TW202416307A - Winding electrolytic capacitor - Google Patents

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 Capacitors

The present invention relates to a wound electrolytic capacitor formed by winding an anode foil and a cathode foil.

Electrolytic capacitors are passive components that store and discharge electric charge by electrostatic capacitance. Electrolytic capacitors include valve metals such as tantalum or aluminum as anode foil and cathode foil. Anode foil and cathode foil are foil bodies of valve metal. A dielectric oxide film is formed on the foil surface of the anode foil. An electrolyte is interposed between the anode foil and the cathode foil.

The electrolyte is in 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 capacitance appearance rate of the electrolytic capacitor. The capacitance appearance rate is the ratio of the measured electrostatic capacitance of the electrolytic capacitor to the theoretical electrostatic capacitance (measured electrostatic capacitance/theoretical electrostatic capacitance×100).

Theoretical electrostatic capacitance is the resultant electrostatic capacitance when the electrolytic capacitor is regarded as a capacitor with the anode side and the cathode side connected in series. It can be obtained by dividing the product of the anode side electrostatic capacitance and the cathode side electrostatic capacitance by the sum of the anode side electrostatic capacitance and the cathode side electrostatic capacitance ((anode side electrostatic capacitance × cathode side electrostatic capacitance) / (anode side electrostatic capacitance + cathode side electrostatic capacitance)).

The anode side electrostatic capacitance and cathode side electrostatic capacitance are measured in the following manner: a test piece of a specified area is cut out from the foil, a platinum plate is used as an opposing electrode in the anode side electrostatic capacitance, and two test pieces are used as opposing electrodes in the cathode side electrostatic capacitance, and the test pieces are immersed in an electrostatic capacitance measurement solution in a glass measurement tank, and the measurement is performed using an electrostatic capacitance meter in accordance with the Japan Electronic Information Technology Association (JEITA) standard RC-2364A.

In recent years, the high output of server power supplies and radio base stations has been rapidly advancing with the utilization of massive amounts of data. The number of scenarios where electrolytic capacitors are required to have higher capacitance has increased. The anode foil is expanded by forming a valve metal into a sintered body or an etched foil, and a dielectric oxide film is formed on the expanded surface. This allows electrolytic capacitors to have higher capacitance.

In addition, as the output of equipment increases, the withstand voltage required of electrolytic capacitors also increases. In order to increase the spark voltage of the electrolyte, a withstand voltage enhancer is added to the electrolyte. Examples of withstand voltage enhancers include polymer compounds such as polyvinyl alcohol or polyethylene glycol, or inorganic microparticles such as silicon dioxide or aluminum oxide (for example, see Patent Document 1). [Prior Art Document] [Patent Document]

[Patent Document 1] Japanese Patent Publication No. 2011-176102

[The problem that the invention wants to solve]

As such, electrolytic capacitors are required to have higher capacitance, and the present invention provides an electrolytic capacitor with a good capacitance appearance rate so as to achieve higher capacitance. [Means for solving the problem]

To solve the above-mentioned problem, the electrolytic capacitor of the present embodiment includes 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 wound with the separator, the anode foil and the cathode foil, and an electrolyte impregnated in the capacitor element, wherein the electrolyte contains polyoxyethylene glycerol, and the strip width of the anode foil along the winding axis of the capacitor element exceeds 37 mm.

The strip width of the anode foil along the winding axis of the capacitor element may be 150 mm or less.

The average density of the separator may be greater than 0.85 g/cm ³ .

The cathode foil may include a carbon layer laminated on the cathode foil. [Effect of the invention]

According to the present invention, the capacitance appearance rate of the electrolytic capacitor is well maintained, and the capacitance can be easily increased.

An electrolytic capacitor is a passive element that stores and discharges electric charge by electrostatic capacitance. An electrolytic capacitor includes a capacitor element in which an anode foil and a cathode foil are placed opposite each other via a separator. A dielectric oxide film is formed on the foil surface of the anode foil. The capacitor element contains an electrolyte. The electrolyte exists between the anode foil and the cathode foil as a separator, and is in close contact with the dielectric oxide film of the anode foil, becoming a true cathode.

