Electrolytic capacitor and method of manufacturing the same

Abstract

An electrolytic capacitor (20) includes a capacitor element (10) comprising a porous anode body (1), a dielectric layer (3) formed on a surface of the anode body (1), and a solid electrolyte layer (4) covering at least a portion of the dielectric layer (3). The anode body (1) has a plurality of main surfaces and a corner portion, wherein the corner portion includes a plurality of side portions connecting the plurality of main surfaces to each other and one or more vertex portions connecting the plurality of main surfaces to each other. A surface layer X of at least a portion of the corner portion is denser than a surface layer Y of a main surface adjacent to the surface layer X.

Description

[0001] This application is a divisional application of an application filed on February 26, 2020, with application number 202080024652.2 and invention name “Electrolytic capacitor and its manufacturing method”. Technical Field

[0002] The present invention relates to an electrolytic capacitor and a method for manufacturing the same. Background Art

[0003] Electrolytic capacitors have low equivalent series resistance (ESR) and excellent frequency characteristics, making them suitable for use in various electronic devices. Electrolytic capacitors typically comprise a capacitor element with an anode and a cathode. The anode comprises a porous anode body, with a dielectric layer formed on the surface of the anode body. The dielectric layer is in contact with an electrolyte. Some electrolytic capacitors use solid electrolytes such as conductive polymers as the electrolyte (e.g., Patent Document 1).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2009-182157 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] Improve the reliability of electrolytic capacitors using solid electrolytes.

[0009] Means for solving problems

[0010] One aspect of the present invention relates to an electrolytic capacitor comprising 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 anode body has multiple main surfaces and corner portions, the corner portions including multiple side portions and apex portions connecting the multiple main surfaces to each other, and a surface layer X of at least a portion of the corner portion being denser than a surface layer Y of the main surface adjacent to the surface layer X.

[0011] Another aspect of the present invention relates to a method for manufacturing an electrolytic capacitor, the method being a method for manufacturing a solid electrolytic capacitor having a capacitor element, the 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 comprises: preparing the 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. The anode body has a plurality of principal surfaces and a corner portion, the corner portion including a plurality of side portions and a vertex portion connecting the plurality of principal surfaces to each other. The step of preparing the anode body includes irradiating at least a portion of the corner portion with a laser.

[0012] Yet another aspect of the present invention relates to a method for manufacturing an electrolytic capacitor, the method being a method for manufacturing a solid electrolytic capacitor having a capacitor element, the capacitor element comprising 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 comprises: preparing the 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. The anode body has a plurality of principal surfaces and corner portions, the corner portions comprising side portions and vertices connecting the plurality of principal surfaces to each other. The step of preparing the anode body includes causing dielectric particles to collide with at least a portion of the corner portions.

[0013] Yet another aspect of the present invention relates to a method for manufacturing an electrolytic capacitor, the method being a method for manufacturing a solid electrolytic capacitor having a capacitor element, the 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 manufacturing method comprises: a step of preparing the anode body; a step of covering at least a portion of the anode body with the dielectric layer; and a step of covering at least a portion of the dielectric layer with the solid electrolyte layer. The anode body has a plurality of principal surfaces and a corner portion, the corner portion including a side portion and a vertex portion connecting the plurality of principal surfaces to each other. The step of preparing the anode body includes a step of vibrating the anode body together with a vibrating member.

[0014] Effects of the Invention

[0015] The reliability of electrolytic capacitors is improved.

[0016] The novel features of the present invention, both in terms of structure and content, are described in the attached technical solutions and can be better understood together with other objects and features of the present invention through the following detailed description with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a perspective view schematically showing the shape of an anode body used in an electrolytic capacitor according to one embodiment of the present invention.

[0018] Figure 2 It is a cross-sectional view schematically showing an electrolytic capacitor according to one embodiment of the present invention.

[0019] Figure 3 This is an electron microscope photograph of a cross section of a corner portion of the anode body after laser irradiation. DETAILED DESCRIPTION

[0020] [Electrolytic capacitors]

[0021] An electrolytic capacitor according to one embodiment of the present invention includes a capacitor element comprising 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 anode body has multiple main surfaces and corner portions. The corner portions include, for example, multiple side portions connecting the multiple main surfaces to each other, and one or more vertex portions connecting the multiple main surfaces to each other. At least a portion of the corner portion has a curved surface or is chamfered.

[0022] In the anode body, by having at least a portion of its sides and / or vertices curved or chamfered, damage to the dielectric layer at the corners is suppressed, enabling the realization of an electrolytic capacitor with low leakage current. Consequently, the reliability of the electrolytic capacitor can be improved.

[0023] The side portion refers to the side where the two main surfaces of the anode body intersect, and the area near it. The vertex portion refers to the vertex where the three main surfaces of the anode body intersect, and the area near it. Herein, the side portions and vertex portions are collectively referred to as "corner portions." "At least a portion of a corner portion has a curved surface or is chamfered" means, for example, that at least one side portion and / or at least one vertex portion has a curved surface or is chamfered. This also includes cases where a portion of a side portion has a curved surface or is chamfered.

