Preparation method of biaxially oriented polypropylene composite film material for preparing thin-film capacitor

Abstract

The invention discloses a preparation method of a biaxially oriented polypropylene composite membrane material for preparing a thin-film capacitor in the field of high-performance polypropylene materials, which comprises the following steps of: performing liquid-phase bulk polymerization on propylene, vinyl toluene and methyl methacrylate to obtain a terpolymer; then adding maleic anhydride grafted polypropylene and lauryl amine polyoxyethylene ether into the terpolymer, and mixing; preparing the terpolymer and polypropylene into a composite membrane by adopting a tape casting process; and carrying out two-way stretching, then carrying out one-way stretching, and then carrying out vacuum evaporation of a metal layer on the surface of one side of the terpolymer to obtain the two-way stretching polypropylene composite film material for thin-film capacitor preparation. The material can be used for manufacturing a thin-film capacitor, the technical problem of low dielectric constant of a thin-film insulating material can be solved, high strength and high toughness of the insulating material can be ensured while the energy storage density of the capacitor is improved, and meanwhile, the peeling strength of a metal layer is high.

Description

Technical Field

[0001] This invention relates to a high-performance polypropylene material for capacitor manufacturing, and more particularly to a method for preparing a biaxially oriented polypropylene composite film material for thin-film capacitor fabrication. Background Technology

[0002] In existing technologies, the dielectric constant of polypropylene film is approximately 2.2, classifying it as a low-dielectric-constant material. For polypropylene insulation materials used in film capacitors, a higher dielectric constant is preferable, as a higher dielectric constant results in a larger capacitance. According to the capacitance formula C=εS / d, where ε is the dielectric constant, S is the plate area, and d is the plate spacing, the dielectric constant is directly proportional to the capacitance when the plate area and spacing are fixed. Therefore, increasing the dielectric constant of polypropylene material can effectively reduce the size of the capacitor, enabling miniaturization and weight reduction of the equipment.

[0003] In practical applications, the dielectric constant of polypropylene can be increased from 2.2 by adding high dielectric constant additives (such as barium titanate and titanium dioxide), thereby significantly improving the energy storage density and performance of capacitors. However, this leads to a problem: the tensile properties of polypropylene films containing barium titanate and titanium dioxide deteriorate, and the addition of inorganic fillers significantly reduces the elongation at break of the polypropylene film. Taking titanium dioxide as an example, when the addition amount is 1%, the tensile strength of the composite material can be increased by 41.2%, but the elongation at break will decrease significantly. This is because inorganic rigid particles form stress concentration points in the polypropylene matrix, hindering the slippage and orientation of molecular chains, making the material more prone to brittle fracture during stretching.

[0004] Existing film capacitors use polypropylene film material. During vacuum evaporation, the surface of the polypropylene film material needs to be pre-coated with oil shielding and grid pattern printing. The ink coating is applied to the film surface by a printing machine, and then dried in a drying oven at 45-85℃. This step provides a good adhesion surface for subsequent metal evaporation; otherwise, the bonding strength between the evaporated metal layer and the polypropylene film material will be insufficient. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing biaxially oriented polypropylene composite film material for thin-film capacitors, aiming to solve the technical problem of the contradiction between dielectric constant and tensile strength of thin-film insulating materials. While ensuring that the composite film insulating material has a high dielectric constant, it further ensures the high strength and high toughness of the material. At the same time, the bonding strength between the metal layer and the composite film is high.

