Preparation method of modified polypropylene capacitor base film resistant to heat, flame and electric breakdown

Abstract

This invention discloses a method for preparing a heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film, comprising the following steps: S1, preparing composite intercalated organic montmorillonite and microcapsule-type reinforcing particles; S2, preparing modified polypropylene masterbatch: mixing polypropylene masterbatch, composite intercalated organic montmorillonite, microcapsule-type reinforcing particles, initiator, and additives, heating and stirring to obtain modified polypropylene masterbatch; S3, adding polyvinylidene fluoride to the premix, heating and stirring, and melting and extruding the resulting mixture; S4, cooling and casting; S5, biaxial stretching, heat setting, cooling, and corona treatment to obtain a heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film. This invention, by filling and modifying polypropylene with composite intercalated organic montmorillonite and microcapsule-type reinforcing particles, and by compounding with polyvinylidene fluoride, comprehensively improves the heat resistance, flame retardancy, electrical breakdown resistance, and mechanical strength of the polypropylene capacitor base film.

Description

Technical Field

[0001] This invention relates to the field of capacitor base film materials, and in particular to a method for preparing a heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film. Background Technology

[0002] Capacitor film is the core material of film capacitors. Polypropylene (PP) has high strength, good insulation, and chemical resistance, making it a widely used capacitor film substrate. PP has poor flame retardancy, with a limiting oxygen index (LOI) generally only around 17-18. Adding flame retardants is a common method to improve its flame retardancy. Among flame retardants, inorganic flame retardants (such as magnesium hydroxide and zinc borate hydrate) are widely used due to their non-toxic and environmentally friendly properties and good flame retardancy. Examples include a aging-resistant and flame-retardant polypropylene composite material disclosed in patent CN116218080B, a halogen-free flame-retardant polypropylene composite material disclosed in patent CN104774376A, and a nano-anti-aging flame-retardant polypropylene resin composition disclosed in patent CN1769341A. However, nano-magnesium hydroxide and nano-zinc borate hydrate, as inorganic particles, are prone to agglomeration. When used in polypropylene, they can easily lead to uneven dispersion in the system, causing localized stress concentration, which increases the brittleness of polypropylene and reduces its mechanical strength. Furthermore, during long-term use, nano-magnesium hydroxide and nano-hydrated zinc borate, as inorganic components, are prone to surface migration, precipitation, or aggregation in polypropylene organic systems, resulting in problems such as reduced local flame retardant concentration, gradual decrease in flame retardant performance, or even failure of the flame retardant.

[0003] Furthermore, with the increasing demands on capacitor films, higher requirements are being placed on their high-temperature resistance, flame retardancy, and breakdown resistance. In some of the applicant's previous studies, enhanced talc powder was constructed by using expanded-layer modified talc as a carrier, titanium dioxide-carbon dot composite particles as a loading component, and grafting organic matter onto it. This improved the breakdown resistance of polypropylene films (CN120399357A High-Temperature Resistant and High-Voltage Breakdown-Resistant Capacitor Base Film and its Preparation Method). In other previous studies, ultraviolet irradiation crosslinking treatment of polypropylene base films was used as an improvement process to enhance the heat resistance and voltage resistance of the base film. Introducing antioxidant modified alumina nanoparticles with antioxidant properties into the system through modified excipients can overcome the problem of free radicals introduced into the system by the ultraviolet irradiation crosslinking process, and can improve the heat resistance and mechanical strength of the polypropylene film (CN118772538B High-Temperature Resistant High-Performance Polypropylene Capacitor Base Film and its Preparation Method). However, none of these solutions improved the flame retardancy of the polypropylene film.

[0004] Therefore, it is now necessary to improve existing technologies to provide more reliable solutions. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing a heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film, which addresses the shortcomings of the prior art.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing a heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film, comprising the following steps:

[0007] S1. Preparation of composite intercalated organic montmorillonite and microcapsule-type reinforcing particles;

[0008] S2. Preparation of modified polypropylene masterbatch: Polypropylene masterbatch, composite intercalated organic montmorillonite, microcapsule reinforcing particles, initiator and additives are mixed, heated and stirred to obtain modified polypropylene masterbatch;

[0009] S3. Add polyvinylidene fluoride to the premix, heat and stir, and then melt and extrude the resulting mixture.

[0010] S3, Cooling castings;

[0011] S4. Biaxial stretching, heat setting, cooling, and corona treatment yield a heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film.

[0012] Preferably, the raw material content for preparing the heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film is as follows, by weight:

[0013] 85-95 parts of polypropylene masterbatch;

[0014] 7-16 parts of polyvinylidene fluoride;

[0015] 4-11 parts of composite intercalated organic montmorillonite;

[0016] Microencapsulated reinforcing particles, 8-23 parts;

[0017] Initiator 0.025-0.07 parts;

[0018] Additives: 1.8-6 parts.

[0019] Preferably, the additives include 1.5-5 parts by weight of a crosslinking agent and 0.3-1 parts by weight of an antioxidant.

[0020] Preferably, the crosslinking agent is pentaerythritol triacrylate and the antioxidant is antioxidant 1010.

[0021] Preferably, the initiator is at least one selected from dicumyl peroxide, ammonium persulfate, potassium persulfate, benzoyl peroxide, and azobisisobutyronitrile.

[0022] Preferably, the preparation method of the heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film includes the following steps:

[0023] S1. Preparation of composite intercalated organic montmorillonite and microcapsule-type reinforcing particles;

[0024] S2. Preparation of modified polypropylene masterbatch: Mix polypropylene masterbatch, composite intercalated organic montmorillonite, microcapsule reinforcing particles, initiator and additives, and stir at 75-90℃ for 0.5-2h to obtain modified polypropylene masterbatch;

[0025] S3. Add polyvinylidene fluoride to the premix, stir at 160-190℃ for 10-30 min, and melt-extrude the resulting mixture at 260-275℃.

[0026] S3. Cooling the casting sheet, with a cooling temperature of 65-80℃;

[0027] S4. The casting obtained in step S3 is preheated at 110-140℃ and then biaxially stretched at 165-180℃. It is then heat-set at 170-180℃ for 5-20s, cooled to room temperature, and corona treated at 55-80℃ to obtain a heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film.

[0028] The longitudinal stretch ratio is 2-5.5 times, and the transverse stretch ratio is 3.5-6 times.

[0029] Preferably, the composite intercalated organic montmorillonite is prepared by the following method:

[0030] S1-1. Add montmorillonite to deionized water, disperse by ultrasonication, then add hexadecyltrimethylammonium bromide, stir under heating, centrifuge, wash, and dry to obtain pretreated montmorillonite;

[0031] S1-2. Take pretreated montmorillonite, sodium dodecylbenzenesulfonate, styrene, and maleic anhydride and add them to diethyl ether. Disperse by ultrasonication, add ammonium persulfate dropwise, and then stir the reaction under heating. After the reaction is completed, cool, centrifuge, filter, wash, and dry to obtain composite intercalated organic montmorillonite.

[0032] Preferably, the composite intercalated organic montmorillonite is prepared by the following method:

[0033] S1-1. Take 5-20g of montmorillonite and add it to 100-400mL of deionized water. Disperse it ultrasonically for 0.5-2h. Then add 1-4g of cetyltrimethylammonium bromide. Stir at 60-80℃ for 2-8h. Centrifuge, wash with deionized water, and vacuum dry at 70-90℃ for 6-24h to obtain pretreated montmorillonite.

