Modified polypropylene composition, biaxially stretched polypropylene film and applications and polypropylene capacitor film

Abstract

The application belongs to the field of polymers and relates to a modified polypropylene composition, a biaxially stretched polypropylene film and a polypropylene capacitor film. The modified polypropylene composition comprises a modified polypropylene grafted with an alkenyl-containing functional monomer, an antioxidant and a processing aid. The modified polypropylene grafted with the alkenyl-containing functional monomer comprises structural units derived from polypropylene as a matrix phase and structural units derived from the alkenyl-containing functional monomer as a dispersed phase. The mass ratio of the structural units derived from the alkenyl-containing functional monomer and in a grafted state to the structural units derived from the alkenyl-containing functional monomer and in a self-polymerized state in the modified polypropylene grafted with the alkenyl-containing functional monomer is greater than or equal to 1.5. The modified polypropylene composition, the biaxially stretched polypropylene film and the polypropylene capacitor film prepared therefrom have a wide working temperature range and can maintain good dielectric properties and energy storage properties at a high working temperature.

Description

Technical Field

[0001] This invention belongs to the field of polymers, specifically relating to a modified polypropylene composition, a biaxially oriented polypropylene film made from the modified polypropylene composition, the application of the biaxially oriented polypropylene film in the preparation of energy storage dielectrics, and a polypropylene capacitor film with a high operating temperature. Background Technology

[0002] Energy is the driving force of modern societal development. In recent years, with the rapid development of new energy, aerospace, underground resource extraction, and national defense industries, the demand for dielectric capacitors has increased year by year, and they are required to operate under more stringent temperature conditions. However, thin-film capacitors, primarily composed of polymer dielectric materials, have poor thermal stability and cannot operate stably in high-temperature environments. Especially under high electric fields, the temperature rise causes the leakage current inside the polymer dielectric to increase exponentially, resulting in a sharp decrease in charging and discharging efficiency and energy storage density, failing to meet application requirements. More seriously, the leakage current is converted into Joule heat, causing the capacitor temperature to rise continuously, ultimately leading to damage.

[0003] Biaxially oriented polypropylene (BOPP) is currently the most commercially available and widely used polymer film capacitor dielectric material. It has excellent comprehensive performance and mature large-scale preparation process, and is now widely used in industries such as electric vehicles, wind power, photovoltaics, lighting and railway locomotives.

[0004] However, an inherent drawback of polypropylene film capacitors is their poor dielectric energy storage performance and significantly reduced reliability at high temperatures. For example, at room temperature, BOPP can still achieve a charge-discharge efficiency of over 95% even when close to its breakdown field strength, but at 120°C, its efficiency drops to about 70%. This not only significantly reduces its energy storage density but also generates a large amount of waste heat that accumulates inside the device, ultimately leading to overheating and damage (thermal runaway).

[0005] Currently, there are two main types of methods to improve the operating temperature of polymer capacitor films from a materials perspective. The first type is to improve the thermal stability of the polymer dielectric material, that is, to synthesize materials with a high glass transition temperature (T0). g The first method involves polymer dielectric materials. The second method involves introducing a second-phase filler into the polymer dielectric material to prepare a composite material. This filler particles capture and scatter charge carriers to suppress leakage current in the polymer under high temperature and high electric field conditions. However, both methods suffer from complex manufacturing processes, making large-scale industrial production difficult.

[0006] Therefore, it is necessary to find a new type of polypropylene dielectric energy storage material with obvious controllability of dielectric energy storage characteristics, simple preparation process, and good fit for practical engineering applications.

[0007] Grafting modification is a common method for functionalizing polypropylene. Commonly used methods include melt grafting and solid-phase grafting. Melt grafting equipment is simple and inexpensive, but the reaction temperature is high, the process is difficult to control, and there are many byproducts. It is also limited to a limited range of applicable monomers and is currently only used for the preparation of anhydride-based or a few acrylate-based compatibilizers. Solid-phase grafting occurs at temperatures below the melting point of polypropylene, resulting in fewer side reactions, higher grafting efficiency, and a wider range of applicable graft monomers. For example, Y. Pan et al. studied the reaction conditions for solid-phase grafting of glycidyl methacrylate (GMA) onto polypropylene in "Solid-phase grafting of glycidyl methacrylate onto polypropylene." (Journal of Applied Polymer Science, 1997, 65(10): 1905-1912), and pointed out that the influencing factors of solid-phase grafting and melt grafting are significantly different. Suspension grafting is a special type of solid-phase grafting. By introducing an aqueous medium as a dispersant into the reaction system, the reaction temperature is further reduced, improving the uniformity of grafting and reducing the formation of byproducts. In addition, Li Qiaojun et al. discussed the reaction conditions and influencing factors of polypropylene suspension grafting with styrene in "Study on polypropylene suspension grafting with styrene" (Synthetic Resins and Plastics, 1996, 13(1):7-10.). Zhu Baodong et al. reported obtaining a polypropylene dimonomer graft with a grafting rate of 8.97% by aqueous suspension grafting in "Polypropylene aqueous suspension grafting with styrene and maleic anhydride" (Modern Plastics Processing and Application, 2009, 5:3.). Currently, there are no reports of bulk grafted modified polypropylene as a dielectric energy storage material.

[0008] Improving the heat and oxygen aging resistance of polypropylene by using antioxidant compounding is a common method. CN111378229A discloses a polypropylene composition resistant to long-term heat aging and its preparation method. The composition comprises 84.55-57.9% polypropylene, 15-40% talc, 0.1-0.3% primary antioxidant, 0.1-0.3% secondary antioxidant, 0.05-0.2% hindered amine antioxidant, 0.1-0.3% thioester antioxidant, and 0.1-1% acid scavenger. CN112430363A discloses a low-density, high-transmittance polypropylene material resistant to long-term heat and oxygen aging, wherein the primary antioxidant is a compound of high molecular weight hindered phenolic antioxidant and low molecular weight hindered phenolic antioxidant. Summary of the Invention

[0009] The purpose of this invention is to provide a modified polypropylene composition containing a novel alkenyl functional monomer grafted onto modified polypropylene, which can be further processed into a polypropylene film through a biaxial stretching process. The modified polypropylene composition and the polypropylene film can maintain high energy storage efficiency and energy storage density even at high operating temperatures.

[0010] A first aspect of the present invention provides a modified polypropylene composition comprising modified polypropylene grafted with an alkenyl functional monomer, an antioxidant, and a processing aid.

[0011] The modified polypropylene grafted with alkenyl functional monomers comprises structural units derived from polypropylene as the matrix phase and structural units derived from alkenyl functional monomers as the dispersed phase; the ash content of the modified polypropylene grafted with alkenyl functional monomers is less than 50 ppm, preferably less than 36 ppm, more preferably less than 30 ppm; the mass ratio of structural units derived from alkenyl functional monomers and in the grafted state to structural units derived from alkenyl functional monomers and in the self-polymerized state in the modified polypropylene grafted with alkenyl functional monomers is greater than or equal to 1.5, preferably greater than or equal to 2; the DC volume resistivity of the modified polypropylene grafted with alkenyl functional monomers at 120℃ and 200 MV / m electric field is 1.5 × 10⁻⁶. 14 Ω·m~0.9×10 20 Ω·m.

[0012] A second aspect of the present invention provides a biaxially oriented polypropylene film, which is prepared from the above-described modified polypropylene composition.

[0013] A third aspect of the present invention provides the application of the above-described biaxially oriented polypropylene film in energy storage media, particularly high-temperature energy storage media.

[0014] A fourth aspect of the present invention provides a polypropylene capacitor film, which is one or more layers, wherein at least one layer is the above-described biaxially oriented polypropylene film.

[0015] The modified polypropylene composition of the present invention, as well as the biaxially oriented polypropylene film and polypropylene capacitor film made therefrom, have a wide operating temperature range. In particular, they maintain good dielectric and energy storage properties even at higher operating temperatures, making them especially suitable for high-temperature and high-field-strength operating conditions. The biaxially oriented polypropylene film and high-performance polypropylene capacitor film of the present invention have the advantage of good tensile properties, and can balance mechanical and electrical properties at higher operating temperatures, making them suitable for high-temperature and high-field-strength operating conditions.

[0016] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0017] Exemplary embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

[0018] Figure 1 The results shown are the TSDC test results of the products in Example 3 and Comparative Example 1. Detailed Implementation

[0019] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0020] The present invention provides a modified polypropylene composition comprising modified polypropylene grafted with an alkenyl functional monomer, an antioxidant, and a processing aid.

[0021] The modified polypropylene grafted with alkenyl functional monomers comprises structural units derived from polypropylene as the matrix phase and structural units derived from alkenyl functional monomers as the dispersed phase; the ash content of the modified polypropylene grafted with alkenyl functional monomers is less than 50 ppm, preferably less than 36 ppm, more preferably less than 30 ppm; the mass ratio of structural units derived from alkenyl functional monomers and in the grafted state to structural units derived from alkenyl functional monomers and in the self-polymerized state in the modified polypropylene grafted with alkenyl functional monomers is greater than or equal to 1.5, preferably greater than or equal to 2; the DC volume resistivity of the modified polypropylene grafted with alkenyl functional monomers at 120℃ and 200 MV / m electric field is 1.5 × 10⁻⁶. 14 Ω·m~0.9×10 20 Ω·m.

[0022] According to the present invention, preferably, the modified polypropylene grafted with the alkenyl functional monomer has at least one of the following characteristics: a melt flow rate of 1–10 g / 10 min at 230°C and a load of 2.16 kg, preferably 1.5–8 g / 10 min, more preferably 2–5 g / 10 min. Melting temperature T m The temperature range is 155–168℃, preferably 157–165℃. The flexural modulus is 1400–2000 MPa, preferably 1500–1800 MPa.

[0023] In this invention, the term "structural unit" refers to a portion of modified polypropylene grafted with an alkenyl functional monomer, and its form is not limited. Specifically, "structural unit derived from polypropylene" refers to a product formed from polypropylene, which includes both "group" and "polymer" forms. "Structural unit derived from alkenyl functional monomer" refers to a product formed from an alkenyl functional monomer, which includes both "group" and "self-polymerized" forms. The "structural unit" can be a repeating unit or a non-repeating independent unit. A structural unit derived from an alkenyl functional monomer in a "grafted state" refers to a structural unit derived from an alkenyl functional monomer that has formed a covalent bond (graft) with polypropylene.

[0024] According to the present invention, preferably, the modified polypropylene grafted with the alkenyl functional monomer is prepared by a grafting reaction of polypropylene and the alkenyl functional monomer, more preferably by a suspension grafting reaction. The grafting reaction of the present invention is a free radical polymerization reaction; therefore, "in the grafted state" refers to the state in which the monomer, after free radical polymerization, forms a bond with another reactant. "The self-polymerized state" refers to the state in which the monomer forms a self-polymer and is not bonded (grafted) to another reactant. The bond includes both direct and indirect bonds.

