A polypropylene composite material, a polypropylene composite film and a preparation method thereof

Abstract

This invention relates to the field of polymer materials technology, specifically disclosing a polypropylene composite material, a polypropylene composite film, and a method for preparing the same. The invention provides a polypropylene composite material comprising polypropylene, 1,3:2,4-di-p-methylbenzyl sorbitol, and other additives. The 1,3:2,4-di-p-methylbenzyl sorbitol used as an organic nucleating agent can effectively regulate and improve the microstructure of polypropylene, significantly increasing its crystallinity and reducing density defects in the resulting polypropylene film. This provides a reliable material basis for preparing polypropylene composite films with high electrical insulation properties, excellent high-temperature resistance, and long-term high-temperature cycling stability, solving the problem of insufficient long-term stable cycling performance in existing polypropylene films due to low energy storage density and poor high-temperature resistance.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a polypropylene composite material, a polypropylene composite film, and a method for preparing the same. Background Technology

[0002] With increasingly severe global energy and environmental problems, energy storage technology has become a cutting-edge research topic and a key industrial support. As the microelectronics and power industries develop, energy storage devices face increasingly stringent requirements for lightweight design, high energy density, and resistance to long-term high-temperature cycling. Thin-film capacitors are core energy storage devices, and the polymer dielectric materials involved are crucial for high-energy-density pulse capacitors. Developing new dielectric materials that combine high energy density, high voltage resistance, and long-term high-temperature cycling stability has become an urgent priority. Simultaneously, the complex and variable operating environment of capacitors (especially high-temperature and high-voltage conditions) places even higher demands on materials. Therefore, there is an urgent need for an alternative polypropylene composite material that can maintain excellent dielectric properties, high energy density, and stable long-term cycling characteristics under high-temperature and high-voltage conditions.

[0003] Currently, a common method to improve polypropylene composites is to prepare polypropylene-based composites by doping with high-dielectric ceramics such as barium titanate. Although this method can improve energy density and dielectric constant, the poor compatibility and weak bonding between the organic and inorganic interfaces can easily lead to a significant decrease in discharge efficiency and poor cycling stability at high temperatures. Another common approach is to enhance the dielectric properties of polypropylene materials under high temperature and high pressure by physically blending and adding small organic molecules. However, the distribution of small organic molecules in the material is uneven, and it is difficult to completely consume the free radicals generated by thermal decomposition. This may increase conductivity and reduce voltage withstand performance, failing to meet the requirements for long-term cycling at high temperatures. In addition, the dielectric properties and oxidation resistance can be improved by chemically modifying the side groups of the polypropylene polymer chain and grafting specific functional monomers. However, the grafting efficiency is low and it is not suitable for large-scale production, making it difficult to meet the needs of industrial applications. Based on the aforementioned improvements, the breakdown field strength of domestically produced polypropylene film is 600–650 MV / m, which is close to the material performance limit, but still 50–100 MV / m lower than that of imported film. Furthermore, the breakdown field strength decreases significantly at high temperatures, and the long-term cycle stability is insufficient. This severely limits the energy storage density and service life of domestically produced film capacitors, thereby restricting their application in demanding scenarios.

[0004] It is evident that existing polypropylene films suffer from problems such as low energy storage density and poor high-temperature resistance, resulting in insufficient long-term stable cycling performance. This severely restricts their application in high-energy-storage pulse devices, new energy vehicles, aerospace, electromagnetic catapults, and other scenarios. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a polypropylene composite material, a polypropylene composite film, and a method for preparing the same, in order to solve the problem that existing polypropylene films have insufficient long-term stable cycling performance due to low energy storage density and poor high-temperature resistance.

[0006] To achieve the above-mentioned technical objectives, the present invention provides a polypropylene composite material comprising the following components by volume percentage:

[0007] Organic nucleating agent 0.01%–5%, including sorbitol benzylidene derivatives; other auxiliaries 0.01%–1.00%; balance polypropylene.

[0008] Furthermore, the polypropylene is at least one of homopolymer polypropylene, block copolymer polypropylene, high-impact polypropylene, random copolymer polypropylene, and metallocene polypropylene.

[0009] Furthermore, organic nucleating agents also include at least one of carboxylic acid metal salt nucleating agents, phosphate metal salt nucleating agents, aromatic diamide nucleating agents, and rare earth compound nucleating agents.

