Method for preparing cyclic olefin copolymer composite insulating dielectric film

Abstract

A method for preparing a cyclic olefin copolymer composite insulating dielectric film, belonging to the field of capacitors. This invention addresses the problem of deteriorating insulation properties and reduced energy storage efficiency in existing polymer dielectric film capacitors under high temperature or high electric field conditions. The method includes the following steps: 1. Preparing a cyclic olefin copolymer solution; 2. Preparing an anhydride-grafted cyclic olefin copolymer solution; 3. Adding a high-polarity diamine monomer to the anhydride-grafted cyclic olefin copolymer solution for reaction, followed by coating and gradient-heating thermal imidization treatment. This method is used to prepare a cyclic olefin copolymer composite insulating dielectric film.

Description

Technical Field

[0001] The invention belongs to the field of capacitors. Background Art

[0002] Polymer dielectric film capacitors are gaining increasing attention due to their high breakdown voltage, low cost, easy processing, fast charge and discharge speeds, and excellent operational stability. However, at high temperatures or in high electric fields, film capacitors experience insulation degradation and reduced energy storage efficiency due to a dramatic increase in conductivity losses. Therefore, improving the high-temperature resistance of capacitor films is of great research value.

[0003] In recent years, inorganic nanofillers with low dielectric constants and wide bandgap fillers have been added to polymers to improve high-temperature performance in order to reduce conductivity losses. However, good modification effects can only be achieved when small-sized nanoparticles are uniformly dispersed in the matrix. Once agglomeration occurs, the electrical properties will be severely degraded. To eliminate or avoid the adverse effects of inorganic fillers and improve the electrical properties of polymers, organic fillers have been introduced into polymers. However, the difference in thermal properties between the matrix and the organic filler can lead to thermal runaway and thermal separation. Multilayer structure design can synergize the characteristics of each membrane and improve the energy storage performance of the membrane. However, due to the poor compatibility between adjacent layers of multilayer polymer composites, delamination during the stretching process will pose a huge safety hazard to the operation of film capacitors. Therefore, finding a simple and effective preparation method and modification means to obtain dielectric thin film polymers with excellent insulation and energy storage properties at high temperatures has become one of the important research directions.

[0004] The rigid structure of cyclic olefin copolymer (COC) itself gives it a large band gap and a high glass transition temperature (Tg), reducing high-temperature conduction losses. These properties make COC promising for the development of high-temperature polymer capacitors, meeting the current requirements for dielectric capacitors. However, it still cannot solve the existing problems of deteriorating insulation properties and reduced energy storage efficiency of polymer dielectric film capacitors under high temperature or high electric field conditions. Summary of the Invention

[0005] The present invention aims to solve the problems of deterioration of insulation performance and reduced energy storage efficiency of polymer dielectric film capacitors under high temperature or high electric field conditions, and further provides a method for preparing a cycloolefin copolymer composite insulating dielectric film.

[0006] A method for preparing a cycloolefin copolymer composite insulating dielectric film is carried out according to the following steps:

[0007] 1. dissolving the cyclic olefin copolymer in an organic solvent under heating conditions to obtain a cyclic olefin copolymer solution;

[0008] 2. Under protective atmosphere and heating conditions, adding a high-polarity dianhydride monomer and an initiator to a cycloolefin copolymer solution and dissolving them, then stirring and carrying out a grafting reaction for 4 to 6 hours under protective atmosphere, a temperature of 110° C. to 140° C., and a rotation speed of 200 r / min to 400 r / min, separating the grafted polymer after the reaction and drying it, and finally dissolving the dried grafted polymer in an organic solvent to obtain an anhydride-grafted cycloolefin copolymer solution;

[0009] 3. Adding a high-polarity diamine monomer to the anhydride-grafted cycloolefin copolymer solution, reacting at a temperature of 110° C. to 140° C. for 3 to 5 hours, then coating the solution on a substrate, and finally performing a gradient temperature-increasing thermal imidization treatment to obtain a cycloolefin copolymer composite insulating dielectric film;

[0010] The thickness of the cycloolefin copolymer composite insulating dielectric film is 6 μm to 20 μm; the mass percentage of the grafted polyimide in the cycloolefin copolymer composite insulating dielectric film is 10% to 20%.

