JPH0423410B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for manufacturing a capacitor using a conductive polymer as a solid electrolyte. (Prior Art) In recent years, with the development of digital equipment, the emergence of large-capacity capacitors with low impedance and excellent high-frequency characteristics in the high-frequency region has been awaited, and research in this field has become active. Currently known capacitors with excellent high frequency characteristics include capacitors made of film, mica, ceramics, etc.
If you try to obtain a capacitance of 1 μF or more, the size will become large and the price will become extremely high. Furthermore, electrolytic capacitors, which are known as large-capacity capacitors, include electrolyte type and solid type. The former electrolytic capacitor uses a liquid electrolyte and is ionic conductive, so the resistance increases significantly in the high frequency range and the impedance of the capacitor increases. The latter electrolytic capacitors include those that use manganese dioxide and those that use 7,7,8,8-tetracyanoquinodimethane (abbreviated to TCNQ) complex as a solid electrolyte. In capacitors using manganese dioxide as a solid electrolyte, since manganese dioxide is an insoluble solid, manganese dioxide obtained by thermally decomposing manganese nitrate is used as the solid electrolyte.
This thermal decomposition is usually repeated several times. Manganese dioxide has drawbacks such as high impedance and large leakage current due to its relatively high resistivity and its tendency to damage the oxide film of its derivative during repeated thermal decomposition.
In capacitors using TCNQ complexes as solid electrolytes (JP-A-58-191414, JP-A-58-17609, etc.), the TCNQ complex shows high conductivity.
Due to its poor thermal stability, it may decompose during the capacitor manufacturing process and become an insulator, which has disadvantages in the capacitor's thermal characteristics. Although it has not yet reached the level of practical use, a method for manufacturing capacitors using electrolytic polymerization of a polymer of a heterocyclic compound as a solid electrolyte has been proposed (Japanese Patent Application Laid-Open No. 1989-1999).
244017, JP-A-61-2315, etc.). The above method is a method of forming a polymer thin film layer of a heterocyclic compound on an anodic oxide film by electrolytic oxidation. In this method, the anodic oxide film layer is insulated, so
It is impossible or very difficult to electrolytically polymerize a heterocyclic compound onto an anodic oxide film layer by electrolytic oxidation. Furthermore, even if electrolytic oxidation polymerization occurs from pinholes in the anodic oxide film layer, the film will be non-uniform, which poses a serious problem in practice. (Problem to be solved by the invention) There are chemical oxidation polymerization methods and electrolytic oxidation polymerization methods to synthesize conductive polymers, but chemical oxidation polymerization methods cannot form a strong film on the anodic oxide film layer. In addition, in the electrolytic oxidation polymerization method, since the anodic oxide film layer is an electrical insulator, it does not conduct current, making it impossible to form a strong conductive polymer film thereon. The present inventors formed a dielectric oxide film on a film-forming metal, formed a chemically oxidized conductive polymer film on the dielectric oxide film, and further formed an electrolytic polymer film of a conductive polymer on top of this. We proposed a solid electrolytic capacitor with a structure in which it was formed (Patent Application No. 62-4053). This capacitor is a solid electrolytic capacitor with large capacitance and excellent electrical and temperature characteristics, but there is still room for consideration regarding its manufacturing method, and in particular, there are areas that need improvement regarding the efficiency of electrolytic polymerization. It remained. (Means for Solving the Problems) As a result of various studies in order to improve the efficiency of electrolytic polymerization, the present inventors formed a dielectric oxide film on a film-forming metal foil, and added an oxidized film on the dielectric oxide film. After forming a conductive polymer film by chemically oxidizing and polymerizing pyrrole, thiophene, aniline, or furan using a chemical agent, cut the edge of the metal foil and place it on top of the conductive polymer film while leaving the metal part exposed. By laminating conductive polymer films obtained by electrolytic polymerization, the electrolytic polymerization time is 1/5 that of forming an electrolytic polymer film on a chemically oxidized polymer film without cutting. We found that it can be shortened to ~1/10. To explain the present invention in more detail with reference to FIG. 1 showing the structure of a capacitor obtained by the method of the present invention, a film-forming metal foil 1 whose surface has been roughened by etching is subjected to electrolytic oxidation or air oxidation to remove oxides of the metal. A dielectric oxide film 2 is created.
