Electric field distortion resistant metallized film capacitor and preparation method thereof

Abstract

The invention discloses an electric field distortion resistant metallized film capacitor and a processing method thereof, and relates to the technical field of capacitors. The inner electrode of the metallized film capacitor resistant to electric field distortion is mainly composed of three layers of structures, namely a polymer film substrate, an electrostatic shielding layer and a metallized layer. The inner electrode is manufactured through the steps of film slitting, antistatic layer deposition, metallized layer evaporation, metal spraying, winding, energizing, welding, packaging and the like. The electrostatic shielding layer is located between the polymer film substrate and the metallization layer and plays a role in relieving the phenomena of electric field distortion and metallization layer metal migration and accumulation caused by space charge accumulation and uneven temperature rise in the capacitor in the working process of the capacitor, so that the service life of the capacitor is prolonged, and the reliability of the capacitor is improved. The method is suitable for large-scale production and has remarkable economic benefits and application prospects.

Description

Technical Field

[0001] The present invention relates to the field of capacitors, and particularly to a metalized film capacitor resistant to electric field distortion and a processing method thereof. Background Art

[0002] As an electronic component capable of storing and releasing electrical energy, the capacitor has become an essential basic component in modern electronic technology and power systems since its invention in the mid-18th century, playing a huge role in many fields such as information technology, energy technology, transportation, and medical equipment. The metalized film capacitor (MFC) is an important branch of capacitors. Compared with other types of capacitors, the metalized film capacitor has the characteristics of small volume, good self-healing property, high safety, good stability, and environmental friendliness, so it is widely used in many fields such as high-voltage power transmission, electric vehicles, and aerospace.

[0003] The inner electrode of the metalized film capacitor is a key component that determines the performance of the metalized film capacitor. The inner electrode consists of a dielectric film and a metallization layer: usually, polymer films such as polypropylene (PP) film, polystyrene (PS) film, and polyethylene terephthalate (PET) film are used as the dielectric film, and a metallization layer with a nanometer-level thickness (usually metals Zn, Al, and their series alloys) is formed on the surface of the dielectric film by vacuum evaporation technology. Then, an electrode structure in which the metallization layer is wrapped inside the dielectric film and alternately laminated is formed by winding or stacking.

[0004] However, during the operation of the metalized film capacitor, the accumulation and migration of space charges caused by the complex electric field will lead to serious electric field distortion, and the temperature rise inside the capacitor during operation will also cause breakdown and thermal aging of the dielectric film of its inner electrode. These are the two most critical factors affecting the life and stability of the capacitor and have a direct impact on the failure of the capacitor.

[0005] At present, the overall structural design of the capacitor is gradually improved, and its influence on the performance is gradually reduced. The fundamental factor affecting the development of the capacitor gradually focuses on the dielectric properties of the inner electrode. The quality of the inner electrode directly affects various performance indicators such as the capacitance stability, voltage resistance performance, use safety, and life cycle of the capacitor. The key to the dielectric properties of the inner electrode lies in: how to solve the serious electric field distortion caused by the accumulation and migration of space charges in the inner electrode under the action of a complex electric field, and the problem of temperature rise inside the capacitor during operation. Solving these two problems is of great significance for improving the dielectric properties and stability of the metalized film capacitor at high temperatures.

[0006] The present invention proposes a new processing method. By depositing an electrostatic shielding layer between the dielectric film and the metallization layer, it effectively alleviates the electric field distortion and the metal migration and accumulation phenomena in the metallization layer caused by the space charge accumulation and uneven temperature rise inside the capacitor, thereby improving the service life and reliability of the capacitor. Summary of the Invention

[0007] The main object of the present invention is to provide a metallized film capacitor resistant to electric field distortion, which alleviates the space charge accumulation phenomenon and the uneven temperature rise phenomenon inside the capacitor during the operation of the metallized film capacitor, thereby improving the service life and reliability of the capacitor.

[0008] To achieve the above-mentioned invention object, the technical solution adopted by the present invention is as follows.

[0009] The present invention first provides an electrode structure, which includes a dielectric film layer, an electrostatic shielding layer, and a metallization layer that are sequentially stacked to form a sandwich structure, wherein the electrostatic shielding layer is a conductive material.

