Flame-retardant modified metallized film for capacitors and method for preparing the same

Abstract

The application relates to a flame-retardant modified metallized film for capacitors and a preparation method thereof, and belongs to the technical field of capacitor materials. The metallized film comprises the following components in parts by weight: 50-60 parts of terephthalic acid, 30-40 parts of ethylene glycol, 5-10 parts of cyclobutane-1,3-dicarboxylic acid, 0.5-1 part of antimony trioxide, 0.5-1 part of a stabilizer, 4-6 parts of a composite flame retardant, 0.1-0.3 part of 4-dimethylaminopyridine and 0.1-0.2 part of a cage polysilsesquioxane. The prepared metallized film has excellent flame-retardant performance.

Description

Technical Field

[0001] This invention belongs to the field of capacitor material technology, and relates to a flame-retardant modified metallized film for capacitors and its preparation method. Background Technology

[0002] Film capacitors, as key components in electronic circuits, are widely used in consumer electronics, industrial automation, and new energy fields. With the miniaturization and high-performance development of electronic devices, the performance requirements for film capacitors are increasing. Traditional metallized film capacitors are prone to insufficient flame retardancy and poor thermal stability under harsh environments such as high temperature and high humidity, leading to capacitor failure and even safety accidents. Currently, although there is some research on flame-retardant modified metallized films, they generally suffer from uneven flame retardant dispersion, insufficient thermal stability, and poor mechanical properties, affecting the reliability and lifespan of the capacitors.

[0003] Therefore, it is of great significance to develop a flame-retardant modified metallized thin film for capacitors and its preparation method. Summary of the Invention

[0004] The purpose of this invention is to provide a flame-retardant modified metallized film for capacitors and its preparation method, which has excellent flame-retardant properties.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A flame-retardant modified metallized film for capacitors, the metallized film comprising, by weight, 50-60 parts terephthalic acid, 30-40 parts ethylene glycol, 5-10 parts cyclobutane-1,3-dicarboxylic acid, 0.5-1 part antimony trioxide, 0.5-1 part stabilizer, 4-6 parts composite flame retardant, 0.1-0.3 parts 4-dimethylaminopyridine, and 0.1-0.2 parts cage-like polysilsesquioxane;

[0007] The preparation method of the composite flame retardant is as follows:

[0008] S1-1: Dissolve magnesium nitrate and aluminum nitrate in deionized water at a molar ratio of 2:1, add urea, stir at 90-95 °C for 10-12 h, wash with deionized water and vacuum dry at 60 °C for 10-14 h to obtain powder A;

[0009] S1-2: Disperse powder A in an aqueous solution containing 10-20% ammonium polyphosphate by mass, sonicate at 45-55 °C for 4-6 h, wash with deionized water and dry at 60 °C for 10-14 h to obtain powder B;

[0010] S1-3: Mix powder B with modified boron nitride, add 1-3% by weight of powder B of silane coupling agent KH550, ball mill for 1-2 h at a speed of 200-300 rpm, and then vacuum dry at 60 °C for 10-14 h to obtain the composite flame retardant.

[0011] Furthermore, the method for preparing the modified boron nitride in S1-3 is as follows:

[0012] S2-1: Boron nitride was dispersed in an ethanol solution with a mass fraction of 50-60%, silane coupling agent KH550 was added, and the mixture was stirred at 80°C for 6 h. The mixture was then washed with deionized water and dried at 60°C for 10-14 h to obtain powder C.

[0013] S2-2: Diethylphosphoacetic acid and powder C are mixed at a molar ratio of (5-7):1 and added to MES buffer solution with pH 5-6. Then EDC and NHS are added, and the mixture is stirred at 45-55℃ for 4-6 h. The mixture is washed with deionized water and dried at 60℃ for 10-14 h to obtain modified boron nitride.

[0014] Furthermore, the stabilizer is triphenyl phosphite.

[0015] Furthermore, the total molar ratio of urea to metal salt in S1-1 is (1-3):1.

