Preparation method of cycloolefin copolymer composite insulating dielectric film

Abstract

The invention discloses a preparation method of a cycloolefin copolymer composite insulating dielectric film, and belongs to the field of capacitors. The invention solves the problems that the insulating property of the polymer dielectric thin film capacitor is degraded and the energy storage efficiency is reduced under the condition of high temperature or high electric field in the prior art. The method comprises the following steps: 1, preparing a cycloolefin copolymer solution; 2, preparing an anhydride grafted cycloolefin copolymer solution; and 3, adding a high-polarity diamine monomer into the anhydride grafted cycloolefin copolymer solution to react, and then coating and carrying out gradient heating thermal imidization treatment. The method is used for preparing the cycloolefin 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 more and more attention due to their advantages such as high breakdown voltage, low cost, easy processing, fast charge and discharge speed, and excellent operating stability. However, under high temperature or high electric field conditions, the film capacitors suffer from problems such as deterioration of insulation performance and reduced energy storage efficiency due to the sharp increase in conductivity loss. Therefore, improving the high temperature resistance of capacitor films is of great research value.

[0003] In order to reduce the conductivity loss, in recent years, inorganic nanofillers with low dielectric constant and wide bandgap fillers have been added to polymers to improve high temperature performance, but only when small-sized nanoparticles are evenly dispersed in the matrix can a good modification effect be obtained. Once agglomeration occurs, its electrical properties will be seriously deteriorated; in order to eliminate or avoid the adverse effects of inorganic fillers and improve the electrical properties of polymers, organic fillers are introduced into polymers, but the difference in thermal properties between the matrix and the organic filler material will lead to thermal runaway and thermal separation; multi-layer design of the structure can coordinate the characteristics of each membrane and improve the energy storage performance of the membrane, but due to the poor compatibility between adjacent layers of multi-layer polymer composite materials, if stratification occurs during the stretching process, it will bring huge safety hazards 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 performance at high temperatures has become one of the important directions of current research.

[0004] The rigid structure of cyclic olefin copolymer (COC) itself gives it a larger band gap and a higher glass transition temperature (Tg), reducing high-temperature conduction losses. These properties make COC promising for the development of high-temperature polymer capacitors, which meets the current requirements for dielectric capacitors. However, it still cannot solve the existing problems of deterioration of insulation performance 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 cycloolefin copolymer in an organic solvent under heating conditions to obtain a cycloolefin copolymer solution;

[0008] 2. Under protective atmosphere and heating conditions, adding high polar dianhydride monomer and initiator to the cycloolefin copolymer solution to dissolve, then stirring the grafting reaction for 4h to 6h under protective atmosphere, temperature of 110°C to 140°C and rotation speed of 200r / min to 400r / 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 3h to 5h, then coating the substrate, and finally performing a gradient temperature-raising 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, and under the action of an initiator, a polyimide and the cycloolefin copolymer are subjected to a grafting reaction, and a cycloolefin copolymer composite insulating dielectric film is finally obtained by high-temperature solution polymerization. A trace amount of polyimide (mass fraction of 10% to 20%) is grafted onto the cycloolefin copolymer, a large number of fluorine atoms and large benzene ring side groups are introduced, and then the polymer chain conformation and local arrangement are changed to introduce trap sites, so that under high temperature or high electric field conditions, the dielectric breakdown field strength, discharge energy density and charge and discharge efficiency are significantly improved. That is, the cycloolefin copolymer composite insulating dielectric film prepared by the present invention 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.

[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, so 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 more than 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 films prepared in the comparative experiment;

[0016] Figure 2 It is a comparison diagram of 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;

[0017] Figure 3 Weibull distribution probability diagram of breakdown voltage 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 at room temperature;

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

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

[0022] Figure 8 The stress-strain curves 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;

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

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

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

[0026] 2. Under protective atmosphere and heating conditions, adding high polar dianhydride monomer and initiator to the cycloolefin copolymer solution to dissolve, then stirring the grafting reaction for 4h to 6h under protective atmosphere, temperature of 110°C to 140°C and rotation speed of 200r / min to 400r / 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 3h to 5h, then coating the substrate, and finally performing a gradient temperature-raising 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, the 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 (mass fraction of 10% to 20%) on the cycloolefin copolymer, a large number of fluorine atoms and large benzene ring side groups are introduced, thereby changing the polymer chain conformation and local arrangement to introduce trap sites, so that under high temperature or high electric field conditions, the dielectric breakdown field strength, discharge energy density and charge and discharge efficiency are significantly improved. 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 existing problems of deterioration of insulation performance and reduced energy storage efficiency of 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 polymer chains, so 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 more than 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 present embodiment has the advantages of simple process flow, environmental protection and no pollution, low production cost, etc., and is suitable for industrial production.

