JPS62257717A - Manufacture of solid electrolytic capacitor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a solid electrolytic capacitor with good performance, in which a conductive layer is made of lead dioxide formed by chemical precipitation on a dielectric film layer.

2. Description of the Related Art Solid electrolytic capacitors using lead dioxide as a conductive layer are known, for example, as described in Japanese Patent Publication No. 58-21414. However, in the conventional solid electrolytic capacitors described above, the method of forming lead dioxide on the dielectric film layer is to thermally decompose a reaction mother liquor containing lead ions. However, there is a problem that the metal can crack due to heat or even be chemically damaged by the generated gas. Therefore, when a voltage is applied to this solid electrolytic capacitor, current may concentrate at the defective portion of the dielectric film, causing dielectric breakdown. Therefore, in order to increase the reliability of the withstand voltage, the formation voltage must be increased to 3 to 5 times the rated voltage, and in order to obtain the specified capacity, a large positive rod with a large area must be used. The problem is that you don't get it.

Furthermore, as described in Japanese Patent Publication No. 49-29374, a method is known in which a lead dioxide layer is formed on a dielectric film layer by chemical precipitation. However, this method requires silver ions as a catalyst when chemically depositing lead dioxide, so silver or silver compounds adhere to the dielectric film, reducing insulation resistance. There is.

As a method to solve these drawbacks, a method is known in which tetracyanoquinodimethane salt, which is an organic semiconductor, is used as a conductive layer (Japanese Patent Application Laid-open No. 173928/1983, etc.); Disadvantages include that the cost of the dimethane salt is rather high and, being a salt, it is unstable to moisture.

The present inventors have previously provided a method for manufacturing a solid electrolytic capacitor in which lead dioxide is formed on a conductive film by chemical precipitation from a reaction mother liquor containing extremely high concentrations of lead ions and persulfate ions ( (Patent Application No. 1988-19318). However, in this method, the stability of the reaction mother liquor in which lead dioxide is chemically precipitated is poor, and a solid electrolytic capacitor having sufficiently satisfactory performance cannot necessarily be obtained.

The purpose of the present invention is to solve the above-mentioned drawbacks of the prior art, and to provide a method that is low in cost, does not use thermal decomposition reactions, and does not use catalysts such as silver catalysts that adversely affect capacitor performance.
An object of the present invention is to provide a method for manufacturing a solid electrolytic capacitor in which a lead dioxide layer is formed on a dielectric film layer by chemical precipitation from a reaction mother liquor with improved stability.

According to the present invention, in the method for manufacturing a solid electrolytic capacitor in which the conductive layer is lead dioxide formed by chemical precipitation from a reaction mother liquor containing lead ions and persulfate ions,
The lead ion concentration in the reaction mother liquor is within the range of 0.1 mol/l to less than the saturation solubility, and the molar ratio of persulfate ions to lead ions is 0.1 mol/l. - A method for manufacturing a solid electrolytic capacitor is provided, characterized in that the value is within a range of 0.05 or more and less than 0.5.

The dielectric film in the present invention refers to an oxide film on foil, wire, or sintered body of valve metal such as aluminum, tantalum, niobium, etc., 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 conductor layer of lead dioxide on the dielectric film layer by chemical precipitation.

There are no particular restrictions on lead ion species and persulfate ion species;
Typical examples of compounds that provide lead ion species include lead citrate, lead 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, lead bromate, etc. On the other hand, typical examples of compounds that provide persulfate ion species include ammonium persulfate, potassium persulfate, sodium persulfate, etc. can be given. Two or more of these compounds that provide lead ion species and persulfate ion species may be used in combination.

The lead ion concentration in the reaction mother liquor is from 0.1 mol/l to below the saturation solubility, preferably from 0.5 mol/l to below the saturation solubility. The concentration of lead ions is 0.1 mol/12 J:D
If it is low, the lead ion concentration in the reaction mother liquor is too low and the number of applications must be increased. In addition, if the concentration of lead ions exceeds the saturation solubility,
No benefit was observed by adding an increased amount. On the other hand, the persulfate ion concentration in the reaction mother liquor is within a molar ratio of 0.05 or more and less than 0.5 with respect to lead ions. When the concentration of persulfate ions is 0.5 or more in molar ratio to lead ions, the stability of the reaction mother liquor deteriorates and precipitates are deposited. Furthermore, if the concentration of persulfate ions is less than 0.05 in molar ratio to lead ions, the reaction will not proceed sufficiently, making it impossible to obtain a solid electrolytic capacitor with good performance.

The reaction mother liquor may be used by simultaneously dissolving a compound that provides lead ion species and a compound that provides persulfate ion species in urine, or an aqueous solution of a compound that provides lead ion species and a compound that provides persulfate ion species in advance. They may be prepared separately and mixed immediately before use.

