JP2008004860A - Manufacturing method of solid electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce manufacturing cost of a solid electrolytic capacitor, and also to control increase in equivalent series resistance. <P>SOLUTION: A capacitor element is formed (etching to cut end formation/carbonization treatment) having an anode object wherein anodic oxidation film is formed in the surface, the capacitor element is impregnated with an oxidant (oxidant impregnation), and then the capacitor element is impregnated with a monomer wherein an oxidant is diluted with a soluble dilution solvent (monomer impregnation). Then, a solid electrolyte consisting of a conductive polymer is formed on an oxidation film by carrying out chemical polymerization of the oxidant and the monomer impregnated to the capacitor element (solid electrolyte formation). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a solid electrolytic capacitor, and more particularly to a method for manufacturing a solid electrolytic capacitor having a solid electrolyte made of a conductive polymer.

A capacitor element of an electrolytic capacitor is made of a valve metal such as aluminum, tantalum, or niobium, and has an anode body (anode foil or sintered body) having a large number of etching pits and fine holes formed on the surface. Further, an oxide film serving as a dielectric is formed on the surface of the anode body, and electrodes are drawn from the oxide film.
An electrolyte is in contact with the oxide film, and this electrolyte functions as a true cathode for drawing an electrode from the oxide film.
Here, since the electrolyte as the true cathode has a great influence on the electrical characteristics of the electrolytic capacitor, electrolytic capacitors employing various types of electrolytes have been conventionally proposed.

Among them, the solid electrolytic capacitor uses a solid electrolyte having electronic conductivity instead of a liquid electrolyte having inferior impedance characteristics in a high frequency region because of its ionic conductivity.
In this solid electrolytic capacitor, a capacitor element is immersed in a mixed solution of a monomer and an oxidant to impregnate the capacitor element with a mixed solution of a monomer and an oxidant, and then a polymerization reaction between the monomer and the oxidant is performed. A method for promoting formation of a solid electrolyte is known (see Patent Document 1).
The polymerization reaction of the monomer and the oxidizing agent starts from the time when the mixed liquid of the monomer and the oxidizing agent is prepared. Therefore, if the timing at which the capacitor element is immersed in the mixed solution is different, the degree of polymerization of the monomer and the oxidizing agent in the mixed solution impregnated in the capacitor element is different.
For this reason, the formation state of the solid electrolyte differs depending on the capacitor element, and the electrical characteristics such as equivalent series resistance may differ between the solid electrolytic capacitors.
Furthermore, when the degree of polymerization in the mixed solution increases, the viscosity of the mixed solution increases, so that the mixed solution may not penetrate into the deep part of the etching pits of the anode body. In this case, the oxide film in the deep part of the etching pit is exposed, and the electrical characteristics of the solid electrolytic capacitor are deteriorated.
Therefore, in order to allow the mixed solution to penetrate into the deep part of the etching pit, it is necessary to shorten the replacement cycle of the mixed solution, but there is a problem that the manufacturing cost of the solid electrolytic capacitor is increased.

  Therefore, without impregnating the above-mentioned mixed solution, the capacitor element is impregnated with the oxidant, and then the monomer is impregnated with the capacitor element. Further, the polymerization reaction between the impregnated monomer and the oxidant is promoted, thereby solid electrolyte. There is known a technique for forming (see, for example, Patent Document 2).

Japanese Patent Laid-Open No. 10-340830 JP 2003-272953 A

  According to the above-described technique, when the capacitor element is impregnated with the monomer, the polymerization reaction between the oxidant and the monomer is rapidly started from the surface of the anode body, so that a solid electrolyte is formed from the surface of the anode body. At this time, since the solid electrolyte formed on the surface of the anode body inhibits the penetration of the monomer into the deep part of the etching pit, the solid electrolyte may not be formed in the deep part of the etching pit. In this case, the equivalent series resistance of the solid electrolytic capacitor is increased.

  The objective of this invention is providing the manufacturing method of the solid electrolytic capacitor which can suppress the increase in an equivalent series resistance while reducing manufacturing cost.

