Manufacturing method of electrolytic capacitor

Abstract

To suppress increase in a leakage current even if an ambient operating temperature of an electrolytic capacitor changes rapidly.SOLUTION: An electrolytic capacitor 1 includes an exterior body 4 and a capacitor element 5 accommodated in the exterior body 4. The capacitor element 5 includes an anode with an oxide film, a cathode, a separator disposed between the anode and the cathode, and a conductive polymer and liquid which are held on at least the separator. A method of manufacturing the electrolytic capacitor 1 includes: a first step of applying, to a capacitor body 10 in which the capacitor element 5 is accommodated in the exterior body 4, a voltage higher than a rated voltage for 30 minutes or more in an environment at a category lower limit temperature; and a second step of applying, to the capacitor body, the rated voltage or a voltage higher than the rated voltage for 30 minutes or more in an environment at a category upper limit temperature.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing an electrolytic capacitor. [Background technology]

[0002] When manufacturing electrolytic capacitors, aging treatment is performed to form a dielectric oxide film (hereinafter simply referred to as "oxide film") on the anode end surface and to repair any damage caused by the manufacturing process of the oxide film formed on the anode, thereby suppressing the increase in leakage current.

[0003] Patent Document 1 describes a method for manufacturing a solid electrolytic capacitor in which an oxide film is formed on an anode body, and a manganese dioxide layer and a cathode layer are sequentially laminated on the oxide film. Patent Document 1 describes a method in which, after forming a manganese dioxide layer, a voltage is applied in an atmosphere at a temperature of 0°C to 40°C and a relative humidity of 70% or more (claims of Patent Document 1, etc.). According to this method, by applying a voltage under atmospheric conditions that allow manganese dioxide to exhibit its maximum conversion properties, the deteriorated parts of the oxide film can be directly repaired by the manganese dioxide that covers it, so that the deteriorated parts of the oxide film can be repaired in a concentrated manner, and the variation in withstand voltage characteristics and the variation in leakage current can be reduced (functions, examples, etc. of Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 63-268240 Summary of the Invention [Problem to be solved by the invention]

[0005] The inventors' research has revealed that when the temperature of the environment in which an electrolytic capacitor is used changes suddenly, defects occur in the oxide film, which tends to increase the leakage current.

[0006] An object of the present invention is to manufacture an electrolytic capacitor capable of suppressing an increase in leakage current even when the temperature of the environment in which it is used changes suddenly. [Means for solving the problem]

[0007] The method for manufacturing an electrolytic capacitor of the present invention is a method for manufacturing an electrolytic capacitor comprising an anode having an oxide film, a cathode, a separator disposed between the anode and the cathode, a capacitor element having at least a conductive polymer and a liquid held by the separator, and an outer casing in which the capacitor element is housed, and includes a first step of applying a voltage higher than the rated voltage for 30 minutes or more to a capacitor body in which the capacitor element is housed in the outer casing in an environment of a lower category temperature limit, and a second step of applying a rated voltage or a voltage higher than the rated voltage for 30 minutes or more in an environment of an upper category temperature limit.

[0008] According to the present invention, in the first step, the portion (e.g., loss of oxide film) weakened in the lower limit temperature environment of the category is exposed, and a voltage is applied to the capacitor body in the lower limit temperature environment of the category, thereby enabling the weakened portion to be repaired. In addition, in the second step, the portion (e.g., loss of oxide film) weakened in the upper limit temperature environment of the category is exposed, and a voltage is applied to the capacitor body in the upper limit temperature environment of the category, thereby enabling the weakened portion to be repaired. This makes it possible to manufacture an electrolytic capacitor that can suppress an increase in leakage current even if the temperature of the usage environment changes suddenly. The lower limit temperature of the category and the upper limit temperature of the category include a normal fluctuation range (temperature error, fluctuation width, temperature distribution of the thermostatic bath, for example, set value ±1.6°C).

[0009] In the above method, it is preferable that the second step is carried out after the first step.

[0010] In the upper category temperature environment of the second step, the movement of ions in the electrolyte is relatively faster than in the lower category temperature environment of the first step. Therefore, it is considered that the oxide film is more easily repaired in the upper category temperature environment of the second step than in the lower category temperature environment of the first step. It is also considered that the repair of the oxide film is faster. Even if there are areas in which the oxide film is not sufficiently repaired in the first step, by carrying out the second step after the first step, that area is more likely to be repaired in the second step. In addition, the oxide film can be strengthened in the second step.

[0011] In the first step, a voltage that is 1.15 times or more the rated voltage is preferably applied to the capacitor body.

[0012] By applying a voltage slightly higher than the rated voltage in the lower limit temperature environment of the category, the repair performance of the oxide film in the lower limit temperature environment of the category can be improved.

[0013] In the first step, it is preferable that the time for applying a voltage to the capacitor body in the category lower limit temperature environment is 120 minutes or less.

[0014] By setting the application time in the first step to 120 minutes or less, the manufacturing time of the electrolytic capacitor is not too long, and the productivity of the electrolytic capacitor can be improved.

[0015] In the second step, it is preferable that the time for applying a voltage to the capacitor body in an environment of the upper category temperature limit is 120 minutes or less.

[0016] By setting the application time in the second step to 120 minutes or less, the production time of the electrolytic capacitor is not too long, and the productivity of the electrolytic capacitor can be improved. Effect of the Invention

[0017] It is possible to manufacture an electrolytic capacitor that can suppress an increase in leakage current even if the temperature of the environment in which it is used changes suddenly. [Brief description of the drawings]

[0018] [Figure 1] 1 is a cutaway front view of a main portion of an electrolytic capacitor produced by a method according to an embodiment of the present invention. [Diagram 2] 2 is a schematic diagram for explaining the configuration of the capacitor element shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[0020] An electrolytic capacitor 1 produced by a method according to an embodiment of the present invention is shown in Fig. 1. As shown in Fig. 1, the electrolytic capacitor 1 includes an exterior body 4 having an exterior case 2 and a sealing body 3, a capacitor element 5 housed in the exterior body 4, and a base plate 6.

[0021] The outer case 2 is, for example, a case made of metal. The sealing body 3 is, for example, made of an elastic material such as rubber. The sealing body 3 seals the opening of the outer case 2. The seat plate 6 is disposed so as to face the sealing body 3.

[0022] Fig. 2 shows capacitor element 5 before being housed in exterior body 4. As shown in Fig. 2, capacitor element 5 has anode 11, cathode 12, and separator 13. Anode 11 and cathode 12 are wound into a cylindrical shape with separator 13 interposed therebetween, and the winding is stopped by tape 14 attached to the outer circumferential surface.

[0023] Lead tabs (not shown) are connected to the anode 11 and the cathode 12, respectively. The anode 11 is connected to a lead terminal 21 via a lead tab. The cathode 12 is connected to a lead terminal 22 via a lead tab. The lead terminals 21 and 22 are led out to the outside through holes 31 and 32, respectively, formed in the sealing body 3, as shown in FIG.

[0024] The anode 11 (see FIG. 2) is a valve metal having a dielectric oxide film formed on its surface. The valve metal may be at least one selected from the group consisting of aluminum, tantalum, niobium, and titanium. The oxide film is formed, for example, by roughening the surface of a foil of the valve metal by etching, and then subjecting it to a chemical oxidation treatment.

[0025] The cathode 12 is formed using a valve metal. For example, a valve metal foil whose surface is roughened by etching, or a foil whose surface is roughened and then subjected to chemical conversion treatment is used as the cathode 12. A plain foil that is not subjected to etching may be used as the cathode 12. Furthermore, a coating foil in which a metal thin film containing at least one metal selected from the group consisting of titanium, nickel, titanium carbide, nickel carbide, titanium nitride, nickel nitride, titanium carbonitride, and nickel carbonitride is formed on the surface of the roughened foil or plain foil may be used. A coating foil in which a carbon thin film is formed on the surface of the roughened foil or plain foil may be used.

[0026] There is no particular limitation on the material of the separator 13. For example, a material mainly made of cellulose fiber may be used as the separator 13, or a mixed fiber containing chemical fiber may be used. Examples of chemical fibers include synthetic fibers such as polyester fiber, polyamide fiber, acrylic fiber, polyimide fiber, aramid fiber, and nylon fiber.

[0027] The separator 13 holds a solvent or electrolyte as the "liquid" of the present invention and a conductive polymer. The electrolyte is not particularly limited. The electrolyte may contain, for example, a low-viscosity solvent and a poorly volatile solvent, or may contain one of a low-viscosity solvent and a poorly volatile solvent. Examples of low-viscosity solvents include solvents containing lactone, specifically, γ-butyrolactone, γ-valerolactone, and the like. Examples of poorly volatile solvents include ethylene glycol, polyalkylene glycol (polyethylene glycol, polypropylene glycol, and the like), sulfolane, and derivatives thereof. The electrolyte may contain, for example, inorganic acids, carboxylic acids, hydroxy acids, and their ammonium salts, amine salts, and amidine salts, and may contain additives such as nitro compounds. For example, an electrolyte having a boiling point of 180°C or higher and a resistivity of 1 kΩ·cm or higher may be used as the electrolyte. Also, only a solvent that does not dissolve the solute may be used.

[0028] The conductive polymer is formed on the surface of the oxide film of the anode 11, the surface of the cathode 12, and the fiber surface constituting the separator 13. The conductive polymer is not particularly limited. For example, polythiophene, polypyrrole, polyaniline, or a derivative thereof is used as the conductive polymer, and poly3,4-ethylenedioxythiophene (PEDOT) is generally used. For the dopant, p-toluenesulfonic acid, polystyrenesulfonic acid (PSS), or the like is generally used. In addition, the method of forming the conductive polymer is not particularly limited. For example, the conductive polymer is formed by immersing a capacitor element in a solution in which a conductive polymer containing a dopant is dispersed in a solvent and then drying the capacitor element, by immersing a capacitor element in a solution in which a soluble conductive polymer containing a dopant is dissolved in a solvent and then drying the capacitor element, by chemical polymerization of a monomer, a dopant, and an oxidizing agent or a monomer and a dopant having an oxidizing effect, by electrolytic polymerization of a monomer and a dopant, and the like.

[0029] Next, a method for manufacturing the electrolytic capacitor 1 will be described.

[0030] Lead terminals 21 and 22 for external extraction electrodes are connected to anode 11 and cathode 12 (see FIG. 2) that have been cut to a predetermined width, respectively. Anode 11 is a valve metal on which an oxide film is formed. Anode 11 to which lead terminal 21 is connected and cathode 12 to which lead terminal 22 is connected are wound with separator 13 interposed therebetween to produce capacitor element 5.

[0031] Next, the capacitor element 5 is subjected to a chemical conversion treatment in order to repair the cut edge of the capacitor element 5 or the oxide film that was lost during the production of the capacitor element 5. The chemical conversion treatment is performed by applying a voltage to the capacitor element 5 in a chemical conversion liquid. As the chemical conversion liquid, for example, a chemical conversion liquid in which an organic acid having a carboxylic acid group or its salt (solute) is dissolved in an organic solvent or an inorganic solvent, or a chemical conversion liquid in which an inorganic acid such as phosphoric acid or its salt (solute) is dissolved in an organic solvent or an inorganic solvent may be used. As the chemical conversion liquid in which an organic acid having a carboxylic acid group or its salt (solute) is dissolved in an organic solvent or an inorganic solvent, for example, an aqueous solution containing adipic acid and an aqueous solution containing an adipate salt can be used. As the aqueous solution containing an adipate salt, for example, an aqueous solution containing a solute mainly composed of ammonium adipate can be used.

[0032] The chemical conversion treatment may be, for example, a first chemical conversion treatment using a chemical conversion solution in which an organic acid having a carboxylic acid group or its salt (solute) is dissolved in an organic solvent or an inorganic solvent, followed by heat treatment, and then a second chemical conversion treatment using a chemical conversion solution in which an inorganic acid such as phosphoric acid or its salt (solute) is dissolved in an organic solvent or an inorganic solvent. A cycle of the first chemical conversion treatment, heat treatment, the second chemical conversion treatment, and heat treatment may be repeatedly performed. The chemical conversion treatment may be a repeated cycle of the first chemical conversion treatment and heat treatment, or a repeated cycle of the second chemical conversion treatment and heat treatment. A tough oxide film is formed by repeatedly performing the first chemical conversion treatment and / or the second chemical conversion treatment and heat treatment. The heat treatment here is generally performed at a temperature of 100°C to 300°C, and the heat treatment time is about several tens of minutes. The chemical conversion treatment may be a cycle of only the first chemical conversion treatment without the heat treatment, or a cycle of only the second chemical conversion treatment.

[0033] Next, in order to hold the conductive polymer on the separator, the capacitor element 5 that has been subjected to the chemical conversion treatment is immersed in a liquid containing the conductive polymer, and then dried (first step). For example, a dispersion liquid containing PEDOT / PSS may be used as the liquid containing the conductive polymer. PEDOT / PSS is a composite of poly3,4-ethylenedioxythiophene (PEDOT) and polystyrene sulfonic acid (PSS). The capacitor element 5 is immersed in the dispersion liquid containing PEDOT / PSS at least once, and then dried. This removes the solvent, and the conductive polymer (PEDOT / PSS) is held on the separator. Although the above example shows the case where the capacitor element 5 is immersed in the dispersion liquid, the capacitor element 5 may be impregnated with the dispersion liquid. After immersion in the dispersion liquid or impregnation with the dispersion liquid, the capacitor element 5 may be dried. Drying may be performed at room temperature, under vacuum or reduced pressure, or by using a multi-stage dryer. Capacitor element 5 may be dried at a high temperature of, for example, 160° C. or higher.

