Electrolytic capacitors and manufacturing methods

Abstract

The electrolytic capacitor is equipped with an anodic sintered body made of sintered valve metal powder, and the tanδ of the electrolytic capacitor is improved by including a voltage-resistant agent in the electrolyte. [Solution] The electrolytic capacitor comprises an anode sintered body, a cathode body, and an electrolyte, and the manufacturing method includes an anode formation step, a chemical conversion step, an element formation step, a preparation step, and an impregnation step. The anode sintered body has a valve metal substrate, a sintered layer formed by sintering valve metal powder on the surface of the valve metal substrate, and a dielectric film formed on the sintered layer. The electrolyte contains inorganic oxide colloidal particles. The anode formation step forms the anode sintered body by sintering valve metal powder on the valve metal substrate. The chemical conversion step forms a dielectric film on the surface of the sintered layer. The element formation step forms a capacitor element by facing the anode sintered body and the cathode body with a separator in between. The preparation step prepares an electrolyte containing inorganic oxide colloidal particles. The impregnation step impregnates the capacitor element with the electrolyte.

Description

Technical Field

[0001] The present invention relates to an electrolytic capacitor having a sintered body anode and a manufacturing method thereof.

Background Art

[0002] An electrolytic capacitor includes a valve metal such as tantalum or aluminum as an anode body and a cathode body. The anode body is enlarged in surface area by forming the valve metal into a shape such as a sintered body or an etched foil, and has a dielectric film on the enlarged surface by a treatment such as anodic oxidation. An electrolytic solution is interposed between the anode body and the cathode body. The electrolytic solution adheres closely to the uneven surface of the anode body and functions as a true cathode.

[0003] Electrolytic capacitors are used in various applications. For example, in the field of power electronics, in a power supply circuit that converts the power of an AC power supply into DC power by a converter circuit and then converts this DC power into desired AC power by an inverter circuit, a smoothing capacitor is provided to suppress and smooth the DC pulsation output from the converter circuit before inputting it into the inverter circuit. Also, a decoupling capacitor is provided in the vicinity of a semiconductor switching element such as gallium nitride for the stable operation and noise removal of the semiconductor switching element. And with the recent trend towards higher power, the requirements for higher capacitance and higher withstand voltage of electrolytic capacitors have become stronger.

[0004] An electrolytic capacitor can increase the specific surface area by enlarging the surface area of the anode body, and thus has a large capacitance and can meet the requirement for higher capacitance. Also, the contact area between the electrolytic solution and the dielectric film of the anode body increases. Therefore, it is easy to further increase the capacitance of the electrolytic capacitor.

[0005] To increase the capacitance of electrolytic capacitors, improving the capacitance per unit volume is crucial. The capacitance of an electrolytic capacitor is proportional to the surface area of ​​the dielectric film. Therefore, etching is performed to enlarge the surface area, and the etching pits tend to extend deeper than the surface of the electrode foil. In other words, in electrolytic capacitors, the core of the anode body tends to become thinner and thinner. As a result, the anode body is prone to becoming brittle, and bending occurs in places when a winding configuration is used.

[0006] If the anode material becomes bent in places, the capacitor element will become larger. Alternatively, if the anode material becomes bent in places, the capacitance per unit volume will decrease. Otherwise, it will be treated as a defective product, resulting in a decrease in yield.

[0007] Therefore, a method of increasing the surface area by forming an anodic sintered body having a sintered layer of valve-acting metal has been investigated (see, for example, Patent Document 1). The sintered body has a porous structure in which the valve-acting metal powders maintain voids between each other. As a result, the surface area of ​​the anode body is increased.

[0008] Furthermore, to increase the voltage rating of electrolytic capacitors, it is also effective to increase the spark voltage of the electrolyte. Therefore, in response to the demand for higher voltage ratings, a voltage rating enhancer is added to the electrolyte. Examples of voltage rating enhancers include polyethylene glycol, polyglycerin, and colloidal silica (see, for example, Patent Document 2). [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Patent No. 7168823 [Patent Document 2] Japanese Patent Publication No. 2011-176102 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] Electrolytic capacitors that achieve high capacitance by incorporating an anodic sintered body made of sintered valve metal powder, and improve voltage resistance by adding a voltage-reducing agent to the electrolyte, have been found to have inferior dielectric loss tangent (tanδ).

[0011] The present invention was proposed to solve the above problems, and its objective is to provide an electrolytic capacitor and a manufacturing method that includes an anodic sintered body made by sintering powder of a valve-acting metal, and improves tanδ while including a pressure-resistant agent in the electrolyte. [Means for solving the problem]

[0012] To solve the above problems, the electrolytic capacitor of this embodiment comprises a valve-acting metal substrate, a sintered layer formed by sintering valve-acting metal powder on the surface of the valve-acting metal substrate, and an anodic sintered body having a dielectric film formed on the sintered layer, a cathode body facing the anodic sintered body, and an electrolyte containing inorganic oxide colloidal particles.

