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 at least held by the separator. A method of manufacturing the electrolytic capacitor 1 includes a first step of leaving a capacitor body 10 in an environment at a category lower limit temperature for 5 minutes or more; a second step of leaving the capacitor body in an environment at a category upper limit temperature for 5 minutes or more; and a third step of aging the capacitor body. Before the third step, processing (one cycle) of performing the first step and the second step is performed by 10 cycles or more.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 an electrolytic capacitor, 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 parts of the oxide film formed on the anode that were damaged during the manufacturing process. This makes it possible to suppress an increase in leakage current. Patent Document 1 describes a method in which, after aging treatment, a solid electrolytic capacitor is alternately immersed in cooled liquid and heated liquid. The method described in Patent Document 1 makes it possible to reduce the rate of defective products. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 1-261812 Summary of the Invention [Problem to be solved by the invention]

[0004] The inventors' research has revealed that aging alone tends to cause defects in the oxide film, which increases leakage current, when the temperature of the environment in which the electrolytic capacitor is used changes suddenly. In addition, as described in Patent Document 1, it has been found that even if the solid electrolytic capacitor is alternately immersed in cooled liquid and heated liquid after aging, the increase in leakage current cannot be sufficiently suppressed when the temperature of the environment in which the electrolytic capacitor is used changes suddenly.

[0005] 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]

[0006] 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, the method comprising the steps of: a first step of leaving the capacitor body with the capacitor element housed in the outer casing in an environment at a category lower limit temperature for 5 minutes or more; a second step of leaving the capacitor body in an environment at a category upper limit temperature for 5 minutes or more; and a third step of performing an aging treatment, in which, when the first step and the second step are considered to be one cycle, the treatment is performed 10 or more cycles before the third step.

[0007] According to the present invention, before the aging process, a first step of leaving the capacitor body in an environment of the lower category temperature limit and a second step of leaving the capacitor body in an environment of the upper category temperature limit are repeatedly performed. This exposes weak points such as defects in the oxide film that occurred in the environment of the lower category temperature limit and the environment of the upper category temperature limit. These weak points are repaired or strengthened in the subsequent aging process. 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. Note that the lower category temperature limit and the upper category temperature limit include the normal fluctuation range (temperature error, fluctuation width, and temperature distribution of the thermostatic bath, for example, set value ±1.6°C).

[0008] In each cycle of the above method, either the first step or the second step may be performed first. For example, the second step may be performed after the first step. In this case, the second step is performed in an environment of the upper category temperature limit, and then the aging treatment is performed. However, when the aging treatment starts, the temperature of the capacitor body is close to the set temperature of the aging treatment. Therefore, the aging treatment starts promptly.

[0009] In the above method, the treatment is preferably performed for 30 cycles or less.

[0010] By limiting the number of cycles of the first and second steps to 30 or less, the manufacturing time of the electrolytic capacitor is not too long, which improves the productivity of the electrolytic capacitor.

[0011] In the first step of the above method, it is preferable that the time for which the capacitor body is left in an environment at the category lower limit temperature is 60 minutes or less.

[0012] By limiting the time for which the capacitor body is left in an environment with the lowest category temperature in the first step to 60 minutes or less, the manufacturing time for electrolytic capacitors does not become too long, which improves the productivity of electrolytic capacitors.

[0013] In the second step of the above method, it is preferable that the capacitor body is left in an environment of an upper category temperature limit for 60 minutes or less.

[0014] By limiting the time for which the capacitor body is left in an environment with the category upper limit temperature in the second step to 60 minutes or less, the manufacturing time of the electrolytic capacitor is not too long, and therefore the productivity of the electrolytic capacitor can be improved.

[0015] In the above method, the aging treatment is preferably performed by applying a voltage equal to or greater than a rated voltage to the capacitor body in an environment of a category upper limit temperature.

