A fluorine-containing copolymer-modified meta-aramid resin, an aramid insulating film and a preparation method and application thereof

Abstract

The application relates to the technical field of high-performance polymer insulating materials, and discloses a meta-aramid resin containing fluorine copolymerization modification, an aramid insulating film and a preparation method and application thereof. The meta-aramid resin is obtained by low-temperature solution polycondensation reaction of m-phenylenediamine, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane and isophthaloyl chloride; the mole number of the 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane is 5-30% of the mole number of the m-phenylenediamine; and the mole ratio of the m-phenylenediamine and the isophthaloyl chloride is 1.01:1. The -CF3 strong electron-withdrawing group introduced by the HFBAPP forms deep energy level traps in the polymer, effectively inhibits carrier migration, reduces dielectric loss from about 0.15 of a conventional PMIA to below 0.01, and the reduction is more than 90%; the deep trap energy level introduced by the fluorine atom improves the charge injection barrier, meanwhile, the hexafluoropropane structure increases the free volume and reduces the local electric field concentration, and the breakdown strength is increased from about 60 kV / mm of a conventional one to above 90 kV / mm, and the highest can reach 116 kV / mm.

Description

Technical Field

[0001] This application relates to the field of high-performance polymer insulating materials technology, and in particular to a fluorinated copolymer modified meta-aramid resin, an aramid insulating film, its preparation method and application. Background Technology

[0002] Meta-aramid (poly(m-phenylene isophthalamide), PMIA) is a high-performance aromatic polyamide with excellent high-temperature resistance, flame retardancy, chemical stability and electrical insulation. It is widely used in electrical insulation, protective clothing, high-temperature filtration and composite materials.

[0003] In the field of electrical insulation, meta-aramid insulating paper and insulating film are used as key insulating materials for power equipment such as transformers, motors, and generators. Their dielectric properties and heat resistance are directly related to the safe operation and service life of the equipment. However, conventional meta-aramid resins have relatively high dielectric constants (approximately 3.8~4.2, 1 kHz) and dielectric losses (approximately 0.01~0.02), resulting in significant dielectric loss and heat generation under high-frequency and high-voltage conditions. Furthermore, their breakdown strength (approximately 60~80 kV / mm) is relatively low, limiting their application in higher voltage levels and higher frequency power electronic equipment.

[0004] To improve the insulation performance of meta-aramid insulating paper, existing technologies mainly employ physical blending of nanofillers (such as boron nitride, alumina, and mica). For example, patent CN202310692459.1 discloses a fluorinated graphene-modified aramid insulating paper and its preparation method, which improves insulation performance through physical doping of fluorinated graphene; however, physical blending suffers from problems such as uneven filler dispersion, interface defects, and poor long-term stability. Another method to improve its performance is to introduce fluorinated monomers for copolymerization modification, utilizing the strong electronegativity of fluorine atoms to introduce deep-level traps, suppressing carrier migration, thereby improving insulation performance. However, current research on fluorinated copolymerization modification of meta-aramid is limited, especially regarding systematic optimization of insulation performance, which has yet to be reported. Summary of the Invention

[0005] This application provides a fluorinated copolymer modified meta-aramid resin, an aramid insulating film, a preparation method thereof, and its application, aiming to solve the technical problems of high dielectric loss and low breakdown strength of existing meta-aramid resins, so as to improve their insulation performance.

[0006] To achieve the above objectives, the present application adopts the following technical solution.

[0007] In a first aspect, this application provides a fluorinated copolymer-modified meta-aramid resin, the chemical structure of which is shown in formula (1): (1) Where m is an integer from 1 to 3, and n is an integer from 17 to 19.

[0008] A second aspect of this application provides a method for preparing the above-mentioned meta-aramid resin, comprising: The meta-aramid resin was obtained by low-temperature solution polycondensation reaction of m-phenylenediamine, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane and isophthaloyl chloride. The molar amount of 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane is 5-30% of the molar amount of m-phenylenediamine; The molar ratio of m-phenylenediamine to isophthaloyl chloride is 1.01:1.