Then, an oxidizing agent is applied on the dielectric oxide film 2.
After uniformly dispersing a solution containing 0.001mol/~2mol/by a method such as coating or spraying, the conductive polymer and the monomer are brought into contact with a solution containing at least 0.01mol/~2mol/without solvent, or conversely, the conductive polymer and the monomer are brought into contact with a solution containing at least 0.01mol/~2mol/ After uniformly dispersing molecular monomers on the dielectric surface, contact with an oxidizing agent to form a conductive polymer film 3 on the dielectric oxide film layer 2 by chemical oxidation polymerization,
Make the surface conductive. Next, the end of the film-forming metal foil whose surface has been made conductive is cut, used as an anode, and placed in an electrolytic solution containing 0.01 mol/~2 mol/of a supporting electrolyte and 0.01 mol/~5 mol/of a conductive polymer monomer. When electrolytic oxidation polymerization is carried out, a tough conductive polymer film 4 that has been electrolytically oxidized and polymerized is obtained on the conductive polymer film 3 that has been polymerized using an oxidizing agent. The cut surface of the film-forming metal foil exposes the metal and comes into contact with the conductive polymer film 4, resulting in a large leakage current. The surface is chemically repaired to form an oxide film to prevent leakage current. Further, a counter electrode lead is taken out using commonly used silver paste or the like and covered with epoxy resin or the like to obtain a capacitor. The film-forming metal foil of the present invention uses aluminum or tantalum. The oxidizing agents used in the chemical oxidative polymerization of the present invention include crude iodine, bromine, halogens such as bromine iodide, arsenic pentafluoride, antimony pentafluoride, silicon tetrafluoride, phosphorus pentachloride, phosphorus pentafluoride, and chloride. Aluminum, metal halides such as molybdenum chloride, protic acids such as sulfuric acid, nitric acid, fluorosulfuric acid, trifluoromethanesulfuric acid, and chlorosulfuric acid, oxygenated compounds such as sulfur trioxide and nitrogen dioxide, sodium persulfate, potassium persulfate, and ammonium persulfate. Oxidizing agents such as persulfates, hydrogen peroxide, peracetic acid, difluorosulfonyl peroxide, and other peroxides are used. The conductive polymer film formed by chemical oxidative polymerization of the present invention uses polypyrrole, polythiophene, polyaniline, or polyfuran, and particularly preferably uses polypyrrole. The supporting electrolyte in the present invention includes anions such as halide anions such as hexafluoroline, hexafluoroarsenic, and tetrafluoroborine, halogen anions such as iodine, bromine, and chlorine, perchlorate anions, alkylbenzenesulfonic acids, nitrobenzenesulfonic acids, and aminobenzene. Sulfonic acid anions such as sulfonic acid, benzenesulfonic acid, and β-naphthalenesulfonic acid, preferably sulfonic acid anions. Also, the cation is lithium,
These are alkali metal cations such as sodium and potassium, and quaternary ammonium cations such as ammonium and tetraalkylammonium. Compounds include LiPF ₆ , LiAsF ₆ , LiClO ₄ , NaI,
NaPF ₆ , NaClO ₄ , KI, KPF ₆ , KAsF ₆ ,
Examples include KClO ₄ , LiBF ₄ , sodium toluenesulfonate, and tetrabutylammonium trienesulfonate. The conductive polymer obtained by electrolytic oxidative polymerization of the present invention includes polypyrrole, polythiophene, polyaniline, and polyfuran, preferably polypyrrole. In the present invention, the foil may be cut anywhere as long as it is immersed in the electrolytically polymerized solution. EXAMPLES The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to these Examples. Example 1 Chemical conversion treatment was performed to form an aluminum oxide dielectric film on the surface, and the submerged capacity was 2, 5, and 5, respectively.
Thickness 60μm width 15mm with values of 10, 20, 100μF/ ^cm2
Each 25 mm long aluminum anode foil was placed in an aqueous solution of 0.04 mol/ammonium persulfate under reduced pressure.