[0011] The beneficial effects of the present invention are:

[0012] The present invention dissolves a cycloolefin copolymer in an organic solvent, then, under the action of an initiator, grafts polyimide and the cycloolefin copolymer to form a composite insulating dielectric film through high-temperature solution polymerization. By grafting a trace amount of polyimide (10% to 20% by mass) onto the cycloolefin copolymer, a large number of fluorine atoms and large benzene ring side groups are introduced, thereby altering the polymer chain conformation and local arrangement, introducing trap sites. This significantly improves the dielectric breakdown field strength, discharge energy density, and charge-discharge efficiency under high temperature or high electric field conditions. The cycloolefin copolymer composite insulating dielectric film prepared by the present invention significantly improves its breakdown performance and thermal stability, and exhibits excellent energy storage performance, resolving the issues of existing polymer dielectric film capacitors, which suffer from deteriorating insulation performance and reduced energy storage efficiency under high temperature or high electric field conditions.

[0013] (1) Compared with conventional polymer nanocomposites, the cycloolefin copolymer composite insulating dielectric film prepared by the present invention mainly introduces trap sites by changing the conformation and local arrangement of polymer chains, thereby achieving that after 50,000 charge and discharge cycles at 120°C and 200 kV / mm, the discharge energy density and charge and discharge efficiency of the cycloolefin copolymer composite insulating dielectric film show no signs of attenuation, and the charge and discharge efficiency is maintained at above 99%.

[0014] (2) At a relatively high temperature (120°C), the breakdown field strength of the cycloolefin copolymer composite insulating dielectric film reaches 645 kV / mm; the discharge energy density at 120°C and 640 kV / mm is 4.55 J / cm 3, and the charge and discharge efficiency can still be maintained at above 95%. In addition, the present invention has the advantages of simple process flow, environmental protection and pollution-free, low production cost, etc., and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 XRD patterns of the cycloolefin copolymer composite insulating dielectric films prepared in Examples 1 to 3 and the cycloolefin copolymer insulating dielectric film prepared in the comparative experiment;

[0016] Figure 2 Comparison chart of infrared spectra of the cyclic olefin copolymer composite insulating dielectric films prepared in Examples 1 to 3 and the cyclic olefin copolymer insulating dielectric film prepared in the comparative experiment;

[0017] Figure 3 Weibull distribution probability diagram of the breakdown voltage of the cyclic olefin copolymer composite insulating dielectric films prepared in Examples 1 to 3 and the cyclic olefin copolymer insulating dielectric films prepared in the comparative experiment at room temperature;

[0018] Figure 4 Weibull distribution probability diagram of the breakdown voltage of the cyclic olefin copolymer composite insulating dielectric films prepared in Examples 1 to 3 and the cyclic olefin copolymer insulating dielectric films prepared in the comparative experiment at 120° C.;

[0019] Figure 5 The discharge energy density and charge-discharge efficiency of the cyclic olefin copolymer composite insulating dielectric films prepared in Examples 1 to 3 and the cyclic olefin copolymer insulating dielectric films prepared in the comparative experiment at room temperature vary with the electric field;

[0020] Figure 6 The discharge energy density and charge-discharge efficiency of the cyclic olefin copolymer composite insulating dielectric films prepared in Examples 1 to 3 and the cyclic olefin copolymer insulating dielectric films prepared in the comparative experiment at 120°C are shown as a function of the electric field;

[0021] Figure 7 The discharge energy density and charge-discharge efficiency of the cyclic olefin copolymer composite insulating dielectric film prepared in Example 2 are shown in FIG. 1 after 50,000 charge-discharge cycles at 120° C. and 200 kV / mm.