[0025] According to the present invention, preferably, the modified polypropylene grafted with alkenyl functional monomers has at least one of the following characteristics:

[0026] - Maximum operating temperature ≥100℃, preferably 110~160℃, more preferably 120~145℃;

[0027] The breakdown field strength at -120℃ is Eg≥500MV / m, preferably 550~800MV / m;

[0028] The DC volume resistivity at -120℃ and a field strength of 200MV / m is 2.0×10⁻⁶. 14 Ω·m~1.0×10 17 Ω·m; for example, 1.0 × 10 15 Ω·m, 1.0×10 16 Ω·m, and any value within that range;

[0029] The dielectric constant at -120℃ and 100Hz is greater than 2.25, preferably 2.26 to 2.65;

[0030] The dielectric loss at -120℃ and 100Hz is less than 1.0E-3, preferably 1.0E-6 to 9E-4;

[0031] The energy storage density at -120℃ and 300MV / m is greater than 0.780J / cm³. 3 Preferably, it is 0.80–2.0 J / cm³. 3 ;

[0032] The energy storage efficiency at -120℃ and 300MV / m is greater than 90.0%, preferably 92.0% to 99.0%.

[0033] The capacitor film of the present invention has the above-mentioned excellent dielectric properties measured at 120°C. For example, the energy storage efficiency of the film measured in the following embodiments at 120°C and 300MV / m is above 95%. The upper limit of the temperature at which the energy storage efficiency reaches 95% can be used as an indicator of the maximum operating temperature. This confirms that the capacitor film of the present invention has a maximum operating temperature of at least 120°C.

[0034] The aforementioned properties of the modified polypropylene grafted with alkenyl functional monomers described in this invention were measured by fabricating it into a thin film.

[0035] The alkenyl group in the alkenyl-containing functional monomer of the present invention is used for grafting with polypropylene. Therefore, any alkenyl-containing functional monomer with the alkenyl group located in a reactive position is applicable to the present invention.

[0036] Specifically, the alkenyl-containing functional monomer is selected from at least one monomer having the structure shown in Formula 1.

[0037]

[0038] In Equation 1, R b R c R d Each is independently selected from H, substituted or unsubstituted alkyl groups; R a Selected from substituted or unsubstituted alkyl groups, substituted or unsubstituted alkoxy groups, substituted or unsubstituted aryl groups, substituted or unsubstituted ester groups, substituted or unsubstituted carboxyl groups, substituted or unsubstituted cycloalkyl or heterocyclic groups, cyano groups, and substituted or unsubstituted silyl groups; R a and R d Arrange the rings arbitrarily.

[0039] According to a preferred embodiment of the present invention, R b R c R d Each is independently selected from H, substituted or unsubstituted C1-C6 alkyl groups; R a Selected from substituted or unsubstituted C1-C 20 Alkyl, substituted or unsubstituted C1-C 20 Alkoxy, substituted or unsubstituted C6-C 20 aryl, substituted or unsubstituted C1-C 20 Ester group, substituted or unsubstituted C1-C 20 Carboxyl, substituted or unsubstituted C3-C 20 Cycloalkyl or heterocyclic, cyano, substituted or unsubstituted C3-C 20 Silyl group; the substituted group is halogen, -OH, -NH2, =O, C1-C 12 Alkyl, C3-C6 cycloalkyl, C1-C 12 alkoxy groups, C1-C 12 Acyloxy group; R a and R d Optionally, it can form a 4-6 membered heterocycle with a double bond.

[0040] According to a more preferred embodiment of the present invention, wherein R b R c R dEach is independently selected from H, substituted or unsubstituted C1-C6 alkyl groups;

[0041] R a Selected from the groups shown in Formula 2, Formula 3, Formula 4, Formula 5, Formula 6, combinations of the groups shown in Formula 6 and Formula 7, and heterocyclic groups;

[0042]

[0043] In Equation 2, R 4 -R 8 Each is independently selected from H, halogen, hydroxyl, amino, phosphate group, sulfonic acid group, substituted or unsubstituted C1-C. 12 Alkyl, substituted or unsubstituted C3-C 12 cycloalkyl, substituted or unsubstituted C1-C 12 alkoxy, substituted or unsubstituted C1-C 12 ester group, substituted or unsubstituted C1-C 12 The substituted amino group, wherein the substituted group is selected from halogen, hydroxyl, amino, phosphate, sulfonic acid, C1-C 12 Alkyl, C3-C 12 cycloalkyl, C1-C 12 alkoxy groups, C1-C 12 ester group, C1-C 12 The amino group; preferably, R 4 -R 8 Each is independently selected from H, halogen, hydroxyl, amino, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy;

[0044]

[0045] In Equation 3, R4-R 10 Each is independently selected from H, halogen, hydroxyl, amino, phosphate group, sulfonic acid group, substituted or unsubstituted C1-C. 12 Alkyl, substituted or unsubstituted C3-C 12 cycloalkyl, substituted or unsubstituted C1-C 12 alkoxy, substituted or unsubstituted C1-C 12 ester group, substituted or unsubstituted C1-C 12 The substituted amino group, wherein the substituted group is selected from halogen, hydroxyl, amino, phosphate, sulfonic acid, C1-C 12 Alkyl, C3-C 12 cycloalkyl, C1-C 12 alkoxy groups, C1-C 12 ester group, C1-C 12 The amino group; preferably, R4-R10 Each of the groups is independently selected from H, halogen, hydroxyl, amino, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy, wherein the substituted group is selected from halogen, hydroxyl, amino, C1-C6 alkyl, C1-C6 alkoxy;

[0046]

[0047] In Equation 4, R4'-R 10 Each group is independently selected from H, halogen, hydroxyl, amino, phosphate, sulfonic acid, substituted or unsubstituted C1-C. 12 Alkyl, substituted or unsubstituted C3-C 12 cycloalkyl, substituted or unsubstituted C1-C 12 alkoxy, substituted or unsubstituted C1-C 12 ester group, substituted or unsubstituted C1-C 12 The substituted amino group, wherein the substituted group is selected from halogen, hydroxyl, amino, phosphate, sulfonic acid, C1-C 12 Alkyl, C3-C 12 cycloalkyl, C1-C 12 alkoxy groups, C1-C 12 ester group, C1-C 12 The amino group; preferably, R4'-R 10 Each of the following is independently selected from H, halogen, hydroxyl, amino, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy, wherein the substituted group is selected from halogen, hydroxyl, amino, C1-C6 alkyl, C1-C6 alkoxy;

[0048]

[0049] In Equation 5, R', R”, and R”' are each independently selected from substituted or unsubstituted C1-C. 12 Straight-chain alkyl, substituted or unsubstituted C3-C 12 Branched alkyl, substituted or unsubstituted C1-C 12 alkoxy, substituted or unsubstituted C1-C 12 The acyloxy group; preferably, R', R"', R"' are each independently selected from substituted or unsubstituted C1-C6 straight-chain alkyl, substituted or unsubstituted C3-C6 branched alkyl, substituted or unsubstituted C1-C6 alkoxy, substituted or unsubstituted C1-C6 acyloxy.

[0050]

[0051] In Equation 6, R m Selected from the following groups, substituted or unsubstituted: C1-C20 Straight-chain alkyl, C3-C 20 Branched alkyl, C3-C 12 cycloalkyl, C3-C 12 Epoxyalkyl, C3-C 12 Epoxyalkylalkyl, wherein the substituted group is selected from at least one of halogen, amino and hydroxyl groups;

[0052] The heterocyclic group is selected from imidazole, pyrazol, carbazole, pyrrolidone, pyridinyl, piperidinyl, caprolactam, pyrazinyl, thiazolyl, purine, morpholino, and oxazolino.

[0053] According to a specific embodiment of the present invention, the alkenyl-containing functional monomer is a styrene monomer, wherein the styrene monomer is selected from at least one of styrene, α-methylstyrene, 1-vinylnaphthalene, 2-vinylnaphthalene, monosubstituted or polysubstituted styrene, monosubstituted or polysubstituted α-methylstyrene, monosubstituted or polysubstituted 1-vinylnaphthalene, and monosubstituted or polysubstituted 2-vinylnaphthalene; the substituted group is preferably selected from at least one of halogen, hydroxyl, amino, phosphoric acid, sulfonic acid, C1-C8 straight-chain alkyl, C3-C8 branched alkyl or cycloalkyl, C1-C6 straight-chain alkoxy, C3-C8 branched alkoxy or cyclic alkoxy, C1-C8 straight-chain ester, C3-C8 branched ester or cyclic ester, C1-C8 straight-chain amino, and C3-C8 branched amino or cyclic amino; preferably, the styrene monomer is selected from at least one of styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, and 4-methylstyrene.

[0054] According to a specific embodiment of the present invention, the alkenyl-containing functional monomer is an alkenyl-containing silane monomer, wherein the alkenyl-containing silane monomer is selected from at least one of vinyltriethoxysilane, vinyltrimethoxysilane, vinyltriisopropoxysilane, vinyltritert-butoxysilane, vinyltriacetoxysilane, methylvinyldimethoxysilane, ethylvinyldiethoxysilane, allyltriethoxysilane, allyltrimethoxysilane, allyltriisopropoxysilane, vinyltris(β-methoxyethoxy)silane, allyltris(β-methoxyethoxy)silane, allyltritert-butoxysilane, allyltriacetoxysilane, methylallyldimethoxysilane, and ethylallyldiethoxysilane.

[0055] According to one specific embodiment of the present invention, the alkenyl-containing functional monomer is an acrylate monomer and / or an acrylic monomer. Preferably, the acrylate monomer is selected from at least one of methyl methacrylate, sec-butyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, isooctyl methacrylate, dodecyl methacrylate, coconut oleate methacrylate, octadecyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminopropyl methacrylate, and glycidyl methacrylate. Preferably, the acrylic monomer is selected from at least one of acrylic acid, methacrylic acid, and 2-ethylacrylic acid.

[0056] In this invention, C3-C 12 Epoxyalkyl refers to an alkyl group that has 3-12 carbon atoms and is substituted with an epoxyalkyl group, such as ethylene oxide methyl.

