SEPARATOR WITH IMPROVED TENSILE STRENGTH FOR STARVED ELECTROLYTE LEAD/ACID BATTERY

Abstract: Compositions and papers made therefrom useful as separator materials in starved electrolyte lead/acid batteries described. The compositions comprise a mixture of 15 percent to 75 percent by weight of perlite, 20 percent to 70 percent by weight of glass fibers, and 5 percent to 20 percent by weight of acid-insoluble thermoplastic fibers, the latter preferably in the form of staple fibers. The glass fibers have diameters in the range of from 0.3 to 1.0 micrometers while the perlite has particle sizes in the range of from about 30 to about 100 micrometers.

Description: SEPAI*ATOR WITH IMPBOVED TENSILE STRENGTH FOR STARVED E E-CTROLYTΞ LEAD/ACID BATTERY Technical Field The invention herein relates to lead/acid electric storage batteries. More particularly it relates to separators for such batteries. Background of the Prior Art Recently efficient maintenance-free rechargeable sealed lead/acid storage batteries utilizing a "starved electrolyte" concept have " been introduced coπmercially. Various aspects of batteries of this type are disclosed in a number of patents, most notably U.S. Patent No. 3,862,861. Such batteries normally utilize as separators materials such _s microporous rubber, polyvinyl chloride, polyolefins, phenolic resin impregnated paper or (preferably) glass paper made frcm microfiber diameter, unwoven, short staple glass fibers. These batteries, while useful in a wide variety of applications, have been severely limited in the practical sizes which can be cαπraarcially utilized because of the high cost of these batteries per unit of energy density. Thus, while cells of the cαrrnon C, D, "beer can" and similar sizes are practical for sane purposes cattnercially, larger sizes such as the typical autαnotive battery size are far too costly for cαimercial practicality. Similarly, the high unit density cost of eve ' the smaller size batteries have restricted these types of batteries to high value end uses such as in spacecraft and ---mergency equipment, effectively elimi-nating the batteries frcm the fields of conventional consumer use such as flashlights, radios and the like. In these types of batteries a very high proportion of the cost of battery materials lies in the cost of the separator. The preferred microfiber glass paper separators are extremely costly. In the past, however, attempts to substitute lower cost materials have led to battery structures with significantly poorer electrica characteristics. Recently, a low cost high efficiency battery separat composition for starved electrolyte batteries has been developed a described and claimed in U.S. Patent Application Serial No 06/039,708, filed May 17, 1979. this battery separator compositi comprises a mixture of 30 percent to 80 percent by weight of expand perlite and 20 percent to 70 percent by weight of glass fibers, wherei the glass fibers have diameters in the range of frcm about 0.3 to abo 1.0 micrometers and the perlite has particle sizes in the range from about 3 to about 100 micrometers. The electrical performan propercies of these compositions have been found to be eminent suitable for use in the starved electrolyte lead/acid batteries. Continued experience with the perlite/glass fiber separat compositions and separators made therefrcm have brought to light o significant problem, however. In sατte battery production ir-ethcd the separator is in the form of a long paper strip which is wound a spiral fashion with the electrical plate materials to fo cylindrical batteries. Typical of this type of construction are t batteries shown in the aforementioned U.S. Patent fo. 3,862,861. T winding operations to form such batteries .-ire performed at high spe and under high tensile loads. In sane cases with the perlite/gla fiber paper strips, the papers have been unable to sustain that hi tensile loading and have torn apart. When this occurs, of cours the winding operation must be stopped and the paper tear repaired. It would therefore be highly desirable to have a separat material having the same electrical performance characteristics a low cost features of the papers of the prior invention, but havi increased tensile strength sufficient to allow the paper to be wou rapidly into a cylindrical battery shape without significant amoun of tearing of the paper. 3rief Sumrary of the Invention The invention herein comprises an irπproved oomposition use as a separator in a starved electrolyte lead/ cid battery v-hi comprises a mixture of 15 percent to 75 percent by weight of expand perlite, the perlite having particle sizes in the range of from abo 30 to about 100 micrαneters; 20 percent to 70 percent by weight - URfi OMP glass fibers, wherein the glass fibers have diameters in the range of from about 0.3 to about 1.0 micrcmeters and 5 percent to 20 percent by weight of substantially acid-insoluble thermoplastic fibers. These improved ccmpositions have been found to be essentially equivalent in all irtcortant chetiical and electrical properties to the battery separator compositions of the prior i-nvention, but to have tensile strengths seme three to five times greater. The invention also includes a paper article made frcm this iπproved composition and a battery separator made frcm the paper. Detailed Description of the Invention The articles utilizing the cαnpositions of this invention are dencminated "separators" for the starved electrolyte lead/acid batteries, following the nomenclature of the prior patents, especially the aforesaid U.S. Patent No. 3,862,861. However, it will be recognized from the structure of these star-zed electrolyte batteries that the articles, unlike separators in conventional batteries, are multifunctional, in that they possess not only a separator function but also a reservoir function, wherein they serve to retain the electrolyte within