[0022] Figure 8 The stress-strain curves of the cyclic olefin copolymer composite insulating dielectric films prepared in Examples 1 to 3 and the cyclic olefin copolymer insulating dielectric film prepared in the comparative experiment;

[0023] Figure 9 Schematic diagram of molecular orbital energy level distribution and trap capture mechanism. DETAILED DESCRIPTION

[0024] Specific embodiment 1: This embodiment is a method for preparing a cyclic olefin copolymer composite insulating dielectric film, which is as follows:

[0025] 1. dissolving the cyclic olefin copolymer in an organic solvent under heating conditions to obtain a cyclic olefin copolymer solution;

[0026] 2. Under protective atmosphere and heating conditions, adding a high-polarity dianhydride monomer and an initiator to a cycloolefin copolymer solution and dissolving them, then stirring and carrying out a grafting reaction for 4 to 6 hours under protective atmosphere, a temperature of 110° C. to 140° C., and a rotation speed of 200 r / min to 400 r / min, separating the grafted polymer after the reaction and drying it, and finally dissolving the dried grafted polymer in an organic solvent to obtain an anhydride-grafted cycloolefin copolymer solution;

[0027] 3. Adding a high-polarity diamine monomer to the anhydride-grafted cycloolefin copolymer solution, reacting at a temperature of 110° C. to 140° C. for 3 to 5 hours, then coating the solution on a substrate, and finally performing a gradient temperature-increasing thermal imidization treatment to obtain a cycloolefin copolymer composite insulating dielectric film;

[0028] The thickness of the cycloolefin copolymer composite insulating dielectric film is 6 μm to 20 μm; the mass percentage of the grafted polyimide in the cycloolefin copolymer composite insulating dielectric film is 10% to 20%.

[0029] The beneficial effects of this embodiment are:

[0030] In this embodiment, a cycloolefin copolymer is dissolved in an organic solvent, and under the action of an initiator, polyimide and the cycloolefin copolymer are grafted to react, and a cycloolefin copolymer composite insulating dielectric film is finally obtained by high-temperature solution polymerization. By grafting a trace amount of polyimide (10% to 20% by mass) onto the cycloolefin copolymer, a large number of fluorine atoms and large benzene ring side groups are introduced, thereby changing the conformation and local arrangement of the polymer chain and introducing trap sites, thereby significantly improving the dielectric breakdown field strength, discharge energy density, and charge-discharge efficiency under high temperature or high electric field conditions. That is, the cycloolefin copolymer composite insulating dielectric film prepared by this embodiment can greatly improve its breakdown performance and thermal stability, and has excellent energy storage performance, solving the problem of deterioration of insulation performance and reduced energy storage efficiency of existing polymer dielectric film capacitors under high temperature or high electric field conditions.

[0031] (1) Compared with conventional polymer nanocomposites, the cycloolefin copolymer composite insulating dielectric film prepared in this embodiment mainly introduces trap sites by changing the conformation and local arrangement of the polymer chains, thereby achieving that after 50,000 charge and discharge cycles at 120°C and 200 kV / mm, the discharge energy density and charge and discharge efficiency of the cycloolefin copolymer composite insulating dielectric film show no signs of attenuation, and the charge and discharge efficiency is maintained at above 99%.

[0032] (2) At a relatively high temperature (120°C), the breakdown field strength of the cycloolefin copolymer composite insulating dielectric film reaches 645 kV / mm; the discharge energy density at 120°C and 640 kV / mm is 4.55 J / cm 3 , and the charge and discharge efficiency can still be maintained at above 95%. In addition, the process flow of this embodiment is simple, environmentally friendly and pollution-free, and the production cost is low, making it suitable for industrial production.

[0033] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the cyclic olefin copolymer in step 1 is prepared by polymerization of norbornene and ethylene, and the norbornene content in the cyclic olefin copolymer is 50 mol% to 80 mol%. Other aspects are the same as specific embodiment 1.

