Preparation method and application of fluorene polyester-tris (2-hydroxyethyl) cyanurate composite dielectric with high breakdown strength and dielectric performance

Abstract

The application relates to a preparation method and application of a fluorene polyester-tris (2-hydroxyethyl) cyanurate composite dielectric with high breakdown strength and dielectric performance, and relates to the technical field of composite film preparation. The application aims to solve the problem that traditional composite dielectrics cannot have high dielectric constant and high breakdown strength. The fluorene polyester-tris (2-hydroxyethyl) cyanurate composite dielectric prepared by the method has excellent dielectric performance and breakdown performance. The application provides a new material selection for high-performance capacitors and aviation materials, and is widely applied to advanced fields such as electricity, electronics and new energy vehicles. Meanwhile, the preparation equipment is simple in process operation, easy to implement, low in cost, environment-friendly and pollution-free, and provides an extremely favorable way for developing advanced polymer capacitors. The application can obtain a preparation method and application of a fluorene polyester-tris (2-hydroxyethyl) cyanurate composite dielectric with high breakdown strength and dielectric performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite film preparation, and particularly relates to a preparation method and application of fluorene polyester-tris (2-hydroxyethyl) cyanurate composite medium with high breakdown strength and dielectric performance. BACKGROUND

[0002] Over-exploitation of non-renewable energy not only causes air pollution, but also brings serious problems such as world energy shortage. The development and utilization of clean energy provides a solution to these major global problems. However, the full use of new energy needs to overcome the randomness and intermittency of the application system through advanced energy storage devices. As a widely used fast charge-discharge energy storage device, dielectric capacitor plays a crucial role in new energy electric vehicles, pulse power supply and medical equipment. For example, BOPP film is widely used in commercial dielectric medium, which is a biaxially oriented polypropylene film. It belongs to non-polar polymer, and the breakdown field strength can reach 700 kV / mm at room temperature, and the dielectric constant is about 2.25 at a frequency of 1 kHz, and the energy storage density is only 1-2 J / cm 3 Pure polymers are difficult to have both high polarization properties and insulation properties, so the exploration of polymer-based composite medium has become an effective way to improve the energy storage density. The common filling type composite medium is usually filled with inorganic fillers such as ceramics, metal oxides and graphene, which enhances the interface polarization to improve the dielectric constant, but also causes the decline of the field strength. Although the dielectric constant and polarization capacity of the composite medium after random filling are improved, the overall insulation performance of the medium is reduced due to the uneven distribution of electric field and the presence of conductive paths. SUMMARY

[0003] The purpose of the present application is to solve the problem that the traditional composite medium cannot have high dielectric constant and high breakdown strength, and to provide a preparation method and application of fluorene polyester-tris (2-hydroxyethyl) cyanurate composite medium with high breakdown strength and dielectric performance.

[0004] A preparation method of fluorene polyester-tris (2-hydroxyethyl) cyanurate composite medium with high breakdown strength and dielectric performance is as follows:

[0005] Step S1: preparing a mixed solution;

[0006] The fluorene polyester particles and tris (2-hydroxyethyl) cyanurate particles are added to the N-methyl pyrrolidone solution, and after sufficient stirring, the mixed solution is obtained; the tris (2-hydroxyethyl) cyanurate particles account for 0.5%, 1.0%, 1.5% or 2.0% of the total mass of the fluorene polyester particles and the tris (2-hydroxyethyl) cyanurate particles;

[0007] Step S2: preparing fluorene polyester-tris (2-hydroxyethyl) cyanurate composite medium;

[0008] The mixed solution obtained in step S1 is uniformly coated on one side of the pretreated substrate, then the substrate is gradiently heat treated, cooled to room temperature after the heat treatment is completed, the composite medium on the substrate is peeled off, and finally dried to obtain the fluorene polyester-tris (2-hydroxyethyl) cyanurate composite medium with high breakdown strength and dielectric performance.

[0009] The application of the fluorene polyester-tris (2-hydroxyethyl) cyanurate composite medium with high breakdown strength and dielectric performance in capacitors and aerospace materials.

[0010] The principles of the present application:

[0011] The fluorene polyester-tris (2-hydroxyethyl) cyanurate composite medium with high breakdown strength and dielectric performance is composed of fluorene polyester and tris (2-hydroxyethyl) cyanurate, and the composite medium contains multiple concentration components of fluorene polyester and tris (2-hydroxyethyl) cyanurate.

