Method for manufacturing an electrolytic capacitor, and method for evaluating a conductive polymer layer.

Abstract

To provide a manufacturing method of electrolytic capacitor capable of improving performance while reducing manufacturing defects by washing the conductive polymer layer as a solid electrolyte layer under appropriate washing conditions.SOLUTION: The manufacturing method of an electrolytic capacitor has a step of forming a solid electrolyte layer including a conductive polymer on the surface of the anode body on which a dielectric layer is formed. The solid electrolyte layer forming step includes: a step of forming a first conductive polymer layer; and a cleaning step of cleaning an anode body formed with the first conductive polymer layer under predetermined cleaning conditions. The cleaning conditions are determined so that the measured electrical conductivity falls within a predetermined range when the cleaned anode body is immersed in a solvent and when the electrical conductivity of the solvent is measured.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an electrolytic capacitor and a method for evaluating a conductive polymer layer constituting a solid electrolyte layer of an electrolytic capacitor.

Background Art

[0002] Electrolytic capacitors are mounted in various electronic devices because they have a small equivalent series resistance (ESR) and excellent frequency characteristics. An electrolytic capacitor usually includes a capacitor element having an anode portion and a cathode portion. The anode portion includes a porous anode body, and a dielectric layer is formed on the surface of the anode body. The dielectric layer contacts an electrolyte. There is an electrolytic capacitor using a solid electrolyte such as a conductive polymer as the electrolyte (see, for example, Patent Document 1).

[0003] Patent Document 2 describes a step of forming a dielectric film on the surface of an anode body, a step of forming a conductive polymer layer on the dielectric film by polymerizing a precursor of a polymer constituting the conductive polymer layer on the dielectric film, a step of washing the conductive polymer layer with a solvent, a step of drying the washed conductive polymer layer under atmospheric pressure to remove the solvent, and then a step of drying the conductive polymer layer under a reduced pressure lower than atmospheric pressure.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Patent Document 2 states that by cleaning a conductive polymer layer formed by polymerization on a dielectric film using a solvent, unwanted precursors and oxidizing agents that adhered to the conductive polymer layer during polymerization can be removed, resulting in a high-performance electrolytic capacitor. However, it does not specifically suggest how to control the cleaning conditions when cleaning the conductive polymer layer.

[0006] For example, the longer the cleaning time, the more unwanted precursors and oxidizing agents contained in the conductive polymer layer are removed, which can contribute to improving the performance of the electrolytic capacitor. On the other hand, the longer the cleaning time, the more essential components contained in the conductive polymer layer may also be removed, or the more the conductive polymer deteriorates, so depending on the cleaning conditions, it may not lead to an improvement in the performance of the electrolytic capacitor.

[0007] Based on the above, the present invention aims to provide guidelines for determining cleaning conditions when cleaning a conductive polymer layer in the manufacture of electrolytic capacitors, thereby reducing manufacturing defects and improving the performance of electrolytic capacitors. [Means for solving the problem]

[0008] In view of the above, one aspect of the present disclosure relates to a method for manufacturing an electrolytic capacitor comprising: a porous anode body; a dielectric layer formed on the surface of the anode body; a solid electrolyte layer covering at least a portion of the dielectric layer; and a cathode layer covering at least a portion of the solid electrolyte layer, the method comprising the step of forming the solid electrolyte layer containing a conductive polymer on the surface of the anode body on which the dielectric layer is formed, wherein the step of forming the solid electrolyte layer includes the step of forming a first conductive polymer layer and the step of cleaning the anode body on which the first conductive polymer layer is formed under predetermined cleaning conditions, the cleaning conditions being determined such that when the anode body after cleaning is immersed in a solvent and the electrical conductivity of the solvent is measured, the measured electrical conductivity falls within a predetermined range.

[0009] Another aspect of the present disclosure relates to a method for evaluating a conductive polymer layer constituting a solid electrolyte layer in the manufacture of an electrolytic capacitor comprising a porous anode, a dielectric layer formed on the surface of the anode, a solid electrolyte layer covering at least a portion of the dielectric layer, and a cathode layer covering at least a portion of the solid electrolyte layer, the method comprising: a cleaning step of cleaning the anode on which the conductive polymer layer is formed; and a step of immersing the cleaned anode in a solvent and measuring the electrical conductivity of the solvent. [Effects of the Invention]

[0010] In the manufacturing of electrolytic capacitors, the cleaning conditions in the cleaning process of the conductive polymer layer can be appropriately determined, thereby reducing manufacturing defects in electrolytic capacitors and improving their performance. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic cross-sectional view showing an example of a capacitor element of an electrolytic capacitor manufactured by a manufacturing method according to one embodiment of the present disclosure. [Figure 2] This is a schematic cross-sectional view showing an electrolytic capacitor manufactured by a manufacturing method according to one embodiment of the present disclosure. [Figure 3] This flowchart shows an example of the process for forming a fixed electrolyte layer in the manufacturing method of an electrolytic capacitor according to this embodiment. [Figure 4] This graph shows an example of the change in electrical conductivity of pure water over time after an anode body with a conductive polymer layer formed on it is immersed in pure water. [Modes for carrying out the invention]

[0012] A method for manufacturing an electrolytic capacitor according to one embodiment of the present disclosure comprises a porous anode body, a dielectric layer formed on the surface of the anode body, a solid electrolyte layer covering at least a portion of the dielectric layer, and a cathode layer covering at least a portion of the solid electrolyte layer, the method for manufacturing an electrolytic capacitor comprising the step of forming a solid electrolyte layer containing a conductive polymer on the surface of the anode body on which the dielectric layer is formed.

[0013] The solid electrolyte layer formation step includes a step of forming a first conductive polymer layer and a cleaning step of cleaning the anode body on which the first conductive polymer layer has been formed under predetermined cleaning conditions.

[0014] By providing a cleaning step to clean the anode body on which the first conductive polymer layer is formed, unwanted components adhering to the first conductive polymer layer are removed, improving the performance of the electrolytic capacitor, such as its voltage withstand characteristics.

[0015] The amount of unwanted components removed during the cleaning process depends on the cleaning conditions (type of cleaning solution, temperature of the cleaning solution, volume or flow rate, cleaning time, etc.). Generally, longer cleaning times and larger amounts of cleaning solution used can remove more unwanted components, thereby improving the performance of the electrolytic capacitor. However, on the other hand, longer cleaning times and larger amounts of cleaning solution also tend to remove necessary components that make up the first conductive polymer layer, and the degradation of the first conductive polymer layer also accelerates. To achieve high-performance electrolytic capacitors, it is important to appropriately set the cleaning conditions during the cleaning process.

[0016] Therefore, in the manufacturing method according to one embodiment of the present disclosure, the washing conditions are determined such that when the anode body is immersed in the solvent after washing and the electrical conductivity of the solvent is measured, the measured electrical conductivity falls within a predetermined range. The solvent is not particularly limited, but one that has almost no electrical conductivity is preferred, for example, pure water. Here, pure water is defined as a solvent whose electrical conductivity measured without immersing the anode body is 10 μS / cm or less.

[0017] By immersing the anode body with the first conductive polymer layer formed therein in a solvent, components contained in the first conductive polymer layer from the anode body (particularly unnecessary components such as dopant residues and oxidants) elute. As a result, the electrical conductivity of the solvent increases, and the solvent comes to exhibit electrical conductivity. Therefore, by measuring the electrical conductivity of the solvent, the amount of components removed by washing can be estimated, and by determining the washing conditions so that the measured electrical conductivity falls within a predetermined range, the amount of components to be removed can be kept within an appropriate range. As a result, manufacturing defects of the electrolytic capacitor are reduced, and the performance of the electrolytic capacitor is improved. Also, variations in the performance of the electrolytic capacitor after manufacture are reduced.

[0018] The predetermined range of electrical conductivity for determining the washing conditions depends on the configuration of the electrolytic capacitor to be manufactured (such as the size of the anode body (apparent surface area), the material of the conductive polymer, and the coating amount). For example, by fabricating a plurality of prototype electrolytic capacitors while changing the washing conditions and deriving the correlation between the washing conditions and the electrical conductivity when a electrolytic capacitor with few manufacturing defects and high performance is obtained, a predetermined range of electrical conductivity corresponding to the configuration of the electrolytic capacitor can be determined. Specifically, for example, when one or more washed anode bodies are immersed in pure water at a ratio such that the total mass of the conductive polymer layer of the anode body is in the range of 0.5 g to 2 g per 1 kg of pure water, the washing conditions may be determined so that the change in electrical conductivity per hour is 5 μS / cm or less and the electrical conductivity is 70 μS / cm or less. When one or more washed anode bodies having a conductive polymer layer with a total mass of 0.1 g are immersed in 110 g of pure water for 4 hours, the washing conditions may be determined so that the electrical conductivity after immersion is 70 μS / cm or less.

[0019] A plurality of washed anode bodies may be immersed in the solvent. The total mass of the conductive polymer means, in the case of immersing one washed anode body, the mass of the conductive polymer layer contained in the anode body, and in the case of immersing a plurality of washed anode bodies, the sum of the masses of the conductive polymer layers contained in each of the plurality of anode bodies.

[0020] The first conductive polymer layer may be formed by polymerization of a first monomer. The first conductive polymer layer formed by polymerization usually contains unreacted monomers and dopants, and by removing these, the performance of the electrolytic capacitor can be enhanced. The first conductive polymer layer may be formed by chemical polymerization of the first monomer. Note that the first monomer includes oligomers.

[0021] The solid electrolyte layer may be formed by a plurality of conductive polymer layers. For example, a further first conductive polymer layer may be formed on the first conductive polymer layer to serve as the solid electrolyte layer. When the solid electrolyte layer is formed by a plurality of conductive polymer layers, the first conductive polymer layer may be the innermost conductive polymer layer formed to cover the dielectric layer, the conductive polymer layer forming the outermost solid electrolyte layer, or the conductive polymer layer positioned in the middle within the solid electrolyte layer. In other words, when the solid electrolyte layer is formed by a plurality of conductive polymer layers, washing may be performed after forming any of the conductive polymer layers. However, when the solid electrolyte layer contains a conductive polymer layer formed by polymerization, it is desirable to perform washing under predetermined washing conditions determined based on the electrical conductivity immediately after forming the conductive polymer layer formed by polymerization.

[0022] The manufacturing method may further include a step of impregnating the anode body with a solution or dispersion containing a second conductive polymer (polymer dispersion) pre-polymerized after forming the first conductive polymer layer by polymerization, to form a second conductive polymer layer covering the first conductive polymer layer. In this case, after forming the first conductive polymer layer, a washing step is performed, and the second conductive polymer layer is formed so as to cover the surface of the first conductive polymer layer after washing. In this case, when the first conductive polymer layer is the conductive polymer layer formed to cover the dielectric layer, the washing step of the present embodiment is particularly effective.

[0023] The surface of the first conductive polymer layer formed by polymerization has fine irregularities when viewed microscopically. Therefore, when forming the second conductive polymer layer covering the first conductive polymer layer by impregnating the anode body on which the first conductive polymer layer is formed with a solution or dispersion containing the second conductive polymer, the solution or dispersion containing the second conductive polymer may not penetrate deep into the depressions on the surface of the first conductive polymer layer, and it may not be possible to maintain high adhesion between the first conductive polymer layer and the second conductive polymer layer.