[0034] After the conductive polymer is held by the separator, the electrolyte is impregnated into the capacitor element 5. Then, the sealing body 3 is attached to the capacitor element 5, the capacitor element 5 is housed in the exterior case 2, the opening of the exterior case 2 is sealed with the sealing body 3, and the opening of the exterior case 2 is curled to produce the capacitor body 10.

[0035] Then, a first process is performed in which a voltage higher than the rated voltage is applied to the obtained capacitor body 10 in an environment of the lower category temperature limit for 30 minutes or more, and a second process is performed in which the rated voltage or a voltage higher than the rated voltage is applied to the obtained capacitor body 10 in an environment of the upper category temperature limit for 30 minutes or more.

[0036] Here, the "category lower limit temperature of an electrolytic capacitor" is the lowest ambient temperature at which an electrolytic capacitor can be used continuously. If an electrolytic capacitor is used in a temperature environment lower than the category lower limit temperature, the characteristics of the electrolytic capacitor may deteriorate. The "category upper limit temperature of an electrolytic capacitor" is the highest ambient temperature at which an electrolytic capacitor can be used continuously. If an electrolytic capacitor is used in a temperature environment higher than the category upper limit temperature, the characteristics of the electrolytic capacitor may deteriorate. The category lower limit temperature and the category upper limit temperature are the lower limit temperature and the upper limit temperature of the ambient temperature range (category temperature range) at which an electrolytic capacitor can be used continuously, based on the design of the electrolytic capacitor. The category temperature range is determined, for example, based on the electrolyte, conductive polymer (including dopants, additives, etc.), electrodes, separators, and combinations of these that make up the electrolytic capacitor. The category temperature range is determined, for example, in accordance with the Japanese Industrial Standards (JIS). The "rated voltage" is the maximum voltage that can be continuously applied to an electrolytic capacitor at any temperature between the category lower limit temperature and the category upper limit temperature. The rated voltage is determined, for example, by the withstand voltage of the anode foil and electrolyte, the characteristics of other materials that make up the capacitor, and is ultimately determined by confirming product characteristics including reliability. For example, capacitors are designed with a rated voltage that conforms to the Japanese Industrial Standards (JIS).

[0037] In the first step, the voltage applied to the capacitor body 10 is greater than the rated voltage. The applied voltage is not particularly limited as long as it is greater than the rated voltage. The applied voltage may be, for example, 1.05 times or more the rated voltage, or 1.15 times or more the rated voltage. The upper limit of the applied voltage is not particularly limited. The higher the applied voltage, the greater the effect of repairing the oxide film. However, if the applied voltage is too high, the oxide film may be severely damaged, and the damaged portion may not be repaired sufficiently. In consideration of this point, the applied voltage may be, for example, 2.0 times or less the rated voltage, or 1.4 times or less the rated voltage.

[0038] In the first step, a voltage is applied to the capacitor body 10 in an environment of the lower limit temperature of the category. By applying a voltage to the capacitor body 10 in an environment of the lower limit temperature of the category, portions weakened in the environment of the lower limit temperature of the category (such as damage to the oxide film) are repaired. This makes it possible to impart resistance to the environment of the lower limit temperature of the category. For example, when the electrolytic capacitor is used at the lower limit temperature of the category, damage to the oxide film can be suppressed. Also, when the electrolytic capacitor is used at a temperature lower than the lower limit temperature of the category, damage to the oxide film can be suppressed. As a result, even if the temperature of the environment in which the electrolytic capacitor is used drops to the lower limit temperature of the category, damage to the oxide film is suppressed and leakage current is reduced.

[0039] In the first step, the voltage is applied to the capacitor body 10 for 30 minutes or more. Immediately after the voltage application starts, a large current flows through the capacitor body 10 to repair the missing parts of the oxide film on the electrode cut surface and the like, and the capacitor element 5 inside generates heat. This is thought to cause the temperature of the capacitor element 5 to become higher than the category lower limit temperature. When the repair of the oxide film progresses to a certain extent, the current flowing through the capacitor body 10 decreases, and the capacitor element 5 is cooled again and reaches a temperature close to the category lower limit temperature. By applying a voltage to the capacitor body 10 in this state, it is possible to impart resistance to the category lower limit temperature environment. In order to apply a voltage when the capacitor element 5 is at or close to the category lower limit temperature, it is thought that the application time needs to be 30 minutes or more.

[0040] In the first step, the time for applying voltage to the capacitor body 10 is not particularly limited as long as it is 30 minutes or more. The application time may be 40 minutes or more, or 50 minutes or more. There is no upper limit to the application time. The application time may be, for example, 120 minutes or less. By not making the application time too long, the manufacturing time of the electrolytic capacitor does not become too long, and the productivity of the electrolytic capacitor can be improved.