[0012] The advantages of the present application:

[0013] (1) The preparation method of the fluorene polyester-tris (2-hydroxyethyl) cyanurate composite medium with high breakdown strength and dielectric performance, FPE particles and tris (2-hydroxyethyl) cyanurate particles are dissolved in N-methyl pyrrolidone at different mass ratios to form a mixed solution, which is coated and dried. Based on the performance requirements of general electronic devices, the composite medium needs high dielectric constant and high breakdown strength. Tris (2-hydroxyethyl) cyanurate with several times higher dielectric constant than FPE is doped in FPE. Due to the presence of hydroxyl (-OH) and cyanurate ion (-C3N3O3) in tris (2-hydroxyethyl) cyanurate, the dielectric constant of the composite medium after doping tris (2-hydroxyethyl) cyanurate is improved. Pure FPE film itself has very high breakdown strength, and tris (2-hydroxyethyl) cyanurate has lower electronic conductivity, which can absorb a certain degree of carrier injection and transport, so the breakdown strength of the composite medium after doping is improved compared with pure FPE film.

[0014] (2) The fluorene polyester-tris (2-hydroxyethyl) cyanurate composite medium prepared by the method of the present application has excellent dielectric performance and breakdown performance. This provides a new material selection for high-performance capacitors and aerospace materials, and is widely used in advanced fields such as electrical, electronic and new energy vehicles. At the same time, the preparation equipment of the present application is simple and easy to operate, and has low cost and no pollution, which provides an extremely favorable way for the development of advanced polymer capacitors.

[0015] The application can obtain a preparation method and application of fluorene polyester-tris (2-hydroxyethyl) cyanurate composite medium with high breakdown strength and dielectric performance. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 A cross-section scanning electron microscope image of the fluorene polyester-tris (2-hydroxyethyl) cyanurate composite medium prepared in Example 1 is shown;

[0017] Figure 2 Test infrared spectrograms of the pure FPE film and the fluorene polyester-tris (2-hydroxyethyl) cyanurate composite medium prepared by the application are shown, pure represents the pure FPE film, 0.5% represents that the tris (2-hydroxyethyl) cyanurate particles account for 0.5% of the total mass of the fluorene polyester particles and the tris (2-hydroxyethyl) cyanurate particles, 1.0% represents that the tris (2-hydroxyethyl) cyanurate particles account for 1.0% of the total mass of the fluorene polyester particles and the tris (2-hydroxyethyl) cyanurate particles, 1.5% represents that the tris (2-hydroxyethyl) cyanurate particles account for 1.5% of the total mass of the fluorene polyester particles and the tris (2-hydroxyethyl) cyanurate particles, and 2.0% represents that the tris (2-hydroxyethyl) cyanurate particles account for 2.0% of the total mass of the fluorene polyester particles and the tris (2-hydroxyethyl) cyanurate particles;

[0018] Figure 3 A direct current breakdown Weibull distribution diagram of the pure FPE film and the fluorene polyester-tris (2-hydroxyethyl) cyanurate composite medium prepared by the application is shown, ★ represents the FPE film in Comparative Example 1, ▲ represents the composite medium with a tris (2-hydroxyethyl) cyanurate mass fraction of 0.5%, ♦ represents the composite medium with a tris (2-hydroxyethyl) cyanurate mass fraction of 1.0%, ▼ represents the composite medium with a tris (2-hydroxyethyl) cyanurate mass fraction of 1.5%, and ● represents the composite medium with a tris (2-hydroxyethyl) cyanurate mass fraction of 2.0%;

[0019] Figure 4 A dielectric constant test result of the pure FPE film and the fluorene polyester-tris (2-hydroxyethyl) cyanurate composite medium prepared by the application is shown, ★ represents the FPE film in Comparative Example 1, ▲ represents the composite medium with a tris (2-hydroxyethyl) cyanurate mass fraction of 0.5%, ♦ represents the composite medium with a tris (2-hydroxyethyl) cyanurate mass fraction of 1.0%, ▼ represents the composite medium with a tris (2-hydroxyethyl) cyanurate mass fraction of 1.5%, and ● represents the composite medium with a tris (2-hydroxyethyl) cyanurate mass fraction of 2.0%;

