Electrolytic capacitor and paste for forming conductive layer of electrolytic capacitor

Abstract

The electrolytic capacitor includes a capacitor element, wherein the capacitor element includes: an anode body, a dielectric layer covering at least a portion of the anode body, a solid electrolyte layer covering at least a portion of the dielectric layer, and a cathode lead layer covering at least a portion of the solid electrolyte layer. The cathode lead layer includes a conductive layer, and the oxygen permeability of the conductive layer is 7 cc / m when the thickness of the conductive layer is 10 μm. 2 ·day·atm or less.

Description

Technical Field

[0001] The present application relates to an electrolytic capacitor and a paste for forming a conductive layer of the electrolytic capacitor. Background Art

[0002] An electrolytic capacitor includes a capacitor element and an outer casing covering the capacitor element. As an example of an electrolytic capacitor, there is a solid electrolytic capacitor using a conductive polymer or the like as a solid electrolyte. In this case, the capacitor element includes: an anode body, a dielectric layer formed on the anode body, a solid electrolyte layer formed on the dielectric layer, and a cathode lead layer (carbon layer) formed on the solid electrolyte layer (for example, Patent Document 1).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2008-27998 Summary of the invention

[0006] An electrolytic capacitor according to one aspect of the present application includes a capacitor element, the capacitor element comprising: an anode body, a dielectric layer covering at least a portion of the anode body, a solid electrolyte layer covering at least a portion of the dielectric layer, and a cathode lead layer covering at least a portion of the solid electrolyte layer. The cathode lead layer includes a conductive layer, and the oxygen permeability of the conductive layer is 7 cc / m when the thickness of the conductive layer is 10 μm. 2 ·day·atm or less.

[0007] Another aspect of the present invention relates to a paste for forming a conductive layer of an electrolytic capacitor, comprising conductive carbon particles and a dispersion medium. The conductive layer formed using the paste has an oxygen permeability of 7 cc / m when the thickness is 10 μm. 2 ·day·atm or less.

[0008] According to the present application, it is possible to suppress an increase in the ESR of an electrolytic capacitor including a solid electrolyte layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a cross-sectional view schematically showing an electrolytic capacitor according to one embodiment of the present application. DETAILED DESCRIPTION

[0010] Before describing the embodiments, problems in the prior art are briefly described below.

[0011] For electrolytic capacitors with solid electrolyte layers, air (especially oxygen, or oxygen and moisture) sometimes penetrates the outer casing, and then penetrates the cathode lead layer and contacts the solid electrolyte layer, causing the conductive polymer contained in the solid electrolyte layer to deteriorate. Such degradation of conductive polymers is particularly significant under high temperature and / or high humidity. If the conductive polymer deteriorates, the resistance of the solid electrolyte layer increases, and the equivalent series resistance (ESR) of the electrolytic capacitor increases.

[0012] In view of the above problems, the present application provides an electrolytic capacitor including a solid electrolyte layer that suppresses an increase in ESR, an electrolytic capacitor, and a paste for forming a conductive layer of an electrolytic capacitor.

[0013] [Electrolytic capacitors]

[0014] The electrolytic capacitor according to the present embodiment includes a capacitor element, the capacitor element comprising: an anode body, a dielectric layer covering at least a portion of the anode body, a solid electrolyte layer covering at least a portion of the dielectric layer, and a cathode lead layer covering at least a portion of the solid electrolyte layer. The cathode lead layer includes a conductive layer, and the oxygen permeability of the conductive layer is 7 cc / m when the thickness of the conductive layer is 10 μm. 2 ·day·atm or less.

[0015] The oxygen permeability of the membrane is 7cc / m 2 The cathode lead-out layer, which is a conductive layer with high gas barrier properties of ·day·atm or less, covers the solid electrolyte layer, and the contact between the solid electrolyte layer and air is suppressed. The increase in ESR associated with the deterioration of the solid electrolyte layer caused by the above contact is suppressed.

[0016] The oxygen permeability of the conductive layer can be 4cc / m when the thickness is 10μm. 2 ·Day·Atm or less, 2.5cc / m 2 ·day·atm or less.

[0017] From the viewpoint of reducing ESR, the surface resistivity of the conductive layer may be 10 Ω / sq. to 200 Ω / sq., 15 Ω / sq. to 100 Ω / sq., or 15 Ω / sq. to 60 Ω / sq.

[0018] (Carbon material)

[0019] The conductive layer preferably comprises a granular carbon material (hereinafter also referred to as carbon particles) having conductivity. Hereinafter, the conductive layer comprising the carbon material is also referred to as a carbon layer. As the carbon material, for example, graphite, graphene, carbon black, soft carbon, hard carbon, etc. can be cited. As graphite, a material having a graphite-type crystal structure is used, which can be any of artificial graphite and natural graphite. As the carbon material, carbon nanotubes, carbon fibers, etc. can be used. The carbon material can be a fibrous carbon material such as carbon nanotubes and carbon fibers cut into appropriate lengths (also including crushed materials, etc.). These carbon materials can be used alone or in combination of two or more.

[0020] The carbon particles may include spherical particles, preferably flaky particles. In the case of flaky carbon particles, it is easy to fill the carbon particles in a layered overlapping state in the conductive layer. Using a densely formed conductive layer, it is easy to suppress air permeation in the conductive layer. As long as it is a flaky form, the type of carbon material constituting the particle is not particularly limited, and graphite, graphene, etc. are easily in a flaky form, and flaky particles are easy to obtain.

[0021] When the carbon particles include flaky particles, the average aspect ratio of the carbon particles may be 2 or more, or 3 or more. When the average aspect ratio of the carbon particles is in such a range, a large number of flat particles such as flaky particles are included, and it is easy to fill the carbon particles in a stacked state in the conductive layer. Therefore, by using a densely formed conductive layer, it is easy to suppress air permeation in the conductive layer. When the carbon particles include flaky particles, the upper limit of the aspect ratio of the carbon particles is, for example, 200.

