JPH0695493B2 - Method for manufacturing solid electrolytic capacitor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a solid electrolytic capacitor using a conductive polymer as a solid electrolyte.

2. Description of the Related Art In recent years, with the digitalization of circuits for electric devices, there is an increasing demand for capacitors used therein to have a smaller size, a larger capacity and a lower impedance in a high frequency region.

Conventionally, high-frequency capacitors include plastic film capacitors, mica capacitors, laminated ceramic capacitors and the like. However, these capacitors are not suitable for increasing the capacity because they are too large in shape.

On the other hand, examples of large-capacity capacitors include aluminum dry electrolytic capacitors, aluminum solid electrolytic capacitors, and tantalum solid electrolytic capacitors. These capacitors are suitable for large capacity because the oxide film that is the dielectric is extremely thin, but since the oxide film is easily damaged,
An electrolyte for repairing the film damage needs to be provided between the cathode and the cathode. In an aluminum dry electrolytic capacitor, an etched positive and negative aluminum foil is wound around a separator, and the separator is impregnated with a liquid electrolyte for use. Since this liquid electrolyte is ionic conductive and has a large specific resistance, the loss is large and the impedance frequency characteristics and temperature characteristics are significantly inferior.In addition, the capacity decreases and the loss increases due to liquid leakage and liquid evaporation that inevitably occur over time. There was a problem that there was. On the other hand, the solid electrolytic capacitor uses manganese dioxide as the electrolyte, and although the problems of temperature characteristics and deterioration of capacity and loss over time are improved, the loss resistance and impedance of the manganese dioxide are relatively high because manganese dioxide has a relatively high specific resistance. Frequency characteristics are inferior to monolithic ceramic capacitors and film capacitors.

On the other hand, recently, in place of manganese dioxide as a solid electrolyte, an organic semiconductor having high conductivity and high anodizing property, that is, 7,7,8,8-tetracyanoquinodimethane complex salt (TCNQ salt) is used as a solid electrolyte. It has been proposed to use a solid electrolytic capacitor used as an electrolyte (Japanese Patent Publication No. 56-
10777, JP-A-58-17609). Aluminum solid electrolytic capacitors using TCNQ salt are said to have good frequency characteristics and temperature characteristics, good leakage current characteristics, and higher high-temperature life than conventional ones, but the specific resistance when applying organic semiconductors is high. It is not enough because of the rise in the temperature and the lack of adhesion to the valve metal foil.

Furthermore, in recent years, a heterocyclic monomer such as pyrrole or thiophene is electrolytically (oxidized) polymerized using a supporting electrolyte to form a highly conductive polymer containing an anion of the supporting electrolyte as a dopant on an anode body. However, a solid electrolytic capacitor using this as a solid electrolyte has been proposed (JP-A-60-37114, JP-A-60-244017).

Capacitors in which the solid electrolyte is a conductive polymer obtained by electrolytic polymerization have frequency characteristics, temperature characteristics, and life characteristics (high temperature
It can be said to be a solid electrolytic capacitor that is expected because it has excellent long-term reliability under high humidity.

However, the solid electrolytic capacitor in which the solid electrolyte is a conductive polymer obtained by electrolytic polymerization has a problem of increased leakage current.

An object of the present invention is to provide a method for manufacturing a capacitor that prevents an increase in leakage current.

Means for Solving the Problem In order to achieve this object, the inventor examined the cause of the increase in leakage current. As a result, the following findings were obtained.

The electrolytic oxidation polymerization method is a method in which a direct current voltage is applied in an electrolytic solution (electrolytic polymerization solution) containing a polymerizable monomer and a supporting electrolyte to form a conductive polymer film on the surface of an anode by electrolytic oxidation of the monomer. However, generation of hydrogen is unavoidable because this reaction is a hydrogen abstraction reaction. This generated hydrogen is difficult to volatilize from the electrolytic solution, and often not only remains as bubbles at the interface of the electrolytic solution but also tends to be attracted and attached to the surface of the anode. The tendency is that the supporting electrolyte is, for example, ABS (alkylbenzene sulfonate).
Alternatively, it is particularly noticeable in the case of surfactant systems such as alkylsulfates.

