Anode body and manufacturing method thereof, and electrolytic capacitor and manufacturing method thereof

Abstract

A method for manufacturing an anode body for an electrolytic capacitor includes a powder preparation step for preparing anode body powder 110 containing powder of a first metal that is a valve action metal, and a step for sintering the anode body powder to obtain an anode body. The powder of the first metal contains, in addition to the first metal, a small amount of particles containing a second metal having magnetism. The manufacturing method further includes a magnetic separation step for removing particles containing the second metal from the first metal powder by magnetic separation before sintering the anode body powder 110.

Description

Anode body and manufacturing method thereof, and electrolytic capacitor and manufacturing method thereof

[0001] The present disclosure relates to an anode body and a method for manufacturing the same, and an electrolytic capacitor and a method for manufacturing the same.

[0002] Electrolytic capacitors are used in a variety of electronic devices due to their low equivalent series resistance (ESR) and excellent frequency characteristics. An electrolytic capacitor typically includes a capacitor element having an anode portion and a cathode portion. The anode portion includes a porous anode body, and a dielectric layer is formed on the surface of the anode body. The dielectric layer is in contact with an electrolyte. Some electrolytic capacitors use a solid electrolyte, such as a conductive polymer, as the electrolyte (see, for example, Patent Document 1).

[0003] The anode body of an electrolytic capacitor is formed porous by, for example, placing a valve metal powder in a mold and sintering it. As a method for preparing the metal powder used in the anode body, Patent Document 2 describes a method for preparing foil-shaped tantalum powder, which involves a nitriding step at a low temperature of 500°C or less, followed by a high-temperature heat treatment step at 1000°C or more.

[0004] JP 2009-182157 A JP 2019-527300 A

[0005] Improve the reliability of electrolytic capacitors that use solid electrolytes.

[0006] One aspect of the present disclosure relates to a method for producing an anode body for an electrolytic capacitor, the method comprising: a powder preparation step of preparing a powder for the anode body including powder of a first metal that is a valve action metal; and a step of sintering the powder for the anode body to obtain an anode body, wherein the powder of the first metal includes particles containing a second metal that has magnetism in addition to the first metal; and the method further comprises a magnetic separation step of removing particles containing the second metal from the powder of the first metal by magnetic separation before sintering the powder for the anode body.

[0007] Another aspect of the present disclosure relates to a method for manufacturing an electrolytic capacitor including a capacitor element including a porous anode body, a dielectric layer formed on a surface of the anode body, and a solid electrolyte layer covering at least a portion of the dielectric layer, the method including: preparing the anode body by the above-described method for manufacturing an anode body; covering at least a portion of the anode body with the dielectric layer; and covering at least a portion of the dielectric layer with the solid electrolyte layer.

[0008] Yet another aspect of the present disclosure relates to an anode body for an electrolytic capacitor, comprising particles of a first metal that is a valve action metal and particles of a second metal that is magnetic, wherein the content of the second metal is 10 mg or less per kg of the first metal.

[0009] Yet another aspect of the present disclosure relates to an electrolytic capacitor including a capacitor element including a porous anode body, a dielectric layer formed on a surface of the anode body, and a solid electrolyte layer covering at least a portion of the dielectric layer, wherein the anode body includes particles of a first metal that is a valve metal and particles of a second metal that is magnetic, and the content of the second metal in the anode body is 10 mg or less per kg of the first metal.

[0010] According to the present disclosure, the reliability of electrolytic capacitors is improved.

[0011] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0012] 1 is a schematic diagram illustrating an example of a magnetic separation device for separating particles containing a second metal from powder for an anode body; FIG. 2 is a cross-sectional view illustrating an example of a capacitor element according to an embodiment of the present disclosure; and FIG. 3 is a cross-sectional view illustrating an electrolytic capacitor manufactured by a manufacturing method according to an embodiment of the present disclosure.

[0013] Hereinafter, embodiments of the present disclosure will be described using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values, materials, etc. may be exemplified, but other numerical values, materials, etc. may be applied as long as the effects of the present disclosure are obtained. In this specification, the expression "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or more and numerical value B or less." In the following description, when lower and upper limits of numerical values ​​related to specific physical properties or conditions are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not equal to or greater than the upper limit. When multiple materials are exemplified, one of the materials may be selected and used alone, or two or more of the materials may be used in combination.

