1. Field of the Invention
The invention relates to a method of manufacturing a metal foil for an electrolytic capacitor, which is used for an anode foil or a cathode foil, and an electrolytic capacitor using the same.
2. Description of the Related Art
In the modern society, automobiles and electric appliances such as televisions and personal computers have been so widely spread as to be indispensable for daily lives. High performance of electronic parts such as electrolytic capacitors greatly contributes to high functionalization of these products.
In a general electrolytic capacitor, a metal foil made of a valve metal such as aluminum, tantalum, titanium and the like is used for an electrode foil. For example, an electrolytic capacitor, produced by forming a capacitor element in which a rectangular anode foil and a rectangular cathode foil are wound, impregnating a driving electrolytic solution between the rectangular anode foil and the rectangular cathode foil and housing the capacitor element in a casing, has been commercialized. Also, a solid electrolytic capacitor containing a solid electrolyte excellent in electric conductivity such as polythiophene and polypyrrole, instead of the driving electrolytic solution, has been commercialized.
A metal foil for use in such electrolytic capacitors, for example, is manufactured by following method. First, a wide metal strip is subjected to etching treatment to widen the surface area. Next, a wide metal strip for an anode foil having an anodic oxide film which is formed by anodizing the surface of the etched wide metal strip and a wide metal strip for a cathode foil which is only performed the etching treatment are prepared. Thereafter, in a slitting step, these respective wide metal strips are slit in predetermined width with a cutting blade. Further, in a cutting step, the slit metal sheets are cut in pieces by a cutting apparatus to produce rectangular metal foils. (See, for example, Japanese Unexamined Patent Publication No. 2007-152436)
Recently, a variety of electronic parts tend to be installed in automobiles and the like for high functionalization. Therefore, electrolytic capacitors with high withstanding voltage having a rated voltage as high as 25 V or 35 V have been required.
However, such electrolytic capacitors with high withstanding voltage have a problem that a short circuit is likely to be caused at the time of manufacture. According to investigations of the present inventor, it is supposed that burrs and cracks produced at a slit edge surface of an anode foil or a cathode foil to be used for manufacturing an electrolytic capacitor with high withstanding voltage are causes of the problem. Specifically, in the case where the anode foil and the cathode foil of an electrolytic capacitor are produced, as described above, by carrying out the slitting step of slitting the wide metal strip subjected to etching treatment in predetermined width, it is required to use metal foils with large etching pits as the anode foil and the cathode foil to produce the electrolytic capacitor with high withstanding voltage. Therefore, when the wide metal strip is slit, the unevenness of the slit edge surface becomes large and accordingly, burrs and cracks tend to be formed at the slit edge surface. Particularly, because the hard anodic oxide film is formed on the surface of the wide metal strip for the anode foil, the cutting blade becomes dull and whereby, burrs and cracks are easy to be formed at the slit edge surface.
In the case where the metal foil having burrs and cracks at the slit edge surface is used to manufacture an electrolytic capacitor, both electrode foils are electrically conducted with the burrs and whereby, a leak current tends to be increased or a short circuit tends to be occur. Further, due to progression of cracks, the leak current tends to be further increased and the capacity tends to be lowered. Therefore, in the industrial manufacture, there is a problem that defective products causing the short circuit and the like tend to be increased and the production yield tends to be lowered.