[0034] Specific embodiment 3: This embodiment differs from either specific embodiment 1 or 2 in that the organic solvent in steps 1 and 2 is one or a mixture of toluene, xylene, acetone, dimethylformamide, methyl ethyl ketone, and propylene glycol methyl ether. Otherwise, the organic solvent is the same as in specific embodiment 1 or 2.

[0035] Specific embodiment 4: This embodiment differs from one of specific embodiments 1 to 3 in that, in step 1, the cyclic olefin copolymer is dissolved in an organic solvent at a temperature of 110°C to 120°C; and the volume ratio of the cyclic olefin copolymer to the organic solvent in step 1 is 1 g:(7.0-8.5) mL. Other steps are the same as specific embodiments 1 to 3.

[0036] Specific embodiment 5: This embodiment differs from Specific embodiments 1 to 4 in that: the high-polarity dianhydride monomer described in step 2 is one or a mixture of maleic anhydride and succinic anhydride; the initiator described in step 2 is one or a mixture of dicumyl peroxide, di-tert-butyl peroxide, benzoyl peroxide, tert-butyl perbenzoate, dicyclohexyl peroxydicarbonate, cumene hydroperoxide, and azobisisobutyronitrile; and the protective atmosphere described in step 2 is nitrogen, helium, neon, or argon. Other aspects are the same as Specific embodiments 1 to 4.

[0037] Specific embodiment 6: This embodiment differs from Specific embodiments 1 to 5 in that in step 2, a high-polarity dianhydride monomer and an initiator are added to and dissolved in a cyclic olefin copolymer solution under a nitrogen atmosphere at a temperature of 110°C to 140°C. Other steps are the same as Specific embodiments 1 to 5.

[0038] Specific embodiment 7: This embodiment differs from Specific embodiments 1 to 6 in that the mass ratio of the high polarity dianhydride monomer to the initiator in step 2 is 1:(0.09-0.34). Other aspects are the same as Specific embodiments 1 to 6.

[0039] Specific embodiment 8: This embodiment differs from any one of specific embodiments 1 to 7 in that, in step 2, the grafted polymer is separated by precipitation with acetone and then dried to a constant weight under vacuum at a temperature of 60°C to 80°C; and the ratio of the mass of the dried grafted polymer to the volume of the organic solvent in step 2 is 1 g: (6-9) mL. Other aspects are the same as specific embodiments 1 to 7.

[0040] Specific Embodiment 9: This embodiment differs from Specific Embodiments 1 to 8 in that the highly polar diamine monomer described in step 3 is a mixture of one or both of 2,2'-bis(trifluoromethyl)diaminobiphenyl and 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether; and the molar ratio of the highly polar diamine monomer described in step 3 to the highly polar dianhydride monomer described in step 2 is 1:(1.01-1.13). Other aspects are the same as Specific Embodiments 1 to 8.

[0041] Specific Embodiment 10: This embodiment differs from Specific Embodiments 1 to 9 in that the gradient temperature increase thermal imidization treatment described in step 3 is specifically carried out as follows: the temperature is increased in multiple steps to 210°C to 230°C at a heating rate of 1°C / min to 5°C / min, with each step having a temperature interval of 20°C to 50°C, and each step is maintained at a constant temperature for 30 minutes to 420 minutes. Other aspects are the same as Specific Embodiments 1 to 9.

