WO2023190189A1

WO2023190189A1 - Winding electrolytic capacitor

Info

Publication number: WO2023190189A1
Application number: PCT/JP2023/011884
Authority: WO
Inventors: 太一梅原; 光軌相良; 貴大長谷川
Original assignee: 日本ケミコン株式会社
Priority date: 2022-03-30
Filing date: 2023-03-24
Publication date: 2023-10-05

Abstract

Provided is an electrolytic capacitor having a good capacitance appearance rate. This electrolytic capacitor comprises: an anode foil having a dielectric oxidizing coat; a cathode foil facing the anode foil; a separator interposed between the anode foil and the cathode foil; a capacitor element that winds around the anode foil and the cathode foil via the separator; and an electrolyte impregnated into the capacitor element. The electrolyte contains polyoxyethylene glycerin. The anode foil has a band width of more than 37mm along the winding shaft of the capacitor element .

Description

Wound electrolytic capacitor

The present invention relates to a wound electrolytic capacitor in which an anode foil and a cathode foil are wound.

An electrolytic capacitor is a passive element that stores and discharges charge using capacitance. Electrolytic capacitors include valve metals such as tantalum or aluminum as anode and cathode foils. The anode foil and the cathode foil are valve metal foils. A dielectric oxide film is formed on the surface of the anode foil. An electrolytic solution is interposed between the anode foil and the cathode foil.

The electrolyte comes into close contact with the dielectric oxide film of the anode foil and functions as a true cathode. The degree of contact between the electrolyte and the dielectric oxide film of the anode foil affects the rate of capacitance appearance of the electrolytic capacitor. The capacitance appearance rate is the ratio of the measured capacitance to the theoretical capacitance of the electrolytic capacitor (actual capacitance/theoretical capacitance×100).

Theoretical capacitance is a composite capacitance that assumes that an electrolytic capacitor is a capacitor with an anode and a cathode connected in series, and the result of multiplying the anode capacitance by the cathode capacitance is It is obtained by the calculation formula ((anode side capacitance x cathode side capacitance)/(anode side capacitance + cathode side capacitance)) divided by the sum of the capacitance and the cathode side capacitance.

For the anode side capacitance and the cathode side capacitance, cut out a test piece with a specified area from the foil.For the anode side capacitance, use a platinum plate as the opposing electrode, and for the cathode side capacitance, use two test pieces to connect them to each other. as a counter electrode, immerse it in a capacitance measurement liquid in a glass measurement tank, and measure it using a capacitance meter according to JEITA standard RC-2364A.

In recent years, there has been a rapid increase in the power output of server power supplies and radio base stations due to the use of big data. Electrolytic capacitors are also increasingly required to have higher capacitance. The surface of the anode foil is expanded by forming the valve metal into a sintered body or etched foil, and a dielectric oxide film is formed on the expanded surface. This enabled the electrolytic capacitor to have a high capacity.

Additionally, with the increase in the output of devices, the withstand voltage required of electrolytic capacitors is also increasing. In order to increase the spark voltage of the electrolyte, a pressure-resistant improver is added to the electrolyte. Examples of the pressure resistance improver include polymer compounds such as polyvinyl alcohol and polyethylene glycol, and inorganic fine particles such as silica and alumina (see, for example, Patent Document 1).

Japanese Patent Application Publication No. 2011-176102

As described above, electrolytic capacitors are required to have higher capacitance, and the object of the present invention is to provide an electrolytic capacitor that has a good capacity appearance rate so that the capacitance can be increased.

In order to solve the above problems, the electrolytic capacitor of the present embodiment includes an anode foil having a dielectric oxide film, a cathode foil facing the anode foil, and a separator interposed between the anode foil and the cathode foil. , comprising a capacitor element in which the separator, the anode foil, and the cathode foil are wound, and an electrolyte impregnated in the capacitor element, the electrolyte containing polyoxyethylene glycerin, and the anode foil comprising: , the band width along the winding axis of the capacitor element is more than 37 mm.

The anode foil may have a band width of 150 mm or less along the winding axis of the capacitor element.

