Dry cell

Abstract: A dry cell which is so arranged that, with a bottom plate (4) being disposed at the lower portion of a raw cell sealed at its opening (1) by a sealing member (2), an insulative seal packing (5) is applied onto the peripher­ al portion of the bottom plate (4), while the raw cell and the peripheral portion of the bottom plate (4) are surround­ ed by a metal jacket (10) welded by laser at its butted opposite ends. At the peripheral portion of the bottom plate (4), a gas discharge mechanism is formed which is arranged to be normally closed by the seal packing (5), and to be released from the closing by the seal packing (5) due to deformation of the bottom plate (4) upon increase of internal pressure of the dry cell for discharging the gas within the dry cell outside, and thus, a safe dry cell free from a danger of rupture maybe provided.

Description: BACKGROUND OF THE INVENTION The present invention generally relates to a dry cell or dry battery, and more particularly, to a cylindrical type Leclanche cell (referred to merely as a dry cell hereinafter) which is free from a danger of rupture due to an increase of an internal pressure thereof through improvements on its bottom plate for higher safety. It has been a recent trend that the dry cell has been changed from a paper tube cladding or paper tube jacket type to a metal cladding or metal jacket type, with a marked development of its cell performance through improvements in resistance against leakage and also resistance against expansion or swelling thereof. For the metal jacket type as referred to above, there have generally been employed a double-lock type jacket folded into double layers at its opposite edges, a butted-joint type jacket merely butted to each other at opposite edges thereof, and a laser-welded type jacket subjected to laser welding at its opposite butted edges (referred to as a laser-welded type jacket hereinafter), etc. US-A-3 442 716 discloses an alkaline cell comprising an outer metal case constituting the negative terminal of the cell and an inner metal case constituting the positive terminal of the cell. The bottom plate is integrally formed as a part of the outer case. A bottom insulating sealing member is provided as an elastic synthetic resin comprising a body portion sealing the bottom opening of the inner case and a sleeve portion sealing the bottom interspace between the inner case and the outer case. A sleeve of absorbent material is interposed between the outer and inner cases. This absorbent material is porous paper preferably having good resistance to any alkaline electrolyte. Furthermore, a gas discharge mechanism is provided in a cap and is comprised of gas venting holes in the side cylindrical wall of the cap. The bottom insulating sealing member is elastic enough to release from the cell any exessive increase in the internal pressure caused by a swell of the anode material and also to release hydrogen gas pressure which may result from abnormal operating conditions. Such exessive pressure will cause displacement of the body portion of the bottom sealing member. If the gas is to be accidentally forced out, taking any electrolyte with it into the interspace between the outer and inner cases, then such electrolyte will be trapped in the sleeve of absorbent material and the gas alone will pass through the interspace between the top surface of the inner case and a brim-shaped portion of the cap. Then the gas will be released through a venting hole in the cap. From US-A-2 934 584, an alkaline cell is known in which the inner case, the inner insulating packing, and the notched plate are arranged such that air-tightness is maintained by pressing the inner insulating packing against the inner case by the notched plate. In the case where the cell internal pressure is raised, the packing is deformed or pushed up at the notched portion without support of the notched plate disposed behind, thereby to cause the gas to escape. The construction of a further conventional dry cell will be described with reference to figures 1 to 3. As shown in figure 1, the dry cell generally includes a zinc can z containing therein a cathode mixture m, a carbon rod c, a partitioning paper p having a paste layer over its one face, etc., a synthetic resin sealing member 2 for sealing an opening 1 of the zinc can z, a heat-shrinkable synthetic resin tube 6 covering the entire outer periphery of the zinc can z including a bottom plate 4 (anode) at the bottom portion 3 of the zinc can z, a seal packing 5 and a shoulder portion of the sealing member 2, a sealing material 7 such as pitch or the like disposed on a recess formed on the upper surface of the sealing member 2, and a sealing plate 8a integrally formed with a cap 8 (cathode) and disposed on said sealing member 2. The entire dry cell is further clamped, through a resinous packing 9 disposed on the sealing plate 8 and the seal packing 5 provided at the lower portion of the dry cell, by a metallic outer cladding can or metal jacket 10 (referred to as a metal jacket hereinafter) to maintain the dry cell in an air-tight state. When the laser-welded type metal jacket as shown in Fig. 2(B) is employed as a metal jacket instead of the double-lock type metal jacket (Fig. 2(A)) or butted-joint type metal jacket (Fig. 3(B)), as compared, for example, with the double-lock type metal jacket in Fig. 2(A), since the laser-welded portion 22 has a thickness smaller than that of the double-lock portion 21 by a difference α, the laser-welded type metal jacket of Fig. 2(B) can employ a raw cell 23' having a larger external diameter than the raw cell 23 of the double-lock type metal jacket of Fig. 2(A), with a consequent increase of the cell capacity by that extent. Moreover, since the laser-welded metal jacket (Fig. 3(A)) has a tensile strength higher than that of the butted-joint type metal jacket (Fig. 3(B)) in a diametrical direction of the jacket especially at the laser-welded portion 22, said laser-welded metal jacket is free from any separation or opening w at a butted-joint portion 31 as in the butted-joint type metal joint (Fig. 3(B)) even during over-discharging. In the case where a dry cell employing the laser-welded type metal jacket (Fig. 2(B)) is wrongly used, for example, by undesirable charging thereof or by leaving it in a high temperature atmosphere above 85°C, etc., the dry cell may be expanded due to an increase of its internal pressure through generation of a gas therein. The gas thus generated passes through a gap between the zinc can z and the resinous sealing member 2 so as to be collected between the zinc can z and the synthetic resin tube 6, while part of the gas is discharged outside via the seal packing 5 provided at the bottom portion of the zinc can z (Fig. 1). If the internal pressure within the dry cell is rapidly raised, since the tensile strength in the diametrical direction is extremely high in the case of the laser-welded type metal jacket (Fig. 2(B), Fig. 3(A)) as compared with that of the double-lock type metal jacket (Fig. 2(A)) or butted-joint type metal joint (Fig. 3(B)), the dry cell is expanded longitudinally in the direction of its height, thus resulting in problems such as disengagement of the cap 8, integrally formed with the sealing plate 8a and provided at the upper portion, or scattering of the cathode mixture m. Particularly, in the case of scattering of the cathode mixture m, appliances employing the dry cell may be heavily damaged, giving rise to various accidents in some cases. SUMMARY OF THE INVENTION Accordingly, an essential object of the present invention is to provide a dry cell which is provided with an improved gas discharge mechanism with substantial elimination of disadvantageous inherent in the conventional cells and which is simple in contruction, and stable in function, and can be readily manufactured on a large scale at low costs. In accomplishing these objects, the dry cell according to the invention comprises a dry cell which comprising a raw cell sealed at its opening by a sealing material, a bottom plate provided at a first portion of the raw cell, a cap provided at a second portion of said raw cell, a metal jacket covering the outer periphery of said raw cell and the peripheral portion of the bottom plate, and a gas discharge mechanism, and is characterized in that said bottom plate is deformable and clamped by folding the lower edge of the metal jacket inwardly, a seal packing is interposed between the lower edge of said metal jacket and a peripheral edge of said bottom plate, said metal jacket is subjected to laser-welding at its opposite butted ends, said bottom plate is provided, at its peripheral edge, with said gas discharge mechanism, and said gas discharge mechanism is formed by more than one opening means (H; V) in said peripheral edge of said bottom plate covered by said seal packing to be normally closed by said seal packing and to be opened upon deformation of the bottom plate by an increase of an internal pressure of the dry cell for discharging gas from within said dry cell therethrough to the outside. The construction of the gas discharge mechanism and, thus, of the whole dry cell of the invention is very simple. This is achieved by the features that the bottom plate is deformable and is provided, at its peripheral edge, with the gas discharge mechanism which is arranged to be normally closed by the seal packing and to be released from the closing upon deformation of the bottom plate by an increase of the internal pressure of the dry cell. In other words, the gas discharge means is provided in such a position that it is overlapped by the seal packing during normal use. In case of an increase of the internal pressure, the deformable bottom plate swells outwardly, whereby the air-tightness among the bottom plate, the seal packing and the metal jacket is lost and there is formed a small gap, through which the gas directly escapes outside. According to the invention, the gas exhaust cannot be hindered by an expansion of the inner case. The dry cell of the present invention is assembled through employment of parts having functions not adversely affecting the cell performance during normal use, and the order of the arragement of the parts is such that from the interior of the cell towards outside, the zinc can (inner case), the bottom plate provided with the gas discharge means, and the seal packing are sequentially disposed. Furthermore, for effective utilization of the inner volume of the cell of the present invention with the object of improving the cell capacity, the laser-welded metal jacket is employed, whereby the external diameter of the zinc can is enlarged so as to allow to fill more reaction active substances than in the conventional dry cell. In the laser-welded metal jacket, swelling of the cell due to an increase of the internal pressure is prevented by effecting the welding at the butted portions. However, due to an increase of the internal pressure, the cell swells in the direction of the "+"-terminal plate and the "-"-terminal plate by the generation of gas. Therefore, the dry cell of the present invention is provided with the gas discharge means at the bottom plate. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiment thereof with reference to the accompanying drawings, in which; Fig. 1 is a side elevational view, partly in section, showing construction of a typical dry cell conventionally employed (already referred to), Figs. 2(A) and 2(B) are schematic side sectional views of a dry cell employing a double-lock type metal jacket and a dry cell employing a laser-welded type metal jacket for explaining a difference in the external diameter of raw cells contained therein (already referred to), Figs. 3(A) and 3(B) are also schematic side sectional views of a dry cell employing the laser-welded type metal jacket and a dry cell employing a butted-joint type metal jacket for explaining behaviors thereof during over-discharging of the cells (already referred to), Fig. 4 is a top plan view of a bottom plate having gas discharging holes in its peripheral portion and employed in a dry cell (Figs. 5 and 6) according to one preferred embodiment of the present invention, Fig. 5 is a fragmentary side elevational view, partly in section and showing the lower portion of a dry cell employing the bottom plate of Fig. 4 according to one preferred embodiment of the present invention, Fig. 6 is a view similar to Fig. 5, which particularly shows the state of deformation of the bottom plate following gas generation upon undesirable charging of the dry cell. Fig. 7 is a top plan view of a bottom plate having gas discharging notches in its peripheral portion and employed in a dry cell (Figs. 8 and 9) according to a modification of the present invention, Fig. 8 is a fragmentary side elevational view, partly in section and showing the lower portion of a dry cell employing the bottom plate of Fig. 7 according to the modification of the present invention, and Fig. 9 is a view similar to Fig. 8, which particularly shows the state of deformation of the bottom plate following gas generation upon undesirable charging of the dry cell. DETAILED DESCRIPTION OF THE INVENTION Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings. In the first place, it is to be noted that in Figs. 5, 6, 8 and 9, only the lower portions of dry cells including gas discharging mechanism directly related to the present invention are shown for brevity, since the upper portions of the dry cells have construction generally similar to that in the conventional dry cell of Fig. 1, with like parts being designated by like reference numerals. Referring now to the drawings, there is shown in Fig. 5, a dry cell B1 according to one preferred embodiment of the present invention which includes a raw cell sealed at its opening 1 (Fig. 1) by a sealing material 2(Fig. 1), a bottom plate 4A provided at the lower portion of the raw cell, a cap 8(Fig. 1) provided at the upper portion of the raw cell, a metal jacket 10 covering the outer periphery of the raw cell and subjected to laser welding at its opposite butted ends 22 (Fig. 2(B)), and a seal packing 5 interposed between the lower edge of the metal jacket 10 and a peripheral edge of the bottom plate 4A, and characterized in that there is provided a gas discharge mechanism provided at the peripheral edge of the bottom plate 4A, and arranged to be normally closed by the seal packing 5 and to be released from the closing upon deformation by an increase of an internal pressure of the dry cell for discharging gas within the dry cell therethrough. As shown in Fig. 4 the bottom plate 4A is provided with a plurality of gas discharge holes H formed in a peripheral edge 4Af of the bottom plate 4A. More specifically, the gas discharge openings H each having a diameter of 1mm are formed in plurality in positions spaced inwardly from the outer face of the peripheral edge by 1.6mm, at equal intervals as illustrated so as to be closed from below by the seal packing 5. The configuration of the holes H can be modified, for example, to elongated shape besides circular shape, and the size of the holes H may also be selected as desired. As is seen from Fig. 5, the gas discharge openings H are provided in the peripheral edge 4Af of the bottom plate 4A in such positions and size as will be overlapped by the seal packing 5 at the lower side thereof, and the bottom plate 4A is clamped by folding the lower edge of the metal jacket 10 inwardly as in the conventional practice. In this case, it is preferable that the lower end of the metal jacket 10 folded inwardly is also so positioned as to overlap the gas discharge holes H, and this is advantageous in positively closing the gas discharge holes H during normal use, thereby to maintain the resistance against leakage by keeping sufficient liquid tightness and air tightness. By the above construction, connecting terminals (not shown) at the load side are normally connected to the terminal portions of the dry cell B1 by correct polarities, and the dry cell is thus protected against undesirable charging, etc. However, by some causes, if the dry cell is subjected to wrong use such