Chemistry: electrical and wave energy – Processes and products – Electrostatic field or electrical discharge
Patent
1986-04-30
1988-05-03
Valentine, Donald R.
Chemistry: electrical and wave energy
Processes and products
Electrostatic field or electrical discharge
20412975, 204DIG9, 20412943, C25F 304
Patent
active
047418125
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method for etching electrode foil for aluminum electrolytic capacitors.
The so-called aluminum electrolytic capacitor is constituted by rolling an aluminum electrode foil and an insulating paper and impregnating the roll with an electrolyte for its driving. In this capacitor, the aluminum electrode foil has its surface undulated to increase its area by etching it, thereby increasing the elevating surface enlarging factor (surface area after etching/surface area before etching) of the aluminum foil is used. Heretofore, as the methods for etching the electrode foil for the aluminum electrolytic capacitors mainly for use at such a low voltage as less than 100 W.V., the following two methods normally have been normally employed.
Thus a first method is that using an etching solution of hydrochloric acid as its main component. The etching is performed, with placing an aluminum foil between two electrode plates facing each other and in parallelism thereto and with allowing an alternating current flowing to through the etching solution between the two electrode plates, without current directly flow through the aluminum foil.
A second method is that using an etching solution of sodium chloride as its main component. The etching is peformed, with immersing an aluminum foil in this etching solution, and by permitting a direct current or alternating current or alternating current-superposed direct current to flow in the etching solution between the aluminum foil and an electrode or electrodes placed on one or both sides of the aluminum foil.
However the first etching method was disadvantageous in that only a current that has symmetrical wave forms in its positive and negative cycle permits independent changes in its positive and negative wave width and in its positive and negative current densities, thus detracting from adequate enhancement of the surface enlarging factor, all the more so in view of the searching for on further miniaturization hereafter of aluminum electrolytic capacitors. The second etching method had a grave defect in that because of the use of a nearly neutral aqueous solution of sodium chloride as the etching solution, the aluminum ion which dissolves during electrolytic etching deposits on the production equipment or the like as hydroxide thereof (white powder); which interferes with smooth proceeding of production and upgrading of operation rate.
SUMMARY OF THE INVENTION
The present invention, is intended eliminate such prior art difficulties, and aims at enhancing the operation rate of the production equipment as well as producing aluminum foil having a high surface enlarging factor in an acidic hydrochloric acid solution, which does not form white powder.
Thus, according to the present invention, in conducting electrolytic etching with alternating current, using acidic hydrochloric solution which does not produce white powder as the etching solution, by a method of independently setting etching current wave forms of the positive and negative cycle by the etching current flow directly through the aluminum foil, a condition for the electrolytic etching by an alternating current is set that the ratio of the negative to the positive cycle electric charge to be impressed on the aluminum foil is in a range between 0.2 to 2.0, and duty ratio is at 51-90%.
In this way, an aluminum foil which shows higher surface enlarging factor can be obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 A and 1 B are wave form graphs showing wave forms of the current which is impressed on aluminum foil in the method for etching the electrode foil for aluminum electrolytic capacitors of the present invention;
FIG. 2 is a characteristic graph showing the relationship between the ratio of negative to positive cycle part of the electric charge impressed on the aluminum foil and the surface enlarging factor according to the method of the present invention; and
FIG. 3 is a characteristic graph showing the relationship between the duty ratio (=positive wav
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Kanzaki Nobuyoshi
Kojima Kouichi
Okabayashi Masanori
Shimatani Ryouichi
Touyama Kenji
Matsushita Electric - Industrial Co., Ltd.
Valentine Donald R.
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