[0057] According to a specific embodiment of the present invention, the alkenyl-containing functional monomer is an alkenyl-containing heterocyclic compound. The alkenyl-containing heterocyclic monomer of the present invention can be any alkenyl-containing heterocyclic compound capable of free radical polymerization, and can be selected from at least one of the following: imidazoles containing alkenyl substituents, pyrazoles containing alkenyl substituents, carbazoles containing alkenyl substituents, pyrrolidones containing alkenyl substituents, pyridines or pyridine salts containing alkenyl substituents, piperidines containing alkenyl substituents, caprolactams containing alkenyl substituents, pyrazines containing alkenyl substituents, thiazoles containing alkenyl substituents, purines containing alkenyl substituents, morpholines containing alkenyl substituents, and oxazolines containing alkenyl substituents; preferably, the alkenyl-containing heterocyclic monomer is a monoalkenyl-containing heterocyclic monomer.

[0058] Specifically, the alkenyl-containing heterocyclic monomer may be selected from at least one of the following: 1-vinylimidazolium, 2-methyl-1-vinylimidazolium, N-allylimidazolium, 1-vinylpyrazole, 3-methyl-1-vinylpyrazole, vinylcarbazole, N-vinylpyrrolidone, 2-vinylpyridine, 3-vinylpyridine, 4-vinylpyridine, 2-methyl-5-vinylpyridine, vinylpyridine N-oxide, vinylpyridine salt, vinylpiperidine, N-vinylcaprolactam, 2-vinylpyrazine, N-vinylpiperazine, 4-methyl-5-vinylthiazole, N-vinylpurine, vinylmorpholine, and vinyloxazoline.

[0059] According to the present invention, the alkenyl-containing functional monomer may further be at least one selected from maleic anhydride, maleimide and its derivatives, itaconic anhydride, and α-methylene-γ-butyrolactone. Preferably, the alkenyl-containing functional monomer is maleic anhydride.

[0060] In this invention, various types of alkenyl-containing functional monomers can be used alone or in combination with one or more.

[0061] The polypropylene mentioned in this invention refers to the polypropylene portion of the grafted material, or it can refer to ungrafted polypropylene, which can be a propylene homopolymer or a propylene copolymer containing ethylene or butene units. More preferably, the polypropylene powder is a homopolymer polypropylene with an isotacticity greater than 96%, more preferably greater than 96.5%; or a copolymer polypropylene with a total content of ethylene and butene units of less than 3.0 mol% based on the total molar amount of structural units, for example, 2.5 mol%, 2 mol%, 1.5 mol%, 1 mol%, 0.9 mol%, 0.8 mol%, 0.7 mol%, 0.6 mol%, 0.5 mol%, 0.4 mol%, 0.3 mol%, 0.2 mol%, or 0.1 mol%. Preferably, the total content of ethylene and butene units in the copolymer polypropylene is greater than 0 and less than 0.1 mol%, or greater than 0.1 mol% and less than or equal to 3.0 mol%.

[0062] According to the present invention, in order to obtain the polypropylene dielectric energy storage material with the aforementioned characteristics, it is preferable to use polypropylene having the following characteristics: particle size of 16 to 50 mesh; ash content of less than 55 ppm, preferably less than 40 ppm, more preferably less than 35 ppm; and flexural modulus of 1400 to 2000 MPa, preferably 1500 to 1800 MPa.

[0063] In addition to the above-mentioned features, the polypropylene preferably also has at least one of the following features: a melt flow rate of 0.5 to 10 g / 10 min at 230°C and 2.16 kg load, preferably 1 to 5 g / 10 min, more preferably 2 to 4 g / 10 min; and / or a melt temperature Tm of 150°C or higher, preferably 153 to 180°C, more preferably 155 to 167°C.

[0064] The polypropylene powder suitable for this invention is commercially available or can be prepared by the methods described in Chinese patents CN109694427A, CN109694428A, CN104558813A, CN109912734A, CN111019025A, and CN105431459A.

[0065] The modified polypropylene grafted with alkenyl functional monomers of the present invention can be prepared by a method comprising the following steps: in the presence of an inert gas, a reaction mixture comprising polypropylene and alkenyl functional monomers is subjected to a grafting reaction, followed by washing with a washing solvent to obtain the polypropylene dielectric energy storage material.

[0066] The grafting reaction of this invention can be carried out with reference to various methods conventional in the art, preferably a suspension grafting reaction. For example, active grafting sites are formed on polypropylene in the presence of an alkenyl-containing functional monomer for grafting, or active grafting sites are first formed on polypropylene and then treated with a grafting monomer. Grafting sites can be formed by treatment with a free radical initiator, or by high-energy ionizing radiation or microwave treatment. Free radicals generated in the polymer as a result of chemical or radiation treatment form grafting sites on the polymer and initiate monomer polymerization at these sites.

[0067] Preferably, the grafting site is initiated by a free radical initiator and a grafting reaction is further carried out. In this case, the reaction mixture further includes a free radical initiator; more preferably, the free radical initiator is selected from peroxide free radical initiators and / or azo free radical initiators.

[0068] The peroxide radical initiator is preferably selected from at least one of benzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide, lauroyl peroxide, dodecyl peroxide, tert-butyl peroxide, diisopropyl peroxide, tert-butyl peroxide, and dicyclohexyl peroxide; the azo radical initiator is preferably azobisisobutyronitrile and / or azobisisoheptanenitrile.

[0069] More preferably, the grafting site is initiated by a peroxide-based free radical initiator and the grafting reaction is further carried out.

[0070] Furthermore, the grafting reaction of the present invention can also be carried out by the methods described in CN106543369A, CN104499281A, CN102108112A, CN109251270A, CN1884326A and CN101492517B.

[0071] Provided that the above-mentioned product characteristics are met, the present invention does not impose any particular limitation on the amount of each component used in the grafting reaction. Specifically, the mass ratio of the free radical initiator to the alkenyl-containing functional monomer can be 0.1 to 10:100, preferably 0.5 to 5:100. The mass ratio of the alkenyl-containing functional monomer to the polypropylene can be 0.5 to 25:100, preferably 1 to 20:100.

[0072] The present invention does not particularly limit the process conditions for the grafting reaction. Specifically, the temperature of the grafting reaction can be 30-110°C, preferably 60-95°C; the time can be 0.5-10h, preferably 1-6h.

[0073] In this invention, the "reaction mixture" includes all materials added to the grafting reaction system. The materials can be added all at once or at different stages of the reaction.

[0074] The reaction mixture of the present invention also includes deionized water as a dispersant. The amount of deionized water is 300-800% of the total mass of the polypropylene powder and the alkenyl-containing functional monomer.

[0075] The reaction mixture of the present invention may further include an organic solvent as a solvent for dissolving the solid free radical initiator. The organic solvent preferably includes at least one of C2-C5 alcohols, C2-C4 ethers, and C3-C5 ketones; more preferably, it includes at least one of C2-C4 alcohols, C2-C3 ethers, and C3-C5 ketones; and most preferably, it includes at least one of ethanol, diethyl ether, and acetone. The mass content of the organic solvent is preferably 1-35% of the mass of the polypropylene powder.

[0076] According to the present invention, the preparation method of the modified polypropylene grafted with the alkenyl functional monomer can be selected from one of the following methods:

[0077] Method 1, the preparation method includes the following steps:

[0078] a. Place the polypropylene powder in a closed reactor and replace it with an inert gas;

[0079] b. Add the free radical initiator and the alkenyl-containing functional monomer to the closed reactor and stir to mix;

[0080] c. Add deionized water to raise the temperature of the reaction system to the grafting reaction temperature and carry out the grafting reaction; optionally, allow the reaction system to swell before or after adding deionized water;

[0081] d. After the reaction is complete, filter and optionally dry to obtain powder;

[0082] e. The powder is washed with a washing solvent, filtered, and dried to obtain the modified polypropylene grafted with the alkenyl functional monomer.

[0083] Method 2, the preparation method includes the following steps:

[0084] a. Place the polypropylene powder in a closed reactor and replace it with an inert gas;

[0085] b. Mix the organic solvent and the free radical initiator, and add them to the closed reactor;

[0086] c. Remove the organic solvent, add an alkenyl-containing functional monomer, and optionally swell the reaction system;

[0087] d. Add deionized water to raise the temperature of the reaction system to the grafting reaction temperature and carry out the grafting reaction;

[0088] e. After the reaction is complete, the mixture is filtered and optionally dried to obtain a powder;

[0089] f. The powder is washed with a washing solvent, filtered, and dried to obtain the modified polypropylene grafted with the alkenyl functional monomer.

[0090] According to the method of the present invention, the polypropylene powder used can be commercially available as a product with a suitable particle size, or it can be purchased or made in-house and then screened. Therefore, the present invention may also include a step of screening pretreatment of the polypropylene powder. Screening can be achieved using conventional sieving methods. According to a preferred embodiment, the screening pretreatment includes the following steps: screening the powder using a double-layer vibrating screen or linear screen equipped with a screen of appropriate mesh size, and using the polypropylene powder in the middle layer of the screening machine as the reactant to obtain raw material powder with a corresponding particle size range.

[0091] According to a more specific embodiment of the present invention, the method for preparing the modified polypropylene grafted with the alkenyl functional monomer is selected from one of the following methods:

[0092] Method 1, the preparation method includes the following steps:

[0093] a. Use a double-layer vibrating screen or linear screen equipped with 16-mesh and 48-mesh screens to screen the powder, and use the polypropylene powder in the middle layer of the screening machine as the reaction material.

[0094] b. Place the polypropylene powder in the middle layer of the screening machine into a closed reactor for inert gas replacement;

[0095] c. Dissolve the free radical initiator in an alkenyl functional monomer to prepare a solution, add it to a closed reactor containing polypropylene, and stir to mix.

[0096] d. Add deionized water, heat the system to the graft polymerization temperature of 30-110°C, and react for 0.5-10 hours; optionally, allow the reaction system to swell before or after adding deionized water;

[0097] e. After the reaction is complete, the mixture is filtered and optionally dried to obtain a powder;

[0098] f. The powder is washed with a washing solvent at a temperature of 40–130°C for 0.5–10 h. After washing, it is filtered and dried to obtain the modified polypropylene grafted with the alkenyl functional monomer.

[0099] Method 2, the preparation method includes the following steps:

[0100] a. Use a double-layer vibrating screen or linear screen equipped with 16-mesh and 48-mesh screens to screen the powder, and use the polypropylene powder in the middle layer of the screening machine as the reaction material.

[0101] b. Place the polypropylene powder in the middle layer of the screening machine into a closed reactor for inert gas replacement;

[0102] c. Mix the organic solvent and the free radical initiator, and add them to the closed reactor;

[0103] d. Remove the organic solvent, add an alkenyl-containing functional monomer, and optionally swell the reaction system;

[0104] e. Add deionized water, heat the system to the graft polymerization temperature of 30-110℃, and react for 0.5-10 hours;

[0105] f. After the reaction is complete, filter and optionally dry to obtain powder;

[0106] g. The powder is washed with a washing solvent at a temperature of 40–130°C for 0.5–10 h. After washing, it is filtered and dried to obtain the modified polypropylene grafted with the alkenyl functional monomer.

