JPH05243098A - Manufacture of solid-state electrolytic capacitor - Google Patents

Abstract

PURPOSE:To elevate the formation property of a solution, enhance the recovery performance of surface oxide and reduce leakage current by admixing organic acid and inorganic acid aimed to promote cathode oxidation or electrolyte comprising their salt to a pyrrole solution or an oxidizing agent-dissolved solvent solution or their mixed solution. CONSTITUTION:The main body of a capacitor element 1 is immersed in a solution 4 comprising a pyrrole solution to which electrolyte is added for the formation, an oxidizing agent solution or their mixed solution contained in a vessel 5. An anode lead wire 2 is set to positive while a cathode lead wire 3 is set to negative. They are connected to a direct current power source 6 where saturation is carried out under the supply of power. This construction makes it possible to protect a surface oxide layer from damage and prevent an increase in leakage current and hence attain low leakage current. Since it is possible to saturate the solution and recover the surface oxide simultaneously, the aging treatment after the completion of products can be simplified while the efficiency of manufacturing process of a solid-state electrolytic capacitor can be enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solid electrolytic capacitor, and more particularly to a method for manufacturing an electrolytic capacitor using polypyrrole, which is an organic conductor, as a solid electrolyte.

[0002]

2. Description of the Related Art Solid electrolytic capacitors are made of aluminum,
A dielectric film such as tantalum may be formed, so-called valve metal is used for the anode, and manganese dioxide, an inorganic oxide such as lead dioxide on the upper surface of the dielectric oxide film layer, or a tetracyanoquinodimethane complex salt, polypyrrole, polyacetylene, It is formed by using various organic conductors such as polyaniline and polyfuran as electrolytes.

The anode body of a solid electrolytic capacitor has an increased surface area in order to increase the capacitance per unit. Therefore, a porous sintered body or a foil-shaped electrode whose surface is subjected to an etching process is used as the anode.

Therefore, it is difficult to form a solid electrolyte,
Usually, the electrolyte material is used by impregnating the anode with an electrolyte material in the state of a solution in which an electrolyte is dissolved in a solvent or a liquid that is heated and melted, and is transformed into a target solid electrolyte by thermal transformation or polymerization reaction.

Conventionally, solid electrolytes using manganese dioxide have been known. For manganese dioxide, an aqueous solution of manganese nitrate is impregnated with an anode, which is heated and fired to be converted into manganese dioxide.

The solid electrolyte directly contacts the dielectric oxide film layer and functions as a true cathode. Therefore, the conductivity of the solid electrolyte layer directly affects the loss and high frequency impedance of the solid electrolytic capacitor. In recent years, the use of solid electrolytic capacitors with a high frequency is rapidly increasing, and along with this, it is required to improve the electric conductivity of the solid electrolyte layer.

Manganese dioxide has an electric conductivity of 10 ^-2 to 10
It is about ^-1 s / cm, which is not sufficient for use in the recent high frequency region, and there is a demand for a solid electrolyte having higher conductivity.

Under these circumstances, a conductive organic substance has recently attracted attention as a solid electrolyte. There are various kinds of conductive organic substances, and among them, a polymer of pyrrole, which is a five-membered heterocyclic compound, to which conductivity is imparted with an appropriate dopant has a high conductivity of about 10 to 10 ² s / cm. Therefore, commercialization of solid electrolytic capacitors using polypyrrole has attracted attention.

[0009]

An electrolytic capacitor using polypyrrole as a solid electrolyte has excellent electrical characteristics due to its high conductivity. However, since the mechanical strength of the polymer is weak and the function of repairing the defective portion of the dielectric oxide film is not sufficient, the leakage current is high and it is difficult to suppress this leakage current to a low level by film repair.

Conventionally, there has been tried a method of forming a polypyrrole polymer film in order to reduce the leakage current, then immersing the electrode in a chemical conversion solution to perform an anodizing reaction (chemical conversion treatment), and repeating the polymerization again. There is. However, if the chemical conversion treatment is performed after the polymer film of polypyrrole is formed, there is a drawback that the anodizing reaction is blocked by the polymer film of polypyrrole and the film cannot be sufficiently repaired. I had to repeat.

Therefore, the inventor of the present invention applies a voltage to the anode in the course of carrying out the polymerization reaction by immersing the anode in a pyrrole solution, an oxidant solution or a mixed solution thereof, and at the same time, the chemical conversion reaction is allowed to proceed to form an oxide film. We have been considering reducing leakage current by repairing. However, there is a limit to the film formation by the chemical conversion in a solution that does not contain an electrolyte that is suitable for chemical conversion, and in order to form a dense repair oxide film, it is necessary to enhance the chemical conversion of the solution, that is, the anodic oxidation ability.