[0024] As mentioned above, the first conductive polymer layer formed by polymerization contains unreacted monomers, dopants, oxidizing agents, etc., and readily combines with moisture, potentially leaving a significant amount of moisture in the polymerized film. If the adhesion between the first conductive polymer layer and the second conductive polymer layer is insufficient, the moisture remaining in the first conductive polymer layer may vaporize and expand due to the heat generated in subsequent processes. This can cause the outer second conductive polymer layer to peel away from the first conductive polymer layer, widening the gap between the conductive polymer layers and forming a cavity.

[0025] However, by cleaning the first conductive polymer layer under predetermined cleaning conditions and appropriately removing unreacted monomers, dopants, and oxidizing agents that can trigger swelling, it is possible to suppress poor formation of the solid electrolyte layer due to swelling of the conductive polymer layer.

[0026] To improve adhesion between the first conductive polymer layer and the second conductive polymer layer, the anode may be impregnated with a solution or solvent containing a basic compound after the cleaning step and before the formation of the second conductive polymer layer, thereby pre-adhering the basic compound to the surface of the first conductive polymer layer. The cations contained in the basic compound suppress the repulsion of the anionic dopant contained in the conductive polymer, thereby improving adhesion between the second conductive polymer layer and the first conductive polymer layer. As the basic compound, amine compounds such as N,N-dimethyloctylamine and 1,8-diaminooctane, or amidine compounds can be preferably used.

[0027] The first conductive polymer contained in the first conductive polymer layer and the second conductive polymer contained in the second conductive polymer layer may be the same, or they may contain different monomer units. If the second conductive polymer contains the same monomer units as the monomer units that constitute the first conductive polymer, a thick conductive polymer layer having the same monomer skeleton can be formed.

[0028] ≪Evaluation Method for Conductive Polymer Layers≫ A method for evaluating a conductive polymer layer according to one embodiment of the present disclosure is a method for evaluating a conductive polymer layer constituting a solid electrolyte layer in the manufacture of an electrolytic capacitor comprising a porous anode, a dielectric layer formed on the surface of the anode, a solid electrolyte layer covering at least a portion of the dielectric layer, and a cathode layer covering at least a portion of the solid electrolyte layer, the method comprising a cleaning step of cleaning the anode on which the conductive polymer layer is formed, and a step of immersing the cleaned anode in a solvent and measuring the electrical conductivity of the solvent. The solvent is preferably one that has little electrical conductivity, for example, pure water.

[0029] By immersing an anode body with a conductive polymer layer in a solvent, components contained in the conductive polymer layer (especially unwanted components such as dopant residue and oxidizing agents) are leached out from the anode body. This increases the electrical conductivity of the solvent, causing it to become electrically conductive. Therefore, the amount of components removed by washing can be estimated from the magnitude of the electrical conductivity.

[0030] Electrical conductivity increases with the immersion time of the anode, but the rate of increase slows down as the immersion time progresses, and it asymptotically approaches a certain constant value. The conductive polymer layer can be evaluated based on the measured electrical conductivity after an arbitrary immersion time, but it is preferable to evaluate it based on the electrical conductivity after a sufficient amount of time has elapsed since immersion (e.g., 4 hours or more) and when it has sufficiently approached a certain constant value.

[0031] The evaluation of the conductive polymer layer is preferably performed based on the electrical conductivity when the time change of the measured electrical conductivity becomes 5 μS / cm or less per 2 hours.

[0032] The electrical conductivity of the solvent is measured by the AC two-electrode method in accordance with JIS K 0130:2008. The electrical conductivity values ​​are given at 25°C.

[0033] Based on the measurement results of electrical conductivity, the cleaning conditions for the conductive polymer layer during the actual manufacturing of electrolytic capacitors can be determined. The method for evaluating the conductive polymer layer may further include a step of determining the cleaning conditions when the measured electrical conductivity falls within a predetermined range when cleaning the anode during the cleaning process. This makes it possible to keep the amount of components removed during the cleaning process within an appropriate range during the actual manufacturing of electrolytic capacitors. As a result, manufacturing defects in electrolytic capacitors can be reduced, and the performance of the manufactured electrolytic capacitors can be improved.

[0034] A predetermined range of electrical conductivity for determining cleaning conditions can be derived based on the correlation between the cleaning conditions and the electrical conductivity at which electrolytic capacitors with few manufacturing defects and high performance are obtained when the cleaning process is carried out under those cleaning conditions. By prototyping multiple electrolytic capacitors while changing the cleaning conditions and deriving the correlation between the cleaning conditions and electrical conductivity at which electrolytic capacitors with few manufacturing defects and high performance are obtained, a desirable range of electrical conductivity according to the configuration of the electrolytic capacitor can be determined.

[0035] Specifically, for example, the cleaning conditions may be determined such that when one or more cleaned anodes having a conductive polymer layer with a total mass of 0.1 g are immersed in 110 g of pure water for 4 hours, the electrical conductivity after immersion is 70 μS / cm or less.

[0036] The measured electrical conductivity is considered to be roughly proportional to the ratio of the total mass of the conductive polymer layer on the anode to the mass of the solvent in which the anode is immersed. Therefore, even if a cleaned anode with a total mass of 1 g of conductive polymer layer is immersed in 1100 g of pure water for 4 hours, the same electrical conductivity as under the above cleaning conditions can be measured. The amount of pure water and the total mass of the conductive polymer layer on the anode can be increased or decreased as long as the ratio of the total mass of the conductive polymer layer on the anode to the mass of the pure water in which the anode is immersed remains the same. As the amount of pure water is increased or decreased, the total mass of the conductive polymer layer is also adjusted according to the amount of pure water. To adjust the total mass of the conductive polymer layer, the number of anodes immersed in pure water can be increased or decreased. It is preferable to determine the amount of pure water in accordance with the size of the electrical conductivity measuring instrument.

[0037] In electrical conductivity measurements, the total mass of the conductive polymer layer in the anode is not limited to the above-mentioned example (0.1 g per 110 g of pure water), but may be in the range of 0.5 g to 2 g per 1 kg of pure water. Multiple anodes may be immersed in pure water so that the total mass of the conductive polymer layer contained in the anode falls within the above range, and if the anode is large, individual pieces from which a portion of the anode has been cut may be immersed in pure water. Furthermore, the time at which electrical conductivity is measured is not limited to 4 hours after the start of immersion, but the electrical conductivity may be evaluated when it approaches a certain value sufficiently after immersion. For example, the washing conditions may be determined based on the electrical conductivity when the time change of the measured electrical conductivity becomes 5 μS / cm or less per 2 hours.

[0038] In other words, the cleaning conditions may be determined such that when one or more cleaned anodes are immersed in pure water, the total mass of the conductive polymer layer on the anode is in the range of 0.5 g to 2 g per 1 kg of pure water, and the electrical conductivity is 70 μS / cm or less when the change in electrical conductivity per 2 hours becomes 5 μS / cm or less.

[0039] In measuring electrical conductivity, the surface area A of the anode immersed in 110g of pure water is 100-2000mm². 2It may be within the range described above. Here, the surface area A of the anode is the apparent surface area of ​​the anode without a conductive polymer layer (without considering the surface area of ​​the pores of the porous body), and if the anode has a roughly rectangular shape, it is the sum of the areas of the six rectangles that make up the faces of the rectangular body. When multiple anodes are immersed, the surface area A is the sum of the surface areas of each anode. Depending on the size of the anode, one or more anodes or individual pieces of anodes may be immersed so that the surface area A falls within the above range. The surface area A is 100 to 1000 mm². 2 Or 100-500mm 2 It may be within the range.

[0040] ≪Electrolytic Capacitors≫ The electrolytic capacitor and its manufacturing method according to this embodiment will be described below with reference to the drawings as appropriate. However, the present invention is not limited thereto. Figure 1 is a schematic cross-sectional view showing an example of a capacitor element of an electrolytic capacitor manufactured by the manufacturing method according to this embodiment. Figure 2 is a schematic cross-sectional view of an electrolytic capacitor manufactured by the manufacturing method according to this embodiment.

[0041] The electrolytic capacitor 20 comprises a capacitor element 10 having an anode portion 6 and a cathode portion 7, an outer casing 11 that encloses the capacitor element 10, an anode lead terminal 13 electrically connected to the anode portion 6 and partially exposed from the outer casing 11, and a cathode lead terminal 14 electrically connected to the cathode portion 7 and partially exposed from the outer casing 11. The anode portion 6 has an anode body 1 and an anode wire 2. A dielectric layer 3 is formed on the surface of the anode body. The cathode portion 7 has a solid electrolyte layer 4 that covers at least a portion of the dielectric layer 3 and a cathode layer 5 that covers at least a portion of the surface of the solid electrolyte layer 4.

[0042] <Capacitor element> The following will provide a detailed explanation of the capacitor element 10, using the case where a solid electrolyte layer is provided as the electrolyte as an example.

[0043] The anode section 6 comprises an anode body 1 and an anode wire 2 extending from one surface of the anode body 1 and electrically connected to an anode lead terminal 13. The anode 1 is, for example, a rectangular porous sintered body obtained by sintering metal particles. As the metal particles, valve metal particles such as titanium (Ti), tantalum (Ta), and niobium (Nb) are used. One or more types of metal particles are used in the anode 1. The metal particles may be an alloy composed of two or more metals. For example, an alloy containing a valve metal with silicon, vanadium, boron, etc. can be used. Alternatively, a compound containing a valve metal with a typical element such as nitrogen may be used. The valve metal alloy has a valve metal as its main component, for example, containing 50 atomic percent or more of the valve metal.

[0044] The anode wire 2 is made of a conductive material. The material of the anode wire 2 is not particularly limited, and examples include copper, aluminum, aluminum alloy, etc., in addition to the valve metal mentioned above. The materials constituting the anode body 1 and the anode wire 2 may be the same or different. The anode wire 2 has a first portion 2a embedded in the interior of the anode body 1 from one surface of the anode body 1, and a second portion 2b extending from the aforementioned surface of the anode body 1. The cross-sectional shape of the anode wire 2 is not particularly limited, and examples include circular, track-shaped (a shape consisting of parallel straight lines and two curves connecting the ends of these straight lines), elliptical, rectangular, polygonal, etc.

[0045] The anode portion 6 is manufactured, for example, by pressure molding a rectangular parallelepiped shape with the first portion 2a embedded in the powder of the first metal particles, and then 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 so as to be embedded. The second portion 2b is joined to the anode lead terminal 13 by welding or the like, so that the anode wire 2 and the anode lead terminal 13 are electrically connected. The welding method is not particularly limited and can include resistance welding, laser welding, etc.

[0046] A dielectric layer 3 is formed on the surface of the anode 1. The dielectric layer 3 is composed of, for example, a metal oxide. Methods for forming a layer containing a metal oxide on the surface of the anode 1 include, for example, immersing the anode 1 in a chemical conversion solution to anodize the surface of the anode 1, or heating the anode 1 in an oxygen-containing atmosphere. The dielectric layer 3 is not limited to the layer containing the metal oxide described above, and only needs to have insulating properties.