[0010] Further, the dielectric film layer is selected from any one of polymer films such as polypropylene (PP) film, polystyrene (PS) film, and polyethylene terephthalate (PET) film.

[0011] Further, the metallization layer is selected from metal zinc (Zn), metal aluminum (Al) with a nanoscale thickness, or a series of alloys of the two.

[0012] Furthermore, the electrostatic shielding layer is selected from any one or several conductive materials such as aluminum-doped zinc oxide (AZO), indium tin oxide (ITO), fluorine-doped tin oxide (FTO), reduced graphene oxide (rGO), or carbon nanotubes (CNTs). When this electrode structure is applied to the inner electrode of a metallized film capacitor, the electrostatic shielding layer is further preferably an AZO material, because the metallization layer in the inner electrode of a metallized film capacitor is usually metal Zn, Al, and their series alloys. Selecting the AZO material for the electrostatic shielding layer has overlapping elements with the Zn and Al metals in the metallization layer, which is beneficial for interface matching and interlayer bonding.

[0013] Furthermore, the thickness of the electrostatic shielding layer is 20 - 30 nm.

[0014] The present invention also provides a metallized film capacitor, which includes the above electrode structure.

[0015] Further, the metallized film capacitor includes an inner electrode. The above two electrode structures are stacked in a double layer, and a blank area with a certain width is reserved on one side in the width direction of the dielectric film layer of the electrode structure as an insulating margin. When stacking the two layers, the insulating margins of the upper and lower electrode structures are placed on both sides of the double-layer stack; the two electrode structures of the double-layer stack are formed into an alternately stacked structure by winding or stacking to form the inner electrode. The blank area refers to the area where there is no conductive layer on the surface of the dielectric film layer, that is, there is no electrostatic shielding layer and metallization layer.

[0016] Furthermore, the width of the insulating margin is 0.5 - 3 mm.

[0017] The inner electrode of the metallized film capacitor of the present invention uses an inner electrode with the above electrode structure. By depositing an electrostatic shielding layer between the dielectric film layer and the metallization layer, and the electrostatic shielding layer uses a material with good conductivity, a conductive layer can be formed on the surface of the dielectric film layer, reducing its surface resistivity, enabling the generated static charges to leak quickly, and suppressing and reducing the generation of static charges; thus effectively alleviating the electric field distortion and the metal migration and accumulation phenomenon in the metallization layer caused by the accumulation of space charges and uneven temperature rise inside the capacitor, and improving the service life and reliability of the metallized film capacitor.

[0018] The present invention also provides a preparation method for the above electrode structure, including the following steps:

[0019] S1, surface treatment of the dielectric film layer: Select any one of polymer films such as polypropylene (PP) film, polystyrene (PS) film, and polyethylene terephthalate (PET) film as the material of the dielectric film layer, and cut it into a suitable width to ensure that the size of the film meets the requirements of subsequent processing; use the plasma surface treatment process to perform surface plasma bombardment treatment on the polymer film. Through this surface treatment, the surface of the polymer film is cleaned, thereby obtaining macroscopic uniformity on the film surface and forming dangling bonds on the surface of the polymer film, which is conducive to the deposition and adhesion of the subsequent electrostatic shielding layer material and metallization layer.

[0020] S2, preparation of the electrostatic shielding layer: Select conductive materials such as aluminum-doped zinc oxide (AZO), indium tin oxide (ITO), fluorine-doped tin oxide (FTO), reduced graphene oxide (rGO), or carbon nanotubes (CNTs), and use any one of physical deposition methods such as pulsed laser deposition method, plasma-enhanced chemical vapor deposition method, and magnetron sputtering method to form an electrostatic shielding layer on the surface of the polymer film. By using the physical deposition method, the same-mode diffusion of elements during the growth process can form a gradient distribution of common elements when the electrostatic shielding layer and the metallization layer have common elements, which is conducive to the uniformity and homogeneity of performance.

[0021] S3. Preparation of the metallization layer: A nanometer-thick layer of metallic zinc (Zn), metallic aluminum (Al), or a series of alloys thereof is deposited on the surface of the electrostatic shielding layer by vacuum evaporation technology as the metallization layer. This metallization layer provides good electrical conductivity for devices such as metallized film capacitors.