[0016] Furthermore, in S1-3, powder B and modified boron nitride are mixed at a mass ratio of (2-4):1.

[0017] Furthermore, in S2-1, the mass ratio of silane coupling agent KH550 to boron nitride is 1:(8-10).

[0018] Furthermore, the molar ratio of diethylphosphoacetic acid, EDC, and NHS is 2:2:(1-2).

[0019] A method for preparing a flame-retardant modified metallized thin film for capacitors, the specific steps of which are as follows:

[0020] S8-1: Add terephthalic acid, ethylene glycol, cyclobutane-1,3-dicarboxylic acid, antimony trioxide and stabilizer to the reactor according to the formula ratio, introduce nitrogen gas and heat to 210-230℃, pressure 0.3-0.5 MPa;

[0021] S8-2: Subsequently, composite flame retardant, 4-dimethylaminopyridine and cage-type polysilsesquioxane were added to the reactor, stirred for 5-10 min, then heated to 230-250℃, stirred for 30-40 min, further heated to 265-270℃, and stirred for 4-6 h to obtain modified polyester material.

[0022] S8-3: Modified polyester material is extruded through a flat die of an extruder at 230-240℃ to form a sheet with a thickness of 80-120μm, which is then subjected to biaxial stretching to obtain a biaxially stretched film.

[0023] S8-4: Heat-set the film and then anneal it at 110-120°C for 30-60 min to obtain the flame-retardant modified metallized film for the capacitor.

[0024] Furthermore, the biaxial stretching process in S8-3 involves heating the sheet to 80-100°C, stretching it longitudinally at a stretching ratio of 1:(3-5), and then stretching it transversely at 100-120°C at a stretching ratio of 1:(3-4).

[0025] Furthermore, the heat setting time in S8-4 is 5 to 10 seconds, and the temperature is 180 to 200°C.

[0026] During high-temperature operation, MgAl-LDH undergoes interlayer water of crystallization removal, absorbing a significant amount of heat and releasing CO2 and H2O to dilute the concentration of combustible gases. Simultaneously, the MgO and Al2O3 generated from LDH pyrolysis possess Lewis acidic sites, which catalyze the β-splitting of polyester molecular chains to generate olefinic free radicals, promoting cross-linking into carbon and forming a dense insulating layer. Ammonium polyphosphate decomposes into polyphosphoric acid and NH3 at high temperatures. Polyphosphoric acid binds to the terminal hydroxyl groups of the polyester through esterification, enhancing the graphitization of the carbon layer. Polyphosphoric acid undergoes a condensation reaction with the hydroxyl groups on the LDH surface, forming covalent bonds and increasing the shear strength between the carbon layer and the matrix. The layered structure of LDH physically adsorbs ammonium polyphosphate molecules through van der Waals forces, reducing its hygroscopicity. Simultaneously, the cavitation effect generated by ultrasonic treatment allows ammonium polyphosphate to intercalate into the LDH interlayer, improving dispersion uniformity. In addition, LDH and ammonium polyphosphate have a further synergistic effect. The acidic sites of LDH promote the decomposition of ammonium polyphosphate, and the polyphosphate further reacts with the MgO generated by LDH to form magnesium phosphate, forming a three-dimensional network structure, which improves the compressive strength of the carbon layer.

[0027] Boron nitride (BN) possesses high thermal conductivity, improving film heat dissipation and preventing localized overheating that could lead to breakdown. The silane coupling agent KH550 hydrolyzes to generate Si-OH, which condenses with hydroxyl groups on the boron nitride surface to form Si-O-BN bonds. Simultaneously, the amino groups adsorb LDH nanosheets via electrostatic interactions, achieving chemical bonding between BN and the flame retardant. Diethylphosphoacetic acid (DPPA) undergoes an amidation reaction with BN under EDC / NHS catalysis, introducing phosphorus and forming a PNB synergistic flame retardant system. The hexagonal crystal structure of BN is preserved intact through KH550 modification, constructing thermally conductive pathways within the polyester matrix. DPPA decomposes to generate PO· radicals, inhibiting the combustion chain reaction; simultaneously, it releases NH3 to dilute the oxygen concentration. Modified BN reacts with polyphosphoric acid from the decomposition of ammonium polyphosphate to generate borophosphate, enhancing the carbon layer density and significantly improving the film's flame retardant effect.