  According to a first aspect of the present invention, there is provided a method for manufacturing a solid electrolytic capacitor comprising: a capacitor element forming step for forming a capacitor element having an anode body having an anodized film formed on a surface thereof; and an oxidant impregnation for impregnating the capacitor element with an oxidant. A step of impregnating the capacitor element with a monomer diluted with a diluent solvent capable of dissolving the oxidant after the step of impregnating the oxidant, and the oxidant impregnated in the capacitor element. And a solid electrolyte forming step of forming a solid electrolyte made of a conductive polymer on the oxide film by chemically polymerizing the monomer.

The weight ratio of the diluent solvent to the monomer is preferably in the range of 1:10 to 10: 1 (second invention).
The oxidizing agent is preferably one of p-toluenesulfonic acid ferric salt, naphthalenesulfonic acid ferric salt, and triisopropylnaphthalenesulfonic acid ferric salt (third invention). . In addition, the monomer is preferably any one of aniline, pyrrole, thiophene and derivatives thereof (fourth invention).
Further, the thiophene derivative is preferably ethylenedioxythiophene (fifth invention).

According to the first invention, after impregnating the capacitor element with the oxidant, the monomer diluted with the diluting solvent capable of dissolving the oxidant is impregnated. The monomer is impregnated in the capacitor element while being dissolved. For this reason, the polymerization reaction between the monomer and the oxidizing agent proceeds slowly, and the rate at which the solid electrolyte is formed on the surface of the anode body is reduced.
Thus, the monomer sufficiently penetrates deep into the etching pits of the anode body, and a dense and uniform solid electrolyte can be formed. Thereby, an increase in the equivalent series resistance of the solid electrolytic capacitor can be suppressed. Moreover, since it is not necessary to prepare a liquid mixture by mixing an oxidizing agent and a monomer, manufacturing cost can be reduced.

  Further, the inventors of the present invention can efficiently suppress an increase in the equivalent series resistance of the solid electrolytic capacitor when the weight ratio of the diluent solvent and the monomer is in the range of 1:10 to 10: 1. I found.

Embodiments of the present invention will be described with reference to the drawings.
First, as shown in FIG. 1, a capacitor element 10 of a solid electrolytic capacitor 1 manufactured by the manufacturing method of the present embodiment includes an anode foil 2 and a cathode foil 3, and these anode foil 2, cathode foil 3, Has a structure wound around the separator 4.

The anode foil 2 is made of a valve metal such as aluminum. As shown in FIG. 2, the surface of the anode foil 2 is roughened (etching pit formation) by an etching process, and an anodized film 2a is formed by anodic oxidation (chemical conversion).
Similarly to the anode foil 2, the cathode foil 3 is formed of aluminum or the like, and its surface is roughened (formation of etching pits) and a natural oxide film 3a is formed.

Further, the solid electrolyte 5 made of a conductive polymer is held on both surfaces of the separator 4. That is, the solid electrolyte 5 is sandwiched between the anode foil 2 and the cathode foil 3 and the separator 4. As the conductive polymer constituting the solid electrolyte 5, polyaniline, polypyrrole, polyethylenedioxythiophene (PEDT) or the like can be used, and these are generated by chemical polymerization of monomers.
As shown in FIGS. 1 and 2, lead tabs are connected from the anode foil 2 and the cathode foil 3, respectively, and lead wires 6 are drawn from the anode foil 2 and the cathode foil 3 through the lead tabs, respectively.

Next, the manufacturing method of the solid electrolytic capacitor 1 will be further described with reference to FIG.
First, in order to increase the effective surface area of the electrode, the surfaces of the anode foil 2 and the cathode foil 3 are subjected to etching treatment to be roughened. Further, the surface of the roughened anode foil 2 is subjected to a chemical conversion treatment to form an anodic oxide film 2a, and the cathode foil 3 forms a natural oxide film 3a by water resistance treatment and / or heat treatment.
Then, after cutting the anode foil 2 and the cathode foil 3 on which the anodic oxide film 2a and the natural oxide film 3a are formed into predetermined dimensions, the lead wires 6 are connected to the anode foil 2 through lead tabs, respectively. The cathode foil 3 is wound through a separator 4, and further, element formation (cut formation) is performed by applying a voltage in an aqueous solution of ammonium adipate.
Thereafter, the separator is carbonized to produce the cylindrical capacitor element 10.

Next, the cylindrical capacitor element 10 is immersed in an oxidant so that the capacitor element 10 is impregnated with an oxidant and then dried (oxidant impregnation step). Thereafter, the capacitor element 10 is immersed in a monomer solution obtained by diluting the monomer with a diluent solvent in which the oxidizing agent is soluble, thereby impregnating the capacitor element 10 with the monomer solution (monomer) (monomer impregnation step).
Subsequently, the impregnated oxidant and the monomer are chemically polymerized by heating at a predetermined temperature in the polymerization layer for a certain period of time, and a conductive polymer is formed between the electrode foils 2 and 3 and the separator 4. The solid electrolyte 5 is formed (solid electrolyte forming step).

  Here, since the capacitor element 10 is impregnated with the oxidizing agent and then the monomer solution is impregnated, the monomer is impregnated into the capacitor element 10 while the previously impregnated oxidizing agent is dissolved in the diluting solvent. For this reason, the polymerization reaction between the monomer and the oxidizing agent proceeds slowly, and the rate at which the solid electrolyte is formed on the surface of the anode body is reduced. As a result, the monomer sufficiently penetrates deep into the etching pits of the electrode foils 2 and 3, and a dense and uniform solid electrolyte 5 can be formed. Moreover, since it is not necessary to prepare a liquid mixture by mixing an oxidizing agent and a monomer, manufacturing cost can be reduced.

  Subsequently, the solid electrolytic capacitor 1 is assembled. That is, the cylindrical capacitor element 10 obtained by the above-described process is housed in a bottomed cylindrical outer case, and the opening is sealed with a sealing rubber or the like. Finally, aging is performed to complete the manufacturing process.

Next, more specific Example 1 of the present invention will be described together with Comparative Examples 1 and 2. In Example 1 and Comparative Examples 1 and 2 described below, the steps for forming a solid electrolyte (oxidant impregnation, monomer impregnation, solid electrolyte formation shown in FIG. 3) are different, but all other steps are performed. The same.
Hereinafter, only the process for forming the solid electrolyte will be described. Each solid electrolytic capacitor has a rating of 4.0 V-100 μF.

[Example 1] After impregnation with oxidant, impregnation with monomer solution In Example 1, the capacitor element 10 was impregnated with an iron p-toluenesulfonate solution (oxidant) (oxidant impregnation step), and then at 100 ° C. Heated for 30 minutes and dried. Thereafter, the capacitor element 10 is impregnated with a monomer solution diluted with a weight ratio of butanol (diluted solvent) and ethylenedioxythiophene (monomer) of 1: 1 (monomer impregnation step).
Furthermore, the capacitor element 10 was heated at 100 ° C. for 60 minutes to produce PEDT, which is a conductive polymer, by chemical polymerization to form the solid electrolyte 5 (solid electrolyte formation step).

(Comparative example 1) Oxidant / monomer mixed liquid impregnation In Comparative example 1, the capacitor element 10 was impregnated with a solution (mixed liquid) in which iron p-toluenesulfonate and ethylenedioxythiophene were previously mixed. Then, heating was performed at 100 ° C. for 60 minutes, and PEDT, which is a conductive polymer, was generated by chemical polymerization to form a solid electrolyte.

(Comparative Example 2) After impregnation with a monomer solution, impregnation with an oxidizing agent In Comparative Example 2, the capacitor element 10 was impregnated with a monomer solution in which the weight ratio of butanol and ethylenedioxythiophene was 1: 1, and then p- An impregnated iron sulfonate solution was heated at 100 ° C. for 60 minutes to produce PEDT as a conductive polymer by chemical polymerization to form a solid electrolyte.

  The electrical characteristics (capacitance, equivalent series resistance, and leakage current) of the solid electrolytic capacitors obtained by the manufacturing methods of Example 1 and Comparative Examples 1 and 2 were measured. The results are shown in Table 1.

As shown in Table 1, the equivalent series resistance and leakage current of the solid electrolytic capacitor manufactured by the manufacturing method of Example 1 are smaller than the solid electrolytic capacitor manufactured by the manufacturing methods of Comparative Examples 1 and 2. Yes.
As described above, it was confirmed that the equivalent series resistance and leakage current can be suppressed by impregnating the capacitor element 10 with the oxidant and then with the monomer solution.

[Examples 2-7] (Comparative Examples 3-4) After impregnation with oxidant, impregnation with monomer solution In Examples 2-7 and Comparative Examples 3 and 4, the weight of ethylenedioxythiophene relative to butanol in the monomer solution Only the ratio is different, and the other conditions are the same as in the first embodiment.
Specifically, in Example 2, the weight ratio of butanol and ethylenedioxythiophene in the monomer solution was 10: 1. In Example 3, the weight ratio of butanol to ethylenedioxythiophene in the monomer solution was 5: 1.
In Example 4, the weight ratio of butanol and ethylenedioxythiophene in the monomer solution was 2: 1. In Example 5, the weight ratio of butanol and ethylenedioxythiophene in the monomer solution was 1: 2.
In Example 6, the weight ratio of butanol and ethylenedioxythiophene in the monomer solution was 1: 5. In Example 7, the weight ratio of butanol and ethylenedioxythiophene in the monomer solution was 1:10.
In Comparative Example 3, the weight ratio of butanol to ethylenedioxythiophene in the monomer solution was 15: 1. In Comparative Example 4, the weight ratio of butanol and ethylenedioxythiophene in the monomer solution was 1:15.

  The electrical characteristics (capacitance, equivalent series resistance, and leakage current) of the solid electrolytic capacitors obtained by the manufacturing methods of Examples 1 to 7 and Comparative Examples 3 and 4 were measured. The results are shown in Table 2.

As shown in Table 2, the equivalent series resistance and leakage current of the solid electrolytic capacitors manufactured by the manufacturing methods of Examples 1 to 7 are smaller than those of the solid electrolytic capacitors manufactured by the manufacturing methods of Comparative Examples 3 and 4. Yes.
Thus, it was confirmed that the weight ratio of butanol and ethylenedioxythiophene in the monomer solution is preferably in the range of 1:10 to 10: 1.

  Further, in the examples, p-toluenesulfonic acid iron solution was used as an oxidizing agent, but known sulfonic acid-based metal salts other than p-toluenesulfonic acid iron solution (for example, naphthalenesulfonic acid ferric salt, triisopropylnaphthalene). (Sulfuric acid ferric salt) may be used as an oxidizing agent.

  Furthermore, in the examples, ethylenedioxythiophene was used as the monomer, but known solutions other than ethylenedioxythiophene (for example, aniline, pyrrole, and derivatives thereof) may be used as the monomer.

  In addition, in the examples, butanol was used as a diluent solvent, but a known diluent solvent (for example, ethanol or methanol) in which an oxidizing agent other than butanol is dissolved may be used.

  Further, in the examples, a solid electrolytic capacitor having a wound capacitor element has been described, but the present invention is also applicable to a laminated capacitor element of aluminum foil and a solid electrolytic capacitor having a sintered body of tantalum or niobium. Is possible.

It is a disassembled perspective view of the capacitor | condenser element by this invention. It is a figure which shows roughly the laminated structure of a solid electrolytic capacitor. It is a figure which shows the manufacturing process of a solid electrolytic capacitor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solid electrolytic capacitor 2 Anode foil 2a Anodized film 3 Cathode foil 3a Natural oxide film 4 Separator 5 Solid electrolyte 6 Lead wire 10 Capacitor element

Claims (5)

A capacitor element forming step of forming a capacitor element having an anode body having an anodized film formed on the surface;
An oxidizing agent impregnation step of impregnating the capacitor element with an oxidizing agent;
After the oxidant impregnation step, a monomer impregnation step of impregnating the capacitor element with a monomer diluted with a diluting solvent capable of dissolving the oxidant;
A solid electrolyte forming step of forming a solid electrolyte made of a conductive polymer on the oxide film by chemically polymerizing the oxidant impregnated in the capacitor element and the monomer. A method for manufacturing a solid electrolytic capacitor.   2. The method of manufacturing a solid electrolytic capacitor according to claim 1, wherein a weight ratio of the dilution solvent and the monomer is in a range of 1:10 to 10: 1.   3. The oxidizing agent according to claim 1, wherein the oxidizing agent is any one of p-toluenesulfonic acid ferric salt, naphthalenesulfonic acid ferric salt, and triisopropyl naphthalenesulfonic acid ferric salt. The manufacturing method of the solid electrolytic capacitor of description.   The method for producing a solid electrolytic capacitor according to any one of claims 1 to 3, wherein the monomer is any one of aniline, pyrrole, thiophene, and derivatives thereof. The method for producing a solid electrolytic capacitor according to claim 1, wherein the thiophene derivative is ethylenedioxythiophene.

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