An all-organic polymer dielectric film with a five-layer structure and a preparation method thereof

Abstract

The application discloses a full-organic polymer dielectric film with a five-layer structure and a preparation method thereof. The dielectric film comprises five-layer films; the five-layer films comprise two low-loss high-breakdown layer films located at the outermost layers, two intermediate transition layer films arranged between the two low-loss high-breakdown layer films, and a high-dielectric layer film arranged between the two intermediate transition layer films; and the full-organic polymer dielectric film is prepared by bonding the five-layer films in a continuous hot-pressing process. The organic polymers with different properties are combined together by the method of multi-layer continuous hot-pressing, so that the advantages of each component can be fully exerted, the growth of the electric tree branches is inhibited by the differences between the layers of different components, and the breakdown strength is improved. The full-organic composite film has the advantages of high dielectric constant, high breakdown field strength and high discharge energy density.

Description

A five-layer all-organic polymer dielectric membrane and its preparation method Technical Field

[0001] This invention relates to a dielectric polymer material thin film and its preparation method, and more particularly to an all-organic polymer dielectric film with a five-layer structure and its preparation method. Background Technology

[0002] Organic thin-film capacitors have important applications in various fields due to their excellent discharge power density, extremely high operating voltage, and unique self-healing properties. For example, they are used in inverters constructed with thin-film capacitors in electric vehicles to convert DC to AC. They are also used in laser instruments to generate powerful voltages and in electromagnetic catapults to provide powerful power as energy storage devices.

[0003] Currently, commercially available organic film capacitors mainly use biaxially oriented polypropylene (BOPP) material, with a dielectric constant of approximately 2.2 and a typical energy storage density of 3 J / cm³. 3 The lower energy storage density significantly impacts the size of power modules in practical production. For example, thin-film capacitors in inverters and electromagnetic catapult systems occupy considerable space, severely limiting device usability. Therefore, finding a novel polymer film with higher energy storage density is crucial for the miniaturization of related modules.

[0004] Polyvinylidene fluoride (PVDF)-based fluoropolymers exhibit strong polarity and high dielectric constants (8–12), making them potential candidates for novel high-energy-storage polymer films. However, the ferroelectric nature of PVDF leads to significant energy loss during a charge-discharge cycle. PVDF-based binary copolymers (e.g., P(VDF-HFP), P(VDF-CTFE)) introduce larger groups into the main chain, resulting in larger defects during PVDF crystallization. This reduces ferroelectricity, transforming PVDF into a relaxor ferroelectric material and significantly decreasing energy loss during charge-discharge processes.

[0005] Multilayer composite polymer films can effectively improve dielectric energy storage characteristics for two main reasons: First, the interface between different types of polymer dielectrics can effectively suppress the growth of electrical trees, improving the breakdown performance of the composite film; second, each polymer film layer becomes thinner, and the thin-layer reinforcement effect improves the electrical performance of each polymer film layer. There are two commonly used methods for preparing multilayer composite polymer films in existing technologies: one is to use multiple layers of dielectric material when winding the capacitor. When the number of composite film layers is large, a single capacitor requires multiple rolls of film (twice the number of composite film layers), making the process complex and almost impossible to operate. Furthermore, the winding process introduces a large amount of air between the film layers, reducing device performance. The other method is to directly prepare multilayer composite dielectric films through multilayer co-extrusion biaxial stretching technology. However, when the processing temperatures of each layer material differ significantly, simultaneous melt extrusion processing is not possible. Summary of the Invention

[0006] Purpose of the invention: The purpose of this invention is to provide a five-layer all-organic polymer dielectric film that can effectively suppress the growth of electrical trees and improve breakdown performance and dielectric constant.

[0007] A second objective of this invention is to provide a method for preparing the all-organic polymer dielectric membrane with the aforementioned five-layer structure.

[0008] Technical solution: The all-organic polymer dielectric membrane with a five-layer structure of the present invention comprises five thin films; the five thin films include two low-loss, high-breakdown layers located on the outermost layer, two intermediate transition layers between the two low-loss, high-breakdown layers, and a high-dielectric layer between the two intermediate transition layers; the all-organic polymer dielectric membrane is obtained by bonding the five layers of films stacked in sequence together in a continuous hot-pressing process.

[0009] The dielectric constant and dielectric loss of the low-loss high-breakdown layer, the intermediate transition layer, and the high-dielectric layer all increase sequentially.

