JPH0777185B2 - Method for manufacturing solid electrolytic capacitor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a solid electrolytic capacitor, and more particularly to a method for manufacturing a solid electrolytic capacitor in which an anode substrate is well impregnated with a semiconductor layer and has excellent performance.

[Prior Art] Generally, in an element of a solid electrolytic capacitor, an oxide film is formed on an anode substrate made of a valve metal, and a semiconductor layer such as manganese dioxide is formed on the outer surface of the oxide film as a counter electrode. A conductive layer is formed to reduce the contact resistance.

However, the method of forming a semiconductor layer applied to such a solid electrolytic capacitor is, for example, a method of thermally decomposing an aqueous solution containing manganese ions to form a semiconductor layer,
There is a problem that the oxide film is thermally cracked and further chemically damaged by the generated gas.

In order to solve such a problem, for example, Japanese Patent Publication No. 49-2
As described in Japanese Patent No. 9374, a method is known in which lead dioxide is chemically deposited on an oxide film to form a semiconductor layer. However, this method requires silver ions as a catalyst when chemically depositing lead dioxide, and therefore has a problem that silver or a compound of silver is attached to the surface of the oxide film to reduce the insulation resistance.

From this point of view, the inventors of the present invention chemically analyze a semiconductor made of lead dioxide and lead sulfate on an oxide film without using a thermal decomposition reaction and without using a catalyst such as silver ion which adversely affects the capacitor performance. We proposed a solid electrolytic capacitor formed by selective deposition (Japanese Patent Application No. 61-93451).

[Problems to be Solved by the Invention] On the other hand, in the solid electrolytic capacitor proposed by the present inventors in response to the recent demand for smaller volume of electronic components, it is necessary to increase the impregnation rate of the semiconductor layer into the anode substrate. Therefore, it is necessary to increase the capacity in a small volume.

[Means for Solving Problems] The present invention has been made in order to achieve the above-mentioned object, and the gist thereof is to provide a dielectric oxide film, a chemical substance, and a chemical oxide film on the surface of an anode substrate made of a metal having a valve action. In a method for producing a solid electrolytic capacitor, which comprises sequentially forming a semiconductor layer made of lead dioxide or lead dioxide and lead sulfate and a dielectric layer produced by a dynamic deposition method, an anode substrate having the dielectric oxide film is The solid electrolytic capacitor is formed by contacting the reaction mother liquor for chemically depositing the semiconductor layer and leaving it at a temperature not lower than the solidification temperature of the reaction mother liquor and not higher than 10 ° C. and then reacted at a temperature not lower than 28 ° C. to form the semiconductor layer. There is a manufacturing method.

[Specific Configuration and Action of the Invention] Hereinafter, a method for manufacturing the solid electrolytic capacitor of the present invention will be described.

Examples of the valve metal substrate used as the anode of the solid electrolytic capacitor of the present invention include aluminum, tantalum,
Any metal having a valve action such as niobium, titanium and alloys having these as substrates can be used.

The oxide film layer on the surface of the anode substrate may be an oxide layer of the anode substrate itself provided on the surface layer of the anode substrate, or may be a layer of another dielectric oxide provided on the surface of the anode substrate. Is desirable. In any case, a conventionally known method can be used as a method for providing the oxide layer.

The semiconductor layer used in the present invention is made of lead dioxide, or lead dioxide and lead sulfate as main components, and is produced by a conventionally known chemical deposition method.

Examples of the chemical deposition method include a method of chemically depositing from a solution containing a lead-containing compound and an oxidizing agent.

Examples of the lead-containing compound include oxine, acetylacetone, pyromeconic acid, salicylic acid, alizarin, polyvinyl acetate, porphyrin compounds, crown compounds,
Lead-containing compounds in which lead atoms are coordinate-bonded or ionic-bonded to chelate-forming compounds such as cryptate compounds, lead citrate, lead acetate, basic lead acetate, lead chloride, lead bromide, lead perchlorate, Examples thereof include lead chlorate, lead sulfamate, lead silicon hexafluoride, lead bromate, lead borofluoride, lead acetate hydrate, and lead nitrate. These lead-containing compounds are
It is appropriately selected depending on the solvent used for the reaction mother liquor. Moreover, you may use these lead-containing compounds in mixture of 2 or more types.

