A biaxially oriented polypropylene-based capacitor film and a method for making the same

Abstract

The application relates to a two-way stretched polypropylene-based capacitor film and a preparation method thereof, and raw materials include polypropylene resin, fillers, a compatilizer, a nucleating agent and an antioxidant; the compatilizer is obtained by melt extrusion granulation of maleic anhydride grafted polypropylene and BN@SiO2-NH2; BN@SiO2-NH2 is obtained by the following steps: mixing boron nitride and urea in a ball mill, mechanically exfoliating, ultrasonic dispersing in an ethanol aqueous solution, adding tetraethyl orthosilicate and ammonia water, stirring and hydrolyzing to obtain BN@SiO2, and finally reflux grafting with gamma-aminopropyl triethoxysilane to obtain BN@SiO2-NH2. The compatilizer formed by premixing MAH-g-PP and BN@SiO2-NH2 can be uniformly dispersed and avoid agglomeration, and contains BN and SiO2 as fillers, plays a role in strengthening the interface and improving the breakdown strength, and promotes the dispersion of inorganic particles, effectively improving the dielectric constant.

Description

Technical Field

[0001] This invention relates to the field of capacitor film technology, specifically to a biaxially oriented polypropylene-based capacitor film and its preparation method. Background Technology

[0002] Polypropylene (PP) film is widely used in food packaging, medical packaging, production and transportation pipelines, textiles, electronic components and other fields due to its advantages such as low density, good chemical corrosion resistance and low cost.

[0003] Capacitors are one of the three major passive components, found in various electronic products. Film capacitors, in particular, are widely used in new energy fields such as new energy vehicles, photovoltaics, and wind power generation due to their high voltage resistance, temperature resistance, and stability. With continuous technological advancements and rapid development, the performance requirements for film capacitors are becoming increasingly stringent. As the core material of film capacitors, improving the performance of the capacitor film to optimize capacitor performance is currently a major focus in this field. Biaxially oriented polypropylene (BOPP) film is currently the most commercially successful polymer dielectric material, possessing high breakdown strength, excellent temperature stability, relatively low cost, and processability suitable for large-scale automated production. Despite the significant advantages of BOPP film, its physical properties limit its application in some high-end scenarios: while BOPP performs well at low temperatures, its breakdown electric field strength decreases rapidly and dielectric loss increases significantly at high temperatures (>70℃). Furthermore, improving the dielectric constant is difficult, often sacrificing insulation strength and temperature resistance. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention designs a compatibilizer that can serve as both a filler and an aid in the dispersion of inorganic particles in a matrix, effectively improving the dielectric constant while enhancing its heat resistance and breakdown strength.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A biaxially oriented polypropylene-based capacitor film comprises, by weight: 100 parts polypropylene resin, 3-8 parts filler, 5-10 parts compatibilizer, 0.1-0.5 parts nucleating agent, and 0.1-0.5 parts antioxidant;

[0007] The compatibilizer is obtained by melt extrusion granulation of maleic anhydride-grafted polypropylene and BN@SiO2-NH2. The preparation process of BN@SiO2-NH2 is as follows:

[0008] Boron nitride and urea were mixed and placed in a ball mill. After ball milling for 10-20 h, mechanical exfoliation was performed. Then, the mixture was ultrasonically dispersed in an ethanol aqueous solution, and tetraethyl orthosilicate and ammonia were added. The mixture was stirred and hydrolyzed to obtain BN@SiO2. Finally, it was refluxed and grafted with γ-aminopropyltriethoxysilane to obtain BN@SiO2-NH2.

[0009] Furthermore, the mass ratio of maleic anhydride-grafted polypropylene to BN@SiO2-NH2 in the compatibilizer is 100:20~30. The specific preparation process is as follows: maleic anhydride-grafted polypropylene (MAH-g-PP) and BN@SiO2-NH2 are mixed and fed into a twin-screw extruder, and melt-extruded and granulated at 180~220℃ to obtain compatibilizer granules.

[0010] Furthermore, the grafting rate of the maleic anhydride-grafted polypropylene is 1.2% to 1.5%.

[0011] Furthermore, the preparation process of the BN@SiO2-NH2 is as follows:

[0012] 1) Mix boron nitride and urea at a mass ratio of 1:20~40 and place them in a ball mill. The ball-to-material ratio is 80:1~120:1. The speed is 400~600 r / min. The ball milling is carried out for 15~20 h for mechanical stripping to obtain stripped boron nitride, which is denoted as BN.

