Title of Invention	A FIBROUS SHEET PLATE SEPARATOR FOR USE IN A STORAGE BATTERY
Abstract	A lead acid battery having a glass finer separator material is disclose. The separator material is a mass of intermeshed glass or other fibers produced by suspending the fibers in a gaseous medium, and collecting the suspended fibers on a foraminous material. The mass of fibers suspended in the gaseous medium has a BET surface area of from 0.2 to 5m<sup>2</sup> per gram. Abattery having a glass giber separator material with added cellulose fibrils is also disclosed, as is a battery having a glass fiber separator material with added particulate material such as silica.

Title of Invention

A FIBROUS SHEET PLATE SEPARATOR FOR USE IN A STORAGE BATTERY

Abstract

A lead acid battery having a glass finer separator material is disclose. The separator material is a mass of intermeshed glass or other fibers produced by suspending the fibers in a gaseous medium, and collecting the suspended fibers on a foraminous material. The mass of fibers suspended in the gaseous medium has a BET surface area of from 0.2 to 5m<sup>2</sup> per gram. Abattery having a glass giber separator material with added cellulose fibrils is also disclosed, as is a battery having a glass fiber separator material with added particulate material such as silica.

Full Text	The present invention relates generally to the field of batteries and, more specificali^ to batteries in which separators containing glass fibers are positioned between the positive and negative plates and to a method for producing such separators and batteries. As is subsequently discussed in more detail, separators containing glass fibers are well known. Long before glass fiber separators, however, cedar veneers were used as a separator material, and were replaced by microporous, hard rubbery separators and cellulose sepai'ators impregnated with resins. Valve regulated ("sealed" - "recombinant") lead acid (VRLA) batteries are known; they usually comprise a plurality of positive and negative plates, as in a prismatic cell, or layers of separator and positive and negative electrodes wound together, as in a "jelly roll" cell. The plates arc arranged so that they alternate, negative - positive - negative, etc., with separator material separating each plate from adjacent plates. The separator, typically composed of a mat of glass fibers, is an inert material; it stores battery acid, and provides low electric resistance. In addition, in VRLA batteries, the separator material provides innumerable gas channels between the plates through which oxygen can migrate from the positive electrode, when generated there, to the negative electrode where it can be recombined with hydrogen, according to the oxygen cycle. Another important function of a separator is to exert pressure against the plate paste or active material which forces the paste into contact with the plate, and causes a pressure between the plates, ensuring that there is not an interface at which corrosion can occur. Glass fiber separator material has been produced conmiercially by wet processes on paper making equipment including fourdrinjer macliines and rotoformers, inclined fourdrinier machines and extended wire rotoformers. In the production of separator made of glass fibers for VRLA batteries, it is preferred that to organic bmder be added to a furnish from which separator sheets are made; the entanglement of individual fibers serves to maintain the sheet in a cohesive structure, and water glass or any of various sulfate salts, which sometimes form on the fiber surfaces, serves as a binder. Organic binders, however, tend to decrcase. the ability of a separator to wick acid, and to decrease the amount of acid a separator can hold. A great deal of work has been dircted to modifying the glass fiber famish from which separators are produced to improve battery performance and/or lower the cost of the separator. Some of the work has entailed the addition of synthetic fibers for various reasons, such as the use of thermoformable plastic fibers so that the separator can be heat sealed on its edges to envelop a plate. Other work, which pertains to the field of this invention, has been directed to the use of filler, e.g., silica, to provide separators which arc comparable to ail glass fiber separators, at a lower cost. Separators made from glass fibers to which cellulose has been added and polyolefm fibers to which cellulose has been added have also been suggested. Prior art patents are discussed below. US Patent No. 4,465,748 (Harris) discloses glass fiber sheet material for use as a separator in an electrochemical cell, and made from 5 to 35 percent w/w of glass fibers less than 1 µm in diameter; the patent also discloses a glass fiber sheet for such use wherein there are fibers of a continuous range of fiber diameters and lengths, and most of the fibers are not over 5 mm in length. US patent No- 4,216,280, (Kono et al.), discloses glass fiber sheet material for use as a plate separator in a battery, and made from 50 to 95 percent w/w of glass fibers less than 1 \|µm in diameter and 50 to 5 percent w/w of coarser glass fibers. The coarser glass fibers, the reference says, have a fiber diameter larger than 5 µm, preferably larger than 10 µm, and it is advantageous for some of the coarser fibers to have diameters of 10 µm to 30 µm. US Patent No. 4,205,122 (Minra et al.) discloses a battery separator of reduced electric resistance comprising a self supportmg, non woven mat consisting essentially of a mixture of olefanic resin fibers having a coarseness of from 4 to 13 decigrex and olefinic resin fibers having a coarseness of less than 4 decigrex, the latter fibers being present in an amount of not less than 3 paits by weight per 100 parts by weight of fibers; up to about 600 parts by weight of inert filler materials per 100 parts by weight of fibers can also be used. The battery separator is produced by subjecting a suitable aqueous dispersion to a sheet-forming operadon, drying the resulting wet, non-woven mat, and heat treating the dried mat at a temperature ranging from a point 20°C. lower than the melting point of the aforementioned fibers to a point about 50°C. higher than the melting point. us Patent No. 4,216,281 (O'Rell et al.) discloses a separator material produced from a furnish containing 30 to 70 percent w/w of polyolefin synthetic pulp, 15 to 65 percent w/w of a siliceous filler and 1 to 35 percent w/w of "long" fibers which can be polyester fibers, glass fibers, or a mixrure of the two. Cellulose in an amount