JP2008034440A - Method of manufacturing solid-state electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress an increase in leak current of a solid-state electrolytic capacitor. <P>SOLUTION: A capacitor element is provided with a positive electrode with an anodic oxide coating on its surface, and is formed (etching-chemical conversion of cut end/carbonization). The capacitor element is immersed in an oxidant solution to impregnate the capacitor element with the oxidant (oxidant impregnation), and then is immersed in a monomer solution to impregnate it with the monomer (monomer impregnation). In this case, at least either of the oxidant solution and the monomer solution is added with aromatic dicarboxylic acid or dicarboxylic acid salt. Next, the oxidant and the monomer impregnated in the capacitor element are chemically polymerized together, so as to form a solid electrolyte made of conductive high polymer on the oxide film (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 is an electrolytic capacitor in which a solid electrolyte having conductivity is used, and has excellent impedance characteristics in a high frequency region as compared with a liquid electrolyte. As the solid electrolyte, polyethylenedioxythiophene (PEDT), which is a conductive polymer, is widely used.

In this solid electrolyte, the capacitor element is immersed in a mixed solution of an oxidant solution and a monomer solution so that the capacitor element is impregnated with the oxidant and the monomer. A method of forming a solid electrolyte by accelerating the polymerization reaction is known.
At this time, a method of adding phthalic acid or phthalate to the mixed solution is known. By this method, the self-repairing property of the capacitor element can be improved and the leakage current can be reduced (for example, see Patent Document 1).

Japanese Patent Laid-Open No. 5-243098

  In the above-described technique, when phthalic acid or phthalate is added to the mixed solution of the oxidant solution and the monomer solution, the polymerization reaction starts from the time when the oxidant solution and the monomer solution are mixed. Phthalic acid or phthalate is used in the polymerization reaction. Therefore, when the capacitor element is immersed in the mixed solution, the amount of phthalic acid or phthalate is reduced, and the self-repairing property of the capacitor element cannot be sufficiently improved. For this reason, it is difficult to sufficiently suppress the increase in leakage current.

  An object of the present invention is to provide a method for manufacturing a solid electrolytic capacitor in which self-restorability is enhanced and an increase in leakage current is suppressed.

The method for producing a solid electrolytic capacitor according to the present invention includes a capacitor element forming step of forming a capacitor element having an anode body having an oxide film formed on a surface thereof, and immersing the capacitor element in an oxidant solution, thereby An oxidant impregnation step for impregnating the element with an oxidant; a monomer impregnation step for impregnating the capacitor element with a monomer by immersing the capacitor element in a monomer solution after the oxidant impregnation step;
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, and the oxidant An aromatic dicarboxylic acid or an aromatic dicarboxylic acid salt is added to at least one of the solution and the monomer solution.

  At this time, it is preferable that the concentration of the aromatic dicarboxylic acid or the aromatic dicarboxylic acid salt added to at least one of the oxidant solution or the monomer solution is in the range of 0.01 to 0.9 wt%.

In the present invention, the oxidizing agent may contain any one of p-toluenesulfonic acid, methoxybenzenesulfonic acid and dodecylbenzenesulfonic acid.
In addition, the monomer may contain aniline, pyrrole, thiophene, and any one of these dielectrics.

Further, the aromatic dicarboxylic acid may contain any one of phthalic acid, terephthalic acid and isophthalic acid.
Furthermore, the aromatic dicarboxylate salt may contain any one of ammonium salt, tertiary amine salt, secondary amine salt and primary amine salt.
In addition, the aromatic dicarboxylate may contain any one of trimethylamine, triethylamine, dimethylethylamine, diethylmethylamine, dimethylamine, methylethylamine, diethylamine, methylamine, ethylamine and propylamine.

  According to the present invention, the aromatic dicarboxylic acid or aromatic dicarboxylate is added to at least one of the oxidant solution or the monomer solution, so that the aromatic dicarboxylic acid or the aromatic dicarboxylate Before being used for the polymerization reaction with the monomer solution, it is used to enhance the self-healing property of the capacitor element. Thereby, an increase in leakage current can be suppressed.

  In addition, the inventors of the present invention, when the concentration of the aromatic dicarboxylic acid or aromatic dicarboxylic acid salt added to at least one of the oxidant solution or the monomer solution is in the range of 0.01 to 0.9 wt%, It has been found that an increase in leakage current of a solid electrolytic capacitor can be efficiently suppressed.

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, polythiophene, polyethylenedioxythiophene (PEDT) or the like can be used, and these are generated by chemical polymerization of an oxidizing agent and a monomer.
As shown in FIG. 1, 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.

Next, a method for manufacturing the solid electrolytic capacitor 1 will be described with further 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 the lead tabs, respectively. The cathode foil 3 is wound through the separator 4, and further, through cut formation and carbonization of the separator, the cylindrical capacitor element 10 is manufactured.

Next, this cylindrical capacitor element 10 is immersed in an oxidant solution to be impregnated with an oxidant and then dried (oxidant impregnation step). Thereafter, the capacitor element 10 is immersed in a monomer solution to which an aromatic dicarboxylic acid is added to impregnate the monomer (monomer impregnation step).
Subsequently, the impregnated oxidizing agent and the monomer are chemically polymerized by heating at a predetermined temperature in the polymerization tank for a certain period of time, and the conductive polymer is interposed between the anode foil 2 and the cathode foil 3 and the separator 4. A solid electrolyte 5 is formed (solid electrolyte formation step).

  Here, the self-repairing property of the capacitor element 10 can be improved by adding the aromatic dicarboxylic acid to the monomer solution. Thereby, an increase in leakage current can be suppressed.

  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 Example 1. In Example 1 and Comparative Example 1 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 the same. is there.
Hereinafter, only the process for forming the solid electrolyte will be described. In addition, all the rating of each solid electrolytic capacitor is 4.0V-560 micro F.

[Example 1]
In Example 1, the capacitor element 10 was impregnated with iron p-toluenesulfonate (oxidant) by immersing it in an iron p-toluenesulfonate solution (oxidant impregnation step), and then 30 ° C. at 30 ° C. Heated for minutes and dried. Thereafter, the capacitor element 10 is immersed in a 3,4-ethylenedioxythiophene solution having a phthalic acid concentration of 0.1 wt% to impregnate 3,4-ethylenedioxythiophene (monomer) (monomer impregnation step). Let me.
Furthermore, the capacitor element 10 is heated at 180 ° C. for 30 minutes, and PEDT, which is a conductive polymer, is generated by chemical polymerization of iron p-toluenesulfonate and 3,4-ethylenedioxythiophene to form the solid electrolyte 5. (Solid electrolyte forming step).
(Comparative Example 1)
In Comparative Example 1, the capacitor element 10 is immersed in a mixed solution in which iron p-toluenesulfonate having a phthalic acid concentration of 0.1 wt% and 3,4-ethylenedioxythiophene are mixed in advance. To impregnate iron p-toluenesulfonate and 3,4-ethylenedioxythiophene.
Further, the capacitor element 10 is heated at 180 ° C. for 30 minutes, and PEDT which is a conductive polymer is formed by chemical polymerization of iron p-toluenesulfonate and 3,4-ethylenedioxythiophene, thereby forming the solid electrolyte 5. did.

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

As shown in Table 1, the capacitance, tan δ, and equivalent series resistance of the solid electrolytic capacitors manufactured by the manufacturing methods of Example 1 and Comparative Example 1 are equivalent, but manufactured by the manufacturing method of Example 1. The leakage current of the manufactured solid electrolytic capacitor is smaller than the leakage current of the solid electrolytic capacitor manufactured by the manufacturing method of Comparative Example 1.
As described above, by immersing the capacitor element 10 in the oxidant solution, the increase in leakage current of the capacitor element 10 can be suppressed by immersing in the monomer solution to which phthalic acid has been added after impregnation with the oxidant. Was confirmed.

[Examples 2 to 4], (Comparative Examples 2 to 5)
In Examples 2 to 4 and Comparative Examples 2 to 5, only the concentration of phthalic acid in the monomer solution is different, and the other conditions are the same as in Example 1.
Specifically, in Example 2, the concentration of phthalic acid in the monomer solution was 0.01 wt%.
In Example 3, the concentration of phthalic acid in the monomer solution was 0.05 wt%. In Example 4, the concentration of phthalic acid in the monomer solution was 0.9 wt%.
In Comparative Example 2, the concentration of phthalic acid in the monomer solution was 0 wt%. That is, phthalic acid is not added to the monomer solution. In Comparative Example 3, the concentration of phthalic acid in the monomer solution was 0.005 wt%.
In Comparative Example 4, the concentration of phthalic acid in the monomer solution was 1.0 wt%. In Comparative Example 5, the concentration of phthalic acid in the monomer solution was 2.0 wt%.

  The electrical characteristics (capacitance, tan δ, equivalent series resistance, and leakage current) of the solid electrolytic capacitors obtained by the production methods of Examples 1 to 4 and Comparative Examples 2 to 5 were measured. The results are shown in Table 2.

As shown in Table 2, the capacitance, tan δ, and equivalent series resistance of the solid electrolytic capacitors produced by the production methods of Examples 1 to 4 and Comparative Examples 2 to 5 were equivalent values. Moreover, the leakage current of the solid electrolytic capacitor manufactured by the manufacturing method of Examples 1-4 is smaller than the leakage current of the solid electrolytic capacitor manufactured by the manufacturing method of Comparative Examples 2-5.
Thus, it was confirmed that the concentration of phthalic acid in the monomer solution is preferably in the range of 0.01 to 0.9 wt%.

  In the examples described above, phthalic acid is added to the monomer solution, but the same effect can be obtained when phthalic acid is added to the oxidant solution or the oxidant solution and the monomer solution instead of the monomer solution. It was confirmed that

  In the examples, PEDT is used as the solid electrolyte, but a known conductive polymer other than PEDT (for example, polyaniline, polypyrrole, and polythiophene) may be used as the solid electrolyte.

  In the examples, p-toluenesulfonic acid iron was used as an oxidizing agent, but known organic sulfonic acid metal salts (for example, methoxybenzenesulfonic acid, dodecylbenzenesulfonic acid) other than iron p-toluenesulfonate were used. It may be used as an oxidizing agent.

  Furthermore, in the examples, 3,4-ethylenedioxythiophene was used as a monomer, but known substances other than 3,4-ethylenedioxythiophene (for example, aniline, pyrrole, and dielectrics thereof) were used as monomers. May be.

In the examples, phthalic acid is added to the monomer solution, but terephthalic acid and isophthalic acid may be used instead of phthalic acid.
Furthermore, not only phthalic acid, terephthalic acid and isophthalic acid, but also ammonium salts, tertiary amine salts trimethylamine, triethylamine, dimethylethylamine and diethylmethylamine, secondary amine salts dimethylamine, methylethylamine and diethylamine, primary The amine salts ethylamine and propylamine may be used.

  Furthermore, in the examples, a solid electrolytic capacitor having a wound type 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 (7)

A capacitor element forming step of forming a capacitor element having an anode body with an oxide film formed on the surface;
An oxidant impregnation step of impregnating the capacitor element with an oxidant by immersing the capacitor element in an oxidant solution;
After the oxidant impregnation step, a monomer impregnation step of impregnating the capacitor element with a monomer by immersing the capacitor element in a monomer solution;
A solid electrolyte forming step of forming a solid electrolyte composed of a conductive polymer on the oxide film by chemically polymerizing the oxidant impregnated in the capacitor element and the monomer; and
An aromatic dicarboxylic acid or an aromatic dicarboxylate is added to at least one of the oxidant solution or the monomer solution.   The concentration of the aromatic dicarboxylic acid or the aromatic dicarboxylic acid salt added to at least one of the oxidant solution or the monomer solution is in a range of 0.01 to 0.9 wt%. 2. A method for producing a solid electrolytic capacitor according to 1.   The method for producing a solid electrolytic capacitor according to claim 1, wherein the oxidizing agent contains any one of p-toluenesulfonic acid, methoxybenzenesulfonic acid, and dodecylbenzenesulfonic acid.   The method for producing a solid electrolytic capacitor according to any one of claims 1 to 3, wherein the monomer contains aniline, pyrrole, thiophene, or any one of these dielectrics.   The method for producing a solid electrolytic capacitor according to any one of claims 1 to 4, wherein the aromatic dicarboxylic acid contains any one of phthalic acid, terephthalic acid, and isophthalic acid.   The said aromatic dicarboxylate salt contains any one of an ammonium salt, a tertiary amine salt, a secondary amine salt, and a primary amine salt, The any one of Claims 1-4 characterized by the above-mentioned. Manufacturing method for solid electrolytic capacitor.   The aromatic dicarboxylate salt contains any one of trimethylamine, triethylamine, dimethylethylamine, diethylmethylamine, dimethylamine, methylethylamine, diethylamine, methylamine, ethylamine and propylamine. The manufacturing method of the solid electrolytic capacitor of any one of 1-4.

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