[0013] The inorganic oxide colloid particles may be silica.

[0014] The content of the inorganic oxide colloid particles may be 17 wt% or less relative to the total amount of the electrolyte.

[0015] The inorganic oxide colloid particles may be surface-modified with an organic substance.

[0016] The electrolyte may contain the inorganic oxide colloid particles and a solute, and the solute content may be 5 wt% or more and 25 wt% or less of the total amount of the electrolyte.

[0017] The anode sintered body may have a segmented portion that divides the sintered layer.

[0018] In order to solve the above problems, the method for manufacturing an electrolytic capacitor according to the present embodiment includes an anode forming step of forming an anode sintered body having a sintered layer by sintering powder of a valve-acting metal on a valve-acting metal base material, a chemical conversion step of forming a dielectric film on the surface layer of the sintered layer, an element forming step of forming a capacitor element in which the anode sintered body and the cathode body are opposed to each other through a separator, a preparation step of preparing an electrolytic solution containing inorganic oxide colloid particles, and an impregnation step of impregnating the capacitor element with the electrolytic solution.

[0019] The anode forming step may further include a step of dividing the sintered layer.

Effects of the Invention

[0020] According to the present invention, the tanδ of an electrolytic capacitor combining an anode sintered body and a withstand voltage improver in an electrolytic solution can be improved.

Brief Description of the Drawings

[0021] [Figure 1] It is a graph showing the increase rate of tanδ in each example and each comparative example.

Embodiments for Carrying Out the Invention

[0022] Hereinafter, an electrolytic capacitor and a manufacturing method according to an embodiment will be described. Note that the present invention is not limited to the embodiments described below.

[0023] (Electrolytic Capacitor) An electrolytic capacitor is a passive element that obtains capacitance by the dielectric polarization action of a dielectric film and stores and discharges electric charges. The electrolytic capacitor includes a capacitor element. The capacitor element includes an anode sintered body, a cathode body, and an electrolytic solution. A dielectric film is formed on the surface of the anode sintered body. The anode sintered body and the cathode body are opposed to each other with a separator interposed therebetween. The electrolytic solution is impregnated in the capacitor element. By impregnating the capacitor element, the electrolytic solution is interposed between the dielectric film of the anode sintered body and the cathode body and adheres to the dielectric film of the anode sintered body to function as a true cathode.

[0024] (Anode sintered body) The anode sintered body is a laminate of a valve - acting metal base material and a sintered layer. The valve - acting metal base material is a foil body obtained by stretching a valve - acting metal. The sintered layer is formed on one or both sides of the valve - acting metal base material. This sintered layer is a porous structure formed by adhering and sintering a powder of the valve - acting metal to the valve - acting metal base material. Due to the porous structure of the sintered layer, the surface of the anode sintered body is enlarged, and the surface area of the anode sintered body is increased.

[0025] The valve - acting metals are aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, antimony, etc. The purity of the valve - acting metal is desirably 99.9% or more with respect to the anode body, and other elements such as silicon, iron, copper, manganese, magnesium, chromium, zinc, titanium, vanadium, gallium, nickel, boron, and zirconium may be included.

[0026] The electrolytic capacitor can adopt a wound type. The wound - type capacitor element is a wound body. The anode sintered body, the cathode body, and the separator have a long strip shape. After overlapping the anode sintered body and the cathode body with the separator sandwiched therebetween, the laminate of the anode sintered body, the cathode body, and the separator is wound.

[0027] When the electrolytic capacitor adopts a wound type, the sintered layer may have a plurality of dividing portions that divide the sintered layer. The dividing portions are formed by cracking the surface layer of the sintered layer, splitting the surface layer, making a cut in the surface layer, making a notch in the surface layer, or digging into the surface layer. That is, examples of the actual state of the dividing portion are cracks, splits, cuts, notches, or digs. This dividing portion is deep in the direction from the surface of the sintered layer toward the core portion and generally extends in the direction along the winding axis of the winding.

[0028] Because the sintered layer has a segmented section, bending stress is dispersed. In the case of wound electrolytic capacitors, this makes it less likely for cracks that could damage the base foil to occur during winding, allowing for smooth and well-formed winding. Furthermore, the formation of segmented sections makes it easier for the electrolyte to penetrate the sintered layer, i.e., the porous structure, which is thought to improve the capacitance retention rate.

