Composite powder used for producing porous body included in anode body of electrolytic capacitor, method for producing the composite powder, and method for producing anode body for electrolytic capacitor

Abstract

To enhance the reliability of a porous body included in an anode body of an electrolytic capacitor.SOLUTION: A composite powder used for producing a porous body included in an anode body of an electrolytic capacitor, comprises a raw material powder containing a valve metal and an aromatic compound (excluding naphthalene and polymers) adhering to a surface of particles of the raw material powder, wherein the melting point of the aromatic compound is 35°C or more and 120°C or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a composite powder used to manufacture a porous body included in an anode body of an electrolytic capacitor, The present invention relates to a method for producing the composite powder and a method for producing an anode body for an electrolytic capacitor. [Background technology]

[0002] In recent years, electrolytic capacitors with low equivalent series resistance (ESR) and excellent frequency characteristics have been developed. The anode body of an electrolytic capacitor includes, for example, a porous body containing a valve metal and a dielectric layer covering the porous body. The raw material for the porous body is, for example, a raw material powder containing a valve metal to which an additive (binder) has been added.

[0003] Patent Document 1 proposes "a solid electrolytic capacitor including a capacitor element including a sintered porous anode body; a dielectric disposed on the anode body; and a solid electrolyte disposed on the dielectric and including a conductive polymer and a depolarizer." Patent Document 1 lists, as an example of powder used to form the sintered porous anode body, a powder containing tantalum, and lists, as a specific example of a binder used to aggregate the powder particles, polystyrene.

[0004] Patent Document 2 describes a tantalum powder containing tantalum, hydrogen doped in the tantalum, and nitrogen doped in the tantalum, in which the hydrogen (H) content (ppm) of the tantalum powder is determined by the Brunauer-Emmett-Teller (BET) surface area (m 2 / g) (H / BET) is greater than 100, and the tantalum powder has (a) a hydrogen content of 300 ppm to 1200 ppm, (b) a nitrogen content of 500 ppm to 3,500 ppm, and (c) a nitrogen content of 3 m 2 / g~about 10m 2 / g」。 Patent Document 2 lists naphthalene as a specific example of a binder to be added to the tantalum powder.

[0005] Patent Document 3 proposes "a method for making an anode for an electrolytic capacitor, the method comprising the steps of combining a metal powder and an effective amount of dimethyl sulfone as a binder; pressing the powder and dimethyl sulfone to form an anode body; and removing the dimethyl sulfone."

[0006] Patent Document 4 proposes "a method for sintering a tantalum capacitor anode element, characterized in that a tantalum anode element obtained by compression molding tantalum powder mixed with an adhesive is placed in a drying furnace filled with a degreasing solvent, subjected to sealed low-temperature solvent catalytic wet dewaxing, then vacuum dried, and further vacuum sintered." Patent Document 4 lists benzoic acid and the like as specific examples of adhesives.

[0007] Patent Document 5 proposes "a method for manufacturing an element for a solid electrolytic capacitor, which comprises pressure-molding a valve action metal powder containing a binder to obtain a compact element, and then sintering the compact element in a vacuum, characterized in that the compact element is immersed in pure water and subjected to ultrasonic vibrations." Patent Document 5 lists benzoic acid as a specific example of the binder. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Special Publication No. 2022-533161 [Patent Document 2] Special Publication No. 2020-500260 [Patent Document 3] Special Publication No. 2003-509583 [Patent Document 4] Japanese Patent Application Laid-Open No. 2013-135211 [Patent Document 5] Japanese Patent Application Laid-Open No. 2007-273710 Summary of the Invention [Problem to be solved by the invention]

[0009] There is a demand for improved reliability for the porous body contained in the anode body of an electrolytic capacitor. [Means for solving the problem]

[0010] One aspect of the present disclosure relates to a composite powder used for manufacturing a porous body included in an anode body of an electrolytic capacitor, the composite powder including a raw material powder containing a valve action metal and an aromatic compound (excluding naphthalene and a polymer) adhered to the surface of particles of the raw material powder, and the aromatic compound has a melting point of 35°C or higher and 120°C or lower.

[0011] Another aspect of the present disclosure relates to a method for producing a composite powder used to produce a porous body included in an anode body of an electrolytic capacitor, the method including the steps of: preparing a raw material powder containing a valve action metal; preparing an additive solution containing an aromatic compound (excluding naphthalene and a polymer) having a melting point of 35°C or higher and 120°C or lower, and a solvent; adding the additive solution to the raw material powder while stirring the raw material powder to obtain a wet raw material powder; and removing the solvent by drying the wet raw material powder while stirring to obtain a composite powder, wherein the composite powder includes the raw material powder and the aromatic compound adhered to surfaces of the particles of the raw material powder.

[0012] Yet another aspect of the present disclosure relates to a method for manufacturing an anode body for an electrolytic capacitor, the method including the steps of: preparing a composite powder including a raw material powder containing a valve action metal and an aromatic compound (excluding naphthalene and a polymer) adhered to surfaces of particles of the raw material powder; filling the composite powder into a predetermined molding die and pressure-molding it to obtain a molded body; removing the aromatic compound contained in the molded body; sintering the molded body from which the aromatic compound has been removed to obtain a porous body; and forming a dielectric layer on the surface of the porous body to obtain an anode body, wherein the melting point of the aromatic compound is 35°C or higher and 120°C or lower. [Effects of the Invention]

[0013] According to the present disclosure, it is possible to improve the reliability of the porous body included in the anode body of an electrolytic capacitor. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 2 is a diagram showing an example of wet mixing of raw material powder and aromatic compound A. [Figure 2] 2 is a diagram showing an example of a process for producing a compact from a composite powder, in which (a) shows the state of the composite powder when weighed, (b) shows the state of the composite powder before compaction, and (c) shows the state of the composite powder during compaction. [Figure 3] FIG. 2 is a configuration diagram showing an example of equipment used in the step of removing aromatic compound A and the step of sintering the compact. [Figure 4] FIG. 1 is a cross-sectional view schematically illustrating an electrolytic capacitor according to an embodiment of the present disclosure. [Figure 5] FIG. 1 is a cross-sectional view showing a state in which a jig set for measuring bulk density is filled with powder. [Figure 6] FIG. 1 is a perspective view schematically showing a porous body (sintered body) for explaining evaluation methods in Examples. DETAILED DESCRIPTION OF THE INVENTION

[0015] The following describes embodiments of the present disclosure using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and materials may be applied as long as the effects of the present disclosure are obtained. In this specification, the term "numerical value A to numerical value B" includes numerical value A and numerical value B and can be interpreted as "numerical value A or more and numerical value B or less." In the following description, when lower and upper limits are exemplified for numerical values ​​of specific physical properties or conditions, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not equal to or greater than the upper limit. When multiple materials are exemplified, one of the materials may be selected and used alone, or two or more of the materials may be used in combination.

[0016] The anode body of an electrolytic capacitor includes a porous body (porous sintered body) containing a valve metal and a dielectric layer covering the surface of the porous body. The present disclosure relates to a composite powder used to manufacture the porous body included in the anode body of an electrolytic capacitor. The composite powder according to an embodiment of the present disclosure includes a raw material powder containing a valve metal and an aromatic compound (excluding naphthalene and polymers) attached to the surface of the raw material powder particles. The aromatic compound has a melting point of 35°C or higher and 120°C or lower.

[0017] Hereinafter, aromatic compounds (excluding benzoic acid, naphthalene, and polymers) with a melting point of 35°C or more and 120°C or less will also be referred to as "aromatic compound A." Particles of raw material powder will also be referred to as "raw material particles." Particles of composite powder include raw material particles and aromatic compound A attached to the surfaces of the raw material particles. Hereinafter, particles of composite powder will also be referred to as "composite particles."

[0018] In the composite powder disclosed herein, aromatic compound A is added to the raw powder as an additive. Such composite powders can improve the weighing stability (fluidity) of the powder. This can reduce mass variation between porous bodies (between compacts). Furthermore, such composite powders can reduce the bulk density of the composite powder. This reduces density variation within the compact, allowing porous bodies (sintered bodies) with low density variation to be obtained through the sintering process. This can prevent chipping and cracking due to the presence of locally low density areas in the compact (porous body). This reduced density variation facilitates the formation of homogeneous dielectric layers and solid electrolyte layers throughout the porous body, thereby reducing the characteristic variation of electrolytic capacitors, reducing the defect rate, and improving reliability. Furthermore, when aromatic compound A is used as the additive, the carbon content of the porous body derived from the additive can be reduced, thereby suppressing the increase in leakage current when the carbon content is high. By reducing the carbon content of the porous body and reducing mass variation between porous bodies and density variation within the porous body, the reliability of the porous body and electrolytic capacitors manufactured using the porous body can be improved.