[0010] Furthermore, the particle size of the organic nucleating agent is 1 μm to 10 μm.

[0011] Furthermore, other additives include at least one of antioxidants, light stabilizers, voltage stabilizers, plasticizers, and antistatic agents.

[0012] Furthermore, other adjuvants include antioxidants, including at least one of antioxidant 1010, antioxidant 168, antioxidant 1076, antioxidant 1098, antioxidant 3114, antioxidant 2246, antioxidant 626, antioxidant 618, and antioxidant 126.

[0013] This invention provides a method for preparing a polypropylene composite film, which is prepared using polypropylene composite materials and includes the following steps:

[0014] Step S1: The organic nucleating agent is subjected to ultrasonic exfoliation to obtain organic nucleating agent powder with a preset particle size;

[0015] Step S2: Mix the organic nucleating agent powder, polypropylene, and other additives evenly, and then melt-blend to obtain a mixed melt;

[0016] Step S3: The mixed melt is co-extruded to obtain a polypropylene composite film.

[0017] Furthermore, it also includes annealing treatment; the annealing treatment is: annealing the polypropylene composite film at 110℃~130℃ for 8h~10h.

[0018] Furthermore, during the ultrasonic exfoliation process, the ultrasonic exfoliation power is 1800W to 2000W, and the ultrasonic exfoliation time is 6h to 8h; during the melt blending process, the temperature is 130℃ to 250℃.

[0019] This application provides a polypropylene composite film, which is prepared by using polypropylene composite materials or by using a method for preparing polypropylene composite films.

[0020] In summary, this invention provides a polypropylene composite material comprising polypropylene, 1,3:2,4-di-p-methylbenzyl sorbitol, and other additives; 1,3:2,4-di-p-methylbenzyl sorbitol, as an organic nucleating agent, can effectively regulate and improve the micro-aggregate structure of polypropylene, significantly enhance the crystallinity of polypropylene, and reduce the density defects of the prepared polypropylene film, providing a reliable material basis for preparing polypropylene composite films with high electrical insulation properties, excellent high-temperature resistance, and long-term high-temperature cycling stability.

[0021] Compared with the prior art, the polypropylene composite material provided in this application has the technical advantages of simple component composition and convenient preparation process. The polypropylene composite film prepared from this polypropylene composite material can simultaneously achieve a synergistic improvement in high electrical performance, excellent high temperature resistance and long-term high temperature cycling stability, which can meet the stringent requirements of high-end electronic devices such as power capacitors for dielectric materials. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 A process flow diagram for preparing polypropylene composite films provided in embodiments of the present invention;

[0024] Figure 2 Comparison of the breakdown field strength of polypropylene composite film and pure polypropylene film under working conditions of 25°C and 125°C before annealing treatment provided by the present invention.

[0025] Figure 3 Comparison of the breakdown field strength of polypropylene composite film and pure polypropylene film after annealing treatment provided by the present invention under working conditions of 25°C and 125°C.

[0026] Figure 4 Energy storage density diagrams of polypropylene composite film and pure polypropylene film before annealing treatment provided by the present invention.

[0027] Figure 5 Energy storage density diagrams of polypropylene composite film and pure polypropylene film after annealing treatment provided by the present invention.

[0028] Figure 6 Differential scanning calorimetry curves of polypropylene composite film and pure polypropylene film provided by the present invention;

[0029] Figure 7 Thermogravimetric curves of polypropylene composite film and pure polypropylene film provided by the present invention;

[0030] Figure 8 The dielectric constant-frequency relationship curves of the polypropylene composite film and the pure polypropylene film provided by this invention;

[0031] Figure 9 Broadband dielectric loss spectrum of polypropylene composite film and pure polypropylene film provided by the present invention;

[0032] Figure 10 High-temperature long-term cyclic charge-discharge performance test curves of polypropylene composite film and pure polypropylene film provided by the present invention. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments in this specification, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection claimed by the present invention.

[0034] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," indicating orientation or positional relationships, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0035] Unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0036] The raw materials used in this invention are not particularly restricted in their source; they can be purchased on the market or prepared using conventional methods known to those skilled in the art.