[0042] The following examples are used to verify the beneficial effects of the present invention:

[0043] Example 1:

[0044] A method for preparing a cycloolefin copolymer composite insulating dielectric film is carried out according to the following steps:

[0045] 1. dissolving the cyclic olefin copolymer in an organic solvent at a temperature of 110° C. to obtain a cyclic olefin copolymer solution;

[0046] The mass ratio of the cycloolefin copolymer to the volume ratio of the organic solvent is 1 g:7 mL;

[0047] 2. Under the conditions of nitrogen atmosphere and temperature of 110° C., a high-polarity dianhydride monomer and an initiator are added to the cycloolefin copolymer solution and dissolved, and then the grafting reaction is stirred under the conditions of nitrogen atmosphere, temperature of 120° C. and rotation speed of 300 r / min for 5 hours. After the reaction, the grafted polymer is separated by precipitation using acetone, and then dried to constant weight under vacuum at a temperature of 80° C., and finally the dried grafted polymer is dissolved in an organic solvent to obtain an anhydride grafted cycloolefin copolymer solution;

[0048] The mass ratio of the high-polarity dianhydride monomer to the initiator is 1:0.09; the volume ratio of the mass of the dried graft polymer to the organic solvent is 1 g:6 mL;

[0049] 3. Add high polarity diamine monomer to the anhydride grafted cycloolefin copolymer solution, react at a temperature of 120°C for 4 hours, and then apply it on the glass substrate by knife coating. First, increase the temperature to 60°C at a heating rate of 2°C / min, keep the temperature at 60°C for 60 minutes, then increase the temperature to 90°C at a heating rate of 2°C / min, keep the temperature at 90°C for 60 minutes, then increase the temperature to 120°C at a heating rate of 2°C / min, keep the temperature at 120°C for 1 minute. Under the conditions of constant temperature for 60 minutes, the temperature was then increased to 150°C at a heating rate of 2°C / min, and kept constant at 150°C for 60 minutes, then the temperature was increased to 200°C at a heating rate of 2°C / min, and kept constant at 200°C for 60 minutes, and finally the temperature was increased to 220°C at a heating rate of 2°C / min, and kept constant at 220°C for 60 minutes to obtain a cycloolefin copolymer composite insulating dielectric film, recorded as COC-g-10wt%PI;

[0050] The molar ratio of the high-polarity diamine monomer described in step 3 to the high-polarity dianhydride monomer described in step 2 is 1:1; the thickness of the cyclic olefin copolymer composite insulating dielectric film is 10 μm; the mass percentage of the grafted polyimide in the cyclic olefin copolymer composite insulating dielectric film is 10%;

[0051] The cyclic olefin copolymer in step 1 is prepared by polymerization of norbornene and ethylene; and the norbornene content in the cyclic olefin copolymer (TOPAS-6017S-04) is 50 mol% to 80 mol%;

[0052] The organic solvent in step 1 and step 2 is xylene;

[0053] The high polarity dianhydride monomer described in step 2 is maleic anhydride; the initiator described in step 2 is benzoyl peroxide;

[0054] The highly polar diamine monomer described in step three is 2,2'-bis(trifluoromethyl)diaminobiphenyl.

[0055] Example 2: This example differs from Example 1 in that the mass ratio of the high-polarity dianhydride monomer to the initiator in Step 2 is 1:0.22; the mass percentage of the grafted polyimide in the cyclic olefin copolymer composite insulating dielectric film in Step 3 is 15%; and the cyclic olefin copolymer composite insulating dielectric film in Step 3 is designated as COC-g-15wt%PI. All other aspects are the same as in Example 1.

[0056] Example 3: This example differs from Example 1 in that the mass ratio of the high-polarity dianhydride monomer to the initiator in Step 2 is 1:0.34; the mass percentage of the grafted polyimide in the cyclic olefin copolymer composite insulating dielectric film in Step 3 is 20%; and the cyclic olefin copolymer composite insulating dielectric film in Step 3 is designated as COC-g-20wt%PI. All other aspects are the same as in Example 1.

[0057] Comparative experiment:

[0058] At a temperature of 110°C, a cyclic olefin copolymer was dissolved in an organic solvent, and then stirred for 5 hours under a nitrogen atmosphere, a temperature of 120°C and a rotation speed of 300 r / min, and then coated on a glass substrate by a doctor blade method. The temperature was first increased to 60°C at a heating rate of 2°C / min, and kept constant at 60°C for 120 minutes, and then increased to 90°C at a heating rate of 2°C / min, and kept constant at 90°C for 360 minutes. Finally, the temperature was increased to 120°C at a heating rate of 2°C / min, and kept constant at 120°C for 120 minutes to obtain a cyclic olefin copolymer insulating dielectric film, which was recorded as COC.

