Method for producing sealing member for battery

A method for producing a sealing member for a battery includes integrally insert-molding a gasket on a peripheral edge of a metal sealing plate. The gasket is molded on the peripheral edge of the metal sealing plate by inserting the metal sealing plate between the female and male molds, the female mold having a concave surface conforming to the upper surface of the metal sealing plate and provided with a magnet or vacuum suction mouth to attract the metal sealing plate in its center, and the male mold having a surface conforming to the lower surface of the metal sealing plate, then injecting a molten resin into a cavity formed between the female mold and the male mold while pressing the female and male molds against each other by an elastic member.

TITLE OF THE INVENTION 
Method for producing sealing member for battery 
BACKGROUND OF THE INVENTION 
The present invention relates to an improved method for producing a sealing 
member for a battery by integrally molding a gasket on the peripheral edge 
of a metal sealing plate. 
There have been known batteries each having a metal container which 
accommodates a power generating element therein and a sealing member which 
seals the open end of the metal container. The sealing member has a metal 
sealing plate and a resin gasket. Those batteries use various electrolytes 
such as nonaqueous electrolytes, alkaline electrolytes and acid 
electrolytes. The sealing members had been produced by mounting a 
previously formed gasket on the sealing plate. To secure the adhesion 
between the sealing plate and the gasket thereby to achieve high 
electrolyte leakage resistance, an electrolyte-resistant sealing agent is 
interposed between them as necessary. Such process is indispensable 
especially in battery systems using alkaline electrolytes sinse the 
alkaline electrolyte itself exhibits a noticeable tendency to creep or a 
property of rising up along the metal surface. 
As set forth, producing of sealing member required a step of molding a 
gasket and another step of integrally combining the gasket obtained and 
the sealing plate. 
In order to simplify the process of producing such sealing members, there 
are proposed attempts of insert-molding a gasket on the peripheral edge of 
a sealing plate, for example, in Japanese Laid-Open Patent Publication No. 
Sho 50-91720. 
The usual method for producing a sealing member by insert-molding the 
gasket onto a sealing plate is as follows. First, a sealing plate is 
provided between a female or concave mold of a molding apparatus having a 
concave face conforming to the upper surface of the sealing member to be 
obtained and a male or convex mold with a convex face conforming to the 
lower surface of the sealing member. The two molds are then clamped, 
followed by injecting a resin gasket material into a cavity formed on the 
peripheral edge of the sealing plate. 
Usage of such ordinary molding apparatus for the above-mentioned 
insert-molding, however, inevitably brings about faulty moldings such as 
flowing out of resin onto unwanted areas of the sealing plate, detachment 
or dislocation of the sealing plate from the mold. These faults are caused 
by delicate differences or ununiformity in molding conditions including 
configuration of the sealing plate, molding temperature, molding pressure, 
mold clamping pressure, temperature of cooling water and molding cycle. 
Such faults also appears even when a lot of the resin gasket material is 
changed. The other problems encountered include sticking to the mold of 
the sealing agent applied to the sealing plate. Especially fatal is the 
resin flowing over to the inner surface of the sealing plate. Since the 
inner surface is in contact with the power generating element, the resin 
flowing over spoils conductivity of the battery. 
BRIEF SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a method for molding a 
gasket on a metal sealing plate which is free from the foregoing problems 
such as detachment of the sealing plate from the mold, dislocation of the 
sealing plate or adhesion of the resin gasket material to unwanted areas 
of the metal sealing plate. 
The present invention provides a method for producing a sealing member for 
a battery, which has a metal sealing plate and a synthetic resin gasket 
integrally mounted on the peripheral edge of the metal sealing plate 
comprising the steps of: 
inserting a metal sealing plate between a female mold and a male mold, the 
female mold having a concave surface conforming to the upper surface of 
the metal sealing plate and provided with a magnet to attract or vacuum 
suction mouth to suck up the metal sealing plate in its center, and the 
male mold having a surface conforming to the lower surface of the metal 
sealing plate; 
pressing the female and male molds against each other by an elastic member; 
and 
injecting a molten resin into a cavity formed between the female and male 
molds to integrally mold a gasket on the peripheral edge of the metal 
sealing plate. 
According to the present invention, the sealing plate is attracted by the 
magnet or vacuum suction. Therefore, the sealing plate can be prevented 
from the detachment and dislocation. 
In addition, if the magnet is movable up and down, and if the female mold 
is further provided with an elastic member to thrust the magnet on the 
sealing plate, the hold of the sealing plate by the mold will be further 
strengthened. Thus, according to the present invention, it is possible to 
make a sealing plate free from the resin sticking to unwanted areas 
without using a high precision mold. 
Various kinds of resin can be employed as the gasket material. For example, 
polyethylene, polypropylene and polyphenylene sulfide can be used for 
lithium batteries, and polyamide can be used for alkaline batteries. 