[0022] The present invention also provides a method for preparing the inner electrode of a metallized film capacitor: 1) Form the electrode structure as above. The difference is that during the above process of forming the electrode structure, in steps S2 and S3, a blank area with a certain width is left on one side of the surface of the dielectric film layer, that is, the electrostatic shielding layer and the metallization layer are not deposited in this blank area, and the insulating margin is formed on one side of the surface of the dielectric film layer; 2) The two electrode structures with insulating margins are stacked in a double layer. When stacking in a double layer, the insulating margins of the upper and lower electrode structures are placed on both sides of the double-layer stack; the two electrode structures of the double-layer stack are formed into an alternately stacked structure by winding or stacking to form the inner electrode.

[0023] Another task of the present invention is also to provide a processing method for the above-mentioned metallized film capacitor. This method has simple steps and is suitable for large-scale production, with significant economic benefits and application prospects. The processing method includes the following steps:

[0024] Step 1: Using the inner electrode prepared above, spray a metal layer on the two end surfaces of the inner electrode through a metal spraying machine to facilitate subsequent welding of leads.

[0025] Step 3: Use an energizing machine to process the inner electrode to further improve the electrical performance of the capacitor and ensure its stability in actual applications.

[0026] Step 4: Weld an external lead joint on the inner electrode to make a capacitor core. During the welding process, ensure the firmness and electrical conductivity of the lead joint to ensure the reliability of the capacitor.

[0027] Step 5: Package the capacitor core to obtain the metallized film capacitor. During the packaging process, ensure the sealing and mechanical strength of the capacitor to protect the internal structure from the external environment.

[0028] Perform performance tests on the prepared metallized film capacitor, such as capacitance and dielectric loss. It shows that compared with the prior art, the present invention has beneficial effects as follows:

[0029] (1) The electrode structure formed by adding an electrostatic shielding layer between the polymer film and the metallization layer in the present invention serves as the internal electrode of the metallized film capacitor. The electrostatic shielding layer alleviates the electric field distortion and the metal migration and accumulation phenomena in the metallization layer caused by the space charge accumulation and uneven temperature rise inside the capacitor during the operation of the capacitor. The electrostatic shielding layer has excellent electrical conductivity, significantly reducing the dielectric loss generated due to the electric field distortion during the operation of the capacitor. In addition, the anti-electric field distortion characteristic brought by the electrostatic shielding layer improves the breakdown voltage of the capacitor.

[0030] (2) A metallized film capacitor designed by the present invention has improved service life and reliability due to its ability to resist electric field distortion. Under low-voltage working conditions, the average life of the metallized film capacitor provided by the present invention is extended by 30% - 50%. Under high-voltage working conditions, the average life of the capacitor is extended by 80% - 120%.

[0031] (3) The processing method of the present invention is simple and feasible, compatible with the existing manufacturing process of metallized film capacitors, and suitable for large-scale production. Description of the Drawings

[0032] Figure 1 It is a schematic diagram of the electrode structure prepared in each embodiment of the present invention and a schematic diagram of the process of forming the internal electrode of the metallized film capacitor with the electrode structure.

[0033] In the figure: 1 is the dielectric film layer; 2 is the electrostatic shielding layer; 3 is the metallization layer; 4 is the insulating margin; 5 is the internal electrode. Detailed Embodiments

[0034] The following will describe in detail the specific embodiments of the present invention in conjunction with the drawings. However, the description of the embodiments is not a limitation of the technical solution. Any change in form rather than in essence based on the concept of the present invention should be regarded as the protection scope of the present invention.

[0035] In the following detailed embodiments, a polypropylene film is selected as the polymer substrate, i.e., the dielectric film layer, a conductive material such as AZO is selected as the antistatic material for deposition as the electrostatic shielding layer, and metal Al is selected as the metallization layer for detailed description.

