PP film for low-loss capacitor

Abstract

The invention relates to the technical field of high-molecular polypropylene films, and discloses a PP film for a low-loss capacitor, which is prepared from the following ingredients in parts by mass: 80 to 95 parts of heat-resistant polypropylene resin base materials, 3 to 12 parts of dielectric modifiers, 0.1 to 0.2 part of nucleating agents, 0.05 to 0.8 part of lubricating agents and 1 to 3 parts of stabilizing agents. Through the synergistic effect of specific components, for example, large conjugate structures of the dielectric modifier and the stabilizer synergistically absorb and dissipate electric field energy and the like, the dielectric loss of the PP film is effectively reduced, so that the PP film can reduce heating of a capacitor in a high-frequency or high-voltage application scene, the service life of the capacitor is prolonged, and the safety of the capacitor is improved; and the strict standard of modern electronic equipment on dielectric loss of the capacitor is met. The PP film provided by the invention can maintain the stability of dielectric constant and dielectric loss in a high-temperature working environment, solves the problem of performance reduction caused by insufficient heat resistance of a traditional PP film, and expands the applicability of a capacitor in a high-temperature application scene.

Description

Technical Field

[0001] The present invention relates to the technical field of high molecular polypropylene films, and in particular to a PP film for low-loss capacitors. Background Art

[0002] In the field of capacitor technology, polypropylene (PP) film, as a common insulating dielectric material, is widely used in the manufacture of various types of capacitors, including metallized film capacitors, DC link capacitors, AC filter capacitors, and pulse power capacitors. However, existing PP film in capacitor applications presents several challenges that need to be addressed.

[0003] First, as electronic devices continue to evolve toward miniaturization, higher performance, and higher reliability, the performance requirements for capacitors are becoming increasingly stringent, particularly with regard to dielectric loss. In high-frequency or high-voltage applications, excessive dielectric loss in PP film can cause severe heating in capacitors, shortening their service life and potentially posing safety risks such as thermal failure or even damage, affecting the normal operation of the entire electronic device.

[0004] Secondly, traditional PP film has shortcomings in heat resistance. In some high-temperature operating environments, PP film may experience performance degradation, such as unstable dielectric constant and dielectric loss, which makes it difficult for capacitors to meet the needs of certain high-temperature applications.

[0005] Furthermore, various additives are often added to PP film during the processing to improve its performance. However, if the compatibility and stability of these additives are not ideal, they may gradually migrate or volatilize during the long-term use of the capacitor, thereby causing changes in the performance of the PP film and affecting the reliability and stability of the capacitor.

[0006] Furthermore, the existing PP film manufacturing process also limits further performance improvements. For example, during biaxial stretching, inaccurate control of process parameters such as the stretch ratio and stretching temperature can lead to uneven molecular orientation and crystalline structure in the film, thus affecting the uniformity and stability of its dielectric properties. Therefore, there is an urgent need to develop a low-loss PP film for capacitors that offers excellent heat resistance and a precisely controllable manufacturing process to meet the high performance requirements of modern electronic devices. Summary of the Invention

[0007] The purpose of the present invention is to address the problems existing in the prior art and provide a PP film for low-loss capacitors with low loss, excellent heat resistance and precise and controllable preparation process.

[0008] To achieve the above object, the technical solution adopted by the present invention is: a PP film for low-loss capacitors, comprising the following components in the following weight ratios: 80-95 parts of a heat-resistant polypropylene resin base material, 3-12 parts of a dielectric modifier, 0.1-0.2 parts of a nucleating agent, 0.05-0.8 parts of a lubricant, and 1-3 parts of a stabilizer; The stabilizer has a structure shown in Formula 1: Formula 1; The R1 is selected from the group consisting of methyl, ethyl, methoxy and phenyl.

[0009] Furthermore, the thickness of the PP film for low-loss capacitors is 3.0-3.8 μm±3%.

[0010] Furthermore, the tensile strength of the PP film for low-loss capacitors is: MD (longitudinal direction) ≥ 160 MPa, TD (transverse direction) ≥ 200 MPa.

[0011] Furthermore, the dielectric modifier is at least one of silicon dioxide, aluminum oxide or barium titanate, and its particle size range is 20-100 nm.

[0012] Furthermore, the nucleating agent is di(3,4-dimethylbenzylidene)sorbitol.

[0013] Furthermore, the stabilizer is any one of the compounds shown in the following structures: ; .

[0014] Furthermore, the lubricant is oleamide.

