JPH0642446B2 - Method for manufacturing solid electrolytic capacitor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a solid electrolytic capacitor having good performance in which a lead dioxide layer is formed on a dielectric film layer by chemical deposition.

2. Description of the Related Art A solid electrolytic capacitor using lead dioxide as a conductive substance is known, as described in, for example, Japanese Patent Publication No. 58-21414. However, in the conventional solid electrolytic capacitor described above, since the method of forming lead dioxide on the dielectric film layer is a method of thermally decomposing the reaction mother liquor containing lead ions, the dielectric film (oxide film) is formed. Has a problem that it is thermally cracked and is chemically damaged by the generated gas. Therefore, when a voltage is applied to this solid electrolytic capacitor, current may concentrate on the defective portion of the dielectric film, causing dielectric breakdown. Therefore, in order to increase the reliability of the withstand voltage, the formation voltage should be 3 to 5 of the rated voltage.
However, there is a problem in that a large anode body having a large surface area must be used in order to obtain a predetermined capacity.

In order to prevent such a defect, for example, JP-A-54-124
As described in Japanese Patent Publication No. 47, first, manganese nitrate is thermally decomposed to form a manganese dioxide layer on the oxide film layer, and then a solution containing lead ions and persulfate ions at an extremely low concentration is formed. In addition, a method of providing a lead dioxide layer on the manganese dioxide layer by chemical deposition is known. However, since this method causes a thermal reaction when forming the manganese dioxide layer, thermal cracking of the dielectric film and chemical damage due to generated gas are unavoidable.

In addition, as described in Japanese Patent Publication No. 49-29374,
It is known to form a lead dioxide layer on the dielectric film layer by chemical deposition. However, this method requires silver ions as a catalyst when chemically precipitating lead dioxide, so that there is a problem that silver or a compound of silver is attached to the surface of the dielectric film, and the insulation resistance is reduced. is there.

From this point of view, the present inventors have made use of a conductive material of lead dioxide on the dielectric film layer without utilizing a thermal decomposition reaction and without using a catalyst such as silver ion which adversely affects the performance of the capacitor. We proposed a method for producing a solid electrolytic capacitor whose layer was formed by chemical deposition from a reaction mother liquor containing lead ions and persulfate ions (Japanese Patent Application No. 60-193185).

However, the solid electrolytic capacitor obtained by this method, the method of forming lead dioxide on the dielectric film layer is pre-mixed with a compound giving a lead ion and a compound giving a persulfate ion to prepare a reaction mother liquor, Since it is a method of coating on the dielectric film layer or dipping the dielectric film in this reaction mother liquor, the conductivity of the lead dioxide conductive material layer and the value of the dielectric loss tangent of the capacitor are not always satisfactory. It shouldn't be.

In recent years, in some application fields, it has been desired to further improve the conductivity of the conductive material layer of the solid electrolytic capacitor and reduce the value of the dielectric loss tangent.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention An object of the present invention is to reduce the cost, to utilize a thermal decomposition reaction, and without using a catalyst that adversely affects the performance of a capacitor, such as a silver catalyst, on a dielectric film layer. Another object of the present invention is to provide a method of manufacturing a solid electrolytic capacitor having a small dielectric loss tangent, which is obtained by chemically forming lead dioxide.

Means for Solving the Problems As a result of various studies to solve the above-mentioned drawbacks of the prior art, the present inventors have defined a coating order of a solution containing an oxidant and a solution containing a lead-containing compound, and defined a chemical order. The present invention has been found out that the above-mentioned object can be achieved extremely effectively and a solid electrolytic capacitor having good performance can be obtained by using lead oxide that is deposited as a conductive material layer.

That is, according to the present invention, in producing a solid electrolytic capacitor using lead dioxide as a conductive substance, a solution containing an oxidizing agent is applied on the dielectric film layer, and then a solution containing a lead-containing compound is applied. Then, there is provided a method for producing a solid electrolytic capacitor, characterized in that lead dioxide is formed on the dielectric film layer by chemical deposition.

The dielectric film in the present invention means an oxide film of a valve metal foil such as aluminum, tantalum, niobium or a sintered body, which is well known in the art, and can be obtained by a known method.

One component for forming a lead dioxide conductive material on the dielectric film by chemical deposition is a solution containing an oxidant.

The solvent used to prepare the solution containing the oxidizing agent may be any solvent that dissolves the oxidizing agent, and generally water or an organic solvent is used.

Typical examples of the oxidizing agent include quinone, chloranil,
Pyridine-N-oxide, dimethyl sulfoxide,
Chromic acid, potassium permanganate, selenium oxide, mercury acetate, vanadium oxide, sodium chlorate, hydrogen peroxide,
Sodium persulfate, potassium persulfate, ammonium persulfate,
Examples include ferric chloride. You may use 2 or more types of these oxidizing agents. The oxidizing agent may be appropriately selected depending on the solvent used. The use ratio of the oxidizing agent is preferably within the range of 3 to 0.3 times the molar amount of the lead-containing compound in the solution containing the lead-containing compound to be used subsequently. The ratio of the oxidizing agent used is 3 of the molar amount of the lead-containing compound used.
When the amount is more than twice the molar amount, the unreacted oxidizing agent remains, resulting in high cost, and when the amount is less than 0.3 times the molar amount, the unreacted lead-containing compound remains and the electrical conductivity is deteriorated, which is not preferable.