[0047] (Cathode part) The cathode portion 7 has a solid electrolyte layer 4 and a cathode layer 5 that covers the solid electrolyte layer 4. The solid electrolyte layer 4 is formed to cover at least a portion of the dielectric layer 3.

[0048] For the solid electrolyte layer 4, for example, a manganese compound or a conductive polymer can be used. Examples of conductive polymers include polypyrrole, polythiophene, polyfuran, polyaniline, and polyacetylene. These may be used individually or in combination. The conductive polymer may also be a copolymer of two or more monomers. Polythiophene, polyaniline, and polypyrrole may be used because of their excellent conductivity. Polypyrrole may be used in particular because of its excellent water repellency.

[0049] The solid electrolyte layer 4 containing the conductive polymer described above may be composed of two or more solid electrolyte layers. For example, the solid electrolyte layer 4 includes a first conductive polymer layer covering the dielectric layer 3 and a second conductive polymer layer covering the first conductive polymer layer. When the solid electrolyte layer 4 is composed of two or more layers, the composition and formation method (polymerization method) of the conductive polymer used in each layer may differ. For example, the first conductive polymer layer may be formed by polymerizing raw material monomers on the dielectric layer 3. Alternatively, the second conductive polymer layer may be formed by applying a liquid containing the conductive polymer to the dielectric layer 3.

[0050] In this specification, polypyrrole, polythiophene, polyfuran, and polyaniline, etc., refer to polymers that have polypyrrole, polythiophene, polyfuran, and polyaniline as their basic skeletons, respectively. Therefore, polypyrrole, polythiophene, polyfuran, and polyaniline, etc., may also include their respective derivatives. For example, polythiophene includes poly(3,4-ethylenedioxythiophene), etc.

[0051] Various dopants may be added to polymerization solutions, solutions, or dispersions of conductive polymers to improve the conductivity of the conductive polymer. The dopants are not particularly limited, but examples include naphthalene sulfonic acid, p-toluenesulfonic acid, and polystyrene sulfonic acid.

[0052] When conductive polymers are dispersed in a dispersion medium in the form of particles, the average particle size D50 is, for example, between 0.01 μm and 0.5 μm. If the average particle size D50 is within this range, the particles can easily penetrate into the interior of the anode 1.

[0053] The cathode layer 5 includes, for example, a carbon layer 5a formed to cover the solid electrolyte layer 4, and a metal paste layer 5b formed on the surface of the carbon layer 5a. The carbon layer 5a contains a conductive carbon material such as graphite and a resin. The metal paste layer 5b contains, for example, metal particles (e.g., silver) and a resin. However, the configuration of the cathode layer 5 is not limited to this configuration. The configuration of the cathode layer 5 is acceptable as long as it has a current collecting function.

[0054] (Basic compounds) If the solid electrolyte layer 4 is composed of multiple conductive polymer layers, a basic compound may be interposed between the conductive polymer layers to improve adhesion between them. The basic compound may be added to a solution or dispersion of the conductive polymer.

[0055] Examples of basic compounds include inorganic bases such as ammonia, as well as organic bases such as amine compounds. From the viewpoint of effectively suppressing the decrease in conductivity, amine compounds are preferred among the basic compounds. The amine compound may be a primary amine, secondary amine, or tertiary amine. Examples of amine compounds include aliphatic amines and cyclic amines. A single basic compound may be used, or two or more may be used in combination. The amine compound may have substituents as needed. The presence of an amine compound in the conductive polymer layer can be analyzed, for example, by gas chromatography (GC).

[0056] <Anode lead terminal> The anode lead terminal 13 is electrically connected to the anode body 1 via the second portion 2b of the anode wire 2. The material of the anode lead terminal 13 is not particularly limited as long as it is electrochemically and chemically stable and conductive. The anode lead terminal 13 may be a metal such as copper, or a nonmetal. Its shape is not particularly limited as long as it is flat. The thickness of the anode lead terminal 13 (distance between the main surfaces of the anode lead terminal 13) may be 25 μm or more and 200 μm or less, or 25 μm or more and 100 μm or less, from the viewpoint of reducing the profile.

[0057] One end of the anode lead terminal 13 may be joined to the anode wire 2 by conductive adhesive or solder, or by resistance welding or laser welding. The other end of the anode lead terminal 13 is led out to the outside of the housing 11 and is exposed from the housing 11. The conductive adhesive is, for example, a mixture of a thermosetting resin and carbon particles or metal particles, as described later.

[0058] <Cathode lead terminals> The cathode lead terminal 14 is electrically connected to the cathode portion 7 at the junction 14a. The junction 14a is the portion of the cathode lead terminal 14 that overlaps with the cathode layer 5 when viewed from the direction normal to the cathode layer 5.

[0059] The cathode lead terminal 14 is joined to the cathode layer 5, for example, via a conductive adhesive 8. One end of the cathode lead terminal 14 forms part of the joint 14a, for example, and is located inside the casing 11. The other end of the cathode lead terminal 14 is led out to the outside. Therefore, a portion of the cathode lead terminal 14, including the other end, is exposed from the casing 11.

[0060] The material of the cathode lead terminal 14 is not particularly limited, as long as it is electrochemically and chemically stable and conductive. The cathode lead terminal 14 may be a metal such as copper, or a nonmetal. Its shape is also not particularly limited, and for example, it may be long and flat. From the viewpoint of reducing the profile, the thickness of the cathode lead terminal 14 may be 25 μm to 200 μm, or 25 μm to 100 μm.

[0061] <Exterior> The outer casing 11 is provided to electrically insulate the anode lead terminal 13 and the cathode lead terminal 14, and is made of an insulating material (outer casing material). The outer casing material includes, for example, a thermosetting resin. Examples of thermosetting resins include epoxy resin, phenolic resin, silicone resin, melamine resin, urea resin, alkyd resin, polyurethane, polyimide, and unsaturated polyester.

[0062] ≪Manufacturing Method for Electrolytic Capacitors≫ An example of a method for manufacturing an electrolytic capacitor according to this embodiment is described below.

[0063] (1) Preparation process for capacitor elements First, the capacitor element is prepared. The steps for preparing the capacitor element include, for example, preparing an anode, covering at least a portion of the anode with a dielectric layer, covering at least a portion of the dielectric layer with a solid electrolyte layer, and covering at least a portion of the solid electrolyte layer with a carbon layer. The steps for preparing the capacitor element may further include covering at least a portion of the carbon layer with a conductive resin layer.

[0064] (1a) Preparation of the anode A porous sintered body can be used as the anode 1. Valve metal particles and an anode wire 2 are placed in a mold such that the first portion 2a is embedded in the valve metal particles, and after pressure molding, an anode portion 6 including the anode 1, which is a porous body of valve metal, is obtained by sintering. The first portion 2a of the anode wire is embedded in the interior of the porous sintered body from one side. The pressure during pressure molding is not particularly limited. Sintering is preferably carried out under reduced pressure. A binder such as polyacrylic carbonate may be mixed with the valve metal particles as needed.

[0065] Valve-acting metal particles are typically pressure-molded and sintered using a mold with a rectangular internal space. In this case, the shape of the anode body 1 after sintering is also a rectangular parallelepiped and has multiple main surfaces.

[0066] (1b) Dielectric layer formation process Next, the anode 1 is subjected to a chemical treatment to cover at least a portion of the anode 1 with a dielectric layer 3. Specifically, the anode 1 is immersed in a chemical treatment tank filled with an electrolytic aqueous solution (for example, an aqueous phosphoric acid solution), and the second portion 2b of the anode wire 2 is connected to the anode in the chemical treatment tank to perform anodic oxidation, thereby forming a dielectric layer 3 consisting of an oxide film of a valve-acting metal on the surface of the porous portion. As the electrolytic aqueous solution, not only an aqueous phosphoric acid solution but also nitric acid, acetic acid, sulfuric acid, etc., can be used.

[0067] (1c) Process for forming a solid electrolyte layer Next, at least a portion of the dielectric layer 3 is covered with a solid electrolyte layer 4. This gives a capacitor element 10 comprising an anode 1, a dielectric layer 3, and a solid electrolyte layer 4. The solid electrolyte layer 4 may also include multiple conductive polymer layers.

[0068] As an example of forming a solid electrolyte layer 4 containing multiple conductive polymer layers, the solid electrolyte layer formation step may include: (i) impregnating the anode body with a first solution containing a first monomer, which is a raw material for the first conductive polymer, and polymerizing the monomer on the surface of the dielectric layer to form a first conductive polymer layer covering the dielectric layer; (ii) cleaning the anode body on which the first conductive polymer layer has been formed under predetermined cleaning conditions; and (iii) impregnating the anode body with a solution or dispersion containing a second conductive polymer to form a second conductive polymer layer covering the first conductive polymer layer. Figure 3 is a flowchart showing an example of the solid electrolyte layer formation step in the manufacturing method of an electrolytic capacitor according to this embodiment.

[0069] In step (i), a first conductive polymer layer is formed on the anode body 1 on which the dielectric layer 3 is formed by impregnating it with monomers or oligomers, and then polymerizing the monomers or oligomers by chemical polymerization or electrolytic polymerization. The first conductive polymer may contain a dopant. The conductive polymer and dopant can be selected from those exemplified for the solid electrolyte layer 4, respectively.

[0070] In step (i) for forming the first conductive polymer layer, the raw material monomers for the first conductive polymer are oxidatively polymerized (so-called "in-situ polymerization") above the dielectric layer 3 to form the first conductive polymer layer on the dielectric layer 3. As a result, fine irregularities may occur on the surface of the first conductive polymer layer due to non-uniform polymerization reactions and non-uniform layer growth.

[0071] Next, in step (ii), the anode body on which the first conductive polymer layer is formed is washed under predetermined washing conditions to remove unreacted monomers, dopants, oxidizing agents, and other unwanted components contained in the first conductive polymer layer. The washing conditions are set so that when the washed anode body is immersed in a solvent and the electrical conductivity of the solvent is measured, the measured electrical conductivity falls within a predetermined range. This is achieved by pre-evaluating the conductive polymer as described above, resulting in electrolytic capacitors with fewer manufacturing defects and high performance.

[0072] Next, in step (iii), the cleaned anode is impregnated with a solution or dispersion containing the second conductive polymer, thereby covering the surface of the first conductive polymer layer with the second conductive polymer layer. The second conductive polymer layer is formed so as to fit into the recesses on the surface of the first conductive polymer layer, thereby improving the adhesion between the first conductive polymer layer and the second conductive polymer layer.

[0073] In step (iii), prior to impregnating the anode with a solution or dispersion of the second conductive polymer, the anode may be impregnated with a solution or solvent containing a basic compound. The solvent is then removed by drying, and the basic compound is deposited on the surface of the first conductive polymer layer. The solvent is, for example, water. This suppresses electrostatic repulsion between the anionic first dopant doped into the first conductive polymer in the first conductive polymer layer and the anionic second dopant doped into the second conductive polymer in the second conductive polymer layer, thereby improving the adhesion between the first conductive polymer layer and the second conductive polymer layer. The basic compound is pre-coated along the surface irregularities of the first conductive polymer layer.

[0074] Next, the anode body 1, which has a first conductive polymer layer pre-coated with a basic compound, is immersed in a solution or dispersion of the second conductive polymer, removed, and dried after or simultaneously with a vacuum treatment. This forms the second conductive polymer layer on at least a portion of the first conductive polymer layer. The dispersion may contain a binder and / or conductive inorganic particles (e.g., conductive carbon material such as carbon black).

[0075] Following step (iii), the anode body may be impregnated with a solution or dispersion containing the third conductive polymer to form a third conductive polymer layer covering the second conductive polymer layer.

[0076] The second conductive polymer may contain a dopant. The conductive polymer and dopant may be selected from those exemplified for the solid electrolyte layer 4. A known binder can be used. The dispersion may contain known additives used when forming the solid electrolyte layer.

[0077] (1d) Process for forming the carbon layer and the conductive resin layer Next, a cathode layer 5, consisting of a carbon layer 5a and a metal paste layer 5b, is formed by sequentially applying carbon paste and metal paste to the surface of the solid electrolyte layer 4. The configuration of the cathode layer 5 is not limited to this, and any configuration that has a current collection function is acceptable.

[0078] (2) Electrical connection process between the capacitor element and the lead terminals Next, the anode lead terminal 13 and cathode lead terminal 14 are prepared. The second portion 2b of the anode wire 2, which is planted from the anode body 1, is joined to the anode lead terminal 13 by laser welding or resistance welding. After applying conductive adhesive 8 to the cathode layer 5, the cathode lead terminal 14 is joined to the cathode part 7 via the conductive adhesive 8.

[0079] Next, the capacitor element 10 and the materials for the outer casing 11 (for example, uncured thermosetting resin and filler) are placed in a mold, and the capacitor element 10 is sealed by a transfer molding method, compression molding method, or the like. At this time, a portion of the anode lead terminal 13 and cathode lead terminal 14 are exposed from the mold. The molding conditions are not particularly limited, and the time and temperature conditions should be set appropriately considering the curing temperature of the thermosetting resin used.

[0080] Finally, the exposed portions of the anode lead terminal 13 and cathode lead terminal 14 are bent along the outer casing 11 to form a bent portion. This positions parts of the anode lead terminal 13 and cathode lead terminal 14 on the mounting surface of the outer casing 11. By the method described above, the electrolytic capacitor 20 is manufactured.

[0081] [Examples] The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0082] Electrolytic capacitors were manufactured according to the following procedure. (Formation of anode) Tantalum metal particles were used as the valve metal. The tantalum metal particles were formed into a rectangular parallelepiped so that one end of an anode wire made of tantalum metal was embedded in the tantalum metal particles, and then the formed body was sintered in a vacuum. This resulted in an anode section containing an anode body made of a porous sintered tantalum body and an anode wire, one end of which was embedded in the anode body and the remaining part which was planted from one side of the anode body. The size of the anode body after sintering was approximately 1.0 mm × 2.3 mm × 1.7 mm, a roughly rectangular parallelepiped, and the surface area A was approximately 16 mm². 2 The anode wire is planted from a 1.0 mm x 1.7 mm surface.

[0083] Next, the anode body and a portion of the anode wire planted from the anode body were immersed in a chemical conversion tank filled with an electrolytic phosphoric acid solution, and the other end of the anode wire was connected to the anode body in the chemical conversion tank. Then, by performing anodic oxidation, a uniform dielectric layer of tantalum oxide (Ta2O5) was formed on the surface of the anode body (the surface of the porous sintered body including the inner wall surface of the pores) and on the surface of a portion of the anode wire.

[0084] Next, 3,4-ethylenedioxythiophene, the raw material for the first conductive polymer, along with p-iron(III) toluenesulfonate and 1-butanol were mixed to prepare a dispersion (reaction solution) containing the first monomer. After immersing the anode in the dispersion, the anode was removed from the dispersion and heat-treated in the air. In this case, p-iron(III) toluenesulfonate functions as an oxidizing agent. In this manner, the first monomer was polymerized on the dielectric layer, forming a solid electrolyte layer containing poly(3,4-ethylenedioxythiophene) (PEDOT) as the first conductive polymer layer.

[0085] Next, the anode body on which the first conductive polymer layer was formed was cleaned with a cleaning solution for a predetermined period of time.

[0086] Next, a second dispersion was prepared by mixing poly(3,4-ethylenedioxythiophene) as the second conductive polymer with p-toluenesulfonate. After immersing the anode in the second dispersion, the anode was removed from the second dispersion, allowing the second dispersion to permeate the anode. Subsequently, a drying treatment was performed at 80°C for 20 minutes under atmospheric pressure to form a second conductive polymer layer and obtain the anode. The total mass of the 23 anodes was 0.6 g, of which the solid electrolyte layer (first conductive polymer layer) accounted for 0.1 g.

[0087] In this example, multiple anodes A1 to A4 were fabricated by varying the cleaning time of the anodes on which the first conductive polymer layer was formed, as shown in Table 1. In addition, anode B1 was fabricated by forming a second conductive polymer layer on the anodes on which the first conductive polymer layer was formed without cleaning.

[0088] For each of the anodes A1-A4 and B1, 23 anodes that had been washed before the formation of the second conductive polymer layer were immersed in 110g of pure water, and the change in electrical conductivity over time after immersion was measured. Figure 4 shows the change in electrical conductivity over time for each of the anodes A1-A4 and B1. From Figure 4, it can be seen that the electrical conductivity increases with the passage of immersion time, but after approximately 4 hours of immersion, the change in electrical conductivity over time becomes less than 5 μS / cm per 2 hours, asymptotically approaching a constant value.

[0089] Capacitor elements C1 to C4 were fabricated by sequentially applying carbon paste and metal paste to predetermined areas on the surface of the solid electrolyte layer using anodes A1 to A4, thereby forming a cathode layer consisting of a carbon layer and a silver paste layer. Similarly, capacitor element C5 was fabricated by forming a cathode layer on anode B1.