[0029] The dielectric film is formed on the surface layer of one or both sides of the anodic sintered body. Typically, the dielectric film is an oxide film formed on the surface layer of the anodic sintered body, and if the anodic sintered body is made of aluminum, it is an aluminum oxide layer obtained by oxidizing the sintered layer. To obtain the desired withstand voltage, the dielectric film is preferably formed with a thickness of 0.9 to 1.5 nm per 1 V of the desired withstand voltage. A pseudo-boehmite layer may be formed on the dielectric film. The pseudo-boehmite layer contains a hydrated aluminum oxide, such as AlOOH·xH2O or Al2O3·xH2O. On the other hand, the dielectric film is a layer of aluminum oxide containing γ-alumina, which is a crystalline oxide. This pseudo-boehmite layer is dense internally and functions as a resistive layer to improve the withstand voltage of the electrolytic capacitor.

[0030] (Cathole body) The cathode body is, for example, a foil body stretched from a valve metal. The purity of the valve metal is preferably 99% or higher with respect to the cathode body. An expanding layer is formed on the cathode body. A plain foil without an expanding layer may also be used as the cathode body. The expanding layer is a porous structure obtained by treating the anode body to increase its surface area. The expanding layer is an etched layer obtained by etching the foil body, a sintered layer obtained by sintering valve metal powder, or a deposited layer obtained by depositing valve metal particles onto the foil. That is, the expanding layer consists of tunnel-shaped pits, spongy pits, or densely packed powder or voids between particles.

[0031] The cathode body may have a thin oxide film of about 1 to 10 Vfs, formed by a native oxide film or a chemical conversion treatment. The native oxide film is formed when the cathode body reacts with oxygen in the air.

[0032] Furthermore, the cathode body may be provided with a conductive layer. The conductive layer is laminated on the cathode foil. The conductive layer may mainly contain inorganic materials or inorganic compounds. Examples of inorganic materials or inorganic compounds include titanium, zirconium, tantalum, niobium, nitrides or carbides thereof, aluminum carbide, carbon materials, and composites or mixtures thereof. Specifically, examples include a carbon layer which is a conductive layer of carbon material, a conductive layer of titanium nitride, a conductive layer of titanium carbide, a conductive layer which is a mixture of titanium and carbon material, and a conductive layer which is a composite of aluminum carbide (Al4C3) and titanium oxide (TiO2). The conductive layer containing carbon material, i.e., the carbon layer, contains graphite, carbon black, or a mixture thereof as the carbon material.

[0033] (electrolyte) Here, polyhydric alcohols such as polyethylene glycol, polyglycerin, and glycerin derivatives to which ethylene oxide and propylene oxide have been added increase the dielectric strength of electrolytic capacitors, but when the anode is an anodic sintered body, they worsen the tanδ of the electrolytic capacitor. On the other hand, inorganic oxide colloidal particles suppress the deterioration of tanδ in electrolytic capacitors equipped with an anodic sintered body. Therefore, this electrolyte contains inorganic oxide colloidal particles. Examples of inorganic oxide colloidal particles include silica, alumina, zirconia, titania, aluminosilicate, and aluminosilicate-coated silica. Inorganic oxide colloidal particles increase the dielectric strength of electrolytic capacitors.

[0034] Although this is a hypothesis and not limited to this, it is presumed that inorganic oxide colloidal particles, compared to polyethylene glycol, polyglycerin, and glycerin derivatives to which ethylene oxide and propylene oxide have been added, are less likely to cause the sintered grains of the valve metal to detach from the valve metal substrate, thus suppressing the deterioration of tanδ in electrolytic capacitors.

[0035] It is preferable that the inorganic oxide colloid particles are surface-modified with an organic substance. Surface modification of the inorganic oxide colloid particles with an organic substance makes it less likely for the electrolyte to gel and for the inorganic oxide to precipitate. Therefore, the effect of improving the dielectric strength of the inorganic oxide colloid particles is maintained for a long time. Since the surface of the inorganic oxide colloid particles is surface-modified with an organic substance, silica is preferred as the inorganic oxide colloid particle.

[0036] Examples of organic substances used to modify the surface of inorganic oxide colloid particles include silylation agents or silane coupling agents represented by the following general formula (Chemical Formula 1). [ka] [In the formula, X1 is a hydrocarbon group (-R) having 1 to 20 carbon atoms, which may be a carboxyl group, ester group, amide group, cyano group, ketone group, formyl group, ether group, hydroxyl group, amino group, mercapto group, sulfide group, sulfoxide group, sulfone group, isocyanate group, or ureido group, with X2 to X4 being acetoxy groups, alkoxy groups having 1 to 5 carbon atoms, or alkyl groups, and at least two of X2 to X4 being alkoxy groups.]

[0037] The silylating agent or silane coupling agent represented by the general formula (Chemical Formula 1) may be one or more selected from the group consisting of 3-glycidoxypropylmethyldimethoxysilane, 3-methacryloxypropyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, vinyltrimethoxysilane, p-styryltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-isocyanatetopropyltriethoxysilane, and 3-glycidoxypropylmethyldiethoxysilane.