The separator may have an average density of 0.85 g/cm ³ or more.

The cathode foil may include a carbon layer laminated on the cathode foil.

According to the present invention, the capacitance appearance rate of the electrolytic capacitor is maintained well, making it easier to increase the capacitance.

It is a graph of the POEG series and the PO&EO-added glycerin series, with the horizontal axis representing the band width of the anode foil and the vertical axis representing the capacity appearance rate. It is a graph showing the relationship between the band width of the anode foil of the POEG series and the capacity appearance rate based on each capacity appearance rate of the PO&EO-added glycerin series. It is a graph showing approximate straight lines of the PO&EO-added glycerin series and the POEG series. (a) is a photograph of the anode foil of Example 4, and (b) is a photograph of the anode foil of Comparative Example 4.

An electrolytic capacitor is a passive element that stores and discharges charge using capacitance. An electrolytic capacitor includes a capacitor element in which an anode foil and a cathode foil are opposed to each other with a separator in between. A dielectric oxide film is formed on the surface of the anode foil. This capacitor element contains an electrolyte. The electrolytic solution is interposed between the anode foil and the cathode foil, and is in close contact with the dielectric oxide film of the anode foil, forming a true cathode.

This electrolytic capacitor is a wound type. The capacitor element is constructed by winding an anode foil and a cathode foil into a spiral shape. The anode foil and the cathode foil are long foil bodies made of valve metal. The winding axis of the capacitor element coincides with the extending direction of the short sides of the anode foil and the cathode foil, that is, the band width direction. The anode foil and the cathode foil have a winding axis extending along the short side, and are wound along the long side so that the long side is rounded to form a capacitor element.

The band width along the short side of the anode foil, that is, along the winding axis of the capacitor element, is more than 37 mm. The short side of the cathode foil is preferably the same length or longer than the short side of the anode foil so that there is no area in the anode foil that does not face the cathode foil. The long sides of the cathode foil are also preferably the same length or longer than the long sides of the anode foil so that there is no area on the anode foil that does not face the cathode foil. The separator is preferably longer than the long sides of the anode foil and the cathode foil so that it can be wound in advance to form a winding shaft.

When impregnating the capacitor element with an electrolytic solution, the electrolytic solution permeates toward the center of the capacitor element from the flat end face perpendicular to the circumferential surface of the capacitor element. In the electrolytic solution impregnation process, reduced pressure treatment or pressure treatment is added as necessary. The electrolytic solution with which the capacitor element is impregnated contains polyoxyethylene glycerin (hereinafter referred to as POEG). POEG, like polyvinyl alcohol and polyethylene glycol, originally functions as a pressure enhancer.

This electrolytic capacitor satisfies these three conditions: the capacitor element is of a wound type, the length of the anode foil in the direction of the winding axis is over 37 mm, and the electrolyte contains POEG. . When these configurations are combined, the capacitance appearance rate of the electrolytic capacitor becomes relatively good compared to other configurations, and it becomes easier to increase the capacity of the electrolytic capacitor. In addition, as another configuration, although it is a wound type, the length of the anode foil in the winding axis direction is in the range of 27 mm or more and 80 mm, and the electrolytic capacitor whose electrolyte solution contains a voltage resistance improver other than POEG was compared. There is.

The band width along the winding axis of the anode foil is preferably 70 mm or less. Up to 70 mm, the capacitance of the electrolytic capacitor can be increased by satisfying three conditions: it is a wound type, the length of the anode foil in the direction of the winding axis is over 37 mm, and the electrolyte contains POEG. The appearance rate remains at over 95%, which is high compared to other configurations.

Furthermore, the band width along the winding axis of the anode foil is preferably more than 70 mm. Although it is a wound type electrolytic capacitor, the length of the anode foil in the direction of the winding axis is in the range of more than 70 mm, and the electrolytic solution contains a voltage resistance improver other than POEG, and the capacitance appearance rate is significantly reduced. Put it away. However, by satisfying three conditions: the length of the anode foil in the winding axis direction is over 70 mm, the shape is wound, and the electrolyte contains POEG, the capacitance appearance rate of the electrolytic capacitor is The decrease in the capacitance is suppressed, and the capacitance appearance rate is superior to that of an electrolytic capacitor in which the electrolyte contains a voltage resistance improver other than POEG.