the battery. It is believed that the microporous nature and the high specific surface area of the present articles, with their myriads of minute passageways and interstices, impart to the articles their ability to combine these different functions. For the purposes of this specification, therefore, the practice of the aforesaid prior patents in labeling these articles "separators" will be adhered to, but the difference between the present multifunctional articles (with their "separator/reservoir" nature) and conventional battery separators should be recognized. The centpositions herein are formed from a mixture of expanded perlite granules, small diameter glass fibers and acid-insoluble thermoplastic fibers. Perlite is a rhyolitic glassy rock formed by volcanic action. Perlite is unique among the glassy -materials in that it contains a significant proportion of combined wa~er wnich. when the perlite is crushed and rapidly heated, is converted to steam and causes the perlite granules to expand or "pop" to form expanded perlite granules with volumes sane 4 to 20 times greater than the volume of the original unexpended particles. Bulk densities of the expanded materials are cαtmonly in the range of frcm about 0.03 g/cm to abo 0.25 g/cm 3 . The high volume, low bulk density expanded perlite h in the past been used in a variety of applications, including as filt aids, thermal insulation, lightweight concrete aggregates and horticultural use. However, until the invention described in t aforesaid application Serial No. 06/039,708, expanded perlite had nev before been considered as having utility in electric batteries. In the oompositions of this invention the perlite will present in the form of generally irregular particles having nαπin particle sizes in the range of frcm about 3 to about 100 micrometer Most suitable for use in the present invention are those grades perlite having particle sizes in the range of from about 10 to abo 35 micrometers. Suitable grades of perlite are available comτiercial from Johns-Manville Corporation. The perlite will be present in t composition as from about 15 percent to about 75 percent, preferab 40 percent to 60 percent, of the ccπtposition. (Unless otherwi stated, all percentages herein are by weight.) Since perlite is a natural material, the compositions batches taken frcm different ore bodies or even different parts the same ore body will vary, sometimes widely, but normally with fairly well defined limits. Typical perlite chemical analyses sh 71 percent to 75 percent Siθ2, 12 percent to 13 percent AI2 and 7 percent to 9 percent K^O and a2θ with the remainder bei a wide variety of other oxides and elements including materials s as calcium, iron, magnesium and titanium oxides. Typical analys are described in Industrial Minerals, page 17 (May, 1977) . The exa cαπposition of the perlite is not critical in this invention, as lo as the perlite used is chemically and electrically compatible w the other materials in the present separator cat-positions and al in the assembled batteries. The glass fibers used in the present compositions may produced from any of a wide variety of glass fiber formi compositions. The fibers formed from such compositions must h average volume surface diameters in the range of from 0.3 to 1 micrometers. Typical glass compositions for glass fibers useful this invention include those shewn in U.S. Patent No. 3,085,887. T glass fibers will be present in the composition as from about percent to about 70 " percent, preferably 30 percent to 50 percent, of the composition. Compositions containing less than about 20 percent of glass fiber do not produce papers with adequate j-hysical integrity to withstand handling, while those with more than about 70 percent glass fiber give no added electrical properties but are significantly costlier. The third component of the improved separator cαiipositions and articles of the present invention are acid-insoluble thermoplastic fibers in quantities of 5 to 20 percent, preferably 10 to 15 percent Any conventional type of acid-insoluble staple or chopped thermoplastic fibers may be used. Typical among the fibers which are useful in this composition are polypropylene fibers, saran fibers (predominantly Folyvinylidene chloride units in the polymer) , ethylene/propylene copolym---r fibers, polyethylene fiber and vinyon fibers, such as fibers of copolymers of polyvinyl chloride and polyvinyl acetate. The staple fibers or chopped fibers should have an aspect ratio (i.e., length:diameter ratio) on the order of about 1000:1. The aspect ratio may vary widely, however, as long as the staple or chopped fibers have sufficient length to provide significant increases in tensile strength to .the papers and separators as compared to papers and separators of the prior invention not containing such staple or chopped fibers. Since the papers are normally wet-laid frcm slurries of fibers and perlite, the thermoplastic fibers should not be of undue length so that clumping and other formation problems can be avoided. Those skilled in the art of paper making will be irrmediately aware of the maximum and m-i-nimum practical lengths for chopped fibers or staple fibers in order to get good formation during the paper -raking process as described below and have good tensile strength in the finished products. The separator articles of the present inventi i may also contain small amounts (up to a few percent by weight) of other materials such as unexpanded perlite, glass fragments, silica particles and the like. Because the nature of the separator is vitally imporTant to the electrical performance of the finished battery, however, such materials should be present only if -ohey do not detrimentally affect that electrical performance. Since the effect on electrical performance of the various types of potential ---mpurities cannot be OMPI* k ι, 1P -. readily