Biaxially oriented polypropylene dielectric film, modified polypropylene material and uses thereof

Abstract

The present invention belongs to the field of polymers and relates to a biaxially oriented polypropylene dielectric film, a modified polypropylene material and its use. The preparation raw material of the biaxially oriented polypropylene dielectric film includes a modified polypropylene grafted with an alkenyl-containing functional monomer. The modified polypropylene grafted with an alkenyl-containing functional monomer includes structural units derived from polypropylene as a matrix phase and structural units derived from an alkenyl-containing functional monomer as a dispersed phase. The ash content of the modified polypropylene grafted with an alkenyl-containing functional monomer is less than 50 ppm. In the modified polypropylene grafted with an alkenyl-containing functional monomer, 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 is 1.0 or more. The D50 of the dispersed phase is less than 450 nm. The biaxially oriented polypropylene dielectric film of the present invention can maintain good dielectric performance and energy storage performance at a relatively high operating temperature, and is suitable for operating conditions of high temperature and high operating electric field strength.

Description

Detailed Description of the Invention

[0001] [Technical field] The present invention belongs to the field of polymers, and in particular relates to a biaxially oriented polypropylene dielectric film having a high operating temperature, a modified polypropylene material for preparing a dielectric film, the use of the biaxially oriented polypropylene dielectric film and the modified polypropylene material in high temperature energy storage dielectric media, and a polypropylene capacitor film and a polypropylene electrical film having a high operating temperature.

[0002] [Background technology] Energy is the vitality of the development of modern society. In recent years, with the rapid development of new energy, aerospace, underground resource development, national defense, and military industries, as well as other scientific and technological fields, the demand for dielectric capacitors is not only increasing year by year, but also requiring them to be able to be used under more severe temperature conditions. However, thin film capacitors based on polymer dielectric materials have poor thermal stability and cannot be operated stably under high temperature environments. Especially under the action of high electric fields, the leakage current inside the polymer dielectric medium increases exponentially with the increase in temperature, resulting in a sharp decrease in the charge and discharge efficiency and energy storage density, which cannot meet the requirements of the application. More seriously, the leakage current is converted into Joule heat, so that the temperature of the capacitor continues to rise, eventually causing damage to the capacitor.

[0003] Biaxially oriented polypropylene (BOPP) is a polymer film capacitor dielectric material. It is currently the most commercially viable and most widely applied, with excellent comprehensive performance and a mature large-scale preparation process. It is currently widely used in electric vehicles, wind power generation, photovoltaic power generation, lighting, railway locomotives and other industries.

[0004] However, polypropylene film capacitors have the inherent disadvantage that the energy storage performance of the dielectric is poor under high temperature conditions, resulting in a significant decrease in reliability. For example, BOPP can achieve a high charge / discharge efficiency of over 95% even near the breakdown field strength at room temperature, but this drops to around 70% at 120°C. This not only significantly reduces the energy storage density, but also generates a large amount of waste heat that accumulates inside the device, ultimately leading to overheating damage to the device (thermal runaway).

[0005] Currently, from the material point of view, there are two main ways to increase the operating temperature of polymer capacitor films. The first method is to improve the thermal stability of the polymer dielectric material, i.e., to increase the glass transition temperature (T g The first method is to synthesize a polymer dielectric material having a . The second method is to introduce a second phase filler into a polymer medium material to produce a composite material, and to suppress the leakage current of the polymer under high temperature and high electric field by utilizing the carrier capture and scattering effect of the filler particles. However, both methods have problems in that the preparation process is complicated and large-scale industrial production is difficult.

[0006] Therefore, there is a need to find new modified polypropylene compositions that have demonstrable ability to control and tune the dielectric energy storage properties, simple preparation processes, and are suitable for practical engineering applications.

[0007] Graft modification is a common method for functionalizing polypropylene. Commonly used methods include melt grafting and solid-phase grafting. The melt grafting method requires simple equipment and low cost, but is characterized by high reaction temperature, difficult process control, relatively large amount of by-products, and limited range of applicable monomers. At present, the melt grafting method is only used for the preparation of anhydride-based or a few acrylate-based graft compatibilizers. The solid-phase grafting method is characterized by a reaction temperature lower than the melting point of polypropylene, few side reactions, high grafting efficiency, and a wide range of applicable graft monomers. For example, Y. Pan et al., in “Solid-phase grafting of glycidyl methacrylate onto polypropylene” (Journal of Applied Polymer Science, 1997, 65(10):1905-1912), investigated the reaction conditions for solid-phase grafting of glycidyl methacrylate (GMA) onto polypropylene, and pointed out that the influencing factors of solid-phase grafting and melt grafting are significantly different. Suspension grafting is a special solid-phase grafting, and by introducing an aqueous medium as a dispersant into the reaction system, the reaction temperature can be further reduced, the grafting uniformity can be improved, and the generation of by-products can be suppressed. Furthermore, Li Qiaojun et al., in “Studies on Suspension Grafting of Styrene onto Polypropylene” (Synthetic Resins and Plastics, 1996, 13(1):7-10), discussed the reaction conditions and influencing factors of suspension grafting of polypropylene with styrene. Zhu Baodong et al. reported in “Grafting of Styrene and Maleic Anhydride onto Polypropylene in Water Suspension System” (Modern Plastics Processing and Applications, 2009, 5:3) that a polypropylene double monomer graft with a graft rate of 8.97% was obtained by aqueous suspension grafting.To date, there are no reports on solid-phase or suspension graft-modified polypropylene as a primary material for dielectric energy storage.

[0008] It is a common practice to improve the thermal oxidative aging resistance of polypropylene by blending antioxidants. CN111378229A discloses a long-term thermal aging resistant polypropylene composition and its preparation method, the composition comprising 84.55-57.9% polypropylene, 15-40% talcum powder, 0.1-0.3% main antioxidant, 0.1-0.3% auxiliary antioxidant, 0.05-0.2% hindered amine antioxidant, 0.1-0.3% thioester antioxidant and 0.1-1% acid acceptor. CN202011292440.0 discloses a polypropylene material with low density, high light transmittance and long-term thermal oxidative aging resistance, comprising a main antioxidant which is a blend of a high molecular weight hindered phenolic antioxidant and a low molecular weight hindered phenolic antioxidant.

[0009] [Contents of the invention] The object of the present invention is to provide a biaxially oriented polypropylene dielectric film with high operating temperature, which is a novel modified polypropylene material grafted with alkenyl-containing functional monomer. The modified polypropylene material can be used to prepare a polypropylene dielectric film by a biaxially oriented process. The polypropylene dielectric film and modified polypropylene material can maintain high energy storage efficiency and energy storage density at higher operating temperatures.

[0010] A first aspect of the present invention is to provide a biaxially oriented polypropylene dielectric film with high operating temperature, wherein a raw material for preparing the biaxially oriented polypropylene dielectric film comprises a modified polypropylene grafted with an alkenyl-containing functional monomer; 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 modified polypropylene grafted with the alkenyl-containing functional monomer has an ash content of less than 50 ppm, preferably less than 36 ppm, and more preferably less than 30 ppm; in the modified polypropylene grafted with the alkenyl-containing functional monomer, the ratio of the mass of the structural units derived from the alkenyl-containing functional monomer and in a grafted state to the mass of the structural units derived from the alkenyl-containing functional monomer and in a self-polymerized state is 1.0 or more; and the D50 of the dispersed phase is less than 450 nm, preferably 50-400 nm.

[0011] The maximum operating temperature of the biaxially oriented polypropylene dielectric film is 100°C or higher, preferably 110 to 160°C, and more preferably 120 to 145°C.

[0012] The biaxially oriented polypropylene dielectric film has at least one of the following characteristics: Breakdown field strength E at 120°C g is 500 MV / m or more, preferably 550 to 800 MV / m; DC volume resistivity ρ at 120℃ and electric field strength of 200MV / m vg is 6.0 x 10 13 Ω·m or more, preferably 1.0×10 14 Ω m~1.0×10 20 Ω m, preferably 1.5×10 14 Ω m~0.9×10 20 Ω·m, and more preferably 2.0×10 14 Ω m~1.0×10 17 is Ω·m; The dielectric constant at 120°C and 100 Hz is greater than 2.25, preferably 2.26 to 2.65; a dielectric loss at 120° C. and 100 Hz of less than 1.55E-3, preferably less than 1.5E-3, preferably 1.0E-3 or less, more preferably 1.0E-6 to 1.3E-3, and even more preferably 1.0E-6 to 9E-4; The energy storage density at 120°C and 300MV / m is 0.720J / cm 3 Larger, preferably 0.740 to 2.0 J / cm 3 , preferably 0.780 J / cm 3 Greater than 0.780 to 2.0 J / cm 3 , and more preferably 0.80 to 2.0 J / cm 3 is; The energy storage efficiency at 120° C. and 300 MV / m is greater than 90.0%, and preferably 92.0 to 99.0%.

[0013] The biaxially oriented polypropylene dielectric film has at least one of the following characteristics: a tensile strength in the longitudinal direction is 140 MPa or more, and preferably 140 to 170 MPa; a tensile strength in the transverse direction is 200 MPa or more, and preferably 205 to 250 MPa; a breaking elongation in the longitudinal direction is 210% or more, preferably 225% or more; a breaking elongation in the transverse direction is 60% or more, preferably 62% or more; and a thickness of 0.5 to 15 μm, preferably 4 to 10 μm.

[0014] A second aspect of the present invention provides a modified polypropylene material useful for preparing a dielectric film, the modified polypropylene material comprising a modified polypropylene grafted with an alkenyl-containing functional monomer; the modified polypropylene grafted with an 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 modified polypropylene grafted with an alkenyl-containing functional monomer has an ash content of less than 50 ppm, preferably less than 36 ppm, more preferably less than 30 ppm; in the modified polypropylene grafted with an alkenyl-containing functional monomer, the ratio of the mass of the structural units derived from the alkenyl-containing functional monomer and in a grafted state to the mass of the structural units derived from the alkenyl-containing functional monomer and in a self-polymerized state is 1.0 or more; and the D50 of the dispersed phase is less than 450 nm, preferably 50 to 400 nm.

[0015] The maximum operating temperature of the modified polypropylene material is 100°C or higher, preferably 110-160°C, and more preferably 120-145°C.

[0016] The modified polypropylene material has at least one of the following characteristics: Breakdown field strength E at 120℃ g is 500 MV / m or more, preferably 550 to 800 MV / m; DC volume resistivity ρ at 120℃ and electric field strength of 200MV / m vg is 6.0 x 10 13 Ω·m or more, preferably 1.0×10 14 Ω m~1.0×10 20 Ω m, preferably 1.5×10 14 Ω m~0.9×10 20 Ω·m, more preferably 2.0×10 14 Ω m~1.0×10 17 is Ω·m; The dielectric constant at 120°C and 100 Hz is greater than 2.25, preferably 2.26 to 2.65; The dielectric loss at 120° C. and 100 Hz is less than 1.55E-3, preferably less than 1.5E-3, preferably 1.0E-3 or less, more preferably 1.0E-6 to 1.3E-3, and even more preferably 1.0E-6 to 9E-4; The energy storage density at 120°C and 300MV / m is 0.720J / cm 3 Larger, preferably 0.740 to 2.0 J / cm 3 , preferably 0.780 J / cm 3 Greater than 0.780 to 2.0 J / cm 3 , and more preferably 0.80 to 2.0 J / cm 3 is; The energy storage efficiency at 120° C. and 300 MV / m is greater than 90.0%, and preferably 92.0 to 99.0%.

[0017] A third aspect of the present invention provides the use of the biaxially oriented polypropylene dielectric film or modified polypropylene material described above in an energy storage dielectric medium, particularly a high temperature energy storage dielectric medium.

[0018] A fourth aspect of the present invention is to provide a polypropylene capacitor film which is one or more layers, at least one layer being the biaxially oriented polypropylene dielectric film as described above, or at least one layer being produced from a feedstock comprising the modified polypropylene material as described above, preferably by biaxial orientation, and preferably at least one layer being produced from the modified polypropylene material as described above by biaxial orientation.

[0019] A fifth aspect of the present invention is to provide a polypropylene electrical film which is one or more layers, at least one layer being the biaxially oriented polypropylene dielectric film as described above, or at least one layer being produced from a feedstock comprising the modified polypropylene material as described above, preferably by biaxial orientation, and preferably at least one layer being produced from the modified polypropylene material as described above by biaxial orientation.

[0020] The biaxially oriented polypropylene dielectric film, modified polypropylene material, polypropylene capacitor film and polypropylene electric film of the present invention have a wide operating temperature range, and can maintain good dielectric properties and energy storage properties at high operating temperatures, so they are particularly suitable for use conditions of high temperature and high operating electric field strength. The biaxially oriented polypropylene dielectric film and high-performance polypropylene capacitor film and polypropylene electric film have the advantages of good tensile properties, and can take into account both mechanical properties and electrical properties at higher operating temperatures, and are also suitable for working conditions of high temperature and high operating electric field strength.

[0021] Additional features and advantages of the present invention are described in the detailed description of specific embodiments that follow.

[0022] [Brief description of the drawings] Exemplary embodiments of the invention will now be explained in more detail with reference to the figures.

[0023] FIG. 1 is a photograph showing the microstructure of the modified polypropylene sample of Example 1 under an electron microscope at 20,000 times magnification, in which the spherical dispersed phase is an aggregate of styrene structural units.

[0024] FIG. 2 is a photograph showing the microstructure of the modified polypropylene sample of Example 2 under an electron microscope at 20,000 times magnification.

[0025] FIG. 3 is a photograph showing the microstructure of the modified polypropylene sample of Example 3 under an electron microscope at 20,000 times magnification.

[0026] FIG. 4 is a photograph showing the microstructure of the modified polypropylene sample of Example 10 under an electron microscope at 20,000 times magnification.

[0027] FIG. 5 is a photograph showing the microstructure of the modified polypropylene sample of Comparative Example 1 under an electron microscope at 20,000 magnifications, in which no dispersed phase is discernible.

[0028] FIG. 6 shows the TSDC test results for the products of Example 15 and Comparative Example 7.

[0029] [Detailed Description of the Invention] Specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are intended to illustrate and explain the present invention and are not intended to limit the present invention.

[0030] The present invention provides a biaxially oriented polypropylene dielectric film, and raw materials for preparing the biaxially oriented polypropylene dielectric film include a modified polypropylene grafted with an alkenyl-containing functional monomer; the modified polypropylene grafted with an alkenyl-containing functional monomer includes structural units derived from polypropylene as a matrix phase and structural units derived from an alkenyl-containing functional monomer as a dispersed phase; the modified polypropylene grafted with an alkenyl-containing functional monomer has an ash content of less than 50 ppm, preferably less than 36 ppm, and more preferably less than 30 ppm; in the modified polypropylene grafted with an alkenyl-containing functional monomer, the ratio of the mass of the structural units derived from the alkenyl-containing functional monomer and in a grafted state to the mass of the structural units derived from the alkenyl-containing functional monomer and in a self-polymerized state is 1.0 or more; the D50 of the dispersed phase is less than 450 nm, preferably 50 to 400 nm.

[0031] The maximum operating temperature of the biaxially oriented polypropylene dielectric film is 100°C or higher, preferably 110 to 160°C, and more preferably 120 to 145°C.

[0032] The dielectric 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 at 120°C and 300MV / m measured in the examples described below was 90% or more in both cases. The upper limit temperature at which the energy storage efficiency reaches 90% can be used as an indicator of the maximum operating temperature. This confirms that the dielectric film of the present invention has a maximum operating temperature of at least 120°C.

[0033] According to a preferred embodiment of the present invention, the biaxially oriented polypropylene dielectric film has at least one of the following characteristics: Breakdown field strength E at 120°C g is 500 MV / m or more, preferably 550 to 800 MV / m; DC volume resistivity ρ at 120℃ and electric field strength of 200MV / m vg is 6.0 x 10 13 Ω·m or more, preferably 1.0×10 14 Ω m~1.0×10 20 Ω m, preferably 1.5×10 14 Ω m~0.9×10 20 Ω·m, more preferably 2.0×10 14 Ω m~1.0×10 17 Ω m, e.g., 1.0×10 15 Ω m, 1.0×10 16 Ω·m, and any value in this range; The dielectric constant at 120°C and 100 Hz is greater than 2.25, preferably 2.26 to 2.65; a dielectric loss at 120° C. and 100 Hz of less than 1.55E-3, preferably less than 1.5E-3, preferably 1.0E-3 or less, more preferably 1.0E-6 to 1.3E-3, and even more preferably 1.0E-6 to 9E-4; The energy storage density at 120°C and 300MV / m is 0.720J / cm 3 Larger, preferably 0.740 to 2.0 J / cm 3 , more preferably 0.780 to 2.0 J / cm 3 , and more preferably 0.80 to 2.0 J / cm3 is; The energy storage efficiency at 120° C. and 300 MV / m is greater than 90.0%, and preferably 92.0 to 99.0%.

[0034] The biaxially oriented polypropylene dielectric film of the present invention has the following characteristics: a tensile strength in the longitudinal direction of 140 MPa or more, and preferably 140 to 170 MPa; a tensile strength in the transverse direction of 200 MPa or more, and preferably 205 to 250 MPa; a breaking elongation in the longitudinal direction of 210% or more, preferably 225% or more; a breaking elongation in the transverse direction of 60% or more, preferably 62% or more; and a thickness of 0.5 to 15 μm, preferably 4 to 10 μm.

[0035] According to one embodiment of the present invention, in the modified polypropylene grafted with an alkenyl-containing functional monomer, the ratio of the mass of structural units derived from the alkenyl-containing functional monomer and in a grafted state to the mass of structural units derived from the alkenyl-containing functional monomer and in a self-polymerized state is 1.1-1.0, preferably 1.2-6.

[0036] According to another embodiment of the present invention, in the modified polypropylene grafted with alkenyl-containing functional monomer, the ratio of the mass of structural units derived from the alkenyl-containing functional monomer and in a grafted state to the mass of structural units derived from the alkenyl-containing functional monomer and in a self-polymerized state is 1.5 or more, preferably 2 or more.

[0037] According to the present invention, preferably, the modified polypropylene grafted with an alkenyl-containing functional monomer has at least one of the following characteristics: a melt flow rate at 230° C. under a load of 2.16 kg is 1 to 10 g / 10 min, preferably 1.5 to 8 g / 10 min, and more preferably 2 to 5 g / 10 min; a melting temperature T m The bending modulus is 1400 to 2000 MPa, preferably 1500 to 1800 MPa.

[0038] The term "structural unit" means a part of modified polypropylene, and its form is not limited. Specifically, the term "structural unit derived from polypropylene" refers to a product formed from polypropylene, including not only those in "radical" form but also those in "polymer" form. The term "structural unit derived from alkenyl-containing functional monomer" refers to a product formed from alkenyl-containing functional monomer, including not only those in "radical" form but also those in "self-polymerized state". The "structural unit" may be a repeating unit or a non-repeating independent unit. The structural unit derived from an alkenyl-containing functional monomer and in a "grafted state" refers to a structural unit derived from an alkenyl-containing functional monomer that forms a covalent bond (graft) with the polypropylene.

[0039] Specifically, the polypropylene dielectric energy storage material has an islands-sea structure, as shown in Figure 1, where the "sea" is the matrix phase formed from structural units derived from polypropylene, and the "islands" are the dispersed phase formed from structural units derived from alkenyl-containing functional monomers.

[0040] Compared with the doping technology of inorganic fillers, the grafting modification can form a uniformly dispersed nanoscale dispersed phase in the composite material, which can avoid problems such as the difficulty of adding inorganic fillers and their poor dispersion. Compared with the surface modification, the process of bulk modification is simpler, the dispersed phase is uniformly dispersed, the structure is stable, and the functional monomer layer is not easily shed off due to external forces during use.