[0038] The electrolyte is not particularly limited as long as it can contain inorganic oxide colloidal particles. That is, the electrolyte may include an organic acid or its salt, an inorganic acid or its salt, or a composite compound of an organic acid and an inorganic acid or its salt, and may also include an ionic dissociable salt that dissociates into an acidic component and a basic component. The acidic component and the basic component may also be added separately as solute.

[0039] Organic acids that make up the acidic component include carboxylic acids such as oxalic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, adipic acid, benzoic acid, toluic acid, enanthic acid, malonic acid, 1,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, azelaic acid, resorcinic acid, phloroglucic acid, gallic acid, gentisic acid, protocatechuic acid, pyrocatechuic acid, trimellitic acid, pyromellitic acid, undecanediic acid, dodecanediic acid, tridecanediic acid, t-butyladipic acid, and 11-vinyl-8-octadecenediic acid, as well as phenols and sulfonic acids. Inorganic acids include boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, carbonic acid, and silicic acid. Examples of complex compounds of organic and inorganic acids include borodisalicylic acid, borodisuoic acid, borodiglycolic acid, borodimalonic acid, borodisuccinic acid, borodiadipic acid, borodiazelaic acid, borodibenzoic acid, borodimaleic acid, borodilactic acid, borodimalic acid, boroditartaric acid, borodicitric acid, borodiphthalic acid, borodi(2-hydroxy)isobutyric acid, borodiresorcinic acid, borodimethylsalicylic acid, borodinafthoic acid, borodimandelic acid, and borodi(3-hydroxy)propionic acid.

[0040] Basic components include ammonium, quaternary ammonium, amidinium quaternary, amines, sodium, potassium, etc. Quaternary ammonium components include tetramethylammonium, triethylmethylammonium, tetraethylammonium, etc. Amidinium quaternary components include ethyldimethylimidazolinium, tetramethylimidazolinium, etc. Amines include primary amines, secondary amines, and tertiary amines. Primary amines include methylamine, ethylamine, propylamine, etc. Secondary amines include dimethylamine, diethylamine, ethylmethylamine, dibutylamine, etc. Tertiary amines include trimethylamine, triethylamine, tributylamine, ethyldimethylamine, ethyldiisopropylamine, etc.

[0041] The solvent for the electrolyte may be either a protic polar solvent or an aprotic polar solvent. Examples of protic polar solvents include monohydric alcohols, polyhydric alcohols, and oxyalcohol compounds. Examples of aprotic polar solvents include sulfones, amides, lactones, cyclic amides, nitriles, and sulfoxides.

[0042] Examples of monohydric alcohols include ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, and benzyl alcohol. Examples of polyhydric alcohols and oxyalcohol compounds include ethylene glycol, propylene glycol, glycerin, methyl cellosolve, ethyl cellosolve, methoxypropylene glycol, and dimethoxypropanol.

[0043] Examples of sulfones include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, sulfolane, 3-methylsulfolane, and 2,4-dimethylsulfolane. Examples of amides include N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide, N,N-diethylacetamide, and hexamethylphosphoric amide. Examples of lactones and cyclic amides include γ-butyrolactone, γ-valerolactone, δ-valerolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene carbonate, and isobutylene carbonate. Examples of nitriles include acetonitrile, 3-methoxypropionitrile, and glutalonitrile. Examples of sulfoxides include dimethyl sulfoxide.

[0044] Furthermore, other additives can be added to the electrolyte. Examples of additives include complex compounds of boric acid and polysaccharides (such as mannitol and sorbitol), complex compounds of boric acid and polyhydric alcohols, boric acid esters, nitro compounds, phosphoric acid, phosphoric acid esters, and other phosphoric acid compounds. These may be used individually or in combination of two or more. Nitro compounds suppress the generation of hydrogen gas in the electrolytic capacitor. Examples of nitro compounds include o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, p-nitrobenzyl alcohol, and m-nitroacetophenone.

[0045] (Separator) The separators include cellulose and mixed papers such as kraft, Manila hemp, esparto, hemp, and rayon; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and their derivatives; polytetrafluoroethylene resins; polyvinylidene fluoride resins; vinylon resins; polyamide resins such as aliphatic polyamides, semi-aromatic polyamides, and fully aromatic polyamides; polyimide resins; polyethylene resins; polypropylene resins; trimethylpentene resins; polyphenylene sulfide resins; acrylic resins; and polyvinyl alcohol resins, and these resins are used individually or in mixtures.