[0022] The average aspect ratio of the carbon particles can be calculated as follows.

[0023] A scanning electron microscope (SEM) is used to obtain an image of a cross section of the conductive layer or carbon particles. From the obtained SEM image, any number of carbon particles (e.g., 10) are selected, and the maximum diameter D1 of each carbon particle is measured. Next, the maximum diameter D2 in a direction perpendicular to the maximum diameter D1 is measured. For each carbon particle, the ratio of D1 to D2 is calculated: D1 / D2 as the aspect ratio, and these are averaged to calculate the average aspect ratio.

[0024] From the viewpoint of improving gas barrier properties and reducing ESR, the average particle size of the carbon particles measured by dynamic light scattering is preferably 0.1 μm or more and 30 μm or less. When the average particle size of the carbon particles is 30 μm or less, it is easy to suppress the air permeation in the conductive layer. The contact area between the solid electrolyte layer and the carbon particles is increased, and it is easy to reduce the interface resistance between the solid electrolyte layer and the cathode lead layer (conductive layer). In addition, it is easy to densely fill the carbon particles in the conductive layer, and it is easy to ensure high conductivity. The average particle size of the carbon particles can be 0.1 μm or more and 25 μm or less.

[0025] From the perspective of cost, improvement of gas barrier properties, and reduction of ESR, when the carbon particles are flaky, the average particle size of the carbon particles is more preferably from 1 μm to 20 μm, further preferably from 1 μm to 15 μm, and particularly preferably from 1 μm to 10 μm.

[0026] For example, in the case of a conductive layer containing flaky carbon particles with an average particle size of 20 μm or less, the oxygen permeability can be reduced to 4 cc / m at a thickness of 10 μm. 2 ·day·atm or less. In this case, the surface resistivity of the conductive layer is, for example, 15Ω / sq. or more and 60Ω / sq. or less. In addition, in the case of a conductive layer containing flaky carbon particles with an average particle size of 15μm or less, the oxygen permeability can be reduced to 2.5cc / m when the thickness is 10μm. 2 ·day·atm or less.

[0027] The average particle size of the carbon particles can be obtained, for example, by obtaining a sample solution in which carbon particles are dispersed or a sample solution prepared by diluting a conductive layer forming paste described later, and measuring the sample solution using a particle size distribution measuring device (ELS-Z manufactured by Otsuka Electronics Co., Ltd.) by a dynamic light scattering method. The average particle size of the carbon particles is the 50% cumulative value (median particle size) in the scattering intensity distribution obtained by the dynamic light scattering method.

[0028] The cathode extraction layer may be a two-layer structure of a first conductive layer covering at least a portion of the solid electrolyte layer and a second conductive layer covering at least a portion of the first conductive layer. The first conductive layer may be a conductive layer (carbon layer) containing the above-mentioned carbon particles, and the second conductive layer may be a silver paste layer described later.

[0029] (First polymer)

[0030] In addition to the carbon material, the conductive layer may also contain a polymer having an acid group (hereinafter referred to as the first polymer) as an additive. The conductive polymer contained in the solid electrolyte layer is easily positively charged by hole doping. Specifically, for example, the -NH- group or -N= group contained in polypyrrole or polyaniline, or the -S- group contained in polythiophene, each easily changes to -NH 2 + -yl, -NH + = base, or -S += group. The acid group of the first polymer is bonded to these positively charged functional groups, so that the first polymer can be closely attached to the conductive polymer. In addition, the polymer chain of the first polymer is attached to the surface of the carbon particles in a tangled manner, so that the first polymer can be closely attached to the carbon particles. As a result, the adhesion between the carbon particles and the conductive polymer is improved by the first polymer. Therefore, the air permeation from the conductive layer to the solid electrolyte layer can be suppressed, and the increase in the ESR of the electrolytic capacitor caused by the deterioration of the conductive polymer can be further suppressed.

[0031] When the carbon particles include flaky particles, the first polymer is easily sandwiched between the overlapping flaky particles, and the conductive layer and the solid electrolyte layer are easily adhered to each other. Thus, it is easy to suppress air permeation from the conductive layer to the solid electrolyte layer, and it is easy to suppress the degradation of the conductive polymer contained in the solid electrolyte layer.

[0032] In addition, the first polymer is thermally stable compared to its monomer, so the adhesion between the carbon material and the conductive polymer is easily maintained at a high level even in a high temperature environment. Therefore, by including the first polymer, a high effect of suppressing the increase in ESR can be obtained even at high temperatures.

[0033] The acid group may include a sulfonic acid group (-SO 3 H), carboxyl group (-COOH), and at least one of their derivatives. The derivatives include anionic groups formed by the dissociation of protons from the acidic groups, salts of anionic groups and cations (e.g., sodium salts, etc.), and esters formed by the reaction of acidic groups with alcohols. The acidic groups are introduced into the monomers corresponding to the repeating units of the first polymer. The number of acidic groups contained in the first polymer can be 50 or more relative to 100 monomers, or can be 85 or more.

[0034] The content of the first polymer can be more than 1 mass part, more than 2 mass parts, more than 5 mass parts, or more than 10 mass parts relative to 100 mass parts of carbon material. By including more than 1 mass part of the first polymer relative to 100 mass parts of carbon material, the adhesion between the cathode lead layer (carbon layer) and the solid electrolyte layer is improved, and the ESR rise of the electrolytic capacitor can be suppressed. On the other hand, if the content of the first polymer is too large, the viscosity of the paste for forming the conductive layer increases. In addition, sometimes the resistance of the conductive layer becomes large, which will offset the effect of suppressing the rise of ESR. Therefore, in order not to damage the operability of the carbon paste based on coating, the content of the first polymer can be set to less than 5000 mass parts relative to 100 mass parts of carbon material. The content of the first polymer can be less than 1000 mass parts or less than 100 mass parts relative to 100 mass parts of carbon material.