Here, the JIS standard (JIS C 5101-4-1) stipulates that the tolerance of capacitance is preferably ±20%. When this regulation is met, the upper limit of the band width along the winding axis of the anode foil is preferably 150 mm or less. An electrolytic capacitor in which the length of the anode foil in the direction of the winding axis is 150 mm or less is of a wound type, and if the electrolyte contains POEG, a capacity retention rate of 80% can be easily achieved.

The electrolytic solution permeates toward the center of the capacitor element from the flat end face perpendicular to the circumferential surface of the capacitor element, and is retained in the separator. The average density of the separator is preferably 0.85 g/cm ³ or more. If the electrolytic capacitor satisfies these three conditions: the length of the anode foil in the direction of the winding axis is over 37 mm, and the electrolyte contains POEG, the separator density can be Even if it is increased, the capacity appearance rate remains high.

If the separator can be made thinner, the length of the anode foil and cathode foil bands that can be wound around a capacitor element with a constant outer diameter can be extended. If the lengths of the anode foil and cathode foil can be extended, the electrode area will become larger. The high capacitance appearance rate achieved by satisfying the three conditions and the large electrode area achieved by thinning the separator combine to further increase the capacitance of this electrolytic capacitor.

Note that POEG is preferably in a liquid state at room temperature. When the molecular weight of POEG is, for example, about 1000, POEG is in a liquid state at room temperature. When POEG is in a solid state at room temperature, it can be added to the electrolytic solution by dissolving it in the solution by heating. However, POEG, which is in a liquid state at room temperature, is difficult to precipitate even if the solvent evaporates over time, and maintains a good electrostatic capacitance of the electrolytic capacitor.

In such an electrolytic capacitor, known anode foils, cathode foils, electrolytes, and separators can be used and are not particularly limited.

For example, valve metals used for anode foils and cathode foils include aluminum, tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. Although it is desirable that the purity be high, it may contain impurities such as silicon, iron, copper, magnesium, and zinc.

The surface-expanding layer formed on the anode foil and the cathode foil is a sintered body made by sintering valve metal powder, or an etched layer made by etching a stretched foil. It consists of shaped pits or voids between densely packed particles. Tunnel-like pits may be provided through the foil. The dielectric oxide film is typically an oxide film formed on the surface layer of the anode foil, and if the anode foil is made of aluminum, it is an aluminum oxide layer obtained by oxidizing the surface of the surface expanding layer. The cathode foil may have a natural oxide film, or a thin dielectric oxide film (approximately 1 to 10 V) may be formed by chemical conversion treatment.

A carbon layer containing a carbon material as a main material may be formed on the surface of the cathode foil. That is, the cathode side may be a cathode foil in which the cathode foil and a carbon layer are laminated. When a carbon layer is laminated on the cathode foil and the cathode body is on the cathode side, in combination with the three conditions of the present electrolytic capacitor, a large capacity of the electrolytic capacitor is achieved as follows.

That is, when the carbon layer is laminated on the cathode foil, the total amount of hydrogen gas generated within the electrolytic capacitor is suppressed. The reason why the total amount of hydrogen gas generated is suppressed is presumed to be that the reduction reaction of dissolved oxygen becomes more dominant than the reduction reaction of hydrogen ions at the cathode. If the total amount of hydrogen gas generated can be suppressed by measures on the cathode side, some increase in leakage current during repair of the dielectric oxide film, which is the origin of the hydrogen gas generation mechanism, can be tolerated.

If the increase in leakage current is allowed, it becomes possible to reduce the thickness of the dielectric oxide film, which lowers the withstand voltage of the anode foil. When the dielectric oxide film becomes thinner, the distance between the electrodes becomes narrower, and the capacitance of the electrolytic capacitor increases. Therefore, when a carbon layer is laminated on the cathode foil, the rate of appearance of the capacitance increases and the level of the capacitance increases, thereby increasing the capacitance of the electrolytic capacitor.

