Preparation method and application of bifunctional acrylate monomer modified polypropylene coarsening film for extremely cold-resistant oil-immersed capacitor

Abstract

The invention discloses a preparation method and application of a bifunctional acrylate monomer modified polypropylene coarsening film for an extremely cold-resistant oil-immersed capacitor, and belongs to the technical field of manufacturing of electronic and electrical insulating materials. The invention relates to application of a bifunctional acrylate monomer modified polypropylene coarsened film in an extremely cold resistant oil-immersed capacitor or a thin film capacitor. The preparation method comprises the following steps: (1) respectively adding a polypropylene coarsened film, a monomer, an interface agent, a co-monomer, an initiator and deionized water in certain parts by weight into a reactor, and heating for swelling; (2) heating the reaction system to a certain temperature, and carrying out grafting reaction; and (3) washing, extracting and drying. According to the invention, the bifunctional acrylate is used as a monomer to carry out long-chain branching modification on the polypropylene coarsened film, so that the problem of poor performance of a capacitor in an extreme environment caused by low-temperature embrittlement and high-temperature insulation deterioration of the polypropylene coarsened film is solved. The method has the advantages of good effect, environmental protection, simple process, low cost and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of electronic and electrical insulating material manufacturing, and specifically relates to a preparation method and application of a bifunctional acrylate monomer modified polypropylene roughening film for an extreme cold resistant oil-immersed capacitor. In particular, the polypropylene roughening film of the present invention is mainly used for preparing an extreme cold resistant oil-immersed capacitor and a film capacitor. Background Art

[0002] Extremely cold environments place higher demands on the operational stability of capacitors. It is obviously very important to produce oil-immersed capacitors that are suitable for extremely cold regions.

[0003] Polypropylene roughened film is an ideal solid dielectric insulating material for oil-immersed power capacitors. Its surface roughening is achieved by changing the crystal structure inside polypropylene with the help of temperature and external force. High isotactic polypropylene resin is a crystalline polymer. By controlling the temperature of extrusion melt and casting, α and β crystals can be formed on the surface of the casting, and these two crystals can exist at the same time. α crystal is a stable crystal form, and β crystal is a thermodynamically unstable crystal form. Under the action of force field and temperature field, β crystal can be transformed into stable α crystal. Since the density of β crystal is greater than that of α crystal, after β crystal is transformed into α crystal, a large number of fine and interconnected concave and convex rough surfaces are formed on the surface of the film, thus forming a film with roughened surface. The roughened structure allows the rapid diffusion of the impregnant on both surfaces of the film at the same time, greatly improving and enhancing the impregnation performance of the film. The roughening of polypropylene capacitor film is aimed at improving the impregnation effect of its insulating oil, and its impregnation performance is optimized with the increase of the roughness and roughening density of the film. However, its insulation strength will decrease with the increase of roughness, so the average roughness of the roughened film needs to take into account both the impregnation effect and the insulation performance.

[0004] In order to solve the performance problem of oil-immersed capacitors in extremely cold regions and improve the energy storage performance of other film capacitors, the present invention adopts a suspension grafting method to graft a bifunctional acrylate monomer onto the surface of a polypropylene roughened film, and utilizes the generated long-chain branching to improve the electrical properties of the polypropylene roughened film. This method has the advantages of being able to control the grafting rate, reducing the use of solvents, being economical and environmentally friendly, having a simple production process, and reducing the occurrence of side reactions such as gelation. Summary of the invention

[0005] The purpose of the present invention is to solve the problems of low-temperature embrittlement and high-temperature insulation degradation of the existing polypropylene roughened film used as the insulating medium of oil-immersed capacitors in extremely cold regions, thereby affecting the energy storage performance, and to provide a preparation method and application of a bifunctional acrylate monomer modified polypropylene roughened film for extremely cold resistant oil-immersed capacitors.