[0006] The objective of this invention is achieved as follows: a method for preparing a biaxially oriented polypropylene composite film material for thin-film capacitor fabrication, comprising the following steps: S1: Liquid-phase bulk polymerization of propylene, vinyltoluene, and methyl methacrylate, with benzoyl peroxide as the initiator. The weight ratio of each substance is propylene:vinyltoluene:methyl methacrylate:benzoyl peroxide = 1:(0.08-0.11):(0.14-0.26):(0.03-0.05); the polymerization temperature is 75-85℃; the pressure is 2.5-3.0MPa; a terpolymer of propylene, vinyltoluene, and methyl methacrylate is obtained. S2: Maleic anhydride-grafted polypropylene and dodecylamine polyoxyethylene ether are added to the terpolymer and mixed. The maleic anhydride-grafted polypropylene is used as an interface compatibilizer, and the amount added is 3-5% of the copolymer weight. The dodecylamine polyoxyethylene ether is used as an antistatic agent, and the amount added is 0.3-0.8% of the copolymer weight. A homogeneous copolymer is obtained. The maleic anhydride grafting content in the maleic anhydride-grafted polypropylene is 0.8-1.2 wt%. The total amine value of the dodecylamine polyoxyethylene ether is 130-141 mg KOH / g. S3: The terpolymer treated in step S2 is used to form a composite film with polypropylene using a casting process. The overall thickness is 150-240μm, of which the thickness of the terpolymer is 30-60μm. S4: The composite film is heated to a high-elasticity state at 95-115℃ and then biaxially stretched. The longitudinal stretching ratio during biaxial stretching is 4-6 times and the transverse stretching ratio is 3-4 times. The longitudinal stretching is achieved by the speed difference between the fast and slow rollers, and the transverse stretching is performed in the transverse direction by a tenter frame. Then, a second longitudinal stretching is performed with a stretching ratio of 1.5-2.0. The setting temperature after each stretching is 125-130℃ to stabilize the molecular chains in the oriented state and reduce the subsequent shrinkage rate of the film. The thickness of the composite film after stretching is 3.75-16.7μm. S5: Perform corona discharge treatment on one side of the terpolymer surface, with an electrode gap of 1-2 mm, a treatment voltage of 5000-15000V, and a power of 200-2000W, so that the surface tension reaches more than 38dyn / cm. S6: A metal layer is vacuum-deposited on one side of the terpolymer surface. First, an aluminum layer is deposited, then a zinc layer is deposited. After deposition, an aging treatment is performed to obtain a biaxially oriented polypropylene composite film material for the preparation of thin-film capacitors.

[0007] Further, in step S1, the weight ratio of each substance is propylene: vinyltoluene: methyl methacrylate: benzoyl peroxide = 1:0.1:0.21:0.04.

[0008] Furthermore, in step S2, the amount of maleic anhydride-grafted polypropylene added is 4% of the copolymer weight, and the amount of dodecylamine polyoxyethylene ether used is 0.5% of the copolymer weight.

[0009] Furthermore, in step S4, the temperature during biaxial stretching of the composite film is 105-110℃.

[0010] Furthermore, in step S6, the aluminum layer evaporation is performed by using aluminum wire as an evaporation source and heating it to 660-800°C in a steel furnace. After the aluminum melts, it evaporates in the gas phase and condenses and deposits on the surface of the terpolymer to form an aluminum layer with a thickness of 10-30 nm.

[0011] Furthermore, in step S6, the zinc layer is deposited by heating a zinc bar to 420-600°C. After the zinc melts, it evaporates in the gas phase and is deposited on the surface of the terpolymer side to form a zinc layer with a thickness of 5-15 nm.

[0012] Furthermore, the aging treatment in step S6 includes high-temperature aging and room-temperature aging. After the vapor deposition is completed, a high-temperature aging treatment is performed at 150-200℃ for 20-50 minutes to eliminate internal stress and improve film stability. Then, a room-temperature aging treatment is performed at 20-25℃ for 20-24 hours to fully bond the metal layer with the base film and improve adhesion.

[0013] The material obtained by this invention can be used to prepare thin-film capacitors. Compared with the prior art, the advantages of this invention are as follows: 1. The present invention forms a composite film by laminating a terpolymer onto the surface of polypropylene, which has the dual benefits of high strength and high toughness.

[0014] 2. Composite films have a high dielectric constant, which can increase the energy storage density of capacitors.

[0015] 3. Maleic anhydride grafted onto polypropylene and dodecylamine polyoxyethylene ether effectively enhances the interfacial bonding between polypropylene and the terpolymer, and between the terpolymer and the vapor-deposited layer. During vacuum vapor deposition, there is no need for oil shielding or grid pattern printing on the composite film surface, while maintaining strong bonding between the terpolymer and the vapor-deposited layer, reducing production steps and material consumption.