After soaking for 10 minutes, it was dried. This was immersed in an acetonitrile solution containing 2 mol of pyrrole monomer for 10 minutes under reduced pressure to form a polypyrrole thin film on the aluminum oxide dielectric by chemical oxidative polymerization. Next, the aluminum anode foils subjected to the above treatment were cut into pieces of 5 mm in width and 8 mm in length, and were treated with an aqueous solution containing 0.2 mol of pyrrole monomer, 0.02 mol of oxalic acid, and 0.05 mol of tetrabutylammonium toluenesulfonate as a supporting electrolyte. immersed in it. The aluminum anode foil is used as an anode,
Current density 0.5mA/cm ² using stainless steel plate as cathode
Under these conditions, constant current electrolysis was carried out until an electrolytically polymerized film was formed on the entire surface of the aluminum anode foil with the ends cut off, and as a result, a uniform dark green polypyrrole thin film was formed on the surface. Table 1 shows the time required to complete electrolytic polymerization. This foil was placed in an air bath at 130°C, and a constant voltage of 4V was applied for 12 hours using the aluminum anode foil as the anode and the polypyrrole film as the cathode to prevent leakage current. Next, silver paste was applied to this surface to take out the counter electrode lead, which was then covered with epoxy resin to complete the capacitor. Table 2 shows the initial performance of the obtained capacitor. (Comparative Example) A chemical conversion treatment was performed by electrolytic oxidation to form an aluminum oxide dielectric on the surface. Thicknesses with liquid capacitance values of 2, 5, 10, 20, and 100μF/ ^cm2, respectively.
60μm width 15mm length 25mm aluminum anode foil,
A chemically polymerized polypyrrole thin film was formed in the same manner as in Example 1 above. Next, without cutting the aluminum anode foil that had undergone the above treatment, an electrolytic polymer film was formed in the same manner as in Example 1, and a constant current was applied until an electrolytic polymer film was formed on the entire surface of the aluminum anode foil. As a result of electrolysis, a uniform dark green polypyrrole thin film was formed on the surface. The time required to complete electrolytic polymerization is the first
Shown in the table. Table 2 shows the initial performance of the obtained capacitor.

【table】

[Table] (Effects of the invention) As mentioned earlier, a chemical polymer film of conductive polymer is formed on a dielectric oxide film, which is an electrical insulator, and then electrolytic polymerization is performed to form a strong electrolytic polymer film. It has become possible to manufacture solid electrolytic capacitors by forming the film on a chemically polymerized film, but the method of the present invention, that is, after forming the chemically polymerized film, cuts the ends of the metal foil to expose the metal part. The method of performing electrolytic polymerization while the metal is in the same state can significantly shorten the time required to form an electrolytically polymerized film on a thin metal film of the same area as in the previous method.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view showing the structure of a solid electrolytic capacitor obtained by the method of the present invention. 1... Film-forming metal, 2... Dielectric oxide film, 3... Conductive polymer film formed by chemical oxidative polymerization, 4... Conductive polymer film obtained by electrolytic polymerization.

Claims (1)

[Claims] 1. A dielectric oxide film is formed on a film-forming metal foil, and a chemically oxidized and polymerized conductive polymer film of pyrrole, thiophene, aniline, or furan is formed on the dielectric oxide film using an oxidizing agent. After forming, the end of the film-forming metal foil is cut to expose the metal part, and then electrolytically polymerized to form an electrolytically polymerized conductive material of pyrrole, thiophene, aniline, or furan on the chemically oxidized conductive polymer film. 1. A method for manufacturing a foil-type solid electrolytic capacitor, which is characterized by laminating a polymer film. 2. The method for manufacturing a foil solid electrolytic capacitor according to claim 1, wherein the film-forming metal foil is aluminum or tantalum. 3. The method for manufacturing a foil solid electrolytic capacitor according to claim 1, wherein the conductive polymer film subjected to chemical oxidative polymerization using an oxidizing agent is polypyrrole. 4. The method for manufacturing a foil solid electrolytic capacitor according to claim 1, wherein the electrolytically polymerized conductive polymer film laminated on the chemically oxidized conductive polymer film is polypyrrole.