[0006] A bifunctional acrylate monomer modified polypropylene roughening film for extreme cold resistant oil-immersed capacitors is applied in metallized polypropylene films for extreme cold resistant oil-immersed capacitors or film capacitors.

[0007] A method for preparing a bifunctional acrylate monomer modified polypropylene roughening film for an extreme cold resistant oil-immersed capacitor is specifically completed by the following steps:

[0008] 1. Add 1 part of polypropylene roughening film, 0.04-0.8 parts of bifunctional acrylate monomer, 0.05-0.15 parts of interface agent, 0.05-0.4 parts of comonomer, 1-6 parts of deionized water, 0.001-0.01 parts of antioxidant and 0.001-0.01 parts of initiator into the reactor, and swell at a certain temperature for a certain time;

[0009] 2. Heating the reaction system, carrying out a grafting reaction at a certain temperature for a certain time to obtain a reaction product;

[0010] 3. Purify the reaction product and then dry it to obtain a roughened polypropylene film modified with a bifunctional acrylate monomer for an extreme cold resistant oil-immersed capacitor.

[0011] Principle of the present invention:

[0012] The present invention uses a bifunctional acrylate as a grafting monomer, which can be used to perform long-chain branching modification on polypropylene, and can also introduce a cross-linking structure for cross-linking modification, thereby changing the molecular structure of polypropylene and improving the performance of the polypropylene roughening film under extremely cold conditions. Through long-chain branching, the polarity of the molecular chain is enhanced to introduce carrier traps, while the entanglement between the polypropylene macromolecular chains is enhanced, the slip and movement of the molecular chains are hindered, the free volume is reduced, the conductivity loss at high temperature is suppressed, and the breakdown field strength is improved, thereby enhancing the mechanical properties and electrical properties of the polypropylene roughening film. Through cross-linking, a three-dimensional mesh structure is formed in the amorphous region, which enhances the interaction between the molecular chains, limits the movement of the molecular chain segments, reduces the free volume, and reduces the mean free path of the carriers, so that the conductivity loss is suppressed and the breakdown field strength is improved. At the same time, the cross-linking point acts as a carrier trap, which can also improve the energy storage performance of the polypropylene roughening film. Therefore, bifunctional acrylate is used as a grafting monomer to perform long-chain branching on polypropylene. It solves the problems of low-temperature brittleness and high-temperature performance degradation of polypropylene roughened membrane, and meets its application needs in extremely cold areas.

[0013] Beneficial effects of the present invention:

[0014] 1. The present invention uses a polypropylene roughening film, a bifunctional acrylate monomer, an interface agent, a comonomer, ionized water, an antioxidant and an initiator as raw materials, and adopts a suspension grafting method for modification to prepare a long-chain branched modified polypropylene roughening film. At the same time, due to the two functional groups in the molecular structure of the bifunctional acrylate monomer, a small amount of cross-linking structure can also be introduced, and the modified polypropylene molecular structure finally prepared is ideal.

[0015] 2. The long-chain branched polypropylene roughening film prepared by the method of the present invention improves the molecular structure of polypropylene through long-chain branching and cross-linking. On the one hand, it enhances the polarity and entanglement of the polypropylene molecular chain, and on the other hand, it forms a three-dimensional network structure, which can hinder the movement of the molecular chain, reduce the free volume, and improve the electrical properties. In addition, polar functional groups, entanglements and cross-linking points of molecular chains can introduce carrier traps to improve its energy storage performance. In short, the use of long-chain branched modified polypropylene with bifunctional acrylate monomers can significantly improve the mechanical properties and energy storage properties of the polypropylene roughening film and inhibit its deformation caused by temperature, solving the problems of low-temperature embrittlement and high-temperature performance degradation of the polypropylene roughening film. The performance of oil-immersed capacitors using it as an energy storage medium in extremely cold areas is improved. At the same time, the energy storage performance of other thin film capacitors using it as an energy storage medium can also be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is the FT-IR spectrum of the original polypropylene roughened film;