up to about 10 percent w/w is disclosed as an optional ingredient of the furnish. US Patent No, 4,363,856 (Waterhousc) discloses a separator material made from a furnish composed of polyolefin pulp fibers and glass fibers, and names polyester staple fibers, polyolefin staple fibers and cellulose pulp fibers as alternative constituents of the furnish. US Patent No. 4,387,144 (McCallum) discloses a battery separator having a low electrical resistance after extended use which is made by therna]lconsolidation and themal embossing of a paper web formed from a furnish containing a synthetic pulp the fibrils of which are filled with an inorganic filler, the web incorporating a wetting agent which is preferably an organic sulphonate, and organic succinate, or phenol ethoxylaie. US patent No. 4,373,015 (Peters et al.) discloses sheet material for use as a separator in a battery, and "comprising organic polymeric fibers"; boch of the examples of the reference describe the sheet material as "short staple fiber polyester matting about 0.3 mm thick', and indicate that the polyester fibers range from about 1 µm to about 6 µm in diameter. Sheet separators for use in conventional (not valve regulated) batteries and comprising both glass fibers and organic fibers are disclosed in all of the following US patents: No. 4,529,677 (Bodendorf); No. 4,363,856 (Waterhouse); and No. 4,359,511 (Strzempko). US patent No. 4,367,271, Hasegawa, discloses storage batteiy separators composed of acrylic fibrils in an amount of up to about 10 percent w/w, balance glass fibers. Japanese patent document 55/146,872 discloses a separator material comprising glass fibers (50-85 percent w/w) and organic fibers (50-15 percent w/w). US patent No. 4,245,013, Clegg et al,, discloses a separator made by overlaying a first sheet of fibrous material including polyethylene fibers with a second sheet of fibrous material including polyethylene and having a synthetic pulp content higher than the first sheet. US Patent No. 4,908,282, Badger, discloses a separator comprising a sheet made from first fibers which impart to the sheet an absorbency greater than 90% and second fibers i which impart to the sheet an absorbency less than 80% wherein the first and second fibers are present in such proportions thai the sheet has an absorbency of from 75 to 95%. This patent discloses that fine glass fibers have a high absorbency, that coarse glass fibers have a low absorbency, and that hydrophobic organic fibers have an extremely low absorbency, and that, when this separator is saturated with electrolyte, unfilled voids remain so that gas can transfer from plate to plate for recombination. The disclosure of Badger is incorporated herein by reference. US Patent No. 5,091,275 (Brecht et al.) discloses a glass fiber sepaarator which expands when exposed to electrolyte. The separator comprises glass fibers which are impregnated with an aqueous solution of colloidal silica particles and a sulfate salt. The separator is produced by forming a paper making web of glass fibers, impregnating the web with the aqueous mixture of silica and the salt, lightly compressing the impregnated web to remove some of the aqueous solution, pardally drying the web, compressing the web to a final thickness and completing the drying of the web. The web is preferably compressed to a thickness which is less than the distance between plates in a given cell, so that insertion of an assembled cell stack into a case is facilitated. When electrolyte is added to the case, the salt dissolves in the electrolyte and the separator expands to provide good contact between the plates and the separators. According to the patent, the silica contributes to the recombination performance of cells incorporating the pre-compressed separator. The silica also contributes a great deal of stiffness to the separator, so much so that the separator may be characterised as rigid. It has been determined that the production of battery separator by paper-making techniques from a furnish of glass fibers and silica powder leads to problems which are caused by variations in the concentration of the silica powder in the furnish. Typical glass fiber furnishes have a liquid content exceeding 98 percent w/w. In the course of making separator sheets, most of the water is removed from the furnish in the first few feet of a screen on which the furnish is cast. The water, known as white water, is recycled and winds up back in the headbox of the machinc. If the furnish is composed exclusively of glass fibers, virtually none of the fibers pass through the wire and wind up in the white water. However, furnishes comprising glass fibers and silica powder do not fare so well In the absence of a retention aid, significant amounts of silica powder from such furnishes do pass through the paper making wire and wind up in the white water. Left unchecked, this phenomenon causes the concentration of silica powder in the furnish to increase, undesirably changing the properties of the furnish. Heretofore, the problem of silica powder and the like passing through a paper making wire has been avoided though the use of binders and retention aids. US patent No. 2,477,000 discloses a synthetic fiber paper produced from i5brillae and fibers made by methods wherein a solution of the fiber is extruded through very small orifices (spinnerets) and then the extruded solution is allowed to congeal either in a precipitating bath or by evaporation of the solvent or by temperature changes (see column 2, lines 25 and following). The patent says that fibers of cellulose acetate, cellulose nitrate, regenerated cellulose from viscose, "Vinylite (a synthetic resin made by polymerization of vinyl compounds), Araiac (a fibrous product made from skim milk casein), and spun glass" which range in length up to 1 inch and in diameter from 12-80 microns and fibrillae preferably derived from flax, Manila hemp, caroa or hemp can be used to make the paper. At least 90 percent of the fibrillae should be from 0.0015 to 0.0025 inch in length and from 0.0000027 to 0.0000044 inch in width- WO 98/12759, an International Application published March 26, 1998, discloses "A resilient fibrous mat, preferably made of microfibers is especially adapted for use as a battery separator for starved electrolyte batteries. . . . The fibrous mat, with one or two surface layers, can be formed form an air laid fibrous blanket by subjecting one or both surfaces of the blanket to hydro entanglement to increase the entanglement of the fibers at and adjacent the major surface($) relative to the entanglement of the fibers in the resilient fibrous layer. The fibrous mar with a substantially uniform density may be made by flooding the blanket with a liquid and drawing a vacuum through the blanket." A publication (apparently, European Patent Application 98-15, Japan Vilene Co., Ltd., filed September 29, 1997 as application 97116846) shows the kind of entanglement disclosed in W098/12759 to produce the material of Figs. 1 and 2 diercof, but applied to the entire body of the separator material rather than to a region or regions adjacent one or both major surfaces as in W098/12759. An English language absti'act of a published Japanese patent application (07147154, published June 6, 1995), entitled SEPARATOR FOR .