[0024] Furthermore, the fact that at least a portion of a corner portion has a "curved surface" is not limited to cases where the cross-sectional shape of the corner portion is a curve. For example, the cross-sectional shape of the corner portion may also be a broken line having multiple obtuse angles. In cases where the cross-sectional shape is convex, and the straight line corresponding to one principal surface and the straight line corresponding to the other adjacent principal surface are connected via at least one straight line and / or curve in the cross-sectional shape, the corner portion can be said to have a curved surface. In other words, having a "curved surface" in a corner portion also means that the cross-sectional shape of the corner portion in a cross section perpendicular to the two adjacent principal surfaces does not have a sharp area of ​​less than 90°.

[0025] The dielectric layer is usually formed by subjecting the anode to a chemical conversion treatment to grow an oxide film on the surface of the anode. Therefore, the properties of the dielectric layer formed by chemical conversion are affected by the surface condition of the anode before the chemical conversion treatment.

[0026] The anode body usually has the shape of a cuboid. In this case, near the edge connecting the two orthogonal main faces of the cuboid and / or near the vertex where the three mutually orthogonal main faces of the cuboid intersect (corner portion), the surface of the anode body is uneven when observed microscopically, and the surface roughness is large, and it is easy to become a shape with a concave and convex shape. If the dielectric layer is grown by chemical conversion treatment in this state, the dielectric layer is prone to defects in the concave and convex portion. If defects are generated in the dielectric layer, there is the following situation: a path for current to flow between the solid electrolyte and the valve metal via the defective portion is generated, and the leakage current increases.

[0027] Furthermore, the anode body is porous and therefore brittle, making it susceptible to damage. In particular, the corners of the anode body have lower mechanical strength than other areas, and thermal stress is more likely to concentrate. Damage to the porous areas can damage the dielectric layer covering them. This damage to the dielectric layer can increase leakage current.

[0028] In the electrolytic capacitor of this embodiment, by pre-curving at least a portion of the corner portion of the anode body, defects during chemical conversion in the dielectric layer can be reduced. Consequently, leakage current can be reduced. Furthermore, mechanical strength can be improved, and thermal stress can be alleviated. This can suppress damage to the dielectric layer after chemical conversion, ultimately preventing an increase in leakage current.

[0029] The solid electrolyte layer is formed in a manner covering the dielectric layer. In the case where the corner portion of the anode body does not have a curved surface, the thickness of the solid electrolyte layer at the corner portion is easily formed to be thin. In particular, in the case where the solid electrolyte layer contains a conductive polymer and the conductive polymer is formed by chemical polymerization, the thickness of the solid electrolyte layer is easily thinned in the corner portion. However, by forming at least a portion of the corner portion into a curved surface, the thin film of the solid electrolyte layer at the corner portion can be suppressed, and the solid electrolyte layer can be formed with a uniform thickness. As a result, the electrolytic capacitor becomes stronger against stress from the outside, and an increase in leakage current and the occurrence of short circuit defects can be suppressed. In addition, the withstand voltage is improved.

[0030] The surface layer X of at least a portion of the corner portion can be denser than the surface layer Y of the main surface adjacent to the surface layer X. The surface layer Y is the surface layer of the main surface adjacent to the corner portion, where the porous anode body is typically exposed. By densely forming the surface layer X at the corner portion, the mechanical strength of the corner portion can be further improved. Consequently, the effect of suppressing the increase in leakage current through the corner portion can be enhanced.

[0031] Furthermore, when at least a portion of the surface layer X at the corners is densely formed, the dense surface layer X need not be curved or chamfered. Even when the corners are not curved and chamfered, densely forming the surface layer X at the corners can still achieve sufficient mechanical strength. This can suppress the increase in leakage current through the corners. However, if at least a portion of the area containing the surface layer X is curved or chamfered, leakage current can be further suppressed, which is preferable. In this case, the surface layer Y can be an area adjacent to the curved or chamfered portion of the surface layer X.

[0032] The fact that the surface layer X is denser than the surface layer Y means, for example, that the porosity P1 of the surface layer X is smaller than the porosity P2 of the surface layer Y. The surface layer X may have a portion with a porosity P1 of 10% or less. In contrast, the porosity P2 of the surface layer Y is usually 20% or more.

[0033] The surface layer X and the surface layer Y may have a portion where the ratio of porosity P2 to porosity P1, P2 / P1, satisfies, for example, 5 or greater. P2 / P1 may be 10 or greater or 50 or greater. Any portion of the surface layer X and any portion of the surface layer Y may satisfy P2 / P1 of 5 or greater.

[0034] When at least a portion of the corner portion has a curved surface, the curvature of the curved surface is, for example, 0.002 (1 / μm) to 0.05 (1 / μm), and more preferably 0.005 (1 / μm) to 0.02 (1 / μm).

[0035] It should be noted that the curvature and porosity are determined by image analysis of a cross-sectional photograph of the anode body in a specified region. In the electron micrograph of the cross section, the area of ​​the voids in any region A within the surface layer X is determined, and the ratio of the void area to the area of ​​region A is defined as porosity P1. Similarly, the area of ​​the voids in any region B within the surface layer Y is determined, and the ratio of the void area to the area of ​​region B is defined as porosity P2.

[0036] The curved corners can be formed by press-molding the anode body using a mold with a curved surface, or by removing a portion of the corners. However, laser irradiation of the corners can create a curved surface and / or a denser surface layer at the corners. Laser irradiation melts the surface layer X at the corners. The surface layer X after laser irradiation is a molten layer formed by melting the porous portions of the anode body and can be denser than the porous surface layer Y. The porosity P1 of the surface layer X formed by laser irradiation is extremely low, for example, less than 1%.

[0037] Alternatively, the anode body can be placed on a vibrating member such as a sieve or dielectric particles, and the vibrating member can be vibrated to form the corner portion into a curved surface. In this case, the corner portion of the anode body collides with the vibrating member due to vibration, and the corner portion is compressed by the collision, and the corner portion can be formed into a curved surface shape. As a result, the surface layer X of the corner portion can be formed denser (higher density) than the surface layer Y of the main surface that maintains the porous structure.

[0038] Among the corner portions, the portion having a curved surface shape or a chamfered shape includes, for example, a portion having a curvature radius R of 20 μm to 500 μm, and more preferably includes a portion having a curvature radius R of 50 μm to 200 μm. Here, the curvature radius of the corner portion is calculated by taking a picture of the anode body from a certain main surface side and performing image analysis on the contour shape near the obtained corner (vertex). In the contour line of the anode body, the distance from the boundary between the area with the curved surface (chamfered portion) and the side portion without the curved surface (not chamfered) to the vertex position (the position of the intersection of the side portion and the side portion) before the curved surface is formed (before chamfering) is obtained, and is regarded as the curvature radius R. The curvature radius R can also be obtained for each side portion of the anode body and the average value is calculated. For example, in the case where the anode body is a roughly rectangular parallelepiped, the curvature radius R is obtained at both ends of the 12 side portions, and the average value of the curvature radii R in total is obtained. By using a vibrating member, it is easy to obtain an anode body having an average value of the curvature radius R in the above range.

[0039] In the corner portions of the anode body, the curved or chamfered portions may include portions having different radii of curvature R. In this case, the variation in the radii of curvature R among the multiple corner portions of the anode body may be, for example, 350 μm or less, more preferably 150 μm or less. The variation in the radii of curvature R is the difference between the maximum and minimum values ​​of the radii of curvature R of the corner portions calculated by the above method (if the anode body is a substantially rectangular parallelepiped, this is the difference between the maximum and minimum values ​​of the 24 calculated radii of curvature).

[0040] Figure 1 : is a schematic perspective view showing an example of an anode body used in the electrolytic capacitor of this embodiment. Figure 1As shown, anode body 1 has a substantially rectangular parallelepiped shape, with six main surfaces 101A to 101F exposed. 101D to 101F are located at positions hidden from the paper and are therefore not shown.

[0041] In the main surfaces 101A to 101F, near the sides where two adjacent main surfaces intersect each other, a connecting surface is formed by removing the corners of the side portions. Figure 1 In the example, the connecting surface 102C is between the main surfaces 101A and 101B, the connecting surface 102A is between the main surfaces 101B and 101C, and the connecting surface 102A is between the main surfaces 101B and 101C. In addition, near the vertex where the three main surfaces intersect, a second connecting surface is formed by removing the corner of the vertex. Figure 1 In the example, a second connecting surface 103A is provided at the vertex where the main surfaces 101A-101C intersect. Second connecting surface 103A connects connecting surfaces 102A-102C to each other. Connecting surfaces 102A-102C and second connecting surface 103A are processed into curved surfaces with rounded corners. Connecting surfaces 102A-102C and second connecting surface 103A can be curved surfaces or composed of one or more flat surfaces (for example, with chamfered corners).

[0042] By thus forming anode body 1 with no sharp edges, a dielectric layer with fewer defects can be formed on the surface of anode body 1. Consequently, leakage current can be reduced. Furthermore, the mechanical strength of the anode body is improved, and the concentration of thermal stress is alleviated. Consequently, damage to the dielectric layer can be suppressed, and increases in leakage current caused by such damage can be suppressed, allowing leakage current to be kept low.

[0043] The surface layers of connecting surfaces 102A-102C and / or second connecting surface 103A can be made denser than the porous surface layers of main surfaces 101A-101F. In other words, the porosity P1 of the surface layers of connecting surfaces 102A-102C and / or second connecting surface 103A can be smaller than the porosity P2 of the surface layers of main surfaces 101A-101F. This further enhances the mechanical strength of the corners of the anode body.