[0046] The separator may be fibrillated by generating thin fibers that branch out from the surface of the original fibers, such as fibrillated cellulose. Fibrillation can be achieved, for example, by beating. The fibrillated fibers intertwine using the thin fibrillated fibers, improving the strength of the separator. As a result, the separator can be made thinner. Thinning the separator allows for longer anodic sintered bodies and cathode bodies per unit volume, improving the capacitance of the electrolytic capacitor.

[0047] (Manufacturing method) An example of the manufacturing method for this electrolytic capacitor is as follows: The manufacturing method for the electrolytic capacitor includes an anode formation step to form an anode sintered body, a chemical formation step to form a dielectric film, a cathode formation step to form a cathode body, an element formation step to form a capacitor element, a preparation step to prepare an electrolyte, an impregnation step to impregnate the capacitor element with the electrolyte, and a packaging step to seal the capacitor element.

[0048] In the anode formation process, a valve metal powder is sintered to form an anode sintered body. The type of valve metal powder may be the same as or different from that of the valve metal substrate. The sintered layer is produced by pasteuring the valve metal powder, applying it to a foil body, drying it, etc., and then heating and sintering it in a vacuum or reducing atmosphere. The gaps between the sintered grains in the sintered layer can be set according to the desired capacitance; for example, the average particle size, particle size distribution of the valve metal powder, and the type and amount of binder, solvent, surfactant, etc. can be adjusted.

[0049] Furthermore, in the anode formation process, a dielectric film is formed by a chemical conversion treatment. The chemical conversion solution is a halogen-ion-free solution, such as a phosphoric acid-based chemical conversion solution such as ammonium dihydrogen phosphate, a boric acid-based chemical conversion solution such as ammonium borate, or an adipic acid-based chemical conversion solution such as ammonium adipate. Before forming the dielectric film, the anode sintered body may be immersed in pure water at 80°C or above or boiling to form a pseudo-boehmite layer. If a pseudo-boehmite layer is formed, the chemical conversion treatment will transform the pseudo-boehmite layer into a dielectric film layer, starting from the interface between the unconverted valve metal layer and the pseudo-boehmite layer and moving towards the outer surface of the pseudo-boehmite layer.

[0050] In the anode formation process, the divided portion may be formed before the chemical conversion treatment. Alternatively, the divided portion may be formed after the chemical conversion treatment. Furthermore, the chemical conversion treatment may be performed before the formation of the divided portion, and then a second chemical conversion treatment may be performed after the formation of the divided portion. However, since the anode body is wound while opening the divided portion during the element formation process, the divided portion must not be closed before the element formation process, and no chemical conversion treatment should be performed to close the divided portion, nor should a repair chemical conversion treatment be performed to close the divided portion. Most preferably, the divided portion is not closed, and a dielectric film is formed on the inner surface of the divided portion.

[0051] The separation portion divides the sintered layer. The separation portion is formed by cracking, splitting, cutting, notching, or carving into the surface of the sintered layer. In other words, examples of actual separation portions are cracks, fissures, cuts, notches, or carvings. This separation portion may be deep in the direction from the surface of the sintered layer toward the core, reaching the deepest part of the sintered layer, not reaching the deepest part of the sintered layer, or carving into the valve-acting metal substrate. The depth of all separation portions does not need to be uniform.

[0052] The divisions generally extend in the width direction of the strip, in other words, along the winding axis of the winding. The divisions extend either completely or partially across the sintered layer. That is, some divisions extend from one long side of the sintered layer to the other long side. Others extend from one long side of the sintered layer to below or beyond the centerline of the anodic sintered body, but not to the other long side. Others extend from the other long side of the sintered layer to below or beyond the centerline of the anodic sintered body, but not to the other long side. The direction and length of all divisions do not need to be uniform.

[0053] The groove width of the divided portion is preferably 50 μm or less, including 0, when the anodic sintered body is flattened without curving. The groove width of the divided portion is the length along the longitudinal direction of the anodic sintered body. If the divided portion is formed by cracking, splitting, or cutting, the groove width of the divided portion becomes substantially 0. Substantially 0 means that when the anodic sintered body is flattened without curving, the interface of the divided portion is at least partially in contact. If the groove width of the divided portion is 50 μm or less, the decrease in capacitance of the electrolytic capacitor due to the reduction in the surface area of ​​the dielectric film can be suppressed.

[0054] Depolarization treatment may be added to repair voids within the dielectric film. Depolarization treatment includes heat treatment, phosphoric acid treatment, or both. In heat treatment, for example, exposure to a temperature environment of 450°C or higher in air opens isolated voids within the dielectric film. In phosphoric acid treatment, the anodic sintered body is immersed in a phosphoric acid solution or ammonium dihydrogen phosphate solution to enlarge cracks and openings leading to voids. In this phosphoric acid treatment, the anode body is immersed. This makes it easier for the conversion solution to penetrate the voids, and the voids can be repaired by a second conversion treatment.