\LKALINE BATTERY states: "A fiber having a section form shown in (c) of the drawing, for example, is constituted from 0.04 to 0.12 deniers of circular and petal polypropylene component 2 and 0.12 denier of a polyethylene component 1. A hundred percent of this dividing composite fiber with a fineness of 2 deniers and a fiber length of 38mm is opened by atard machine to laminate unidirectional and cross fiber webs with METSUKE of 1.3 and 52f/ml This is treated from both surfaces with a water flow having a water pressure of 130kg/cm2 on a nozzle plate having a nozzle diameter of 0.13mm and a pitch of 0.6mm. This cloth is dipped in fuming sulfuric acid, sulfonated, and then calendered to provide a separator having a METSUKE of 65g/m2 and a thickness of 0.1 5mm. The same treatment can be performed in constitutions other than (c) in the drawing. Thus, excellent electrolyte resistance, oxidizing property, and liquid holding property are provided, and a battery can be smoothly operated for a long period." BRIEF DESCRIPTION OF THE INSTANT INVENTION The instant invendon i.s based upon the discovery that a binderlcss glass fiber mat .suitable for use as a separator for Valve regulated ("sealed" - "recombinant") lead acid (VRLA) batteries can be produced by a dry process by collecting the fibers from fiberizing appai'atus, without subjecting them to a wet paper making or other post forming process. For example, glass fibers produced by the flame blown process, which is subsequendy described in more detail, can be wound on a drum until a mat weighing about 1,000 grams per square meter has been collected; the mat can then be slit transversely, and removed from the drum as sheets weighing about 1,000 grams per square meter, having one dunension which equals the circumference of the drum, and another which equals the width of the drum. This mat wliich, in a typical example, has an average fiber diameter of 0.8 pm, can then be sepai^ated into layers having the weight in grams per square meter desired in a given baaery separator, and the layers can be cut to size and used as separators, as subsequently described in more detail. Web having the targeted grammmage can also be taken direcdy from the drum or glass can be fiberized by another method which is controlled so that a continuous sheet having the targeted grammage is produced. A glass fiber mat which can be used in practicing the instant invention can also be made by what is called "the rotary process" in glass forming apparatus which includes a glass melting tank, a rapidly rotating centrifugal bushing with small openings in a periphery, at least one high pressure hot gas nozzle from which a high velocity fibcrizing jet is directed across the periphery of the centrifuge, and a collectmg conveyor. Molten glass fed ro the centrifugal bushing is caused by centrifugal force to flow through the peripheral openings of the bushing mto the fiberizing jet, by which the streams of glass are attenuated and carried onto a collecting conveyor which is pervious to the gas. The mat from this process can also be collected on a drum, slit transversely, and removed from the drum as sheets which, again can weigh about 1,000 grams per square meter and can be composed of fine fibers, average fiber diameter 0,8 µm when the rotary process is that of US patent No. 5,076,826, or can range up to about 3µm when other rotary processes are used. This mat can also be separated into layers having the weight in grams per square meter desired in a given battery separator, and the layers can be cut to size and used as separators, as subsequently described in more detail. This web having the targeted grammage can also be taken directly from the drum. It has been found by examination, using a scanning electron microscope, of mat produced as described in the two preceding paragraphs and collected on a drum, that the mat is formed in discrete layers, each of which is composed of the fibers deposited during one revolution of the collecting drum, and that there is a fiber diameter gradient within each of the discrete layers, the fibers of the smallest diameter being concentrated adjacent one major surface of each layer, and the fibers of the largest diameter being concentrated adjacent the other major surface. A part of the Increased resilience of battery separator according to the invention is attributed to the observed layering, and another part is attributed to the gradient in fiber diameter within each layer. It will be appreciated that separator material can also be produced by a wet papermaking process where similar layering occurs, for example, by casting a plurality of slurries of glass or other fibers, the first on the screen of paper making apparatus, and the second and subsequent ones on the previously cast fibers, or by assembling a plurality of thin sheets of glass or other fibers made by a wet process to produce a composite separator having the desired thickness and grammage. Accordingly, in one aspect, the invention is a battery separator composed of a plurality of thin sheets of non-woven fabric assembled to constitute the separator, and the thin sheets can be made by an air-laid or wet process. Thinner sheets of the glass fiber mat can also be produced by either the flame blown process or by the rotary process, includmg that of US patent No. 5,076,826, and enough of the thinner sheets to provide the desired grammage, which usually ranges from about 20 to about 1000 g.m"" can be stacked, and then cat to size. To produce the thinner sheets, glass fibers can be produced from softened glass and collected in a conventional manner, usually on a foraminous conveyor, and the speeds of the fiberizing process and of the conveyor can be set so that a mat having the desired grammage is conveyed from the forming operation, and cither rolled for future use, or