Battery Seal

This invention relates to novel battery seals capable of prolonging shelf life of a battery by preventing moisture loss and oxygen ingress, while simultaneously providing a means for venting unusual amounts of gas build-up within the battery cell. The seal thus provides a safer, more effective means for containing a battery's necessary ingredients and/or preventing seepage of by-products of cell storage or discharge.

To provide a combination of functionality and safety, a battery seal should be capable of venting gases on rare occasions when, for reasons such as dead short, heavy load or unusual storage conditions, gas build-up becomes extraordinary. Under normal operating conditions, however, the seal should remain airtight.

It is known that the porous carbon rod of a typical zinc/carbon battery is capable of venting some excess gas. However, this may be quite insufficient when the battery is subjected to high heat or is otherwise used improperly. Porous seals, while able to handle the venting problem, would be undesirable for use as battery seals because they would not be expected to maintain sufficient airtightness under normal operating conditions. They would not, for instance, be expected to properly contain by-products of cell storage and discharge, nor to properly prevent moisture loss or oxygen ingress.

Plastic seals have been used on certain zinc/carbon dry cells, and asphalt has been used as a sealant between the plastic seal and the points within the battery where the seal makes contact. It is believed, for instance, that Matsushita manufactures zinc carbon dry cell batteries with an asphalt seal between the carbon pencil and a plastic seal washer, and that Matsushita has manufactured a product with asphalt at the interface between a seal washer and zinc can. Rayovac, and perhaps Matsushita, uses a solvent dissolved asphalt dispensed on the periphery of a shallow metal container to contact a closure cap and produce an airtight seal. Battery seals such as the Matsushita designs referenced above, however, would not be expected to provide a sufficient means for venting excess gases. A battery's inability to vent excess gas can cause rupture of the battery cell and can render the battery useless. Additionally, the build-up of pressure may, in some types of batteries, cause seepage of by-products and other materials which can be harmful to equipment into which the battery has been placed.

It is therefore an object of the present invention to provide an airtight battery seal which is capable of efficiently venting excess gases within a battery cell before the pressure of such gases reaches a level likely to cause rupture or seepage.

It is a further object of the invention to provide seals capable of venting gases in a non-destructive manner such that the battery remains functional after the venting.

It is a further object of the invention to provide a seal which prolongs battery shelf life by effectively preventing moisture loss from, or oxygen ingress into, the battery.

It is yet another object of the invention to provide a battery seal which is economical to manufacture and install, takes up less space than total asphalt overpour seals and is thoroughly reliable in use.

The above objects and other objects are accomplished by providing a battery seal comprising a plug of air-tight material which fits within an open end of a battery jacket and which has a layer of sealant on at least one of its surfaces which face the interior of the battery, wherein the battery jacket is comprised of a material having sufficiently elastic properties to cause the jacket to regain its original shape after slight distortion under a temporary pressure, and wherein the battery jacket is crimped, along its edge which forms said open end, in a manner which causes the jacket to directly or indirectly compress the plug inward onto a receiving member, such that the receiving member contacts the plug, in the region of the sealant, at a pressure which is sufficient to provide an air-tight seal between the plug and receiving member under normal battery storage and operating conditions yet is low enough to allow the plug to move away from the receiving member in response to force exerted on the plug by abnormal gas pressure within the battery. Under normal operating conditions, gas pressure within a battery cell does not substantially exceed atmospheric pressure. Typically, the pressure is less than about 2 pounds per square inch above atmospheric pressure. It is particularly desirable that a seal be capable of venting gasses when the pressure exceeds atmospheric by appreciably more than about 10 pounds per square inch.

The seal of this invention will, under ordinary conditions, be sufficiently air-tight to prevent substantial moisture loss or oxygen ingress and thus sufficiently airtight to prolong the effective life of a battery in which it is installed.

When excessive gas pressure builds up within a battery cell having the seal of this invention, the plug is pressed away from the receiving member, thus creating an opening between the plug and receiving member through which gas can escape. This motion of the plug slightly deforms the crimped portion of the battery jacket which otherwise acts to compress the plug downward onto the receiving member. Because of the elastic properties of the jacket material, the original crimp of the jacket recovers its former shape once excess gases have been vented and once the upward pressure on the plug is released. This recovery of shape by the battery jacket recompresses the plug into position upon the receiving member such that, together with the sealant along the lower periphery of the plug, the plug and receiving member once again form an air-tight seal. Once excessive pressure within the cell has been relieved by venting of the gases in accordance with the instant invention, the seal returns to its original position and remains fully functional.

The invention is further elucidated by the following detailed description of certain preferred embodiments when read in conjunction with the drawing and description thereof.

The plug of the invention may be comprised of any air-tight material, preferably material which is electrically non-conductive. Most plastics are suitable. Nylon, polyvinyl chloride, polypropylene, and polyethylene are preferred, especially high density polyethylene. In certain preferred embodiments, the plug is in the form of a washer having a central aperture for enclosing a battery's current collector. When the plug is so configured it can aid in centering the current collector.

The sealant of the invention greatly increases airtightness relative to direct interfacing of the plug and receiving member, and makes possible the use of high performance mixes such as all zinc chloride mixes. The sealant can be any compound or mixture of compounds capable of forming an air-tight seal. It is preferable that the sealant be dispersable or dissolvable in a solvent carrier such that, when mixed with solvent, the sealant material flows easily and can be readily applied to appropriate surfaces by known mechanical methods. Organic solvents, particularly toluene, methylene chloride and mineral spirits are preferred. It is also preferable that the sealant be somewhat malleable in the dry state after its carrier solvent has evaporated. This enables the seal to be assembled after the sealant has dried. When the seal is assembled after the sealant has dried, there is no problem with the sealant's running during the assembly process. This renders unnecessary the careful control over orientation of the components of the seal during assembly which might otherwise be necessary, and can allow for more efficient mass production. Examples of sealants appropriate for use in the instant invention include but are not limited to asphalt, caulk, epoxy glues, rubber cement, and airplane glues. An especially preferred sealant is blown asphalt.

The crimped battery jacket of the invention may be comprised of any material having elastic properties such that the crimped portion returns to its original shape after minor deformation under pressure and after the deforming pressure has been released. Preferred jacket materials include but are not limited to metal and plastic compounds, preferably hard metal and hard plastics. Seventy-five pound plate steel is especially preferred. When steel is used, it is often desirable to use steel which has been coated with a rust preventative.

The receiving member which contacts the air-tight plug of the invention may be any member within a battery which is located and oriented in a position where it can contact and form an airtight seal with the plug. For instance, it may be the top portion of the battery's container of active ingredients. In certain preferred embodiments, the receiving member may be the zinc container of a typical zinc/carbon dry cell battery.

FIG. 1 is a cross-sectional view of a cylindrical zinc/carbon dry cell battery incorporating a preferred embodiment of the seal of this invention .

There is shown in FIG. 1 a zinc/carbon dry cell battery encased in jacket 10 which is crimped at its edge 11 so as to exert inward pressure, indirectly through paper sleeve 12 and protective cap 7, onto plug 8 which has peripheral groove 9 etched along the periphery of its inner surface 13. Plug 8 is preferably in the form of a washer having centrally located aperture 14 which encircles and fits snugly against current collector 6. The inward pressure exerted indirectly onto plug 8 by the crimp 11 in steel jacket 10 presses plug 8 inward against zinc container 5. The interface 15 between plug 8 and zinc container 5 contains sealant material 4. It is highly desirable that sealant material 4 also be used at the interface between plug 8 and current collector 6. It is desirable that the edge of container 5 slant such that the edge fits into peripheral groove 9 of plug 8. This can improve the airtightness of the seal.

The terms and descriptions used herein are set forth by way of illustration only and are not meant as limitations. Those skilled in the art will recognize that numerous variations are possible within the spirit and scope of the invention as defined in the following claims.