[0034] S1-2. Take 2.5-10g of pretreated montmorillonite, 0.25-1g of sodium dodecylbenzenesulfonate, 1.5-6g of styrene, and 0.35-1.4g of maleic anhydride and add them to 75-300mL of diethyl ether. Disperse the mixture ultrasonically for 0.5-2h, add 1.5-6mg of ammonium persulfate dropwise, and then stir the mixture at 65-83℃ for 15-60min. Cool to room temperature, centrifuge and filter. Wash the solid product with diethyl ether and ethanol sequentially, and vacuum dry at 40-60℃ for 4-16h to obtain composite intercalated organic montmorillonite.

[0035] Preferably, the microencapsulated reinforcing particles are prepared by the following method:

[0036] S2-1. Preparation of silane coupling agent-grafted modified alumina:

[0037] Add silane coupling agent to acetone and stir until homogeneous to obtain silane coupling agent solution; add nano alumina to silane coupling agent solution, heat and stir under reflux, centrifuge and filter, wash and dry the solid product to obtain modified alumina;

[0038] S2-2, Preparation of microencapsulated reinforcing particles:

[0039] S2-2-1. Add nano-magnesium hydroxide and nano-hydrated zinc borate to acetone and disperse by ultrasonication to obtain a flame-retardant particle dispersion:

[0040] S2-2-2, Sodium dodecylbenzenesulfonate and modified alumina are added to Tris-HCl buffer solution, ultrasonically dispersed, then dopamine hydrochloride is added, and the reaction is stirred to obtain a prepolymer solution;

[0041] S2-2-3. Under stirring, the flame retardant particle dispersion is added dropwise to the prepolymer solution, heated and stirred to react. After the reaction is completed, the mixture is centrifuged and filtered. The solid product is washed and dried to obtain microcapsule-type reinforcing particles.

[0042] Preferably, the microcapsule-type reinforcing particles are prepared by the following method:

[0043] S2-1. Preparation of silane coupling agent-grafted modified alumina:

[0044] Add silane coupling agent KH570 to acetone and stir until homogeneous to obtain a silane coupling agent solution with a concentration of 4-15 wt%. Add 1-4 g of nano-alumina to 60-240 mL of the silane coupling agent solution, stir and reflux at 70-80 °C for 5-20 h, centrifuge and filter, wash the solid product with acetone and ethanol in sequence, and vacuum dry at 70-90 °C for 6-24 h to obtain modified alumina.

[0045] S2-2, Preparation of microencapsulated reinforcing particles:

[0046] S2-2-1. Take 1.25-5g of nano-magnesium hydroxide and 0.75-3g of nano-hydrated zinc borate and add them to 50-200mL of acetone. Disperse the mixture ultrasonically at 60-80℃ for 45-120min to obtain a flame-retardant particle dispersion.

[0047] S2-2-2, Add 0.75-3g sodium dodecylbenzenesulfonate and 1-3g modified alumina to 90-350mL of Tris-HCl buffer solution with a concentration of 5-15mM and a pH of 8-9, and sonicate for 45-180min. Then add 6-24g dopamine hydrochloride and stir at room temperature for 30-90min to obtain the prepolymer solution.

[0048] S2-2-3. Under stirring, the flame retardant particle dispersion is added dropwise to the prepolymer solution. The addition is completed within 30-90 minutes. Then, the temperature is raised to 40-55℃, and the reaction is stirred for 5-20 hours. After centrifugation and filtration, the solid product is washed with acetone and ethanol in sequence, and then vacuum dried overnight at 60-80℃ to obtain microcapsule-type reinforcing particles.

[0049] The beneficial effects of this invention are:

[0050] This invention provides a method for preparing a heat-resistant, flame-retardant, and electrical breakdown-resistant modified polypropylene capacitor base film. By filling and modifying polypropylene with composite intercalated organic montmorillonite and microcapsule-type reinforcing particles, and compounding with polyvinylidene fluoride, the heat resistance, flame retardancy, electrical breakdown resistance, and mechanical strength of the polypropylene capacitor base film can be comprehensively improved.

[0051] In this invention, a two-dimensional composite intercalated organic montmorillonite with a layered structure and a zero-dimensional microcapsule-type reinforcing particles with a spherical structure can be uniformly dispersed and filled in a polypropylene system. The two types of fillers can form a composite filling and reinforcing effect. By cooperating with each other at the microscopic level, they can enhance the heat resistance, strength, and other properties of polypropylene.

[0052] In the composite intercalated organic montmorillonite of the present invention, montmorillonite itself has a layered nanostructure, which can reduce charge accumulation through physical barrier effect, significantly improve the dielectric strength and breakdown voltage of polypropylene, and also improve the thermal stability, mechanical properties and flame retardancy of reinforced polypropylene; after intercalation with hexadecyltrimethylammonium bromide and prepolymerization modification with styrene and maleic anhydride, the problems of easy agglomeration and difficult dispersion of montmorillonite in polypropylene can be solved.

[0053] In this invention, by constructing microcapsule-type reinforcing particles with composite flame-retardant particles as the core material and modified nano-alumina-doped polydopamine membrane as the capsule wall, and adding them to polypropylene, the dispersibility of the composite flame-retardant particles can be significantly improved, their aggregation reduced, and direct contact between the composite flame-retardant particles and the polypropylene system avoided during normal use. This prevents the composite flame-retardant particles from negatively impacting the strength of the polypropylene substrate due to dispersibility issues. Simultaneously, by sealing the composite flame-retardant particles inside the capsule, problems such as surface migration, precipitation, or aggregation of the composite flame-retardant particles in the polypropylene system are effectively solved. In the event of a fire, the capsule wall melts at high temperatures, releasing the internal composite flame-retardant particles without affecting their flame-retardant performance. Attached Figure Description

[0054] Figure 1 The results of the analysis test on the effect of modified alumina content on the melting point of the capsule wall of microcapsule-type reinforcing particles;

[0055] Figure 2 The breakdown voltage test results are for the capacitor base films prepared in Examples 1-3 and Comparative Examples 1-5.

[0056] Figure 3 The longitudinal tensile strength test results are for the capacitor base films prepared in Examples 1-3 and Comparative Examples 1-5;

[0057] Figure 4 The results of the transverse tensile strength test of the capacitor base films prepared in Examples 1-3 and Comparative Examples 1-5;

[0058] Figure 5 The limiting oxygen index test results are for the capacitor base films prepared in Examples 1-3 and Comparative Examples 1-5;

[0059] Figure 6 The limiting oxygen index reduction rate test results are for the capacitor base films prepared in Examples 1-3 and Comparative Examples 1-5.

[0060] Figure 7 The results of thermal shrinkage tests are for the capacitor base films prepared in Examples 1-3 and Comparative Examples 1-5. Detailed Implementation

[0061] The present invention will be further described in detail below with reference to embodiments, so that those skilled in the art can implement it based on the description.

[0062] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0063] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials and reagents used in the following examples are commercially available. For examples where specific conditions are not specified, conventional conditions or conditions recommended by the manufacturer are followed. For reagents or instruments whose manufacturers are not specified, they are all commercially available products.

[0064] This invention provides a method for preparing a heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film, comprising the following steps:

[0065] S1. Preparation of composite intercalated organic montmorillonite and microcapsule-type reinforcing particles;

[0066] S2. Preparation of modified polypropylene masterbatch: Mix polypropylene masterbatch, composite intercalated organic montmorillonite, microcapsule reinforcing particles, initiator and additives, and stir at 75-90℃ for 0.5-2h to obtain modified polypropylene masterbatch;

[0067] S3. Add polyvinylidene fluoride to the premix, stir at 160-190℃ for 10-30 min, and melt-extrude the resulting mixture at 260-275℃.

[0068] S3. Cooling the casting sheet, with a cooling temperature of 65-80℃;

[0069] S4. The casting obtained in step S3 is preheated at 110-140℃ and then biaxially stretched at 165-180℃. It is then heat-set at 170-180℃ for 5-20s, cooled to room temperature, and corona treated at 55-80℃ to obtain a heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film.

[0070] The longitudinal stretch ratio is 2-5.5 times, and the transverse stretch ratio is 3.5-6 times.

[0071] In a preferred embodiment, the raw material content of the modified polypropylene capacitor base film for preparing the heat-resistant, flame-retardant, and electrical breakdown-resistant material is as follows (by weight):

[0072] 85-95 parts of polypropylene masterbatch;

[0073] 7-16 parts of polyvinylidene fluoride;

[0074] 4-11 parts of composite intercalated organic montmorillonite;

[0075] Microencapsulated reinforcing particles, 8-23 parts;

[0076] Initiator 0.025-0.07 parts;

[0077] Additives: 1.8-6 parts.

[0078] In a preferred embodiment, the additive includes 1.5-5 parts by weight of a crosslinking agent and 0.3-1 parts by weight of an antioxidant.

[0079] In a preferred embodiment, the crosslinking agent is pentaerythritol triacrylate, and the antioxidant is antioxidant 1010.

[0080] In a preferred embodiment, the initiator is at least one selected from dicumyl peroxide, ammonium persulfate, potassium persulfate, benzoyl peroxide, and azobisisobutyronitrile.

[0081] Composite intercalated organic montmorillonite was prepared by the following method:

[0082] S1-1. Add montmorillonite to deionized water, disperse by ultrasonication, then add hexadecyltrimethylammonium bromide, stir under heating, centrifuge, wash, and dry to obtain pretreated montmorillonite;

[0083] S1-2. Take pretreated montmorillonite, sodium dodecylbenzenesulfonate, styrene, and maleic anhydride and add them to diethyl ether. Disperse by ultrasonication, add ammonium persulfate dropwise, and then stir the reaction under heating. After the reaction is completed, cool, centrifuge, filter, wash, and dry to obtain composite intercalated organic montmorillonite.

[0084] In a preferred embodiment, the composite intercalated organic montmorillonite is prepared by the following method:

[0085] S1-1. Take 5-20g of montmorillonite and add it to 100-400mL of deionized water. Disperse it ultrasonically for 0.5-2h. Then add 1-4g of cetyltrimethylammonium bromide. Stir at 60-80℃ for 2-8h. Centrifuge, wash with deionized water, and vacuum dry at 70-90℃ for 6-24h to obtain pretreated montmorillonite.

[0086] S1-2. Take 2.5-10g of pretreated montmorillonite, 0.25-1g of sodium dodecylbenzenesulfonate, 1.5-6g of styrene, and 0.35-1.4g of maleic anhydride and add them to 75-300mL of diethyl ether. Disperse the mixture ultrasonically for 0.5-2h, add 1.5-6mg of ammonium persulfate dropwise, and then stir the mixture at 65-83℃ for 15-60min. Cool to room temperature, centrifuge and filter. Wash the solid product with diethyl ether and ethanol sequentially, and vacuum dry at 40-60℃ for 4-16h to obtain composite intercalated organic montmorillonite.

[0087] In a preferred embodiment, the microcapsule-type reinforcing particles are prepared by the following method:

[0088] S2-1. Preparation of silane coupling agent-grafted modified alumina:

[0089] Add silane coupling agent KH570 to acetone and stir until homogeneous to obtain a silane coupling agent solution with a concentration of 4-15 wt%. Add 1-4 g of nano-alumina to 60-240 mL of the silane coupling agent solution, stir and reflux at 70-80 °C for 5-20 h, centrifuge and filter, wash the solid product with acetone and ethanol in sequence, and vacuum dry at 70-90 °C for 6-24 h to obtain modified alumina.

[0090] S2-2, Preparation of microencapsulated reinforcing particles:

[0091] S2-2-1. Take 1.25-5g of nano-magnesium hydroxide and 0.75-3g of nano-hydrated zinc borate and add them to 50-200mL of acetone. Disperse the mixture ultrasonically at 60-80℃ for 45-120min to obtain a flame-retardant particle dispersion.

[0092] S2-2-2, Add 0.75-3g sodium dodecylbenzenesulfonate and 1-3g modified alumina to 90-350mL of Tris-HCl buffer solution with a concentration of 5-15mM and a pH of 8-9, and sonicate for 45-180min. Then add 6-24g dopamine hydrochloride and stir at room temperature for 30-90min to obtain the prepolymer solution.

[0093] S2-2-3. Under stirring, the flame retardant particle dispersion is added dropwise to the prepolymer solution. The addition is completed within 30-90 minutes. Then, the temperature is raised to 40-55℃, and the reaction is stirred for 5-20 hours. After centrifugation and filtration, the solid product is washed with acetone and ethanol in sequence, and then vacuum dried overnight at 60-80℃ to obtain microcapsule-type reinforcing particles.

[0094] Invention Mechanism

[0095] In this invention, polypropylene is modified by composite intercalation of organic montmorillonite and microcapsule-type reinforcing particles, and polyvinylidene fluoride is added in combination, which can comprehensively improve the heat resistance, flame retardancy, electrical breakdown resistance and mechanical strength of polypropylene capacitor base film.

[0096] I. Composite Intercalated Organic Montmorillonite

[0097] In this invention, montmorillonite is first intercalated with hexadecyltrimethylammonium bromide to obtain pretreated montmorillonite, achieving its organic modification to facilitate further modification. Then, the pretreated montmorillonite is blended with styrene and maleic anhydride, and prepolymerized under the action of an initiator, allowing styrene and maleic anhydride to further intercalate and coat the montmorillonite, forming a certain amount of maleic anhydride-styrene prepolymer. Subsequently, after the composite intercalated organic montmorillonite is added to the raw material system of the capacitor base film, styrene and maleic anhydride undergo further copolymerization and grafting reactions under the action of initiators in the raw material system. Maleic anhydride grafts onto polypropylene, thereby promoting a more uniform dispersion of the composite intercalated organic montmorillonite in the polypropylene system and improving the bonding strength between the composite intercalated organic montmorillonite and polypropylene. On the other hand, the maleic anhydride-styrene copolymer formed by copolymerization is a good compatibility material, which can improve the compatibility between microcapsule-type reinforcing particles and the polypropylene system, while promoting the uniform dispersion of microcapsule-type reinforcing particles in the polypropylene system. Finally, a filling structure is formed in which the layered two-dimensional composite intercalated organic montmorillonite and the spherical zero-dimensional microcapsule-type reinforcing particles are uniformly dispersed in the polypropylene system. The two dimensions of fillers can form a composite filling and reinforcing effect. Through mutual cooperation at the microscopic level, it can enhance the heat resistance, strength, and other properties of polypropylene. For example, in improving breakdown resistance, two-dimensional composite intercalated organic montmorillonite with a large specific surface area forms numerous interfaces in the polypropylene matrix through the stacking of its layered structure. These interfaces can induce dipole polarization and trap charge carriers, thereby reducing the risk of electric field distortion and effectively extending charge migration paths, suppressing partial discharge, blocking the development of breakdown paths, and improving breakdown resistance. Furthermore, the large specific surface area of ​​the two-dimensional composite intercalated organic montmorillonite can also provide attachment points for polypropylene molecular chains, reducing the probability of breakdown initiation. Zero-dimensional microcapsule-type reinforcing particles have a high dielectric constant, which can introduce more traps, increase the trap energy level density, improve the internal electric field distribution, and enhance the overall insulation level. The high dielectric constant of the zero-dimensional microcapsule-type reinforcing particles can also attract the development of breakdown paths, achieving directional blocking of breakdown paths in conjunction with the two-dimensional composite intercalated organic montmorillonite.

[0098] In composite intercalated organic montmorillonite, montmorillonite itself has a layered nanostructure, which can reduce charge accumulation through physical barrier effect, and can significantly improve the dielectric strength and breakdown voltage of polypropylene (Xie Jun, Liu Qi, Li Lin, et al. Study on the synergistic improvement of polypropylene film insulation performance by TiO2@SiO2 and montmorillonite nanomaterials [J]. Journal of Electrical Engineering, 2025(7).). It can also improve the thermal stability, mechanical properties and flame retardancy of reinforced polypropylene. After intercalation with hexadecyltrimethylammonium bromide and prepolymerization modification with styrene and maleic anhydride, the problems of easy agglomeration and difficult dispersion of montmorillonite in polypropylene can be solved.

[0099] II. Microencapsulated reinforcing particles

[0100] In this invention, the surface of nano-alumina is first modified by using silane coupling agent KH570, and then a silane coupling agent with double bonds is grafted onto the nano-alumina to obtain modified alumina.

[0101] Nano-sized magnesium hydroxide and nano-sized zinc borate hydrate were used as composite flame retardant particles and dispersed in acetone to obtain a flame retardant particle dispersion, which was used as the oil phase core material liquid; at the same time, modified alumina, sodium dodecylbenzene sulfonate, and dopamine hydrochloride were mixed and prepolymerized to obtain a prepolymer liquid, which was used as the aqueous phase capsule material liquid.

[0102] Finally, the oil-phase core material liquid is dropwise added to the aqueous-phase encapsulation liquid to form an oil-in-water system. The composite flame-retardant particles in the oil-phase core material liquid are then in-situ coated through prepolymerization to form a microcapsule-type reinforcing particle with nano-magnesium hydroxide and nano-zinc borate hydrate composite flame-retardant particles as the core material and a modified alumina-doped polydopamine membrane as the capsule wall. During the preparation process, in the prepolymerization stage, the double bonds modified on the surface of the nano-alumina participate in the prepolymerization reaction of dopamine, forming a prepolymerized film liquid that serves as the encapsulation material. This prepolymerized film liquid is then mixed with the oil-phase core material liquid for further polymerization. Ultimately, nano-alumina is doped into the capsule wall to form a composite encapsulation material that coats the composite flame-retardant particles.

[0103] Among composite flame-retardant particles, nano-magnesium hydroxide is a widely used inorganic flame retardant that combines flame retardancy, smoke suppression, and filling functions. Its decomposition products are magnesium oxide and water vapor (the lowest decomposition temperature range is approximately 340℃±10°C), and it does not produce corrosive gases, exhibiting non-toxic and environmentally friendly properties. Zinc borate hydrate is also a widely used inorganic flame retardant. When the temperature exceeds approximately 300℃, nano-zinc borate hydrate gradually decomposes, releasing water of crystallization, which acts as an endothermic cooling agent and dilutes oxygen in the air. Simultaneously, the decomposition generates boron oxide (B2O3) and halide oxides (such as ZnCl2 and ZnBr2), which adhere to the material surface to form a flame-retardant coating, isolating oxygen and inhibiting the release of flammable gases.

[0104] However, as inorganic particles, nano-magnesium hydroxide and nano-hydrated zinc borate are prone to aggregation.

[0105] When applied to polypropylene, uneven dispersion within the system can easily occur, leading to localized stress concentrations, which increases the brittleness of polypropylene and reduces its mechanical strength. Furthermore, during long-term use, nano-magnesium hydroxide and nano-hydrated zinc borate, as inorganic components, are prone to surface migration, precipitation, or aggregation within the polypropylene organic system, resulting in reduced localized flame retardant concentrations, a gradual decrease in the flame retardant's performance, and even its failure.

[0106] This invention introduces microcapsule-type reinforcing particles into polypropylene, using composite flame-retardant particles as the core material and a modified nano-alumina-doped polydopamine membrane as the capsule wall. This significantly improves the dispersibility of the composite flame-retardant particles, reduces their aggregation, and prevents direct contact between the composite flame-retardant particles and the polypropylene system during normal use. This avoids negative impacts on the strength of the polypropylene substrate caused by issues such as dispersibility of the composite flame-retardant particles. Furthermore, by sealing the composite flame-retardant particles inside the capsule, problems such as surface migration, precipitation, or aggregation of the composite flame-retardant particles in the polypropylene system are effectively solved. In the event of a fire, the capsule wall melts at high temperatures, releasing the internal composite flame-retardant particles without affecting their flame-retardant performance.

[0107] Furthermore, in the microcapsule-type reinforcing particles of the present invention:

[0108] The capsule wall material is a modified nano-alumina-doped polydopamine film. Polydopamine itself has a high volume resistivity and good insulation properties, which helps to improve the electrical breakdown resistance of polypropylene. Polydopamine has a polyphenol structure and can be adsorbed onto the polypropylene matrix through electrostatic interactions, hydrogen bonds, van der Waals forces, etc., to ensure good interfacial strength. Furthermore, polydopamine also has an auxiliary nucleation effect in polypropylene, which can promote the formation of finer spherulite particles in polypropylene, thereby improving crystallization performance (Liu Shixiang; Huang Yajiang; Yang Junlong; Kong Miqiu; Yang Qi; Li Guangxian;. Study on the efficient β-nucleation effect of polydopamine particles on isotactic polypropylene [C] / / National Polymer Academic Paper Conference of Chinese Chemical Society. 2017.).

[0109] Polydopamine itself has good heat resistance (generally it can remain stable at around 200-240℃), but the melting process temperature involved in the preparation of capacitor base film will reach around 250-270℃. (1) In this invention, by doping with nano-alumina, the thermal stability, mechanical strength, barrier properties and insulation properties of polydopamine film can be improved. The improvement in thermal stability allows the melting point of the modified polydopamine film (capsule wall) to be higher than the melting process temperature, so that it can ensure that the microcapsule-type reinforcing particles remain stable in the high-temperature process of preparing capacitor base film and that the internal composite flame-retardant particles will not leak. In addition, by adjusting the doping ratio of nano-alumina, the melting point of the modified polydopamine film can be controlled (for example, it can be controlled in the range of 270-350℃, preferably controlled at around 280-315℃), so that it can cope with melting processes at different temperatures, while not making the melting point too high and affecting the flame-retardant properties (the ignition point of polypropylene is about 350~400℃). (2) Alumina has a high melting point and chemical inertness, which can significantly improve the stability of polypropylene film in high temperature environment; (3) The addition of alumina can improve the tensile strength of polypropylene film and reduce the shrinkage rate during processing; (4) Alumina has a high dielectric constant, and its addition can effectively reduce partial discharge and leakage current, thereby improving the breakdown field strength.