[0019] The aromatic compound A has a melting point of 35°C or higher and is stable in a solid state at room temperature (approximately 20 to 25°C). Therefore, the composite powder can be obtained as a dry powder and can maintain a low bulk density, so that a porous body (molded body) with small density variation can be stably obtained and excellent weighing stability can be ensured. From the viewpoint of facilitating the production of the composite powder, ensuring high productivity, and improving weighing stability, the melting point of the aromatic compound may be 40°C or higher, or 45°C or higher.

[0020] The melting point of the aromatic compound A is 120°C or lower. In this case, the aromatic compound A removal step described below can be easily performed at low cost. High productivity of the porous body can be ensured, and a highly reliable porous body (anode body) with a reduced carbon content can be obtained at low cost. In the aromatic compound A removal step using the equipment of FIG. 3, the piping from the aromatic compound A removal furnace to the recovery tank (heat-insulated piping 540 in FIG. 3) is maintained at approximately 120 to 150°C, thereby preventing the aromatic compound from adhering to the inner wall of the piping. In addition, there is no need to install heat-resistant piping or additional equipment for heating the piping to 150°C or higher, which is advantageous in terms of cost. From the viewpoints of improving productivity, reducing costs, and improving reliability, the melting point of the aromatic compound is preferably 100°C or lower, and more preferably 90°C or lower.

[0021] For example, if the additive is benzoic acid (melting point 122.4°C), even if the temperature of the above-mentioned pipe is set in the range of approximately 120 to 150°C, there may be areas within the pipe (or near the pipe within the removal furnace) where the temperature is below 122°C, and benzoic acid may precipitate and solidify in these areas. The presence of these solidified materials reduces the ability to transport the additive from the removal furnace to the recovery tank, resulting in insufficient removal of the additive and reducing the productivity and reliability of the porous body.

[0022] Composite powders containing aromatic compound A produce porous bodies (compacts) with minimal density variation. Addition of aromatic compound A tends to decrease the bulk density of the powder. This decrease in bulk density increases the proportion of the volume (apparent volume of the powder, including interparticle voids) of the composite powder 300 (raw powder) in the space 460 in Figure 2(b), thereby preventing the composite powder 300 from concentrating at the bottom of the space 460 due to gravity. This decrease in bulk density is presumably one of the factors that reduces density variation within the compact (porous) when the powder is compressed using the press mold 430 to obtain a compact. The bulk density of the composite powder, calculated as the raw powder, may be lower than that of the raw powder. When a small amount of aromatic compound A is added, the bulk density of the composite powder, calculated as the raw powder, may be higher than that of the raw powder due to the influence of the solvent contained in the additive solution. However, the density variation of the porous body (compact) is reduced, and weighing stability is improved. When the amount of aromatic compound A added is large, the bulk density D2 of the composite powder converted into raw material powder becomes lower than the bulk density D1 of the raw material powder, making it easier to reduce the density variation and further improving weighing stability.

[0023] The powder is filled to the level in a predetermined measuring hole. That is, a predetermined amount of powder is filled in the measuring hole of the measuring jig using a leveling jig. For example, powder 300 is filled in measuring hole 420a in FIG. 2(a) using a leveling jig. The bulk density D1 of the raw material powder is calculated by the formula D1=M1 / V, where M1 is the mass of the raw material powder filled to the level in the measuring hole and V is the volume of the measuring hole.

[0024] The bulk density D2 of the composite powder as converted to raw material powder can be calculated from the formula D2 = M2a / V, where M2a is the mass of the composite powder as converted to raw material powder when filled to the level in the measuring hole, and V is the volume of the measuring hole. The mass M2a of the composite powder as converted to raw material powder can be calculated from the formula M2a = M2 / (1 + (X / 100)), where M2 is the mass of the composite powder when filled to the level in the measuring hole, and X is the content of additives in the composite powder (amount (parts by mass) per 100 parts by mass of raw material powder).

[0025] Furthermore, in the composite powder containing aromatic compound A, the variation in the amount of powder filled into the measuring hole is small, and the mass variation between porous bodies (between compacts) can be reduced. The powder is measured, for example, by filling powder 300 into measuring hole 420a in FIG. 2(a).

[0026] If the mass variation between porous bodies is large, the surface area of ​​the porous bodies (anode bodies) will vary greatly, which may lead to increased variation in the capacitance of electrolytic capacitors. Furthermore, when multiple porous bodies are simultaneously subjected to chemical conversion treatment at the same chemical conversion voltage, the chemical conversion current will vary greatly between the porous bodies, leading to increased variation in the film quality of the formed chemical conversion coating, which may in turn increase variation in the leakage current (LC) of the electrolytic capacitors. This can lead to increased variation in the characteristics of electrolytic capacitors. One possible method for reducing the variation in the characteristics of electrolytic capacitors is to remove those outside a specified mass range as defective products at the stage of obtaining the molded bodies. However, this method increases the molding defect rate and is disadvantageous in terms of productivity.

[0027] The boiling point of aromatic compound A is preferably 400°C or lower (or 350°C or lower). In the step of removing aromatic compound A, aromatic compound A can be removed by vaporizing it at a temperature of 400 to 500°C. This temperature range is approximately the same as the temperature range for removing camphor by evaporation and the temperature range for removing acrylic resin by thermal decomposition and evaporation, and the equipment used when camphor or acrylic resin was used as an additive can be used as is.

[0028] The aromatic compound A preferably contains an oxygen atom. The oxygen atom gives the molecules of the aromatic compound A polarity, and it is believed that the polarity causes Coulomb force, which makes them more likely to adhere to the surface of raw material particles containing valve metals. It is presumed that the steric hindrance of the aromatic compound A, which has an aromatic ring, inhibits aggregation of the raw material particles, resulting in a decrease in the bulk density of the composite powder.

[0029] From the viewpoint of easily obtaining stable performance of the electrolytic capacitor, it is preferable that the aromatic compound A is composed only of carbon atoms, hydrogen atoms, and oxygen atoms. If the aromatic compound contains atoms other than carbon atoms, hydrogen atoms, and oxygen atoms, the presence of the other atoms (for example, if the other atoms are sulfur atoms, partial sulfurization of Ta) may affect the performance of the electrolytic capacitor.

[0030] The aromatic compound A may contain a heterocycle in which some of the carbon atoms constituting the benzene ring are replaced with oxygen atoms, or an oxygen atom may be bonded to at least one of the carbon atoms constituting the benzene ring. The oxygen atom may be bonded directly to the carbon atom constituting the benzene ring, or may be bonded to the carbon atom constituting the benzene ring via a methylene group (-CH2-) or an ethylene group (-CH2CH2-). The presence of a bond between a carbon atom and an oxygen atom, which is likely to exhibit polarity, near the heterocycle or benzene ring, which causes steric hindrance, is thought to restrict the arrangement and orientation of the heterocycle or benzene ring, effectively reducing the bulk density of the composite powder.

[0031] The aromatic compound A may have one benzene ring and an oxygen-containing functional group bonded to the benzene ring. Examples of the oxygen-containing functional group include a hydroxyl group, a carboxyl group, a carbonyl group, an ester group, an ether group, etc. The oxygen-containing functional group may be bonded directly to a carbon atom constituting the benzene ring, or may be bonded to a carbon atom constituting the benzene ring via a methylene group (-CH2-) or an ethylene group (-CH2CH2-). The oxygen-containing functional group may be a divalent functional group and may be bonded to two carbon atoms constituting the benzene ring to form a heterocycle.

[0032] The aromatic compound A may be an aromatic compound containing a lactone ring. A lactone ring is a heterocyclic ring containing an ester group (-C(=O)-O-) in the ring. Examples of aromatic compounds containing a lactone ring include coumarin compounds, dehydroacetic acid (melting point 112°C, boiling point 270°C), etc. Coumarin compounds include coumarin and its derivatives. Examples of coumarin compounds include coumarin (melting point 72°C, boiling point 302°C), 6-methylcoumarin (melting point 77°C, boiling point 304°C), etc.

[0033] The aromatic compound A may be a vanilloid compound. A vanilloid compound is a compound having a vanillyl group. Examples of vanilloid compounds include vanillin compounds, vanillic acid compounds, etc. Vanillin compounds include vanillin and its derivatives. Examples of vanillin compounds include vanillin (melting point 82°C, boiling point 285°C) and ethyl vanillin (melting point 76°C, boiling point 295°C). Vanillic acid compounds include vanillic acid and its derivatives. Examples of vanillic acid compounds include methyl vanillate (melting point 65°C, boiling point 287°C) and ethyl vanillate (melting point 43°C, boiling point 293°C).

[0034] The aromatic compound A preferably contains at least one selected from the group consisting of coumarin (melting point 72°C, boiling point 302°C), vanillin (melting point 82°C, boiling point 285°C), thymol (melting point 52°C, boiling point 232°C), p-methoxyphenol (melting point 58°C, boiling point 243°C), phenyl salicylate (melting point 44°C, boiling point 137°C), benzyl (melting point 97°C, boiling point 348°C), and 3-phenylpropionic acid (51°C, 280°C). These compounds have a high solubility of 10 g or more per 100 g of ethanol or the like, as described below, a melting point in the range of 35 to 100°C, and a boiling point of 350°C or less.

