Electrolysis: processes – compositions used therein – and methods – Electrolytic erosion of a workpiece for shape or surface... – Electrolyte composition or defined electrolyte
Utility Patent
1998-12-11
2001-01-02
Gorgos, Kathryn (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic erosion of a workpiece for shape or surface...
Electrolyte composition or defined electrolyte
C205S674000, C205S213000, C361S508000, C361S509000, C361S528000, C361S529000, C428S472200, C428S596000, C428S606000, C428S687000
Utility Patent
active
06168706
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a four-component acid electrolyte composition and method for etching aluminum anode foil to render it suitable for use in electrolytic capacitors, and to such electrolytic capacitors.
2. Related Art
In known processes for etching aluminum foil, an electrolytic bath is used that contains sodium chloride or other salt, as well as sulfate based electrolytes. Such a solution typically has a neutral pH. The etching is usually followed by treatment in nitric or hydrochloric acid.
U.S. Pat. No. 4,213,835 discloses a method for electrolytically etching an aluminum foil. This process involves a pari-potentiostatic etching technique using a constant anode potential in a traveling bath containing chloride ions. Foils are thus provided with tunnel densities greater than 10
7
tunnels/cm
2
of foil surface.
U.S. Pat. No. 4,420,367 discloses a method for etching an aluminum foil for electrolytic capacitors by carrying out an electrolytic tunnel etching process in a first etching stage, as known in the art. Non-electrolytic chemical etching is then used for enlarging the tunnels in one or several additional etching steps. The method is preferably carried out in a halogen-free or chloride-free solution having nitrate ions, such as HNO
3
and/or Al(NO
3
)
3
.
U.S. Pat. Nos. 4,474,657, 4,518,471 and 4,525,249 disclose the etching of aluminum electrolytic capacitor foil by passing the foil through an electrolyte bath. The bath contains 3% hydrochloric acid and 1% aluminum as aluminum chloride. The etching is carried out under a direct current (DC) and at a temperature of 75° C. 4,474,657 is limited to the above single step. 4,518,471 adds a second step where the etched foil is treated in a similar bath with a lower current density and at a temperature of 80-82.5° C. 4,525,249 adds a different second step, where the etched foil is treated in a bath of 8% nitric acid and 2.6% aluminum as a nitrate, at a temperature of 85° C.
However, such methods or compositions, which maintain adequate metal strength and improve capacitance, are not efficient enough to be suitable for use in the commercial production of electrolytic capacitors.
SUMMARY OF THE INVENTION
The present invention provides improved etching of aluminum anode foil for increased capacitance and/or metal strength, relative to known etching methods and compositions. The present invention provides the novel use of a four-component acid electrolyte to greatly improve etching gains in aluminum anode foil, suitable for use in electrolytic capacitors. The type of current, or the amount, ratio and/or concentration of a component used, provides the increased capacitance and/or metal strength.
Accordingly, the present invention provides improved methods and compositions for etching aluminum foil, as well as electrolytic capacitors comprising this foil.
REFERENCES:
patent: 4125674 (1978-11-01), Kimura et al.
patent: 4213835 (1980-07-01), Fickelscher
patent: 4420367 (1983-12-01), Lacher
patent: 4474657 (1984-10-01), Arora
patent: 4518471 (1985-05-01), Arora
patent: 4525249 (1985-06-01), Arora
patent: 5143587 (1992-09-01), Endoh et al.
patent: 5715133 (1998-02-01), Harrington et al.
Hemphill Ralph Jason
Strange Thomas Flavian
Gorgos Kathryn
Keehan Christopher M.
Mitchell Steven M.
Pacesetter Inc.
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