[0028] The nanocage-like structure of cage-like polysilsesquioxane forms a dense SiO2-reinforced char layer during combustion, which synergistically retards flame with antimony trioxide and ammonium polyphosphate, thereby improving the oxygen index of the film. The vibration of Si-O bonds and the resonance of polyester chains construct an efficient thermal conduction pathway, while the SiO2 core maintains high insulation. The rigid cage enhances the tensile strength of the film through physical / chemical cross-linking, and the nanoscale optimization of melt flowability reduces viscosity and improves thickness uniformity. The hydrophobic Si-O-Si skeleton reduces water absorption, inhibits dielectric loss during humid heat aging, and maintains a high strength level after thermal aging.

[0029] The beneficial effects of this invention are:

[0030] This invention significantly improves the flame retardancy and overall performance of thin films through the synergistic effect of MgAl-LDH, ammonium polyphosphate, boron nitride, and cage-like polysilsesquioxane. LDH undergoes interlayer dehydration and endothermic reaction, releasing CO2 / H2O to dilute combustible gases. The pyrolysis product MgO / Al2O3 catalyzes carbonization, forming covalent bonds with ammonium polyphosphate to enhance the graphitization and interfacial bonding of the carbon layer. Ultrasonic intercalation technology further improves dispersibility. Boron nitride, modified with KH550 and diethylphosphoacetic acid, constructs a PNB synergistic flame retardant system. Its hexagonal crystal structure retains high thermal conductivity while releasing NH3 to dilute oxygen and generate borophosphate to strengthen the carbon layer. Cage-like polysilsesquioxane enhances the carbon layer density through nanocage-like SiO2, synergistically retards with antimony trioxide, optimizes the thermal conductivity pathway through Si-O bond vibration, enhances tensile strength through the rigid cage structure, reduces water absorption through the hydrophobic framework, suppresses dielectric loss during humid heat aging, and maintains a high strength level even after thermal aging. Detailed Implementation

[0031] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with embodiments, is provided below.

[0032] In the embodiments and comparative examples of the present invention:

[0033] Terephthalic acid: purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0034] Ethylene glycol: purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0035] Cyclobutane-1,3-dicarboxylic acid: purchased from Shanghai Bid Pharmaceutical Technology Co., Ltd.;

[0036] Antimony trioxide: purchased from Beijing Hailiyang Chemical Technology Co., Ltd.;

[0037] Triphenyl phosphite: purchased from Changhe Chemical New Materials (Jiangsu) Co., Ltd.;

[0038] 4-Dimethylaminopyridine: purchased from Shanghai Kaisai Chemical Co., Ltd.;

[0039] Cage-type polysilsesquioxane: purchased from Guangdong Wengjiang Chemical Reagent Co., Ltd.;

[0040] Ammonium polyphosphate: purchased from Guangzhou Haoyu International Trade Co., Ltd.;

[0041] Silane coupling agent KH550: purchased from Jiangxi Hongbai New Materials Co., Ltd.;

[0042] Boron nitride: purchased from Forsmann Technology (Beijing) Co., Ltd.;

[0043] Diethylphosphoacetic acid: purchased from Shanghai Boteng Pharmaceutical Technology Co., Ltd.;

[0044] EDC: Purchased from Shanghai Xijia Biotechnology Co., Ltd.;

[0045] NHS: Purchased from Shanghai Changming Pharmaceutical Technology Co., Ltd.;

[0046] MES buffer solution: purchased from Shanghai McLean Biochemical Technology Co., Ltd.