The concentration of the lead-containing compound in the reaction mother liquor is in the range of 0.05 mol / l from the concentration giving the saturated solubility, preferably in the range of 0.1 mol / l from the concentration giving the saturated solubility, more preferably the saturated solubility. It is in the range of 0.5 mol / l from the given concentration. The concentration of lead-containing compound in the reaction mother liquor is 0.05 mol
If it is less than / l, a solid electrolytic capacitor with good performance cannot be obtained. Further, when the concentration of the lead-containing compound in the reaction mother liquor exceeds the saturation solubility, the merit of increasing the addition amount is not recognized.

Examples of the oxidizing agent include quinone, chloranil, pyridine-N-oxide, dimethylsulfoxide, chromium, potassium permanganate, selenium oxide, mercury acetate, and the like.
Examples thereof include vanadium oxide, sodium chlorate, ferric chloride, hydrogen peroxide, benzoyl peroxide, calcium hypochlorite, calcium chlorite, calcium chlorate, calcium perchlorate and the like. These oxidizing agents may be appropriately selected depending on the solvent used. Also, two or more oxidizing agents may be mixed and used.

The proportion of the oxidizing agent used is 5 to 5 times the molar amount of the lead-containing compound used.
It is preferably in the range of 0.1 times by mole. If the proportion of the oxidizing agent used is more than 5 times the mole amount of the lead compound used, there is no cost advantage, and if it is less than 0.1 times the mole amount, a solid electrolytic capacitor with good performance cannot be obtained.

Further, when the semiconductor layer is composed of lead dioxide which originally functions as a semiconductor and a layer containing lead sulfate which is an insulating material as a main component, the leakage current of the capacitor can be reduced by mixing lead sulfate. On the other hand, the compounding of lead sulfate lowers the electrical conductivity of the semiconductor layer and thus increases the loss coefficient.
Even if compared with the conventional solid electrolytic capacitor, a high level of performance can be maintained and exhibited. Therefore, when the semiconductor layer is composed of a mixture of lead dioxide and lead sulfate, good capacitor performance is maintained with a wide range of composition of lead sulfate of 10 parts by weight or more and less than 100 parts by weight and lead sulfate of 90 parts by weight or less. 80 to 50 parts by weight of lead sulfate, more preferably 20 to 50 parts by weight of lead dioxide, and more preferably lead dioxide.
A good balance between the leakage current and the loss factor is obtained in the range of 75 to 65 parts by weight of lead sulfate with respect to 25 to 35 parts by weight. Lead dioxide 10
If it is less than part by weight, the conductivity is deteriorated, the loss factor becomes large, and sufficient capacity cannot be obtained.

The semiconductor layer mainly composed of lead dioxide and lead sulfate is, for example,
An aqueous solution containing lead ions and superfluic acid ions can be formed as a reaction mother liquor by chemical deposition. Also, a suitable oxidizing agent containing no persulfate ion may be added.

The concentration of lead ion in the mother liquor is calculated from
0.05 mol / l, preferably from a concentration giving a saturated solubility of 0.
1 mol / l, more preferably from a concentration that gives saturated solubility
Within the range of 0.5 mol / l. If the concentration of lead ions is higher than the saturation solubility, there is no merit by increasing the amount.
When the concentration of lead ions is lower than 0.05 mol / l,
The lead ion in the mother liquor is too thin, so that the number of reactions must be increased.

On the other hand, the concentration of persulfate ions in the mother liquor is in the range of 5 to 0.05 in terms of molar ratio with respect to lead ions. If the concentration of persulfate ion is more than 5 with respect to the lead ion, unreacted persulfate ion remains, resulting in higher cost, and the concentration of persulfate ion is less than 0.05 with respect to the lead ion. If so, unreacted lead ions remain and the conductivity deteriorates, which is not preferable.