[0044] Anode wire 2 extends from main surface 101B of anode body 1 . Anode body 1 and anode wire 2 constitute anode portion 6 .

[0045] Hereinafter, the structure of the electrolytic capacitor according to the present embodiment will be described with reference to the drawings as appropriate. However, the present invention is not limited thereto. Figure 2 1 is a schematic cross-sectional view of the electrolytic capacitor according to this embodiment.

[0046] Electrolytic capacitor 20 includes a capacitor element 10 having an anode portion 6 and a cathode portion 7, an outer casing 11 that seals capacitor element 10, an anode lead terminal 13 electrically connected to anode portion 6 and partially exposed from outer casing 11, and a cathode lead terminal 14 electrically connected to cathode portion 7 and partially exposed from outer casing 11. Anode portion 6 includes an anode body 1 and an anode wire 2. A dielectric layer 3 is formed on the surface of the anode body. Cathode portion 7 includes a solid electrolyte layer 4 that covers at least a portion of dielectric layer 3, and a cathode layer 5 that covers the surface of solid electrolyte layer 4.

[0047] <Capacitor Components>

[0048] Hereinafter, capacitor element 10 will be described in detail by taking as an example a case where a solid electrolyte layer is provided as an electrolyte.

[0049] Anode portion 6 includes an anode body 1 and an anode wire 2 extending from one surface of anode body 1 and electrically connected to an anode lead terminal 13 .

[0050] The anode body 1 is, for example, a porous sintered body of a rectangular parallelepiped obtained by sintering metal particles. As the above-mentioned metal particles, particles of valve metals such as titanium (Ti), tantalum (Ta), and niobium (Nb) are used. One or more metal particles can be used in the anode body 1. The metal particles can be an alloy composed of two or more metals. For example, an alloy containing a valve metal and silicon, vanadium, boron, etc. can be used. In addition, a compound containing a valve metal and a typical element such as nitrogen can also be used. The alloy of the valve metal contains the valve metal as the main component, for example, contains more than 50 atomic % of the valve metal.

[0051] The anode wire 2 is made of a conductive material. The material of the anode wire 2 is not particularly limited. For example, in addition to the above-mentioned valve metals, copper, aluminum, aluminum alloys, etc. can also be mentioned. The materials constituting the anode body 1 and the anode wire 2 can be the same or different. The anode wire 2 has: a first part 2a buried in the interior of the anode body 1 from one side of the anode body 1, and a second part 2b extending from the above-mentioned side of the anode body 1. The cross-sectional shape of the anode wire 2 is not particularly limited. Examples include circular, annular (a shape consisting of parallel straight lines and two curved lines connecting the ends of these straight lines to each other), elliptical, rectangular, polygonal, etc.

[0052] The anode portion 6 is produced, for example, by press-forming the first portion 2a into a rectangular parallelepiped while burying it in the powder of the above-mentioned metal particles and sintering it. As a result, the second portion 2b of the anode wire 2 is drawn out from one side of the anode body 1 in an extended manner. The second portion 2b is joined to the anode lead terminal 13 by welding or the like, and the anode wire 2 is electrically connected to the anode lead terminal 13. The welding method is not particularly limited, and examples thereof include resistance welding, laser welding, and the like. Thereafter, processing to form a curved surface at the corner portion of the rectangular parallelepiped can be performed.

[0053] A dielectric layer 3 is formed on the surface of anode body 1. Dielectric layer 3 is composed of, for example, a metal oxide. Examples of methods for forming a layer composed of a metal oxide on the surface of anode body 1 include immersing anode body 1 in a chemical conversion solution to anodic-oxidize the surface of anode body 1 and heating anode body 1 in an atmosphere containing oxygen. Dielectric layer 3 is not limited to a layer composed of the aforementioned metal oxides; any dielectric layer may be used as long as it has insulating properties.

[0054] (Cathode)

[0055] Cathode portion 7 includes solid electrolyte layer 4 and cathode layer 5 covering solid electrolyte layer 4 . Solid electrolyte layer 4 is formed so as to cover at least a portion of dielectric layer 3 .

[0056] The solid electrolyte layer 4 may be made of, for example, a manganese compound or a conductive polymer. Examples of the conductive polymer include polypyrrole, polythiophene, polyfuran, polyaniline, and polyacetylene. These may be used alone or in combination. Furthermore, the conductive polymer may be a copolymer of two or more monomers. For excellent conductivity, polythiophene, polyaniline, and polypyrrole may be used. In particular, for excellent hydrophobicity, polypyrrole may be used.

[0057] The solid electrolyte layer 4 containing the above-mentioned 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 above-mentioned 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, formation method (polymerization method), etc. of the conductive polymer used in each layer may be different.

