Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Cell enclosure structure – e.g. – housing – casing – container,...
Patent
1990-12-14
1996-12-31
Fourson, George
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Cell enclosure structure, e.g., housing, casing, container,...
429 53, 429 54, 429 82, 429185, H01M 208
Patent
active
055892930
DESCRIPTION:
BRIEF SUMMARY
This invention relates to sealed electrochemical cells, such as primary alkaline cells, and more particularly to an improved sealing and insulating member for such cells. In accordance with the invention, multiple vent sections are provided, each having a thickness which is easier to form by injection molding than the thicknesses necessitated when a single vent section is used.
The general construction of sealed, cylindrical galvanic cells is such that the principal components, an anode and a cathode, are assembled into a can, together with the appropriate separators, electrolyte, etc. Generally, the can into which the principal cell components are assembled is a positive cathode contact, i.e. the can, and usually the bottom end thereof, forms a cathode contact for the cell and the cell is closed by a member placed in the top end of the can. Such member is generally a sealing and insulating member, by which the cell is sealed so as to preclude electrolyte leakage therefrom, and so that the anode contact of the cell is insulated from the can at the opposite end thereof from its closed bottom end. Said sealing and insulating member, hereinafter referred to as the top member is typically formed from a polymeric material which can be injection molded.
It is common to include a vent membrane that is integrally formed in the top member. The vent membrane is generally of a thickness less than the surrounding thickness of the top member so that the membrane can rupture at a predetermined internal pressure. Top members having a variety of vent designs are disclosed in U.S. Pat. Nos. 4,191,806; 4,237,203; and 4,476,200. The top member disclosed in U.S. Pat. No. 4,476,200 is injection molded using a polypropylene material having a melt index between 4 and 30. A melt index in this range permits the injection molding of very thin vent membranes. U.S. Pat. No. 4,191,806 teaches that it is difficult to form thin vent membranes when harder plastics are used to make top members by injection molding. In order to get proper venting, this patent discloses forming grooves in the vent membrane.
Mineral filled polyolefins comprise a class of materials which poses particular problems for making top members by the injection molding process. Mineral filled sealing members are disclosed in Great Britain Patent No. 2,149,198. These materials have a high viscosity when melted, making it difficult to form thin vent membranes in the top member by injection molding. One problem is that vent membranes cannot be made thin enough because the mineral filled polyolefins do not easily flow through the thin section of the injection mold. To overcome this problem the membrane can initially be formed thicker than desired and a moving pin member of the mold used to further compress the vent membrane section down to the desired thickness. In this manner it is possible to form vent membranes having a thickness ranging from 0.0025" to 0.005" depending on the particular cell size. However, this method does not produce consistently uniform top members and there is variability in the pressure required to rupture the membrane. Another problem encountered when using mineral filled polyolefins is that a seam often forms during injection molding where the material flowing from different directions through the mold meet. This seam imparts a fracture zone in the top member.
Thus, it is seen that there is a need for a top member design which can be easily injection molded using filled polyolefins and which incorporates a reliable vent membrane that is easily molded.
The features and advantages of the present invention will be more fully discussed below with reference to the accompanying figures in which:
FIG. 1 shows a top view of a sealing and insulating member made in accordance with the present invention;
FIG. 2 shows a bottom view of the sealing and insulating member of FIG. 1;
FIG. 3 shows a side view of the sealing and insulating member of FIG. 1;
FIG. 4 shows a vertical cross section through the top member of Figure, taken along the line A--A;
FIG. 5 sh
REFERENCES:
patent: 4476200 (1984-10-01), Markin et al.
patent: 4756982 (1988-07-01), McCartney, Jr. et al.
Kirk-Othmer Encyclopedia of Chemical Technology Third Edition vol. 15, p. 437; vol. 18 p. 172;vol. 22 p. 530 (1981).
Pope Peter J.
Willis-Owen Richard B.
Allen Rose M.
Duracell Inc.
Everhart C.
Feltovic Robert J.
Fourson George
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