[0055] In the cathode formation process, a cathode body is formed. When forming a surface expansion layer on the cathode body, the surface expansion layer can be selected from an etched layer obtained by etching, a sintered layer obtained by sintering valve metal powder, or a deposited layer obtained by depositing valve metal particles.

[0056] DC etching creates tunnel-shaped etching pits. These tunnel-shaped etching pits are holes carved in the direction of the foil thickness. Typically, these tunnel-shaped etching pits are formed by passing a DC current through an acidic aqueous solution containing halogen ions, such as hydrochloric acid. The tunnel-shaped etching pits are further expanded by passing a DC current through an acidic aqueous solution, such as nitric acid.

[0057] AC etching creates sponge-like etching pits. These sponge-like etching pits cause the expanded layer to become a sponge-like layer with a series of fine voids. These sponge-like etching pits are formed by passing an alternating current through an acidic aqueous solution containing halogen ions, such as hydrochloric acid.

[0058] The sintered layer is produced by attaching valve metal powder to a foil body and sintering it. The vapor-deposited layer is produced, for example, by resistance heating vapor deposition or electron beam heating vapor deposition. This vapor-deposited layer is formed by heating the same or different type of valve metal as the foil body using resistance heat or electron beam energy to evaporate it, and depositing the vapor of valve metal particles onto the surface of the foil body.

[0059] When forming a conductive layer on a cathode, methods such as vacuum deposition, sputtering, ion plating, CVD, coating, electroplating, and electroless plating can be used. In the coating method, a slurry is prepared by dispersing a conductive material in a dispersion solvent, and the slurry is applied to the cathode and dried using methods such as slurry casting, doctor blade method, or spray atomization. In the deposition method, the conductive material is evaporated by electric heating in a vacuum, or by irradiating a carbon material with an electron beam in a vacuum to evaporate it, and a film is formed on the cathode. In the sputtering method, a target made of conductive material and the cathode are placed in a vacuum chamber, and an inert gas is introduced into the vacuum chamber and a voltage is applied to cause the plasma-generated inert gas to collide with the target, depositing conductive material particles knocked out from the target onto the cathode.

[0060] After laminating the conductive layer, it is preferable to press-form it. In press-form, for example, the cathode body, which consists of the conductive layer and the cathode foil, is sandwiched between press rollers and press pressure is applied. If the press-form is used to press the conductive layer into the pores of the expanded layer and to deform the conductive layer along the uneven surface of the expanded layer, the adhesion and fixation between the conductive layer and the cathode body will be further improved.

[0061] In the capacitor element formation process, the anode sintered body and cathode body are stacked with a separator in between. The separator is stacked so that one end extends beyond the other end of the anode sintered body and cathode body. The core of the capacitor element is created by first winding the protruding separator so that it aligns with the short sides of the anode sintered body and cathode body. Then, using this core as the winding axis, the long sides of the anode sintered body and cathode body are wound around it. As a result, the stack of anode body, cathode body and separator is wound in multiple layers in a spiral shape, forming a cylindrical capacitor element.

[0062] In an anodic sintered body with a divided section, the divided section opens first during winding, and multiple divided sections share and bear the bending stress. Therefore, when winding to form a capacitor element, smooth and well-formed winding of the anodic sintered body becomes possible, and the formation of numerous fine cracks in the anodic sintered body becomes less likely. Numerous fine cracks increase leakage current. However, by forming a divided section in the sintered layer, the occurrence of fine cracks is suppressed, and the leakage current of the electrolytic capacitor is further reduced.

[0063] Prior to this winding, the lead terminals are connected to the anode and cathode, respectively. The lead terminals are conductors that protrude from one of the lead end faces of the capacitor element and electrically connect the electrolytic capacitor to the mounting board. The lead terminals are electrically and mechanically connected to the anode and cathode by methods such as cold welding, ultrasonic welding, or laser welding.

[0064] After the element formation process, a repair and chemical conversion process may be provided to repair the exposed base metal portion of the valve acting metal when the anode sintered body and cathode body are cut to a desired width, as well as any defects in the anode sintered body and cathode body caused by physical stress such as winding.

[0065] In the repair chemical conversion process, the capacitor element is immersed in a conversion solution and a voltage is applied. The conversion solution can be a phosphoric acid-based solution such as ammonium dihydrogen phosphate, a boric acid-based solution such as ammonium borate, an adipic acid-based solution such as ammonium adipate, or a solution made by mixing boric acid and dicarboxylic acids such as citric acid. The voltage is preferably, for example, 0.1 to 1.2 times the conversion voltage. Furthermore, as appropriate, methods for applying the voltage during repair chemical conversion include applying a constant voltage from the start of the repair chemical conversion, or gradually increasing the applied voltage at regular intervals.