The electrolytic capacitor is of a wound type. The capacitor element is formed by spirally winding an anode foil and a cathode foil. The anode foil and the cathode foil are long foil bodies made of valve-acting metal. The winding axis of the capacitor element is consistent with the extension direction of the short sides of the anode foil and the cathode foil, that is, the width direction. The anode foil and the cathode foil have a winding axis extending along the short sides, and are wound along the long side direction in a manner that the long sides are rounded, thereby forming a capacitor element.

The short side of the anode foil, i.e., the width of the strip along the winding axis of the capacitor element, exceeds 37 mm. The short side of the cathode foil is preferably the same length as or longer than the short side of the anode foil so that no area that is not facing the cathode foil can be formed on the anode foil. As for the long side of the cathode foil, it is also preferably the same length as or longer than the long side of the anode foil so that no area that is not facing the cathode foil can be formed on the anode foil. The separator is preferably longer than the long sides of the anode foil and the cathode foil so that it can be wound up first to form a winding axis.

When the electrolyte is impregnated into the capacitor element, the electrolyte penetrates from the flat end surface perpendicular to the peripheral surface of the capacitor element toward the center of the capacitor element. In the electrolyte impregnation step, a pressure reduction treatment or a pressure increase treatment is applied as needed. The electrolyte impregnated into the capacitor element contains polyoxyethylene glycerin (hereinafter referred to as POEG (polyoxyethylene glycerin)). POEG, like polyvinyl alcohol or polyethylene glycol, originally functions as a withstand voltage enhancer.

The electrolytic capacitor satisfies three conditions: the capacitor element is a winding type, the length of the anode foil in the winding direction exceeds 37 mm, and the electrolyte contains POEG. When these structures are combined, the capacitance appearance rate of the electrolytic capacitor becomes relatively good compared with other structures, and it is easy to make the electrolytic capacitor large in capacitance. Furthermore, as another structure, although it is a winding type, the length of the anode foil in the winding direction is greater than 27 mm and within the range of 80 mm, and the electrolyte contains a voltage-resistant improver other than POEG as a comparison object.

The width of the anode foil along the winding axis is preferably 70 mm or less. By satisfying the three conditions of being wound to 70 mm, making the length of the anode foil in the winding axis direction exceed 37 mm, and containing POEG in the electrolyte, the capacitance appearance rate of the electrolytic capacitor is also maintained high and exceeds 95% compared with other structures.

In addition, the strip width of the anode foil along the winding axis is preferably more than 70 mm. Although it is a wound type, if the length of the anode foil in the winding axis direction is more than 70 mm, the capacitance appearance rate of the electrolytic capacitor containing a voltage-resistant enhancer other than POEG in the electrolyte will be significantly reduced. However, by satisfying the three conditions that the length of the anode foil in the winding axis direction exceeds 70 mm, it is a wound type, and POEG is contained in the electrolyte, the decrease in the capacitance appearance rate of the electrolytic capacitor is suppressed, and the capacitance appearance rate is more advantageous than that of the electrolytic capacitor containing a voltage-resistant enhancer other than POEG in the electrolyte.

Here, in the Japanese Industrial Standards (JIS) standard (JIS C 5101-4-1), the permissible error of electrostatic capacitance is preferably specified as ±20%. In compliance with this specification, the upper limit of the width of the anode foil along the winding axis is preferably 150 mm or less. If the length of the anode foil in the winding axis direction is 150 mm or less and the electrolytic capacitor is further a wound type, a capacitance retention rate of 80% can be easily achieved if POEG is included in the electrolyte.

The electrolyte penetrates from the flat end surface perpendicular to the peripheral surface of the capacitor element toward the center of the capacitor element and is maintained by infiltrating the separator. The average density of the separator is preferably above 0.85 g/ ^cm3 . When the electrolytic capacitor meets the three conditions of being a winding type, making the length of the anode foil in the winding direction exceed 37 mm, and containing POEG in the electrolyte, the capacitance appearance rate is maintained high even if the density of the separator is increased.