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

[0034] Specific embodiment 3: This embodiment is different from specific embodiment 1 or 2 in that the organic solvent described in step 1 and step 2 is one or a mixture of toluene, xylene, acetone, dimethylformamide, methyl ethyl ketone and propylene glycol methyl ether. The rest is the same as 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 cycloolefin copolymer is dissolved in an organic solvent at a temperature of 110° C. to 120° C.; the mass ratio of the cycloolefin copolymer to the volume ratio of the organic solvent in step 1 is 1 g: (7.0 to 8.5) mL. The rest is the same as specific embodiments 1 to 3.

[0036] Specific implementation mode 5: This implementation mode is different from specific implementation modes 1 to 4 in that: the high polar dianhydride monomer described in step 2 is one of maleic anhydride and succinic anhydride or a mixture of two of them; the initiator described in step 2 is one of diisopropylbenzene peroxide, di-tert-butyl peroxide, benzoyl peroxide, tert-butyl perbenzoate, dicyclohexyl peroxydicarbonate, isopropylbenzene hydroperoxide and azobisisobutyronitrile or a mixture of several of them; the protective atmosphere described in step 2 is nitrogen, helium, neon or argon. The rest is the same as specific implementation modes 1 to 4.

[0037] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that in step 2, high polarity dianhydride monomer and initiator are added to the cycloolefin copolymer solution and dissolved under nitrogen atmosphere and temperature of 110° C. to 140° C. The rest is 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). Others are the same as Specific embodiments 1 to 6.

[0039] Specific embodiment 8: This embodiment differs from Specific embodiments 1 to 7 in that: in step 2, the grafted polymer is separated by precipitation with acetone, 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 1g:(6-9)mL. Others are the same as Specific embodiments 1 to 7.

[0040] Specific embodiment 9: This embodiment is different from specific embodiments 1 to 8 in that: the high 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; the molar ratio of the high polar diamine monomer described in step 3 to the high polar dianhydride monomer described in step 2 is 1:(1.01-1.13). Others are the same as specific embodiments 1 to 8.

[0041] Specific embodiment 10: This embodiment is different from specific embodiments 1 to 9 in that the gradient temperature rise thermal imidization treatment described in step 3 is specifically carried out according to the following steps: the temperature is raised to 210°C to 230°C in multiple steps 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. The rest is the same as specific embodiments 1 to 9.

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

[0043] Embodiment 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 cycloolefin copolymer in an organic solvent at a temperature of 110° C. to obtain a cycloolefin 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 polar dianhydride monomer and an initiator are added to the cycloolefin copolymer solution to dissolve, and then the grafting reaction is stirred for 5 hours under the conditions of nitrogen atmosphere, temperature of 120°C and rotation speed of 300r / min. After the reaction, the grafted polymer is separated by acetone precipitation, and then dried to constant weight under vacuum at a temperature of 80°C. 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 polar dianhydride monomer to the initiator is 1:0.09; the mass ratio of the dried graft polymer to the volume ratio of the organic solvent is 1 g:6 mL;

[0049] 3. Add the 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 blade coating. First, increase the temperature to 60°C at a heating rate of 2°C / min, keep the temperature constant at 60°C for 60 minutes, then increase the temperature to 90°C at a heating rate of 2°C / min, keep the temperature constant at 90°C for 60 minutes, then increase the temperature to 120°C at a heating rate of 2°C / min, and keep the temperature constant at 120°C. Under the condition of constant temperature for 60 minutes, then the temperature was increased to 150°C at a heating rate of 2°C / min, and the temperature was kept constant for 60 minutes at 150°C, then the temperature was increased to 200°C at a heating rate of 2°C / min, and the temperature was kept constant for 60 minutes at 200°C, and finally the temperature was increased to 220°C at a heating rate of 2°C / min, and the temperature was kept constant for 60 minutes at 220°C 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 cycloolefin copolymer composite insulating dielectric film is 10 μm; the mass percentage of the grafted polyimide in the cycloolefin copolymer composite insulating dielectric film is 10%;

