Method for improving electrical properties of dielectric film and application thereof
By annealing the dielectric film, its crystallinity is improved, the problem of poor breakdown resistance at high temperatures is solved, and the performance and application range of the capacitor are improved.
Patent Information
- Application Number
- CN202411553210.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-01
- Publication Date
- 2025-01-10
AI Technical Summary
The existing dielectric films have poor breakdown resistance at high temperatures, resulting in a decrease in the charge and discharge efficiency of the capacitor and a decrease in the breakdown intensity, affecting normal use.
By annealing the dielectric film, its crystallinity is improved, thereby improving the breakdown characteristics and temperature resistance. The specific method includes annealing treatment for 1-12 hours at a temperature of 60-150°C, especially annealing conditions of 130-140°C. The optimal breakdown characteristics can be achieved.
It improves the breakdown and temperature resistance of the dielectric film, extends the service life of the capacitor, and expands its application scenarios.
Smart Images
Figure CN119296965A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of capacitors, and in particular relates to a method for improving the electrical performance of a dielectric film and an application thereof. Background Art
[0002] As the core component of the converter valve, the operating reliability and safety of dry DC capacitors greatly depend on the structure and performance of dielectric films. Common dielectric films include polypropylene (PP), polyvinylidene fluoride (PVDF), polyimide (PI), polyethylene terephthalate (PET), biaxially oriented polypropylene (BOPP), etc. Among them, polypropylene (PP) film is widely used in the field of metallized film capacitors due to its low dielectric loss (about 0.02%), excellent insulation performance (about 700MV / m), excellent processing performance, and good self-healing performance. However, under the influence of multiple physical fields such as electricity and heat, the rated operating temperature of PP film and capacitor is only 85℃. When the temperature is higher than this temperature, the breakdown strength may decrease and the leakage current may increase, affecting normal use. When the electric field strength is 400MV / m and the temperature is 120℃, the charge and discharge efficiency (η) of the biaxially oriented polypropylene (BOPP) film is reduced to 70% of the original charge and discharge. In general, the capacitor is defined as a failure when the capacity decay exceeds 5%. Under variable temperature, the dual effects of electric field and temperature will reduce the charging and discharging efficiency of capacitors. When an external electric field is applied to the dielectric film, electrons are accelerated under the action of the electric field force. This movement usually occurs in the loose amorphous region of the spherulite chain segment. When the energy obtained by the electron is sufficient to cause it to collide from the valence band to the conduction band, electron-hole pairs will be generated, which will lead to a sharp increase in conductivity, forming a conductive channel and eventually breakdown. Therefore, how to improve the breakdown resistance and temperature resistance of polypropylene capacitors has become a difficult and hot research topic. Summary of the invention
[0003] The present application provides a method for improving the electrical performance of a dielectric film and its application, aiming to solve the problem of poor breakdown resistance of existing dielectric films.
[0004] A first aspect of the present application provides a method for improving the electrical properties of a dielectric film, the method comprising annealing the dielectric film.
[0005] The crystallinity of the dielectric film increases with the increase of annealing temperature, and the maximum crystallinity can reach 63%. The BOPP film annealed at 140°C obtains the best breakdown characteristics, that is, the breakdown characteristics of the dielectric film can be improved after annealing, which will help improve the breakdown performance of the material at high temperature and have guiding significance for industrial production.
[0006] According to some embodiments of the method for improving electrical properties of dielectric films described in the present application, the annealing temperature is 60-150°C.
[0007] According to some embodiments of the method for improving the electrical properties of a dielectric film described in the present application, the annealing time is 1-12 hours.
[0008] According to some embodiments of the method for improving electrical properties of a dielectric film described in the present application, the annealing temperature is 130-140°C.
[0009] According to some implementations of the method for improving the electrical properties of a dielectric film described in the present application, the annealing time is 4-10 hours.
[0010] According to some embodiments of the method for improving electrical properties of a dielectric film described in the present application, the dielectric film includes a plastic film.
[0011] According to some embodiments of the method for improving electrical properties of a dielectric film described in the present application, the dielectric film includes one or more of polyvinylidene fluoride, polyimide, polyethylene terephthalate, polypropylene and biaxially oriented polypropylene film.
[0012] According to some embodiments of the method for improving electrical properties of a dielectric film described in the present application, the dielectric film is a biaxially oriented polypropylene film.