[0107] The inert gas described in this invention can be any of the inert gases commonly used in the art, including but not limited to nitrogen and argon.

[0108] According to a preferred embodiment of the present invention, the washing solvent is selected from one or a mixture of two or more of n-hexane, cyclohexane, n-heptane, petroleum ether, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, acetone, methyl ethyl ketone, tetrahydrofuran, 2-methyltetrahydrofuran, benzene, toluene, and xylene. Preferably, the washing solvent is a mixture of solvent A and solvent B, wherein solvent A is selected from at least one of n-hexane, cyclohexane, n-heptane, petroleum ether, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, acetone, methyl ethyl ketone, tetrahydrofuran, and 2-methyltetrahydrofuran, and solvent B is at least one of toluene and xylene.

[0109] According to a preferred embodiment of the present invention, the mass of the washing solvent is 2 to 20 times the mass of the grafted polypropylene powder. As mentioned above, the washing temperature can be 40 to 130°C, preferably 55 to 100°C; the washing time can be 0.5 to 10 hours, preferably 1 to 8 hours.

[0110] The drying step after the reaction is preferably carried out. Both the drying step and the drying step after washing with the washing solvent are preferably carried out by vacuum drying, and the temperature can be 60-90°C.

[0111] According to some embodiments of the present invention, the antioxidant is selected from one or more of hindered phenols, hindered amines, phosphites, thiolated compounds, and benzofuranones. Based on 100 parts by weight of modified polypropylene, the content of the antioxidant can be 0.1 to 0.8 parts by weight, preferably 0.1 to 0.6 parts by weight.

[0112] The inventors of this invention discovered in their research that selecting appropriate antioxidant compound combinations and ratios can significantly improve the heat and oxygen aging resistance of modified polypropylene compositions and greatly extend the oxidation induction period, thereby resulting in film products with excellent thermal stability. Specifically, the antioxidant is obtained by compounding antioxidant component A and antioxidant component B. Antioxidant component A is selected from at least one of hindered phenols, hindered amines, phosphites, and thiolated compounds, and antioxidant component B is at least one benzofuranone. Preferably, the weight ratio of antioxidant component A to antioxidant component B is 1:0.01-0.03.

[0113] More specifically, the antioxidant component A is selected from at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010), tris[2,4-di-tert-butylphenyl] phosphite (antioxidant 168), octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (antioxidant 1076), 2,2'-thiobis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1035), 2,2'-methylenebis(4-methyl-6-tert-butylphenol) (antioxidant 2246), 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane (antioxidant CA), and bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite (antioxidant 626). The antioxidant component B is selected from at least one of 3-butyl-1(3-hydro)-isobenzofuranone (antioxidant 501), 5-methyl-7-tert-butyl-3-(3,4-dimethyl)-3-hydro-benzofuran-2-one, 5-methyl-7-tert-butyl-3-(2,5-dimethyl)-3-hydro-benzofuran-2-one, and 5-methyl-7-tert-butyl-3-(2-hydroxy-5-methyl)-3-hydro-benzofuran-2-one.

[0114] According to a specific embodiment of the present invention, the antioxidant is selected from a combination of antioxidant 1010 and / or antioxidant 168 and / or antioxidant 501. According to a preferred embodiment of the present invention, in the modified polypropylene composition, the content of the antioxidant is preferably 0.2 to 0.4 parts by weight per 100 parts by weight of the modified polypropylene composition.

[0115] According to the present invention, the processing aids include, but are not limited to, lubricants, acid absorbers, slip agents, antistatic agents, and anti-sticking agents. The amounts of each aid can be conventionally selected in the art, as those skilled in the art will know, and will not be elaborated upon here. The processing aids used will not adversely affect the stretching film-forming properties or mechanical properties of the modified polypropylene composition. Based on 100 parts by weight of modified polypropylene, the content of the processing aid can be 0.05 to 1 part by weight, preferably 0.05 to 0.5 parts by weight.

[0116] According to some embodiments of the present invention, the processing aid is a lubricant. The lubricant may be selected from one or more of the following: polyethylene glycol lubricants, fluoropolymer lubricants, silicone lubricants, fatty alcohol lubricants, fatty acid lubricants, fatty acid ester lubricants, stearamide lubricants, fatty acid metal soap lubricants, alkane and oxidized alkane lubricants, and micro / nano particle lubricants.

[0117] Specifically, the PEG-based lubricant can be, for example, a PEG molecule with a molecular weight of 500 to 50,000, which can be end-capped, grafted, cross-linked, or subjected to other chemical or physical modifications. The fluoropolymer lubricant can be, for example, at least one of polytetrafluoroethylene, polyvinylidene fluoride, and polyhexafluoropropylene, or other unimodal or multimodal fluoropolymers, as well as crystalline or semi-crystalline fluoropolymers. The silicone lubricant can be any existing compound with carbon or silicon atoms as the main molecular chain and oligomers or oligomers with organic groups such as methyl, phenyl, alkoxy, and vinyl as side chains. The fatty alcohol lubricant can be, for example, at least one of soft fatty alcohol, stearic alcohol, and tallow fatty alcohol. The fatty acid lubricant can be, for example, stearic acid and / or 12-hydroxystearic acid. The fatty acid ester lubricant can be, for example, at least one of butyl stearate, glyceryl monostearate, hexadecyl palmitate, and octadecyl stearate. The stearamide lubricant may be at least one of stearamide, oleamide, erucamide, n,n-ethylene bis-stearamide (EBS), etc. The fatty acid metal soap lubricant may be at least one of lead stearate, calcium stearate, magnesium stearate, synthetic calcium acetate, etc. The alkane and alkane oxide lubricant may be at least one of liquid paraffin, solid paraffin, polyethylene wax, polypropylene wax, ethylene oxide wax, etc. The micro / nano particle lubricant may be, for example, powdered rubber and / or silica gel microparticles.

[0118] According to a specific embodiment of the present invention, the processing aid is a fluoropolymer.

[0119] All of the above processing aids are commercially available.

[0120] The modified polypropylene composition of the present invention is prepared by mixing the components.

[0121] The present invention also provides a biaxially oriented polypropylene film, which is prepared from the above-described modified polypropylene composition.

[0122] The method for forming polymer films from the modified polypropylene composition granules of the present invention can be carried out with reference to the prior art. For example, the granules can be processed by hot pressing or extrusion casting, or by biaxial stretching, to form a film.

[0123] According to a specific embodiment of the present invention, the biaxially oriented polypropylene film is prepared by a method comprising the following steps:

[0124] (1) The modified polypropylene composition is mixed and granulated;

[0125] (2) The obtained granules are melt-extruded and cast into sheets to obtain modified polypropylene sheets;

[0126] (3) The modified polypropylene casting is biaxially stretched to obtain the biaxially stretched polypropylene film.

[0127] The process of mixing and extruding the modified polypropylene with antioxidants and processing aids in step (1) typically includes: mixing the modified polypropylene composition evenly in a high-speed mixer; adding the evenly mixed material to a twin-screw extruder or a single-screw extruder for melt mixing and uniform extrusion granulation; and drying to obtain granules. The processing temperature of the twin-screw extruder can be controlled between 190 and 230°C.

[0128] According to the present invention, the temperature of the melt extrusion in step (2) is 190-230°C; the temperature of the casting quench roll of the cast sheet is 15-50°C. The modified polypropylene cast sheet may be a single-layer structure or a multi-layer structure.

[0129] According to the present invention, preferably, the longitudinal tensile strength of the biaxially oriented polypropylene film is ≥140 MPa, more preferably 140-170 MPa; the transverse tensile strength is ≥200 MPa, more preferably 205-250 MPa; the longitudinal elongation at break is ≥210%, more preferably ≥225%; the transverse elongation at break is ≥60%, more preferably ≥62%; the oxidation induction period is ≥5 min, more preferably ≥10 min; and the thickness is 0.5-15 micrometers, more preferably 4-10 micrometers.

[0130] The biaxially oriented polypropylene film of this invention can be used as an energy storage dielectric, and is particularly suitable as a high-temperature energy storage dielectric due to its high operating temperature. The dielectric is preferably a membrane dielectric, which can be single-layer or multi-layered, including but not limited to capacitor films, roughened films, supercapacitor films, electrostatic films, or battery separators. The biaxially oriented polypropylene film of this invention is particularly suitable for preparing films for use in membrane capacitors, and can be directly applied as a polypropylene capacitor film, or used to prepare polypropylene capacitor films.

[0131] The capacitor film, also known as an electrical film or capacitor film, refers to capacitor films, electrical films, etc., used in the electrical field. Its specific definition is well known to those in the industry.

[0132] Specifically, the present invention provides a polypropylene capacitor film, which may be one or more layers, and at least one layer of the polypropylene capacitor film is the aforementioned biaxially oriented polypropylene film.

[0133] The preparation of polypropylene capacitor film specifically includes: adding the modified polypropylene composition granules obtained in step (1) into a casting equipment for extrusion casting, and then stretching the resulting casting in a film biaxial stretching equipment. During the extrusion casting process, the casting die can be selected according to the desired film structure. For example, when a film with a single-layer structure is required, a single-layer die can be used; when a film with a multi-layer structure is required (e.g., a film with a three-layer structure of upper surface layer, core layer, and lower surface layer), a multi-layer composite die can be used, and at least one layer (e.g., the core layer) of the multi-layer composite die is connected to the extruder hopper containing the modified polypropylene composition, so that at least one layer (e.g., the core layer) of the resulting film is a modified polypropylene layer formed by the modified polypropylene composition. During the extrusion process, the extrusion temperature can be 100-200℃, and the temperature of the casting quenching roller can be 15-50℃.

[0134] In this invention, the biaxial stretching includes simultaneous stretching (i.e., simultaneous longitudinal (MD) and transverse (TD) stretching of the film) or step-by-step stretching (i.e., first longitudinal stretching of the film, then transverse stretching of the film).

[0135] The simultaneous stretching method includes: first, preheating the modified polypropylene composition casting sheet at a temperature of 120–170°C, and then simultaneously performing MD and TD stretching; the conditions for the simultaneous stretching method include: stretching temperature of 150–175°C, MD stretching ratio of more than 3 times, TD stretching ratio of more than 3 times, MD stretching rate of 50–300% / s, and TD stretching rate of 50–300% / s.

[0136] The stepwise stretching method includes: first preheating the modified polypropylene composition casting sheet, then performing MD stretching, then preheating again and then performing TD stretching; the conditions for the stepwise stretching method include: MD stretching temperature of 150-170℃, TD stretching temperature of 155-175℃, MD stretching ratio of 3 times or more, TD stretching ratio of 5 times or more, MD stretching rate of 50-300% / s, and TD stretching rate of 50-300% / s.