[0035] The content of the first polymer may be 1 to 5000 parts by mass, 2 to 1000 parts by mass, 5 to 100 parts by mass, or 10 to 100 parts by mass based on 100 parts by mass of the carbon material.

[0036] The weight average molecular weight of the first polymer is, for example, in the range of 2,000 to 1,000,000. By using the first polymer having a molecular weight in such a range, the conductive layer and the solid electrolyte layer are closely attached, air permeation from the conductive layer to the solid electrolyte layer is reduced, and an increase in ESR can be suppressed.

[0037] As the first polymer, for example, as an example with a sulfonic group, a polymer having an aromatic sulfonic acid in a monomer structure and a polymer having an aliphatic sulfonic acid in a monomer structure can be utilized. As a polymer having an aromatic sulfonic acid in a monomer structure, polystyrene sulfonic acid, phenolsulfonic acid novolac resin, etc. can be cited. As a polymer having an aliphatic sulfonic acid in a monomer structure, polyvinyl sulfonic acid, polyallyl sulfonic acid, etc. can be cited. In addition, as an example of the first polymer with a carboxyl group (or its derivative), acrylic resins such as polyacrylic acid, polymethacrylic acid, polymethyl acrylate, polymethyl methacrylate, or polyethylene terephthalate, etc. can be cited. In addition, as the first polymer, polyacrylic acid ethyl sulfonic acid, polyacrylic acid butyl sulfonic acid, polymethacrylic acid sulfonic acid, poly-2-acrylamide-2-methylpropane sulfonic acid, etc. can be used.

[0038] (Second polymer)

[0039] In the conductive layer, in addition to the first polymer, a second polymer different from the first polymer may be included as an additive. The second polymer can synergistically improve the ESR rise suppression effect or enable the second polymer to have other functions. The second polymer may or may not have an acid group, similar to the first polymer.

[0040] The second polymer may be water-soluble. The water-soluble second polymer is easy to bond with other second polymers or the first polymer through hydrogen bonds, and it is easy to obtain a dense structure by utilizing hydrogen bonds within the molecular chain. Therefore, there is little space for diffusion of gases such as oxygen in the polymer, and it is difficult for gases to permeate through the polymer. Therefore, the use of the second polymer can further suppress the permeation of air from the conductive layer to the solid electrolyte layer, and can further suppress the increase in the ESR of the electrolytic capacitor.

[0041] Among water-soluble polymers, cellulose-based polymers and polyvinyl alcohol have high oxygen barrier properties and can therefore be preferably used as the second polymer. It should be noted that cellulose-based polymers include cellulose ethers and cellulose esters, such as carboxymethyl cellulose or hydroxyethyl cellulose, which are derivatives chemically modified from the hydroxyl group of glucose as a monomer constituting cellulose.

[0042] The weight average molecular weight of the second polymer is, for example, in the range of 2,000 to 1,000,000. The content of the second polymer is not limited, and for example, in consideration of operability, it may be 10 parts by mass or less relative to 100 parts by mass of the carbon material. As with the first polymer, the second polymer may have an acid group. The content of the second polymer may be 5 to 50 parts by mass, 5 to 35 parts by mass, 8 to 35 parts by mass, or 8 to 32 parts by mass relative to 100 parts by mass of the first polymer.

[0043] [Paste for forming a conductive layer of an electrolytic capacitor]

[0044] The conductive layer forming paste of the electrolytic capacitor according to the present embodiment contains conductive carbon particles and a dispersion medium. The conductive layer formed by using the paste containing conductive carbon particles (hereinafter also referred to as carbon paste) has a conductivity of 7 cc / m when the thickness is 10 μm. 2 Oxygen permeability of ·day·atm or less. The surface resistivity of the conductive layer formed using the above-mentioned paste may be 10 Ω / sq. or more and 200 Ω / sq. or less.

[0045] The oxygen permeability of the conductive layer was determined by the following method using a conductive layer forming paste.

[0046] A conductive layer-forming paste is applied to a polyethylene terephthalate (PET) film, and dried (cured) by heating at 130° C. for 30 minutes to form a conductive layer having a thickness of 10 μm. The oxygen permeability of the conductive layer formed on the PET film is determined using an oxygen permeability measuring device (e.g., a measuring device manufactured by Hitachi High-Tech Science Corporation). Specifically, the oxygen permeability of the laminate of the PET film and the conductive layer is measured, and the oxygen permeability of the conductive layer is determined by subtracting the oxygen permeability of the PET film from the measured value.

[0047] The surface resistivity of the conductive layer was determined by the following method using a conductive layer forming paste.

[0048] The conductive layer-forming paste was applied on a PET film using a bar coater and dried (cured) by heating at 130° C. for 30 minutes to form a conductive layer. The thickness of the conductive layer may be, for example, 10 μm. The surface resistivity of the formed conductive layer was measured by a four-probe method.

[0049] The conductive carbon particles can use the above-mentioned carbon particles contained in the conductive layer. As the dispersion medium, water, an organic medium, or a mixture thereof is used. The above-mentioned paste can contain additives and / or a binder as required. In the above-mentioned paste, as an additive, the above-mentioned first polymer can be contained, and the first polymer and the above-mentioned second polymer can also be contained simultaneously.

[0050] The binder is not particularly limited, and any known binder used in the preparation of the conductive layer may be used. For example, a polymer binder such as a thermoplastic resin (polyester resin, etc.) or a thermosetting resin (polyimide resin, epoxy resin, etc.) is preferred.