[0010] The high-dielectric-layer thin film material comprises a polymer matrix and an organic blend phase. The polymer matrix is ​​at least one of polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene), poly(vinylidene fluoride-co-chlorotrifluoroethylene), poly(vinylidene fluoride-co-chlorotrifluoroethylene-co-chlorotrifluoroethylene), or poly(vinylidene fluoride-co-chlorotrifluoroethylene-co-chlorofluoroethylene). The organic blend phase is at least one of poly(methyl methacrylate-co-styrene), polymethyl methacrylate, polyurea, or polythiourea. The mass ratio of the polymer matrix to the organic blend phase is (99–70):(1–30). The polymer matrix and the organic blend phase are preferably thoroughly mixed, and the high-dielectric-layer thin film is prepared using a melt extrusion biaxial stretching process. Specifically, poly(vinylidene fluoride-co-hexafluoropropylene) resin and polymethyl methacrylate resin are mixed together at a mass ratio of (99–70):(1–30), melt extruded using a twin-screw extruder, and then cast and biaxially stretched to form a film. The extruder temperature to the die is set to gradually increase from 170 to 240°C, and the screw speed is set to 40 to 200 r / min.

[0011] The intermediate transition layer film material is at least one of polyethylene terephthalate, polyphenylene sulfide, polyethylene naphthalate, polycarbonate, polyimide, or polyetherimide.

[0012] The low-loss, high-breakdown layer film material is preferably polypropylene.

[0013] The thickness of the five-layer all-organic polymer dielectric film is 10–18 μm.

[0014] The preparation method of the above-mentioned all-organic polymer dielectric film with a five-layer structure includes the following steps:

[0015] (A1) The low-loss high-breakdown layer film (1), the intermediate transition layer film (2), the high-dielectric layer film (3), the intermediate transition layer film (2), and the low-loss high-breakdown layer film (1) are stacked in order from top to bottom.

[0016] (B1) The five layers of film stacked in step (A1) are bonded together by continuous hot pressing to form the all-organic polymer dielectric film with the five-layer structure.

[0017] Specifically, it includes the following steps:

[0018] (A2) The film layers are rolled up and installed on different rollers. The film layers are stacked in sequence by the rollers. The pre-stacked film is sandwiched between the rollers and continuously moved forward by the rollers.

[0019] (B2) The pre-stacked film is preheated by passing it through a heated roller at a constant temperature;

[0020] (C2) The preheated film is hot-pressed by continuous hot pressing rollers. The hot-pressed film leaves and is then cooled by shaping rollers. The resulting film is then wound up to obtain a five-layer all-organic polymer dielectric film.

[0021] The preheating process described above is preferably completed using a roller heated by high-temperature oil, with a preheating temperature of 80–160°C. Preferably, the temperature is increased gradually, and the preheating temperature is determined by factors such as the low-loss, high-breakdown layer film material, the high-dielectric layer film material, the preheating path length, and the hot-pressing line speed. Under these preheating conditions, both the low-loss, high-breakdown layer film material and the high-dielectric layer film material are thoroughly heated and begin to soften, preparing for hot pressing.

[0022] The hot-pressing temperature is 170–200°C. This temperature is lower than the melting point of the intermediate transition layer but higher than the melting points of the low-loss, high-breakdown layer and the high-dielectric layer. Under these hot-pressing temperatures, the low-loss, high-breakdown layer and the high-dielectric layer reach a viscous flow state, while the intermediate transition layer remains in a highly elastic state. After cooling, the five layers bond together, forming a single-layer film with a five-layer structure.

[0023] The pressure applied during the hot pressing process is 5–100 MPa. Under these pressure conditions, the viscous, low-loss, high-breakdown layer and the high-dielectric layer thin film material are tightly pressed onto the intermediate transition layer, which is in a highly elastic state.

[0024] In this invention, after a brief hot pressing with rollers, the film enters the cooling and setting stage to obtain the finished film. To avoid introducing dust and other contaminants between layers and in the film roll, the entire process from unwinding, lamination, preheating, hot pressing, setting to winding is carried out in a clean environment.

[0025] Beneficial effects: Compared with the prior art, the present invention achieves the following significant effects:

[0026] (1) The dielectric film of the present invention is a single-layer film consisting of five independent thin films bonded together, which has the advantages of high breakdown strength, low dielectric loss, good machinability, high dielectric constant and high energy storage density; the relative dielectric constant of the five-layer film of the present invention can be as high as 5.5, while the dielectric loss is only 0.024; (2) The present invention is close to a "gradient material", from the low loss high breakdown layer film, to the intermediate transition layer film, and then to the high dielectric layer film, the dielectric constant increases and the dielectric loss decreases in turn; (3) The present invention enables the five independent thin films stacked in a certain order to bond together under continuous hot pressing to form a single-layer film. This method avoids the problem that the processing temperature of each layer material is large in the prior art and cannot be melted and extruded at the same time; (4) The present invention combines organic polymers with different properties using a multilayer composite method, which can give full play to the advantages of each component. The difference between different component layers will inhibit the growth of electrical trees and play a role in improving the breakdown strength; (5) The present invention can significantly improve the energy storage density of polymer films, effectively improve the breakdown strength of polymer films and reduce dielectric loss. Attached Figure Description