[0059] The mass ratio of the cyclic olefin copolymer to the volume ratio of the organic solvent is 1 g:7 mL; the thickness of the cyclic olefin copolymer insulating dielectric film is 10 μm;

[0060] The cyclic olefin copolymer in step 1 is prepared by polymerization of norbornene and ethylene, and the norbornene content in the cyclic olefin copolymer (TOPAS-6017S-04) is 50 mol% to 80 mol%;

[0061] The organic solvent is xylene.

[0062] Figure 1The XRD patterns of the cycloolefin copolymer composite insulating dielectric films prepared in Examples 1 to 3 and the cycloolefin copolymer insulating dielectric films prepared in the comparative experiment are shown. As can be seen from the figure, the cycloolefin copolymer composite insulating dielectric films prepared in Examples 1 to 3 exhibit typical "steamed bun-shaped" amorphous diffraction peaks in the diffraction angle range of 10° to 30°, proving that the crystallinity of the cycloolefin copolymer is not affected.

[0063] Figure 2 The infrared spectra of the cycloolefin copolymer composite insulating dielectric film prepared in Examples 1 to 3 and the cycloolefin copolymer insulating dielectric film prepared in the comparative experiment are compared. As can be seen from the figure, the characteristic absorption peaks of the imide ring appear at 1776 cm -1 、1720cm -1 (symmetric and asymmetric stretching vibration peaks of C=O) and 1370 cm -1 (CN stretching vibration peak), 1120cm -1 (Stretching vibration peak of CF), proving that the anhydride on the cycloolefin copolymer successfully reacted with 2,2'-bis(trifluoromethyl)diaminobiphenyl.

[0064] A DC breakdown test was performed on the cycloolefin copolymer composite insulating dielectric films prepared in Examples 1 to 3 and the cycloolefin copolymer insulating dielectric film prepared in the comparative experiment, with a voltage rise rate of 300 V / s and a peak voltage of 15,000 V. Figure 3 Weibull distribution probability plots of the breakdown voltages of the cyclic olefin copolymer composite insulating dielectric films prepared in Examples 1 to 3 and the comparative experiment at room temperature are shown. As can be seen from the plots, the breakdown field strengths of the cyclic olefin copolymer composite insulating dielectric films are significantly improved, with the COC-g-15wt% PI composite dielectric film having the best breakdown performance of 720 kV / mm, a 15% improvement over pure COC film.

[0065] A DC breakdown test was performed on the cycloolefin copolymer composite insulating dielectric films prepared in Examples 1 to 3 and the cycloolefin copolymer insulating dielectric film prepared in the comparative experiment, with a voltage rise rate of 300 V / s and a peak voltage of 15,000 V. Figure 4 Weibull distribution probability plots of the breakdown voltages of the cyclic olefin copolymer composite insulating dielectric films prepared in Examples 1 to 3 and the cyclic olefin copolymer insulating dielectric films prepared in the comparative experiment at 120°C are shown. As can be seen from the figure, the breakdown field strength of the cyclic olefin copolymer composite insulating dielectric films is significantly improved, with the COC-g-15wt% PI composite dielectric film having the best breakdown performance of 645kV / mm, a 43% improvement over pure COC film.