[0035] Among these, coumarin and vanillin are preferred as aromatic compound A. These compounds are not corrosive solids, so no special precautions are required for transportation, and they do not fall under the category of substances notified under the Industrial Safety and Health Act in Japan, simplifying management. Because they have a relatively high melting point of 70°C or higher, no special temperature control is required for the storage environment of the composite powder from the time the composite powder is prepared until the molded product is obtained. These compounds are known to be contained in foods, etc., and are therefore of low toxicity to the human body.

[0036] Aromatic compound A does not contain polymers. Examples of polymers include polystyrene, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyimide, and polyether ether ketone. Polymers are often added in large amounts to the raw powder to improve weighing stability. They often fail to thermally decompose below 500°C, or even if they do, they tend to remain incompletely and leave decomposition products. This can result in a high carbon content in the porous material. Furthermore, because harmful substances such as benzene and toluene are produced during the thermal decomposition process, special care is required for the recovery and disposal of the decomposition products. When using polymers to obtain composite powders, the polymers tend to form tightly adhered particle agglomerates (e.g., 300 μm or larger) after the solvent removal process. These agglomerates can lead to problems such as increased powder filling variability in the weighing holes, increased density variability within the porous material (molded body), and irregularly shaped sintered bodies, reducing the reliability of the porous material. Therefore, a separate step for removing the agglomerates is required, which leads to a loss of powder and is disadvantageous in terms of productivity.

[0037] Aromatic Compound A does not include naphthalene. Naphthalene is an aromatic compound with a melting point of 79°C, but it is included in the list of specified chemical substances, is harmful, and is difficult to handle. Naphthalene is included in the list of substances for which the American Conference of Governmental Industrial Hygienists (ACGIH) has determined that the permissible concentration is 10 ppm or less in time-weighted average (TWA).

[0038] The content of aromatic compound A in the composite powder is preferably 0.01 parts by mass or more per 100 parts by mass of raw material powder. When the content of aromatic compound A is 0.01 parts by mass or more, good weighing stability of the composite powder is easily ensured, and a porous body (molded body) with small density variation is obtained. The higher the content of aromatic compound A, the more improved the weighing stability of the composite powder becomes, the lower the bulk density of the composite powder converted into raw material powder, and the smaller the density distribution index of the side surface of the sintered body described below tends to become. The content of aromatic compound A in the composite powder may be 0.01 parts by mass or more and 2 parts by mass or less per 100 parts by mass of raw material powder. When the content of aromatic compound A is 2 parts by mass or less, the carbon content of the porous body is reduced, and leakage current is reduced. From the viewpoint of further improving weighing stability and further reducing density variation of the porous body (molded body), the content of aromatic compound A may be 0.5 parts by mass or more and 2 parts by mass or less per 100 parts by mass of raw material powder. From the viewpoint of further reducing leakage current (carbon content of the porous body), the content of aromatic compound A may be 0.01 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of raw material powder. When the content of aromatic compound A exceeds 0.5 parts by mass, the leakage current can be sufficiently reduced by introducing a step of immersing the molded body in an organic solvent before the heating step in the aromatic compound A removal step described below.

[0039] If the additive is an acrylic polymer, the carbon content of the porous body may increase, resulting in an increase in leakage current (LC). While the exact reason for this is unclear, it is presumed that adding a large amount of acrylic polymer (e.g., 1 part by mass or more of acrylic polymer per 100 parts by mass of raw material powder) is necessary to improve weighing stability, and that some of the pyrolysis products generated by thermal decomposition during the additive removal process tend to remain rather than be removed by evaporation. Examples of acrylic polymers include poly(meth)acrylic acid and its salts, and (meth)acrylic acid ester polymers (acrylic resins). "(Meth)acrylic acid" refers to at least one selected from the group consisting of "acrylic acid" and "methacrylic acid." Furthermore, even if a process for removing the additive involves immersing a molded body made from a composite powder containing the acrylic polymer in toluene to elute the acrylic polymer, the acrylic polymer tends to remain firmly attached to the molded body, making it difficult to reduce the carbon content of the porous body and to achieve the desired effect of suppressing leakage current.

[0040] The content of the additive (aromatic compound A) in the composite powder (amount per 100 parts by mass of raw material powder) can be determined as follows: The composite powder is placed in an organic solvent such as ethanol, stirred, and then the raw material powder (e.g., Ta powder) is separated from the liquid (a solution containing the additive) by filtration or centrifugation. The liquid is dried to obtain a precipitate (additive). The masses of the raw material powder and the precipitate are measured, and the mass ratio (percentage) of the precipitate to the raw material powder is determined.

[0041] The components of the additive can be determined, for example, by gas chromatography-mass spectrometry. The melting point and boiling point are measured by a general method described in, for example, the Japanese Industrial Standards (JIS). If necessary, the melting point may be measured by differential scanning calorimetry (DSC). If necessary, the boiling point may be measured by thermogravimetric differential thermal analysis (TG / DTA).

[0042] (Raw material powder) The raw material powder contains a valve metal. Examples of the valve metal include aluminum (Al), titanium (Ti), tantalum (Ta), niobium (Nb), zirconium (Zr), and hafnium (Hf). The raw material particles may be particles of the valve metal, particles of an alloy containing the valve metal, or particles of a compound containing the valve metal. Only one type of particle may be used, or two or more types may be mixed together.

[0043] The average particle size of the raw material powder may be 100 μm or less, or may be 80 μm or less. In this case, it is possible to suppress the increase in density variation of the green body due to the uneven distribution of coarse particles in the green body, and the dimensional variation of the green body can be reduced by improving the flatness of the surface of the green body. Furthermore, since it is relatively difficult to achieve an average particle size of 100 μm or more with powders having a CV value of 100 μFV / g (100 kCV) or more, there is also the advantage of broadening the options when selecting raw material powders. The addition of aromatic compound A can improve the weighing stability of raw material powders having an average particle size of 100 μm or less. If camphor is added to raw material powders having an average particle size of 100 μm or less, the weighing stability of the powder may be reduced.

[0044] Furthermore, from the viewpoint of preventing the powder from floating in the air, the average particle size of the raw material powder may be 10 μm or more. In this case, the loss of powder due to the powder floating in the air when transferring from one container to another can be prevented, and the risk of workers inhaling the powder can be reduced. Furthermore, the small particle size can prevent particles from scattering through gaps in the molded parts.

[0045] The average particle size referred to here is the median diameter (D50) in the volume particle size distribution determined by a laser diffraction particle size distribution measuring device.

[0046] [Method of manufacturing composite powder] A method for producing a composite powder according to an embodiment of the present disclosure includes a step of preparing a raw material powder containing a valve action metal, a step of preparing a solution of an aromatic compound A (hereinafter also referred to as "additive solution A"), a step of mixing the raw material powder with the additive solution A, and a step of removing the solvent.

[0047] When adding a small amount (e.g., 2 parts by mass or less or 1 part by mass or less) of aromatic compound A to 100 parts by mass of raw powder, a homogeneous composite powder can be produced by dissolving aromatic compound A in a solvent and mixing it with the raw powder to create a wet raw powder (wet mixing). If a small amount of aromatic compound A is dry-mixed with the raw powder at a temperature above the melting point of aromatic compound A, it is difficult to distribute the molten aromatic compound A over the entire surface of the raw powder, making it difficult to produce a homogeneous composite powder. Furthermore, with this method, the molten aromatic compound A tends to adhere to the walls of the mixing vessel, which can result in a large proportion not contributing to the compounding, making it difficult to control the amount of aromatic compound A added to the raw powder.

[0048] (raw powder preparation process) The raw material powder may be any of those exemplified above.

[0049] (Additive solution A preparation process) The additive solution A contains an aromatic compound A and a solvent. The aromatic compound A may be any of those exemplified above. The concentration of the aromatic compound A in the additive solution A is, for example, 0.005 mass % or more and 10 mass % or less. When it is necessary to lower the concentration of the additive solution A, a high-concentration additive solution A may be prepared first, and then the solution A may be diluted with a solvent to lower the concentration.

[0050] The solvent is preferably a relatively less harmful solvent rather than a highly harmful solvent such as toluene. Examples of relatively less harmful solvents include ethanol, isopropanol, and butyl acetate (hereinafter also referred to as "ethanol, etc."). One solvent may be used alone, or two or more solvents may be used in combination.

[0051] The solvent is preferably ethanol, isopropanol, or butyl acetate, and the solubility of aromatic compound A per 100 g of solvent at 20°C is preferably 10 g or more. It is preferable that the solubility in at least one of the three solvents is within the above range. In this case, the dissolution rate of aromatic compound A in the solvent is fast, and additive solution A can be easily prepared. In this case, the occurrence of uneven mixing is sufficiently suppressed, making it easy to mix the raw material particles and aromatic compound A homogeneously.