The carbon material contained in the carbon layer is graphite, carbon black, activated carbon, carbon nanohorn, fibrous carbon, or a mixture thereof. Examples of graphite include natural graphite, artificial graphite, and graphitized Ketjenblack. Examples of carbon black include Ketjen black, acetylene black, channel black, and thermal black. Activated carbon is made from natural plant tissues such as coconut shells, synthetic resins such as phenol, and materials derived from fossil fuels such as coal, coke, and pitch. Examples of fibrous carbon include carbon nanotubes (hereinafter referred to as CNTs), carbon nanofibers (hereinafter referred to as CNFs), and the like.

Activated carbon and fibrous carbon are preferable as carbon materials to be included in the carbon layer because pi electrons are delocalized and the specific surface area is large. The carbon material may be subjected to porous treatment such as activation treatment or opening treatment.

In order to improve the adhesion between the carbon layer and the cathode foil, a surface-expanding layer may be formed on the surface of the cathode foil, and a carbon layer may be formed on the surface-expanding layer. Further, in order to improve the adhesion between the carbon layer and the cathode foil, it is preferable to press the cathode foil on which the carbon layer is formed. In press processing, for example, the carbon layer and cathode foil are sandwiched between press rollers and press linear pressure is applied. The press pressure is preferably about 0.01 to 100 t/cm. When the carbon layer and the cathode foil are brought into pressure contact, the carbon material enters the pores of the surface-expanding layer, and the carbon material deforms along the uneven surface of the surface-expanding layer, improving the adhesion and fixation between the carbon layer and the cathode foil. The quality will further improve.

The carbon material contained in the carbon layer is not particularly limited, but carbon black, which is spherical carbon, is also preferred. If the surface-expanding layer formed on the surface of the cathode foil is an etching pit, using carbon black with a particle size smaller than the opening diameter of the etching pit will allow the carbon black to penetrate deeper into the etching pit, and the carbon layer will come into close contact with the cathode foil. do.

Further, the carbon material contained in the carbon layer may be flaky or scaly graphite and carbon black, which is spherical carbon. The scale-like or scaly graphite preferably has an aspect ratio of a short axis to a long axis in the range of 1:5 to 1:100. Carbon black, which is spherical carbon, preferably has a primary particle diameter of 100 nm or less on average. When a carbon layer containing this combination of carbon materials is laminated on a cathode foil, carbon black is easily rubbed into the pores of the surface-expanding layer by graphite. Graphite is easily deformed along the uneven surface of the surface-expanding layer and easily piled up on the uneven surface. The graphite then acts as a pressure cap and holds down the spherical carbon that has been rubbed into the pores. Therefore, the adhesion and fixing properties between the carbon layer and the cathode foil are further improved.

The electrolytic solution contains an anion component and a cation component in addition to POEG. Examples of the solvent for the electrolytic solution include protic organic polar solvents and aprotic organic polar solvents, which may be used alone or in combination of two or more. Examples of the protic organic polar solvent include monohydric alcohols, polyhydric alcohols, and oxyalcohol compounds, such as ethylene glycol, propylene glycol, and glycerin. Representative examples of aprotic organic polar solvents include sulfonic, amide, lactone, cyclic amide, nitrile, and sulfoxide solvents, such as γ-butyrolactone, ethylene carbonate, propylene carbonate, and acetonitrile.

Organic acids that serve as anionic components include 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, and 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, etc. Examples include carboxylic acids, phenols, and sulfonic acids. In addition, examples of inorganic acids serving as anionic components include boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, carbonic acid, and silicic acid. Examples of composite compounds of organic acids and inorganic acids that serve as anionic components include borodisalicylic acid, borodisoxalic acid, borodiglycolic acid, borodismalonic acid, borodisuccinic acid, borodiadipic acid, borodiazelaic acid, borodisbenzoic acid, borodismaleic acid, and borodisilactic acid. , borodimalic acid, boroditartaric acid, borodiccitric acid, borodiphthalic acid, borodi(2-hydroxy)isobutyric acid, borodiresorcinic acid, borodimethylsalicylic acid, borodinaphthoic acid, borodimandelic acid, and borodi(3-hydroxy)propionic acid.