[0041] According to the present invention, the modified polypropylene is preferably prepared by grafting reaction, preferably suspension grafting reaction, between polypropylene and alkenyl-containing functional monomer. The grafting reaction of the present invention is a radical polymerization reaction, and therefore the term "grafted state" refers to the state in which the monomer forms a linkage with other reactants after radical polymerization. "Self-polymerized state" refers to the state in which the monomer forms a self-polymer and is not linked (grafted) with other reactants. Linkage includes both direct linkage and indirect linkage.

[0042] Since the alkenyl group in the alkenyl-containing functional monomers of the present invention is used for grafting with polypropylene, any alkenyl-containing functional monomer having an alkenyl group in a reactive position is suitable for use in the present invention.

[0043] Specifically, the alkenyl-containing functional monomer is at least one selected from monomers having a structure represented by Formula 1: [ka] In formula 1, R b , R c , R d are each independently selected from H, substituted or unsubstituted alkyl; R a is selected from substituted or unsubstituted alkyl, substituted or unsubstituted alkoxy, substituted or unsubstituted aryl, substituted or unsubstituted ester groups, substituted or unsubstituted carboxyl, substituted or unsubstituted cycloalkyl or heterocyclyl, cyano, substituted or unsubstituted silyl; R a and R d optionally forms a ring.

[0044] According to a preferred embodiment of the present invention, R b , R c , R d are each independently selected from H, substituted or unsubstituted C1-C6 alkyl; R a is a substituted or unsubstituted C1-C 20Alkyl, substituted or unsubstituted C1-C 20 Alkoxy, substituted or unsubstituted C6-C 20 Aryl, substituted or unsubstituted C1-C 20 Ester groups, substituted or unsubstituted C1-C 20 Carboxyl, substituted or unsubstituted C3-C 20 Cycloalkyl or heterocyclyl, cyano, substituted or unsubstituted C3-C 20 silyl; the substituents are selected from halogen, -OH, -NH2, =O, C1-C 12 Alkyl, C3-C6 cycloalkyl, C1-C 12 Alkoxy, C1-C 12 acyloxy; R a and R d are optionally joined together through a double bond to form a 4- to 6-membered heterocycle.

[0045] According to a more preferred embodiment of the present invention, b , R c , R d are each independently selected from H, substituted or unsubstituted C1-C6 alkyl; R a is at least one selected from a group represented by formula 2, a group represented by formula 3, a group represented by formula 4, a group represented by formula 5, a group represented by formula 6, and a heterocyclic group; [ka] In formula 2, R 4 -R 8 are each independently H, halogen, hydroxy, amino, phosphate, sulfonate, 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 groups, substituted or unsubstituted C1-C 12 amine groups, and the substituents are selected from halogen, hydroxy, amino, phosphate, sulfonate, C1-C 12Alkyl, C3-C 12 Cycloalkyl, C1-C 12 Alkoxy, C1-C 12 Ester group, C1-C 12 amine groups; preferably, R 4 -R 8 are each independently selected from H, halogen, hydroxy, amino, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy; [ka] In formula 3, R4-R 10 are each independently H, halogen, hydroxy, amino, phosphate, sulfonate, 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 groups, substituted or unsubstituted C1-C 12 amine groups, and the substituents are selected from halogen, hydroxy, amino, phosphate, sulfonate, C1-C 12 Alkyl, C3-C 12 Cycloalkyl, C1-C 12 Alkoxy, C1-C 12 Ester group, C1-C 12 amine groups; preferably, R-R 10 are each independently selected from H, halogen, hydroxy, amino, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy, wherein the substituents are selected from halogen, hydroxy, amino, C1-C6 alkyl, C1-C6 alkoxy; [ka] In formula 4, R4'-R 10 ' are each independently H, halogen, hydroxy, amino, phosphate, sulfonate, substituted or unsubstituted C1-C 12Alkyl, substituted or unsubstituted C3-C 12 Cycloalkyl, substituted or unsubstituted C1-C 12 Alkoxy, substituted or unsubstituted C1-C 12 Ester groups, substituted or unsubstituted C1-C 12 amine groups, and the substituents are selected from halogen, hydroxy, amino, phosphate, sulfonate, C1-C 12 Alkyl, C3-C 12 Cycloalkyl, C1-C 12 Alkoxy, C1-C 12 Ester group, C1-C 12 amine groups; preferably, R4'-R 10 ' are each independently selected from H, halogen, hydroxy, amino, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy, wherein the substituents are selected from halogen, hydroxy, amino, C1-C6 alkyl, C1-C6 alkoxy; [ka] In formula 5, R', R'', and R''' are each independently a 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; preferably, R1 is a C2-C6 alkenyl, preferably a monounsaturated alkenyl; R2, R3, R4 are each independently selected from substituted or unsubstituted C1-C6 linear alkyl, substituted or unsubstituted C3-C6 branched alkyl, substituted or unsubstituted C1-C6 alkoxy, substituted or unsubstituted C1-C6 acyloxy; [ka] In formula 6, R m is hydrogen and / or the following substituted or unsubstituted groups: C1-C 20 Straight chain alkyl, C3-C 20Branched alkyl, C3-C 12 Cycloalkyl, C3-C 12 Epoxy alkyl, C3-C 12 epoxyalkylalkyl, the substituents being at least one selected from halogen, amino and hydroxy; The heterocyclic group is selected from imidazolyl, pyrazolyl, carbazolyl, pyrrolidinonyl, pyridyl, piperidinyl, caprolactamyl, pyrazinyl, thiazolyl, purinyl, morpholinyl, oxazolinyl.

[0046] According to a particular embodiment of the present invention, the alkenyl-containing functional monomer is a styrene monomer, the styrene monomer being at least one selected from styrene, α-methylstyrene, 1-vinylnaphthalene, 2-vinylnaphthalene, mono- or poly-substituted styrene, mono- or poly-substituted α-methylstyrene, mono- or poly-substituted 1-vinylnaphthalene and mono- or poly-substituted 2-vinylnaphthalene; the substituents are preferably at least one selected from halogen, hydroxy, amino, phosphate, sulfonate, C1-C8 linear alkyl, C3-C8 branched alkyl or cycloalkyl, C1-C6 linear alkoxy, C3-C8 branched alkoxy or cycloalkoxy, C1-C8 linear ester, C3-C8 branched ester or cyclic ester, C1-C8 linear amine, and C3-C8 branched amine or cyclic amine; preferably, the styrene monomer is at least one selected from styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene and 4-methylstyrene.

[0047] According to certain embodiments of the present invention, the alkenyl-containing functional monomer is an alkenyl-containing silane monomer, the alkenyl-containing silane monomer being at least one selected from vinyltriethoxysilane, vinyltrimethoxysilane, vinyltriisopropoxysilane, vinyltri-tert-butoxysilane, vinyltriacetoxysilane, methylvinyldimethoxysilane, ethylvinyldiethoxysilane, allyltriethoxysilane, allyltrimethoxysilane, allyltriisopropoxysilane, vinyltris(β-methoxyethoxy)silane, allyltris(β-methoxyethoxy)silane, allyltri-tert-butoxysilane, allyltriacetoxysilane, methylallyldimethoxysilane, and ethylallyldiethoxysilane.

[0048] According to a particular embodiment of the present invention, the alkenyl-containing functional monomer is an acrylate monomer and / or an acrylic monomer, and preferably the acrylate monomer is at least one selected from methyl(methyl)acrylate, sec-butyl(methyl)acrylate, ethyl(methyl)acrylate, n-butyl(methyl)acrylate, isobutyl(methyl)acrylate, tert-butyl(methyl)acrylate, isooctyl(methyl)acrylate, dodecyl(methyl)acrylate, cosine(methyl)acrylate, octadecyl(methyl)acrylate, dimethylaminoethyl(methyl)acrylate, diethylaminoethyl(methyl)acrylate, dimethylaminopropyl(methyl)acrylate, and glycidyl(methyl)acrylate.Preferably, the acrylic monomer is at least one selected from acrylic acid, methacrylic acid, and 2-ethylacrylic acid.

[0049] In the present invention, C3-C 12 Epoxyalkylalkyl refers to epoxyalkyl-substituted alkyl having 3 to 12 carbon atoms, such as oxiranylmethyl.

[0050] According to a particular embodiment of the present invention, the alkenyl-containing functional monomer is an alkenyl-containing heterocyclic monomer.The alkenyl-containing heterocyclic monomer of the present invention can be any alkenyl-containing heterocyclic compound that can undergo radical polymerization, and can be at least one selected from alkenyl-substituted imidazole, alkenyl-substituted pyrazole, alkenyl-substituted carbazole, alkenyl-substituted pyrrolidone, alkenyl-substituted pyridine or pyridinium, alkenyl-substituted piperidine, alkenyl-substituted caprolactam, alkenyl-substituted pyrazine, alkenyl-substituted thiazole, alkenyl-substituted purine, alkenyl-substituted morpholine and alkenyl-substituted oxazoline;preferably, the alkenyl-containing heterocyclic monomer is a monoalkenyl-containing heterocyclic monomer.

[0051] Specifically, the alkenyl-containing heterocyclic monomer is at least one selected from: 1-vinylimidazole, 2-methyl-1-vinylimidazole, N-allylimidazole, 1-vinylpyrazole, 3-methyl-1-vinylpyrazole, vinylcarbazole, N-vinylpyrrolidone, 2-vinylpyridine, 3-vinylpyridine, 4-vinylpyridine, 2-methyl-5-vinylpyridine, vinylpyridine N-oxide, vinylpyridinium, vinylpiperidine, N-vinylcaprolactam, 2-vinylpyrazine, N-vinylpiperazine, 4-methyl-5-vinylthiazole, N-vinylpurine, vinylmorpholine, and vinyloxazoline.

[0052] According to the present invention, the alkenyl-containing functional monomer may also 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.

[0053] Various alkenyl-containing functional monomers may be used in the present invention either alone or in combination with one or more other monomers.

[0054] Preferably, the content of structural units derived from an alkenyl-containing functional monomer in the modified polypropylene grafted with an alkenyl-containing functional monomer is 1.0 to 28% by weight, preferably 1.5 to 24% by weight, more preferably 2.0 to 20% by weight.

[0055] The polypropylene part of the modified polypropylene in the present invention can also refer to ungrafted polypropylene, which may be a propylene homopolymer or a propylene copolymer containing ethylene or butylene units. More preferably, the polypropylene powder is a homopolypropylene with an isotacticity of more than 96%, preferably more than 96.5%; or a propylene copolymer with a total content of ethylene and butene units of less than 3.0 mol%, 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%, 0.1 mol%, based on the total molar content of structural units. Preferably, the propylene copolymer has a total content of ethylene and butene units of more than 0 and less than 0.1 mol%, or more than 0.1 mol% and less than or equal to 3.0 mol%.

[0056] According to the present invention, in order to obtain the modified polypropylene having the above-mentioned characteristics, it is preferable to use a polypropylene having the following characteristics: particle size is 16-50 mesh; ash content is less than 55 ppm, preferably less than 40 ppm, more preferably less than 35 ppm; flexural modulus is 1400-2000 MPa, preferably 1500-1800 MPa.

[0057] In addition to having the above mentioned characteristics, the polypropylene may be a homopolypropylene or a propylene copolymer and preferably has at least one of the following characteristics: 2. A melt flow rate at 230°C under a load of 16 kg is 0.5 to 10 g / 10 min, preferably 1 to 5 g / 10 min, and more preferably 2 to 4 g / 10 min; Melting temperature T m is 150°C or higher, preferably 153 to 180°C, and more preferably 155 to 167°C; the isotacticity is greater than 96%, preferably greater than 96.5%; or the combined content of ethylene units and butene units is less than 3.0 mol%, preferably greater than 0 and less than 0.1 mol%, or greater than 0.1 mol% and equal to or less than 3.0 mol%.

[0058] Polypropylene powder suitable for the present invention is commercially available or can be prepared by the methods described in Chinese patents CN109694427A, CN109694428A, CN104558813A, CN109912734A, CN111019025A and CN105431459A.

[0059] The modified polypropylene grafted with alkenyl-containing functional monomer can be prepared by a process comprising the steps of: subjecting a reaction mixture comprising polypropylene powder and alkenyl-containing functional monomer to a grafting reaction in the presence of an inert gas, optionally washing with a washing solvent to obtain the modified polypropylene grafted with alkenyl-containing functional monomer.

[0060] The grafting reaction of the present invention can be carried out with reference to various conventional methods in the art, preferably suspension grafting reactions, such as forming active grafting sites on polypropylene in the presence of alkenyl-containing functional monomers for grafting, or forming active grafting sites on polypropylene first, followed by treatment with monomers for grafting. The grafting sites may be formed by treatment with free radical initiators, or by treatment with high energy ionizing radiation or microwaves. Free radicals generated in the polymer as a result of chemical or radiation treatment form grafting sites on the polymer and initiate polymerization of the monomers at these sites.

[0061] Preferably, the grafting sites are initiated by a free radical initiator and the grafting reaction proceeds further, in which case the reaction mixture comprises a free radical initiator; more preferably, the free radical initiator is selected from peroxide-based free radical initiators and / or azo-based free radical initiators.

[0062] Here, the peroxide-based radical initiator is preferably at least one selected from the group consisting of dibenzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide, lauroyl peroxide, dodecyl peroxide, tert-butyl peroxybenzoate, diisopropyl peroxydicarbonate, tert-butyl peroxy(2-ethylhexanoate) and dicyclohexyl peroxydicarbonate; the azo-based radical initiator is preferably azobisisobutyronitrile and / or azobisisoheptonitrile.

[0063] More preferably, the grafting sites are initiated by a peroxide-based free radical initiator and the grafting reaction proceeds further.

[0064] In addition, the grafting reaction of the present invention can also be carried out according to the methods described in CN106543369A, CN104499281A, CN102108112A, CN109251270A, CN1884326A and CN101492517B.

[0065] The amount of each component used in the grafting reaction of the present invention is not particularly limited, provided that the above product characteristics are satisfied, and specifically, the mass ratio of the free radical initiator to the alkenyl-containing functional monomer may be 0.1-10:100, preferably 0.5-5:100. The mass ratio of the alkenyl-containing functional monomer to the polypropylene may be 0.5-25:100, preferably 1-20:100.

[0066] The present invention also has no special limitations on the technical conditions of the grafting reaction, specifically, the temperature of the grafting reaction can be 30-110°C, preferably 60-95°C; the time can be 0.5-10 hours, and preferably 1-6 hours.

[0067] In the present invention, the term "reaction mixture" includes all materials added to the grafting reaction system, which materials may be added all at once or at different stages of the reaction.

[0068] The reaction mixture of the present invention may further contain deionized water as a dispersant. The mass content of the deionized water is 300-800% of the total mass of the polypropylene powder and the alkenyl-containing functional monomer.

[0069] The reaction mixture of the present invention may further comprise an organic solvent as a solvent for dissolving the solid radical initiator, and the organic solvent preferably comprises at least one selected from C2-C5 alcohols, C2-C4 ethers and C3-C5 ketones, more preferably at least one selected from C2-C4 alcohols, C2-C3 ethers and C3-C5 ketones, and most preferably at least one selected from ethanol, diethyl ether and acetone. The mass content of the organic solvent is preferably 1-35% of the mass of the polypropylene powder.

[0070] According to one embodiment of the present invention, a method for preparing a modified polypropylene grafted with an alkenyl-containing functional monomer comprises the steps of: a. placing polypropylene powder in a closed reactor and then flushing with an inert gas; b. adding a free radical initiator and an alkenyl-containing functional monomer to a closed reactor and mixing with stirring; c. adding deionized water and heating the reaction system to a grafting reaction temperature to carry out the grafting reaction; optionally swelling the reaction system before or after adding the deionized water; d. After completion of the reaction, filtering and optionally drying to obtain a powder; e. optionally washing the powder with a washing solvent, filtering, and drying; f. Obtaining a modified polypropylene grafted with an alkenyl-containing functional monomer; or The method for preparing modified polypropylene grafted with alkenyl-containing functional monomers comprises the steps of: a. placing polypropylene powder in a closed reactor and then flushing with an inert gas; b. mixing an organic solvent and a free radical initiator and adding the mixture to a closed reactor; c. removing the organic solvent, adding an alkenyl-containing functional monomer, and optionally swelling the reaction system; d. adding deionized water and heating the reaction system to a grafting reaction temperature to carry out the grafting reaction; e. After completion of the reaction, filtering and optionally drying to obtain a powder; f. optionally washing the powder with a washing solvent, filtering and drying; g. Obtaining a modified polypropylene grafted with an alkenyl-containing functional monomer.

[0071] According to one embodiment of the present invention, a method for preparing a modified polypropylene grafted with an alkenyl-containing functional monomer comprises the following steps:

[0072] Approach I, the preparation method includes the steps of: a. placing polypropylene powder in a closed reactor and then flushing with an inert gas; b. adding a free radical initiator and an alkenyl-containing functional monomer to a closed reactor and mixing with stirring; c. adding deionized water and heating the reaction system to a grafting reaction temperature to carry out the grafting reaction; optionally swelling the reaction system before or after adding the deionized water; d. After the reaction is completed, filtering and drying to obtain the modified polypropylene grafted with alkenyl-containing functional monomer.

[0073] In approach II, the preparation method comprises the steps of: a. placing polypropylene powder in a closed reactor and then flushing with an inert gas; b. mixing an organic solvent and a free radical initiator and adding the mixture to a closed reactor; c. removing the organic solvent, adding an alkenyl-containing functional monomer, and optionally swelling the reaction system; d. adding deionized water and heating the reaction system to a grafting reaction temperature to carry out the grafting reaction; e. After the reaction is completed, filtering and drying to obtain the modified polypropylene grafted with alkenyl-containing functional monomer.

[0074] According to another embodiment of the present invention, a method for preparing a modified polypropylene grafted with an alkenyl-containing functional monomer comprises the following steps:

[0075] Approach I, the preparation method includes the steps of: a. placing polypropylene powder in a closed reactor and then flushing with an inert gas; b. adding a free radical initiator and an alkenyl-containing functional monomer to a closed reactor and mixing with stirring; c. adding deionized water and heating the reaction system to a grafting reaction temperature to carry out the grafting reaction; optionally swelling the reaction system before or after adding the deionized water; d. After completion of the reaction, filtering and optionally drying to obtain a powder; e. Washing the powder with a washing solvent, filtering and drying to obtain the modified polypropylene grafted with alkenyl-containing functional monomer.

[0076] In approach II, the preparation method comprises the steps of: a. placing polypropylene powder in a closed reactor and then flushing with an inert gas; b. mixing an organic solvent and a free radical initiator and adding the mixture to a closed reactor; c. removing the organic solvent, adding an alkenyl-containing functional monomer, and optionally swelling the reaction system; d. adding deionized water and heating the reaction system to a grafting reaction temperature to carry out the grafting reaction; e. After completion of the reaction, filtering and optionally drying to obtain a powder; f. Washing the powder with a washing solvent, filtering and drying to obtain the modified polypropylene grafted with alkenyl-containing functional monomer.

[0077] According to the method of the present invention, the polypropylene powder used may be directly purchased as a product with an appropriate particle size, or may be screened after purchase or self-preparation. Therefore, the present invention may also include a screening pretreatment step of the polypropylene powder. Screening can be achieved using conventional screening methods. According to a preferred embodiment, the screening pretreatment includes screening the powder using a double-layer vibrating screen or linear screen with a screen mesh of a corresponding mesh number, and using the polypropylene powder in the middle layer of the screen as a reaction material to obtain a raw powder with a corresponding particle size range.

[0078] According to a more specific embodiment of the present invention, the method for the preparation of the modified polypropylene grafted with alkenyl-containing functional monomers is selected from one of the following approaches:

[0079] Approach I, the preparation method includes the steps of: a. Screening the powder using a double-layer vibrating screen or a linear screen having a 16 mesh and a 48 mesh screen, and using the polypropylene powder in the middle layer of the screen as the reactive material; b. placing polypropylene powder in the middle layer of a screen in a closed reactor and then replacing it with an inert gas; c. dissolving a free radical initiator in an alkenyl-containing functional monomer to prepare a solution and adding the solution to a closed reactor filled with polypropylene and mixing with stirring; d. adding deionized water and heating the system to a grafting reaction temperature of 30-110°C for reaction for 0.5-10 hours; optionally swelling the reaction system before or after adding deionized water; e. After the reaction is completed, filtering and drying to obtain the modified polypropylene grafted with alkenyl-containing functional monomer.