[0051] As the additive, in addition to the first polymer and the second polymer, known additives used in the preparation of the conductive layer may be used, for example, a dispersant, a surfactant, an antioxidant, a preservative, an alkali, and / or an acid.

[0052] Hereinafter, the structure of the electrolytic capacitor will be described in more detail with reference to the drawings as appropriate. Figure 1 This is a cross-sectional view schematically showing the structure of an electrolytic capacitor according to the present embodiment. In the example shown in the figure, an electrolytic capacitor 1 includes a capacitor element 2, a resin outer casing 3 that seals the capacitor element 2, and an anode lead terminal 4 and a cathode lead terminal 5, each of which has at least a portion exposed to the outside of the outer casing 3. The outer casing 3 has a substantially rectangular parallelepiped shape, and the electrolytic capacitor 1 also has a substantially rectangular parallelepiped shape.

[0053] Capacitor element 2 includes anode body 6 constituting an anode portion, dielectric layer 7 covering anode body 6 , and cathode portion 8 covering dielectric layer 7 .

[0054] The anode body 6 includes a region facing the cathode portion 8 and a region not facing the cathode portion 8. In the region of the anode body 6 not facing the cathode portion 8, an insulating separation layer 13 is formed in a band-shaped manner covering the surface of the anode body 6 in a portion adjacent to the cathode portion 8, thereby limiting the contact between the cathode portion 8 and the anode body 6. In the region of the anode body 6 not facing the cathode portion 8, another portion is electrically connected to the anode lead terminal 4 by welding. The cathode lead terminal 5 is electrically connected to the cathode portion 8 via an adhesive layer 14 formed of a conductive adhesive.

[0055] The cathode portion 8 includes a solid electrolyte layer 9 covering the dielectric layer 7 and a cathode lead layer 10 covering the solid electrolyte layer 9. The cathode lead layer 10 includes a carbon layer 11 and a silver paste layer 12. The carbon layer 11 is composed of the above-mentioned conductive layer. Therefore, even if air intrudes into the interior of the outer casing 3, the contact between the solid electrolyte layer 9 and the air can be suppressed, and the deterioration of the conductive polymer contained in the solid electrolyte layer 9 can be suppressed.

[0056] Hereinafter, the structure of the electrolytic capacitor will be described in more detail.

[0057] (Capacitor element 2)

[0058] Capacitor element 2 includes an anode body 6 constituting an anode portion, a dielectric layer 7 , and a cathode portion 8 including a solid electrolyte layer 9 . Cathode portion 8 includes solid electrolyte layer 9 and cathode extraction layer 10 covering solid electrolyte layer 9 .

[0059] The electrolytic capacitor only needs to include at least one capacitor element 2, and may include one capacitor element 2 or a plurality of capacitor elements. The number of capacitor elements included in the electrolytic capacitor may be determined according to the intended use.

[0060] (Anode 6)

[0061] The anode body 6 can include: a valve metal, an alloy containing a valve metal, and a compound containing a valve metal. These materials can be used alone or in combination of two or more. As the valve metal, for example, aluminum, tantalum, niobium, and titanium are preferably used. The anode body 6 having a porous surface can be obtained, for example, by roughening the surface of a substrate (a foil-shaped or plate-shaped substrate, etc.) containing a valve metal by etching or the like. In addition, the anode body 6 can also be a formed body of particles containing a valve metal or a sintered body thereof. It should be noted that the sintered body has a porous structure. That is, when the anode body 6 is a sintered body, the anode body 6 as a whole can be porous.

[0062] (Dielectric layer 7)

[0063] The dielectric layer 7 is formed by anodizing the valve metal on the surface of the anode body 6 by chemical conversion treatment or the like. The dielectric layer 7 may be formed so as to cover at least a portion of the anode body 6. The dielectric layer 7 is usually formed on the surface of the anode body 6. Since the dielectric layer 7 is formed on the porous surface of the anode body 6, it is formed along the inner wall surface of the pores and depressions (pits) on the surface of the anode body 6.

[0064] The dielectric layer 7 contains an oxide of a valve metal. For example, when tantalum is used as the valve metal, the dielectric layer contains Ta. 2 O 5 When aluminum is used as the valve metal, the dielectric layer contains Al 2 O 3 It should be noted that dielectric layer 7 is not limited thereto, and may function as a dielectric. When the surface of anode body 6 is porous, dielectric layer 7 is formed along the surface of anode body 6 (including the inner wall surface of the pores).

[0065] (Cathode portion 8)

[0066] The solid electrolyte layer 9 constituting the cathode portion 8 includes a conductive polymer and may further include a dopant, an additive, etc. as required. As the conductive polymer, for example, polypyrrole, polythiophene, polyaniline, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, and / or polythiophene vinylene, and derivatives thereof, etc. can be used.

[0067] (Solid Electrolyte Layer 9)

[0068] The solid electrolyte layer 9 can be formed, for example, by chemically polymerizing and / or electrolytically polymerizing a raw material monomer on the dielectric layer 7. Alternatively, it can be formed by bringing a solution in which a conductive polymer is dissolved or a dispersion in which a conductive polymer is dispersed into contact with the dielectric layer 7. The solid electrolyte layer 9 may be formed so as to cover at least a portion of the dielectric layer 7.

[0069] (Cathode extraction layer 10)

[0070] Cathode lead layer 10 constituting cathode portion 8 includes carbon layer 11 and silver paste layer 12 . Cathode lead layer 10 is formed so as to cover at least a portion of solid electrolyte layer 9 .

[0071] (Carbon layer 11)

[0072] The carbon layer 11 includes the above-mentioned carbon particles and, if necessary, may include a binder and / or an additive, etc. The carbon layer 11 may include the above-mentioned first polymer as an additive, or may include both the above-mentioned first polymer and the second polymer.