[0020] Figure 5The dielectric loss test results of the pure FPE film and the fluorene polyester-tris (2-hydroxyethyl) cyanurate composite medium prepared in the present application are shown in the figure, the ★ represents the FPE medium in Comparative Example 1, the ▲ represents the composite medium with a mass fraction of 0.5% of tris (2-hydroxyethyl) cyanurate, the ♦ represents the composite medium with a mass fraction of 1.0% of tris (2-hydroxyethyl) cyanurate, the ▼ represents the composite medium with a mass fraction of 1.5% of tris (2-hydroxyethyl) cyanurate, and the ● represents the composite medium with a mass fraction of 2.0% of tris (2-hydroxyethyl) cyanurate;

[0021] Figure 6 The AC conductivity test results of the pure FPE film and the fluorene polyester-tris (2-hydroxyethyl) cyanurate composite medium prepared in the present application are shown in the figure, the ★ represents the FPE medium in Comparative Example 1, the ▲ represents the composite medium with a mass fraction of 0.5% of tris (2-hydroxyethyl) cyanurate, the ♦ represents the composite medium with a mass fraction of 1.0% of tris (2-hydroxyethyl) cyanurate, the ▼ represents the composite medium with a mass fraction of 1.5% of tris (2-hydroxyethyl) cyanurate, and the ● represents the composite medium with a mass fraction of 2.0% of tris (2-hydroxyethyl) cyanurate. DETAILED DESCRIPTION

[0022] Specific implementation mode one: the preparation method of the fluorene polyester-tris (2-hydroxyethyl) cyanurate composite medium with high breakdown strength and dielectric performance in the present embodiment is carried out according to the following steps:

[0023] Step S1: preparation of a mixed solution;

[0024] The fluorene polyester particles and the tris (2-hydroxyethyl) cyanurate particles are added to the N-methyl pyrrolidone solution, and after being fully stirred, a mixed solution is obtained; the mass fraction of the tris (2-hydroxyethyl) cyanurate particles in the total mass of the fluorene polyester particles and the tris (2-hydroxyethyl) cyanurate particles is 0.5%, 1.0%, 1.5% or 2.0%;

[0025] Step S2: preparation of a fluorene polyester-tris (2-hydroxyethyl) cyanurate composite medium;

[0026] The mixed solution obtained in step S1 is uniformly coated on one side of the pretreated substrate, and then the substrate is subjected to gradient heat preservation. After the heat preservation is completed, the substrate is cooled to room temperature, the composite medium on the substrate is then peeled off, and finally the substrate is dried to obtain the fluorene polyester-tris (2-hydroxyethyl) cyanurate composite medium with high breakdown strength and dielectric performance.

[0027] Specific implementation mode two: the difference between the present embodiment and specific implementation mode one is that the ratio of the total mass of the fluorene polyester particles and the tris (2-hydroxyethyl) cyanurate particles to the volume of the N-methyl pyrrolidone solution in step S1 is (0.4-0.5) g:(3.5-4) mL.

[0028] The other steps are the same as in Embodiment One.

[0029] Embodiment Three: The difference between this embodiment and Embodiments One or Two is that the stirring in Step S1 is performed at a temperature of 20-25°C for 8-10 hours.

[0030] The other steps are the same as in Embodiments One or Two.

[0031] Embodiment Four: The difference between this embodiment and any one of Embodiments One to Three is that the stirring in Step S1 is performed using a magnetic stirrer.

[0032] The other steps are the same as in Embodiments One to Three.

[0033] Embodiment Five: The difference between this embodiment and any one of Embodiments One to Four is that the stirring speed in Step S1 is 300-400 r / min.

[0034] The other steps are the same as in Embodiments One to Four.

[0035] Embodiment Six: The difference between this embodiment and any one of Embodiments One to Five is that the pretreated substrate in Step S2 is treated according to the following steps: first washing the substrate with water added with dishwashing liquid for 3-5 times, then rinsing with clean water for 3-5 times, then washing with deionized water for 3-5 times, and finally washing with anhydrous ethanol for 3-5 times, and then drying with a hair dryer and wiping with non-woven fabric, to obtain the pretreated substrate, wherein the substrate is a glass plate with a size of (10-15) cm * (30-35) cm.

[0036] The other steps are the same as in Embodiments One to Five.