[0080] Approach II, the preparation method includes the steps of: a. Screening the powder using a double-layer vibrating screen or a linear screen having a 16 mesh and a 48 mesh screen, and using the polypropylene powder in the middle layer of the screen as the reactive material; b. placing polypropylene powder in the middle layer of a screen in a closed reactor and then replacing it with an inert gas; c. mixing an organic solvent and a free radical initiator and adding the mixture to a closed reactor; c. removing the organic solvent, adding an alkenyl-containing functional monomer, and optionally swelling the reaction system; d. adding deionized water, heating the system to a grafting reaction temperature of 30-110°C, and reacting for 0.5-10 hours; e. After the reaction is completed, filtering and drying to obtain the modified polypropylene grafted with alkenyl-containing functional monomer.

[0081] According to a more specific embodiment of the present invention, the method for the preparation of the modified polypropylene grafted with alkenyl-containing functional monomers is selected from one of the following approaches:

[0082] Approach I, the preparation method includes the steps of: a. Screening the powder using a double-layer vibrating screen or a linear screen having a 16 mesh and a 48 mesh screen, and using the polypropylene powder in the middle layer of the screen as the reactive material; b. placing polypropylene powder in the middle layer of a screen in a closed reactor and then replacing it with an inert gas; c. dissolving a free radical initiator in an alkenyl-containing functional monomer to prepare a solution and adding the solution to a closed reactor filled with polypropylene and mixing with stirring; d. adding deionized water and heating the system to a grafting reaction temperature of 30-110°C and reacting for 0.5-10 hours; optionally swelling the reaction system before or after adding deionized water; e. After completion of the reaction, filtering and optionally drying to obtain a powder; f. Washing the powder with a washing solvent at a temperature of 40-130° C. for 0.5-10 hours, filtering and drying to obtain a modified polypropylene grafted with an alkenyl-containing functional monomer.

[0083] Approach II, the preparation method includes the steps of: a. Screening the powder using a double-layer vibrating screen or a linear screen having a 16 mesh and a 48 mesh screen, and using the polypropylene powder in the middle layer of the screen as the reactive material; b. placing polypropylene powder in the middle layer of a screen in a closed reactor and then replacing it with an inert gas; c. mixing an organic solvent and a free radical initiator and adding the mixture to a closed reactor; d. removing the organic solvent, adding an alkenyl-containing functional monomer, and optionally swelling the reaction system; e. adding deionized water and heating the system to a grafting reaction temperature of 30-110°C for reaction for 0.5-10 hours; f. After completion of the reaction, filtering and optionally drying to obtain a powder; g. Washing the powder with a washing solvent at a temperature of 40-130° C. for 0.5-10 hours, filtering and drying to obtain a modified polypropylene grafted with an alkenyl-containing functional monomer.

[0084] The inert gas in the present invention may be any of the various inert gases commonly used in the art, including, but not limited to, nitrogen and argon.

[0085] According to a preferred embodiment of the present invention, the cleaning solvent is one or a mixture of two or more selected from the group consisting 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 cleaning solvent is a mixture of solvent A and solvent B, where solvent A is one selected from the group consisting 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 selected from the group consisting of toluene and xylene.

[0086] 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.

[0087] As described above, the washing temperature may be 40 to 130° C., preferably 55 to 100° C., and the washing time may be 0.5 to 10 hours, preferably 1 to 8 hours.

[0088] The drying step after the reaction is carried out in advance. The drying step after the reaction and the drying step after washing with a washing solvent are preferably carried out by vacuum drying, and the temperature may be 60 to 90°C.

[0089] According to the present invention, the biaxially oriented polypropylene dielectric film comprises modified polypropylene as the main or only resin component, and further, the raw material for preparing the biaxially oriented polypropylene dielectric film may further comprise antioxidant and optionally processing aid, or other resin components in a controlled amount.Preferably, the content of modified polypropylene grafted with alkenyl-containing functional monomer is 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more, for example 75% by weight, 80% by weight, 85% by weight, 90% by weight, 95% by weight, based on the weight of the dielectric film.

[0090] The method for preparing a polymer dielectric film from modified polypropylene can be carried out with reference to the prior art. According to one embodiment of the present invention, a biaxially oriented polypropylene dielectric film is prepared by a method including the following steps: (1) mixing modified polypropylene grafted with alkenyl-containing functional monomers with antioxidants and optionally processing aids and pelletizing; (2) melt-extruding and casting the pellets obtained in step (1) to obtain a modified polypropylene cast sheet; (3) biaxially stretching the modified polypropylene cast sheet to obtain a biaxially oriented polypropylene dielectric film.

[0091] The present invention further provides a modified polypropylene material for preparing a dielectric film, the modified polypropylene material comprising a modified polypropylene grafted with an alkenyl-containing functional monomer, the modified polypropylene grafted with an alkenyl-containing functional monomer comprising structural units derived from polypropylene as a matrix phase and structural units derived from the alkenyl-containing functional monomer as a dispersed phase; the modified polypropylene grafted with an alkenyl-containing functional monomer has an ash content of less than 50 ppm, preferably less than 36 ppm, and more preferably less than 30 ppm; in the modified polypropylene grafted with an alkenyl-containing functional monomer, the ratio of the mass of the structural units derived from the alkenyl-containing functional monomer and in a grafted state to the mass of the structural units derived from the alkenyl-containing functional monomer and in a self-polymerized state is 1.0 or more; the D50 of the dispersed phase is less than 450 nm, preferably 50-400 nm.

[0092] The maximum operating temperature of the modified polypropylene material is above 100°C, preferably 110-160°C, and more preferably 120-145°C.

[0093] According to a preferred embodiment of the present invention, the modified polypropylene material has at least one of the following characteristics: Breakdown field strength E at 120°C g is 500 MV / m or more, preferably 550 to 800 MV / m; DC volume resistivity ρ at 120℃ and electric field strength of 200MV / m vg is 6.0 x 10 13 Ω·m or more, preferably 1.0×10 14 Ω m, ~1.0×10 20 Ω m, preferably 1.5×10 14 Ω m~0.9×10 20 Ω·m, more preferably 2.0×10 14 Ω m~1.0×10 17 Ω m, e.g. 1.0×10 15 Ω m, 1.0×10 16 Ω·m, and any value in this range; The dielectric constant at 120°C and 100 Hz is greater than 2.25, preferably 2.26 to 2.65; The dielectric loss at 120° C. and 100 Hz is less than 1.55E-3, preferably less than 1.5E-3, preferably 1.0E-3 or less, more preferably 1.0E-6 to 1.3E-3, and more preferably 1.0E-6 to 9E-4; The energy storage density at 120°C and 300MV / m is 0.720J / cm 3 Larger, preferably 0.740 to 2.0 J / cm 3 , more preferably 0.780 to 2.0 J / cm 3 , and more preferably 0.80 to 2.0 J / cm 3 is; The energy storage efficiency at 120° C. and 300 MV / m is greater than 90.0%, and preferably 92.0-99.0%.

[0094] Other specific definitions of the modified polypropylene grafted with alkenyl-containing functional monomers are as stated above and will not be described again herein.

[0095] Additionally, the modified polypropylene material may also include antioxidants and optionally processing aids.

[0096] According to the present invention, the content of the antioxidant is preferably 0.1 to 0.8 parts by weight, preferably 0.1 to 0.6 parts by weight, based on 100 parts by weight of the modified polypropylene, and the content of the processing aid is preferably 0.05 to 1 part by weight, preferably 0.05 to 0.5 parts by weight.

[0097] According to some embodiments of the present invention, the antioxidant is one or a mixture of two or more selected from the group consisting of hindered phenols, hindered amines, phosphites, thiols, and benzofuranones. The content of the antioxidant can be 0.1-0.8 parts by weight, preferably 0.1-0.6 parts by weight, based on 100 parts by weight of the modified polypropylene.

[0098] In this study, the inventors of the present invention found that the appropriate antioxidant combination and blending ratio can obviously improve the thermal oxidative aging resistance of the modified polypropylene material, and the prepared film product has excellent thermal stability. Specifically, the antioxidant is obtained by mixing antioxidant component A and antioxidant component B, where antioxidant component A is at least one selected from the group consisting of hindered phenol, hindered amine, phosphite and thio, 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.

[0099] More specifically, antioxidant component A is selected from the group consisting of pentaerythrityl tetrakis[β-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010), tris[2,4-di-t-butylphenyl]phosphite (antioxidant 168), n-octadecyl β-(3,5-di-t-butyl-4-hydroxyphenyl)propionate (antioxidant 1076), 2,2'-thiobis[3-(3,5-di-t-butyl bis(2,4-di-tert-butylphenol)pentaerythritol diphosphite (Antioxidant 626). The antioxidant component B is one selected from the group consisting of 3-butyl-1-(3-hydrogen)-isobenzofuranone (antioxidant 501), 5-methyl-7-tert-butyl-3-(3,4-dimethyl)-3-hydrogen-benzofuran-2-one, 5-methyl-7-tert-butyl-3-(2,5-dimethyl)-3-hydrogen-benzofuran-2-one and 5-methyl-7-tert-butyl-3-(2-hydroxy-5-methyl)-3-hydrogen-benzofuran-2-one.

[0100] According to a particular 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, the content of the antioxidant in the modified polypropylene material is preferably 0.2-0.4 parts by weight based on 100 parts by weight of the modified polypropylene material.

[0101] According to the present invention, the processing aids include, but are not limited to, lubricants, acid acceptors, slip agents, antistatic agents, antiblock agents, etc. The amount of each aid can be conventionally selected in the art, is known to those skilled in the art, and will not be described herein. The processing aids used do not adversely affect the tensile film-forming properties and mechanical properties of the modified polypropylene material. The content of the processing aid may be 0.05 to 1 part by weight, preferably 0.05 to 0.5 parts by weight, based on 100 parts by weight of the modified polypropylene.

[0102] According to some embodiments of the present invention, the processing aid is a lubricant.The lubricant can be one or more selected from polyethylene glycol lubricants, fluoropolymer lubricants, organosilicon lubricants, fatty alcohol lubricants, fatty acid lubricants, fatty acid ester lubricants, stearic acid amide lubricants, fatty acid metal soap lubricants, alkane and alkane oxide lubricants, and micro-nanoparticle lubricants.

[0103] Specifically, the PEG lubricant may be, for example, a PEG molecule having a molecular weight of 500 to 50,000, which may have been subjected to end-capping, grafting, and crosslinking, or may have been subjected to other chemical or physical modifications. The fluoropolymer lubricant may be, for example, at least one selected from polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, etc., or other monomodal or polymodal fluoropolymers, crystalline or semicrystalline fluoropolymers. The organosilicon lubricant may be various existing compounds containing carbon atoms and silicon atoms as the molecular backbone and containing oligomers or oligopolymers of organic groups such as methyl, phenyl, alkoxy, and vinyl as side chains. The fatty alcohol lubricant may be, for example, at least one selected from soft fatty alcohols, hard fatty alcohols, tallow fatty alcohols, etc. The fatty acid lubricant may be, for example, at least one selected from stearic acid and / or 12-hydroxystearic acid. The fatty acid ester lubricant may be, for example, at least one selected from butyl stearate, monoglyceryl stearate, cetyl palmitate, stearyl stearate, etc. The stearic acid amide lubricant may be, for example, at least one selected from stearic acid amide, oleic acid amide, erucic acid amide, n,n-ethylene bisstearic acid amide (EBS), etc. The fatty acid metal soap lubricant may be, for example, at least one selected from lead stearate, calcium stearate, magnesium stearate, synthetic calcium acetate, etc. The alkane and alkane oxide lubricant may be, for example, at least one selected from liquid paraffin, solid paraffin, polyethylene wax, polypropylene wax, ethylene oxide wax, etc. The micro-nanoparticle lubricant may be, for example, powdered rubber and / or silica gel particles.

[0104] According to a specific embodiment of the present invention, the processing aid is a fluoropolymer.

[0105] The various processing aids mentioned above are commercially available.

[0106] The modified polypropylene material of the present invention is prepared by mixing the various ingredients.

[0107] The process of preparing pellets of the modified polypropylene material into a polymeric dielectric film can be carried out according to conventional techniques, for example, the pellets can be processed by hot pressing or extrusion casting, or the pellets can be processed by biaxial stretching to form a dielectric film.

[0108] The pellets can be prepared according to conventional pelletizing methods in the art, for example, by pelletizing in a twin-screw extruder.

[0109] According to a specific embodiment of the present invention, a biaxially oriented polypropylene dielectric film is prepared by a method comprising the steps of: (1) mixing and pelletizing a modified polypropylene material; (2) melt-extruding and casting the pellets obtained in step (1) to obtain a modified polypropylene cast sheet; (3) biaxially stretching the modified polypropylene cast sheet to obtain a biaxially oriented polypropylene dielectric film.

[0110] In step (1), the step of mixing the modified polypropylene material with an antioxidant and a processing aid and pelletizing it may generally include a step of uniformly mixing the modified polypropylene material with a high-speed agitator, adding the uniformly mixed material to a twin-screw extruder or a single-screw extruder, melting, mixing, uniformly extruding and pelletizing, and drying to obtain pellets. Here, the processing temperature of the twin-screw extruder can be controlled to 190-230°C.

[0111] According to the present invention, in step (2), the melt extrusion temperature is 190-230° C., and the temperature of the casting quench roller is 15-50° C. The modified polypropylene cast sheet may have a single-layer structure or a multi-layer structure.

[0112] According to a specific embodiment of the present invention, a method for preparing a dielectric film includes the steps of: putting modified polypropylene material pellets into a hot air oven to dry; putting the dried pellets into a melt extrusion casting machine to cast a cast sheet, where the temperature of the melt extrusion extruder is 230°C, the temperature of the screen exchange area is controlled at 230°C, the temperature of the machine head is controlled at 230°C, the temperature of the casting roller is controlled at 25°C, and making a thick cast sheet with a thickness of 230±20 μm. The thick cast sheet of polypropylene is put into the stretching fixture of a film biaxial stretching device and biaxial synchronous stretching is performed.

[0113] In order to improve the properties of the dielectric film, the dielectric film preferably further contains a film-forming aid. The film-forming aid may be at least one selected from the group consisting of anti-halogen agents, light stabilizers, heat stabilizers, colorants, fillers, slip agents, antiblocking agents, and antistatic agents. The specific type of film-forming aid is a matter of routine choice in the art and will not be detailed here.

[0114] The biaxially oriented polypropylene dielectric film, modified polypropylene material according to the present invention can be used as an energy storage dielectric medium, and is particularly suitable for use as a high-temperature energy storage dielectric medium due to its high operating temperature. The dielectric medium is preferably a film dielectric medium, which may be single-layered or multi-layered, for example, but not limited to, a capacitor film, an electric film, a rough film, a supercapacitor film, an electrostatic film, or a battery separator film. The polypropylene-based dielectric energy storage material of the present invention is particularly suitable for making a capacitor film. The capacitor film, which is a functional film material with electric polarization as its basic electrical property, is excellent in insulating and dielectric properties and is therefore used as a dielectric material for thin-film capacitors. The electric film is a film with a thickness of 350 μm or less and excellent electrical performance, which is usually produced using a polymer polymer as a raw material and may contain some auxiliary materials that meet the requirements of electrical products such as corrosion resistance and radiation resistance, and is generally used in electronic component insulation materials, automotive wiring, electric wire winding, insulation protection, etc.

[0115] Specifically, the present invention provides one or more layers of a polypropylene capacitor film, at least a portion of at least one layer being a biaxially oriented polypropylene dielectric film as described above, or at least one layer being produced from a feedstock comprising the modified polypropylene material as described above, preferably by biaxial orientation, and preferably at least one layer being produced from the modified polypropylene material as described above, by biaxial orientation.

[0116] The present invention further provides one or more layers of polypropylene electrical film, at least a portion of at least one layer being a biaxially oriented polypropylene dielectric film as described above, or at least one layer being produced from a raw material comprising the modified polypropylene material as described above, preferably by biaxial orientation, and preferably at least one layer being produced from the modified polypropylene material as described above, by biaxial orientation.

[0117] The method for preparing a polypropylene capacitor film / electrical film includes a step of adding the pellets of the modified polypropylene material obtained in step (1) to a casting device for extrusion casting to obtain a cast sheet, and then a step of stretching the obtained cast sheet with a film biaxial stretching device. In the extrusion casting, a die for the cast sheet can be selected according to the structure of the film to be obtained. For example, a single-layer die can be used to obtain a film having a single layer structure, and a multi-layer composite die can be used to obtain a film having a multi-layer structure (for example, a film having a three-layer structure of an upper layer, a core layer, and a lower layer). At least one layer (for example, a core layer) of the multi-layer composite die can be communicated with an extruder hopper containing the modified polypropylene material described above, so that at least one layer (for example, a core layer) of the obtained film can be a modified polypropylene layer formed of the modified polypropylene material. In the extrusion step, the extrusion temperature can be 100 to 200°C, and the temperature of the cast quench roller can be 15 to 50°C.

[0118] In the present invention, biaxial stretching includes synchronous stretching (i.e., stretching the film in the machine direction (MD) and transverse direction (TD) simultaneously) or step stretching (i.e., stretching the film first in MD and then in TD).

[0119] The synchronous stretching includes a step of preheating the cast sheet of the modified polypropylene material at a preheat temperature which may be 120-170°C, followed by simultaneous MD and TD stretching, and the synchronous stretching conditions include a stretching temperature of 150-175°C, an MD stretching ratio of 3 times or more, a TD stretching ratio of 3 times or more, an MD stretching speed of 50-300% / sec, and a TD stretching speed of 50-300% / sec.

[0120] The stepwise stretching includes a step of preheating a cast sheet of the modified polypropylene-based material, followed by MD stretching and then TD stretching, and the stepwise stretching conditions include an MD stretching temperature of 150-170°C, a TD stretching temperature of 155-175°C, an MD stretching ratio of 3 times or more, a TD stretching ratio of 5 times or more, an MD stretching speed of 50-300% / sec, and a TD stretching speed of 50-300% / sec.

[0121] According to the present invention, the method may or may not include performing an annealing set treatment on the stretched film, and preferably, the method includes performing an annealing set treatment on the stretched film, and when performing the annealing set treatment, the temperature of the annealing set treatment is preferably 160 to 180° C. The time of the annealing set treatment is preferably 5 to 60 seconds. By performing the annealing set treatment on the stretched film, the dimensional stability of the film can be improved.

[0122] According to the present invention, the method may further include subjecting the obtained polypropylene film to surface corona treatment, edge cut treatment and winding treatment, which are conventional operations in the art, and the present invention has no special restrictions thereon.

[0123] The present invention will be further described with reference to the following examples, but the scope of the present invention is not limited to these examples.

[0124] In the following examples and comparative examples, A model LCR400 film casting apparatus was purchased from Labtech, Sweden. A model Karo IV film biaxial stretching apparatus was purchased from Bruckner, Germany.

[0125] The properties of the modified polypropylene materials and films were measured according to the following methods.

[0126] (1. Measurement of Ash Content of Polypropylene / Modified Polypropylene Materials) The measurements were carried out according to the method specified in GB / T 9345-2008.

[0127] (2. Measurement of isotacticity of polypropylene) The measurements were carried out according to the method specified in GB / T 2412-2008.

[0128] (3. Measurement of Melt Flow Rate (MFR)) The MFR of polypropylene / modified polypropylene materials was measured at 230°C under a load of 2.16 kg using a CEAST 7026 melt indexer according to the method specified in GB / T3682-2018.