as charging or the like, with the cell being expanded as a gas is generated therein, the bottom plate 4A swells outwardly to be deformed as at D in Fig. 6, and between the bottom plate 4A and the seal packing 5, there is formed a small gap, through which the gas within the dry cell B1 escapes outside via a passage as indicated by arrows. Referring further to Fig. 7, there is shown a modification of the bottom plate 4A described so far with reference to Figs. 4 to 6. In the modified bottom plate 4B in Fig. 7, the gas discharge holes H described as formed in the peripheral edge 4Af of the bottom plate 4A are replaced by four gas discharge notches V formed at the outer face of a peripheral edge 4Bf of the bottom plate 4B at equal intervals. Each of the notches V in a V-shape has two sides forming an angle of 60° therebetween and each measuring 1.5mm in length as shown. These notches V may be formed, e.g. into a U-shape besides the V-shape as described above, and the size thereof may also be altered as desired. Fig. 8 shows a dry cell B2 in which the bottom plate 4A in the dry cell B1 of Figs. 4 to 6 is replaced by the modified bottom plate 4B in Fig. 7. In the above arrangement of Fig. 8 also, the positional relation among the notches V of the bottom plate 4B, the seal packing 5 and the metal jacket 10 should preferably be similar to that in the bottom plate 4A having the gas discharge holes H in Figs. 4 to 6. In this case also, upon expansion of the dry cell due to generation of gas by the wrong use such as undesirable charging of the cell, etc., the bottom plate 4B is deformed as at D and the gas escapes outside through a passage indicated by arrows in Fig. 9. Table 1 below shows comparison of scattering of the cathode mix due to rupture of dry cells having or not having the gas discharge mechanism in the bottom plates. Each of dry cells used for the experiments in Table 1 was prepared in a normal process by filling a zinc can with a cathode mix prepared by mixing 20 parts by weight of acetylene black, 83 parts by weight of electrolyte mainly composed of zinc chloride, and 1 part by weight of zinc chloride, with respect to 100 parts by weight of manganese dioxide, through a separating paper having a paste layer on its one surface. As is seen in the above Table 1, in the dry cells provided with the gas discharge mechanism according to the present invention, even when the internal pressure of the dry cells is raised by wrong use such as short-time charging by a large current or long-time charging by a small current, the gas is discharged outside through the gas discharge mechanism without giving rise to rupture of the cell even if the swelling in the longitudinal direction of the dry cell takes place, and therefore, no external scattering of the cathode mix was noticed. As is clear from the foregoing description, according to the dry cell of the present invention, the laser-welded type metal jacket is employed, with the gas discharging mechanism being provided at the peripheral edge of the bottom plate, and therefore, even when the dry cell expands due to gas generation during wrong use of the dry sell such as undesirable charging, etc., so as to be deformed at its bottom plate, the gas rapidly escapes outside through the gas discharge mechanism provided in the bottom plate, and thus, scattering of the cathode mix can be advantageously prevented.

Claims: A dry cell comprising a raw cell sealed at its opening (1) by a sealing material (2), a bottom plate (4A, 4B) provided at a first portion of the raw cell, a cap (8) provided at a second portion of said raw cell, a metal jacket (10) covering the outer periphery of said raw cell and the peripheral portion of the bottom plate (4A, 4B), and a gas discharge mechanism, characterized in that said bottom plate (4A, 4B) is deformable and clamped by folding the lower edge of the metal jacket (10) inwardly, a seal packing (5) is interposed between the lower edge of said metal jacket (10) and a peripheral edge of said bottom plate (4A; 4B), said metal jacket (10) is subjected to laser-welding at its opposite butted ends, said bottom plate (4A; 4B) is provided, at its peripheral edge (4Af; 4Bf), with said gas discharge mechanism, and said gas discharge mechanism is formed by more than one opening means (H; V) in said peripheral edge (4Af; 4Bf) of said bottom plate (4A; 4B) covered by said seal packing (5) to be normally closed by said seal packing (5) and to be opened upon deformation of the bottom plate (4A, 4B) by an increase of an internal pressure of the dry cell for discharging gas from within said dry cell therethrough to the outside. A dry cell as claimed in claim 1, wherein said opening means (H) includes a plurality of circular holes or elongated holes formed in said peripheral edge (4Af) of said bottom plate (4A) at equal intervals. A dry cell as claimed in claim 1, wherein said opening means are formed by notches (V) in said peripheral edge (4Bf) of said bottom plate (4B). A dry cell as claimed in claim 3, wherein said notches (V) include a plurality of V-shaped or U-shaped removed portions formed in said peripheral edge (4Bf) at equal intervals.

Inventors: ASHIHARA RYOHEI, MIYOSHI JUN, SUEHIRO KIKUMITSU, SUGINO KAZUO, ASHIHARA, RYOHEI, MIYOSHI, JUN, SUEHIRO, KIKUMITSU, SUGINO, KAZUO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1988
Main classification: H01M2
IPC codes: H01M2