[0137] According to the present invention, the method may or may not involve annealing and setting the stretched film. Preferably, the method includes annealing and setting the stretched film, wherein, when setting is performed, the annealing and setting temperature is preferably 160–180°C. The annealing and setting time is preferably 5–60 seconds. This annealing and setting treatment of the stretched film can improve the dimensional stability of the film.

[0138] According to the present invention, the method may further include subjecting the obtained polypropylene film to surface corona treatment, edge trimming, and winding, which are conventional operations in the art and are not particularly limited thereto.

[0139] The present invention will be further described below with reference to the embodiments, but the scope of the present invention is not limited to these embodiments.

[0140] In the following examples and comparative examples:

[0141] The film casting equipment was purchased from Labtech GmbH in Sweden, model LCR400.

[0142] The biaxial stretching equipment for thin films was purchased from Brückner GmbH, Germany, model Karo IV.

[0143] The properties of the modified polypropylene composition and the film were tested according to the following methods, and the film test results are shown in Tables 2 and 3.

[0144] 1. Ash content determination of polypropylene / polypropylene dielectric energy storage materials:

[0145] The determination shall be carried out in accordance with the method specified in GB / T 9345.1-2008.

[0146] 2. Isotacticity determination of polypropylene:

[0147] The determination shall be carried out in accordance with the method specified in GB / T 2412-2008.

[0148] 3. Determination of Melt Flow Rate (MFR):

[0149] The MFR of polypropylene / polypropylene dielectric energy storage materials was determined using a CEAST 7026 melt flow indexer at 230°C and a load of 2.16 kg, according to the method specified in GB / T 3682-2018.

[0150] 4. Melting temperature T m Measurement:

[0151] Differential scanning calorimetry (DSC) was used to analyze the melting and crystallization processes of polypropylene / polypropylene dielectric energy storage materials. The specific procedure was as follows: Under nitrogen protection, 5 mg of sample was placed in a crucible, and the temperature was increased from 20 °C to 200 °C at a rate of 10 °C / min, held for 5 min to eliminate thermal history, then decreased to 20 °C at a rate of 10 °C / min, held for 1 min, and finally increased to 200 °C at a rate of 10 °C / min. The scanning data from the third heating was recorded, and the melting temperature Tm was calculated according to GB / T 19466.3-2004.

[0152] 5. Determination of parameter η:

[0153] Boil 1-2g of the grafted product under reflux in an appropriate amount of xylene until the particles are completely dissolved. While still hot, pour the xylene solution into 6 times its volume of organic solvent (ethyl acetate or acetone) to precipitate. Let the mixture stand for 1 hour until all insoluble matter precipitates out. Filter the mixture using a vacuum funnel. The filtered insoluble matter is the pure grafted product, which is then dried and weighed. The ratio of the grafted portion to the self-polymerized portion of the functional monomer structural unit is:

[0154]

[0155] In the formula, w0 is the mass of ungrafted polypropylene, w1 is the mass of the grafted product, and w2 is the mass of the insoluble matter.

[0156] 6. Determination of flexural modulus:

[0157] The determination shall be carried out in accordance with the method specified in GB / T 9341-2008.

[0158] 7. Determination of DC volume resistivity:

[0159] The determination was carried out according to the method specified in GB / T 13542.2-2009. The test method was the contact electrode method, and the electrode material was conductive rubber.

[0160] 8. Determination of breakdown field strength:

[0161] The determination was carried out according to the method specified in GB / T 13542.2-2009, and the test method was the 50-point electrode method.

[0162] 9. Measurement of energy storage density and energy storage efficiency:

[0163] The determination should be performed according to the methods specified in the following literature.

[0164] Yuan,C.,Zhou,Y.,Zhu,Y.et al.Polymer / molecular semiconductor all-organic composites for high-temperature dielectric energystorage.Nat.Commun.11,3919(2020).

[0165] 10. Determination of dielectric constant and dielectric loss factor:

[0166] The determination should be performed according to the methods specified in the following literature.

[0167] Yuan,C.,Zhou,Y.,Zhu,Y.et al.Polymer / molecular semiconductor all-organic composites for high-temperature dielectric energystorage.Nat.Commun.11,3919(2020).

[0168] 11. Thickness of the capacitor film:

[0169] The determination was carried out according to the method specified in GB / T 13542.3-2006, and the measurement method was the micrometer method.

[0170] 12. Measurement of TSDC:

[0171] The determination should be performed according to the methods specified in the following literature.

[0172] Tian Fuqiang,Bu Wenbin, Shi Linshuang,et al.Theory of modifiedthermally stimulated current and direct determination of trap leveldistribution[J].Journal of Electrostatics,2011,69(1):7-10.

[0173] The material was pressed into a thin film with an average thickness of 50 μm, and a circular gold electrode with a diameter of 20 mm was sputtered onto the surface. During testing, the material was first polarized at a specific polarization temperature with a DC field strength of 20 kV / mm for 30 min, then the electric field was maintained while the temperature was rapidly reduced to -100 °C. The electric field was then removed for 15 min to eliminate any unfrozen trapped charges. The temperature was then linearly increased from -100 °C to 150 °C at a rate of 3 °C / min, while simultaneously measuring the temperature-depolarization current curve.

[0174] 13. Determination of tensile strength and elongation at break of thin films:

[0175] The determination shall be carried out in accordance with the method specified in GB / T 13542.2-2009.

[0176] 14. Determination of Oxidation Induction Period (OIT):

[0177] The oxidation induction period was determined according to the method specified in GB / T19466.6-2009.

[0178] The raw materials used in the examples are described in Tables A and B below.

[0179] Table A

[0180]

[0181]

[0182] *PP1: Polypropylene used in Examples 1, 3 and Comparative Example 1.

[0183] *PP2: Polypropylene used in Examples 2 and 4.

[0184] Properties of the powders used in the examples in Table B

[0185]

[0186] In all embodiments, the polypropylene powder used was sieved using a vibrating screen equipped with 16-mesh and 48-mesh sieves before the grafting reaction.

[0187] Example 1

[0188] (1) Preparation of modified polypropylene

[0189] 5.0 kg of PP1 powder, sieved through a sieve, was added to a 50 L reactor equipped with a double-layer four-bladed agitator and baffles. The reaction system was sealed, and nitrogen was used for purging to remove oxygen. A homogeneous solution of 7.2 g of tert-butyl peroxide (2-ethylhexanoate) and 400 g of styrene was added to the reactor and stirred for 30 minutes. Then, 17.8 kg of deoxygenated deionized water was added, and the mixture was heated to 50 °C for 2 hours to allow swelling. The swollen powder was then heated to 95 °C and reacted for 4 hours. After the reaction, the mixture was cooled, the liquid components were filtered off, and the product was vacuum dried at 70 °C for 10 hours to obtain polypropylene-g-styrene powder C1.

[0190] Weigh 1.5 kg of the above-mentioned polypropylene-g-styrene powder C1, add 3 kg of xylene and 20 kg of tetrahydrofuran, seal the reaction system, and heat to 70°C while stirring and washing for 5 hours. After stirring, filter out the liquid phase, and vacuum dry the product at 70°C for 10 hours to obtain polypropylene-g-styrene powder B1.

[0191] (2) Preparation of modified polypropylene composition

[0192] Weigh the above-mentioned polypropylene-g-styrene powder (C1 or B1), antioxidant 1010 / 168 / 501 (weight ratio 1:1:0.03), and processing aids, and place them in a high-speed mixer. Mix at high speed for 30 seconds. Granulate using a Coperion WP25 twin-screw extruder. During processing, the twin-screw zone temperature is 190-200-210-220-230-230-210℃, and the screw speed is 300 rpm. Based on 100 parts by weight of modified polypropylene, the total amount of antioxidant is 0.3 parts by weight, and the amount of fluoropolymer processing aid is 0.1 parts by weight.

[0193] (3) Preparation of polypropylene capacitor film

[0194] The modified polypropylene composition granules obtained in step (2) were added to a hot air oven for drying, and the dried polypropylene composition granules were added to an LCR400 extrusion casting machine purchased from Labtech, Sweden for melt extrusion and casting. The temperature of the melt extrusion extruder was 230°C, the temperature of the screen changing zone was controlled at 230°C, the temperature of the die head was controlled at 230°C, and the temperature of the casting roller was controlled at 25°C to produce a thick cast sheet of modified polypropylene composition.

[0195] The modified polypropylene composition was cast into a thick sheet and placed in the stretching fixture of a biaxial stretching apparatus. A biaxial step-by-step stretching process was employed, involving longitudinal (MD) stretching followed by transverse (TD) stretching. The process conditions for each step are shown in Table 1: MD preheating temperature was 155℃, MD stretching temperature was 155℃, MD stretching ratio was 5 times, and MD stretching rate was 200% / s; TD preheating temperature was 170℃, TD stretching temperature was 170℃, TD stretching ratio was 7 times, and film TD stretching rate was 300% / s; the film setting temperature was 175℃. Biaxially stretched polypropylene capacitor films MC1 and MB1 were obtained.

[0196] The obtained capacitor film was subjected to performance tests such as tensile properties and electrical properties. The performance parameters of the biaxially oriented polypropylene capacitor film are shown in Tables 2 and 3.

[0197] Example 2

[0198] (1) Preparation of modified polypropylene

[0199] 3.0 kg of PP2 powder, sieved through a sieve, was added to a 50 L reactor equipped with a double-layer four-bladed agitator and baffles. The reaction system was sealed, and nitrogen was used for purging to remove oxygen. A homogeneous solution of 8.2 g of tert-butyl peroxide (2-ethylhexanoate), 63 g of styrene, and 470 g of methyl methacrylate was added to the reactor and mixed with the powder. The mixture was then heated to 60 °C for 2 hours to allow swelling. Next, 18.1 kg of deoxygenated and preheated deionized water (to 60 °C) was added through a feed tank, and the reactor was heated to 90 °C and reacted for 6 hours. After the reaction, the mixture was cooled and the liquid components were filtered off. 23 kg of acetone and 2 kg of n-heptane were added, and the mixture was heated to 55 °C and stirred for 3 hours. After stirring, the liquid phase was filtered off, and the product was vacuum dried at 70 °C for 10 hours to obtain polypropylene-g-methyl methacrylate / styrene powder B2.