[0066] In the preparation step for preparing the electrolyte, the electrolyte is prepared by adding inorganic oxide colloid particles, a solute, and additives to the solvent. In the impregnation step for impregnating the capacitor element with the electrolyte, the capacitor element is immersed in the electrolyte, allowing the electrolyte to penetrate the voids within the capacitor element. To penetrate even finer voids, vacuum or pressure treatment may be performed as needed. The electrolyte impregnation step may be repeated multiple times. For example, the inside of the capacitor element may be depressurized, and the electrolyte may be injected into the capacitor element while pressurizing the electrolyte.

[0067] In the packaging process for sealing capacitor elements, the electrolyte-impregnated capacitor elements are housed in an outer case. The outer case is made of aluminum, an aluminum or manganese-containing aluminum alloy, or stainless steel. The outer case is, for example, a cylindrical body with one end closed and the other end open. A pressure relief valve may be formed at the bottom of the outer case. The pressure relief valve opens when the internal pressure of the outer case exceeds a set pressure.

[0068] The opening of the outer casing is sealed by a sealing body. The sealing body is an elastic insulator such as a rubber sheet, or a laminate of a rigid substrate insulating board such as a synthetic resin sheet and an elastic insulator. The sealing body is attached to the opening of the outer casing. Then, by crimping, the sealing body is folded and crushed inward around the opening edge of the outer casing, and it adheres tightly to the entire circumference of the opening edge of the outer casing. A press-fit hole is formed in the sealing body, and the lead terminal is pulled out to the outside through the press-fit hole.

[0069] After sealing the capacitor elements in the outer casing, the electrolytic capacitor undergoes an aging process to complete its manufacturing. In the aging process, a DC voltage is applied to the electrolytic capacitor to repair any defects in the dielectric film layer and other areas. [Examples]

[0070] The electrolytic capacitors and manufacturing methods of the embodiments will be described in more detail below. However, the present invention is not limited to the embodiments described below.

[0071] Electrolytic capacitors of Example 1, Comparative Examples 1 to 3, and Reference Examples 1 to 4 were fabricated. Each electrolytic capacitor differs in the type of anode. The anode is either an anodic sintered body or an anodic etched foil. Each electrolytic capacitor is equipped with one of four types of electrolyte. That is, each electrolytic capacitor has a different combination of anode type and electrolyte type.

[0072] The valve-acting metal substrate of the anodic sintered body was made of a foil body formed by stretching aluminum. The sintered layer of the anodic sintered body was formed by attaching aluminum powder to both sides of the valve-acting metal substrate and heating and sintering it. A dielectric film was formed on the sintered layer by chemical conversion treatment. Then, by winding the anodic sintered body around a roller and cracking it, numerous divisions were formed in the sintered layer.

[0073] The anodic etching foil was made from stretched aluminum foil. This aluminum foil was immersed in an aqueous hydrochloric acid solution, and a DC current was passed through the aluminum foil in the hydrochloric acid solution to form an expanded surface layer consisting of tunnel-shaped etching pits. Then, a chemical conversion treatment was applied to the aluminum foil with the expanded surface layer to form a dielectric film along the irregularities of the expanded surface layer. An aqueous ammonium borate solution was used as the chemical conversion solution. The dielectric film was formed by applying voltage in the chemical conversion solution.

[0074] The cathode and separator in each electrolytic capacitor are identical. The cathode is an enlarged aluminum foil. The aluminum foil was immersed in an ammonium borate aqueous solution at a liquid temperature of 85°C, and a constant current was applied until a voltage of 3V was achieved. Lead wires were connected to the anodic sintered body or anodic etched foil and the cathode, and the anodic sintered body or etched foil and the cathode were wound together with a cellulose-based separator in between.

[0075] Capacitor elements fabricated by winding were immersed in an electrolyte solution, impregnating the voids within the capacitor elements with the electrolyte. The compositions of the four types of electrolytes are shown in Table 1 below. The values ​​in Table 1 below represent the weight of each element when the total volume of the electrolyte is 100 parts by weight.

[0076] (Table 1) TIFF2026059597000003.tif131161

[0077] As shown in Table 1 above, electrolyte 1 contains inorganic oxide colloidal particles. Electrolyte 2 contains an EO·PO-added glycerin derivative. Electrolyte 3 contains polyethylene glycol with a molecular weight of 1000. Electrolyte 4 contains polyethylene glycerin. The inorganic oxide colloidal particles, EO·PO-added glycerin derivative, polyethylene glycol, and polyethylene glycerin are pressure-resistant agents. The inorganic oxide colloidal particles are silica surface-modified with 3-glycidoxypropylmethyldimethoxysilane as an organic substance. EO is an abbreviation for ethylene oxide, PO is an abbreviation for propylene oxide, and the EO·PO-added glycerin derivative is a glycerin derivative to which ethylene oxide and propylene oxide have been added.