[0047] Example 1

[0048] A flame-retardant modified metallized film for capacitors, the metallized film comprising, by weight, 55 parts terephthalic acid, 35 parts ethylene glycol, 8 parts cyclobutane-1,3-dicarboxylic acid, 0.8 parts antimony trioxide, 0.8 parts triphenyl phosphite, 5 parts composite flame retardant, 0.2 parts 4-dimethylaminopyridine, and 0.15 parts cage-type polysilsesquioxane;

[0049] The preparation method of the composite flame retardant is as follows:

[0050] S1-1: Dissolve magnesium nitrate and aluminum nitrate in deionized water at a molar ratio of 2:1, add urea (the total molar ratio of urea to metal salt is 2:1), stir at 92 °C for 11 h, wash with deionized water and vacuum dry at 60 °C for 12 h to obtain powder A.

[0051] S1-2: Powder A is dispersed in an aqueous solution containing 15% ammonium polyphosphate by mass, ultrasonically treated at 50 °C for 5 h, washed with deionized water and dried at 60 °C for 12 h to obtain powder B;

[0052] S1-3: Mix powder B and modified boron nitride at a mass ratio of 3:1, add 2% by mass of silane coupling agent KH550 of powder B, ball mill for 1.5 h at a ball milling speed of 250 rpm, and then vacuum dry at 60 ℃ for 12 h to obtain the composite flame retardant.

[0053] The method for preparing the modified boron nitride in S1-3 is as follows:

[0054] S2-1: Boron nitride was dispersed in a 55% ethanol solution, and silane coupling agent KH550 was added. The mass ratio of silane coupling agent KH550 to boron nitride was 1:9. The mixture was stirred at 80°C for 6 h, washed with deionized water, and dried at 60°C for 12 h to obtain powder C.

[0055] S2-2: Diethylphosphoacetic acid and powder C were mixed at a molar ratio of 6:1 and added to MES buffer at pH 5.5. Then EDC and NHS were added. The molar ratio of diethylphosphoacetic acid, EDC and NHS was 2:2:1.5. The mixture was stirred at 50 °C for 5 h, washed with deionized water and dried at 60 °C for 12 h to obtain modified boron nitride.

[0056] A method for preparing a flame-retardant modified metallized thin film for capacitors, the specific steps of which are as follows:

[0057] S8-1: Add terephthalic acid, ethylene glycol, cyclobutane-1,3-dicarboxylic acid, antimony trioxide and stabilizer to the reactor according to the formula ratio, introduce nitrogen gas and heat to 220℃, pressure 0.4 MPa;

[0058] S8-2: Subsequently, composite flame retardant, 4-dimethylaminopyridine and cage-type polysilsesquioxane were added to the reactor, stirred for 8 min, then heated to 240℃, stirred for 35 min, further heated to 268℃, and stirred for 5 h to obtain modified polyester material.

[0059] S8-3: Modified polyester material is extruded through a flat die at 235°C to form a sheet with a thickness of 100 μm. Then, it is subjected to biaxial stretching treatment. The sheet is heated to 90°C and stretched longitudinally at a stretch ratio of 1:4. Then, it is stretched transversely at 110°C at a stretch ratio of 1:3.5 to obtain a biaxially stretched film.

[0060] S8-4: Heat-set the film for 8 seconds at 190°C, then anneal at 115°C for 45 minutes to obtain the flame-retardant modified metallized film for the capacitor.

[0061] Example 2

[0062] A flame-retardant modified metallized film for capacitors, the metallized film comprising, by weight, 50 parts terephthalic acid, 30 parts ethylene glycol, 5 parts cyclobutane-1,3-dicarboxylic acid, 0.5 parts antimony trioxide, 0.5 parts triphenyl phosphite, 4 parts composite flame retardant, 0.1 parts 4-dimethylaminopyridine, and 0.1 parts cage-type polysilsesquioxane;

[0063] The preparation method of the composite flame retardant is as follows:

[0064] S1-1: Dissolve magnesium nitrate and aluminum nitrate in deionized water at a molar ratio of 2:1, add urea (the total molar ratio of urea to metal salt is 1:1), stir at 90 °C for 10 h, wash with deionized water and vacuum dry at 60 °C for 10 h to obtain powder A.

