Preparation method and application of difurfuryl sulfide long-chain branched modified polypropylene coarsening film for extremely cold-resistant oil-immersed capacitor

Abstract

The invention discloses a preparation method and application of a difurfuryl sulfide long-chain branched 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 difurfuryl sulfide modified polypropylene coarsened film is prepared from a polypropylene coarsened film, difurfuryl sulfide, an interface agent, a co-monomer, deionized water, a main antioxidant, an auxiliary antioxidant and an initiator as raw materials. The difurfuryl sulfide long-chain branched modified polypropylene coarsened film is applied to an oil-immersed capacitor or a thin-film capacitor. According to the invention, the difurfuryl sulfide 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 simple process, environmental protection, low cost, good processing effect and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of electronic and electrical insulating material manufacturing, and specifically relates to a preparation method and application of a diffuryl sulfide long-chain branched modified polypropylene roughening film for an extreme cold resistant oil-immersed capacitor. Background Art

[0002] Polypropylene is one of the five general-purpose plastics. It has the characteristics of high melting point, good heat resistance, low density, excellent mechanical properties and good chemical stability. It has been successfully used in the field of oil-immersed power capacitors. However, due to the linear structure of the molecular chain of conventional polypropylene, the temperature difference between the outdoor low temperature environment and the operating temperature of the capacitor in the extremely cold environment (-60℃~-40℃) has a great influence on the insulation and thermal shrinkage of the capacitor film material. Long-term hot and cold cycles will cause the breakdown field strength of the capacitor film to decrease and the dielectric loss to increase. Under low temperature conditions, the molecular chain of polypropylene film moves slowly, the brittleness increases, the breakdown field strength decreases and the dielectric loss increases, and even the film is mechanically damaged due to the generation of electrical stress, which seriously affects the insulation performance. Therefore, how to improve the performance of polypropylene roughening film under low temperature conditions is crucial for the application of oil-immersed capacitors in extremely cold areas.

[0003] Introducing long-chain branching structure into the polypropylene molecular chain is an effective method to solve the application performance of polypropylene roughening film under low temperature conditions. At present, the preparation methods of long-chain branched polypropylene are generally divided into two categories, one is the post-modification method, that is, modifying commercial polypropylene, and the other is the catalytic polymerization method, that is, introducing the long-chain branching structure into the polypropylene molecular chain through catalytic polymerization. Since the post-modification method is simple to operate and easy to implement, it is a method that is widely used in the preparation of long-chain branched polypropylene. It mainly modifies linear polypropylene through free radical reactions. Due to the complexity of free radical reactions, there are two major problems in the preparation of long-chain branched polypropylene using the post-modification method. One is the degradation and gelation of polypropylene, and the other is the competition between polymer grafting and monomer homopolymerization, and the competition between polymer main chain bond breaking and crosslinking and branching.

[0004] In order to solve the shortcomings of existing polypropylene roughening membranes, such as unsatisfactory mechanical properties at low temperatures and decreased energy storage performance at high temperatures, which in turn affect their application, the present invention proposes a method for long-chain branched modified polypropylene roughening membranes so that they can adapt to extremely cold climates. Summary of the invention

[0005] The purpose of the present invention is to solve the problem that the polypropylene roughened film used as the insulating medium of oil-immersed capacitors in extremely cold areas has the defects of low-temperature embrittlement and high-temperature insulation degradation, which further affects the energy storage performance, and to provide a preparation method and application of diffuryl sulfide long-chain branched modified polypropylene roughened film for extremely cold resistant oil-immersed capacitors.

[0006] A diffuryl sulfide long-chain branched modified polypropylene roughening film for extreme cold resistant oil-immersed capacitors is prepared from polypropylene roughening film, diffuryl sulfide, an interfacial agent, a comonomer, deionized water, a primary antioxidant, an auxiliary antioxidant and an initiator; the diffuryl sulfide long-chain branched modified polypropylene roughening film is used in oil-immersed capacitors or film capacitors.