[0037] Embodiment Seven: The difference between this embodiment and any one of Embodiments One to Six is that the drying temperature in Step S2 is 80°C.

[0038] The other steps are the same as in Embodiments One to Six.

[0039] Embodiment Eight: The difference between this embodiment and any one of Embodiments One to Seven is that the gradient temperature holding step in Step S2 is: first heating the substrate to 50-60°C, and holding at 50-60°C for 8-10 hours, and then increasing the temperature to 80-90°C, and continuing to hold for 8-10 hours.

[0040] The other steps are the same as in Embodiments One to Seven.

[0041] Specific embodiment nine: the difference between this embodiment and one of the specific embodiments one to eight is that the thickness of the fluorene polyester-tris (2-hydroxyethyl) cyanurate composite medium with high breakdown strength and dielectric performance in step S2 is 8-12 μm.

[0042] The other steps are the same as specific embodiments one to eight.

[0043] Specific embodiment ten: the application of a fluorene polyester-tris (2-hydroxyethyl) cyanurate composite medium with high breakdown strength and dielectric performance, the application of the fluorene polyester-tris (2-hydroxyethyl) cyanurate composite medium with high breakdown strength and dielectric performance in capacitors and aerospace materials.

[0044] The beneficial effects of the present application are verified by the following examples:

[0045] Example 1: a preparation method of a fluorene polyester-tris (2-hydroxyethyl) cyanurate composite medium with high breakdown strength and dielectric performance, which is carried out according to the following steps:

[0046] Step S1: preparation of a mixed solution;

[0047] The fluorene polyester (FPE) particles and tris (2-hydroxyethyl) cyanurate particles are added to 3.5 mL of N-methyl pyrrolidone (NMP) solution, and are magnetically stirred at a speed of 350 r / min at a temperature of 25°C for 10 h to obtain a mixed solution; the total mass of the fluorene polyester particles and tris (2-hydroxyethyl) cyanurate particles is 0.4 g, and the mass fraction of tris (2-hydroxyethyl) cyanurate particles is 0.5%.

[0048] Step S2: preparation of a fluorene polyester-tris (2-hydroxyethyl) cyanurate composite medium;

[0049] First, the substrate is washed with water added with detergent for 3 times, then washed with clean water for 3 times, then washed with deionized water for 3 times, and finally washed with anhydrous ethanol for 3 times; after washing, the anhydrous ethanol is evaporated under a hair dryer, the non-woven fabric is used to dry, and the pretreated substrate is placed on a glass plate rack; the substrate is a glass plate with a size of 10*30 cm;

[0050] The mixed solution obtained in step S1 is uniformly coated on one side of the pretreated glass plate, and then the glass plate is placed in a forced air oven, heated to 60°C, and kept at 60°C for 10 h, then heated to 80°C, and kept at 80°C for 10 h to remove the solvent in the composite medium; after the heat preservation is completed, it is cooled to room temperature at room temperature, then the composite medium on the glass plate is peeled off, and finally it is placed in a vacuum oven at 80°C for drying, to obtain a fluorene polyester-tris (2-hydroxyethyl) cyanurate composite medium with high breakdown strength and dielectric performance (such as Figure 1(As shown), the thickness is 8-12 μm.

[0051] Example 2: In this example, tri(2-hydroxyethyl) cyanurate particles accounted for 1.0% of the total mass of fluorene polyester particles and tri(2-hydroxyethyl) cyanurate particles. All other experimental conditions were the same as in Example 1.

[0052] Example 3: In this example, tri(2-hydroxyethyl) cyanurate particles accounted for 1.5% of the total mass of fluorene polyester particles and tri(2-hydroxyethyl) cyanurate particles. All other experimental conditions were the same as in Example 1.

[0053] Example 4: In this example, tri(2-hydroxyethyl) cyanurate particles accounted for 2.0% of the total mass of fluorene polyester particles and tri(2-hydroxyethyl) cyanurate particles. All other experimental conditions were the same as in Example 1.

[0054] Comparative Example 1: Preparation of FPE film;

[0055] S1: Take FPE and N-methylpyrrolidone solutions according to the mass ratio of FPE to N-methylpyrrolidone of 0.4g:3.5mL respectively; add FPE to N-methylpyrrolidone and mechanically stir at 25℃ for 10h to obtain pure FPE solution; place the coated glass plate in an 80℃ forced-air oven for heating and heat preservation for 10h.

[0056] S2: Remove the glass plate and cool it to room temperature. Finally, use deionized water to peel off the composite medium and dry it in a vacuum oven at 60°C to obtain a pure FPE film.

[0057] Figure 2 The image shows the infrared spectra of the pure FPE film and the fluorene polyester-tris(2-hydroxyethyl) cyanurate composite medium prepared according to the present invention. "pure" indicates pure FPE film; "0.5%" indicates that the tris(2-hydroxyethyl) cyanurate particles account for 0.5% of the total mass of the fluorene polyester particles and tris(2-hydroxyethyl) cyanurate particles; "1.0%" indicates that the tris(2-hydroxyethyl) cyanurate particles account for 1.0% of the total mass of the fluorene polyester particles and tris(2-hydroxyethyl) cyanurate particles; "1.5%" indicates that the tris(2-hydroxyethyl) cyanurate particles account for 1.5% of the total mass of the fluorene polyester particles and tris(2-hydroxyethyl) cyanurate particles; and "2.0%" indicates that the tris(2-hydroxyethyl) cyanurate particles account for 2.0% of the total mass of the fluorene polyester particles and tris(2-hydroxyethyl) cyanurate particles.

[0058] like Figure 2 As shown, 1742cm -1 The peak corresponds to the stretching vibration of the C=O bond in the FPE matrix. Compared with pure FPE film, the fluorene polyester-tris(2-hydroxyethyl) cyanurate composite medium exhibits a peak at 3067 cm⁻¹.-1 A new characteristic peak was observed at 1613 cm⁻¹, corresponding to the stretching vibration peak of the hydroxyl group (-OH) in tris(2-hydroxyethyl) cyanurate. -1 The vibrational peaks corresponding to the carbonyl group (-C=O) indicate that tris(2-hydroxyethyl) cyanurate was successfully introduced into the FPE matrix.

[0059] Figure 3 The diagram shows the DC breakdown Weibull distribution of the pure FPE film and the fluorene polyester-tris(2-hydroxyethyl) cyanurate composite dielectric prepared in this invention. ★ represents the FPE film in Comparative Example 1, ▲ represents the composite dielectric with a tris(2-hydroxyethyl) cyanurate mass fraction of 0.5%, ◆ represents the composite dielectric with a tris(2-hydroxyethyl) cyanurate mass fraction of 1.0%, ▼ represents the composite dielectric with a tris(2-hydroxyethyl) cyanurate mass fraction of 1.5%, and ● represents the composite dielectric with a tris(2-hydroxyethyl) cyanurate mass fraction of 2.0%.

[0060] like Figure 3 As shown, the breakdown field strengths of pure FPE film and fluorene polyester-tris(2-hydroxyethyl) cyanurate composite dielectric are 713.9, 517.8, 580.4, 629.2, and 904.3 MV / m, respectively. Compared with pure FPE film, the breakdown field strength of the composite dielectric with a tris(2-hydroxyethyl) cyanurate mass fraction of 2.0% is significantly improved. Since the breakdown field strength of tris(2-hydroxyethyl) cyanurate is relatively low, a small amount of doping will decrease the overall breakdown field strength of the composite dielectric; however, when tris(2-hydroxyethyl) cyanurate is doped to a certain concentration, it will introduce a composite interface, thereby increasing the breakdown field strength.

[0061] Figure 4 The dielectric constant test results of the pure FPE film and the fluorene polyester-tris(2-hydroxyethyl) cyanurate composite medium prepared by this invention are shown. ★ indicates the FPE film in Comparative Example 1, ▲ indicates the composite medium with a tris(2-hydroxyethyl) cyanurate mass fraction of 0.5%, ◆ indicates the composite medium with a tris(2-hydroxyethyl) cyanurate mass fraction of 1.0%, ▼ indicates the composite medium with a tris(2-hydroxyethyl) cyanurate mass fraction of 1.5%, and ● indicates the composite medium with a tris(2-hydroxyethyl) cyanurate mass fraction of 2.0%.

[0062] like Figure 4As shown, the relative permittivity of all composite films gradually decreases with increasing frequency. This is because, at high frequencies, the dipole moment reversal of the polymer medium cannot quickly follow changes in the electric field, resulting in a hysteresis effect of polarization, which further induces relaxation. At the same frequency, the composite medium doped with tris(2-hydroxyethyl) cyanurate has a higher relative permittivity than the pure FPE film. At 1 Hz, the relative permittivity of the prepared pure FPE film and the FPE and tris(2-hydroxyethyl) cyanurate composite medium are 3.7, 3.7, 3.8, 3.3, and 3.7, respectively.

[0063] Figure 5 The values ​​represent the dielectric loss test results of the pure FPE film and the fluorene polyester-tris(2-hydroxyethyl) cyanurate composite dielectric prepared in this invention. ★ represents the FPE dielectric in Comparative Example 1, ▲ represents the composite dielectric with a tris(2-hydroxyethyl) cyanurate mass fraction of 0.5%, ◆ represents the composite dielectric with a tris(2-hydroxyethyl) cyanurate mass fraction of 1.0%, ▼ represents the composite dielectric with a tris(2-hydroxyethyl) cyanurate mass fraction of 1.5%, and ● represents the composite dielectric with a tris(2-hydroxyethyl) cyanurate mass fraction of 2.0%.

[0064] like Figure 5 As shown, the dielectric loss of all composite dielectrics exhibits a trend of first decreasing and then increasing with increasing frequency. At low frequencies, the electric field changes relatively slowly, making it difficult for electrons in the dielectric to respond quickly to changes in the electric field, leading to a decrease in dielectric loss. However, at high frequencies, the electric field changes more rapidly, causing the inherent losses in the dielectric to gradually increase, resulting in an increase in dielectric loss. At the same frequency, the dielectric loss of the fluorene polyester-tris(2-hydroxyethyl) cyanurate composite dielectric is higher than that of the pure FPE film, and it decreases continuously with increasing overall and gradient concentrations of tris(2-hydroxyethyl) cyanurate.

[0065] Figure 6 The figures represent the AC conductivity test results of the pure FPE film and the fluorene polyester-tris(2-hydroxyethyl) cyanurate composite medium prepared in this invention. ★ represents the FPE medium in Comparative Example 1, ▲ represents the composite medium with a tris(2-hydroxyethyl) cyanurate mass fraction of 0.5%, ◆ represents the composite medium with a tris(2-hydroxyethyl) cyanurate mass fraction of 1.0%, ▼ represents the composite medium with a tris(2-hydroxyethyl) cyanurate mass fraction of 1.5%, and ● represents the composite medium with a tris(2-hydroxyethyl) cyanurate mass fraction of 2.0%.

[0066] like Figure 6 As shown, the AC conductivity of all polymer media increases with increasing frequency, which is attributed to increased polarization loss and space charge effect at high frequencies.

Claims

1. A method for preparing a fluorene polyester-tris(2-hydroxyethyl) cyanurate composite dielectric with both high breakdown strength and dielectric properties, characterized in that... The preparation method is carried out according to the following steps: Step S1: Prepare a mixed solution; Fluorene polyester particles and tris(2-hydroxyethyl) cyanurate particles were added to 3.5 mL of N-methylpyrrolidone solution and magnetically stirred at 350 r / min for 10 h at 25 °C to obtain a mixed solution; the total mass of fluorene polyester particles and tris(2-hydroxyethyl) cyanurate particles was 0.4 g, and the mass fraction of tris(2-hydroxyethyl) cyanurate particles was 2%; Step S2: Preparation of fluorene polyester-tris(2-hydroxyethyl) cyanurate composite medium; First, the substrate is washed three times with water containing detergent, then rinsed three times with clean water, then washed three times with deionized water, and finally washed three times with anhydrous ethanol. After washing, the anhydrous ethanol is evaporated under a hair dryer, dried with a non-woven cloth, and placed on a glass plate holder to obtain a pre-treated substrate. The substrate is a glass plate with a size of 10*30cm. The mixed solution obtained in step S1 is uniformly coated on one side of a pretreated glass plate. The glass plate is then placed in a forced-air oven and heated to 60°C for 10 hours. The temperature is then increased to 80°C and maintained for another 10 hours to remove the solvent from the composite medium. After the heat treatment is completed, the plate is cooled to room temperature, and the composite medium is peeled off from the glass plate. Finally, the plate is dried in an 80°C vacuum oven to obtain a fluorene polyester-tris(2-hydroxyethyl) cyanurate composite medium with high breakdown strength and dielectric properties, with a thickness of 8–12 μm.

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