If the separator can be made thinner, the length of the anode foil and cathode foil that can be wound around a capacitor element with a certain outer diameter can be extended. If the length of the anode foil and cathode foil can be extended, the electrode area becomes larger. The high capacitance appearance rate achieved by satisfying the three conditions and the large electrode area achieved by thinning the separator interact with each other, further increasing the electrostatic capacitance of the electrolytic capacitor.

Furthermore, POEG is preferably in a liquid state at room temperature. If 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 dissolved in a solution by heating and added to an electrolyte. However, POEG in a liquid state at room temperature is not easily precipitated even if the solvent evaporates over time, thereby maintaining the electrostatic capacitance of the electrolytic capacitor well.

In such an electrolytic capacitor, the anode foil, cathode foil, electrolyte and separator can be any known ones and are not particularly limited.

For example, valve metals used in anode foil and cathode foil are aluminum, tantalum, niobium, titanium, uranium, zirconium, zinc, tungsten, bismuth, and antimony. They are ideally of high purity, but may contain impurities such as silicon, iron, copper, magnesium, and zinc.

The diffusion layer formed on the anode foil and cathode foil is a sintered body formed by sintering the powder of the valve metal, or an etched layer formed by etching the stretched foil, and includes tunnel-shaped pits, sponge-shaped pits, or gaps between dense powders. The tunnel-shaped pits can be set through the foil. The dielectric oxide film is typically an oxide film formed on the surface of the anode foil. If the anode foil is made of aluminum, it is an aluminum oxide layer formed by oxidizing the surface of the diffusion layer. The cathode foil can have a natural oxide film, or a thin dielectric oxide film (about 1 V to 10 V) can be formed by chemical synthesis.

A carbon layer containing a carbon raw material as a main material may be formed on the surface of the cathode foil. That is, the cathode side may also be a cathode foil formed by laminating the cathode foil and the carbon layer. The three conditions of the cathode foil being laminated, the cathode side being a cathode body, and the present electrolytic capacitor interact with each other to achieve a large capacitance of the electrolytic capacitor in the following manner.

That is, when the carbon layer is deposited on the cathode foil, the total amount of hydrogen gas generated in 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 in the cathode is more advantageous than the reduction reaction of hydrogen ions. If the total amount of hydrogen gas generated can be suppressed by measures on the cathode side, the increase in leakage current when repairing the dielectric oxide film that is the start of the hydrogen gas generation mechanism can be tolerated to some extent.

If the leakage current is allowed to increase, the dielectric oxide film can be thinned to reduce the withstand voltage of the anode foil. When the dielectric oxide film is thinned, the distance between the electrodes becomes narrower, and the capacitance of the electrolytic capacitor is improved. Therefore, when a carbon layer is stacked on the cathode foil, the increase in the capacitance appearance rate and the increase in the capacitance interact with each other, thereby achieving a larger capacitance of the electrolytic capacitor.

The carbon raw materials contained in the carbon layer are graphite, carbon black, activated carbon, carbon nanotubes, fibrous carbon or a mixture of these. Examples of graphite include natural graphite, artificial graphite, graphitized Ketjen black, etc. Examples of carbon black include Ketjen black, acetylene black, channel black, and thermal black, etc. Activated carbon is made from natural plant tissues such as coconut shells, synthetic resins such as phenol, coal, coke, asphalt, etc., which are derived from fossil fuels. Examples of fibrous carbon include carbon nanotubes (hereinafter referred to as CNT (carbon nanotube)), carbon nanofibers (hereinafter referred to as CNF (carbon nanofiber)), etc.

Activated carbon or fibrous carbon is preferred as a carbon material to be contained in the carbon layer because of its large specific surface area due to the delocalization of π electrons. The carbon material may be subjected to a porosity treatment such as activation treatment or opening treatment.

In order to improve the adhesion between the carbon layer and the cathode foil, a diffusion layer may be formed on the surface of the cathode foil, and the carbon layer may be formed on the diffusion layer. In addition, in order to improve the adhesion between the carbon layer and the cathode foil, it is preferred to perform a press process on the cathode foil formed with the carbon layer. During the press process, for example, the carbon layer and the cathode foil are clamped by a pressing roller, and a pressing line pressure is applied. The pressing pressure is ideally about 0.01 t/cm to 100 t/cm. When the carbon layer and the cathode foil are pressed, the carbon raw material enters the pores of the diffusion layer, and the carbon raw material is deformed along the concave and convex surface of the diffusion layer, and the adhesion and fixation between the carbon layer and the cathode foil are further improved.