[0016] 4. During the stretching process, the molecular chains of polypropylene and terpolymer gradually untangle and extend from a disordered coiled state, arranging themselves into an ordered structure along the stretching direction. As the stretching ratio increases, the orientation of the molecular chains continuously improves, and the tensile strength of the film in the stretching direction is significantly enhanced. In particular, when the longitudinal and transverse stretching ratios are different, and after secondary longitudinal stretching, the longitudinal strength is much greater than the transverse strength, which facilitates the subsequent tension winding of the film capacitor.

[0017] 5. The transverse tear strength of the stretched film is higher than that of pure polypropylene film material, which makes the capacitors made thereafter have high impact resistance. Detailed Implementation

[0018] The raw materials used in this invention and their sources are as follows: Propylene, vinyltoluene, methyl methacrylate, and benzoyl peroxide are common chemicals, produced by numerous manufacturers, and are available commercially.

[0019] Maleic anhydride-grafted polypropylene: manufactured by Mitsui Chemicals, Ltd. of Japan, model QB510; maleic anhydride grafting content is stable at 0.8-1.2wt%; heat resistance range -20℃ to 130℃; melt flow rate is about 5.0g / 10min (230℃ / 2.16kg).

[0020] Dodecylamine polyoxyethylene ether: The manufacturer is Haian (Linyi) Guoli Chemical Co., Ltd., the model is AC1205, it is a yellow viscous liquid with a total amine value of 130-141 mgKOH / g.

[0021] Polypropylene: The manufacturer is Wanhua Chemical Group Co., Ltd., with a number average molecular weight (Mn) of 80,000-100,000 and a weight average molecular weight (Mw) of 350,000-400,000. Example 1

[0022] A method for preparing a biaxially oriented polypropylene composite film material for thin-film capacitor fabrication includes the following steps: S1: Liquid-phase bulk polymerization of propylene, vinyltoluene, and methyl methacrylate is carried out, with benzoyl peroxide as the initiator. The weight ratio of each substance is propylene:vinyltoluene:methyl methacrylate:benzoyl peroxide = 1:0.1:0.21:0.04. The polymerization temperature is 75-85℃ and the pressure is 2.5-3.0MPa. A terpolymer of propylene, vinyltoluene, and methyl methacrylate is obtained. The number average molecular weight (Mn) of the obtained terpolymer is 70,000-90,000, and the weight average molecular weight (Mw) is 320,000-380,000.

[0023] S2: Maleic anhydride-grafted polypropylene and dodecylamine polyoxyethylene ether are added to the terpolymer and mixed. The maleic anhydride-grafted polypropylene acts as an interfacial compatibilizer, with an addition amount of 4% of the copolymer weight. The dodecylamine polyoxyethylene ether acts as an antistatic agent, with an addition amount of 0.5% of the copolymer weight. A homogeneous copolymer is obtained. The maleic anhydride-grafted polypropylene is manufactured by Mitsui Chemicals Co., Ltd. of Japan, model QB510; the maleic anhydride grafting content is stable at 0.8-1.2 wt%; the heat resistance range is -20℃ to 130℃, and the melt flow rate is approximately 5.0 g / 10 min (230℃ / 2.16 kg). The dodecylamine polyoxyethylene ether is manufactured by Haian (Linyi) Guoli Chemical Co., Ltd., model AC1205, a yellow viscous liquid with a total amine value of 130-141 mg KOH / g.

[0024] S3: The terpolymer treated in step S2 and polypropylene are used to form a composite film with an overall thickness of 240μm, of which the thickness of the terpolymer is 60μm; the polypropylene masterbatch material used is manufactured by Wanhua Chemical Group Co., Ltd., with a number average molecular weight (Mn) of 80,000-100,000 and a weight average molecular weight (Mw) of 350,000-400,000.

[0025] S4: The composite film is heated to a high-elasticity state at 105-110℃ and then biaxially stretched. The longitudinal stretching ratio is 5 times and the transverse stretching ratio is 4 times. The longitudinal stretching is achieved by the speed difference between the fast and slow rollers. The transverse stretching is carried out in the transverse direction by a tenter frame. Then, a second longitudinal stretching is performed with a stretching ratio of 2.0. The setting temperature after each stretching is 125-130℃ to stabilize the molecular chains in the oriented state and reduce the subsequent shrinkage rate of the film. The thickness of the composite film after stretching is 7.5μm.

[0026] S5: Perform corona discharge treatment on one side of the terpolymer surface, with an electrode gap of 1-2 mm, a treatment voltage of 10000V, and a power of 1500W, so that the surface wetting tension reaches more than 38 dynes / cm². The corona treatment generates polar functional groups on the surface of the plastic film through high-voltage discharge, thereby increasing the surface tension of the non-polar material and significantly enhancing the adhesion between the aluminum coating layer and the substrate.

[0027] S6: A metal layer is vacuum-deposited on one side of the terpolymer surface, first an aluminum layer, then a zinc layer, followed by aging treatment to obtain a biaxially oriented polypropylene composite film material for thin-film capacitor fabrication. The specific steps include the following: S6-1: Aluminum layer evaporation deposition uses aluminum wire as the evaporation source and heats it to 660-800℃ in a steel furnace. After the aluminum melts, it evaporates in the gas phase and condenses and deposits on the surface of the terpolymer to form an aluminum layer with a thickness of 20nm.

[0028] S6-2: Zinc layer evaporation is achieved by heating a zinc bar to 420-600℃, melting the zinc, evaporating it in the gas phase, and depositing it on the surface of the terpolymer side to form a zinc layer with a thickness of 10nm.

[0029] S6-3: Aging treatment includes high-temperature aging and room-temperature aging. After vapor deposition, high-temperature aging is performed at 180℃ for 30 minutes to eliminate internal stress and improve film stability. Then, room-temperature aging is performed at 20-25℃ for 24 hours to fully bond the metal layer with the base film and improve adhesion.

[0030] The specific properties of the prepared polypropylene composite membrane material are as follows: Electrical properties: Dielectric constant: 3.55 (1kHz), stable dielectric properties, essentially unaffected by applied electric field. Dielectric loss: <0.0005 (1kHz), extremely low loss, excellent performance stability at high frequencies. Breakdown field strength: ≥770kV / mm, excellent corona resistance. Insulation resistance: ≥10 15 It has an insulation strength of Ω·cm and excellent insulation properties.

[0031] Mechanical properties: longitudinal tensile strength up to 288MPa, transverse tensile strength up to 165MPa, longitudinal elongation at break: 50-70%; transverse elongation at break: 150-190%.

[0032] Thermal properties: Heat shrinkage rate (120℃, 15min): 2.5%, good dimensional stability; Operating temperature range: -40℃ to 120℃, with good temperature resistance.

[0033] The metal layer peel strength test conditions in the biaxially oriented polypropylene composite film material of this invention were conducted according to the national standard GB / T 13542.4-2009. As mentioned above, the substrate of the test material is a composite film made of terpolymer and polypropylene. According to the national standard, the metal layer peel speed during the test was 300 mm / min, the peel angle was 180°, the test temperature was 23±2℃, and the relative humidity was 50±5% (the same below). The test showed that the metal layer adhesion and peel strength reached 2.95 N / mm. Example 2

[0034] Based on Example 1, only the amount of each substance used in the liquid-phase bulk polymerization in step S1 was changed, and the product was tested. The results are shown in Tables 1-3 below: Table 1: Changing only the amount of vinyltoluene

[0035] Table 1 shows that with the increase of vinyltoluene content, the dielectric constant gradually increases, and the values ​​are all much greater than 2.2 of pure polypropylene material; the breakdown field strength gradually decreases; the dielectric constant and breakdown field strength are within a good range. Taking all factors into consideration, the optimal weight ratio of propylene to vinyltoluene is 1:(0.08-0.11). Within this range, the metal layer peel strength is high, and at the same time, the transverse and longitudinal tensile strengths are also high.

[0036] Table 2: Changing only the amount of methyl methacrylate

[0037] Table 2 shows that as the amount of methyl methacrylate increases, the dielectric constant gradually decreases, but the values ​​are all much greater than the 2.2 of pure polypropylene; the breakdown field strength gradually increases; and the dielectric constant and breakdown field strength are within a good range. Considering the longitudinal tensile strength, transverse tensile strength, and metal layer peel strength, the preferred weight ratio of propylene to methyl methacrylate is 1:(0.14-0.26).

[0038] Table 3: Variation of Benzoyl Peroxide Dosage

[0039] The table above shows that without benzoyl peroxide, the polymer lacks an initiator and cannot polymerize normally. When the amount of benzoyl peroxide is less than 0.03%, the reaction rate is slow, the chain length is short, and the strength is low. When the amount is greater than 0.05%, the decomposition of benzoyl peroxide generates too many free radicals, which accelerates the copolymerization reaction of vinyltoluene and methyl methacrylate, resulting in a decrease in the uniformity of molecular chain distribution and a reduction in strength. The amount of initiator has little effect on the dielectric constant.

[0040] In summary, in step S1, the preferred range of propylene: vinyltoluene: methyl methacrylate: benzoyl peroxide is 1: (0.08-0.11): (0.14-0.26): (0.03-0.05); the optimal value is 1: 0.1: 0.21: 0.04.

[0041] In step S2, the amount (by weight) of maleic anhydride-grafted polypropylene was changed, and the results are shown in Table 4 below.

[0042] Table 4: Test results of varying maleic anhydride-grafted polypropylene addition (by weight)

[0043] The table above shows that when the amount of maleic anhydride-grafted polypropylene is less than 0.03%, the tensile strength and metal layer peel strength decrease significantly, while when the amount is greater than 0.05%, the increase in tensile strength and metal layer peel strength is not significant. Maleic anhydride-grafted polypropylene, as an interfacial compatibilizer, is preferably added at 3-5% of the copolymer weight, with 4% being the most preferred. Its main effect is on the overall tensile strength and the interfacial bonding force between the metal layer and the ternary composite layer.

[0044] In step S2, the amount (by weight) of dodecylamine polyoxyethylene ether added was changed, and the results are shown in Table 5 below.

[0045] Table 5: Test results of varying dodecylamine polyoxyethylene ether addition (by weight)

[0046] The table above shows that dodecylamine polyoxyethylene ether is preferred as an antistatic agent at a dosage of 0.3-0.8% of the copolymer weight. It has low dielectric loss, with the most preferred dosage being 0.3%. Its main effects are on dielectric loss and volume resistivity.

[0047] Based on steps S1-S2 of Example 1, the propylene-vinyl toluene-methyl methacrylate terpolymer was further prepared into a film separately without being compounded with polypropylene material. After biaxial stretching under the conditions of S4, the strength was compared with that of polypropylene film under the same conditions, as shown in Table 6 below.

[0048] Table 6: Performance Comparison of Terpolymer Films and Polypropylene Films

[0049] The table above shows that the longitudinal and transverse tensile strength of the terpolymer film is significantly greater than that of the polypropylene film, but the elongation at break is lower than that of polypropylene. This makes the tensile strength of the composite material more similar to that of the terpolymer, which is the fundamental reason why the longitudinal and transverse tensile strength of the polypropylene composite material of this invention is greater than that of existing polypropylene.

[0050] In this invention, in step S1, the polymerization temperature can be 75-85℃; the pressure is 2.5-3.0MPa. In step S4, the overall thickness of the composite film can be 150-240μm, of which the thickness of the terpolymer is 30-60μm. In step S4, biaxial stretching can be carried out at 95-115℃, with a longitudinal stretching ratio of 4-6 times and a transverse stretching ratio of 3-4 times. The second longitudinal stretching ratio is 1.5-2.0. The setting temperature after each stretching is 125-130℃, which stabilizes the molecular chains in the oriented state and reduces the subsequent shrinkage rate of the film. The thickness of the composite film after stretching is 3.75-16.7μm. In step S5, the processing voltage is 5000-15000V and the power is 200-2000W.

[0051] This invention is not limited to the above embodiments. Based on the technical solutions disclosed in this invention, those skilled in the art can make some substitutions and modifications to some of the technical features without creative effort, and all such substitutions and modifications are within the protection scope of this invention.

Claims

1. A method for preparing a biaxially oriented polypropylene composite film material for thin-film capacitor fabrication, characterized in that... Includes the following steps: S1: Liquid-phase bulk polymerization of propylene, vinyltoluene, and methyl methacrylate, with benzoyl peroxide as the initiator. The weight ratio of each substance is propylene:vinyltoluene:methyl methacrylate:benzoyl peroxide = 1:(0.08-0.11):(0.14-0.26):(0.03-0.05); the polymerization temperature is 75-85℃; the pressure is 2.5-3.0MPa; a terpolymer of propylene, vinyltoluene, and methyl methacrylate is obtained. S2: Maleic anhydride-grafted polypropylene and dodecylamine polyoxyethylene ether are added to the terpolymer and mixed. The maleic anhydride-grafted polypropylene is used as an interface compatibilizer, and the amount added is 3-5% of the copolymer weight. The dodecylamine polyoxyethylene ether is used as an antistatic agent, and the amount added is 0.3-0.8% of the copolymer weight. A homogeneous copolymer is obtained. The maleic anhydride grafting content in the maleic anhydride-grafted polypropylene is 0.8-1.2 wt%. The total amine value of the dodecylamine polyoxyethylene ether is 130-141 mgKOH / g. S3: The terpolymer treated in step S2 is used to form a composite film with polypropylene using a casting process. The overall thickness is 150-240μm, of which the thickness of the terpolymer is 30-60μm. S4: The composite film is heated to a high-elasticity state at 95-115℃ and then biaxially stretched. The longitudinal stretching ratio during biaxial stretching is 4-6 times and the transverse stretching ratio is 3-4 times. The longitudinal stretching is achieved by the speed difference between the fast and slow rollers, and the transverse stretching is performed in the transverse direction by a tenter frame. Then, a second longitudinal stretching is performed with a stretching ratio of 1.5-2.

0. The setting temperature after each stretching is 125-130℃ to stabilize the molecular chains in the oriented state and reduce the subsequent shrinkage rate of the film. The thickness of the composite film after stretching is 3.75-16.7μm. S5: Perform corona discharge treatment on one side of the terpolymer surface, with an electrode gap of 1-2mm, a treatment voltage of 5000-15000V, and a power of 200-2000W, so that the surface tension reaches more than 38dyn / cm. S6: A metal layer is vacuum-deposited on one side of the terpolymer surface. First, an aluminum layer is deposited, then a zinc layer is deposited. After deposition, an aging treatment is performed to obtain a biaxially oriented polypropylene composite film material for the preparation of thin-film capacitors.

2. The method for preparing a biaxially oriented polypropylene composite film material for thin-film capacitor fabrication according to claim 1, characterized in that, In step S1, the weight ratio of each substance is propylene: vinyltoluene: methyl methacrylate: benzoyl peroxide = 1:0.1:0.21:0.

04.

3. The method for preparing a biaxially oriented polypropylene composite film material for thin-film capacitor fabrication according to claim 1, characterized in that, In step S2, the amount of maleic anhydride-grafted polypropylene added is 4% of the copolymer weight, and the amount of dodecylamine polyoxyethylene ether used is 0.5% of the copolymer weight.

4. A method for preparing a biaxially oriented polypropylene composite film material for thin-film capacitor fabrication according to any one of claims 1-3, characterized in that, In step S4, the temperature during biaxial stretching of the composite film is 105-110℃.

5. A method for preparing a biaxially oriented polypropylene composite film material for thin-film capacitor fabrication according to any one of claims 1-3, characterized in that, In step S6, aluminum layer evaporation involves using aluminum wire as an evaporation source and heating it to 660-800°C in a steel furnace. After the aluminum melts, it evaporates in the gas phase and condenses and deposits on one side of the terpolymer to form an aluminum layer with a thickness of 10-30 nm.

6. A method for preparing a biaxially oriented polypropylene composite film material for thin-film capacitor fabrication according to any one of claims 1-3, characterized in that, In step S6, the zinc layer is deposited by heating a zinc bar to 420-600°C. After the zinc melts, it evaporates in the gas phase and is deposited on the surface of the terpolymer to form a zinc layer with a thickness of 5-15 nm.

7. A method for preparing a biaxially oriented polypropylene composite film material for thin-film capacitor fabrication according to any one of claims 1-3, characterized in that, The aging treatment in step S6 includes high-temperature aging and room-temperature aging. After the vapor deposition is completed, a high-temperature aging treatment is performed at 150-200℃ for 20-50 minutes to eliminate internal stress and improve film stability. Then, a room-temperature aging treatment is performed at 20-25℃ for 20-24 hours to fully bond the metal layer with the base film and improve adhesion.

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