[0016] By carrying out the aging treatment as described above after the first and second steps, it is possible to manufacture an electrolytic capacitor that can suppress an increase in leakage current even if the temperature of the usage environment changes suddenly. 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 (lead tab terminals) 21, 22 for external extraction electrodes are connected to the anode 11 and cathode 12 (see FIG. 2) that have been cut to a predetermined width. The anode 11 to which the lead terminal 21 is connected and the cathode 12 to which the lead terminal 22 is connected are wound with a separator 13 interposed therebetween to produce a capacitor element 5. The anode 11 is a valve metal having an oxide film formed thereon.

[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). As the liquid containing the conductive polymer, for example, a dispersion liquid containing PEDOT / PSS may be used. 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 describes 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 supported on the separator, capacitor element 5 is impregnated with an electrolyte. Thereafter, sealing body 3 is attached to capacitor element 5, capacitor element 5 is housed in outer case 2, the opening of outer case 2 is sealed with sealing body 3, and the opening of outer case 2 is curled to produce capacitor body 10.

[0035] Then, the first step is performed in which the obtained capacitor body 10 is left in an environment of a lower limit temperature of the category for 15 minutes or more, and the second step is performed in which the obtained capacitor body 10 is left in an environment of an upper limit temperature of the category for 15 minutes or more. When the first step and the second step are regarded as one cycle, this process is performed for 10 cycles 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 time for which the capacitor body 10 is left in an environment with a category lower limit temperature is not particularly limited as long as it is 5 minutes or more. The leaving time may be 10 minutes or more, or 15 minutes or more. There is no upper limit to the leaving time. The leaving time may be, for example, 60 minutes or less. By not leaving the leaving time too long, the manufacturing time of the electrolytic capacitor is not too long, and the productivity of the electrolytic capacitor can be improved.

[0038] In the second step, the time for which the capacitor body 10 is left in the environment of the upper category temperature limit is not particularly limited as long as it is 5 minutes or more. The leaving time may be 10 minutes or more, or 15 minutes or more. There is no upper limit to the leaving time. The leaving time may be, for example, 60 minutes or less. By not leaving the leaving time too long, the manufacturing time of the electrolytic capacitor is not too long, and the productivity of the electrolytic capacitor can be improved.

[0039] When the process of performing the first step and the second step is defined as one cycle, the number of cycles is not particularly limited as long as the process is performed 10 or more times. It may be 15 or more, or 20 or more. There is no upper limit to the number of cycles. The number of cycles may be, for example, 30 or less. By not increasing the number of cycles too much, the manufacturing time of the electrolytic capacitor is not too long, and the productivity of the electrolytic capacitor can be improved.

[0040] In the process (one cycle) in which the first step and the second step are performed, the first step may be performed first, or the second step may be performed first. When the first step is performed first, the first step is performed first in every cycle. When the second step is performed first, the second step is performed first in every cycle. This causes the first step and the second step to be performed alternately.

[0041] The leaving time of the capacitor body 10 in the first step and the leaving time of the capacitor body 10 in the second step may be the same or different. The leaving time of the capacitor body 10 in the first step may be the same in all cycles or may be different in at least one cycle. The leaving time of the capacitor body 10 in the second step may be the same in all cycles or may be different in at least one cycle.

[0042] After performing the above-mentioned first and second steps (1 cycle) for 10 or more cycles, the capacitor body 10 is subjected to an aging treatment (third step). The aging treatment here is an aging treatment generally known to those skilled in the art, and specifically, it is a treatment in which a rated voltage or a voltage higher than the rated voltage is applied to the capacitor body 10 in an environment of the upper category temperature limit with the capacitor element 5 (see FIG. 1) housed in the exterior body 4. The application time is not particularly limited. The application time may be, for example, 20 minutes or more, or 30 minutes or more. The upper limit of the application time is also not limited. 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 is not too long, and the productivity of the electrolytic capacitor can be improved.

[0043] 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.