[0013] 2) BN was ultrasonically dispersed in an ethanol aqueous solution, and the pH was adjusted to 8-9 with dilute ammonia. Tetraethyl orthosilicate was slowly added dropwise to the BN dispersion. The mixture was stirred at 40°C for 6 hours, centrifuged and washed to obtain BN@SiO2.

[0014] 3) BN@SiO2 is dispersed in ethanol, and 30-50% by weight of γ-aminopropyltriethoxysilane is added for reflux grafting to obtain BN@SiO2-NH2.

[0015] Furthermore, the filler is selected from one or more of alumina, calcium carbonate, titanium dioxide, and barium titanate.

[0016] Furthermore, the nucleating agent is talc powder with a particle size of 100-200 nm; the antioxidant is antioxidant 1010 or antioxidant 168.

[0017] A second objective of this invention is to provide a method for preparing the biaxially oriented polypropylene-based capacitor film as described above, comprising the following steps:

[0018] S1. After drying the polypropylene resin, mix it with filler, compatibilizer, nucleating agent and antioxidant, stir it in a high-speed mixer, and then feed it into a twin-screw extruder. Melt extrusion is carried out at 210~230℃ to cast sheets.

[0019] S2. The casting sheet is subjected to biaxial stretching. First, it is preheated to 70~90℃, and then longitudinally stretched at 110~130℃ with a stretching ratio of 4~5 times. Then, it is transversely stretched at 120~150℃ with a stretching ratio of 5~6 times.

[0020] S3. The film is heat-set after biaxial stretching, then cooled at 50°C, corona treated, drawn, and wound to obtain the final product.

[0021] Boron nitride (BN), as a two-dimensional layered material, possesses high thermal conductivity, excellent insulation properties, and low dielectric loss, making it an ideal filler for polymer modification. However, BN has a highly inert surface and poor interfacial compatibility with the polypropylene matrix. Direct blending can easily lead to agglomeration, affecting the overall performance of the composite material.

[0022] In this application, boron nitride is first mechanically exfoliated. Urea exfoliation of boron nitride has been shown to significantly reduce the average flake size, effectively inhibit inter-flake aggregation, and introduce active amino groups. Building upon this, the exfoliated boron nitride is impregnated in an ethanol-water solution, followed by the addition of tetraethyl orthosilicate for hydrolysis. This hydrolysis partially allows the growth of silica particles between the boron nitride layers. Furthermore, the addition of γ-aminopropyltriethoxysilane forms an organic bridge, resulting in stable BN@SiO2-NH2 composite particles. These particles act as active sites in the subsequent melt blending with MAH-g-PP, forming chemical bonds. Through this series of reactions, the final product is added to the PP matrix as a compatibilizer. This effectively disperses fillers, prevents aggregation, and, while containing the boron nitride structure, also acts as a filler to enhance the interface and improve breakdown strength.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. BN@SiO2-NH2 forms a covalent bond with MAH-g-PP through pre-reaction, and when it is blended with the polypropylene matrix, a strongly chemically bonded interface layer is formed between the filler and the matrix; at the same time, BN maintains its two-dimensional layered structure and is loaded with SiO2 particles, which significantly improves the breakdown strength of the film; 2. The compatibilizer formed by premixing MAH-g-PP and BN@SiO2-NH2 can be uniformly dispersed like a common compatibilizer when blended with polypropylene, avoiding the agglomeration problem caused by the high surface energy when BN@SiO2-NH2 is directly added, and also promoting the dispersion of inorganic particle fillers; 3. The uniformly dispersed high dielectric constant inorganic particles such as barium titanate and alumina introduce a high dielectric phase into the polypropylene matrix, effectively improving the dielectric constant. Detailed Implementation

[0024] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0026] Example 1: I. Preparation of compatibilizer

[0027] 1) Take 10g of hexagonal boron nitride powder (Suzhou Sailon Nano New Material Industry Co., Ltd., BN-2) and mix it with 300g of urea. Add the mixture to a ball mill jar with a ball-to-material ratio of 100:1 and mill at 500r / min for 20 hours. Take out the product, wash it three times with deionized water, and vacuum dry it at 60℃ for 12 hours to obtain exfoliated boron nitride BN.