[0129] (4. Melting temperature T m (Decision on The melting and crystallization processes of polypropylene / modified polypropylene materials were analyzed by differential scanning calorimetry. The specific procedure is as follows: Under nitrogen protection, 5 mg of sample was placed in a crucible, heated from 20°C to 200°C at a heating rate of 10°C / min, and held for 5 minutes to remove thermal history. Then, cooled to 20°C at a heating rate of 10°C / min, held for 1 minute, and finally heated to 200°C at a heating rate of 10°C / min. The scan data during the third heating were recorded, and the melting temperature T was determined according to GB / T19466.3-2004. m was calculated.

[0130] (5. Determination of parameter η) 1-2 g of the grafted product was refluxed in an appropriate amount of xylene until the particles were completely dissolved. The xylene solution was poured hot into 6 times the amount of organic solvent (ethyl acetate or acetone) for precipitation. The mixture was left for 1 hour until the insoluble matter was completely precipitated. The mixture was filtered through a vacuum funnel, and the filtered insoluble matter (i.e., the pure grafted product) was dried and weighed. The ratio of the grafted portion to the self-polymerized portion of the structural units derived from the functional monomer was as follows:

number

[0131] (6. Measurement of flexural modulus) The measurements were carried out according to the method specified in GB / T9341-2008.

[0132] (7. Measurement of DC volume resistivity) The measurement was carried out according to the method specified in GB / T13542.2-2009, the measurement method was the contact electrode method, and the electrode material was conductive rubber.

[0133] (8. Measurement of breakdown field strength) The measurement was carried out according to the method specified in GB / T13542.2-2009, and the measurement method was the 50-point electrode method.

[0134] (9. Measurement of Energy Storage Density and Energy Storage Efficiency) The measurements were performed with reference to the method described in the following literature: Yuan, C., Zhou, Y., Zhu, Y. et al. Polymer / molecular semiconductor all-organic composites for high-temperature dielectric energy storage. Nat. Commun. 11, 3919 (2020).

[0135] (10. Measurement of dielectric constant and dielectric loss factor) The measurements were performed with reference to the method described in the following literature: Yuan, C., Zhou, Y., Zhu, Y. et al. Polymer / molecular semiconductor all-organic composites for high-temperature dielectric energy storage. Nat. Commun. 11, 3919 (2020).

[0136] (11. Film Thickness Measurement) The measurement was carried out according to the method specified in GB / T13542.3-2006, and the measurement method was the micrometer method.

[0137] 12. Characterization of the Dispersed Phase and Calculation of D50 The specimens obtained by hot pressing and extrusion of modified polypropylene were immersed in liquid nitrogen for 15 min and then subjected to brittle fracture. The fracture surface was subjected to metal spray treatment and then characterized by thermal field emission scanning electron microscope (NanoSEM 450, FEI, USA) to obtain micromorphology images. Through Nano Measurer 1.2 analysis software, 200 dispersed phases were taken for each sample, the diameter was measured, and the D50 was calculated using data processing software. D50 represents the median particle size, i.e. the particle size of the sample where the cumulative particle size distribution rate reaches 50%.

[0138] (13. Measurement of tensile strength and elongation at break of film) The measurements were carried out according to the method specified in GB / T 13542.2-2009.

[0139] (14. TSDC Measurement) The measurements were performed with reference to the method described in the following literature: Tian Fuqiang, Bu Wenbin, Shi Linshuang, et al. Theory of modified thermally stimulated current and direct determination of trap level distribution[J]. Journal of Electrostatics, 2011, 69 (1) : 7-10.

[0140] The material was pressed into a film with an average thickness of 50 μm, and a circular gold electrode with a diameter of 20 mm was sputtered onto its surface. During the measurements, the sample was first polarized at a constant polarization temperature for 30 min using a DC electric field of 20 kV / mm, and then the temperature was rapidly decreased to -100 °C while maintaining the electric field. The electric field was then removed for 15 min to remove any unfrozen trapped charges. The temperature was then linearly increased from -100 °C to 150 °C at a heating rate of 3 °C / min, and the depolarization current was measured simultaneously.

[0141] [Example] The materials used in the examples are shown in Tables A and B below.

[0142] [Table 1]

[0143] [Table 2]

[0144] The polypropylene powder used in all the examples was sieved through a vibrating sieve equipped with 16 mesh and 48 mesh sieves prior to the grafting reaction.

[0145] [Example 1] 5.0 kg of PP1 powder sieved from the middle layer of the sieving device was added to a 50 L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen substitution. 7.2 g of tert-butylperoxy (2-ethylhexanoate) and 400 g of styrene were mixed into a uniform solution, then added to the reaction kettle and mixed with the powder while stirring for 30 minutes. Then, 17.8 kg of degassed deionized water was added, and the reaction mixture was heated to 50°C and swollen for 2 hours. The swollen powder was heated to 95°C and reacted for 4 hours. After the reaction was completed, the reaction product was cooled and filtered to remove the liquid components, and then vacuum dried at 70°C for 10 hours to obtain polypropylene-g-styrene powder. Figure 1 is a photograph of the microstructure of the product of Example 1 observed with a 20,000x electron microscope, and the bright spherical parts are the dispersed phase formed by the styrene structural unit. It can be seen that the particle size of the dispersed phase is small and the morphology is regular. The graft / self-polymerization ratio η, D50, ash content, MFR, Tm and flexural modulus of the obtained graft-modified polypropylene were tested. The results are shown in Table 1.

[0146] The resulting polypropylene-g-styrene powder and antioxidant 1010 / 168 (weight ratio 1:1) were weighed and added to a high-speed stirrer to mix uniformly. The material was pelletized using a Coperion Co. WP25 twin screw extruder at cutoff temperatures of 190-200-210-220-230-230-220°C and a screw speed of 300 rpm to obtain polypropylene-g-styrene pellets. The amount of antioxidant added was 0.3 parts by weight based on 100 parts by weight of polypropylene-g-styrene powder.

[0147] The obtained pellets were dried in a hot air oven, and the dried pellets were added to an LCR400-type extrusion casting device from Labtech Co., Sweden, for melt extrusion and casting to obtain a cast sheet, the temperature of the extruder for melt extrusion was 230°C, the temperature of the screen exchange area was controlled at 230°C, the temperature of the device head was controlled at 230°C, and the temperature of the casting roller was controlled at 25°C, and a cast sheet with a thickness of 230±20 μm was prepared.

[0148] The resulting thick polypropylene cast sheet was placed in the stretching fixture of a film biaxial stretching device and subjected to a biaxial synchronous stretching process. The processing conditions for each process included the following: preheating temperature was 160°C, stretching temperature was 160°C, stretching ratio was 5.5x5.5x, film stretching speed was 100% / sec, and film set temperature was 160°C. Various electrical property parameters were tested for the resulting polypropylene film. The results are shown in Table 2.

[0149] [Example 2] 5.0 kg of PP2 powder sieved from the middle layer of the sieving device was added to a 50L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen substitution. 13.5 g of tert-butylperoxy (2-ethylhexanoate) and 1001 g of styrene were mixed into a homogeneous solution, then added to the reaction kettle and mixed with the powder while stirring. The reaction mixture was heated to 40°C and swollen for 3 hours. Next, 36.0 kg of degassed and preheated to 40°C was added through a filling tank, the reaction kettle was heated to 90°C, and the reaction was carried out for 6 hours. After the reaction was completed, the reaction product was cooled and filtered to remove the liquid components, and then vacuum dried at 70°C for 10 hours to obtain polypropylene-g-styrene powder. Figure 2 is a photograph of the microstructure of the product of Example 2 observed with an electron microscope at 20,000 times, and the bright spherical parts are the dispersed phase formed by the styrene structural unit.

[0150] The resulting powder was pelletized and a film product was prepared as in Example 1, and the resulting graft modified polypropylene and the resulting polypropylene film were tested for various structural and performance parameters. The results are shown in Tables 1 and 2.

[0151] [Example 3] 5.0 kg of PP2 powder sieved from the middle layer of the sieving device was added to a 50L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen replacement. 3.1 g of dibenzoyl peroxide, 112 g of styrene, and 13.9 g of maleic anhydride were mixed into a homogeneous solution, then added to the reaction kettle and mixed with the powder while stirring. The resulting mixture was allowed to swell at room temperature for 8 hours and then heated to 92°C. Next, 16.4 kg of deionized water that had been degassed and preheated to 92°C was added through a filling tank, the reaction kettle was heated to 92°C, and the reaction was carried out for 4 hours. After the reaction was completed, the reaction product was cooled and filtered to remove the liquid components, and then vacuum dried at 70°C for 10 hours to obtain polypropylene-g-maleic anhydride / styrene powder. FIG. 3 is a photograph of the microstructure of the powder of Example 3 observed with an electron microscope at 20,000 times magnification, in which the bright spherical parts are the dispersed phase formed by maleic anhydride / styrene structural units.

[0152] The resulting powder was pelletized and a film product was prepared as in Example 1, and the resulting graft modified polypropylene and the resulting polypropylene film were tested for various structural and performance parameters. The results are shown in Tables 1 and 2.

[0153] [Example 4] 5.0 kg of PP1 powder sieved from the middle layer of the sieving device was added to a 50L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen replacement. 2.5 g of dibenzoyl peroxide and 250.5 g of methyl methacrylate were mixed into a homogeneous solution and then added to the reaction kettle, mixed with the powder while stirring for 30 minutes, and 26.3 kg of degassed deionized water was added. The reaction kettle was heated to 91°C and the reaction was carried out for 3 hours. After the reaction was completed, the reaction product was cooled and filtered to remove the liquid components, and then vacuum dried at 70°C for 10 hours to obtain polypropylene-g-methyl methacrylate powder.

[0154] The resulting powder was pelletized and a film product was prepared as in Example 1, and the resulting graft modified polypropylene and the resulting polypropylene film were tested for various structural and performance parameters. The results are shown in Tables 1 and 2.

[0155] [Example 5] 5.0 kg of PP2 powder sieved from the middle layer of the sieving device was added to a 50L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen replacement. 6.2 g of dibenzoyl peroxide, 198.0 g of styrene, and 52.0 g of maleic anhydride were mixed into a homogeneous solution, then added to the reaction kettle and mixed with the powder while stirring. The resulting mixture was allowed to swell at room temperature for 6 hours and heated to 90°C. Then, 22.6 kg of deionized water that had been degassed and preheated to 90°C was added through a filling tank, and the reaction was carried out for 4 hours. After the reaction was completed, the reaction product was cooled and filtered to remove the liquid components, and then vacuum dried at 70°C for 10 hours to obtain polypropylene-g-maleic anhydride / styrene powder.

[0156] The resulting powder was pelletized and a film product was prepared as in Example 1, and the resulting graft modified polypropylene and the resulting polypropylene film were tested for various structural and performance parameters. The results are shown in Tables 1 and 2.

[0157] [Example 6] 5.0 kg of PP1 powder sieved from the middle layer of the sieving device was added to a 50L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen replacement. 31 g of lauroyl peroxide and 603 g of vinyltriethoxysilane were mixed into a homogeneous solution, then added to the reaction kettle, mixed with the powder while stirring for 20 minutes, and 19.6 kg of degassed deionized water was added. The reaction kettle was heated to 91°C and the reaction was carried out for 7 hours. After the reaction was completed, the reaction product was cooled and filtered to remove the liquid components, and then vacuum dried at 70°C for 10 hours to obtain polypropylene-g-vinyltriethoxysilane powder.

[0158] The resulting powder was pelletized and a film product was prepared as in Example 1, and the resulting graft modified polypropylene and the resulting polypropylene film were tested for various structural and performance parameters. The results are shown in Tables 1 and 2.

[0159] [Example 7] 5.0 kg of PP2 powder sieved from the middle layer of the sieving device was added to a 50L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen replacement. 6.2 g of dibenzoyl peroxide, 115.0 g of methyl acrylate, and 38.0 g of acrylic acid were mixed into a homogeneous solution, then added to the reaction kettle and mixed with the powder for 40 minutes while stirring. The resulting mixture was heated to 95°C. Next, 36.1 kg of deionized water that had been degassed and preheated to 90°C was added through a filling tank, and the reaction was carried out for 4 hours. After the reaction was completed, the reaction product was cooled and filtered to remove the liquid components, and then vacuum dried at 70°C for 10 hours to obtain polypropylene-g-methyl acrylate / acrylic acid powder.

[0160] The resulting powder was pelletized and a film product was prepared as in Example 1, and the resulting graft modified polypropylene and the resulting polypropylene film were tested for various structural and performance parameters. The results are shown in Tables 1 and 2.

[0161] [Example 8] The PP1 powder in Example 1 was replaced with the PP3 powder sieved from the middle layer of the sieving device, and other preparation conditions and methods were the same as those in Example 1, and the obtained graft-modified polypropylene and the obtained polypropylene film were tested for various structure and performance parameters. The results are shown in Tables 1 and 2.

[0162] [Example 9] 5.0 kg of PP2 powder sieved from the middle layer of the sieving device was added to a 50L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen replacement. 8.8 g of dibenzoyl peroxide and 355 g of 4-vinylpyridine were mixed into a homogeneous solution and then added to the reaction kettle, mixed with the powder while stirring for 30 minutes, 27.8 kg of degassed deionized water was added, and the reaction mixture was heated to 50 ° C and allowed to swell for 2 hours. The reaction kettle was heated to 92 ° C, and the reaction was carried out for 6 hours. After the reaction was completed, the reaction product was cooled, filtered to remove the liquid components, and then vacuum dried at 70 ° C for 10 hours to obtain polypropylene-g-4-vinylpyridine powder.

[0163] The resulting powder was pelletized and a film product was prepared as in Example 1, and the resulting graft modified polypropylene and the resulting polypropylene film were tested for various structural and performance parameters. The results are shown in Tables 1 and 2.

[0164] [Example 10] 5.0 kg of PP1 powder sieved from the middle layer of the sieving device was added to a 50L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen replacement. 1.35 g of dibenzoyl peroxide and 76 g of glycidyl methacrylate were mixed into a homogeneous solution, then added to the reaction kettle, mixed with the powder while stirring for 30 minutes, and 16.7 kg of degassed deionized water was added. The reaction kettle was heated to 93°C and the reaction was carried out for 2.5 hours. After the reaction was completed, the reaction product was cooled, filtered to remove the liquid components, and then vacuum dried at 70°C for 10 hours to obtain polypropylene-g-glycidyl methacrylate powder. Figure 4 is a photograph of the microstructure of the powder of Example 10 observed with an electron microscope at 20,000 times, and the bright spherical parts are the dispersed phase.

[0165] The resulting powder was pelletized and a film product was prepared as in Example 1, and the resulting graft modified polypropylene and the resulting polypropylene film were tested for various structural and performance parameters. The results are shown in Tables 1 and 2.

[0166] [Example 11] The PP1 powder sieved from the middle layer of the sieving device in Example 1 was replaced with the PP1 powder sieved from the upper layer of the sieving device, and other preparation conditions and methods were the same as those in Example 1. The obtained graft-modified polypropylene and the obtained polypropylene film were tested for various structure and performance parameters. The results are shown in Tables 1 and 2.

[0167] [Example 12] The PP1 powder sieved from the middle layer of the sieving device in Example 1 was replaced with the PP1 powder sieved from the lower layer of the sieving device, and other preparation conditions and methods were the same as those in Example 1. The obtained graft-modified polypropylene and the obtained polypropylene film were tested for various structure and performance parameters. The results are shown in Tables 1 and 2.

[0168] [Example 13] 5.0 kg of PP1 powder sieved from the middle layer of the sieving device was added to a 50 L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, oxygen was removed by nitrogen replacement, 7.2 g of tert-butylperoxy (2-ethylhexanoate) and 400 g of styrene were mixed into a uniform solution, added to the reaction kettle, and mixed with the powder for 30 minutes while stirring, to which 17.8 kg of degassed deionized water was added, and the reaction mixture was heated to 50 ° C to swell for 2 hours. The swollen powder was heated to 95 ° C to react for 4 hours. After the reaction was completed, the reaction product was cooled, filtered to remove the liquid components, and vacuum dried at 70 ° C for 10 hours to obtain polypropylene-g-styrene powder C13. The obtained graft-modified polypropylene was tested for the properties of graft / self-polymerization ratio η, D50, ash content, MFR, Tm and flexural modulus. The results are shown in Table 1.

[0169] 1.5 kg of the above polypropylene-g-styrene powder C13 was weighed, 3 kg of xylene and 20 kg of THF were added, and the reaction system was sealed, heated to 70 ° C, and stirred for 5 hours for cleaning. After the stirring was completed, the liquid phase was removed by filtration, and the product was vacuum dried at 70 ° C for 10 hours to obtain polypropylene-g-styrene powder B13. The obtained graft-modified polypropylene was tested for the properties of graft / self-polymerization ratio η, D50, ash content, MFR, Tm and flexural modulus. The results are shown in Table 1.

[0170] The polypropylene-g-styrene powder (C13 or B13) and antioxidant 1010 / 168 (weight ratio 1:1) were weighed and added to a high-speed mixer to mix uniformly. The materials were pelletized using a Coperion Co. WP25 twin screw extruder at cutoff temperatures of 190-200-210-220-230-230-220°C and a screw speed of 300 rpm to obtain polypropylene-g-styrene pellets. The amount of antioxidant added was 0.3 parts by weight based on 100 parts by weight of polypropylene-g-styrene powder.

[0171] The obtained pellets were dried in a hot air oven, and the dried pellets were added to an LCR400-type extrusion casting device from Labtech Co., Sweden, for melt extrusion and casting to obtain a cast sheet, the temperature of the extruder for melt extrusion was 230°C, the temperature of the screen exchange area was controlled at 230°C, the temperature of the device head was controlled at 230°C, and the temperature of the casting roller was controlled at 25°C, and a cast sheet with a thickness of 230±20 μm was prepared.

[0172] The resulting thick polypropylene cast sheet was placed in the stretching fixture of a film biaxial stretching device and subjected to a biaxial synchronous stretching process. The processing conditions for each process included the following: preheating temperature was 160°C, stretching temperature was 160°C, stretching ratio was 5.5x5.5x, film stretching speed was 100% / sec, and film set temperature was 160°C. Various electrical property parameters were tested for the resulting polypropylene films C13 and B13. The results are shown in Table 2.

[0173] [Example 14] 3.0 kg of PP2 powder sieved from the middle layer of the sieving device was added to a 50 L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen substitution. 8.2 g of tert-butylperoxy (2-ethylhexanoate), 63 g of styrene, and 470 g of methyl methacrylate were mixed into a homogeneous solution, then added to the reaction kettle and mixed with the powder under stirring. The reaction mixture was allowed to swell at 60°C for 2 hours. Then, 18.1 kg of deionized water, which had been degassed and preheated to 60°C, was added through a filling tank. The reaction kettle was heated to 90°C, and the reaction was carried out for 6 hours. After the reaction was completed, the reaction product was cooled and filtered to remove the liquid components. 23 kg of acetone and 2 kg of n-heptane were added, and the resulting mixture was heated to 55°C and stirred for 3 hours. After the stirring was completed, the liquid phase was removed by filtration, and the mixture was dried in vacuum at 70° C. for 10 hours to obtain polypropylene-g-methyl methacrylate / styrene powder B14.

[0174] The resulting powder was pelletized and a film product was prepared as in Example 13, and the resulting graft modified polypropylene and polypropylene film B14 were tested for various structural and performance parameters. The results are shown in Tables 1 and 2.

[0175] [Example 15] 5.0 kg of PP1 powder sieved from the middle layer of the sieving device was added to a 50L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen replacement. 2.5 g of dibenzoyl peroxide and 250.5 g of methyl methacrylate were mixed into a homogeneous solution, then added to the reaction kettle and mixed with the powder while stirring for 30 minutes, to which 26.3 kg of degassed deionized water was added. The reaction kettle was heated to 91°C and the reaction was carried out for 3 hours. After the reaction was completed, the reaction product was cooled, filtered to remove the liquid components, and vacuum dried at 70°C for 10 hours to obtain polypropylene-g-methyl methacrylate powder C15.