[0110] Therefore, the doping of nano-alumina in polydopamine membranes can improve the thermal stability, mechanical strength, barrier properties, and insulation properties of the microcapsule-type reinforcing particle wall, and can also significantly enhance the breakdown resistance and mechanical strength of the capacitor base film.

[0111] III. Polyvinylidene fluoride (PVDF)

[0112] Polyvinylidene fluoride (PVDF) has a high dielectric constant, which can improve the insulation properties of polypropylene and enhance its resistance to electrical breakdown. At the same time, the high temperature resistance and flexibility of PVDF can improve the heat resistance and mechanical strength of polypropylene films.

[0113] The above is the general concept of the present invention. Based on this, detailed embodiments and comparative examples are provided below to further illustrate the present invention.

[0114] The main sources of raw materials in the following examples and comparative examples are as follows:

[0115] Polypropylene, brand SK, grade R370Y, purchased from Suzhou Yitianli Plastics Co., Ltd.

[0116] Polyvinylidene fluoride, grade 5130, Shanghai Yiqiang Plastics Technology Co., Ltd.

[0117] Montmorillonite, average particle size 10μm, Zhejiang Huatai New Materials Co., Ltd.

[0118] Styrene, Jinan Anqi Chemical Co., Ltd.;

[0119] Maleic anhydride, Shanghai Yongzheng Chemical Co., Ltd.

[0120] Nano-alumina, average particle size 100nm, Yangzhou Zhongtianli New Material Co., Ltd.

[0121] Silane coupling agent KH570, Nanjing Chemical Reagent Co., Ltd.;

[0122] Nano-sized magnesium hydroxide, average particle size 200nm, Shanghai Yingcheng New Materials Co., Ltd.

[0123] Nano-hydrated zinc borate, average particle size 250nm, Guangdong Shengke Biochemical Technology Co., Ltd.

[0124] Dopamine hydrochloride, Shanghai Maclean Biochemical Technology Co., Ltd.

[0125] Sodium dodecylbenzenesulfonate, pentaerythritol triacrylate, Shanghai Maclean Biochemical Technology Co., Ltd.;

[0126] Antioxidant 1010, Jiangsu Runfeng Synthetic Technology Co., Ltd.

[0127] Example 1

[0128] A method for preparing a heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film includes the following steps:

[0129] S1. Preparation of composite intercalated organic montmorillonite and microcapsule-type reinforcing particles;

[0130] S2. Preparation of modified polypropylene masterbatch: Polypropylene masterbatch, composite intercalated organic montmorillonite, microcapsule reinforcing particles, initiator and additives are mixed and stirred at 85°C for 1 hour to obtain modified polypropylene masterbatch.

[0131] S3. Add polyvinylidene fluoride to the premix, stir at 180°C for 15 minutes, and melt-extrude the resulting mixture at 265°C.

[0132] S3. Cooling the casting sheet, with a cooling temperature of 70℃;

[0133] S4. The casting obtained in step S3 is preheated at 125°C and then biaxially stretched at 170°C. It is then heat-set at 170°C for 15 seconds, cooled to room temperature, and corona treated at 65°C to obtain a heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film.

[0134] The longitudinal stretch ratio is 4 times, and the transverse stretch ratio is 5 times.

[0135] Specifically, the corona treatment involves simultaneously applying corona treatment to both sides of the stretched sheet using two electrodes. During corona treatment, the output power of the two electrodes is 8 kW, the output voltage is 7 kW, the pulse frequency is 18 kHz, the discharge gap is 2 mm, and the bombardment intensity of the electrodes is 10 W·min / m. 2 The corona treatment in the remaining embodiments and comparative examples is the same as in this embodiment.

[0136] The proportions of each raw material in the preparation of the heat-resistant, flame-retardant, and electrically-breakdown-resistant modified polypropylene capacitor base film, by weight, are as follows:

[0137] 90 parts of polypropylene masterbatch;

[0138] 11 parts of polyvinylidene fluoride;

[0139] Seven portions of composite intercalated organic montmorillonite;

[0140] 15 parts of microencapsulated reinforcing particles;

[0141] 0.04 parts initiator;

[0142] 3.5 parts of additives.

[0143] The additives include 3 parts by weight of a crosslinking agent and 0.5 parts by weight of an antioxidant. The crosslinking agent is pentaerythritol triacrylate, and the antioxidant is antioxidant 1010.

[0144] The initiator is benzoyl peroxide.

[0145] In this example, the composite intercalated organic montmorillonite was prepared by the following method:

[0146] S1-1. Take 10g of montmorillonite and add it to 200mL of deionized water. Disperse it by ultrasonication for 1h, then add 2g of cetyltrimethylammonium bromide. Stir at 70℃ for 4h, centrifuge, wash with deionized water, and vacuum dry at 80℃ for 12h to obtain pretreated montmorillonite.

[0147] S1-2. Take 4.5g of pretreated montmorillonite, 0.5g of sodium dodecylbenzenesulfonate, 3g of styrene, and 0.7g of maleic anhydride and add them to 150mL of diethyl ether. Disperse the mixture by sonication for 1h, add 3mg of ammonium persulfate dropwise, and then stir the mixture at 75℃ for 25min. Cool to room temperature, centrifuge and filter. Wash the solid product with diethyl ether and ethanol in sequence, and dry it under vacuum at 50℃ for 8h to obtain composite intercalated organic montmorillonite.

[0148] In this example, the microencapsulated reinforcing particles were prepared by the following method:

[0149] S2-1. Preparation of silane coupling agent-grafted modified alumina:

[0150] Add silane coupling agent KH570 to acetone and stir until homogeneous to obtain a silane coupling agent solution with a concentration of 8wt%. Add 2g of nano alumina to 120mL of silane coupling agent solution, stir and reflux at 75℃ for 10h, centrifuge and filter, wash the solid product with acetone and ethanol in sequence, and vacuum dry at 80℃ for 12h to obtain modified alumina.

[0151] S2-2, Preparation of microencapsulated reinforcing particles:

[0152] S2-2-1. Take 2.5g of nano-magnesium hydroxide and 1.5g of nano-hydrated zinc borate and add them to 100mL of acetone. Disperse them ultrasonically at 70℃ for 90min to obtain a flame-retardant particle dispersion.

[0153] S2-2-2, 1.5g sodium dodecylbenzenesulfonate and 2g modified alumina were added to 180mL of Tris-HCl buffer solution with a concentration of 10mM and a pH of 8.5, and ultrasonically dispersed for 90min. Then, 12g dopamine hydrochloride was added, and the mixture was stirred at room temperature for 45min to obtain the prepolymer solution.

[0154] S2-2-3. Under stirring, the flame retardant particle dispersion is added dropwise to the prepolymer solution. The addition is completed within 60 minutes. Then, the temperature is raised to 45°C, and the reaction is stirred for 10 hours. After centrifugation and filtration, the solid product is washed with acetone and ethanol in sequence, and then dried under vacuum at 70°C overnight to obtain microcapsule-type reinforcing particles.

[0155] Example 2

[0156] A method for preparing a heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film includes the following steps:

[0157] S1. Preparation of composite intercalated organic montmorillonite and microcapsule-type reinforcing particles;

[0158] S2. Preparation of modified polypropylene masterbatch: Polypropylene masterbatch, composite intercalated organic montmorillonite, microcapsule reinforcing particles, initiator and additives are mixed and stirred at 85°C for 1 hour to obtain modified polypropylene masterbatch.

[0159] S3. Add polyvinylidene fluoride to the premix, stir at 180°C for 15 minutes, and melt-extrude the resulting mixture at 265°C.

[0160] S3. Cooling the casting sheet, with a cooling temperature of 70℃;

[0161] S4. The casting obtained in step S3 is preheated at 125°C and then biaxially stretched at 170°C. It is then heat-set at 175°C for 10 seconds, cooled to room temperature, and corona treated at 65°C to obtain a heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film.

[0162] The longitudinal stretch ratio is 4 times, and the transverse stretch ratio is 5 times.

[0163] The proportions of each raw material in the preparation of the heat-resistant, flame-retardant, and electrically-breakdown-resistant modified polypropylene capacitor base film, by weight, are as follows:

[0164] 90 parts of polypropylene masterbatch;

[0165] 11 parts of polyvinylidene fluoride;

[0166] 7.5 parts of composite intercalated organic montmorillonite;

[0167] 15 parts of microencapsulated reinforcing particles;

[0168] 0.04 parts initiator;

[0169] 3.5 parts of additives.

[0170] The additives include 3 parts by weight of a crosslinking agent and 0.5 parts by weight of an antioxidant. The crosslinking agent is pentaerythritol triacrylate, and the antioxidant is antioxidant 1010.

[0171] The initiator is benzoyl peroxide.

[0172] In this example, the composite intercalated organic montmorillonite was prepared by the following method:

[0173] S1-1. Take 10g of montmorillonite and add it to 200mL of deionized water. Disperse it by ultrasonication for 1h, then add 2g of cetyltrimethylammonium bromide. Stir at 70℃ for 4h, centrifuge, wash with deionized water, and vacuum dry at 80℃ for 12h to obtain pretreated montmorillonite.

[0174] S1-2. Take 5g of pretreated montmorillonite, 0.5g of sodium dodecylbenzenesulfonate, 3g of styrene, and 0.7g of maleic anhydride and add them to 150mL of diethyl ether. Disperse the mixture by sonication for 1h, add 3mg of ammonium persulfate dropwise, and then stir the mixture at 75℃ for 25min. Cool to room temperature, centrifuge and filter. Wash the solid product with diethyl ether and ethanol in sequence, and dry it under vacuum at 50℃ for 8h to obtain composite intercalated organic montmorillonite.

[0175] In this example, the microencapsulated reinforcing particles were prepared by the following method:

[0176] S2-1. Preparation of silane coupling agent-grafted modified alumina:

[0177] Add silane coupling agent KH570 to acetone and stir until homogeneous to obtain a silane coupling agent solution with a concentration of 8wt%. Add 2g of nano alumina to 120mL of silane coupling agent solution, stir and reflux at 75℃ for 10h, centrifuge and filter, wash the solid product with acetone and ethanol in sequence, and vacuum dry at 80℃ for 12h to obtain modified alumina.

[0178] S2-2, Preparation of microencapsulated reinforcing particles:

[0179] S2-2-1. Take 2.5g of nano-magnesium hydroxide and 1.5g of nano-hydrated zinc borate and add them to 100mL of acetone. Disperse them ultrasonically at 70℃ for 90min to obtain a flame-retardant particle dispersion.

[0180] S2-2-2, 1.5g sodium dodecylbenzenesulfonate and 2g modified alumina were added to 180mL of Tris-HCl buffer solution with a concentration of 10mM and a pH of 8.5, and ultrasonically dispersed for 90min. Then, 12g dopamine hydrochloride was added, and the mixture was stirred at room temperature for 45min to obtain the prepolymer solution.

[0181] S2-2-3. Under stirring, the flame retardant particle dispersion is added dropwise to the prepolymer solution. The addition is completed within 60 minutes. Then, the temperature is raised to 45°C, and the reaction is stirred for 10 hours. After centrifugation and filtration, the solid product is washed with acetone and ethanol in sequence, and then dried under vacuum at 70°C overnight to obtain microcapsule-type reinforcing particles.

[0182] Example 3

[0183] A method for preparing a heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film includes the following steps:

[0184] S1. Preparation of composite intercalated organic montmorillonite and microcapsule-type reinforcing particles;

[0185] S2. Preparation of modified polypropylene masterbatch: Polypropylene masterbatch, composite intercalated organic montmorillonite, microcapsule reinforcing particles, initiator and additives are mixed and stirred at 85°C for 1 hour to obtain modified polypropylene masterbatch.

[0186] S3. Add polyvinylidene fluoride to the premix, stir at 180°C for 15 minutes, and melt-extrude the resulting mixture at 265°C.

[0187] S3. Cooling the casting sheet, with a cooling temperature of 70℃;

[0188] S4. The casting obtained in step S3 is preheated at 125°C and then biaxially stretched at 170°C. It is then heat-set at 170°C for 10 seconds, cooled to room temperature, and corona treated at 65°C to obtain a heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film.

[0189] The longitudinal stretch ratio is 4 times, and the transverse stretch ratio is 5 times.

[0190] The proportions of each raw material in the preparation of the heat-resistant, flame-retardant, and electrically-breakdown-resistant modified polypropylene capacitor base film, by weight, are as follows:

[0191] 90 parts of polypropylene masterbatch;

[0192] 11 parts of polyvinylidene fluoride;

[0193] 7.5 parts of composite intercalated organic montmorillonite;

[0194] 13.5 parts of microencapsulated reinforcing particles;

[0195] 0.04 parts initiator;

[0196] 3.5 parts of additives.

[0197] The additives include 3 parts by weight of a crosslinking agent and 0.5 parts by weight of an antioxidant. The crosslinking agent is pentaerythritol triacrylate, and the antioxidant is antioxidant 1010.

[0198] The initiator is benzoyl peroxide.

[0199] In this example, the composite intercalated organic montmorillonite was prepared by the following method:

[0200] S1-1. Take 10g of montmorillonite and add it to 200mL of deionized water. Disperse it by ultrasonication for 1h, then add 2g of cetyltrimethylammonium bromide. Stir at 70℃ for 4h, centrifuge, wash with deionized water, and vacuum dry at 80℃ for 12h to obtain pretreated montmorillonite.

[0201] S1-2. Take 5g of pretreated montmorillonite, 0.5g of sodium dodecylbenzenesulfonate, 3.5g of styrene, and 0.7g of maleic anhydride and add them to 150mL of diethyl ether. Disperse the mixture by sonication for 1h, add 3mg of ammonium persulfate dropwise, and then stir the mixture at 75℃ for 25min. Cool to room temperature, centrifuge and filter. Wash the solid product with diethyl ether and ethanol in sequence, and dry it under vacuum at 50℃ for 8h to obtain composite intercalated organic montmorillonite.

[0202] In this example, the microencapsulated reinforcing particles were prepared by the following method:

[0203] S2-1. Preparation of silane coupling agent-grafted modified alumina:

[0204] Add silane coupling agent KH570 to acetone and stir until homogeneous to obtain a silane coupling agent solution with a concentration of 8wt%. Add 2g of nano alumina to 120mL of silane coupling agent solution, stir and reflux at 75℃ for 10h, centrifuge and filter, wash the solid product with acetone and ethanol in sequence, and vacuum dry at 80℃ for 12h to obtain modified alumina.

[0205] S2-2, Preparation of microencapsulated reinforcing particles:

[0206] S2-2-1. Take 2.5g of nano-magnesium hydroxide and 1.5g of nano-hydrated zinc borate and add them to 100mL of acetone. Disperse them ultrasonically at 70℃ for 90min to obtain a flame-retardant particle dispersion.

[0207] S2-2-2, 1.5g sodium dodecylbenzenesulfonate and 2g modified alumina were added to 180mL of Tris-HCl buffer solution with a concentration of 10mM and a pH of 8.5, and ultrasonically dispersed for 90min. Then, 12g dopamine hydrochloride was added, and the mixture was stirred at room temperature for 45min to obtain the prepolymer solution.

[0208] S2-2-3. Under stirring, the flame retardant particle dispersion is added dropwise to the prepolymer solution. The addition is completed within 60 minutes. Then, the temperature is raised to 45°C, and the reaction is stirred for 10 hours. After centrifugation and filtration, the solid product is washed with acetone and ethanol in sequence, and then dried under vacuum at 70°C overnight to obtain microcapsule-type reinforcing particles.

[0209] Comparative Example 1

[0210] The only difference between this example and Example 1 is that the raw materials used to prepare the heat-resistant, flame-retardant, and electrically broken-down modified polypropylene capacitor base film do not contain composite intercalated organic montmorillonite.

[0211] Comparative Example 2

[0212] The only difference between this example and Example 1 is that the composite intercalated organic montmorillonite in the raw materials for preparing the heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film is replaced with pretreated montmorillonite, and the amount added is modified to 5 parts by weight; wherein, the preparation method of the pretreated montmorillonite is the same as in Example 2.

[0213] Comparative Example 3

[0214] The only difference between this example and Example 1 is that the raw materials used to prepare the heat-resistant, flame-retardant, and electrically-breakdown-resistant modified polypropylene capacitor base film do not contain microcapsule-type reinforcing particles.

[0215] Comparative Example 4

[0216] A method for preparing a heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film includes the following steps:

[0217] S1. Preparation of composite intercalated organic montmorillonite;

[0218] S2. Preparation of modified polypropylene masterbatch: Polypropylene masterbatch, composite intercalated organic montmorillonite, nano magnesium hydroxide, nano zinc hydrated borate, initiator and additives are mixed and stirred at 85°C for 1 hour to obtain modified polypropylene masterbatch.

[0219] S3. Add polyvinylidene fluoride to the premix, stir at 180°C for 15 minutes, and melt-extrude the resulting mixture at 265°C.

[0220] S3. Cooling the casting sheet, with a cooling temperature of 70℃;

[0221] S4. The casting obtained in step S3 is preheated at 125°C and then biaxially stretched at 170°C. It is then heat-set at 175°C for 10 seconds, cooled to room temperature, and corona treated at 65°C to obtain a heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film.

[0222] The longitudinal stretch ratio is 4 times, and the transverse stretch ratio is 5 times.

[0223] The proportions of each raw material in the preparation of the heat-resistant, flame-retardant, and electrically-breakdown-resistant modified polypropylene capacitor base film, by weight, are as follows:

[0224] 90 parts of polypropylene masterbatch;

[0225] 11 parts of polyvinylidene fluoride;

[0226] 7.5 parts of composite intercalated organic montmorillonite;

[0227] 2.5 parts of nano-magnesium hydroxide;

[0228] 1.5 parts of nano-hydrated zinc borate;

[0229] 0.04 parts initiator;

[0230] 3.5 parts of additives.

[0231] The preparation method of the composite intercalated organic montmorillonite is the same as in Example 2.

[0232] Comparative Example 5

[0233] The only difference between this example and Example 1 is that modified alumina is not added in step S2-2-2 of preparing microcapsule-type reinforcing particles.

[0234] I. Analysis of the Influence of Modified Alumina Content on the Melting Point of Microcapsule-Type Reinforcing Particles

[0235] Following the method of Example 2, the amount of modified alumina added in step S2-2-2 was adjusted to obtain different microcapsule-type reinforcing particles. The melting point of the capsule wall of the microcapsule-type reinforcing particles was tested by differential scanning calorimetry (DSC), and the test results are shown in Table 1 below. Figure 1 As shown.

[0236] Table 1

[0237]

[0238] The test results show that as the amount of modified alumina added increases, the melting point of the capsule wall gradually increases within a certain range. Therefore, by controlling the amount of modified alumina added, the melting point of the capsule wall can be ensured to be higher than the melting process temperature during the preparation of polypropylene film. This ensures that the nano-magnesium hydroxide and nano-hydrated zinc borate inside the capsule wall will not leak, while also preventing the melting point from being too high and affecting the flame retardant performance.

[0239] II. The following performance tests were performed on the capacitor base films prepared in the examples and comparative examples:

[0240] 1. Breakdown voltage test

[0241] An insulation withstand voltage tester (HZJY-115, Hezhong Electric) was used. The test time was 20s, the cutoff voltage was 5kV, and the test was conducted at arbitrary points at 0.2m intervals along the 1.5m TD direction. The test data were recorded, and the average value of all test data was recorded as the breakdown voltage test result.

[0242] 2. Tensile strength test

[0243] The tensile breaking strength of the polypropylene capacitor base film prepared in the examples and comparative examples was tested using a universal tensile testing machine in accordance with the standard ASTM D882-12 "Standard Test Methods for Tensile Properties of Films and Sheets".

[0244] 3. Flame retardant properties

[0245] The limiting oxygen index is tested using the standard JIS-K7201-3-2008. The higher the value, the better the flame retardant performance.

[0246] 4. Long-lasting flame retardant performance

[0247] The polypropylene capacitor base film was aged at "double 85" (85℃, 85%RH) for 500 hours, and then its flame retardant properties were tested using the same method as above to simulate its performance after long-term use. The limiting oxygen index decrease rate η was calculated:

[0248] ;

[0249] LOI0 and LOI1 represent the limiting oxygen index before and after aging, respectively.

[0250] 5. Heat shrinkage rate test

[0251] The thermal shrinkage rate of polypropylene capacitor base film prepared according to the ASTM D2732 test examples and comparative examples at 160°C;

[0252] The test results are shown in Table 1 below. Figure 1-5 As shown:

[0253] Table 1

[0254]

[0255] The test results show that the polypropylene capacitor base film prepared in Examples 1-3 has high heat resistance, flame retardancy, electrical breakdown resistance and mechanical strength, and also has long-lasting flame retardancy, with excellent overall performance.

[0256] In Comparative Example 1, without the addition of composite intercalated organic montmorillonite, the overall performance decreased, especially the heat resistance, flame retardancy and electrical breakdown resistance were significantly reduced.

[0257] In Comparative Example 2, styrene and maleic anhydride were not used for further intercalation and coating of montmorillonite, resulting in poor dispersibility of montmorillonite and the lack of the compatibility improvement effect of maleic anhydride-styrene copolymer on the microcapsule-type reinforcing particles and polypropylene system, thus leading to a decline in overall performance.

[0258] In Comparative Example 3, the flame retardant and electrical breakdown resistance properties of the unadded microencapsulated reinforcing particles decreased significantly.

[0259] In Comparative Example 4, directly adding nano-magnesium hydroxide and nano-hydrated zinc borate to polypropylene failed to improve the problems of easy agglomeration of nano-magnesium hydroxide and nano-hydrated zinc borate, making it difficult to fully exert the flame retardant properties and damaging the mechanical strength of polypropylene. At the same time, its flame retardant properties had poor long-term effectiveness.

[0260] In Comparative Example 5, the microcapsule-type reinforcing particles were not doped with nano-alumina to modify the polydopamine capsule wall, which affected the strength and thermal stability of the composite microcapsules, resulting in a decrease in the long-term flame retardant performance. At the same time, the enhancement effect of alumina on the puncture resistance and strength of the polypropylene system was lost, ultimately leading to a decline in the overall performance of the capacitor base film.