[0200] (2) Preparation of modified polypropylene composition

[0201] The above-mentioned polypropylene-g-methyl methacrylate / styrene powder, antioxidants 1035 / 168 / 501 (weight ratio 1:1:0.03), and processing aids were placed in a high-speed mixer and stirred at high speed for 30 seconds. Granulation was then performed using a Coperion WP25 twin-screw extruder. During processing, the twin-screw zone temperature was 190-200-210-220-230-230-210℃, and the screw speed was 300 rpm. Based on 100 parts by weight of modified polypropylene, the total amount of antioxidants was 0.5 parts by weight, and the amount of fluoropolymer processing aids was 0.2 parts by weight.

[0202] (3) Preparation of polypropylene capacitor film

[0203] The preparation method of the thin film is the same as in Example 1, except that the biaxial stretching process conditions are different, as shown in Table 1. The performance parameters of the obtained polypropylene capacitor film MB2 are shown in Tables 2 and 3.

[0204] Example 3

[0205] (1) Preparation of modified polypropylene

[0206] 5.0 kg of PP1 powder, sieved through a sieve, was added to a 50 L reactor equipped with a double-layer four-bladed agitator and baffles. The reaction system was sealed, and nitrogen was used for purging to remove oxygen. A homogeneous solution of 2.5 g benzoyl peroxide and 250.5 g methyl methacrylate was added to the reactor and stirred for 30 min. Then, 26.3 kg of deoxygenated deionized water was added. The reactor was heated to 91 °C and reacted for 3 hours. After the reaction, the mixture was cooled, the liquid components were filtered off, and the product was vacuum dried at 70 °C for 10 hours to obtain polypropylene-g-methyl methacrylate powder C3.

[0207] Weigh 3 kg of the above-mentioned polypropylene-g-methyl methacrylate powder C3, add 10 kg of xylene and 20 kg of ethyl acetate, seal the reaction system, and heat to 70°C with stirring and washing for 7 hours. After stirring, filter out the liquid phase, and vacuum dry the product at 70°C for 10 hours to obtain 3.103 kg of polypropylene-g-methyl methacrylate powder B3. The TSDC determination results are as follows. Figure 1 As shown.

[0208] (2) Preparation of modified polypropylene composition

[0209] The above-mentioned polypropylene-g-methyl methacrylate powder (C3 or B3), antioxidant 1076 / 168 / 501 (weight ratio 1:1:0.04), and fluoropolymer were placed in a high-speed mixer and stirred at high speed for 30 seconds. Granulation was then performed using a Coperion WP25 twin-screw extruder. During processing, the twin-screw zone temperature was 190-200-210-220-230-230-210℃, and the screw speed was 300 rpm. Based on 100 parts by weight of modified polypropylene, the total amount of antioxidant was 0.3 parts by weight, and the amount of fluoropolymer was 0.1 parts by weight.

[0210] (3) Preparation of polypropylene capacitor film

[0211] The preparation method of the thin film is the same as in Example 1, except that the biaxial stretching process conditions are different, as shown in Table 1. The performance parameters of the obtained polypropylene capacitor films MC3 and MB3 are shown in Tables 2 and 3.

[0212] Example 4

[0213] (1) Preparation of modified polypropylene

[0214] 1.5 kg of PP2 powder, sieved from the middle layer of a sieve, was added to a 50 L reactor equipped with a double-layer four-bladed agitator and baffles. The reaction system was sealed, and nitrogen was used for purging to remove oxygen. A homogeneous solution of 1.9 g benzoyl peroxide, 59.7 g styrene, and 15.6 g maleic anhydride was prepared and added to the reactor along with the powder. The mixture was stirred and allowed to swell at room temperature for 6 hours, then heated to 90 °C. 7.0 kg of deionized water, preheated to 90 °C and deoxygenated, was then added through a feed tank, and the reaction was continued for 4 hours. After the reaction, the mixture was cooled and the liquid component was filtered off. 25 kg of acetone was added, and the mixture was heated to 55 °C and stirred for 5 hours. After stirring, the liquid phase was filtered off, and the product was vacuum dried at 70 °C for 10 hours to obtain polypropylene-g-maleic anhydride / styrene powder B4.

[0215] (2) Preparation of modified polypropylene composition

[0216] The above-mentioned polypropylene-g-maleic anhydride / styrene powder, antioxidant 1010 / 168 / 501 (weight ratio 1:1:0.05), and fluoropolymer were placed in a high-speed mixer and stirred at high speed for 30 seconds. Granulation was then performed using a Coperon WP25 twin-screw extruder. During processing, the twin-screw zone temperature was 190-200-210-220-230-230-210℃, and the screw speed was 300 rpm. Based on 100 parts by weight of modified polypropylene, the total amount of antioxidant was 0.3 parts by weight, and the amount of fluoropolymer was 0.1 parts by weight.

[0217] (3) Preparation of polypropylene capacitor film

[0218] The preparation method of the thin film is the same as in Example 1, except that the biaxial stretching process conditions are different, as shown in Table 1. The performance parameters of the obtained polypropylene capacitor film MB4 are shown in Tables 2 and 3.

[0219] Comparative Example 1

[0220] (1) Preparation of modified polypropylene

[0221] 5.0 kg of PP1 powder, sieved from the middle layer of a sieve, was added to a 50 L reactor equipped with a double-layer four-bladed agitator and baffles. The reaction system was sealed, and nitrogen was used for purging to remove oxygen. A homogeneous solution of 2.0 g benzoyl peroxide and 188.2 g methyl methacrylate was prepared and added to the reactor, where it was stirred and mixed with the powder for 30 min. Then, 25.9 kg of deoxygenated deionized water was added. The reactor was heated to 90 °C and reacted for 3 hours. After the reaction, the mixture was cooled, the liquid components were filtered off, and the product was vacuum dried at 70 °C for 10 hours to obtain 5.168 kg of polypropylene-g-methyl methacrylate powder D1. The TSDC determination results are as follows: Figure 1 As shown.

[0222] (2) Preparation of modified polypropylene composition

[0223] The above-mentioned polypropylene-g-methyl methacrylate powder, antioxidants 1076 / 168 / 501 (weight ratio 1:1:0.04), and fluoropolymer were placed in a high-speed mixer and stirred at high speed for 30 seconds. Granulation was then performed using a Coperion WP25 twin-screw extruder. During processing, the twin-screw zone temperature was 190-200-210-220-230-230-210℃, and the screw speed was 300 rpm. Based on 100 parts by weight of modified polypropylene, the total amount of antioxidant was 0.3 parts by weight, and the amount of fluoropolymer was 0.1 parts by weight.

[0224] (3) Preparation of polypropylene capacitor film

[0225] The preparation method of the thin film is the same as in Example 1. The performance parameters of the obtained polypropylene capacitor film MD1 are shown in Tables 2 and 3.

[0226]

[0227]

[0228] By comparing MB1 and MC1, and MB3 and MC3, it can be seen that using solvent washing process to reduce the influence of self-polymers can effectively improve the dielectric properties of the materials (significantly increasing DC volume resistivity).

[0229] The final products of MB3 and MD1 contain the same total amount of grafted monomers. By comparing MB3 and MD1 and measuring with TSDC, it can be seen that, under the same total content of grafted monomers, MB3, which has a higher grafting / self-polymerization ratio η, has a significantly changed grafted phase composition, thereby generating different charge traps, which can ultimately effectively improve the dielectric properties of the material.

[0230] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

[0231] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

Claims

1. A modified polypropylene composition comprising modified polypropylene grafted with an alkenyl functional monomer, an antioxidant, and a processing aid; The modified polypropylene grafted with alkenyl functional monomers comprises structural units derived from polypropylene as the matrix phase and structural units derived from alkenyl functional monomers as the dispersed phase; the ash content of the modified polypropylene grafted with alkenyl functional monomers is less than 50 ppm; the mass ratio of structural units derived from alkenyl functional monomers and in the grafted state to structural units derived from alkenyl functional monomers and in the self-polymerized state in the modified polypropylene grafted with alkenyl functional monomers is greater than or equal to 1.5; the DC volume resistivity of the modified polypropylene grafted with alkenyl functional monomers at 120 ℃ and 200 MV / m is 1.5 × 10⁻⁶. 14 Ω m ~ 0.9 × 10 20 Ω m.

2. The modified polypropylene composition according to claim 1, wherein, The ash content of the modified polypropylene grafted with the alkenyl functional monomer is less than 36 ppm.

3. The modified polypropylene composition according to claim 2, wherein, The ash content of the modified polypropylene grafted with the alkenyl functional monomer is less than 30 ppm.

4. The modified polypropylene composition according to claim 1, wherein, In the modified polypropylene grafted with alkenyl functional monomers, the mass ratio of structural units derived from alkenyl functional monomers and in the grafted state to structural units derived from alkenyl functional monomers and in the self-polymerized state is greater than or equal to 2.

5. The modified polypropylene composition according to claim 1, wherein, The modified polypropylene grafted with the alkenyl functional monomer has at least one of the following characteristics: a melt flow rate of 1~10 g / 10min at 230 °C and 2.16 kg load; and a melting temperature T. m Temperature range: 155~168 ℃; flexural modulus range: 1400~2000 MPa.

6. The modified polypropylene composition according to claim 5, wherein, The modified polypropylene grafted with the alkenyl functional monomer had a melt flow rate of 1.5~8 g / 10min at 230 °C and 2.16 kg load.

7. The modified polypropylene composition according to claim 6, wherein, The modified polypropylene grafted with the alkenyl functional monomer had a melt flow rate of 2~5 g / 10min at 230 °C and 2.16 kg load.

8. The modified polypropylene composition according to claim 5, wherein, The melting temperature T of the modified polypropylene grafted with the alkenyl functional monomer is... m The temperature ranges from 157 to 165 degrees Celsius.

9. The modified polypropylene composition according to claim 5, wherein, The flexural modulus of the modified polypropylene grafted with the alkenyl functional monomer is 1500~1800 MPa.

10. The modified polypropylene composition according to claim 1, wherein, The modified polypropylene grafted with alkenyl functional monomers has at least one of the following characteristics: - Maximum operating temperature ≥100 ℃; Breakdown field strength E at -120 ℃ g ≥500 MV / m; The DC volume resistivity at -120 ℃ and a field strength of 200 MV / m is 2.0 × 10⁻⁶. 14 Ω m~1.0×10 17 Ω m; The dielectric constant at -120 ℃ and 100 Hz is greater than 2.25; The dielectric loss at -120 ℃ and 100 Hz is less than 1.0E-3; The energy storage density at -120 ℃ and 300 MV / m is greater than 0.780 J / cm³. 3 ; The energy storage efficiency at -120 ℃ and 300 MV / m is greater than 90.0%.

11. The modified polypropylene composition according to claim 10, wherein, The maximum operating temperature of the modified polypropylene grafted with the alkenyl functional monomer is 110~160 ℃.

12. The modified polypropylene composition according to claim 11, wherein, The maximum operating temperature of the modified polypropylene grafted with the alkenyl functional monomer is 120~145 ℃.