When bubbles are generated by hydrogen generated on the surface of the anode, the electrolytic polymerized film formation is hindered and thinned at that portion, and the phenomenon that the conductive polymer film for solid electrolyte having a uniform thickness as a whole is not formed occurs. After forming the conductive polymer film, a colloidal graphite layer and an Ag paste layer are sequentially coated and the cathode lead is taken out. A capacitor in which a part of the conductive polymer film for solid electrolyte has a very thin thickness causes leakage current increase, which is one of the most important characteristics, and is not suitable for practical use. If the colloidal silicon layer and the Ag paste layer are provided so as to avoid the conductive polymer film portion formed near the electrolyte interface, the increase in leakage current can be prevented, but in this case, increase in loss and high frequency range It is not a drastic solution because it causes another problem of low capacity.

The inventor, who has obtained the above knowledge, has made a deeper study in order to solve the problem by removing bubbles due to generated hydrogen. As a result, it was found that it is effective to add an antifoaming agent to the electrolytic solution, and the present invention could be completed thereby.

Therefore, the method for producing a solid electrolytic capacitor according to any one of claims 1 to 6 is characterized in that at least a polymerizable monomer, a supporting electrolyte and an antifoaming agent are electrolytically polymerized (electrolytically oxidatively polymerized) in an electrolytic solution to form a dielectric substance. The conductive polymer film for solid electrolyte is formed on the valve metal substrate on which the film is formed.

Examples of the defoaming agent used in the present invention include silicone defoaming agents. Specific examples of the silicone defoaming agent include:
For example, as in claim 2, there is a compound represented by the following general formula.

However: n is 0 or a positive integer, and the concentration of the defoaming agent in the electrolyte solution is usually in the range of 10 to 1000 ppm as in claim 3.

As the polymerizable monomer in the electrolytic solution, a heterocyclic compound is usually used as in claim 4, and specifically, as in claim 5, of pyrrole, thiophene, and dielectrics thereof. Try to use at least one of.

As the supporting electrolyte in the electrolytic solution, alkylbenzene sulfonate, alkyl sulfate, etc. are used. The supporting electrolyte has a function of increasing the conductivity of the electrolytic solution so that the electrolytic oxidative polymerization proceeds smoothly, and a function of supporting electrolyte anions entering the electrolytic polymerization film as a dopant and increasing the conductivity of the same.

Further, as the valve metal of the valve metal base material having the dielectric film formed on its surface, aluminum, tantalum, etc. may be mentioned as in the sixth aspect.

Before forming the conductive polymer film for the solid electrolyte,
Usually, a conductive layer (for example, a manganese oxide layer) is laminated on the surface of the dielectric film to impart conductivity, and then electrolytic polymerization is performed.

Action In the method for producing a solid electrolytic capacitor of the present invention, an antifoaming agent is added to the electrolytic solution for electrolytic oxidative polymerization, and bubbles due to hydrogen generated as the polymerization reaction proceeds are easily broken at the electrolytic solution interface. It does not stay, and the phenomenon of bubbles adhering to the surface of the anode is eliminated. Therefore, the conductive polymer film for solid electrolyte formed by electrolytic polymerization has a uniform thickness without a thin portion. Therefore, the inconvenience of increasing the leakage current is eliminated.

When the defoaming agent is a silicone-based defoaming agent, there are advantages that the addition amount is small, and the substances of other components are not corroded and unnecessary harmful reactions do not occur.

When the addition amount of the defoaming agent is less than 10 ppm, the defoaming effect tends to be insufficient, and when the addition amount of the defoaming agent exceeds 1000 ppm, the leakage property to the cathode forming material such as colloidal graphite tends to be deteriorated. .

Examples Examples of the present invention will be described below.

-Example 1-Anode leads were attached to an 8 x 10 mm aluminum etched foil, and a 70% aqueous solution of ammonium adipate was used to prepare about 70
Anodizing was performed under conditions of ℃ and applied voltage of 35 V to form a dielectric film, and a valve metal substrate having the dielectric film formed on the surface was obtained. Next, an aqueous solution of manganese nitrate was applied and pyrolyzed at 250 ° C. for 10 minutes to adhere a conductive layer made of a manganese oxide film to the surface, and then electrolytic polymerization was carried out as follows using this as an anode.

As an electrolyte, pyrrole (0.3 mol / l), sodium dodecylbenzene sulfonate (0.15 mol / l), a self-emulsifying silicone defoamer that can be used for both aqueous and non-aqueous foaming liquid systems (KS506 manufactured by Shin-Etsu Chemical) : Addition amount of 100 ppm) and water, the anode (valve metal base material) is immersed in an electrolytic solution, the first electrode for electrolytic polymerization previously coated with polypyrrole is brought into contact, and the electrolysis is provided separately from the first electrode. A voltage of 3 V was applied between the second polymerization electrodes to form a polypyrrole conductive polymer film for a solid electrolyte. This polypyrrole contains the dodecylbenzene sulfonate anion as a dopant.

No bubbles were generated at the interface during the electrolytic polymerization, and it was confirmed by visual observation of the completed conductive polymer film that the film was a very smooth film.

After electrolytic polymerization, remove the electrode, wash with water and dry,
A carbon paste layer is laminated on the conductive polymer film by coating, and then an Ag paste layer is laminated on the conductive polymer film by coating, and then the cathode lead is taken out and then externally sealed with an epoxy resin. Completed the capacitor. The number of manufactured solid electrolytic capacitors is 10.

-Examples 2 to 6-Example 1 except that the concentration of the defoaming agent KS506 is as follows.
A capacitor was obtained in the same manner as in.

Example 2 ... 5 ppm Example 3 ... 10 ppm Example 4 ... 500 ppm Example 5 ... 1000 ppm Example 6 ... 2000 ppm-Examples 7 to 10-In addition to the defoaming agent KS506, the following silicone defoaming agent was used. A capacitor was obtained in the same manner as in Example 1.

During the electropolymerization, no bubbles were generated at the interface,
When the completed conductive polymer film was visually observed, it was confirmed that it was a very smooth film.

Example 7 ... Fast-acting emulsion type defoaming agent using non-ionic emulsifier manufactured by Shin-Etsu Chemical KM68-1F Example 8 ... Emulsion type de-foaming using non-ionic emulsifier manufactured by Shin-Etsu Chemical and complying with the standards of the Food Sanitation Law. Agent KM72 Example 9 ... Emulsion defoaming agent using nonionic emulsifier manufactured by Shin-Etsu Chemical and having excellent sustainability and high-temperature stability KM75 Example 10 ... Usable for both water-based and non-aqueous foaming systems manufactured by Shin-Etsu Chemical Highly Diluting Stable Self-Emulsifying Defoamer X-50-711B-Examples 11-14-Example 1 except that sodium dodecylbenzene sulfonate (SDBS) as the supporting electrolyte was replaced with the following: A capacitor was obtained in the same manner as in. The defoaming effect of the defoaming agent was sufficiently exhibited, no bubbles were generated at the interface during the electrolytic polymerization, and the completed conductive polymer film was observed with the naked eye to find that it was a very smooth film.

Example 11 ... Sodium Dodecyl Sulfate (SDS) Example 12 ... n-Butyl Phosphate (NBP) Example 13 ... Sodium Monobutylnaphthalene Sulfonate (SMBNS) Example 14 ... Sodium Triisoflupyrnaphthalene Sulfonate (STIPNS) Similarly to the case of Example 1, the polypyrrole contains each supporting electrolyte anion as a dopant.