[0014] The present disclosure also encompasses combinations of two or more features arbitrarily selected from the appended claims, i.e., two or more features arbitrarily selected from the appended claims can be combined unless a technical contradiction arises.

[0015] The present disclosure is based on the finding that one of the factors (modes) that cause poor reliability in electrolytic capacitors is due to metal impurities contained in trace amounts in the anode body, and that defects can occur even when the amount of metal impurities is extremely small.

[0016] A method for manufacturing an anode body of an electrolytic capacitor according to one embodiment of the present disclosure is a method for manufacturing an anode body of an electrolytic capacitor, and includes a powder preparation step of preparing a powder for the anode body including powder of a first metal that is a valve action metal, and a step of sintering the powder for the anode body to obtain the anode body.

[0017] In addition to the first metal, the powder of the first metal contains a trace amount of particles containing a magnetic second metal (e.g., iron (Fe)). Typically, the particles containing the second metal are removed to some extent by the supplier of the anode body powder. For example, as described in Patent Document 2, the content of iron impurities in the anode body powder is at most about 20 ppm by mass. However, it has been found that even such a low content of the second metal can cause poor reliability.

[0018] If the anode body contains particles containing the second metal, when a dielectric film is formed on the surface of the anode body by chemical conversion treatment, current flows concentratedly in the particles containing the second metal, degrading the properties of the surrounding dielectric layer, and the dielectric layer may become thinner or not be formed near the particles containing the second metal, resulting in poor insulation.

[0019] The second metal may not be uniformly distributed among particles of the first metal constituting the main component of the anode body powder, but may be contained in the form of particles containing the second metal. In other words, the anode body powder is a mixed powder containing a majority of particles of the first metal and a trace amount of particles containing the second metal. Therefore, even if the content of the second metal in the anode body powder is small, when a required amount of the anode body powder is divided into small portions and multiple anode bodies are produced, most anode bodies may contain substantially no second metal, but specific anode bodies may contain the second metal at a relatively high concentration. As a result, electrolytic capacitors produced using anode bodies containing a high concentration of the second metal may exhibit performance degradation due to poor chemical formation of the dielectric layer.

[0020] Although some electrolytic capacitors with poor chemical formation can be removed in an initial defect detection process after production, if the anode body powder contains a large number of particles containing the second metal, the yield of electrolytic capacitor production will decrease. Furthermore, some electrolytic capacitors that contain particles containing the second metal but pass the initial defect detection process will exhibit early performance degradation with use, which is one of the causes of reduced reliability. In order to suppress chemical formation defects, it is preferable that the proportion of particles containing the second metal contained in the anode body of the electrolytic capacitor be 10 ppm or less (i.e., 10 mg or less per kg of the first metal).

[0021] The method for manufacturing an anode body further includes a magnetic separation step of magnetically removing particles containing a second metal from the powder of the first metal before sintering the anode body powder. This reduces the number of anode bodies containing particles containing the second metal. Therefore, by using an anode body manufactured by this method, the yield of electrolytic capacitor manufacturing is improved and highly reliable electrolytic capacitors can be obtained.

[0022] In the step of removing particles containing the second metal from the powder of the first metal, the particles containing the second metal are preferably removed by magnetic separation so that the ratio of the particles containing the second metal in the powder of the first metal is 10 mg or less (i.e., 10 ppm or less) per 1 kg of the powder of the first metal. The ratio of the particles containing the second metal in the powder of the first metal after the removal step is more preferably 5 mg or less (i.e., 5 ppm or less) or 3 mg or less (i.e., 3 ppm or less) per 1 kg of the powder of the first metal. Approximately 10,000 anode bodies can be produced per kg of powder of the first metal, depending on the size of the anode body. When the ratio is 10 mg or less per 1 kg of powder of the first metal, the number of particles containing the second metal contained in 1 kg of powder of the first metal is, for example, 50 or less.