[0009] Preferably, the preparation method includes the following steps: S1, under an inert atmosphere, m-phenylenediamine and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane are dissolved in a polar organic solvent and cooled to a set temperature; under vigorous stirring, isophthaloyl chloride is added in batches to carry out a prepolymerization reaction to obtain a precursor solution; S2, the precursor solution is heated to carry out a polymerization reaction, and the pH is adjusted to 7.0~8.0 to obtain a meta-aramid resin solution.

[0010] More preferably, the polar organic solvent is at least one of N,N-dimethylacetamide, N-methylpyrrolidone, dimethylformamide, or dimethyl sulfoxide; The total concentration of m-phenylenediamine and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane in a polar organic solvent is 10-25%.

[0011] More preferably, the set temperature is -5℃ to 5℃; The polymerization reaction is carried out at a temperature of 45℃~50℃.

[0012] Further preferably, the reaction temperature is controlled to be ≤10℃ after each addition of isophthaloyl chloride; The rate of vigorous stirring is ≥500 rpm.

[0013] A third aspect of this application provides the use of the above-mentioned fluorinated copolymerized meta-aramid resin in the preparation of insulating films, insulating papers, insulating fibers or insulating composite materials.

[0014] A fourth aspect of this application provides an aramid insulating film, which is prepared by the following method: The meta-aramid resin solution prepared according to claim 2 was degassed under vacuum to obtain a film-forming stock solution; the film-forming stock solution was cast and coated on a substrate at room temperature to obtain a wet film; The wet film is dried by segmented heating and then subjected to hot pressing to obtain an aramid insulating film; Preferably, the segmented heating and drying specifically involves: The wet film was dried at 60℃ for 1 hour, then heated to 80℃ for 3 hours, and then heated to 100℃ for 24 hours. The hot pressing process is performed at a temperature of 200~220℃, a pressure of 10 MPa, and a time of 10 min.

[0015] Preferably, the vacuum degree of the vacuum degassing is ≤100 mmHg, and the degassing time is 2~4h; The coating speed of the casting process is 10~30mm / s.

[0016] Compared with the prior art, the beneficial effects of this application are as follows: This application significantly reduces dielectric loss and substantially improves breakdown strength by introducing the fluorinated diamine monomer 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP) into meta-aramid resin. Specifically, the -CF3 strong electron-withdrawing group introduced by HFBAPP forms a deep-level trap in the polymer, effectively suppressing carrier migration and reducing dielectric loss from approximately 0.15 kV / mm in conventional PMIA to below 0.01 kV / mm, a reduction of over 90%. The deep-trap energy level introduced by the fluorine atom increases the charge injection barrier, while the hexafluoropropane structure increases the free volume and reduces local electric field concentration, increasing the breakdown strength from approximately 60 kV / mm to over 90 kV / mm, with a maximum of 116 kV / mm. Furthermore, this application uses copolymerization modification to covalently link the fluorinated groups to the molecular backbone, avoiding phase separation and interfacial defects, resulting in better long-term material stability.

[0017] The preparation method of this application only requires the addition of a diamine monomer to the existing low-temperature solution polycondensation process, without the need for additional complex equipment, and is highly compatible with the existing meta-aramid production process. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 SEM image of H-PMIA-10 insulating film; Figure 2 The EDS spectrum of the H-PMIA-10 insulating film; Figure 3 XPS images of the H-PMIA-10 insulating film (Figure b) and the PMIA insulating film of Comparative Example 1 (Figure a); Figure 4 Frequency spectra of dielectric constant and dielectric loss of the insulating films in the examples and comparative examples; Figure 5 The breakdown strength diagrams of the insulating films in the examples and comparative examples are shown at a frequency of 1 kHz. Figure 6 Frequency spectrum of dielectric constant and dielectric loss of H-PMIA-10 insulating film before and after hot pressing; Figure 7 The diagram shows the breakdown strength of the H-PMIA-10 insulating film before and after hot pressing at a frequency of 1kHz. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0021] In the following description of this embodiment, the terms "including", "comprising", "having", and "containing" are all open-ended terms, meaning that they include but are not limited to.

[0022] In the following description of this embodiment, the term "and / or" is used to describe the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, B existing alone, and A and B existing simultaneously. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0023] In the following description of this embodiment, the term "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0024] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0025] Those skilled in the art should understand that, in the following description of the embodiments of this application, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0026] Those skilled in the art will understand that the numerical ranges in the embodiments of this application should be understood as each intermediate value between the upper and lower limits of the specifically disclosed range. Each smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this application. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0027] Unless otherwise stated, the technical / scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. While this application describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this application. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0028] This application provides a fluorinated copolymer-modified meta-aramid resin, the chemical structure of which is shown in formula (1): (1) Where m is an integer from 1 to 3, and n is an integer from 17 to 19.

[0029] The applicant accidentally discovered that introducing the fluorinated diamine monomer 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP) into meta-aramid resin can significantly reduce dielectric loss and substantially improve breakdown strength. This is because the strong electron-withdrawing -CF3 group introduced by HFBAPP forms a deep-level trap in the polymer, effectively suppressing carrier migration and thus significantly reducing dielectric loss. Furthermore, the deep-trap energy level introduced by the fluorine atom raises the charge injection barrier, while the hexafluoropropane structure increases the free volume, reducing local electric field concentration and further improving breakdown strength.

[0030] This application describes the preparation of meta-aramid resin by a low-temperature solution polycondensation reaction of m-phenylenediamine (MPD), 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP), and isophthaloyl chloride (IPC).

[0031] The molar amount of HFBAPP is 5-30% of the molar amount of MPD, more preferably 10%; the molar ratio of m-phenylenediamine to isophthaloyl chloride is 1.01:1.

[0032] In this application, the amount of HFBAPP introduced is a core parameter for controlling the dielectric and mechanical properties of the resin. When the proportion of HFBAPP in the molar number of m-phenylenediamine is less than 5%, the density of fluorine atoms in the molecular chain is too low, making it difficult to form effective deep-level traps. The dielectric loss remains above 0.012, and the breakdown strength improvement is less than 20%. When the proportion of HFBAPP exceeds 30%, the large molecular volume of HFBAPP significantly hinders the close packing of the molecular chains, leading to a decrease in the glass transition temperature of the resin (below 260°C). Simultaneously, the film-forming properties deteriorate, making it difficult to prepare thin films, and the polymerization reactivity decreases, making it difficult to obtain high molecular weight products. Based on this, this application preferably uses 5-30% of the total molar number of HFBAPP in the diamine, and more preferably 10%. Within this range, the dielectric loss can be reduced to below 0.01, and the breakdown strength is improved by more than 70% compared to conventional meta-aramid resins.

[0033] The fluorinated copolymer-modified meta-aramid resin of this application has a dielectric constant of 2.34 at 1 kHz, a dielectric loss tangent (tan δ) of 0.021 at 1 kHz, and an AC breakdown strength of 92.15 kV / mm.

[0034] In this application, the preparation method of the fluorinated copolymer-modified meta-aramid resin specifically includes the following steps: S1, under an inert atmosphere, m-phenylenediamine and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane are dissolved in a polar organic solvent and cooled to a set temperature; under vigorous stirring, isophthaloyl chloride is added in batches to carry out a prepolymerization reaction to obtain a precursor solution; In this application, a highly efficient desiccant (calcium hydride) can be added to the polar organic solvent to remove moisture.

[0035] In this application, the total concentration of MPD and HFBAPP in the solution obtained by dissolving MPD and HFBAPP in a polar organic solvent is 10-25 wt%, preferably 15-20 wt%.

[0036] The polar organic solvent may be at least one of N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), dimethylformamide (DMF) or dimethyl sulfoxide (DMSO), preferably DMAc.

[0037] In this application, after preparing the solution, it is cooled to a set temperature, i.e., -5℃ to 5℃. Then, under a stirring speed of ≥500 rpm, isophthaloyl chloride is added to the solution in batches, and the reaction temperature is controlled to ≤10℃ after each addition of isophthaloyl chloride. For example, isophthaloyl chloride can be added to the solution in 4 batches, with an interval of more than 5 minutes between each addition, to carry out the prepolymerization reaction.

[0038] S2, the precursor solution is heated to carry out a polymerization reaction, and the pH is adjusted to 7.0~8.0 to obtain a meta-aramid resin solution.

[0039] In this application, the polymerization reaction temperature is 45℃~50℃. After the reaction, the pH is tested and controlled at 7.0~8.0. The viscous solution after the reaction is filtered through a 400-mesh filter to obtain a fluorinated copolymerized modified meta-aramid resin solution.

[0040] The preparation method of this application only requires the addition of a diamine monomer to the existing low-temperature solution polycondensation process, without the need for additional complex equipment, and is highly compatible with the existing meta-aramid production process.

[0041] The fluorinated copolymer-modified meta-aramid resin prepared in this application has low dielectric loss, high breakdown strength, high long-term stability, and excellent insulation properties. Its dielectric constant is 2.34 at 1 kHz, its dielectric loss tangent (tan δ) is 0.021 at 1 kHz, and its AC breakdown strength is 92.15 kV / mm. It can be used to prepare insulating films, insulating papers, insulating fibers, or insulating composite materials.

[0042] This application also provides an aramid insulating film, which is prepared by the following method: The above-mentioned meta-aramid resin solution is degassed under vacuum to obtain a film-forming stock solution; the film-forming stock solution is cast and coated on a substrate at room temperature to obtain a wet film; wherein, the vacuum degree of the vacuum degasing is ≤100 mmHg and the degasing time is 2~4h; the coating speed of the casting coating is 10~30mm / s.

[0043] The wet film is dried by segmented heating and then subjected to hot pressing to obtain an aramid insulating film.

[0044] Specifically, the segmented heating and drying process involves drying the wet film at 60°C for 1 hour, then heating it to 80°C for 3 hours, and finally heating it to 100°C for 24 hours.

[0045] In this application, the three-stage heating and drying process is crucial to avoiding defects in the aramid insulating film. The first stage involves drying at 60°C for 1 hour: this temperature is below the boiling point of DMAc (165°C), allowing the solvent to evaporate slowly. If the temperature is directly raised to 120°C, the solvent will rapidly vaporize, forming bubbles inside the film and causing "pinhole" or "crater" defects on the surface. The second stage involves drying at 80°C for 3 hours: further evaporating the solvent. At this point, the film has preliminarily set and can withstand a slightly faster evaporation rate. The third stage involves drying at 120°C for 24 hours: completely removing residual solvent. If drying is incomplete, the residual solvent will vaporize during subsequent hot pressing, leading to interlayer blistering.

[0046] If the drying temperature is too low (e.g., only 80℃ at most), the residual solvent in the film will exceed 5%, and the breakdown strength after hot pressing will be less than 80 kV / mm; if the drying temperature is too high (e.g., directly 150℃), the film surface will quickly form a skin, and the internal solvent will not be able to escape, forming internal voids and causing the film to crack.

[0047] In this application, the hot pressing treatment is performed at a temperature of 200~220℃, a pressure of 10 MPa, and a time of 10 min. After hot pressing, the pressure is kept constant, and the mixture is allowed to cool naturally to room temperature (approximately 2~3 h). After the temperature drops below 50℃, the pressure is released to obtain a fluorinated copolymer-modified meta-aramid insulating film.

[0048] In this application, the hot-pressing temperature is the most critical parameter affecting the film's density and insulation performance. Below 180°C, the PMIA molecular chain segments lack sufficient mobility, failing to effectively eliminate intrafilm porosity; the breakdown strength is typically below 60 kV / mm, and the dielectric loss is greater than 0.8. Within the temperature range of 180–250°C, as the temperature increases, the degree of molecular chain rearrangement and interfacial fusion increases, gradually improving the breakdown strength. However, above 250°C, the PMIA backbone may undergo thermal oxidative cross-linking or even degradation, resulting in a darker and more brittle film. Therefore, this application preferably uses a hot-pressing high-pressure temperature of 200–220°C, with 220°C being the most preferred.

