A novel polyimide composite film material with high surface electrical strength, its preparation method and application

Abstract

This application discloses a novel polyimide composite film material with high surface electrical strength, comprising a polyimide base layer and an electrospun polyimide composite nanofiber surface layer, wherein the electrospun polyimide composite nanofiber surface layer contains a metal compound; the thickness of the polyimide composite film material is 25–250 μm. The polyimide composite film material provided in this application is composed of a polyimide resin base layer and an electrospun polyimide composite nanofiber surface layer, which are ultimately subjected to high-temperature imidization. After a chemical reaction, the layers are bonded together to form a single unit, exhibiting strong interlayer adhesion. This novel polyimide composite film material, while maintaining excellent mechanical properties, possesses a lower secondary electron emission coefficient, higher surface conductivity, and faster surface charge dissipation capability, thereby improving the surface electrical strength of the polyimide film material through multiple pathways, meeting the needs of spacecraft manufacturing for insulating materials.

Description

Technical Field

[0001] This application relates to a novel polyimide composite film material with high surface electrical strength, its preparation method and application, belonging to the technical field of high voltage insulating materials. Background Technology

[0002] Polyimide film is the world's best-performing thin-film insulating material, often referred to as "golden" film. Due to its superior comprehensive properties, including resistance to high and low temperatures, high mechanical strength, wear resistance, radiation resistance, good chemical stability, and dielectric properties, polyimide film has been widely used as a special engineering material in fields such as electrical insulation, microelectronics, space technology, and aerospace.

[0003] In space construction, polyimide films are frequently used to manufacture solar cell array substrates, thermal insulation coatings, and external coatings for spacecraft. However, the space environment is complex and variable, with various uncertainties such as plasma environments, strong radiation environments, high-energy particle bombardment, extreme temperature fluctuations, micrometeoroids and orbital debris, and solar activity. These factors can all damage spacecraft operating in space, inducing charge-discharge effects, a phenomenon particularly severe in geosynchronous orbit (GEO). When spacecraft operate in GEO, they are affected by geomagnetic substorms, placing them in a high-energy (0–50 keV) and low-density (10…) environment. 5 ~10 6 m 3 In a plasma environment, the charging and discharging phenomena become more pronounced upon entering a geomagnetic substorm plasma environment. Surface charging reaches tens of kV or higher, creating a high potential difference locally. This leads to field emission, generating primary electrons, which then collide with the surface to emit secondary electrons. This repeated electron emission and collision develops into secondary electron avalanche, ultimately triggering electrostatic discharge (ESD). ESD causes the deterioration and aging of insulating materials, and the generated electromagnetic pulse interference can affect the normal operation of electronic communication equipment. Discharge can also directly damage critical spacecraft components such as solar cell arrays and their drive mechanisms, high-power cables, and circuit boards, potentially causing spacecraft malfunctions or even complete satellite disconnection. Polyimide film, as an important insulating material in spacecraft, has a surface dielectric strength far lower than its breakdown strength. Therefore, the surface dielectric strength of polyimide film is a crucial factor limiting the insulation performance of spacecraft.

[0004] Polymer doping with nanoparticles and surface treatment are effective ways to improve the surface electrical conductivity of polymers. However, existing methods often suffer from problems such as nanoparticle agglomeration, poor interlayer bonding, reduced mechanical properties, and greater insulation risks to polyimide films. For example, patent CN104292488A provides a method for preparing a highly conductive polyimide composite film. This method mixes graphite oxide and carbon nanotubes into anhydrous hydrazine as a conductive solution, and uses dianhydride and diamine as raw materials to add to the conductive solution to prepare the polyimide composite film. Although the graphite oxide and carbon nanotubes introduced by this method can improve the conductivity of the film to a certain extent, they will destroy the excellent properties of polyimide itself. For example, after being corroded by atomic oxygen in space, the insulation performance of the polyimide film will be greatly reduced, and gases such as carbon dioxide and carbon monoxide will be generated, which will aggravate the degree of discharge damage.

