Electrolytic capacitor and manufacturing method

Abstract

To provide an electrolytic capacitor that achieves both a high withstand voltage and a low equivalent series resistance (ESR), and a manufacturing method of the same.SOLUTION: An electrolytic capacitor includes an anode body having a dielectric film, a cathode body, a separator, and an electrolytic solution. The anode body includes an anode foil made of a valve metal and a powder layer made of a valve metal powder and formed on the anode foil. The electrolytic solution contains a carboxylic acid having 12 or less total carbon atoms in a molecule. A manufacturing method of the electrolytic capacitor includes an anode body forming step of forming the anode body having the dielectric film, an element forming step of forming the capacitor element by superimposing the cathode body on the anode body via the separator, and an impregnation step of impregnating the capacitor element with the electrolytic solution. In the anode body forming step, the powder layer of the valve metal powder is formed on the anode foil of the valve metal. In the impregnation step, the capacitor element is impregnated with the electrolytic solution containing the carboxylic acid having 12 or more total carbon atoms in the molecule.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrolytic capacitor that obtains capacitance by the dielectric polarization of a dielectric film and stores and discharges electric charge, and to a method for manufacturing the same. [Background technology]

[0002] Electrolytic capacitors have valve metals such as tantalum or aluminum as anode and cathode bodies. The anode body is enlarged by forming the valve metal into a sintered body or etched foil, and a dielectric film is applied to the enlarged surface. This enlarged surface allows electrolytic capacitors to achieve a large capacitance despite their small size. In this electrolytic capacitor, the gap between the dielectric film on the anode body and the counter electrode is filled with electrolyte to ensure close contact.

[0003] The electrolyte is interposed between the dielectric oxide layer of the anode foil and the cathode foil, and provides ionic conduction between the anode and cathode foils. The electrolyte is in direct contact with the dielectric film and acts as a true cathode. The composition of the electrolyte significantly affects the electrical properties of the electrolytic capacitor, such as withstand voltage, impedance, dielectric dissipation factor (tanδ), and equivalent series resistance (ESR).

[0004] Such electrolytic capacitors are used in a variety of applications. For example, in the field of power electronics, power from an AC power source is converted into DC power by a converter circuit, and this DC power is then converted into desired AC power by an inverter circuit. A smoothing capacitor is provided in a power supply circuit to suppress pulsation in the DC output from the converter circuit and smooth the DC before inputting it to the inverter circuit. Furthermore, a decoupling capacitor is provided near a semiconductor switching element such as gallium nitride to ensure stable operation of the semiconductor switching element and to remove noise.

[0005] With the recent trend toward higher power consumption, electrolytic capacitors are required to have a higher withstand voltage. To address this, a method has been proposed in which a long-chain carboxylic acid, such as 1,9-nonanedicarboxylic acid, 1,6-decanedicarboxylic acid, 1,10-decanedicarboxylic acid, azelaic acid, sebacic acid, dodencanedioic acid, α-methylazelaic acid, or 11-vinyl-8-octadecenedioic acid, is added to the electrolyte as a solute (see Patent Documents 1 and 2). These long-chain carboxylic acids are known as solutes that can maintain a high sparkover voltage. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 09-17697 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-70020 Summary of the Invention [Problem to be solved by the invention]

[0007] Recent electrolytic capacitors are expected to be used in temperature ranges including high-temperature environments, such as in automotive applications, etc. However, electrolytic capacitors using electrolytes containing these long-chain carboxylic acids experience an increase in ESR (equivalent series resistance) when exposed to high-temperature environments such as 150°C.

[0008] The present invention has been proposed to solve the above problems, and its object is to provide an electrolytic capacitor that achieves both high withstand voltage and low ESR, and a manufacturing method thereof. [Means for solving the problem]

[0009] In order to solve the above-described problems, the electrolytic capacitor of the present embodiment includes an anode body having a dielectric coating, a cathode body facing the anode body, a separator interposed between the anode body and the cathode body, and an electrolyte interposed between the anode body and the cathode body, wherein the anode body has an anode foil made of a valve metal and a powder layer made of valve metal powder and formed on the anode foil, and the electrolyte contains a carboxylic acid having a total carbon number of 12 or less in the molecule.