[0023] In response to demands for miniaturization of electrolytic capacitors, the smaller the size of the anode body, the larger the proportion of particles containing the second metal in the entire anode body, which makes the above-mentioned chemical formation failure more apparent. Therefore, it is important to reduce the proportion of particles containing the second metal contained in the anode body powder in advance.

[0024] The particles containing the second metal may contain a non-magnetic metal (excluding the first metal) in addition to the second metal. The particles containing the second metal may be particles of an alloy of the second metal and the non-magnetic metal. In this case, the proportion of the particles containing the second metal in the powder of the first metal is calculated based on the mass of the entire alloy in the particles, not just the mass of the second metal. The particles containing the second metal may include, for example, stainless steel (SUS) particles. In this case, the particles containing the second metal include the second metals iron (Fe) and chromium (Cr).

[0025] The removal of the particles containing the second metal may be performed on the anode body powder before powder-blending, or may be performed on the anode body powder after powder-blending. However, when the anode body powder contains a binder, it is preferable to perform the removal on the anode body powder after powder-blending, as described below.

[0026] The powder preparation step may be a step of mixing a binder with powder of the first metal and stirring the mixture to prepare a powder for the anode body. Molding and sintering the powder for the anode body containing the binder improves the sinterability of the anode body and improves the quality of the porous anode body. In this case, the removal of particles containing the second metal may be performed on the powder for the anode body containing the binder after the powder preparation step.

[0027] In the powder preparation process, a powder of the first metal and a binder are placed in a container and shaken to prepare the anode body powder. At this time, the inner surface of the container may be scraped by collision with particles of the first metal, and particles of the metal constituting the container may be mixed into the powder of the first metal. For example, if the container is made of stainless steel, particles containing metals such as iron (Fe), chromium (Cr), and nickel (Ni) may be mixed into the powder of the first metal. In particular, if the first metal contains tantalum (Ta), the inner surface of the container is likely to be scraped by collision with the tantalum particles because the tantalum particles are hard, and particles of the metal constituting the container may be easily mixed into the powder for the anode body as particles containing the second metal.

[0028] Therefore, by providing a magnetic separation process for removing particles containing the second metal from the anode body powder after the powder preparation process, the number of anode bodies containing particles containing the second metal is reduced, improving the yield of electrolytic capacitor production and obtaining highly reliable electrolytic capacitors.

[0029] The first metal may include, for example, tantalum (Ta), and the second metal may include, for example, at least one selected from the group consisting of iron (Fe) and nickel (Ni).

[0030] A magnetic sieve may be used to remove particles containing the second metal. By passing the anode body powder through a sieve, particles of the first metal pass through the sieve, while particles containing the second metal adhere to the sieve. Thus, particles containing the second metal can be separated and removed from the anode body powder. The anode body powder may be passed through the sieve while vibrating the sieve horizontally and / or vertically. To prevent the anode body powder particles from being separated and removed in the form of large aggregated particles, a gas flow may be supplied toward the sieve from the side through which the anode body powder passes (the side opposite to the side into which the anode body powder is introduced). The anode body powder may be passed through multiple sieves. For example, the step of passing the anode body powder through a magnetic sieve may be performed multiple times.

[0031] As another example, a belt conveyor may be used as shown in Fig. 1. However, the method for separating particles containing the second metal is not limited to the above-described method using a sieve and the method using a belt conveyor.

[0032] In the example shown in FIG. 1 , magnetic separation device 100 includes belt 101 and belt conveyor 103 having magnetic roller 102. Anode body powder 110 placed on belt 101 is conveyed on belt 101 toward magnetic roller 102 while being leveled to a uniform thickness by doctor blade 104, and falls at the end of magnetic roller 102 (e.g., position P in FIG. 1 ). At this time, an attractive force due to the magnetic force of magnetic roller 102 acts on the particles containing the second metal, counteracting the downward gravity, so that the falling position of the particles containing the second metal is closer to the rotation direction of the magnetic roller than the particles of the first metal (e.g., position Q in FIG. 1 ). This allows the particles containing the second metal to be separated from the anode body powder.

