JP2657932B2 - Method for manufacturing solid electrolytic capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a method for manufacturing a solid electrolytic capacitor using a conductive polymer film as a solid electrolyte.

(Prior Art) In recent years, as a solid electrolytic capacitor responding to the demand for miniaturization and high performance, Japanese Patent Application Laid-Open No. 60-244017 or Japanese Patent Application Laid-open No.
There is one disclosed in Japanese Patent Publication No. 08-No.

In the technology disclosed in these publications, an anode body obtained by forming a valve action metal having a roughened surface and forming an oxide film is immersed in an electrolytic solution as an anode and energized to form an oxide film on the oxide film. Although the electropolymerized film is used as a solid electrolyte, since the oxide film is an insulator, effective energization with the cathode is not performed, and current concentrates on a defective portion of the oxide film or where the distance from the cathode is short. It has been extremely difficult to obtain a uniform electrolytic polymerized film as a solid electrolyte.

Therefore, the anode body is immersed in, for example, a pyrrole solution, and then a chemical oxidative polymerization method is performed by immersing the anode body in an oxidizing agent solution. The electrolytic oxidation polymerization is performed in the inside to form an electrolytic polymerization film integrated with the oxide film via the chemical polymerization film.

However, in general, chemical oxidative polymerization is performed at room temperature. At this time, the outflow time of the pyrrole solution into the oxidant solution is extremely shorter than the formation time of the chemical polymerization film at the interface between the pyrrole solution and the oxidant solution and in the pits. Due to the short length, uniform and sufficient formation of the chemically polymerized film on the oxide film surface was not performed,
The capacity appearance rate was low. In addition, since the particulate polymer formed by the polymerization of pyrrole diffused in the oxidizing agent solution in the oxidizing agent solution adheres to the chemically polymerized film formed on the oxide film surface, the chemically polymerized film is thin. A uniform film has a state in which there are particulate protrusions. Therefore, the electrolytic oxidation polymerization performed in the next step is performed using the chemically polymerized film having the thin, non-uniform, and particulate projections as an anode. , An electric field concentration is generated there, and a current flows toward the electric field, and selectively occurs at the protrusion. For this reason, the formed electropolymerized film is very uneven, leaving very thin portions and portions that are not formed at all, and wraps the entire surface of the anode body on average through the chemical polymerized film. Cannot obtain the desired electrolytic polymerized film, deteriorating the tan δ characteristics. In addition, during the subsequent formation of the graphite and silver paste layers, graphite and silver paste penetrate from the insufficiently formed electrolytically polymerized film and directly oxidize. This causes deterioration of leakage current characteristics and occurrence of short-circuit failure due to contact with the film surface.

In addition, since the adhesion between the chemically polymerized film and the oxide film is generally poor, where the formation of the electrolytic polymerized film is insufficient, the chemical polymerized film and the oxide film are peeled off with time, and the capacitance and tanδ characteristics This causes deterioration of life characteristics.

(Problems to be Solved by the Invention) As described above, a solid electrolytic capacitor using a conductive polymer film as a solid electrolyte is worthy of attention as meeting the demand for miniaturization and high performance. There is a problem to be solved in forming a desired electrolytic polymerized film.

The present invention has been made in view of the above points, and is a method of manufacturing a solid electrolytic capacitor capable of forming an excellent chemically polymerized film on an oxide film constituting an anode body, which is a condition for obtaining a desired electrolytic polymerized film. The purpose is to provide.

[Constitution of the Invention] (Means for Solving the Problems) In the method for manufacturing a solid electrolytic capacitor of the present invention, a chemical polymerization film is formed by chemical oxidation polymerization on an oxide film formed on a valve metal, and then the chemical polymerization is performed. In a method of manufacturing a solid electrolytic capacitor in which an electrolytic polymerized film is formed on a film by electrolytic oxidation polymerization, the valve action metal having the oxide film formed thereon is immersed in a solution of a five-membered heterocyclic compound comprising pyrrole, thiophene or furan, and thereafter The chemical oxidative polymerization is immediately performed in an oxidant solution at a temperature lower than at least the compound solution.

(Action) According to the above configuration, the solution of the complex five-membered ring compound is oxidized during the chemical oxidative polymerization performed by immersing the anode body in the solution of the five-membered heterocyclic compound and immediately immersing it in the solution of the oxidant. It hardly diffuses into the solution, the polymerization is carried out at once at the interface between the heteropentacyclic compound solution and the oxidizing agent solution on the surface of the anode body, and then held in the pits by the oxidizing solution that has permeated sequentially. Since all of the five-membered heterocyclic compounds are also polymerized in the pits, a uniform and sufficient chemically polymerized film is formed on the entire surface of the anode body including the pits. In addition, because there is no diffusion of the five-membered heterocyclic compound into the oxidizing agent solution,
The particulate polymer does not adhere to the chemically polymerized film formed on the surface of the anode body, and the surface of the obtained chemically polymerized film is extremely smooth without protrusions.

Therefore, it greatly contributes to the formation of a uniform electrolytic polymerized film by the subsequent electrolytic oxidative polymerization, and the resulting electrolytically polymerized film is integrated with the oxide film in a state of wrapping the entire surface of the anode body on average through the chemical polymerized film. It becomes a thing.

(Example) An example of the present invention will be described below. That is, as shown in FIG. 1, the anode foil 2 made of, for example, high-purity aluminum, having an oxide film 1 formed on the surface through a chemical conversion step by etching to increase the surface area, is immersed in pyrrole, thiophene, or a furan / ethanol aqueous solution for 5 minutes After that, the film is further immersed in an aqueous solution of ammonium persulfate at least lower than the aqueous solution of pyrrole, thiophene, or furan / ethanol to perform chemical oxidation polymerization to form a chemical polymerization film 4 made of a conductive polymer on the oxide film 1. Thereafter, the anode foil 2 on which the chemically polymerized film 4 is formed is formed.
Is immersed in an electrolytic solution containing a supporting electrolyte and a five-membered heterocyclic compound such as pyrrole, thiophene or furan, and subjected to electrolytic oxidative polymerization to form a conductive electrolytic polymer film 5 on the chemical polymer film 4.
Generate Next, a colloidal carbon or silver paste is applied and baked on the electrolytic polymerized film 5 to form a cathode layer 6, a cathode lead (not shown) is attached to the cathode layer 6, and finally, the exterior is covered. It is something that is given.

According to the method for manufacturing a solid electrolytic capacitor having the above-described configuration, it is possible to form a uniform and sufficiently smoothed chemical polymer film 4 on the anode foil 2, and the electrolytic polymer film 5 as a solid electrolyte obtained by electrolytic oxidation polymerization. Can be formed uniformly and sufficiently on the entire surface of the anode foil 2 via the chemical polymerized film 4 with the oxide film 1 to improve the capacitance and the tan δ characteristics, and the graphite and silver paste can be formed. Without directly contacting the oxide film 1, it greatly contributes to the improvement of leakage current characteristics and short-circuit failure.

Further, since the electrolytically polymerized film 5 wraps around the uniformized chemically polymerized film 4 and is formed uniformly, the adhesion of the chemically polymerized film 4 to the oxide film 1 via the electrolytically polymerized film 5 is improved, and there is little change over time and the life is short. It greatly contributes to the improvement of characteristics.

Next, comparison of various characteristics between the solid electrolytic capacitor obtained by the present invention and the solid electrolytic capacitors obtained by the conventional example and the comparative example will be described.

The following table shows a comparison of the characteristics of the solid electrolytic capacitors rated at 10V-3 μF according to Examples A to C, Conventional Example D and Comparative Example E described below. FIGS. 2 to 4 show the characteristics at 105 ° C. It shows life characteristics with respect to time.

The values in the table excluding short-circuit defects are the average values of 100 samples, and the values in parentheses indicate variations.

Example A (1) Chemical oxidative polymerization conditions After immersing a chemically treated aluminum anode foil in a pyrrole / ethanol solution at 45 ° C. for 5 minutes, 0.05 mol / mol of tetraethylammonium paratoluenesulfonate was used as a supporting electrolyte.
l in a 0.1 mol / l aqueous solution of ammonium persulfate at 10 ° C
Soak for a minute.

(2) Capacitor element shape Flat plate shape (3) Electrolytic oxidation polymerization conditions Immersion in an electrolytic solution composed of acetonitrile containing 1 mol / l of pyrrole monomer and 1 mol / l of tetraethylammonium paratoluenesulfonate as a supporting electrolyte, and constant-current oxidative polymerization ( 1 mA / cm ² for 30 minutes).

Example B (1) Chemical Oxidation and Polymerization Conditions After immersing a chemical conversion-treated aluminum anode foil in a pyrrole / ethanol solution at 35 ° C. for 5 minutes, 0.05 mol / mol of tetraethylammonium paratoluenesulfonate was used as a supporting electrolyte.
l in a 0.1 mol / l aqueous solution of ammonium persulfate at 10 ° C
Soak for a minute.

(2) Capacitor element shape Same as Example A (3) Electrolytic oxidation polymerization conditions Same as Example A Example C (1) Chemical oxidation polymerization conditions Aluminum anode foil chemically treated with a pyrrole / ethanol solution at 15 ° C. for 5 minutes After immersion, 0.05 mol / mol of tetraethylammonium paratoluenesulfonate as a supporting electrolyte
l in a 0.1 mol / l aqueous solution of ammonium persulfate at 10 ° C
Soak for a minute.

(2) Capacitor element shape Same as Example A (3) Electrolytic oxidation polymerization conditions Same as Example A Conventional example D (1) Chemical oxidation polymerization conditions An aluminum anode foil chemically treated with a pyrrole / ethanol solution at 25 ° C. for 5 minutes After immersion, 0.05 mol / mol of tetraethylammonium paratoluenesulfonate as a supporting electrolyte
l in a 0.1 mol / l ammonium persulfate aqueous solution at 25 ° C containing
Soak for a minute.

(2) Capacitor element shape Same as Example A (3) Electrolytic oxidation polymerization conditions Same as Example A Comparative example E (1) Chemical oxidation polymerization conditions An aluminum anode foil chemically treated with a pyrrole / ethanol solution at 25 ° C. for 5 minutes After immersion, 0.05 mol / mol of tetraethylammonium paratoluenesulfonate as a supporting electrolyte
l in a 0.1 mol / l aqueous solution of ammonium persulfate at 40 ° C
Soak for a minute.

(2) Capacitor element shape Same as Example A (3) Electrolytic oxidation polymerization conditions Same as Example A As is clear from the above table, those according to Examples A to C have significantly improved capacitance, tan δ, and leakage current characteristics as compared with those according to Conventional Example D and Comparative Example E. Significant improvement effect of short-circuit failure is seen.

2 to 4, it can be seen that it contributes to the improvement of the life characteristics of the rate of change of capacitance and the tan δ, as well as to the significant improvement of the leakage current in the life characteristics.

Further, from the experimental results shown in the above table and FIGS. 2 to 4, the temperature of the heterocyclic five-membered ring compound solution and the temperature of the oxidizing agent solution become larger as the difference between the oxidizing agent solution and the heterocyclic five-membered ring compound solution becomes larger. It is effective on the initial characteristics and the life characteristics, and it is understood that when this relationship is reversed, it is less preferable than when there is no temperature difference between the two.

In the above-described embodiment, an example in which an aluminum foil is used as the anode foil has been described. However, the present invention can be applied to a case in which a valve action metal foil such as a tantalum foil or a niobium foil is used. It is needless to say that the present invention can be applied to a product obtained by winding a sintered body or by sintering a powder made of these valve action metals.

[Effects of the Invention] According to the present invention, a uniform, sufficient, and smooth chemical polymerized film can be formed on an anode foil, and an electrolytic polymerized film formed using the film as an anode can be formed uniformly and sufficiently. Thus, it is possible to obtain a method of manufacturing a solid electrolytic capacitor that can greatly contribute to improvement of initial characteristics and also contribute to improvement of life characteristics.

[Brief description of the drawings]

FIG. 1 is a partially cut-away schematic cross-sectional view showing a configuration of a capacitor element during manufacture according to an embodiment of the present invention, FIG. 2 is a time-capacitance change rate characteristic curve, and FIG. 3 is a time-tan δ characteristic curve. FIG. 4 is a time-leakage current characteristic curve. 1 ... oxide film, 2 ... anode foil 4 ... chemically polymerized film, 5 ... electrolytic polymerized film

Claims (1)

(57) [Claims] 1. A method for manufacturing a solid electrolytic capacitor, comprising: forming a chemically polymerized film by chemical oxidation polymerization on an oxide film formed on a valve metal and then forming an electrolytic polymerized film by electrolytic oxidation polymerization on the chemically polymerized film. The valve metal having the oxide film formed thereon is immersed in a solution of a five-membered heterocyclic compound comprising pyrrole, thiophene or furan, and then immediately subjected to chemical oxidative polymerization in an oxidant solution at least lower than the compound solution. A method for manufacturing a solid electrolytic capacitor, comprising: