Temperature-resistant insulating mica powder / polypropylene composite film and preparation method thereof

Abstract

The invention discloses a temperature-resistant insulating mica powder / polypropylene composite film and a preparation method thereof, and belongs to the field of polymer film processing. The preparation method of the composite film comprises the following steps: (1) loading an olefin polymerization catalyst on the surfaces of mica powder particles, and carrying out in-situ polymerization on the prepared particles loaded with the olefin polymerization catalyst in a mixed component of alpha-olefin and propylene to prepare polypropylene / mica powder composite particles; and (2) blending polypropylene resin, the polypropylene / mica powder composite particles, a viscosity modifier and an auxiliary agent, granulating, and calendaring to obtain the polypropylene composite material. A firm polypropylene shell layer is formed on the surface of the mica powder, so that the interfacial compatibility of the mica powder and polypropylene is enhanced, good dispersion is realized, and the insulativity of the polypropylene is remarkably improved; meanwhile, the melt viscosity of polypropylene matched with the viscosity modifier is constructed, the molecular entanglement density of a composite system is remarkably improved, the movement of a polypropylene molecular chain is effectively limited, and the thermal stability of the composite film is improved.

Description

Technical Field

[0001] This invention belongs to the field of polymer film processing, specifically relating to a heat-resistant insulating mica powder / polypropylene composite film and its preparation method. Background Technology

[0002] Polypropylene (PP) film possesses excellent mechanical, thermal, and insulating properties, making it widely used in capacitors, power batteries, high-voltage direct current (HVDC) transmission systems, and new energy power generation. However, with increasing voltage levels and the growing scale of flexible HVDC transmission projects, the requirements for the insulation and temperature resistance of PP film as a dielectric material are also gradually increasing. Furthermore, during actual operation, under the combined effects of electro-thermal fields, PP film can experience microstructural damage such as molecular chain breakage, creating electrical weaknesses that may ultimately lead to insulation failures, thus threatening the safe and stable operation of the entire system.

[0003] Currently, particle doping modification is the most widely used method to explore ways to improve the insulation and heat resistance properties of polypropylene films. For example, in the literature "Trap and DC Breakdown Characteristics of Polypropylene / Alumina Nanodielectrics", Acta Physica Sinica, 2017, 66(06), 281-289, nano-alumina is doped into polypropylene to prepare PP composite films with significantly improved breakdown field strength. The invention patent application CN202411874191.4 discloses the modification of mica powder using compounds containing carboxyl groups and benzene rings and / or palm wax, followed by blending the modified mica powder with PP resin and preparing heat-resistant PP films through a biaxial stretching process. The literature, "Study on Synergistic Improvement of Insulation Performance of Polypropylene Film by TiO2@SiO2 and Montmorillonite Nanomaterials", Journal of Electrical Engineering, 2025, 40(07), 2282-2294, describes the use of sintering process to combine spherical nanoparticles (TiO2@SiO2) with sheet-like montmorillonite to form multidimensional nanofillers. Further, the multidimensional nanofillers are combined with the PP matrix through melt extrusion and hot pressing to obtain a PP composite film. DC breakdown strength test results show that the introduction of 1.0 wt% multidimensional nanofillers increases the DC breakdown strength of the composite film by 34.5%.

[0004] However, the doped inorganic particles are prone to forming submicron or micron-sized agglomerates, which significantly reduces the breakdown field strength and thermal stability of polypropylene composite films, limiting the practical application of polypropylene films. Summary of the Invention

[0005] Purpose of the invention: The first objective of this invention is to provide a heat-resistant insulating mica powder / polypropylene composite film, and the second objective of this invention is to provide a method for preparing the above-mentioned heat-resistant insulating mica powder / polypropylene composite film.

[0006] Technical solution: The temperature-resistant insulating mica powder / polypropylene composite film of the present invention comprises, by weight, the following raw materials: 100 parts polypropylene resin, 0.3-30 parts polypropylene / mica powder composite particles, 10-40 parts viscosity modifier and 0.1-3 parts additives, wherein the polypropylene / mica powder composite particles are particles with a propylene / α-olefin copolymer shell layer formed by in-situ polymerization on the surface.

[0007] More preferably, the mica powder / polypropylene composite film comprises, by weight, the following raw materials: 100 parts polypropylene resin, 15-25 parts polypropylene / mica powder composite particles, 13-30 parts viscosity modifier and 0.9-2.4 parts additives.