[0012] Therefore, an object of the present invention is to obtain a solid electrolytic capacitor having excellent electrical characteristics by enhancing the chemical conversion property of the solution to improve the repairability of the oxide film to further reduce the leakage current.

[0013]

SUMMARY OF THE INVENTION According to the present invention, a capacitor element formed by winding or laminating an anode having a dielectric oxide film layer formed on its surface with a separator interposed, is formed by a pyrrole solution and an oxidant solution, respectively. Or by impregnating a mixed solution of a pyrrole solution and an oxidant solution, and simultaneously applying a voltage between the anode and the solution, a solid oxide layer of polypyrrole is formed by a polymerization reaction of the solid electrolyte, and a dielectric oxide film layer is formed. In the method for producing a solid electrolytic capacitor for repairing the deteriorated or damaged part of the organic acid, an inorganic acid or a salt thereof as an electrolyte is added to the pyrrole solution, the oxidant solution or a mixed solution thereof to accelerate anodic oxidation. It has a feature.

The electrolyte added to the pyrrole solution or the oxidant solution should be selected from acids, bases or salts which do not dissolve the anode material or the oxide film already formed. Particularly when the anode is aluminum, it is not preferable that it exhibits strong acidity or alkalinity. Generally, weak acids and their salts are selected. Particularly preferred inorganic acids are boric acid and phosphoric acid. As the organic acid, a carboxylic acid is suitable, and specific examples thereof include adipic acid, maleic acid, phthalic acid, succinic acid, malic acid and the like.

Further, not only these acids but also ammonia may be added for pH adjustment or ammonium salt or amine salt may be added. Each of these is used as an electrolyte of an electrolytic capacitor using a chemical conversion solution or an electrolytic solution.

The amount of these electrolytes added is not particularly limited, but is usually in the range of about 1% to 10%.

The voltage application is preferably within a range not exceeding the formation voltage for forming the dielectric oxide film of the anode. When a voltage exceeding the formation voltage is applied, the oxide film may grow more than the desired thickness and the capacitance value per unit may decrease.

The applied voltage may be normally supplied from a DC power source, but it may be a pulsating current or a pulsed voltage, and it does not matter if the polarity is not changed.

The current is regulated by the applied voltage and the internal resistance component, but generally 0.1 mA to 10 mA / cm ²
It is a degree.

The application time is also not particularly limited, but it may be the entire period during impregnation in the solution or a part thereof. Further, not only a method of immersing the capacitor element in the solution but also a method of dropping a required amount of the solution on the capacitor element may be used.

The pyrrole solution and the oxidizing agent solution used in the present invention are not particularly limited as long as they can polymerize and form a pyrrole monomer by an appropriate oxidizing action, but if a concrete example is shown, pyrrole is dissolved. The solvent is
Methanol, ethanol, acetone, acetonitrile,
Examples include water, tetrahydrofuran, or a mixed solvent thereof.

As the oxidizing agent, ammonium persulfate, hydrogen peroxide, etc. are used. Regarding the solvent of the oxidant,
There is no particular limitation as long as it can dissolve an oxidant in a predetermined concentration, has a viscosity that does not hinder impregnation, and does not affect materials such as the anode, and is common with the solvent of the above-mentioned pyrrole solution. Good.

[0023]

In the present invention, the process of polymerizing pyrrole on the surface of the anode by chemical polymerization, that is, the pyrrole solution or the oxidant solution or a mixed solution thereof is impregnated with the anode for chemical polymerization. By containing an electrolyte for promoting the oxidation reaction and applying a voltage between the anode and the solution, the impregnation of the solution and the anodization reaction proceed in parallel. Moreover, due to the presence of the electrolyte, the defective portion and the deteriorated portion of the oxide film of the anode are promptly repaired and the generation of the leakage current is suppressed.

[0024]

EXAMPLES The present invention will be described below with reference to examples. FIG. 1 is an explanatory view showing a state of voltage application according to the present invention. In the figure, reference numeral 1 is a capacitor element, and a positive electrode lead wire 2 is connected to a strip-shaped foil of high-purity aluminum on a surface of which a dielectric oxide film layer is formed,
This is laminated and wound together with the separator and the strip-shaped electrode for drawing out the electrode on the cathode side to form the capacitor element 1. The cathode lead wire 3 is connected to the above-mentioned strip-shaped foil on the cathode side, and each is led out upward from the winding end face.

The main body of the capacitor element 1 is impregnated into a container 5 containing a solution 4 consisting of a pyrrole solution or an oxidizer solution to which an electrolyte for chemical conversion is added, or a mixed solution of both. Then, the anode lead wire 2 is set to the positive side and the cathode lead wire 3 is set to the negative side.

