Electrolytic capacitor and method of preparing it

Details Electrolytic capacitor and method of preparing it Electrolytic capacitor and method of preparing it

1989-03-29

1990-11-13

Griffin, Donald A.

Electricity: electrical systems and devices

Electrolytic systems or devices

Liquid electrolytic capacitor

29 2503, H01G 902

Patent

active

049706268

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to an electrolytic capacitor using aluminum as electrode foil, utilized in various electronic equipments, and a method of preparing it.


BACKGROUND ART

Electrolytic capacitors of this type have been hitherto constituted of an anode foil on which an anodized dielectric film is formed, comprising a high purity aluminum foil electrolytically etched to expand its effective areas and then subjected to formation treatment, and a cathode foil employing an aluminum foil electrolytically etched to expand its effective areas, which foils are wound interposing a separator followed by impregnation with a driving electrolyte (hereinafter "paste").
Such electrolytic capacitors used in commonly available electronic equipments are strongly demanded to be made more compact and thinner with the trend of making various electronic equipments more compact and thinner.
Incidentally, the capacitance C of electrolytic capacitors is the composite capacitance of the anode capacitance C.sub..sym. with the cathode capacitance C.sub..crclbar., and represented by the following formula: ##EQU1## Accordingly, it has been attempted to increase not only the electrostatic capacitance of the anode foil but also that of the cathode foil, but an excessive etching causes surface dissolution of aluminum foils to proceed and prevents the electrostatic capacitance from increasing, and also the etching resulting from non-uniform dissolution brings about an extreme lowering of foil strength, so that, since the foils are made to have smaller widths to make them compact, it has been further impossible to wind foils in a high speed, thus leaving a limit in increasing the electrostatic capacitance of cathode foils by using electrolytic etching techniques.
As a means for improving it, it is known to form a titanium-deposited film on the roughened surfaces of aluminum foils (for example, Japanese Unexamined Patent Publications No. 180420/1986 and No. 214420/1986).
The cathode foils obtained by such a titanium vacuum deposition process can have a greater surface area and a more increased electrostatic capacitance than those obtained by the electrolytic etching process, but have had the disadvantages that they have too dense a structure to be impregnated with the paste with ease and therefore the electrostatic capacitance can be effectively exhibited with difficulty as capacitors.
They also have had the disadvantage that a lowering of capacitance is caused when vacuum deposition is continuously carried out.


DISCLOSURE OF THE INVENTION

The present invention aims at eliminating these disadvantages conventionally involved, and an object thereof is to provide an electrolytic capacitor that employs a high-capacitance cathode foil obtainable as a result of studying titanium vacuum deposition.
Namely, the present invention employs as the cathode foil an aluminum foil obtained by vacuum deposition of titanium with a deposition angle on the deposition surface, said vacuum deposition being carried out in an argon gas atmosphere kept within the range of from 1.0.times.10.sup.-5 to 1.0.times.10.sup.-4 Torr, while controlling to from 50.degree. to 200.degree. C. the temperature on the deposition surface of an aluminum foil substrate made to have an enlarged surface area.
Such titanium vacuum deposition results in the formation of a titanium film with a rough column-like structure comprising columns independent from each other. Employment of such an electrode enables the titanium column-like structure film to be impregnated with the paste through its details, resulting in an increase in the effective surface area, an improvement in the electrostatic capacitance, and an improvement in the electrostatic capacitance of electrolytic capacitors.


BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-a and 1-b are cross sections of aluminum foils;
FIG. 2 is a schematic view to illustrate a vacuum deposition method by which the deposition angle .theta. is given;
FIGS. 3 and 4 are views to show the relationship between the vacuum deposit

REFERENCES:
patent: 2647079 (1953-07-01), Burnham
patent: 2722637 (1955-11-01), Brennan
patent: 3245888 (1966-04-01), West et al.
patent: 4309810 (1982-01-01), Drake

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