[0058] It should be noted that, in this specification, polypyrrole, polythiophene, polyfuran, and polyaniline refer to polymers with polypyrrole, polythiophene, polyfuran, and polyaniline as their basic skeletons, respectively. Therefore, polypyrrole, polythiophene, polyfuran, and polyaniline may also include their respective derivatives. For example, polythiophene includes poly(3,4-ethylenedioxythiophene).

[0059] Various dopants may be added to the polymer solution, solution, or dispersion for forming the conductive polymer to improve the conductivity of the conductive polymer. The dopant is not particularly limited, and examples thereof include naphthalenesulfonic acid, p-toluenesulfonic acid, and polystyrenesulfonic acid.

[0060] 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 to 0.5 μm. When the average particle size D50 of the particles is within this range, the particles easily penetrate into the interior of the anode body 1 .

[0061] Cathode layer 5 includes, for example, a carbon layer 5a formed to cover solid electrolyte layer 4, and a metal paste layer 5b formed on the surface of carbon layer 5a. Carbon layer 5a comprises a conductive carbon material such as graphite and a resin. Metal paste layer 5b comprises, for example, metal particles (e.g., silver) and a resin. The configuration of cathode layer 5 is not limited to this. Any configuration of cathode layer 5 is acceptable as long as it has a current collecting function.

[0062] <Anode lead terminal>

[0063] 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, for example, a metal such as copper, or a non-metal. Its shape is not particularly limited as long as it is flat. From the perspective of thinning, the thickness of the anode lead terminal 13 (the distance between the main surfaces of the anode lead terminal 13) may be greater than 25 μm and less than 200 μm, or may be greater than 25 μm and less than 100 μm.

[0064] One end of the anode lead terminal 13 may be bonded to the anode wire 2 by a conductive adhesive or solder, or may be bonded to the anode wire 2 by resistance welding or laser welding. The other end of the anode lead terminal 13 is led outward from the outer casing 11 and exposed from the outer casing 11. The conductive adhesive may be, for example, a mixture of a thermosetting resin described later and carbon particles or metal particles.

[0065] <Cathode lead terminal>

[0066] Cathode lead terminal 14 is electrically connected to cathode portion 7 at joint portion 14a. Joint portion 14a is a portion of cathode lead terminal 14 that overlaps cathode layer 5 when cathode layer 5 and cathode lead terminal 14 joined thereto are viewed from the normal direction of cathode layer 5.

[0067] Cathode lead terminal 14 is bonded to cathode layer 5 via, for example, conductive adhesive 8. One end of cathode lead terminal 14, for example, constitutes a portion of bonding portion 14a and is disposed within exterior body 11. The other end of cathode lead terminal 14 is externally extended. Therefore, a portion of cathode lead terminal 14, including the other end, is exposed from exterior body 11.

[0068] The material of cathode lead terminal 14 is not particularly limited, as long as it is electrochemically and chemically stable and conductive. Cathode lead terminal 14 can be made of a metal such as copper, or a non-metallic material. Its shape is also not particularly limited, and for example, it can be a long, flat plate. To minimize thickness, the thickness of cathode lead terminal 14 can be between 25 μm and 200 μm, or between 25 μm and 100 μm.

[0069] <Exterior body>

[0070] The outer casing 11 is provided to electrically insulate the anode lead terminal 13 from the cathode lead terminal 14 and is made of an insulating material (outer casing material). The outer casing material may be, for example, a thermosetting resin. Examples of thermosetting resins include epoxy resins, phenolic resins, silicone resins, melamine resins, urea resins, alkyd resins, polyurethanes, polyimides, and unsaturated polyesters.

[0071] <<Method for Manufacturing Electrolytic Capacitor>>

[0072] Hereinafter, an example of a method for manufacturing the electrolytic capacitor according to this embodiment will be described.

[0073] A method for manufacturing an electrolytic capacitor is a method for manufacturing a solid electrolytic capacitor having a capacitor element, the 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 comprises the steps of preparing the 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. The anode body has a plurality of principal surfaces and a corner portion including a plurality of side portions and a vertex portion connecting the plurality of principal surfaces to each other. The step of preparing the anode body includes forming a curved surface at at least a portion of the corner portion or chamfering at least a portion of the corner portion.

[0074] (1) Anode body preparation process

[0075] As the anode body 1, a porous sintered body can be used. Valve metal particles and the anode wire 2 are placed in a mold in such a manner that the first part 2a is embedded in the valve metal particles, and after press-forming, sintering is performed to obtain the anode portion 6 of the anode body 1 comprising a porous body of valve metal. The first part 2a of the anode wire is embedded in the interior of the porous sintered body from one side. The pressure during press-forming is not particularly limited. Sintering is preferably performed under reduced pressure. A binder such as polyacrylic carbonate can be mixed into the valve metal particles as needed.

