Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Cell enclosure structure – e.g. – housing – casing – container,...
Reexamination Certificate
2001-01-29
2002-11-26
Maples, John S. (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Cell enclosure structure, e.g., housing, casing, container,...
C429S163000
Reexamination Certificate
active
06485863
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns a container where alkaline solution is packed.
More specifically, it concerns a battery exterior container of alkali manganese batteries and the nickel cadmium batteries. Moreover, it concerns the surface treated steel sheet that is suitable for making thereof.
PRIOR ART
A method of barrel plating after press forming cold-rolled steel strip into a battery container or a method of press forming nickel-plated steel strip into a battery container have been adopted for manufacturing a battery container for such as alkali-manganese batteries and nickel cadmium batteries in which strong alkaline solution is packed. The reason why nickel plating is used for batteries such as alkali manganese batteries and nickel cadmium batteries is as follows. Nickel having excellent corrosion resistance to alkali is suitable for these batteries whose electrolyte is chiefly strong alkaline potassium hydroxide. Moreover, nickel is suitable for batteries since nickel has steady contact resistance when the battery is connected with an external terminal. Furthermore, nickel has excellent spot welding properties in case where each component is spot welded when assembled into a battery in the battery manufacturing process.
By the way, recently the main current of the plating method has been pre-plating, in which a steel strip is nickeled beforehand, replacing past barrel plating. It was difficult to manufacture products of high quality steadily by the past barrel plating because the difference of the plating thickness was large and it was especially difficult to nickel inside the container uniformly. As for pre-plating, the method of giving thermal diffusion processing after nickel plating has come to be applied chiefly to improve corrosion resistance. Now, the relation between the battery performance of the alkali manganese battery and the positive electrode container (battery container) is described hereafter. The said battery performance and the properties of the inside of positive electrode container are closely related. It is said that the lower the contact resistance between the inside of the positive electrode container and the positive electrode mix of the alkali manganese battery (consisting of manganese dioxide as a positive electrode active material, graphite as a conductor, and potassium hydroxide as electrolyte), the more excellent the battery performance. As for alkali manganese battery, the positive electrode mix and the positive electrode container are in contact, and the positive electrode container serves as not only a container of the battery but also as a conductor which transfers electrons.
Therefore, when the contact resistance between the positive electrode mix and the inner surface of the positive electrode container is great, the internal resistance of the battery rises. It causes decrease in the operation voltage, and in the electrical discharge duration, obstructing the battery performance. So, it is desirable to decrease the contact resistance between the positive electrode mix and the inner surface of the positive electrode container. Therefore, roughing the surf ace inner surf ace the positive electrode container, making a ditch on the positive electrode container in the vertical direction, and applying conductive coating or a conducting material made by adding binder to graphite are proposed to decrease the contact resistance between the positive electrode mix and the inner surf ace of the positive electrode container.
Next, the press-forming method of the battery container is described. Recently, DI (drawing and ironing) forming method is increasingly used as a method of thinning wall to increase the capacity of the battery replacing the past multi step deep drawing method (see Published Japanese Patent Hei 7-99686). This DI forming method and DTR (drawing thin and redraw) forming method is capable of increasing the battery capacity because the container side wall being thinner than the bottom thickness allows more positive electrode and negative electrode active materials to be contained. Moreover, the thick bottom has an advantage to improve the pressure resistance of the battery.
OBJECTS OF THE PRESENT INVENTION
By the way, although the DI forming method and the DTR forming method are effective for increasing battery capacity as mentioned above, there is a disadvantage when they are used for continuous forming because the deformation resistance of the material in those methods is greater than in the conventional multi step deep-drawing forming method. Concretely, when the powdering quality (powdery dropout of the plating layer) in the cupping process of the DI forming method and the DTR forming method is inferior, the powder adheres to the die and the punch in the ironing process causing a defect in the container sidewall. Although the similar phenomenon happens in the deep drawing forming, the above-mentioned defect is more remarkable in the DI forming method and the DTR forming method because the container wall has small surface roughness, which produced more lustrous appearance.
Moreover, powdering quality is more critical in the DI forming method and the DTR forming method. Also, because the contact pressure of the material and the tool is greater in the DI forming method and the DTR forming method than that in the drawing method, favorable lubrication is requested for tool life. Therefore, materials which have a favorable powdering quality and retention of the press lubricant are requested.
When using nickel plated steel sheet, one of the ways to improve the retention of the lubricant is to cause cracks in the plating layer at the press-forming step and to hold the lubricant in the part where cracks are caused. As a means for this, gloss nickel-plating producing a hard plating layer is generally brought to mind. However, although the gloss nickel plating produces a hard gloss plating layer, it is brittle and it has inferior powdering quality at the press-forming. In addition, since gloss plating involves organic additives containing sulfur (for example, sulfonic acid having ═C SO
2
-group) to make electrolytic ally deposited crystal grains fine, sulfur is absorbed in the plating layer, which causes the embrittlement with sulfur promoted by the temperature rise of the material in the ironing and the stretching process of the DI forming and the DTR forming resulting in a deteriorated powdering quality.
The inventors of the present invention examined various materials for a battery container having excellent formability in the DI forming method and the DTR forming method from such viewpoints, and found that nickel-cobalt alloy plating is suitable.
The present invention is based on such findings and it is aimed at a battery container having high quality and excellent continuous formability and a surf ace treated steel sheet which is suitable for producing the said battery container. Another objective of the present invention is to improve the removability DTR forming. This is taken into consideration since the difficulty of stripping the container from the punch (strippability) in the final pressing process is critical in the container manufacturing in addition to the above-mentioned powdering quality. At stripping where the container is pulled out from the punch hitching fingernails on the edge of the container, there was a problem that an inferior stripping caused breaking and split at the open edge portion of the container more frequently, which deteriorated the productivity.
THE BEST MANNER REALIZING THE PRESENT INVENTION
A battery container which achieves the above mentioned purpose is obtained by forming a surface treated steel sheet, of which inside and outside are plated with nickel-cobalt alloy, using DI forming method or DTR forming method. The cobalt content of the above-mentioned nickel-cobalt alloy plating is preferably from 0.5 to 10 percent by weight, and the thickness of the above-mentioned nickel cobalt-alloy plating is from 0.5 to 3 &mgr;m for the inside of the container and from 1.0 to 4 9 &m
Ohmura Hideo
Ohmura Hitoshi
Tomomori Tatsuo
Browdy and Neimark , P.L.L.C.
Maples John S.
Toyo Kohan Co., LTD
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