JPH0719727B2 - Method for manufacturing solid electrolytic capacitor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a solid electrolytic capacitor having good performance in which lead dioxide formed by chemical deposition on a dielectric film layer is used as a semiconductor layer.

2. Description of the Related Art A solid electrolytic capacitor using lead dioxide as a semiconductor layer is known as described in, for example, Japanese Patent Publication No. 58-21414. However, in the conventional solid electrolytic capacitor described above, the method of forming lead dioxide on the dielectric film layer is a method of thermally decomposing it from a reaction mother liquor containing lead ions. 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 the rated voltage.
It has to be increased by 5 times, and there is a problem that a large anode having a large surface area cannot be used in order to obtain a predetermined capacity.

Further, as described in JP-B-49-29374, a method of forming a lead dioxide layer on a dielectric film layer by chemical deposition is known. 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.

As a method for solving such a drawback, a method of using a tetracyanoquinodimethane salt which is an organic semiconductor as a semiconductor layer is known (Japanese Patent Laid-Open No. 173928/1982, etc.). The cost of methane salt is extremely high, and since it is a salt, it is unstable to moisture.

The present inventors have previously provided a method for producing a solid electrolytic capacitor in which lead dioxide is formed on a dielectric film by chemical deposition from a reaction mother liquor containing extremely high concentrations of lead ions and persulfate ions (Patent application Sho 60-19318). However, according to this method, the stability of the reaction mother liquor for chemically precipitating lead dioxide is poor, and a solid electrolytic capacitor having a sufficiently satisfactory performance cannot be obtained.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The object of the present invention is to solve the above-mentioned drawbacks of the prior art, to use a solvent, such as a silver catalyst, which is low in cost, does not utilize a thermal decomposition reaction, and has a bad influence on the performance of a capacitor. Without,
It is an object of the present invention to provide a method of manufacturing a solid electrolytic capacitor in which a lead dioxide layer is formed on a dielectric film layer by chemical deposition from a reaction mother liquor with improved stability.

Means for Solving the Problems According to the present invention, in a method for producing a solid electrolytic capacitor having a semiconductor layer of lead dioxide formed by chemical deposition from a reaction mother liquor containing lead ions and persulfate ions,
The solid electrolytic capacitor, wherein the lead ion concentration in the reaction mother liquor is in the range of 0.1 mol / to the saturated solubility or less, and the molar ratio of persulfate ion to lead ion is in the range of 0.05 or more and less than 0.5. A method of manufacturing the same is provided.

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

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

There is no particular limitation on the lead ion species and vinegar sulfate ion species,
As typical examples of compounds giving lead ion species, for example, lead citrate, acetate, basic lead acetate, lead borofluoride, lead acetate hydrate, lead nitrate, lead chloride, lead bromide, lead perchlorate, Examples include lead chlorate, lead sulfamate, lead hexafluoride, and lead bromate. 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.

The lead ion concentration in the reaction mother liquor is 0.1 mol / to the saturated solubility or less, preferably 0.5 mol / to the saturated solubility or less. When the concentration of lead ions is lower than 0.1 mol / l, the lead ion concentration in the reaction mother liquor is too low, and there is a drawback that the number of times of coating must be increased. Further, when the concentration of lead ions exceeds the saturation solubility, the merit of increasing the amount is not recognized. On the other hand, the persulfate ion concentration in the reaction mother liquor is 0.05 or more in molar ratio with respect to lead ions.
Within the range of less than 5. When the concentration of persulfate ion is 0.8 or more in molar ratio with respect to lead ion, the stability of the reaction mother liquor deteriorates and a precipitate is deposited. When the concentration of persulfate ion is less than 0.05 in terms of molar ratio with respect to lead ion, the reaction does not proceed sufficiently and a solid electrolytic capacitor with good performance cannot be obtained.

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. You may adjust separately and may mix and use just before use.

Since the reaction mother liquor of the present invention is stable for several hours to several days, a large amount of the reaction mother liquor can be prepared and retained.

The solid electrolytic capacitor in the present invention, the reaction mother liquor is applied to a valve working metal such as aluminum, tantalum or niobium having a dielectric coating, or the valve working metal having a dielectric coating is immersed in the reaction mother liquor to obtain a reaction mother liquor. Is introduced into the dielectric film, reacted at room temperature, preferably heated and reacted, washed with water and dried.

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 film layer without heating to a high temperature, there is no risk of damaging the dielectric film of the anode, and there is no need to perform anodic oxidation (reformation) for repair. Therefore, the rated voltage can be increased several times that of the conventional one, and the size of the capacitor can be made smaller than that of the conventional one to obtain a capacitor having the same capacity and the same rated voltage.

