speed of 5°C / min at room temperature, and the temperature is kept at 130°C for 5min, 210°C for 5min, 310°C for 5min, and 380°C for 5min, respectively. Then a punch is used to punch holes in the gap between the glass mesh cloths, and the hole spacing is 10cm.

[0059] 8) In the flat tooling, lay 8 layers of 0.14mm cyanate ester glass fiber prepreg, the polyimide functional interlayer, and 8 layers of 0.14mm cyanate ester glass fiber prepreg in sequence, and then lay the release cloth, the hole isolation film, and the vacuum bag film in sequence. After curing with a hot press, the product is demolded.

[0060] Example 3

[0061] The polyamic acid solution preparation, substrate preparation containing polyamic acid film, and conductive functional layer printing of Example 3 are basically the same as those of Example 1, except that:

[0062] 5) 10*10 mm / 40 g.m -2 Quartz fiber mesh cloth is laid on the surface of the substrate coated with polyamide acid resin, and pre-baking treatment (drying treatment in a drying oven at 80°C for 6h) is used to remove the solvent. The substrate is placed in a high-temperature oven for pre-curing. The pre-curing conditions are as follows: the temperature is raised in the following manner, i.e., the temperature is raised at a speed of 5°C / min at room temperature, and the temperature is kept at 130°C for 5 min, at 210°C for 5 min, at 300°C for 5 min, and at 360°C for 5 min.

[0063] 6) After curing, the substrate is cooled to room temperature, and then the substrate is soaked in water. The polyimide film is peeled off from the surface of the glass substrate, and the smooth surface of the peeled polyimide film is fixed on the surface of a flat tooling.

[0064] 7) 10*10 mm / 40 g.m -2 The quartz fiber mesh cloth is pre-impregnated with polyamide acid resin, and then laid on the smooth surface of the peeled polyimide film. Pre-baking treatment is used to remove the solvent, and the film is cured together with the flat tooling in a high-temperature oven. The curing conditions are as follows: the temperature is raised in the following manner, i.e., the temperature is raised at a speed of 3°C / min at room temperature, and the temperature is kept at 110°C for 15 min, at 190°C for 15 min, at 290°C for 20 min, and at 350°C for 30 min. Then, a puncher is used to punch holes in the mesh gap, and the hole spacing is 1 cm.

[0065] 8) The phthalonitrile resin is dissolved in acetone to form a resin glue solution, and the resin glue solution is brushed on both sides of the polyimide functional interlayer. The solvent is removed by drying at 80°C in a vacuum oven for 1 hour.

[0066] In the flat tooling, 8 layers of 0.14 mm phthalonitrile quartz fiber prepreg, the polyimide functional interlayer, and 8 layers of 0.14 mm phthalonitrile quartz fiber prepreg are laid in sequence, and then release cloth, hole isolation film, and vacuum bag film are laid in sequence. After curing by using a hot press, the product is demolded.

[0067] Example 4

[0068] Example 4 is basically the same as Example 3, except that the interlayer composite material is molded by using a molding method. In the flat tooling, 8 layers of 0.14 mm phthalonitrile quartz fiber prepreg, the polyimide functional interlayer, and 8 layers of 0.14 mm phthalonitrile quartz fiber prepreg are laid in sequence, and then the upper and lower molds of the molding mold are assembled. After curing by using a hot press, the product is demolded.

[0069] Comparative Example 1

[0070] 90g of 4,4-diaminodiphenyl ether monomer and 1070g of N,N-dimethylacetamide were mixed and stirred to dissolve at a temperature of 5°C, and then 97g of pyromellitic dianhydride was added and stirred at a temperature of 5°C, to obtain a polyamic acid solution. The polyamic acid solution was coated on the surface of a glass plate using a coating device, and pre-baking was performed to remove the solvent, to obtain a substrate with a polyamic acid film. The substrate with the polyamic acid film was placed in a high-temperature oven for pre-curing.