[0010] The electrolyte may contain a glycol compound.

[0011] The capacitor element may be a wound body formed by winding the strip-shaped anode body and the cathode body, and the anode body may have a plurality of dividing portions extending in the width direction of the strip and dividing the powder layer.

[0012] In order to solve the above-described problems, the method for manufacturing an electrolytic capacitor according to the present embodiment includes an anode body-forming step of forming an anode body having a dielectric coating, an element-forming step of overlapping the anode body with a cathode body via a separator to form a capacitor element, and an impregnation step of impregnating the capacitor element with an electrolyte, wherein the anode body-forming step forms a powder layer of valve action metal powder on an anode foil made of a valve action metal, and the impregnation step impregnates the capacitor element with an electrolyte containing a carboxylic acid having a total of 12 or more carbon atoms in the molecule. [Effects of the Invention]

[0013] According to the present invention, the electrolytic capacitor achieves both high withstand voltage and low ESR. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a scatter diagram showing the relationship between the number of carbon atoms in the molecule of the solute acid component of the electrolyte and the leakage current for each of the powder laminate foil and the etched foil. DETAILED DESCRIPTION OF THE INVENTION

[0015] DETAILED DESCRIPTION OF THE INVENTION An electrolytic capacitor and a manufacturing method thereof according to an embodiment of the present invention will be described below. However, the present invention is not limited to the following embodiment.

[0016] (Overall composition) An electrolytic capacitor is a passive device that obtains capacitance through the dielectric polarization of a dielectric film and stores and discharges electric charge. This electrolytic capacitor has a capacitor element. The capacitor element includes an anode body, a cathode body, a separator, and an electrolyte. The anode body has a dielectric film on its surface. The separator is interposed between the anode body and the cathode body. The anode body and the cathode body face each other via the separator. The electrolyte is impregnated in the voids within the capacitor element, particularly between the anode body and the cathode body. The electrolyte is interposed between the dielectric film of the anode body and the cathode body, and provides ionic conduction between the anode foil and the cathode foil. The electrolyte is in direct contact with the dielectric film and acts as a true cathode. The electrolyte is in close contact with the dielectric film and acts as a true cathode.

[0017] External terminals are connected to the anode body and the cathode body and extend outside the capacitor element. The external terminals are electrically and mechanically connected to the anode body and the cathode body by cold welding, ultrasonic welding, laser welding, or the like. The capacitor element is formed by alternately stacking the anode body and the cathode body, to which the external terminals are connected, with a separator sandwiched between them, and then winding the stack. The capacitor element is inserted into a cylindrical case with a bottom, and the open end of the case is sealed with a sealing body by crimping.

[0018] In such an electrolytic capacitor, the anode body is a powder laminate foil. The powder laminate foil includes an anode foil and a powder layer. The powder laminate foil is formed by using a valve action metal anode foil as a base material and laminating a powder layer of agglomerated valve action metal powder on the anode foil. The electrolyte contains a carboxylic acid having a total carbon number of 12 or more in its molecular structure. When the anode body is a powder laminate foil and the electrolyte contains a carboxylic acid having a total carbon number of 12 or more in its molecular structure, deterioration of the ESR of the electrolytic capacitor is suppressed even when exposed to a high-temperature environment such as 150°C, and the electrolytic capacitor achieves both high withstand voltage and low ESR.

[0019] (anode body) The anode foil is a long, strip-shaped foil made by stretching a valve metal. Valve metals include aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. The purity of the valve metal for the anode foil is preferably 99.9% or higher, and other elements such as silicon, iron, copper, manganese, magnesium, chromium, zinc, titanium, vanadium, gallium, nickel, boron, and zirconium may also be included.

[0020] The powder layer is formed on one or both sides of the anode foil. The powder layer is formed by laminating valve action metal particles. The valve action metal particles in the powder layer may be the same type as or different from the anode foil. This powder layer has a porous structure formed by voids between the agglomerated valve action metal particles. This powder layer expands the surface area of ​​the anode body, resulting in a surface area that exceeds one time the projected area. In other words, this powder layer becomes the surface expansion layer of the anode body.

[0021] The powder layer is a sintered layer formed by sintering valve action metal particles, or a vapor-deposited layer formed by vapor-depositing valve action metal particles onto a foil. The sintered layer is produced by attaching valve action metal particles to a foil and then heating and sintering the particles in a vacuum or reducing atmosphere. The vapor-deposited layer is produced, for example, by a resistance heating vapor deposition method or an electron beam heating vapor deposition method. This vapor-deposited layer is formed by heating and evaporating the valve action metal using resistance heat or electron beam energy, and then depositing the vapor of the valve action metal particles on the surface of the foil.

[0022] The dielectric coating is formed on one or both sides of the anode body. The dielectric coating is typically an oxide coating formed on the surface layer of the anode body, and if the anode body is made of aluminum, it is an aluminum layer. In the chemical conversion treatment to form the dielectric coating, a voltage is applied to the anode body in a chemical conversion solution so as to achieve a desired withstand voltage. In the chemical conversion treatment, it is preferable to form a dielectric coating with a thickness of 1.1 to 1.5 nm to achieve a withstand voltage of 1 V. The chemical conversion solution is a solution free of halogen ions, and examples thereof include phosphoric acid-based chemical conversion solutions such as ammonium dihydrogen phosphate, boric acid-based chemical conversion solutions such as ammonium borate, and adipic acid-based chemical conversion solutions such as ammonium adipate.

[0023] This anode body preferably has a plurality of dividing portions that divide the powder layer. The dividing portions are formed by cracking, splitting, slitting, notching, or digging into the surface layer of the powder layer. That is, examples of the actual dividing portions are cracks, fissures, slits, notches, or digging. The dividing portions are deep in the direction from the surface of the powder layer toward the core, and may be deep enough to reach the deepest part of the powder layer, deep enough not to reach the deepest part of the powder layer, or deep enough to penetrate into the anode foil. It is not necessary for all dividing portions to have the same depth.

[0024] The dividing portions generally extend in the width direction of the ribbon, in other words, in the direction along the winding axis. The dividing portions may extend completely or partially across the powder layer. That is, some dividing portions extend from one long side of the powder layer to the other long side. Other dividing portions may extend from one long side of the powder layer to a point less than or beyond the foil centerline, but not to the other long side. Other dividing portions may extend from the other long side of the powder layer to a point less than or beyond the foil centerline, but not to the other long side. It is not necessary for all dividing portions to extend in the same direction or for the same length.

[0025] The divided portions of the powder layer disperse bending stress. This allows for smooth, well-wound anode body during winding to form a capacitor element, reducing the likelihood of numerous fine cracks forming in the anode body. This also prevents stress concentration from damaging the anode foil and causing the anode body to bend during winding. If the anode body is bent during winding, the diameter of the capacitor element increases. Therefore, maintaining the capacitance of the electrolytic capacitor results in an increase in size. Alternatively, maintaining the diameter of the electrolytic capacitor results in a decrease in the capacitance. Otherwise, the electrolytic capacitor will be treated as a defective product, resulting in a decrease in yield.

[0026] Incidentally, after the powder layer is formed, the dividing portion may be formed before the chemical conversion treatment of the dielectric coating. The dividing portion may be formed after the chemical conversion treatment. Alternatively, the chemical conversion treatment may be performed before the dividing portion is formed, and then the chemical conversion treatment may be performed again after the dividing portion is formed. However, since the anode body is wound while the dividing portion is open in the element formation step, the chemical conversion treatment is not performed to close the dividing portion before the element formation step, and repair chemical conversion is not performed to close the dividing portion. However, preferably, a dielectric coating is also formed on the inner surface of the dividing portion.

[0027] The groove width of the dividing portion is preferably 50 μm or less (including 0) when the anode body is flattened without bending. The groove width of the dividing portion is the length along the longitudinal direction of the anode body. When the dividing portion is formed by splitting, tearing, or notching, the groove width of the dividing portion is substantially 0. "Substantially 0" refers to a state in which the interfaces of the dividing portion are at least partially in contact when the anode body is flattened without bending. If the groove width of the dividing portion is 50 μm or less, a decrease in the capacitance of the electrolytic capacitor due to a decrease in the surface area of ​​the dielectric film can be suppressed.

[0028] (cathode body) The cathode body is a long strip of cathode foil made by stretching valve metal. The purity of the valve metal for the cathode body is preferably 99% or higher. A surface-expanding layer is formed on the cathode foil as needed. The surface-expanding layer can be a sintered layer, a vapor-deposited layer, or an etched layer obtained by etching the cathode foil. In other words, the surface-expanding layer has a porous structure and consists of tunnel-like pits, spongy pits, or voids between densely packed powder or particles.

[0029] The tunnel-shaped etching pits are holes dug in the foil thickness direction. These tunnel-shaped etching pits are typically formed by passing a direct current in an acidic aqueous solution containing halogen ions, such as hydrochloric acid. The tunnel-shaped etching pits are further expanded by passing a direct current in an acidic aqueous solution, such as nitric acid. The spongy etching pits turn the surface-expanding layer into a sponge-like layer with fine, interconnected voids. These spongy etching pits are formed by passing an alternating current in an acidic aqueous solution containing halogen ions, such as hydrochloric acid.

[0030] The cathode body may have a natural oxide film or a thin oxide film of about 1 to 10 V formed by chemical conversion treatment. The natural oxide film is formed when the cathode body reacts with oxygen in the air.

[0031] The cathode body may further include a conductive layer. The conductive layer is laminated on the cathode foil. The conductive layer may primarily contain an inorganic substance or an inorganic compound. Examples of inorganic substances or inorganic compounds include titanium, zirconium, tantalum, niobium, nitrides or carbides of these, aluminum carbide, carbon materials, and composites or mixtures of these. Specific examples include a carbon layer, which is a conductive layer of a carbon material, a conductive layer of titanium nitride, a conductive layer of titanium carbide, a conductive layer made of a mixture of titanium and a carbon material, and a conductive layer made of a composite of aluminum carbide (Al4C3) and titanium oxide (TiO2).

[0032] The conductive layer containing a carbon material, i.e., the carbon layer, contains graphite, carbon black, or a mixture thereof as the carbon material. Examples of graphite include natural graphite, artificial graphite, and graphitized ketjen black. Examples of carbon black include ketjen black, acetylene black, channel black, and thermal black. In addition, the carbon layer may contain activated carbon, carbon nanohorn, or fibrous carbon as the carbon material. Activated carbon is derived from natural plant tissues such as coconut husks, synthetic resins such as phenol, and fossil fuels such as coal, coke, and pitch. Examples of fibrous carbon include carbon nanotubes (hereinafter referred to as CNTs) and carbon nanofibers (hereinafter referred to as CNFs).

[0033] (electrolyte) An electrolyte is a mixed solution in which a solute is dissolved in a solvent, and additives are added as needed. Examples of the solvent for the electrolyte include water, protic organic polar solvents, and aprotic organic polar solvents, which may be used alone or in combination of two or more. The solute for the electrolyte includes an anion component and a cation component. The solute is typically a salt of an organic acid, a salt of an inorganic acid, or a salt of a complex compound of an organic acid and an inorganic acid, which may be used alone or in combination of two or more.

[0034] A carboxylic acid having a total of 12 or more carbon atoms in the molecule is added as a solute to the electrolyte. Examples of carboxylic acids having a total of 12 or more carbon atoms in the molecule include 1,6-decanedicarboxylic acid having 12 carbon atoms and 11-vinyl-8-octadecenedioic acid having 20 carbon atoms. One or more types of carboxylic acids having a total of 12 or more carbon atoms in the molecule may be contained in the electrolyte.

[0035] In addition to carboxylic acids having a total carbon number of 12 or more in the molecule, other types of solutes can also be contained in the electrolyte. For example, organic 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, 1,7-octanedicarboxylic acid, azelaic acid, 1-methylazelaic acid, undecanedioic acid, t-butyladipic acid, resorcylic acid, phloroglucinic acid, gallic acid, gentisic acid, protocatechuic acid, pyrocatechuic acid, trimellitic acid, and pyromellitic acid, as well as phenols, sulfonic acids, or a combination thereof can be added to the electrolyte.

[0036] Examples of inorganic acids include boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, carbonic acid, silicic acid, etc. Examples of composite compounds of organic acids and inorganic acids include borodisalicylic acid, borodioxalic 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, borodiresorcylic acid, borodimethylsalicylic acid, borodinaphthoic acid, borodimandelic acid, and borodi(3-hydroxy)propionic acid, or a combination of these, can be added to the electrolyte.

[0037] Examples of at least one salt of an organic acid, an inorganic acid, or a complex compound of an organic acid and an inorganic acid include ammonium salts, quaternary ammonium salts, quaternized amidinium salts, amine salts, sodium salts, and potassium salts. Examples of quaternary ammonium ions of quaternary ammonium salts include tetramethylammonium, triethylmethylammonium, and tetraethylammonium. Examples of quaternized amidinium salts include ethyldimethylimidazolinium and tetramethylimidazolinium. Examples of amine salts include salts of primary amines, secondary amines, and tertiary amines. Examples of primary amines include methylamine, ethylamine, and propylamine. Examples of secondary amines include dimethylamine, diethylamine, ethylmethylamine, and dibutylamine. Examples of tertiary amines include trimethylamine, triethylamine, tributylamine, ethyldimethylamine, and ethyldiisopropylamine. The acid that forms the anion and the base that forms the cation may be added separately to the solvent.

[0038] Examples of the protic organic polar solvent include monohydric alcohols, polyhydric alcohols, and oxyalcohol compounds. Examples of the monohydric alcohols include ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, and benzyl alcohol. Examples of the polyhydric alcohols and oxyalcohol compounds include ethylene glycol, propylene glycol, diethylene glycol, glycerin, methyl cellosolve, ethyl cellosolve, methoxypropylene glycol, dimethoxypropanol, and alkylene oxide adducts of polyhydric alcohols such as polyethylene glycol and polyoxyethylene glycerin.

[0039] Representative examples of aprotic organic polar solvents include sulfones, amides, lactones, cyclic amides, and nitriles. Examples of sulfones include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, sulfolane, 3-methyl sulfolane, and 2,4-dimethyl sulfolane. 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 glutaronitrile.

[0040] Glycol compounds are preferred as the solvent for the electrolyte. Glycol compounds are compounds in which hydrogen atoms bonded to two or more carbon atoms in an aliphatic hydrocarbon or cyclic aliphatic hydrocarbon are replaced with hydroxyl groups. Glycol compounds have a high boiling point of 150°C or higher. These glycol compounds improve the chemical conversion properties of the dielectric film, reducing the ESR and improving the withstand voltage of electrolytic capacitors. Examples of glycol compounds include ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, and polyoxyethylene glycol. The electrolyte may contain one type of glycol compound solvent, or two or more types of glycol compound solvents. Furthermore, glycol compounds may be used alone as the solvent, or may be combined with other glycol compounds.

[0041] Furthermore, other additives can be added to the electrolyte solution. Examples of additives include alkylene oxide adducts of polyhydric alcohols such as polyethylene glycol and polyoxyethylene glycerin, complex compounds of boric acid and polysaccharides (mannite, sorbite, etc.), complex compounds of boric acid and polyhydric alcohols, boric acid esters, nitro compounds (o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, p-nitrobenzyl alcohol, m-nitroacetophenone, etc.), and phosphate esters. These may be used alone or in combination of two or more.

[0042] (separator) Examples of materials for the separator include cellulose papers such as kraft, Manila hemp, esparto, hemp, cotton, and rayon, and mixtures thereof; polyester-based resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and derivatives thereof; polytetrafluoroethylene-based resins, polyvinylidene fluoride-based resins, vinylon-based resins; polyamide-based resins such as aliphatic polyamides, semi-aromatic polyamides, and wholly aromatic polyamides; polyimide-based resins, polyethylene resins, polypropylene resins, trimethylpentene resins, polyphenylene sulfide resins, acrylic resins, and polyvinyl alcohol resins. These resins can be used alone or in combination.

[0043] (Manufacturing method) This electrolytic capacitor is fabricated through an element formation process, an impregnation process, and a packaging process. The element formation process includes an anode body formation process for forming an anode body, a cathode body formation process for forming a cathode body, and a winding process for overlapping the anode body and the cathode body with a separator interposed therebetween and winding them. The impregnation process is a process for impregnating the capacitor element with an electrolyte. The packaging process is a process for housing and sealing the capacitor element in a case.

[0044] Before proceeding to the winding process, aluminum lead terminals are connected to the anode foil and cathode foil by stitching, cold welding, ultrasonic welding, laser welding, or the like. In the winding process, the separator is overlapped so that one end protrudes beyond one end of the anode foil and cathode foil. The protruding separator is wound first so that the core of the wound body is aligned with the short sides of the anode body and cathode body, creating a winding core. Next, the winding is completed by rolling up the long sides of the anode body and cathode body using the winding core as a winding shaft.

[0045] In an anode body with divided sections, the divided sections open first during winding, and multiple divided sections share the bending stress. This reduces the bending stress at each location and suppresses the occurrence of microcracks. The anode body is then wound with a smooth curve without bending. As microcracks are suppressed, an increase in leakage current is suppressed.

[0046] After the element formation process, a repair chemical conversion process may be performed to repair defects in the bare valve metal portions exposed when the anode body and cathode body are cut to the desired width, as well as defects formed in the dielectric coating of the anode body due to physical stress such as winding. In the repair chemical conversion process, the wound body is immersed in a chemical conversion solution and a voltage is applied. The chemical conversion solution may be a phosphoric acid-based chemical conversion solution such as ammonium dihydrogen phosphate, a boric acid-based chemical conversion solution such as ammonium borate, an adipic acid-based chemical conversion solution such as ammonium adipate, or a chemical conversion solution containing a mixture of boric acid and a dicarboxylic acid such as citric acid. The repair chemical conversion voltage is preferably, for example, 0.1 to 1.2 times the chemical conversion voltage applied to the anode body. The voltage application method during repair chemical conversion may be, for example, a method of applying a constant voltage from the start of repair chemical conversion or a method of increasing the applied voltage stepwise at regular intervals.

[0047] In the impregnation step, the capacitor element is immersed in the electrolyte solution to impregnate the voids within the capacitor element. A depressurization or pressurization process may be performed as necessary to impregnate the electrolyte solution into smaller voids. The electrolyte impregnation step may be repeated multiple times. For example, the pressure inside the capacitor element may be reduced, and the electrolyte solution may be injected into the capacitor element while pressurizing the electrolyte solution.

[0048] In the packaging process, the capacitor element impregnated with the electrolyte is housed in a case. The case is made of aluminum, an aluminum alloy containing manganese, or stainless steel, and is, for example, a cylinder with a bottom and an open end. A pressure release valve is formed at the bottom of the case. A seal is attached to the opening of the case housing the capacitor. The seal is made of an elastic insulator such as a rubber plate, or a laminate of a hard substrate insulating plate such as a synthetic resin plate and an elastic insulator, and is crimped from the outside of the case. After the capacitor element is sealed in the case, the electrolytic capacitor undergoes an aging process to complete its production. In the aging process, a DC voltage is applied to the electrolytic capacitor to repair defects in the dielectric coating, etc.

[0049] The case may be a cylindrical body with one end closed and the other end open, or may be, for example, a laminate film. The case may also be formed by molding the element with a resin such as a heat-resistant resin or an insulating resin, or the case may be formed in the form of a thin film by dip-coating or printing the resin on the element. [Example]

[0050] The electrolytic capacitor and the manufacturing method of the present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples.

[0051] Examples 1 and 2 Electrolytic capacitors were produced in Examples 1 and 2 and Comparative Examples 1 and 2. The electrolytic capacitors in Examples 1 and 2 and Comparative Examples 1 and 2 have in common the anode body being a powder laminated foil, but differ in the type of anion component contained in the electrolytic solution.

[0052] The anode foil is a long strip of aluminum foil. The anode body is a sintered anode body made of an aluminum substrate with a sintered layer made of sintered aluminum grains and a dielectric coating formed on the sintered layer. This sintered layer has a divided section.