[0073] The average thickness of the carbon layer 11 is, for example, 0.01 μm to 50 μm. The average thickness can be determined by measuring the thickness of a plurality of locations (for example, 10 locations) of the carbon layer 11 in a cross-sectional SEM image of the carbon layer 11 and averaging the measured thicknesses.

[0074] As the binder and additive contained in the carbon layer 11, known components used in the carbon layer of the electrolytic capacitor can be used without particular limitation. The carbon layer 11 may contain a metal element such as silver.

[0075] (Silver paste layer 12)

[0076] The silver paste layer 12 includes, for example, silver particles and a binder. The silver particles may contain other metal elements. The content of the other metal elements in the silver particles is preferably 0.1 mass % or less.

[0077] The silver content in silver paste layer 12 is, for example, greater than 50% by mass, preferably 70% by mass or more. When the silver content is within this range, high conductivity of silver paste layer 12 can be ensured, thereby improving current collection from capacitor element 2.

[0078] The binder contained in the silver paste layer 12 is not particularly limited, but a cured product of a curable resin is preferred. Examples of the curable resin include thermosetting resins such as epoxy resins.

[0079] The silver paste layer 12 may contain additives and the like as necessary. Examples of the additives include known substances used in the silver paste layer. The silver paste layer 12 may contain the above-mentioned first polymer and / or second polymer.

[0080] (Exterior body 3)

[0081] External package 3 covers capacitor element 2. Usually, part of lead terminals 4 and 5 are also covered by external package 3. External package 3 is formed by sealing capacitor element 2 and part of lead terminals 4 and 5 with a resin material.

[0082] The outer casing 3 preferably contains a cured product of a curable resin composition, and may contain a thermoplastic resin or a composition containing a thermoplastic resin. As the curable resin composition and the thermoplastic resin (composition), those described below can be used.

[0083] For the outer casing 3 formed of a resin material, the resin material is easily degraded or easily damaged by mechanical impact, and the external air easily penetrates the outer casing 3 and intrudes into the outer casing. According to this embodiment, the gas barrier property of the cathode lead layer is high, and when the outer casing 3 formed of a resin material is used, the contact between the solid electrolyte layer 9 and the air can also be suppressed.

[0084] (Lead terminals 4, 5)

[0085] One end of the lead terminal 4, 5 is electrically connected to the capacitor element 2, and the other end is led out to the outside of the outer casing 3. In the electrolytic capacitor 1, one end side of the lead terminal 4, 5 is covered by the outer casing 3 together with the capacitor element 2. As the lead terminal 4, 5, the lead terminal used in the electrolytic capacitor can be used without particular limitation, for example, the lead terminal called the lead frame can be used. As the raw material of the lead terminal 4, 5, for example, metals such as copper or alloys thereof can be cited.

[0086] [Method for manufacturing electrolytic capacitor]

[0087] The above-mentioned electrolytic capacitor is manufactured by a manufacturing method including the following steps: a step of forming a dielectric layer in a manner covering at least a portion of the anode body, a step of forming a solid electrolyte layer in a manner covering at least a portion of the dielectric layer, and a step of forming a cathode lead layer on at least a portion of the solid electrolyte layer. The step of forming the cathode lead layer includes, for example, a step of forming a carbon layer, and a step of forming a silver paste layer on at least a portion of the carbon layer. The manufacturing method of the electrolytic capacitor may further include a step of preparing the anode body before the step of forming the dielectric layer. In addition, the manufacturing method of the electrolytic capacitor may further include a step of electrically connecting the lead terminal to the capacitor element, and a step of covering the capacitor element and a portion of the lead terminal with an outer casing (sealing step).

[0088] Hereinafter, each step will be described in more detail.

[0089] (Step of Preparing Anode Body 6)

[0090] In this step, anode body 6 constituting the anode portion is formed by a known method depending on the type of anode body 6 .

[0091] Anode body 6 can be prepared, for example, by roughening the surface of a foil or plate-shaped substrate containing a valve metal. Roughening can be performed by forming irregularities on the substrate surface, for example, by etching the substrate surface (for example, electrolytic etching).

[0092] In addition, without being limited to the above, the valve-acting metal powder is formed into a desired shape (for example, a block shape) to obtain a formed body. The formed body can be sintered to form the anode body 6 having a porous structure.

[0093] (Step of Forming Dielectric Layer 7)

[0094] In this process, a dielectric layer 7 is formed on the anode body 6. The dielectric layer 7 is formed by anodizing the anode body 6. Anodization can be performed by a known method, such as a chemical conversion treatment. The chemical conversion treatment can be performed, for example, by immersing the anode body 6 in a chemical conversion solution, allowing the chemical conversion solution to penetrate the surface of the anode body 6, and applying a voltage between the anode body 6 and a cathode immersed in the chemical conversion solution. As the chemical conversion solution, for example, a phosphoric acid aqueous solution is preferably used.

[0095] (Step of Forming Solid Electrolyte Layer 9)

[0096] In this process, a solid electrolyte layer 9 is formed on the dielectric layer 7. The solid electrolyte layer 9 is formed, for example, by electrolytically polymerizing a raw material monomer of a conductive polymer on the dielectric layer 7. The anode body 6 formed with the dielectric layer 7 is immersed in a polymerization solution prepared by premixing the raw material monomer and the dopant and then adding a solvent, and in the polymerization solution, an electrode for polymerization initiation is brought close to the surface of the anode body 6, a cathode is arranged at a position away from the anode body 6 and opposite to it, and a voltage is applied between the electrode for polymerization initiation and the cathode to perform electrolytic polymerization. The raw material monomer can be, for example, pyrrole, thiophene, aniline, acetylene, phenylene, phenylene vinylene, acene, and / or thiophene vinylene, and derivatives thereof. The solvent can be, for example, water, an organic solvent, or a mixture thereof.