[0049] The present application will be further described below through specific embodiments.

[0050] Example 1 This embodiment provides a meta-aramid resin and an aramid insulating film, wherein the molar number of HFBAPP is 5% of the molar number of MPD, and the preparation method is as follows: S1. In a dry 1L four-necked reaction flask, connect a mechanical stirrer, thermometer, nitrogen inlet / outlet, and feed port. Purge the air with high-purity nitrogen for 30 minutes. Add 250 g of dry DMAc and 10 g of dry CaH, start stirring, and add 20.75 g of m-phenylenediamine and 5.24 g of HFBAPP to the reaction flask, stirring until completely dissolved. Place the reaction flask in an ice-salt bath and cool to an internal temperature of 0°C.

[0051] Take 40.60g of isophthaloyl chloride and place it in a dry feeder. Add the isophthaloyl chloride to the reaction flask in four batches at a stirring speed of 500 rpm, with an interval of about 5 minutes between each batch. Control the reaction temperature after each batch is added to not exceed 5℃.

[0052] S2, after all IPC has been added, remove the ice-salt bath and allow the reaction system to naturally heat up to room temperature. Then place it in a constant temperature water bath at 30°C and continue to stir at 300 rpm for 3 hours.

[0053] After the reaction was completed, the pH of the system was measured to be approximately 7.5 using precision pH test paper. The resulting viscous solution was filtered through a 400-mesh stainless steel filter and degassed under vacuum at 40°C for 2 hours to obtain a meta-aramid resin solution.

[0054] S3, the above meta-aramid resin solution was degassed under vacuum for 30 min, and then uniformly coated onto a smooth stainless steel plate at 10 mm / s using a doctor blade coating method, with the coating thickness controlled at 200 μm. It was then placed in an oven and dried at 60℃ for 1 h, then at 80℃ for 1 h, and then at 120℃ for 24 h. After cooling, it was peeled off from the steel plate to obtain the initial film. The initial film was placed in a hot press and hot-pressed at 200℃ and 10 MPa for 10 minutes. After natural cooling to room temperature, an aramid insulating film with a thickness of about 0.2 mm was obtained, which was designated as H-PMIA-5.

[0055] Example 2 This embodiment provides a meta-aramid resin and an aramid insulating film, wherein the molar number of HFBAPP is 10% of the molar number of MPD, and the preparation method is as follows: S1 differs from Example 1 in that the amount of m-phenylenediamine is changed to 19.66 g and the amount of HFBAPP is changed to 10.47 g, while the rest are the same as in Example 1.

[0056] S2 is the same as in Example 1; S3 is the same as in Example 1.

[0057] The aramid insulating film prepared in Example 2 is designated as H-PMIA-10.

[0058] Example 3 This embodiment provides a meta-aramid resin and an aramid insulating film, wherein the molar number of HFBAPP is 15% of the molar number of MPD, and the preparation method is as follows: S1 differs from Example 1 in that the amount of m-phenylenediamine is changed to 18.56 g and the amount of HFBAPP is changed to 15.71 g, while the rest are the same as in Example 1.

[0059] S2 is the same as in Example 1; S3 is the same as in Example 1.

[0060] The aramid insulating film prepared in Example 3 is designated as H-PMIA-15.

[0061] Comparative Example 1 Comparative Example 1 does not use HFBAPP. The difference between Comparative Example 1 and Example 1 is that the amount of HFBAPP used is 0. The other two are the same as in Example 1. The aramid insulating film prepared in Comparative Example 1 is denoted as PMIA.