[0041] In the second step, the voltage applied to the capacitor body 10 is equal to or greater than the rated voltage. The applied voltage is not particularly limited as long as it is equal to or greater than the rated voltage. The applied voltage may be, for example, the rated voltage, 1.05 times the rated voltage, or 1.15 times the rated voltage. The upper limit of the applied voltage is not particularly limited. The higher the applied voltage, the greater the effect of repairing the oxide film. However, if the applied voltage is too high, the oxide film may be severely damaged, and the damaged portion may not be repaired sufficiently. In consideration of this, the applied voltage may be, for example, 2.0 times or less than the rated voltage, or 1.4 times or less than the rated voltage.

[0042] In the second step, a voltage is applied to the capacitor body 10 in an environment of the maximum category temperature. By applying a voltage to the capacitor body 10 in an environment of the maximum category temperature, portions weakened in the environment of the maximum category temperature (such as damage to the oxide film) are repaired. This makes it possible to provide resistance to the maximum category temperature environment. For example, when the electrolytic capacitor is used at the maximum category temperature, damage to the oxide film can be suppressed. Also, when the electrolytic capacitor is used at a high temperature lower than the minimum category temperature, damage to the oxide film can be suppressed. As a result, even if the temperature of the environment in which the electrolytic capacitor is used rises to the maximum category temperature, damage to the oxide film is suppressed and leakage current is reduced.

[0043] In the second step, the voltage is applied to the capacitor body 10 for 30 minutes or more. By setting the application time to 30 minutes or more, the capacitor body 10 can be sufficiently repaired and the leakage current can be sufficiently reduced. The time for applying the voltage to the capacitor body 10 is not particularly limited as long as it is 30 minutes or more. The application time may be 40 minutes or more, or 50 minutes or more. There is no upper limit to the application time. The application time may be, for example, 120 minutes or less. By not setting the application time too long, the manufacturing time of the electrolytic capacitor does not become too long, and the productivity of the electrolytic capacitor can be improved.

[0044] Either the first step or the second step may be carried out first, and the first step and the second step may be carried out alternately multiple times.

[0045] The applied voltage in the first step and the applied voltage in the second step may be the same or different. When the first step is performed two or more times, the applied voltage in all the first steps may be the same, or the applied voltage in at least one of the first steps may be different. When the second step is performed two or more times, the applied voltage in all the second steps may be the same, or the applied voltage in at least one of the second steps may be different.

[0046] The application time of the first step and the application time of the second step may be the same or different. When the first step is performed two or more times, the application times of all the first steps may be the same, or at least one of the first steps may be different. When the second step is performed two or more times, the application times of all the second steps may be the same, or at least one of the second steps may be different.

[0047] As a result, it is possible to manufacture an electrolytic capacitor capable of suppressing an increase in leakage current even if the temperature of the environment in which it is used changes suddenly.

[0048] Conventionally, aging treatment has been performed at the upper limit temperature of the category, but according to the manufacturing method of the electrolytic capacitor of this embodiment, a first step of applying a voltage to the capacitor body 10 in an environment of the lower limit temperature of the category, and a second step of applying a voltage to the capacitor body 10 in an environment of the upper limit temperature of the category are performed. In other words, the aging treatment is performed at both the lower limit temperature of the category and the upper limit temperature of the category.

[0049] By performing aging treatment at the lower limit temperature of the category (first step), it is possible to expose the parts that would be weakened in the lower limit temperature environment of the category (such as damage to the oxide film) and repair the weakened parts. This makes it possible to impart resistance to the lower limit temperature environment of the category. Furthermore, by performing aging treatment in the upper limit temperature environment of the category (second step), it is possible to expose the parts that would be weakened in the upper limit temperature environment of the category (such as damage to the oxide film) and repair the weakened parts. This makes it possible to impart resistance to the upper limit temperature environment of the category.

[0050] It was found that the electrolytic capacitor manufactured by the above method is an electrolytic capacitor that can suppress an increase in leakage current even if the temperature of the environment in which it is used changes suddenly, and also that it can suppress an increase in leakage current even if the change in the temperature of the environment in which it is used is small.

[0051] Either the first step or the second step may be carried out first, but if the first step is carried out before the second step, it is believed that the following effects can be obtained. In the upper category temperature environment of the second step, the movement of ions in the electrolyte is relatively faster than in the lower category temperature environment of the first step. Therefore, it is considered that the oxide film is more easily repaired in the upper category temperature environment of the second step than in the lower category temperature environment of the first step. It is also considered that the repair of the oxide film is faster. Even if there are areas in which the oxide film is not sufficiently repaired in the first step, by carrying out the second step after the first step, that area is more likely to be repaired in the second step. In addition, the oxide film can be strengthened in the second step. EXAMPLES

[0052] The present invention will be described in more detail below with reference to examples. However, the following examples do not limit the present invention, and all modifications and variations within the scope of the present invention are included in the technical scope of the present invention.