[0028] 2) Take 5 g of BN and disperse it in 100 mL of ethanol-water mixed solvent (volume ratio 4:1). Adjust the pH to 8-9 with dilute ammonia water, slowly add 10 g of tetraethyl orthosilicate, stir at 40 °C for 6 h, centrifuge the product, wash it 3 times with ethanol, and dry it at 60 °C to obtain BN@SiO2.

[0029] 3) Disperse 3g of BN@SiO2 in 100mL of anhydrous ethanol, add 1.5g of 3-aminopropyltriethoxysilane, and reflux at 70℃ for 8 hours. Centrifuge the product, wash it three times with ethanol, and dry it under vacuum at 60℃ for 12 hours to obtain BN@SiO2-NH2.

[0030] 4) Take 100 g of MAH-g-PP (Jiangsu Runfeng Synthetic Technology Co., Ltd., density 0.92 g / cm³). 3 A pre-reacting compatibilizer was obtained by mixing 20 g of the above BN@SiO2-NH2 (grafting rate 1.2%) with 20 g of the above BN@SiO2-NH2, adding it to a twin-screw extruder, and melt-extruded and granulating at 200°C.

[0031] II. Preparation of Polypropylene Capacitor Film

[0032] S1. After drying 100 parts of polypropylene resin (Suzhou Yitianli Plastics Co., Ltd., brand R370Y), it is mixed with 3 parts of filler (alumina and calcium carbonate 2:1 mixture), 5 parts of compatibilizer, 0.1 parts of nucleating agent talc powder and 0.1 parts of antioxidant 1010. The mixture is stirred in a high-speed mixer and then fed into a twin-screw extruder for melt extrusion at 210℃ to cast sheets.

[0033] S2. The casting sheet is subjected to biaxial stretching. First, it is preheated to 80°C, and then longitudinally stretched at 110°C with a stretching ratio of 4.2 times. Then, it is transversely stretched at 130°C with a stretching ratio of 5.5 times.

[0034] S3. The film is heat-set after biaxial stretching, then cooled at 50°C, corona treated, drawn, and wound to obtain the final product.

[0035] Example 2: I. Preparation of compatibilizer

[0036] Same as Example 1.

[0037] II. Preparation of Polypropylene Capacitor Film

[0038] S1. After drying 100 parts of polypropylene resin (Suzhou Yitianli Plastics Co., Ltd., brand R370Y), it is mixed with 6 parts of filler (a 2:1 mixture of titanium dioxide and barium titanate), 8 parts of compatibilizer, 0.3 parts of nucleating agent talc powder and 0.3 parts of antioxidant 1010. The mixture is stirred in a high-speed mixer and then fed into a twin-screw extruder for melt extrusion at 210℃ to cast sheets.

[0039] S2. The casting sheet is subjected to biaxial stretching. First, it is preheated to 80°C, and then longitudinally stretched at 110°C with a stretching ratio of 4.2 times. Then, it is transversely stretched at 130°C with a stretching ratio of 5.5 times.

[0040] S3. The film is heat-set after biaxial stretching, then cooled at 50°C, corona treated, drawn, and wound to obtain the final product.

[0041] Example 3: I. Preparation of compatibilizer

[0042] Same as Example 1.

[0043] II. Preparation of Polypropylene Capacitor Film

[0044] S1. After drying 100 parts of polypropylene resin (Suzhou Yitianli Plastics Co., Ltd., brand R370Y), it is mixed with 8 parts of filler (a 2:1 mixture of titanium dioxide and calcium carbonate), 10 parts of compatibilizer, 0.3 parts of nucleating agent talc powder and 0.5 parts of antioxidant 1010. The mixture is stirred in a high-speed mixer and then fed into a twin-screw extruder for melt extrusion at 210℃ to cast sheets.

[0045] S2. The casting sheet is subjected to biaxial stretching. First, it is preheated to 80°C, and then longitudinally stretched at 110°C with a stretching ratio of 4.2 times. Then, it is transversely stretched at 130°C with a stretching ratio of 5.5 times.

[0046] S3. The film is heat-set after biaxial stretching, then cooled at 50°C, corona treated, drawn, and wound to obtain the final product.

[0047] Comparative Example 1: I. Preparation of Compatibilizer

[0048] 1) Take 5 g of hexagonal boron nitride powder and disperse it in 100 mL of ethanol-water mixed solvent (volume ratio 4:1). Adjust the pH to 8-9 with dilute ammonia water, slowly add 10 g of tetraethyl orthosilicate, stir at 40 °C for 6 h, centrifuge the product, wash it 3 times with ethanol, and dry it at 60 °C to obtain BN@SiO2.

[0049] 2) Disperse 3g of BN@SiO2 in 100mL of anhydrous ethanol, add 1.5g of 3-aminopropyltriethoxysilane, and reflux at 70℃ for 8 hours. Centrifuge the product, wash it three times with ethanol, and dry it under vacuum at 60℃ for 12 hours to obtain BN@SiO2-NH2.

[0050] 3) Take 100 g of MAH-g-PP (Jiangsu Runfeng Synthetic Technology Co., Ltd., density 0.92 g / cm³). 3 A pre-reacting compatibilizer was obtained by mixing 20 g of the above BN@SiO2-NH2 (grafting rate 1.2%) with 20 g of the above BN@SiO2-NH2, adding it to a twin-screw extruder, and melt-extruded and granulating at 200°C.

[0051] II. Prepare polypropylene capacitor film in the same manner as in Example 2.

[0052] Comparative Example 2: I. Preparation of Compatibilizer

[0053] 1) Mix 10g of hexagonal boron nitride powder with 300g of urea, add it to a ball mill jar, ball ratio 100:1, and ball mill at 500r / min for 20 hours. Take out the product, wash it three times with deionized water, and vacuum dry it at 60℃ for 12 hours to obtain exfoliated boron nitride (BN).

[0054] 2) Take 100 g of MAH-g-PP (Jiangsu Runfeng Synthetic Technology Co., Ltd., density 0.92 g / cm³). 3 A pre-reacting compatibilizer was obtained by mixing 20 g of the above BN with a grafting rate of 1.2% and adding it into a twin-screw extruder, and then melt-extruded and granulating it at 200°C.

[0055] II. Preparation of Polypropylene Capacitor Film

[0056] Same as Example 2.

[0057] Comparative Example 3: S1. 100 parts of polypropylene resin (Suzhou Yitianli Plastics Co., Ltd., grade R370Y) were dried and mixed with 6 parts of filler (a 2:1 mixture of titanium dioxide and barium titanate) and 6.7 parts of MAH-g-PP (Jiangsu Runfeng Synthetic Technology Co., Ltd., density 0.92 g / cm³). 3The grafting rate was 1.2%, 1.3 parts of BN@SiO2-NH2 prepared in Example 1, 0.3 parts of nucleating agent talc powder and 0.3 parts of antioxidant 1010 were mixed and stirred in a high-speed mixer, and then fed into a twin-screw extruder for melt extrusion at 210°C to cast sheets;

[0058] S2. The casting sheet is subjected to biaxial stretching. First, it is preheated to 80°C, and then longitudinally stretched at 110°C with a stretching ratio of 4.2 times. Then, it is transversely stretched at 130°C with a stretching ratio of 5.5 times.

[0059] S3. The film is heat-set after biaxial stretching, then cooled at 50°C, corona treated, drawn, and wound to obtain the final product.

[0060] The polypropylene-based capacitor films prepared in the above embodiments and comparative examples were subjected to the following performance tests:

[0061] 1. Dielectric constant and dielectric loss: According to ASTM D150, test conditions: standard atmospheric pressure, 50±5%RH, 23±2℃.

[0062] 2. Breakdown strength: ASTM D149, standard atmospheric pressure, 50±5%RH, the breakdown strength was tested at 25℃ and 70 and 120℃ respectively.

[0063] 3. Heat shrinkage rate: GB / T 13542.2-2021, 120℃ / 150℃, 30min.