[0078] Each electrolytic capacitor was completed by placing an electrolyte-impregnated capacitor element into an outer case, sealing the opening of the outer case with a sealing body, and then performing an aging treatment. Here, the electrolytic capacitors of Example 1 and Comparative Examples 1 to 3 include an anodic sintered body. The electrolytic capacitors of Reference Examples 1 to 4 include an anodic etched foil. Of each group, the electrolytic capacitors of Example 1 and Reference Example 1 include an electrolyte 1 to which inorganic oxide colloid particles are added. Of each group, the electrolytic capacitors of Comparative Example 1 and Reference Example 2 include an electrolyte 2 to which an EO·PO-added glycerin derivative is added. Of each group, the electrolytic capacitors of Comparative Example 2 and Reference Example 3 include an electrolyte 3 to which polyethylene glycol is added. Of each group, the electrolytic capacitors of Comparative Example 3 and Reference Example 4 include an electrolyte 4 to which polyethylene glycerin is added.

[0079] The electrolytic capacitors of Example 1, Comparative Examples 1 to 3, and Reference Examples 1 to 4 were left in a 150°C environment for 320 hours. The tanδ was then measured before and after being left in this high-temperature environment. The tanδ was measured at room temperature using an LCR meter. The measurement frequency of tanδ was 120 Hz, and the AC signal level was a sine wave of 0.5 Vrms.

[0080] The percentage increase in tanδ after exposure to a high-temperature environment was calculated relative to the tanδ before exposure. Table 2 below shows the percentage increase in tanδ for the electrolytic capacitors of Example 1, Comparative Examples 1 to 3, and Reference Examples 1 to 4, along with the type of anode and electrolyte used in each electrolytic capacitor. Based on Table 2, Figure 1 shows a graph of the percentage increase in tanδ for each electrolytic capacitor.

[0081] (Table 2) TIFF2026059597000004.tif93161

[0082] As shown in Table 2 and Figure 1 above, the electrolytic capacitors of Comparative Examples 1 to 3 showed an increase in tanδ of 35% or 42%. In contrast, the electrolytic capacitor of Example 1 suppressed the increase in tanδ to 19%. This indicates that even when an anodic sintered body is included and a voltage booster is added to the electrolyte, the deterioration of tanδ is suppressed when the voltage booster is inorganic oxide colloidal particles.

[0083] Furthermore, in the electrolytic capacitors of Reference Examples 1 to 4, the rate of increase in tanδ was low regardless of which voltage enhancer was used, and in the case of anodic etched foil, the problem of deterioration of tanδ did not occur even when a voltage enhancer was added to the electrolyte. In other words, deterioration of tanδ is a problem specific to electrolytic capacitors equipped with an anodic sintered body, and it was confirmed that deterioration of tanδ is suppressed when an anodic sintered body is combined with inorganic oxide colloidal particles.

Claims

1. An anodic sintered body having a valve-acting metal substrate, a sintered layer formed by sintering valve-acting metal powder onto the surface of the valve-acting metal substrate, and a dielectric film formed on the sintered layer, A cathode body facing the aforementioned anode sintered body, An electrolyte containing inorganic oxide colloidal particles, To be equipped, An electrolytic capacitor characterized by the following features.

2. The inorganic oxide colloid particles are silica. The electrolytic capacitor according to claim 1, characterized by the above.

3. The content of the inorganic oxide colloid particles is 17 wt% or less relative to the total amount of the electrolyte. The electrolytic capacitor according to claim 1, characterized by the above.

4. The inorganic oxide colloid particles are surface-modified with organic material. The electrolytic capacitor according to claim 1, characterized by the above.

5. The electrolyte comprises the inorganic oxide colloid particles and a solute. The content of the solute shall be 5 wt% or more and 25 wt% or less relative to the total amount of the electrolyte. The electrolytic capacitor according to claim 1, characterized by the above.

6. The anode sintered body has a segmented portion that divides the sintered layer. An electrolytic capacitor according to any one of claims 1 to 5, characterized by the above.

7. An anode forming step in which a valve metal powder is sintered onto a valve metal substrate to form an anode sintered body having the sintered layer, A conversion step in which a dielectric film is formed on the surface of the sintered layer, A device formation step for forming a capacitor element in which the anode sintered body and the cathode body are facing each other with a separator in between, A preparation step for preparing an electrolyte containing inorganic oxide colloidal particles, The capacitor element is impregnated in the electrolyte solution, Including, A method for manufacturing electrolytic capacitors characterized by the following.

8. The anode formation step further includes a step of dividing the sintered layer. A method for manufacturing an electrolytic capacitor according to claim 7, characterized by the above.

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