[0071] After pre-curing, the substrate with the polyamic acid film was cooled to room temperature, and conductive silver paint was printed on the surface of the pre-cured substrate with the polyamic acid film by screen printing to form a conductive functional layer. The polyamic acid solution after defoaming treatment was coated on the surface of the substrate with the polyamic acid film on which the conductive functional layer was printed. After curing, the substrate was cooled to room temperature, and then immersed in water, and the polyimide film was peeled off from the surface of the glass substrate. Punching was performed using a puncher, and the hole spacing was 5cm.

[0072] In a flat mold, 8 layers of 0.14mm phthalonitrile quartz fiber prepreg, the polyimide functional interlayer, 8 layers of 0.14mm phthalonitrile quartz fiber prepreg were sequentially laid, and then release cloth, hole isolation film, and vacuum bag film were sequentially laid. After curing using a hot press, demolding was performed.

[0073] After the interlayer composite material in Comparative Example 1 was demolded, the material had visible delamination defects, and the composite material and the polyimide functional interlayer were debonded. Examples 1-4 had no visible delamination, bulging, and other defects. Table 1 below is the test results of the interlaminar shear strength of the material, and the results show that the composite materials prepared in Examples 1-4 have good mechanical properties.

[0074] Table 1: Mechanical property test of composite material

[0075]

[0076] Note: ① Example 2 used a low-cost solution for room temperature application scenarios, and used a glass mesh that was not resistant to high temperatures, so no 300°C high temperature test was performed, and therefore there is no 300°C interlaminar shear strength data. ② In Comparative Example 1, the composite material had delamination defects, i.e., the composite material layers had separated, and there was no meaning to test the interlaminar shear strength, so there is no test data.

[0077] Although the present application has been disclosed as above with examples, it is not intended to limit the present application, and appropriate modifications or equivalent replacements of the technical solutions of the present application made by those skilled in the art should be covered within the protection scope of the present application, and the protection scope of the present application is defined by the claims.

Claims

1. A method for preparing a conductive polyimide film, characterized in that, Includes the following steps: 1) Preparation of polyamic acid solution; 2) Use a coating device to coat the polyamic acid solution onto the surface of the glass substrate, perform a pre-baking treatment to remove the solvent, form a polyamic acid film on the substrate surface, obtain a substrate containing a polyamic acid film, and then place the substrate containing the polyamic acid film in a high-temperature oven for pre-curing. 3) Cool the pre-cured substrate containing the polyamic acid film from step 2) to room temperature, and then use screen printing to print a periodic array structure onto the surface of the substrate containing the polyamic acid film to form a conductive functional layer. 4) Degas the polyamic acid solution and then coat it onto the substrate surface of the polyamic acid film with the periodic array structure obtained in step 3), and pre-bake it in an oven. 5) Lay the inorganic fiber mesh on the surface of the polyamic acid-coated substrate that has been pre-baked in step 4), then pre-bake it in a drying oven to remove the solvent, and then place the substrate in a high-temperature oven for pre-curing. 6) After pre-curing and cooling to room temperature, immerse the substrate in water to peel the generated polyimide film off the substrate surface; fix the peeled polyimide film with the smooth side facing up on the surface of the flat panel fixture. 7) The inorganic fiber mesh is pre-impregnated with polyamic acid solution and then laid on the smooth surface of the polyimide film peeled off in step 6). The solvent is removed by pre-baking in a drying oven, and the film is cured in a high-temperature oven along with a flatbed device to obtain a conductive polyimide film.