[0076] Valve action metal particles are typically press-formed and sintered using a mold having a rectangular interior space. In this case, the sintered anode body 1 is also in the shape of a rectangular parallelepiped, having multiple main faces. In this case, the multiple main faces are directly connected to each other to form edges and vertices, and the leading ends of the edges and / or vertices, i.e., the corners, that connect the multiple main faces are sharp.

[0077] Anode bodies with a sharp tip can be processed to form a curved surface at least partially at the corner portion, or at least partially at the corner portion can be chamfered. This removes the corner of the tip portion, allowing for a rounded shape, for example. Curving the corner portion can be achieved by, for example, shaving off a portion of the corner portion and removing the tip portion.

[0078] In the processing step of forming a curved surface or chamfering at least a portion of the corner portion, at least a portion of the corner portion can be formed at a high density. For example, by irradiating the corner portion with a laser, the corner portion is formed into a curved surface, and at least a portion of the corner portion can be formed at a high density. Alternatively, the anode body can be vibrated together with a vibrating member. During the vibration, the anode body, particularly the corner portion, collides with the vibrating member, compressing the corner portion, thereby forming a curved surface, and at least a portion of the corner portion can be formed at a high density.

[0079] It is also possible to create curved surfaces at the corners by irradiating them with laser light. By irradiating the corners with laser light, the corners melt, changing the tip from a sharp shape to a curved surface. The resulting molten layer is denser than the porous portion of the anode body and has extremely low porosity. This significantly improves the mechanical strength of the corners and effectively suppresses damage to the dielectric layer at the corners. The thickness of the molten layer can be, for example, 1 μm to 100 μm.

[0080] The laser used for laser irradiation is not limited, and for example, a YAG (Yttrium Aluminum Garnet) laser (wavelength: 1064 nm) can be used.

[0081] During formation of the solid electrolyte layer, from the perspective of facilitating the expulsion of air present in the pores of the anode body, it is preferred that the corner portions be irradiated with laser light, and that the main surface of the anode body adjacent to the corner portions be substantially not irradiated with laser light. It should be noted that the above description refers to not irradiating the majority of the main surface with laser light, and does not exclude irradiating a portion of the main surface (e.g., the area on the main surface adjacent to the corner portion) with laser light.

[0082] Laser irradiation can be performed on the sintered anode body or on the valve metal particles that have been press-formed before sintering. However, considering the deformation caused by volume shrinkage after sintering, it is preferable to irradiate the sintered anode body with laser.

[0083] When the anode body is vibrated together with the vibrating member, for example, the removal of the front end can be performed by placing the anode body on a base (vibrating member) having an uneven surface, such as a sieve (screen) or a file, and vibrating the base in the up-down and / or left-right directions. As the base vibrates, the anode body jumps and rolls on the base. As a result, a portion of the front end of the corner portion is cut off, forming a curved surface at the corner portion. However, most of the front end portion can remain in a compressed state on the surface of the corner portion without being cut off. As a result, the surface of the corner portion with a curved surface can be formed at a high density. A sieve can be used as the base because the residue scraped off the front end portion can easily fall downward and be removed, and the static friction coefficient is moderately small, making it easy to roll the anode body. The mesh of the sieve can be smaller than the minimum value of the outer diameter of the anode body so that the anode body does not fall through the opening of the sieve. The mesh of the sieve can be greater than 1 mm, or greater than 2 mm and less than 3.4 mm. When the mesh size is 1 mm or larger, it is easy to reduce the variation in the curvature radius R of the corner portion to a certain value or less.

[0084] Alternatively, the anode body may be placed on the dielectric particles and an external force may be applied to the dielectric particles so that the anode body and the dielectric particles are vibrated together. For example, the anode body and the dielectric particles may be mixed, and the anode body and the dielectric particles may be placed together in an oscillator, and the oscillator may be operated. The oscillator is preferably capable of applying vertical vibration in addition to horizontal vibration. The dielectric particles may include aluminum oxide particles, zirconium oxide particles, and the like. The particle size (average particle size) of the dielectric particles may be, for example, 0.1 mm to 3 mm, or 0.5 mm to 2 mm.

[0085] The dielectric particles, introduced into the oscillator along with the anode body, vibrate as the oscillator operates, causing them to collide with the anode body. The corners of the anode body, due to their low mechanical strength, are susceptible to deformation caused by collisions, and the porous portions at these corners are easily crushed and compressed. This allows for a high-density surface layer to be formed at these corners.

[0086] The density of the dielectric particles can be 0.15 to 0.4 times the density (true density) of the anode body. When the density of the dielectric particles is within this range, the energy generated by the collisions of the dielectric particles can be effectively utilized to compress and deform the corners. Furthermore, the percentage of corners that are chipped off due to collisions can be reduced.

[0087] The method of vibrating the dielectric particles while the anode body and dielectric particles are mixed together can form a curved surface or chamfer at the corners in a shorter time than the method of vibrating the sieve on which the anode body is placed. This makes it easier to reduce the variation in the curvature radius R at the corners.

