Preparation method and application of polyetherimide-based tri-phase blended dielectric film

Abstract

This invention belongs to the field of dielectric materials technology and discloses a method for preparing a polyetherimide-based three-phase blend dielectric film and its application. Using polyetherimide as the base, polyvinylidene fluoride and polymethyl methacrylate are added for three-phase blending. The mass ratio of the three components is controlled at 1-1.4:0.1-0.3:0.03-0.20. The microphase separation structure and molecular chain stacking state of the three-phase blend system are precisely controlled through sequential dissolution and gradient drying processes. The prepared film has a thickness of 8-15 μm, is mainly amorphous, has a maximum breakdown strength of 571 MV / m at 150℃, and a storage density of up to 10.07 J / cm². 3 The energy storage efficiency is 82%. The process of this invention is simple and easy to industrialize. The resulting thin film can be used in high-temperature energy storage capacitors with an operating temperature of ≥150℃, and has important application value in aerospace, power electronics, new energy equipment and other fields.

Description

Technical Field

[0001] This invention belongs to the field of dielectric materials technology, and particularly relates to a method for preparing a polyetherimide-based three-phase blend dielectric film and its application. Background Technology

[0002] As aerospace, power electronics, rail transportation, and new energy equipment develop towards higher power density, higher operating temperature, and reliability in extreme environments, dielectric energy storage capacitors, as core energy storage and pulse power components, directly determine the safety and stability of system operation.

[0003] Compared to electrochemical energy storage devices, dielectric capacitors offer significant advantages such as fast charging and discharging speeds, high power density, long cycle life, and short response times, making them an irreplaceable device type for high-frequency, high-temperature, and high-pulse environments. However, the most widely used commercial dielectric films, such as polypropylene (PP), suffer from a significant temperature resistance bottleneck. Their dielectric breakdown strength and energy density decrease significantly at 105–110℃, making it difficult to meet the stable energy storage requirements of aerospace, power electronics, and radar systems at 120–150℃ or even higher temperatures. Therefore, developing polymer dielectric materials capable of stable operation at high temperatures has become a research hotspot.

[0004] Polyetherimide (PEI) possesses excellent heat resistance and structural strength, but its dielectric constant is relatively low; polyvinylidene fluoride (PVDF) exhibits high polarizability, but its dielectric loss is significant at high temperatures; polymethyl methacrylate (PMMA) demonstrates good film-forming properties and dielectric uniformity. Blending different polymers is an effective method for improving the overall performance of materials. However, due to differences in polarity, solubility, and molecular structure among polymers, traditional blending methods often result in significant phase separation, leading to defective structures within the film and thus reducing the material's breakdown strength and energy storage performance. Therefore, developing a preparation method capable of controlling the structure of a three-phase blend is of great significance for obtaining high-performance polymer dielectric films. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a method for preparing a polyetherimide-based three-phase blend dielectric film and its application. Through component synergistic design, sequential dissolution process, and gradient drying film-forming technology, a PEI / PMMA / PVDF three-phase blend system is constructed. Ultimately, a synergistic unity of high dielectric constant, low dielectric loss, and high breakdown strength is achieved under high temperature conditions. Furthermore, the resulting film maintains stable energy storage performance at temperatures of 150°C and above, meeting the application requirements of high-temperature energy storage capacitors in aerospace, power electronics, and rail transportation fields.

[0006] To achieve the above objectives, the present invention provides a method for preparing a polyetherimide-based triphase blend dielectric film, comprising the following steps: S1. Dry the polymer powder of polyetherimide, polymethyl methacrylate and polyvinylidene fluoride; S2. Weigh the polyetherimide, polymethyl methacrylate, and polyvinylidene fluoride according to a mass ratio of 1-1.4:0.1-0.3:0.03-0.20. First, dissolve the polyetherimide in a polar solvent and heat and stir until completely dissolved. Then add the polymethyl methacrylate and stir until completely dissolved. Finally, add the polyvinylidene fluoride, keep warm and stir until completely dissolved to form a blended solution. S3. Remove air bubbles from the blended solution, and then uniformly coat the solution onto a clean carrier using a solution casting method; S4. The carrier coated with the solution is subjected to gradient drying in sequence to obtain a carrier with a thin film attached. S5. Cool the carrier with the film attached to room temperature, soak it in warm water, peel off the film, and dry it to obtain a polyetherimide-based three-phase blend dielectric film.