13. The modified polypropylene composition according to claim 10, wherein, The breakdown field strength E of the modified polypropylene grafted with the alkenyl functional monomer at 120 °C g It ranges from 550 to 800 MV / m.

14. The modified polypropylene composition according to claim 10, wherein, The dielectric constant of the modified polypropylene grafted with the alkenyl functional monomer is 2.26~2.65 at 120 °C and 100 Hz.

15. The modified polypropylene composition according to claim 10, wherein, The dielectric loss of the modified polypropylene grafted with the alkenyl functional monomer at 120 °C and 100 Hz is 1.0E-6 to 9E-4.

16. The modified polypropylene composition according to claim 10, wherein, The modified polypropylene grafted with the alkenyl functional monomer has a storage density of 0.80~2.0 J / cm³ at 120 °C and 300 MV / m. 3 .

17. The modified polypropylene composition according to claim 10, wherein, The modified polypropylene grafted with the alkenyl functional monomer has an energy storage efficiency of 92.0 ~ 99.0% at 120 °C and 300 MV / m.

18. The modified polypropylene composition according to claim 1, wherein, The alkenyl-containing functional monomer is selected from at least one monomer having the structure shown in Formula 1. Formula 1 In Equation 1, R b R c R d Each is independently selected from H, substituted or unsubstituted alkyl groups; R a Selected from substituted or unsubstituted alkyl groups, substituted or unsubstituted alkoxy groups, substituted or unsubstituted aryl groups, substituted or unsubstituted ester groups, substituted or unsubstituted carboxyl groups, substituted or unsubstituted cycloalkyl or heterocyclic groups, cyano groups, and substituted or unsubstituted silyl groups; R a and R d Arrange the rings arbitrarily.

19. The modified polypropylene composition according to claim 18, wherein, R b R c R d Each is independently selected from H, substituted or unsubstituted C1-C6 alkyl groups; R a Selected from substituted or unsubstituted C1-C 20 Alkyl, substituted or unsubstituted C1-C 20 Alkoxy, substituted or unsubstituted C6-C 20 aryl, substituted or unsubstituted C1-C 20 Ester group, substituted or unsubstituted C1-C 20 Carboxyl, substituted or unsubstituted C3-C 20 Cycloalkyl or heterocyclic, cyano, substituted or unsubstituted C3-C 20 Silyl group; the substituted group is halogen, -OH, -NH2, =O, C1-C 12 Alkyl, C3-C6 cycloalkyl, C1-C 12 alkoxy groups, C1-C 12 Acyloxy group; R a and R d Optionally, it can form a 4-6 membered heterocycle with a double bond.

20. The modified polypropylene composition according to claim 19, wherein, R b R c R d Each is independently selected from H, substituted or unsubstituted C1-C6 alkyl groups; R a Selected from the groups shown in Formula 2, Formula 3, Formula 4, Formula 5, Formula 6, combinations of the groups shown in Formula 6 and Formula 7, and heterocyclic groups; Formula 2 In Equation 2, R 4 -R 8 Each is independently selected from H, halogen, hydroxyl, amino, phosphate group, sulfonic acid group, substituted or unsubstituted C1-C. 12 Alkyl, substituted or unsubstituted C3-C 12 cycloalkyl, substituted or unsubstituted C1-C 12 alkoxy, substituted or unsubstituted C1-C 12 ester group, substituted or unsubstituted C1-C 12 The substituted amino group, wherein the substituted group is selected from halogen, hydroxyl, amino, phosphate, sulfonic acid, C1-C 12 Alkyl, C3-C 12 cycloalkyl, C1-C 12 alkoxy groups, C1-C 12 ester group, C1-C 12 The amino group; Formula 3 In Equation 3, R4-R 10 Each is independently selected from H, halogen, hydroxyl, amino, phosphate group, sulfonic acid group, substituted or unsubstituted C1-C. 12 Alkyl, substituted or unsubstituted C3-C 12 cycloalkyl, substituted or unsubstituted C1-C 12 alkoxy, substituted or unsubstituted C1-C 12 ester group, substituted or unsubstituted C1-C 12 The substituted amino group, wherein the substituted group is selected from halogen, hydroxyl, amino, phosphate, sulfonic acid, C1-C 12 Alkyl, C3-C 12 cycloalkyl, C1-C 12 alkoxy groups, C1-C 12 ester group, C1-C 12 The amino group; Formula 4 In Equation 4, R4'-R 10 Each group is independently selected from H, halogen, hydroxyl, amino, phosphate, sulfonic acid, substituted or unsubstituted C1-C. 12 Alkyl, substituted or unsubstituted C3-C 12 cycloalkyl, substituted or unsubstituted C1-C 12 alkoxy, substituted or unsubstituted C1-C 12 ester group, substituted or unsubstituted C1-C 12 The substituted amino group, wherein the substituted group is selected from halogen, hydroxyl, amino, phosphate, sulfonic acid, C1-C 12 Alkyl, C3-C 12 cycloalkyl, C1-C 12 alkoxy groups, C1-C 12 ester group, C1-C 12 The amino group; Formula 5 In Equation 5, R', R'', and R''' are each independently selected from substituted or unsubstituted C1-C. 12 Straight-chain alkyl, substituted or unsubstituted C3-C 12 Branched alkyl, substituted or unsubstituted C1-C 12 alkoxy, substituted or unsubstituted C1-C 12 Acyloxy group; Formula 6 Formula 7 In Equation 6, R m Selected from the following groups, substituted or unsubstituted: C1-C 20 Straight-chain alkyl, C3-C 20 Branched alkyl, C3-C 12 cycloalkyl, C3-C 12 Epoxyalkyl, C3-C 12 Epoxyalkylalkyl, wherein the substituted group is selected from at least one of halogen, amino and hydroxyl groups; The heterocyclic group is selected from imidazole, pyrazol, carbazole, pyrrolidone, pyridinyl, piperidinyl, caprolactam, pyrazinyl, thiazolyl, purine, morpholino, and oxazolino.

21. The modified polypropylene composition according to claim 20, wherein, In Equation 2, R 4 -R 8 Each is independently selected from H, halogen, hydroxyl, amino, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy.

22. The modified polypropylene composition according to claim 20, wherein, In Equation 3, R4-R 10 Each of the groups is independently selected from H, halogen, hydroxyl, amino, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy, wherein the substituted group is selected from halogen, hydroxyl, amino, C1-C6 alkyl, C1-C6 alkoxy.

23. The modified polypropylene composition according to claim 20, wherein, In Equation 4, R4'-R 10 Each of the groups is independently selected from H, halogen, hydroxyl, amino, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy, wherein the substituted group is selected from halogen, hydroxyl, amino, C1-C6 alkyl, C1-C6 alkoxy.

24. The modified polypropylene composition according to claim 20, wherein, In Formula 5, R', R'', and R''' are each independently selected from substituted or unsubstituted C1-C6 straight-chain alkyl, substituted or unsubstituted C3-C6 branched alkyl, substituted or unsubstituted C1-C6 alkoxy, and substituted or unsubstituted C1-C6 acyloxy.

25. The modified polypropylene composition according to claim 20, wherein, The alkenyl-containing functional monomer is a styrene monomer, which is selected from at least one of styrene, α-methylstyrene, 1-vinylnaphthalene, 2-vinylnaphthalene, monosubstituted or polysubstituted styrene, monosubstituted or polysubstituted α-methylstyrene, monosubstituted or polysubstituted 1-vinylnaphthalene, and monosubstituted or polysubstituted 2-vinylnaphthalene.

26. The modified polypropylene composition according to claim 25, wherein, The substituted group is selected from at least one of halogen, hydroxyl, amino, phosphate, sulfonic acid, C1-C8 straight-chain alkyl, C3-C8 branched alkyl or cycloalkyl, C1-C6 straight-chain alkoxy, C3-C8 branched alkoxy or cycloalkoxy, C1-C8 straight-chain ester, C3-C8 branched ester or cycloester, C1-C8 straight-chain amino, and C3-C8 branched amino or cycloamino.

27. The modified polypropylene composition according to claim 25, wherein, The styrene monomer is selected from at least one of styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, and 4-methylstyrene.

28. The modified polypropylene composition according to claim 20, wherein, The alkenyl-containing functional monomer is an alkenyl-containing silane monomer, which is selected from at least one of vinyltriethoxysilane, vinyltrimethoxysilane, vinyltriisopropoxysilane, vinyltritert-butoxysilane, vinyltriacetoxysilane, methylvinyldimethoxysilane, ethylvinyldiethoxysilane, allyltriethoxysilane, allyltrimethoxysilane, allyltriisopropoxysilane, vinyltri(β-methoxyethoxy)silane, allyltri(β-methoxyethoxy)silane, allyltritert-butoxysilane, allyltriacetoxysilane, methylallyldimethoxysilane, and ethylallyldiethoxysilane.

29. The modified polypropylene composition according to claim 20, wherein, The alkenyl-containing functional monomer is an acrylate monomer and / or an acrylic monomer.

30. The modified polypropylene composition according to claim 29, wherein, The acrylate monomers are selected from at least one of methyl methacrylate, sec-butyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, isooctyl methacrylate, dodecyl methacrylate, coconut oil ester methacrylate, octadecyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminopropyl methacrylate, and glycidyl methacrylate; the acrylic monomers are selected from at least one of acrylic acid, methacrylic acid, and 2-ethylacrylic acid.

31. The modified polypropylene composition according to claim 18, wherein, The alkenyl-containing functional monomer is at least one of maleic anhydride, maleimide and its derivatives, itaconic anhydride, and α-methylene-γ-butyrolactone.

32. The modified polypropylene composition according to claim 31, wherein, The alkenyl-containing functional monomer is maleic anhydride.

33. The modified polypropylene composition according to claim 1, wherein, The polypropylene has a particle size of 16-50 mesh, an ash content of less than 55 ppm, and a flexural modulus of 1400-2000 MPa.

34. The modified polypropylene composition according to claim 33, wherein, The ash content of the polypropylene is less than 40 ppm.

35. The modified polypropylene composition according to claim 34, wherein, The ash content of the polypropylene is less than 35 ppm.

36. The modified polypropylene composition according to claim 33, wherein, The flexural modulus of the polypropylene is 1500~1800 MPa.

37. The modified polypropylene composition according to claim 1, wherein, The polypropylene is either homopolymer polypropylene or copolymer polypropylene.

38. The modified polypropylene composition according to claim 37, wherein, The polypropylene has at least one of the following characteristics: The melt flow rate at -230 ℃ and 2.16 kg load is 0.5~10 g / 10 min; -Melting temperature T m Temperatures above 150°C; -Isotacticity greater than 96%; or, the total content of ethylene and butene units is less than 3.0 mol.