[0088] When a vibrating member is used to curve or chamfer corners, it is preferable to curve or chamfer the corners of the porous body before sintering because sintering increases the mechanical strength and makes the corners less likely to be compressed.

[0089] By using a mold from which corners have been removed in advance, valve action metal particles are press-molded and sintered, an anode body having curved surfaces formed at the corners can be obtained.

[0090] (2) Dielectric layer formation process

[0091] Next, anode body 1 is subjected to a chemical conversion treatment, whereby at least a portion of anode body 1 is covered with dielectric layer 3. Specifically, anode body 1 is immersed in a chemical conversion tank filled with an electrolytic aqueous solution (e.g., an aqueous phosphoric acid solution), and second portion 2b of anode wire 2 is connected to the anode body of the chemical conversion tank to perform anodization. This allows dielectric layer 3, which is composed of an oxide film of the valve-acting metal, to be formed on the surface of the porous portion. The aqueous electrolytic solution is not limited to an aqueous phosphoric acid solution; nitric acid, acetic acid, sulfuric acid, and the like can be used.

[0092] (3) Solid electrolyte layer formation process

[0093] Next, at least a portion of dielectric layer 3 is covered with solid electrolyte layer 4. Thus, capacitor element 10 including anode body 1, dielectric layer 3, and solid electrolyte layer 4 is obtained.

[0094] The solid electrolyte layer 4 comprising 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 is formed with a monomer or 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 is formed with a solution or dispersion of the conductive polymer and drying it.

[0095] The solid electrolyte layer 4 can be formed, for example, by impregnating the anode body 1 formed with the dielectric layer 3 in a dispersion containing a conductive polymer, a binder and a dispersion medium, taking it out and drying it. The dispersion may contain a binder and / or conductive inorganic particles (for example, a conductive carbon material such as carbon black). In addition, a dopant may be contained in the conductive polymer. As the conductive polymer and the dopant, each can be selected from the substances exemplified for the solid electrolyte layer 4. A well-known binder can be used as the binder. The dispersion may contain a well-known additive used when forming the solid electrolyte layer.

[0096] Next, a carbon paste and a metal paste are sequentially applied 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 structure of the cathode layer 5 is not limited thereto, and any structure having a current collecting function may be used.

[0097] Next, the anode lead terminal 13 and the 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. Furthermore, after applying a conductive adhesive 8 to the cathode layer 5, the cathode lead terminal 14 is joined to the cathode portion 7 via the conductive adhesive 8.

[0098] Next, the materials for capacitor element 10 and outer casing 11 (e.g., uncured thermosetting resin and filler) are placed in a mold, and capacitor element 10 is sealed by transfer molding, compression molding, or the like. At this point, anode lead terminal 13 and cathode lead terminal 14 are partially exposed from the mold. Molding conditions are not particularly limited; time and temperature conditions can be appropriately set, taking into account the curing temperature of the thermosetting resin used.

[0099] Finally, the exposed portions of anode lead terminal 13 and cathode lead terminal 14 are bent along exterior body 11 to form bent portions. As a result, portions of anode lead terminal 13 and cathode lead terminal 14 are disposed on the mounting surface of exterior body 11 .

[0100] The electrolytic capacitor 20 is manufactured by the above method.

[0101] Figure 3 This is an electron microscope photograph showing a cross section of a corner portion of an anode body after laser irradiation. Figure 3 In the figure, the white portion contains valve metal (Ta), while the black portion is voids. It can be seen that the corners have curved surfaces, and the surface layer X of the curved corners is densely formed. Meanwhile, the interior of the surface layer X remains porous.

[0102] Industrial applicability

[0103] The present invention can be used in electrolytic capacitors, and can be suitably used in electrolytic capacitors using a porous body as an anode body.

[0104] The present invention has been described with respect to the presently preferred embodiments, but such disclosure should not be construed in a limiting sense. Upon reading the above disclosure, various modifications and variations will undoubtedly be apparent to those skilled in the art in the art to which the present invention belongs. Therefore, the attached technical solutions should be construed as including all modifications and variations without departing from the true spirit and scope of the present invention.

[0105] Description of Reference Numerals

[0106] 20: Electrolytic capacitor

[0107] 10: Capacitor components

[0108] 1: Anode

[0109] 2: Anode wire

[0110] 2a: Part 1

[0111] 2b: Part 2

[0112] 3: Dielectric layer

[0113] 4: Solid electrolyte layer

[0114] 5: Cathode layer

[0115] 5a: Carbon layer

[0116] 5b: Metal paste layer

[0117] 6: Anode

[0118] 7: Cathode

[0119] 8: Conductive adhesive material

[0120] 11: Exterior body

[0121] 13: Anode lead terminal

[0122] 14: Cathode lead terminal

[0123] 14a: Joint

[0124] 101A to 101C: Main surface of anode body

[0125] 102A~102C:Connection surface

[0126] 103A: Second connection surface

Claims

1. An electrolytic capacitor comprising a capacitor element, the capacitor element comprising: 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 anode body has a plurality of main faces and corner portions, The corner portion includes a plurality of side portions and a vertex portion connecting the plurality of main surfaces to each other, The surface layer X of at least a portion of the corner portion is denser than the surface layer Y of the main surface adjacent to the surface layer X. The porosity P1 in the surface layer X is smaller than the porosity P2 in the surface layer Y. Any portion of the surface layer X and any portion of the surface layer Y satisfy P2 / P1 of 5 or more.