[0007] A method for preparing a diffuryl sulfide long-chain branched 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, 0.05-0.8 parts of difurfuryl sulfide, 0.05-0.2 parts of interface agent, 0.1-0.4 parts of comonomer, 1-10 parts of deionized water, 0.01-0.08 parts of primary antioxidant, 0.001-0.006 parts of auxiliary antioxidant and 0.001-0.008 parts of initiator into the reaction kettle, and swell at a certain temperature for a certain time;

[0009] 2. Raising the temperature of the reactor, and then carrying out a grafting reaction at a certain temperature for a certain time to obtain a reaction product;

[0010] 3. First, the reaction product is soaked and washed with a solvent for a certain period of time, then extracted with acetone for a certain period of time, and finally dried at a certain temperature to obtain a diffuryl sulfide modified polypropylene roughened membrane.

[0011] Principle of the present invention:

[0012] The present invention uses difurfuryl sulfide 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, and the mechanical properties and electrical properties of the polypropylene roughening film are enhanced; through cross-linking, a three-dimensional network structure is formed in the amorphous region, the interaction between the molecular chains is enhanced, the movement of the molecular chain segments is restricted, the free volume is reduced, and the mean free path of the carriers is reduced, so that the conductivity loss is suppressed and the breakdown field strength is improved. At the same time, the cross-linking points and the polar groups in the molecules act as carrier traps, which can also improve the energy storage performance of the polypropylene roughening film. Therefore, difurfuryl sulfide is used as a grafting monomer to carry out long-chain branching of polypropylene; the problems of low-temperature brittleness and high-temperature performance degradation of the polypropylene roughened film are solved, meeting its application needs in extremely cold regions.

[0013] Beneficial effects of the present invention:

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

[0015] Second, 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, which on the one hand enhances the polarity and entanglement of the polypropylene molecular chain, and on the other hand forms a three-dimensional network structure, which can hinder the movement of the molecular chain, reduce the free volume, and improve the electrical performance. In addition, the polar functional groups at the cross-linking points, the polar groups in the molecular chain, the entanglement of the molecular chain and the cross-linking points can all introduce carrier traps to improve its energy storage performance; in short, the use of diffuryl sulfide monomer long-chain branched modified polypropylene can significantly improve the mechanical properties and energy storage performance 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; improving the performance of oil-immersed capacitors using it as an energy storage medium in extremely cold areas; at the same time, it can also improve the energy storage performance of other film capacitors using it as an energy storage medium. 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 modified polypropylene roughened film prepared using difurfuryl sulfide monomer in Example 1;

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

[0022] 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 modified polypropylene roughened membrane using diffuryl sulfide monomer in Example 1;

[0023] Figure 8 The energy storage density and efficiency spectrum of the long-chain branched modified polypropylene roughened membrane prepared using diffuryl sulfide monomer at 25°C and 85°C in Example 1;

[0024] Fig. 9 FT-IR spectrum of the difurfuryl sulfide long-chain branched modified polypropylene roughened film prepared using difurfuryl sulfide monomer in Example 2;

[0025] Fig.10 The XRD pattern of the difurfuryl sulfide long-chain branched modified polypropylene roughened film prepared using difurfuryl sulfide monomer in Example 2;

[0026] Fig.11 The breakdown field intensity spectra at 25°C, 85°C and 105°C fitted by Weibull distribution analysis method for the difurfuryl sulfide long-chain branched modified polypropylene roughened membrane prepared using difurfuryl sulfide monomer in Example 2;

[0027] Fig.12 The FT-IR spectrum of the difurfuryl sulfide long-chain branched modified polypropylene roughened membrane prepared using difurfuryl sulfide monomer in Example 3;

[0028] Fig.13 The XRD pattern of the difurfuryl sulfide long-chain branched modified polypropylene roughened film prepared using difurfuryl sulfide monomer in Example 3;

