JPH0727849B2 - Manufacturing method of solid electrolytic capacitor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a solid electrolytic capacitor in which an oxide film, a lead dioxide semiconductor layer, a carbon layer and / or a metal layer are sequentially provided on the surface of a metal having a valve action. And a solid electrolytic capacitor with improved tan δ (dielectric loss tangent), characterized in that the capacitor is heat-treated.

2. Description of the Related Art Some of the inventors of the present invention have previously found that the cost is low, the thermal decomposition reaction is not used, and a catalyst that adversely affects the performance of the capacitor, such as a silver catalyst, is not used for the chemical reaction on the oxide film layer. We proposed a solid electrolytic capacitor in which a lead dioxide semiconductor layer was provided by selective deposition, and a carbon layer and a metal layer were sequentially provided on the lead dioxide semiconductor layer.

However, in the case of the above-mentioned solid electrolytic capacitor having a high capacity, tan δ was not always sufficiently satisfactory.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention An object of the present invention is to form an oxide film, a semiconductor layer of lead dioxide, a carbon layer and / or a metal layer sequentially on the surface of a metal having a small tan δ even in a high capacity and having a valve action. It is to provide a solid electrolytic capacitor.

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to solve the drawbacks of the conventional solid electrolytic capacitors, and as a result, heat-treating the solid electrolytic capacitors at a specific temperature to effectively achieve the above object. The present invention has been completed and the present invention has been completed.

That is, the gist of the present invention is that an oxide film layer is formed on the surface of a metal having a valve action, and a semiconductor layer of lead dioxide is formed thereon by a chemical deposition method.
Alternatively, the method for producing a solid electrolytic capacitor is characterized in that after providing the metal layer, heat treatment is performed at a temperature of 40 ° C. or higher and 300 ° C. or lower.

The metal having a valve action used in the present invention is tantalum, niobium, aluminum or the like, which is obtained as a foil or a sintered body.

In the present invention, as a method of forming an oxide film on the surface of a metal having a valve action such as tantalum, niobium, aluminum or the like, a method known in the art can be adopted. Alternatively, a commercially available high-capacity chemical conversion foil, such as a high-voltage etched aluminum chemical foil or a low-voltage etched aluminum chemical foil, having an oxide film formed on the surface of a metal having a valve action may be used.

As a method of forming the lead dioxide semiconductor layer on the oxide film, for example, a so-called chemical deposition method is employed in which a reaction mother liquor containing lead ions and persulfate ions is chemically oxidized on the oxide film layer.

An aqueous solution containing lead ions and persulfate ions is used as a reaction mother liquor for forming a lead dioxide semiconductor layer on the oxide film layer by chemical deposition.

There are no particular restrictions on the lead ion species and persulfate ion species,
Representative examples of compounds that give lead ion species include lead citrate, lead acetate, basic lead acetate, lead borofluoride, lead acetate hydrate, and the like. On the other hand, typical examples of the compound that gives a persulfate ion species include ammonium persulfate, potassium persulfate, and sodium persulfate. Two or more kinds of these compounds giving the lead ion species and the persulfate ion species may be mixed and used.

Lead ion concentration in the reaction mother liquor is from 7 mol / l to 0.1 mol / l
It is desirable to be in the range of 1, preferably 5 to 1.3 mol / l. If the concentration of lead ions is higher than 7 mol / l, the viscosity of the reaction mother liquor becomes too high, which makes it difficult to use, and if the concentration of lead ions is lower than 0.1 mol / l, the lead mother liquor in the reaction mother liquor is reduced. Since the ion concentration is too low, there is a drawback that the number of times of coating must be increased. On the other hand, the concentration of persulfate ions in the reaction mother liquor is preferably within the range of 5 to 0.5 in terms of molar ratio with respect to lead ions. If the concentration of persulfate ion is more than 5 with respect to lead ion in molar ratio, unreacted persulfate ion remains, resulting in high cost.
Also, the concentration of persulfate ion is 0.
If it is less than 5, unreacted lead ions remain and the electrical conductivity deteriorates, which is not preferable.

The reaction mother liquor may be used by dissolving a compound giving a lead ion species and a compound giving a persulfate ion species in water at the same time, or an aqueous solution of a compound giving a lead ion species and a compound giving a persulfate ion species in advance. They may be prepared separately and mixed immediately before use.

To provide a lead dioxide semiconductor layer on the oxide film layer, a valve action metal having an oxide film is immersed in a reaction mother liquor (an aqueous solution containing lead ions and persulfate ions), or a valve action compound having an oxide film is formed. A method in which a reaction mother liquor is applied to a metal, the reaction mother liquor is allowed to enter the oxide film, left to stand, and then washed with water and dried is adopted.

In the present invention, a part of the lead dioxide semiconductor layer penetrates into the pores of the valve metal foil or the oxide film of the sintered body.

Next, a carbon layer and / or a metal layer is provided on the lead dioxide semiconductor layer. As a method for providing the carbon layer on the lead dioxide semiconductor layer, a conventionally known method is adopted. As a method of providing the metal layer on the carbon layer, for example, a method of applying a paste containing silver, aluminum, copper or the like, or a method of depositing silver, aluminum, copper or the like can be mentioned.

The solid electrolytic capacitor thus obtained is then heat treated. The heat treatment temperature is 40 ° C or higher and 300 ° C or lower, preferably 7
It is 0 ° C or higher and 300 ° C or lower. When the heat treatment temperature is lower than 40 ° C., the treatment time is extremely long, which is not practical, and when the heat treatment temperature is higher than 300 ° C., the lead dioxide conductor layer causes decomposition, which is not preferable.

The heat treatment time varies depending on the heat treatment time and cannot be determined unconditionally, but it is usually several hours, preferably 1 to 5 hours.

The heat treatment in the present invention uses a high-capacity conversion foil (for example, a low-voltage etched aluminum conversion foil) and is particularly suitable for a solid electrolytic capacitor in which a lead dioxide semiconductor layer, a carbon layer and / or a metal layer are sequentially provided on the conversion foil. It is effective.

Effects of the Invention The solid electrolytic capacitor manufactured by the method of the present invention has the following advantages over the conventionally known solid electrolytic capacitors.

Small leakage current.

Tanδ is small even with high capacity.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. The characteristic values of the solid electrolytic capacitors of each example are shown in the table.

Example 1 A reaction mother liquor was obtained by mixing an aqueous solution having a lead acetate concentration of 2.0 mol / l and an aqueous solution having a potassium persulfate concentration of 2.5 mol / l at a volume ratio of 1: 1. Immediately apply this reaction mother liquor to a 4 cm long, 0.3 cm wide low-pressure etched aluminum conversion foil (capacity is approximately 8 μF / cm ² when using an electrolyte solution of ethylene glycol and ammonium adipate) and apply it under reduced pressure. When left for 3 hours, a lead dioxide layer was formed on the formed foil. Then, the lead dioxide layer was thoroughly washed with water and then dried under reduced pressure at 110 ° C. for 3 hours. A carbon paste was applied on the lead dioxide layer and dried, and then a silver paste was further applied and dried. An aluminum foil was used as the cathode, and the resin was sealed to produce a solid electrolytic capacitor.

Then, this solid electrolytic capacitor was placed in a thermostatic chamber at 110 ° C for 4 hours.
Left for hours.

Comparative Example 1 A solid electrolytic capacitor was produced in the same manner as in Example 1 except that heat treatment was not performed at 110 ° C. in Example 1.

Example 2 A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the carbon layer was not provided on the lead dioxide layer in Example 1.

Claims (1)

[Claims] 1. An oxide film layer is formed on the surface of a metal having a valve action, a lead dioxide semiconductor layer is formed thereon by a chemical deposition method, and a carbon layer and / or a metal layer is further provided. A method for producing a solid electrolytic capacitor, characterized by performing heat treatment at a temperature of 40 ° C or higher and 300 ° C or lower.