Examples of at least one salt of an organic acid, an inorganic acid, or a composite compound of an organic acid and an inorganic acid include ammonium salts, quaternary ammonium salts, quaternized amidinium salts, amine salts, sodium salts, potassium salts, etc. can be mentioned. Examples of the quaternary ammonium ion of the quaternary ammonium salt 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. Primary amines include methylamine, ethylamine, propylamine, etc. Secondary amines include dimethylamine, diethylamine, ethylmethylamine, dibutylamine, etc. Tertiary amines include trimethylamine, triethylamine, tributylamine, ethyldimethylamine, Examples include ethyldiisopropylamine.

Other additives can also be added to the electrolyte. Examples of additives include phosphoric acid compounds containing phosphoric acid, boric acid compounds containing boric acid, complex compounds of boric acid and sugar alcohols such as mannitol and sorbitol, colloidal silica, and silicone oil.

As the electrolyte, a solid electrolyte may be used in addition to the electrolytic solution. The solid electrolyte is, for example, a conductive polymer. The conductive polymer is a self-doped type doped with an intramolecular dopant molecule or a conjugated polymer doped with an external dopant molecule. Conjugated polymers are obtained by chemical oxidative polymerization or electrolytic oxidative polymerization of monomers having π-conjugated double bonds or derivatives thereof. Any known conjugated polymer or dopant can be used without particular limitation.

As the conductive polymer, poly(3,4-ethylenedioxythiophene) called PEDOT doped with polystyrene sulfonic acid called PSS is particularly preferred. A solid electrolyte is formed by immersing a capacitor element in a dispersion liquid in which a solid electrolyte is dispersed in a solvent and then drying it. The anode foil, cathode foil, and separator may be separately dipped in the dispersion before assembly, or may be applied dropwise or sprayed. The electrolytic solution may be impregnated into the capacitor element after the solid electrolyte layer is formed on the capacitor element.

The separator is interposed between the anode foil and the cathode foil to prevent short circuits between the anode foil and the cathode foil or the cathode body, and also holds the electrolyte. Separators can be made of cellulose such as kraft, Manila hemp, esparto, hemp, rayon, and mixed papers thereof, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and their derivatives, polytetrafluoroethylene resins, and polyfluoride. Polyamide resins such as vinylidene resins, vinylon resins, aliphatic polyamides, semi-aromatic polyamides, and fully aromatic polyamides, polyimide resins, polyethylene resins, polypropylene resins, trimethylpentene resins, polyphenylene sulfide resins, acrylic resins, etc. These resins can be used alone or in combination, and can be used in combination with cellulose.

Here, electrolytic capacitors are required to have high capacity as well as high withstand voltage. In order to achieve high capacity, it is necessary to increase the size of the anode foil in addition to expanding the area of the anode foil. Therefore, electrolytic capacitors tend to have a larger band width along the winding axis of the capacitor element. In server power supplies, the casing in which electrolytic capacitors are placed is becoming smaller, and as a result, the electrolytic capacitors mounted in the casing are required to be lower in height and occupy less space on the board. For this reason, it is becoming mainstream to place electrolytic capacitors horizontally in order to reduce their height, and in order to increase the capacitance of electrolytic capacitors, it is necessary to make them longer. Furthermore, rather than using a plurality of short electrolytic capacitors in parallel, there is a need to increase the length of the electrolytic capacitor to ensure capacitance and reduce the number of electrolytic capacitors to be mounted.

In contrast, in the electrolytic capacitor of this embodiment, the capacitance appearance rate is maintained high even if the winding axis direction of the capacitor element is extended. Therefore, by having an elongated capacitor element whose winding axis direction is longer than the outer diameter, it is possible to reduce the height in the direction perpendicular to the spread of the mounting board, making it suitable for horizontal use. Furthermore, since it is possible to increase the capacity of the electrolytic capacitor, the number of electrolytic capacitors to be mounted can be reduced.

Hereinafter, this electrolytic capacitor will be explained in more detail based on Examples. Note that the present invention is not limited to the following examples.

Electrolytic capacitors of each Reference Example, each Example, and each Comparative Example were manufactured as follows. A strip-shaped aluminum foil was used as the anode foil. On the cathode side, a cathode body was made by laminating a cathode foil and a carbon layer, and the cathode foil was a strip-shaped aluminum foil like the anode foil.

The aluminum foil on the anode side was subjected to direct current etching to form a surface-expanding layer consisting of tunnel-shaped etching pits. The DC etching process uses a first step to form pits and a second step to enlarge the pits.The first step is to electrochemically etch the aluminum foil using a direct current in an aqueous solution containing chlorine ions. I did it.

After forming the surface-expanding layer, the anode foil was subjected to a chemical conversion treatment to form a dielectric oxide film on the surface of the surface-expanding layer. Specifically, a voltage of 650 V was applied in a chemical solution of 4 wt% boric acid at a liquid temperature of 85°C.

The aluminum foil on the cathode side was subjected to AC etching treatment, and a surface-expanding layer consisting of spongy etching pits was formed on both sides of the foil. Next, the aluminum foil was subjected to a chemical conversion treatment to form an oxide film on the surface of the surface expanding layer. In the chemical conversion treatment, after removing chlorine deposited during AC etching with a phosphoric acid aqueous solution, a voltage was applied in an aqueous solution of ammonium dihydrogen phosphate.

The carbon layer laminated on the cathode foil contained carbon black as a carbon material. First, a slurry was prepared by mixing and kneading carbon black powder, styrene butadiene rubber (SBR) as a binder, and an aqueous solution of carboxymethyl cellulose ammonium (CMC-NH ₃ ) as an aqueous solution containing a dispersant.

This slurry was uniformly applied to the cathode foil. After the slurry was heated and dried to volatilize the solvent, the cathode foil was pressed. In the press processing, the cathode foil was sandwiched between press rollers and a press linear pressure of 5.38 kN/cm was applied to fix the carbon layer on the cathode foil.

Separators with different densities were stacked and used as separators. Specifically, a separator made of kraft paper with a density of 0.85 g/cm ³ and a thickness of 15 μm and a separator made of kraft paper with a density of 0.95 g/cm ³ and a thickness of 25 μm were used in layers. The electrolytic solution contains ethylene glycol as a solvent, and ethylamine azelaate as a solute, along with a pressure improver. A capacitor element was produced by sandwiching and winding a separator between an anode foil and a cathode foil, and the capacitor element was immersed in an electrolytic solution, so that the electrolytic solution was impregnated from both end surfaces of the capacitor element.

An aluminum foil-shaped lead terminal is connected to the anode foil and the cathode foil by cold pressure welding. After being impregnated with the electrolytic solution, the lead-out terminal led out from the capacitor element is connected to an external terminal attached to a sealing body made of a phenol laminate. Thereafter, the capacitor element was housed in an aluminum case, and the opening of the case was sealed with a sealant. After being sealed with the sealing body, the electrolytic capacitor was subjected to an aging treatment. In the aging treatment, a voltage of 490 V was applied for 90 minutes at room temperature (30° C.).

Each Reference Example, each Example, and each Comparative Example differs in the type of pressure resistance improver included in the electrolytic solution and the band width of the anode foil. Differences among each reference example, each example, and comparative example are shown in Table 1 below. Note that the anode foil and the cathode foil are of the same length, and only the anode foil is shown as a representative.

(Table 1)

As shown in Table 1, in Reference Examples 1 and 3 and Examples 1 to 6, POEG was contained in the electrolytic solution as a pressure resistance improver. In Table 1, PO&EO-added glycerin is a glycerin derivative in which a propylene oxide polymer (PO) and an ethylene oxide polymer (EO) are added to two hydroxy group positions of glycerin. In Reference Examples 2 and 4 and Comparative Examples 1 to 6, PO&EO-added glycerin is contained in the electrolyte as a pressure-resistant improver. The concentration of the withstand voltage improver added to the electrolytic solution was the same in each Reference Example, each Example, and each Comparative Example.