[0062] Comparative Example 2 Comparative Example 2 uses a physical blending method, as detailed below: S1 is the same as Comparative Example 1; S2 is the same as Comparative Example 1; S3, add 5.24 g of HFBAPP to the above meta-aramid resin solution and stir until homogeneous; degas the meta-aramid resin solution under vacuum for 30 min, and then uniformly coat it onto a smooth stainless steel plate at a speed of 10 mm / s using a doctor blade coating method, controlling the coating thickness to 200 μm. Then place it in an oven and dry it first at 60℃ for 1 h, then at 80℃ for 1 h, and then at 120℃ for 24 h. After cooling, peel it off from the steel plate to obtain the initial film; The initial film was placed in a hot press and hot-pressed at 200℃ and 10 MPa for 10 minutes. After natural cooling to room temperature, an aramid insulating film with a thickness of about 0.2 mm was obtained, denoted as PMIA / HFBAPP-blend.

[0063] The microstructure and composition of the aramid insulating film prepared in Example 2 were tested. Figure 1 Its SEM image, Figure 2 Its EDS plot.

[0064] from Figure 1 It can be seen that the H-PMIA-10 insulating film has a good morphology. The film surface exhibits a continuous, non-porous, and dense morphology. No obvious phase separation, microcracks, or agglomerates were found, indicating that the resin obtained by copolymerization of MPD, HFBAPP, and IPC has good film-forming properties and forms a highly uniform condensed structure during solution casting and subsequent hot pressing.

[0065] from Figure 2 It can be seen that the H-PMIA-10 insulating film has a uniform microstructure; the fluorine content on its surface is 4%, the fluorine-containing CF3 groups are uniformly polymerized, and the fluorine-containing side groups do not undergo significant aggregation, indicating that the polymerization reaction of the fluorine-containing groups is successful.

[0066] Figure 3XPS images of the H-PMIA-10 insulating film of Example 2 (Figure b) and the PMIA insulating film of Comparative Example 1 (Figure a). From Figure 3 It can be seen that the C1s peak at 284.8 eV belongs to the aromatic carbon and amide carbon in the polymer backbone, and the N1s peak at 399.5 eV is the nitrogen atom in the amide bond, proving that the polymer chain retains the complete amide structure; while the F1s peak at 688.5 eV proves that the third monomer HFBAPP was successfully introduced.

[0067] The insulation performance of the aramid insulating films prepared in the examples and comparative examples was tested, and the specific test methods are as follows: 1. The dielectric constant and dielectric loss in the range of 1 Hz to 1 MHz at room temperature were measured using a broadband dielectric spectrometer (Novocontrol Concept 80).

[0068] 2. The AC breakdown strength was tested using a withstand voltage tester (Beijing Huace Testing Instruments, HCDJC-100kV) according to ASTM D149 standard, using spherical-plate electrodes, in transformer oil.

[0069] The frequency spectra of dielectric constant and dielectric loss of the insulating films in the examples and comparative examples are as follows: Figure 4 As shown. From Figure 4 As can be seen, compared with the conventional PMIA and physically blended insulating films of the comparative example, the insulating film prepared by the fluorinated copolymer modified resin of this application has lower dielectric constant and dielectric loss at different frequencies. This change is mainly attributed to the densification of the film and the elimination of interface defects during the hot pressing process, which reduces polarization centers and charge traps, thereby achieving a simultaneous reduction in dielectric constant and loss. Among them, the overall performance is optimal when the HFBAPP content is 10 mol%.

[0070] Table 1 shows the insulation performance test data of the insulating films of the examples and comparative examples at a frequency of 1 kHz, and the breakdown strength test graph is shown in the figure. Figure 5 As shown.

[0071] Table 1. Insulation performance test data of aramid insulating film From Table 1 and Figure 5 As can be seen, compared with conventional PMIA, the insulating film prepared by the fluorinated copolymer modified resin of this application has a dielectric loss reduced by more than 66%, a breakdown strength increased by more than 54%, and at the same time maintains excellent mechanical properties and heat resistance.