[0052] (Mixing process of raw material powder and additive solution A) This step is a step of wet-mixing the raw material powder with the aromatic compound A. That is, in the mixing step, the additive solution is added to the raw material powder while stirring the raw material powder, thereby obtaining a wet raw material powder.

[0053] The amount of aromatic compound A added may be 0.01 parts by mass or more and 2 parts by mass or less per 100 parts by mass of raw material powder. When the amount of aromatic compound A added is 2 parts by mass or less, the carbon content of the porous body is sufficiently reduced. When the amount of aromatic compound A added is 0.01 parts by mass or more, a composite powder with excellent weighing stability is easily obtained, and density variation within the porous body (molded body) is easily reduced.

[0054] From the viewpoint of sufficiently suppressing the occurrence of uneven mixing and facilitating the production of a homogeneous composite powder, the amount of additive solution A added is preferably 5 parts by mass or more and 20 parts by mass or less per 100 parts by mass of raw material powder. When the amount of additive solution A added is within the above range, it is easy to adjust the entire raw material powder to a moderately wet state. When the amount of additive solution A added is small, it may be difficult for aromatic compound A to be uniformly distributed throughout the entire raw material powder. When the amount of additive solution A added is large, the raw material powder may become a slurry, and a large amount of additive solution A and raw material powder may adhere to the wall of the mixing container, and a large amount of aromatic compound A may precipitate on the wall of the mixing container during drying (solvent removal process).

[0055] (Solvent removal process) In the solvent removal step, the wet raw material powder is dried while being stirred to remove the solvent, thereby obtaining a composite powder. The composite powder contains the raw material powder and aromatic compound A attached to the surface of the raw material powder particles. Drying can be performed by heating, reducing pressure, or the like. When the solvent is ethanol, drying by heating can be performed at about 50 to 90°C.

[0056] When heat drying is performed, it is preferable to maintain the stirring state until the temperature of the raw material powder drops below the melting point of aromatic compound A. If the stirring is stopped before the temperature of the raw material powder drops below the melting point of aromatic compound A, the molten aromatic compound A may move, resulting in uneven mixing.

[0057] FIG. 1 shows an example of wet mixing of raw material powder and aromatic compound A. Raw material powder 100 is placed in a mixing container 110. A solution 200 of aromatic compound A is added to raw material powder 100 while stirring the raw material powder 100. In this manner, wet raw material powder 100 is obtained. Thereafter, the wet raw material powder 100 placed in the mixing container 110 is dried while being stirred to remove the solvent. In this manner, a composite powder is obtained.

[0058] [Method of manufacturing an anode body for electrolytic capacitors] The anode body for an electrolytic capacitor according to an embodiment of the present disclosure includes a composite powder preparation step, a composite powder molding step, an aromatic compound A removal step, a compact sintering step, and a dielectric layer formation step.

[0059] (Composite powder preparation process) In this step, the composite powder of the present disclosure is prepared. In this step, for example, the composite powder obtained by the above-described manufacturing method is prepared.

[0060] (Composite powder molding process) In the composite powder molding process, the composite powder is filled into a predetermined molding die and pressure-molded to obtain a compact. This compact contains aromatic compound A. In this process, a portion of an anode wire may be embedded in the compact. By including aromatic compound A in the composite powder, mass variation between compacts is reduced. Furthermore, density variation within the compact is reduced, and sufficient density is ensured even at the edges, which tend to have locally low density, ensuring strength and suppressing cracking or chipping at the edges of the compact.

[0061] FIG. 2 is a diagram showing an example of a process for producing a compact from a composite powder. First, as shown in Fig. 2(a), composite powder 300 is poured into a measuring hole 420a having a certain volume, which is formed by a weighing mold 420 and a lower mold 440, and the composite powder 300 is filled into the measuring hole 420a using a leveling slider 410. In this manner, the composite powder 300 is weighed. The composite powder 300 containing aromatic compound A has excellent weighing stability, and the powder 300 can be stably weighed by filling the measuring hole 420a using the leveling slider 410.

[0062] 2(b), the weighed composite powder 300 is placed in a predetermined space 460 formed by a pressing die 430 and a lower die 440. After that, an upper die 450 is placed above the space 460, and an anode wire 6 is inserted into a predetermined hole in the upper die 450 so that a portion of the anode wire 6 is placed in the space 460. 2(c), the pressing die 430 is moved in the direction of the arrow to compress and mold the composite powder 300. In this way, a compact 310 is formed in which a part of the anode wire 6 is embedded.

[0063] For example, as shown in FIGS. 2(b) and 2(c), the powder 300 is piled up at the bottom of the space 460, and then the press die 430 pushes the powder 300 upward to form the compact 310. When a compact is produced using raw powder without adding aromatic compound A, the density is higher at the bottom and lower at the top, resulting in greater density variation within the compact. The strength of the upper corners is particularly low, making them prone to cracking and chipping. In contrast, when a compact is produced using the composite powder of the present disclosure containing aromatic compound A, the density difference between the vertical direction (gravity direction) of the composite powder within the space is reduced, resulting in less density variation within the compact and less reduction in strength at the corners. The composite powder has a low bulk density, and the volume of the powder 300 piled up at the bottom of the space 460 (the apparent volume of the powder including voids between particles) is large. Furthermore, since aromatic compound A is adsorbed to the raw powder, friction between particles in the composite powder is reduced, and powder 300 can easily rise above space 460 during pressure molding using press die 430. These factors are presumed to contribute to the reduction of density variations inside the compact.

[0064] (Aromatic Compound A Removal Step) In the aromatic compound A removal step, the aromatic compound A contained in the compact is removed. The removal step can reduce the amount of aromatic compound A remaining in the compact. As a result, the carbon content derived from aromatic compound A in the sintered compact obtained in the subsequent step can be sufficiently reduced.

[0065] For example, the aromatic compound A contained in the molded body may be removed by vaporization. That is, the removal step may include a step (heating step) of heating the molded body to a predetermined temperature (a temperature equal to or higher than the boiling point of the aromatic compound A) under reduced pressure. When the boiling point of the aromatic compound A is 400°C or lower, the aromatic compound A can be removed at a temperature of about 400 to 500°C under reduced pressure. The reduced pressure in the removal step may be under vacuum, or may be under an atmosphere in which a small amount of inert gas such as Ar gas is introduced while evacuation is being performed using a vacuum pump.

[0066] The removal step may also include a step (immersion step) of immersing the molded body in an organic solvent to dissolve the aromatic compound A in the organic solvent. In the immersion step, the molded body may be immersed while being rocked. Examples of organic solvents include ethanol, isopropanol, and butyl acetate. In the removal step, it is preferable to perform the immersion step followed by a heating step. In this case, the carbon content derived from the aromatic compound A in the sintered body obtained in the subsequent step can be further reduced. When the aromatic compound A is removed by heating a molded body containing a large amount of aromatic compound A (for example, the amount of aromatic compound A added is 1 part by mass), the heating time required for removal may be long. In this case, by combining the immersion step and the heating step, the aromatic compound A can be removed quickly and easily when the amount of aromatic compound A added is large.

[0067] (Sintering process of compact) In the sintering step of the compact, the compact from which the aromatic compound A has been removed is sintered to obtain a porous body (sintered body). Details of the porous body will be described later. The sintering of the compact can be carried out, for example, under reduced pressure at a temperature of 1200 to 1500°C. Note that the reduced pressure in the sintering step is preferably under high vacuum.

[0068] Fig. 3 is a configuration diagram showing an example of equipment used in the step of removing aromatic compound A (heating step) and the step of sintering the compact. In Fig. 3, compact A is a compact containing aromatic compound A (a compact before the treatment of removing aromatic compound A (heating treatment) (including a compact after the immersion step)), and compact B is a compact after the treatment of removing aromatic compound A (heating treatment).

[0069] The equipment 500 includes a removal furnace 510 that removes aromatic compound A from compact A to obtain compact B, a sintering furnace 520 that sinters compact B, a recovery tank 530 that recovers aromatic compound A removed from compact A, heat-insulating piping 540, and a vacuum pump 550. The heat-insulating piping 540 is disposed between the removal furnace 510 and the recovery tank 530.

[0070] The temperature inside the heat-insulating pipe 540 is adjusted to a temperature equal to or higher than the melting point of aromatic compound A. This prevents the aromatic compound A from precipitating inside the pipe 540. For example, if the melting point of aromatic compound A is 120°C or lower (or 100°C or lower), the temperature inside the pipe 540 may be maintained at approximately 120 to 150°C. In this case, there is no need to provide a pipe with a special heat-insulating structure, which is advantageous in terms of manufacturing costs.