[0066] Energy storage tests were conducted on the cyclic olefin copolymer composite insulating dielectric films prepared in Examples 1 to 3 and the cyclic olefin copolymer insulating dielectric films prepared in the comparative experiment. The electrode area was 0.0707 cm 2 , the signal period is 0.1S. Figure 5 The discharge energy density and charge-discharge efficiency of the cyclic olefin copolymer composite insulating dielectric films prepared in Examples 1 to 3 and the comparative experiment at room temperature are shown as a function of the electric field. As can be seen from the figure, the discharge energy density of the cyclic olefin copolymer composite insulating dielectric films is significantly improved. Among them, the COC-g-15wt% PI composite dielectric film prepared in Example 2 has the best performance, with a discharge energy density of 6.15 J / cm at room temperature and 720 kV / mm. 3 , an increase of 18% over the COC dielectric film, and the charge and discharge efficiency remains above 96% at room temperature and 720kV / mm.

[0067] Energy storage tests were conducted on the cyclic olefin copolymer composite insulating dielectric films prepared in Examples 1 to 3 and the cyclic olefin copolymer insulating dielectric films prepared in the comparative experiment. The electrode area was 0.0707 cm 2 , the signal period is 0.1S. Figure 6 The discharge energy density and charge-discharge efficiency of the cyclic olefin copolymer composite insulating dielectric films prepared in Examples 1 to 3 and the comparative experiment at 120°C are shown as a function of the electric field. As can be seen from the figure, the discharge energy density of the cyclic olefin copolymer composite insulating dielectric films is significantly improved. Among them, the COC-g-15wt% PI composite dielectric film prepared in Example 2 has the best performance, with a discharge energy density of 4.55 J / cm at 120°C and 640 kV / mm. 3 , an increase of 71% over COC dielectric film, and the charge and discharge efficiency remains above 95% at 120°C and 640kV / mm.

[0068] The cyclic test of the cyclic olefin copolymer composite insulating dielectric film prepared in Example 2 was carried out, and the electrode area was 0.0707 cm 2 , the signal period is 0.1S. Figure 7 The discharge energy density and charge-discharge efficiency of the cyclic olefin copolymer composite insulating dielectric film prepared in Example 2 are shown in FIG. 1 , which is a graph showing the changing trends of the discharge energy density and charge-discharge efficiency after 50,000 charge-discharge cycles at 120°C and 200 kV / mm. As can be seen from the figure, after 50,000 charge-discharge cycles, neither the discharge energy density nor the charge-discharge efficiency showed any signs of attenuation, and the charge-discharge efficiency remained stable at over 99%, indicating that the cyclic olefin copolymer composite insulating dielectric film has excellent long-term stability in practical high-temperature applications.

[0069] Tensile tests were performed on the cycloolefin copolymer composite insulating dielectric films prepared in Examples 1 to 3 and the cycloolefin copolymer insulating dielectric film prepared in the comparative experiment. Starting from the middle of the sample, marks were made with a marker pen at 10 mm and 25 mm in the left and right directions, respectively, to obtain standard areas of 20 mm and 50 mm in length. The marks were then clamped using a fixture on the experimental apparatus. The sample was stretched at a rate of 50 mm / min until it broke, and the stress-strain curve of the film was recorded during this process. Figure 8 The stress-strain curves are for the cycloolefin copolymer composite insulating dielectric films prepared in Examples 1 to 3 and the cycloolefin copolymer insulating dielectric film prepared in the comparative experiment. As can be seen from the figure, the tensile strength of the films is improved after polyimide grafting. Among them, the COC-g-15wt% PI composite dielectric film prepared in Example 2 is the best, with the tensile strength increased to 90 MPa, an increase of 1.8 times, and the elongation at break is 2.97%, which can still be maintained at a stable level.

[0070] The electrostatic potential distribution and molecular orbital energy levels of COC and COC-g-PI were calculated by density functional theory (DFT). Figure 9 Schematic diagram of the molecular orbital energy level distribution and trapping mechanism. The figure shows that the lowest unoccupied molecular orbital (LUMO) energy level of COC-g-PI (-1.0398 eV) is lower than that of COC (1.8999 eV), while the highest occupied molecular orbital (HOMO) energy level of COC-g-PI (-5.8787 eV) is higher than that of COC (-7.3391 eV), indicating that COC-g-PI has a stronger ability to capture electrons and holes than COC. Therefore, the low-content polyimide grafting changes the conformation and local arrangement of the polymer chains, introducing trap sites. This is the primary reason for the significant improvements in the dielectric breakdown field strength, discharge energy density, and charge-discharge efficiency of the cycloolefin copolymer composite insulating dielectric film.