[0029] Fig.14 The breakdown field intensity spectra at 25°C, 85°C and 105°C fitted by Weibull distribution analysis method for the difurfuryl sulfide long-chain branched modified polypropylene roughened membrane prepared using difurfuryl sulfide monomer in Example 3;

[0030] Fig.15 FT-IR spectrum of the difurfuryl sulfide long-chain branched modified polypropylene roughened film prepared using difurfuryl sulfide monomer in Example 4;

[0031] Fig.16 The XRD pattern of the difurfuryl sulfide long-chain branched modified polypropylene roughened film prepared using difurfuryl sulfide monomer in Example 4;

[0032] Fig.17 The breakdown field intensity spectra at 25° C., 85° C. and 105° C. are fitted by Weibull distribution analysis method for the difurfuryl sulfide long-chain branched modified polypropylene roughened membrane prepared using difurfuryl sulfide monomer in Example 4. DETAILED DESCRIPTION

[0033] The present invention is further explained below in conjunction with specific embodiments. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0034] Specific implementation method 1: In this implementation method, a diffuryl sulfide long-chain branched modified polypropylene roughening film for extreme cold resistant oil-immersed capacitors is prepared from polypropylene roughening film, diffuryl sulfide, an interfacial agent, a comonomer, deionized water, a primary antioxidant, an auxiliary antioxidant and an initiator as raw materials; the diffuryl sulfide long-chain branched modified polypropylene roughening film is used in oil-immersed capacitors or film capacitors.

[0035] Specific embodiment 2: The difference between this embodiment and specific embodiment 1 is that the breakdown field strength of the diffuryl sulfide long-chain branched modified polypropylene roughened film for extreme cold resistant oil-immersed capacitors is 400kV / mm-850kV / mm at 25°C, 350kV / mm-800kV / mm at 85°C, and 300kV / mm-700kV / mm at 105°C; the energy storage density reaches 2J / cm at 25°C. 3 ~7J / cm 3 , the energy storage density reached 1.5J / cm at 85℃ 3 ~6.5J / cm 3 , the energy storage efficiency at 25° C. and 85° C. is higher than 90%. The other steps are the same as those in the first embodiment.

[0036] Specific implementation method three: This implementation method is a method for preparing a diffuryl sulfide long-chain branched modified polypropylene roughening film for an extreme cold resistant oil-immersed capacitor, which is specifically completed in the following steps:

[0037] 1. Add 1 part of polypropylene roughening film, 0.05-0.8 parts of difurfuryl sulfide, 0.05-0.2 parts of interface agent, 0.1-0.4 parts of comonomer, 1-10 parts of deionized water, 0.01-0.08 parts of primary antioxidant, 0.001-0.006 parts of auxiliary antioxidant and 0.001-0.008 parts of initiator into the reaction kettle, and swell at a certain temperature for a certain time;

[0038] 2. Raising the temperature of the reactor, and then carrying out a grafting reaction at a certain temperature for a certain time to obtain a reaction product;

[0039] 3. First, the reaction product is soaked and washed with a solvent for a certain period of time, then extracted with acetone for a certain period of time, and finally dried at a certain temperature to obtain a diffuryl sulfide modified polypropylene roughened membrane.

[0040] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the interface agent in step 1 is one or more of xylene and cyclohexane. The other steps are the same as those of specific embodiments 1 to 3.

[0041] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that the comonomer in step 1 is styrene. The other steps are the same as those in specific embodiments 1 to 4.

[0042] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that the primary antioxidant described in step 1 is one or more of tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] pentaerythritol ester, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate n-octadecyl alcohol ester, 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 1.1.3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane and bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite. The other steps are the same as specific embodiments 1 to 5.

[0043] Specific embodiment 7: This embodiment differs from specific embodiments 1 to 6 in that the auxiliary antioxidant described in step 1 is one or more of tris(2,4-di-tert-butylphenyl)phosphite, triphenyl phosphite, trinonylphenyl phosphite, dilauryl thiodipropionate and octadecyl thiodipropionate. The other steps are the same as those of specific embodiments 1 to 6.

[0044] Specific embodiment 8: This embodiment differs from specific embodiments 1 to 7 in that the initiator in step 1 is one or more of dicumyl peroxide, dibenzoyl peroxide, azobisisobutyronitrile and ammonium persulfate. The other steps are the same as those in specific embodiments 1 to 7.

[0045] 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; the swelling time is 20min to 240min; the grafting reaction temperature in step 2 is 80°C to 95°C; the grafting reaction time is 0.5h to 10h. The other steps are the same as those in specific embodiments 1 to 8.

[0046] Specific embodiment 10: This embodiment differs from specific embodiments 1 to 9 in that the drying temperature in step 3 is 35° C. to 80° C. The other steps are the same as those in specific embodiments 1 to 9.

[0047] The following examples are used to verify the beneficial effects of the present invention:

[0048] Example 1: A method for preparing a diffuryl sulfide long-chain branched modified polypropylene roughening film for an extreme cold resistant oil-immersed capacitor, which is specifically completed by the following steps:

[0049] 1. Add 10g of polypropylene roughened film, 4g of difurfuryl sulfide, 2g of xylene, 4g of styrene, 25g of deionized water, 0.02g of antioxidant 1010 and 0.04g of DCP into a beaker and swell at 60°C for 1 hour.

[0050] 2. raising the temperature of the reaction kettle to 90° C. and carrying out a grafting reaction at 90° C. for 4 hours to obtain a reaction product;

[0051] 3. The reaction product was washed three times with deionized water and anhydrous ethanol respectively, extracted with acetone for 12 hours, and finally dried at 60°C to obtain a diffuryl sulfide long-chain branched modified polypropylene roughened film for extreme cold resistant oil-immersed capacitors.

[0052] Example 2: A method for preparing a diffuryl sulfide long-chain branched modified polypropylene roughening film for an extreme cold resistant oil-immersed capacitor, which is specifically completed by the following steps:

[0053] 1. Add 10g of polypropylene roughened film, 0.5g of difurfuryl sulfide, 1g of cyclohexane, 25g of deionized water, 0.01g of antioxidant 1076, 0.001g of antioxidant 168 and 0.02g of DCP into a beaker and swell at 60°C for 2 hours.

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

[0055] 3. The reaction product was washed three times with anhydrous ethanol, extracted with acetone for 8 hours, and finally dried at 45°C to obtain a diffuryl sulfide long-chain branched modified polypropylene roughened film for extreme cold resistant oil-immersed capacitors.

[0056] Example 3: A method for preparing a roughened film of diffuryl sulfide long-chain branched modified polypropylene for an extreme cold resistant oil-immersed capacitor, which is specifically completed by the following steps:

[0057] 1. Add 10g of polypropylene roughened film, 1g of furfuryl sulfide, 2g of xylene, 3g of styrene, 40g of deionized water, 0.02g of antioxidant 1076 and 0.08g of BPO into a beaker and swell at 60°C for 1 hour.

[0058] 2. raising the temperature of the reaction kettle to 90° C. and carrying out a grafting reaction at 90° C. for 2 hours to obtain a reaction product;

[0059] 3. The reaction product was washed three times with anhydrous ethanol, extracted with acetone for 12 hours, and finally dried at 50°C to obtain a diffuryl sulfide long-chain branched modified polypropylene roughened film for extreme cold resistant oil-immersed capacitors.

[0060] Example 4: A method for preparing a diffuryl sulfide long-chain branched modified polypropylene roughening film for an extreme cold resistant oil-immersed capacitor, which is specifically completed by the following steps:

[0061] 1. Add 10g of polypropylene roughened film, 2g of difurfuryl sulfide, 1g of xylene, 2g of styrene, 25g of deionized water, 0.01g of antioxidant CA, 0.002g of antioxidant DLTP and 0.04g of AIBN into a beaker and swell at 60°C for 1 hour.

[0062] 2. raising the temperature of the reaction kettle to 90° C. and carrying out a grafting reaction at 90° C. for 4 hours to obtain a reaction product;

[0063] 3. The reaction product was washed three times with deionized water and anhydrous ethanol in turn, extracted with acetone for 24 hours, and finally dried at 60°C to obtain a diffuryl sulfide long-chain branched modified polypropylene roughened film for extreme cold resistant oil-immersed capacitors.

[0064] Figure 1 is the FT-IR spectrum of the original polypropylene roughened film;

[0065] Figure 2 is the XRD pattern of the original polypropylene roughened film;

[0066] 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;

[0067] Figure 4 The energy storage density and efficiency spectrum of the original polypropylene roughened membrane at 25℃ and 85℃;

[0068] Figure 5 The FT-IR spectrum of the long-chain branched modified polypropylene roughened film prepared using difurfuryl sulfide monomer in Example 1;

[0069] Figure 6 The XRD pattern of the long-chain branched modified polypropylene roughened film prepared using difurfuryl sulfide monomer in Example 1;

[0070] 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 modified polypropylene roughened membrane using diffuryl sulfide monomer in Example 1;

[0071] Figure 8The energy storage density and efficiency spectrum of the long-chain branched modified polypropylene roughened membrane prepared using diffuryl sulfide monomer at 25°C and 85°C in Example 1;

[0072] Fig. 9 FT-IR spectrum of the difurfuryl sulfide long-chain branched modified polypropylene roughened film prepared using difurfuryl sulfide monomer in Example 2;

[0073] Fig.10 The XRD pattern of the difurfuryl sulfide long-chain branched modified polypropylene roughened film prepared using difurfuryl sulfide monomer in Example 2;

[0074] Fig.11 The breakdown field intensity spectra at 25°C, 85°C and 105°C fitted by Weibull distribution analysis method for the difurfuryl sulfide long-chain branched modified polypropylene roughened membrane prepared using difurfuryl sulfide monomer in Example 2;

[0075] Fig.12 The FT-IR spectrum of the difurfuryl sulfide long-chain branched modified polypropylene roughened membrane prepared using difurfuryl sulfide monomer in Example 3;

[0076] Fig.13 The XRD pattern of the difurfuryl sulfide long-chain branched modified polypropylene roughened film prepared using difurfuryl sulfide monomer in Example 3;

[0077] Fig.14 The breakdown field intensity spectra at 25°C, 85°C and 105°C fitted by Weibull distribution analysis method for the difurfuryl sulfide long-chain branched modified polypropylene roughened membrane prepared using difurfuryl sulfide monomer in Example 3;

[0078] Fig.15 FT-IR spectrum of the difurfuryl sulfide long-chain branched modified polypropylene roughened film prepared using difurfuryl sulfide monomer in Example 4;

[0079] Fig.16 The XRD pattern of the difurfuryl sulfide long-chain branched modified polypropylene roughened film prepared using difurfuryl sulfide monomer in Example 4;

[0080] Fig.17 The breakdown field intensity spectra at 25° C., 85° C. and 105° C. are fitted by Weibull distribution analysis method for the difurfuryl sulfide long-chain branched modified polypropylene roughened membrane prepared using difurfuryl sulfide monomer in Example 4.

[0081] From the attached Figures 1 to 17It 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 diffuryl sulfide as a monomer long-chain branch in Example 1 of the present invention shows that diffuryl sulfide is successfully grafted onto the polypropylene roughened film, and the XRD spectrum of the polypropylene roughened film modified by using diffuryl sulfide as a monomer long-chain branch shows that the crystalline structure is ideal. The electrical performance spectrum of the polypropylene roughened film modified by using diffuryl sulfide as a monomer long-chain branch shows that the electrical performance at 25°C, 85°C and 105°C is greatly improved, the breakdown field strength at 25°C is increased by 50-80%, the breakdown field strength at 85°C is increased by 30-70%, and the breakdown field strength at 105°C is increased by 40-75%, and the energy storage density at 25°C and 85°C reaches 3.51 J / cm 3 and 2.69 J / cm 3 , the energy storage efficiency is higher than 90%.

Claims

1. Application of a diffuryl sulfide long-chain branched modified polypropylene roughening film for extreme cold resistant oil-immersed capacitors, characterized in that The diffuryl sulfide long-chain branched modified polypropylene roughened film for extreme cold resistant oil-immersed capacitors is prepared from polypropylene roughened film, diffuryl sulfide, interface agent, comonomer, deionized water, primary antioxidant, auxiliary antioxidant and initiator as raw materials; the diffuryl sulfide long-chain branched modified polypropylene roughened film is used in oil-immersed capacitors or film capacitors.

2. The use of the diffuryl sulfide long-chain branched modified polypropylene roughening film for extreme cold resistant oil-immersed capacitors according to claim 1, characterized in that The breakdown field strength of the diffuryl sulfide long-chain branched modified polypropylene roughened film for the extreme cold resistant oil-immersed capacitor is 400kV / mm-850kV / mm at 25°C, 350kV / mm-800kV / mm at 85°C, and 300kV / mm-700kV / mm at 105°C; the energy storage density reaches 2J / cm at 25°C. 3 ~7J / cm 3 , the energy storage density reached 1.5J / cm at 85℃ 3 ~6.5J / cm 3 , the energy storage efficiency at 25℃ and 85℃ is higher than 90%.

3. The method for preparing a diffuryl sulfide long-chain branched 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, 0.05-0.8 parts of difurfuryl sulfide, 0.05-0.2 parts of interface agent, 0.1-0.4 parts of comonomer, 1-10 parts of deionized water, 0.01-0.08 parts of primary antioxidant, 0.001-0.006 parts of auxiliary antioxidant and 0.001-0.008 parts of initiator into the reaction kettle, and swell at a certain temperature for a certain time; 2. Raising the temperature of the reactor, and then carrying out a grafting reaction at a certain temperature for a certain time to obtain a reaction product; 3. First, the reaction product is soaked and washed with a solvent for a certain period of time, then extracted with acetone for a certain period of time, and finally dried at a certain temperature to obtain a diffuryl sulfide modified polypropylene roughened membrane.

4. The method for preparing a diffuryl sulfide long-chain branched modified polypropylene roughening film for an extreme cold resistant oil-immersed capacitor according to claim 3, characterized in that The interfacial agent described in step 1 is one or more of xylene and cyclohexane.

5. The method for preparing a diffuryl sulfide long-chain branched 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.

6. The method for preparing a diffuryl sulfide long-chain branched modified polypropylene roughening film for an extreme cold resistant oil-immersed capacitor according to claim 3, characterized in that The main antioxidant described in step 1 is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 1.

1. One or more of 3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane and bis(2,4-di-tert-butylphenol)pentaerythritol diphosphite.

7. The method for preparing a diffuryl sulfide long-chain branched modified polypropylene roughening film for an extreme cold resistant oil-immersed capacitor according to claim 3, characterized in that The auxiliary antioxidant described in step 1 is one or more of tris(2,4-di-tert-butylphenyl) phosphite, triphenyl phosphite, trinonylphenyl phosphite, dilauryl thiodipropionate and octadecyl thiodipropionate.

8. The method for preparing a diffuryl sulfide long-chain branched modified polypropylene roughening film for an extreme cold resistant oil-immersed capacitor according to claim 3, characterized in that The initiator type described in step 1 is one or more of dicumyl peroxide, dibenzoyl peroxide, azobisisobutyronitrile and ammonium persulfate.

9. The method for preparing a diffuryl sulfide long-chain branched 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; the swelling time is 20min to 240min; the grafting reaction temperature in step 2 is 80°C to 95°C; the grafting reaction time is 0.5h to 10h.

10. The method for preparing a diffuryl sulfide long-chain branched modified polypropylene roughening film for extreme cold resistant oil-immersed capacitors according to claim 3, characterized in that The drying temperature described in step 3 is 35°C to 80°C.

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