[0017] Figure 2 is the XRD pattern of the original polypropylene roughened film;

[0018] Figure 3 The breakdown field intensity spectra of the original polypropylene roughened film at 25℃, 85℃ and 105℃ were fitted by Weibull distribution analysis method;

[0019] Figure 4 The energy storage density and efficiency spectrum of the original polypropylene roughened membrane at 25℃ and 85℃;

[0020] Figure 5 The FT-IR spectrum of the long-chain branched polypropylene roughened film prepared using 1,6-hexanediol diacrylate monomer in Example 1;

[0021] Figure 6 The XRD pattern of the long-chain branched polypropylene roughened film prepared using 1,6-hexanediol diacrylate monomer in Example 1;

[0022] Figure 7The breakdown field intensity spectra at 25°C, 85°C and 105°C fitted by the Weibull distribution analysis method for preparing the long-chain branched polypropylene roughened film using 1,6-hexanediol diacrylate monomer in Example 1;

[0023] Figure 8 The energy storage density and efficiency spectrum of the long-chain branched polypropylene roughened film prepared using 1,6-hexanediol diacrylate monomer at 25° C. and 85° C. in Example 1;

[0024] Fig. 9 The FT-IR spectrum of the long-chain branched polypropylene roughened film prepared using 1,6-hexanediol diacrylate monomer in Example 2;

[0025] Fig.10 The XRD pattern of the long-chain branched polypropylene roughened film prepared using 1,6-hexanediol diacrylate monomer in Example 2;

[0026] Fig.11 The breakdown field intensity spectra at 25°C, 85°C and 105°C fitted by the Weibull distribution analysis method for preparing the long-chain branched polypropylene roughened film using 1,6-hexanediol diacrylate monomer in Example 2;

[0027] Fig.12 The FT-IR spectrum of the long-chain branched polypropylene roughened film prepared using 1,6-hexanediol diacrylate monomer in Example 3;

[0028] Fig.13 The XRD pattern of the long-chain branched polypropylene roughened film prepared using 1,6-hexanediol diacrylate monomer in Example 3;

[0029] Fig.14 The breakdown field intensity spectra at 25°C, 85°C and 105°C fitted by the Weibull distribution analysis method for preparing the long-chain branched polypropylene roughened film using 1,6-hexanediol diacrylate monomer in Example 3;

[0030] Fig.15 The FT-IR spectrum of the long-chain branched polypropylene roughened film prepared using 1,6-hexanediol diacrylate monomer in Example 4;

[0031] Fig.16 The XRD pattern of the long-chain branched polypropylene roughened film prepared using 1,6-hexanediol diacrylate monomer in Example 4;

[0032] Fig.17 The breakdown field intensity spectra at 25° C., 85° C. and 105° C. were fitted using the Weibull distribution analysis method for preparing the long-chain branched polypropylene roughened film using 1,6-hexanediol diacrylate monomer in Example 4. DETAILED DESCRIPTION

[0033] Specific implementation method 1: In this implementation method, a bifunctional acrylate monomer-modified polypropylene roughening film for extreme cold resistant oil-immersed capacitors is applied in metallized polypropylene films for extreme cold resistant oil-immersed capacitors or film capacitors.

[0034] Specific embodiment 2: The difference between this embodiment and specific embodiment 1 is that the breakdown field strength of the bifunctional acrylate monomer modified polypropylene roughened film for extreme cold resistant oil-immersed capacitors at 25°C is 300kV / mm~850kV / mm, the breakdown field strength at 85°C is 280kV / mm~800kV / mm, and the breakdown field strength at 105°C is 250kV / mm~700kV / mm; the energy storage density at 25°C is 1.5J / cm 3 ~8J / cm 3 , the energy storage efficiency is over 90%, and the energy storage density at 85°C is 1J / cm 3 ~5J / cm 3 , the energy storage efficiency is above 90%. The other steps are the same as those in the first embodiment.

[0035] Specific embodiment 3: This embodiment differs from specific embodiment 1 or 2 in that: a method for preparing a roughened polypropylene film modified with a bifunctional acrylate monomer for an extreme cold resistant oil-immersed capacitor is specifically completed in the following steps:

[0036] 1. Add 1 part of polypropylene roughening film, 0.04-0.8 parts of bifunctional acrylate monomer, 0.05-0.15 parts of interface agent, 0.05-0.4 parts of comonomer, 1-6 parts of deionized water, 0.001-0.01 parts of antioxidant and 0.001-0.01 parts of initiator into the reactor, and swell at a certain temperature for a certain time;

[0037] 2. Heating the reaction system, carrying out a grafting reaction at a certain temperature for a certain time to obtain a reaction product;

[0038] 3. Purify the reaction product and dry it to obtain a roughened polypropylene film modified with a bifunctional acrylate monomer for an extremely cold-resistant oil-immersed capacitor. The other steps are the same as those in the first or second embodiment.

[0039] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the bifunctional acrylate monomer described in step 1 is one or more of dipropylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, polyethylene glycol (200) diacrylate, polyethylene glycol (400) diacrylate, polyethylene glycol (600) diacrylate or polyethylene glycol (1000) diacrylate. The other steps are the same as those of specific embodiments 1 to 3.

[0040] Specific implementation method 5: This implementation method is different from specific implementation methods 1 to 4 in that the interface agent in step 1 is xylene. The other steps are the same as those of specific implementation methods 1 to 4.

[0041] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that the comonomer in step 1 is styrene. The other steps are the same as those in specific embodiments 1 to 5.

[0042] Specific embodiment 7: This embodiment differs from specific embodiments 1 to 6 in that the antioxidant described in step 1 is one or more of tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]pentaerythritol, β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl alcohol or 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane. The other steps are the same as specific embodiments 1 to 6.

[0043] Specific embodiment eight: This embodiment differs from specific embodiments one to seven in that the initiator described in step one is one or more of dicumyl peroxide, dibenzoyl peroxide, tert-butyl perbenzoate or bis(2-phenylethoxy) peroxydicarbonate. The other steps are the same as those of specific embodiments one to seven.

[0044] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that: the swelling temperature in step 1 is 40°C to 80°C, and the swelling time is 30min to 300min; the grafting reaction temperature in step 2 is 80°C to 95°C; and the grafting reaction time is 30min to 480min. The other steps are the same as those in specific embodiments 1 to 8.

[0045] Specific embodiment 10: This embodiment differs from specific embodiments 1 to 9 in that: the process for purifying the reaction product in step 3 is: first, the reaction product is soaked and washed 2 to 4 times with deionized water, then soaked and washed 2 to 4 times with anhydrous ethanol, and then extracted with acetone for 2h to 24h; the drying temperature in step 3 is 35°C to 70°C. The other steps are the same as those in specific embodiments 1 to 9.

[0046] The following examples are used to verify the beneficial effects of the present invention:

[0047] Example 1: A method for preparing a bifunctional acrylate monomer-modified polypropylene roughening film for an extreme cold-resistant oil-immersed capacitor, which is specifically completed by the following steps:

[0048] 1. Add 10 g of polypropylene roughened film, 4 g of 1,6-hexanediol diacrylate monomer, 2 g of xylene, 4 g of styrene, 25 g of deionized water, 0.02 g of antioxidant 1010 and 0.04 g of DCP into a reactor and swell at 60° C. for 1 h;

[0049] 2. raising the temperature of the reaction system to 90° C. and performing a grafting reaction at 90° C. for 4 hours to obtain a reaction product;

[0050] 3. Purify the reaction product and dry it at 60°C to obtain a bifunctional acrylate monomer modified polypropylene roughened film for extreme cold resistant oil-immersed capacitors;

[0051] The process for purifying the reaction product in step three is: first, the reaction product is soaked and washed 3 times with deionized water, then the reaction product is soaked and washed 3 times with anhydrous ethanol, and then extracted with acetone for 12 hours.

[0052] Example 2: A method for preparing a roughened polypropylene film modified with a bifunctional acrylate monomer for an extreme cold resistant oil-immersed capacitor, which is specifically completed by the following steps:

[0053] 1. Add 10 g of polypropylene roughened film, 2 g of polyethylene glycol (1000) diacrylate monomer, 4 g of xylene, 3 g of styrene, 25 g of deionized water, 0.04 g of antioxidant 1010 and 0.1 g of DCP into the reactor and swell at 60 °C for 1 h;

[0054] 2. raising the temperature of the reaction system to 90° C. and performing a grafting reaction at 90° C. for 4 hours to obtain a reaction product;

[0055] 3. Purify the reaction product and dry it at 60°C to obtain a bifunctional acrylate monomer modified polypropylene roughened film for extreme cold resistant oil-immersed capacitors;

[0056] The process for purifying the reaction product in step three is: first, the reaction product is soaked and washed twice with deionized water, then the reaction product is soaked and washed twice with anhydrous ethanol, and then extracted with acetone for 12 hours.

[0057] Example 3: A method for preparing a roughened polypropylene film modified with a bifunctional acrylate monomer for an extreme cold resistant oil-immersed capacitor, which is specifically completed by the following steps:

[0058] 1. Add 10 g of polypropylene roughened film, 1 g of polyethylene glycol (1000) diacrylate monomer, 4 g of xylene, 4 g of styrene, 30 g of deionized water, 0.02 g of antioxidant 1076 and 0.04 g of BPO into the reactor and swell at 60 °C for 1 h;

[0059] 2. raising the temperature of the reaction system to 90° C. and carrying out a grafting reaction at 90° C. for 6 hours to obtain a reaction product;

[0060] 3. Purify the reaction product and dry it at 60°C to obtain a bifunctional acrylate monomer modified polypropylene roughened film for extreme cold resistant oil-immersed capacitors;

[0061] The process for purifying the reaction product in step three is: first, the reaction product is soaked and washed 3 times with deionized water, then the reaction product is soaked and washed 3 times with anhydrous ethanol, and then extracted with acetone for 24 hours.

[0062] Example 4: A method for preparing a bifunctional acrylate monomer-modified polypropylene roughening film for an extreme cold resistant oil-immersed capacitor is specifically completed by the following steps:

[0063] 1. Add 10 g of polypropylene roughened film, 4 g of polyethylene glycol (600) diacrylate monomer, 1 g of xylene, 4 g of styrene, 20 g of deionized water, 0.01 g of antioxidant 1076 and 0.04 g of BPO into the reactor and swell at 60 °C for 1 h;

[0064] 2. raising the temperature of the reaction system to 90° C. and carrying out a grafting reaction at 90° C. for 8 hours to obtain a reaction product;

[0065] 3. Purify the reaction product and dry it at 60°C to obtain a bifunctional acrylate monomer modified polypropylene roughened film for extreme cold resistant oil-immersed capacitors;

[0066] The process for purifying the reaction product in step three is: first, the reaction product is soaked and washed 4 times with deionized water, then the reaction product is soaked and washed 4 times with anhydrous ethanol, and then extracted with acetone for 6 hours.

[0067] Figure 1 is the FT-IR spectrum of the original polypropylene roughened film;

[0068] Figure 2 is the XRD pattern of the original polypropylene roughened film;

[0069] Figure 3 The breakdown field intensity spectra of the original polypropylene roughened film at 25℃, 85℃ and 105℃ were fitted by Weibull distribution analysis method;

[0070] Figure 4The energy storage density and efficiency spectrum of the original polypropylene roughened membrane at 25℃ and 85℃;

[0071] Figure 5 The FT-IR spectrum of the long-chain branched polypropylene roughened film prepared using 1,6-hexanediol diacrylate monomer in Example 1;

[0072] Figure 6 The XRD pattern of the long-chain branched polypropylene roughened film prepared using 1,6-hexanediol diacrylate monomer in Example 1;

[0073] Figure 7 The breakdown field intensity spectra at 25°C, 85°C and 105°C fitted by the Weibull distribution analysis method for preparing the long-chain branched polypropylene roughened film using 1,6-hexanediol diacrylate monomer in Example 1;

[0074] Figure 8 The energy storage density and efficiency spectrum of the long-chain branched polypropylene roughened film prepared using 1,6-hexanediol diacrylate monomer at 25° C. and 85° C. in Example 1;

[0075] Fig. 9 The FT-IR spectrum of the long-chain branched polypropylene roughened film prepared using 1,6-hexanediol diacrylate monomer in Example 2;

[0076] Fig.10 The XRD spectrum of the long-chain branched polypropylene roughened film prepared using 1,6-hexanediol diacrylate monomer in Example 2;

[0077] Fig.11 The breakdown field intensity spectra at 25°C, 85°C and 105°C fitted by the Weibull distribution analysis method for preparing the long-chain branched polypropylene roughened film using 1,6-hexanediol diacrylate monomer in Example 2;

[0078] Fig.12 The FT-IR spectrum of the long-chain branched polypropylene roughened film prepared using 1,6-hexanediol diacrylate monomer in Example 3;

[0079] Fig.13 The XRD pattern of the long-chain branched polypropylene roughened film prepared using 1,6-hexanediol diacrylate monomer in Example 3;

[0080] Fig.14 The breakdown field intensity spectra at 25°C, 85°C and 105°C fitted by the Weibull distribution analysis method for preparing the long-chain branched polypropylene roughened film using 1,6-hexanediol diacrylate monomer in Example 3;

[0081] Fig.15The FT-IR spectrum of the long-chain branched polypropylene roughened film prepared using 1,6-hexanediol diacrylate monomer in Example 4;

[0082] Fig.16 The XRD pattern of the long-chain branched polypropylene roughened film prepared using 1,6-hexanediol diacrylate monomer in Example 4;

[0083] Fig.17 The breakdown field intensity spectra at 25° C., 85° C. and 105° C. were fitted using the Weibull distribution analysis method for preparing the long-chain branched polypropylene roughened film using 1,6-hexanediol diacrylate monomer in Example 4.

[0084] From the attached Figures 1 to 17 It can be seen from the test data in that compared with the characterization and test of the original polypropylene roughened film, the FT-IR spectrum of the polypropylene roughened film modified by using 1,6-hexanediol diacrylate monomer as the monomer long-chain branch in Examples 1, 2, 3 and 4 of the present invention shows that the bifunctional acrylate is successfully grafted onto the polypropylene roughened film, and the XRD spectrum of the polypropylene roughened film modified by using 1,6-hexanediol diacrylate monomer as the monomer long-chain branch shows that the crystalline structure is ideal. The electrical performance spectrum of the polypropylene roughened film modified by using 1,6-hexanediol diacrylate monomer as the monomer long-chain branch shows that the breakdown field strength at 25°C, 85°C and 105°C, the energy storage density and energy storage efficiency at 25°C and 85°C are greatly improved, the breakdown field strength at 25°C, 85°C and 105°C are increased by 130-200%, 110-200% and 90-180%, respectively, and the energy storage density at 25°C and 85°C reaches 6.2 J / cm 3 and 3.2 J / cm 3 , the energy storage efficiency has also been greatly improved.

Claims

1. Application of a bifunctional acrylate monomer modified polypropylene roughening film for extreme cold resistant oil-immersed capacitors, characterized in that A bifunctional acrylate monomer modified polypropylene roughening film for extreme cold resistant oil-immersed capacitors is applied in metallized polypropylene films for extreme cold resistant oil-immersed capacitors or film capacitors.

2. The use of a bifunctional acrylate monomer modified polypropylene roughening film for an extreme cold resistant oil-immersed capacitor according to claim 1, characterized in that The bifunctional acrylate monomer modified polypropylene roughened film for extreme cold resistant oil-immersed capacitors has a breakdown field strength of 300 kV / mm to 850 kV / mm at 25°C, a breakdown field strength of 280 kV / mm to 800 kV / mm at 85°C, and a breakdown field strength of 250 kV / mm to 700 kV / mm at 105°C; the energy storage density at 25°C is 1.5 J / cm 3 ~8J / cm 3 , the energy storage efficiency is over 90%, and the energy storage density at 85°C is 1J / cm 3 ~5J / cm 3 , the energy storage efficiency is over 90%.

3. The method for preparing a bifunctional acrylate monomer modified polypropylene roughening film for an extreme cold resistant oil-immersed capacitor according to claim 1, characterized in that The preparation method is specifically completed according to the following steps:

1. Add 1 part of polypropylene roughening film, 0.04-0.8 parts of bifunctional acrylate monomer, 0.05-0.15 parts of interface agent, 0.05-0.4 parts of comonomer, 1-6 parts of deionized water, 0.001-0.01 parts of antioxidant and 0.001-0.01 parts of initiator into the reactor, and swell at a certain temperature for a certain time; 2. Heating the reaction system, carrying out a grafting reaction at a certain temperature for a certain time to obtain a reaction product; 3. Purify the reaction product and then dry it to obtain a roughened polypropylene film modified with a bifunctional acrylate monomer for an extreme cold resistant oil-immersed capacitor.

4. The method for preparing a bifunctional acrylate monomer modified polypropylene roughening film for an extreme cold resistant oil-immersed capacitor according to claim 3, characterized in that The bifunctional acrylate monomer described in step 1 is one or more of dipropylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, polyethylene glycol (200) diacrylate, polyethylene glycol (400) diacrylate, polyethylene glycol (600) diacrylate or polyethylene glycol (1000) diacrylate.

5. The method for preparing a bifunctional acrylate monomer modified polypropylene roughening film for an extreme cold resistant oil-immersed capacitor according to claim 3, characterized in that The interface agent described in step 1 is xylene.

6. The method for preparing a bifunctional acrylate monomer modified polypropylene roughening film for an extreme cold resistant oil-immersed capacitor according to claim 3, characterized in that The comonomer described in step 1 is styrene.

7. The method for preparing a bifunctional acrylate monomer modified polypropylene roughening film for an extreme cold resistant oil-immersed capacitor according to claim 3, characterized in that The antioxidant described in step 1 is one or more of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, n-octadecylβ-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate or 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane.

8. The method for preparing a bifunctional acrylate monomer modified polypropylene roughening film for an extreme cold resistant oil-immersed capacitor according to claim 3, characterized in that The initiator described in step 1 is one or more of dicumyl peroxide, dibenzoyl peroxide, tert-butyl perbenzoate or bis(2-phenylethoxy) peroxydicarbonate.

9. The method for preparing a bifunctional acrylate monomer modified polypropylene roughening film for an extreme cold resistant oil-immersed capacitor according to claim 3, characterized in that The swelling temperature in step 1 is 40°C to 80°C, and the swelling time is 30min to 300min; the grafting reaction temperature in step 2 is 80°C to 95°C; and the grafting reaction time is 30min to 480min.

10. The method for preparing a bifunctional acrylate monomer modified polypropylene roughening film for an extreme cold resistant oil-immersed capacitor according to claim 3, characterized in that The process for purifying the reaction product in step three is: first, the reaction product is soaked and washed 2 to 4 times with deionized water, then the reaction product is soaked and washed 2 to 4 times with anhydrous ethanol, and then extracted with acetone for 2h to 24h; the drying temperature described in step three is 35°C to 70°C.

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