Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Involving measuring – analyzing – or testing
Reexamination Certificate
2001-04-03
2004-04-27
Nicolas, Wesley A. (Department: 1742)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Involving measuring, analyzing, or testing
C205S082000, C205S081000, C205S316000, C205S324000, C205S323000, C205S138000
Reexamination Certificate
active
06726825
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for manufacturing a positive electrode foil of an aluminum electrolytic capacitor.
BACKGROUND OF THE INVENTION
Aluminum electrolytic capacitors are widely used in the circuits of electronic apparatuses. A common type of aluminum electrolytic capacitor comprises a capacitor element having a positive electrode foil and a negative electrode foil separated by a separator and wound to a roll, a driving liquid electrolyte permeated into the capacitor element, and a metal case accommodating the capacitor element.
The positive electrode foil is conventionally manufactured by the following procedure. An aluminum foil is etched to increase its effective surface area and coated by anodizing process with a dielectric oxide film. The effective surface area is controlled with determining the etching conditions, Controlling an applied voltage in an anodizing process determines a thickness of the film, and thereby, a rated voltage and a capacitance of a finished capacitor can be controlled.
FIG. 7
is a flowchart of a conventional procedure of manufacturing the positive electrode foil. In the etching process, an aluminum foil
71
having a thickness of 0.05 to 0.11 mm and a length of about 5000 m provided in a coil form is continuously etched by the etching operation
72
in an etching apparatus. The apparatus is equipped with a control panel
73
manually preset with the etching conditions for a desired effective surface area. The etched foil
74
is rolled in every 1,000 m into a coil specified with a lot number. Each lot of the etched foil
74
is then subjected to a characteristic inspection
75
(conforming to EIAJ RC-2364A).
In general, a number of the etching apparatuses are used for manufacturing the etched foils
74
having the same effective surface area.
In the anodizing process, each etched foil
76
is continuously impressed with a constant voltage in the anodizing operation
77
in an anodizing apparatus to obtain a dielectric oxide film, i.e., an anodized foil
79
. The anodizing apparatus is equipped with a control panel
78
preset manually with the anodizing conditions based on the rated voltage and the desired effective surface area of the etched foil
74
. The anodizing conditions may include predetermined levels (data from the preceding experiments and production) of applied voltage and current and temperatures in the anodizing process.
The anodized foil
79
is then subjected to a characteristic inspection
80
(conforming to EIAJ RC-2364A) and a judgment
81
before a finished positive electrode foil
82
is released.
If, in the characteristic inspection
80
, it is judged that the resultant rated voltage and capacitance are not desired values, the anodizing conditions are updated to obtain them.
FIG. 8
illustrates such an anodizing apparatus. The anodizing apparatus is fed with an etched foil
91
generally having a thickness of 0.05 to 0.11 mm, a width of 500 mm, and a length of 500 to 1,000 m. The etched foil
91
is passed over a feed roller
92
connected to the positive electrode of a first direct-current source
97
and introduced by a running roller
93
into an anodizing tank
96
. The anodizing tank
96
has a plurality of cathode electrodes
95
arranged therein in parallel with the etched foil
91
to be passed and is filled with an anodizing processing liquid. In the anodizing tank
96
, the etched foil
91
serving as the positive electrode is anodized to obtain a dielectric oxide film thereon. The etched foil
91
coated with the dielectric oxide film is pulled out from the anodizing tank
96
, and then, conveyed via a depolarization tank
98
to a first re-anodizing tank
99
and a second re-anodizing tank
101
. Each of the re-anodizing tanks
99
and
101
has a plurality of cathode electrodes arranged therein and connected to a second direct-current source
100
for a continuous re-anodizing process of the etched foil
91
. Finally, the etched foil
91
is passed through a post-process tank
102
and rolled for obtaining a roll of a positive electrode foil
103
. The voltage of the second direct-current source
100
is determined based on a measured voltage detected with a voltage-detecting roller
104
provided before the roll of positive electrode foil
103
.
Another anodizing process is disclosed in Japanese Patent Laid-open Publication No. 2-128415. When impressed with different levels of the anodizing voltage in steps, an aluminium foil is depolarized in a certain period between any two steps of the anodizing. This will minimize a leakage current on the positive electrode foil.
Also, a manufacturing apparatus disclosed in Japanese Patent Laid-open Publication No. 58-197713 includes a pair of current electrode and voltage electrode sandwiching the electrode foil in a processing liquid. While the current electrode is fed with an alternating current, the voltage at the voltage electrode is measured by a phase sensitive voltmeter and used for controlling the anodizing process.
The conventional method of manufacturing the positive electrode foil
82
however causes the effective surface area of the etched foil
76
to vary between the etching apparatuses. This hardly ensures a constant capacitance in any capacitor with the positive electrode foil
82
manufactured from an aluminum foil
76
by the anodizing process
77
even under the predetermined anodizing conditions. That is because the dielectric oxide film is not uniform in the thickness due to a change of the current for the anodizing process
77
. The change is caused by variations of the effective surface area of the foil
76
.
Therefore, the step of judgment
81
is provided after the step
80
for inspecting the properties of the anodized foil
79
in the beginning of the anodizing process. When the judgment
81
is negative, the anodizing conditions are modified and re-set. This hence produces a loss in the time for manufacturing the anodized foil
79
.
For continuously manufacturing the positive electrode foils
82
of different rated voltages with a single anodizing apparatus, an aluminum foil is inserted between the anodized foils
79
of different voltages for inhibiting the anodizing conditions for the preceding lot from affecting to the succeeding lot. This makes the procedure more difficult, and in worse case, produce defectives of the anodized foil
79
.
Moreover, as the anodizing conditions are set by an operator, they may often have artificial errors.
The etched foil
76
is varied in the effective surface area along the lengthwise direction. This will hardly be overcome by the anodizing conditions calculated in each lot. In the conventional anodizing apparatus shown in
FIG. 8
, while the output of the second direct-current source
100
is controlled based on a measured voltage detected by the voltage sensor roller
104
, the voltage in the tank
99
may vary corresponding to the specific resistance of the etched foil
91
between the first re-anodizing tank
99
and the voltage sensor roller
104
. As a result, the positive electrode foil
103
is hardly uniform in the capacitance and the withstanding voltage along the lengthwise direction.
In the method disclosed in Japanese Patent Laid-open Publication No. 02-128415, the aluminum foils is impressed with different levels of the anodizing voltage at multiple steps, and more specifically, with a constant anodizing voltage at each tank for the anodizing process. Consequently, the withstanding voltage of the finished anodizing film can hardly be examined. As a result, a capacitor employing the positive electrode foil may hardly be uniform in the capacitance and the withstanding voltage.
In the apparatus disclosed in Japanese Patent Laid-open Publication No. 58-197713, the electrode foil is measured at a particular portion for measuring anodizing conditions using a pair of the current electrode and the voltage electrode. And thus, the anodizing condition is hardly controlled throughout the length based on the measurement at the particular position.
S
Kurihara Naomi
Nakamura Katsuyuki
Nakanishi Kazuaki
Nakano Hiroyuki
Okabayashi Masanori
Matsushita Electric - Industrial Co., Ltd.
Nicolas Wesley A.
Parkhurst & Wendel L.L.P.
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