[0008] Furthermore, the viscosity modifier comprises a molecular weight of 50-150*10 in a mass ratio of 1-1.6:1. 4 g / mol of ultra-high molecular weight polypropylene A and molecular weight of 200-450*10 4 g / mol of ultra-high molecular weight polypropylene B.

[0009] Furthermore, the mica powder particles have a flake-like morphology and an average particle size of less than 10 μm; the feed molar ratio of propylene to α-olefin in the propylene / α-olefin copolymer shell is 85:15-95:5, preferably 88:12-95:5.

[0010] Further, the additives include one or more of antioxidants, lubricants, or antistatic agents, wherein the antioxidant is one or more of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 2,6-di-tert-butyl-p-cresol, tris(2,4-di-tert-butylphenyl) phosphite, bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite, dilauryl thiodipropionate, and N-isopropyl-N'-phenyl-p-phenylenediamine; the lubricant is one or more of oleamide, glyceryl stearate, pentaerythritol stearate, high molecular weight silicone masterbatch, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, ethylene-tetrafluoroethylene copolymer, and hexafluoropropylene-vinylidene fluoride copolymer; and the antistatic agent is one or more of polyether block amide, polyether ester amide, and ethoxylated alkylamine.

[0011] The preparation method of the above-mentioned mica powder / polypropylene composite film includes the following steps: (1) First, an olefin polymerization catalyst is loaded on the surface of mica powder particles, and then the particles loaded with the olefin polymerization catalyst are polymerized in situ in a mixture of α-olefin and propylene to obtain polypropylene / mica powder composite particles. (2) Polypropylene resin, polypropylene / mica powder composite particles, viscosity modifier and additives are blended and granulated, and then calendered to obtain particle / polypropylene composite film.

[0012] Further, in step (1), the specific preparation steps of the polypropylene / mica powder composite particles are as follows: (11) After pretreating the mica powder particles, place them in a solvent, add an aminosilane compound, and after fully reacting, obtain amino-functionalized particles. (12) Disperse the amino-functionalized particles in a solvent, slowly add the protonating agent solution to obtain a mixture, and then prepare the amino-protonated particles after the reaction. (13) Add the amino protonated particles to the solvent, mix them, and then add the olefin polymerization catalyst solution. After the reaction is complete, particles loaded with the olefin polymerization catalyst are obtained. (14) The particles loaded with olefin polymerization catalyst are mixed with solvent in a reactor, and then propylene gas is introduced into the reactor. Then the pressure is slowly released to atmospheric pressure to completely remove the air in the reactor. Then, α-olefin is added into the reactor and enough propylene gas is introduced to the initial pressure of 2-4 bar. The reactor is stirred continuously at 70-80 °C and 4-6 bar propylene partial pressure until the reaction is completed to obtain polypropylene / mica powder composite particles.

[0013] Further, in step (11), the pretreatment method is as follows: adding mica powder to a concentrated hydrochloric acid aqueous solution and stirring thoroughly to react, and then obtaining the product; wherein, the concentration of the concentrated hydrochloric acid aqueous solution is 3-6 mol / L; the mass ratio of mica powder to concentrated hydrochloric acid aqueous solution is 10:100-120, and the parameters for stirring the reaction are: reacting at 60-75℃ for 2-3 h; the mass ratio of the pretreated mica powder particles to the aminosilane compound is 5-10:2-5, preferably 5-7:2-3.5; the aminosilane compound is one or more of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, phenylaminomethyltrimethoxysilane, γ-aminopropylmethyldiethoxysilane, and N-ethyl-γ-aminopropyltrimethoxysilane, and the parameters for thorough reaction are: continuously reacting at 80-85℃ for 6-10 h. h, the solvent is toluene; in step (12), the mass ratio of amino-functionalized particles to protonating agent solution is 1-5:1-5, preferably 1-1.5:1; the concentration of protonating agent solution is 1-2 mol / L; the protonating agent is one or more of perchloric acid, trifluoromethanesulfonic acid, hexafluorophosphoric acid, tetrafluoroboric acid, trifluoroacetic acid, and hydrochloric acid; the solvent is diethyl ether, and the reaction parameters are: stirring reaction at 20-30 ℃ for 1.5-3 h.