[0090] Multiple samples were prepared for each capacitor element C1 to C5. Visual inspection was performed to check for blistering in the conductive polymer layer after the formation of the second conductive polymer layer, the carbon layer, and the silver paste layer. The number of samples p showing blistering was calculated relative to the total number of samples N, and the blistering rate (%) was calculated as (p / N) × 100. The evaluation results are shown in Table 1. Table 1 also shows the number of samples N for capacitor elements C1 to C5, and the cleaning time during the cleaning process of the first conductive polymer layer.

[0091] Table 1 shows that in capacitor elements C1 to C4, which have a cleaning step for the first conductive polymer layer, the adhesion between the first conductive polymer layer and the second conductive polymer layer is improved compared to capacitor element C5, which does not have a cleaning step. As a result, the occurrence of blistering in the conductive polymer layer is significantly suppressed.

[0092] As shown in Figure 4, the electrical conductivity of the anodes A1 to A4 used in capacitor elements C1 to C4 is 0.07 mS / cm or less (70 μS / cm or less). If the measured electrical conductivity of the anode is 70 μS / cm or less, the adhesion between the conductive polymer layers is enhanced, and the occurrence of blistering is suppressed. When using anodes of different sizes from anodes A1 to A4, the ratio of the total mass of conductive polymer contained in the anode to the mass of pure water should be kept the same, and the electrical conductivity should be measured. In this case as well, if the measured electrical conductivity of the anode is 70 μS / cm or less, it is presumed that the capacitor elements manufactured using that anode have enhanced adhesion between the conductive polymer layers, and the occurrence of blistering is suppressed.

[0093] In this embodiment, the ratio of the conductive polymer layer content in the anode to the mass of pure water is 0.1 g per 110 g of pure water, but it is not limited to this, and any ratio in the range of 0.5 g to 2 g per 1 kg of pure water is acceptable.

[0094] [Table 1] [Industrial applicability]

[0095] The present invention can be used in electrolytic capacitors, and preferably in electrolytic capacitors that use a porous material as the anode. [Explanation of Symbols]

[0096] 20: Electrolytic capacitors 10: Capacitor element 1: Anode 2: Anode wire 2a:First part 2b:Second part 3: Dielectric layer 4: Solid electrolyte layer 5: Cathode layer 5a: Carbon layer 5b: Metal paste layer 6: Anode section 7: Cathode 8: Conductive adhesive 11: Exterior 13: Anode lead terminal 14: Cathode lead terminals 14a: Joint

Claims

1. A method for manufacturing an electrolytic capacitor comprising a porous anode, a dielectric layer formed on the surface of the anode, a solid electrolyte layer covering at least a portion of the dielectric layer, and a cathode layer covering at least a portion of the solid electrolyte layer, The process includes forming the solid electrolyte layer containing a conductive polymer on the surface of the anode on which the dielectric layer is formed, The process for forming the solid electrolyte layer is as follows: A step of impregnating the anode body with a first solution containing a first monomer, and forming a first conductive polymer layer by chemical polymerization of the first monomer, The process includes a cleaning step of cleaning the anode body on which the first conductive polymer layer is formed under predetermined cleaning conditions, A method for manufacturing an electrolytic capacitor, wherein the cleaning conditions are determined such that, after cleaning, the anode is immersed in a solvent to dissolve the dopant residue and oxidizing agent into the solvent, and the electrical conductivity of the solvent is measured, and the measured electrical conductivity falls within a predetermined range.

2. The method for manufacturing an electrolytic capacitor according to claim 1, wherein the first conductive polymer layer is formed so as to cover the dielectric layer.

3. A method for manufacturing an electrolytic capacitor according to claim 1 or 2, further comprising the step of impregnating the anode body with a solution or dispersion containing a second conductive polymer after the formation of the first conductive polymer layer to form a second conductive polymer layer covering the first conductive polymer layer.

4. A method for evaluating a conductive polymer layer constituting the solid electrolyte layer in the manufacture of an electrolytic capacitor comprising a porous anode, a dielectric layer formed on the surface of the anode, a solid electrolyte layer covering at least a portion of the dielectric layer, and a cathode layer covering at least a portion of the solid electrolyte layer, wherein The conductive polymer layer includes a first conductive polymer layer formed by impregnating the anode body with a first solution containing a first monomer and chemical polymerization of the first monomer. A cleaning step for cleaning the anode body on which the first conductive polymer layer is formed, A method for evaluating a conductive polymer layer, comprising the steps of: immersing the anode body after cleaning in a solvent to dissolve dopant residue and oxidizing agent into the solvent; and then measuring the electrical conductivity of the solvent.

5. The method for evaluating a conductive polymer layer according to claim 4, further comprising the step of determining cleaning conditions such that the measured electrical conductivity falls within a predetermined range when cleaning the anode in the cleaning step.

6. The method for evaluating a conductive polymer layer according to claim 5, wherein the cleaning conditions are determined such that the anode body after cleaning is immersed in pure water in a ratio such that the total mass of the conductive polymer layer on the anode body is in the range of 0.5 g to 2 g per 1 kg of pure water, and the electrical conductivity is 70 μS / cm or less when the change in electrical conductivity per 2 hours becomes 5 μS / cm or less.

7. The method for evaluating a conductive polymer layer according to claim 5, wherein the cleaning conditions are determined such that when the cleaned anode body having a total mass of 0.1 g of the conductive polymer layer is immersed in 110 g of pure water for 4 hours, the electrical conductivity after immersion is 70 μS / cm or less.

8. The surface area of ​​the anode body to be immersed is 100 to 2000 mm². ２ A method for evaluating a conductive polymer layer according to claim 7, which falls within the range of the specified range.

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