[0071] An insulated pipe 540 and a recovery tank 530 are arranged between the removal furnace 510 and the vacuum pump 550. The interiors of the removal furnace 510, the insulated pipe 540, and the recovery tank 530 are depressurized by the vacuum pump 550. The interior of the sintering furnace 520 is also depressurized by the vacuum pump 550. The recovery tank 530 is cooled with liquid nitrogen or the like, and the aromatic compound A is solidified and recovered. Valves may be provided between the removal furnace 510 and the sintering furnace 520, between the removal furnace 510 and the insulated pipe 540, between the insulated pipe 540 and the recovery tank 530, between the recovery tank 530 and the vacuum pump 550, and between the sintering furnace 520 and the vacuum pump 550. The valves may be opened and closed depending on the location and timing where depressurization is required.

[0072] The removal step (heating step) and sintering step using the apparatus of FIG. 3 will be described below. The compact A is supplied to a removal furnace 510 under reduced pressure, where the aromatic compound A is removed from the compact A, thereby producing a compact B. Next, the compact B is supplied to a sintering furnace 520 under reduced pressure and sintered, thereby producing a sintered body. Meanwhile, the aromatic compound A removed by evaporation in the removal furnace 510 passes through a heat-insulating pipe 540 and is recovered in a recovery tank 530.

[0073] In FIG. 3, the removal furnace and the sintering furnace are provided separately, but a single furnace may be provided that serves both the removal furnace and the sintering furnace. That is, the removal step and the sintering step may be performed in a single furnace. The removal furnace and / or the sintering furnace may be configured as a single furnace or may be configured as multiple furnaces. In addition, regarding the vacuum pump, a vacuum pump connected to the collection tank and a vacuum pump connected to the sintering furnace may be provided separately.

[0074] (Dielectric layer forming process) In the dielectric layer forming step, a dielectric layer is formed on the surface of the porous body to obtain an anode body. The dielectric layer is formed, for example, by chemical conversion treatment. Details of the dielectric layer will be described later. By reducing the carbon content of the porous body, the film quality of the dielectric layer formed by chemical conversion treatment is improved, and the performance of the electrolytic capacitor is improved. For example, the leakage current of the electrolytic capacitor can be reduced.

[0075] The electrolytic capacitor will be described in detail below.

[0076] [Electrolytic capacitor] The electrolytic capacitor includes a capacitor element. The capacitor element includes an anode body and a cathode portion. The anode body includes a porous body and a dielectric layer covering the surface of the porous body. The cathode portion is formed to cover the dielectric layer. The cathode portion includes at least a solid electrolyte layer.

[0077] The anode body may include a rod-shaped anode wire partially embedded in the porous body. When the porous body is a rectangular parallelepiped, the anode wire is embedded in one end face of the rectangular parallelepiped. The anode wire may include a valve metal. A portion of the anode wire is embedded in the porous body, and the remainder protrudes from the porous body. The remainder is connected to an anode lead terminal by welding or the like.

[0078] (porous body) The porous body contains a valve metal, such as aluminum (Al), titanium (Ti), tantalum (Ta), niobium (Nb), zirconium (Zr), or hafnium (Hf).

[0079] The porous body is a sintered compact of raw material particles (raw material powder) containing a valve metal. The particles may be particles of a valve metal, particles of an alloy containing a valve metal, or particles of a compound containing a valve metal. The particles may be of one type, or a mixture of two or more types.

[0080] The porous body can be obtained by press-molding raw material particles into a predetermined shape to obtain a compact, and then sintering the compact. For example, an anode wire may be placed in a predetermined position in a mold, raw material particles may be introduced into the mold, and the compact may be press-molded to obtain a compact. A porous body in which a portion of the anode wire is embedded may be obtained by sintering the compact. The porous body is typically a rectangular parallelepiped.

[0081] (dielectric layer) The dielectric layer is formed so as to cover the outer surface of the porous body and the inner wall surfaces of the pores of the porous body. The dielectric layer is formed, for example, by subjecting the porous body to a chemical conversion treatment to grow an oxide film on the surface of the porous body. The chemical conversion treatment may be performed by immersing the porous body in a chemical conversion solution to anodize the surface of the porous body. Alternatively, the surface of the porous body may be oxidized by heating the porous body in an oxygen-containing atmosphere.

[0082] (solid electrolyte layer) The solid electrolyte layer is disposed so as to cover at least a portion of the dielectric layer. The solid electrolyte layer may be filled in the pores of the porous body via the dielectric layer and formed on the outer surface of the porous body. The solid electrolyte layer may be a laminate of two or more different solid electrolyte layers.

[0083] The solid electrolyte layer includes a conductive polymer. The conductive polymer may be a π-conjugated polymer, and examples of the conductive polymer include polypyrrole, polythiophene, polyaniline, and derivatives thereof. These may be used alone or in combination. The conductive polymer may also be a copolymer of two or more monomers. Note that a derivative of a conductive polymer refers to a polymer having a conductive polymer as its basic skeleton. For example, an example of a polythiophene derivative is poly(3,4-ethylenedioxythiophene) (PEDOT).

[0084] A dopant may be added to the conductive polymer. That is, the solid electrolyte layer may include a conductive polymer and a dopant. The conductive polymer may be contained in the solid electrolyte layer in a doped state with the dopant. The dopant can be selected depending on the conductive polymer, and known dopants may be used. Examples of dopants include benzenesulfonic acid, alkylbenzenesulfonic acid, naphthalenesulfonic acid, alkylnaphthalenesulfonic acid, polystyrenesulfonic acid (PSS), and salts thereof. The solid electrolyte layer may include, for example, PEDOT doped with PSS.

[0085] A solid electrolyte layer containing a conductive polymer can be formed, for example, by impregnating a porous body (anode body) having a dielectric layer formed on its surface with a first treatment liquid containing a monomer (or oligomer), and then polymerizing the monomer (or oligomer) by electrolytic polymerization or chemical polymerization. In the case of chemical polymerization, the first treatment liquid contains, for example, a monomer (or oligomer), an oxidizing agent, and a solvent (or dispersion medium). Examples of the monomer include 3,4-ethylenedioxythiophene (EDOT) and pyrrole. The first treatment liquid may also contain a dopant.

[0086] Alternatively, the solid electrolyte layer may be formed by impregnating a porous body (anode body) having a dielectric layer formed on its surface with a treatment liquid containing a conductive polymer, followed by drying. The treatment liquid contains, for example, a conductive polymer, a solvent (or a dispersion medium), and, if necessary, a dopant.

[0087] (others) The capacitor element may include a cathode layer covering at least a portion of the solid electrolyte layer. The electrolytic capacitor may include an anode lead terminal and a cathode lead terminal electrically connected to the capacitor element, and an exterior resin disposed around the capacitor element. The cathode lead terminal is connected to the cathode part via a conductive member. The anode lead terminal is connected to an end of the anode wire protruding from the porous body. The shape, size, etc. of the capacitor element are not particularly limited, and may be a known capacitor element or a capacitor element having a similar configuration.

[0088] (cathode layer) The cathode layer may include a carbon layer formed on the solid electrolyte layer and a metal paste layer formed on the carbon layer. The carbon layer may be formed of a conductive carbon material such as graphite and a resin. The metal paste layer may be formed of metal particles (e.g., silver particles) and a resin, for example, a known silver paste.

[0089] (Conductive material) The cathode layer is connected to the connection portion of the cathode lead terminal by a conductive member. That is, the cathode layer (cathode portion) is electrically connected to the cathode lead terminal. The conductive member is made of a conductive material. The conductive member may be formed using a material containing metal particles (e.g., silver particles) and a resin, or may be formed using, for example, a known metal paste (e.g., silver paste). The conductive member is formed by heating the metal paste. The conductive member may be made of a plurality of conductive layers of different types.

[0090] (exterior resin) The exterior resin is disposed around the capacitor element so that the capacitor element is not exposed on the surface of the electrolytic capacitor. Furthermore, the exterior resin insulates the anode lead terminal from the cathode lead terminal. The exterior resin may be a known exterior resin used for electrolytic capacitors. For example, the exterior resin may be formed using an insulating resin material used to seal the capacitor element. The exterior resin may be formed by placing the capacitor element in a mold, introducing an uncured thermosetting resin and a filler into the mold by transfer molding, compression molding, or the like, and curing the resin.

[0091] Examples of the exterior resin include epoxy resin, phenolic resin, silicone resin, melamine resin, urea resin, alkyd resin, polyurethane, polyimide, unsaturated polyester, etc. The exterior resin may contain substances other than resin (such as inorganic fillers).

[0092] (cathode lead terminal) A portion of the cathode lead terminal is exposed from the exterior resin and is used as a cathode external terminal. The material of the cathode lead terminal may be any material that can be used as a cathode lead terminal of an electrolytic capacitor. For example, a known cathode lead terminal material used in electrolytic capacitors may be used. The cathode lead terminal may be formed by processing a metal sheet (including a metal plate and a metal foil) made of a metal (copper, copper alloy, etc.) using a known metal processing method.