[0005] Patent CN115073794A provides a method for introducing nano-alumina into a polyimide matrix using in-situ polymerization, and then constructing an alumina film on the surface of the polyimide using ion exchange. Although this method can improve the electrical strength of the film, the nano-alumina particles are prone to agglomeration in the polyimide matrix, which leads to defects and reduces the insulation performance. At the same time, the adhesion between the surface alumina film and the polyimide is weak, and it is easy to fall off quickly after being bombarded by high-energy particles in space, which will damage the stability and mechanical properties of the polyimide. Summary of the Invention

[0006] To address the aforementioned issues, this application proposes a novel polyimide composite film material with high surface electrical strength, its preparation method, and its application. Compared to the original polyimide film, this composite film material maintains excellent mechanical properties while exhibiting higher surface flashover voltage, lower surface secondary electron emission coefficient, higher surface conductivity, and faster surface charge dissipation capability, resulting in high surface electrical strength.

[0007] According to one aspect of this application, a novel high surface electrical strength polyimide composite film material is provided, comprising a polyimide base layer and an electrospun polyimide composite nanofiber surface layer, wherein the electrospun polyimide composite nanofiber surface layer contains a metal compound; the thickness of the polyimide composite film material is 25–250 μm.

[0008] Specifically, the novel polyimide composite film material provided in this application retains the polyimide resin base layer while introducing an electrospun polyimide composite nanofiber surface layer on top. The polyimide resin base layer possesses the excellent mechanical properties of polyimide films. As the surface layer, the polyimide composite nanofibers, being a network structure formed by multiple one-dimensional nanowires, can provide a more direct path for charge dissipation, accelerating the dissipation of surface charge and thus increasing conductivity. Furthermore, the metal compounds introduced during the preparation of the polyimide composite nanofibers will form metal oxides inside or on the surface of the nanofibers after high-temperature heating. These metal oxides can reduce the secondary electron emission coefficient of the material and also improve its electrical conductivity. Moreover, since the polyimide resin base layer and the electrospun polyimide composite nanofiber surface layer are simultaneously subjected to high-temperature imidization, the layers bond together after chemical reaction, resulting in strong interlayer bonding and higher structural stability of the material.

[0009] Optionally, the thickness of the polyimide composite film material is not fixed. The thickness of both the polyimide resin base layer and the electrospun polyimide composite nanofiber surface layer can be adjusted. Preferably, the thickness of the polyimide film material is 25–250 μm, which is commonly used in industry.

[0010] Furthermore, when the thickness of the polyimide film material is 25–250 μm, the thickness of the polyimide resin base layer is 24–245 μm, and the thickness of the polyimide composite nanofiber surface layer is 1–5 μm.

[0011] Optionally, the polyimide base layer is obtained by polyamic acid solution after diamine and dianhydride undergo condensation acylation reaction in solvent A, and the polyamic acid solution is prepared by coating process.

[0012] Optionally, the diamine is selected from one or more of 4,4'-diaminodiphenyl ether (ODA), p-phenylenediamine (PDA), 4,4'-diaminobiphenyl (BPA), 2,2'-bis(4-aminophenyl)hexafluoropropane (6FAP), 4,4'-diaminophenyl sulfone (DDS), hexamethylenediamine (HMDA), 2,2'-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (6F-BAPP), 4,4'-(4,4'-isopropylidene diphenyl-1,1'-dimethyldioxy)diphenylamine (IDDA) and related derivatives;

[0013] The dianhydride is selected from one or more of the following: pyromellitic dianhydride (PMDA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 4,4'-(hexafluoroisopropene) phthalic anhydride (6FDA), 4,4'-terephthalodioxydiphthalic anhydride (HQDA), 4,4'-diphenyl ether dianhydride (ODPA), and related derivatives.

[0014] Solvent A is selected from one of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and N-methylpyrrolidone (NMP).

[0015] Optionally, the surface layer of the electrospun polyimide composite nanofiber is prepared by using a polyamic acid solution as solution α, then dissolving a metal compound in solvent B as solution β, mixing solution α and solution β to form a viscous solution γ, and using solution γ as a precursor solution for electrospinning through an electrospinning process.

[0016] Solvent A is the same as solvent B.

[0017] Optionally, the metal compound is selected from one or more of chromium-containing compounds, copper-containing compounds, zinc-containing compounds, tin-containing compounds, iron-containing compounds, cobalt-containing compounds, and aluminum-containing compounds.

[0018] Preferably, the metal compound is selected from one or more of chromium-containing compounds and copper-containing compounds.