[0007] Preferably, in step S1, the drying process specifically involves drying at 80°C for 4 hours. Since polymer powder is prone to absorbing water, pre-drying can reduce the impact of moisture on the dissolution process and dielectric properties.

[0008] Preferably, in step S2, the mass ratio of polyetherimide, polymethyl methacrylate, and polyvinylidene fluoride is 1.30:0.15:0.05.

[0009] Preferably, in step S2, the polar solvent is any one of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide, and the amount added is 8 mL; the amount of polyetherimide added is 1-1.4 g; the mixture is heated and stirred until completely dissolved at 50°C and 500 rpm for 3 h; the amount of polymethyl methacrylate added is 0.1-0.3 g; the mixture is stirred until completely dissolved at 70°C and 300 rpm for 3 h; and the amount of polyvinylidene fluoride added is 0.03-0.2 g; the mixture is kept warm and stirred until completely dissolved at 80°C and 600 rpm for 10 h.

[0010] Stirring should be performed in a sealed container to minimize the absorption of moisture from the air, which could affect experimental performance. There is no fixed requirement for stirring speed; it should be set according to specific conditions (such as the amount of polymer powder, rotor size, and dissolving container size). Ideally, the speed should create a vortex at 1 / 3 of the solution volume. Too low a speed will result in uneven dispersion and aggregation of polymer particles, preventing them from fully contacting the solvent and leading to low dissolution efficiency. Too high a speed will easily generate a large number of bubbles, increasing the difficulty of subsequent degassing and potentially damaging the polymer molecular chain structure.

[0011] Preferably, in step S3, bubble removal is performed by degassing at a vacuum of 80 kPa and a temperature of 60°C for 1 hour; the carrier is a glass plate.

[0012] Preferably, in step S4, the gradient drying specifically involves: first heat treatment at 80°C for 8 hours, then heat treatment at 120°C for 4 hours, and finally heat treatment under vacuum at 150°C for 2 hours. This gradient drying process allows the solvent to gradually evaporate, reducing the porosity or defect structures caused by rapid evaporation, thereby obtaining a dense and uniform dielectric film.

[0013] Preferably, in step S5, the drying is carried out at 60°C for 5-24 hours.

[0014] A polyetherimide-based three-phase blend dielectric film is also provided, which is prepared by the method for preparing polyetherimide-based three-phase blend dielectric films. The dielectric film has a thickness of 8-15 μm, is an amorphous structure, and forms a uniform microphase separation structure.

[0015] An application of polyetherimide-based three-phase blend dielectric film is also provided for the preparation of high-temperature energy storage capacitors, pulse power devices or power electronic insulation components, wherein the operating temperature of the high-temperature energy storage capacitor is ≥150℃.

[0016] In this invention, a three-phase blend system is constructed using a sequential dissolution method. Because polyetherimide (PEI) molecular chains are relatively rigid and difficult to dissolve, PEI is first dissolved in a solvent to form a stable solution. Polymethyl methacrylate (PMMA) has good polarity and compatibility; adding the PEI solution can, to some extent, adjust the interfacial structure of the system, thereby mitigating the polarity difference between PEI and PVDF. Subsequently, polyvinylidene fluoride (PVDF) is added to prevent PVDF from agglomerating or prematurely precipitating during the initial dissolution phase, thus enabling the three polymers to form a more homogeneous and stable blend system in solution.

[0017] Compared with the prior art, the present invention has the following advantages and technical effects: This invention uses polyetherimide (PEI) as a base and incorporates polyvinylidene fluoride (PVDF) and polymethyl methacrylate (PMMA) in a three-phase blend. By designing the ratio of these three components and the film-forming process, PEI provides skeletal rigidity and heat resistance, ensuring the film maintains good structural strength and insulation properties at around 150°C. Simultaneously, PMMA improves the system's compatibility and interfacial state, reducing the phase separation tendency between PEI and PVDF while retaining the high dielectric constant provided by PVDF. This results in a three-phase blend film with both high dielectric constant and low dielectric loss at high temperatures. Experimental results demonstrate that the three-phase blend dielectric film exhibits a maximum breakdown strength of 571 MV / m and a storage density of 10.07 J / cm² at 150°C. 3It has an efficiency of up to 82% and excellent overall performance.

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0019] Figure 1 Fourier transform infrared spectra of the three-phase blend dielectric thin film samples prepared in Examples 1-4; Figure 2 The XRD patterns of the three-phase blend dielectric films prepared in Examples 1-4 are shown below. Figure 3 Figure 1 shows the curves of dielectric constant and dielectric loss of the three-phase blend dielectric films prepared in Examples 1-4 as a function of temperature and frequency. In Figure 1, (a) shows the relationship between dielectric constant and dielectric loss of the three-phase blend dielectric films prepared in Examples 1-4 as a function of temperature, and (b) shows the relationship between dielectric constant and dielectric loss of the three-phase blend dielectric films prepared in Examples 1-4 as a function of frequency. Figure 4 The images show the surface and cross-sectional SEM images of the three-phase blend dielectric film prepared in Example 1, as well as the corresponding N and F element mapping images. In the figures, (a) is the surface SEM image of the three-phase blend dielectric film (scale bar is 5 μm), (b) is the F element mapping test image of the surface of the three-phase blend dielectric film, (c) is the N element mapping test image of the surface of the three-phase blend dielectric film, (d) is the cross-sectional SEM image of the three-phase blend dielectric film (scale bar is 10 μm), (e) is the F element mapping test image of the cross-section of the three-phase blend dielectric film, and (f) is the N element mapping test image of the cross-section of the three-phase blend dielectric film. Figure 5 The breakdown strength curves of the three-phase blend dielectric films prepared in Examples 1-4 are shown. Figure 6 The curves show the relationship between the recovered energy storage density and energy storage efficiency of the three-phase blend dielectric films prepared in Examples 1-4 and the electric field. Detailed Implementation

[0020] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0021] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0022] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. Experimental instruments, equipment, and reagents in the following embodiments that do not specify their sources are all commercially available materials.

[0023] Unless otherwise defined or stated, all technical and scientific terms used in this invention have the same meaning as those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein can be applied to the methods of this invention. It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other.

[0024] Example 1 A method for preparing a polyetherimide-based triphase blend dielectric film includes the following steps: (1) Weigh the required polymer powder according to the mass ratio of polyetherimide, polymethyl methacrylate and polyvinylidene fluoride 1.30:0.15:0.05, put it into a vacuum drying oven, dry at 80℃ for 4h.

[0025] (2) First, according to the experimental design, polyetherimide was added to 8 ml of N-methylpyrrolidone (NMP) and stirred for 3 h at 50 °C and 500 rpm.

[0026] (3) After it is completely dissolved, add 0.15g of polymethyl methacrylate and stir continuously at 70℃ and 300 rpm for 3h; finally add 0.05g of polyvinylidene fluoride and keep warm and stir at 80℃ and 600 rpm for 10h until it is completely dissolved and forms a homogeneous and stable blend solution.

[0027] (4) The blend solution was placed in a vacuum drying oven and degassed for 1 hour under a vacuum of 80 kPa and 60°C. The solution was then uniformly coated onto a glass plate using a solution casting method. The plate was then dried in a drying oven at 80°C for 8 hours, in a drying oven at 120°C for 4 hours, and finally in a vacuum drying oven at 150°C for 2 hours. After drying, the glass plate was removed, and the film was peeled off by immersing it in warm water. The film was then dried in a 60°C oven for 24 hours to obtain a blend film with a thickness of 9 μm. The resulting blend dielectric film was designated as 4% PVDF.

[0028] Example 2 A method for preparing a polyetherimide-based triphase blend dielectric film includes the following steps: (1) Weigh the required polymer powder according to the mass ratio of polyetherimide, polymethyl methacrylate and polyvinylidene fluoride 1.32:0.15:0.03, put it into a vacuum drying oven, set the temperature to 80℃ and dry for 4h.

[0029] (2) First, according to the experimental design, polyetherimide was added to 8 ml of N-methylpyrrolidone (NMP) and stirred for 3 h at 50 °C and 500 rpm.

[0030] (3) After it is completely dissolved, add 0.15g of polymethyl methacrylate and stir continuously at 70℃ and 300 rpm for 3h; finally add 0.03g of polyvinylidene fluoride and keep warm and stir at 80℃ and 600 rpm for 10h until it is completely dissolved and forms a homogeneous and stable blend solution.

[0031] (4) The blend solution was placed in a vacuum drying oven and degassed for 1 hour under a vacuum of 80 kPa and 60°C. The solution was then uniformly coated onto a glass plate using a solution casting method. The plate was then dried in a drying oven at 80°C for 8 hours, in a drying oven at 120°C for 4 hours, and finally in a vacuum drying oven at 150°C for 2 hours. After drying, the glass plate was removed, and the film was peeled off by immersing it in warm water. The film was then dried in a 60°C oven for 24 hours to obtain a blend film with a thickness of 11 μm. The resulting blend dielectric film was designated as 2% PVDF.

[0032] Example 3 A method for preparing a polyetherimide-based triphase blend dielectric film includes the following steps: (1) Weigh the required polymer powder according to the mass ratio of polyetherimide, polymethyl methacrylate and polyvinylidene fluoride 1.20:0.20:0.10, put it into a vacuum drying oven, set the temperature to 80℃ and dry for 4h.

[0033] (2) First, according to the experimental design, polyetherimide was added to 8 ml of N-methylpyrrolidone (NMP) and stirred for 3 h at 50 °C and 500 rpm.

[0034] (3) After it is completely dissolved, add 0.20g of polymethyl methacrylate and stir continuously at 70℃ and 300 rpm for 3h; finally add 0.10g of polyvinylidene fluoride and keep warm and stir at 80℃ and 600 rpm for 10h until it is completely dissolved and forms a homogeneous and stable blend solution.

[0035] (4) The blend solution was placed in a vacuum drying oven and degassed for 1 hour under a vacuum of 80 kPa and 60°C. The solution was then uniformly coated onto a glass plate using a solution casting method. The plate was then dried in a drying oven at 80°C for 8 hours, in a drying oven at 120°C for 4 hours, and finally in a vacuum drying oven at 150°C for 2 hours. After drying, the glass plate was removed, and the film was peeled off after immersion in warm water. The film was then dried in a 60°C oven for 24 hours to obtain a blend film with a thickness of 8 μm. The resulting blend dielectric film was designated as 6% PVDF.

[0036] Example 4 A method for preparing a polyetherimide-based triphase blend dielectric film includes the following steps: (1) Weigh the required polymer powder according to the mass ratio of polyetherimide, polymethyl methacrylate and polyvinylidene fluoride 1.00:0.30:0.20, put it into a vacuum drying oven, set the temperature to 80℃, and dry for 4 hours.

[0037] (2) First, according to the experimental design, polyetherimide was added to 8 ml of N-methylpyrrolidone (NMP) and stirred for 3 h at 50 °C and 500 rpm.

[0038] (3) After it is completely dissolved, add 0.30g of polymethyl methacrylate and stir continuously at 70℃ and 300 rpm for 3h; finally add 0.20g of polyvinylidene fluoride and keep warm and stir at 80℃ and 600 rpm for 10h until it is completely dissolved and forms a homogeneous and stable blend solution.

[0039] (4) The blend solution was placed in a vacuum drying oven and degassed for 1 hour under a vacuum of 80 kPa and 60°C. The solution was then uniformly coated onto a glass plate using a solution casting method. The plate was then dried in a drying oven at 80°C for 8 hours, in a drying oven at 120°C for 4 hours, and finally in a vacuum drying oven at 150°C for 2 hours. After drying, the glass plate was removed, and the film was peeled off by immersing it in warm water. The film was then dried in a 60°C oven for 24 hours to obtain a blend film with a thickness of 12 μm. The resulting blend dielectric film was designated as 13% PVDF.

[0040] Experimental Example 1 Performance testing.

[0041] (1) Structural characterization: Fourier transform infrared spectra of the dielectric thin film samples obtained in Examples 1-4 were tested. The results are as follows: Figure 1 As shown, at 829.1cm -1 1144.3cm -1 1721.5cm -1 1774.8cm -1 The peaks at the positions correspond to β-PVDF, the CF vibration of PVDF, the carbonyl group of PMMA, and the imide group of PEI, respectively. No new absorption peaks were observed, indicating that the components were successfully blended and no new chemical reactions occurred, and the system structure is stable.

[0042] (2) Crystal structure analysis: XRD tests were performed on the samples from Examples 1-4. The results are as follows: Figure 2As shown, all dielectric thin film samples exhibit broad diffraction halos, indicating that they are primarily amorphous. Notably, with increasing PVDF content, the diffraction peak positions gradually shift from 8.5 Å to 9.4 Å. Correspondingly, the average interchain spacing decreases from 10.4 Å to 9.41 Å. This trend suggests that the molecular chain packing density gradually increases with increasing PVDF content. The introduction of polyethyleneimine (PEI) and polyethylene glycol (PMMA) disrupts the original ordered structure of the PVDF chains and, to some extent, promotes chain rearrangement. This change in chain packing structure is expected to affect polarization behavior under an electric field, thereby optimizing the dielectric properties and energy storage characteristics of the material.

[0043] (3) Dielectric property testing: The dielectric constant and loss of the dielectric films obtained in Examples 1-4 were tested to determine their relationship with temperature and frequency. The results are as follows: Figure 3 As shown in the figure, all dielectric films in Examples 1-4 exhibited high dielectric constants, and the dielectric constant increased sequentially with increasing PVDF content. Among them, the dielectric constant and loss of Example 1 (sample 4% PVDF) were lower than the other three. This is because the microphase separation in the three phases restricted its operation, achieving a balance between high polarization and low loss. This balance is beneficial for achieving higher polarization during charging while minimizing losses during discharging, which is far superior to other sample ratios.

[0044] (4) Morphology and elemental distribution analysis: Surface and cross-sectional SEM tests, as well as N and F elemental mapping tests, were performed on the dielectric thin film sample of Example 1. The results are as follows: Figure 4 As shown, scanning electron microscopy (SEM) images reveal that the composite material containing 4 wt% PVDF blend has a smooth, crack-free surface with no observed pores or agglomerates. It also exhibits high transparency, flexibility, and homogeneity, indicating that the three-phase blend achieved high-quality blending. Energy dispersive spectroscopy (EDS) analysis shows that nitrogen (N) exhibits a cyclic distribution pattern, while fluorine (F) is uniformly distributed within the nitrogen matrix, indicating slight phase separation between the two. Cross-sectional SEM images show that the sample has a uniform and dense morphology, with layered structures and blurred phase interfaces, further confirming the formation of microphase-separated structures and good interfacial compatibility.