The adhesion between the sealing plate and the gasket can be increased by 
interposing a sealing agent therebetween. The sealing agent is provided on 
the peripheral edge of the sealing plate or where a gasket is to be 
molded, prior to molding the gasket. Effective sealing agents are epoxy 
resin and heat-resistant organic silicon compounds such as a silane 
coupling agent. 
While the novel features of the invention are set forth particularly in the 
appended claims, the invention, both as to organization and content, will 
be better understood and appreciated, along with other objects and 
features thereof, from the following detailed description taken in 
conjunction with the drawings.

DETAILED DESCRIPTION OF THE INVENTION 
Now, as the preferred embodiments of the present invention, methods for 
producing the sealing member used for a coin-type battery will be 
described in detail with reference to the attached drawings. 
EXAMPLE 1 
In the present example, there will be explained the method for producing a 
sealing member used in a coin-type manganese dioxide lithium primary 
battery shown in FIG. 1. 
A sealing member 8 has a metal sealing plate 1 which is concurrently a 
negative electrode terminal and a gasket 2 integrated on a bent peripheral 
edge of the sealing plate 1. The gasket 2 is made of polypropylene, for 
example. The sealing member 8 seals the open end of a container 6 which 
accommodates a power generating element including a positive electrode 5, 
a separator 4 and a negative electrode active material 3. The container 6 
also serves as the positive electrode terminal. 
The main part of a molding apparatus used in the present example is shown 
in FIG. 2 and FIG. 3. A female mold 10 has a concave portion 12 conforming 
to the shape of the upper surface of the sealing plate 1 on its bottom 
surface. A magnet 16 and spring 17 movable up and down for thrusting the 
magnet 16 downward are provided in the center of the concave portion 12. A 
male mold 11 has a convex portion 13 conforming to the shape of the lower 
surface of the sealing plate 1. The male mold 11 is provided with a 
fitted-in movable core 14 which cooperates with the male mold 11 and a 
spring 15 for thrusting the movable core 14 upward. The female mold 10 is 
provided with a gate 18 and a runner 19 which lead a resin material for 
the gasket 2. The runner 19 is connected to the sprue of a sprue bush (not 
shown). 
In molding the sealing member 8 using this molding apparatus, the sealing 
plate 1 is first put on the convex portion 13 of the male mold 11, and the 
female mold 10 is moved down. Then, the sealing plate 1 is clamped by the 
magnet 16, and the female mold 10 is further moved downward, thereby 
pressing down the movable core 14 outdoing the elastic force of the 
springs 15. With the sealing plate 1 clamped between the female mold 10 
and the male mold 11 in this way, the molds 10 and 11 are pressed against 
each other by the elastic force of the springs 15, and the sealing plate 1 
is compressed by the spring 17. Then, there is formed a cavity surrounded 
by a step portion 12a of the female mold 10, a side of the convex portion 
13 of the male mold 11, a shoulder portion 13a connected to the convex 
portion 13 and the top end face of the movable core 14. In this state, a 
molten resin is fed in that cavity through the runner 19 and the gate 18 
to integrally mold a gasket 2 on the peripheral edge of the sealing plate 
1. 
In molding the gasket 2 using the female mold 10 and the male mold 11 
mentioned above, the sealing plate 1 is clamped by a magnet 16 and will 
not detach or dislocate. Even if there is an uniformity in thickness of 
the metal sealing plate 1, the resin material will not flow out to other 
than the specific area, because the spring 15 presses the molds 10 and 11 
against each other and the spring 17 forces the magnet 16 to press the 
sealing plate 1, thereby bringing the molds 10 and 11 in close contact 
with the sealing plate 1. In this way, a specific gasket can be formed on 
a metal sealing plate. 
Actually, 5 lots, one lot made up of 5,000 pieces, of sealing members 8 
were produced using this molding apparatus. 
COMATIVE EXAMPLE 1 
As a comparative example, 5 lots, one lot made up of 5,000 pieces, of 
sealing members 8 were produced in the same way but using male and female 
molds with no magnet and spring. 
Table 1 shows the yields (percentage nondefective) in comparison. 
TABLE 1 
______________________________________ 
Yield (percent nondefective) 
Lot No. Example 1 Comparative Example 1 
______________________________________ 
1 100 85 
2 100 96 
3 99 92 
4 100 82 
5 100 83 
______________________________________ 
Next, coin-type manganese dioxide lithium primary batteries as shown in 
FIG. 1 were assembled using those sealing members 8 obtained. 
A pellet-shaped positive electrode 5 contains manganese dioxide as an 
active material. The positive electrode 5 was prepared as follows. At 
first, 100 parts by weight of manganese dioxide heat-treated at 
400.degree. C. and 7 parts by weight of graphite as a conductive material 
were mixed. Then, 430 mg of thus obtained mixture was press-molded using a 
mold 15.7 mm in diameter under a pressure of 4 t/cm.sup.2, followed by 
drying at 250.degree. C. 