Examples of compounds that give lead ion species include lead citrate, lead perchlorate, lead nitrate, lead acetate, basic lead acetate, lead chlorate, lead sulfamate, lead hexafluoride, lead bromate, and chloride. Examples thereof include lead and lead bromide. Two or more kinds of compounds that give these lead ion species may be mixed and used.
On the other hand, examples of the compound that gives a persulfate ion species include potassium persulfate, sodium persulfate, and ammonium persulfate. Two or more kinds of these compounds giving the persulfate ion species may be mixed and used.

On the other hand, examples of the oxidizing agent include hydrogen peroxide, calcium hypochlorite, calcium chlorite, calcium chlorate, calcium perchlorate, and the like.

When the semiconductor layer described above is produced by the chemical deposition method,
An anode substrate having an oxide film is immersed in a reaction mother liquor obtained by mixing a solution containing a lead-containing compound and a solution containing an oxidant.

In the present invention, first, while keeping the anode substrate having an oxide film in contact with the reaction mother liquor, the solidification temperature of the reaction mother liquor or more 10
It is important to leave it in the temperature range of ℃ or less, preferably -5 ℃ ~ 6 ℃. When the standing temperature is lower than the solidification temperature of the mother liquor or when it exceeds 10 ° C, the effect of increasing the capacity of the manufactured solid electrolytic capacitor cannot be expected. Further, the leaving time of the reaction mother liquor is generally several tens of minutes,
It may be left under reduced pressure within the above temperature range.

Next, the reaction mother liquor left in the above-mentioned temperature range is
The semiconductor layer is formed by reacting as it is at a temperature of 28 ° C. or higher, preferably 28 ° C. or higher and lower than 45 ° C. The solid electrolytic capacitor manufactured according to the present invention has a structure in which a part of this semiconductor layer has entered the pores having the oxide film of the valve metal foil, wire, and sintered body described above. If the reaction temperature is lower than 28 ° C, the reaction rate becomes slow, which is industrially disadvantageous.

Thus, when a semiconductor layer composed of lead dioxide or lead dioxide and lead sulfate is formed from the reaction mother liquor at a relatively low temperature, a solid electrolytic capacitor having a large capacitance can be obtained because lead hydroxide does not easily precipitate and Even so, since the particle size is small,
It is considered that these particles easily enter the pores of the oxide film.

A conductor layer is formed by forming a metal layer or a carbon layer on the semiconductor layer formed by the present invention, or by forming a metal layer on the carbon layer. The method of forming the carbon layer on the semiconductor layer is not particularly limited, and a conventionally known method, for example, a method of applying a carbon paste is adopted. As a method of providing the metal layer, for example, a method of applying a paste containing silver, nickel, or copper, or the inventors of the present invention, Japanese Patent Application No. 61-192499
And a method of applying a conductive paste proposed in Japanese Patent Application No. 61-266092, etc., or a method of plating or vapor depositing silver, nickel, copper or the like.

The solid electrolytic capacitor element according to the present invention described above can be made into a general-purpose capacitor product for various applications by, for example, a resin mold, a resin case, a metal outer case, an outer case of a resin dipping laminate film, or the like.

[Examples] Hereinafter, the present invention will be described with reference to Examples and Comparative Examples.