The capacitance appearance rates of the electrolytic capacitors of each reference example, each example, and comparative example shown in Table 1 above were measured. The ratio of the measured capacitance to the theoretical capacitance of the electrolytic capacitor (actual capacitance/theoretical capacitance x 100) was calculated, and the calculation result was taken as the capacity appearance rate. The theoretical capacitance was calculated using the formula ((anode side capacitance×cathode side capacitance)/(anode side capacitance+cathode side capacitance)).

To measure the anode side capacitance and cathode side capacitance, disassemble the electrolytic capacitor after aging treatment, take out the anode foil and cathode foil, cut out a test piece from the foil, use a platinum plate as the counter electrode, and measure the cathode side capacitance. Here, two test pieces were used as electrodes facing each other, immersed in a capacitance measurement liquid in a glass measurement tank, and measured using a capacitance meter according to JEITA standard RC-2364A.

Table 2 below shows the capacitance appearance rates of the electrolytic capacitors of each Reference Example, Example, and Comparative Example.
(Table 2)

Also, based on Table 2, the graph in FIG. 1 was created. Here, Reference Examples 1 and 3 and Examples 1 to 6 using polyoxyethylene glycerin are referred to as POEG series. Reference Examples 2 and 4 and Comparative Examples 1 to 6 using PO&EO-added glycerin are referred to as the PO&EO-added glycerin series. Then, the horizontal axis is the band width of the anode foil, the vertical axis is the capacity appearance rate, and the same series are included in the same graph. The POEG series including Examples is represented by a graph plotted with circles, and the PO&EO-added glycerin series including Comparative Examples is represented by a graph plotted with x marks.

Furthermore, based on Table 2, the graph in FIG. 2 was created. In FIG. 2, each capacity appearance rate in the PO&EO-added glycerin series is used as a reference (100%), and the ratio of each capacity appearance rate in the POEG series is plotted. The POEG series including Examples is represented by a graph plotted with circles, and the PO&EO-added glycerin series including Comparative Examples is represented by a graph plotted with x marks.

As shown in Table 1, FIGS. 1 and 2, the POEG series has a higher capacity appearance rate than the PO&EO-added glycerin series in all anode foil band widths. In the PO&EO-added glycerin series, the capacity appearance rate drops significantly when the band width of the anode foil exceeds 37 mm, the capacity appearance rate sharply decreases when the band width becomes 62 mm, and the capacity appearance rate decreases significantly when the band width exceeds 70 mm. On the other hand, in the POEG series, the capacity appearance rate is maintained for all anode foil band widths of 62 mm or less, and even when the anode foil band width is increased to more than 70 mm, the decrease in capacity appearance rate is suppressed. There is.

Therefore, when the band width of the anode foil exceeds 37 mm, the difference in capacity appearance rate between the POEG series and the PO&EO-added glycerin series widens, and the capacity appearance rate is relatively improved compared to the PO&EO-added glycerin series. Furthermore, when the band width of the anode foil is, for example, 32 mm, the difference in capacity appearance rate between the POEG series and the PO&EO-added glycerin series was 1.9%, but when the band width of the anode foil becomes 62 mm, the difference in capacity appearance rate is 4. When the rate increases to 9%, the POEG series becomes noticeably superior, and when the band width of the anode foil exceeds 70 mm, the rate increases to 8.7%, making the POEG series extremely superior.

As a result, if the capacitor element is made into a wound type, the band width along the winding axis of the anode foil is made to exceed 37 mm, and the electrolyte contains POEG, the capacitance appearance rate of the electrolytic capacitor can be maintained well and the capacity can be increased. It was confirmed that it would be easier.