[0033] An anode element according to an embodiment of the present disclosure includes particles of a first metal that is a valve metal and particles of a second metal that is magnetic, and the content of the second metal is 10 mg or less per kg of the first metal, i.e., 100 × (10 / 1000000) mass % or less (0.001 mass % or less).

[0034] A method for manufacturing an electrolytic capacitor according to an embodiment of the present disclosure is a method for manufacturing an electrolytic capacitor including a capacitor element including a porous anode body, a dielectric layer formed on the surface of the anode body, and a solid electrolyte layer covering at least a portion of the dielectric layer, the method including the steps of: preparing an anode body, covering at least a portion of the anode body with the dielectric layer, and covering at least a portion of the dielectric layer with the solid electrolyte layer. In the step of preparing an anode body, an anode body manufactured by the above-described method for manufacturing an anode body is prepared.

[0035] An electrolytic capacitor according to an embodiment of the present disclosure includes a capacitor element including a porous anode body, a dielectric layer formed on the surface of the anode body, and a solid electrolyte layer covering at least a portion of the dielectric layer. The anode body includes particles of a first metal, which is a valve metal, and also includes a trace amount of particles of a second metal other than the first metal that has magnetic properties. The content of the second metal in the anode body is 10 mg or less per kg of the first metal, or 0.001 mass % or less. The content of the second metal in the anode body can be calculated, for example, by elemental analysis such as ICP emission spectroscopy.

[0036] The method for manufacturing an anode body and a method for manufacturing an electrolytic capacitor according to this embodiment will be described below with reference to the drawings as appropriate. However, the present invention is not limited thereto. Fig. 2 is a cross-sectional view schematically showing an example of a capacitor element according to this embodiment. Fig. 3 is a cross-sectional view schematically showing an electrolytic capacitor manufactured by the manufacturing method according to this embodiment.

[0037] Electrolytic capacitor 20 includes capacitor element 10 having anode portion 6 and cathode portion 7, exterior body 11 sealing capacitor element 10, anode lead terminal 13 electrically connected to anode portion 6 and partially exposed from exterior body 11, and cathode lead terminal 14 electrically connected to cathode portion 7 and partially exposed from exterior body 11. Anode portion 6 includes anode body 1 and anode wire 2. Dielectric layer 3 is formed on the surface of the anode body. Cathode portion 7 includes solid electrolyte layer 4 covering at least a portion of dielectric layer 3, and cathode layer 5 covering the surface of solid electrolyte layer 4.

[0038] <Capacitor Element> Hereinafter, the capacitor element 10 will be described in detail, taking as an example a case where the capacitor element 10 includes a solid electrolyte layer as the electrolyte.

[0039] The anode part 6 includes an anode body 1 and an anode wire 2 extending from one surface of the anode body 1 and electrically connecting to an anode lead terminal 13. The anode body 1 is, for example, a rectangular porous sintered body obtained by sintering particles of a first metal. The particles of the first metal are particles of a valve metal such as titanium (Ti), tantalum (Ta), or niobium (Nb). The anode body 1 includes particles of one or more types of the first metal. The particles of the first metal may be an alloy of two or more metals, at least one of which is the first metal. For example, an alloy containing a valve metal (first metal) and silicon, vanadium, boron, or the like may be used. Alternatively, a compound containing a valve metal and a typical element such as nitrogen may be used. The valve metal alloy contains the valve metal (first metal) as a main component, for example, at least 50 atomic % of the valve metal (first metal).

[0040] The anode wire 2 is made of a conductive material. The material of the anode wire 2 is not particularly limited and includes, for example, copper, aluminum, aluminum alloys, and the like, in addition to the valve metals described above. The anode body 1 and the anode wire 2 may be made of the same material or different materials. The anode wire 2 has a first portion 2a that is embedded inside the anode body 1 from one surface of the anode body 1, and a second portion 2b that extends from the above surface of the anode body 1. The cross-sectional shape of the anode wire 2 is not particularly limited and includes, for example, a circle, a track shape (a shape consisting of parallel straight lines and two curves connecting the ends of these straight lines), an ellipse, a rectangle, a polygon, and the like.

