Battery plate separator envelope and method of forming battery plate assemblies including the same

Abstract: Battery plate envelopes (12) include a sheet of porous film material having a folded widthwise bottom edge (12a) and overlapped lateral edges (12b1,12c1,12b2,12c2) to thereby form a pocket for receiving a battery plate (10) therein. The overlapped lateral edges are joined to one another by a lengthwise extending series of discontinuous joining regions (12d,12e) with adjacent ones of the discontinuous joining regions being separated by respective unsealed regions (12f,12g). These unsealed regions thereby establish respective lateral channels through which fluid (e.g., electrolyte employed in a wet storage battery) may pass to the interior pocket, and hence to the battery plate. The discontinuous joining regions are most preferably formed by passing the sheet material through the nip between opposed joining rings, each of which is provided with a series of triangularly-shaped teeth with smooth land areas formed between adjacent teeth series.

Description: The present invention relates generally to the field of wet cell storage batteries, and particularly to the battery plates and separators employed therein. BACKGROUND OF THE INVENTION Wet cell storage batteries having alternating positive and negative battery plates with interposed separators to prevent physical contact between the plates are notoriously well known. It is also well known from U.S. Patent No. 4,026,000 to Anderson that the individual battery plates may be enveloped in a folded sheet of porous film material. According to the Anderson patent, the overlapped edges of the sheet are continuously sealed to one another along their entire longitudinal extent. Other patent publications in the battery plate separator art which may be of interest include U.S. Patent Nos. 4,407,063 to Johnson; 4,080,727 to Stolle et al and 4,085,560 to McClosky as well as UK Patent Specification No. 1,497,364. The disclosure of GB-A-1 415 958 is of a battery plate envelope made of folded resin sheet having overlapping side edges joined by discontinuous sealed regions separated by unsealed regions. The joining is effected by heat welding. Further examples of envelopes having sealed regions formed by welding are in EP-A-0 472 232; Patent Abstracts of Japan, volume 10, No 251 (E-432); Patent Abstracts of Japan, volume 16, No 482 (E-1275) and Patent Abstracts of Japan, volume 17, No 525 (E-1436). The present invention is concerned with the provision of a viable alternative to this prior proposal and to that end provides the battery plate envelope defined in claim 1; further preferred features being defined in claims 2 to 5. The invention also provides the related process for forming a battery plate assembly as defined in claim 6. Broadly stated therefore the invention provides a battery plate envelope comprising a sheet of porous film material having a folded bottom edge and overlapped lateral edges which form a pocket for receiving a battery plate, characterized in that said overlapped lateral edges are secured to one another by an extended series of discontinuous non-welded but mechanically joined regions being separated by respective unsealed regions which establish a lateral channel through which fluid may pass. BRIEF DESCRIPTION OF THE DRAWINGS Reference will hereinafter be made to the accompanying drawings wherein like reference numerals throughout the various FIGURES denote like structural elements, and wherein: FIGURE 1 is a schematic perspective view of a battery plate positioned in a discontinuous edge-sealed microporous film envelope according to the present invention; FIGURE 2 is a schematic representation of the enveloping and apparatus employed to obtain the discontinuous edge-sealed battery plate envelope shown in FIGURE 1; FIGURE 3 is a side elevational view showing a presently preferred pair of discontinuous edge-joining rollers to obtain the battery plate envelope shown in FIGURE 1; and FIGURE 4 is a detailed elevation view of a region of the edge-joining rollers which is bounded by the chain line in FIGURE 3. DETAILED DESCRIPTION OF THE PREFERRED EXEMPLARY EMBODIMENTS Accompanying FIGURE 1 shows an exemplary enveloped battery plate BP which includes a battery plate 10 positioned within the interior pocket of a plate envelope 12. As is shown, the plate envelope 12 has a bottom edge 12a formed along a fold line between opposite side panels 12b, 12c. The widthwise dimension of the side panels 12a, 12b is greater than the widthwise dimension of the battery plate 10 so that the lateral edges 12b 1 , 12c 1 and 12b 2 , 12c 2 of the side panels 12b, 12c overlap one another in a region outside the lateral extent of the battery plate 10. These overlapped side edges 12b 1 , 12c 1 and 12b 2 , 12c 2 of the side panels 12b, 12c are joined to one another by a longitudinally extending series of corrugated joining regions 12d, 12e, respectively. Adjacent ones of the corrugated joining regions 12d, 12e thus