[0019] More preferably, the metal compound is selected from chromium-containing compounds, such as chromium trichloride, chromium acetate, and chromium nitrate. After heat treatment in an oxygen-containing atmosphere (such as air), the metal will be fully oxidized into metal oxides that exist inside or on the surface of the polyimide nanofibers. This reduces the secondary electron emission coefficient of the material surface, accelerates the dissipation of surface charge, and improves the material conductivity, thereby significantly increasing the surface flashover voltage of the insulating material.

[0020] According to another aspect of this application, a method for preparing the above-mentioned novel high surface electrical strength polyimide composite film material is provided, comprising the following steps:

[0021] Step 1: Sublimate the diamine and dianhydride separately in a vacuum drying oven for 2-5 hours before use;

[0022] Step 2: Weigh dianhydride and diamine using an analytical balance to make the molar ratio of dianhydride to diamine (1.01-1.05):1. Add the diamine to a three-necked flask, weigh solvent A and pour it into the three-necked flask, stir well, and after the diamine is completely dissolved, add the dianhydride to the three-necked flask in several batches, with an interval of 15-30 minutes each time. Then stir for 12 hours under nitrogen or air atmosphere to form a yellow polyamic acid (PAA) solution.

[0023] Step 3: Take the PAA solution obtained in Step 2, spread it evenly on a glass plate covered with aluminum foil, coat it with a vacuum coating machine using a scraper, and then place it in a vacuum drying oven at 80°C for 40 minutes before taking it out.

[0024] Step 4: Take the PAA solution obtained in Step 2 as solution α, then dissolve the metal compound in solvent B, and ultrasonically disperse it to form solution β. Stir the solutions α and β (volume ratio of 19:1) evenly to form a viscous solution γ (in which the content of the metal compound ranges from 0.5wt% to 5wt%), which is the precursor solution for electrospinning, with a solid content range of 15wt% to 20wt%.

[0025] Step 5: The precursor solution obtained in Step 4 is loaded into a plastic syringe with a stainless steel needle. The aluminum foil paper with a polyamic acid film covering the surface obtained after drying in Step 3 is wrapped on the rotating drum used to collect the spinning as the receiving end of electrospinning. The distance between the needle and the receiving end is 15cm. A 20kV DC high voltage is applied to the needle. The rotation speed of the rotating drum is 50-120rpm. The pushing speed of the syringe pusher is 3-6μL / min. Electrospinning is carried out for 12h, that is, a layer of polyamic acid composite nanofibers is obtained on the polyamic acid film.

[0026] Step Six: Remove the aluminum foil covering the polyamic acid composite nanofiber-polyamic acid film from Step Five, place it in an 80℃ vacuum drying oven for 1 hour, and then place it in a high-temperature drying oven to complete high-temperature imidization, thereby obtaining a novel multilayer polyimide composite film material.

[0027] Specifically, the initial liquid volume in steps three and four can be selected according to actual needs. If a large membrane area is required, take more solution; otherwise, take less.

[0028] Specifically, the above preparation method first utilizes the polycondensation acylation reaction of diamine and dianhydride to generate a polyamic acid (PAA) solution, then uses a coating method to obtain a polyamic acid film, and dries it in a vacuum oven for a period of time. This is to remove the gas mixed in on the surface and inside of the polyamic acid film, and to thermocure the polyamic acid film so that it can maintain its shape in subsequent processes, laying the foundation for the material to have good mechanical and insulating properties. Next, a polyamic acid nanofiber layer of composite metal compound is constructed on the polyamic acid film using an electrospinning process. Finally, it is placed in a high-temperature forced-air drying oven to complete high-temperature imidization. During this process, the metal compound reacts with oxygen to generate metal oxides.

[0029] On the one hand, the presence of metal oxides enables polyimide composite film materials to obtain a lower secondary electron emission coefficient and higher electrical conductivity. On the other hand, the nanofiber structure provides a good channel for charge movement, and the charge can be quickly and effectively dissipated along the nanofiber. Reducing surface secondary electron emission and slowing down charge accumulation can significantly suppress the occurrence of surface flashover. In addition, since the polyimide resin base layer and the polyimide composite nanofiber surface layer are simultaneously imidized at high temperature, the layers are bonded together after chemical reaction to form a whole. The interlayer bonding force is strong, which makes the structure of this composite material more stable.

[0030] Furthermore, in step four, the metal compound solution is placed in a clean container and ultrasonically dispersed at 40°C for 10 minutes.

[0031] Furthermore, in step four, the metal compound is selected from one or more of the following: sulfates, sulfites, nitrates, nitrites, and halides of monovalent, divalent, and / or trivalent metal ions.

[0032] In one embodiment, the soluble metal salt may be any one or more of the following: tin chloride, tin nitrate, stannous sulfate, copper bromide, copper chloride, copper sulfate, copper nitrate, copper nitrite, copper formate, copper acetate, ferrous chloride, ferrous chloride, ferrous nitrate, ferrous nitrate, ferrous sulfate, ferrous sulfate, ferrous bromide, ferrous bromide, zinc nitrate, zinc sulfate, zinc nitrite, zinc bromide, zinc chloride, zinc chlorate, zinc sulfate, aluminum nitrate, aluminum chloride, aluminum sulfate, chromium chloride, chromium nitrate, chromium sulfate, chromium acetate, cobalt bromide, cobalt chloride, cobalt iodide, cobalt nitrate, cobalt nitrite, and cobalt sulfate.

[0033] Furthermore, the solid content of the viscous solution γ obtained in step four is maintained at 15–20 wt%.

[0034] Furthermore, in step six, the high-temperature imidization adopts a gradient heating and holding method. Specifically, the heating process is as follows: heating at a rate of 5℃ / min to 120℃, 150℃, 240℃, and 300℃, holding at each temperature stage for 20 minutes, and finally heating to 350℃ and holding for 1 hour.

[0035] According to another aspect of this application, this application also provides the above-mentioned novel high surface electrical strength polyimide composite film material, and / or the application of the novel high surface electrical strength polyimide composite film material prepared by the above-mentioned preparation method in the manufacture of spacecraft insulation materials, wherein the spacecraft insulation materials include solar cell array substrates, heat insulation layers, cable insulation components and external coatings for spacecraft.

[0036] The beneficial effects that this application may produce include, but are not limited to:

[0037] 1. The novel high surface electrical strength polyimide composite film material provided in this application, structurally, uses a polyimide film as a base layer upon which an electrospun polyimide composite nanofiber surface layer is constructed. This maintains the mechanical properties of the composite film material. The overall double-layer or even multi-layer polyimide film material is equivalent to setting multiple layers of insulation protection without changing the original excellent properties of polyimide. The film surface layer exhibits a nanofiber structure, which can provide a rapid channel for charge movement, thus improving the material's conductivity and surface charge dissipation ability, and suppressing the generation of surface discharge.

[0038] 2. The novel high surface electrostatic strength polyimide composite film material provided in this application has the following composition: the added metal compound undergoes an oxidation reaction to form a metal oxide. The metal oxide has a low secondary electron emission coefficient, which can effectively weaken the development of secondary electron avalanche and reduce the surface flashover voltage.

[0039] 3. The novel high surface electrical strength polyimide composite film material provided in this application utilizes electrospinning, a method that can improve the aggregation of nanoparticles in the matrix and achieve uniform dispersion of metal oxide particles. Furthermore, the polyimide resin base layer and the surface layer of the electrospun polyimide composite nanofiber are simultaneously subjected to high-temperature imidization, resulting in chemical reactions between the layers, which enhances interlayer bonding and adhesion, maintaining the structural stability of the multilayer composite film material. The entire preparation process is relatively simple, highly operable, low in cost, safe, and does not pollute the environment, thus possessing broad prospects for aerospace applications. Attached Figure Description

[0040] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0041] Figure 1 This is a schematic diagram of the structure of the novel polyimide composite film material provided in this application;

[0042] Figure 2 This is a flowchart of the method for preparing the novel polyimide composite film material provided in this application;

[0043] Figure 3 This is a SEM microstructure image of the surface layer of the polyimide composite nanofibers in Example 1 of this application;

[0044] Figure 4 This is a schematic diagram of the polyamic acid resin base layer of Embodiment 1 of this application.

[0045] List of components and reference numerals:

[0046] 1. Polyimide resin base layer; 2. Electrospun polyimide composite nanofiber surface layer. Detailed Implementation

[0047] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of skill in the art. The reagents and raw materials used in this invention are readily available through conventional means, and unless otherwise specified, they shall be used in accordance with conventional methods in the art or as per the product instructions. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention. The preferred embodiments and materials described in this patent are for illustrative purposes only.

[0049] like Figure 1 As shown, the novel high surface electrical strength polyimide composite film material has a polyimide resin base layer as its bottom layer, and an electrospun polyimide composite nanofiber surface layer is superimposed on top of the polyimide resin base layer. The specific process for preparing the novel polyimide composite film material provided in this application is as follows: Figure 2 As shown.

[0050] Example 1

[0051] The polyimide composite material provided in Example 1 was prepared using the following method:

[0052] 1) Weigh PMDA and ODA in a molar ratio of 1.05:1, measure 40 mL of DMAc and pour it into a three-necked flask, then add ODA and stir until it is completely dissolved. After that, add PMDA into the three-necked flask in four portions, with an interval of 15 min between each portion, and stir for 12 h to obtain a yellow polyamic acid (PAA) solution.

[0053] 2) Take 7 mL of the PAA solution obtained in step 1), spread it evenly on a glass plate covered with aluminum foil, coat it with a vacuum coating machine using a scraper, and then place it in a vacuum drying oven at 80°C for 40 min before taking it out.

[0054] 3) Take 30 mL of the PAA solution obtained in step 1) as solution α, then dissolve chromium acetate in DMAc, place it in a clean container and ultrasonically disperse it at 40℃ for 10 min to form solution β. After stirring solution α and solution β evenly, a viscous solution γ (in which the content of chromium acetate is 1 wt%) is formed, which is the precursor solution for electrospinning with a solid content of 15 wt%.

[0055] 4) The precursor solution obtained in step 3) is loaded into a plastic syringe with a stainless steel needle. The aluminum foil paper with a polyamic acid film on the surface obtained after drying in step 2) is wrapped on the rotating drum used to collect the spinning as the receiving end of electrospinning. The distance between the needle and the receiving end is 15cm. A 20kV DC high voltage is applied to the needle. The rotating drum speed is 120rpm. The pushing device of the syringe is pushed at a rate of 3-6μL / min. Electrospinning is carried out for 12h, that is, a layer of polyamic acid composite nanofibers is obtained on the polyamic acid film.

[0056] 5) Remove the aluminum foil covering the polyamic acid composite nanofiber-polyamic acid film from step 4), place it in an 80℃ vacuum drying oven for 1 hour, and then place it in a high-temperature forced-air drying oven for imidization. The gradient heating process is as follows: heat to 120℃, 150℃, 240℃, and 300℃ at a rate of 5℃ / min, hold at each temperature stage for 20 minutes, and finally heat to 350℃ and hold for 1 hour. Finally, a novel double-layer polyimide composite film material with polyimide resin as the base layer and Cr2O3-containing polyimide composite nanofibers as the surface layer is obtained.

[0057] The polyimide composite film material prepared by the above method was tested for thickness using a professional thickness gauge, and the thickness of the novel polyimide composite film material was found to be 53.86 μm. The surface of the novel polyimide composite film material was characterized by AFM atomic force microscopy, and the surface roughness RMS of the treated novel polyimide composite film material was found to be 17.32 nm. Figure 3 This is a SEM microstructure image of the surface layer of the polyimide composite nanofibers in Example 1 of this application. Figure 4 This is a schematic diagram of the polyamic acid resin base layer of Embodiment 1 of this application.

[0058] Examples 2-7

[0059] The preparation methods of Examples 2-7 are the same as those of Example 1, except that the metal compounds used in step 3) are different. Examples 2-7 are SnCl2·2H2O, AlCl3·6H2O, CoCl2·6H2O, ZnCl2·H2O, CuCl2·2H2O, and FeCl2·6H2O, respectively. The remaining steps are the same.

[0060] Example 8

[0061] The preparation method of Example 8 is the same as that of Example 1, except that the highest heat treatment temperature of high-temperature imidization in step 5) is 300°C for 1 hour to obtain metal oxide layers with different surface roughness.

[0062] The novel polyimide composite film material prepared by this method was tested for thickness using a professional thickness gauge, and the thickness of the novel polyimide composite film material was found to be 53.72 μm. The surface of the material was characterized by AFM atomic force microscopy, and the surface roughness RMS of the treated novel polyimide composite film material was found to be 1.41 nm.

[0063] Example 9

[0064] The preparation method of Example 9 is the same as that of Example 1, except that the highest heat treatment temperature of high-temperature imidization in step 5) is 320°C and held for 1 hour to obtain metal oxide layers with different surface roughness.

[0065] The thickness of the novel polyimide composite film material prepared by this method was tested by a professional thickness gauge and found to be 53.75 μm. The surface of the novel polyimide composite film material was characterized by AFM atomic force microscopy and the RMS surface roughness of the treated material was found to be 1.69 nm.