predetermined, it is preferred that the amount of i-ir -irit be ra-i-ni-T-ized and the compositions herein be composed essentia entirely of the expanded perlite, glass fibers and thermoplas fibers. The oppositions of the present invention are formed i sheets of paper, frαn which the separator materials of the pres invention are made, in the manner of conventional paper making. glass fibers, expanded perlite and thermoplastic fibers are disper in an aqueous acid slurry (pH of about 3) which is stirred so as cause the perlite and fibers to became thoroughly and randcmly mi with each other. The perlite/fiber mixture is then deposited f the slurry onto a conventional paper making screen or wire as in Fourdrinier machine or a Potoformer machine to form a matted pap For these purposes the perlite in the furnish should not contain m than about 5 percent, preferably not more than about 1 percent, "floaters," which are perlite particles which float on the surf of the water slurry. Floaters are detrimental because they do get incorporated into the fiber matrix of the paper, but are deposi last as the slurry drains and thus form a loose dusty layer on surface of the paper. Quantities of floaters greater than th mentioned above merely increase the problem. The paper formed of fibers and perlite particles is then dried and collected in conventional manner. Following collection of the dry paper, the pa is heat treated to "seal in" the fibers. This is accomplished heating the paper at a temperature of approximately 260"F to 28 (125 β C to 135°C) for a short period. In ccπmercial operation, t would normally be carried on by passing the dry paper through hot pr rolls where the paper would be in αoncact with the rolls for a seconds. Thereafter, the paper may be cut to sizes appropriate the various size batteries in which the separator materials are be used. As examples of the itproved composition and papers of present invention, wo sets of materials were hand formed i-n she in the laboratory. The first sample contained 50 percent of perli 35 percent of glass microfibers and 15 percent of staple vinyσn fib comprising a copolymer of polyvinyl chloride and polyvinyl aceta Fiber diameters were approximately 20 micrometers. The paper was h __? • treated as described above. In the second set of experiments, an identical composition was made up with the exception that the staple fibers tested were polyethylene staple fibers produced cαnτ-ercially by the Crown Zellerbach Company and sold under the name "synthetic weed pulp." Estimated fiber diameter of the staple materials was in the -range of 1 to 5 micrometers. Test results on samples of these two materials indicated that papers of the present invention including the thermoplastic fiber had from three to five times greater tensile strength than the perlite/glass fiber papers of the prior invention. The papers of the present invention will not be expected to show any significant change or deterioration in electrical properties as compared to the perlite/glass fiber papers of the prior invention. Statement of Industrial Application The materials of the present invention find application as separators and reservoirs in starved electrolyte lead/acid storage batteries. Batteries using such materials will in turn find application for many electrical power generating uses including automotive electrical systems.

Claims: Claims 1. A composition, useful as a separator material in star electrolyte lead/acid batteries, which ocmprises a mixture of percent to 75 percent by weight of expanded perlite, 20 percent ' 5 70 percent by weight of glass fibers and 5 percent to 20 percent weight of acid-insoluble thermoplastic fibers, said glass fibers hav diameters in the range of frcm about 0.3 to about 1.0 micrcraeters said perlite having particle sizes in the range of from about 3 about 100 micrometers. 10 2. A composition as in Claim 1 consisting essentially said expanded perlite, glass fibers and thermoplastic fibers. 3. A composition as in Claims 1 or 2 wherein said expan perlite is present as from 40 percent to 60 percent by weight of composition, said glass fibers are present as from 30 percent to 15 percent by weight of the composition, and said -thermoplastic fib are present as en the order of about 10 to 15 percent by weight. 4. A composition as in Claims 1 or 2 wherein said expan perlite " has particle sizes in the range of from about 10 to about micrometers. 20 5. A composition as in Claims 1 or 2 wherein s thermoplastic fibers are selected from the group consisting of sa fibers, polypropylene fibers, ethylene/propylene copolymer fibe vinyσn fibers and polyethylene fibers. 6. A composition as in Claim 5 wherein said thermoplas 25 fibers are in the form of staple fibers. 7. A paper useful as a separator material in a star electrolyte lead/acid battery comprising the composition of Clai in matted form. 8. A paper useful as separator material in a star 30 electrolyte lead/acid battery comprising the cαi- osition of Clai in matted form. 9. A paper useful as separator material in a star electrolyte lead/ cid battery comprising the ccmposisiσn of Clai in matted form. 35 10. A paper useful as separator material in a star electrolyte lead/acid battery comprising the composition of Clai in matted form. "BUR OM ^ WI 11. A battery separator for a starved electrolyte lead/acid battery formed frcm a paper as in Claim 7. - 12. A battery separator for a starved electrolyte lead/acid battery formed from a paper as in Claim 8. 13. A battery separator for a starved electrolyte lead/ cid battery formed from a paper as in Claim 9. 14. A battery separator for a starved electrolyte lead/acid battery formed from a paper as in Claim 10. -^\jR£ • ■ lϊ'_

Inventors: GROSS S, SCHEFFEL N
Applicants: JOHNS MANVILLE, JOHNS MANVILLE CORP
Application year: 1981
Main classification: H01M2
IPC codes: D21H13, D21H17, H01M2