[0036] Such as Figure 1Schematic diagrams of the electrode structures prepared for the following examples and the process of forming the inner electrodes of the electrode structures into metallized film capacitors. As shown in the figure, a dielectric film layer 1 is made of a polymer material, and then an electrostatic shielding layer 2 and a metallization layer 3 are sequentially deposited on the surface of the dielectric film layer 1 to obtain the electrode structure of the present invention; the two prepared electrode structures are stacked in a double layer, and a certain blank area is reserved on one side in the width direction of the dielectric film layer 1 as an insulating margin 4, and when the two electrode structures are stacked in a double layer, the insulating margins 4 of the upper and lower layers are placed on both sides. The double-layer stacked electrode structures are evenly and tightly wound through a winding system using the current process to form the inner electrode 5 of the metallized film capacitor. In each example, the obtained inner electrode 5 is further formed into a capacitor core and then subjected to subsequent packaging to form a metallized film capacitor.

[0037] Example 1

[0038] In this example, a metallized film capacitor with anti-electric field distortion is obtained. Specifically, the formation of the electrode structure used in the metallized film capacitor of this example includes: the dielectric film layer 1 is a polypropylene film with a thickness of 9 μm; the electrostatic shielding layer 2 is made of AZO material and deposited into an AZO conductive film with a thickness of 20 - 30 nm; the metallization layer 3 is a metal layer with a thickness of 20 - 50 nm formed by aluminum evaporation. When the electrode structure forms the inner electrode and is encapsulated into the capacitor core, a blank of 0.5 - 3 mm is reserved on one side in the width direction of the dielectric film layer 1 as the insulating margin 4.

[0039] It includes the following steps:

[0040] S1: Select a high-quality polypropylene film with a thickness of 9 μm as the dielectric film layer, cut it into a film with a suitable width according to the capacitor size requirements, ensure that the size of the film meets the requirements of subsequent processing, and use the plasma surface treatment process to perform surface plasma bombardment on the polymer dielectric film layer, clean the surface of the dielectric film layer in an Ar atmosphere to obtain surface macroscopic uniformity, and form dangling bonds on the surface of the dielectric film layer, which is beneficial to the deposition and adhesion of the electrostatic shielding material and the metallization layer.

[0041] S2: Select AZO conductive material and use the magnetron sputtering process to deposit an AZO film with a thickness of 20 - 30 nm on the surface of the dielectric film layer. During deposition, a blank area is left un-deposited with AZO film on one side in the width direction of the dielectric film layer, and the width of the blank area is 0.5 - 3 mm. The deposition conditions are: the distance between the substrate and the target is 100 mm, and the growth chamber is pumped to a vacuum degree of 1.0×10 - 3Above mTorr, Ar and O2 are introduced into the growth chamber. The flow ratio of Ar to O2 is 100:6, the sputtering pressure is controlled at 3.7 mTorr, the sputtering power is adjusted to 150 W, and growth is carried out at room temperature for 10 min. The AZO thin film, as an electrostatic shielding layer, can alleviate the space charge accumulation phenomenon and the uneven internal temperature rise phenomenon during the operation of the metallized film capacitor, and improve the service life and reliability of the capacitor.

[0042] S3: By means of vacuum evaporation technology, the vacuum degree is controlled at 10 -5 ~10 -6 Torr, the temperature of the aluminum evaporation source is controlled at 1100 - 1500 °C, the evaporation rate is set at 0.5 nm / s, and a 20 - 50 nm metal aluminum film is evaporated on the surface of the electrostatic shielding layer to form a metallized layer, thus obtaining the electrode structure. During the deposition of the metallized layer in this step, the blank area left in the above S2 step still does not deposit the metallized layer, that is, an insulating margin with a width of 0.5 - 3 mm is formed in the blank area.

[0043] S4: The two electrode structures prepared in S3 are stacked in a double layer, and when the two electrode structures are stacked in a double layer, the insulating margins of the upper and lower layers are placed on both sides respectively.

[0044] S5: The double - layer stacked electrode structure is wound by a winding system using the current process to form an inner electrode: at 25 °C and an air humidity of 20% RH - 30% RH, through the winding system, the winding tension is controlled between 15 - 45 G, and the winding pressure is controlled between 10 - 15 MPa to ensure that the film is wound flat, tight and without air gaps, thus forming the inner electrode of the capacitor.