A polypropylene unwoven fabric was used as a separator 4. An active 
material 3 of the negative electrode was a disk of lithium 0.25 mm in 
thickness and 20 mm in diameter. An electrolyte was prepared by dissolving 
lithium perchlorate as a solute in 0.5 mol/liter in a mixed solvent of 
propylene carbonate and dimethoxyethane. 
Five lots, one lot made up of 1,000 pieces, of batteries were assembled 
using the sealing members obtained in the example and the comparative 
example, respectively. Thus obtained batteries were put to an electrolyte 
leakage resistance test. In the test, a cycle of storing the battery in a 
thermostat maintained at 70.degree. C. for one hour then storing the 
battery in a thermostat maintained at 15.degree. C. for one hour was 
repeated 100 times. The results are shown in Table 2. 
TABLE 2 
______________________________________ 
Percent leakage 
Lot No. Example 1 Comparative Example 1 
______________________________________ 
1 0 13 
2 0 10 
3 0 5 
4 0 16 
5 0.1 4 
______________________________________ 
EXAMPLE 2 
A sealing member 9 shown in FIG. 4 which is identical with the one in 
Example 1 but provided with a sealing agent layer 7 on the peripheral edge 
of the sealing plate 1 was produced using the same molding apparatus as in 
Example 1. 
COMATIVE EXAMPLE 2 
As a comparative example, a sealing member also having the sealing agent 
layer 7 was produced using male and female molds with no magnet and 
spring. 
In these examples, prior to the molding, the sealing agent layer 7 was 
formed by applying a toluene solution of a polypropylene modified with 
maleic acid (trade name "HARDLEN" by Toyo Kasei Kogyo Co., Ltd.) on the 
peripheral edge of the sealing plate 1, followed by baking for 30 seconds 
at 130.degree. C. 
The yield (percent nondefective) of sealing members per 5,000-piece lot (5 
lots) is shown in Table 3. 
TABLE 3 
______________________________________ 
Yield (percent nondefective) 
Lot No. Example 2 Comparative Example 2 
______________________________________ 
1 100 75 
2 100 60 
3 100 67 
4 100 80 
5 99 66 
______________________________________ 
Next, five lots, one lot made up of 1,000 pieces, of coin-type manganese 
dioxide lithium primary batteries as shown in FIG. 4, were assembled with 
the sealing members thus obtained. 
COMATIVE EXAMPLE 3 
In a comparative example, five 1,000-piece lots of coin-type manganese 
dioxide lithium primary batteries shown in FIG. 5 were assembled using a 
sealing member by mounting a gasket 2' previously formed onto the sealing 
plate 1. Sealing agent layer 7' is positioned between the inner surface of 
the sealing plate 1 and the gasket 2'. 
The batteries thus obtained were subjected to the electrolyte leakage test 
in the same manner as in Example 1. The results are shown in Table 4. 
TABLE 4 
______________________________________ 
Percent leakage 
Lot No. Example 2 Comparative Example 3 
______________________________________ 
1 0 14 
2 0 18 
3 0 7 
4 0 21 
5 0 12 
______________________________________ 
EXAMPLE 3 
The molding apparatus of the present example is shown in FIG. 6. In this 
apparatus, a female mold 20 has a concave portion 22 and a step portion 
22a conforming to a shape of a sealing member. The female mold 20 used in 
the present example has a suction mouth 21 in the center of the concave 
portion 22. Further, a spring 23 to thrust the female mold 20 downward is 
provided above the female mold 20. 
In this example, the male mold 11 is provided with a movable core 14 which 
cooperates with the male mold 11. It is also possible for the shoulder 
portion 13a of the male mold 11 to take place of the movable core 14. The 
springs 15 and 23 are a coil spring, for example. The spring 23 can be a 
belleville spring. 
As set forth above, the present invention can keep down the percent 
operation defectives resulted from detachment of the sealing plate from 
the mold or dislocation in production by the insert-molding of the sealing 
member for batteries. It is also possible to obtain sealing members of 
uniform quality without the resin sticking to other than the specific 
area. Thus, the invention can reduce the costs of producing sealing 
members and ensure a high quality stably, and can also provide batteries 
with an improved electrolyte leakage resistance and a high reliability. 
Although the present invention has been described in terms of the presently 
preferred embodiments, it is to be understood that such disclosure is not 
to be interpreted as limiting. Various alterations and modifications will 
no doubt become apparent to those skilled in the art to which the present 
invention pertains, after having read the above disclosure. Accordingly, 
it is intended that the appended claims be interpreted as covering all 
alterations and modifications as fall within the true spirit and scope of 
the invention.