Example 1 An aluminum foil having a length of 2 cm and a width of 0.5 cm was used as an anode, the surface of the foil was electrochemically etched by an alternating current, and then the anode terminal was caulked to the etched aluminum foil to connect the anode terminal. Next, electrochemical treatment is performed in an aqueous solution of boric acid and ammonium borate to form an oxide film of alumina, and low-voltage etched aluminum conversion foil (about 10
μF / cm ² ) was obtained. Then, after winding the formed foil in a spiral shape, it is immersed in a reaction mother liquor in which an aqueous solution of lead acetate trihydrate 2.4 mol / l and an aqueous solution of aluminum persulfate 4 mol / l are mixed,
It was left at 3 ° C. for 1 hour. Then, the reaction mother liquor was reacted at 35 ° C. for 1 hour to form a semiconductor layer. After the formed foil was washed with water and dried, a conductor layer was formed with a silver paste, the cathode lead was connected, and the foil was housed in an aluminum can and sealed with a resin to produce a solid electrolytic capacitor. The produced semiconductor layer was composed of lead dioxide and lead sulfate, and it was confirmed by mass analysis, X-ray analysis, and infrared spectroscopic analysis that lead dioxide was contained in an amount of about 25% by weight.

Example 2 A solid electrolytic capacitor was prepared in the same manner as in Example 1 except that the reaction mother liquor was allowed to stand at -5 ° C for 40 minutes in Example 1.

Example 3 A solid electrolytic capacitor was prepared in the same manner as in Example 1 except that the reaction mother liquor was allowed to stand at 10 ° C. for 90 minutes.

Example 4 Example 4 was repeated except that the reaction mother liquor was prepared by adding a 1.0 mol / l aqueous solution of lead acetate trihydrate and a 0.5-fold molar diluted aqueous solution of hydrogen peroxide to lead acetate trihydrate. A solid electrolytic capacitor was produced in the same manner as in Example 1. It was confirmed that the semiconductor layer at this time consisted only of lead dioxide.

Example 5 A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the reaction temperature of the reaction mother liquor was changed to 50 ° C.

Comparative Example 1 A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the reaction mother liquor was allowed to react at 35 ° C. for 1 hour without leaving the formed foil in the reaction mother liquor at 3 ° C.

Comparative Example 2 A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the leaving temperature of the reaction mother liquor was changed to 23 ° C in Example 1.

Comparative Example 3 A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the leaving temperature of the reaction mother liquor was changed to −15 ° C. below the freezing point of the reaction mother liquor in Example 1.

Comparative Example 4 When the reaction temperature of the reaction mother liquor was set to 26 ° C. in Example 1, no semiconductor layer was formed.

Table 1 collectively shows the average performance values of the five solid electrolytic capacitors produced in each of Examples 1 to 5 and Comparative Examples 1 to 3.

EFFECTS OF THE INVENTION According to the present invention, there is provided a solid electrolytic capacitor in which a dielectric oxide film, a lead dioxide or a semiconductor layer made of lead dioxide and lead sulfate, and a conductor layer are formed on the surface of an anode substrate made of a valve metal. When manufacturing, the anode substrate having a dielectric oxide film in the reaction mother liquor for chemically depositing the semiconductor layer is left for a predetermined time at a temperature not lower than the solidification temperature of the reaction mother liquor and not higher than 10 ° C, and then at a temperature not lower than 28 ° C. When the semiconductor layer is formed by reacting with, the semiconductor layer well enters the pores of the anode substrate, so that the surface area of the semiconductor layer becomes large and a solid electrolytic capacitor with a large capacitance can be manufactured even with the same volume. .

Claims (3)

[Claims] 1. A solid electrolysis comprising a dielectric oxide film, a semiconductor layer made of lead dioxide or a mixture of lead dioxide and lead sulfate, and a conductor layer sequentially formed on the surface of an anode substrate made of a metal having a valve action. In the method of manufacturing the capacitor,
The anode substrate on which the dielectric oxide film is formed is brought into contact with a reaction mother liquor for chemically depositing the semiconductor layer, and allowed to stand for a predetermined time within a temperature range of the reaction mother liquor to a solidification temperature of 10 ° C. A method for manufacturing a solid electrolytic capacitor, which comprises reacting at a temperature to form the semiconductor layer. 2. The method for producing a solid electrolytic capacitor according to claim 1, wherein the reaction mother liquor is an aqueous solution containing lead ions and an oxidizing agent. 3. The method for producing a solid electrolytic capacitor according to claim 1, wherein the reaction mother liquor is an aqueous solution containing lead ions and persulfate ions.