JPS6328027A - Electrode foil for electrolytic capacitor and manufacture of the same - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an electrode foil for electrolytic capacitors and a method for manufacturing the same.

BACKGROUND OF THE INVENTION Conventional techniques have conventionally been used to increase the surface area of electrode foils for electrolytic capacitors by etching their surfaces as skillfully as possible, with the aim of making capacitors smaller and larger in capacity. For example, Japanese Patent Publication No. 57-17080 discloses a method in which electrode foil is anodized and then etched, and Japanese Patent Publication No. 60-38861 discloses a method in which the surface of electrode foil is enlarged by a multi-step etching method. , also published in Japanese Unexamined Patent Publication No. 55
No. 11364 discloses a method of etching in tripolyphosphate. Furthermore, JP-A-61-5
No. 187 and also Japanese Unexamined Patent Application Publication No. 61-5188 disclose a method in which a large number of fine pores are formed on the surface of an aluminum foil that are resistant to an electrolytic etching solution and should form etching nuclei. Aluminum electrode material for electrolytic capacitors has a coating integrally attached to it, and when forming micropores, a coating material mixed with metal or non-metallic particles is applied to the surface of the aluminum foil, and then the particles are removed. It is disclosed that by doing so, it is possible to form a resistant coating in which a large number of micropores are formed.

Problems to be Solved by the Invention Among the conventional techniques, in the structure disclosed in the first three inventions, the surface of the electrode foil is always in uniform contact with the etching solution during etching. As a result, excessive machining and notching as shown in Figure 2 is inevitable.
However, the degree of surface roughening is poor. In addition, in the configurations according to the latter two inventions, if a corrosion-resistant film such as a photoresist that is insoluble in an etching solution is attached to the capacitor electrode material on the aluminum, a step of removing the resist film after etching is essential. At that time, when immersed in the removal solution,
Because resist components enter the inside of the aluminum electrode material, which has already been finely etched, it takes time and effort to remove it, and furthermore, it is extremely difficult to remove it sufficiently, resulting in a decline in capacitor characteristics. It also becomes.

In view of the above problems, the present invention provides an electrode foil for an electrode capacitor that can prevent excessive etching of the electrode foil and form etched bits evenly and uniformly on the valve metal that is the capacitor material. A manufacturing method is provided.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides an oxide of the valve metal itself having a large number of micropores on the surface of the valve metal. This involves forming resin bumps on the surface of the valve metal, oxidizing the metal surface, and then removing the bumps.

According to the above-described structure, the metal in the etched portion is exposed before etching the electrode foil, and the remaining portion is covered with metal oxide. In this case, the metal part is much more easily etched than the oxide part (excessive etching is also prevented, and the desired etching with a large surface area is performed).

EXAMPLES Below, the configuration of the present invention will be explained in an easy-to-understand manner based on FIG. As the metal having a valve action, metals well known for use in electrolytic capacitors such as aluminum, tantalum, and titanium are used.

Bumps 2 are formed on these valve metals Fi1.

Bump 2 is most suitable for raising with resin.
Specifically, the valve metal 1 is immersed in a suspension containing particles of thermoplastic resin such as styrene, acrylic, vinyl chloride, cellulose acetate, polycarbonate, polyethylene, etc., and heated after drying to dissolve the particles. It is made to adhere to the valve metal 1 by softening. Another method for forming resin bumps on metal foil is by electrodeposition coating or by introducing a heated valve metal foil into an atmosphere in which resin particles are suspended.

The particle size of the resin particles can be selected as desired according to the etching bit diameter, but considering that the purpose is to form an etched bit for an electrode capacitor, it is not a good idea to use particles that are too large. , a particle size of 0.1 to 10 microns, which is about the same as that of an etch bit, is suitable. Further, the number of bits can be easily adjusted by controlling, for example, the number of particles in the suspension and the coating thickness. Such resin particles having a relatively small particle size may be synthesized by flotation or suspension polymerization, or may be obtained by mechanically crushing large particles into fine particles. The valve metal foil 1 on which the bumps 2 have been formed in this way has an oxide film 3 formed thereon by anodizing or using various oxidizing agents to oxidize the exposed metal surface with no bumps formed thereon. Form. Electrode oxidation can be carried out by a conventional anodic oxidation method using a relatively conductive solution such as an organic acid such as carboxylic acid, halonic acid or phosphoric acid, or a salt thereof. In the case of chemical oxidation, oxidizing agents such as nitric acid, nitrates, hydrogen peroxide, etc. may be used, or simply immersion in a hot solution may be used. The valve metal foil 1 having the resin bumps 2 and the oxide film 3 adhered to its surface in this way is immersed in a solvent to remove the bumps 2.

The state when the bump 2 is removed is shown at 4 in FIG.

When the metal in the portion covered with the bumps 2 is exposed by the above procedure, a metal foil for an electrode capacitor electrode is obtained in which a valve metal oxide selectively having micropores is formed on the surface. Thereafter, this is immersed in an etching solution to form desired etch pits 5 in the metal part.

