Stock material or miscellaneous articles – All metal or with adjacent metals – Surface feature
Reexamination Certificate
1999-04-07
2001-05-29
Valentine, Donald R. (Department: 1741)
Stock material or miscellaneous articles
All metal or with adjacent metals
Surface feature
C205S684000, C205S658000, C205S676000, C205S675000, C361S509000, C361S529000
Reexamination Certificate
active
06238810
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the use of a surface active agent that can also act as a viscosity modifier to promote the initiation of tunnels during the etching of high purity cubicity 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. 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. U.S. Pat. No. 4,474,657 is limited to the above single step. U.S. Pat. No. 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. U.S. Pat. No. 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 methods and compositions for the etching of anode foils, resulting in increased tunnel initiation and tunnel length control, relative to known etching methods and compositions. This invention makes use of surface active, viscosity modifying agents to promote tunnel initiation during the etching process, as well to control the length, depth and width of the etched tunnels, resulting in improved capacitance and increased foil strength. The present invention describes an etch suitable for the making of high gain anode foil to support 150 to 700 Volts of oxide.
The present invention provides the novel use of surface active, viscosity modifying agents to promote additional tunnel initiation during the etching process by modifying the surface energy such that additional sites are energetically favorable, and modifying the transition point between laminar flow and turbulent flow (the Reynolds number) such that initiation sites are less disturbed by adjacent active tunnel growth sites. Known etch electrolytes do not include this feature, and tunnel initiation is 10% to 20% lower than with the use of the agents of the present invention. This increased tunnel initiation results in a foil having a much higher surface area, providing increased capacitance, relative to known etching methods and compositions.
Tunnel length control can be obtained by varying the concentration of the surface active, viscosity modifying agent used. A higher concentration results in shorter tunnel lengths, producing a thicker web in the center of the foil (i.e., a larger amount of foil left behind in the center of the foil after tunnel initiation). This thicker web provides for an overall increase in foil strength, relative to known etching methods and compositions.
Surface active, viscosity modifying agents according to the present invention include but are not limited to the alcohols, specifically the diols such as ethylene glycol, glycerol, and butoxyethanol (butyl cellosolve). Other agents known to be surface active include: diacetin, propylene glycol, and butyrolactone. These agents are added in concentrations of 0.5% to 50% by weight to the etch electrolyte and the anode foil is etched in a manner known to those skilled in the art.
Accordingly, the present invention provides improved methods and compositions for etching anode foil, as well as electrolytic capacitors comprising this foil.
REFERENCES:
patent: 4213835 (1980-07-01), Fickelscher
patent: 4420367 (1983-12-01), Locher
patent: 4474657 (1984-10-01), Arora
patent: 4518471 (1985-05-01), Arora
patent: 4549944 (1985-10-01), Pliefke
patent: 5143587 (1992-09-01), Endoh et al.
Hemphill Ralph Jason
Strange Thomas Flavian
Mitchell Steven M.
Pacesetter Inc.
Valentine Donald R.
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