2. The method for preparing the conductive polyimide film according to claim 1, characterized in that, Step 1) involves preparing a polyamic acid solution using existing methods, including: mixing an aromatic diamine monomer and a solvent and stirring once at -5 to 15°C; then adding aromatic dianhydride in portions and stirring a second time at -5 to 15°C to obtain a polyamic acid solution; the molar ratio of the aromatic diamine to the aromatic dianhydride is 1:(0.9 to 1.1); the mass percentage of the aromatic diamine to the aromatic dianhydride in the polyamic acid solution is 5% to 35%; and / or The aromatic diamine is 4,4-diaminodiphenyl ether, m-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4-diaminobiphenyl, p-phenylenediamine, 3,4-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,3'-diaminodiphenyl sulfone, 3,3'-dimethyl-4,4-diaminobiphenyl, 3,3'-diamino-benzophenone, 4,4'-diamino-benzophenone, 2,2'-bis( At least one of the following: (trifluoromethyl)-4,4'-diaminobiphenyl, 4,4'-diaminobenzoylaniline, 2,2'-bis(4-aminophenyl)hexafluoropropane, 1,3-bis(4-aminophenoxy)benzene, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 1,4-bis(2-trifluoromethyl4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, and 2,2-bis[4-(4-aminophenoxy)phenyl]propane; and / or The aromatic dianhydride is at least one selected from 3,3',4,4'-benzophenone tetracarboxylic dianhydride, pyromellitic dianhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, 4,4-hexafluoroisopropylphthalic anhydride, 2,3,3',4''-biphenyl tetracarboxylic dianhydride, 2,3,3',4''-diphenyl ether tetracarboxylic dianhydride, and 4,4'-(4,4'-isopropyldiphenoxy)bis(phthalic anhydride).

3. The method for preparing the conductive polyimide film according to claim 1, characterized in that, In step 4), the degassing treatment of the polyamic acid solution shall be performed for 20 to 40 minutes; and / or, the pre-drying treatment in the oven shall not exceed 1 hour.

4. The method for preparing the conductive polyimide film according to claim 1, characterized in that, The inorganic fiber mesh fabric in steps 5) and 7) is made of either glass fiber or quartz fiber.

5. The method for preparing the conductive polyimide film according to claim 1, characterized in that, The pre-drying conditions in step 5) are: pre-drying at 35~80℃ for 6~24h; and / or Pre-curing is thermosetting, using the following programmed temperature rise method: start heating at room temperature at a rate of 3~5℃ / min, hold at 110~130℃ for 5~15min, hold at 190~210℃ for 5~15min, and hold at 290~360℃ for 5~20min.

6. The method for preparing the conductive polyimide film according to claim 1, characterized in that, The pre-drying conditions in step 7) are: pre-drying at 35~80℃ for 6~24h; and / or Curing is achieved through heat curing, using the following programmed temperature rise method: start heating at room temperature at a rate of 3~5℃ / min, hold at 110~130℃ for 5~15min, hold at 190~210℃ for 5~15min, hold at 290~310℃ for 5~20min, and hold at 350~380℃ for 5~30min.

7. A method for preparing a conductive polyimide film sandwich composite material, characterized in that, Includes the following steps: A conductive polyimide film prepared by any one of claims 1-6 and two layers of inorganic fiber mesh fabric are placed in the mold cavity of an RTM molding die. The conductive polyimide film is located between the two layers of inorganic fiber mesh fabric, and resin is added. Then the mold is closed, cured, and demolded to obtain a composite material with a polyimide film sandwich.

8. The method for preparing the conductive polyimide film sandwich composite material as described in claim 7, characterized in that, The material of the inorganic fiber mesh is selected from one of glass fiber and quartz fiber; and / or The added resin is one of polyarylacetylene resin, cyanate ester resin, or phthalonitrile resin.

9. The method for preparing the conductive polyimide film sandwich composite material as described in claim 7, characterized in that, Resin can be added by injection after the upper and lower molds of the RTM molding die are closed; or by pre-impregnating the inorganic fiber mesh with resin and placing the two pre-impregnated layers of inorganic fiber mesh in the mold cavity of the RTM molding die.

10. A conductive polyimide film sandwich composite material, characterized in that, It is prepared by the method for preparing conductive polyimide film sandwich composite material according to any one of claims 7-9.

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