[0037] This invention provides a polypropylene composite material comprising the following components by volume percentage:

[0038] Organic nucleating agent 0.01%–5%, including sorbitol benzylidene derivatives; other auxiliaries 0.01%–1.00%; balance polypropylene.

[0039] It should be noted that organic nucleating agents, as heterogeneous organic nucleating agents, can control the grain size / crystal form of polypropylene. Through the heterogeneous nucleation effect, they can improve crystallinity, enhance the microstructure of polypropylene, reduce the defect density of polypropylene films, and achieve a dual improvement in heat resistance and mechanical strength. At the same time, organic nucleating agents can also form an interface with polypropylene and work synergistically with other additives (such as antioxidants). This interface can effectively inhibit local charge accumulation, reduce leakage current, inhibit the growth and expansion of electrical trees, and reduce the local electric field enhancement effect. In addition, organic nucleating agents can also endow polypropylene with higher thermal conductivity, which can quickly conduct heat generated under the action of electric field, prevent local overheating and breakdown effect, and significantly extend the long-term cycle life of polypropylene composite films prepared by polypropylene composite materials in high-temperature environments, making them suitable for harsh scenarios such as high-energy storage pulse devices, new energy vehicles, and aerospace.

[0040] In some preferred embodiments, the volume percentage of the organic nucleating agent is 0.1% to 0.15%.

[0041] It should be noted that within this volume percentage range, the annealed polypropylene composite film exhibits superior electrical properties.

[0042] In some specific embodiments, the volume percentage of the organic nucleating agent is 0.01%, 0.1%, 1.0%, 3.0%, or 5.0%; and the volume percentage of other auxiliaries is 0.01%, 0.05%, 0.1%, or 1.0%.

[0043] In some embodiments, the polypropylene is at least one of homopolymer polypropylene, block copolymer polypropylene, high-impact polypropylene, random copolymer polypropylene, and metallocene polypropylene.

[0044] It should be noted that when selecting polypropylene, priority should be given to polypropylene with a narrow molecular weight distribution and a moderate melt flow rate, so that it can form good compatibility with organic nucleating agents and other additives in subsequent blending and processing.

[0045] In some embodiments, the organic nucleating agent further includes at least one of carboxylic acid metal salt nucleating agents, phosphate metal salt nucleating agents, aromatic diamide nucleating agents, and rare earth compound nucleating agents.

[0046] In some embodiments, the particle size of the organic nucleating agent is 1 μm to 10 μm.

[0047] It should be noted that organic nucleating agents with the above-mentioned particle size have better dispersing effect, which can effectively reduce powder agglomeration, reduce the formation of large particles, and improve the uniformity of distribution, ensuring that they can be evenly dispersed with polypropylene and other additives. This ensures that the polypropylene composite film prepared from polypropylene composite materials can always have high energy storage density and stable and reliable high-temperature long-term cycling performance in various energy storage applications.

[0048] In some embodiments, other additives include at least one of antioxidants, light stabilizers, voltage stabilizers, plasticizers, and antistatic agents.

[0049] In some embodiments, other adjuvants include antioxidants, which include at least one of antioxidant 1010, antioxidant 168, antioxidant 1076, antioxidant 1098, antioxidant 3114, antioxidant 2246, antioxidant 626, antioxidant 618, and antioxidant 126.

[0050] It should be noted that antioxidants can effectively scavenge free radicals at high temperatures and inhibit the high-temperature oxidative degradation of polypropylene composites or polypropylene composite films. When combined with organic nucleating agents, antioxidants can impart higher thermal conductivity to polypropylene composites and polypropylene composite films, which can quickly conduct heat generated under the action of an electric field, prevent local overheating from causing breakdown, and extend their long-term cycle life in high-temperature environments.

[0051] In some preferred embodiments, the adjuvant is an antioxidant, which includes antioxidant 1010 and antioxidant 168, with a volume ratio of antioxidant 1010 to antioxidant 168 of 1-2:1-2. In some specific embodiments, the volume ratio of antioxidant 1010 to antioxidant 168 is 2:1.

[0052] It should be noted that when the polypropylene composite material contains both 1,3:2,4-di-p-methylbenzyl sorbitol and the aforementioned antioxidant, the organic nucleating agent and antioxidant can more efficiently regulate the polypropylene crystal structure. The polypropylene composite film prepared from this polypropylene composite material, after annealing, has a significantly higher breakdown field strength than pure polypropylene material, polypropylene and antioxidant composite material, and polypropylene and 1,3:2,4-di-p-methylbenzyl sorbitol composite material.

[0053] See Figure 1This invention provides a method for preparing a polypropylene composite film, which is prepared using polypropylene composite materials and includes the following steps:

[0054] Step S1: The organic nucleating agent is subjected to ultrasonic exfoliation to obtain organic nucleating agent powder with a preset particle size;

[0055] Step S2: Mix the organic nucleating agent powder, polypropylene, and other additives evenly, and then melt-blend to obtain a mixed melt;

[0056] Step S3: The mixed melt is co-extruded to obtain a polypropylene composite film.

[0057] In some embodiments, the polypropylene composite film is wound up at a speed of 5–20 r / min.

[0058] In some preferred embodiments, an annealing treatment is also included, wherein the wound polypropylene composite film is annealed at 110°C to 130°C for 8 to 10 hours.

[0059] It should be noted that annealing can reduce the internal stress of polypropylene composite films, improve the interfacial bonding effect between organic nucleating agents and other additives, enhance the uniformity and structural stability of polypropylene composite films, further optimize the synergistic effect of organic nucleating agents and other additives, regulate the crystallization properties of polypropylene composite films, and inhibit the oxidative degradation of polypropylene composite films.

[0060] In some embodiments, during the ultrasonic stripping process, the ultrasonic stripping power is 1800W to 2000W, and the ultrasonic stripping time is 6h to 8h; during the melt blending process, the melt blending temperature is 130℃ to 250℃.

[0061] This application provides a polypropylene composite film, which is prepared by using polypropylene composite materials or by using a method for preparing polypropylene composite films.

[0062] In some embodiments, the thickness of the polypropylene composite film is 3–30 μm. Under the conditions of heat shrinkage test temperature of 50–150°C and time of 10–100 minutes, the sum of the longitudinal heat shrinkage rate and the transverse heat shrinkage rate of the polypropylene composite film is less than or equal to 1%–50%.

[0063] It should be noted that the polypropylene composite film possesses high mechanical breakdown strength and high overheat-induced breakdown resistance, maintaining good dielectric and breakdown resistance properties even at high temperatures, with an energy storage density increased to 6.2 J / cm² compared to pure polypropylene. 3It exhibits excellent long-term cycle stability under high-temperature conditions of 125℃ and can be widely used in fields with stringent requirements for high energy storage density and long-term cycle life, such as high-energy-storage pulse equipment, hybrid electric vehicles, electromagnetic catapult equipment, smart power grid equipment, aerospace equipment, and military and defense equipment.

[0064] This application provides an application of a polypropylene composite film, which can be used in any of the following: high-energy-storage pulse capacitors, automotive capacitors, power system capacitors, aerospace capacitors, electromagnetic catapult capacitors, and military and defense capacitors.

[0065] The applicant further provides the following specific embodiments to describe the present invention. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0066] Example 1

[0067] This embodiment provides a polypropylene composite material and a polypropylene composite film.

[0068] The polypropylene composite material comprises the following components by volume percentage: antioxidant 1010 0.10%, antioxidant 168 0.05%, 1,3:2,4-di-p-methylbenzyl sorbitol 0.05%, with the balance being polypropylene (purchased from Sinopec Zhongyuan Petrochemical Co., Ltd.).

[0069] Polypropylene composite films are prepared from polypropylene composite materials, and the preparation steps are as follows:

[0070] Step S1: Polypropylene, antioxidant, and organic nucleating agent are dried in an oven at 50°C for 12 hours to completely remove residual moisture and avoid affecting the compatibility and synergistic effect of each component. The organic nucleating agent is placed in pure water and ultrasonically exfoliated at 2000W for 7 hours. During the ultrasonic process, an ice bath can be used to prevent the temperature from getting too high. After centrifugation, the organic nucleating agent is placed in an oven for drying to obtain organic nucleating agent powder with a particle size range of 1μm to 10μm. The particle size of the organic nucleating agent is refined by ultrasonic exfoliation, which can improve the dispersion uniformity of the antioxidant and polypropylene.

[0071] Step S2: Place the polypropylene powder in a ball mill jar, set the speed of the two-roll mill to 100 r / min, and mix for 20 minutes. Then remove and set aside. Subsequently, place the mixed polypropylene, antioxidant, and organic nucleating agent in a ball mill jar, set the speed of the two-roll mill to 60 r / min, and mix for 8 hours until all components are uniformly mixed to obtain a mixed powder. Note that the volume of the ball mill jar used should not exceed 2 / 3 of the jar's capacity.

[0072] Step S3: The mixed powder is placed in a melt extrusion casting film machine at a temperature of 187.5℃ for melt blending to obtain a mixed melt; at this temperature, the compatibility of each component can be guaranteed and their synergistic mechanism can be preserved.

[0073] In step S4, a polypropylene composite film is prepared at a temperature of 187°C and a winding speed of 12.5 r / min. Then, the polypropylene composite film is annealed at 120°C for 9 h to obtain a polypropylene composite film with a thickness of 15 μm. The annealing treatment helps to further enhance the synergistic effect of the organic nucleating agent and the antioxidant, and optimize the crystal structure and thermal stability of the polypropylene composite film.

[0074] Example 2

[0075] This embodiment provides a polypropylene composite material and a polypropylene composite film. The difference between this embodiment and Embodiment 1 lies in the component ratio of the polypropylene composite material, as detailed below:

[0076] The polypropylene composite material comprises the following components by volume percentage: antioxidant 1010 0.10%, antioxidant 168 0.05%, 1,3:2,4-di-p-methylbenzyl sorbitol 0.10%, with the balance being polypropylene (purchased from Sinopec Zhongyuan Petrochemical Co., Ltd.).

[0077] In this embodiment, the polypropylene composite film is prepared from polypropylene composite material, and its preparation method is the same as that in Example 1.

[0078] Example 3

[0079] This embodiment provides a polypropylene composite material and a polypropylene composite film. The difference between this embodiment and Embodiment 1 lies in the component ratio of the polypropylene composite material, as detailed below:

[0080] The polypropylene composite material comprises the following components by volume percentage: antioxidant 1010 0.10%, antioxidant 168 0.05%, 1,3:2,4-di-p-methylbenzyl sorbitol 0.15%, with the balance being polypropylene (purchased from Sinopec Zhongyuan Petrochemical Co., Ltd.).

[0081] In this embodiment, the polypropylene composite film is prepared from polypropylene composite material, and its preparation method is the same as that in Example 1.

[0082] Example 4

[0083] This embodiment provides a polypropylene composite material and a polypropylene composite film. The difference between this embodiment and Embodiment 1 lies in the component ratio of the polypropylene composite material, as detailed below:

[0084] The polypropylene composite material comprises the following components by volume percentage: antioxidant 1010 0.10%, antioxidant 168 0.05%, and the balance being polypropylene (purchased from Sinopec Zhongyuan Petrochemical Co., Ltd.).

[0085] Polypropylene composite films are prepared from polypropylene composite materials, and the preparation steps are as follows:

[0086] Step S1: Place the polypropylene and antioxidant in an oven at 50°C for 12 hours to dry them.

[0087] Step S2: Place the polypropylene powder in a ball mill jar, set the speed of the two-roll mill to 100 r / min, and mix for 20 min. Then take it out for later use. Subsequently, place the mixed polypropylene and antioxidant in a ball mill jar, set the speed of the two-roll mill to 60 r / min, and mix for 8 h until all components are mixed evenly to obtain a mixed powder.

[0088] Step S3: The mixed powder is placed in a melt extrusion casting film machine at a temperature of 187.5℃ for melt blending to obtain a mixed melt;

[0089] In step S4, a polypropylene composite film is prepared at a temperature of 187°C and a winding speed of 12.5 r / min. Then, the polypropylene composite film is annealed at 120°C for 9 h to obtain a polypropylene composite film with a thickness of 15 μm.

[0090] Example 5

[0091] This embodiment provides a polypropylene composite material and a polypropylene composite film. The difference between this embodiment and Embodiment 1 lies in the component ratio of the polypropylene composite material, as detailed below:

[0092] The polypropylene composite material comprises the following components by volume percentage: 1,3:2,4-di-p-methylbenzyl sorbitol 0.10%, with the balance being polypropylene (purchased from Sinopec Zhongyuan Petrochemical Co., Ltd.).

