JPH0145941B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to improvement of alkaline batteries, and an object thereof is to provide an alkaline battery with improved leakage resistance. Generally, when sealing a battery, a gasket made of synthetic resin such as polyethylene, polypropylene, or nylon is interposed between the anode can and the cathode current collector, and the gasket is used to collect the cathode by tightening the opening edge of the anode can inward. Press the anode can against the electric object.
By bringing the contact surfaces between the gasket and the cathode current collector into close contact with each other, leakage of the electrolyte from these contact surfaces is prevented. However, in batteries that use an alkaline electrolyte such as caustic potash, the electrolyte creeps up the surface of the cathode current collector and leaks out to the outside, so the synthetic resin gasket described above is not suitable. To prevent electrolyte leakage due to the creep phenomenon described above, compressive stress (resistance force generated inside the gasket when the gasket is compressed, acts as a pushing force on the outside of the gasket, that is, on the cathode current collector, etc.) is not sufficient, and water absorption causes a decrease in compressive stress, so leakage resistance tends to be low. For this reason, to date, the shape of the cathode current collector has been improved to improve leakage resistance, and asphalt pitch has been added to the contact surfaces of the gasket, anode can, and cathode current collector.
Many proposals have been made, including the use of liquid packing materials such as fatty polyamides and fluorine-based oils, but these alone do not necessarily provide a high degree of leakage resistance. In view of the current situation, the inventors conducted various research and found that nylon was used as a gasket material.
When using 610 and increasing the crystallinity of the obtained gasket to a certain range, the compressive stress of the gasket increases and the water absorption decreases, thereby preventing electrolyte leakage. He discovered that the effect can be suppressed by using a large cloth, and completed this invention. That is, the present invention provides a gasket made of nylon 610 with increased crystallinity of 40 to 60% over the entire gasket from the surface to the inside between the anode can and the cathode current collector. The present invention relates to an alkaline battery in which the interior of the battery is made liquid-tight by disposing and sealing the anode can and the cathode current collector with a liquid packing material interposed between the contact surfaces of the anode can and the cathode current collector. The nylon 610 used as the gasket material in this invention has high tensile strength and hardness, and also has high compressive stress, making it superior to polyethylene, polypropylene, etc. as a gasket material. When molded into gaskets for alkaline batteries by
It has a crystallinity of about 38%. Therefore, heat treatment of these gaskets increases the degree of crystallinity and improves compressive stress, and at the same time reduces the amorphous portion and reduces the water absorption caused by this portion, suppressing the decrease in compressive stress due to water absorption. Become so. In this invention, the crystallinity of the gasket when incorporated into a battery is limited to 40 to 60%, because if the crystallinity is less than 40%, the increase in crystallinity is small and the compressive stress will not be sufficiently high. In addition, since the decrease in water absorption is small, compressive stress is likely to decrease due to water absorption, and as a result, the force with which the gasket pushes against the anode can and cathode current collector in the battery after sealing is reduced.
As a result, leakage of electrolyte occurs from the interface between the gasket and the anode can or cathode current collector, resulting in insufficient leakage resistance.On the other hand, when the crystallinity exceeds 60%,
Since the gasket is heated at high temperature for a long time to increase the degree of crystallinity, the gasket suffers thermal deterioration, and the surface hardening of the gasket progresses, making the gasket too hard, and when the gasket is tightened for sealing. This is because cracks occur and the electrolyte leaks from the cracked portions, resulting in a decrease in leakage resistance. Heat treatment to increase the crystallinity of the gasket is performed before the gasket is assembled into the battery.
In this case, the treatment temperature can be anything above the glass transition temperature of nylon 610 (the temperature at which a polymer substance changes from a glass-like hard state to a rubber-like state when heated) and below its melting point.
However, since the crystallization rate is slow at low temperatures, it is preferable to employ a temperature of 100°C or higher. Note that if the heat treatment time is short, the temperature during the heat treatment may exceed the melting point of nylon 610 by about 10°C. The heat treatment time varies depending on the treatment temperature and the degree to which the degree of crystallinity is to be increased, but is usually 1 to 10 hours. The atmosphere for the heat treatment may be air, but preferably vacuum or a gas inert to nylon 610, such as nitrogen, argon, helium, or water vapor. However, it is not preferable to carry out the heat treatment in a liquid such as liquid paraffin because it is necessary to remove the liquid remaining on the gasket surface after the treatment. Heat treatment of a gasket can be carried out, for example, by placing the gasket in a container that can be placed in a vacuum and heated, and vacuuming the inside of the container (usually 1 mmHg to 1 x 10 ^-2 mm).
Hg or once vacuumed, nylon such as nitrogen, argon, helium, water vapor, etc.
This is carried out by introducing a gas inert to 610 into the container to return the pressure inside the container to normal pressure, and then heating it. After heating for a predetermined period of time, the gasket is placed in the container and allowed to cool (standing cooling) to cool to room temperature. The reason why the gasket is left to cool in the container is to prevent the gasket from being exposed to oxygen at high temperatures and being damaged. When a gasket undergoes heating and cooling as described above, the temperature on the surface and inside of the gasket is slightly higher during heating, and the temperature inside is slightly lower.
By cooling, the temperature decreases from the surface, and the temperature decreases slower inside than at the surface. Therefore, the increase in crystallinity of the gasket is almost uniform from the surface to the inside, and the crystallinity increases throughout the gasket from the surface to the inside. When cooling the gasket after heating, it is possible to immerse the gasket in a refrigerant such as a dry ice-methanol solution to rapidly cool it, but if the gasket is rapidly cooled after heating, the crystallinity of the gasket surface will increase, so rapid cooling is the method. cannot be adopted. In other words, if the gasket is heat treated as described above and allowed to cool naturally, the degree of crystallinity will increase throughout the gasket from its surface to its interior. The degree of crystallinity in this invention is expressed by a numerical value calculated from the measured density. To measure the degree of crystallinity using the density method, the degree of crystallinity of the sample is x,
When the mist degree of crystalline is d _c , the density of amorphous is d _a , and the density of the sample is d, the degree of crystallinity x is x=d _c (d - d _a )/d (d _c - _{d a} ), where the crystalline density d _c and the amorphous density d _a
The method is based on the principle that the degree of crystallinity can be determined by measuring the density d of the sample, since these can be determined from standard samples or literature. Density is determined using the float-sink method, in which a sample is placed in a container such as a beaker, carbon tetrachloride of known density is poured in to float the sample on the carbon tetrachloride, and then toluene of known density is gradually added dropwise using a biuret while stirring. However, the sample is not floating in the liquid,
It is determined by continuing to drip toluene until it reaches a state where it is not even sinking, reading the amount of toluene dripped at that point, and calculating it using the following formula. d=d ₁・V ₁ +d ₂・V ₂ /V ₁ +V ₂ (where d is the density of the sample, d ₁ is the density of carbon tetrachloride, V ₁ is the injection amount of carbon tetrachloride, and d ₂ is toluene density, V ₂ is the dropping volume of toluene). FIG. 1 is a cross-sectional view showing an example of a button-type alkaline battery according to the present invention.
A separator 3 is placed on top of the separator 3, a cathode agent 4 is filled therein, and the peripheral folded portion 8 has a crystallinity of 40 to 60%.
The anode can 1 is fitted to the cathode current collector 5 fitted with an annular gasket 6 made of nylon 610 having an L-shaped cross section adjusted to the shape of the anode, and a gasket is inserted between the anode can 1 and the cathode current collector 5. 6, the opening edge of the anode can 1 is tightened inward and sealed to make the inside of the battery liquid-tight. The anode can 1 in this battery is formed from a nickel-plated iron plate, and the anode mixture 2 is an anode active material such as ferrous oxide, manganese dioxide, ferrous oxide, mercury oxide, or nickel peroxide. It is made of a conductive additive such as phosphorous graphite, and has a metal annular pedestal 7 fixed to its periphery. The separator 3 is made of a stack of hydrophilically treated microporous polypropylene film, cellophane and vinylon-rayon mixed paper, and the cathode material 4 is made by adding a gelling dispersant such as sodium polyacrylate or carboxymethylcellulose. It is made by injecting most of the alkaline electrolyte such as caustic potash into amalgamated zinc. The cathode current collector 5 is a clad steel plate having a nickel layer on the outer surface of the steel plate to satisfy aesthetics and corrosion resistance, and a copper layer on the inner surface to prevent the formation of local batteries with the zinc active material. A plate is formed into a can shape having a peripheral folded portion 8 by drawing, or a steel plate is formed in advance by a similar method, and then a nickel layer and a copper layer are formed by a plating method, and Although not shown, the gasket can be prepared by forming a film of a liquid packing material such as asphalt pitch, fatty polyamide, or fluorine-based oil on the surface of the gasket before the battery is assembled by coating or dipping. 6 and anode can 1
A liquid packing material is interposed on the contact surface between the gasket 6, the anode can 1, and the cathode current collector 5, and the liquid packing material is used to fill the fine gaps that occur at the contact surfaces between the gasket 6, anode can 1, and the cathode current collector 5. This is to prevent electrolyte from leaking out. Next, the present invention will be explained in more detail with reference to Examples. An annular gasket having an L-shaped cross section was manufactured by injection molding nylon 610. The crystallinity of this gasket was 25%. These gaskets were individually heat treated in vacuum at 150°C for 2 hours to increase the degree of crystallinity to 35%, heat treated in vacuum at 160°C for 2 hours to increase the crystallinity to 37%, and then heated in vacuum at 160°C for 2 hours to increase the crystallinity to 37%. 175℃
Heat treatment at 200℃ for 2 hours to increase crystallinity to 40%, heat treatment at 200℃ in vacuum for 2 hours to increase crystallinity to 45%, and heat treatment at 200℃ in vacuum for 10 hours to increase crystallinity. Increase the temperature to 55% and 200℃ in vacuum
The crystallinity was increased to 60% by heat treatment at 200°C for 100 hours in vacuum, and the crystallinity was increased to 63% by heat treatment at 200°C in vacuum for 100 hours. Note that the gasket was cooled after the heat treatment by allowing it to cool. Nylon with increased crystallinity as described above
Using a gasket made of 610 and a gasket made of untreated nylon 610 with a crystallinity of 25%, the first
Eight types of SR44 type button-type alkaline batteries (Batteries A to H) were assembled with the structure shown in the figure. The gasket of battery A is untreated, that is, the crystallinity is 25.
% nylon 610 gasket, the gasket for battery B is a nylon 610 gasket with an increased crystallinity of 35%, and the gasket for battery C is a nylon 610 gasket with an increased crystallinity of 37%. The gasket for battery D is a nylon 610 gasket with increased crystallinity of 40%, the gasket for battery E is a nylon 610 gasket with increased crystallinity of 45%, and the gasket for battery F is a nylon 610 gasket with increased crystallinity of 45%. The gasket for battery G is made of nylon 610 with increased crystallinity of 60%. In addition, the gasket for battery H is made of nylon 610 with increased crystallinity of 63%.
It is a manufactured gasket. In addition, both batteries use ferrous oxide as the anode active substance, and the electrolyte is water with 5% by weight of zinc oxide and 35% by weight of caustic potassium.
The dissolved version is used. In each of the batteries, the gasket is immersed in a toluene solution of asphalt pitch before being assembled into the battery, and after being pulled up, it is dried to form a film of asphalt pitch on the gasket, and the cathode current collector is also Before fitting with the gasket, apply asphalt pitch toluene solution (however,
The viscosity is adjusted to be higher than that described above) and dries to form a film of asphalt pitch, thereby coating the contact surfaces of the gasket with the anode can and the cathode current collector in a liquid state made of asphalt pitch. Packing material was interposed. 100 of these batteries were heated at 60℃ and 90% relative humidity.
The batteries were stored in an atmosphere for the period shown in Table 1, and the number of batteries in which leakage occurred was determined. The results are shown in Table 1.

【table】

[Table] As shown in Table 1, batteries D, E, and
Compared to other batteries A, B, C, and H, F and G had a smaller number of leaking cells and had excellent leakage resistance. Note that this invention is not limited to button-type alkaline batteries as exemplified in the examples;
It is also applicable to cylindrical alkaline batteries. As explained above, in this invention, nylon
By increasing the crystallinity of the 610 gasket to a range of 40 to 60%, we were able to improve its leakage resistance.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of a button-type alkaline battery according to the present invention. 1... Anode can, 5... Cathode current collector, 6... Gasket.

Claims (1)

[Claims] 1 Between the anode can 1 and the cathode current collector 5, a gasket 6 made of nylon 610 with an increased crystallinity of 40 to 60% is placed over the entire gasket 6 from its surface to the inside. An alkaline battery in which the gasket 6, the anode can 1, and the cathode current collector 5 are disposed so that a liquid packing material is interposed between the contact surfaces and sealed to make the inside of the battery liquid-tight.