[0093] (Anode lead terminal) A portion of the anode lead terminal is exposed from the exterior resin and is used as an external anode terminal. The material of the anode lead terminal may be any material that can be used as a material for an anode lead terminal of an electrolytic capacitor. For example, a known anode lead terminal material used in electrolytic capacitors may be used. The anode lead terminal may be formed by processing a metal sheet (including a metal plate and a metal foil) made of a metal (copper, copper alloy, etc.) using a known metal processing method.

[0094] 4 is a cross-sectional view schematically illustrating an example of the electrolytic capacitor according to this embodiment, but the electrolytic capacitor according to this embodiment is not limited to this.

[0095] Electrolytic capacitor 20 includes capacitor element 10, exterior resin 11 that seals capacitor element 10, and anode lead terminal 12 and cathode lead terminal 13 that are electrically connected to capacitor element 10. A portion of anode lead terminal 12 and cathode lead terminal 13 are each exposed from exterior resin 11. A portion of anode lead terminal 12 and cathode lead terminal 13 are covered by exterior resin 11 together with capacitor element 10.

[0096] Capacitor element 10 includes an anode body 1, a solid electrolyte layer 2 formed on anode body 1, and a cathode layer 3 formed on solid electrolyte layer 2. Anode body 1 includes a porous body 4 containing a valve metal, and a dielectric layer 5 covering porous body 4. Dielectric layer 5 is formed so as to cover the outer surface of porous body 4 and the inner wall surfaces of the pores.

[0097] The porous body 4 has a substantially rectangular parallelepiped shape and six side surfaces. A portion of the anode wire 6 extends from one side surface of the porous body 4. That is, the anode wire 6 has a first portion 6a that is embedded inside the porous body 4 from one side surface of the porous body 4, and a second portion 6b that extends from the one side surface of the porous body 4. The second portion 6b is joined to an anode lead terminal 12 by welding or the like.

[0098] The solid electrolyte layer 2 is formed so as to cover at least a portion of the dielectric layer 5. The solid electrolyte layer 2 fills the pores of the porous body 4 (anode body 1). The solid electrolyte layer 2 is formed so as to cover the outer surface S of the porous body 4 and the inner wall surfaces of the pores, with the dielectric layer 5 interposed therebetween.

[0099] The cathode layer 3 is formed to cover the surface of the solid electrolyte layer 2. The cathode layer 3 has a carbon layer 3a formed to cover the solid electrolyte layer 2 and a metal paste layer 3b formed on the surface of the carbon layer 3a. The cathode lead terminal 13 is joined to the cathode layer 3 (metal paste layer 3b) via a conductive member 8. The carbon layer 3a contains a conductive carbon material such as graphite and a resin. The metal paste layer 3b contains, for example, metal particles (e.g., silver) and a resin. The configuration of the cathode layer 3 is not limited to this configuration. The cathode layer 3 may have any configuration as long as it has a current collecting function.

[0100] <<Notes>> The above description of the embodiments discloses the following techniques. (Technology 1) A composite powder used to manufacture a porous body included in an anode body of an electrolytic capacitor, The composite powder includes a raw material powder containing a valve action metal and an aromatic compound (excluding naphthalene and a polymer) attached to the surface of particles of the raw material powder, The composite powder has a melting point of 35°C or higher and 120°C or lower. (Technology 2) 2. The composite powder according to claim 1, wherein the aromatic compound has a boiling point of 400°C or less. (Technology 3) 3. The composite powder according to claim 1 or 2, wherein the aromatic compound contains an oxygen atom. (Technology 4) 3. The composite powder according to claim 1 or 2, wherein the aromatic compound is composed of only carbon atoms, hydrogen atoms, and oxygen atoms. (Technology 5) 3. The composite powder according to claim 1, wherein in the aromatic compound, a part of the carbon atoms constituting the benzene ring is substituted with an oxygen atom, or an oxygen atom is bonded to at least one of the carbon atoms constituting the benzene ring. (Technology 6) 3. The composite powder according to claim 1 or 2, wherein the aromatic compound comprises at least one selected from the group consisting of coumarin, vanillin, thymol, p-methoxyphenol, phenyl salicylate, benzyl, and 3-phenylpropionic acid. (Technology 7) the solubility of the aromatic compound in 100 g of a solvent at 20°C is 10 g or more; 7. The composite powder according to any one of techniques 1 to 6, wherein the solvent is ethanol, isopropanol, or butyl acetate. (Technology 8) 8. The composite powder according to any one of techniques 1 to 7, wherein the content of the aromatic compound in the composite powder is 0.01 parts by mass or more and 2 parts by mass or less per 100 parts by mass of the raw material powder. (Technology 9) 9. The composite powder according to any one of techniques 1 to 8, wherein the bulk density of the composite powder is lower than the bulk density of the raw material powder. (Technology 10) 10. The composite powder according to any one of techniques 1 to 9, wherein the anode body comprises the porous body containing the valve metal and a dielectric layer covering the surface of the porous body. (Technology 11) A method for producing a composite powder used to produce a porous body included in an anode body of an electrolytic capacitor, comprising: preparing a raw material powder containing a valve action metal; A step of preparing an additive solution containing an aromatic compound (excluding naphthalene and polymers) having a melting point of 35°C or higher and 120°C or lower, and a solvent; adding the additive solution to the raw material powder while stirring the raw material powder to obtain the raw material powder in a wet state; and a step of removing the solvent by drying the wet raw material powder while stirring to obtain a composite powder, The composite powder comprises the raw material powder and the aromatic compound adhered to the surface of particles of the raw material powder. (Technology 12) 12. The method for producing a composite powder according to claim 11, wherein the aromatic compound has a boiling point of 400°C or less. (Technology 13) 13. The method for producing a composite powder according to claim 11 or 12, wherein the aromatic compound includes at least one selected from the group consisting of coumarin, vanillin, thymol, p-methoxyphenol, phenyl salicylate, benzyl, and 3-phenylpropionic acid. (Technology 14) 14. The method for producing a composite powder according to any one of techniques 11 to 13, wherein the content of the aromatic compound in the composite powder is 0.01 parts by mass or more and 2 parts by mass or less per 100 parts by mass of the raw material powder. (Technology 15) 15. The method for producing a composite powder according to any one of techniques 11 to 14, wherein the amount of the additive solution added is 5 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the raw material powder. (Technology 16) 16. The method for producing a composite powder according to any one of techniques 11 to 15, wherein the solvent includes at least one selected from the group consisting of ethanol, isopropanol, and butyl acetate. (Technology 17) 17. The method for producing a composite powder according to any one of techniques 11 to 16, wherein the anode body comprises the porous body containing the valve metal and a dielectric layer covering the surface of the porous body. (Technology 18) 18. The method for producing a composite powder according to any one of techniques 11 to 17, wherein the solubility of the aromatic compound in 100 g of ethanol, isopropanol, or butyl acetate at 20° C. is 10 g or more. (Technology 19) A step of preparing a composite powder including a raw material powder containing a valve action metal and an aromatic compound (excluding naphthalene and polymers) attached to the surface of particles of the raw material powder; a step of filling the composite powder into a predetermined molding die and press-molding the composite powder to obtain a molded body; removing the aromatic compound contained in the molded body; sintering the compact from which the aromatic compound has been removed to obtain a porous body; forming a dielectric layer on the surface of the porous body to obtain an anode body; Including, The method for producing an anode body for an electrolytic capacitor, wherein the aromatic compound has a melting point of 35°C or higher and 120°C or lower. (Technology 20) 20. The method for producing an anode body for an electrolytic capacitor according to claim 19, wherein the aromatic compound has a boiling point of 400° C. or lower. (Technology 21) 21. The method for producing an anode body for an electrolytic capacitor according to claim 19, wherein the aromatic compound includes at least one selected from the group consisting of coumarin, vanillin, thymol, p-methoxyphenol, phenyl salicylate, benzyl, and 3-phenylpropionic acid. (Technology 22) 22. The method for producing an anode body for an electrolytic capacitor according to any one of claims 19 to 21, wherein the content of the aromatic compound in the composite powder is 0.01 parts by mass or more and 2 parts by mass or less per 100 parts by mass of the raw material powder. (Technology 23) 23. The method for producing an anode body for an electrolytic capacitor according to any one of claims 19 to 22, wherein the step of removing the aromatic compound contained in the compact includes a heating step of heating the compact to vaporize the aromatic compound. (Technology 24) The step of removing the aromatic compound contained in the molded body includes: an immersion step of immersing the molded body in an organic solvent to dissolve the aromatic compound into the solvent; and a heating step performed after the immersion step. (Technology 25) 25. The method for producing an anode body for an electrolytic capacitor according to claim 24, wherein the organic solvent is ethanol, isopropanol, or butyl acetate.