[0097] In addition, a treatment liquid containing a conductive polymer can be attached to the anode body 6 formed with the dielectric layer 7, and then dried to form a solid electrolyte layer 9. The treatment liquid may also contain other components such as a dopant. For example, poly (3, 4-ethylenedioxythiophene) (PEDOT) is used as the conductive polymer. For example, polystyrene sulfonic acid (PSS) is used as the dopant. The treatment liquid is, for example, a dispersion or solution of the conductive polymer. As the dispersion medium (solvent), for example, water, an organic solvent, or a mixture thereof can be cited. The solid electrolyte layer 9 can be formed by chemically polymerizing the raw material monomers of the conductive polymer on the dielectric layer 7.

[0098] (Step of Forming Cathode Leading Layer 10)

[0099] In this step, the carbon layer 11 and the silver paste layer 12 are sequentially stacked on the solid electrolyte layer 9 , thereby forming the cathode lead layer 10 .

[0100] (Step of Forming Carbon Layer 11)

[0101] In this step, the conductive layer forming paste (carbon paste) is attached to at least a portion of solid electrolyte layer 9 to form carbon layer 11. Carbon layer 11 may be formed by further heating the carbon paste coating formed on at least a portion of solid electrolyte layer 9.

[0102] The carbon layer 11 can be formed by attaching a carbon paste to at least a portion of the solid electrolyte layer 9 to form a coating and drying the coating. The coating may be further heated after formation. The temperature when heating the carbon paste coating is, for example, 150° C. to 300° C.

[0103] The carbon paste may be brought into contact with solid electrolyte layer 9 . For example, anode body 6 including solid electrolyte layer 9 may be immersed in the carbon paste, or the carbon paste may be applied to the surface of solid electrolyte layer 9 using a known coater or the like.

[0104] (Step of Forming Silver Paste Layer 12)

[0105] In this process, a silver paste layer 12 is formed on at least a portion of the carbon layer 11. The silver paste layer 12 can be formed by attaching a silver paste to at least a portion of the carbon layer 11. The silver paste can contain silver particles, a binder, a dispersion medium, and additives as required. As for the silver particles, the binder, and the additive, reference can be made to the description of the silver paste layer 12. The silver paste can also contain the first polymer and / or the second polymer. As the dispersion medium, water, an organic medium, and a mixture thereof can be cited.

[0106] The silver paste layer 12 can be formed by drying and / or heating a coating of the silver paste formed on at least a portion of the carbon layer 11. For example, when a thermosetting resin is used as a binder, the silver paste layer 12 is formed by heating the coating of the silver paste to cure the binder.

[0107] (Lead terminal connection process)

[0108] In this process, the anode lead terminal 4 and the cathode lead terminal 5 are electrically connected to the capacitor element 2. The connection of each lead terminal can be performed after the capacitor element 2 is manufactured. The connection of the cathode lead terminal 5 to the capacitor element 2 is performed after the capacitor element 2 is manufactured, but the connection of the anode lead terminal 4 to the anode body 6 can be performed at an appropriate stage of the process of manufacturing the capacitor element 2. For example, in the case of forming an anode body with a porous structure by sintering, a molded body formed into a desired shape is obtained in a state where one end of the anode lead terminal in the longitudinal direction of a rod-shaped body is buried in the powder of a valve-acting metal. Then, the molded body can be sintered to form an anode body with a porous structure in which one end of the anode lead terminal is buried.

[0109] When a stack of multiple capacitor elements is used, anode lead terminal 4 can be connected to anode body 6 in the same manner as described above. Cathode lead terminal 5 can be connected to the capacitor element in the same manner as described above, or one end of cathode lead terminal 5 can be connected to a stack of multiple capacitor elements that electrically connect cathode portions 8 to each other.

[0110] (Sealing process)

[0111] In this step, capacitor element 2 and a part of lead terminals 4 and 5 are covered with outer package 3, thereby sealing capacitor element 2 with outer package 3. More specifically, capacitor element 2 and lead terminals 4 and 5 can be sealed by covering a part of capacitor element 2 and lead terminals 4 and 5 with a resin constituting the resin outer package after capacitor element 2 and lead terminals 4 and 5 are electrically connected.

[0112] The outer casing 3 can be formed using a molding technique such as injection molding, insert molding, and compression molding. The outer casing 3 can be formed, for example, by filling a curable resin composition or a thermoplastic resin (composition) to a predetermined position using a predetermined mold so as to cover the capacitor element 2 and one end of the lead terminals 4 and 5. In the case of a laminate of multiple capacitor elements, it is sufficient to form a resin outer casing so as to cover a portion of the laminate and the lead terminals.

[0113] In addition to the curable resin, the curable resin composition may also contain a filler, a curing agent, a polymerization initiator, and / or a catalyst, etc. As the curable resin, for example, epoxy resins, phenolic resins, urea resins, polyimides, polyamide-imides, polyurethanes, diallyl phthalate, unsaturated polyesters, etc. can be cited. The curable resin composition may contain a variety of curable resins.

[0114] As fillers, for example, insulating particles (inorganic, organic) and / or fibers are preferred. As insulating materials constituting the fillers, for example, insulating compounds (oxides, etc.) such as silica and alumina, glass, mineral materials (talc, mica, clay, etc.) and the like can be cited. The resin casing may contain one of the above-mentioned fillers, or a combination of two or more thereof. The content of the filler in the resin casing is, for example, 10 to 90% by mass.

[0115] As the thermoplastic resin, for example, polyphenylene sulfide (PPS), polybutylene terephthalate (PBT), etc. can be used. The composition containing the thermoplastic resin may contain the above-mentioned filler and the like in addition to the thermoplastic resin.