39. The modified polypropylene composition according to claim 38, wherein, The melt flow rate of the polypropylene at 230 °C and 2.16 kg load is 1~5 g / 10 min.

40. The modified polypropylene composition according to claim 39, wherein, The melt flow rate of the polypropylene at 230 °C and 2.16 kg load is 2~4 g / 10 min.

41. The modified polypropylene composition according to claim 38, wherein, The melting temperature T of the polypropylene m The temperature ranges from 153 to 180 ℃.

42. The modified polypropylene composition according to claim 41, wherein, The melting temperature T of the polypropylene m The temperature ranges from 155 to 167 degrees Celsius.

43. The modified polypropylene composition according to claim 38, wherein, The isotacticity of the polypropylene is greater than 96.5%.

44. The modified polypropylene composition according to claim 38, wherein, The total content of ethylene units and butene units in the polypropylene is greater than 0 and less than 0.1 mol%, or greater than 0.1 mol% and less than or equal to 3.0 mol%.

45. The modified polypropylene composition according to claim 1, wherein, The modified polypropylene grafted with the alkenyl functional monomer is prepared by a method comprising the following steps: in the presence of an inert gas, a reaction mixture comprising polypropylene powder and an alkenyl functional monomer is subjected to a grafting reaction, followed by washing with a washing solvent to obtain the modified polypropylene grafted with the alkenyl functional monomer.

46. ​​The modified polypropylene composition according to claim 45, wherein, The reaction mixture also includes a free radical initiator.

47. The modified polypropylene composition according to claim 46, wherein, The free radical initiator is selected from peroxide free radical initiators and / or azo free radical initiators.

48. The modified polypropylene composition according to claim 47, wherein, The peroxide radical initiator is selected from at least one of benzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide, lauroyl peroxide, dodecyl peroxide, tert-butyl peroxide, diisopropyl peroxide, tert-butyl peroxide, and dicyclohexyl peroxide; the azo radical initiator is azobisisobutyronitrile and / or azobisisoheptanenitrile.

49. The modified polypropylene composition according to claim 46, wherein, The mass ratio of the free radical initiator to the alkenyl-containing functional monomer is 0.1~10:

100.

50. The modified polypropylene composition according to claim 49, wherein, The mass ratio of the free radical initiator to the alkenyl-containing functional monomer is 0.5~5:

100.

51. The modified polypropylene composition according to claim 46, wherein, The reaction mixture further includes at least one of the following components: deionized water and / or an organic solvent, wherein the mass content of the deionized water is 300-800% of the total mass of the polypropylene powder and the alkenyl functional monomer, and the mass content of the organic solvent is 1-35% of the mass of the polypropylene powder.

52. The modified polypropylene composition according to claim 51, wherein, The preparation method of the modified polypropylene grafted with the alkenyl functional monomer includes the following steps: a. Place the polypropylene powder in a closed reactor and replace it with an inert gas; b. Add the free radical initiator and the alkenyl-containing functional monomer to the closed reactor and stir to mix; c. Add deionized water and heat the reaction system to the grafting reaction temperature to carry out the grafting reaction; optionally, allow the reaction system to swell before or after adding deionized water; d. After the reaction is complete, filter and optionally dry to obtain powder; e. The powder is washed with a washing solvent, filtered, and dried to obtain the modified polypropylene grafted with the alkenyl functional monomer.

53. The modified polypropylene composition according to claim 51, wherein, The preparation method of the modified polypropylene grafted with the alkenyl functional monomer includes the following steps: a. Place the polypropylene powder in a closed reactor and replace it with an inert gas; b. Mix the organic solvent and the free radical initiator, and add them to the closed reactor; c. Remove the organic solvent, add an alkenyl-containing functional monomer, and optionally swell the reaction system; d. Add deionized water to raise the temperature of the reaction system to the grafting reaction temperature and carry out the grafting reaction; e. After the reaction is complete, filter and optionally dry to obtain powder; f. The powder is washed with a washing solvent, filtered, and dried to obtain the modified polypropylene grafted with the alkenyl functional monomer.

54. The modified polypropylene composition according to any one of claims 45-53, wherein, It also includes a screening and pretreatment step for polypropylene powder.

55. The modified polypropylene composition according to claim 54, wherein, The screening pretreatment includes the following steps: screening the powder using a double-layer vibrating screen or linear screen equipped with a screen of appropriate mesh size, and using the polypropylene powder in the middle layer of the screening machine as the reaction material.

56. The modified polypropylene composition according to any one of claims 45-53, wherein, The grafting reaction is carried out at a temperature of 30~110 ℃ for 0.5~10 h.

57. The modified polypropylene composition according to claim 56, wherein, The grafting reaction is carried out at a temperature of 60-95°C for 1-6 hours.

58. The modified polypropylene composition according to any one of claims 45-53, wherein, The washing solvent is selected from one or a mixture of two or more of the following: n-hexane, cyclohexane, n-heptane, petroleum ether, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, acetone, methyl ethyl ketone, tetrahydrofuran, 2-methyltetrahydrofuran, benzene, toluene, and xylene. The mass of the washing solvent is 2 to 20 times the mass of the grafted polypropylene powder.

59. The modified polypropylene composition according to claim 58, wherein, The washing solvent is a mixture of solvent A and solvent B. Solvent A is selected from at least one of n-hexane, cyclohexane, n-heptane, petroleum ether, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, acetone, methyl ethyl ketone, tetrahydrofuran, and 2-methyltetrahydrofuran. Solvent B is at least one of toluene and xylene.

60. The modified polypropylene composition according to any one of claims 45-53, wherein, The washing temperature is 40~130℃; the washing time is 0.5~10 h.

61. The modified polypropylene composition according to claim 60, wherein, The washing temperature is 55~100 ℃, and the time is 1~8 h.

62. The modified polypropylene composition according to any one of claims 1-53, wherein, Based on 100 parts by weight of modified polypropylene, the content of the antioxidant is 0.1 to 0.8 parts by weight; the content of the processing aid is 0.05 to 1 part by weight.

63. The modified polypropylene composition according to claim 62, wherein, Based on 100 parts by weight of modified polypropylene, the content of the antioxidant is 0.1 to 0.6 parts by weight, and the content of the processing aid is 0.05 to 0.5 parts by weight.

64. The modified polypropylene composition according to any one of claims 1-53, wherein, The antioxidant is selected from one or more of hindered phenols, hindered amines, phosphites, thiolated compounds, and benzofuranones.

65. The modified polypropylene composition according to claim 64, wherein, The antioxidant is obtained by compounding antioxidant component A and antioxidant component B. Antioxidant component A is selected from at least one of hindered phenols, hindered amines, phosphites and thiolated compounds, and antioxidant component B is at least one benzofuranone.

66. The modified polypropylene composition according to claim 65, wherein, The antioxidant component A is selected from pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris[2,4-di-tert-butylphenyl]phosphite, octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 2,2'-thiobis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane and bis(2-methyl-4-hydroxy-5-tert-butylphenyl)butane. At least one of (2,4-di-tert-butylphenol) pentaerythritol diphosphite; wherein the antioxidant component B is selected from at least one of 3-butyl-1(3-hydro)-isobenzofuranone, 5-methyl-7-tert-butyl-3-(3,4-dimethyl)-3-hydro-benzofuran-2-one, 5-methyl-7-tert-butyl-3-(2,5-dimethyl)-3-hydro-benzofuran-2-one, and 5-methyl-7-tert-butyl-3-(2-hydroxy-5-methyl)-3-hydro-benzofuran-2-one.

67. The modified polypropylene composition according to claim 65, wherein, The weight ratio of antioxidant component A to antioxidant component B is 1:0.01-0.

03.

68. The modified polypropylene composition according to any one of claims 1-53, wherein, The processing aid is selected from at least one of lubricants, acid absorbers, slip agents, antistatic agents, and anti-sticking agents; The lubricant is selected from at least one of the following: polyethylene glycol lubricants, fluoropolymer lubricants, organosilicon lubricants, fatty alcohol lubricants, fatty acid lubricants, fatty acid ester lubricants, stearamide lubricants, fatty acid metal soap lubricants, alkane and oxidized alkane lubricants, and micro / nanoparticle lubricants.

69. A biaxially oriented polypropylene film, wherein the biaxially oriented polypropylene film is prepared from the modified polypropylene composition according to any one of claims 1-68.

70. The biaxially oriented polypropylene film according to claim 69, wherein, The biaxially oriented polypropylene film is prepared by a method comprising the following steps: (1) The modified polypropylene composition according to any one of claims 1-68 is mixed and granulated; (2) The obtained granules are melt-extruded and cast into sheets to obtain modified polypropylene sheets; (3) The modified polypropylene casting is biaxially stretched to obtain the biaxially stretched polypropylene film.

71. The biaxially oriented polypropylene film according to claim 69 or 70, wherein, The biaxially oriented polypropylene film has a longitudinal tensile strength ≥140MPa; a transverse tensile strength ≥200MPa; a longitudinal elongation at break ≥210%; a transverse elongation at break ≥60%; an oxidation induction period ≥5min; and a thickness of 0.5~15 micrometers.

72. The biaxially oriented polypropylene film according to claim 71, wherein, The longitudinal tensile strength of the biaxially oriented polypropylene film is 140~170 MPa.

73. The biaxially oriented polypropylene film according to claim 71, wherein, The transverse tensile strength of the biaxially oriented polypropylene film is 205~250 MPa.

74. The biaxially oriented polypropylene film according to claim 71, wherein, The longitudinal elongation at break of the biaxially oriented polypropylene film is ≥225%.

75. The biaxially oriented polypropylene film according to claim 71, wherein, The transverse elongation at break of the biaxially oriented polypropylene film is ≥62%.

76. The biaxially oriented polypropylene film according to claim 71, wherein, The oxidation induction period of the biaxially oriented polypropylene film is ≥10 min.

77. The biaxially oriented polypropylene film according to claim 71, wherein, The thickness of the biaxially oriented polypropylene film is 4 to 10 micrometers.

78. The use of the biaxially oriented polypropylene film according to any one of claims 69-77 in the preparation of energy storage dielectrics.

79. The application according to claim 78, wherein, The energy storage medium is a high-temperature energy storage medium.

80. The application according to claim 78, wherein, The dielectric is a single-layer or multi-layer film dielectric.

81. The application according to claim 80, wherein, The dielectric is a capacitor film, a roughening film, a supercapacitor film, an electrostatic film, or a battery separator.

82. A polypropylene capacitor film, wherein the polypropylene capacitor film is one or more layers, wherein at least one layer is a biaxially oriented polypropylene film as described in any one of claims 69-77.

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