[0014] Further, in step (13), the olefin polymerization catalyst solution includes a main catalyst, a co-catalyst, and a solvent; the solvent is toluene, and the main catalyst is a metallocene catalyst, specifically zirconium dichlorodi ... The mixture comprises one or more of the following: tetramethylcyclopentadienyl zirconium dichloride (tert-butyramide) and tetramethylcyclopentadienyl hafnium dichloride; the co-catalyst comprises one or more of the following: methylaluminoxane, triphenylcarbium tetra(pentafluorophenyl)borate, N,N-dimethylaniline tetra(pentafluorophenyl)borate, and modified methylaluminoxane; the mass ratio of amino protonated particles, main catalyst, and co-catalyst in the mixture is 1-5:1-3:3-9, preferably 2-3:1.2-2.5:4-6.5; the reaction parameters are: stirring at 20-30 °C for 12-24 h.

[0015] Further, in step (14), the mass ratio of the particles loaded with the olefin polymerization catalyst to the α-olefin is 0.5-4:5-30, preferably 1-3:5-15; the α-olefin is one or more of 1-butene, 1-hexene, and 1-octene, and the solvent is hexane.

[0016] Further, in step (2), the process parameters for the blending and granulation are: first, mix evenly, then melt and blend using a twin-screw extruder, and extrude and granulate, with a screw speed of 50-200 rpm and a barrel temperature of 190-250 ℃; the process parameters for the calendering are: roller temperature of 190-250 ℃ and roller speed of 20-50 m / min.

[0017] Invention Principle: This invention introduces catalytically active centers for olefin polymerization onto the surface of flake mica powder particles, initiating copolymerization of propylene and α-olefins. This forms a robust propylene / α-olefin copolymer shell on the surface, enhancing the interfacial compatibility between mica powder and PP resin. This achieves good dispersion of flake mica powder in the PP matrix, significantly hindering the formation of conductive pathways and greatly improving the insulation properties of PP. Simultaneously, ultra-high molecular weight polypropylene (UHMWPP) with molecular weights of 500,000-1,500,000 and 2,000,000-4,500,000 is introduced to construct a melt viscosity gradient matching the PP resin and UHMWPP. This significantly increases the molecular entanglement density of the composite system, effectively restricting the movement of PP molecular chains and improving the thermal stability of the composite film. Ultimately, a heat-resistant insulating mica powder / polypropylene composite film is obtained, which has wide applications in capacitors, power batteries, and high-voltage direct current transmission systems.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) Mica powder particle doping modification is an effective method to improve the insulation and heat resistance of polypropylene film. However, the interaction between mica powder particles and polypropylene interface is weak and agglomeration is very easy to occur, which leads to the deterioration of composite film performance. Therefore, the present invention innovatively introduces metallocene catalytic active centers that can initiate olefin polymerization into mica powder particles, so that propylene and α-olefins copolymerize on the surface of mica powder, thereby forming a strong propylene / α-olefin copolymer shell, which significantly improves the interfacial compatibility between mica powder and PP resin matrix, realizes good dispersion of mica powder in PP matrix, and forms a "maze effect" of extended leakage channels. (1) “Should” significantly hinder the formation of conductive pathways and greatly improve the insulation of PP; (2) Introduce ultra-high molecular weight polypropylene with a molecular weight of 500,000 to 1,000,000 and 2,000,000 to 4,500,000 at a mass ratio of 1 to 1.6:1 into the composite system to construct a viscosity gradient that matches the PP resin and ultra-high molecular weight polypropylene. The proportion of low molecular weight ultra-high molecular weight polypropylene can effectively improve melt flowability, promote diffusion between interfacial molecules, significantly increase the molecular entanglement density of the composite system, effectively restrict the movement of PP molecular chains, and thus significantly improve the thermal stability of the composite film; (3) According to the experiment, the composite film prepared by the present invention has a transverse and longitudinal thermal shrinkage rate of 0.98-1.36% and 1.23-1.51% (120 ℃ / 120 s), respectively, and a breakdown strength of 573.28-589.31kV / mm (25 ℃) / 554.97-578.29kV / mm (50 ℃). Detailed Implementation

[0019] The present invention will now be further described with reference to specific embodiments.

[0020] Example 1: The heat-resistant insulating mica powder / polypropylene composite film provided in this example comprises the following raw materials by weight: 100 parts polypropylene resin, 25 parts polypropylene / mica powder composite particles, 30 parts viscosity modifier, 0.1 parts antioxidant pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 0.5 parts lubricant pentaerythritol stearate, and 0.3 parts antistatic agent polyether ester amide. The viscosity modifier comprises a 130*10 molecule with a molecular weight of 130*10 ppm in a mass ratio of 1:1. 4 g / mol of ultra-high molecular weight polypropylene A and a molecular weight of 360*10 4 The ultra-high molecular weight polypropylene B (g / mol) is polypropylene / mica powder composite particles. The polypropylene / mica powder composite particles are mica powder with a propylene / α-olefin copolymer shell formed by in-situ polymerization on the surface. The feed molar ratio of propylene to α-olefin is 95:5.