[0053] [Conventional example] (Making a capacitor) Lead terminals for external extraction electrodes were connected to the anode foil and cathode foil cut to a specified width. The anode foil was made of a valve metal with a dielectric oxide film formed on the surface of the aluminum foil. The oxide film was formed by roughening the surface of the aluminum foil by etching, and then performing a chemical oxidation treatment. The cathode foil was aluminum foil with an etched surface. The anode foil and cathode foil were wound with a cellulose fiber separator between them to produce a capacitor element.

[0054] In order to repair the oxide film on the cut edge of the anode foil and the oxide film that was damaged when the external extraction electrode was attached, a chemical conversion treatment was performed. In this experiment, the chemical conversion treatment was performed by the following method. A chemical conversion solution was prepared by dissolving a solute mainly made of ammonium adipate in an aqueous solvent and adjusting the ammonium adipate concentration to 0.1wt% to 2wt%. With the capacitor element immersed in this chemical conversion solution, a voltage close to the chemical conversion voltage value of the oxide film was applied (first chemical conversion treatment). After that, the capacitor element was heat-treated at a temperature of 200°C to 300°C for several tens of minutes, and then a solute mainly made of phosphoric acid was dissolved in an aqueous solvent and the phosphoric acid concentration was adjusted to 0.1wt% to 0.5wt%. With the capacitor element immersed in this chemical conversion solution, a voltage close to the chemical conversion voltage value of the oxide film was applied (second chemical conversion treatment).

[0055] Next, in order to retain the conductive polymer on the separator, the capacitor element after the chemical conversion treatment was impregnated with an aqueous solution in which the conductive polymer was dispersed in water. Here, the so-called dispersion method was used. 1 / 3 to 2 / 3 of the capacitor element was immersed in a 2.0 wt% PEDOT / PSS dispersion aqueous solution under a reduced pressure of 80 to 100 kPa for 20 minutes, and then the capacitor element was pulled out and dried to remove moisture. This formed the surface of the oxide film of the anode 11, the surface of the cathode 12, and the surface of the fibers that make up the separator 13.

[0056] The capacitor element on which the conductive polymer was formed was impregnated with an electrolyte, which was a solution of 1.0 wt % malic acid in ethylene glycol solvent.

[0057] The obtained capacitor element was fitted with a sealing body made of butyl rubber, and then housed in a metal case. The opening of the metal case was sealed, and the periphery of the opening of the case was curled to produce a capacitor body. In an environment of the upper limit temperature of the category (125°C), a voltage of rated voltage (80V) x 1.15 [V] was applied to the obtained capacitor body for 1 hour to perform an aging treatment, and then the lead terminals were inserted into the insertion holes formed in the base plate 6 made of insulating resin, and the lead terminals were bent in a direction away from each other to produce a surface-mounted electrolytic capacitor. In this way, a conventional electrolytic capacitor was produced. This electrolytic capacitor has a category temperature range of -55°C to +125°C, a rated voltage of 80V, a rated capacitance of 15μF, and a volume of φ6.3 x 7.7L. The electrolytic capacitors of Comparative Examples 1 to 5 and Example 1 described below also have a category temperature range of -55°C to +125°C, a rated voltage of 80V, a rated capacitance of 15µF, and a volume of φ6.3×7.7L.

[0058] [Comparative Example 1] After the curling process, the capacitor body was left in an environment with the lower limit of the category temperature (-55°C) for 30 minutes before undergoing aging treatment at the upper limit of the category temperature (125°C).Other than the above, the electrolytic capacitor was produced in the same manner as the conventional example.

[0059] [Example 1] After curling, a voltage of rated voltage (80V) x 1.15[V] was applied to the capacitor body for 30 minutes in an environment of the lower limit of the category temperature (-55℃) before aging at the upper limit of the category temperature (125℃).Other than the above, the electrolytic capacitor was manufactured in the same way as the conventional example.

[0060] [Example 2] After curling, a voltage of rated voltage (80V) x 1.25[V] was applied to the capacitor body for 30 minutes in an environment of the lower limit of the category temperature (-55℃) before aging at the upper limit of the category temperature (125℃).Other than the above, the electrolytic capacitor was manufactured in the same way as the conventional example.

[0061] [Comparative Example 2] After curling, before aging at the upper category temperature (125°C), a voltage of rated voltage (80V) x 1.15[V] was applied to the capacitor body for 30 minutes in a -20°C environment. Other than the above, the electrolytic capacitor was manufactured in the same way as the conventional example.

[0062] [Comparative Example 3] After curling, before aging at the upper category temperature (125°C), a voltage of rated voltage (80V) x 1.15[V] was applied to the capacitor body for 30 minutes in a -40°C environment. Other than the above, the electrolytic capacitor was manufactured in the same way as the conventional example.

[0063] [Comparative Example 4] After curling, a voltage of rated voltage (80V) x 1.15[V] was applied to the capacitor body for 15 minutes in an environment of the lower limit of the category temperature (-55℃) before aging at the upper limit of the category temperature (125℃).Other than the above, the electrolytic capacitor was manufactured in the same way as the conventional example.

[0064] [Comparative Example 5] After curling, the rated voltage (80V) was applied to the capacitor body for 30 minutes in an environment of the lower limit of the category temperature (-55°C) before aging at the upper limit of the category temperature (125°C).Other than the above, the electrolytic capacitor was fabricated in the same way as the conventional example.

[0065] (evaluation) A temperature cycle test was conducted in which an electrolytic capacitor was left in an environment with the lowest category temperature (-55°C) for 30 minutes and then left in an environment with the highest category temperature (125°C) for 30 minutes, with this cycle being counted as 500 cycles. After the temperature cycle test, the rated voltage was applied to the electrolytic capacitor and the leakage current (LC) was measured two minutes after the application. In addition, before the temperature cycle test, the rated voltage was applied to the electrolytic capacitor and the leakage current (LC) was measured two minutes after the application. In this experiment, the leakage current of 20 electrolytic capacitors was measured both before and after the temperature cycle test and the average value was calculated. Table 1 shows the average leakage current.

[0066] [Table 1]

[0067] In Table 1, "1.15WV application" means that 1.15 times the rated voltage (80V) (92V) was applied. "1.25WV application" means that 1.25 times the rated voltage (80V) (100V) was applied. "1WV application" means that the rated voltage (80V) was applied. From past experience, if the leakage current is 6.0μA or less (= 0.005 x rated capacitance x rated voltage or less), it can be determined that the leakage current is low.

[0068] As can be seen from Table 1, in the conventional example, aging treatment (conventional aging treatment) was performed at the upper category temperature limit. In Comparative Example 1, in addition to the conventional aging treatment, the capacitor body was left in an environment at the lower limit temperature of the category. In addition to the conventional aging treatment, aging treatment was performed in a low temperature environment in Examples 1 and 2 and Comparative Examples 2 to 5. The conditions of the aging treatment in the low temperature environment (temperature, voltage, application time) are different between Examples 1 and 2 and Comparative Examples 2 to 5.

[0069] In the conventional example, the leakage current after the temperature cycle test was large at 9.8 μA, exceeding 6.0 μA. In Comparative Example 1, the leakage current after the temperature cycle test was large at 7.8 μA, exceeding 6.0 μA. From the above, it was found that the increase in leakage current after the temperature cycle test cannot be suppressed by the conventional aging treatment alone. It was also found that the increase in leakage current after the temperature cycle test cannot be suppressed even if the capacitor body is left in a low temperature environment in addition to the conventional aging treatment.

[0070] On the other hand, in Examples 1 and 2 in which aging treatment was performed in a low temperature environment (low temperature aging treatment) in addition to the conventional aging treatment, the leakage current was 6.0 μA or less. However, in Comparative Examples 2 to 5, the leakage current exceeded 6.0 μA.

[0071] From Examples 1 and 2 and Comparative Examples 2 to 5, the following was found. In Examples 1 and 2, in which the low-temperature aging treatment was performed at the lower limit temperature of the category, the increase in leakage current was suppressed. However, in Comparative Examples 2 and 3, in which the low-temperature aging treatment was performed at a temperature higher than the lower limit temperature of the category, the increase in leakage current could not be suppressed. From this, it is considered that in order to suppress the increase in leakage current, it is necessary to perform the low-temperature aging treatment at the lower limit temperature of the category. In Comparative Example 4, the low-temperature aging treatment was performed at the lower limit temperature of the category, but the increase in leakage current could not be suppressed. The application time of the low-temperature aging treatment in Comparative Example 4 is shorter than the application time of the low-temperature aging treatment in Example 1. From this, it is considered that the application time of the low-temperature aging treatment needs to be 30 minutes or more in order to suppress the increase in leakage current. In Comparative Example 5, the low-temperature aging treatment was performed for 30 minutes or more at the lower limit temperature of the category, but the increase in leakage current could not be suppressed. The applied voltage in Comparative Example 5 is the rated voltage, which is smaller than the applied voltage value in Example 1. From this, it is considered that the applied voltage needs to be made larger than the rated voltage in order to suppress the increase in leakage current.