cut to size, in which case it can be used immediately to produce batteries, or stacked for future use. The continuous sheet can also be collected with a cross-lappcr to hnprove its uniformity. When a battery is produced, at least one stack of alternating positive and negative plates is assembled, with separator between adjacent plates, and the separator of each stack is compressed so that the stack can be slipped into a pocket which is a part of the case of the battery. It is important that the separator have sufficient resiliency, after such compression, that it exerts the required pressure against the paste or active material on each plate to force the paste into contact with the plate, and to cause a pressure between the plates, ensuring that there is an interface, along the faces of the plates, among the plate paste or active material, the electrolyte and oxygen. A standard test has been developed to measure the resiliency of a separator material. The results of this test, as is subsequently explained in more detail, indicate that separators in batteries according to the invention are significantly more resilient than otherwise identical separators made from different samples of the same glass fibers, but by a conventional wet paper making process, OBJECTS OF THE INVENTION It is, therefore, an object of the instant invention to provide an improved VRLA or other battery contaning a separator composed, at least predominandy, of glass fibers as collected from a fiber forming process, i.e., without having been subjected to a wet paper making process or to a post fomiing process such as that called an "airlaid" or spunlaced, or to another post forming, secondan' process.. It is another object to provide a method for producing a battery separator composed predominantly of glass fibers. It is yet another object to provide a glass fiber VRLA separator which has better resiliency than a separator made by the wet paper making process from the same fibers. It is still another object to provide a glass fiber VRLA battery separator which has greater resiliency, by comparison with previously known separators, and, as a consequence, can be 10 to 50 percent lighter in weight per unit of area (grammage) but still provide the same "BCI" (Battery Council International) thickness as conventional wet laid separator, i.e., 300 grams per square meter for separator having a BCI thickness of 2.13 millimeters. It is yet another object to provide a VRLA battery separator which has improved resilience and shock absorbing properties because it is composed of a plurality of separate layers. It is a further object to provide a glass fiber VRLA separator which has greater absorbency for a battery electrolyte than does a separator made by the wet paper making process from the same fibers. It is still another object to provide a glass fiber VRLA separator material in which the average fiber length is greater than in a separator made by the wet paper making process from the same fibers because the fiber breakage associated with the paper making or post fonning redispersing and forming processes does not occur. It is yet another object to provide a separator that is composed of multiple, separately formed layers of glass or other fibers. Other objects and advantages will be apparent from the description which follows, reference being made to the attached drawings. DEFINITIONS As used herein, the term "percent v/v" means percent by volume; the term "percent w/w" and the symbol % mean percent by weight; the term "wire", as applied to a paper making machine, means the surface of the machine on which a furnish is cast in producing paper, and can be, for example, the screen of a Fourdrinier machine or the vacuum drum of a rotoformer machine; pore sizes reported herein, unless otherwise indicated, are in microns, and are determined by the first bubble method or by liquid porosimetry, Coulter; all temperatures are in °C.; and the following abbreviations have the meanings indicated: µm = micron or microns; mg-milligram or milligrams; g=gram or grams; kg-kilogram or kilograms; l=liter or liters; ml=miliiliter or milliliters; cc=cubic centimeter or cubic centimeters; pcf=pound per cubic foot or pounds per cubic foot; m=meter or meters; cm=centimeter or centimeters; mm=millumeter or millimeters; mil=inch x 10-3 or inches x lO-3 (multiply times 25.4 to convert to mm); kPa=ressure in thousands of Newtons per square meter; psi=pounds per square inch (multiply times 6.89 to convert to kPa); and kN=force in thousands of Newtons. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view with parts broken away to show details of construction of a VRLA battery according to the invention. Figs. 2 and 2a are vertical sectional views which show different parts of apparatus for producing a glass fiber mat by what is called "the rotary process" that can be used as collected from the fiber forming process, i.e., without having been subjected to a wet paper making process, to produce a battery according to the invention; together, Figs. 2 and 2a constitute a schcmadc representation of the apparatus. Fig, 3 is a schematic representation similar to a part of the apparatus of Fig. 2a, showing different apparatus which can be used to produce a glass fiber mat by what is called "the flame blown" process; the apparatus of Fig. 3 can be used alone to produce a mat or with the apparatus of Fig. 2 to produce a glass fiber mat that can be used as collected from the fiber forming process to produce a battery according to the invendon. Fig. 4 is a schematic representation similar to Fig. 3 of still another apparatus which can be used with that of Fig. 2 for producing a glass fiber mat that can be used as collected from the fiber forming process to produce a battery according to the invention. Fig. 5 and 7 are plots of thickness in mm of separator materials that can be used in batteries according to the invention, when compressed (the compression curve), vs. force in kPa applied to compress the separator to that thickness and of rebound thickness in mm (the rebound curve) vs. force applied before rebound thickness was detennined, Figs. 6 and 8 are plots of the data represented in Figs 5 and 7 and, in addition, plots of thickness of a wet-laid glass fiber separator in mm when compressed vs. force in kPa applied to compress the separator to that thickness and of rebound thickness in mm vs. force applied before rebound thickness was determined for commercial separator materials that have been used in batteries. Fig. 9 is a plot of separator thickness in mm