[0176] 3 kg of the above polypropylene-g-methyl methacrylate powder C15 was weighed, 10 kg of xylene and 20 kg of ethyl acetate were added, and the reaction system was sealed, heated to 70°C, and stirred for 7 hours for cleaning. After stirring, the liquid phase was removed by filtration, and the mixture was vacuum dried at 70°C for 10 hours to obtain 2.965 kg of polypropylene-g-methyl methacrylate powder B15. The measurement results of TSDC are shown in Figure 6.

[0177] The resulting powder was pelletized and film products were prepared as in Example 13, and the resulting graft modified polypropylene and the resulting polypropylene films C15 and B15 were tested for various structural and performance parameters. The results are shown in Tables 1 and 2.

[0178] [Example 16] 1.5 kg of PP2 powder sieved from the middle layer of the sieving device was added to a 50L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen replacement. 1.9 g of dibenzoyl peroxide, 59.7 g of styrene, and 15.6 g of maleic anhydride were mixed into a homogeneous solution, then added to the reaction kettle and mixed with the powder under stirring. The resulting mixture was allowed to swell at room temperature for 6 hours and heated to 90°C. Then, 7.0 kg of deionized water, which had been degassed and preheated to 90°C, was added through a filling tank, and the reaction was carried out for 4 hours. After the reaction was completed, the reaction product was cooled and filtered to remove the liquid components. 25 kg of acetone was added, and the resulting solution was heated to 55°C and stirred for 5 hours. After the stirring was completed, the liquid phase was removed by filtration, and the mixture was dried in vacuum at 70°C for 10 hours to obtain polypropylene-g-maleic anhydride / styrene powder B16.

[0179] The resulting powder was pelletized and a film product was prepared as in Example 13, and the resulting graft modified polypropylene and polypropylene film B16 were tested for various structural and performance parameters. The results are shown in Tables 1 and 2.

[0180] [Comparative Example 1] 5.0 kg of PP1 powder sieved from the middle layer of the sieving device was pelletized to prepare a film product. The preparation conditions and method were the same as in Example 1. Various structure and performance parameters were tested for the polypropylene and the resulting polypropylene film. The results are shown in Tables 1 and 2. Figure 5 is a photograph showing the microstructure of PP1 powder under an electron microscope at 20,000 times magnification, and no dispersed phase is observed.

[0181] [Comparative Example 2] The PP1 powder in Example 1 was replaced with the PP4 powder sieved from the middle layer of the sieving device, 10.8 kg of deionized water was added, and other preparation conditions and methods were the same as those in Example 1. The obtained graft-modified polypropylene and the obtained polypropylene film were tested for various structural and electrical property parameters. The results are shown in Tables 1 and 2.

[0182] [Comparative Example 3] 5.0 kg of PP2 powder sieved from the middle layer of the sieving device was added to a 50L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen replacement. 18.6 g of dibenzoyl peroxide and 735 g of 4-vinylpyridine were mixed into a homogeneous solution and then added to the reaction kettle, and mixed with the powder while stirring for 30 minutes, to which 36.7 kg of degassed deionized water was added, and the reaction mixture was heated to 50 ° C and allowed to swell for 2 hours. The reaction kettle was heated to 92 ° C, and the reaction was carried out for 6 hours. After the reaction was completed, the reaction product was cooled, filtered to remove the liquid components, and vacuum dried at 70 ° C for 10 hours to obtain polypropylene-g-4-vinylpyridine powder.

[0183] The resulting powder was pelletized and film products were made as in Example 1, and the resulting graft modified polypropylene and polypropylene films were tested for various structural and electrical property parameters, with the results shown in Tables 1 and 2.

[0184] [Comparative Example 4] 5.0 kg of PP1 powder sieved from the middle layer of the sieving device and 400 g of polystyrene GPPS-123 were pelletized to prepare a film product. Other preparation conditions and methods were the same as those in Example 1. Various electrical property parameters were tested for the obtained polypropylene film. The results are shown in Table 2.

[0185] [Comparative Example 5] 5.0 kg of PP1 powder sieved from the middle layer of the sieving device and 1000 g of polystyrene GPPS-123 were pelletized to prepare a film product. The other preparation conditions and methods were the same as those in Example 2. When biaxially oriented, the film broke.

[0186] [Comparative Example 6] Tongfeng MPP03 high temperature film was tested for various performance parameters, and the results are shown in Table 2.

[0187] [Comparative Example 7] 5.0 kg of PP1 powder sieved from the middle layer of the sieving device was added to a 50L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen replacement. 2.0 g of dibenzoyl peroxide and 188.2 g of methyl methacrylate were mixed into a homogeneous solution and added to the reaction kettle, and mixed with the powder while stirring for 30 minutes, to which 25.9 kg of degassed deionized water was added. The reaction kettle was heated to 90°C and the reaction was carried out for 3 hours. After the reaction was completed, the reaction product was cooled and filtered to remove the liquid components, and then vacuum dried at 70°C for 10 hours to obtain 5.168 kg of polypropylene-g-methyl methacrylate powder D7. The results of the TSDC measurement are shown in Figure 6.

[0188] The resulting powder was pelletized and a film product was prepared as in Example 13, and the resulting graft modified polypropylene and polypropylene film D7 were tested for various structural and performance parameters. The results are shown in Tables 1 and 2.

[0189] [Table 3]

[0190] [Table 4]

[0191] Comparing D1 and C1, it can be seen that the dielectric and energy storage properties of polypropylene can be significantly improved by graft modification.

[0192] Comparing D2 and C1, it can be seen that when high-ash polypropylene is used as the reaction raw material, the size of the grafted phase becomes smaller, and the energy storage efficiency and energy storage properties are significantly lower than when low-ash polypropylene modifier is used under the same preparation conditions.

[0193] Comparing D3 with C9 and D1, it can be seen that when the size of the dispersed phase is too large, the breaking strength of the product is hardly improved compared with D1, other dielectric properties and energy storage properties are not obviously improved compared with D1, and the properties of the product are significantly different from those of Example C9 with graft modification.

[0194] Comparing D4 with C1-C12, it can be seen that when the graft monomer polymer is directly added, the interfacial action force of the mixture of the graft monomer polymer and polypropylene is weaker than that of D1, the breaking strength is lower, and the energy storage properties are reduced to a certain extent.

[0195] Comparing D5 and C2, it can be seen that the graft modified polypropylene material can form a film normally when the functional monomer loading is increased, but after adding a large amount of functional monomer polymer, it cannot form a film because the film was destroyed during processing.

[0196] Comparing D6 with C1-C12, it can be seen that the film according to the present invention has the advantages that the energy storage efficiency at 120°C is obviously higher than that of the commercially available high-temperature capacitor films, and the energy storage density and dielectric properties are equivalent to or slightly better than those of the commercially available high-temperature capacitor films.

[0197] From C11 to C12, it can be seen that by controlling the particle size of the polypropylene base material within a preferred range, a product having better heat insulation and energy storage properties can be obtained.

[0198] Comparing B13 with C13 and B15 with C15, it can be seen that the solvent cleaning process can effectively improve the dielectric properties of the material (significantly improving the DC volume resistivity) by reducing the effect of the self-polymerization products.

[0199] The final products of B15 and D7 have the same total amount of graft monomer. Through comparison of B15 and D7 and TSDC measurement, it can be seen that under the condition of the same total content of graft monomer, B15 with a higher graft / self-polymerization ratio η has an obvious change in the composition of the grafted phase, which leads to different charge trapping, and finally can effectively improve the dielectric properties of the material.

[0200] [Example 17] 5.0 kg of PP1 powder sieved from the middle layer of the sieving device was added to a 50 L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, oxygen was removed by nitrogen replacement, 7.2 g of tert-butylperoxy (2-ethylhexanoate) and 400 g of styrene were mixed into a uniform solution, added to the reaction kettle, and mixed with the powder for 30 minutes while stirring, to which 17.8 kg of degassed deionized water was added, and the reaction mixture was heated to 50 ° C and swollen for 2 hours. The swollen powder was heated to 95 ° C and reacted for 4 hours. After the reaction was completed, the reaction product was cooled, filtered to remove the liquid components, and vacuum dried at 70 ° C for 10 hours to obtain polypropylene-g-styrene powder. The obtained graft-modified polypropylene was tested for the properties of graft / self-polymerization ratio η, D50, ash content, MFR, Tm and flexural modulus. The results are shown in Table 4.

[0201] The polypropylene-g-styrene powder, antioxidant 1010 / 168 / 501 (weight ratio 1:1:0.03) and processing aid were weighed and added to a high-speed mixer and mixed at high speed for 30 seconds. The materials were pelletized using a Coperion Co. WP25 twin screw extruder at cutoff temperatures of 190-200-210-220-230-230-210°C and a screw speed of 300 rpm. Based on 100 parts by weight of modified polypropylene, the total amount of antioxidant was 0.3 parts by weight and the fluoropolymer as processing aid was 0.1 parts by weight.

[0202] The obtained pellets were dried in a hot air oven, and the dried pellets were added to an extrusion casting device of LCR400 type manufactured by Labtech Co., Sweden, for melt extrusion and casting to obtain a cast sheet, the temperature of the extruder for melt extrusion was 230°C, the temperature of the screen exchange area was controlled at 230°C, the temperature of the device head was controlled at 230°C, and the temperature of the casting roller was controlled at 25°C to prepare a thick cast sheet.

[0203] The thick cast sheet was placed in the stretching jig of a film biaxial stretching device and subjected to a biaxial step stretching process (i.e., first MD stretching, then TD stretching). The processing conditions of each process were as shown in Table 3: MD preheating temperature was 155°C, MD stretching temperature was 155°C, MD stretching ratio was 5 times, MD stretching speed was 200% / sec, TD preheating temperature was 170°C, TD stretching temperature was 170°C, TD stretching ratio was 7 times, TD stretching speed was 300% / sec, and film setting temperature was 175°C. Thus, a biaxially stretched polypropylene film was obtained.

[0204] The obtained film was tested for tensile properties, electrical properties, etc. The performance parameters of the obtained polypropylene film are shown in Tables 5 and 6.

[0205] [Example 18] 5.0 kg of PP2 powder sieved from the middle layer of the sieving device was added to a 50 L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen substitution. 13.5 g of tert-butylperoxy (2-ethylhexanoate) and 1001 g of styrene were mixed into a homogeneous solution, then added to the reaction kettle and mixed with the powder while stirring. The reaction mixture was heated to 40°C and allowed to swell for 3 hours. Next, 36.0 kg of deionized water, which had been degassed and preheated to 40°C, was added through a filling tank. The reaction kettle was heated to 90°C and the reaction was carried out for 6 hours. After the reaction was completed, the reaction product was cooled and filtered to remove the liquid components, and then vacuum dried at 70°C for 10 hours to obtain polypropylene-g-styrene powder.

[0206] The polypropylene-g-styrene powder, antioxidant 1035 / 168 / 501 (weight ratio 1:1:0.03) and processing aid were added to a high speed mixer and mixed at high speed for 30 seconds. The material was pelletized using a Coperion Co. WP25 twin screw extruder at cutoff temperatures of 190-200-210-220-230-230-210°C and a screw speed of 300 rpm. Based on 100 parts by weight of modified polypropylene, the total amount of antioxidant was 0.5 parts by weight and the fluoropolymer as processing aid was 0.2 parts by weight.

[0207] In this example, the film was prepared according to the same method as in Example 17, except that the biaxial stretching processing conditions were different, as shown in Table 3. The structure and performance parameters of the obtained graft modified polypropylene and the obtained polypropylene film are shown in Tables 4, 5, and 6.

[0208] [Example 19] 5.0 kg of PP2 powder sieved from the middle layer of the sieving device was added to a 50L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen replacement. 3.1 g of dibenzoyl peroxide, 112 g of styrene, and 13.9 g of maleic anhydride were mixed into a homogeneous solution, then added to the reaction kettle and mixed with the powder while stirring. The resulting mixture was allowed to swell at room temperature for 8 hours and then heated to 92°C. Next, 16.4 kg of deionized water that had been degassed and preheated to 92°C was added through a filling tank, the reaction kettle was heated to 92°C, and the reaction was carried out for 4 hours. After the reaction was completed, the reaction product was cooled and filtered to remove the liquid components, and then vacuum dried at 70°C for 10 hours to obtain polypropylene-g-maleic anhydride / styrene powder.

[0209] The modified polypropylene, antioxidant 1010 / 168 / 501 (weight ratio 1:1:0.05) and fluoropolymer were weighed and added to a high speed mixer and stirred at high speed for 30 seconds. The materials were pelletized using a Coperion Co. WP25 twin screw extruder at cutoff temperatures of 190-200-210-220-230-230-210°C and a screw speed of 300 rpm. Based on 100 parts by weight of modified polypropylene, the total amount of antioxidant was 0.3 parts by weight and the fluoropolymer was 0.1 parts by weight.

[0210] In this example, the film was prepared according to the same method as in Example 17, except that the biaxial stretching processing conditions were different, as shown in Table 3. The structure and performance parameters of the obtained graft modified polypropylene and the obtained polypropylene film are shown in Tables 4, 5, and 6.

[0211] [Example 20] 5.0 kg of PP1 powder sieved from the middle layer of the sieving device was added to a 50L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen replacement. 2.5 g of dibenzoyl peroxide and 250.5 g of methyl methacrylate were mixed into a homogeneous solution and then added to the reaction kettle, mixed with the powder while stirring for 30 minutes, and 26.3 kg of degassed deionized water was added. The reaction kettle was heated to 91°C and the reaction was carried out for 3 hours. After the reaction was completed, the reaction product was cooled and filtered to remove the liquid components, and then vacuum dried at 70°C for 10 hours to obtain polypropylene-g-methyl methacrylate powder.

[0212] The polypropylene-g-methyl methacrylate, antioxidant 1076 / 168 / 501 (weight ratio 1:1:0.04) and fluoropolymer were weighed and added to a high speed mixer and mixed at high speed for 30 seconds. The materials were pelletized using a Coperion Co. WP25 twin screw extruder at cutoff temperatures of 190-200-210-220-230-230-210°C and a screw speed of 300 rpm. Based on 100 parts by weight of modified polypropylene, the total amount of antioxidant was 0.3 parts by weight and the fluoropolymer was 0.1 parts by weight.

[0213] In this example, the film was prepared according to the same method as in Example 17, except that the biaxial stretching processing conditions were different, as shown in Table 3. The structure and performance parameters of the obtained graft modified polypropylene and the obtained polypropylene film are shown in Tables 4, 5, and 6.

[0214] [Example 21] 5.0 kg of PP2 powder sieved from the middle layer of the sieving device was added to a 50L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen replacement. 6.2 g of dibenzoyl peroxide, 198.0 g of styrene, and 52.0 g of maleic anhydride were mixed into a homogeneous solution, then added to the reaction kettle and mixed with the powder while stirring. The resulting mixture was allowed to swell at room temperature for 6 hours and heated to 90°C. Then, 22.6 kg of deionized water that had been degassed and preheated to 90°C was added through a filling tank, and the reaction was carried out for 4 hours. After the reaction was completed, the reaction product was cooled and filtered to remove the liquid components, and then vacuum dried at 70°C for 10 hours to obtain polypropylene-g-maleic anhydride / styrene powder.

[0215] The polypropylene-g-styrene / maleic anhydride, antioxidant 1010 / 168 / 501 (weight ratio 1:1:0.05) and fluoropolymer were weighed and added to a high speed mixer and mixed at high speed for 30 seconds. The materials were pelletized using a Coperion Co. WP25 twin screw extruder at cutoff temperatures of 190-200-210-220-230-230-210°C and a screw speed of 300 rpm. Based on 100 parts by weight of modified polypropylene, the total amount of antioxidant was 0.3 parts by weight and the fluoropolymer was 0.1 parts by weight.

[0216] In this example, the film was prepared according to the same method as in Example 17, except that the biaxial stretching processing conditions were different, as shown in Table 3. The structure and performance parameters of the obtained graft modified polypropylene and the obtained polypropylene film are shown in Tables 4, 5, and 6.

[0217] [Example 22] 5.0 kg of PP1 powder sieved from the middle layer of the sieving device was added to a 50L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen replacement. 31 g of lauroyl peroxide and 603 g of vinyltriethoxysilane were mixed into a homogeneous solution, then added to the reaction kettle, mixed with the powder while stirring for 20 minutes, and 19.6 kg of degassed deionized water was added. The reaction kettle was heated to 91°C and the reaction was carried out for 7 hours. After the reaction was completed, the reaction product was cooled and filtered to remove the liquid components, and then vacuum dried at 70°C for 10 hours to obtain polypropylene-g-vinyltriethoxysilane powder.

[0218] The resulting powder was pelletized and film products were prepared in the same manner and under the same conditions as in Example 17. The structure and performance parameters of the resulting graft modified polypropylene and polypropylene film are shown in Tables 4, 5 and 6.

[0219] [Example 23] 5.0 kg of PP2 powder sieved from the middle layer of the sieving device was added to a 50L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen replacement. 6.2 g of dibenzoyl peroxide, 115.0 g of methyl acrylate, and 38.0 g of acrylic acid were mixed into a homogeneous solution, then added to the reaction kettle, mixed with the powder while stirring for 40 minutes, and heated to 95 ° C. Next, 36.1 kg of degassed and preheated to 90 ° C was added through a filling tank, and the reaction was carried out for 4 hours. After the reaction was completed, the reaction product was cooled and filtered to remove the liquid components, and then vacuum dried at 70 ° C for 10 hours to obtain polypropylene-g-methyl acrylate / acrylic acid powder.

[0220] The resulting powder was pelletized and film products were prepared in the same manner and under the same conditions as in Example 17. The structure and performance parameters of the resulting graft modified polypropylene and polypropylene film are shown in Tables 4, 5 and 6.

[0221] [Example 24] The PP1 powder in Example 17 was replaced with the PP3 powder sieved from the middle layer of the sieving device, and other preparation conditions and methods were the same as those in Example 17. Various performance parameters were tested for the obtained polypropylene film. The structure and performance parameters of the obtained graft-modified polypropylene and polypropylene film are shown in Tables 4, 5, and 6.

[0222] [Example 25] 5.0 kg of PP2 powder sieved from the middle layer of the sieving device was added to a 50L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen replacement. 8.8 g of dibenzoyl peroxide and 355 g of 4-vinylpyridine were mixed into a homogeneous solution and then added to the reaction kettle, mixed with the powder while stirring for 30 minutes, 27.8 kg of degassed deionized water was added, and the reaction mixture was heated to 50 ° C and allowed to swell for 2 hours. The reaction kettle was heated to 92 ° C, and the reaction was carried out for 6 hours. After the reaction was completed, the reaction product was cooled, filtered to remove the liquid components, and then vacuum dried at 70 ° C for 10 hours to obtain polypropylene-g-4-vinylpyridine powder.

[0223] The resulting powder was pelletized and film products were prepared in the same manner and under the same conditions as in Example 17. The structure and performance parameters of the resulting graft modified polypropylene and polypropylene film are shown in Tables 4, 5 and 6.

[0224] [Example 26] 5.0 kg of PP1 powder sieved from the middle layer of the sieving device was added to a 50L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen replacement. 1.35 g of dibenzoyl peroxide and 76 g of glycidyl methacrylate were mixed into a homogeneous solution and then added to the reaction kettle, mixed with the powder while stirring for 30 minutes, and 16.7 kg of degassed deionized water was added. The reaction kettle was heated to 93°C and the reaction was carried out for 2.5 hours. After the reaction was completed, the reaction product was cooled and filtered to remove the liquid components, and then vacuum dried at 70°C for 10 hours to obtain polypropylene-g-glycidyl methacrylate powder.

[0225] The resulting powder was pelletized and film products were prepared in the same manner and under the same conditions as in Example 17. The structure and performance parameters of the resulting graft modified polypropylene and polypropylene film are shown in Tables 4, 5 and 6.