[0101] [Example] Hereinafter, the present disclosure will be specifically described based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0102] Examples 1 to 7, 9 to 10 (Preparation of composite powder) Ta powder (average particle size: 80 μm, CV value: 70 kCV (nominal capacitance: 70,000 μF / g)) was prepared as the raw material powder. An additive solution containing an additive and a solvent was prepared. As the additive, coumarin or vanillin was used as aromatic compound A. Ethanol was used as the solvent. Coumarin and vanillin have melting points in the range of 35 to 120°C, boiling points of 400°C or less, and a solubility of 10 g or more in 100 g of ethanol.

[0103] The additive solution was added to the raw powder while stirring, to obtain a wet raw powder (Figure 1). The amount of additive added was the value (parts by mass) shown in Table 1 per 100 parts by mass of raw powder. The concentration of the additive solution was adjusted appropriately so that the amount of additive solution added was within the range of 5 to 20 parts by mass per 100 parts by mass of raw powder. The wet raw powder was heated and dried at a temperature of 90°C or less while stirring, to remove the solvent. In this way, a composite powder containing the raw powder and the additive attached to the surface of the raw powder particles (Ta particles with additives attached to their surfaces: composite particles) was obtained.

[0104] (Production of molded body) A predetermined amount of composite powder was filled into a predetermined molding die by leveling and weighing (Fig. 2(a)). One end of an anode wire was embedded in the part filled with composite powder (Fig. 2(b)). The composite powder was then pressed to obtain a compact (Fig. 2(c)). The outer shape of the compact was a rectangular parallelepiped (0.8mm x 3.7mm x 5.2mm). Ta wire was used as the anode wire.

[0105] (Removal of additives) The compact was heated under reduced pressure at 400 to 500° C. to remove the additives contained in the compact (a compact heating step).

[0106] (Production of sintered body) Next, the compact from which the additives had been removed was sintered under reduced pressure at 1300 to 1400°C. The sintering temperature and time were adjusted so that the shrinkage rate was about 10%. In this way, a porous body (Ta sintered body) with a portion of the anode wire embedded was obtained.

[0107] Example 8 In the additive removal step, the compact was subjected to an immersion step, and then the compact was subjected to a heating step.

[0108] Specifically, the immersion process for the compacts was carried out as follows. The compacts were placed in a stainless steel basket-shaped container, and the basket-shaped container containing the compacts was immersed in ethanol in a beaker for 10 minutes. During the immersion, the basket-shaped container was swung up and down within the beaker at a speed of approximately one reciprocating movement per 2 seconds. The basket-shaped container was then removed from the beaker, and the compacts in the basket-shaped container were transferred to a petri dish and dried at 80°C.

[0109] Except for the above, a composite powder was prepared, a compact was prepared, and a sintered body was prepared in the same manner as in Example 5.

[0110] Comparative Example 1 An acrylic resin solution (solvent: toluene) was prepared as an additive solution instead of a coumarin solution. The amount of acrylic resin added was 1.5 parts by mass per 100 parts by mass of the raw material powder. Other than the above, a composite powder was prepared in the same manner as in Example 1, a compact was prepared, and a sintered body was prepared.

[0111] Comparative Example 2 Instead of the coumarin solution, a camphor solution (solvent: methanol) was prepared as the additive solution. The amount of camphor added was 1.5 parts by mass per 100 parts by mass of the raw material powder. Other than the above, a composite powder was prepared in the same manner as in Example 1, a compact was prepared, and a sintered body was prepared.

[0112] Comparative Example 3 A compact was produced in the same manner as in Example 1, except that the raw material powder was used as is instead of the composite powder, and then a sintered body was produced.

[0113] Comparative Example 4 While stirring the raw powder, only a solvent was added to the raw powder instead of the additive solution, to obtain a wet raw powder. Ethanol was used as the solvent. The wet raw powder was heated and dried at a temperature of 90°C or less while stirring to remove the solvent, to obtain a dry raw powder. A compact was produced in the same manner as in Example 1, except that this raw powder was used instead of the composite powder, and a sintered body was then produced.

[0114] The green bodies and sintered bodies produced in the above examples and comparative examples were evaluated as follows.

[0115] [evaluation] (Quality rate of molded products) To evaluate the weighing stability of the powder, the yield rate of the molded products was calculated. Specifically, 300 molded products were produced using an automatic molding machine, and the masses of the 300 molded products were measured. The percentage of the 300 molded products whose mass was within ±0.5% of the target mass (good products) was calculated as the yield rate of the molded products. When the weighing stability of the powder is high, the mass variation of the molded products is reduced, and the yield rate of the molded products increases.

[0116] (Carbon content of sintered body) The carbon content (ppm by mass) of the sintered body was determined using approximately 1 g of the sintered body. The measurement device used was a carbon / sulfur analyzer (manufactured by Horiba, Ltd.).

[0117] (LC in liquid) The sintered body with the anode wire partially embedded therein was subjected to chemical conversion treatment (anodization). The chemical conversion treatment was carried out in a 0.02 mass% aqueous solution of phosphoric acid at a chemical conversion voltage of 80 V and a temperature of 60°C. A predetermined voltage of less than 80 V was applied to the sintered body (anode body) after the chemical conversion treatment in the phosphoric acid aqueous solution, and the current value at the time a predetermined time had elapsed since the start of voltage application was determined as the in-liquid LC (leakage current).

[0118] (Ratio of bulk density D2 of composite powder converted to raw powder to bulk density D1 of raw powder) (Bulk density of raw powder D1) The bulk density D1 of the raw material powder was determined by the following method using a measuring jig set shown in FIG.

[0119] A measuring jig set 600 shown in FIG. 5 was prepared. Specifically, a stainless steel hollow cylindrical filling jig 610 (inner diameter 20 mm), a stainless steel plate-shaped weighing jig 620 (thickness 8 mm) having a circular cross-section hole 620a (diameter 8 mm, depth 8 mm) in the center, and a metal plate 640 were prepared. As shown in FIG. 5, the weighing jig 620 was placed on the metal plate 640, and the filling jig 610 was placed on the weighing jig 620. At this time, the filling jig 610 was placed in a position that did not overlap with the weighing hole 620a. Five grams of raw powder 700 was loaded into the hollow portion 610a of the filling jig 610, and the filling jig 610 was reciprocated once (in the direction of the arrow shown in FIG. 5) so as to pass through the weighing hole 620a of the weighing jig 620. In this way, the powder 700 was filled into the weighing hole 620a. Next, the powder 700 filled in the measuring hole 620a was removed and its mass was measured. This measurement was repeated 10 times. The average of the 10 measurements was calculated as the mass M1 of the raw material powder filled in the measuring hole 620a. The bulk density D1 of the raw material powder was calculated by dividing the mass M1 by the volume V of the measuring hole 620, i.e., by calculating M1 / V.

[0120] (Bulk density D2 of composite powder converted to raw powder) The mass M2 of the composite powder filled in the measuring hole 620a was determined using the same method as above. The mass M2a of the composite powder converted into raw material powder was determined by calculating M2 / (1+(X / 100)). Note that "X" in the formula is the content of the additive in the composite powder (amount (parts by mass) per 100 parts by mass of raw material powder), and is the amount of additive added (parts by mass) in Table 1.

[0121] The mass M2a of the obtained composite powder in terms of raw material powder was divided by the volume V of the weighing hole 620, ie, M2a / V was calculated to determine the bulk density D2 of the composite powder in terms of raw material powder.

[0122] Using the obtained D1 and D2, calculate D2 / D1.

[0123] (Sintered body density distribution index) In order to evaluate the density variation of the sintered body, the density distribution index of the side surface of the sintered body was determined as follows.

[0124] Here, FIG. 6 is a perspective view that schematically shows a porous body (sintered body) in which a part of the anode wire is embedded. The porous body (sintered body) 4 shown in Figure 6 has a first surface 4a and a second surface 4b, a third surface 4c and a fourth surface 4d, a fifth surface 4e and a sixth surface (not shown) opposite the fifth surface 4e. The third surface 4c and the fourth surface 4d are narrower than the fifth surface 4e and the sixth surface 4d. A portion of the anode wire 6 is embedded in the porous body 4, and the remainder extends from the first surface 4a of the porous body 4 to the outside.

[0125] First, three straight lines were drawn on the fourth surface 4d of the porous body (sintered body) 4 in the longitudinal direction of the anode wire 6. The central line Lc divided the width of the fourth surface 4d perpendicular to the longitudinal direction into two equal parts. Two lines L1 and L2 were drawn 0.25 mm away from the central line Lc, sandwiching the central line Lc. Next, 12 straight lines M1 to M12 were drawn in a direction perpendicular to the longitudinal direction of the anode wire 6. The line M1 closest to the first surface 4a was drawn 0.25 mm away from the end of the fourth surface 4d on the first surface 4a side. The line M12 closest to the second surface 4b was similarly drawn 0.25 mm away from the end of the fourth surface 4d on the second surface 4b side. The remaining 10 straight lines were drawn so as to divide the space between lines M1 and M2 into 11 equal parts. The Vickers hardness was measured at 36 points where the lines Lc, L1, and L2 intersected with the lines M1 to M12 (see FIG. 6). The Vickers hardness was measured in accordance with JIS Z 2244. The average value and standard deviation of the measurements at the 36 points were determined, and the coefficient of variation was calculated by dividing the standard deviation by the average value.