 LC (leakage current) is small.

 A high breakdown voltage capacitor can be manufactured.

Since the electrical conductivity of lead dioxide is sufficiently high as 10 ^-1 to 10 ¹ S · cm ^-1 , its impedance is low.

 Good high frequency characteristics.

 tanδ (loss factor) is small.

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 Table 1.

Example 1 An aluminum foil (purity: 99.99%) having a thickness of 100 μm was used as an anode, and the surface of the foil was electrochemically etched by direct current to have an average pore diameter of 2 μm and a specific surface area of 12 m ² / g. The etched aluminum foil was then electrochemically treated in an aqueous solution of boric acid and ammonium borate to form a thin layer of dielectric (alumina) on the aluminum foil.

An aqueous solution of lead acetate trihydrate with a concentration of 4 mol / mol and an ammonium persulfate concentration of 1.2 mol / mol with a volume of 1: 1
To prepare a reaction mother liquor. The lead ion concentration of the reaction mother liquor is 2 mol /, and the molar ratio of persulfate ion to lead ion is 0.3. The obtained reaction mother liquor was stable, and no precipitate was formed even if left for 1 hour. This reaction mother liquor was applied to the above-mentioned aluminum foil having a dielectric coating layer and left at 80 ° C. for 30 minutes, whereby a lead dioxide layer was formed on the dielectric coating layer. Next, the lead dioxide layer was thoroughly washed with water to remove unreacted substances, and then dried under reduced pressure at 110 ° C. for 3 hours. A carbon paste was applied onto the lead dioxide layer and dried, and then a silver paste was applied and dried, the cathode was taken out with a copper wire, and the resin was sealed to produce a solid electrolytic capacitor.

Example 2 A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the concentration of ammonium persulfate for adjusting the reaction mother liquor (before mixing) was changed to 0.32 mol / in Example 1.

The lead ion concentration of the reaction mother liquor is 2 mol / mole, and the molar ratio of persulfate ion to lead ion is 0.08.

Example 3 In Example 1, an aqueous solution having a concentration of lead citrate of 0.5 mol / min was used in place of the aqueous solution of lead acetate trihydrate having a concentration of 4 mol / min.
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the reaction mother liquor prepared from an aqueous solution of 0.15 mol / sodium persulfate was used.

The lead ion concentration of the reaction mother liquor is 0.25 mol /, and the molar ratio of persulfate ion to lead ion is 0.3.

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

Comparative Example 2 The method described in JP-B-49-29374, that is,
A mixture of 250 ml of a solution of 0.3 mol of lead acetate dissolved in concentrated ammonium acetate, a saturated aqueous solution of ammonium persulfate (4 mol /) 1 and 8 × 10 ^-5 mol of silver nitrate was prepared as in Example 1. It was applied to an aluminum foil having a thin body layer, and a solid electrolytic capacitor was produced in the same manner as in Example 1. The lead ion concentration of the reaction mother liquor was 0.24 mol / mol, and the molar ratio of persulfate ion to lead ion was 4 / 0.3 (about 13.3).

Comparative Example 3 In Example 1, the concentration of the ammonium persulfate aqueous solution was 6 mol /
A reaction mother liquor was prepared in the same manner as in Example 1 except that The reaction mother liquor had a lead ion concentration of 2 mol / mol, and the molar ratio of persulfate ion to lead ion was 1.5. When the obtained reaction mother liquor was allowed to stand for 1 hour, a large amount of precipitate was generated. Then, using this reaction mother liquor, a solid electrolytic capacitor was produced in the same manner as in Example 1.

In this example, the capacitor using the aluminum foil as the anode body was described, but the capacitor of the present invention is
The present invention is not limited to such a structure, and the metal forming the anode may be another film forming metal such as tantalum or an alloy thereof. Further, it is not limited to such a foil type, and may be a porous body obtained by sintering a film-forming metal powder.

Further, as for the exterior structure, in this example, a resin-molded one was illustrated, but the exterior body uses a resin case, a metal exterior case, a resin dip, a laminate film exterior, or the like. However, this does not depart from the invention.

Claims (1)

[Claims] 1. A method for producing a solid electrolytic capacitor having a semiconductor layer of lead dioxide formed by chemical deposition from a reaction mother liquor containing lead ions and persulfate ions, wherein the concentration of lead ions in the reaction mother liquor is 0.1 mol. The method for producing a solid electrolytic capacitor is characterized in that the molar ratio of persulfate ion to lead ion is within a range of 0.05 or more and less than 0.5, and is within a range from / to a saturated solubility or less.