[0226] [Example 27] The modified polypropylene and polypropylene film were prepared according to the method of Example 17, except that the antioxidant was antioxidant 1010 / 168 (weight ratio 1:1). The structure and performance parameters of the obtained graft modified polypropylene and polypropylene film are shown in Tables 4, 5 and 6.

[0227] [Example 28] The modified polypropylene and polypropylene film were prepared according to the method of Example 18, except that the antioxidant was Antioxidant 501. The structure and performance parameters of the obtained graft modified polypropylene and polypropylene film are shown in Tables 4, 5 and 6.

[0228] [Example 29] The modified polypropylene and polypropylene film were prepared according to the method of Example 19, except that the antioxidant was antioxidant 1010 / 168 / 501 (weight ratio 1:1:0.01). The structure and performance parameters of the obtained graft modified polypropylene and polypropylene film are shown in Tables 4, 5 and 6.

[0229] [Example 30] The PP1 powder sieved from the middle layer of the sieving device in Example 17 was replaced with the PP1 powder sieved from the upper layer of the sieving device, and other preparation conditions and methods were the same as those in Example 17. The structure and performance parameters of the obtained graft-modified polypropylene and polypropylene film are shown in Tables 4, 5 and 6.

[0230] [Example 31] The PP1 powder sieved from the middle layer of the sieving device in Example 17 was replaced with the PP1 powder sieved from the lower layer of the sieving device, and other preparation conditions and methods were the same as those in Example 17. The structure and performance parameters of the obtained graft-modified polypropylene and polypropylene film are shown in Tables 4, 5 and 6.

[0231] [Example 32] 5.0 kg of PP1 powder sieved from the middle layer of the sieving device was added to a 50 L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, oxygen was removed by nitrogen replacement, 7.2 g of tert-butyl peroxy (2-ethylhexanoate) and 400 g of styrene were mixed into a uniform solution, added to the reaction kettle, and mixed with the powder for 30 minutes while stirring, to which 17.8 kg of degassed deionized water was added, and the reaction mixture was heated to 50 ° C to swell for 2 hours. The swollen powder was heated to 95 ° C to react for 4 hours. After the reaction was completed, the reaction product was cooled, filtered to remove the liquid components, and vacuum dried at 70 ° C for 10 hours to obtain polypropylene-g-styrene powder C32. The obtained graft-modified polypropylene was tested for the properties of graft / self-polymerization ratio η, D50, ash content, MFR, Tm and flexural modulus. The results are shown in Table 4.

[0232] 1.5 kg of the above polypropylene-g-styrene powder C32 was weighed, 3 kg of xylene and 20 kg of THF were added, and the reaction system was sealed, heated to 70 ° C, and stirred for 5 hours for cleaning. After the stirring was completed, the liquid phase was removed by filtration, and the product was vacuum dried at 70 ° C for 10 hours to obtain polypropylene-g-styrene powder B32. The obtained graft-modified polypropylene was tested for the properties of graft / self-polymerization ratio η, D50, ash content, MFR, Tm and flexural modulus. The results are shown in Table 4.

[0233] The polypropylene-g-styrene powder (C32 or B32), antioxidant 1010 / 168 / 501 (weight ratio 1:1:0.3) and processing aid were weighed and added to a high-speed mixer and mixed at high speed for 30 seconds. The materials were pelletized using a Coperion Co. WP25 twin screw extruder at cutoff temperatures of 190-200-210-220-230-230-210°C and a screw speed of 300 rpm. Based on 100 parts by weight of modified polypropylene, the total amount of antioxidant was 0.3 parts by weight and the fluoropolymer as processing aid was 0.1 parts by weight.

[0234] The obtained pellets were dried in a hot air oven, and the dried pellets were added to an extrusion casting device of LCR400 type manufactured by Labtech Co., Sweden, for melt extrusion and casting to obtain a cast sheet, the temperature of the extruder for melt extrusion was 230°C, the temperature of the screen exchange area was controlled at 230°C, the temperature of the device head was controlled at 230°C, and the temperature of the casting roller was controlled at 25°C to prepare a thick cast sheet.

[0235] The thick cast sheet was placed in the stretching jig of a film biaxial stretching device and subjected to a biaxial step stretching process (i.e., first MD stretching, then TD stretching). The processing conditions of each process were as shown in Table 3: MD preheating temperature was 155°C, MD stretching temperature was 155°C, MD stretching ratio was 5 times, MD stretching speed was 200% / sec, TD preheating temperature was 170°C, TD stretching temperature was 170°C, TD stretching ratio was 7 times, TD stretching speed was 300% / sec, and film setting temperature was 175°C. Thus, biaxially stretched polypropylene films C32 and B32 were obtained.

[0236] The obtained film was tested for tensile properties, electrical properties, etc. The performance parameters of the obtained polypropylene film are shown in Tables 5 and 6.

[0237] [Example 33] 3.0 kg of PP2 powder sieved from the middle layer of the sieving device was added to a 50 L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen substitution. 8.2 g of tert-butylperoxy (2-ethylhexanoate), 63 g of styrene, and 470 g of methyl methacrylate were mixed into a homogeneous solution, then added to the reaction kettle and mixed with the powder under stirring. The reaction mixture was heated to 60°C and allowed to swell for 2 hours. Then, 18.1 kg of deionized water, which had been degassed and preheated to 60°C, was added through a filling tank. The reaction kettle was heated to 90°C, and the reaction was carried out for 6 hours. After the reaction was completed, the reaction product was cooled and filtered to remove the liquid components. 23 kg of acetone and 2 kg of n-heptane were added, and the resulting solution was heated to 55°C and stirred for 3 hours. After the stirring was completed, the liquid phase was removed by filtration, and the mixture was dried in vacuum at 70° C. for 10 hours to obtain polypropylene-g-methyl methacrylate / styrene powder B33.

[0238] The polypropylene-g-methyl methacrylate / styrene powder, antioxidant 1035 / 168 / 501 (weight ratio 1:1:0.03) and processing aid were weighed and added to a high-speed mixer and mixed at high speed for 30 seconds. The materials were pelletized using a Coperion Co. WP25 twin screw extruder at cutoff temperatures of 190-200-210-220-230-230-210°C and a screw speed of 300 rpm. Based on 100 parts by weight of modified polypropylene, the total amount of antioxidant was 0.5 parts by weight and the fluoropolymer as processing aid was 0.2 parts by weight.

[0239] The film was prepared according to the same method as in Example 32, except that the biaxial stretching processing conditions were different, as shown in Table 3. The structure and performance parameters of the obtained graft modified polypropylene and the obtained polypropylene film B33 are shown in Tables 4, 5 and 6.

[0240] [Example 34] 5.0 kg of PP1 powder sieved from the middle layer of the sieving device was added to a 50L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen replacement. 2.5 g of dibenzoyl peroxide and 250.5 g of methyl methacrylate were mixed into a homogeneous solution and then added to the reaction kettle, and mixed with the powder while stirring for 30 minutes, to which 26.3 kg of degassed deionized water was added. The reaction kettle was heated to 91°C and the reaction was carried out for 3 hours. After the reaction was completed, the reaction product was cooled, filtered to remove the liquid components, and vacuum dried at 70°C for 10 hours to obtain polypropylene-g-methyl methacrylate powder C34.

[0241] 3 kg of the polypropylene-g-methyl methacrylate powder C34 was weighed, 10 kg of xylene and 20 kg of ethyl acetate were added, and the reaction system was sealed, heated to 70° C., and stirred for 7 hours for cleaning. After stirring, the liquid phase was removed by filtration, and the mixture was vacuum-dried at 70° C. for 10 hours to obtain 2.965 kg of polypropylene-g-methyl methacrylate powder B34.

[0242] The polypropylene-g-methyl methacrylate powder (C34 or B34), antioxidant 1076 / 168 / 501 (weight ratio 1:1:0.04) and fluoropolymer were weighed and added to a high speed mixer and mixed at high speed for 30 seconds. The materials were pelletized using a Coperion Co. WP25 twin screw extruder at cutoff temperatures of 190-200-210-220-230-230-210°C and a screw speed of 300 rpm. Based on 100 parts by weight of modified polypropylene, the total amount of antioxidant was 0.3 parts by weight and the fluoropolymer was 0.1 parts by weight.

[0243] The films were prepared according to the same method as in Example 32, except that the biaxial stretching processing conditions were different, as shown in Table 3. The structure and performance parameters of the obtained graft modified polypropylene and the obtained polypropylene films C34 and B34 are shown in Tables 4, 5, and 6.

[0244] [Example 35] 1.5 kg of PP2 powder sieved from the middle layer of the sieving device was added to a 50L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen replacement. 1.9 g of dibenzoyl peroxide, 59.7 g of styrene, and 15.6 g of maleic anhydride were mixed into a homogeneous solution, then added to the reaction kettle and mixed with the powder under stirring. The resulting mixture was allowed to swell at room temperature for 6 hours and heated to 90°C. Then, 7.0 kg of deionized water that had been degassed and preheated to 90°C was added through a filling tank, and the reaction was carried out for 4 hours. After the reaction was completed, the reaction product was cooled and filtered to remove the liquid components. 25 kg of acetone was added, and the resulting solution was heated to 55°C and stirred for 5 hours. After the stirring was completed, the liquid phase was removed by filtration, and the mixture was dried in vacuum at 70°C for 10 hours to obtain polypropylene-g-maleic anhydride / styrene powder B35.

[0245] The polypropylene-g-maleic anhydride / styrene powder, antioxidant 1010 / 168 / 501 (weight ratio 1:1:0.05) and fluoropolymer were weighed and added to a high speed mixer and mixed at high speed for 30 seconds. The materials were pelletized using a Coperion Co. WP25 twin screw extruder at cutoff temperatures of 190-200-210-220-230-230-210°C and a screw speed of 300 rpm. Based on 100 parts by weight of modified polypropylene, the total amount of antioxidant was 0.3 parts by weight and the fluoropolymer was 0.1 parts by weight.

[0246] The film was prepared according to the same method as in Example 32, except that the biaxial stretching processing conditions were different, as shown in Table 3. The structure and performance parameters of the obtained graft modified polypropylene and the obtained polypropylene film B35 are shown in Tables 4, 5 and 6.

[0247] [Comparative Example 8] 5.0 kg of PP1 powder sieved from the middle layer of the sieving device was pelletized to prepare a film product. The antioxidant was antioxidant 1010 / 168 (weight ratio 1:1), and other preparation conditions and methods were the same as in Example 17. Various performance parameters were tested for the obtained product. The structure and performance parameters of the obtained polypropylene and the obtained polypropylene film are shown in Tables 4, 5, and 6.

[0248] [Comparative Example 9] The PP1 powder in Example 17 was replaced with the PP4 powder sieved from the middle layer of the sieving device, 10.8 kg of deionized water was added, and other preparation conditions and methods were the same as those in Example 1. Various performance parameters were tested for the obtained products. The structures and performance parameters of the obtained graft modified polypropylene and polypropylene film are shown in Tables 4, 5, and 6.

[0249] [Comparative Example 10] 5.0 kg of PP2 powder sieved from the middle layer of the sieving device was added to a 50L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen replacement. 18.6 g of dibenzoyl peroxide and 735 g of 4-vinylpyridine were mixed into a homogeneous solution and then added to the reaction kettle, and mixed with the powder while stirring for 30 minutes, to which 36.7 kg of degassed deionized water was added, and the reaction mixture was heated to 50 ° C and allowed to swell for 2 hours. The reaction kettle was heated to 92 ° C, and the reaction was carried out for 6 hours. After the reaction was completed, the reaction product was cooled, filtered to remove the liquid components, and vacuum dried at 70 ° C for 10 hours to obtain polypropylene-g-4-vinylpyridine powder.

[0250] The resulting powder was pelletized to prepare film products. The antioxidant was antioxidant 1010 / 168 (weight ratio 1:1), and the process and conditions were the same as in Example 17. The structure and performance parameters of the resulting graft modified polypropylene and the resulting polypropylene film are shown in Tables 4, 5, and 6.

[0251] [Comparative Example 11] 5.0 kg of PP1 powder sieved from the middle layer of the sieving device and 400 g of polystyrene GPPS-123 were pelletized to prepare a film product. Other preparation conditions and methods were the same as those in Example 17. Various performance parameters were tested for the obtained product. The performance parameters of the obtained polypropylene film are shown in Tables 5 and 6.

[0252] [Comparative Example 12] 5.0 kg of PP1 powder sieved from the middle layer of the sieving device and 1000 g of polystyrene GPPS-123 were pelletized to prepare a film product. The antioxidant was antioxidant 1010 / 168 (weight ratio 1:1), and other preparation conditions and methods were the same as those in Example 18. When biaxially stretched, the film broke.

[0253] [Comparative Example 13] Tongfeng MPP03 high temperature film was tested for various performance parameters, and the results are shown in Tables 5 and 6.

[0254] [Comparative Example 14] 5.0 kg of PP1 powder sieved from the middle layer of the sieving device was added to a 50L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen replacement. 2.0 g of dibenzoyl peroxide and 188.2 g of methyl methacrylate were mixed into a homogeneous solution and added to the reaction kettle, and mixed with the powder while stirring for 30 minutes, to which 25.9 kg of degassed deionized water was added. The reaction kettle was heated to 90°C and the reaction was carried out for 3 hours. After the reaction was completed, the reaction product was cooled, filtered to remove the liquid components, and vacuum dried at 70°C for 10 hours to obtain 5.168 kg of polypropylene-g-methyl methacrylate powder D14.

[0255] The polypropylene-g-methyl methacrylate powder, antioxidant 1076 / 168 / 501 (weight ratio 1:1:0.04) and fluoropolymer were weighed and added to a high speed mixer and mixed at high speed for 30 seconds. The materials were pelletized using a Coperion Co. WP25 twin screw extruder at cutoff temperatures of 190-200-210-220-230-230-210°C and a screw speed of 300 rpm. Based on 100 parts by weight of modified polypropylene, the total amount of antioxidant was 0.3 parts by weight and the fluoropolymer was 0.1 parts by weight.

[0256] The film was prepared according to the same method as in Example 32. The structure and performance parameters of the obtained graft modified polypropylene and polypropylene film D14 are shown in Tables 4, 5 and 6.

[0257] [Comparative Example 15] 5.0 kg of PP1 powder sieved from the middle layer of the sieving device was added to a 50 L reaction kettle equipped with a double-layered four-blade stirring paddle and baffle, the reaction system was sealed, and oxygen was removed by nitrogen replacement. 3.9 g of tert-butylperoxy (2-ethylhexanoate) and 200 g of styrene were mixed into a homogeneous solution, then added to the reaction kettle and mixed with the powder while stirring for 30 minutes, to which 17.2 kg of degassed deionized water was added, and the reaction mixture was heated to 50 ° C and swollen for 2 hours. The swollen powder was heated to 95 ° C and reacted for 4 hours. After the reaction was completed, the reaction product was cooled, filtered to remove the liquid components, and vacuum dried at 70 ° C for 10 hours to obtain 5.168 kg of polypropylene-g-styrene powder with a graft / self-polymerization ratio η of 2.11.

[0258] The resulting polypropylene-g-styrene powder was mixed with 159 g of polystyrene GPPS-123 and pelletized to prepare a film product. Other preparation conditions and methods were the same as in Example 17. The resulting mixture and the resulting polypropylene film were tested for various structural and performance parameters. The results are shown in Tables 4, 5, and 6.

[0259] [Table 5]

[0260] [Table 6]

[0261] [Table 7]

[0262] [Table 8]

[0263] Comparing D8 and C17, it can be seen that the dielectric and energy storage properties of polypropylene can be significantly improved by graft modification.

[0264] Comparing D9 and C17, it can be seen that when high-ash polypropylene is used as the reaction raw material, the size of the grafted phase becomes smaller, and the energy storage efficiency and energy storage properties are significantly lower than when low-ash polypropylene modifier is used under the same preparation conditions.

[0265] Comparing D10 with C25 and D8, it can be seen that when the size of the dispersed phase is too large, the breaking strength of the product is little improved compared with D8, other dielectric properties and energy storage properties are not obviously improved compared with D8, and the properties of the product are significantly different from those of example C25 with graft modification.

[0266] Comparing D11 with C17-C31, it can be seen that when the graft monomer polymer is directly added, the interfacial action force of the mixture of the graft monomer polymer and polypropylene is weaker than that of D8, the breaking strength is lower, and the energy storage properties are reduced to a certain extent.

[0267] Comparing D12 and C18, it can be seen that the graft modified polypropylene material can form a film normally when the functional monomer loading is increased, but after adding a large amount of functional monomer polymer, it cannot form a film because the film was destroyed during processing.

[0268] Comparing D13 with C17-C31, it can be seen that the film according to the present invention has the advantages that the energy storage efficiency at 120°C is obviously higher than that of the commercially available high-temperature capacitor films, and the energy storage density and dielectric properties are equivalent to or slightly better than those of the commercially available high-temperature capacitor films.

[0269] From C30 to C31, it can be seen that by controlling the particle size of the polypropylene base material within a preferred range, a product having better heat insulation and energy storage properties can be obtained.

[0270] Comparing B32 with C32 and B34 with C34, it can be seen that the solvent cleaning process can effectively improve the dielectric properties of the material (significantly improving the DC volume resistivity) by reducing the influence of the self-polymerization products.

[0271] The final products of B34 and D14 have the same total amount of graft monomer. Through comparison between B34 and D14 and TSDC measurement, it can be seen that under the condition of the same total content of graft monomer, B34 with a higher graft / self-polymerization ratio η has an obvious change in the composition of the grafted phase, which leads to different charge trapping, and finally can effectively improve the dielectric properties of the material.

[0272] Comparing D15 and C17, it can be seen that when the total styrene content is the same, the product with a higher graft / self-polymerization ratio η has better thermal insulation and energy storage properties.

[0273] Although the embodiments of the present invention have been described above, the above description is illustrative and not exhaustive, and the present invention is not limited to the embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the embodiments.

[0274] The range endpoints and any values ​​disclosed herein are not limited to the exact range or value, but should be understood to encompass values ​​close to those ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and the individual point values, and the individual point values ​​may be combined with each other to produce one or more new numerical ranges, which numerical ranges should be considered as specifically disclosed herein.

[0275] As used herein, the terms "comprise" and "containing" are used interchangeably and include "consisting essentially of," "consisting of," and "being." [Brief description of the drawings]

[0276] [Figure 1] 1 is a photograph showing the microstructure of the modified polypropylene sample of Example 1 under an electron microscope at 20,000 times magnification, in which the spherical dispersed phase is an aggregate of styrene structural units. [Diagram 2] 1 is a photograph showing the microstructure of a modified polypropylene sample of Example 2 under an electron microscope at 20,000 times magnification. [Diagram 3] 1 is a photograph showing the microstructure of a modified polypropylene sample of Example 3 under an electron microscope at 20,000 times magnification. [Figure 4] 1 is a photograph showing the microstructure of a modified polypropylene sample of Example 10 under an electron microscope at 20,000 times magnification. [Diagram 5] 1 is a photograph showing the microstructure of the modified polypropylene sample of Comparative Example 1 under an electron microscope at 20,000 times magnification, in which no dispersed phase is discernible. [Figure 6] TSDC test results for the products of Example 15 and Comparative Example 7 are shown.

Claims

1. A biaxially oriented polypropylene dielectric film, wherein raw materials for preparing said biaxially oriented polypropylene dielectric film include modified polypropylene grafted with an alkenyl-containing functional monomer; A biaxially oriented polypropylene dielectric film, characterized in that the modified polypropylene grafted with an 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 modified polypropylene grafted with an alkenyl-containing functional monomer has an ash content of less than 50 ppm, preferably less than 36 ppm, and more preferably less than 30 ppm; in the modified polypropylene grafted with an alkenyl-containing functional monomer, the ratio of the mass of structural units derived from the alkenyl-containing functional monomer and in a grafted state to the mass of structural units derived from the alkenyl-containing functional monomer and in a self-polymerized state is 1.0 or more; and the D50 of the dispersed phase is less than 450 nm, preferably 50 to 400 nm.

2. 2. The biaxially oriented polypropylene dielectric film according to claim 1, wherein the biaxially oriented polypropylene dielectric film has a maximum operating temperature of 100°C or higher, preferably 110-160°C, and more preferably 120-145°C.

3. The biaxially oriented polypropylene dielectric film according to claim 1 or 2, wherein the biaxially oriented polypropylene dielectric film has at least one of the following characteristics: Breakdown field strength E at 120°C ｇ is 500 MV / m or more, preferably 550 to 800 MV / m; DC volume resistivity ρ at 120° C. and an electric field strength of 200 MV / m ｖｇ But 6.0 x 10 １３ Ω·m or more, preferably 1.0×10 １４ Ω m to 1.0 x 10 ２０ Ω·m, preferably 1.5×10 １４ Ω m to 0.9 x 10 ２０ Ω·m, more preferably 2.0×10 １４ Ω m to 1.0 x 10 １７ Ω·m; A dielectric constant at 120° C. and 100 Hz is greater than 2.25, preferably 2.26 to 2.65; a dielectric loss at 120° C. and 100 Hz of less than 1.55E-3, preferably less than 1.5E-3, preferably 1.0E-3 or less, more preferably 1.0E-6 to 1.3E-3, and even more preferably 1.0E-6 to 9E-4; Energy storage density at 120°C and 300MV / m is 0.720J / cm ３ Greater than 0.740 to 2.0 J / cm ３ , more preferably 0.780 to 2.0 J / cm ３ and more preferably 0.80 to 2.0 J / cm ３ is; The energy storage efficiency at 120° C. and 300 MV / m is greater than 90.0%, and preferably 92.0-99.0%.

4. The biaxially oriented polypropylene dielectric film according to any one of claims 1 to 3, wherein the biaxially oriented polypropylene dielectric film has at least one of the following characteristics: a longitudinal tensile strength of 140 MPa or more, and preferably 140 to 170 MPa; a transverse tensile strength of 200 MPa or more, and preferably 205 to 250 MPa; a longitudinal breaking elongation of 210% or more, preferably 225% or more; a transverse breaking elongation of 60% or more, preferably 62% or more; a thickness of 0.5 to 15 μm, preferably 4 to 10 μm.

5. The biaxially oriented polypropylene dielectric film according to claim 1, wherein in the modified polypropylene grafted with the alkenyl-containing functional monomer, the ratio of the mass of structural units derived from the alkenyl-containing functional monomer and in a grafted state to the mass of structural units derived from the alkenyl-containing functional monomer and in a self-polymerized state is 1.1 to 1.0, preferably 1.2 to 6.

6. 2. The biaxially oriented polypropylene dielectric film according to claim 1, wherein in the modified polypropylene grafted with the alkenyl-containing functional monomer, the ratio of the mass of structural units derived from the alkenyl-containing functional monomer and in a grafted state to the mass of structural units derived from the alkenyl-containing functional monomer and in a self-polymerized state is 1.5 or more, preferably 2 or more.

7. The biaxially oriented polypropylene dielectric film according to any one of claims 1 to 6, wherein the modified polypropylene grafted with alkenyl-containing functional monomer has at least one of the following characteristics: a melt flow rate of 1 to 10 g / 10 min, preferably 1.5 to 8 g / 10 min, and more preferably 2 to 5 g / 10 min at 230°C under a load of 2.16 kg; a melting temperature T ｍ is 155-168° C., and preferably 157-165° C.; flexural modulus is 1400-2000 MPa, and preferably 1500-1800 MPa.

8. The alkenyl-containing functional monomer has Formula 1: 【Chemistry 1】 At least one monomer having a structure represented by In formula 1, R ｂ , R ｃ , R ｄ are each independently selected from H, substituted or unsubstituted alkyl; R ａ is selected from substituted or unsubstituted alkyl, substituted or unsubstituted alkoxy, substituted or unsubstituted aryl, substituted or unsubstituted ester groups, substituted or unsubstituted carboxyl, substituted or unsubstituted cycloalkyl or heterocyclyl, cyano, substituted or unsubstituted silyl; R ａ and R ｄ optionally forms a ring; The biaxially oriented polypropylene dielectric film according to any one of claims 1 to 7.

9. R ｂ , R ｃ , R ｄ are each independently H, substituted or unsubstituted C １ -C ６ alkyl; R ａ is a substituted or unsubstituted C １ -C ２０ Alkyl, substituted or unsubstituted C １ -C ２０ Alkoxy, substituted or unsubstituted C ６ -C ２０ Aryl, substituted or unsubstituted C １ -C ２０ Ester group, substituted or unsubstituted C １ -C ２０ Carboxyl, substituted or unsubstituted C ３ -C ２０ Cycloalkyl or heterocyclyl, cyano, substituted or unsubstituted C ３ -C ２０ silyl; said substituents are selected from halogen, —OH, —NH ２ , =O, C １ -C １２ Alkyl, C ３ -C ６ Cycloalkyl, C １ -C １２ Alkoxy, C １ -C １２ acyloxy; R ａ and R ｄ are optionally joined together via a double bond to form a 4- to 6-membered heterocyclic ring; The biaxially oriented polypropylene dielectric film of claim 8.

10. R ｂ , R ｃ , R ｄ each independently represents H, substituted or unsubstituted C １ -C ６ alkyl; R ａ is at least one selected from a group represented by formula 2, a group represented by formula 3, a group represented by formula 4, a group represented by formula 5, a group represented by formula 6, and a heterocyclic group; 【Chemistry 2】 In formula 2, R ４ -R ８ are each independently H, a halogen, a hydroxyl, an amino, a phosphate group, a sulfonate group, a substituted or unsubstituted C １ -C １２ Alkyl, substituted or unsubstituted C ３ -C １２ Cycloalkyl, substituted or unsubstituted C １ -C １２ Alkoxy, substituted or unsubstituted C １ -C １２ Ester group, substituted or unsubstituted C １ -C １２ amine groups, the substituents being selected from halogen, hydroxy, amino, phosphate groups, sulfonate groups, C １ -C １２ Alkyl, C ３ -C １２ Cycloalkyl, C １ -C １２ Alkoxy, C １ -C １２ Ester group, C １ -C １２ amine groups; preferably, R ４ -R ８ are each independently H, halogen, hydroxy, amino, substituted or unsubstituted C １ -C ６ Alkyl, substituted or unsubstituted C １ -C ６ alkoxy; 【Chemistry 3】 In formula 3, R ４ -R １０ are each independently H, a halogen, a hydroxyl, an amino, a phosphate group, a sulfonate group, a substituted or unsubstituted C １ -C １２ Alkyl, substituted or unsubstituted C ３ -C １２ Cycloalkyl, substituted or unsubstituted C １ -C １２ Alkoxy, substituted or unsubstituted C １ -C １２ Ester group, substituted or unsubstituted C １ -C １２ amine groups, the substituents being selected from halogen, hydroxy, amino, phosphate groups, sulfonate groups, C １ -C １２ Alkyl, C ３ -C １２ Cycloalkyl, C １ -C １２ Alkoxy, C １ -C １２ Ester group, C １ -C １２ amine groups; preferably, R ４ -R １０ are each independently H, halogen, hydroxy, amino, substituted or unsubstituted C １ -C ６ Alkyl, substituted or unsubstituted C １ -C ６ alkoxy, said substituents being selected from halogen, hydroxy, amino, C １ -C ６ Alkyl, C １ -C ６ alkoxy; 【Chemistry 4】 In formula 4, R ４ '-R １０ ' are each independently H, halogen, hydroxy, amino, a phosphate group, a sulfonate group, a substituted or unsubstituted C １ -C １２ Alkyl, substituted or unsubstituted C ３ -C １２ Cycloalkyl, substituted or unsubstituted C １ -C １２ Alkoxy, substituted or unsubstituted C １ -C １２ Ester group, substituted or unsubstituted C １ -C １２ amine groups, the substituents being selected from halogen, hydroxy, amino, phosphate groups, sulfonate groups, C １ -C １２ Alkyl, C ３ -C １２ Cycloalkyl, C １ -C １２ Alkoxy, C １ -C １２ Ester group, C １ -C １２ amine groups; preferably, R ４ '-R １０ Each ' is independently H, halogen, hydroxy, amino, substituted or unsubstituted C １ -C ６ Alkyl, substituted or unsubstituted C １ -C ６ alkoxy, said substituents being selected from halogen, hydroxy, amino, C １ -C ６ Alkyl, C １ -C ６ alkoxy; 【Chemistry 5】 In formula 5, R′, R″, and R′″ are each independently a substituted or unsubstituted C １ -C １２ Straight chain alkyl, substituted or unsubstituted C ３ -C １２ Branched alkyl, substituted or unsubstituted C １ -C １２ Alkoxy, substituted or unsubstituted C １ -C １２ acyloxy; preferably, R １ is C ２ -C ６ alkenyl, preferably monounsaturated alkenyl; R ２ , R ３ , R ４ each independently represents a substituted or unsubstituted C １ -C ６ Straight chain alkyl, substituted or unsubstituted C ３ -C ６ Branched alkyl, substituted or unsubstituted C １ -C ６ Alkoxy, substituted or unsubstituted C １ -C ６ acyloxy; 【Chemistry 6】 In formula 6, R ｍ is hydrogen and / or the following substituted or unsubstituted groups: １ -C ２０ Straight chain alkyl, C ３ -C ２０ Branched alkyl, C ３ -C １２ Cycloalkyl, C ３ -C １２ Epoxy alkyl, C ３ -C １２ epoxyalkylalkyl, wherein said substituents are at least one selected from halogen, amino and hydroxy; the heterocyclic group is selected from imidazolyl, pyrazolyl, carbazolyl, pyrrolidinonyl, pyridyl, piperidinyl, caprolactamyl, pyrazinyl, thiazolyl, purinyl, morpholinyl, oxazolinyl; The biaxially oriented polypropylene dielectric film of claim 9.

11. The alkenyl-containing functional monomer is a styrene monomer, the styrene monomer being at least one selected from styrene, α-methylstyrene, 1-vinylnaphthalene, 2-vinylnaphthalene, mono- or poly-substituted styrene, mono- or poly-substituted α-methylstyrene, mono- or poly-substituted 1-vinylnaphthalene, and mono- or poly-substituted 2-vinylnaphthalene; the substituent is preferably a halogen, a hydroxy, an amino, a phosphoric acid group, a sulfonic acid group, C １ -C ８ Straight chain alkyl, C ３ -C ８ Branched alkyl or cycloalkyl, C １ -C ６ Linear alkoxy, C ３ -C ８ Branched alkoxy or cycloalkoxy, C １ -C ８ Linear ester group, C ３ -C ８ A branched ester group or a cyclic ester group, C １ -C ８ Linear amine groups and C ３ -C ８ at least one selected from a branched amine group or a cyclic amine group; preferably, the styrene monomer is at least one selected from styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene and 4-methylstyrene; The biaxially oriented polypropylene dielectric film of claim 10.

12. 11. The biaxially oriented polypropylene dielectric film of claim 10, wherein the alkenyl-containing functional monomer is an alkenyl-containing silane monomer, and the alkenyl-containing silane monomer is at least one selected from vinyltriethoxysilane, vinyltrimethoxysilane, vinyltriisopropoxysilane, vinyltri-tert-butoxysilane, vinyltriacetoxysilane, methylvinyldimethoxysilane, ethylvinyldiethoxysilane, allyltriethoxysilane, allyltrimethoxysilane, allyltriisopropoxysilane, vinyltris(β-methoxyethoxy)silane, allyltris(β-methoxyethoxy)silane, allyltri-tert-butoxysilane, allyltriacetoxysilane, methylallyldimethoxysilane, and ethylallyldiethoxysilane.

13. The biaxially oriented polypropylene dielectric film of claim 10, wherein the alkenyl-containing functional monomer is an acrylate monomer and / or an acrylic monomer, preferably the acrylate monomer is at least one selected from methyl(methyl)acrylate, sec-butyl(methyl)acrylate, ethyl(methyl)acrylate, n-butyl(methyl)acrylate, isobutyl(methyl)acrylate, tert-butyl(methyl)acrylate, isooctyl(methyl)acrylate, dodecyl(methyl)acrylate, cosinine(methyl)acrylate, octadecyl(methyl)acrylate, dimethylaminoethyl(methyl)acrylate, diethylaminoethyl(methyl)acrylate, dimethylaminopropyl(methyl)acrylate, and glycidyl(methyl)acrylate; preferably the acrylic monomer is at least one selected from acrylic acid, methacrylic acid, and 2-ethylacrylic acid.

14. 10. The biaxially oriented polypropylene dielectric film of claim 9, wherein the alkenyl-containing functional monomer is 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.

15. The biaxially oriented polypropylene dielectric film according to any one of claims 1 to 14, wherein the polypropylene has the following characteristics: particle size of 16-50 mesh; ash content less than 55 ppm, preferably less than 40 ppm, more preferably less than 35 ppm; flexural modulus of 1400-2000 MPa, preferably 1500-1800 MPa.

16. The biaxially oriented polypropylene dielectric film according to any one of claims 1 to 15, wherein the polypropylene is a homopolypropylene or a propylene copolymer, preferably having at least one of the following characteristics:

2. A melt flow rate at 230° C. under a load of 16 kg is 0.5 to 10 g / 10 min, preferably 1 to 5 g / 10 min, and more preferably 2 to 4 g / 10 min; Melting temperature T ｍ is 150°C or higher, preferably 153 to 180°C, more preferably 155 to 167°C; the isotacticity is greater than 96%, preferably greater than 96.5%; or the combined content of ethylene units and butene units is less than 3.0 mol%, preferably greater than 0 and less than 0.1 mol%, or greater than 0.1 mol% and equal to or less than 3.0 mol%.

17. The biaxially oriented polypropylene dielectric film according to any one of claims 1 to 16, wherein the modified polypropylene grafted with alkenyl-containing functional monomer is prepared by a method comprising the steps of: subjecting a reaction mixture comprising polypropylene powder and alkenyl-containing functional monomer to a grafting reaction in the presence of an inert gas, and optionally washing with a washing solvent to obtain the modified polypropylene grafted with the alkenyl-containing functional monomer.

18. 18. The biaxially oriented polypropylene dielectric film of claim 17, wherein the reaction mixture further comprises a free radical initiator and at least one of the following components: deionized water and / or an organic solvent, the mass content of the deionized water being 300-800% of the sum of the mass of the polypropylene powder and the alkenyl-containing functional monomer, and the mass content of the organic solvent being 1-35% of the mass of the polypropylene powder.

19. The method for preparing the modified polypropylene grafted with the alkenyl-containing functional monomer comprises the following steps: a. placing polypropylene powder in a closed reactor and then flushing with an inert gas; b. adding a free radical initiator and an alkenyl-containing functional monomer to the closed reactor and mixing with stirring; c) adding deionized water and heating the reaction system to a grafting reaction temperature to carry out the grafting reaction; optionally swelling the reaction system before or after adding the deionized water; d. After completion of the reaction, filtering and optionally drying to obtain a powder; e. optionally washing the powder with a washing solvent, filtering and drying; f. Obtaining a modified polypropylene grafted with said alkenyl-containing functional monomer; Contains or The method for preparing the modified polypropylene grafted with the alkenyl-containing functional monomer comprises the following steps: a. placing polypropylene powder in a closed reactor and then flushing with an inert gas; b. mixing an organic solvent and a free radical initiator and adding said mixture to said closed reactor; c) removing the organic solvent and adding an alkenyl-containing functional monomer and optionally swelling the reaction system; d. adding deionized water and heating the reaction system to a grafting reaction temperature to carry out the grafting reaction; e. After the reaction is complete, filtering and optionally drying to obtain a powder; f. Optionally, washing the powder with a washing solvent, filtering and drying; g. Obtaining a modified polypropylene grafted with said alkenyl-containing functional monomer; Including, The biaxially oriented polypropylene dielectric film according to claim 18, wherein the temperature of the grafting reaction is 30-110°C, and preferably 60-95°C; and the time is 0.5-10 hours, and preferably 1-6 hours.

20. 18. The biaxially oriented polypropylene dielectric film according to claim 17, wherein the method further comprises a step of screening the polypropylene powder pre-treatment, preferably the screening pre-treatment comprises a step of screening the powder using a double-layer vibrating screen or a linear screen having a screen mesh of a corresponding mesh number, and a step of using the polypropylene powder of the middle layer of the screen as a reactive material.

21. The cleaning solvent is one or a mixture of two or more selected from the group consisting 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 cleaning solvent is a mixture of solvent A and solvent B, wherein solvent A is at least one selected from the group consisting 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 selected from the group consisting of toluene and xylene; 18. The biaxially oriented polypropylene dielectric film of claim 17, wherein the mass of the washing solvent is 2 to 20 times the mass of the grafted polypropylene powder.

22. The biaxially oriented polypropylene dielectric film according to claim 17, wherein the washing temperature is 40-130°C, preferably 55-100°C, and the washing time is 0.5-10 hours, preferably 1-8 hours.

23. The biaxially oriented polypropylene dielectric film according to any one of claims 1 to 22, wherein the raw material for preparing the biaxially oriented polypropylene dielectric film further comprises an antioxidant and optionally a processing aid, and based on 100 parts by weight of the modified polypropylene, the content of the antioxidant is 0.1 to 0.8 parts by weight, preferably 0.1 to 0.6 parts by weight, and the content of the processing aid is 0.05 to 1 part by weight, preferably 0.05 to 0.5 parts by weight; based on the weight of the dielectric film, the content of the modified polypropylene grafted with the alkenyl-containing functional monomer is 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more.

24. The antioxidant is one or a mixture of two or more selected from the group consisting of hindered phenols, hindered amines, phosphites, thios, and benzofuranones; Preferably, the antioxidant is obtained by combining antioxidant component A and antioxidant component B, wherein the antioxidant component A is at least one selected from the group consisting of hindered phenols, hindered amines, phosphites and thios, and the antioxidant component B is at least one benzofuranone; More preferably, the antioxidant component A is selected from the group consisting of pentaerythrityl tetrakis[β-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], tris[2,4-di-t-butylphenyl]phosphite, n-octadecyl β-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-thiobis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, and bis(2,4-di-t said antioxidant component B being at least one selected from the group consisting of 3-butyl-1-(3-hydrogen)-isobenzofuranone, 5-methyl-7-tert-butyl-3-(3,4-dimethyl)-3-hydrogen-benzofuran-2-one, 5-methyl-7-tert-butyl-3-(2,5-dimethyl)-3-hydrogen-benzofuran-2-one and 5-methyl-7-tert-butyl-3-(2-hydroxy-5-methyl)-3-hydrogen-benzofuran-2-one; The biaxially oriented polypropylene dielectric film according to claim 23, wherein the weight ratio of the antioxidant component A to the antioxidant component B is 1:0.01-0.

03.

25. the processing aid is at least one selected from the group consisting of a lubricant, an acid acceptor, a slip agent, an antistatic agent, and an antiblock agent; 24. The biaxially oriented polypropylene dielectric film of claim 23, wherein the lubricant is at least one selected from the group consisting of polyethylene glycol lubricants, fluoropolymer lubricants, organosilicon lubricants, fatty alcohol lubricants, fatty acid lubricants, fatty acid ester lubricants, stearic acid amide lubricants, fatty acid metal soap lubricants, alkane and alkane oxide lubricants, and micro-nanoparticle lubricants.

26. The biaxially oriented polypropylene dielectric film according to any one of claims 1 to 25, wherein the biaxially oriented polypropylene dielectric film is prepared by a method comprising the steps of: (1) mixing and pelletizing the raw materials for preparation; (2) melt-extruding and casting the pellets obtained in step (1) to obtain a modified polypropylene cast sheet; (3) A step of biaxially stretching the modified polypropylene cast sheet to obtain the biaxially oriented polypropylene dielectric film.