[0065] S1-2: Powder A is dispersed in an aqueous solution containing 10% ammonium polyphosphate by mass, ultrasonically treated at 45°C for 4 hours, washed with deionized water and dried at 60°C for 10 hours to obtain powder B;

[0066] S1-3: Mix powder B with modified boron nitride at a mass ratio of 2:1, add 1% by mass of silane coupling agent KH550 of powder B, ball mill for 1 h at a ball milling speed of 200 rpm, and then vacuum dry at 60 ℃ for 10 h to obtain the composite flame retardant.

[0067] The method for preparing the modified boron nitride in S1-3 is as follows:

[0068] S2-1: Boron nitride was dispersed in a 50% ethanol solution, and silane coupling agent KH550 was added. The mass ratio of silane coupling agent KH550 to boron nitride was 1:8. The mixture was stirred at 80°C for 6 h, washed with deionized water, and dried at 60°C for 10 h to obtain powder C.

[0069] S2-2: Diethylphosphoacetic acid and powder C were mixed at a molar ratio of 5:1 and added to MES buffer at pH 5. Then EDC and NHS were added. The molar ratio of diethylphosphoacetic acid, EDC and NHS was 2:2:1. The mixture was stirred at 45 °C for 4 h, washed with deionized water and dried at 60 °C for 10 h to obtain modified boron nitride.

[0070] A method for preparing a flame-retardant modified metallized thin film for capacitors, the specific steps of which are as follows:

[0071] S8-1: Add terephthalic acid, ethylene glycol, cyclobutane-1,3-dicarboxylic acid, antimony trioxide and stabilizer to the reactor according to the formula ratio, introduce nitrogen gas and heat to 210℃, pressure 0.3 MPa;

[0072] S8-2: Subsequently, composite flame retardant, 4-dimethylaminopyridine and cage-type polysilsesquioxane were added to the reactor, stirred for 5 min, then heated to 230℃, stirred for 30 min, further heated to 265℃, and stirred for 4 h to obtain modified polyester material.

[0073] S8-3: Modified polyester material is extruded through a flat die of an extruder at 230°C to form a sheet with a thickness of 80 μm. Then, it is subjected to biaxial stretching treatment. The sheet is heated to 80°C and stretched longitudinally at a stretch ratio of 1:3. Then, it is stretched transversely at 100°C at a stretch ratio of 1:3 to obtain a biaxially stretched film.

[0074] S8-4: Heat-set the film for 5 seconds at 180°C, then anneal at 110°C for 30 minutes to obtain the flame-retardant modified metallized film for the capacitor.

[0075] Example 3

[0076] A flame-retardant modified metallized film for capacitors, the metallized film comprising the following components, by weight: 60 parts terephthalic acid, 40 parts ethylene glycol, 10 parts cyclobutane-1,3-dicarboxylic acid, 1 part antimony trioxide, 1 part triphenyl phosphite, 6 parts composite flame retardant, 0.3 parts 4-dimethylaminopyridine, and 0.2 parts cage-type polysilsesquioxane;

[0077] The preparation method of the composite flame retardant is as follows:

[0078] S1-1: Dissolve magnesium nitrate and aluminum nitrate in deionized water at a molar ratio of 2:1, add urea, and the total molar ratio of urea to metal salt is 3:1. Stir at 95 °C for 12 h, wash with deionized water and vacuum dry at 60 °C for 14 h to obtain powder A.

[0079] S1-2: Powder A was dispersed in an aqueous solution containing 20% ​​ammonium polyphosphate by mass, ultrasonically treated at 55 °C for 6 h, washed with deionized water and dried at 60 °C for 14 h to obtain powder B;

[0080] S1-3: Mix powder B with modified boron nitride at a mass ratio of 4:1, add 3% by mass of silane coupling agent KH550 of powder B, ball mill for 2 h at a ball milling speed of 300 rpm, and then vacuum dry at 60 ℃ for 14 h to obtain the composite flame retardant.

[0081] The method for preparing the modified boron nitride in S1-3 is as follows:

[0082] S2-1: Boron nitride was dispersed in a 60% ethanol solution, and silane coupling agent KH550 was added. The mass ratio of silane coupling agent KH550 to boron nitride was 1:10. The mixture was stirred at 80°C for 6 h, washed with deionized water, and dried at 60°C for 14 h to obtain powder C.

[0083] S2-2: Diethylphosphoacetic acid and powder C were mixed at a molar ratio of 7:1 and added to MES buffer at pH 6. Then EDC and NHS were added. The molar ratio of diethylphosphoacetic acid, EDC and NHS was 1:1:1. The mixture was stirred at 55 °C for 6 h, washed with deionized water and dried at 60 °C for 14 h to obtain modified boron nitride.

[0084] A method for preparing a flame-retardant modified metallized thin film for capacitors, the specific steps of which are as follows:

[0085] S8-1: Add terephthalic acid, ethylene glycol, cyclobutane-1,3-dicarboxylic acid, antimony trioxide and stabilizer to the reactor according to the formula ratio, introduce nitrogen gas and heat to 230℃, pressure 0.5 MPa;

[0086] S8-2: Subsequently, composite flame retardant, 4-dimethylaminopyridine and cage-type polysilsesquioxane were added to the reactor, stirred for 10 min, then heated to 250℃, stirred for 40 min, further heated to 270℃, and stirred for 6 h to obtain modified polyester material.

[0087] S8-3: Modified polyester material is extruded through a flat die of an extruder at 240°C to form a sheet with a thickness of 120 μm. Then, it is subjected to biaxial stretching treatment. The sheet is heated to 100°C and stretched longitudinally at a stretch ratio of 1:5. Then, it is stretched transversely at 120°C at a stretch ratio of 1:4 to obtain a biaxially stretched film.

[0088] S8-4: Heat-set the film for 10 seconds at 200°C, then anneal it at 120°C for 60 minutes to obtain the flame-retardant modified metallized film for the capacitor.

[0089] Comparative Example 1

[0090] Ammonium polyphosphate was not added in the preparation of the composite flame retardant, and the remaining steps were the same as in Example 1.

[0091] Comparative Example 2

[0092] Modified boron nitride was not added in the preparation of the composite flame retardant, and the remaining steps were the same as in Example 1.

[0093] Comparative Example 3

[0094] No modification of boron nitride was performed; the remaining steps were the same as in Example 1.

[0095] Comparative Example 4

[0096] Diethylphosphoacetic acid was not added in the preparation of modified boron nitride, and the remaining steps were the same as in Example 1.

[0097] Comparative Example 5

[0098] Without adding cage-like polysilsesquioxane, the remaining steps are the same as in Example 1.

[0099] Comparative Example 6

[0100] Without adding composite flame retardants, the remaining steps are the same as in Example 1.

[0101] Flame retardant performance test

[0102] According to GB / T 2406.2-2009 standard, the limiting oxygen index of the films prepared in the examples and comparative examples was determined using an oxygen index meter. Each group of samples was tested three times, and the average value was taken. The experimental data are recorded in the table below.

[0103]

[0104] As can be seen from the examples and comparative data, the metallized film prepared by the present invention has excellent flame retardant properties.

[0105] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention are still within the scope of the present invention.