Subsequently, an approximate straight line was set using four points in the graph of FIG. 1 where the band width length of the anode foil was 52 mm or more. A graph of this approximate straight line is shown in FIG. Also in FIG. 3, the POEG series including Examples is represented by a plot of circles, and the PO&EO-added glycerin series including Comparative Examples is represented by a plot of x marks. As shown in FIG. 3, the approximate straight line of the POEG series showed that the capacity appearance rate was 80% when the band width length of the anode foil was 150 mm. In other words, when the capacitor element is of a wound type and the electrolyte contains POEG, the JIS stipulates that the capacitance tolerance is ±20% when the band width along the winding axis of the anode foil is 150 mm or less. It was confirmed that the standards were met.

Next, Example 4 in which the length along the winding axis of the anode foil is 62 mm and POEG is included in the electrolyte, and a comparative example in which the length along the winding axis of the anode foil is 62 mm and PO&EP-added glycerin is included in the electrolyte. Regarding No. 4, the capacitor element was taken out from the case, and the taken out capacitor element was disassembled. Figure 3 shows a photograph of the surface of the anode foil after decomposition. 3(a) is a photograph of the anode foil of Example 4, and FIG. 3(b) is a photograph of the anode foil of Comparative Example 4.

As shown in FIGS. 3(a) and (b), the anode foils of Example 4 and Comparative Example 4 have lines Le and Lc along the belt length direction in the central region in the winding axis direction. There is. The components constituting line Le of Example 4 and line Lc of Comparative Example 4 were analyzed. As a result, both line Le and line Lc contained the pressure resistance improver.

However, as can be seen by comparing FIGS. 3A and 3B, the line Le in Example 4 is thin and thin. On the other hand, the line Lc of Comparative Example 4 is thicker and darker than that of Example 4. That is, in the comparison between Example 4 and Comparative Example 4, in Comparative Example 4, PO&EP-added glycerin is unevenly distributed in the central region of the anode foil in the winding axis direction. On the other hand, in a comparison between Example 4 and Comparative Example 4, in Example 4, there is less POEG unevenly distributed in the central region of the anode foil in the winding axis direction.

It has been confirmed that the parts of the anode foil marked with the lines Le and Lc were wet and impregnated with the electrolyte, and that the electrolyte was in close contact with the anode foil. From this, in Comparative Example 4, the electrolyte is in close contact with the anode foil even in the central region of the capacitor element in the winding axis direction, but due to the uneven distribution of the pressure improver, the electrolyte and the anode foil are in close contact with each other. A value close to the theoretical value of capacitance according to the adhesion area could not be obtained, and it is presumed that the capacitance appearance rate decreased significantly.

In other words, in a high concentration region of the withstand voltage improver, the appearance rate of capacitance decreases. If the region where the withstand voltage improver is unevenly distributed is thick and dense, the region where the appearance rate of capacitance decreases becomes wider, and the degree of decrease in the appearance rate of capacitance increases. Therefore, the capacitance appearance rate of the electrolytic capacitor as a whole also decreases. In Examples 1 to 4, compared to Comparative Examples 1 to 4, the pressure resistance improver was dispersed relatively uniformly throughout the anode foil, and there were fewer areas where the appearance rate of capacitance decreased, and the appearance rate of capacitance decreased. It is assumed that the decline was small and the capacity appearance rate remained good. Moreover, such a phenomenon occurs significantly when the density of the separator is 0.85 g/cm ³ or more.

Claims

an anode foil having a dielectric oxide film;
a cathode foil facing the anode foil;
a separator interposed between the anode foil and the cathode foil;
a capacitor element in which the separator, the anode foil, and the cathode foil are wound;
an electrolytic solution impregnated in the capacitor element;
Equipped with
The electrolytic solution contains polyoxyethylene glycerin,
The anode foil has a band width of more than 37 mm along the winding axis of the capacitor element;
A wound type electrolytic capacitor featuring:
The anode foil has a band width of 150 mm or less along the winding axis of the capacitor element;
The wound type electrolytic capacitor according to claim 1, characterized in that:
The separator has an average density of 0.85 g/cm 3 or more;
The wound type electrolytic capacitor according to claim 1, characterized in that:
The cathode foil includes a carbon layer laminated on the cathode foil;
The wound type electrolytic capacitor according to any one of claims 1 to 3, characterized in that: