JP7629835B2 - Manufacturing method of electrolytic capacitor - Google Patents

Description

The present invention relates to a method for manufacturing an electrolytic capacitor.

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 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 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 top of 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 the manganese dioxide to exert its chemical conversion properties to the maximum, the deteriorated parts of the oxide film can be directly repaired with the manganese dioxide that covers it, and therefore 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).

Japanese Unexamined Patent Publication No. 63-268240

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.

The objective of the present invention is to manufacture an electrolytic capacitor that can suppress an increase in leakage current even if the temperature of the operating environment changes suddenly.

The method for manufacturing an electrolytic capacitor of the present invention is a method for manufacturing an electrolytic capacitor having an anode with 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, and includes a first step of applying a voltage higher than the rated voltage for 30 minutes or more in a category lower limit temperature environment to the capacitor body housing the capacitor element in the exterior body, and a second step of applying the rated voltage or a voltage higher than the rated voltage for 30 minutes or more in a category upper limit temperature environment.

According to the present invention, in the first step, the portion that is weakened in the lower limit temperature environment of the category (such as a loss of oxide film) 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 that is weakened in the upper limit temperature environment of the category (such as a loss of oxide film) 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 operating environment changes suddenly. Note that the lower limit temperature and the upper limit temperature of the category include the range of fluctuation that can normally occur (temperature error of the thermostatic bath, fluctuation range, temperature distribution, for example, set value ±1.6°C).

In the above method, it is preferable to carry out the second step after the first step.

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

In the first step, it is preferable to apply a voltage to the capacitor body that is at least 1.15 times the rated voltage.

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

In the first step, it is preferable that the time for which voltage is applied to the capacitor body in the category lower limit temperature environment is 120 minutes or less.

By setting the application time for the first step to 120 minutes or less, the manufacturing time for electrolytic capacitors does not become too long. This improves the productivity of electrolytic capacitors.

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

By setting the application time of the second step to 120 minutes or less, the manufacturing time of the electrolytic capacitor does not become too long. This improves the productivity of the electrolytic capacitor.

It is possible to manufacture electrolytic capacitors that can suppress increases in leakage current even if the operating environment temperature changes suddenly.

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. 2 is a schematic diagram for explaining the configuration of the capacitor element shown in FIG. 1 .

A preferred embodiment of the present invention will be described below with reference to the drawings.

Figure 1 shows an electrolytic capacitor 1 produced by a method according to an embodiment of the present invention. As shown in Figure 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 seat plate 6.

The outer case 2 is, for example, a metal case. 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.

Figure 2 shows the capacitor element 5 before it is housed in the exterior body 4. As shown in Figure 2, the capacitor element 5 has an anode 11, a cathode 12, and a separator 13. The anode 11 and the cathode 12 are wound into a cylindrical shape with the separator 13 interposed between them, and the winding is secured by tape 14 attached to the outer periphery.

Lead tabs (not shown) are connected to the anode 11 and the cathode 12. 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 respectively led out to the outside through holes 31 and 32 formed in the sealing body 3 as shown in FIG. 1.

The anode 11 (see FIG. 2) is a valve metal with 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 valve metal foil by etching, and then subjecting it to a chemical oxidation treatment.

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 chemically treated, is used as the cathode 12. A plain foil that is not etched 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 also be used.

The material of the separator 13 is not particularly limited. For example, the separator 13 may be made mainly of cellulose fiber, or may be made of a mixed fiber containing chemical fiber. Examples of chemical fibers include synthetic fibers such as polyester fiber, polyamide fiber, acrylic fiber, polyimide fiber, aramid fiber, and nylon fiber.

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 difficult-to-volatile solvent, or may contain one of a low-viscosity solvent and a difficult-to-volatile solvent. Examples of low-viscosity solvents include solvents containing lactones, specifically, γ-butyrolactone and γ-valerolactone. Examples of difficult-to-volatile solvents include ethylene glycol, polyalkylene glycols (polyethylene glycol, polypropylene glycol, etc.), 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.

The conductive polymer is 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. 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), etc. are generally used. 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 it to form it, 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 it to form it, by chemical polymerization of a monomer, a dopant, and an oxidizing agent or a monomer and a dopant having an oxidizing effect to form a capacitor element, or by electrolytic polymerization of a monomer and a dopant to form a capacitor element.

Next, we will explain the manufacturing method of the electrolytic capacitor 1.

Lead terminals 21 and 22 for external extraction electrodes are connected to the anode 11 and cathode 12 (see Figure 2), which have been cut to a specified width. The anode 11 is a valve metal on which an oxide film is formed. 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 the capacitor element 5.

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 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 inorganic solvent may be used. As 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 inorganic solvent, for example, an aqueous solution containing adipic acid and an aqueous solution containing an adipate salt are examples. As an aqueous solution containing an adipate salt, for example, an aqueous solution containing a solute mainly composed of ammonium adipate is examples.

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 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 inorganic solvent. A cycle of the first chemical conversion treatment, heat treatment, the second chemical conversion treatment, and heat treatment may be repeated. 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. By repeatedly performing the first chemical conversion treatment and/or the second chemical conversion treatment and heat treatment, a tough oxide film is formed. 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 in which only the first chemical conversion treatment is performed without the above heat treatment, or a cycle in which only the second chemical conversion treatment is performed.

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 poly 3,4-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. The capacitor element 5 may be dried at a high temperature, for example, of 160°C or higher.

After the conductive polymer is held by the separator, the capacitor element 5 is impregnated with an electrolyte. 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.

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 a 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.

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 anode foil, the withstand voltage of the electrolyte, and the characteristics of other materials that make up the capacitor, and is ultimately determined by checking the product characteristics, including reliability. For example, capacitors are designed with a rated voltage that conforms to the Japanese Industrial Standards (JIS).

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. There is no particular upper limit to the applied voltage. 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 sufficiently repaired. Taking this into consideration, the applied voltage may be, for example, 2.0 times or less the rated voltage, or 1.4 times or less the rated voltage.

In the first step, a voltage is applied to the capacitor body 10 in an environment at the lowest category temperature. By applying a voltage to the capacitor body 10 in an environment at the lowest category temperature, any parts weakened in the environment at the lowest category temperature (such as damage to the oxide film) are repaired. This makes it possible to provide resistance to the lowest category temperature environment. For example, when the electrolytic capacitor is used at the lowest category temperature, damage to the oxide film can be suppressed. Also, when the electrolytic capacitor is used at a temperature lower than the lowest 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 drops to the lowest category temperature, damage to the oxide film is suppressed and leakage current is reduced.

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 missing parts of the oxide film on the electrode cut surface and other parts, causing the internal capacitor element 5 to heat up. This is thought to cause the temperature of the capacitor element 5 to rise above the category lower limit temperature. Once the oxide film has been repaired to a certain extent, the current flowing through the capacitor body 10 decreases, and the capacitor element 5 is cooled again, reaching 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 provide 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.

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.

In the second step, the voltage applied to the capacitor body 10 is the rated voltage or higher. The applied voltage is not particularly limited as long as it is equal to or higher 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. Taking this into consideration, the applied voltage may be, for example, 2.0 times the rated voltage or less, or 1.4 times the rated voltage or less.

In the second step, a voltage is applied to the capacitor body 10 in an environment of the upper category temperature limit. By applying a voltage to the capacitor body 10 in an environment of the upper category temperature limit, any parts weakened in the environment of the upper category temperature limit (such as damage to the oxide film) are repaired. This makes it possible to provide resistance to the upper category temperature limit environment. For example, when the electrolytic capacitor is used at the upper category temperature limit, damage to the oxide film can be suppressed. Also, when the electrolytic capacitor is used at a high temperature lower than the lower category temperature limit, 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 upper category temperature limit, damage to the oxide film is suppressed and leakage current is reduced.

In the second step, the time for applying voltage to the capacitor body 10 is 30 minutes or more. By making the application time 30 minutes or more, the capacitor body 10 can be sufficiently repaired and the leakage current can be sufficiently reduced. 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.

Either the first step or the second step may be performed first. In addition, the first step and the second step may be performed alternately multiple times.

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

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 the application time of 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 the application time of at least one of the second steps may be different.

As a result, it is possible to create an electrolytic capacitor that can suppress an increase in leakage current even if the temperature of the operating environment changes suddenly.

Conventionally, aging treatment was performed at the upper category temperature limit, but according to the manufacturing method of the electrolytic capacitor of this embodiment, a first step is performed in which a voltage is applied to the capacitor body 10 in an environment of the lower category temperature limit, and a second step is performed in which a voltage is applied to the capacitor body 10 in an environment of the upper category temperature limit. In other words, aging treatment is performed at both the lower category temperature limit and the upper category temperature limit.

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

It was found that the electrolytic capacitor produced 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 an increase in leakage current can be suppressed even if the change in the temperature of the environment in which it is used is small.

Either the first step or the second step may be carried out first, but when 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 a portion of the oxide film is not sufficiently repaired in the first step, by carrying out the second step after the first step, that portion is more likely to be repaired in the second step. In addition, the oxide film can be strengthened in the second step.

The present invention will be described in more detail below with reference to the following examples. However, the following examples do not limit the present invention, and all modifications and implementations that do not deviate from the spirit of this specification are included within the technical scope of the present invention.

[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.

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 0.1 wt% to 2 wt%. A voltage close to the chemical conversion voltage of the oxide film was applied while the capacitor element was immersed in this chemical conversion solution (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 a voltage close to the chemical conversion voltage of the oxide film was applied while the capacitor element was immersed in the chemical conversion solution, which had a phosphoric acid concentration adjusted to 0.1 wt% to 0.5 wt% (second chemical conversion treatment).

Next, in order to retain the conductive polymer on the separator, the capacitor element after 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 for 20 minutes under a reduced pressure of 80 to 100 kPa, and then the capacitor element was pulled out and dried to remove the moisture. This formed the surface of the oxide film on the anode 11, the surface of the cathode 12, and the surface of the fibers that make up the separator 13.

The capacitor element on which the conductive polymer was formed was impregnated with an electrolyte. Here, the electrolyte used was 1.0 wt% malic acid dissolved in ethylene glycol solvent.

A sealing body made of butyl rubber was attached to the obtained capacitor element, which was then placed in a metal case. The opening of the metal case was then sealed, and the periphery of the opening of the case was then curled to produce a capacitor body. The obtained capacitor body was subjected to an aging treatment by applying a voltage of rated voltage (80V) x 1.15 [V] for one hour in an environment of the upper category temperature limit (125°C), and then the lead terminals were inserted into the insertion holes formed in the seat plate 6 made of insulating resin, and the lead terminals were bent in directions away from each other to produce a surface-mount 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 in 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.

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

[Example 1]
After the curling process, a voltage of rated voltage (80 V) 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 ° C) before aging treatment at the upper limit of the category temperature (125 ° C). Other than the above, an electrolytic capacitor was produced in the same manner as the conventional example.

[Example 2]
After the curling process, 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°C) before aging at the upper limit of the category temperature (125°C). Other than the above, an electrolytic capacitor was produced in the same manner as the conventional example.

[Comparative Example 2]
After the curling process, and 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 an environment of -20°C. Other than the above, an electrolytic capacitor was produced in the same manner as the conventional example.

[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 an environment of -40°C. Other than the above, an electrolytic capacitor was produced in the same manner as the conventional example.

[Comparative Example 4]
After the curling process, 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°C) before aging treatment at the upper limit of the category temperature (125°C). Other than the above, an electrolytic capacitor was produced in the same manner as the conventional example.

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

(evaluation)
A temperature cycle test was conducted in which the electrolytic capacitor was left in an environment of the lower category temperature (-55°C) for 30 minutes and then left in an environment of the upper 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 2 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 2 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.

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

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 Examples 1 and 2 and Comparative Examples 2 to 5, aging treatment was performed in a low temperature environment in addition to the conventional aging treatment. 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.

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.

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.

The following was found from Examples 1 and 2 and Comparative Examples 2 to 5.
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 was 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.

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 category temperature limit, 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 category temperature limit. It was found that electrolytic capacitors made using this method are able to suppress the increase in leakage current even if the temperature of the operating environment changes suddenly.

Although the embodiments of the present invention have been described above based on 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, not the above description, and includes all modifications that are equivalent in meaning to and within the scope of the claims.

For example, in the above Example 1, aging treatment is performed at the lower category temperature before aging treatment at the upper category temperature. However, aging treatment may be performed at the lower category temperature after aging treatment at the upper category temperature. In this case, the first aging treatment exposes parts that are weakened in the upper category temperature environment (such as defects in the oxide film) and can repair the weakened parts. Furthermore, the latter aging treatment exposes parts that are weakened in the lower category temperature environment (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 operating environment temperature changes suddenly.

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

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

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

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 can 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.

REFERENCE SIGNS LIST 1 electrolytic capacitor 2 exterior case 3 sealing body 4 exterior body 5 capacitor element 6 seat plate 10 capacitor body 11 anode 12 cathode 13 separator 21, 22 lead terminals

Claims (5)

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 lower category temperature limit;
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. The method for manufacturing an electrolytic capacitor according to claim 1, characterized in that the second step is carried out after the first step. The method for manufacturing an electrolytic capacitor according to claim 1 or 2, characterized in that in the first step, a voltage of 1.15 times or more the rated voltage is applied to the capacitor body. The method for manufacturing an electrolytic capacitor according to any one of claims 1 to 3, characterized in that in the first step, the time for applying voltage to the capacitor body is 120 minutes or less. The method for manufacturing an electrolytic capacitor according to any one of claims 1 to 4, characterized in that in the second step, the time for applying voltage to the capacitor body is 120 minutes or less.

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