Claims

1. A flame-retardant modified metallized film for capacitors, characterized in that, The metallized film comprises the following components, by weight: 50-60 parts terephthalic acid, 30-40 parts ethylene glycol, 5-10 parts cyclobutane-1,3-dicarboxylic acid, 0.5-1 part antimony trioxide, 0.5-1 part stabilizer, 4-6 parts composite flame retardant, 0.1-0.3 parts 4-dimethylaminopyridine, and 0.1-0.2 parts cage-like polysilsesquioxane; The preparation method of the composite flame retardant is as follows: S1-1: Dissolve magnesium nitrate and aluminum nitrate in deionized water at a molar ratio of 2:1, add urea, stir at 90-95 °C for 10-12 h, wash with deionized water and vacuum dry at 60 °C for 10-14 h to obtain powder A; S1-2: Disperse powder A in an aqueous solution containing 10-20% ammonium polyphosphate by mass, sonicate at 45-55 °C for 4-6 h, wash with deionized water and dry at 60 °C for 10-14 h to obtain powder B; S1-3: Mix powder B with modified boron nitride, add 1-3% by weight of powder B of silane coupling agent KH550, ball mill for 1-2 hours at a speed of 200-300 rpm, and then vacuum dry at 60 °C for 10-14 hours to obtain the composite flame retardant; The method for preparing the modified boron nitride in S1-3 is as follows: S2-1: Boron nitride was dispersed in an ethanol solution with a mass fraction of 50-60%, silane coupling agent KH550 was added, and the mixture was stirred at 80°C for 6 h. The mixture was then washed with deionized water and dried at 60°C for 10-14 h to obtain powder C. S2-2: Diethylphosphoacetic acid and powder C are mixed at a molar ratio of (5-7):1 and added to MES buffer solution with pH 5-6. Then EDC and NHS are added, and the mixture is stirred at 45-55℃ for 4-6 h. The mixture is washed with deionized water and dried at 60℃ for 10-14 h to obtain modified boron nitride. In S1-3, powder B and modified boron nitride are mixed at a mass ratio of (2-4):

1.

2. The flame-retardant modified metallized film for capacitors according to claim 1, characterized in that, The stabilizer is triphenyl phosphite.

3. The flame-retardant modified metallized film for capacitors according to claim 1, characterized in that, The total molar ratio of urea to metal salt in S1-1 is (1-3):

1.

4. The flame-retardant modified metallized film for capacitors according to claim 1, characterized in that, In S2-1, the mass ratio of silane coupling agent KH550 to boron nitride is 1:(8-10).

5. The flame-retardant modified metallized film for capacitors according to claim 1, characterized in that, The molar ratio of diethylphosphoacetic acid, EDC and NHS is 2:2:(1-2).

6. A method for preparing a flame-retardant modified metallized thin film for capacitors as described in any one of claims 1 to 5, characterized in that, The specific steps of the preparation method are as follows: S8-1: Add terephthalic acid, ethylene glycol, cyclobutane-1,3-dicarboxylic acid, antimony trioxide and stabilizer to the reactor according to the formula ratio, introduce nitrogen gas and heat to 210-230℃, pressure 0.3-0.5 MPa; S8-2: Subsequently, composite flame retardant, 4-dimethylaminopyridine and cage-type polysilsesquioxane were added to the reactor, stirred for 5-10 min, then heated to 230-250℃, stirred for 30-40 min, further heated to 265-270℃, and stirred for 4-6 h to obtain modified polyester material. S8-3: Modified polyester material is extruded through a flat die of an extruder at 230-240℃ to form a sheet with a thickness of 80-120 μm, which is then subjected to biaxial stretching treatment to obtain a biaxially stretched film. S8-4: Heat-set the film and then anneal it at 110-120°C for 30-60 min to obtain the flame-retardant modified metallized film for the capacitor.

7. The method for preparing a flame-retardant modified metallized thin film for capacitors according to claim 6, characterized in that, The biaxial stretching process in S8-3 involves heating the sheet to 80-100°C, stretching it longitudinally at a stretching ratio of 1:(3-5), and then stretching it transversely at 100-120°C at a stretching ratio of 1:(3-4).

8. The method for preparing a flame-retardant modified metallized thin film for capacitors according to claim 6, characterized in that, The heat setting time in S8-4 is 5-10 seconds, and the temperature is 180-200℃.

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