[0041] The anode part 6 is fabricated, for example, by press-molding the first portion 2a into a rectangular parallelepiped shape while the first portion 2a is embedded in a powder of particles of the first metal, followed by sintering. This results in the second portion 2b of the anode wire 2 extending from one surface of the anode body 1 in an upright manner. The second portion 2b is joined to the anode lead terminal 13 by welding or the like, thereby electrically connecting the anode wire 2 and the anode lead terminal 13. The welding method is not particularly limited, and examples include resistance welding and laser welding. The corners of the rectangular parallelepiped may then be processed to form curved surfaces.

[0042] A dielectric layer 3 is formed on the surface of the anode body 1. The dielectric layer 3 is made of, for example, a metal oxide. Methods for forming a layer containing a metal oxide on the surface of the anode body 1 include, for example, a method of immersing the anode body 1 in a chemical conversion solution to anodize the surface of the anode body 1, and a method of heating the anode body 1 in an oxygen-containing atmosphere. The dielectric layer 3 is not limited to the above-mentioned layer containing a metal oxide, and may be any layer that is insulating.

[0043] (Cathode Section) The cathode section 7 has a solid electrolyte layer 4 and a cathode layer 5 covering the solid electrolyte layer 4. The solid electrolyte layer 4 is formed so as to cover at least a portion of the dielectric layer 3.

[0044] For example, a manganese compound or a conductive polymer is used for the solid electrolyte layer 4. Examples of conductive polymers include polypyrrole, polythiophene, polyfuran, polyaniline, and polyacetylene. These may be used alone or in combination. The conductive polymer may also be a copolymer of two or more monomers. In terms of excellent conductivity, polythiophene, polyaniline, and polypyrrole may be used. In particular, in terms of excellent water repellency, polypyrrole may be used.

[0045] The solid electrolyte layer 4 containing the conductive polymer is formed, for example, by polymerizing a raw material monomer on the dielectric layer 3. Alternatively, it is formed by applying a liquid containing the conductive polymer to the dielectric layer 3. The solid electrolyte layer 4 is composed of one or more solid electrolyte layers. When the solid electrolyte layer 4 is composed of two or more layers, the composition and formation method (polymerization method) of the conductive polymer used in each layer may be different.

[0046] In this specification, polypyrrole, polythiophene, polyfuran, polyaniline, etc. refer to polymers having polypyrrole, polythiophene, polyfuran, polyaniline, etc. as their basic skeletons, respectively. Therefore, polypyrrole, polythiophene, polyfuran, polyaniline, etc. may also include their respective derivatives. For example, polythiophene includes poly(3,4-ethylenedioxythiophene).

[0047] Various dopants may be added to the polymerization liquid for forming the conductive polymer, or the solution or dispersion of the conductive polymer in order to improve the conductivity of the conductive polymer. The dopant is not particularly limited, but examples thereof include naphthalenesulfonic acid, p-toluenesulfonic acid, and polystyrenesulfonic acid.

[0048] When the conductive polymer is dispersed in the dispersion medium in the form of particles, the average particle size D50 of the particles is, for example, 0.01 μm or more and 0.5 μm or less. If the average particle size D50 of the particles is in this range, the particles can easily penetrate into the interior of the anode body 1.

[0049] The cathode layer 5 has, for example, a carbon layer 5a formed to cover the solid electrolyte layer 4 and a metal paste layer 5b formed on the surface of the carbon layer 5a. The carbon layer 5a contains a conductive carbon material such as graphite and a resin. The metal paste layer 5b contains, for example, metal particles (e.g., silver) and a resin. The configuration of the cathode layer 5 is not limited to this configuration. The configuration of the cathode layer 5 may be any configuration that has a current collecting function.

[0050] <Anode lead terminal> The anode lead terminal 13 is electrically connected to the anode body 1 via the second portion 2b of the anode wire 2. The material of the anode lead terminal 13 is not particularly limited as long as it is electrochemically and chemically stable and conductive. The anode lead terminal 13 may be made of a metal such as copper, or a non-metal. The shape of the anode lead terminal 13 is not particularly limited as long as it is flat. The thickness of the anode lead terminal 13 (the distance between the main surfaces of the anode lead terminal 13) may be 25 μm or more and 200 μm or less, or may be 25 μm or more and 100 μm or less, from the viewpoint of reducing the height.

