Electricity: electrical systems and devices – Electrolytic systems or devices – Liquid electrolytic capacitor
Reexamination Certificate
2000-07-31
2002-04-02
Reichard, Dean A. (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Liquid electrolytic capacitor
C361S527000, C361S502000, C361S512000, C361S519000, C361S523000
Reexamination Certificate
active
06366447
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an electrolytic capacitor, and more specifically, to an electrolytic capacitor with an improved sealing structure.
BACKGROUND OF THE INVENTION
(1) Conventional Electrolytic Capacitor
As shown in
FIG. 22
, the electrolytic capacitor structurally comprises capacitor element
20
formed by winding both anode and cathode electrode foils connected with lead terminal
10
as electrode drawing unit via a separator, and outer case
30
made of aluminium and a rigid resin in a bottomed cylindrical shape, where the capacitor element
20
is sealed. In this case, the lead terminal
10
is drawn outside through through-hole
41
of sealing body
40
fitted on the inner periphery of the opening of the outer case
30
. Herein, rubber of a low elasticity modulus has been used as the sealing body
40
, from the respect of retaining the air tightness between the lead terminal
10
passing through the sealing body
40
and the outer case
30
. As shown in
FIG. 23
, alternatively, the lead terminal
10
comprises plain portion
11
connected to an electrode foil, round rod portion
12
for passing through the sealing body, and external connection portion
13
.
Electrolytic capacitor as shown in
FIGS. 22 and 23
is generally produced by the following procedures. As shown in
FIG. 23
, more specifically, a high-purity aluminium foil in a band shape is subjected to a chemical or electrochemical etching process so that the surface of the aluminium foil can be enlarged; and then, the aluminium foil is subjected to a chemical process in chemical solutions such as aqueous ammonium borate solution. Thus, anode electrode foil
21
with an oxide film layer formed on the surface thereof and cathode electrode foil
22
made of the high-purity aluminium foil singly processed with etching are prepared. As shown in
FIG. 23
, then, the plain portions
11
,
11
of a pair of the lead terminals
10
,
10
are individually connected to these anode electrode foil
21
and cathode electrode foil
22
; then, the resulting both anode and cathode electrode foils
21
,
22
are wound via a separator made of manila paper and the like, to form the capacitor element
20
(element formation process).
Subsequently, the formed capacitor element
20
is impregnated with an electrolyte solution for driving electrolytic capacitor (electrolyte solution impregnation process). Continuously, the capacitor element
20
is placed and sealed in the outer case
30
in the bottomed cylindrical shape (assembly process). At the assembly process, firstly, the lead terminal drawn out of the capacitor element
20
is inserted in the through-hole of the sealing body
40
, thereby moving the lead terminal
10
relative to the sealing body
40
; by subsequently drawing the whole external connection portion
13
of the lead terminal
10
from the through-hole, the round rod portion
12
of the lead terminal
10
is fixed in the through-hole of the sealing body
40
. As shown in
FIG. 22
, then, the capacitor element
20
is placed in the outer case
30
; after the sealing body
40
is fitted on the opening of the outer case
30
, subsequently, the opening of the outer case
30
is subjected to a drawing process, which serves to seal the outer case
30
(assembly process).
(2) Conventional Sealing Body
As the sealing body
40
for sealing the opening of the outer case
30
in such conventional electrolytic capacitor as described above, rubber at a high elasticity modulus has been used from the respect of retaining the air tightness between the lead terminal
10
through the sealing body
40
and the outer case
30
. Because rubber has a larger gas permeability constant, the electrolyte solution permeates through the rubber and is dispersed outside or exogenous gas (water, oxygen and the like) infiltrates into the inside of the case, when the rubber is used as the sealing body. Accordingly, the capacitor performance has thereby been deteriorated.
So as to prevent such occurrence, the use of a metal material or a rigid resin or the like with a small gas permeability constant as the sealing body is suggested. Because materials with small gas permeability constants generally have large elasticity moduli and are of high rigidity compared with rubber, it is difficult to retain the air tightness of the contact portion between the lead terminal passing through the sealing body and the outer case.
As shown in
FIG. 22
, therefore, a technique has been developed, so as to attain the reduction of the gas permeability and the enhancement of the air tightness of the contact portion between the lead terminal and the sealing body by drawing the lead terminal from the elastic body, and the technique comprises constituting a sealing body by bonding a tube-like elastic body made of rubber or a fluorine resin or the like to a sealing plate made of a rigid resin or the like or imbedding the tube-like elastic body in the sealing plate and drawing the lead terminal from the elastic body. Additionally, such technique is disclosed in for example Japanese Utility Model Laid-open Nos. 7317/1980, 115041/1980 and 132936/1980.
(3) Problems of Such Sealing Structure
As mentioned above, however, the elastic body bonded to the sealing plate or integrally imbedded in the sealing plate can have high shape stability but is relatively not readily deformable.
In conventional elastic bodies integrated with sealing plates with high rigidity, the deformation of the elastic bodies along the longitudinal direction is disturbed by the sealing plates and therefore, the elastic bodies cannot elongate along the longitudinal direction, even when the round rod portion of the lead terminal applies pressure to the elastic bodies during the insertion of the lead terminal through the elastic bodies. Consequently, the elastic bodies are compressed, leading to the volume reduction and the emergence of high stress, so that a high insertion pressure is disadvantageously applied to the lead terminal. Additionally, the elastic bodies cannot be made of materials with high elasticity moduli, involving large gas permeability constants. Hence, gas permeation can never be reduced.
So as to reduce the pressure during the insertion of the lead terminal, alternatively, the inner diameter of an elastic body can be almost equal to the outer diameter of the round rod portion of the lead terminal. In that case, however, slight error in the dimension of the elastic body occurs in a dependent manner on the processing precision and dimensional precision of the elastic body, which reduces the air tightness between the elastic body and the lead terminal, involving the enlargement of the variation of the life profile, disadvantageously.
On contrast, a modification of the production method of sealing bodies enables the procurement of a higher processing precision and a higher dimensional precision than conventional ones, but such modification induces the reduction of the productivity and also raises the production cost, undesirably.
Furthermore, the conventional methods comprising bonding an elastic body to the inner face of the through-hole of a sealing plate or imbedding an elastic body in the inner face thereof during the molding of the sealing plate requires complicated procedures, disadvantageously, leading to the reduction of the productivity.
(4) Problems due to Electrolyte Solution
Various types of electrolyte solutions for the impregnation of capacitor element
3
and for driving electrolytic capacitor have been known, and the performance of an electrolyte capacitor depends on the electrolyte solutions used therein. Among them, an electrolyte solution using y- butyrolactone as the principal solvent and so-called quaternary ammonium salt as the dissolving substance, namely a salt comprising tetraalkylammonium ion as the cation component and an acid-conjugated base as the anion component has been known.
The electrolyte solution using the quaternary ammonium salt characteristically has low electric resistance and has great thermal stability, but is nevertheless li
Nguyen Ha
Nippon Chemi-Con Corporation
Price and Gess
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