[0051] The cyclic olefin copolymer described in step 1 is polymerized from norbornene and ethylene; and the percentage of norbornene in the cyclic olefin copolymer (TOPAS-6017S-04) is 50 mol% to 80 mol%;

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

[0053] The high polar 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] Embodiment 2: This embodiment is different from Embodiment 1 in that the mass ratio of the high polar dianhydride monomer to the initiator in step 2 is 1:0.22; the mass percentage of the grafted polyimide in the cycloolefin copolymer composite insulating dielectric film in step 3 is 15%; the cycloolefin copolymer composite insulating dielectric film in step 3 is recorded as COC-g-15wt%PI. The rest is the same as Embodiment 1.

[0056] Embodiment 3: This embodiment is different from Embodiment 1 in that: the mass ratio of the high polar dianhydride monomer to the initiator in step 2 is 1:0.34; the mass percentage of the grafted polyimide in the cycloolefin copolymer composite insulating dielectric film in step 3 is 20%; the cycloolefin copolymer composite insulating dielectric film in step 3 is recorded as COC-g-20wt%PI. The rest is the same as Embodiment 1.

[0057] Comparative experiment:

[0058] At a temperature of 110°C, a cycloolefin 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 scraping method, firstly the temperature was raised to 60°C at a heating rate of 2°C / min, and the temperature was kept constant at 60°C for 120 minutes, and then the temperature was raised to 90°C at a heating rate of 2°C / min, and the temperature was kept constant at 90°C for 360 minutes, and finally the temperature was raised to 120°C at a heating rate of 2°C / min, and the temperature was kept constant at 120°C for 120 minutes, to obtain a cycloolefin copolymer insulating dielectric film, which was recorded as COC;

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

[0060] The cyclic olefin copolymer described in step 1 is polymerized from norbornene and ethylene, and the percentage of norbornene 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 as follows; 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 1776cm -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] 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 were subjected to a DC breakdown test, with a voltage rise rate of 300 V / s and a peak voltage of 15,000 V. Figure 3 The Weibull distribution probability diagram of the breakdown voltage of the cyclic olefin copolymer composite insulating dielectric film prepared in Examples 1 to 3 and the cyclic olefin copolymer insulating dielectric film prepared in the comparative experiment at room temperature; it can be seen from the figure that the breakdown field strength of the cyclic olefin copolymer composite insulating dielectric film is greatly improved, among which the COC-g-15wt% PI composite dielectric film has the best breakdown performance of 720kV / mm, which is 15% higher than that of the pure COC film.

[0065] 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 were subjected to a DC breakdown test, with a voltage rise rate of 300 V / s and a peak voltage of 15,000 V. Figure 4 The Weibull distribution probability diagram of the breakdown voltage of the cyclic olefin copolymer composite insulating dielectric film prepared in Examples 1 to 3 and the cyclic olefin copolymer insulating dielectric film prepared in the comparative experiment at 120°C; it can be seen from the figure that the breakdown field strength of the cyclic olefin copolymer composite insulating dielectric film is greatly improved, among which the COC-g-15wt% PI composite dielectric film has the best breakdown performance of 645kV / mm, which is 43% higher than that of the pure COC film.

[0066] Energy storage tests were performed on 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. 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 cycloolefin copolymer composite insulating dielectric films prepared in Examples 1 to 3 and the cycloolefin copolymer insulating dielectric films prepared in the comparative experiment at room temperature are shown in the figure. As can be seen from the figure, the discharge energy density of the cycloolefin copolymer composite insulating dielectric film is significantly improved, among which the COC-g-15wt%PI composite dielectric film prepared in Example 2 has the best performance, with a discharge energy density of 6.15J / cm at room temperature and 720kV / 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 performed on 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. 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 cycloolefin copolymer composite insulating dielectric films prepared in Examples 1 to 3 and the cycloolefin copolymer insulating dielectric films prepared in the comparative experiment at 120°C are shown in the figure. As can be seen from the figure, the discharge energy density of the cycloolefin copolymer composite insulating dielectric films is significantly improved, among which the COC-g-15wt%PI composite dielectric film prepared in Example 2 has the best performance, with a discharge energy density of 4.55J / cm at 120°C and 640kV / mm. 3 , an increase of 71% over the COC dielectric film, and the charge and discharge efficiency remains above 95% at 120°C and 640kV / mm.