[0053] The cathode body is a long strip of aluminum foil. The cathode body was surface-enlarged by AC etching. In the cathode foil surface-enlarging process, an AC current was passed through the aluminum foil in an aqueous solution containing hydrochloric acid, forming a surface-enlarged layer consisting of spongy etching pits. In addition, an oxide film was formed on the surface of the foil by chemical conversion treatment. In the chemical conversion treatment of the cathode body, the cathode body was immersed in a boric acid aqueous solution, and an oxide film 1 was formed by applying voltage.

[0054] After connecting the lead terminals to the anode and cathode bodies, the anode and cathode bodies of the same length and width were overlapped with a cellulose separator and wound together. The dimensions of the wound body consisting of the anode and cathode bodies and separator were 10 mm in diameter and 20 mm in height.

[0055] This wound body was impregnated with electrolyte solutions containing different types of acid components in Examples 1 and 2 and Comparative Examples 1 and 2. The electrolyte solutions were composed of water, ethylene glycol, an acid component, paranitrobenzyl alcohol, a pressure resistance improver, and diethylamine. The pressure resistance improver was a glycerin derivative in which a propylene oxide polymer and an ethylene oxide polymer were added to the two hydroxyl groups of glycerin. The water content was 10.0 wt% of the total electrolyte, the paranitrobenzyl alcohol content was 1.0 wt% of the total electrolyte, the pressure resistance improver was 17.0 wt% of the total electrolyte, and the diethylamine content was 2.0 wt% of the total electrolyte.

[0056] The acid component of Comparative Example 1 is suberic acid having a total of 8 carbon atoms in the molecule, and the acid component of Comparative Example 2 is azelaic acid having a total of 9 carbon atoms in the molecule. That is, Comparative Examples 1 and 2 are carboxylic acids having a total of less than 12 carbon atoms in the molecule.

[0057] The acid component in Example 1 was 1,6-decanedicarboxylic acid, which has a total of 12 carbon atoms in the molecule, and the acid component in Example 2 was 11-vinyl-8-octadecenedioic acid, which has a total of 20 carbon atoms in the molecule. In Examples 1 and 2, the carboxylic acids used were those with a total of 12 or more carbon atoms in the molecule. The acid components mixed into the electrolyte in Examples 1 and 2 and Comparative Examples 1 and 2 were mixed in equimolar amounts: 3.7 wt% suberic acid, 4.0 wt% azelaic acid, 4.9 wt% 1,6-decanedicarboxylic acid, and 6.8 wt% 11-vinyl-8-octadecenedioic acid. The remainder of the electrolyte was ethylene glycol.

[0058] After the wound body was impregnated with an electrolyte to create a capacitor element, each capacitor element was placed in a case and the opening of the case was sealed with a sealing member to complete the electrolytic capacitor. This electrolytic capacitor has a rated voltage of 450V and a capacitance of 18μF.

[0059] Furthermore, electrolytic capacitors of Comparative Examples 3 to 6 were fabricated. The electrolytic capacitors of Comparative Examples 3 to 6 differ from the electrolytic capacitors of Examples 1 and 2 and Comparative Examples 1 and 2 in that no powder layer was laminated on the anode body and the anode body was subjected to an etching process to enlarge the surface. The compositions of the electrolytic solutions of Comparative Examples 3 to 6 were the same as those of the corresponding electrolytic capacitors of Examples 1 and 2 and Comparative Examples 1 and 2. However, the electrolytic capacitors of Comparative Examples 3 to 6 had a capacitance of 15 μF.

[0060] In the electrolytic capacitors of Comparative Examples 3 to 6, the anode body was a long strip of aluminum foil. The anode body was immersed in an aqueous solution containing hydrochloric acid, and a direct current was passed through the anode body to form a surface-expanded layer consisting of tunnel-shaped etching pits. Next, the anode body was subjected to a chemical conversion treatment to form an oxide film on the surface layer of the anode body. In the chemical conversion treatment process, the anode body was immersed in an ammonium borate aqueous solution and a voltage was applied. The powder layer was not laminated, and the anode body whose surface was expanded by etching was called an etched foil.

[0061] The composition and composition ratio of the electrolyte solution of Comparative Example 3 are the same as those of Comparative Example 1, and the acid component in the electrolyte solution is suberic acid. The composition and composition ratio of the electrolyte solution of Comparative Example 4 are the same as those of Comparative Example 2, and the acid component in the electrolyte solution is azelaic acid. The composition and composition ratio of the electrolyte solution of Comparative Example 5 are the same as those of Example 1, and the acid component in the electrolyte solution is 1,6-decanedicarboxylic acid. The composition and composition ratio of the electrolyte solution of Comparative Example 6 are the same as those of Example 2, and the acid component in the electrolyte solution is 11-vinyl-8-octadecenedioic acid.

[0062] (Characteristics test) The ΔESR of each electrolytic capacitor of Examples 1 and 2, Comparative Examples 1 and 2, and Comparative Examples 3 to 6 was measured after exposure to a high-temperature environment. First, the initial ESR was measured before exposure to the high-temperature environment, and then the post-test ESR was measured after the electrolytic capacitors were exposed to a temperature environment of 150°C for 500 hours. The rate of change in the post-measurement ESR relative to the initial ESR, ΔESR, was then calculated. The ESR measurement conditions were an ambient temperature of 20°C, an LCR meter (Agilent Technologies, E4980A), an AC current level of 1.0 Vrms sine wave, and a measurement frequency of 100 kHz.

[0063] The ΔESR results are shown in Tables 1 and 2 below. The relationship between the total number of carbon atoms in the molecule and ΔESR for the powder laminated foil series of Examples 1 and 2 and Comparative Examples 1 and 2, in which the anode body is a powder laminated foil, and the etched foil series of Comparative Examples 3 to 6, in which the anode body is an etched foil, is shown in the graph of Figure 1. The powder laminated foil series is plotted with circles, and the etched foil series is plotted with triangles.

[0064] (Table 1) TIFF2025151545000002.tif54165

[0065] (Table 2) TIFF2025151545000003.tif54168

[0066] As shown in Table 2 above and Figure 1, the ESR of all of the electrolytic capacitors of Comparative Examples 3 to 6 deteriorates significantly when exposed to a high-temperature environment. On the other hand, as shown in Table 1 and Figure 1, the ESR of the electrolytic capacitors of Comparative Examples 1 and 2 deteriorates significantly when exposed to a high-temperature environment, but the degree of deterioration in ESR of the electrolytic capacitors of Examples 1 and 2 is suppressed compared to Comparative Examples 1 to 6. The electrolytic capacitors of Examples 1 and 2 differ from Comparative Examples 1 to 6 in that the anode body is a powder laminate foil and the electrolyte contains a carboxylic acid with a total carbon number of 12 or more in the molecule.

[0067] In this way, the anode body is made of valve action metal powder and has a powder layer laminated on the anode foil, and the electrolyte contains a carboxylic acid with a total carbon number of 12 or more in the molecule, which allows the electrolytic capacitor to achieve both high withstand voltage and low ESR.

Claims

1. an anode body having a dielectric coating; a cathode body facing the anode body; a separator interposed between the anode body and the cathode body; an electrolyte interposed between the anode body and the cathode body; Equipped with The anode body is a valve metal anode foil; a powder layer formed on the anode foil, the powder layer being made of a valve action metal powder; and the electrolyte solution contains a carboxylic acid having a total carbon number of 12 or more in the molecule; An electrolytic capacitor characterized by:

2. the electrolyte solution contains a glycol compound; 2. The electrolytic capacitor according to claim 1,

3. the capacitor element is a wound body formed by winding the strip-shaped anode body and the strip-shaped cathode body, the anode body has a plurality of dividing portions extending in a width direction of the strip and dividing the powder layer; 3. The electrolytic capacitor according to claim 1 or 2,

4. an anode body forming step of forming an anode body having a dielectric coating; an element forming step of overlapping the cathode body with the anode body via a separator to form a capacitor element; an impregnation step of impregnating the capacitor element with an electrolyte; Including, The anode body forming step includes forming a powder layer of a valve action metal powder on an anode foil of a valve action metal, the impregnation step includes impregnating the capacitor element with an electrolyte solution containing a carboxylic acid having a total carbon number of 12 or less in the molecule; A method for manufacturing an electrolytic capacitor, comprising:

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