2. The electrolytic capacitor according to claim 1, wherein At least a portion of the corner portion including the surface layer X has a curved shape or a chamfered shape.

3. The electrolytic capacitor according to claim 2, wherein The surface layer Y is adjacent to a portion of the corner portion having the curved shape or the chamfered shape.

4. The electrolytic capacitor according to claim 2, wherein Among the corner portions, the portion having the curved surface shape or the chamfered shape includes a portion having a curvature radius R of 20 μm to 500 μm.

5. The electrolytic capacitor according to claim 2, wherein The portion having the curved or chamfered shape in the corner portion includes portions having different curvature radii R, and a difference between a maximum value and a minimum value of the different curvature radii is 350 μm or less.

6. The electrolytic capacitor according to claim 1, wherein The surface layer X and the surface layer Y have portions satisfying a ratio P2 / P1 of the porosity P2 to the porosity P1 of 10 or more.

7. The electrolytic capacitor according to any one of claims 1 to 5, wherein The solid electrolyte layer includes a conductive polymer.

8. The electrolytic capacitor according to any one of claims 1 to 5, wherein The anode body is a sintered body of valve metal particles.

9. A method for manufacturing an electrolytic capacitor, comprising: manufacturing a solid electrolytic capacitor having a capacitor element, the capacitor element comprising 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 comprising: a step of preparing the anode body; covering at least a portion of the anode body with the dielectric layer; as well as a step of covering at least a portion of the dielectric layer with the solid electrolyte layer, The anode body has a plurality of main surfaces and a corner portion, wherein the corner portion includes a plurality of side portions and a vertex portion connecting the plurality of main surfaces to each other. The step of preparing the anode body includes irradiating at least a portion of the corner portion with a laser, wherein a surface layer X of at least a portion of the corner portion is denser than a surface layer Y of the main surface adjacent to the surface layer X, and a porosity P1 in the surface layer X is smaller than a porosity P2 in the surface layer Y. Any portion of the surface layer X and any portion of the surface layer Y satisfy P2 / P1 of 5 or more.

10. The method for manufacturing an electrolytic capacitor according to claim 9, wherein: At least a portion of the main surface of the anode body adjacent to the corner portion is not irradiated with the laser beam.

11. The method for manufacturing an electrolytic capacitor according to claim 9 or 10, wherein: The anode body is a sintered body of metal powder, The laser irradiation is performed after the metal powder is sintered.

12. A method for manufacturing an electrolytic capacitor, comprising: manufacturing a solid electrolytic capacitor having a capacitor element, the capacitor element comprising 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 comprising: a step of preparing the anode body; covering at least a portion of the anode body with the dielectric layer; as well as a step of covering at least a portion of the dielectric layer with the solid electrolyte layer, The anode body has a plurality of main surfaces and a corner portion, wherein the corner portion includes a side portion and a vertex portion connecting the plurality of main surfaces to each other. The step of preparing the anode body includes causing dielectric particles to collide with at least a portion of the corner portion, wherein a surface layer X of at least a portion of the corner portion is denser than a surface layer Y of the main surface adjacent to the surface layer X, and a porosity P1 in the surface layer X is smaller than a porosity P2 in the surface layer Y. Any portion of the surface layer X and any portion of the surface layer Y satisfy P2 / P1 of 5 or more.

13. The method for manufacturing an electrolytic capacitor according to claim 12, wherein: The average particle size of the medium particles is 0.1 mm to 3 mm.

14. A method for manufacturing an electrolytic capacitor, the method comprising manufacturing a solid electrolytic capacitor having a capacitor element, the capacitor element comprising 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 comprising: a step of preparing the anode body; covering at least a portion of the anode body with the dielectric layer; as well as a step of covering at least a portion of the dielectric layer with the solid electrolyte layer, The anode body has a plurality of main surfaces and a corner portion, wherein the corner portion includes a side portion and a vertex portion connecting the plurality of main surfaces to each other. The step of preparing the anode body includes vibrating the anode body together with a vibrating member, wherein a surface layer X of at least a portion of the corner portion is denser than a surface layer Y of the main surface adjacent to the surface layer X, and a porosity P1 in the surface layer X is smaller than a porosity P2 in the surface layer Y. Any portion of the surface layer X and any portion of the surface layer Y satisfy P2 / P1 of 5 or more.

15. The method for manufacturing an electrolytic capacitor according to claim 14, wherein: The vibrating component is a sieve.

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