[0051] One end of the anode lead terminal 13 may be joined to the anode wire 2 with a conductive adhesive or solder, or may be joined to the anode wire 2 by resistance welding or laser welding. The other end of the anode lead terminal 13 is extended to the outside of the exterior body 11 and is exposed from the exterior body 11. The conductive adhesive is, for example, a mixture of a thermosetting resin (described later) with carbon particles or metal particles.

[0052] <Cathode lead terminal> The cathode lead terminal 14 is electrically connected to the cathode part 7 at the joint portion 14a. The joint portion 14a is a portion of the cathode lead terminal 14 that overlaps with the cathode layer 5 when the cathode layer 5 and the cathode lead terminal 14 joined to the cathode layer 5 are viewed from the normal direction of the cathode layer 5.

[0053] The cathode lead terminal 14 is joined to the cathode layer 5 via, for example, a conductive adhesive 8. One end of the cathode lead terminal 14 constitutes, for example, a part of the joining portion 14a and is disposed inside the exterior body 11. The other end of the cathode lead terminal 14 is led out to the outside. Therefore, a part of the cathode lead terminal 14, including the other end, is exposed from the exterior body 11.

[0054] The material of the cathode lead terminal 14 is not particularly limited as long as it is electrochemically and chemically stable and conductive. The cathode lead terminal 14 may be made of a metal such as copper, or a non-metal. The shape of the cathode lead terminal 14 is also not particularly limited, and may be, for example, a long, flat plate. From the viewpoint of reducing the height, the thickness of the cathode lead terminal 14 may be 25 μm or more and 200 μm or less, or 25 μm or more and 100 μm or less.

[0055] <Exterior Body> The exterior body 11 is provided to electrically insulate the anode lead terminal 13 and the cathode lead terminal 14, and is made of an insulating material (exterior body material). The exterior body material includes, for example, a thermosetting resin. Examples of thermosetting resins include epoxy resin, phenolic resin, silicone resin, melamine resin, urea resin, alkyd resin, polyurethane, polyimide, and unsaturated polyester.

[0056] <Method for Manufacturing Electrolytic Capacitor> An example of a method for manufacturing the electrolytic capacitor according to this embodiment will be described below.

[0057] (1) Anode Body Preparation Step First, an anode body is prepared by a manufacturing method including a powder preparation step of preparing an anode body powder containing a powder of a first metal that is a valve action metal, and a step of sintering the anode body powder to obtain the anode body.

[0058] In the powder-mixing step, for example, powder of the first metal is placed in a shaker and stirred to obtain powder for the anode body.

[0059] The anode body powder may be prepared by adding a binder to a shaker together with the powder of the first metal. This improves the fluidity of the anode body powder and improves its formability. Furthermore, the particles are firmly bonded together during the sintering process, resulting in dense pores. Examples of binders include polyacrylic carbonate. The binder may be mixed with the powder of the first metal in the form of a solution or dispersion in a solvent such as butanol or methanol.

[0060] Next, the anode body powder and the anode wire 2 are placed in a mold and pressure-molded so that the first portion 2a is embedded in the anode body powder. The compact is then sintered to obtain an anode part 6 including the anode body 1, which is a porous sintered body of the first metal. The first portion 2a of the anode wire is embedded inside the porous sintered body from one surface. The pressure during pressure molding is not particularly limited. Sintering is preferably performed under reduced pressure. The sintering temperature is a high temperature, for example, 1200°C to 1400°C. The high temperature during sintering removes organic components, such as the binder and solvent, contained in the anode body powder. Prior to sintering, a heat treatment at a relatively low temperature, for example, 300°C to 500°C, may be performed to remove the binder. Sintering melts the surfaces of the particles of the first metal, maintaining gaps between the particles of the first metal, thereby bonding the particles of the first metal to each other and to the first portion 2a of the anode wire, thereby electrically connecting them.

