JPH03200313A - Manufacture of solid electrolytic capacitor - Google Patents

Abstract

PURPOSE:To contrive to improve the capacitance value per unit area of an electrode part by conducting the chemical polymerization of polypyrrole within a specific temperature range. CONSTITUTION:In the manufacture of a solid electrolytic capacitor including a process for forming, at least by a chemical polymerization, a solid electrolyte layer of pyrrole in an anode electrode with a dielectric oxide film layer formed on the surface, the chemical polymerization of pyrrole is conducted within the temperature range from 10 deg.C to -70 deg.C. That is, when the chemical polymerization for polypyrrole is conducted under the cold condition in a predetermined temperature range, orientation properties of pyrrole at the time of polymerization become excellent to enable forming a polypyrrole thin film being compact and satisfactory in the degree of adhesion. Further, because of excellent orientation properties, a high electric conductivity is obtained and a compact polypyrrole layer can also evenly be formed on the anode electrode surface with fine irregularity formed by a face-expanding process. Thus, it is possible to increase the capacitance per unit area.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method for manufacturing a solid electrolytic capacitor using an organic conductive polymer as an electrolyte.

[Conventional technology]

Solid electrolytic capacitors use a so-called valve metal such as aluminum or tantalum, which has an insulating oxide film layer on its surface, or an alloy of these metals for the anode. Forms an oxide film layer. A solid electrolyte layer, which is a semiconductor, is formed on the upper surface of this oxide film layer, and an external cathode terminal is further formed on the upper surface of the solid electrolyte layer through carbon paste, silver paste, conductive adhesive, or the like. Conventionally, conductive metal oxides such as manganese dioxide and lead dioxide, or various conductive organic polymers such as TCNQ (tetracyanoquinodimethane), polyacetylene, polyaniline, and polypyrrole have been used for the solid electrolyte layer. Solid electrolytes made of organic polymers have recently been attracting attention as they have excellent properties and manufacturing processes.Among these, polypyrrole has high conductivity in terms of electrical properties, and is suitable for use at high frequencies in capacitors. It has the advantage of lowering impedance. In addition, polypyrrole can be easily formed as a solid electrolyte layer on an electrode by chemical polymerization, electrolytic polymerization, gas phase polymerization, etc. at room temperature without the need for heating or baking, and a stable thin film can be obtained. Unlike conventional manganese dioxide electrolytes, it does not require repeated firing and can be processed in a short time, simplifying the process.
There is also little effect on the properties of the dielectric film due to temperature rise during firing. Although polypyrrole has excellent properties as described above, higher performance is required in recent electronic devices. For example, switching power supplies are designed with higher switching frequencies in order to achieve high efficiency and miniaturization, and as a result, electrolytic capacitors are required to be smaller and have lower impedance at high frequencies.

[Problem to be solved by the invention]

The solid electrolyte layer of polypyrrole is generally formed by oxidative polymerization. For oxidative polymerization, for example, JP-A-62-
4312, by gas phase polymerization in which pyrrole monomer is polymerized in gas. As in JP-A-63-173313, a combination of chemical polymerization in which a pyrrole monomer is brought into contact with a solution containing an oxidizing agent, or electrolytic polymerization in which electricity is applied to the material to be treated as an anode in a solution containing a supporting electrolyte. It has been known. In addition, there are publications such as JP-A-62-189714 that discuss the reaction temperature during electrolytic polymerization. Among these methods, electrolytic polymerization makes it easy to obtain a film with high conductivity and good adhesion, but it requires electricity to be applied to the material to be treated, and the anode side electrode of the electrolytic capacitor, which is the material to be treated, is not exposed to the surface. Since an insulating dielectric film is formed,
Direct electrolytic polymerization cannot be used. For this reason, attempts have been made to form a conductive thin film layer in advance on the surface of the material to be treated by another means called precoat and then perform electrolytic polymerization. There are pre-coating methods such as forming polypyrrole using a polymerization method other than electrolytic polymerization, and forming a layer of conductive metal oxide such as manganese dioxide, but all of these methods yield a film with high conductivity and good adhesion. Even if a highly conductive film is formed by electrolytic polymerization in the next step, the properties of the precoat layer are affected and the properties cannot be dramatically improved. In addition, the surface of the anode electrode is subjected to a corrugated process such as etching to ensure capacitance, resulting in a microscopically uneven surface.It is important to form a precoat layer uniformly on this uneven surface. is essential for increasing the capacitance value per unit. This invention improves the high frequency characteristics of solid electrolytic capacitors by improving the chemical polymerization method used to form a precoat layer or a first solid electrolyte layer on the surface of the anode electrode. The aim is to improve the capacitance value of each unit and obtain a compact, large-capacity solid electrolytic capacitor.