[0116] [Example]

[0117] Hereinafter, the present application will be described in more detail based on examples, but the present application is not limited to the following examples.

[0118] 《Examples 1 to 5》

[0119] Follow the steps below to make Figure 1 The electrolytic capacitor 1 shown was manufactured and its characteristics were evaluated.

[0120] (1) Fabrication of capacitor elements

[0121] Aluminum foil (thickness 100 μm) was prepared as a substrate, and the surface of the aluminum foil was etched to obtain an anode body 6. The anode body 6 was immersed in a phosphoric acid solution (liquid temperature 70° C.) with a concentration of 0.3 mass %, and a DC voltage of 70 V was applied for 20 minutes, thereby forming a layer of aluminum oxide (Al2O3) on the surface of the anode body 6. 2 O 3) dielectric layer 7. Thereafter, an insulating anti-corrosion tape (separation layer 13) is attached to a predetermined portion of the anode body 6.

[0122] The anode body 6 and the counter electrode formed with the dielectric layer 7 are immersed in a polymerization solution containing pyrrole as a raw material monomer of the conductive polymer, and electrolytic polymerization is performed at a polymerization solution temperature of 25° C. and a polymerization voltage of 3 V, and the film-like polymer formed on the dielectric layer 7 is washed with water. In this way, a solid electrolyte layer 9 containing polypyrrole is formed on the dielectric layer 7.

[0123] The carbon material, the first polymer, and the second polymer are dispersed in water to obtain a carbon paste, and the pH of the carbon paste is adjusted to 5 using aqueous ammonia.

[0124] The carbon material used was a powder of flaky natural graphite having an average particle size shown in Table 1. It should be noted that the above average particle size was obtained by the method described above. In addition, for the powder of flaky natural graphite having an average particle size shown in Table 1, the average aspect ratio obtained by the method described above was 2 or more.

[0125] The first polymer is phenolsulfonic acid novolac resin (weight average molecular weight 30,000). The phenolsulfonic acid novolac resin is a sodium salt having 100 acid groups (sulfonic groups) per 100 monomers. The second polymer is carboxymethyl cellulose (CMC) (weight average molecular weight 100,000). The CMC is an ammonium salt having 30 acid groups (carboxyl groups) per 100 monomers.

[0126] The ratio of the carbon material in the carbon paste is set to 5 mass parts. The content of the phenolsulfonic acid phenolic resin in the carbon paste is set to 25 mass parts relative to 100 mass parts of the carbon material. The content of CMC in the carbon paste is set to 8 mass parts relative to 100 mass parts of the carbon material. In Table 1, the carbon pastes of Examples 1 to 5 are a1 to a5, respectively. The carbon paste of Comparative Example 1 is b1.

[0127] After the carbon paste is applied to the solid electrolyte layer 9, it is heated at 200°C to form a carbon layer 11 (the thickness of the central part of the element is 7 to 10 μm) on the surface of the solid electrolyte layer. Next, a silver paste containing silver particles and a binder resin (epoxy resin) is applied to the surface of the carbon layer 11, and then heated to cure the binder resin to form a silver paste layer 12. In this way, a cathode extraction layer 10 composed of the carbon layer 11 and the silver paste layer 12 is formed.

[0128] By operating as described above, capacitor element 2 is obtained.

[0129] (2) Assembly of electrolytic capacitors

[0130] An electrolytic capacitor was prepared by further placing an anode lead terminal 4, a cathode lead terminal 5, and an adhesive layer 14 on the capacitor element 2, and forming an outer casing 3 using a resin containing silica particles as a filler. In Table 1, the electrolytic capacitors of Examples 1 to 5 are A1 to A5, respectively. The electrolytic capacitor of Comparative Example 1 is B1.

[0131] 《Examples 6-7》

[0132] Carbon pastes a6 to a7 of Examples 6 to 7 were obtained by the same method as the carbon paste a1 of Example 1, except that spherical natural graphite powder having an average particle size shown in Table 1 was used instead of the flaky natural graphite powder. Electrolytic capacitors A6 to A7 of Examples 6 to 7 were obtained by the same method as the electrolytic capacitor A1 of Example 1, except that carbon pastes a6 to a7 were used instead of the carbon paste a1.

[0133] 《Example 8》

[0134] Carbon paste a8 of Example 8 was obtained by the same method as that of carbon paste a1 of Example 1, except that a mixed powder of flaky natural graphite powder (average particle size 20 μm) and spherical natural graphite powder (average particle size 20 μm) was used instead of the flaky natural graphite powder (mass ratio 1:1). Electrolytic capacitor A8 of Example 8 was obtained by the same method as that of electrolytic capacitor A1 of Example 1, except that carbon paste a8 was used instead of carbon paste a1.

[0135] 《Examples 9-11》

[0136] Carbon pastes a9 to a11 of Examples 9 to 11 were obtained by the same method as the carbon pastes a1 to a3 of Examples 1 to 3 except that the first polymer and the second polymer were not added. Electrolytic capacitors A9 to A11 of Examples 9 to 11 were obtained by the same method as the electrolytic capacitors A1 to A3 of Examples 1 to 3 except that the carbon pastes a9 to a11 were used instead of the carbon pastes a1 to a3.

[0137] 《Examples 12-13》

[0138] Carbon pastes a12 to a13 of Examples 12 to 13 were obtained by the same method as the carbon pastes a1 to a2 of Examples 1 to 2 except that the second polymer was not added. Electrolytic capacitors A12 to A13 of Examples 12 to 13 were obtained by the same method as the electrolytic capacitors A1 to A2 of Examples 1 to 2 except that the carbon pastes a12 to a13 were used instead of the carbon pastes a1 to a2.