[0045] S6: A metal layer is sprayed on the two end faces of the inner electrode by a metal spraying machine to facilitate subsequent welding of leads.

[0046] S7: Under the constant temperature condition of 25 °C, the inner electrode is processed by an energizing machine. By applying 1.5 times the rated voltage, two treatments are carried out for 20 s each time, so that local evaporation occurs at the defects of the metallized layer to repair the micro - defects in the film and improve the reliability and stability of the capacitor.

[0047] S8: External lead joints are welded to the inner electrode to make a capacitor core. The welding points are ensured to be smooth, without false soldering, cracks and charring phenomena, and the firmness and conductivity of the lead joints are ensured to guarantee the mechanical reliability of the capacitor.

[0048] S9: The capacitor core is encapsulated, and the encapsulation process ensures the sealing and mechanical strength of the capacitor to protect the internal structure from the external environment.

[0049] Example 2

[0050] Compared with Example 1, the electrostatic shielding layer in step S2 is: an ITO conductive thin film layer with a thickness of 20 - 30 nm made of tin-doped indium oxide (ITO) material by magnetron sputtering; others are the same as in Example 1.

[0051] Example 3

[0052] Compared with Example 1, the electrostatic shielding layer in step S2 is: a carbon nanotube (CNTs) conductive thin film layer with a thickness of 20 - 30 nm made by plasma-enhanced chemical vapor deposition; others are the same as in Example 1.

[0053] Comparative Example 1

[0054] In this comparative example, the electrode structure of the inner electrode does not contain an electrostatic shielding layer. Compared with the preparation steps of Example 1, step S2 is removed, and others are the same as in Example 1.

[0055] For the metallized film capacitors prepared in the above examples and comparative examples, instruments such as a capacitance tester, a withstand voltage tester, an insulation resistance tester, a precision high-voltage bridge, and an AC / DC withstand voltage test device are used to test the finished products for withstand voltage, capacitance, loss, internal resistance, and cycle life, etc., to determine the performance of each capacitor.

[0056] The test results show that a metallized film capacitor made by the present invention has the ability to resist electric field distortion, and its electrical performance, reliability, and life have been significantly improved, especially it performs more excellently in a high electric field or high-temperature environment. For example, the specific performance parameters of an anti-electric-field-distortion metallized polypropylene film capacitor made in Example 1 are listed in Table 1. In this table, the performance parameters of Comparative Example 1 without an electrostatic shielding layer are also compared. The records of 1000 surge discharges of the metallized film capacitors in Example 1 and Comparative Example 1 are shown in Table 2, in which the cycle reliability of the two is compared.

[0057] Table 1. List of relevant performance parameters of the metallized film capacitors prepared in Example 1 and Comparative Example 1

[0058]

[0059] Table 2. Record of 1000 surge discharge performance parameters of the metallized film capacitors prepared in Example 1 and Comparative Example 1

[0060]

[0061] From the comparison of the data in the table, it can be seen that: (1) In terms of the capacitance parameter, a metallized film capacitor made by the present invention mainly solves the accumulation of space charges generated during the operation of the capacitor, that is, the function of resisting electric field distortion, and has almost no influence on the capacitance; (2) In terms of dielectric loss: The electrostatic shielding layer has excellent conductivity, significantly reducing the dielectric loss generated due to electric field distortion during the operation of the capacitor; (3) Breakdown voltage: The anti-electric field distortion characteristic brought by the electrostatic shielding layer improves the breakdown voltage of the capacitor.

[0062] The test results also show that: Due to the ability to resist electric field distortion, the service life and reliability of the capacitor are both improved. Under low-voltage working conditions, the average life of the metallized film capacitor provided by the present invention is extended by 30% - 50%; under high-voltage working conditions, the average life of the capacitor is extended by 80% - 120%.

Claims

1. An electrode structure, characterized in that: The electrode structure includes a dielectric thin film layer, an electrostatic shielding layer, and a metallization layer that are stacked in sequence to form a sandwich structure. The electrostatic shielding layer is a conductive material, the dielectric thin film layer is a non-conductive polymer thin film layer, and the metallization layer is a metal thin film layer or an alloy thin film layer.