[0021] The preparation method of the above-mentioned mica powder / polypropylene composite film includes (the parts used in the following steps are parts by weight): (1) Preparation of polypropylene / mica powder composite particles, the steps are as follows: (11) 10 parts of mica powder (average particle size of 5 μm) were added to 100 parts of 6 mol / L concentrated hydrochloric acid aqueous solution. The reaction was carried out at 60 °C under magnetic stirring for 2 h. After the reaction was completed, vacuum filtration was carried out while hot. The filter cake was washed repeatedly with a large amount of deionized water until the filtrate was neutral. Then, the obtained mica powder was placed in a vacuum oven and dried at 70 °C for 4 h to obtain pretreated mica powder. 5 parts of pretreated mica powder were dispersed in 100 parts of toluene. Then, 2 parts of γ-aminopropyltriethoxysilane were added dropwise. The reaction was carried out at 80 °C for 10 h under magnetic stirring. After the reaction was completed, the mixture was filtered, washed and dried to obtain amino-functionalized mica powder. (12) Disperse 1 part of amino-functionalized mica powder in 40 parts of diethyl ether, and then slowly add 1 part of 1 mol / L perchloric acid diethyl ether solution. Stir magnetically for 3 h at 20 °C to obtain amino-protonated mica powder. (13) Add 2 parts of aminoprotonated mica powder to 60 parts of toluene to form a suspension; dissolve 1.2 parts of ethylidene-bridged silyl (tert-butamide) tetramethylcyclopentadienyl titanium dichloride and 4 parts of methylaluminoxane in toluene and react with magnetic stirring at 20°C for 1 h to obtain a catalyst solution; slowly add the catalyst solution to the suspension and react with magnetic stirring at 30°C for 12 h. After thorough washing and drying, mica powder loaded with metallocene catalyst is obtained. (14) Add 1 part of mica powder loaded with metallocene catalyst and 50 parts of hexane to the reactor and stir to mix evenly; introduce 4 bar of propylene gas into the reactor and then slowly depressurize to atmospheric pressure to completely remove the air in the reactor; then, add 5 parts of 1-hexene into the reactor and introduce enough propylene gas to the initial pressure of 2 bar. Stir continuously for 1 hour at 70 °C and 4 bar of propylene partial pressure until the reaction is finished. Further separate, wash and dry to finally obtain polypropylene / mica powder composite particles. (2) Mix 100 parts of polypropylene resin, 25 parts of polypropylene / mica powder composite particles, and 15 parts of ultra-high molecular weight polypropylene A (molecular weight of 130*10). 4 g / mol) and 15 parts of ultra-high molecular weight polypropylene B (molecular weight 360*10 g / mol) 4 The following ingredients were added to a high-speed mixer and mixed evenly: 0.1 parts of antioxidant pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid], 0.5 parts of lubricant pentaerythritol stearate, and 0.3 parts of antistatic agent polyether ester amide. Then, the mixture was melt-blended and extruded using a twin-screw extruder at a screw speed of 80 rpm and a barrel temperature of 190 ℃. The mixture was then further calendered at a roller temperature of 195 ℃ and a roller speed of 20 m / min to finally obtain a mica powder / polypropylene composite film.

[0022] Example 2: The heat-resistant insulating mica powder / polypropylene composite film provided in this example comprises the following raw materials by weight: 100 parts polypropylene resin, 20 parts polypropylene / mica powder composite particles, 18 parts viscosity modifier, 0.5 parts antioxidant 2,6-di-tert-butyl-p-cresol, and 1 part lubricant ethylene-tetrafluoroethylene copolymer. The viscosity modifier comprises a 70*10 ppm polymer with a mass ratio of 1.25:1. 4 g / mol of ultra-high molecular weight polypropylene and a molecular weight of 200*10 4 g / mol, the polypropylene / mica powder composite particles are mica powder with a propylene / α-olefin copolymer shell formed by in-situ polymerization on the surface, and the feed molar ratio of propylene to α-olefin is 90:10.

