JP2810100B2 - Method for manufacturing solid electrolytic capacitor - Google Patents

Description

The present invention relates to a method for manufacturing a solid electrolytic capacitor having good high-frequency performance.

[Conventional technology]

The solid electrolytic capacitor has a structure in which a solid electrolyte is attached to a valve metal such as aluminum, tantalum, or niobium having a dielectric oxide film on the surface.

Conventionally, manganese dioxide formed mainly by thermal decomposition of manganese nitrate has been used as a solid electrolyte of this type of solid electrolytic capacitor. However, the high heat required during this thermal decomposition and the oxidizing action of the generated NO ₂ gas, etc., damage the dielectric oxide film such as aluminum and tantalum, which lowers the withstand voltage and reduces the leakage current. It has a large drawback, such as an increase in the dielectric properties. Also, several steps of re-chemical formation are required.

In order to compensate for these disadvantages, a method of forming a solid electrolyte without applying high heat, that is, a method of using a polymer semiconductor material having high conductivity as a solid electrolyte has been attempted. As an example, a solid electrolytic capacitor using a conductive polymer obtained by doping a polymer obtained by polymerizing a monomer represented by the following general formula (I) with a dopant is known. .

As a method for producing a solid electrolytic capacitor using a conductive polymer compound of this type as a solid electrolyte, a method of producing the same by electrolytic polymerization in a solution in which a monomer represented by the general formula (I) is dissolved is also known. I have.

[Problems to be solved by the invention]

However, when a solid electrolyte is formed by the above-described electrolytic polymerization, electric current also passes through a dielectric oxide film described later, so that a pinhole is generated in the film, and as a result, a leakage current value of the manufactured solid electrolytic capacitor is obtained. Requires a process for lowering the temperature. In general, as the size of the pinhole increases, it becomes difficult to reduce the leakage current, or a very long time is required.

[Means for solving the problem]

The present invention has been made to solve the above-mentioned problems, and has been made by the general formula (I) In producing a solid electrolytic capacitor using a conductive polymer compound obtained by doping a polymer compound obtained by polymerizing a monomer represented by the above with a dopant as a solid electrolyte, the dielectric formed on the surface of the valve action metal A method for manufacturing a solid electrolytic capacitor, wherein the solid electrolyte is formed on a body oxide film by electrolytic polymerization in an electrolyte in which a nonmetallic conductive substance is suspended.

 Hereinafter, the present invention will be described in detail.

As the valve action metal used as the anode of the solid electrolytic capacitor in the present invention, any metal having a valve action such as aluminum, tantalum, niobium, titanium and an alloy using the same as a substrate can be used.

The dielectric oxide film provided on the surface of the valve action metal may be an oxide layer of the valve action metal itself provided on the surface portion of the valve action metal, or may be an oxide layer provided on the surface of the valve action metal. May be used, but it is particularly preferably a layer made of an oxide of the valve metal itself. In any case, as a method of providing an oxide layer,
A conventionally known method such as an anodizing method using an electrolytic solution can be used.

Next, the monomer used in the present invention has the structure of the above general formula (I).

Representative examples include thiophene, pyrrole, furan, N-
Methylpyrrole, 3-methylthiophene and the like are mentioned. Two or more of these monomers may be used. In the electropolymerization, the above-mentioned monomer is dissolved, the formed valve action metal is immersed in an appropriate electrolyte solution in which a nonmetallic conductive substance is suspended, and an electrolytic reaction is performed with a separately prepared cathode. Thereby, a polymer compound is deposited on the surface of the valve metal. In this case, the monomer is doped at the same time as the polymerization because the electrolyte ion in the electrolyte serves as a dopant, and becomes a conductive polymer compound.

As the nonmetallic conductive substance used in the present invention, those having an electric conductivity of 10 Scm ^-1 or more are preferable, and typical examples thereof include graphite carbon, a substance mainly containing carbon such as carbon fiber, and polythiophene. And conductive polymer powders such as polypyrrole. Substances having an electric conductivity of less than 10 S · cm ⁻¹ , for example, metal oxides such as manganese dioxide and lead dioxide have no effect, and metal powders have a problem in that the leakage current value becomes large.

The amount of floating conductive material cannot be specified unconditionally because it varies depending on the type of conductive material and the amount of electrolyte used, but it is generally sufficient to cover the formed valve metal that is immersed in the electrolyte. good.

As the electrolytic solution used in the present invention, a conventionally known electrolytic solution can be used. For example, propylene carbonate, ethylene carbonate, .gamma.-butyrolactone, acetonitrile, dimethylformamide, sulfolane, methyl sulfoxide, nitromethane, in a solvent such as water I ^-, Cl ^-, B
_{^{r -, F -, ClO 4}} -, BF 4 -, AsF 6 -, AsF 4 -, PF 6 -, F 3 CSO 4 -,
_{^{BCl 4 -, NO 3 -,}} POF 4 -, CN -, SiF 5 -, CH 3 COO -, C 6 H 5 CO
_{^{O -, CH 3 C 6 H}} 4 SO 4 -, C 6 H 5 SO 4 -, SO 4 -, SiF 6 2-, HF 2 - and the like electrolyte comprising an ammonium salt except alkali metal salts or halogen ions It is dissolved.

Further, the above-described conductive polymer compound is further doped with an electron acceptor such as I ₂ , Br ₂ , SO ₃ , AsF ₅ , SbF ₅ , toluenesulfonic acid, benzenesulfonic acid, or the like as a dopant using a chemical method. or, ^{_{or, BF 4 -, ClO 4 -}} , PF 6
^-, AsF ₆ ^-, toluenesulfonic acid ion, the anion may be used by doping using electrochemical methods such as benzenesulfonate ion.

The solid electrolyte used in the present invention is electric conductivity of 10 ⁰ ~10 ² S · cm
^{A value of -1} order is obtained, and the higher the electric conductivity, the lower the tan δ at a high frequency of the manufactured solid electrolytic capacitor, and the better it becomes.

The solid electrolytic capacitor according to the method of the present invention is obtained by taking out a cathode layer with a carbon paste and / or silver paste or the like on the above-mentioned solid electrolyte layer, and further sealing it with a conventionally known method such as a resin or a case to obtain a product. You.

[Operation] When the formed valve-action metal used as the anode of the solid electrolytic capacitor is immersed in the electrolyte in which the nonmetallic conductive material is suspended, the surface of the valve-action metal is covered with the nonmetallic conductive material. When electrolytic polymerization is performed in this state, current flows uniformly through the valve action metal, and even if a pinhole occurs in the dielectric oxide film formed on the surface of the valve action metal, it is a small pinhole. . Therefore, the pinhole can be easily repaired in a process of repairing the pinhole by aging later.

 Hereinafter, examples and comparative examples will be described.

Examples 1 to 6 1 cm small pieces of aluminum etching foil (hereinafter referred to as chemical conversion foil) (10 μF / cm ² ) having a dielectric oxide film formed on the surface by a chemical conversion treatment in an aqueous solution of phosphoric acid and ammonium phosphate.
120 sheets of × 1 cm were prepared, and 20 sheets were used for each example. The small pieces described above were immersed in a 0.05 MBu ₄ NBF ₄ —CH ₃ CN solution in which the monomer and the conductive substance shown in Table 1 were dissolved and suspended, respectively, and electrolytic polymerization was performed. After about 2 hours, the conductive polymer compound formed on the chemical conversion foil was sufficiently washed with water and dried. The conductivity of the formed solid electrolyte is
It was approximately 10 to 200 S · cm ⁻¹ . Next, the chemical conversion foil on which the solid electrolyte layer was formed was immersed in a silver paste bath to form a cathode layer, and then sealed with a resin to produce a solid electrolytic capacitor. Aging was performed for 2 hours.

Comparative Example 1 Pyrrole was dissolved as a monomer using 20 chemical conversion foils similar to those in the example. Except that the conductive substance was not suspended, a solid electrolyte was formed in the same manner as in the example to produce a solid electrolytic capacitor, and aging was also performed for 2 hours. The conductivity of the formed solid electrolyte was approximately 25 S · cm ⁻¹ .

Table 2 shows the performance of the solid electrolytic capacitor manufactured as described above.

[Effects of the Invention] As described above, according to the method for manufacturing a solid electrolytic capacitor of the present invention, when the solid electrolyte is formed by polymerization, the solid electrolyte is formed in an electrolytic solution in which a nonmetallic conductive substance is suspended. Even if the time is short, a solid electrolytic capacitor having a small leakage current value and good performance can be manufactured.

Claims (1)

(57) [Claims] 1. The compound of the general formula (I) When manufacturing a solid electrolytic capacitor using a conductive polymer compound obtained by doping a polymer compound obtained by polymerizing a monomer represented by the above with a dopant as a solid electrolyte, a dielectric formed on the surface of a valve action metal A method for producing a solid electrolytic capacitor, characterized in that the solid electrolyte is formed on a body oxide film by electrolytic polymerization in an electrolytic solution in which a nonmetallic conductive substance having a conductivity of 10 S · cm ⁻¹ or more is suspended.