JP7491863B2 - Manufacturing method of electrolytic capacitor - Google Patents

Description

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

A known electrolytic capacitor is one that includes a capacitor element having an anode with a dielectric oxide film, a cathode, and a separator disposed between the anode and the cathode, and an exterior body that houses the capacitor element.

Patent Document 1 describes a method for manufacturing a wound-type solid electrolytic capacitor. The method described in Patent Document 1 includes a step of applying a conductive composition containing a soluble conductive polymer and a solvent (water and/or an organic solvent) and having a surface tension adjusted to 65 mN/m or less to a capacitor element, and a step of drying the composition to form a conductive polymer layer.

JP 2011-192983 A

In the method of Patent Document 1, a soluble conductive polymer that dissolves in a solvent is used as the conductive polymer. When a conductive composition containing a soluble conductive polymer and a solvent as described in Patent Document 1 is applied to a capacitor element, the conductive composition penetrates deep into the etching pits on whose surface a dielectric oxide film is formed. This forms a conductive polymer layer deep into the etching pits. This results in a capacitor with high capacitance. However, defects may remain in the dielectric oxide film formed at the deepest part of the etching pit. If the conductive composition penetrates into the defects, the leakage current will increase.

The inventors therefore investigated the use of a particulate conductive polymer that is insoluble but disperses in a solvent (hereinafter, sometimes referred to as a dispersible conductive polymer) as the conductive polymer. As a result, they found that there was a risk of an increase in leakage current and a high ESR (equivalent series resistance).

The object of the present invention is to obtain an electrolytic capacitor that has high capacitance, low leakage current, and low ESR when using a dispersible conductive polymer.

The inventors have investigated the use of particulate conductive polymers dispersed in a solvent as the conductive polymer, and have found the following:

When the capacitor element body is immersed in a dispersion liquid in which particulate conductive polymer is dispersed, the particulate conductive polymer has a certain size and therefore does not easily reach the deepest part of the etching pit. Therefore, the probability that the particulate conductive polymer will come into contact with the defect at the deepest part of the etching pit is low. Therefore, it is believed that leakage current can be reduced.

However, the dispersion liquid in which the particulate conductive polymer is dispersed has low impregnation into the capacitor element. If the amount of conductive polymer impregnated into the capacitor element is small, the capacitance will be small. Therefore, it is thought that adding a surfactant to the dispersion liquid will reduce the surface tension of the dispersion liquid, thereby increasing the impregnation of the particulate conductive polymer. This can increase the capacitance, but it has been found that the following separate problems occur.

The lead terminal of the capacitor element is formed with a round bar portion (e.g., "round bar portion 21a" in FIG. 2) made of aluminum or the like, and a lead portion (e.g., "lead portion 21b" in FIG. 2) made of CP wire or the like. The round bar portion and the lead portion are joined by welding, but since different metals are joined, an oxide film cannot be formed at these joints. If the impregnation of the dispersion liquid is too high, the dispersion liquid may seep into the joints between the lead portion and the round bar portion, forming a conductive polymer layer at these joints. If a conductive polymer layer is formed at these joints, leakage current increases.
Although the above improves the impregnation of the capacitor element with the dispersion, the amount of the dispersion held by the capacitor element decreases as the surface tension of the dispersion decreases, making it difficult to thicken the conductive polymer layer and therefore difficult to reduce the ESR.

The inventors therefore conducted further research into the use of dispersible conductive polymers and discovered a method for producing electrolytic capacitors that have high capacitance, low ESR, and small leakage current.

Specifically, the method for producing an electrolytic capacitor of the present invention includes a first step of obtaining an impregnation liquid having a surface tension adjusted to 35 mN/m or more and 50 mN/m or less by adding an acetylene-based surfactant, or an acetylene-based surfactant and an organic solvent, to a dispersion liquid in which a conductive polymer having repeating units of 3,4-ethylenedioxythiophene or a derivative thereof is dispersed in a solvent; and a second step of impregnating a capacitor element body having an anode with a dielectric oxide film, a cathode, and a separator disposed between the anode and the cathode with the impregnation liquid obtained in the first step, and then performing a heat treatment to form a conductive polymer layer on the capacitor element body.

The inventors have found that, according to the above method, when using a dispersible conductive polymer having repeating units of 3,4-ethylenedioxythiophene or its derivatives, an impregnation liquid is used whose surface tension is adjusted to the above range by an acetylene-based surfactant, or an acetylene-based surfactant and an organic solvent. This makes it possible to manufacture an electrolytic capacitor that has a high capacitance, a low ESR, and a small leakage current.

In the above configuration, the organic solvent may be at least one of polyalkylene glycol, polyglycerin, and derivatives thereof.

In the above configuration, the polyalkylene glycol may be at least one selected from the group consisting of polyethylene glycol, polypropylene glycol, and a copolymer of ethylene glycol and propylene glycol.

By using an organic solvent, it becomes easier to adjust the surface tension of the impregnation liquid. In addition, by using the organic solvent, it is possible to expect effects such as supporting the self-repairing performance of the dielectric oxide film, increasing the capacity of the capacitor, and improving the voltage resistance.

According to the present invention, when a dispersible conductive polymer is used, it is possible to manufacture an electrolytic capacitor that has a high capacitance, a low ESR, and a small leakage current.

FIG. 2 is a front view of the electrolytic capacitor according to the embodiment of the present invention. FIG. 2 is an exploded perspective view of the capacitor element shown in FIG. 1 .

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

As shown in FIG. 1, the electrolytic capacitor 1 is an electrolytic capacitor that includes an outer case 2, a capacitor element 3 housed in the outer case 2, and a sealing body 4 that seals the opening of the outer case 2.

As shown in FIG. 2, the capacitor element 3 is formed by winding an anode foil (anode) 11 and a cathode foil (cathode) 12 into a cylindrical shape with a separator 13 between them, and is secured by tape 14 attached to the outer periphery.

Lead terminal 21 and lead terminal 22 are connected to anode 11 and cathode 12, respectively. Lead terminal 21 has a tab portion (not shown), round bar portion 21a, and lead portion 21b. Lead terminal 22 has a tab portion (not shown), round bar portion 22a, and lead portion 22b.

The round bar portion 21a is made of aluminum or the like. The lead portion 21b is made of CP wire, Cu wire or the like. The round bar portion 21a and the lead portion 21b are joined by welding. Because the round bar portion 21a and the lead portion 21b are made of different materials, no oxide film is formed at the joint between the round bar portion 21a and the lead portion 21b.

The round bar portion 22a and the lead portion 22b are made of the same material as the round bar portion 21a and the lead portion 21b, respectively. The round bar portion 22a and the lead portion 22b are joined by welding. Because the round bar portion 22a and the lead portion 22b are made of different materials, no oxide film is formed at the joint between the round bar portion 22a and the lead portion 22b.

Lead terminal 21 and lead terminal 22 are inserted through through holes 31 and 32, respectively, of sealing body 4 shown in FIG. 1.

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

The cathode 12 is formed using a valve metal. For example, the cathode 12 may be a valve metal foil whose surface is roughened by etching, or a foil whose surface is roughened and then chemically treated. The cathode 12 may be a plain foil that is not etched. The cathode 12 may be 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 or plain foil. The cathode 12 may be a coating foil in which a carbon thin film is formed on the surface of the roughened or plain foil.

The material of the separator 13 is not particularly limited. For example, a material mainly made of cellulose may be used as the separator 13.

Between the dielectric oxide film of the anode 11 and the cathode 12, a conductive polymer layer is formed, which is supported by a separator 13. The conductive polymer layer is a layer containing a dispersible conductive polymer that is dispersed in a solvent. A method for forming the conductive polymer layer will be described later. The conductive polymer layer may further be formed on the dielectric oxide film, or may be formed on the cathode 12.

A dispersible conductive polymer is a conductive polymer that does not dissolve in a solvent and exists in the form of colloidal particles in the solvent. The dispersible conductive polymer has repeating units of 3,4-ethylenedioxythiophene or a derivative thereof. Derivatives of 3,4-ethylenedioxythiophene include, for example, 3,4-ethylenedioxythiophene in which the ethylene group is replaced by another alkyl group, and 3,4-ethylenedioxythiophene in which the hydrogen atom of the ethylene group is replaced by another substituent. Examples of dispersible conductive polymers include at least one selected from poly(3,4-ethylenedioxythiophene) and derivatives of poly(3,4-ethylenedioxythiophene). Derivatives of poly(3,4-ethylenedioxythiophene) include, for example, poly(3,4-ethylenedioxythiophene) in which the ethylene group is replaced by another alkyl group, and poly(3,4-ethylenedioxythiophene) in which the hydrogen atom of the ethylene group is replaced by another substituent such as an alkyl group.

The dopant constituting the dispersible conductive polymer may be, for example, at least one selected from polystyrene sulfonic acid, p-toluenesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, and 1-naphthalenesulfonic acid.

The conductive polymer layer may contain additives such as antioxidants.

The electrolytic capacitor 1 described above is manufactured, for example, by the following method.

Lead tabs 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 and cathode 12 to which the lead tabs are connected are wound with a separator 13 in between to create the capacitor element body. The anode 11 is a valve metal on which a dielectric oxide film is formed.

The capacitor element body is chemically treated to repair the cut edges of the capacitor element body and the dielectric oxide film that was damaged during production. The chemical treatment is carried out by applying a voltage to the capacitor element body in a chemical conversion solution. The chemical conversion solution used for the chemical treatment is, for example, an aqueous solution containing at least one of adipic acid and an adipate salt.

To form a conductive polymer layer, a dispersion liquid in which a conductive polymer is dispersed in a solvent is prepared.
An acetylene-based surfactant, or an acetylene-based surfactant and an organic solvent are added to a dispersion liquid in which a conductive polymer having a repeating unit of 3,4-ethylenedioxythiophene or a derivative thereof is dispersed in water as a solvent, to obtain an impregnation liquid having a surface tension adjusted to 35 mN/m or more and 50 mN/m or less (first step). The surface tension can be measured, for example, by a pendant drop method.

As the conductive polymer, the conductive polymers exemplified above can be used. As the dispersion liquid, for example, a liquid in which PEDOT/PSS containing polyethylenedioxythiophene (PEDOT) as a conductive polymer and polystyrenesulfonic acid (PSS) as a dopant is dispersed in water can be used. The concentration of the conductive polymer in the dispersion liquid is not particularly limited. The concentration of the conductive polymer is, for example, 1.6 wt% or more and 2.5 wt% or less.

The organic solvent is not particularly limited. For example, at least one of polyalkylene glycol, polyglycerin, and derivatives thereof may be used as the organic solvent. For example, the polyalkylene glycol and derivatives thereof may be at least one selected from the group consisting of polyethylene glycol, polypropylene glycol, copolymers of ethylene glycol and propylene glycol, and derivatives thereof. The concentration of the organic solvent is not particularly limited.

By using an organic solvent, it is easy to adjust the surface tension of the above-mentioned liquid containing the conductive polymer. In addition, polyalkylene glycol, polyglycerin, and their derivatives can be expected to have effects such as assisting the self-repairing performance of the dielectric oxide film, improving the capacitance of the capacitor, and improving the voltage resistance.

Acetylene-based surfactants are a type of nonionic surfactant. Acetylene-based surfactants are surfactants that have an acetylene structure in the molecule. Examples of acetylene-based surfactants include acetylene glycols, acetylene diols, and acetylene alcohols. Examples of acetylene-based surfactants include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 3,5-dimethyl-1-hexyne-3-ol, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, and ethoxylated versions of these.

The concentration of the acetylene surfactant is not particularly limited. The concentration of the acetylene surfactant is preferably 0.01 wt% or more, more preferably 0.02 wt% or more. The concentration of the acetylene surfactant is preferably 0.07 wt% or less, more preferably 0.05 wt% or less.

The impregnation liquid whose surface tension has been adjusted in the first step may contain additives such as antioxidants.

The capacitor element body, which includes the anode 11, the cathode 12, and the separator 13, is immersed in the impregnation liquid whose surface tension has been adjusted in the first step, so that the capacitor element body is impregnated with the impregnation liquid. At this time, the impregnation liquid is also impregnated into the dielectric oxide film surface of the anode 11 and the separator 13. The capacitor element body is heat-treated (for example, by heating at 40°C or higher and 220°C or lower) to obtain a capacitor element 3 on which a conductive polymer layer is formed (second step). The conductive polymer layer is mainly held by the separator 13. The conductive polymer layer may also be formed on the dielectric oxide film of the anode 11, on the cathode 12, between the anode 11 and the separator 13, and/or between the cathode 12 and the separator 13.

As a result of the above, the capacitor element 3 is obtained. The capacitor element 3 is housed in the exterior case 2 (see FIG. 1), and the opening of the exterior case 2 is closed with the sealing body 4. This results in the electrolytic capacitor 1.

In the above, an example was given of a dispersion liquid in which a conductive polymer having repeating units of 3,4-ethylenedioxythiophene or a derivative thereof is dispersed in water as the solvent. However, a dispersion liquid in which a conductive polymer having repeating units of 3,4-ethylenedioxythiophene or a derivative thereof is dispersed in an organic solvent, or in water and an organic solvent, may also be used as the dispersion liquid.

The present inventors have obtained the following findings.
When a dispersible conductive polymer is used as the conductive polymer, the conductive polymer particles have a certain size and therefore are unlikely to reach the deepest part of the etching pit. Therefore, the probability that the conductive polymer particles will come into contact with the defective part at the deepest part of the etching pit is low. Therefore, it is believed that the leakage current can be reduced.

In addition, it is presumed that the use of an impregnation liquid whose surface tension has been adjusted to 35 mN/m or more and 50 mN/m or less with an acetylene-based surfactant will provide the following effects.
When the capacitor element body is immersed in the impregnation liquid, the impregnation liquid is unlikely to seep up into the joints between the round bar portion 21a and the lead portion 21b of the lead terminal 21 and the joints between the round bar portion 22a and the lead portion 22b of the lead terminal 22, as shown in Fig. 2. Furthermore, the impregnation liquid containing an acetylene surfactant is unlikely to foam when impregnated into the capacitor element body, so that the impregnation liquid is unlikely to adhere to the joints between the round bar portion 21a and the lead portion 21b of the lead terminal 21 and the joints between the round bar portion 22a and the lead portion 22b of the lead terminal 22 due to bubbles or splashes caused by the bubbles breaking. The impregnation liquid is prevented from coming into contact with these joints, which prevents the leakage current from increasing.
Furthermore, by adjusting the surface tension to 35 mN/m or more and 50 mN/m or less, the amount of impregnation liquid retained in the capacitor element body is increased, and the conductive polymer layer becomes thick to a certain extent, thereby lowering the ESR.
Furthermore, since the impregnating liquid does not come into contact with the defect at the innermost part of the etching pit but easily penetrates into the vicinity of the opening of the etching pit, it is presumed that a conductive polymer layer is formed near the opening of the etching pit, which is believed to suppress the decrease in capacitance.

From the above, it has been found that it is possible to manufacture an electrolytic capacitor 1 that has a high capacitance, a low ESR, and a small leakage current.

The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

The electrolytic capacitor was made using the following method.

Aluminum lead rods for external extraction electrodes were connected to the anode and cathode foils cut to a specified width. For the anode foil, an anode aluminum foil was used, on which the surface of the valve metal aluminum foil was roughened by etching, and then chemically treated at 100 V to form a dielectric oxide film. For the cathode foil, a cathode aluminum foil on which carbon was vapor-deposited was used. The anode and cathode aluminum foils were wound with nylon-based electrolytic paper (separator) between them to produce the capacitor element body.

A chemical conversion treatment was performed to repair the dielectric oxide film that was missing on the cut edge of the anode foil and the attachment part of the lead tab. The chemical conversion treatment was performed by immersing the main body of the capacitor element in a chemical conversion solution and applying a voltage that was close to the chemical conversion voltage value of the dielectric oxide film. The chemical conversion solution used was an aqueous solution of ammonium adipate with an ammonium adipate concentration of 2 wt%.

Next, an impregnation liquid adjusted under the following conditions (see [Conditions for preparing the conductive polymer layer] described below) was prepared for the capacitor element body. The capacitor element body was immersed in the impregnation liquid for 30 minutes in an environment reduced to 90 kPa, thereby impregnating the capacitor element body with the impregnation liquid. After that, as a heat treatment, the capacitor element body was held in a thermostatic chamber set at 40°C for 30 minutes, and then held in a thermostatic chamber set at 160°C for 30 minutes and dried. This resulted in a capacitor element with a conductive polymer layer formed thereon.

The lead wires of the resulting capacitor element were inserted into the holes in the sealing body, and the capacitor element and sealing body were housed in an aluminum case, after which the periphery of the opening of the case was curled. A rated voltage (50 V) was applied to the capacitor element housed in the case in a thermostatic chamber set at 135°C, and an aging process was performed to produce an electrolytic capacitor. The electrolytic capacitor produced in this experiment had a rated voltage of 50 WV, a rated capacitance of 8.2 μF, and product dimensions of φ6.3 × 6 L (mm).

[Conditions for preparing conductive polymer layer]
<No.1>
The impregnation liquid was a dispersion of PEDOT/PSS (concentration 2.0 wt%) dispersed in a water solvent. The surface tension of the impregnation liquid was 68.0 mN/m. The surface tension was measured by the pendant drop method. The surface tension was also measured in the following No. 2 to No. 12 by the same method.
<No.2>
An impregnation solution with a surface tension adjusted to 29.0 mN/m was obtained by adding 0.1 wt% of a surfactant, polyethylene glycol-mono-2-ethylhexyl ether (Newcol 1004, manufactured by Nippon Nyukazai Co., Ltd.), to a dispersion of PEDOT/PSS (concentration 2.0 wt%) in a water solvent. This surfactant is not an acetylene-based surfactant.
<No.3>
An impregnation solution with a surface tension adjusted to 35.0 mN/m was obtained by adding 5 wt% polyethylene glycol (PEG400) and 5 wt% ethylene glycol (EG) (total of 10 wt%), and 0.05 wt% of a surfactant, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, ethoxylated (Dynol 604, manufactured by Air Products) to a dispersion of PEDOT/PSS (concentration 2.0 wt%) in a water solvent. Here, "PEG400" refers to polyethylene glycol with a number average molecular weight of 400.
<No.4>
An impregnation solution with a surface tension adjusted to 41.0 mN/m was obtained by adding 5 wt % polyethylene glycol (PEG400) and 5 wt % ethylene glycol (EG) (total of 10 wt %), which was a polyalkylene glycol, and 0.025 wt % of a surfactant, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, ethoxylated (Dynol 604, manufactured by Air Products) to a dispersion of PEDOT/PSS (concentration: 2.0 wt %) dispersed in a water solvent.
<No.5>
An impregnation solution with a surface tension adjusted to 47.0 mN/m was obtained by adding 5 wt % polyethylene glycol (PEG400) and 5 wt % ethylene glycol (EG) (total of 10 wt %), that is, 5 wt % polyethylene glycol, 5 wt % ethylene glycol, 5 wt % polyalkylene glycol, and 0.01 wt % of a surfactant, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, ethoxylated (Dynol 604, manufactured by Air Products) to a dispersion of PEDOT/PSS (concentration: 2.0 wt %) in a water solvent.
<No.6>
An impregnation solution with a surface tension adjusted to 40.0 mN/m was obtained by adding 5 wt % polyethylene glycol (PEG400) and 2.5 wt % polyglycerin (PolyG) (total of 7.5 wt %) and 0.05 wt % of a surfactant, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, ethoxylated (Dynol 604, manufactured by Air Products) to a dispersion of PEDOT/PSS (concentration 2.0 wt %) in an aqueous solvent.
<No.7>
An impregnation solution with a surface tension adjusted to 50.0 mN/m was obtained by adding 5 wt % polyethylene glycol (PEG400) and 1 wt % polypropylene glycol (PPG400) to a dispersion of PEDOT/PSS (concentration 2.0 wt %) in a water solvent, a total of 6 wt % polyalkylene glycol, and 0.05 wt % of a surfactant, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, ethoxylated (Dynol 604, manufactured by Air Products). Here, "PPG400" refers to polypropylene glycol with a number average molecular weight of 400.
<No.8>
An impregnation solution with a surface tension adjusted to 39.0 mN/m was obtained by adding 0.025 wt % of a surfactant, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, ethoxylated (Dynol 604, manufactured by Air Products) to a dispersion in which PEDOT/PSS (concentration: 2.0 wt %) was dispersed in a water solvent.
<No.9>
An impregnation solution with a surface tension adjusted to 26.0 mN/m was obtained by adding 5 wt % polyethylene glycol (PEG400) and 5 wt % ethylene glycol (EG) (total of 10 wt %), which were polyethylene glycol (PEG400) and ethylene glycol (EG), and 0.5 wt % of a surfactant, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, ethoxylated (Dynol 604, manufactured by Air Products) to a dispersion of PEDOT/PSS (concentration: 2.0 wt %) in a water solvent.
<No.10>
An impregnation solution with a surface tension adjusted to 27.0 mN/m was obtained by adding 5 wt % polyethylene glycol (PEG400) and 5 wt % ethylene glycol (EG) (total of 10 wt %), which was a polyalkylene glycol, and 0.1 wt % of a surfactant, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, ethoxylated (Dynol 604, manufactured by Air Products) to a dispersion of PEDOT/PSS (concentration: 2.0 wt %) in a water solvent.
<No.11>
An impregnation solution with a surface tension adjusted to 55.0 mN/m was obtained by adding 5 wt % of polyethylene glycol (PEG400) and 5 wt % of polypropylene glycol (PPG400) (total of 10 wt %), and 0.01 wt % of a surfactant, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, ethoxylated (Dynol 604, manufactured by Air Products) to a dispersion of PEDOT/PSS (concentration 2.0 wt %) in an aqueous solvent.

The following Chemical Formula 1 is the structural formula of the acetylene-based surfactant Dynol 604 (manufactured by Air Products Co.) added in Nos. 3 to 11.

(evaluation)
The electrostatic capacitance (Cap.), equivalent series resistance (ESR) and leakage current (L.C.) of the electrolytic capacitor were measured in an environment of 20°C. In addition, the weight per unit volume of the electrolytic capacitor was measured for the conductive polymer layer formed on the capacitor element. The weight per unit volume of the electrolytic capacitor was calculated by (weight of the capacitor element after the conductive polymer layer is formed - weight of the capacitor element before immersion in the impregnation liquid) / volume of the capacitor element body.

Table 1 shows the experimental conditions.

Table 2 shows the experimental conditions and the evaluation results.

As shown in Tables 1 and 2, the surface tension of the impregnating liquid in No. 2 is 29.0 mN/m, that in No. 9 is 26.0 mN/m, and that in No. 10 is 27.0 mN/m, which are small. As shown in Table 2, No. 2, No. 9, and No. 10, which have small surface tensions, had high capacitance, but also high ESR and large leakage current.
In No. 2, No. 9, and No. 10, it is considered that the surface tension of the impregnation liquid was low, and therefore the impregnation liquid was highly penetrative into the capacitor element body, resulting in a large capacitance.
However, considering that the weight per unit volume of the electrolytic capacitor is small and that the ESR is high, it is presumed that the amount of impregnation liquid retained by the separator was small, resulting in a thin conductive polymer layer and a high ESR.
In addition, in No. 2, bubbles were generated on the liquid surface when the capacitor element body was impregnated with the impregnation liquid, and the adhesion of the bubbles to the joint between the lead part and the round bar part of the lead terminal was observed. In No. 2, No. 9, and No. 10, it is presumed that the impregnation liquid had a low surface tension, so the impregnation liquid seeped up to the joint between the lead part and the round bar part of the lead terminal, causing the leakage current to increase.

As shown in Tables 1 and 2, in No. 11, the surface tension of the impregnation liquid is large at 55.0 mN/m.
In No. 1, in which no organic solvent or surfactant was added, the surface tension of the impregnation liquid was as high as 68.0 mN/m.
As shown in Table 2, the capacitance is small in No. 1 and No. 11. Considering the large surface tension and the small weight per unit volume of the electrolytic capacitor, it is presumed that the capacitance was small because the impregnation of the capacitor element body with the impregnation liquid was low.

As shown in Table 2, No. 3 to No. 8 had large capacitance, small ESR, and small leakage current. No. 3 to No. 8 had large weight per unit volume of electrolytic capacitor. No. 3 to No. 8 had surface tension of 35.0 mN/m to 50.0 mN/m. Furthermore, in No. 3 to No. 8, no bubbles were generated on the liquid surface when the impregnation liquid was impregnated into the capacitor element body, and no bubbles were observed at the joint between the lead portion and the round bar portion of the lead terminal.
From the above, it is presumed that the impregnation liquids No. 3 to No. 8 have high impregnation ability into the capacitor element body, retain a large amount in the separator, and are unlikely to seep up into the joint between the lead portion and the round bar portion of the lead terminal.

From the above experiment, the following was found.
It has been found that when a dispersible conductive polymer having a repeating unit of 3,4-ethylenedioxythiophene is used as the conductive polymer, an electrolytic capacitor having a high capacitance, a low ESR, and a small leakage current can be manufactured by using an acetylene-based surfactant and an impregnation liquid in which the surface tension is adjusted to 35 mN/m or more and 50 mN/m or less by the acetylene-based surfactant, or by a combination of an acetylene-based surfactant and an organic solvent.

In the above experiment, PEDOT/PSS was used as the conductive polymer. However, the dispersible conductive polymer is not limited to PEDOT as long as it has a repeating unit of 3,4-ethylenedioxythiophene or a derivative thereof. For example, the dispersible conductive polymer may have a repeating unit of a 3,4-ethylenedioxythiophene derivative. Furthermore, the dopant is not limited to PSS. The same effect as above can be obtained when a conductive polymer other than PEDOT/PSS is used. The same effect as above can be obtained when another dopant is used.

In the above experiment, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, ethoxylated was used as the acetylene surfactant. However, acetylene surfactants other than 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, ethoxylated may be used. Also, one type of acetylene surfactant may be used, or two or more types of acetylene surfactants may be used. In these cases, the same effects as above can be obtained.

In the above experiment, the surface tension was adjusted by adding an acetylene-based surfactant, or an acetylene-based surfactant and an organic solvent, to a dispersion in which a dispersible conductive polymer is dispersed in a water solvent. However, the surface tension may also be adjusted by adding an acetylene-based surfactant, or an acetylene-based surfactant and an organic solvent, to a dispersion in which a dispersible conductive polymer is dispersed in water and an organic solvent, or to a dispersion in which a dispersible conductive polymer is dispersed in an organic solvent. This also achieves the same effect as above.

In addition, in the above experiments, polyethylene glycol, ethylene glycol, and/or polyglycerin were used as the organic solvent. However, organic solvents other than the polyalkylene glycols used in the experiments may be used. One type of polyalkylene glycol may be used, or two or more types of polyalkylene glycols may be used.

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.

In the above experiment, an electrolytic capacitor with a rated voltage of 50 WV, a rated capacity of 8.2 μF, and a product size of φ6.3 × 6 L (mm) was produced, but the rated voltage, rated capacity, and product size of the electrolytic capacitor of the present invention are not limited to the above.

In addition, although it has been described above that the conductive polymer layer is held by the separator, the conductive polymer layer may also be formed in voids in the capacitor element body (e.g., etching pits in the dielectric oxide film, pits in the cathode, between the anode and the separator, between the cathode and the separator).

Furthermore, after forming a conductive polymer layer on the capacitor element body, the electrolyte may be impregnated.

REFERENCE SIGNS LIST 1 electrolytic capacitor 2 exterior case 3 capacitor element 4 sealing body 11 anode 12 cathode 21, 22 lead terminals 21a, 22a round bar portion 21b, 22b lead portion

Claims (3)

a first step of adding an acetylene-based surfactant, or an acetylene-based surfactant and an organic solvent, to a dispersion obtained by dispersing a conductive polymer having a repeating unit of 3,4-ethylenedioxythiophene or a derivative thereof in a solvent to obtain an impregnation solution having a surface tension adjusted to 35 mN/m or more and 50 mN/m or less;
a second step of impregnating a capacitor element body having an anode with a dielectric oxide film, a cathode, and a separator disposed between the anode and the cathode with the impregnation liquid obtained in the first step, and then performing a heat treatment to form a conductive polymer layer on the capacitor element body. The method for producing an electrolytic capacitor according to claim 1, characterized in that the organic solvent is at least one selected from polyalkylene glycol, polyglycerin, and derivatives thereof. The method for producing an electrolytic capacitor according to claim 2, characterized in that the polyalkylene glycol is at least one selected from the group consisting of polyethylene glycol, polypropylene glycol, and a copolymer of ethylene glycol and propylene glycol.

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