[0044] According to the method for manufacturing an electrolytic capacitor of this embodiment, a first step of leaving the capacitor body 10 in an environment of the lower limit temperature of the category and a second step of leaving the capacitor body 10 in an environment of the upper limit temperature of the category are alternately and repeatedly performed before the aging treatment. This allows weak points (weakened parts) of the capacitor body 10 to be exposed before the aging treatment. The weak points here are defects (such as defects in the oxide film) caused by a sudden temperature difference, defects (such as defects in the oxide film) caused in an environment of the lower limit temperature of the category, defects caused in an environment of the upper limit temperature of the category, etc. By performing the aging treatment in a state where the weak points are exposed, the weak points are repaired and the oxide film is strengthened.

[0045] 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. It was also found that the increase in leakage current can be suppressed even if the change in the temperature of the environment in which it is used is small. Furthermore, it was found that the increase in leakage current can be suppressed whether the capacitor is used in an environment with a lower limit of the category temperature or an environment with an upper limit of the category temperature, as long as the temperature of the environment in which it is used is within the category temperature range. If temperature cycling is performed after the aging treatment, weak points will be exposed after the aging treatment and the product will remain with those weak points exposed, so the above-mentioned effect will not be obtained. EXAMPLES

[0046] 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.

[0047] [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.

[0048] 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).

[0049] Next, in order to hold 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 the moisture. As a result, a conductive polymer was formed on the surface of the oxide film of the anode 11, the surface of the cathode 12, and the surface of the fibers constituting the separator 13.

[0050] 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.

[0051] 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 Example 1, Comparative Example 2 and Examples 1 to 4 described later 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.

[0052] [Comparative Example 1] After the curling process and before the aging process, the capacitor body 10 was left in an environment of the lower limit temperature of the category (-55°C) for 30 minutes, and then left in an environment of the upper limit temperature of the category (125°C) for 30 minutes (1 cycle).Other than the above, an electrolytic capacitor was produced in the same manner as the conventional example.

[0053] [Example 1] After the curling process and before the aging process, the capacitor body 10 was left in an environment of the lower limit temperature of the category (-55°C) for 30 minutes, and then left in an environment of the upper limit temperature of the category (125°C) for 30 minutes (1 cycle), and this process was repeated 10 times. Except for the above, an electrolytic capacitor was produced in the same manner as the conventional example.

[0054] [Example 2] After the curling process and before the aging process, the capacitor body 10 was left in an environment of the lower limit temperature of the category (-55°C) for 30 minutes, and then left in an environment of the upper limit temperature of the category (125°C) for 30 minutes (1 cycle), and this process was repeated 18 times. Except for the above, an electrolytic capacitor was produced in the same manner as the conventional example.

[0055] [Example 3] After the curling process and before the aging process, the capacitor body 10 was left in an environment of the lower limit temperature of the category (-55°C) for 30 minutes, and then left in an environment of the upper limit temperature of the category (125°C) for 30 minutes (1 cycle), and this process was repeated 30 times. Except for the above, an electrolytic capacitor was produced in the same manner as the conventional example.

[0056] [Comparative Example 2] After the curling process and before the aging process, the capacitor body 10 was left in an environment of -40°C, which is higher than the lower limit temperature of the category, for 30 minutes, and then left in an environment of the upper limit temperature of the category (125°C) for 30 minutes (1 cycle), and this process was repeated 18 times. Except for the above, an electrolytic capacitor was produced in the same manner as the conventional example.

[0057] [Example 4] After the curling process and before the aging process, the capacitor body 10 was left in an environment of the lower limit temperature of the category (-55°C) for 15 minutes, and then left in an environment of the upper limit temperature of the category (125°C) for 15 minutes (1 cycle), and this process was repeated 18 times. Except for the above, an electrolytic capacitor was produced in the same manner as the conventional example.

[0058] [Example 5] After the curling process and before the aging process, the capacitor body 10 was left in an environment of the lower limit temperature of the category (-55°C) for 15 minutes, and then left in an environment of the upper limit temperature of the category (125°C) for 15 minutes (1 cycle), and this process was repeated 10 times. Except for the above, the electrolytic capacitor was produced in the same manner as the conventional example.

[0059] In this experiment, performing a process (one cycle) of leaving the capacitor body 10 in a low-temperature environment or a high-temperature environment, and then leaving the capacitor body 10 in the opposite high-temperature environment or a low-temperature environment, is referred to as "performing a temperature cycle." In the conventional example, no temperature cycle was performed, but in Comparative Example 1, Comparative Example 2, and Examples 1 to 4, a temperature cycle was performed after the curling process and before the aging process.

[0060] (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.

[0061] [Table 1]

[0062] From past experience, leakage current can be determined to be low when it is 6.0 μA or less (= 0.005 x rated capacitance x rated voltage or less). In the conventional example in which the temperature cycle was not performed before the aging treatment, the leakage current after the temperature cycle test was large at 9.8 μA, exceeding 6.0 μA. In Comparative Examples 1 and 2, a temperature cycle was performed before the aging treatment, but the leakage current after the temperature cycle test exceeded 6.0 μA. On the other hand, in Examples 1 to 5, the leakage current after the temperature cycle test was 6.0 μA or less.

[0063] From the above, the following findings were obtained. If the temperature cycle is not performed before the aging treatment, the leakage current is large after the temperature cycle test in which the temperature of the usage environment changes suddenly. Even if temperature cycles are performed before aging treatment, the leakage current after the temperature cycle test is large if the number of cycles is small (see Comparative Example 1).In addition, even if temperature cycles are performed before aging treatment, the leakage current after the temperature cycle test is large if the temperature cycles are not performed at the lower and upper category temperatures (see Comparative Example 2). When performing temperature cycling before aging treatment, it was found that by leaving the capacitor body at both the lower and upper category temperatures for 15 minutes or more and repeating this for 10 or more cycles, it is possible to suppress the increase in leakage current after the temperature cycle test.

[0064] 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.

[0065] For example, in the above Examples 1 to 5, before the aging treatment, the capacitor body is left in an environment of the lower limit temperature of the category, and then left in an environment of the upper limit temperature of the category, for multiple cycles (1 cycle). However, before the aging treatment, the capacitor body may be left in an environment of the upper limit temperature of the category, and then left in an environment of the lower limit temperature of the category, for multiple cycles (1 cycle). This also makes it possible to expose weak points before the aging treatment, so that the weak points can be repaired or the oxide film can be strengthened in the subsequent aging treatment. This makes it possible to manufacture an electrolytic capacitor that can suppress an increase in leakage current even if the temperature of the operating environment changes suddenly.

[0066] 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.

[0067] 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]

[0068] 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 housed in the exterior body, A first step of leaving the device in an environment having a category lower limit temperature for 5 minutes or more; A second step of leaving the device in an environment with a category upper limit temperature for 5 minutes or more; A third step of aging treatment; having A method for manufacturing an electrolytic capacitor, characterized in that, when a process comprising the first step and the second step is defined as one cycle, the process is performed 10 or more cycles before the third step.

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

3. 3. The method for producing an electrolytic capacitor according to claim 1, wherein the treatment is repeated for 30 cycles or less.

4. 4. The method for manufacturing an electrolytic capacitor according to claim 1, wherein in the first step, the capacitor body is left in an environment having a category lower limit temperature for a period of 60 minutes or less.

5. 5. The method for manufacturing an electrolytic capacitor according to claim 1, wherein in the second step, the capacitor body is left in an environment of an upper category temperature limit for a period of 60 minutes or less.

6. 6. The method for producing an electrolytic capacitor according to claim 1, wherein the aging treatment comprises applying a voltage equal to or greater than a rated voltage to the capacitor body in an environment of a category upper limit temperature.

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