27. A modified polypropylene material for preparing a dielectric film, comprising: The modified polypropylene material comprises a modified polypropylene grafted with an alkenyl-containing functional monomer, the modified polypropylene grafted with an 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 modified polypropylene grafted with an alkenyl-containing functional monomer has an ash content of less than 50 ppm, preferably less than 36 ppm, more preferably less than 30 ppm; the modified polypropylene grafted with an alkenyl-containing functional monomer has a ratio of the mass of structural units derived from the alkenyl-containing functional monomer and in a grafted state to the mass of structural units derived from the alkenyl-containing functional monomer and in a self-polymerized state of 1.0 or more; and the D50 of the dispersed phase is less than 450 nm, preferably 50 to 400 nm.

28. The modified polypropylene material according to claim 27, wherein the maximum operating temperature of the modified polypropylene material is 100°C or higher, preferably 110-160°C, and more preferably 120-145°C.

29. 29. The modified polypropylene material according to claim 27 or 28, wherein the modified polypropylene material has at least one of the following characteristics: Breakdown field strength E at 120°C ｇ is 500 MV / m or more, preferably 550 to 800 MV / m; DC volume resistivity ρ at 120° C. and an electric field strength of 200 MV / m ｖｇ But 6.0 x 10 １３ Ω·m or more, preferably 1.0×10 １４ Ω m to 1.0 x 10 ２０ Ω·m, preferably 1.5×10 １４ Ω m to 0.9 x 10 ２０ Ω·m, more preferably 2.0×10 １４ Ω m to 1.0 x 10 １７ Ω·m; A dielectric constant at 120° C. and 100 Hz is greater than 2.25, preferably 2.26 to 2.65; a dielectric loss at 120° C. and 100 Hz of less than 1.55E-3, preferably less than 1.5E-3, preferably 1.0E-3 or less, more preferably 1.0E-6 to 1.3E-3, and even more preferably 1.0E-6 to 9E-4; Energy storage density at 120°C and 300MV / m is 0.720J / cm ３ Greater than 0.740 to 2.0 J / cm ３ , more preferably 0.780 to 2.0 J / cm ３ and more preferably 0.80 to 2.0 J / cm ３ is; The energy storage efficiency at 120° C. and 300 MV / m is greater than 90.0%, and preferably 92.0-99.0%.

30. 28. The modified polypropylene material according to claim 27, wherein in the modified polypropylene grafted with alkenyl-containing functional monomer, the ratio of the mass of structural units derived from the alkenyl-containing functional monomer and in the grafted state to the mass of structural units derived from the alkenyl-containing functional monomer and in the self-polymerized state is between 1.1 and 1.0, preferably between 1.2 and 6.

31. 28. The modified polypropylene material according to claim 27, wherein in the modified polypropylene grafted with alkenyl-containing functional monomer, the ratio of the mass of structural units derived from the alkenyl-containing functional monomer and in a grafted state to the mass of structural units derived from the alkenyl-containing functional monomer and in a self-polymerized state is 1.5 or more, preferably 2 or more.

32. The modified polypropylene material according to any one of claims 27 to 31, wherein the modified polypropylene grafted with alkenyl-containing functional monomer has at least one of the following characteristics: a melt flow rate of 1 to 10 g / 10 min, preferably 1.5 to 8 g / 10 min, and more preferably 2 to 5 g / 10 min at 230°C under a load of 2.16 kg; a melting temperature T ｍ is 155-168° C., and preferably 157-165° C.; flexural modulus is 1400-2000 MPa, and preferably 1500-1800 MPa.

33. The alkenyl-containing functional monomer has Formula 1: 【Chemistry 7】 At least one monomer having a structure represented by In formula 1, R ｂ , R ｃ , R ｄ are each independently selected from H, substituted or unsubstituted alkyl; R ａ is selected from substituted or unsubstituted alkyl, substituted or unsubstituted alkoxy, substituted or unsubstituted aryl, substituted or unsubstituted ester groups, substituted or unsubstituted carboxyl, substituted or unsubstituted cycloalkyl or heterocyclyl, cyano, substituted or unsubstituted silyl; R ａ and R ｄ optionally forms a ring; The modified polypropylene material according to any one of claims 27 to 32.

34. R ｂ , R ｃ , R ｄ are each independently H, substituted or unsubstituted C １ -C ６ alkyl; R ａ is a substituted or unsubstituted C １ -C ２０ Alkyl, substituted or unsubstituted C １ -C ２０ Alkoxy, substituted or unsubstituted C ６ -C ２０ Aryl, substituted or unsubstituted C １ -C ２０ Ester group, substituted or unsubstituted C １ -C ２０ Carboxyl, substituted or unsubstituted C ３ -C ２０ Cycloalkyl or heterocyclyl, cyano, substituted or unsubstituted C ３ -C ２０ silyl; said substituents are selected from halogen, —OH, —NH ２ , =O, C １ -C １２ Alkyl, C ３ -C ６ Cycloalkyl, C １ -C １２ Alkoxy, C １ -C １２ acyloxy; R ａ and R ｄ are optionally joined together via a double bond to form a 4- to 6-membered heterocyclic ring; 34. The modified polypropylene material of claim 33.

35. R ｂ , R ｃ , R ｄ each independently represents H, substituted or unsubstituted C １ -C ６ alkyl; R ａ is at least one selected from a group represented by formula 2, a group represented by formula 3, a group represented by formula 4, a group represented by formula 5, a group represented by formula 6, and a heterocyclic group; 【Chemistry 8】 In formula 2, R ４ -R ８ are each independently H, a halogen, a hydroxyl, an amino, a phosphate group, a sulfonate group, a substituted or unsubstituted C １ -C １２ Alkyl, substituted or unsubstituted C ３ -C １２ Cycloalkyl, substituted or unsubstituted C １ -C １２ Alkoxy, substituted or unsubstituted C １ -C １２ Ester group, substituted or unsubstituted C １ -C １２ amine groups, the substituents being selected from halogen, hydroxy, amino, phosphate groups, sulfonate groups, C １ -C １２ Alkyl, C ３ -C １２ Cycloalkyl, C １ -C １２ Alkoxy, C １ -C １２ Ester group, C １ -C １２ amine groups; preferably, R ４ -R ８ are each independently H, halogen, hydroxy, amino, substituted or unsubstituted C １ -C ６ Alkyl, substituted or unsubstituted C １ -C ６ alkoxy; 【Chemistry 9】 In formula 3, R ４ -R １０ are each independently H, a halogen, a hydroxyl, an amino, a phosphate group, a sulfonate group, a substituted or unsubstituted C １ -C １２ Alkyl, substituted or unsubstituted C ３ -C １２ Cycloalkyl, substituted or unsubstituted C １ -C １２ Alkoxy, substituted or unsubstituted C １ -C １２ Ester group, substituted or unsubstituted C １ -C １２ amine groups, the substituents being selected from halogen, hydroxy, amino, phosphate groups, sulfonate groups, C １ -C １２ Alkyl, C ３ -C １２ Cycloalkyl, C １ -C １２ Alkoxy, C １ -C １２ Ester group, C １ -C １２ amine groups; preferably, R ４ -R １０ are each independently H, halogen, hydroxy, amino, substituted or unsubstituted C １ -C ６ Alkyl, substituted or unsubstituted C １ -C ６ alkoxy, said substituents being selected from halogen, hydroxy, amino, C １ -C ６ Alkyl, C １ -C ６ alkoxy; 【Chemistry 10】 In formula 4, R ４ '-R １０ ' are each independently H, halogen, hydroxy, amino, a phosphate group, a sulfonate group, a substituted or unsubstituted C １ -C １２ Alkyl, substituted or unsubstituted C ３ -C １２ Cycloalkyl, substituted or unsubstituted C １ -C １２ Alkoxy, substituted or unsubstituted C １ -C １２ Ester group, substituted or unsubstituted C １ -C １２ amine groups, the substituents being selected from halogen, hydroxy, amino, phosphate groups, sulfonate groups, C １ -C １２ Alkyl, C ３ -C １２ Cycloalkyl, C １ -C １２ Alkoxy, C １ -C １２ Ester group, C １ -C １２ amine groups; preferably, R ４ '-R １０ Each ' is independently H, halogen, hydroxy, amino, substituted or unsubstituted C １ -C ６ Alkyl, substituted or unsubstituted C １ -C ６ alkoxy, said substituents being selected from halogen, hydroxy, amino, C １ -C ６ Alkyl, C １ -C ６ alkoxy; 【Chemistry 11】 In formula 5, R′, R″, and R′″ are each independently a substituted or unsubstituted C １ -C １２ Straight chain alkyl, substituted or unsubstituted C ３ -C １２ Branched alkyl, substituted or unsubstituted C １ -C １２ Alkoxy, substituted or unsubstituted C １ -C １２ acyloxy; preferably, R １ is C ２ -C ６ alkenyl, preferably monounsaturated alkenyl; R ２ , R ３ , R ４ each independently represents a substituted or unsubstituted C １ -C ６ Straight chain alkyl, substituted or unsubstituted C ３ -C ６ Branched alkyl, substituted or unsubstituted C １ -C ６ Alkoxy, substituted or unsubstituted C １ -C ６ acyloxy; 【Chemistry 12】 In formula 6, R ｍ is hydrogen and / or the following substituted or unsubstituted groups: １ -C ２０ Straight chain alkyl, C ３ -C ２０ Branched alkyl, C ３ -C １２ Cycloalkyl, C ３ -C １２ Epoxy alkyl, C ３ -C １２ epoxyalkylalkyl, wherein said substituents are at least one selected from halogen, amino and hydroxy; the heterocyclic group is selected from imidazolyl, pyrazolyl, carbazolyl, pyrrolidinonyl, pyridyl, piperidinyl, caprolactamyl, pyrazinyl, thiazolyl, purinyl, morpholinyl, oxazolinyl; 35. The modified polypropylene material of claim 34.

36. The alkenyl-containing functional monomer is a styrene monomer, the styrene monomer being at least one selected from styrene, α-methylstyrene, 1-vinylnaphthalene, 2-vinylnaphthalene, mono- or poly-substituted styrene, mono- or poly-substituted α-methylstyrene, mono- or poly-substituted 1-vinylnaphthalene and mono- or poly-substituted 2-vinylnaphthalene; the substituents are preferably halogen, hydroxy, amino, phosphoric acid, sulfonic acid, C １ -C ８ Straight chain alkyl, C ３ -C ８ Branched alkyl or cycloalkyl, C １ -C ６ Linear alkoxy, C ３ -C ８ Branched alkoxy or cycloalkoxy, C １ -C ８ Linear ester group, C ３ -C ８ A branched ester group or a cyclic ester group, C １ -C ８ Linear amine groups and C ３ -C ８ at least one selected from a branched amine group or a cyclic amine group; preferably, the styrene monomer is at least one selected from styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene and 4-methylstyrene; 36. The modified polypropylene material of claim 35.

37. 36. The modified polypropylene material of claim 35, wherein the alkenyl-containing functional monomer is an alkenyl-containing silane monomer, the alkenyl-containing silane monomer being at least one selected from vinyltriethoxysilane, vinyltrimethoxysilane, vinyltriisopropoxysilane, vinyltri-tert-butoxysilane, vinyltriacetoxysilane, methylvinyldimethoxysilane, ethylvinyldiethoxysilane, allyltriethoxysilane, allyltrimethoxysilane, allyltriisopropoxysilane, vinyltris(β-methoxyethoxy)silane, allyltris(β-methoxyethoxy)silane, allyltri-tert-butoxysilane, allyltriacetoxysilane, methylallyldimethoxysilane, and ethylallyldiethoxysilane.

38. 36. The modified polypropylene material of claim 35, wherein the alkenyl-containing functional monomer is an acrylate monomer and / or an acrylic monomer, preferably the acrylate monomer is at least one selected from methyl(methyl)acrylate, sec-butyl(methyl)acrylate, ethyl(methyl)acrylate, n-butyl(methyl)acrylate, isobutyl(methyl)acrylate, tert-butyl(methyl)acrylate, isooctyl(methyl)acrylate, dodecyl(methyl)acrylate, cosinine(methyl)acrylate, octadecyl(methyl)acrylate, dimethylaminoethyl(methyl)acrylate, diethylaminoethyl(methyl)acrylate, dimethylaminopropyl(methyl)acrylate, and glycidyl(methyl)acrylate; preferably the acrylic monomer is at least one selected from acrylic acid, methacrylic acid, and 2-ethylacrylic acid.

39. 35. The modified polypropylene material of claim 34, wherein the alkenyl-containing functional monomer is 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.

40. The modified polypropylene material according to any one of claims 27 to 39, wherein the polypropylene has the following characteristics: a particle size of 16-50 mesh; an ash content of less than 55 ppm, preferably less than 40 ppm, more preferably less than 35 ppm; and a flexural modulus of 1400-2000 MPa, preferably 1500-1800 MPa.

41. The modified polypropylene material according to any one of claims 27 to 40, wherein the polypropylene is a homopolypropylene or a propylene copolymer, preferably having at least one of the following characteristics:

2. A melt flow rate at 230° C. under a load of 16 kg is 0.5 to 10 g / 10 min, preferably 1 to 5 g / 10 min, and more preferably 2 to 4 g / 10 min; Melting temperature T ｍ is 150°C or higher, preferably 153 to 180°C, more preferably 155 to 167°C; the isotacticity is greater than 96%, preferably greater than 96.5%; or the combined content of ethylene units and butene units is less than 3.0 mol%, preferably greater than 0 and less than 0.1 mol%, or greater than 0.1 mol% and equal to or less than 3.0 mol%.

42. The modified polypropylene material of any one of claims 27 to 41, wherein the modified polypropylene grafted with alkenyl-containing functional monomer is prepared by a process comprising the steps of: subjecting a reaction mixture comprising polypropylene powder and alkenyl-containing functional monomer to a grafting reaction in the presence of an inert gas, and optionally washing with a washing solvent to obtain the modified polypropylene grafted with alkenyl-containing functional monomer.

43. 43. The modified polypropylene material of claim 42, wherein the reaction mixture further comprises a free radical initiator and at least one of the following components: deionized water and / or an organic solvent, the mass content of the deionized water being 300-800% of the sum of the mass of the polypropylene powder and the alkenyl-containing functional monomer, and the mass content of the organic solvent being 1-35% of the mass of the polypropylene powder.

44. The method for preparing the modified polypropylene grafted with the alkenyl-containing functional monomer comprises the following steps: a. placing polypropylene powder in a closed reactor and then flushing with an inert gas; b. adding a free radical initiator and an alkenyl-containing functional monomer to the closed reactor and mixing with stirring; c) adding deionized water and heating the reaction system to a grafting reaction temperature to carry out the grafting reaction; optionally swelling the reaction system before or after adding the deionized water; d. After the reaction is complete, filtering and optionally drying to obtain a powder; e. optionally washing the powder with a washing solvent, filtering and drying; f. Obtaining a modified polypropylene grafted with said alkenyl-containing functional monomer; Contains or The method for preparing the modified polypropylene grafted with the alkenyl-containing functional monomer comprises the following steps: a. placing polypropylene powder in a closed reactor and then flushing with an inert gas; b. mixing an organic solvent and a free radical initiator and adding said mixture to said closed reactor; c) removing the organic solvent and adding an alkenyl-containing functional monomer and optionally swelling the reaction system; d. adding deionized water and heating the reaction system to a grafting reaction temperature to carry out the grafting reaction; e. After the reaction is complete, filtering and optionally drying to obtain a powder; f. Optionally, washing the powder with a washing solvent, filtering and drying; g. Obtaining a modified polypropylene grafted with said alkenyl-containing functional monomer; Including, The modified polypropylene material according to claim 43, wherein the temperature of the grafting reaction is 30-110°C, and preferably 60-95°C; and the time is 0.5-10 hours, and preferably 1-6 hours.

45. 43. The modified polypropylene material of claim 42, wherein the method further comprises a step of screening the polypropylene powder pre-treatment, preferably the screening pre-treatment comprises a step of screening the powder using a two-layer vibrating screen or a linear screen having a screen mesh of a corresponding mesh number, and a step of using the polypropylene powder of the middle layer of the screen as a reactive material.

46. The cleaning solvent is one or a mixture of two or more selected from the group consisting 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 cleaning solvent is a mixture of solvent A and solvent B, wherein solvent A is at least one selected from the group consisting 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 selected from the group consisting of toluene and xylene; 43. The modified polypropylene material of claim 42, wherein the mass of the washing solvent is 2 to 20 times the mass of the grafted polypropylene powder.

47. The modified polypropylene material according to claim 42, wherein the washing temperature is 40-130°C, preferably 55-100°C, and the washing time is 0.5-10 hours, preferably 1-8 hours.

48. The modified polypropylene material further comprises an antioxidant and optionally a processing aid, the content of the antioxidant being 0.1 to 0.8 parts by weight, preferably 0.1 to 0.6 parts by weight, and the content of the processing aid being 0.05 to 1 part by weight, preferably 0.05 to 0.5 parts by weight, based on 100 parts by weight of the modified polypropylene. The modified polypropylene material according to any one of claims 27 to 47.

49. The antioxidant is one or a mixture of two or more selected from the group consisting of hindered phenols, hindered amines, phosphites, thios, and benzofuranones; Preferably, the antioxidant is obtained by combining antioxidant component A and antioxidant component B, wherein the antioxidant component A is at least one selected from the group consisting of hindered phenols, hindered amines, phosphites and thios, and the antioxidant component B is at least one benzofuranone; More preferably, the antioxidant component A is selected from the group consisting of pentaerythrityl tetrakis[β-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], tris[2,4-di-t-butylphenyl]phosphite, n-octadecyl β-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-thiobis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, and bis(2,4-di-t said antioxidant component B being at least one selected from the group consisting of 3-butyl-1-(3-hydrogen)-isobenzofuranone, 5-methyl-7-tert-butyl-3-(3,4-dimethyl)-3-hydrogen-benzofuran-2-one, 5-methyl-7-tert-butyl-3-(2,5-dimethyl)-3-hydrogen-benzofuran-2-one and 5-methyl-7-tert-butyl-3-(2-hydroxy-5-methyl)-3-hydrogen-benzofuran-2-one; The modified polypropylene material according to claim 48, wherein the weight ratio of the antioxidant component A to the antioxidant component B is 1:0.01-0.

03.

50. the processing aid is at least one selected from the group consisting of a lubricant, an acid acceptor, a slip agent, an antistatic agent, and an antiblock agent; 49. The modified polypropylene material of claim 48, wherein the lubricant is at least one selected from the group consisting of polyethylene glycol lubricants, fluoropolymer lubricants, organosilicon lubricants, fatty alcohol lubricants, fatty acid lubricants, fatty acid ester lubricants, stearic acid amide lubricants, fatty acid metal soap lubricants, alkane and alkane oxide lubricants, and micro-nanoparticle lubricants.

51. 51. Use of the biaxially oriented polypropylene dielectric film according to any one of claims 1 to 26, or the modified polypropylene material according to any one of claims 27 to 50, in the manufacture of an energy storage dielectric medium, in particular a high temperature energy storage dielectric medium, said dielectric medium being preferably a monolayer / multilayer dielectric film, preferably a capacitor film, an electrical film, a roughened film, a supercapacitor film, an electrostatic film or a battery separator film.

52. A polypropylene capacitor film, which is monolayer or multilayer, at least one layer being a biaxially oriented polypropylene dielectric film according to any one of claims 1 to 26, or at least one layer being produced from a raw material comprising the modified polypropylene material according to any one of claims 27 to 50, preferably by biaxial orientation, and preferably at least one layer being produced from the modified polypropylene material according to any one of claims 27 to 50 by biaxial orientation.

53. A polypropylene electrical film, which is monolayer or multilayer, at least one layer being a biaxially oriented polypropylene dielectric film according to any one of claims 1 to 26, or at least one layer being produced from a raw material comprising a modified polypropylene material according to any one of claims 27 to 50, preferably by biaxial orientation, preferably at least one layer being produced from a modified polypropylene material according to any one of claims 27 to 50 by biaxial orientation.

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