[0072] To verify the effect of hot pressing on the insulation performance of aramid insulating film, the insulation performance of the initial film before hot pressing and the insulating film after hot pressing in Example 2 were compared. The test results of dielectric loss and dielectric constant before and after hot pressing were obtained. Figure 6 As shown. From Figure 6 Test results show that the dielectric constant and dielectric loss of the insulating film after hot pressing are lower than those before hot pressing at different frequencies, indicating improved insulation performance. This is because hot pressing eliminates micropores and interface defects inside the film, optimizes the electric field distribution, and thus improves insulation performance.

[0073] Table 2 shows the insulation performance test data of the initial film before hot pressing and the insulating film after hot pressing in Example 2 at a frequency of 1kHz. The breakdown strength test diagram is shown below. Figure 7 As shown.

[0074] Table 2. Insulation performance test data of aramid insulating film before and after hot pressing in Example 2. From Table 2 and Figure 7 It can be seen that the dielectric constant and dielectric loss are significantly reduced after hot pressing; the breakdown strength before hot pressing is 92.15 kV / mm, which increases to 116.64 kV / mm after hot pressing, an increase of 26.6%. This is because hot pressing eliminates micropores and interface defects inside the film and optimizes the electric field distribution, thereby significantly improving the breakdown resistance.

[0075] Although this application has been described in detail in this specification with general descriptions and specific embodiments, some modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, such modifications or improvements made without departing from the spirit of this application are all within the scope of protection claimed in this application.

Claims

1. A fluorinated copolymer-modified meta-aramid resin, characterized in that, Its chemical structure is shown in formula (1): (1) Where m is an integer from 1 to 3, and n is an integer from 17 to 19.

2. The method for preparing the meta-aramid resin according to claim 1, characterized in that, include: The meta-aramid resin was obtained by low-temperature solution polycondensation reaction of m-phenylenediamine, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane and isophthaloyl chloride. The molar amount of 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane is 5-30% of the molar amount of m-phenylenediamine; The molar ratio of m-phenylenediamine to isophthaloyl chloride is 1.01:

1.

3. The preparation method according to claim 2, characterized in that, Includes the following steps: S1, under an inert atmosphere, m-phenylenediamine and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane are dissolved in a polar organic solvent and cooled to a set temperature; under vigorous stirring, isophthaloyl chloride is added in batches to carry out a prepolymerization reaction to obtain a precursor solution; S2, the precursor solution is heated to carry out a polymerization reaction, and the pH is adjusted to 7.0~8.0 to obtain a meta-aramid resin solution.

4. The preparation method according to claim 3, characterized in that, The polar organic solvent is at least one of N,N-dimethylacetamide, N-methylpyrrolidone, dimethylformamide, or dimethyl sulfoxide; The total concentration of m-phenylenediamine and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane in a polar organic solvent is 10-25%.

5. The preparation method according to claim 3, characterized in that, The set temperature is -5℃ to 5℃; The polymerization reaction is carried out at a temperature of 45℃~50℃.

6. The preparation method according to claim 5, characterized in that, After each addition of isophthaloyl chloride, the reaction temperature should be controlled to be ≤10℃; The rate of vigorous stirring is ≥500 rpm.

7. The use of the fluorinated copolymerized meta-aramid resin according to claim 1 in the preparation of insulating films, insulating papers, insulating fibers or insulating composite materials.

8. An aramid insulating film, characterized in that, It is prepared by the following method: The meta-aramid resin solution prepared according to claim 2 was degassed under vacuum to obtain a film-forming stock solution; the film-forming stock solution was cast and coated on a substrate at room temperature to obtain a wet film; The wet film is dried by segmented heating and then subjected to hot pressing to obtain an aramid insulating film.

9. The aramid insulating film according to claim 8, characterized in that, The segmented heating and drying process specifically involves: The wet film was dried at 60℃ for 1 hour, then heated to 80℃ for 3 hours, and then heated to 100℃ for 24 hours. The hot pressing process is performed at a temperature of 200~220℃, a pressure of 10 MPa, and a time of 10 min.

10. The aramid insulating film according to claim 8, characterized in that, The vacuum degree of the vacuum degassing is ≤100mmHg, and the degassing time is 2~4h; The coating speed of the casting process is 10~30mm / s.

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