2. The electrode structure according to claim 1, wherein: The electrostatic shielding layer is selected from any one or several conductive materials of aluminum-doped zinc oxide (AZO), indium tin oxide (ITO), tin-doped fluorine oxide (FTO), reduced graphene oxide (rGO), or carbon nanotubes (CNTs).

3. An electrode structure according to claim 1, characterized in that: The dielectric thin film layer is selected from any one of polypropylene (PP) film, polystyrene (PS) film, and polyethylene terephthalate (PET) film in polymer thin films.

4. An electrode structure according to claim 1, characterized in that: The metallization layer is selected from metal zinc (Zn) or metal aluminum (Al) with a nanoscale thickness or a series of alloys of the two.

5. An electrode structure according to claim 1, characterized in that: The thickness of the electrostatic shielding layer is 20 - 30 nm.

6. A metallized film capacitor, characterized in that: The metallized thin film capacitor includes the electrode structure according to any one of claims 1 - 5.

7. A metallized film capacitor according to claim 6, characterized in that: The metallized thin film capacitor includes an inner electrode; the inner electrode is formed by winding or stacking the electrode structure: Two of the electrode structures are double-layer stacked, and a certain width of blank area is reserved on one side in the width direction of the dielectric thin film layer of the electrode structure as an insulating margin. When double-layer stacking, the insulating margins of the upper and lower electrode structures are placed on both sides of the double-layer stack; the two electrode structures of the double-layer stack are formed into an alternately stacked structure by winding or stacking to form the inner electrode; The blank area refers to that there is no conductive layer on the surface of the dielectric thin film layer in this area, that is, it does not contain the electrostatic shielding layer and the metallization layer.

8. A metallized film capacitor according to claim 7, wherein: The width of the insulating margin is 0.5 - 3 mm.

9. The metallized film capacitor according to any one of claims 6-8, characterized in that: The metallized thin film capacitor alleviates the electric field distortion and the metal migration and accumulation phenomenon in the metallization layer caused by space charge accumulation and uneven internal temperature rise of the capacitor through the electrostatic shielding layer, and improves the service life and reliability of the metallized thin film capacitor; under low-voltage working conditions, the average life of the metallized thin film capacitor is extended by 30% - 50%; under high-voltage working conditions, the average life of the metallized thin film capacitor is extended by 80% - 120%.

10. A method for manufacturing the metallized thin film capacitor according to any one of claims 6 - 9, comprising the following steps: S1, surface treatment of the dielectric thin film layer: Select any one of polypropylene (PP) film, polystyrene (PS) film, and polyethylene terephthalate (PET) film in polymer thin films as the dielectric thin film layer; use a plasma surface treatment process to perform surface plasma bombardment treatment on the polymer thin film; S2, prepare the electrostatic shielding layer: Select any one of aluminum-doped zinc oxide (AZO), indium tin oxide (ITO), tin-doped fluorine oxide (FTO), reduced graphene oxide (rGO), or carbon nanotubes (CNTs), and use any one of the physical deposition methods to form an electrostatic shielding layer on the surface of the dielectric thin film layer; during deposition, leave a certain width of blank area on one side in the width direction of the dielectric thin film layer without depositing the AZO film; S3. Preparation of the metallization layer: A nanoscale-thick layer of metallic zinc (Zn), metallic aluminum (Al), or a series of alloys of the two is deposited on the surface of the electrostatic shielding layer by vacuum evaporation technology to form the metallization layer, thus obtaining the electrode structure; during the deposition of the metallization layer in this step, the blank area left in the above S2 step still does not deposit the metallization layer, that is, an insulating margin is formed in the blank area. S4. Double-layer lamination of the two electrode structures obtained in S3: When the two electrode structures are double-layer laminated, the insulating margins of the upper and lower layers are placed on both sides. S5. The double-layer laminated electrode structure is wound by a winding system to form the inner electrode. S6. A metal layer is sprayed on the two end faces of the inner electrode to facilitate subsequent welding of the leads. S7. The inner electrode is processed using an energizing machine. S8. An external lead joint is welded to the metal layer on the end face of the inner electrode to make the capacitor core. S9. The capacitor core is encapsulated to obtain the metallized film capacitor.

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