[0068] The cyclic test of the cycloolefin 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 Figure 1 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 was stabilized at more than 99%, which indicates that the cyclic olefin copolymer composite insulating dielectric film has excellent long-term stability in practical high-temperature applications.

[0069] 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 were subjected to a tensile test. Starting from the middle of the sample, marks were made with a marker at 10 mm and 25 mm in the left and right directions to obtain standard areas of 20 mm and 50 mm in length. The marks were then clamped with a fixture on the experimental instrument. The sample was stretched at a stretching rate of 50 mm / min until the sample broke, and the stress-strain curve of the film was recorded during the process. Figure 8 The stress-strain curves are 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; as can be seen from the figure, the tensile strength of the film is improved after grafting with polyimide, among which the COC-g-15wt% PI composite dielectric film prepared in Example 2 is the best, with the tensile strength increased to 90MPa, 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 analysis (DFT). Fig. 9 The figure is a schematic diagram of the molecular orbital energy level distribution and trap capture mechanism; it can be seen from the figure that the lowest unoccupied molecular orbital (LUMO) energy level of COC-g-PI (-1.0398eV) is lower than that of COC (1.8999eV); the highest occupied molecular orbital (HOMO) energy level of COC-g-PI (-5.8787eV) is higher than that of COC (-7.3391eV), indicating that COC-g-PI has a stronger ability to capture electrons and holes than COC. Therefore, grafting low-content polyimide changes the polymer chain conformation and local arrangement, introducing trap sites. This is the main reason for the significant improvement of 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 cycloolefin copolymer in an organic solvent under heating conditions to obtain a cycloolefin copolymer solution; 2. Under protective atmosphere and heating conditions, adding high polar dianhydride monomer and initiator to the cycloolefin copolymer solution to dissolve, then stirring the grafting reaction for 4h to 6h under protective atmosphere, temperature of 110°C to 140°C and rotation speed of 200r / min to 400r / 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; 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 3h to 5h, then coating the substrate, and finally performing a gradient temperature-raising thermal imidization treatment to obtain a cycloolefin copolymer composite insulating dielectric film; 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%.

2. The method for preparing a cyclic olefin copolymer composite insulating dielectric film according to claim 1, characterized in that The cycloolefin copolymer described in step 1 is prepared by polymerization of norbornene and ethylene; and the content of norbornene in the cycloolefin copolymer is 50 mol% to 80 mol%.

3. The method for preparing a cyclic olefin 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.

4. The method for preparing a cycloolefin copolymer composite insulating dielectric film according to claim 1, characterized in that In step 1, the cycloolefin copolymer is dissolved in an organic solvent at a temperature of 110° C. to 120° C.; the volume ratio of the cycloolefin copolymer in step 1 to the organic solvent is 1 g: (7.0 to 8.5) mL.

5. The method for preparing a cyclic olefin copolymer composite insulating dielectric film according to claim 1, characterized in that The high polarity dianhydride monomer described in step 2 is one of maleic anhydride and succinic anhydride or a mixture of two of them; the initiator described in step 2 is one of diisopropylbenzene peroxide, di-tert-butyl peroxide, benzoyl peroxide, tert-butyl perbenzoate, dicyclohexyl peroxydicarbonate, isopropylbenzene hydroperoxide and azobisisobutyronitrile or a mixture of several of them; the protective atmosphere described in step 2 is nitrogen, helium, neon or argon.

6. The method for preparing a cyclic olefin copolymer composite insulating dielectric film according to claim 1, characterized in that In step 2, under the conditions of nitrogen atmosphere and temperature of 110° C. to 140° C., a high polarity dianhydride monomer and an initiator are added into the cycloolefin copolymer solution to dissolve.

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

8. The method for preparing a cyclic olefin 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.

9. The method for preparing a cyclic olefin copolymer composite insulating dielectric film according to claim 1, characterized in that The high polarity diamine monomer described in step three is a mixture of one or both of 2,2'-bis(trifluoromethyl)diaminobiphenyl and 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether; the molar ratio of the high polarity diamine monomer described in step three to the high polarity dianhydride monomer described in step two is 1:(1.01-1.13).

10. The method for preparing a cyclic olefin copolymer composite insulating dielectric film according to claim 1, characterized in that The gradient temperature rise thermal imidization treatment described in step 3 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.

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