The other component used to form lead dioxide conductive material on the dielectric film by chemical deposition is a solution containing a lead-containing compound.

The solvent used for preparing the solution containing the lead-containing compound may be any solvent as long as it dissolves the lead-containing compound, and generally water or an organic solvent is used.

Representative examples of lead-containing compounds used include, for example, oxine, acetylacetone, pyromeconic acid, salicylic acid,
Alizarin, polyvinyl acetate, porphyrin compounds,
Lead-containing compounds in which lead atoms are coordinate-bonded or ionic-bonded to chelate-forming compounds such as crown compounds and cryptate compounds, lead citrate, lead acetate, basic lead acetate,
Examples thereof include lead borofluoride, lead acetate hydrate and lead nitrate.
Two or more kinds of these lead-containing compounds may be used. The lead-containing compound is appropriately selected depending on the solvent used.
The concentration of the lead-containing compound used is preferably within the range of 0.05 mol / concentration from the concentration giving the saturated solubility. The concentration of the lead-containing compound in the solution containing the lead-containing compound is 0.05
If it is lower than mol / mol, the concentration of the lead-containing compound is too low, so that it is necessary to increase the number of times of coating. Further, when the concentration of the lead-containing compound in the solution containing the lead-containing compound exceeds the saturation solubility, the merit of increasing the addition amount is not recognized.

The method for producing a solid electrolytic capacitor of the present invention comprises applying a solution containing an oxidant to a valve metal such as aluminum having a dielectric film, tantalum, or niobium, and then applying a solution containing a lead-containing compound. After each solution is allowed to enter the dielectric film and left to stand, it is washed and dried. The temperature for leaving it is not generally determined, but generally a temperature of room temperature to 100 ° C. is preferable. Alternatively, the valve action metal having the dielectric film may be sequentially dipped in the solution to be manufactured by the same method as described above. The coating in the present invention is called coating including this dipping method.

In the present invention, even if the solution containing the lead-containing compound is applied and then the solution containing the oxidant is applied, a solid electrolytic capacitor having good performance cannot be obtained.

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

Since the lead dioxide layer can be formed on the dielectric coating layer without heating to a high temperature, there is no risk of damaging the dielectric coating of the anode and there is no need to perform anodic oxidation (reformation) for repair. Therefore, the rated voltage can be raised several times higher than before, and to obtain a capacitor with the same capacity and rated voltage,
The shape can be made smaller than the conventional one.

Small leakage current.

A high breakdown voltage capacitor can be manufactured.

The electrical conductivity of lead dioxide is 7 × 10 ⁻¹ to 10 ¹ s · cm ^{−1, which} is sufficiently high so that the impedance is low.

Good high frequency characteristics.

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 An aluminum foil having a thickness of 100 μm (purity 99.99%) was used as an anode, and the surface of the foil was electrochemically etched by alternating use of direct current and alternating current to have an average pore diameter of 2 μm and a specific surface area of 12 m ² / g. And Next, this etched aluminum foil was electrochemically treated in a solution of ammonium borate to form a thin layer (alumina) of a dielectric material on the aluminum foil.

An aqueous solution of ammonium persulfate having a concentration of 2.0 mol / ammonium persulfate is applied to the above-mentioned dielectric thin layer, and then an aqueous solution of lead acetate having a concentration of 1.5 mol / mole of lead acetate is applied,
When left at 90 ° C. for 40 minutes, a lead dioxide layer was formed on the thin dielectric layer. After thoroughly washing the lead dioxide layer with water,
It was 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. Next, the lead wire was soldered and then packaged to form a solid electrolytic capacitor.

Example 2 In Example 1, an alcohol solution of selenium oxide having a selenium oxide concentration of 0.3 mol / min was used in place of the ammonium persulfate aqueous solution, and a lead oxine concentration of 0.2 mol / lead was used instead of the lead acetate aqueous solution. A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the chloroform solution of was used.

Comparative Example 1 A solid electrolytic capacitor was prepared by forming lead dioxide on an aluminum foil having the same dielectric layer as that of Example 1 by thermal decomposition of conventionally known lead nitrate.

Comparative Example 2 A solid electrolytic capacitor was produced in the same manner as in Example 2 except that the alcohol solution of selenium oxide and the chloroform solution of lead oxine in Example 2 were mixed and immediately applied to the dielectric film.

Claims (1)

[Claims] 1. A method for producing a solid electrolytic capacitor using lead dioxide as a conductive substance, a solution containing an oxidizing agent is applied on a dielectric film layer, and then a solution containing a lead-containing compound is applied, A method for producing a solid electrolytic capacitor, characterized in that lead dioxide is formed on the dielectric film layer by chemical deposition.