against compression force in kPa for each of two different materials under compression, and rebound thickness for each of the same two materials after they have recovered after being unloaded. Fig. 10 is a vertical sectional view which shows, schematically, apparatus similar- to that of Fig. 3 for producing a glass fiber mat by what is called "the flame blown method" that can be used as collected from the fiber forming process, i.e., without having been subjected to a wet paper making process, to produce a battery according to the invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS A single cell batter}' according to the invention with a total of 9 plates is indicated generally at 10 in Fig. 1. Except for the identity of the separator material therein, the battery' 10 is conventional; the separator can be used in other otherwise conventional batteries. The battery 10 comprises four positive plates 11 which are electrically connected to a positive terminal 12 and five negative plates 13 electrically connected to a negative terminal 14. The plates 11 and 13 are housed within a batteiy case 15 which is covered by a top 16. There is an opening through a boss 17 on the top 16 of the battery, Separators 18 are composed of . sheets of separator material wrapped around the bottom and both major faces of each positive plate 11. In a specific example, five, 8A-U1 batteries similar to the batteries 10, but having four negative and four positive plates were produced from separator material composed of glass fibers collected, as the fibers were formed, into a mat weighing about 310 g.m-2; the fibers had an average diameter of substantially 0.8µm. A control battery was also produced using a separator that is commercially available under the designation BG 30005; this material, which is made by the wet paper making process, weighs 300 +/-15 g.m'-2 This control was made so that assembly and properties of the five 8A-U1 batteries could be compared with the assembly and properties of a control made with separator having the same general target grammage. It was noted that the drylaid separator used to produce the five batteries had a substantially greater thickness and resiliency than the control separator; this confirmed laboratory findings concerning drylaid separator. An assembly of three pairs of positive and negative plates with the drylaid separator had approximately the same thickness as an assembly of five pairs of positive and negative plates with the BG 30005 separator, indicating that drylaid separator for a given battery should have about three fifths the grammage of conventional wetlaid separator for that batteiy. Difficulties were encountered in the assembly of the batteries from the drylaid separator because of the high resiliency of the airlaid separator. These difficulties arose when attempts were made to cast straps on the assemblies of plates with separators and in inserting assemblies of plates and separators into batteries. The cases of batteries that were made were deformed by forces exerted by the separator. One assembly of plates and drylaid separator was compressed in a press with one ton of force for fifteen minutes; since the plate surfaces were 4.85 inches by 4.85 inches, this amounted to an applied force of about 87 psi. This assembly was then inserted into a battery case, which it did not defoim. In another example an outer wrap of the separator was removed and batteries similar to the batteries 10, but having 4 positive plates and 4 negative plates were assembled from the rest of the separator, which had a grammage of about 250 g.cm-2. The batteries were found to have cycling characteristics substantially equivalent to those of the control battery. In another specific example, a glass fiber mat was produced which weighed 1000 g-m-2- and was composed of fibers having an average diameter of substantially 0.8 µm; a layer which weighed 318 g.m-2, which was separated from this mat, is the separator in the battery described above m this paragraph. The separator was subjected to "Compression" and "rebound". Compression thicknesses were determined by the method described in U.S, patent No, 5,336,275 under various apphed loads, and after the excess of each applied load above 3.79 kPa was released; the former measurements are the "Compression" thicknesses while the latter are "rebound" thicknesses. The average results arc presented graphically in Fig. 5, which is a plot of the thicknesses of the separator 18 in mm (designated A) at various applied loads in kPa and of the thicknesses in mm (designated B) after the excess above 3.79 kPa of each applied load was released. Each data point for one of the curves of Fig. 5 is indicated by"+' (this is the curve for "rebound" thickness) and each data point for the other curve is indicated by a dot (this is the curve for "Compression" thicknesses). The data plotted in Fig. 5 indicate that the separator is an outstanding material. Compression and rebound thicknesses were determined for a commercially available separator material that is produced by a wet process using paper making equipment. The material tested is available under the trade designadon HOVOSORB BG 30005, grammage318 g.m'-2. The average results of this testing are presented gi'aphically in Fig. 6, which is a plot similar to Fig. 5, showing the data plotted in Fig. 5 and the Compression thicknesses (designated C) of the HOVOSORB BG 30005 separator in mm and the Rebound thicknesses in mm (designated D) against the applied load in kPa. In yet another specific example, a glass fiber mat was produced which weighed 1000 g.m-2 and was composed of fibers having an average diameter of substantially 0.8 µn; a layer which weighed 130 g.m-2, which was separated from this mat, has been used as the separator in the battery 10. The separator was subjecred to "Compression" and "rebound" testing. The average results are presented graphically in Fig. 7, which is a plot of the Compression thicknesses of the separator in mm (designated E) and of the rebound thicknesses in mm (designated F) against the applied load in kPa. The data points for one of the curves of Fig- 7 are shown by plus marks (these are the data points for the 'Rebound" curve), while those for the other curve are indicated by dots (these are for the "compression" curve). The data plotted in Fig, 7 indicate that the separator is an outstanding material. Compression and rebound thicknesses were determined for a another separator material that is commercially available, this one under the trade designation BGC140, grammage 130 g.m-3. The average results of the BGC140 material are also presented graphicalJy in Fig. 9, which includes a plot of the compression thicknesses of the BGC140 separator in mm (designated G) and of the rebound diicknesses in mm (designated H) against the applied load in kPa. The data points for one of the BGC140 curves are shown by open circles (these are the data points for the "Rebound" curve), while an * indicates each data point for the other BGC140 (these are the "compression" curves). Compression and rebound testing of otlier separator materials composed of the 608 MP mat which ranged in grammage from 130 to 1151 g-m"", indicated that they arc all outstanding separator materials. In another example, a glass fiber mat was produced which weighed 258 g.m-2 and was composed of fibers having an average diameter of substantially 0.8 µm This separator was subjected to "Compression" and "rebound" testing. The average results are presented graphically in Fig. 9, which is a plot of the Compression thicknesses of the separator in mm and of the rebound thicknesses in mm against the applied load in kPa. The data points for one of the curves of Fig. 9 (designated I) are the data points for the "Rebound" curve), while those for another cur\'e (designated J arc for the "compression" curve). Compression and rebound thicknesses were also determined for a wetlaid separator material, grammage 244 g.m-2. The average results of the wetlaid separator material are also presented grapliically in Fig, 9, showing the compression thicknesses of the wedaid separator in mm (designated K) and the rebound thicknesses in mm (designated L) against the applied load in kPa. It has been considered desirable for glass fiber separator material used in VRLA catteries to contain a substantial proportion of fine fibers, e.g., finer than about 5 µm. The separators, if they contain a sufficient proportion of fine fibers, are capable of holding enough of the relatively small amount of electroJyte that is used in such batteries to make :ontact with the plates, and to enable an electric current to flow through the separators. It is usually desirable that the separators also contain a substantial proportion of coarser fibers in order to impart strength and, incidentally, to reduce the cost per pound. The finest presently known glass fibers have been produced by the flame blown process, for example, that shown in Figs. 2 and 2a, attached, and described herein with reference thereto. This is the method by which the glass fiber mats from which separator material for the battery 10 was separated, as described above. Accordingly, the flame blown process has been used to produce separator material for a battery according to the invention. The flame blown process, as is known, if such variables as the temperature and velocity of the blast of hoc gases that attenuates the glass filaments which are drawn from a melting tank are suitably varied, can also be used to produce fibers that are either coarser or finer than 0.8 \xm in diameter. Apparatus shown in Figs. 3 and 10 also produces glass fibers by the flame blown process, but produces fibers somewhat coarser than that of Figs. 2 and 2a. Dryland mat produced as described above has been examined under a scanning electron microscope. It was observed that the material which was collected on a drum while that drum rotated more than one revolution was composed of a plurality of discrete layers, one for each rotation of the drum during the collection process and that there was a fiber diameter gradient within each of the discrete layers, the fibers of the smallest diameter being concentrated adjacent one major surface of each layer, and the fibers of the largest diameter being concenti'ated adjacent the other major surface. The tests described above demonstrate that this separator material has improved resilience, by compaiison with wetlaid separator. An experunent that has been performed with plural sheets of wetlaid glass fiber separator demonstrated that the separator composed of discrete layers also has improved shock resistance by comparison with conventional wetlaid separator. The experiment involved compressing a stack of wetlaid sepai'ator sheets using a compression fixmre on a conventional tensile testing machine. Scanning electron microscope examination of the compressed material revealed that substantially all of the defonnation occurred in one of the outside sheets of the stack. This indicates that the layered sepai'ator material would also have improved shock resistance by comparison with material which is substantially uniform throughout its thickness. It will be appreciated that the separator material can also be produced by a wet papermaking process where similar layering occurs, for example, by casting a plurality of slurries of glass or other fibers, the first on the screen of paper making apparatus, and the second and subsequent ones on the previously cast fibers, or by assembling a plurality of thin sheets of glass or other fibers made by a conventional wet process to produce a composite separator having the desired thickness and gramnage. It will also be appreciated that dry-laid webs of fibers made by the process described in Chapter 7: Dry-Laid Systems by Albin F, Turbak, Nonwovens: Theory, Process, Performance, and Testing" can also be used as separator material in batteries according to the present invention. This process involves carding bundled fibers that can be purchased from manufacturers, and suspending the carded fibers in air or another gas inside a hood, and usmg vacuum to draw the suspended fibers onto a foramnious conveyor so that they form a web of a desired thickness. Figs. 2 and 2a show apparatus which can be used to produce battery separator material composed of first glass fibers having a first average fiber diameter and second glass fibers having a second average fiber diameter. The apparatus has two different fiberizeis, one of which is indicated generally at 1.9, and the other of which is indicated generally at 19. The two fiberizers 19 and 19' are identical; each includes a spinner assembly 20,20' carried by a rotatable spindle 21,21' which can be rotated at high speed about its longitudinal axis 22, 22' by a motor (not illustrated) which drives a belt-driven pulley 23,23' that is keyed to the upper end of the spindle 21. 