[0023] The preparation method of the above-mentioned mica powder / polypropylene composite film includes (the parts used in the following steps are parts by weight): (1) Preparation of polypropylene / mica powder composite particles, the steps are as follows: (11) Ten parts of mica powder (average particle size 7 μm) were added to 100 parts of 4 mol / L concentrated hydrochloric acid aqueous solution and reacted continuously at 70 °C with magnetic stirring for 3 h. After the reaction was completed, vacuum filtration was performed while hot, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral. Then, the obtained mica powder was placed in a vacuum oven and dried at 80 °C for 3 h to obtain pretreated mica powder. Seven parts of pretreated mica powder were dispersed in 160 parts of toluene, and then 3.5 parts of N-ethyl-γ-aminopropyltrimethoxysilane were added dropwise. The reaction was carried out continuously at 80 °C for 7 h with medium-speed magnetic stirring. After the reaction was completed, the mixture was filtered, washed, and dried to obtain amino-functionalized mica powder. (12) Disperse 3 parts of amino-functionalized mica powder in 80 parts of diethyl ether, and then slowly add 2 parts of 1.5 mol / L hexafluorophosphate diethyl ether solution. Stir magnetically at 25 °C for 2 h to obtain amino-protonated mica powder. (13) Add 2 parts of aminoprotonated mica powder to 65 parts of toluene to form a suspension; dissolve 2 parts of dimethylsilyl (tert-butamide)tetramethylcyclopentadienyl hafnium dichloride and 6 parts of modified methylaluminoxane in toluene and react with magnetic stirring at 25°C for 1 h to obtain a catalyst solution; slowly add the catalyst solution to the suspension and react with magnetic stirring at 25°C for 20 h. After thorough washing and drying, mica powder loaded with metallocene catalyst is obtained. (14) Add 3 parts of mica powder supported on metallocene catalyst and 350 parts of hexane to the reactor and stir at low speed to mix evenly; introduce 5 bar of propylene gas into the reactor and then slowly depressurize to atmospheric pressure to completely remove the air in the reactor; then, add 20 parts of 1-octene into the reactor and introduce enough propylene gas to the initial pressure of 4 bar. Stir continuously for 2 hours at 70 °C and 4 bar of propylene partial pressure until the reaction is completed, and then further separate, wash and dry to finally obtain polypropylene / mica powder composite particles; (2) Mix 100 parts of polypropylene resin, 20 parts of polypropylene / mica powder composite particles, and 10 parts of ultra-high molecular weight polypropylene A (molecular weight 70*10). 4 g / mol) and 8 parts of ultra-high molecular weight polypropylene B (molecular weight 200*10 g / mol) 4 0.5 parts of antioxidant 2,6-di-tert-butyl-p-cresol and 1 part of lubricant ethylene-tetrafluoroethylene copolymer were added to a high-speed mixer and mixed evenly. Then, the mixture was melt-blended and extruded into granules using a twin-screw extruder at a screw speed of 120 rpm and a barrel temperature of 210°C. Finally, the mixture was calendered at a roller temperature of 220°C and a roller speed of 35 m / min to obtain a mica powder / polypropylene composite film.

[0024] Example 3: The heat-resistant insulating mica powder / polypropylene composite film provided in this example comprises, by weight, the following raw materials: 100 parts polypropylene resin, 15 parts polypropylene / mica powder composite particles, 13 parts viscosity modifier, 1 part antioxidant dilaurate thiodipropionate, 0.8 parts lubricant high molecular weight silicone masterbatch, and 0.6 parts antistatic agent ethoxylated alkylamine. The viscosity modifier comprises a 100*10 ppm silicone resin with a molecular weight of 100*10 ppm in a mass ratio of 1.6:1. 4 g / mol of ultra-high molecular weight polypropylene A and a molecular weight of 280*10 4 The ultra-high molecular weight polypropylene B (g / mol) is polypropylene / mica powder composite particles. The polypropylene / mica powder composite particles are mica powder with a propylene / α-olefin copolymer shell formed by in-situ polymerization on the surface. The feed molar ratio of propylene to α-olefin is 88:12.