[0015] A method for preparing a PP film for a low-loss capacitor comprises the following steps: S1. The heat-resistant polypropylene resin substrate, dielectric modifier, nucleating agent, lubricant and stabilizer are premixed in a mixer to obtain a premix; S2. The premix is melt-extruded and cast into a base film; S3. The base film is biaxially stretched, the longitudinal stretch ratio is 4.5-5.5, the transverse stretch ratio is 8-10, and the base film is stretched; S4. The stretched base film is subjected to heat setting treatment to obtain a PP film for low-loss capacitors.

[0016] Furthermore, the premixing temperature in S1 is 180-200°C.

[0017] Furthermore, the temperature of the biaxial stretching in S3 is 150-160°C.

[0018] Furthermore, the heat setting temperature in S4 is 155-165° C., and the relaxation heat setting is 10-20 seconds.

[0019] The invention discloses an application of a PP film for low-loss capacitors in manufacturing metallized film capacitors, DC support capacitors, AC filter capacitors or pulse power capacitors.

[0020] The core design of the stabilizer described in the present invention includes long alkyl chains, hydroxyl groups, and a large conjugated structure. These elements work synergistically to significantly improve the thermal stability, dielectric properties, and overall reliability of PP films. The long alkyl chains impart hydrophobicity to the stabilizer, significantly enhancing its compatibility with the polypropylene resin substrate. Polypropylene itself is a non-polar hydrocarbon polymer. The long alkyl chains form a good match with the polypropylene molecular chains through van der Waals forces, reducing phase separation, thereby reducing local stress concentration and dielectric loss. As a highly polar functional group, the main function of hydroxyl groups is to capture free radicals generated during processing and use. During the processing stage of PP film, high temperatures (150-160°C) and shear forces can easily cause polypropylene chains to break, generating free radicals and leading to oxidative degradation. On the one hand, hydroxyl groups neutralize free radicals to prevent chain oxidation reactions; on the other hand, during the heat setting step, hydrogen bonds can stabilize the molecular conformation and reduce heat-induced molecular chain motion. The large conjugated structure efficiently absorbs and dissipates external energy through the π electron delocalization system. In high-voltage or high-frequency applications, external electric fields can easily induce electron migration, leading to dielectric loss. The large conjugated structure significantly suppresses dielectric loss and improves thermal stability.

[0021] The present invention achieves deep synergy between key components through an optimized system consisting of a heat-resistant polypropylene resin substrate, a dielectric modifier, a nucleating agent, a lubricant, and a stabilizer, combined with precise processes of premixing, extrusion, biaxial stretching, and heat setting. The heat-resistant polypropylene resin substrate provides the main strength and high-temperature foundation; the large conjugated structure of the dielectric modifier and the stabilizer synergistically absorbs and dissipates electric field energy; the nucleating agent is evenly dispersed with the assistance of the lubricant, inducing the formation of fine crystals and reducing grain boundary losses; the stabilizer enhances compatibility through long chains, stabilizes the molecular conformation to prevent oxidation by capturing free radicals with hydroxyl groups, and improves energy dissipation efficiency through large conjugation; the lubricant ensures processing fluidity and uniform dispersion of components, avoiding local stress and hot spots. Ultimately, this synergistic effect significantly reduces dielectric loss, improves the stability of the dielectric constant at high temperatures to enhance heat resistance, and ensures uniform thickness, high strength, and long-term performance stability (no component migration and no drift), fundamentally solving the drawbacks of high loss, poor heat resistance, and unstable performance of traditional PP films, and ensuring the reliability and life of capacitors in high-frequency / high-voltage applications.

[0022] Compared with the prior art, the present invention has the following beneficial effects: 1. Significantly Reduced Dielectric Loss: This invention effectively reduces the dielectric loss of PP film through the synergistic effect of specific components, such as the large conjugated structure of the dielectric modifier and stabilizer that synergistically absorbs and dissipates electric field energy. This reduces capacitor heat generation in high-frequency or high-voltage applications, improves the service life and safety of capacitors, and meets the strict standards for capacitor dielectric loss required by modern electronic devices.

[0023] 2. Significantly enhanced heat resistance: By adopting a heat-resistant polypropylene resin substrate and combining the effects of components such as stabilizers, the PP film of the present invention can maintain the stability of the dielectric constant and dielectric loss in high-temperature working environments, solving the problem of performance degradation caused by insufficient heat resistance of traditional PP films and expanding the applicability of capacitors in high-temperature application scenarios.

[0024] 3. Improved processing stability and long-term performance stability: The components in the optimized formula system have good compatibility, and the components are not easy to migrate or volatilize during processing. At the same time, precise control of the preparation process parameters ensures uniform film thickness, high strength and long-term performance stability, ensuring the reliability and stability of the capacitor during long-term use, and fundamentally overcoming the drawbacks of existing PP film such as unstable performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 For the stabilizer 1 of the present invention 1 HNMR spectrum. DETAILED DESCRIPTION

[0026] The following will clearly and completely describe the technical solution of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0027] Synthesis Example 1 Synthesis of Stabilizer 1: ; Step 1: Under a nitrogen atmosphere, 20.00 g of raw material 1, 16.29 g of raw material 2, 40.80 g of potassium phosphate trihydrate, 0.1 g of pyridine-2-carboxylic acid, 0.73 g of CuI and 300 g of DMSO were added to the reaction system, and the mixture was heated to 85°C for 16 hours; after cooling, the reaction mixture was extracted with an ammonia solution and methyl tert-butyl ether, and the organic phase was washed five times with water and twice with a saturated NaCl solution; finally, the combined organic phase was dried over anhydrous Na2SO4, dried by spin drying, and purified by silica gel column using a mixed solution of petroleum ether and ethyl acetate as eluent, and the solution was dried by spin drying to obtain 21.94 g of intermediate 1.

[0028] The second step: under a nitrogen atmosphere, 21.94g of intermediate 1, 21.08g of raw material 3, 0.6g of tri-tert-butyl phosphine, 0.2g of palladium carbon, 16.97g of anhydrous potassium carbonate and 250g of toluene were added to the reaction system, and the temperature was raised to 120°C and refluxed for 12 hours; after the reaction was completed, the temperature was slightly lowered, and diatomaceous earth was used for filtration. After the filtrate was cooled to room temperature, it was washed three times with water, the organic phase was retained, and the aqueous phase was then extracted with ethyl acetate. After the organic phases were combined, the organic phase was dried over anhydrous magnesium sulfate, filtered, and spin-dried for silica gel column chromatography. A mixture of petroleum ether and ethyl acetate was used as eluent, and spin-dried to obtain 34.54g of stabilizer 1.

[0029] Structure identification: MS (m / z) of intermediate 1: [M+H] + =358; MS (m / z) of Stabilizer 1: [M+H] + =563; Stabilizer 1 1 HNMR-CDCl3: δ7.66-7.49(m,3H),7.32(d,1H),7.19-6.98(m,3H),6.92(dd,1H),6.78 (dd,1H),5.42(qt,1H),3.84-3.65(m,8H),3.53-3.24(m,6H),2.88-2.7 2(m,4H),2.72-2.52(m,4H),2.41(t,3H),1.98-1.71(m,4H),1.63(s,3H) .

[0030] Synthesis Example 2 - Synthesis Example 4 In Synthesis Examples 2-4, stabilizers 2-4 were synthesized in sequence, referring to the synthesis method of Synthesis Example 1, replacing raw material 1, and remaining the same as Synthesis Example 1. Specific structures of raw material 1, stabilizers 2-4, and MS (m / z): [M+H] + See Table 1 for data. Table 1 Structure of raw material 1, structure of stabilizer 2-stabilizer 4 involved in synthesis examples 2-4, MS (m / z): [M+H] + data Example 1 Preparation of PP film for low-loss capacitors: 1. Raw material ratio by mass: 90 parts of heat-resistant polypropylene resin base material (a heat-resistant grade polypropylene resin with a melt index of 2.0 g / 10 min and a melting point of 165°C is selected), 8 parts of dielectric modifier (silicon dioxide, particle size 50 nm), 0.15 parts of nucleating agent (di(3,4-dimethylbenzylidene) sorbitol), 0.4 parts of lubricant (oleamide), and 2 parts of stabilizer (stabilizer 1 synthesized in Synthesis Example 1).

[0031] 2. Preparation method: S1. The heat-resistant polypropylene resin substrate, dielectric modifier, nucleating agent, lubricant and stabilizer were placed in a high-speed mixer and premixed, the premix temperature was controlled to 190 ° C, the premix speed was 500 rpm, the mixing time was 30 minutes to obtain a premix; S2. The premix was melt-extruded into a twin-screw extruder (screw diameter 50 mm, L / D ratio 40:1) at 110°C. The melt was then cast through a T-die onto a chill roll (temperature 25°C) to form a uniform base film (initial thickness approximately 50 μm). S3. The base film was placed in a biaxial stretching machine and first stretched longitudinally: stretch ratio 5.0, stretching temperature 155 ° C; then stretched transversely: stretch ratio 9.0, stretching temperature 155 ° C. The total stretching time was 15 seconds to obtain a stretched base film; S4. The stretched base film is treated in a heat setting zone: temperature 160 ° C, relaxation heat setting time 15 seconds, and after setting, it is cooled and reeled by a cooling roller (temperature 30 ° C) to obtain a low-loss capacitor PP film.

[0032] Example 2-Example 4 A PP film for low-loss capacitors was prepared by referring to the preparation method of Example 1, except that the stabilizers therein were replaced with stabilizers 2 to 4 synthesized in Synthesis Examples 2 to 4, and the rest remained the same as Example 1.

[0033] Comparative Example 1 A PP film for low-loss capacitors was prepared by referring to the preparation method of Example 1, except that the stabilizer was not added, and the rest of the steps were the same as those of Example 1.

[0034] Comparative Example 2 A PP film for low-loss capacitors was prepared by referring to the preparation method of Example 1, except that the mass fraction of the heat-resistant polypropylene resin substrate was replaced with 120 parts, and the rest remained the same as in Example 1.

[0035] Comparative Example 3 A PP film for low-loss capacitors was prepared by referring to the preparation method of Example 1, except that the mass fraction of the dielectric modifier was changed to 0.5 parts, and the rest remained the same as Example 1.

[0036] Performance testing: 1. The tensile strength and elongation at break of the sample (a low-loss PP film for capacitors prepared in the examples and comparative examples) were measured in accordance with GB T 13541-1992. The test conditions were 23°C, 50% RH, and a tensile speed of 100 mm / min. The data are shown in Table 2.

[0037] 2. After irradiation with 350nm UV light for 500h, the tensile strength retention of the samples was measured according to GB T 13541-1992. The data are shown in Table 2.

[0038] Table 2 Performance test data of a PP film for low-loss capacitors prepared in the examples and comparative examples The mechanical properties of all embodiments are significantly better than those of the comparative examples. In particular, comparative example 1 performs the weakest among all indicators, confirming the key supporting role of the stabilizer in the integrity of the film structure. After ultraviolet accelerated aging, the strength retention rate of the embodiment is much higher than that of the comparative example, highlighting the synergistic anti-degradation ability of the free radical capture group and the large conjugated structure in the stabilizer. Due to the lack of stabilizer protection, the performance of comparative example 1 drops sharply after aging, further verifying its necessity. Although the retention rate of comparative example 2 after aging is slightly better than that of comparative example 1, the initial mechanical properties deteriorate due to the destruction of the component ratio balance, indicating that excessive substrate will weaken the synergistic effect of the dielectric modifier and the stabilizer. The initial strength and aging resistance of comparative example 3 are weaker than those of the embodiment, but better than comparative example 1, indicating that although the dielectric modifier is not a core stabilizing component, it still makes a fundamental contribution to performance.

[0039] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A PP film for low-loss capacitors, characterized in that: The invention comprises the following components in the following weight ratios: 80-95 parts of heat-resistant polypropylene resin base material, 3-12 parts of dielectric modifier, 0.1-0.2 parts of nucleating agent, 0.05-0.8 parts of lubricant, and 1-3 parts of stabilizer; The stabilizer has a structure shown in Formula 1: Formula 1; The R1 is selected from the group consisting of methyl, ethyl, methoxy and phenyl.

2. The PP film for low-loss capacitors according to claim 1, characterized in that: The dielectric modifier is at least one of silicon dioxide, aluminum oxide or barium titanate, and its particle size ranges from 20 to 100 nm.

3. The PP film for low-loss capacitors according to claim 1, characterized in that: The nucleating agent is di(3,4-dimethylbenzylidene)sorbitol.

4. The PP film for low-loss capacitors according to claim 1, characterized in that: The stabilizer is any one of the compounds shown in the following structures: ； 。 5. The PP film for low-loss capacitors according to claim 1, characterized in that: The lubricant is oleamide.

6. A method for preparing a PP film for low-loss capacitors according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. The heat-resistant polypropylene resin substrate, dielectric modifier, nucleating agent, lubricant and stabilizer are premixed in a mixer to obtain a premix; S2. The premix is melt-extruded and cast into a base film; S3. The base film is biaxially stretched, the longitudinal stretch ratio is 4.5-5.5, the transverse stretch ratio is 8-10, and the base film is stretched; S4. The stretched base film is subjected to heat setting treatment to obtain a PP film for low-loss capacitors.

7. The method for preparing a PP film for low-loss capacitors according to claim 6, characterized in that: The premixing temperature in S1 is 180-200°C.

8. The method for preparing a PP film for low-loss capacitors according to claim 6, characterized in that: The temperature of the biaxial stretching in S3 is 150-160°C.

9. The method for preparing a PP film for low-loss capacitors according to claim 6, characterized in that: The heat setting temperature in S4 is 155-165° C., and the relaxation heat setting is 10-20 seconds.

10. Use of a PP film for low-loss capacitors according to any one of claims 1 to 5 in the manufacture of metallized film capacitors, DC support capacitors, AC filter capacitors or pulse power capacitors.

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