[0064] Table 1

[0065]

[0066] Comparative Example 1, without urea ball milling, did not achieve good mechanical exfoliation of BN, making it prone to agglomeration. Furthermore, it failed to allow silica particles to grow between its layers, resulting in poor BN-SiO2 composite effects and exacerbating agglomeration. Premixing with MAH-g-PP barely managed to disperse it in the PP matrix to form a base film. However, due to BN@SiO2-NH2 agglomeration, neither BN nor SiO2 functioned effectively, leading to a significant decrease in breakdown strength and poor heat resistance, with an even more pronounced decrease in breakdown strength at elevated temperatures. Comparative Example 2 used mechanically exfoliated BN premixed and granulated with MAH-g-PP. Compared to Example 2, the unfunctionalized BN did not significantly improve the dielectric and breakdown strength properties of the film. However, the premixed dispersion was better than Comparative Example 3, and the breakdown strength retention at high temperatures was relatively good. Comparative Example 3 showed improved performance at room temperature and pressure compared to Comparative Example 2, but due to poor dispersion, more defects were exposed at high temperatures, resulting in a larger decrease in breakdown strength at high temperatures than Comparative Example 2. In Examples 1 to 3, the dielectric constant increased with the increase of filler and compatibilizer, but the dielectric loss and breakdown strength decreased slightly. Example 2 reached a balance.

[0067] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details.

Claims

1. A biaxially oriented polypropylene-based capacitor film, characterized in that, The composition by weight includes: 100 parts polypropylene resin, 3-8 parts filler, 5-10 parts compatibilizer, 0.1-0.5 parts nucleating agent, and 0.1-0.5 parts antioxidant; The compatibilizer is obtained by melt extrusion granulation of maleic anhydride-grafted polypropylene and BN@SiO2-NH2. The preparation process of BN@SiO2-NH2 is as follows: Boron nitride and urea were mixed and placed in a ball mill. After ball milling for 10-20 h, mechanical exfoliation was performed. Then, the mixture was ultrasonically dispersed in an ethanol aqueous solution, and tetraethyl orthosilicate and ammonia were added. The mixture was stirred and hydrolyzed to obtain BN@SiO2. Finally, it was refluxed and grafted with γ-aminopropyltriethoxysilane to obtain BN@SiO2-NH2. The filler is selected from one or more of alumina, calcium carbonate, titanium dioxide, and barium titanate; The nucleating agent is talc powder with a particle size of 100-200 nm; the antioxidant is antioxidant 1010 or antioxidant 168.

2. The biaxially oriented polypropylene-based capacitor film according to claim 1, characterized in that, The mass ratio of maleic anhydride-grafted polypropylene to BN@SiO2-NH2 in the compatibilizer is 100:20~30. The specific preparation process is as follows: maleic anhydride-grafted polypropylene and BN@SiO2-NH2 are mixed and fed into a twin-screw extruder, and melt-extruded and granulated at 180~220℃ to obtain compatibilizer granules.

3. The biaxially oriented polypropylene-based capacitor film according to claim 1, characterized in that, The grafting rate of the maleic anhydride-grafted polypropylene is 1.2% to 1.5%.

4. The biaxially oriented polypropylene-based capacitor film according to claim 1, characterized in that, The preparation process of BN@SiO2-NH2 is as follows: 1) Mix boron nitride and urea at a mass ratio of 1:20~40 and place them in a ball mill. The ball-to-material ratio is 80:1~120:

1. The speed is 400~600 r / min. The ball milling is carried out for 15~20 h for mechanical stripping to obtain stripped boron nitride, which is denoted as BN. 2) BN was ultrasonically dispersed in an ethanol aqueous solution, and the pH was adjusted to 8-9 with dilute ammonia. Tetraethyl orthosilicate was slowly added dropwise to the BN dispersion. The mixture was stirred at 40°C for 6 hours, centrifuged and washed to obtain BN@SiO2. 3) BN@SiO2 is dispersed in ethanol, and 30-50% by weight of γ-aminopropyltriethoxysilane is added for reflux grafting to obtain BN@SiO2-NH2.

5. The method for preparing a biaxially oriented polypropylene-based capacitor film according to any one of claims 1-4, characterized in that, Includes the following steps: S1. After drying the polypropylene resin, mix it with filler, compatibilizer, nucleating agent and antioxidant, stir it in a high-speed mixer, and then feed it into a twin-screw extruder. Melt extrusion is carried out at 210~230℃ to cast sheets. S2. The casting sheet is subjected to biaxial stretching. First, it is preheated to 70~90℃, and then longitudinally stretched at 110~130℃ with a stretching ratio of 4~5 times. Then, it is transversely stretched at 120~150℃ with a stretching ratio of 5~6 times. S3. The film is heat-set after biaxial stretching, then cooled at 50°C, corona treated, drawn, and wound to obtain the final product.

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