[0025] The preparation method of the above-mentioned mica powder / polypropylene composite film includes (the parts used in the following steps are parts by weight): (1) Preparation of polypropylene / mica powder composite particles, the steps are as follows: (11) 10 parts of mica powder (average particle size of 8 μm) were added to 100 parts of 3 mol / L concentrated hydrochloric acid aqueous solution and reacted continuously at 75℃ with magnetic stirring for 2.5 h. After the reaction was completed, vacuum filtration was performed while hot, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral. Then, the obtained mica powder was placed in a vacuum oven and dried at 85 ℃ for 2.5 h to obtain pretreated mica powder. 6 parts of pretreated mica powder were dispersed in 140 parts of toluene, and then 3.5 parts of phenylaminomethyltrimethoxysilane were added dropwise. The reaction was carried out continuously at 80 ℃ for 7.5 h with medium-speed magnetic stirring. After the reaction was completed, the mixture was filtered, washed, and dried to obtain amino-functionalized mica powder. (12) Disperse 3.5 parts of amino-functionalized mica powder in 125 parts of diethyl ether, and then slowly add 3.5 parts of 1.6 mol / L trifluoromethanesulfonic acid diethyl ether solution. Stir the reaction magnetically at 30 °C for 2.5 h to obtain amino-protonated mica powder. (13) Add 3 parts of aminoprotonated mica powder to 65 parts of toluene to form a suspension; dissolve 2.5 parts of dimethylsilyl (tert-butamide)tetramethylcyclopentadienyl titanium dichloride and 6.5 parts of triphenylcarbium tetra (pentafluorophenyl)borate in toluene and react with magnetic stirring at 30 °C for 1 h to obtain a catalyst solution; slowly add the catalyst solution to the suspension and react with magnetic stirring at 30 °C for 22 h. After thorough washing and drying, mica powder loaded with metallocene catalyst is obtained. (14) Add 3 parts of mica powder supported on a metallocene catalyst and 300 parts of hexane to a reactor and mix them evenly by stirring at low speed; introduce 4 bar of propylene gas into the reactor, and then slowly depressurize to atmospheric pressure to completely remove the air from the reactor; then add 15 parts of 1-hexene into the reactor and introduce enough propylene gas to the initial pressure of 4 bar, and continue stirring for 2 h at 70 °C and a propylene partial pressure of 4 bar until the reaction is complete. Further separation, washing, and drying are then performed to finally obtain polypropylene / mica powder composite particles; (2) Mix 100 parts of polypropylene resin, 15 parts of polypropylene / mica powder composite particles, and 8 parts of ultra-high molecular weight polypropylene A (molecular weight of 100*10). 4 g / mol) and 5 parts of ultra-high molecular weight polypropylene B (molecular weight 280*10 g / mol) 4 The following ingredients were added to a high-speed mixer and mixed evenly: 1 part of the antioxidant dilaurate thiodipropionate, 0.8 parts of the lubricant high molecular weight silicone masterbatch, and 0.6 parts of the antistatic agent ethoxylated alkylamine. Then, the mixture was melt-blended and extruded using a twin-screw extruder at a screw speed of 150 rpm and a barrel temperature of 230°C. Finally, the mixture was calendered at a roller temperature of 235°C and a roller speed of 45 m / min to obtain the mica powder / polypropylene composite film.

[0026] Comparative Example 1: Compared with Example 1, Comparative Example 1 differs in that the average particle size of the mica powder is 60 μm, while the other components, preparation steps and parameters are the same.

[0027] Comparative Example 2: Compared with Example 1, Comparative Example 2 differs in that 50 parts of polypropylene / mica powder composite particles were added, while the other components, preparation steps and parameters were the same.

[0028] Comparative Example 3: Compared with Example 1, Comparative Example 3 differs in that untreated flake mica powder (without a propylene / α-olefin copolymer shell on the surface of the mica powder) was directly compounded with PP resin to prepare a polypropylene composite film, while the other components, preparation steps and parameters were the same.

[0029] Comparative Example 4: Compared with Example 1, Comparative Example 4 differs in that ultra-high molecular weight polypropylene A is not added, while the other components, preparation steps and parameters are the same.

[0030] Comparative Example 5: Compared with Example 1, Comparative Example 5 differs in that it does not contain ultra-high molecular weight polypropylene A and ultra-high molecular weight polypropylene B, while the other components, preparation steps and parameters are the same.

[0031] Comparative Example 6: Compared with Example 1, the difference in Comparative Example 6 is that flake mica powder was directly physically blended with the propylene / α-olefin copolymer obtained by the method of Example 1 to form a polypropylene / mica powder composite. The other components, preparation steps and parameters were the same.