[0126] The coefficient of variation was determined for each of the five sintered bodies, and the average of the five coefficients of variation was calculated and used as the density distribution index of the side surface of the sintered body. A small density distribution index indicates small density variation of the sintered body.

[0127] The evaluation results are shown in Table 1. The amounts of additives added in Table 1 are the amounts per 100 parts by mass of the raw material powder.

[0128] [Table 1]

[0129] In Examples 1 to 10, in which aromatic compound A was used as an additive, the yield rate of the compacts was high and the mass variation between the compacts was small. Furthermore, because the density variation within the compacts was small, the density distribution index on the side of the sintered compact was small, and the density variation within the sintered compact was also small. The carbon content of the sintered compact was reduced, and the liquid LC was reduced. Because the density variation within the compacts was small, the occurrence of cracks and chips at the corners of the compacts was suppressed. When the amount of aromatic compound A added was large, the ratio of the bulk density of the composite powder converted into raw material powder to the bulk density of the raw material powder tended to decrease, and the density distribution index on the side of the sintered compact tended to decrease (Examples 1 to 7 for coumarin, and Examples 9 to 10 for vanillin).

[0130] When the amount of aromatic compound A added was large, the weighing stability of the powder improved and the yield of the compacts increased.When the amount of aromatic compound A added was small, the carbon content of the sintered compacts was reduced and the LC in the liquid was reduced.

[0131] When the immersion step and the heating step were used in combination in the aromatic compound A removal step, the carbon content of the sintered body was significantly reduced while maintaining a small value of the density distribution index on the side surface of the sintered body, and the LC in the liquid was significantly reduced (Examples 5 and 8), compared to when the aromatic compound A removal was performed by the heating step alone.

[0132] In Comparative Example 1, where the additive was an acrylic resin, the carbon content was high and the LC in the liquid increased. In Comparative Example 2, camphor was added to Ta powder with an average particle size of less than 100 μm, which reduced weighing stability, the yield of non-defective molded products, and the molding yield.

[0133] In Comparative Example 4, the bulk density of the raw material powder was greater than that of Comparative Example 3. This is presumably because the raw material powder was more likely to aggregate than in Comparative Example 3 due to the influence of ethanol used as a solvent in Comparative Example 4. [Industrial Applicability]

[0134] The composite powder according to the present disclosure is suitable for use in producing a porous body included in an anode body of an electrolytic capacitor. [Explanation of symbols]

[0135] 1: anode body, 2: solid electrolyte layer, 3: cathode layer, 3a: carbon layer, 3b: metal paste layer, 4: porous body, 5: dielectric layer, 6: anode wire, 6a: first part, 6b: second part, 8: conductive member, 10: capacitor element, 11: exterior resin, 12: anode lead terminal, 13: cathode lead terminal, 20: electrolytic capacitor, 100: raw material powder, 110: mixing container, 200: solution of aromatic compound A, 300: composite powder, 310: Compacted body, 410: leveling slider, 420: weighing mold, 430: pressing mold, 440: lower mold, 450: upper mold, 460: space, 500: equipment, 510: aromatic compound A removal furnace, 520: sintering furnace, 530: aromatic compound A recovery tank, 540: heat-insulating piping, 550: vacuum pump, 600: evaluation jig set, 610: filling jig, 610a: hollow portion, 620: weighing jig, 620a: weighing hole, 640: metal plate, 700: powder

Claims

1. A composite powder used to manufacture a porous body included in an anode body of an electrolytic capacitor, the composite powder includes a raw material powder containing a valve action metal and an aromatic compound (excluding naphthalene and a polymer) attached to the surface of particles of the raw material powder, The composite powder, wherein the melting point of the aromatic compound is 35°C or higher and 120°C or lower.

2. 2. The composite powder according to claim 1, wherein the aromatic compound has a boiling point of 400°C or less.

3. The composite powder of claim 1 , wherein the aromatic compound contains an oxygen atom.

4. 2. The composite powder of claim 1, wherein the aromatic compound is composed of only carbon, hydrogen, and oxygen atoms.

5. 2. The composite powder according to claim 1, wherein in the aromatic compound, a portion of the carbon atoms constituting the benzene ring is substituted with an oxygen atom, or an oxygen atom is bonded to at least one of the carbon atoms constituting the benzene ring.

6. 2. The composite powder according to claim 1, wherein the aromatic compound comprises at least one selected from the group consisting of coumarin, vanillin, thymol, p-methoxyphenol, phenyl salicylate, benzyl, and 3-phenylpropionic acid.

7. the solubility of the aromatic compound in 100 g of a solvent at 20°C is 10 g or more; 2. The composite powder of claim 1, wherein the solvent is ethanol, isopropanol, or butyl acetate.

8. 2. The composite powder according to claim 1, wherein the content of the aromatic compound in the composite powder is 0.01 parts by mass or more and 2 parts by mass or less per 100 parts by mass of the raw material powder.

9. The composite powder according to claim 1 , wherein the bulk density of the composite powder in terms of the raw material powder is lower than the bulk density of the raw material powder.

10. The composite powder according to claim 1 , wherein the anode body comprises the porous body containing the valve metal and a dielectric layer covering a surface of the porous body.

11. A method for producing a composite powder used to produce a porous body included in an anode body of an electrolytic capacitor, comprising: preparing a raw material powder containing a valve action metal; preparing an additive solution containing an aromatic compound (excluding naphthalene and polymers) having a melting point of 35°C or higher and 120°C or lower, and a solvent; adding the additive solution to the raw material powder while stirring the raw material powder to obtain the raw material powder in a wet state; and a step of removing the solvent by drying the wet raw material powder while stirring to obtain a composite powder, The composite powder comprises the raw material powder and the aromatic compound adhered to the surface of particles of the raw material powder.

12. The method for producing a composite powder according to claim 11, wherein the aromatic compound has a boiling point of 400°C or less.

13. 12. The method for producing a composite powder according to claim 11, wherein the aromatic compound includes at least one selected from the group consisting of coumarin, vanillin, thymol, p-methoxyphenol, phenyl salicylate, benzyl, and 3-phenylpropionic acid.

14. The method for producing a composite powder according to claim 11, wherein the content of the aromatic compound in the composite powder is 0.01 parts by mass or more and 2 parts by mass or less per 100 parts by mass of the raw material powder.

15. The method for producing a composite powder according to claim 11, wherein the amount of the additive solution added is 5 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the raw material powder.

16. The method for producing a composite powder according to claim 11 , wherein the solvent includes at least one selected from the group consisting of ethanol, isopropanol, and butyl acetate.

17. The method for producing a composite powder according to claim 11 , wherein the anode body comprises the porous body containing the valve metal and a dielectric layer covering a surface of the porous body.

18. 12. The method for producing a composite powder according to claim 11, wherein the solubility of the aromatic compound in 100 g of ethanol, isopropanol, or butyl acetate at 20°C is 10 g or more.

19. preparing a composite powder including a raw material powder containing a valve action metal and an aromatic compound (excluding naphthalene and polymers) attached to the surface of particles of the raw material powder; a step of filling the composite powder into a predetermined molding die and press-molding the composite powder to obtain a molded body; removing the aromatic compound contained in the molded body; sintering the compact from which the aromatic compound has been removed to obtain a porous body; forming a dielectric layer on the surface of the porous body to obtain an anode body; Including, The method for producing an anode body for an electrolytic capacitor, wherein the aromatic compound has a melting point of 35°C or higher and 120°C or lower.

20. 20. The method for producing an anode body for an electrolytic capacitor according to claim 19, wherein the aromatic compound has a boiling point of 400°C or lower.

21. 20. The method for producing an anode body for an electrolytic capacitor according to claim 19, wherein the aromatic compound includes at least one selected from the group consisting of coumarin, vanillin, thymol, p-methoxyphenol, phenyl salicylate, benzyl, and 3-phenylpropionic acid.

22. 20. The method for producing an anode body for an electrolytic capacitor according to claim 19, wherein a content of the aromatic compound in the composite powder is 0.01 parts by mass or more and 2 parts by mass or less per 100 parts by mass of the raw material powder.

23. 20. The method for manufacturing an anode body for an electrolytic capacitor according to claim 19, wherein the step of removing the aromatic compound contained in the compact includes a heating step of heating the compact to vaporize the aromatic compound.

24. The step of removing the aromatic compound contained in the molded body includes: an immersion step of immersing the molded body in an organic solvent to dissolve the aromatic compound into the solvent; The method for manufacturing an anode body for an electrolytic capacitor according to claim 23 , further comprising:

25. 25. The method for producing an anode body for an electrolytic capacitor according to claim 24, wherein the organic solvent is ethanol, isopropanol, or butyl acetate.

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