Etching can be performed using any known method, but a typical method is to immerse the metal foil in an aqueous solution containing chlorine ions and conduct the etching while applying electricity.

Next, Examples 1 and 2 show the electrode foil of the present invention and the characteristics of a capacitor made using the electrode foil.

Example 1 An aluminum foil with a thickness of 100 microns and a purity of 99.99% was immersed in an aqueous solution containing 0.8% by weight of PMMA particles with an average particle size of 0.2 microns. Apply evenly to the foil. By heating and drying at 60° C. for 15 minutes and heating at 140 to 170° C. for 5 minutes, PMMA bumps are evenly formed on the aluminum electrode foil. Next, the exposed aluminum portion is chemically converted in a 7% aqueous solution of boric acid at 55 V to form an oxide film. This is thoroughly washed with water, dried, and then immersed in methyl ethyl ketone to dissolve and remove the PMMA bumps.

Next, it was immersed in an aqueous solution consisting of 5% hydrochloric acid and 0.03% oxalic acid, and etched for 2 minutes at a liquid temperature of 80° C. and a current density of 3.5 mA/ant. Afterwards, when this aluminum foil was chemically converted in a 10% aqueous oxalic acid solution at 380 μm,
The capacitance of the obtained electrode foil was 0.88μF/cut
Met. As a comparative example, the capacitance of aluminum electrode foil when no resin bumps are formed is 0.73 μF/cot.
Therefore, an increase in capacity of about 20% was achieved with the aluminum electrode foil of the present invention.

Example 2 An aqueous solution containing suspended polystyrene particles with an average particle size of 0.45 microns and a concentration of 5% was prepared, and an aluminum foil with a thickness of 104 microns and a purity of 99.99% was immersed in this solution. The suspension was then uniformly applied to aluminum foil to a thickness of about 10 microns. After drying at 70° C. for 10 minutes, heat treatment is performed at 120 to 150° C. for 7 minutes to fuse the polystyrene particles onto the aluminum, thereby forming resin bumps evenly on the aluminum. This is chemically converted at 75V in a 5% phosphoric acid aqueous solution to form an oxide film on the exposed parts of the metal aluminum where no bumps are formed, washed with water, dried, and then treated with a toluene solution to form polystyrene bumps. Remove.

Next, etching was carried out for 2 minutes in a 5% hydrochloric acid and 0.03% oxalic acid aqueous solution at a liquid temperature of 85° C. and a current density of 3.0 mA/cnl. Thereafter, the aluminum electrode foil was immersed in a 10% aqueous oxalic acid solution and chemically converted at 380 μm, and the capacitance was measured, and a value of 0.82 μF/cal was obtained.

As a comparative example, the electrostatic capacitance of an electrode foil obtained by etching polystine resin bumps on aluminum without forming them and subsequent chemical conversion treatment was 0.69 μF.
/d. As is clear from the above results, a 17% increase in capacity was observed by using the resin hump-forming electrode of the present invention.

Effects of the Invention As described above, the present invention forms a large number of micro bumps on the surface of a valve metal, then oxidizes the surface,
An oxide film of the valve metal is formed on the exposed surface of the valve metal, and then the bumps are removed and an etching process is performed to prevent excessive etching and ensure uniform and even etching. As a result, the surface roughness of the electrode foil becomes much greater than in the past, which greatly contributes to downsizing and increasing the capacity of electrolytic capacitors.

Furthermore, it is possible to some extent to control the pit diameter and the number of focuses by selecting the particle diameter of the resin hump, which is advantageous for stabilizing quality. Furthermore, since the present invention does not use an insoluble, corrosion-resistant resist material in the etching solution, it is not necessary to remove this material, and the capacitor characteristics will not be deteriorated due to the presence of this component on the electrode material. Further, the present invention can be applied to fine spot etching on general metals other than valve metals for electrolytic capacitors.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an electrode droplet for an electrolytic capacitor according to an embodiment of the present invention, and FIG. 2 is a sectional view of a conventional electrode foil for an electrolytic capacitor. 1... Valve metal foil, 2... Bump,
3...Oxide film, 5...Esochip 7, 6...Excessive etching. Name of agent: Patent attorney Toshio Nakao Hakaichimeika 1 Figure /-Ichito action court foil Figure 2

Claims (2)

[Claims] (1) An electrode foil for an electrolytic capacitor comprising an oxide of a valve metal having a large number of micropores on the surface of the valve metal. (2) Forming a large number of micro bumps on the surface of the valve metal,
Thereafter, the surface is oxidized to form an oxide film of the valve metal on the exposed surface of the valve metal, and then the bumps are removed and the surface of the valve metal is oxidized. A method for manufacturing an electrode foil for an electrolytic capacitor, comprising forming an oxide of the valve metal having a large number of micropores.