[Means to solve the problem]

The method for manufacturing a solid electrolytic capacitor of the present invention includes the step of forming a solid electrolyte layer of pyrrole by at least chemical polymerization on an anode electrode having a dielectric oxide film layer formed on the surface. The chemical polymerization is carried out at a temperature range of 10°C to -70°C. Chemical polymerization of pyrrole is carried out by first applying an oxidizing agent such as ammonium persulfate, iron trichloride, or hydrogen peroxide to an anode electrode with a dielectric oxide film layer formed on the surface of the material to be treated, or placing it in a solution of these oxidizing agents. Then, pyrrole is chemically oxidized and polymerized by immersion in a solution in which pyrrole monomer is dissolved at a predetermined concentration using water or an organic solvent such as alcohol, ketone, acetone, glycol, or hydrocarbon as a solvent. A polypyrrole layer can be formed on the surface of the anode electrode. Previously, the chemical polymerization reaction of pyrrole was carried out at room temperature.
In this invention, the chemical polymerization reaction is carried out in the range of 10°C to 70°C, and the solution in which the pyrrole monomer is dissolved is kept within a predetermined temperature range, and the anode electrode is immersed in the solution at this temperature to conduct the chemical polymerization reaction for a predetermined period of time. Desired properties can be obtained by polymerization. When the temperature on the high temperature side exceeds 10° C., this polymerization reaction is no different from the conventional polymerization reaction at room temperature, and desired characteristics cannot be obtained. In addition, on the low temperature side, lowering the temperature improves the conductivity and increases the capacitance value per unit area, but when the temperature exceeds -70℃, both the conductivity and the capacitance value become noticeable. Improvements will no longer be recognized. Further, it is not preferable because it makes it difficult to use equipment for maintaining the temperature and immersion treatment. As described above, the oxidizing agent may be applied to or immersed in the anode electrode surface before immersion in the pyrrole solution, but the oxidizing agent can also be dissolved in the pyrrole solution at the same time. In this case, since the oxidation of pyrrole proceeds in the solution, it is necessary to quickly perform the immersion treatment of the anode electrode. Furthermore, the remaining pyrrole solution cannot be used repeatedly.

[For production]

According to this invention, by carrying out the chemical polymerization of polypyrrole under low temperature conditions within a predetermined temperature range, the orientation of the pyrrole during polymerization is improved, and a polypyrrole thin film that is dense and has good adhesion can be formed. Since the orientation is good, high conductivity can be obtained. Furthermore, a dense polypyrrole layer can be formed evenly on the surface of the anode electrode, which has fine irregularities formed on the surface by the wave treatment, thereby increasing the capacitance per unit area.

【Example】

The present invention will be explained below based on Examples. First, aluminum foil was electrochemically etched to expand the surface area of the anode electrode. The surface of this aluminum foil was oxidized by anodizing treatment to form a dielectric oxide film layer. Note that the voltage for anodic oxidation was 50V. This anode foil was cut into a piece having a width of 2.2M and a length of 10mm, and an aluminum lead for leading out the electrode was connected to the end of the anode foil. Next, this anode electrode was immersed in an aqueous solution containing 10% ammonium persulfate, and after the immersion, it was dried through ventilation. After this treatment, the anode electrode was placed in a 5% concentration pyrrole-E/7-solution using hexane as a solvent at different temperatures for 3 hours.
A chemical polymerization reaction was performed by dipping for 0 seconds to form a polypyrrole film. The temperature of the solution is from <40°C to -90°C as shown in Table 1.
There were eight levels of temperature. This anode electrode foil was washed with water and dried, and the electrical conductivity of the chemically polymerized polypyrrole film formed on the surface was examined. The results are shown in Table 1. 1-TABLE ABOVE *Measurement of electrical conductivity was performed at 30°C. As can be seen from these results, it was found that lowering the temperature of the chemical polymerization reaction increased the electrical conductivity. However, when the temperature of the pyrrole solution drops below 140°C, the conductivity does not change. Next, a polypyrrole film was formed by electrolytic polymerization on the surface of each anode electrode in Table 1, a cathode electrode was formed, and an exterior was applied to complete the solid electrolytic capacitor, and its characteristics were investigated. The electrolytic polymerization conditions were the same for all anode electrodes, using a solution in which pyrrole monomer and borodisalicylic acid triethylamine salt as a supporting electrolyte were dissolved in an acetonitrile solvent at a concentration of 0.1 M #2, at room temperature. Electrolytic polymerization was performed for 60 seconds with a current of 0.5 mA to form a polypyrrole film. To draw out the cathode from this anode electrode, silver paste was applied to the entire surface of the electrolyte membrane, a lead wire was connected to a part of it, and epoxy resin was then applied to the entire outer surface and hardened to complete the solid electrolytic capacitor. . After aging this solid electrolytic capacitor, the electrical characteristics (capacitance, loss (Tanδ), equivalent series resistance value (ES
When R)) was measured, the results shown in Table 2 were obtained. Note that Tan δ is a value at 120 Hz, and ESR is a value at 100 KHz. A polypyrrole film with good orientation can be formed by chemical polymerization on the anode electrode on which the L-th surface conductor oxide film is formed. As a result, the electrical conductivity of polypyrrole is improved, and the impedance characteristics at high frequencies are improved. In addition, since a film that is dense and has good adhesion to the dielectric oxide film is obtained, the capacitance value per unit area of the electrode is increased, and a small-sized, large-capacity solid electrolytic capacitor can be obtained. As can be seen from the second result, the solid electrolytic capacitor produced by the method of the present invention has a higher capacitance value than the method of the comparative example, and has an equal density at high frequencies, which affects high frequency impedance. Series resistance (ESR
) is found to be low.

【Effect of the invention】

Claims (1)

[Claims] (1) A method for producing a solid electrolytic capacitor including a step of forming a solid electrolyte layer of polypyrrole by at least chemical polymerization on an anode electrode having a dielectric oxide film layer formed on the surface, wherein the chemical polymerization of the polypyrrole is carried out at 10°C to -
A method for manufacturing a solid electrolytic capacitor, characterized in that the manufacturing method is carried out in a temperature range of 70°C.