[0139] [Evaluation of carbon layer]

[0140] Using the carbon pastes of Examples and Comparative Examples prepared above, the oxygen permeability and surface resistivity of the carbon layer were determined by the methods described above.

[0141] [Evaluation of electrolytic capacitors]

[0142] The following evaluations were performed using the electrolytic capacitors of Examples and Comparative Examples produced as described above.

[0143] (Initial Characteristics)

[0144] In an environment of 20°C, use a 4-terminal LCR meter to measure the ESR value (mΩ) of the electrolytic capacitor at a frequency of 100kHz as the initial ESR value (X 0 )(mΩ).

[0145] (Heat resistance)

[0146] Next, the electrolytic capacitor was left in an environment of 125° C. for 1000 hours. The ESR value (X 1 Then, the rate of change of ESR R1 is calculated from the following formula.

[0147] ESR change rate R1 = X 1 / X 0

[0148] (moisture resistance)

[0149] In addition, the electrolytic capacitor was placed in an environment of temperature 60°C and humidity 90% for 500 hours. The ESR value (X 2 Then, the rate of change of ESR R2 is calculated by the following formula.

[0150] ESR change rate R2 = X 2 / X 0

[0151] The evaluation results are shown in Table 1. In Table 1, the initial ESR is expressed as a relative value when the initial ESR of the electrolytic capacitor B1 of Comparative Example 1 is set to 100.

[0152] [Table 1]

[0153]

[0154] The carbon layer obtained by using the carbon pastes a1 to a13 had a surface resistivity of more than 10 Ω / sq. and less than 200 Ω / sq., and an oxygen permeability of 7 cc / m 2·day·atm or less. Electrolytic capacitors A1 to A13 have smaller initial ESR, smaller change rates R1 and R2, and improved heat resistance and moisture resistance than electrolytic capacitor B1.

[0155] For electrolytic capacitors A1 to A3 to which the first polymer and the second polymer are added, the heat resistance and moisture resistance are further improved compared to electrolytic capacitors A9 to A11 to which the first polymer and the second polymer are not added. For electrolytic capacitors A12 to A13 to which the first polymer is added, the heat resistance is greatly improved compared to electrolytic capacitors A9 to A10 to which the first polymer is not added. For electrolytic capacitor A5 using scaly carbon particles, the oxygen permeability is further reduced compared to electrolytic capacitor A6 using spherical carbon particles.

[0156] The carbon layer obtained using carbon paste b1 has a high oxygen permeability of 8.1 cc / m 2 ·day·atm, the heat resistance and moisture resistance of the electrolytic capacitor B1 decreased. In addition, the average particle size of the carbon particles contained in the carbon layer was large, 40 μm, and the interface resistance between the carbon layer and the solid electrolyte layer increased, and the initial ESR of the electrolytic capacitor B1 increased.

[0157] Industrial Applicability

[0158] The electrolytic capacitor of the present application can suppress the degradation of the conductive polymer contained in the solid electrolyte layer and suppress the increase of ESR even when exposed to a high temperature atmosphere or a high humidity atmosphere. Therefore, it can be used in various applications requiring low ESR.

[0159] Description of Reference Numerals

[0160] 1: electrolytic capacitor, 2: capacitor element, 3: outer casing, 4: anode lead terminal, 5: cathode lead terminal, 6: anode body, 7: dielectric layer, 8: cathode part, 9: solid electrolyte layer, 10: cathode lead layer, 11: carbon layer, 12: silver paste layer, 13: separation layer, 14: adhesive layer

Claims

1. An electrolytic capacitor comprising a capacitor element, the capacitor element comprising: an anode body, a dielectric layer covering at least a portion of the anode body, a solid electrolyte layer covering at least a portion of the dielectric layer, and a cathode lead layer covering at least a portion of the solid electrolyte layer, The cathode lead-out layer comprises a conductive layer, The conductive layer comprises conductive carbon particles, a polymer having an acid group as a first polymer, and a second polymer different from the first polymer, wherein the acid group comprises at least one selected from a sulfonic group, a carboxyl group, and derivatives thereof, and the second polymer comprises at least one selected from a cellulose-based polymer and polyvinyl alcohol. The oxygen permeability of the conductive layer when the thickness is 10 μm is 7 cc / m 2 ·day·atm or less.

2. The electrolytic capacitor according to claim 1, wherein: The conductive layer has a surface resistivity of 10 Ω / sq. or more and 200 Ω / sq. or less.

3. The electrolytic capacitor according to claim 1, wherein: The average particle size of the carbon particles measured by a dynamic light scattering method is 0.1 μm or more and 30 μm or less.

4. The electrolytic capacitor according to claim 1 or 2, wherein: The carbon particles include flaky particles.

5. A paste for forming a conductive layer of an electrolytic capacitor, comprising conductive carbon particles, a polymer having an acid group as a first polymer, a second polymer different from the first polymer, and a dispersion medium, The acid group includes at least one selected from a sulfonic group, a carboxyl group, and derivatives thereof, and the second polymer includes at least one selected from a cellulose-based polymer and polyvinyl alcohol. The oxygen permeability of the conductive layer formed using the paste when the thickness was 10 μm was 7 cc / m 2 ·day·atm or less.

6. The paste for forming a conductive layer of an electrolytic capacitor according to claim 5, wherein The conductive layer has a surface resistivity of 10 Ω / sq. or more and 200 Ω / sq. or less.

7. The paste for forming a conductive layer of an electrolytic capacitor according to claim 5 or 6, wherein The average particle size of the carbon particles measured by a dynamic light scattering method is 0.1 μm or more and 30 μm or less.

8. The conductive layer forming paste for an electrolytic capacitor according to claim 5 or 6, wherein The carbon particles include flaky particles.

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