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

The solid electrolytic capacitor of the present invention is produced by applying a reaction mother liquor to a valve metal such as aluminum, tantalum, or niobium having a dielectric film or a dielectric film, or by immersing a valve metal having a dielectric film in a reaction mother liquor. The reaction mother liquor is introduced into the dielectric film, reacted at room temperature, preferably heated, and then washed with water and dried to produce the dielectric film.

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

■ Deposit carbon dioxide on the dielectric film layer without heating to high temperatures.
Since the A layer can be formed, there is no risk of damaging the dielectric film of the anode, and there is no need to perform anodization (reformation) for repair. Therefore, the rated voltage can be increased several times compared to conventional capacitors, and the shape can be made smaller compared to conventional capacitors with the same capacity and rated voltage.

(■ LC (leakage current) is small.

■ Capacitors with high withstand voltage can be manufactured.

■ Conductivity of lead dioxide 10 ~ 101S-CTL-1
is sufficiently high, so the impedance is low.

■ Good high frequency characteristics.

■ Tan δ (loss coefficient) is small.

Example 511 The invention will be described in more detail below with reference to Examples and Comparative Examples. Note that the characteristic values of the solid electrolytic capacitors on each side are shown in Table 1.

Example 1 Aluminum foil with a thickness of 100 μm (purity 99.99%)
The surface of the foil was electrochemically etched using direct current to produce an average hole diameter of 2 μm and a specific surface area of 12 m/'9.
And so. This etched aluminum foil is then electrochemically treated in a solution of boric acid and ammonium borate to form a thin layer of dielectric (
alumina) was formed.

A reaction mother liquor was prepared by mixing an aqueous solution of lead acetate trihydrate with a concentration of 4 mol/l and an aqueous ammonium persulfate solution of 0.3 moles per mol of lead acetate trihydrate.

The resulting reaction mother liquor was stable, and no precipitation occurred even after it was left to stand for 1 hour. When this reaction mother liquor was applied to the aluminum foil having the dielectric film layer described above and left at 80° C. for 30 minutes, a lead dioxide layer was formed on the dielectric film 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. After applying one coat of carbon onto the lead dioxide layer and drying, 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 a reaction mother liquor was used in which the amount of ammonium persulfate used was 0.08 times the mole of lead acetate trihydrate in Example 1. .

Example 3 In Example 1, an aqueous solution with a lead citrate concentration of 0.5 mol/l was used instead of an aqueous solution with a lead acetate trihydrate concentration of 1 mol/l, and an aqueous solution of lead citrate with a concentration of 0.5 mol/l was used instead of the ammonium persulfate aqueous solution. A solid electrolytic capacitor was produced in the same manner as in Example 1, except that a reaction mother liquor containing 0.3 mole of sodium persulfate water subliquid based on lead citrate was used.

Comparative Example 1 A solid electrolytic capacitor was manufactured by forming a lead dioxide layer on an aluminum foil having the same dielectric thin layer as in Example 1 by thermally decomposing lead nitrate as known in the art.

Comparative Example 2 The method described in Japanese Patent Publication No. 19-29374 was used, ie, 250 ml of a solution consisting of 0.3 mol of lead acetate dissolved in concentrated ammonium acetate and a saturated aqueous solution of ammonium persulfate 11 and 8 x 10 A solid electrolytic capacitor was prepared in the same manner as in Example 1 by applying a mixture of molar silver nitrate to an aluminum foil having a thin layer of dielectric material similar to that in Example 1.

Comparative Example 3 A reaction mother liquor was prepared in the same manner as in Example 1, except that the amount of ammonium persulfate used in Example 1 was changed to 1.5 times the molar amount of the acetic acid I-benzene hydrate. The obtained reaction mother liquor was
After leaving it for a while, a thick precipitate appeared. Then,
Using this reaction mother liquor, a solid chamber was prepared in the same manner as in Example 1.
・6 capacitors were manufactured.

Table 1 * Value at 120 Hz ** Value at 30 V Although Tari described a capacitor using aluminum foil as the anode body, the capacitor of the present invention
The structure is not limited to this, and the metal constituting the anode may be other film-forming metals such as tantalum, or alloys thereof. Furthermore, the material is not limited to such a foil type, but may be a porous body made by sintering film-forming metal powder.

Furthermore, regarding the exterior structure, in this 8th example, a resin molded one was shown, but other exterior structures such as a resin case, a metal exterior case, a resin-dipped one, or a laminated film exterior were also used. Even if there is, it does not deviate from this invention.

Claims (1)

[Claims] In a method for manufacturing a solid electrolytic capacitor in which a conductive layer is lead dioxide formed by chemical precipitation from a reaction mother liquor containing lead ions and persulfate ions, the lead ion concentration in the reaction mother liquor is 0.1 mol/l. A method for manufacturing a solid electrolytic capacitor, characterized in that the molar ratio of persulfate ions to lead ions is within a range of 0.05 or more and less than 0.5.