[0072] From the above, it was found that in order to suppress the increase in leakage current after temperature cycle testing, in addition to the conventional aging treatment at the upper limit temperature of the category, it is necessary to perform a low-temperature aging treatment in which a voltage higher than the rated voltage is applied to the capacitor body for 30 minutes or more in an environment at the lower limit temperature of the category. It was found that electrolytic capacitors made by this method can suppress the increase in leakage current even if the temperature of the usage environment changes suddenly.

[0073] Although the embodiment of the present invention has been described above based on the examples, the specific configuration should not be considered to be limited to these embodiments. The scope of the present invention is indicated by the claims rather than the above description, and includes all modifications within the meaning and scope of the claims.

[0074] For example, in the above-mentioned Example 1, the aging treatment at the lower limit temperature of the category is performed before the aging treatment at the upper limit temperature of the category. However, the aging treatment at the lower limit temperature of the category may be performed after the aging treatment at the upper limit temperature of the category. In this case, the first aging treatment exposes the parts that are weakened in the upper limit temperature environment of the category (such as defects in the oxide film) and can repair the weakened parts. Furthermore, the second aging treatment exposes the parts that are weakened in the lower limit temperature environment of the category (such as defects in the oxide film) and can repair the weakened parts. This makes it possible to manufacture an electrolytic capacitor that can suppress an increase in leakage current even if the temperature of the usage environment changes suddenly.

[0075] In addition, in the above-mentioned Examples 1 and 2, when the aging treatment is performed at the lower limit temperature of the category, a voltage of rated voltage (80V)×1.15 [V] or rated voltage (80V)×1.25 [V] is applied to the capacitor body. However, the applied voltage when the aging treatment is performed at the lower limit temperature of the category is not limited to the above voltage. The applied voltage when the aging treatment is performed at the lower limit temperature of the category may be, for example, another voltage higher than the rated voltage.

[0076] In addition, in the above-mentioned Examples 1 and 2, a voltage is applied to the capacitor body for 30 minutes when the aging treatment is performed at the lower limit temperature of the category. However, the application time when the aging treatment is performed at the lower limit temperature of the category may exceed 30 minutes.

[0077] In the above experiment, an electrolytic capacitor was fabricated with a category temperature range of -55°C to +125°C, a rated voltage of 80V, a rated capacitance of 15μF, and a volume of φ6.3×7.7L. However, the category temperature range, rated voltage, rated capacitance, and volume of the electrolytic capacitor of the present invention are not limited to those described above.

[0078] The anode, cathode, separator, conductive polymer, and electrolyte of the electrolytic capacitor of the present invention are not limited to those used in the experiment, and may be changed. For example, even if the electrolyte is a liquid that is only a solvent (does not dissolve solutes), a solid electrolytic capacitor that can suppress an increase in leakage current even if the temperature of the operating environment changes suddenly, as in this embodiment, can be manufactured. [Explanation of symbols]

[0079] 1. Electrolytic capacitor 2 Outer case 3 Sealing body 4 Exterior body 5 Capacitor elements 6 Seat board 10 Capacitor body 11 Anode 12 Cathode 13 Separator 21, 22 Lead terminal

Claims

1. A method for manufacturing an electrolytic capacitor comprising: an anode having an oxide film, a cathode, a separator disposed between the anode and the cathode, a capacitor element having at least a conductive polymer and a liquid held by the separator, and an exterior body housing the capacitor element, A capacitor body in which the capacitor element is accommodated in the exterior body, A first step of applying a voltage higher than the rated voltage for 30 minutes or more in an environment of a category lower limit temperature; A second step of applying the rated voltage or a voltage higher than the rated voltage for 30 minutes or more in an environment with the upper category temperature limit; 2. A method for manufacturing an electrolytic capacitor comprising the steps of:

2. 2. The method for producing an electrolytic capacitor according to claim 1, wherein the second step is carried out after the first step.

3. 3. The method for producing an electrolytic capacitor according to claim 1, wherein in the first step, a voltage that is 1.15 times or more the rated voltage is applied to the capacitor body.

4. 4. The method for manufacturing an electrolytic capacitor according to claim 1, wherein in the first step, a time for applying a voltage to the capacitor body is set to 120 minutes or less.

5. 5. The method for manufacturing an electrolytic capacitor according to claim 1, wherein in the second step, a time for applying a voltage to the capacitor body is set to 120 minutes or less.

Images