[0261] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details.

Claims

1. A method for preparing a heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film, characterized in that, Includes the following steps: S1. Preparation of composite intercalated organic montmorillonite and microcapsule-type reinforcing particles; S2. Preparation of modified polypropylene masterbatch: Polypropylene masterbatch, composite intercalated organic montmorillonite, microcapsule reinforcing particles, initiator and additives are mixed, heated and stirred to obtain modified polypropylene masterbatch; S3. Add polyvinylidene fluoride to the premix, heat and stir, and then melt and extrude the resulting mixture. S4, Cooling castings; S5. Biaxial stretching, heat setting, cooling, and corona treatment yield a heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film. The composite intercalated organic montmorillonite was prepared by the following method: S1-1-1. Add montmorillonite to deionized water, disperse by ultrasonication, then add hexadecyltrimethylammonium bromide, stir under heating, centrifuge, wash, and dry to obtain pretreated montmorillonite; S1-1-2. Take pretreated montmorillonite, sodium dodecylbenzenesulfonate, styrene, and maleic anhydride and add them to diethyl ether. Disperse by ultrasonication, add ammonium persulfate dropwise, and then stir the reaction under heating. After the reaction is completed, cool, centrifuge, filter, wash, and dry to obtain composite intercalated organic montmorillonite. Microencapsulated reinforcing particles were prepared by the following method: S1-2-1, Preparation of modified alumina grafted with silane coupling agent: Add silane coupling agent to acetone and stir until homogeneous to obtain silane coupling agent solution; add nano alumina to silane coupling agent solution, heat and stir under reflux, centrifuge and filter, wash and dry the solid product to obtain modified alumina; S1-2-2, Preparation of microencapsulated reinforcing particles: S1-2-2-1. Add nano-magnesium hydroxide and nano-hydrated zinc borate to acetone and disperse by ultrasonication to obtain a flame-retardant particle dispersion: S1-2-2-2: Sodium dodecylbenzenesulfonate and modified alumina are added to Tris-HCl buffer solution, ultrasonically dispersed, and then dopamine hydrochloride is added and stirred to react, thus obtaining a prepolymer solution. S1-2-2-3. Under stirring, the flame retardant particle dispersion is added dropwise to the prepolymer solution, heated and stirred to react. After the reaction is completed, the mixture is centrifuged and filtered. The solid product is washed and dried to obtain microcapsule-type reinforcing particles.

2. The method for preparing the heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film according to claim 1, characterized in that, The raw material content (by weight) for preparing the heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film is as follows: 85-95 parts of polypropylene masterbatch; 7-16 parts of polyvinylidene fluoride; 4-11 parts of composite intercalated organic montmorillonite; Microencapsulated reinforcing particles, 8-23 parts; Initiator 0.025-0.07 parts; Additives: 1.8-6 parts.

3. The method for preparing the heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film according to claim 2, characterized in that, The additives include 1.5-5 parts by weight of crosslinking agent and 0.3-1 parts by weight of antioxidant.

4. The method for preparing the heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film according to claim 3, characterized in that, The crosslinking agent is pentaerythritol triacrylate, and the antioxidant is antioxidant 1010.

5. The method for preparing the heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film according to claim 2, characterized in that, The initiator is at least one of dicumyl peroxide, ammonium persulfate, potassium persulfate, benzoyl peroxide, and azobisisobutyronitrile.

6. The method for preparing the heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film according to claim 1, characterized in that, Includes the following steps: S1. Preparation of composite intercalated organic montmorillonite and microcapsule-type reinforcing particles; S2. Preparation of modified polypropylene masterbatch: Mix polypropylene masterbatch, composite intercalated organic montmorillonite, microcapsule reinforcing particles, initiator and additives, and stir at 75-90℃ for 0.5-2h to obtain modified polypropylene masterbatch; S3. Add polyvinylidene fluoride to the premix, stir at 160-190℃ for 10-30 min, and melt-extrude the resulting mixture at 260-275℃. S4. Cool the casting sheet at a temperature of 65-80℃; S5. The casting obtained in step S4 is preheated at 110-140℃ and then biaxially stretched at 165-180℃. It is then heat-set at 170-180℃ for 5-20s, cooled to room temperature, and corona treated at 55-80℃ to obtain a heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film. The longitudinal stretch ratio is 2-5.5 times, and the transverse stretch ratio is 3.5-6 times.

7. The method for preparing the heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film according to claim 6, characterized in that, The composite intercalated organic montmorillonite was prepared by the following method: S1-1-1. Take 5-20g of montmorillonite and add it to 100-400mL of deionized water. Disperse it ultrasonically for 0.5-2h. Then add 1-4g of cetyltrimethylammonium bromide. Stir at 60-80℃ for 2-8h. Centrifuge, wash with deionized water, and vacuum dry at 70-90℃ for 6-24h to obtain pretreated montmorillonite. S1-1-2. Take 2.5-10g of pretreated montmorillonite, 0.25-1g of sodium dodecylbenzenesulfonate, 1.5-6g of styrene, and 0.35-1.4g of maleic anhydride and add them to 75-300mL of diethyl ether. Disperse the mixture ultrasonically for 0.5-2h, add 1.5-6mg of ammonium persulfate dropwise, and then stir the mixture at 65-83℃ for 15-60min. Cool to room temperature, centrifuge and filter. Wash the solid product with diethyl ether and ethanol sequentially, and vacuum dry at 40-60℃ for 4-16h to obtain composite intercalated organo-modified montmorillonite.

8. The method for preparing the heat-resistant, flame-retardant, and electrically breakdown-resistant modified polypropylene capacitor base film according to claim 1, characterized in that, Microencapsulated reinforcing particles were prepared by the following method: S1-2-1, Preparation of modified alumina grafted with silane coupling agent: Add silane coupling agent KH570 to acetone and stir until homogeneous to obtain a silane coupling agent solution with a concentration of 4-15 wt%. Add 1-4 g of nano-alumina to 60-240 mL of the silane coupling agent solution, stir and reflux at 70-80 °C for 5-20 h, centrifuge and filter, wash the solid product with acetone and ethanol in sequence, and vacuum dry at 70-90 °C for 6-24 h to obtain modified alumina. S1-2-2, Preparation of microencapsulated reinforcing particles: S1-2-2-1. Take 1.25-5g of nano-magnesium hydroxide and 0.75-3g of nano-hydrated zinc borate and add them to 50-200mL of acetone. Disperse the mixture ultrasonically at 60-80℃ for 45-120min to obtain a flame-retardant particle dispersion. S1-2-2-2: Add 0.75-3g sodium dodecylbenzenesulfonate and 1-3g modified alumina to 90-350mL of Tris-HCl buffer solution with a concentration of 5-15mM and a pH of 8-9, and sonicate for 45-180min. Then add 6-24g dopamine hydrochloride and stir at room temperature for 30-90min to obtain the prepolymer solution. S1-2-2-3. Under stirring, the flame retardant particle dispersion is added dropwise to the prepolymer solution. The addition is completed within 30-90 minutes. Then, the temperature is raised to 40-55℃, and the reaction is stirred for 5-20 hours. After centrifugation and filtration, the solid product is washed with acetone and ethanol in sequence, and then vacuum dried overnight at 60-80℃ to obtain microcapsule-type reinforcing particles.

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