[0032] Comparative Example 7: Compared with Example 1, the difference in Comparative Example 7 is that the mass ratio of ultra-high molecular weight polypropylene A to ultra-high molecular weight polypropylene B is 1:2.5, while the other components, preparation steps and parameters are the same.

[0033] The composite films prepared in Examples 1-3 and Comparative Examples 1-7 were tested for thermal shrinkage according to GB / T 10003-2008 and DC breakdown strength according to GB / T 1408.1-2016. The test results are shown in Table 1.

[0034] Table 1 Thermal stability and breakdown strength of heat-resistant / insulating polypropylene composite films

[0035] As shown in Table 1, for Examples 1-3, on the one hand, by introducing active centers for olefin polymerization onto the surface of mica powder, a strong propylene / α-olefin copolymer shell is formed on the surface of mica powder, achieving good dispersion of flake mica powder in the PP matrix, significantly hindering the formation of conductive pathways, and greatly improving the insulation of PP; on the other hand, by introducing ultra-high molecular weight polypropylene with molecular weights of 500,000-1,500,000 and 2,000,000-4,500,000, a viscosity gradient matching PP resin and ultra-high molecular weight polypropylene is constructed, significantly increasing the molecular entanglement density of the composite system, effectively restricting the movement of PP molecular chains, and improving the thermal stability of the composite film, a temperature-resistant insulating mica powder / polypropylene composite film is finally obtained, with transverse and longitudinal thermal shrinkage rates of 0.98-1.36% and 1.23-1.51%, respectively, and breakdown strength of 573.28-589.31 kV / mm (25℃) / 554.97-578.29 kV / mm (50℃).

[0036] For Comparative Example 1, the mica powder particle size is too large, which makes it impossible to form a large number of dense and parallel sheet barriers, and the leakage channel cannot be effectively extended and blocked. At the same time, the large particle size causes its specific surface area to decrease sharply, which weakens the restriction on the PP molecular chain, resulting in a decrease in the insulation and heat resistance of the composite film.

[0037] In Comparative Example 2, the excessive polypropylene / mica powder composite particles achieve uniform dispersion and perfect coating, leading to a surge in interfacial defects such as pores and agglomeration, which weakens the insulation and heat resistance of the composite film.

[0038] For Comparative Example 3, when untreated mica powder was directly mixed with PP resin, a large amount of mica powder agglomerated significantly in the PP resin matrix, resulting in a substantial reduction in the insulation and heat resistance of the composite film.

[0039] For Comparative Example 4, without the addition of ultra-high molecular weight polypropylene A, the PP resin and ultra-high molecular weight polypropylene B cannot form a matching viscosity gradient, the molecular entanglement density of the composite system decreases, the ability to confine the PP molecular chains is weaker, and ultimately the insulation and heat resistance of the composite film deteriorate.

[0040] For Comparative Example 5, without the addition of ultra-high molecular weight polypropylene A and ultra-high molecular weight polypropylene B, the molecular entanglement of the system was significantly reduced, and the insulation and heat resistance of the polypropylene composite film were further deteriorated.

[0041] For Comparative Example 6, flake mica powder was directly physically blended with the propylene / α-olefin copolymer obtained by the method of Example 1 to form a mica powder / polypropylene composite. The mica powder exhibited significant agglomeration in the propylene / α-olefin copolymer. Further, the mica powder / polypropylene composite particles were compounded with PP resin. The mica powder showed poor dispersibility in the PP resin matrix, and the insulation and heat resistance of the composite film were significantly reduced.

[0042] For Comparative Example 7, the mass ratio of ultra-high molecular weight polypropylene A to ultra-high molecular weight polypropylene B was 1:2.5. Excess ultra-high molecular weight polypropylene B could not form a matching viscosity gradient with PP resin, which reduced the molecular entanglement density of the composite system and decreased the insulation and heat resistance of the composite film.

Claims

1. A temperature-resistant insulating mica powder / polypropylene composite film, characterized in that, The product comprises, by weight, the following raw materials: 100 parts polypropylene resin, 0.3-30 parts polypropylene / mica powder composite particles, 10-40 parts viscosity modifier and 0.1-3 parts additives, wherein the polypropylene / mica powder composite particles are particles with a propylene / α-olefin copolymer shell formed by in-situ polymerization on the surface.

2. The composite film according to claim 1, characterized in that, The viscosity modifier comprises, by mass ratio 1-1.6:1, a molecular weight of 50-150*10. 4 g / mol of ultra-high molecular weight polypropylene A and molecular weight of 200-450*10 4 g / mol of ultra-high molecular weight polypropylene B.