The carbon raw material contained in the carbon layer is not particularly limited, but carbon black as spherical carbon is also preferred. When the expansion layer formed on the surface of the cathode foil is an etched pit, when using carbon black with a smaller particle size than the opening diameter of the etched pit, it is easy to enter the deeper part of the etched pit, so that the carbon layer and the cathode foil are in close contact.

In addition, the carbon raw material contained in the carbon layer may also be flaky or scaly graphite and carbon black as spherical carbon. The flaky or scaly graphite preferably has an aspect ratio of the short diameter to the long diameter in the range of 1:5 to 1:100. The carbon black as spherical carbon preferably has an average primary particle size of 100 nm or less. When the carbon layer containing the carbon raw material of this combination is stacked on the cathode foil, the carbon black is easily ground into the pores of the diffusion layer by the graphite. Graphite is easily deformed along the concave and convex surface of the diffusion layer and is easily stacked on the concave and convex surface. In addition, the graphite becomes a pressing cover to prevent the spherical carbon from being ground and mixed into the pores. Therefore, the adhesion and fixation between the carbon layer and the cathode foil are further improved.

In addition to POEG, the electrolyte also contains anionic components and cationic components. As the solvent of the electrolyte, protic organic polar solvents or non-protic organic polar solvents can be listed, and they can be used alone or in combination of two or more. Regarding protic organic polar solvents, monohydric alcohols, polyhydric alcohols and oxygen-containing alcohol compounds can be listed, such as ethylene glycol, propylene glycol or glycerol. Regarding non-protic organic polar solvents, sulfone series, amide series, lactone series, cyclic amide series, nitrile series, sulfone series, etc. can be listed as representatives, such as γ-butyrolactone, ethyl carbonate, propyl carbonate, acetonitrile, etc.

Examples of organic acids that serve as anionic components 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, resorcinolic acid, 2,4,6-trihydroxybenzoic acid (phloroglucinic acid), gallic acid, gentisic acid, protocatechuic acid, pyrocatechuic acid, trimellitic acid, and pyromellitic acid, or phenols and sulfonic acids. In addition, examples of inorganic acids that serve as anionic components include boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, carbonic acid, and silicic acid. Examples of complex compounds of organic acids and inorganic acids that serve as anionic components include borodihydroxysalicylic acid, borodioxalic acid, borodiglycolic acid, borodimalonic acid, borodisucinic acid, borodiadipic acid, borodiazelaic acid, borodibenzoic acid, borodimaleic acid, borodilactic acid, borodimalic acid, boroditartaric acid, borodicitric acid, borodiphthalic acid, borodi(2-hydroxy)isobutyric acid, borodiresorcinolic acid, borodimethylsalicylic acid, borodinaphthoic acid, borodimandelic acid, and borodi(3-hydroxy)propionic acid.

In addition, as salts of at least one of organic acids, inorganic acids, and complex compounds of organic acids and inorganic acids, for example, ammonium salts, quaternary ammonium salts, quaternary amidine salts, amine salts, sodium salts, potassium salts, etc. can be listed. As quaternary ammonium ions of quaternary ammonium salts, tetramethylammonium, triethylmethylammonium, tetraethylammonium, etc. can be listed. As quaternary amidine salts, ethyldimethylimidazolium, tetramethylimidazolium, etc. can be listed. As amine salts, salts of primary amines, secondary amines, and tertiary amines can be listed. Examples of the primary amine include methylamine, ethylamine, and propylamine, examples of the secondary amine include dimethylamine, diethylamine, ethylmethylamine, and dibutylamine, and examples of the tertiary amine include trimethylamine, triethylamine, tributylamine, ethyldimethylamine, and ethyldiisopropylamine.

Other additives may be added to the electrolyte. Examples of the additives include phosphoric acid compounds including phosphoric acid, boric acid compounds including boric acid, complexes of boric acid and sugar alcohols such as mannitol or sorbitol, colloidal silicon dioxide, and silicone oil.

As an electrolyte, a solid electrolyte may be used in addition to an electrolyte solution. The solid electrolyte is, for example, a conductive polymer. The conductive polymer is a self-doped polymer doped with a dopant molecule within the molecule or a conjugated polymer doped with an external dopant molecule. The conjugated polymer is obtained by chemical oxidation polymerization or electrolytic oxidation polymerization of a monomer having a π-conjugated double bond or a derivative thereof. The conjugated polymer or dopant may be a known one without particular limitation.

As a conductive polymer, poly(3,4-ethylenedioxythiophene) called PEDOT (Poly(3,4-ethylenedioxythiophene)) doped with polystyrene sulfonic acid called PSS (polystyrene sulfonate) is particularly preferred. The solid electrolyte is formed by immersing the capacitor element in a dispersion in which the solid electrolyte is dispersed in a solvent and drying it. The anode foil, cathode foil and separator can be immersed in the dispersion before assembly, or they can be dripped, sprayed, etc. The electrolyte can be impregnated in the capacitor element after the solid electrolyte layer is formed in the capacitor element.

In order to prevent short circuit between the anode foil and the cathode foil or the cathode body, a separator is interposed between the anode foil and the cathode foil and retains the electrolyte. Examples of the partition include kraft paper, Manila hemp, esparto, hemp, rayon and other cellulose and mixed papers thereof, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate and derivatives thereof, polytetrafluoroethylene resins, polyvinylidene fluoride resins, vinylon resins, aliphatic polyamides, semi-aromatic polyamides, wholly aromatic polyamides and other polyamide resins, polyimide resins, polyethylene resins, polypropylene resins, trimethylpentene resins, polyphenylene sulfide resins, acrylic resins and the like. These resins can be used alone or in combination and can be mixed with cellulose.

Here, in addition to requiring high withstand voltage, electrolytic capacitors are also required to have high capacitance. In order to achieve high capacitance, in addition to expanding the area of the anode foil, the anode foil also needs to be enlarged. Therefore, the band width of the electrolytic capacitor along the winding axis of the capacitor element tends to increase. In server power supplies, the frame for configuring electrolytic capacitors is miniaturized, and along with this, the electrolytic capacitors mounted on the frame are also required to be thinner or the dedicated area on the substrate is reduced. Therefore, horizontally configuring electrolytic capacitors for the purpose of thinning has gradually become the mainstream, and in order to increase the capacitance of the electrolytic capacitor, it is inevitable to extend the product. In addition, compared with using a plurality of short electrolytic capacitors in parallel, it is required to extend the length of the electrolytic capacitor to ensure the electrostatic capacitance and reduce the number of electrolytic capacitors to be mounted.

In contrast, the electrolytic capacitor of the present embodiment can maintain a high capacitance appearance rate even if the winding direction of the capacitor element is extended. Therefore, a thin and long capacitor element that is long in the winding direction relative to the outer diameter can promote thinning in a direction perpendicular to the expansion of the mounting substrate, and is preferably used for horizontal placement. In addition, since the capacitance of the electrolytic capacitor can be increased, the number of electrolytic capacitors mounted can be reduced. [Example]

The electrolytic capacitor is further described in detail below based on the embodiments. Furthermore, the present invention is not limited to the following embodiments.

Electrolytic capacitors of each reference example, each embodiment, and each comparative example were produced as follows. A strip of aluminum foil was used as the anode foil. The cathode side was a cathode body formed by laminating cathode foil and carbon layer, and the cathode foil was a strip of aluminum foil similar to the anode foil.

The aluminum foil on the anode side is subjected to a direct current etching process to form an expanded surface layer including tunnel-shaped etched pits. In the direct current etching process, a first step of forming pits and a second step of expanding the pits are used. The first step is to electrochemically etch the aluminum foil with a direct current in an aqueous solution containing chlorine ions.

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

The aluminum foil on the cathode side is subjected to AC etching to form a diffusion layer containing sponge-like etching pits on both sides of the foil. Next, the aluminum foil is subjected to chemical synthesis to form an oxide film on the surface of the diffusion layer. In the chemical synthesis, chlorine attached during the AC etching treatment is removed with a phosphoric acid aqueous solution, and then a voltage is applied to an aqueous solution of ammonium dihydrogen phosphate.

The carbon layer laminated on the cathode foil contains carbon black as a carbon raw material. First, carbon black powder, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose ammonium (CMC (carboxymethyl cellulose)-NH ₃ ) aqueous solution as an aqueous solution containing a dispersant are mixed and kneaded to prepare slurry.

The slurry is evenly applied to the cathode foil. After the slurry is heated and dried to volatilize the solvent, the cathode foil is pressed. During the pressing process, the cathode foil is sandwiched by pressing rolls and a pressing linear pressure of 5.38 kN/cm is applied to fix the carbon layer on the cathode foil.

As separators, separators with different densities are stacked and used. Specifically, a separator comprising kraft paper with a density of 0.85 g/cm ³ and a thickness of 15 μm and a separator comprising kraft paper with a density of 0.95 g/cm ³ and a thickness of 25 μm are stacked and used. The electrolyte contains a withstand voltage enhancer, ethylene glycol as a solvent, and ethylamine azelaic acid as a solute. The capacitor element is made by winding the separator between the anode foil and the cathode foil, and the capacitor element is immersed in the electrolyte, and the electrolyte is impregnated from both end faces of the capacitor element.

The anode foil and cathode foil are connected to an aluminum foil lead terminal by cold pressure welding. After being impregnated with electrolyte, the lead terminal from the capacitor element is connected to the external terminal mounted on the sealing body containing the phenol laminate. After that, the capacitor element is housed in an aluminum casing, and the opening of the casing is sealed with the sealing body. After sealing with the sealing body, the electrolytic capacitor is subjected to aging treatment. The aging treatment is to apply a voltage of 490 V for 90 minutes at room temperature (30°C).

In each reference example, each embodiment, and each comparative example, the type of withstand voltage enhancer contained in the electrolyte and the width of the anode foil are different. The differences among each reference example, each embodiment, and comparative example are shown in the following Table 1. In addition, the anode foil and the cathode foil have the same length, and only the anode foil is representatively shown.

(Table 1) Pressure Improver Anode foil width (mm) Width of partition board (mm) Capacitor element diameter (mm) Capacitor reel length (mm) Reference Example 1 POEG 27 31 30 35 Reference Example 2 PO&EO Added Glycerin 27 31 30 35 Reference Example 3 POEG 32 36 30 40 Reference Example 4 PO&EO Added Glycerin 32 36 30 40 Embodiment 1 POEG 37 41 30 45 Comparison Example 1 PO&EO Added Glycerin 37 41 30 45 Embodiment 2 POEG 42 46 30 50 Comparison Example 2 PO&EO Added Glycerin 42 46 30 50 Embodiment 3 POEG 52 56 30 60 Comparison Example 3 PO&EO Added Glycerin 52 56 30 60 Embodiment 4 POEG 62 66 30 70 Comparison Example 4 PO&EO Added Glycerin 62 66 30 70 Embodiment 5 POEG 70 75 35 80 Comparison Example 5 PO&EO Added Glycerin 70 75 35 80 Embodiment 6 POEG 80 85 35 90 Comparative Example 6 PO&EO Added Glycerin 80 85 35 90

As shown in Table 1, in Reference Example 1 and Reference Example 3 and Examples 1 to 6, POEG is included in the electrolyte as a withstand voltage enhancer. In Table 1, propylene oxide & ethylene oxide (PO & EO) added glycerol is a glycerol derivative obtained by adding a polymer of propylene oxide (PO) and a polymer of ethylene oxide (EO) to two hydroxyl positions of glycerol. In Reference Example 2 and Reference Example 4 and Comparative Examples 1 to 6, PO & EO added glycerol is included in the electrolyte as a withstand voltage enhancer. The concentration of the withstand voltage enhancer added to the electrolyte is the same in each reference example, each example and each comparative example.

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

The anode side electrostatic capacitance and cathode side electrostatic capacitance are measured in the following manner: the electrolytic capacitor after aging treatment is disassembled, the anode foil and cathode foil are taken out, and test pieces are cut out from the foils. A platinum plate is used as a counter electrode. In the cathode side electrostatic capacitance, two test pieces are used as counter electrodes and immersed in the electrostatic capacitance measurement solution in a glass measurement tank. The electrostatic capacitance meter is used to measure according to JEITA standard RC-2364A.

The capacitance appearance ratio of the electrolytic capacitors of each reference example, embodiment and comparative example is shown in Table 2 below. (Table 2) Anode foil width (mm) Capacitor appearance rate (%) POEG Series PO&EO Addition Glycerin Series 27 97.6 95.9 32 97.7 95.8 37 97.7 95.8 42 97.6 94.6 52 98.4 94.4 62 96.2 91.3 70 95.5 90.6 80 93.0 84.3

In addition, based on Table 2, the graph of Figure 1 was prepared. Here, Reference Examples 1 and 3 using polyoxyethylene glycerol and Examples 1 to 6 are set as the POEG series. Reference Examples 2 and 4 using PO&EO added glycerol and Comparative Examples 1 to 6 are set as the PO&EO added glycerol series. And, with the horizontal axis being the width of the anode foil and the vertical axis being the capacitance appearance rate, the same series are included in the same graph. The POEG series including the examples is represented by a curve marked with circular marks, and the PO&EO added glycerol series including the comparative examples is represented by a curve marked with x marks.

Furthermore, a graph of FIG2 was prepared based on Table 2. In FIG2, the ratio of each capacitance appearance rate of the POEG series is plotted with the capacitance appearance rate of each PO&EO addition glycerol series as the standard (100%). The POEG series including the embodiment is represented by a curve marked with a circle, and the PO&EO addition glycerol series including the comparative example is represented by a curve marked with an x.

As shown in Table 1, Figure 1, and Figure 2, the POEG series has a higher capacitance appearance rate than the PO&EO glycerol series in all anode foil widths. In addition, in the PO&EO glycerol series, if the anode foil width exceeds 37 mm, the capacitance appearance rate decreases significantly, and if it reaches 62 mm, the capacitance appearance rate decreases sharply, and if it exceeds 70 mm, the capacitance appearance rate decreases significantly. In contrast, the POEG series maintains the capacitance appearance rate at all anode foil widths below 62 mm, and even if the anode foil width is expanded to more than 70 mm, the decrease in capacitance appearance rate is suppressed.

Therefore, if the width of the anode foil exceeds 37 mm, the difference in capacitance appearance rate between the POEG series and the PO&EO plus glycerol series will be enlarged, and the capacitance appearance rate of the POEG series will be relatively optimized compared with the PO&EO plus glycerol series. Moreover, when the width of the anode foil is, for example, 32 mm, the difference in capacitance appearance rate between the POEG series and the PO&EO plus glycerol series is 1.9%. If the width of the anode foil becomes 62 mm, it will be enlarged to 4.9%, and the POEG series will obviously have an advantage. Furthermore, if the width of the anode foil exceeds 70 mm, it will be enlarged to 8.7%, and the POEG series will have a great advantage.

This confirmed that when the capacitor element is made into a wound type, the strip width of the anode foil along the winding axis exceeds 37 mm, and POEG is contained in the electrolyte, the capacitance appearance rate of the electrolytic capacitor is well maintained and it is easy to achieve a large capacitance.

Next, in the graph of FIG1 , an approximate straight line is set using four points where the width of the anode foil is 52 mm or more. The curve of the approximate straight line is shown in FIG3 . In FIG3 , the POEG series including the embodiment is also represented by a circular mark, and the PO&EO addition glycerol series including the comparative example is also represented by an x mark. As shown in FIG3 , the approximate straight line of the POEG series indicates that the capacitance appearance rate becomes 80% when the width of the anode foil is 150 mm. That is, it was confirmed that when the capacitor element is made into a winding type and POEG is contained in the electrolyte, when the width of the anode foil along the winding axis is less than 150 mm, the JIS standard that stipulates an allowable error of electrostatic capacitance of ±20% is satisfied.

Next, for Example 4 in which the length of the anode foil along the reel is 62 mm and the electrolyte contains POEG, and Comparative Example 4 in which the length of the anode foil along the reel is 62 mm and the electrolyte contains PO&EP plus glycerol, the capacitor element is taken out from the casing and the taken out capacitor element is decomposed. A photograph of the surface of the decomposed anode foil is shown in FIG3. FIG3 (a) is a photograph of the anode foil of Example 4, and FIG3 (b) is a photograph of the anode foil of Comparative Example 4.

As shown in (a) and (b) of Figure 3, in the anode foil of Example 4 and Comparative Example 4, the wire Le and the wire Lc along the length direction of the wire are provided in the center region in the winding direction. The components constituting the wire Le of Example 4 and the wire Lc of Comparative Example 4 were analyzed. As a result, the wire Le and the wire Lc both contain a withstand voltage improver.

However, as can be seen from a comparison between (a) and (b) of FIG. 3 , the line Le of Example 4 is thin and shallow. On the other hand, compared with Example 4, the line Lc of Comparative Example 4 is thick and deep. That is, in the comparison between Example 4 and Comparative Example 4, in Comparative Example 4, PO&EP-added glycerol tends to exist in the central area of the axial direction of the anode foil. On the other hand, in the comparison between Example 4 and Comparative Example 4, in Example 4, the amount of POEG tending to exist in the central area of the axial direction of the anode foil is small.

Furthermore, it can be confirmed that the part of the anode foil with the line Le and the line Lc is wet and impregnated with the electrolyte, and the electrolyte is in close contact with the anode foil. Based on this, it is speculated that in Comparative Example 4, the electrolyte is also in close contact with the anode foil in the center area of the winding axis direction of the capacitor element, but due to the bias of the withstand voltage improver, it is impossible to obtain a value close to the theoretical value of the electrostatic capacitance of the close contact area obtained by the close contact between the electrolyte and the anode foil, and the capacitance appearance rate is significantly reduced.

That is, in the high concentration area of the withstand voltage enhancer, the appearance rate of the electrostatic capacitance decreases. If the area where the withstand voltage enhancer tends to exist is coarse and deep, the area where the appearance rate of the electrostatic capacitance decreases becomes wider, and the decrease in the appearance rate of the electrostatic capacitance becomes greater. Therefore, the capacitance appearance rate of the electrolytic capacitor as a whole also becomes lower. It is speculated that compared with Comparative Examples 1 to 4, the withstand voltage enhancers of Examples 1 to 4 are more evenly dispersed in the entire anode foil, the area where the appearance rate of the electrostatic capacitance decreases is smaller, the decrease in the appearance rate of the electrostatic capacitance is small, and the capacitance appearance rate is well maintained. In addition, this phenomenon occurs significantly when the density of the separator is 0.85 g/ ^cm3 or more.

Le, Lc: line

FIG1 is a graph of the POEG series and the PO&EO addition glycerol series, with the horizontal axis being the width of the anode foil and the vertical axis being the capacitance appearance rate. FIG2 is a graph showing the relationship between the width of the anode foil and the capacitance appearance rate of the POEG series based on the capacitance appearance rates of the PO&EO addition glycerol series. FIG3 is a graph showing the approximate straight line of the PO&EO addition glycerol series and the POEG series. FIG4 (a) is a photograph of the anode foil of Example 4, and FIG4 (b) is a photograph of the anode foil of Comparative Example 4.

Claims (4)

A wound electrolytic capacitor is characterized by comprising: 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 wound with the separator, the anode foil and the cathode foil; and an electrolyte impregnated in the capacitor element, the electrolyte containing polyoxyethylene glycerol, the anode foil having a strip width exceeding 37 mm along the winding axis of the capacitor element. A wound electrolytic capacitor as described in claim 1, wherein the strip width of the anode foil along the winding axis of the capacitor element is 150 mm or less. A wound electrolytic capacitor as described in claim 1, wherein the average density of the separator is greater than 0.85 g/ ^cm3 . A wound electrolytic capacitor as described in any one of claims 1 to 3, wherein the cathode foil includes a carbon layer laminated on the cathode foil.

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