[0013] A second aspect of the present application provides a dielectric film, which is prepared by the method described in the first aspect of the present application.
[0014] The capacitors made of the dielectric film described in this application have higher breakdown resistance and wider application scenarios.
[0015] According to some embodiments of the dielectric film described in the present application, the thickness of the dielectric film is 5-7 μm.
[0016] The third aspect of the present application provides an application of the dielectric film described in the second aspect of the present application in capacitor film. The capacitor prepared by using the dielectric film described in the present application has higher breakdown resistance and wider application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Figure 1 The melting curves of biaxially oriented polypropylene dielectric films obtained at different annealing temperatures;
[0018] Figure 2 The crystallinity of biaxially oriented polypropylene dielectric films obtained at different annealing temperatures;
[0019] Figure 3Weibull distribution of biaxially oriented polypropylene dielectric films obtained at different annealing temperatures;
[0020] Figure 4 The biaxially oriented polypropylene dielectric films obtained at different annealing temperatures have a peak at 1153 cm -1 The peak intensity at φ varies with temperature. DETAILED DESCRIPTION
[0021] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.
[0022] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.
[0023] An embodiment of the present application provides a method for improving the electrical properties of a dielectric film, the method comprising annealing the dielectric film.
[0024] Annealing can cause amorphous polymer chains to be arranged into the crystalline region, forming thicker sheets. Therefore, the crystallinity increases with the increase of annealing temperature. Researchers generally believe that the higher the crystallinity of dielectric films, the more difficult it is for electrons to pass through, and the breakdown characteristics of the film will also be improved.
[0025] The crystallinity of the dielectric film increases with the increase of annealing temperature, and the maximum crystallinity can reach 63%. The BOPP film annealed at 140°C obtains the best breakdown characteristics, that is, the breakdown characteristics of the dielectric film can be improved after annealing, which will help improve the breakdown performance of the material at high temperature and have guiding significance for industrial production.
[0026] In some embodiments of the present application, the annealing temperature is 60-150° C., such as 60° C., 90° C., 110° C., 120° C., 130° C., 140° C., 150° C., etc. The annealing temperature is selected according to the melting temperature of the product to be annealed.
[0027] In some embodiments of the present application, the annealing time is 1-12 h, for example, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, etc.
[0028] In some embodiments of the present application, the annealing temperature is 130-140°C, for example, 130°C, 135°C, 138°C, 140°C, etc.
[0029] In some embodiments of the present application, the annealing time is 4-10 hours, for example, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 10 hours, etc.
[0030] In some embodiments of the present application, the dielectric film includes a plastic film. Annealing is one of the important processes for plastic modification. During the annealing process, the oriented chains of the annealed sample relax and are accompanied by the rearrangement of the chain segments, resulting in changes in structure and performance. Annealing is an effective method to change the structure and performance of semi-crystalline polymers by repairing defects and reducing stress and strain.
[0031] In some embodiments of the present application, the dielectric film includes one or more of polyvinylidene fluoride, polyimide, polyethylene terephthalate, polypropylene and biaxially oriented polypropylene film.
[0032] In some embodiments of the present application, the dielectric film is a biaxially oriented polypropylene film. Annealing can cause amorphous polymer chains to be arranged into the crystalline region to form thicker lamellae, thereby increasing the crystallinity of the product.
[0033] An embodiment of the present application also provides a dielectric film, which is prepared by the method described in the first aspect of the present application.
[0034] The dielectric film obtained by the method described in the first aspect of the present application has a higher breakdown field strength, and the capacitors prepared therefrom have a wider range of uses.
[0035] In some embodiments of the present application, the thickness of the dielectric film is 5-7 μm, for example, 5 μm, 5.8 μm, 6 μm, 6.2 μm, 7 μm, etc.
[0036] The embodiment of the present application also provides an application of the dielectric film described in the second aspect of the present application in capacitor film. The capacitor prepared by using the dielectric film described in the present application has a wider range of application scenarios.
[0037] The discharge energy density of dielectric film capacitors can be calculated by the formula Calculate. Where ε 0 is the dielectric constant of vacuum; ε ris the relative dielectric constant of the dielectric film; E is the electric field strength. Therefore, many researchers have improved the energy storage density of capacitors by improving the breakdown characteristics of dielectric films.
[0038] The biaxially oriented polypropylene film used in the examples of the present application was purchased from Ningbo Dadongnan Wanxiang Technology Co., Ltd.
[0039] Example 1
[0040] A method for improving the electrical properties of a dielectric film comprises annealing a biaxially oriented polypropylene dielectric film at 60° C. for 12 hours to obtain a dielectric film with a thickness of 5.8 μm.
[0041] Example 2
[0042] A method for improving the electrical properties of a dielectric film comprises annealing a biaxially oriented polypropylene dielectric film at 90° C. for 12 hours to obtain a dielectric film with a thickness of 5.8 μm.
[0043] Example 3
[0044] A method for improving the electrical properties of a dielectric film comprises annealing a biaxially oriented polypropylene dielectric film at a temperature of 110° C. for 12 hours to obtain a dielectric film with a thickness of 5.8 μm.
[0045] Example 4
[0046] A method for improving the electrical properties of a dielectric film comprises annealing a biaxially oriented polypropylene dielectric film at 120° C. for 12 hours to obtain a dielectric film with a thickness of 5.8 μm.
[0047] Example 5
[0048] A method for improving the electrical properties of a dielectric film comprises annealing a biaxially oriented polypropylene dielectric film at 130° C. for 12 hours to obtain a dielectric film with a thickness of 5.8 μm.
[0049] Example 6
[0050] A method for improving the electrical properties of a dielectric film comprises annealing a biaxially oriented polypropylene dielectric film at 140° C. for 12 hours to obtain a dielectric film with a thickness of 5.8 μm.
[0051] Example 7
[0052] A method for improving the electrical properties of a dielectric film comprises annealing a biaxially oriented polypropylene dielectric film at 150° C. for 12 hours to obtain a dielectric film with a thickness of 5.8 μm.
[0053] Study on the electrical properties of the dielectric films described in Examples 1-7 of the present application:
[0054] 1. Melting of the dielectric film (biaxially oriented polypropylene film, BOPP) at different annealing temperatures
[0055] The melting state of the dielectric film was analyzed using a DSCQ 200 differential scanning calorimeter (DSC) from TA instruments.
[0056] The specific operation method is as follows: 5-10 mg of biaxially oriented polypropylene dielectric film is placed in a small crucible, and then the crucible is placed in a test instrument for testing. The test temperature range is 30°C to 200°C, and the heating rate of the DSCQ 200 differential scanning calorimeter is set to 10°C / min. The melting curves of the biaxially oriented polypropylene dielectric film at 60°C, 90°C, 110°C, 120°C, 130°C, 140°C, and 150°C are recorded. The results are as follows: Figure 1 shown.
[0057] from Figure 1 It can be seen that with the increase of annealing temperature, the melting peak of the biaxially oriented polypropylene dielectric film becomes wider, because the sample annealed at a lower temperature forms an imperfect or thinner layer, while the sample annealed at a higher temperature becomes a perfect or thicker layer.
[0058] 2. Crystallinity of dielectric films (biaxially oriented polypropylene film, BOPP) obtained at different annealing temperatures
[0059] Test method: A TA instruments DSCQ 200 differential scanning calorimeter (DSC) was used to obtain the melting curve of the film. 5-10 mg of the sample was placed in a small crucible, and the crucible was placed in the instrument. The test temperature range was 30°C to 200°C, and the heating rate was set to 10°C / min.
[0060] Test instrument: TA instruments DSCQ 200 differential scanning calorimeter (DSC)
[0061] The calculation formula of crystallinity is: Where ΔH 0 The melting enthalpy of 100% crystalline PP is 209 J / g; ΔH 1 is the melting enthalpy of the sample; Xc is the crystallinity of the sample. The test results are as follows: Figure 2 shown.
[0062] from Figure 2It can be seen that as the annealing temperature increases, the crystallinity of the sample also increases. When the annealing temperature reaches 130°C, the crystallinity of the sample reaches the highest. After that, as the temperature increases, the crystallinity of the sample basically stops increasing. Annealing at 130°C for 12 hours can make the sample crystallinity reach 63%, and the crystallinity of the sample is increased by about 7% compared with that of the unannealed sample, that is, the breakdown characteristics of the dielectric film are improved.
[0063] 3. Room temperature DC breakdown test of dielectric films (biaxially oriented polypropylene film, BOPP) obtained at different annealing temperatures
[0064] The GJW-50E voltage breakdown tester produced by Huazhi Welding Test High Technology (Suzhou) Co., Ltd. was used to test 15 points of the dielectric film, and the Weibull distribution model was used to perform statistical analysis on the breakdown data.
[0065] The Weibull distribution model can reflect the probability of dielectric breakdown under a certain field strength and the dispersion of the breakdown. The statistical formula of the Weibull distribution model is:
[0066]
[0067] Where P is the cumulative breakdown probability, E is the breakdown field strength, β is the shape parameter, reflecting the dispersion of the breakdown data; α is the scale parameter, which is the breakdown field strength when the breakdown probability is 63.2%, representing the characteristic value of the breakdown data. The breakdown field strength and shape factor of BOPP films treated at different annealing temperatures are shown in Table 1. The Weibull distribution graph is shown in Figure 3 shown.
[0068] Table 1
[0069]
[0070]
[0071] Note: The test method of shape factor is the shape factor obtained by fitting and calculating through the above formula.
[0072] from Figure 3 It can be seen from Table 1 that when the annealing temperature is lower than 130°C, the breakdown field strength of the BOPP dielectric film is only slightly improved or basically unchanged compared with the unannealed sample. When the annealing temperature is higher than 130°C, the breakdown performance of the BOPP dielectric film is significantly improved, among which the breakdown field strength of the BOPP film annealed at 140°C is increased by about 21MV / m compared with the unannealed sample. However, the shape factor of the sample annealed at 150°C decreases significantly, which may be due to the high annealing temperature. At this time, the BOPP film has shrunk slightly, affecting the uniformity of the film.
[0073] Since the maximum discharge energy density of dielectric films is calculated to be related to the square of the electric field strength, it is worth paying attention to improving the breakdown field strength of samples through simple and feasible means such as heat treatment.
[0074] 4. Dielectric films (biaxially oriented polypropylene film, BOPP) obtained at different annealing temperatures at 1153 cm -1 The infrared absorption intensity at the temperature changes with the value of Figure 4 shown.
[0075] Note: BOPP film at 1153cm -1 The absorption peak at belongs to the absorption peak of the amorphous region of the BOPP film. The absorption intensity of this characteristic peak gradually increases with the increase of temperature. The more obvious the increasing trend with temperature, the higher the sensitivity to temperature, and the easier it is to be broken down under high temperature conditions. The smoother the increasing trend with temperature, the lower the sensitivity to temperature, and the less likely it is to be broken down under high temperature conditions.
[0076] from Figure 4 It can be seen that as the annealing temperature increases, the amorphous region of the BOPP film gradually becomes smoother with temperature changes, indicating that high annealing temperature is not only conducive to the arrangement of molecular chains into the lattice, but also conducive to the regularization of the amorphous region, making it less sensitive to temperature. As the annealing temperature increases, the amorphous region of the BOPP film becomes more stable, which is conducive to the improvement of the high-temperature breakdown performance of the BOPP film.
[0077] Although the above embodiments have been shown and described, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. Changes, modifications, substitutions and variations of the above embodiments by those of ordinary skill in the art are all within the scope of protection of the present invention.
Claims
1. A method for improving the electrical properties of a dielectric film, characterized in that: The method includes annealing the dielectric film.
2. The method for improving the electrical properties of a dielectric film according to claim 1, characterized in that: The annealing temperature is 60-150°C; And / or, the annealing time is 1-12h.
3. The method for improving the electrical properties of a dielectric film according to claim 1, characterized in that: The annealing temperature is 130-140°C.
4. The method for improving the electrical properties of a dielectric film according to claim 1, characterized in that: The annealing time is 4-10h.
5. The method for improving the electrical properties of a dielectric film according to claim 1, characterized in that: The dielectric film includes a plastic film.
6. The method for improving the electrical properties of a dielectric film according to claim 1, characterized in that: The dielectric film includes one or more of polyvinylidene fluoride, polyimide, polyethylene terephthalate, polypropylene and biaxially oriented polypropylene film.
7. The method for improving the electrical properties of a dielectric film according to claim 1, characterized in that: The dielectric film is a biaxially oriented polypropylene film.
8. A dielectric film, characterized in that: The dielectric film is prepared by the method according to any one of claims 1 to 7.
9. The dielectric film according to claim 8, characterized in that: The thickness of the dielectric film is 5-7 μm.
10. Use of the dielectric film according to any one of claims 8 to 9 in capacitor films.