[0093] Polypropylene composite films are prepared from polypropylene composite materials, and the preparation steps are as follows:

[0094] Step S1: The polypropylene and organic nucleating agent are placed in an oven at 50°C for 12 hours for drying. The organic nucleating agent is placed in pure water and ultrasonically exfoliated at 2000W for 7 hours. During the ultrasonic process, an ice bath can be used to prevent the temperature from getting too high. After centrifugation, the organic nucleating agent is placed in an oven for drying to obtain organic nucleating agent powder with a particle size range of 1μm to 10μm.

[0095] Step S2: Place the polypropylene powder in a ball mill jar, set the speed of the two-roll mill to 100 r / min, and mix for 20 min. Then take it out for later use. Subsequently, place the mixed polypropylene and organic nucleating agent in a ball mill jar, set the speed of the two-roll mill to 60 r / min, and mix for 8 h until all components are mixed evenly to obtain a mixed powder.

[0096] Step S3: The mixed powder is placed in a melt extrusion casting film machine at a temperature of 187.5℃ for melt blending to obtain a mixed melt;

[0097] In step S4, a polypropylene composite film is prepared at a temperature of 187°C and a winding speed of 12.5 r / min. Then, the polypropylene composite film is annealed at 120°C for 9 h to obtain a polypropylene composite film with a thickness of 15 μm.

[0098] Comparative Example 1

[0099] This comparative example provides a pure polypropylene composite material and a polypropylene film.

[0100] The pure polypropylene composite material is polypropylene (specifically, metallocene polypropylene). The polypropylene film is prepared from polypropylene, and the specific steps are as follows:

[0101] Step S1: Place the polypropylene in an oven at 50°C and keep it at that temperature for 12 hours for drying.

[0102] Step S2: Place the polypropylene powder in the ball mill jar, set the speed of the two roller mill to 100 r / min, mix for 20 min, and then take it out for later use.

[0103] Step S3: The mixed polypropylene powder is placed in a melt extrusion casting film machine at a temperature of 187.5℃ for melt blending to obtain a mixed melt;

[0104] In step S4, a polypropylene film is prepared at a temperature of 187°C and a winding speed of 12.5 r / min. The polypropylene film is then annealed at 120°C for 9 h to obtain a polypropylene composite film with a thickness of 15 μm.

[0105] The polypropylene composite films or polypropylene films prepared in Examples 1-5 and Comparative Example 1 were subjected to the following characterization tests: (1) The DC breakdown field strength of the film under normal temperature and 125℃ high temperature conditions was measured using a standard electrical breakdown test instrument to evaluate its insulation withstand capability; (2) The energy storage density and energy release efficiency of the film under different electric field strengths were quantified by capacitor charge-discharge test to characterize its energy storage and output characteristics; (3) The thermal decomposition temperature and structural stability of the film at high temperature were tested using a thermogravimetric analyzer. The relevant test results are detailed in [reference needed]. Figures 2 to 10 .

[0106] (1) The DC breakdown field strength of the film before and after annealing was measured using a standard electrical breakdown test instrument at room temperature (25℃) and high temperature (125℃) to evaluate its insulation withstand capability. The relevant test results are detailed in [link to relevant test results]. Figure 2 , Figure 3 (2) The energy storage density and energy release efficiency of the film before and after annealing under different electric field strengths were quantified by capacitor charge-discharge tests to characterize its energy storage and output characteristics. For details of the relevant test results, please refer to [link to relevant test results]. Figure 4 , Figure 5 (3) The melting behavior, crystallinity, and thermal transformation characteristics of the annealed film were tested using a differential scanning calorimeter to analyze its crystalline structure and thermal properties. The relevant test results are detailed in [reference needed]. Figure 6 (4) The thermal decomposition temperature and structural stability at high temperatures of the annealed film were tested using a thermogravimetric analyzer to evaluate its thermal resistance. The relevant test results are detailed in [link to relevant test results]. Figure 7 (5) The dielectric constant and dielectric loss of the annealed film were tested over a wide frequency range using a broadband dielectric spectrometer to characterize its dielectric response. The relevant test results are detailed in [reference needed]. Figure 8 , Figure 9 (6) The cycling stability and service life of the annealed film under high temperature conditions of 125℃ were evaluated by high temperature long-term charge-discharge performance test. For details of the relevant test results, please refer to Figure 10 .

[0107] Example 1: Before annealing, the room temperature breakdown electric field strength of the polypropylene composite film can reach 652 MV / m, and the breakdown electric field strength remains at 503 MV / m at 125°C. At room temperature and an electric field of 550 MV / m, the energy storage density is 4.0 J / cm³. 3 The release efficiency is 92.6%; after annealing, the room temperature breakdown field strength of the polypropylene composite film reaches 649 MV / m, and the breakdown field strength remains at 532 MV / m at 125℃; the energy storage density is 4.5 J / cm³ at a room temperature and an electric field of 600 MV / m. 3 The release efficiency is 90.7%.

[0108] Example 2: Before annealing, the room temperature breakdown field strength of the polypropylene composite film can reach 682 MV / m, and the breakdown field strength remains at 522 MV / m at a high temperature of 125℃. Under a room temperature electric field of 600 MV / m, the energy storage density is 4.58 J / cm³. 3 The release efficiency is 89.7%; after annealing, the room temperature breakdown field strength of the polypropylene composite film reaches 743 MV / m, and the breakdown field strength remains at 597 MV / m at a high temperature of 125℃; the energy storage density is 6.2 J / cm³ at a room temperature electric field of 700 MV / m. 3 It has a release efficiency of 88.8%. It exhibits optimal long-term cycling stability at high temperatures, making it suitable for demanding scenarios.

[0109] Example 3: Before annealing, the room temperature breakdown field strength of the polypropylene composite film can reach 669 MV / m, and the breakdown field strength remains at 497 MV / m at a high temperature of 125℃. Under a room temperature electric field of 550 MV / m, the energy storage density is 3.8 J / cm³. 3 The release efficiency is 91.3%; after annealing, the room temperature breakdown field strength of the polypropylene composite film reaches 706 MV / m, and the breakdown field strength remains at 551 MV / m at a high temperature of 125℃; at room temperature and under an electric field of 650 MV / m, the energy storage density is 5.7 J / cm³. 3 It has a release efficiency of 91.1%. It maintains good structural and performance stability even at high temperatures.

[0110] Example 4: Before annealing, the room temperature breakdown field strength of the polypropylene composite film reached 607 MV / m, and the breakdown field strength remained at 501 MV / m at 125°C. At a room temperature and an electric field of 550 MV / m, the energy storage density was 3.8 J / cm³, with a release efficiency of 90.7%. After annealing, the room temperature breakdown field strength of the polypropylene composite film reached 583 MV / m, and the breakdown field strength remained at 489 MV / m at 125°C. At a room temperature and an electric field of 650 MV / m, the energy storage density was 5.4 J / cm³. 3 It has a release efficiency of 90.5%. It maintains good structural and performance stability even at high temperatures.

[0111] Example 5: Before annealing, the room temperature breakdown field strength of the polypropylene composite film can reach 703 MV / m, and the breakdown field strength remains at 483 MV / m at a high temperature of 125°C. Under a room temperature electric field of 550 MV / m, the energy storage density is 3.7 J / cm³. 3 The release efficiency is 91.8%; after annealing, the room temperature breakdown field strength of the polypropylene composite film reaches 625 MV / m, and the breakdown field strength remains at 452 MV / m at a high temperature of 125℃; the energy storage density is 5.3 J / cm³ at a room temperature electric field of 650 MV / m. 3 It has a release efficiency of 91.0%. It maintains good structural and performance stability even at high temperatures.

[0112] Comparative Example 1: Before annealing, the room temperature breakdown field strength of the polypropylene film reached 623 MV / m, and the breakdown field strength remained at 425 MV / m at a high temperature of 125℃. Under a room temperature electric field of 550 MV / m, the energy storage density was 3.6 J / cm³. 3 The release efficiency is 90.3%; after annealing, the room temperature breakdown field strength of the polypropylene film can reach 601 MV / m, and the breakdown field strength at 125℃ still remains at 403 MV / m; at room temperature and an electric field of 650 MV / m, the energy storage density is 5.2 J / cm³. 3It has a release efficiency of 89.5%. It maintains good structural and performance stability even at high temperatures.

[0113] The experimental results from Example 5 and Comparative Example 1 show that adding an organic nucleating agent alone can significantly improve the breakdown field strength of the polypropylene composite film before annealing; however, this performance improvement effect decreases significantly after annealing. This indicates that although the organic nucleating agent can improve the breakdown field strength under normal and high temperature conditions before annealing to some extent, its heat resistance and annealing stability are insufficient, and annealing treatment will significantly inhibit its performance advantages.

[0114] The comparison data between Example 4 and Comparative Example 1 show that when an antioxidant is added alone, both the ambient and high-temperature breakdown field strengths decrease to varying degrees, regardless of whether the film is before or after annealing. This indicates that the introduction of a single antioxidant cannot optimize the breakdown field strength of the polypropylene composite film; on the contrary, it may adversely affect its dielectric properties.

[0115] Further analysis of the experimental data from Examples 1-3 reveals that when both antioxidants and organic nucleating agents are added simultaneously, the breakdown field strength of the polypropylene composite film is improved to varying degrees under both room temperature and high temperature conditions compared to Comparative Example 1. Furthermore, after annealing, the increases in breakdown field strength at both room temperature and high temperature are even more significant in Examples 2 and 3. This result confirms that the combined use of antioxidants and organic nucleating agents not only effectively avoids the performance degradation caused by a single antioxidant but also compensates for the performance degradation defects that occur after annealing with a single organic nucleating agent, achieving a synergistic effect and significantly improving the annealing stability and overall dielectric properties of the polypropylene composite film.

[0116] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to examples, those skilled in the art can still modify the technical solutions described in the foregoing examples or make equivalent substitutions for some of the technical features. However, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A polypropylene composite material, characterized in that, Includes the following components by volume percentage: Organic nucleating agent 0.01% to 5%, including sorbitol benzylidene derivatives; other auxiliaries 0.01% to 1.00%; balance polypropylene.

2. The polypropylene composite material according to claim 1, characterized in that, The polypropylene is at least one of homopolymer polypropylene, block copolymer polypropylene, high-impact polypropylene, random copolymer polypropylene, and metallocene polypropylene.

3. The polypropylene composite material according to claim 1, characterized in that, The organic nucleating agent also includes at least one of carboxylic acid metal salt nucleating agents, phosphate metal salt nucleating agents, aromatic diamide nucleating agents, and rare earth compound nucleating agents.

4. The polypropylene composite material according to claim 1, characterized in that, The particle size of the organic nucleating agent is 1 μm to 10 μm.

5. The polypropylene composite material according to claim 1, characterized in that, The other additives include at least one of antioxidants, light stabilizers, voltage stabilizers, plasticizers, and antistatic agents.

6. The polypropylene composite material according to any one of claims 1 or 5, characterized in that, The other adjuvants include antioxidants, which include at least one of antioxidant 1010, antioxidant 168, antioxidant 1076, antioxidant 1098, antioxidant 3114, antioxidant 2246, antioxidant 626, antioxidant 618, and antioxidant 126.

7. A method for preparing a polypropylene composite film, characterized in that, The polypropylene composite material according to any one of claims 1 to 6 is prepared by the following steps: Step S1: The organic nucleating agent is subjected to ultrasonic exfoliation to obtain organic nucleating agent powder with a preset particle size; Step S2: Mix the organic nucleating agent powder, polypropylene, and other additives evenly, and then melt-blend to obtain a mixed melt; Step S3: The mixed melt is co-extruded to obtain a polypropylene composite film.

8. The method for preparing the polypropylene composite film according to claim 7, characterized in that, It also includes annealing; The annealing process is as follows: the polypropylene composite film is annealed at 110℃ to 130℃ for 8h to 10h.

9. The method for preparing the polypropylene composite film according to claim 7, characterized in that, During the ultrasonic ablation process, the ultrasonic ablation power is 1800W to 2000W, and the ultrasonic ablation process lasts for 6 hours to 8 hours; during the melt blending process, the temperature is 130℃ to 250℃.

10. A polypropylene composite film, characterized in that, It is prepared by using the polypropylene composite material according to any one of claims 1 to 6, or by using the method for preparing polypropylene composite film according to any one of claims 7 to 9.

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