Claims

1. A method for preparing a cycloolefin copolymer composite insulating dielectric film, characterized in that It is carried out in the following steps:

1. dissolving the cyclic olefin copolymer in an organic solvent at a temperature of 110° C. to 120° C. to obtain a cyclic olefin copolymer solution; The cyclic olefin copolymer is formed by polymerization of norbornene and ethylene; and the norbornene content in the cyclic olefin copolymer is 50 mol% to 80 mol%; 2. Under the conditions of nitrogen atmosphere and temperature of 110° C. to 140° C., adding a high-polarity dianhydride monomer and an initiator to a cycloolefin copolymer solution and dissolving them, then stirring and carrying out a grafting reaction for 4 h to 6 h under the conditions of protective atmosphere, temperature of 110° C. to 140° C. and rotation speed of 200 r / min to 400 r / min, separating the grafted polymer after the reaction and drying it, and finally dissolving the dried grafted polymer in an organic solvent to obtain an anhydride-grafted cycloolefin copolymer solution; The high polarity dianhydride monomer is maleic anhydride; the initiator is benzoyl peroxide; 3. Adding a high-polarity diamine monomer to the anhydride-grafted cycloolefin copolymer solution, reacting at a temperature of 110° C. to 140° C. for 3 to 5 hours, then coating the solution on a substrate, and finally performing a gradient temperature-increasing thermal imidization treatment to obtain a cycloolefin copolymer composite insulating dielectric film; The high-polarity diamine monomer is 2,2'-bis(trifluoromethyl)diaminobiphenyl; the thickness of the cycloolefin copolymer composite insulating dielectric film is 6 μm to 20 μm; the mass percentage of the grafted polyimide in the cycloolefin copolymer composite insulating dielectric film is 10% to 20%; The gradient temperature rise thermal imidization treatment is specifically carried out according to the following steps: the temperature is increased in multiple steps to 210°C to 230°C at a heating rate of 1°C / min to 5°C / min, and the temperature of each section is 20°C to 50°C, and each section is kept at a constant temperature for 30min to 420min.

2. The method for preparing a cycloolefin copolymer composite insulating dielectric film according to claim 1, characterized in that The organic solvent described in step 1 and step 2 is one of toluene, xylene, acetone, dimethylformamide, methyl ethyl ketone and propylene glycol methyl ether, or a mixture of several of them.

3. The method for preparing a cyclic olefin copolymer composite insulating dielectric film according to claim 1, characterized in that The volume ratio of the mass of the cycloolefin copolymer described in step 1 to the organic solvent is 1 g: (7.0-8.5) mL.

4. The method for preparing a cycloolefin copolymer composite insulating dielectric film according to claim 1, characterized in that The protective atmosphere in step 2 is nitrogen, helium, neon or argon.

5. The method for preparing a cycloolefin copolymer composite insulating dielectric film according to claim 1, characterized in that The mass ratio of the high polarity dianhydride monomer to the initiator in step 2 is 1:(0.09-0.34).

6. The method for preparing a cycloolefin copolymer composite insulating dielectric film according to claim 1, characterized in that In step 2, the grafted polymer is separated by acetone precipitation and then dried to constant weight under vacuum at a temperature of 60° C. to 80° C.; the mass ratio of the dried grafted polymer to the volume of the organic solvent in step 2 is 1 g: (6 to 9) mL.

7. The method for preparing a cycloolefin copolymer composite insulating dielectric film according to claim 1, characterized in that The molar ratio of the high polarity diamine monomer described in step 3 to the high polarity dianhydride monomer described in step 2 is 1:(1.01-1.13).

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