[0027] Figure 1 is a schematic diagram of the structure of the all-organic polymer dielectric membrane with a five-layer structure of the present invention;

[0028] Figure 2 is a flowchart of the method for preparing a five-layer all-organic composite film according to the present invention;

[0029] Figure 3 is a schematic diagram of continuous hot pressing in the method for preparing an all-organic composite film with a five-layer structure;

[0030] Figure 4 shows the dielectric spectrum test results of the five-layer thin film in Example 1;

[0031] Figure 5 shows the Weber distribution test results of the pressure resistance of the polymer dielectric membrane in Example 1. Detailed Implementation

[0032] The present invention will now be described in further detail.

[0033] Example 1

[0034] As shown in Figure 1, this invention provides an all-organic polymer dielectric film with a five-layer structure, comprising five thin films. The five thin films include two low-loss, high-breakdown layers 1 located on the outermost layer, two intermediate transition layers 2 disposed between the two low-loss, high-breakdown layers 1, and a high-dielectric layer 3 disposed between the two intermediate transition layers 2. The all-organic polymer dielectric film of this invention is prepared by bonding the five sequentially stacked thin films together in a continuous hot-pressing process. The dielectric constant and dielectric loss of the low-loss, high-breakdown layers 1, the intermediate transition layers 2, and the high-dielectric layer 3 all increase sequentially.

[0035] The low-loss, high-breakdown layer film 1 of the present invention is a biaxially oriented polypropylene film, the intermediate transition layer film 2 is a biaxially oriented polyethylene terephthalate film, and the high-dielectric layer film 3 is a poly(vinylidene fluoride-co-hexafluoropropylene) / polymethyl methacrylate composite film.

[0036] As shown in Figures 2 and 3, the method for preparing the all-organic polymer dielectric membrane with a five-layer structure of the present invention includes the following steps:

[0037] (1) Prepare each layer of film:

[0038] a. Preparation of high dielectric film: Film is prepared by melt extrusion biaxial stretching process. Poly(vinylidene fluoride-co-hexafluoropropylene) resin and polymethyl methacrylate resin are mixed together at a mass ratio of 80:20 and fed into a twin-screw extruder. The film is formed by melt extrusion biaxial stretching process. The extruder temperature is set to gradually increase from 170 to 220℃, the screw speed is set to 80 r / min, and the biaxial stretching parameters are set to longitudinal stretching of 3.5 times and transverse stretching of 4.5 times.

[0039] b. Intermediate transition layer film: Polyethylene terephthalate film was prepared using a commercially available 2μm melt extrusion biaxial stretching process with good uniformity;

[0040] c. Low-loss, high-breakdown layer film: Polypropylene film was prepared using a commercially available 2μm melt extrusion biaxial stretching process with good uniformity;

[0041] (2) Cut the roll of low-loss high-breakdown layer film, intermediate transition layer film, and high-dielectric layer film into the same width of 62cm. Stack the different polymer layers together in the order of low-loss high-breakdown layer film, intermediate transition layer film, high-dielectric layer film, intermediate transition layer film, and low-loss high-breakdown layer film. Adjust the linear speed of all rollers to 20m / min and rotate them continuously at a uniform speed. The pre-stacked film is sandwiched between the rollers and is continuously moved forward by the rollers. In Figure 3, ① is the roller that winds the biaxially oriented polypropylene film, ② is the roller that winds the biaxially oriented polyethylene terephthalate film, ③ is the roller that winds the high-dielectric layer film, ④ is the preheating, hot pressing, and cooling shaping roller, and ⑤ is the winding film roller.

[0042] (3) The pre-stacked film is preheated by a hot roller at a constant temperature of 150°C;

[0043] (4) The preheated film passes through several continuous hot-pressing rollers. The temperature of the continuous hot-pressing rollers is set to 160°C and the roller pressure is 10MPa. After hot pressing, the film leaves and is cooled at room temperature for a period of time. Then it passes through a roller with a temperature of 60°C and a pressure of 1MPa. The resulting film is collected by a winding machine to obtain a five-layer all-organic polymer dielectric film.

[0044] Because the PET layer has high temperature resistance, it is placed in the middle, while the PP and P(VDF-HFP) / PMMA layers, which have lower temperature resistance, are placed on either side of the PET layer. The hot-pressing temperature should be lower than the melting point of PET but slightly higher than the melting points of PP and P(VDF-HFP) / PMMA. During hot pressing, the PP and P(VDF-HFP) / PMMA adhere to the surface of the PET layer. After curing, the five separate film layers are bonded together into a single film.