establish therebetween discrete regions 12f, 12g where the side edges 12b 1 , 12c 1 and 12b 2 , 12c 2 are not sealed to one another. The unsealed regions 12f, 12g established between the lengthwise extending corrugated joining regions 12d, 12e, respectively, thereby define lateral or widthwise extending channels through which fluid (e.g., electrolyte) may flow into and out of the interior pocket of the plate envelope 12 and thus into contact with the battery plate disposed therewithin. As such, circulation of the electrolyte within the storage battery cell is improved while maintaining the necessary physical separation between adjacent battery plates. Any suitable porous material which is inert to the components employed in wet cell storage batteries may be employed in the practice of this invention. Most preferably, the material forming the plate envelope 12 is a microporous film material formed of a polyolefin-based plastics as described more fully in U.S. Patent No. 3,351,495. A commercially available separator material is available under the tradename SUBMICRO®. The film material most preferably is formed with longitudinally extending rib elements 12h as shown in FIGURE 1 so as to maintain slight separation between the battery plate 10 and the side panels 12b, 12c of the plate envelope 12. A presently preferred automated apparatus 14 for enveloping the battery plate 10 with the plate envelope 12 is shown in accompanying FIGURE 2. The apparatus is generally comprised of (i) a battery plate infeed conveyor system 16 which sequentially presents battery plates 10 to the envelope-forming section 18, (ii) an enveloped battery plate discharge conveyor system 20 which transports the enveloped battery plates BP to a downstream location where they may be further processed and eventually assembled in a battery case (not shown), and (iii) a film feeding system 22 which feeds the microporous film material FM ultimately forming the envelope 12 to the envelope-forming section 18. The film material FM is fed from a rotatable supply roll 22a around a guide roller 22b and then between a pair of driven feed rollers 22c, 22d. The rollers 22c, 22d may be driven at a desired speed ratio relative to the downstream sizing cylinder 22e so as to present a sufficient length of the film material FM to the envelope-forming station 18. In this regard, the film material FM is cut into sheets of sufficient length by the sizing cylinder 22e which rotates in opposition to the platen cylinder 22f. A cutting blade 22e 1 cuts the film material to form a film sheet FS which had previously been acted upon by creasing blade 22e 2 forming a widthwise extending crease C in the film sheet FS which will ultimately form the bottom edge 12a of the plate envelope 12. The battery plates 10 are fed by conveyor system 16 bottom-edge-first into the envelope-forming station 18. In this regard, the bottom edge of the battery plate will be fed into registry with the crease C formed in the film sheet FS and is propelled into the nip formed between the driven joining cylinders 24, 26. The film sheet FS is thus folded rearwardly over the battery plate 10 causing its conveyance through the nip formed between the joining cylinders 24, 26 thereby enveloping the same. At the same time, the lateral intermeshed pairs of widthwise-separated, serrated edge-joining rings 24a, 26a carried at the lateral sides of joining cylinders 24, 26 will respectively form the series of corrugations of the discontinuous joining regions 12d, 12e and the unsealed regions 12f, 12g therebetween at the side edges 12b 1 , 12c 1 of the envelope 12. An exemplary pair of the intermeshed joining rings 24a, 26a is shown more clearly in accompanying FIGURES 3 and 4. In this regard, it will be observed that each of the peripheries of the joining rings 24a, 26a includes a series of sharp, triangularly-shaped teeth (a representative few of which are identified in FIGURES 3 and 4 by reference numerals 24b, 26b), with adjacent series of teeth being separated by non-serrated (smooth), substantially flat land regions (a representative few of which are identified in FIGURES 3 and 4 by reference numerals 24c, 26c), respectively. Moreover, these land regions 24d, 26d are substantially in opposed registry with one another during rotation of the joining rings 24a, 26b. Most preferably, the individual teeth 24a, 26a form an isosceles triangle having an included apex angle α which is less than the angle β formed by the space between adjacent ones of the teeth 24b, 26b. In a presently preferred embodiment, the included angle α formed by any one tooth is about 79°, and the angle β between adjacent teeth is about 82°. The land regions 24d, 26d, on the other hand, occupy a sufficient peripheral arc of the rings 24a, 26a so as to establish the unsealed regions 12f, 12g of meaningful length. At present, the land regions 24d, 26d established by removing between two to six, preferably three, of the teeth 24b, 26b from what was initially a continuously toothed ring. The structure of the joining rings 24a, 26a and the tooth configuration described above establishes a non-uniform clearance between the teeth 24b, 26b which thereby translates into a non-uniform compressive force being applied to the overlapped edges 12b 1 , 12c 1 and 12b 2 , 12c 2 . The rings are adjustable in the sense that they may be moved toward or away from each other in any conventional manner. In a preferred arrangement, the rings 24a, 26a are initially set in contact with one another, and due to the inherent, albeit slight, flexibility of the shafts on which the rings 24a, 26a are mounted, the thickness of the film material FM itself causes the joining rings to separate by an amount substantially equal to the film material thickness. In this manner, the overlapped edges 12b 1 , 12c 1 and 12b 2 , 12c 2 may be mechanically joined to one another via the formation of the discontinuous joining regions 12d, 12e without excessive stretching or distortion of the film material forming the overlapped edges 12b 1 , 12c 1 and 12b 2 , 12c 2 . Thus, it is not necessary to form an integral seal in the nature of a "weld". At the same time, the unsealed regions 12d, 12g are formed which facilitate the flow of electrolyte therethrough, into and out of the interior pocket of the plate envelope 12b thereby improving electrolyte circulation within the battery cell in which the enveloped battery plate BP is employed. While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

Claims: A battery plate envelope comprising: a sheet of porous film material having a folded bottom edge and overlapped lateral edges which form a pocket for receiving a battery plate (10); characterized in that said overlapped lateral edges are secured to one another by an extended series of discontinuous non-welded but mechanically joined regions (12d, 12e) being separated by respective unsealed regions (12f, 12g) which establish a lateral channel through which fluid may pass. The battery plate envelope as in claim 1, wherein said porous film material includes a plurality of lengthwise extending rib elements (12h). The battery plate envelope as in claim 2, wherein said rib elements (12h) are disposed within the pocket. The battery plate envelope as in claim 1, wherein said porous film material is a microporous polyolefin film. The battery plate envelope as in claim 1, wherein said jointed regions are corrugated. A method of forming a battery plate assembly for a wet storage cell battery comprising the following steps: (i) advancing a battery plate toward a sheet of porous plastics film and folding the sheet of porous plastics film over the battery plate to form a pocket in which the battery plate is disposed and such that lateral edges of the folded porous film overlap one another; and characterized in that (ii) the overlapped lateral edges of the folded porous plastics film are then secured to one another by forming an extended series of discontinuous nonwelded but mechanically joined regions (12d, 12e), with adjacent ones of the joined regions being separated by respective unjoined regions (12f, 12g) to thereby establish lateral channels through which fluid in the wet storage cell battery may pass; and wherein (iii) said joining step includes the steps of (1) forming a nip between opposed pairs of intermeshed joining rings (24a, 26a) having a peripheral series of opposed teeth regions (24b, 26b) separated by a series of smooth land regions (24c, 26c), said opposed teeth of said teeth regions being configured and positioned to establish non-uniform clearance therebetween so as to exert a non-uniform compressive force on the overlapped edges of the porous plastics film when passed through said nip, and then (2) passing the overlapped lateral edges of the folded porous plastics film through said nip between said joining rings to thereby form said discontinuous joined regions (12d, 12e) and unjoined regions (12f, 12g). The method of claim 6, wherein step (ii) includes advancing the battery plate into the sheet material so that the battery plate and sheet material are collectively moved through a nip formed between a pair of opposed joining cylinders (24, 26) each having laterally separated pairs of joining rings (24a, 26a). The method of claim 6, wherein said land regions (24c, 26c) represent between two to six missing teeth. The method of claim 6, wherein said land regions (24c, 26c) represent three missing teeth. The method of claim 6 wherein each of said teeth form an equilateral triangle having an included angle α which is less than an angle β of spaces formed between adjacent ones of said teeth. The method of claim 10, wherein angle α is about 79° and angle β is about 82°. A battery plate assembly for a wet storage cell battery when produced by the method defined in any one of claims 6 to 11.

Inventors: LUZADER REX E, REDDEN GALEN, LUZADER, REX E., REDDEN, GALEN
Applicants: EXIDE CORP, EXIDE CORPORATION
Application year: 1996
Main classification: H01M2
IPC codes: H01M2, H01M4, B29C65