Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Cell enclosure structure – e.g. – housing – casing – container,...
Reexamination Certificate
2000-12-11
2004-04-13
Chaney, Carol (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Cell enclosure structure, e.g., housing, casing, container,...
C429S184000, C429S185000
Reexamination Certificate
active
06720108
ABSTRACT:
The present invention relates to an alkali battery, which employs a strongly alkaline liquid as electrolyte and of which aperture of the battery casing is hermetically sealed by a sealing unit chiefly including resin.
BACKGROUND OF THE INVENTION
The typical construction of a cylindrical alkali battery, for example an alkali dry battery is as shown in
FIG. 5
, which shows a longitudinal cross-section thereof. Specifically, within a battery casing (positive electrode)
1
of cylindrical shape having a head with a positive electrode terminal
8
projecting at its upper end face and an ornamental label
2
stuck on to its outer circumferential surface, there are inserted pellets of positive electrode mixture
3
which are molded in cylindrical shape and consist of manganese dioxide and graphite added as conductive material. On the inside of this positive electrode mixture
3
, there is poured in, separated by a separator
4
, a gel-form zinc negative electrode
7
obtained by uniformly dispersing gelling agent and zinc alloy powder in an alkaline electrolyte in which is dissolved potassium hydroxide.
The aperture
1
a
of battery causing
1
is sealed as follows. In aperture
1
a
at the bottom of battery casing
1
, a rod-shaped negative electrode current collector
10
made of brass is pressed into an insertion hole
9
a
and a resin sealing element (gasket)
9
on to which is fitted an insulating washer
11
made of metal is fitted thereon. Negative electrode current collector
10
is then covered in electrically contacting fashion by a negative electrode terminal plate
12
contacting its head
10
a
and a folded-back portion
9
b
formed on resin sealing element
9
is strongly pressed against negative electrode terminal plate
12
by bending and crimping inwards the edges of the bottom aperture of battery casing
1
.
In the resin forming of sealing element
9
, as shown in
FIG. 6
, a cavity
18
constituting a molding space for sealing element
9
is formed by mold assembly of lower metal mold
13
, upper metal mold
14
and mandrel metal mold
17
, and molten resin
20
passing through a resin passage
19
a
of annular transverse cross-section of resin injection nozzle
19
is poured into this cavity
18
through a resin injection port
18
a
formed in annular shape by upper metal mold
14
, resin injection nozzle
19
and mandrel metal mold
17
. When the resin
20
that has been injected has solidified, the mold assembly constituted by lower metal mold
13
, upper metal mold
14
and mandrel metal mold
17
is broken open to obtain a sealing element
9
as described above.
FIG. 7
shows a sealing unit
21
assembled using a resin sealing element
9
formed by the molding steps described above. Sealing unit
21
is assembled by pressing in and inserting negative electrode current collector
10
from the open end on the opposite side to resin injection gate
9
c
corresponding to resin injection port
18
a
when molding, into insertion hole
9
a
in sealing element
9
. Insulating washer
11
is then mounted by bringing it into contact with inner seat
9
d
and outer seat
9
e,
after which negative electrode terminal plate
12
is placed over insulating washer
11
, by bringing its central portion into contact with and mounting it on head
10
a
of negative electrode current collector
10
. In fitting this sealing unit
21
into aperture
1
a
of battery casing
1
, when bending the bottom aperture
1
a
of battery casing
1
inwards, the folded-back portion
9
b
of resin sealing element
9
is strongly pushed on to negative electrode terminal plate
12
as shown by the arrow.
Due to their use of a strongly alkaline liquid which is an alkaline aqueous solution of high concentration and large ion conductivity even at low temperature as electrolyte, such alkali batteries are able to withstand severe loading, have large capacity, and excellent low-temperature characteristics, and as a result are employed in equipment where power such as in particular motor drive power is needed. On the other hand, the strongly alkaline liquid that is used as electrolyte, due to its high permeability, is subject to the problem that leakage tends to occur due to creeping. Accordingly, sealing of aperture
1
a
of battery casing
1
is performed by forcing negative electrode current collector
10
into the insertion hole
9
a,
setting its external diameter to a value larger than the hole diameter of insertion hole
9
a
of resin sealing element
9
, and bending and strongly crimping the aperture rim of battery casing
1
.
However, in the case of the prior art sealing unit
21
shown in
FIG. 7
, small cracks appear in the resin injection gate
9
c
when negative electrode current collector
10
is inserted into insertion hole
9
a
of sealing element
9
by forcing it in from one end aperture at the opposite side to resin injection gate
9
c
on molding, whilst piercing and breaking flash
9
f
of resin injection gate
9
c
that closes the aperture at the other end, thereby widening this by pushing outwards. Since the resin injection gate
9
c
where these cracks start is arranged in contact with the electrolyte, electrolyte permeates into the cracks.
Also, in the case of high-temperature storage, heat cycle repetition, or prolonged storage at normal temperature, alkali batteries are subject to environmental stress cracking at locations subjected to excessive stress in a high-concentration alkaline aqueous solution (electrolyte) atmosphere. In particular, resin injection gate
9
c,
due to the fact that resin deterioration tends to occur there because of the presence of residual stress on resin injection when molding, tends to constitute a starting point for the environmental stress cracks referred to above which are generated and develop continuously. For example, where 6,6-nylon is employed as the raw material of the sealing element
9
, it is inferred that the high-concentration alkaline aqueous solution is selectively absorbed into non-crystalline portions that are present in the crystalline layer, and cracks are created in the gaps between non-crystalline portions in the spherical crystals due to the joint action of external stress and force of the absorbed alkaline aqueous solution tending to wet and spread.
As a result, due to electrolyte that has permeated into the small cracks generated in the resin injection gate
9
c
creeping up by the creeping phenomenon between the negative electrode current collector
10
and the hole circumferential surface of insertion hole
9
a
of sealing element
9
, cracks are continuously generated and developed originating from the resin injection gate
9
c
which acquires residual stress during resin molding. In this way, electrolyte permeates as the cracks develop and eventually leaks to the outside.
The present invention has been devised in view of the above problems, its object being to provide an alkali battery wherein the generation of environmental stress cracks can be reliably prevented by a simple construction and whereby excellent resistance to leakage can be obtained.
DISCLOSURE OF THE INVENTION
According to the present invention, in order to achieve the above object, in an alkali battery wherein, after a negative electrode current collector has been inserted into an insertion hole therein, a resin sealing element and negative electrode terminal plate are successively inserted into an aperture of a battery casing, and the aperture rim of said battery casing is then bent inwards and crimped to seal the aperture of said battery casing, said sealing element is accommodated within said battery casing in an arrangement facing said negative electrode terminal plate, with a resin injection gate corresponding to a resin injection port of a metal mold during resin molding thereof positioned at the aperture end of said battery casing.
With this alkali battery, since the resin injection gate corresponding to the resin injection port of the metal mold during resin molding of the sealing element is of a construction arranged at the aperture end of the b
Kaneko Toshikazu
Okubo Takeshi
Saeki Toshina
Yamamoto Kenji
Jordan and Hamburg LLP
Yuan Dah-Wei
LandOfFree
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