[0045] Figure 4 shows the dielectric spectrum test diagram of the dielectric film in this embodiment. At a frequency of 1 kHz, the relative dielectric constant of the five-layer film is 5.5 and the dielectric loss is 0.024. Compared with the single high dielectric layer, the dielectric loss is lower, and compared with the single-layer PP and PET films, the relative dielectric constant is higher.

[0046] Figure 5 shows the withstand voltage test of the five-layer membrane. The intrinsic breakdown strength was calculated to be 574 kV / mm based on the Weber distribution, and the withstand voltage capability meets the requirements of dielectric materials.

[0047] Example 2

[0048] Based on Example 1, the difference is that in step (1), the polymer matrix is ​​poly(vinylidene fluoride-co-chlorotrifluoroethylene), the organic blend phase is poly(methyl methacrylate-co-styrene), and the mass ratio of the two is 99:1; in step (3), the preheating temperature is 160°C. In step (4), the continuous hot press roller temperature is set to 170°C, and the roller pressure is 10 MPa.

[0049] Example 3

[0050] Based on Example 1, the difference from Example 1 is that in step (1), the polymer matrix is ​​poly(vinylidene fluoride-co-trifluoroethylene-co-trifluorochloroethylene), the organic blend phase is polyurea, and the mass ratio of the two is 70:30; in step (3), the preheating temperature is 80°C. In step (4), the continuous hot press roller temperature is set to 200°C, and the roller pressure is 5 MPa.

Claims

1. A five-layer all-organic polymer dielectric membrane, characterized in that, The film comprises five thin films; the five thin films include two low-loss, high-breakdown layers (1) located on the outermost layer, two intermediate transition layers (2) between the two low-loss, high-breakdown layers (1), and a high-dielectric layer (3) between the two intermediate transition layers (2); the all-organic polymer dielectric film is obtained by bonding the five layers of films stacked in sequence together in a continuous hot-pressing process; the high-dielectric layer film material includes a polymer matrix and an organic blend phase, wherein the polymer matrix is ​​polyvinylidene fluoride, poly(vinylidene fluoride-co-hexafluoropropylene), poly( The material comprises at least one of vinylidene fluoride-co-trifluorochloroethylene, poly(vinylidene fluoride-co-trifluorochloroethylene-co-trifluorochloroethylene), or poly(vinylidene fluoride-co-trifluoroethylene-co-chlorofluoroethylene); the organic blend phase comprises at least one of poly(methyl methacrylate-co-styrene), polymethyl methacrylate, polyurea, or polythiourea; the intermediate transition layer film material comprises at least one of polyethylene terephthalate, polyphenylene sulfide, polyethylene naphthalate, polycarbonate, polyimide, or polyetherimide; and the low-loss, high-breakdown layer film material comprises polypropylene.

2. The all-organic polymer dielectric membrane with a five-layer structure according to claim 1, characterized in that, The thickness of the all-organic polymer dielectric film is 10~18μm.

3. A method for preparing a five-layer all-organic polymer dielectric membrane as described in claim 1, characterized in that, Includes the following steps: (A1) Stack the low-loss high-breakdown layer film (1), intermediate transition layer film (2), high dielectric layer film (3), intermediate transition layer film (2), and low-loss high-breakdown layer film (1) in order from top to bottom; (B1) Bond the five layers of film stacked in order in step (A1) into one piece by continuous hot pressing to form the all-organic polymer dielectric film with the five-layer structure.

4. The method for preparing a five-layer all-organic polymer dielectric membrane according to claim 3, characterized in that, In step (B1), a preheating process is performed before continuous hot pressing.

5. The method for preparing a five-layer all-organic polymer dielectric membrane according to claim 4, characterized in that, The preheating temperature is 80~160℃.

6. The method for preparing a five-layer all-organic polymer dielectric membrane according to claim 3, characterized in that, In step (B1), the temperature of the hot pressing is 170~200 ℃; the pressure is 5~100 MPa.

7. The method for preparing a five-layer all-organic polymer dielectric membrane according to claim 3, characterized in that, Specifically, the following steps are included: (A2) The film layers are mounted on different rollers and stacked sequentially by the rollers. The pre-stacked film is sandwiched between the rollers and continuously moved forward by the rollers; (B2) The pre-stacked film is preheated by hot rollers with a constant temperature; (C2) The preheated film is hot-pressed by continuous hot-pressing rollers. The hot-pressed film leaves and is then cooled by shaping rollers. The resulting film is then wound up to obtain a five-layer all-organic polymer dielectric film.

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