A popular method employed in the manufacture of Leclanche or zinc-carbon dry cell batteries utilizes a so-called "paper liner" inside the zinc can to physically and electrically separate the zinc can (negative terminal) from the "depolarizer mix" surrounding the carbon rod (positive terminal). During manufacture, the inorganic salts and the water, which are to eventually become the battery's electrolyte, have been mixed into the depolarizer mix. Subsequent to manufacture the paper liner absorbs the electrolyte, becoming saturated with it, and for all practical purposes, the paper liner and the electrolyte become one and the same. It is important to recognize, at this point, that the depolarizer mix consists of materials which yield an electrically conductive mixture of low resistivity. Therefore, the electrical potential or e.m.f., measured at any point on the surface of, or within the mass of, the depolarizer mix is essentially the same potential or e.m.f. as measured at the carbon rod.
From the foregoing, it may be seen that three distinct electrical circuit elements may be identified in the finished battery, as follows:
(1) The zinc can (the negative terminal); PA1 (2) The saturated paper liner and the electrolyte; and PA1 (3) The carbon rod (the positive terminal) along with the surrounding mass of depolarizer mix.
Numerous techniques have been devised and employed to introduce the battery's various components into the zinc can in the proper sequence and under the required conditions. While no effort will be made here to review all of these techniques, two will be mentioned in order to illustrate the nature of the problem which the subject invention is intended to overcome.
Technique A. A rolled sheet of liner paper of appropriate size is first inserted into the zinc can, and then allowed to unroll against the inner wall of the can. A flat disc or "bottom washer" of paper, slightly larger than the can's inside diameter, is then pushed down to the bottom of the can. A controlled quantity of depolarizer mix is deposited within the paper enclosure formed by the sheet and disc, then a wipe-down washer and the carbon rod are placed in position. While the carbon rod is still held in place, a suitably shaped plunger is pressed against the wipe-down washer atop the depolarizer mix for the purpose of compacting the depolarizer mix around the carbon rod and against the paper liner, the compacted depolarizer mix forming a "bobbin."
Technique B. A preformed liner paper bag of suitable dimensions is filled with a controlled quantity of depolarizer mix, the filled bag is inserted into the zinc can, and then the carbon rod is inserted, with subsequent steps essentially those of Technique A.
The difficulty that results in the rapid spoilage of a significant percentage of batteries being manufactured is the production of "smears." These smears consist of a quantity of depolarizer mix which somehow, despite all efforts directed toward prevention, is deposited in a location which effectively "short circuits" the cell.
In Technique A, for example, a quantity of depolarizer mix may coat the paper liner while the mix is being inserted into the cell. If this coating extends to and over the top edge of the paper liner, it will eventually "bridge" or "short circuit" across the linear. In Technique B, for example, the relationship of the dimensions of the preformed liner paper bag relative to those of the can is critical, and any gap between bag and can permits the bag to burst during the compacting operation. Here again, mix leaking through the burst point will constitute a "bridge" or "short circuit" across the liner.
It is an object of the present invention to provide a method of making paper-lined dry cell batteries by Technique A which avoids the possibility of smear formation.
It is another object to provide such a method which does not reduce the efficiency of the battery.
It is a further object to provide such a method which is economical relative to a conventional battery making process.
Another object is to provide batteries made by such a method.