[0066] Example 10

[0067] The preparation method of Example 10 is the same as that of Example 1, except that the highest heat treatment temperature of high-temperature imidization in step 5) is 400°C and held for 1 hour to obtain metal oxide layers with different surface roughness.

[0068] The novel polyimide composite film material prepared by this method was tested for thickness using a professional thickness gauge, and the thickness of the novel polyimide composite film material was found to be 53.93 μm. The surface of the material was characterized by AFM atomic force microscopy, and the surface roughness RMS of the novel polyimide composite film material after treatment was found to be 20.04 nm.

[0069] Comparative Example 1

[0070] Comparative Example 1 is a single-layer polyimide film, which was obtained directly using a coating mechanism with the same amount of PAA solution as in Example 1 and a doctor blade of the same height.

[0071] Comparative Example 2

[0072] Comparative Example 2 is a single-layer polyimide composite nanofiber film, prepared by using steps 3) to 5) in Example 1, to obtain a single-layer electrospun polyimide composite nanofiber film containing Cr2O3.

[0073] Comparative Example 3

[0074] The polyimide film material provided in Comparative Example 3 was prepared using steps 1) to 5) of Example 1, but no metal compound was added in step 3). The resulting material is an integral double-layer polyimide film material with polyimide resin as the base layer and pure polyimide nanofibers as the surface layer.

[0075] Experimental Example

[0076] The tensile strength, vacuum surface flashover voltage, maximum secondary electron emission coefficient, and surface resistivity of the polyimide composite film materials prepared in the above embodiments were tested using a universal testing machine, a vacuum surface flashover voltage testing device, a secondary electron emission coefficient testing system, and a Keithley 6517B electrometer. The results are shown in Table 1.

[0077] Table 1 Performance test data

[0078]

[0079]

[0080] As shown in Table 1, compared to single-layer polyimide films, single-layer electrospun polyimide composite nanofiber films, and bilayer polyimide film materials with pure polyimide nanofibers as the surface layer without any metal compounds, the polyimide composite film material provided in this application embodiment exhibits significantly increased initial flash voltage, aging voltage, and withstand voltage. However, not all metal oxides have the same improvement effect. Alumina, which has a high secondary electron emission coefficient, does not show a significant improvement effect, while chromium oxide and copper oxide, which have low secondary emission coefficients, have better improvement effects. When chromium oxide is selected as the metal oxide, the improvement effect is the best.

[0081] Furthermore, since the imidization heat treatment temperature affects the surface roughness of the nanofiber layer, the imidization heat treatment temperature will also have a certain impact on the electrical properties of the final polyimide composite film material. In Example 1, when the final metal oxide is chromium oxide, the heat treatment temperature of 350°C has the best effect on increasing the surface flashover voltage and reducing the maximum secondary electron emission coefficient.

[0082] Furthermore, the tensile strength was tested using a universal testing machine. As shown in the table, the polyimide prepared by pure coating in Comparative Example 1 exhibits high tensile strength and excellent mechanical properties. In contrast, the mechanical properties of the pure electrospun polyimide composite nanofiber membrane in Comparative Example 2 are poor. The method of using polyimide resin as a base layer to prepare the nanofiber surface layer improves this problem, as the polyimide base layer bears a significant portion of the force applied to the membrane, resulting in a substantial increase in tensile strength. Surface conductivity testing using an electrometer shows that the nanofiber structure significantly improves conductivity compared to the pure polyimide film. Data from Comparative Example 3 indicates that the metal oxides formed by oxidation after addition in this embodiment also improve the film's conductivity to some extent. Therefore, the method of introducing a nanofiber structure on the polyimide film and introducing metal oxides within the nanofibers in this embodiment is a more preferable approach.

[0083] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments.

[0084] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A novel polyimide composite film material with high surface electrical strength, characterized in that, It includes a polyimide base layer and an electrospun polyimide composite nanofiber surface layer, wherein the electrospun polyimide composite nanofiber surface layer contains a metal compound; The thickness of the polyimide composite film material is 25–250 μm; The polyimide base layer is obtained by polyamic acid solution after diamine and dianhydride undergo condensation acylation reaction in solvent A. The polyamic acid solution is then prepared by coating process. The surface layer of the electrospun polyimide composite nanofiber is prepared by using polyamic acid solution as solution α, then dissolving a metal compound in solvent B as solution β, mixing solution α and solution β to form viscous solution γ, and using solution γ as the precursor solution for electrospinning by electrospinning process. Solvent A is the same as solvent B.

2. The novel high surface electrical strength polyimide composite film material according to claim 1, characterized in that, The diamine is selected from one or more of 4,4'-diaminodiphenyl ether, p-phenylenediamine, 4,4'-diaminobiphenyl, 2,2'-bis(4-aminophenyl)hexafluoropropane, 4,4'-diaminophenyl sulfone, hexamethylenediamine, 2,2'-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 4,4'-(4,4'-isopropylidene diphenyl-1,1'-dimethyldioxy)diphenylamine and related derivatives; The dianhydride is selected from one or more of the following: pyromellitic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-(hexafluoroisopropene) phthalic anhydride, 4,4'-terephthalodioxydiphthalic anhydride, 4,4'-diphenyl ether dianhydride and related derivatives. Solvent A is selected from one of N,N-dimethylacetamide, N,N-dimethylformamide, and N-methylpyrrolidone.

3. The novel high surface electrical strength polyimide composite film material according to claim 1, characterized in that, The metal compound is selected from one or more of the following: chromium-containing compounds, copper-containing compounds, zinc-containing compounds, tin-containing compounds, iron-containing compounds, cobalt-containing compounds, and aluminum-containing compounds.

4. A method for preparing a novel high surface electrical strength polyimide composite film material as described in any one of claims 1-3, characterized in that, Includes the following steps: Step 1: Sublimate the diamine and dianhydride separately in a vacuum drying oven before use; Step 2: Weigh dianhydride and diamine using an analytical balance to make the molar ratio of dianhydride to diamine (1.01-1.05):

1. Add the diamine to a three-necked flask, weigh solvent A and pour it into the three-necked flask, stir well, and after the diamine is completely dissolved, add the dianhydride to the three-necked flask in several batches, with an interval of 15-30 minutes each time. Then stir under nitrogen or air atmosphere to form a yellow polyamic acid solution. Step 3: Take the polyamic acid solution obtained in Step 2, spread it evenly on a glass plate covered with aluminum foil, coat it with a vacuum coating machine using a scraper, and then place it in a vacuum drying oven to dry before taking it out. Step 4: Take the polyamic acid solution obtained in Step 2 as solution α, then dissolve the metal compound in solvent B, and ultrasonically disperse it to form solution β. After stirring solution α and solution β evenly, a viscous solution γ is formed, which is the precursor solution for electrospinning. Step 5: Load the precursor solution obtained in Step 4 into a plastic syringe with a stainless steel needle, wrap the aluminum foil paper with a polyamic acid film on the surface obtained after drying in Step 3 onto the rotating roller used for collecting spinning as the receiving end of electrospinning, and perform electrospinning to obtain a layer of polyamic acid composite nanofibers on the polyamic acid film. Step Six: Remove the aluminum foil covering the polyamic acid composite nanofiber-polyamic acid film from Step Five, place it in a vacuum drying oven for vacuum drying, and then place it in a high-temperature drying oven to complete high-temperature imidization, thereby obtaining a novel polyimide composite film material with high surface electrical strength.

5. The preparation method according to claim 4, characterized in that, In step four, the metal compound solution is placed in a clean container and ultrasonically dispersed at a temperature of 28℃-45℃ for 8-12 minutes.

6. The preparation method according to claim 4, characterized in that, The solid content of the viscous solution γ obtained in step four is maintained at 15-20 wt%. The content of metal compounds in the viscous solution γ obtained in step four ranges from 0.5 wt% to 5 wt%.

7. The preparation method according to claim 4, characterized in that, In step six, the high-temperature imidization adopts a gradient heating and holding method, with a heating rate of 5℃ / min to 120℃, 150℃, 240℃, and 300℃, and holding at each temperature stage for 20 minutes, and finally heating to 350℃ and holding for 1 hour.

8. The application of a novel high surface electrical strength polyimide composite film material as described in any one of claims 1-3, and / or the novel high surface electrical strength polyimide composite film material prepared by the preparation method as described in any one of claims 4-7, in the manufacture of spacecraft insulation materials, wherein the spacecraft insulation materials include solar cell array substrates, heat insulation layers, cable insulation components, and external coatings for spacecraft.

Images