3. The composite film according to claim 1, characterized in that, The average particle size of the mica powder is less than 10 μm; the feed molar ratio of propylene to α-olefin in the propylene / α-olefin copolymer shell is 85:15-95:

5.

4. The composite film according to claim 1, characterized in that, The additives include one or more of antioxidants, lubricants, or antistatic agents.

5. A method for preparing the mica powder / polypropylene composite film according to claim 1, characterized in that, Includes the following steps: (1) First, an olefin polymerization catalyst is loaded on the surface of mica powder particles, and then the mica powder particles loaded with the olefin polymerization catalyst are subjected to in-situ polymerization in a mixture of α-olefin and propylene to obtain polypropylene / mica powder composite particles. (2) Polypropylene resin, polypropylene / mica powder composite particles, viscosity modifier and additives are blended and granulated, and then calendered to obtain mica powder / polypropylene composite film.

6. The preparation method according to claim 5, characterized in that, In step (1), the specific preparation steps of the polypropylene / mica powder composite particles are as follows: (11) After pretreating the mica powder particles, place them in a solvent, add an aminosilane compound, and after fully reacting, obtain amino-functionalized particles. (12) Disperse the amino-functionalized particles in a solvent, slowly add the protonating agent solution to obtain a mixture, and then prepare the amino-protonated particles after the reaction. (13) Add the amino protonated particles to the solvent, mix them, and then add the olefin polymerization catalyst solution. After the reaction is complete, particles loaded with the olefin polymerization catalyst are obtained. (14) The particles loaded with olefin polymerization catalyst are mixed with solvent in a reactor, and then propylene gas is introduced into the reactor. Then the pressure is slowly released to atmospheric pressure to completely remove the air in the reactor. Then, α-olefin is added into the reactor and enough propylene gas is introduced to the initial pressure of 2-4 bar. The reactor is stirred continuously at 70-80 °C and 4-6 bar propylene partial pressure until the reaction is completed to obtain polypropylene / mica powder composite particles.

7. The preparation method according to claim 6, characterized in that, In step (11), the pretreatment method is as follows: mica powder is added to a concentrated hydrochloric acid aqueous solution and stirred thoroughly to react. After the reaction is completed, the mica powder is obtained. The concentration of the concentrated hydrochloric acid aqueous solution is 3-6 mol / L. The mass ratio of the pretreated mica powder particles to the aminosilane compound is 5-10:2-5. The aminosilane compound is one or more of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, phenylaminomethyltrimethoxysilane, γ-aminopropylmethyldiethoxysilane, and N-ethyl-γ-aminopropyltrimethoxysilane. The parameters for a complete reaction are: continuous reaction at 80-85 °C for 6-10 minutes. h; In step (12), the mass ratio of amino-functionalized particles to protonating agent solution is 1-5:1-5; the concentration of protonating agent solution is 1-2 mol / L; the protonating agent is one or more of perchloric acid, trifluoromethanesulfonic acid, hexafluorophosphoric acid, tetrafluoroboric acid, trifluoroacetic acid, and hydrochloric acid; the reaction parameters are: stirring reaction at 20-30 ℃ for 1.5-3 h.

8. The preparation method according to claim 6, characterized in that, In step (13), the olefin polymerization catalyst solution includes a main catalyst, a co-catalyst, and a solvent; the main catalyst is a metallocene catalyst, and the co-catalyst is one or more of methylaluminoxane, triphenylcarbazide tetra(pentafluorophenyl)borate, N,N-dimethylaniline tetra(pentafluorophenyl)borate, and modified methylaluminoxane; the mass ratio of amino protonated particles, main catalyst, and co-catalyst in the mixture is 1-5:1-3:3-9; the reaction parameters are: stirring at 20-30 °C for 12-24 h.

9. The preparation method according to claim 6, characterized in that, In step (14), the mass ratio of the particles loaded with the olefin polymerization catalyst to the α-olefin is 0.5-4:5-30; the α-olefin is one or more of 1-butene, 1-hexene, and 1-octene.

10. The preparation method according to claim 5, characterized in that, In step (2), the process parameters for blending and granulation are: first, mix evenly, then melt and blend using a twin-screw extruder, and extrude and granulate, with a screw speed of 50-200 rpm and a barrel temperature of 190-250 ℃; the process parameters for calendering are: roller temperature of 190-250 ℃ and roller speed of 20-50 m / min.

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