Battery containing foam polyurethane resin and method of making

A sealed lead acid battery including a container; a cover connected to the container; a plurality of plate groups disposed in the container, each of the plate groups comprising a plurality of pairs of positive plates and negative plates separated, each from the other, by separators; an upper space within the container extending from the plates to the cover; a pair of straps disposed in the upper space; each of the plates having an upstanding lug; each of the lugs extending from the negative plates being connected to one of the straps; each of the lugs extending from the positive plates being connected to the other of the straps; and foam polyurethane resin filling a sufficient amount of the upper space to control the possibility of an explosion occurring due to the collection of gases within the container, the foam polyurethane having an apparent specific gravity of from 2 g/l to 50 g/l and an open cell structure.

BACKGROUND ART 
1. Industrial Useful Field 
This invention relates to a sealed lead acid battery. 
2. Prior Art 
Since a sealed lead acid battery is so constructed that oxygen gas produced 
on the positive plate at the time of charging is absorbed in the negative 
plate, there is generally no chance for the oxygen gas to disperse outside 
of the battery. When charging is carried out with a large current in the 
sealed lead acid battery, a produced quantity of oxygen gas on the 
positive plate becomes larger than an absorbed quantity of it on the 
negative plate, so that hydrogen gas is also produced from the negative 
plate. For, this reason, when the battery is completely sealed, the inside 
of the battery is filled with oxygen gas and hydrogen gas so as to cause 
an increase in inside pressure. In the event when these gases catch fire 
by some accident, explosion of the battery would occur. 
In order to restrain or prevent such an explosion of the battery, the 
following methods (a) and (b), for example, are tried now. (a) Method in 
which a safety valve that opens when the battery inside pressure rises is 
installed and the produced gas is exhausted by this valve. (b) Method in 
which a porous material is filled in a space on upper parts of positive 
and negative plate groups under a cover on a container. 
In the method (a), however, an extent of explosion can be lessened but 
breaking-into-fragments of the container or other parts by the explosion 
can not be prevented. A method, in which the cover is put in place after 
filling plastic etc. in the space on upper parts of positive and negative 
plate groups, is generally adopted for the method (b). However, this 
method includes such problems that the work becomes troublesome and 
manufacturing cost increases. 
On the other hand, when the sealed lead acid battery is overcharged during 
use, the positive plate will be corroded. Many of corroded materials 
produced in this instance are formed on grain boundaries of lead alloy 
composing the positive plate. Since the corroded material increases in its 
volume, it will widen the grain boundary so as to elongate the positive 
plate. FIG. 5 is a vertical sectional view showing a case where the 
positive plate is elongated. In FIG. 5, 10 denotes positive and negative 
plate groups composed of plural positive plates 1 and negative plates 2 
arranged through separators 3. A lug 2a which is formed on an upper edge 
of the negative plate 2 and extends upward, is joined to a strap 4 from 
under side. When the positive plate 1 is corroded so as to be elongated, 
an elongated portion 11 will sometimes contact with the lug 2a or the 
strap 4 as shown by FIG. 5. For this reason, a short-circuiting has 
sometimes occurred so as to exhaust the life of the battery before the 
life of plate has been exhausted. 
As a method for obstructing the elongation of the positive plate 1 to 
prevent the short-circuiting, a method is tried, for example, in which a 
combed plate made of plastic having acid resistance and insulation 
property is inserted in such a way that each combed piece is located 
between adjoining lugs 2a. However, this method was able to prevent the 
positive plate 1 from directly contacting with the strap 4 but was not 
completely able to prevent the positive plate 1 from contacting with the 
lug 2a. Therefore, the short-circuiting could not be prevented completely. 
The foregoing insertion of plate 1 was carried out by hand work after 
putting the positive and negative plate groups 10 in a container, but 
spaces between the lugs 2a could not be kept constant when welding the 
lugs 2a by means of a cast-on method used frequently in recent years. For 
this reason, the above plate-insertion work was difficult and automization 
of the insertion work was also difficult. 
This invention is made in consideration of the problems described above. 
Namely, an object of this invention is to provide a sealed lead acid 
battery which can prevent the explosion of the sealed lead acid battery, 
prevent short-circuiting and provide a simple method of manufacturing a 
sealed lead acid battery. 
Summary Of The Invention 
This invention provides a sealed lead acid battery, in which positive and 
negative plate groups composed of plural positive plates and negative 
plates arranged through separators, are installed in a container. Each 
plate has a lug extending upward on its upper edge, a lug of each positive 
plate and a lug of each negative plate are connected to different straps 
from under side respectively, and a space exists on upper parts of the 
positive and negative plate groups under the condition where a cover is 
put on the container; characterized by that a foam polyurethane resin 
having an apparent specific gravity of 2to 50g/l and including an open 
cell is filled in a space on upper parts of the positive and negative 
plate groups also in spaces surrounded by the straps, the adjoining lugs, 
and upper surfaces of the plates and separators. 
Further, this invention provides a manufacturing method of a sealed lead 
acid battery, in which positive and negative plate groups composed of 
plural positive plates and negative plates arranged through separators, 
are installed in a container. Each plate has a lug extending upward on its 
upper edge, a lug of each positive plate and a lug of each negative plate 
are connected to different straps from under side respectively, a space 
exists on upper parts of the positive and negative plate groups under the 
condition where a cover is put on the container, and the space also 
includes spaces surrounded by the straps, the adjoining lugs, and upper 
surfaces of the plates and separators; characterized by that a stock 
solution of foam polyurethane resin is filled and foamed in the space on 
upper parts of positive and negative plate groups, and a solution is used 
for the stock solution of foam polyurethane resin, in which foaming can be 
completed within 30 seconds, and the expansion ratio and the quantity 
consumed are so prescribed that a volume after completion of the foaming 
becomes more than or equal to 80 percent of that of the space on upper 
parts of positive and negative plate groups and an apparent specific 
gravity after completion of the foaming becomes 2to 50g/l. 
A hardening agent mainly composed of isocyanate and a principal agent 
mainly composed of polyole and including a foaming agent such as water 
can, for example, be prepared and mixed immediately before filling by 
using a mixer with a specified mixing ratio. This mixture is used as the 
stock solution for foam polyurethane resin. 
According to the sealed lead acid battery of the present invention, the 
following functions and effects are obtainable. (1) The foam polyurethane 
resin having the open cell is filled in the space at upper parts of the 
positive and negative plate groups (abbreviated to "upper space" 
hereunder) including spaces surrounded by the strap, the adjoining lugs, 
and the upper surfaces of the plates and separators (abbreviated to "strap 
lower space " hereunder), so that the upper space is divided into many 
fine spaces connected to each other. For this reason, even when the gases 
produced during charging catch fire, there is no chance for the gases to 
burn quickly and extensively. Consequently, the explosion of battery due 
to fire that might be caught by the gases can be prevented. 
(2) Since the foam polyurethane resin is filled in the strap lower space, 
the positive plate is prevented from elongating and contacting with the 
strap and the lug of negative plate. Accordingly, short-circuiting due to 
the elongation of positive plate can be prevented. 
(3) Since the foam polyurethane resin includes an open cell structure, the 
gas produced at the time of overcharging is exhausted from an exhaust port 
of the cover through the open cell structure. Consequently, there is no 
possibility that the battery inside pressure increases excessively due to 
the gas produced at the time of overcharging and the battery is 
consequently broken due to the increase in battery inside pressure. 
(4) When diameters of the open cells of foam polyurethane resin are 
excessively large, the effect of dividing the upper space is lessened so 
that the effect of controlling the explosion becomes insufficient. When 
diameters of the open cells of foam polyurethane resin are excessively 
small, the gas produced at the time of overcharging becomes hard to pass 
through so that troubles caused by the increase in battery inside pressure 
are apt to occur. However, in the present invention, the diameters of open 
cells are not excessively large because the apparent specific gravity of 
the foam polyurethane resin is more than or equal to 2g/l, and the 
diameters of open cells are not excessively small because the apparent 
specific gravity of the foam polyurethane resin is less than or equal to 
50g/l. Therefore, the explosion of battery and troubles due to the 
increase in battery inside pressure can be prevented satisfactorily. 
Further, since the foam polyurethane resin has an apparent specific 
gravity of more than or equal to 2g/l , a weight of the foam polyurethane 
resin can be adjusted with a high precision. 
(5) Since the foam polyurethane resin has acid resistance, there is no 
possibility that it is dissolved by the acid of the electrolyte to damage 
to the battery. 
(6) Since the weight of the foam polyurethane resin is small, the weight of 
battery scarcely increases. Therefore, the invention is not adverse to the 
needs of the industry for reducing the weight of batteries. 
According to the manufacturing method of the sealed lead acid battery of 
this invention, the following functions and effects are obtainable. 
(1) The stock solution of foam polyurethane resin is filled and foamed, so 
that the work is simple, the manufacturing cost is reduced and the 
automization of work becomes easy. 
(2) Since the stock solution of foam polyurethane resin is one in which the 
foaming is completed within 30 seconds, there is no chance for the stock 
solution to fall in drops and disadvantageously enter surroundings and 
clearances of the positive and negative plate groups so that the solution 
is consumed economically for filling the upper space. Therefore, there is 
no chance for battery performance to be affected and the foam polyurethane 
resin is filled in the upper space with a high efficiency. 
(3) The solution, in which the expansion ratio and the quantity consumed 
are so prescribed that the volume after completion of the foaming becomes 
more than or equal to 80 percent of that of the upper space and the 
apparent specific gravity after completion of the foaming becomes 2to 
50g/l , is used as the stock solution for foam polyurethane resin, so that 
the following effects are obtainable. Data showing the following functions 
and effects are listed in Table 1. 
[1] More than or equal to 80 percent of the upper space becomes filled with 
the foam polyurethane resin, so that the explosion of the battery is 
sufficiently controlled. 
[2] If the apparent specific gravity after completion of the foaming is 
less than 2g/l, the foam polyurethane resin does not enter the strap lower 
space sufficiently because of a weak expansion force. However, if the 
apparent specific gravity after completion of the foaming is more than or 
equal to 2g/l in the present invention, then the strap lower space is 
sufficiently filled with the foam polyurethane resin. Consequently, 
short-circuiting due to the elongation of positive plate is prevented. 
[3] When the apparent specific gravity after completion of the foaming 
exceeds 50 g/l, an excessive pressure is applied on the container so as to 
deform it because the expansion force becomes excessively large. However, 
in the present invention, the apparent specific gravity after completion 
of the foaming is less than or equal to 50 g/l so that the container is 
not deformed. 
TABLE 1 
__________________________________________________________________________ 
Apparent specific gravity of foam polyurethane resin 
1 g/l 2 g/l 10 g/l 50 g/l 60 g/l 
__________________________________________________________________________ 
Filling volume 
20 80-100 100 100 100 
factor*.sup.2 of 
space*.sup.1 (%) 
Affect Resin does not 
Resin enters 
Resin enters 
Bulging to an 
Large bulging 
enter strap 
strap lower 
strap lower 
inconspicuous degree 
exists on 
lower space 
space space exists on side wall 
side wall of 
of container*.sup.3 
container*.sup.3 
__________________________________________________________________________ 
*.sup.1 Space surrounded by strap, adjoining lugs and upper surfaces of 
plates and separators 
##STR1## 
*.sup.3 Container made of polypropylene resin having wall thickness of 5 
mm 
(4) Since the electrolyte works in such a way that water included in it 
accelerates the foaming, the electrolyte does not obstruct the foaming. 
Accordingly, the stock solution of foam polyurethane resin may be filled 
after the initial charging.

DETAILED DESCRIPTION OF THE INVENTION 
An embodiment of this invention will be described hereunder with reference 
to the drawings. 
FIG. 1 is a partially fragmental oblique view showing an embodiment of 
sealed lead acid battery according to the present invention. FIG. 2 is a 
sectional view taken on a line II--II of FIG. 1. In these figures, 
components which are similar to those of FIG. 5 are attached with the same 
symbols. 5 denotes a container, 6 denotes a cover, and 7 denotes a sealing 
plug which plugs an opening 6a a forming an exhaust opening of the cover 
6. The sealing plug 7 has an exhaust valve 7a and an exhaust port 7b . 
Positive and negative plate groups 10 composed of plural positive plates 1 
and negative plates 2 arranged through separators 3 are housed in each 
chamber of the container 5. As shown in FIG. 3 which is the partial 
oblique view of the positive and negative plate groups 10; spaces 
surrounded by the strap 4, the adjoining lugs 2a and upper surfaces of the 
plates 1 & 2 and the separators 3 (strap lower space) 31 are also included 
in a space on upper parts of the positive and negative plate groups 10 
(upper space) 30. The space 31 opens in a lateral direction. 
A foam polyurethane resin 40 is filled in the space 30 also including the 
space 31. The foam polyurethane resin 40 has an apparent specific gravity 
of 2to 50g/l and includes an open cell structure. 
The sealed lead acid battery thus constructed is manufactured in the 
following manner. In the first place, a battery in a state of FIG. 4 is to 
be prepared and filled with electrolyte and subjected to initial charging. 
The sealed lead acid battery is in the state of FIG. 4 before being 
subjected to the initial charging. Since the electrolyte is absorbed and 
held in fine pores of active material for plates and the separators 3 so 
that flowable electrolyte scarcely exists in the upper parts of the 
positive and negative plate groups 10 even after the initial charging, the 
upper parts of the positive and negative plate groups 10 form a space. 
Next, the stock solution for foam polyurethane resin is filled from the 
opening 6a into the space 30. A solution, in which foaming is completed 
within 30 seconds, and an expansion ratio and a quantity consumed are so 
prescribed that the volume after completion of the foaming becomes more 
than or equal to 80 percent of that of the space 30 and an apparent 
specific gravity after completion of the foaming becomes 2to 50g/l, is 
used as the stock solution for foam polyurethane resin. Specifically, a 
hardening agent mainly composed of isocyanate and a principal agent mainly 
composed of polyole and including a foaming agent such as water, for 
example, were mixed immediately before filling with a specified mixing 
ratio by using a mixer. After filling the stock solution, the opening 6a 
was plugged by the sealing plug 7 until the foaming was completed. 
Blowing-off of the foam polyurethane resin from the opening 6a was thus 
prevented. Diameters of cells of the filled foam polyurethane resin 40 
were from 0.5to 1.5mm. The stock solution may be filled in advance of the 
initial charging. In this case, however, much time is required for filling 
the resin because the electrolyte has to be filled through the foam 
polyurethane resin 40 and pass through the open cell of the foam 
polyurethane resin 40. Further, the electrolyte should be filled 
excessively when taking into account the amount of loss due to evaporation 
and electrolysis at the time of initial charging. Therefore, it is 
preferable that the stock solution is filled after the initial charging. 
The opening 6a may be plugged by a temporary sealing plug in place of the 
sealing plug 7, then it may be replaced by the sealing plug 7 after 
completion of the foaming. 
According to the above-mentioned manufacturing method, it is required only 
to fill and foam the stock solution for foam polyurethane resin; so that 
the work is simple, the manufacturing cost is reduced, and the 
automization of the work becomes easy. Since the stock solution is one 
which completes its foaming within 30 seconds, there is no chance for the 
stock solution to fall in drops so as to disadvantageously enter 
surroundings and clearances of the positive and negative plate groups 10 
so that the solution is consumed economically in filling the upper space 
30. Therefore, there is no chance for the battery performance to be 
affected, and the foam polyurethane resin 40 is filled in the upper space 
30 with a high efficiency. The solution, in which the expansion ratio and 
the quantity consumed are so prescribed that the volume after completion 
of the foaming becomes more than or equal to 80 percent of that of the 
space 30 and the apparent specific gravity after completion of foaming 
becomes 2 to 50g/l, is used as the stock solution for foam polyurethane 
resin, so that the following functions and effects are obtainable. [ 1] 
More than or equal to 80 percent of the upper space 30 become filled with 
the foam polyurethane resin 40, so that the possibility of explosion of 
the battery is sufficiently controlled. [2] The apparent specific gravity 
after completion of foaming is more than or equal to 2g/l, so that the 
space 31 is sufficiently filled with the foam polyurethane resin 40. 
Consequently, short-circuiting due to the elongation of positive plate 1 
is prevented. [3] The apparent specific gravity after completion of 
foaming is less than or equal to 50g/l so that there is no chance for the 
container 5 to be deformed. 
According to the sealed lead acid battery thus constructed, since the foam 
polyurethane resin 40 having the open cell is filled in the space 30 also 
including the space 31, the space 30 is divided into many fine spaces 
connected each other so that the explosion of battery due to fire due to 
caught gas can be prevented. Further, since the foam polyurethane resin 40 
is filled in the space 31, short-circuiting due to the elongation of 
positive plate 1 can be prevented. Moreover, since the foam polyurethane 
resin 40 includes the open cell structure, the gas produced at the time of 
overcharging is exhausted from an exhaust port of the cover through the 
open cells, so that there is no possibility that the battery is broken due 
to the increase in interior pressure caused by the gas produced at the 
time of overcharging. The diameters of open cell are not excessively large 
or small because the apparent specific gravity of the foam polyurethane 
resin 40 lies within a range of 2to 50g/l. Therefore, the possibility of 
explosion of the battery is controlled sufficiently and the trouble due to 
the increase in battery inside pressure does not occur. Further, since the 
foam polyurethane resin 40 has the apparent specific gravity of more than 
or equal to 2g/l, the weight of foam polyurethane resin 40 can be adjusted 
with a high precision. 
Occurrence of explosion was tested by using the sealed lead acid battery of 
this embodiment. Twenty sealed lead acid batteries of this embodiment 
having 45 Ah at 5 hour rate were prepared. A large quantity of hydrogen 
was produced in the space 30 by means of electrolysis caused by 
overcharging, and a spark was generated between lead wires previously 
attached to a lower part of the cover 6. As the result, no explosion was 
produced in all the batteries. 
Charge/discharge cycle life tests were carried out on the sealed lead acid 
battery of this embodiment and a conventional sealed lead acid battery. 
Results are shown in Table 2. The conventional battery is in a state as 
shown in FIG. 4. Test conditions were set as follows. After being charged 
completely, the batteries were subjected to 50 repeated cycles described 
below and left as they were for 40 hours. One cycle consisted of a 
discharging for 2 seconds at 250 A, twice repeated chargings for 1 hour at 
a constant voltage of 14.2 V (Max. current: 70 A), a discharging for 4 
minutes at 25 A, and a charging for 30 minutes at a voltage of 14.2 V 
(Max. current: 40 A). The battery life was judged to be exhausted when the 
current after 30 minutes at the last charging of cycle exceeded 5 A. For 
both the battery of this embodiment and the conventional battery, five 
test samples having 70 Ah were prepared and subjected to the tests under 
an ambient temperature of 60.degree. C. 
TABLE 2 
______________________________________ 
Battery of this 
Conventional 
embodiment battery 
______________________________________ 
Number of life 
About 600 cycles 
About 300 cycles 
cycle (mean) 
Cause of Rib corrosion Short-circuiting 
exhaustion of positive due to elongation 
of life plate of positive plate 
______________________________________ 
As seen from Table 2, according to the battery of this embodiment, the 
contact of positive plate 1 with the strap 4 or the lug 2a due to the 
elongation of positive plates was prevented so as to prolong the battery 
life remarkedly. The batteries were disassembled after completion of the 
tests, and the plate 1 was elongated to be in contact with the strap 4 in 
the conventional battery. However, in the battery of this embodiment, in 
spite of conspicuous progress of corrosion in the positive plate 1, the 
positive plate 1 cut into the foam polyurethane resin 40 so that changes 
of size and shape of the positive plate 1 were restrained.