[0061] Particles of the first metal usually contain a small amount of particles of a second metal, which is magnetic. If particles of the second metal are contained in the sintered anode body, the formation of a dielectric layer by a subsequent chemical conversion treatment may be insufficient, which may reduce the reliability of the electrolytic capacitor. Therefore, before pressure molding, a magnetic separation process is separately performed to remove particles containing the second metal from particles of the first metal. In the magnetic separation process, as described above, particles containing the second metal may be removed using a magnetic sieve, or particles containing the second metal may be removed using a belt conveyor as shown in FIG. 1. The removal method is not limited to these methods.

[0062] The removal of particles containing the second metal may be performed before or after the powder preparation step. However, in the powder preparation step, when the powder of the first metal is introduced into a shaker and stirred to obtain the anode body powder, metal components on the inner wall of the shaker container may be scraped off by collision with the powder of the first metal and may be mixed into the anode body powder. For example, if the container is made of stainless steel (SUS), particles containing metals such as iron, chromium, and nickel may be contained in the anode body powder. The magnetic separation step is preferably performed after the powder preparation step in order to remove magnetic metal particles originating from the shaker container.

[0063] The powder for the anode body is usually pressure-molded using a mold having a rectangular parallelepiped internal space, and then sintered. In this case, the shape of the anode body 1 after sintering is also rectangular parallelepiped.

[0064] (2) Dielectric Layer Forming Step Next, the anode body 1 is subjected to a chemical conversion treatment to cover at least a portion of the anode body 1 with the dielectric layer 3. Specifically, the anode body 1 is immersed in a chemical conversion tank filled with an aqueous electrolytic solution (e.g., an aqueous phosphoric acid solution), the second portion 2b of the anode wire 2 is connected to the anode body in the chemical conversion tank, and anodization is performed to form the dielectric layer 3 made of an oxide film of a valve metal on the surface of the porous portion. The aqueous electrolytic solution is not limited to an aqueous phosphoric acid solution, and nitric acid, acetic acid, sulfuric acid, or the like can also be used.

[0065] (3) Solid Electrolyte Layer Forming Step Subsequently, at least a portion of the dielectric layer 3 is covered with the solid electrolyte layer 4. This results in a capacitor element 10 including the anode body 1, the dielectric layer 3, and the solid electrolyte layer 4. The solid electrolyte layer 4 containing a conductive polymer is formed on at least a portion of the dielectric layer 3 by, for example, impregnating the anode body 1 on which the dielectric layer 3 has been formed with a monomer or an oligomer and then polymerizing the monomer or oligomer by chemical polymerization or electrolytic polymerization, or by impregnating the anode body 1 on which the dielectric layer 3 has been formed with a solution or dispersion of the conductive polymer and drying it.

[0066] The solid electrolyte layer 4 can be formed, for example, by immersing the anode body 1 on which the dielectric layer 3 has been formed in a dispersion liquid containing a conductive polymer, a binder, and a dispersion medium, removing the anode body 1, and drying the anode body 1. The dispersion liquid may contain a binder and / or conductive inorganic particles (e.g., a conductive carbon material such as carbon black). The conductive polymer may also contain a dopant. The conductive polymer and the dopant may each be selected from those exemplified for the solid electrolyte layer 4. A known binder can be used. The dispersion liquid may contain known additives used in forming a solid electrolyte layer.

[0067] Next, a carbon paste and a metal paste are applied in this order to the surface of the solid electrolyte layer 4 to form a cathode layer 5 composed of a carbon layer 5a and a metal paste layer 5b. The configuration of the cathode layer 5 is not limited to this, and any configuration may be used as long as it has a current collecting function.

[0068] Next, an anode lead terminal 13 and a cathode lead terminal 14 are prepared. The second portion 2b of the anode wire 2 extending from the anode body 1 is joined to the anode lead terminal 13 by laser welding, resistance welding, or the like. After applying a conductive adhesive 8 to the cathode layer 5, the cathode lead terminal 14 is joined to the cathode part 7 via the conductive adhesive 8.

[0069] Next, the capacitor element 10 and the materials for the exterior body 11 (e.g., uncured thermosetting resin and filler) are placed in a mold, and the capacitor element 10 is sealed by transfer molding, compression molding, or the like. At this time, a portion of the anode lead terminal 13 and the cathode lead terminal 14 are exposed from the mold. The molding conditions are not particularly limited, and the time and temperature conditions may be set appropriately taking into consideration the curing temperature of the thermosetting resin used, etc.

[0070] Finally, the exposed portions of the anode lead terminal 13 and the cathode lead terminal 14 are bent along the exterior package 11 to form bent portions, whereby a portion of the anode lead terminal 13 and the cathode lead terminal 14 is disposed on the mounting surface of the exterior package 11. By the above method, the electrolytic capacitor 20 is manufactured.

[0071] The present disclosure can be used in electrolytic capacitors, and preferably in electrolytic capacitors that use a porous body as an anode body.

[0072] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0073] 20: Electrolytic capacitor 10: Capacitor element 1: Anode body 2: Anode wire 2a: First portion 2b: Second portion 3: Dielectric layer 4: Solid electrolyte layer 5: Cathode layer 5a: Carbon layer 5b: Metal paste layer 6: Anode portion 7: Cathode portion 8: Conductive adhesive 11: Exterior body 13: Anode lead terminal 14: Cathode lead terminal 14a: Joint portion 100: Magnetic separation device 103: Belt conveyor 101: Belt 102: Magnetic roller 104: Doctor blade 110: Powder for anode body

Claims

1. A method for manufacturing an anode body of an electrolytic capacitor, comprising: a powder preparation step of preparing a powder for the anode body containing powder of a first metal which is a valve-acting metal; a step of sintering the powder for the anode body to obtain an anode body; wherein the powder of the first metal contains particles containing a second metal having magnetism in addition to the first metal; A method for manufacturing an anode body, further comprising a magnetic separation step of removing particles containing the second metal from the powder of the first metal by magnetic separation before sintering the powder for the anode body.

2. The method for manufacturing an anode body according to claim 1, wherein the magnetic separation step is a step of removing particles containing the second metal by magnetic separation so that the ratio of particles containing the second metal in the powder of the first metal is 10 mg or less per 1 kg of the powder of the first metal.

3. The powder preparation step is a step of mixing and stirring a binder with the powder of the first metal to prepare the powder for the anode body, The method for manufacturing an anode body according to claim 1, wherein the magnetic separation step is performed on the powder for the anode body containing the binder after the powder preparation step.

4. The method for manufacturing an anode body according to claim 1, wherein the magnetic separation step includes removing particles containing the second metal using a sieving screen with magnetism.

5. The method for manufacturing an anode body according to claim 1, wherein the magnetic separation step includes removing particles containing the second metal using a belt conveyor having a magnetic roller.

6. The first metal contains tantalum, The method for manufacturing an anode body according to claim 1, wherein the second metal contains at least one selected from the group consisting of iron and nickel.

7. A method for manufacturing an electrolytic capacitor including a capacitor element including a porous anode body, a dielectric layer formed on the surface of the anode body, and a solid electrolyte layer covering at least a part of the dielectric layer, comprising: a step of preparing the anode body by the method for manufacturing an anode body according to any one of claims 1 to 6; a step of covering at least a part of the anode body with the dielectric layer; a step of covering at least a part of the dielectric layer with the solid electrolyte layer.

8. An anode body for an electrolytic capacitor, containing particles of a first metal which is a valve-acting metal and particles of a second metal having magnetism, wherein the content ratio of the second metal is 10 mg or less per 1 kg of the first metal.

9. The first metal contains tantalum, The anode body for an electrolytic capacitor according to claim 8, wherein the second metal contains at least one selected from the group consisting of iron and nickel.

10. An electrolytic capacitor comprising a capacitor element including a porous anode body, a dielectric layer formed on the surface of the anode body, and a solid electrolyte layer covering at least a part of the dielectric layer, wherein the anode body contains particles of a first metal that is a valve action metal and particles of a second metal having magnetism, and the content ratio of the second metal in the anode body is 10 mg or less with respect to 1 kg of the first metal.