In this embodiment, since the cathode side electrode is installed inside the capacitor element 1 so as to face the anode, the negative side of the DC power supply 6 is connected to this cathode. When a device in which only the anode and the separator are wound is used without using the above, the container 5 containing the solution is used as the cathode, or a counter electrode is installed in the container 5 to connect the negative side of the DC power supply 6 to the device. It can also be connected and energized.

Next, the results of the experiment conducted according to the above procedure will be shown. The capacitor element used is 3 mm wide on the anode,
Using a strip-shaped aluminum foil having a length of 18 mm, the surface was etched and then anodized at a direct current of 22 V to form a dielectric oxide film layer on the surface.

The separator has a width of 4 mm and a thickness of 100 μ.
m glass paper was used. In addition, the cathode foil has a width of 4
A strip-shaped aluminum foil having a length of 25 mm and a length of 25 mm (without anodic oxidation treatment) was used and wound together with the anode foil to obtain a cylindrical capacitor element. In addition, an electrode lead wire is connected to each of the anode foil and the cathode foil at a predetermined position by ultrasonic welding and is drawn from the winding end surface.

First, as Example 1 of the present invention, the capacitor element was prepared by using a pyrrole solution (ethanol of pyrrole monomer 20
% Solution) at room temperature under normal pressure for 5 minutes. Next, ammonium adipate (concentration 5%) was added as an electrolyte to an ammonium persulfate aqueous solution (concentration 30%), and the mixture was impregnated at room temperature and atmospheric pressure for 10 minutes. At this time, a DC voltage of 22 V was applied to the capacitor element immersed in the oxidant solution by applying 22 V from the lead wire.
It was applied for a minute. Then, the capacitor element was pulled out of the solution, washed with water, and dried by heating. After repeating this step 5 times, the outside of the capacitor element was sealed with resin to complete the solid electrolytic capacitor.

Next, as Example 2 of the present invention, an oxidant solution was prepared in which the triethylamine salt of maleic acid (concentration 5%) was added to the electrolyte instead of the ammonium adipate described above.
A solid electrolytic capacitor was completed under the same conditions as in Inventive Example 1.

Further, for comparison with the embodiment of the present invention, a solid electrolytic capacitor was prepared under the same conditions except that an electrolyte was not added, and used as a comparative example.

When the electrical characteristics of the completed solid electrolytic capacitor were examined, the results shown in Table 1 were obtained. In addition, Tan
δ is a value of 120 Hz, leakage current is a value of 2 minutes after voltage application,
ESR (equivalent series resistance) is a measurement result at 100 KHz.

[0033]

[Table 1]

As can be seen from these results, it was confirmed that the solid electrolytic capacitor according to the present invention had a greatly reduced leakage current as compared with the comparative example.

[0035]

As described above, according to the present invention, in an electrolytic capacitor using polypyrrole as a solid electrolyte, it is possible to prevent an increase in leakage current due to damage or deterioration of an oxide film layer and achieve a low leakage current.

Further, since the oxide film can be repaired at the same time as the impregnation with the solution, the aging treatment after the completion of the product can be greatly simplified and the efficiency of the manufacturing process of the solid electrolytic capacitor can be improved.

[Brief description of drawings]

FIG. 1 is an explanatory view illustrating a manufacturing process of a solid electrolytic capacitor of the present invention.

[Explanation of symbols]

 1 Capacitor element 2 Anode lead wire 3 Cathode lead wire 4 Solution 5 Container 6 DC power supply

Claims (2)

[Claims] 1. A capacitor element formed by winding or laminating an anode having a dielectric oxide film layer formed on the surface thereof with a separator interposed, in a pyrrole solution and an oxidant solution, or in a pyrrole solution and an oxidizer. In a method for producing a solid electrolytic capacitor, which comprises impregnating a mixed solution with a solution, and applying a DC voltage to the capacitor element during the impregnation, and forming a solid electrolyte layer of polypyrrole on the dielectric oxide film layer surface by a polymerization reaction, A solid electrolytic capacitor characterized by adding an electrolyte composed of an organic acid, an inorganic acid or a salt thereof for accelerating anodization to a pyrrole solution used for impregnation, an oxidant solution or both, or a mixed solution thereof. Manufacturing method. 2. The electrolyte added to the pyrrole solution, the oxidant solution or a mixed solution thereof is boric acid, phosphoric acid, adipic acid, maleic acid, phthalic acid, succinic acid, malic acid or a salt thereof. A method for producing the solid electrolytic capacitor described.