[0045] (5) Breakdown performance test: Figure 5The statistical results of Weibull breakdown of the films in Examples 1-4 at 150°C are presented. All samples exhibit a good linear fit, indicating that their breakdown behavior conforms to a two-parameter Weibull distribution. The fitting results show that the 4 wt% PVDF sample has the highest breakdown field strength (E_b = 571 MV / m) and a relatively high Weibull shape parameter β (14.6), indicating that it not only possesses excellent breakdown capability but also has a more concentrated breakdown data distribution, demonstrating higher reliability. In contrast, the breakdown field strength of the 13 wt% PVDF sample decreases to 365 MV / m, and the β value decreases to 8.8, indicating that its internal structural uniformity deteriorates, and local defects have a more significant impact on the breakdown behavior.

[0046] (6) Energy storage performance test: The energy storage performance of the dielectric films obtained in Examples 1-4 was tested at 150℃ and 200℃, and the results are as follows. Figure 5-6 As shown in Table 1, the performance test results at 150℃ were obtained.

[0047] Table 1. Breakdown strength and energy storage performance of dielectric thin film samples from Examples 1-4 at 150°C.

[0048] The test results show that the thin film exhibits the best overall energy storage performance when the PEI:PMMA:PVDF mass ratio is 1.30:0.15:0.05 (Example 1), reaching an energy storage density of 10.07 J / cm³ at 150°C. 3 The efficiency is 82%. As the PVDF content further increases, the dielectric constant improves, but the phase separation phenomenon intensifies, leading to a significant decrease in breakdown strength and energy storage efficiency.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a polyetherimide-based three-phase blend dielectric film, characterized in that, Includes the following steps: S1. Dry the polymer powder of polyetherimide, polymethyl methacrylate and polyvinylidene fluoride; S2. Weigh the polyetherimide, polymethyl methacrylate, and polyvinylidene fluoride according to a mass ratio of 1-1.4:0.1-0.3:0.03-0.

20. First, dissolve the polyetherimide in a polar solvent and heat and stir until completely dissolved. Then add the polymethyl methacrylate and stir until completely dissolved. Finally, add the polyvinylidene fluoride and stir to dissolve, forming a blended solution. S3. Remove air bubbles from the blended solution, and then uniformly coat the solution onto a clean carrier using a solution casting method; S4. The carrier coated with the solution is subjected to gradient drying in sequence to obtain a carrier with a thin film attached. S5. Cool the carrier with the film attached to room temperature, soak it in warm water, peel off the film, and dry it to obtain a polyetherimide-based three-phase blend dielectric film.

2. The preparation method according to claim 1, characterized in that, In step S1, the drying process specifically involves drying at 80°C for 4 hours.

3. The preparation method according to claim 1, characterized in that, In step S2, the mass ratio of polyetherimide, polymethyl methacrylate, and polyvinylidene fluoride is 1.30:0.15:0.

05.

4. The preparation method according to claim 1, characterized in that, In step S2, the polar solvent is any one of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide, with an addition amount of 8 mL. The amount of polyetherimide added is 1-1.4 g. The mixture is heated and stirred until completely dissolved at 50°C and 500 rpm for 3 h. The amount of polymethyl methacrylate added is 0.1-0.3 g. The mixture is stirred until completely dissolved at 70°C and 300 rpm for 3 h. The amount of polyvinylidene fluoride added is 0.03-0.2 g. The mixture is kept at 80°C and 600 rpm for 10 h.

5. The preparation method according to claim 1, characterized in that, In step S3, bubble removal is performed under vacuum conditions of 80 kPa and 60°C for 1 hour; the carrier is a glass plate.

6. The preparation method according to claim 1, characterized in that, In step S4, the gradient drying process specifically involves: first heat treatment at 80°C for 8 hours, then heat treatment at 120°C for 4 hours, and finally heat treatment at 150°C under vacuum for 2 hours.

7. The preparation method according to claim 1, characterized in that, In step S5, drying is carried out at 60℃ for 5-24 hours.

8. A polyetherimide-based three-phase blend dielectric film, characterized in that, The dielectric film is prepared by the preparation method according to any one of claims 1-7, and the thickness is 8-15 μm.

9. An application of the polyetherimide-based three-phase blend dielectric film as described in claim 8, characterized in that, Used to manufacture high-temperature energy storage capacitors.

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