-Example 15-Pyrrole in thiophene, SDBS in tetraethylammonium p-toluenesulfonate (TEApTS), antifoaming agent
KS506 is an oil-based silicone defoamer for non-aqueous foaming systems KS6
A capacitor was obtained in the same manner as in Example 1, except that water (solvent) was replaced by acetonitrile in 9 (manufactured by Shin-Etsu Chemical Co., Ltd.).
Also in this case, the defoaming agent exhibited a good defoaming effect.

-Example 16-After embossing, using a 10% phosphoric acid aqueous solution at about 90 ° C.,
A capacitor was obtained in the same manner as in Example 1 except that anodic oxidation was carried out under the condition of applied voltage of 35 V to form a dielectric film on the surface.

-Comparative Example 1-A capacitor was obtained in the same manner as in Example 1 except that an electrolytic solution containing no defoaming agent was used.

-Comparative Example 2-A capacitor was obtained in the same manner as in Example 16 except that an electrolytic solution containing no antifoaming agent was used.

Each of the 10 capacitors in the examples and comparative
Aging by applying the voltage of, capacity (120Hz), loss (1
20Hz), the leakage current was measured. The measurement results (average value) are shown in Table 1.

As shown in Table 1, each capacitor of the embodiment has a capacitance
It can be seen that it has excellent impedance and leakage current characteristics and is suitable for practical use.

Comparing the leakage current characteristics between Example 1 and Comparative Example 1, or between Example 16 and Comparative Example 2, it can be clearly seen that the addition of the defoaming agent has a function of suppressing an increase in leakage current.

From the leakage current data of Examples 2 to 6, the concentration of the defoaming agent was 10
It is also well understood that ~ 1000ppm is suitable.

The present invention is not limited to the above embodiment. For example, in the examples, the conductive layer was formed of pyrolytic manganese oxide before forming the conductive polymer for the solid electrolyte, but the conductive layer may be formed of a conductive material other than manganese oxide. .
In the examples, the first polyelectrolyte-coated polypyrrole coating is used.
Electrolytic polymerization was performed by applying an electrode.However, an electrode coated with a material other than polypyrrole may be used, an uncoated electrode may be directly applied, or an anode lead may be used to initiate the electropolymerization. You may make it electrify. Although pyrrole or thiophene was used as the monomer for polymerization, those having a substituent introduced therein may be used alone or in combination.

Effect of the Invention As described above, in the method for producing a solid electrolytic capacitor of the present invention, since electrolytic polymerization is performed using an electrolytic solution to which a defoaming agent is added, a conductive polymer film for a solid electrolyte is A film having a uniform thickness without a thin portion can be obtained, and a capacitor having excellent characteristics in which an increase in leakage current is suppressed can be obtained.

Claims (6)

[Claims] 1. A solid electrolyte on a valve metal substrate having a dielectric film formed on its surface by electrolytic polymerization in an electrolytic solution in which at least a polymerizable monomer, a supporting electrolyte and an antifoaming agent are dispersed in a solvent. A method for manufacturing a solid electrolytic capacitor, which comprises forming a conductive polymer film. 2. The method for producing a solid electrolytic capacitor according to claim 1, wherein the defoaming agent is a compound represented by the following general formula. However: n is 0 or a positive integer 3. The concentration of the defoaming agent in the electrolyte solution is 10 to 1000 pp.
The method for producing a solid electrolytic capacitor according to claim 1 or 2, wherein the range is m. 4. The method for producing a solid electrolytic capacitor according to claim 1, wherein the polymerizable monomer is a heterocyclic compound. 5. The heterocyclic compound is pyrrole, thiophene,
And the method for producing a solid electrolytic capacitor according to any one of claims 1 to 4, which is at least one of these derivatives. 6. The method for producing a solid electrolytic capacitor according to claim 1, wherein the valve metal is one of aluminum and tantalum.