2 1. Each of the spinner assemblies 20, 20' includes an internal bowl 24,24' wliich rotates with the spindle 21,21'. Each bowl 24,24' has a peripheral wall 25, 25' through which there are several small diameter openings 26,26'.Each spinner assembly 20,20' also has an insulating heat shield 27, 27' which minimizes heat loss from the bowl 24, 24', As each spinner assembly 20, 20' is rotated, molten glass 28,28' flows from a melting tank (not illustrated) through a mbe 29,29' into one of the bowls 24,24' from which centiifugal force causes streams of the glass to flow through die openings 26, 26'. An annular nozzle 30, 30' surrounds each of the spinner assemblies 20, 20'. Combustion of a fuel gas in a chamber 31,31' forces a jet of heated gas to flow downwardly through the nozzles 30,30'. The gas jets flowing from the nozzles 30, 30' attenuate streams of molten glass which flow through the openings 26,26' into fine fibers 32, 32' and direct them downwardly onto a conveyor 33, 33' where they collect as a mat. Each fiberizer 19 and 19' also includes a riser tube 34, 34' which is connected to a source for compressed air (nor illustrated) and to an end tube 35, 35' which extends vertically upwardly, and teminates just below the heat shields 27, 27'. As is indicated by arrows 36, 36', air flows upwardly through the riser tubes 34, 34' and the end tubes 35, 35' until it is deflected outwardly by the spinner assembly against the intedor of a veil 37, 37' of fibers. The fiberizcrs 19 and 19' are disclosed in US patent No. 5,076,826, which explains that the upward flow of air indicated by the arrows 36, 36' prevents a low pressure zone beneath the spinner assemblies 20,20', and, as a consequence, reduces the amount of remelt which forms in the fiber veils 37, 37'. The patent also discloses that the fiberizers, except for the parts thereof which cause the upward flow of air, were prior art. The apparatus of Figs. 2 and 2a can be operated to produce separator material for use in batteries according to the invention. For example, the fiberizers 19 and 19' can both be operated to produce fibers having an average diameter of 0.8 µm, in which case the speed of the conveyors 33 and 33' can be controlled so that a mat 38 having the desired grammagc is accumulated on the conveyors before it is conveyed from within the housing 39' for delivery to an upwardly inclined conveyor 40 and collection on a take-up roll 4L Ultimately, the mat 38 can be slit to width and used, for example, as described in US patent No. 5,344,466 to produce batteries. Alternatively, the fiberizer 19 can be operated to produce fibers having an average diameter of 0.8 µm, and the Gberizer 19' can be operated to produce fibers having a larger fiber diameter say 1.5 µm, and the speed of the conveyors 33 and 33' can be controlled to provide mat having a desired grammage and a desired proportion of fibers of the two diameters. Since it is usually desirable that the finest fibers of a separator be adjacent the plates of a banery, two layers of the separator described in this paragraph can be placed on top of one another, with their coarse fiber sides adjacent one another, to provide a particularly advantageous separator material. Another apparatus (not illustrated) that can also be used to produce separator material composed of two outer layers of fine fibers and a center layer of coarser fibers comprises the apparatus of Figs. 2 and 2a plus a third fiberizer, identical to the fiberizers 19 and 19' which is positioned between the two so that it deposits fibers on a mat that has already been formed in the fiberizer 19 and the fiberizer 19' deposits fibers on the mat discharged by the third fiberizer. In this case, the fiberizers 19 and 19' are preferably operated to produce fine fibers, and the third fiberizer is operated to produce coarser fibers, Refcrrmg to Fig. 3, still another apparatus that can be used in producing separator material that can be used in a battery according to the invention is indicated generally at 42. The apparatus 42 comprises a fiber collection zone 43 in which primary filarnents 44 drawn by pull rolls 45 from a fiber forming bushing 46 in a glass melting tank 47 pass over a filament support 48 and into a blast of hot gases from a high pressure hot gas nozzle 49, The blast of hot gas softens the filaments, attenuates them into fine fibers SO, and projects them to the right inside the coUecdon zone 43. As is indicated by arrows 51, atmospheric air can enter the region where the fibers 50 are projected. A glass fiber mat 52, which can be one discharged from the fiberizcr 19 enters the collection zone 43 on a conveyor 53, which passes over a suction box 54, holding the mat 52 in contact with the conveyor 53, and drawing fibers 50 to the bottom of the collecting zone 43 and onto the mat 52 and a mat 55 which forms inside the coilection zone as fibers 50 are deposited, first, onto the mat 52, and then onto fibers 50 that have previously been so deposited. The mat 55 can be conveyed into the fiberizer 19' for augmentation, or it can be slit, stacked, and used as previously described to produce a battery according to the mvention, or it can be wound on a roll for subsequent processing. Referring to Fig. 4, still another apparams that can be used in producing separator material that can be used in a battery according to the invention is indicated generally at 56. The apparams 56 comprises a fiber collection zone 57 m which a strand 58 of textile glass fibers is drawn by pull rolls 59 to pull individual fibers 60 fi'om a textile fiber bushing (not illustrated) in a glass melting tank (not illustrated), through a gathering shoe 61 and to second pull rolls 62 by which it is directed into a blast of gases from a high pressure gas nozzle 63, The blast of gas breaks up thr strand 58, and projects the tlbers 60 to the right inside the collection zone 57. A glass fiber mat 63, which can be one discharged from the fiberizer 19 enters the collection zone 57 on a conveyor 64, which passes over a suction box 65, holding the mat 63 in contact with the conveyor 64, and drawing fibers 60 to the bottom of the collecting zone 57 and onto the mat 63 and a mat 66 which forms inside the collection zone as fibers 60 are deposited, first, onto the mat 63, and then onto fibers 60 that have previously been so deposited. The mat 66 can be conveyed into the fiberizer 19' for augmentation, or it can be slit, stacked, and used as previously described to produce a battery according to the invention, or it can be wound on a roll for subsequent processing. The appatatus of Figs. 2 and 2a can also be used to produce a multilayer sepai'ator matetial, e.g., by operadng the fiberizing apparatus 19 of Fig. 2 to deposit a mat composed of a thill layer of fine fibers on the conveyor 33, advancing this thin layer of mat into the fiberlzing apparatus of Fig. 2a and depositing additional fibers and silica on top of the thin layer of mat. The fibers can be deposited in the apparatus of Fig. 2a as previously described, and an aqueous slurry of the silica can be fed at a suitable rate to a rotating dish 67 with veins 68 so that the slurry is thrown outwai'dly by centrifugal force in the dish 67 aud then projected radially outwardly by the veins 68 into the veil 37. Any of the slurry that falls onto the thin layer of the mat on the conveyor 33' is merely collected there, becoming a part of the separator material just like that which impinges on the veil 37. Similaily, the apparatus of Figs. 2 and 2a can be used to produce still another multilayer separator material, e.g., by operating the fiberizing apparatus 19 of Fig. 2 to deposit a mat composed of fine fibers on the conveyor 33, advancing this layer of mat into the fiberizing apparatus of Fig. 2a and depositing additional fibers and a concentrated slurry of extremely fine cellulose fibrils on top of the layer of mat. The fibers can be deposited in the apparams of Fig. 2a as previously described, and an aqueous sluny of the cellulose fibrils can be fed at a suitable rate to a rotating dish 67 with veins 68 so that the sluny is thrown outwai'dly by centrifugal force in the dish 67 and then projected radially outwardly (as indicated at 70) by the veins 68 into the veil 37. Any of the slurry that falls onto the thin layer of the mat on the conveyor 33' is merely collected there, becoming a part of the separator material just like that which impinges on the veil 37. There can also be a dish 67 (not illustrated) in [he fiberizer 19 of Fig. 2, which can be operated as just described to introduce cellulose fibrils into the fibers formed in the fiberizer 19. Referring now to Fig. 10, apparatus indicated generally at 69 is sumilar' to that of Fig. 3, except that a drum collector 70 has been substituted for the conveyor 53 of the Fig, 3 apparatus. The apparatus 69 comprises a fiber collecdon zone 71 in which primary filaments 44 drawn by pull rolls 45 from a fiber forming bushing 46 in a glass melting tank 47 pass over a filament support 48 and into a blast of hot gases from a high pressure hot gas nozzle 49. The blast of hot gas softens the filaments, attenuates them into fine fibers 50, and projects them to the right inside the collection zone 43. As is indicated by arrows 51, atmospheric air can enter the region where the fibers 50 are projected. A mat 72 which is collected on a foraminous surface 73 of the drum 70 is removed from the drum by a roll 74 from which it is delivered to a collection zone, not shown. It will be appreciated that the intant invention, as described above, may be subjected 10 various modifications without departing from the spirit of the invention disclosed and claimed herein. For example, separator according to the invention and comprised of a plurality of sheets or layers may be needled or sewn together to provide added physical integrity for the separator. Additionally or alternatively, layers of material can be cross-lapped. In addition, additives which do not affect the essential characteristics of the separator may be incorporated. I claim: 1. In a storage battery comprising a plurality of lead plares in a closed case, a fibrous sheer plate separator between adjacent ones of said plates, and a body of a sulfuric acid electrolyte absorbed by each of said separators and maintained in contact with each of the adjacent ones of said plates, the improvement wherein said separator sheets consist essentially of intermeshed glass fibers produced by suspending glass fibers in a gaseous medium, and collecting the suspended glass fibers on a foraminous material, with the proviso that the mass of fibers has a BET surface area of from 0.2 to 5 m2 per gram. 2. A glass fiber separator material which is a mass of intermeshed glass fibers produced by suspending glass fibers in a gaseous medium, spraying an aqueous slurry containing from 0.2 percent w/w to 20 percent w/w of cellulose fibrils, based upon the weight of glass fibers and cellulose fibrils, into contact with the suspended glass fibers, said fibrils being from a slurry having a Canadian freeness sufficiently low that the separator material has a tensile strength greater than an otherwise identical separator where glass fibers having an average diameter greater than I µm replace the cellulose fibrils, and collecting the suspended glass fibers and the cellulose fibrils on a foraminous material, with the proviso that the mass of glass fibers suspended and collected has a BET surface area of horn 0.2 lo 5 m2 per gram. 3. A glass fiber separator material as claimed in claim 2 wherein the cellulose fibrils are impregnated with a solidified, synthedc latex. 4. A glass fiber scparator material as claimed in claim 2 wherein the cellulose fibrils are from a slurry which has a Canadian freeness not greater than 100 cc. 5. A glass fiber separator material as claimed in claim 2 wherem the cellulose fibrils adjacent one of the two opposed major surfaces are impregnated with a solidified, synthetic latex, while the cellulose fibrils adjacent the other of the two opposed major surfaces are not so impregnated. 6. A multi-layer sheet useful as a separator in a valve regulated lead acid battery, said sheet comprising at least a first layer and a second layer, said sheet being produced by the method consisting of the steps of forming said first layer by suspending glass fibers in a gaseous medium, collecting a mat of the glass fibers on a foraminous material, and forming said second layer by suspending glass fibers and a powder that is inert to battery reactions in a gaseous medium, collecting the glass fibers and the powder on said first layer, said powder having a mean particle size ranging from 0.001 µm to 20 µm, said first layer having a sufficiently small pore size that substandally all of the powder is collected on said fh'st layer and is retained in the multi-layer sheet, with the proviso that the BET surface area of the fibers in the multi-layer sheet is from 0.2 to 5 m' per gram. 7. A multi-layer sheet as claimed in claim 6 wherein said first layer has a grammage less than 50 g/m2, 8. A multi-layer sheet as claimed in claim 6 which additionally includes a third layer, and wherein said third layer was formed by suspending glass fibers in a gaseous medium, and collecting the suspended glass fibers as said third layer on said first and second layers while they are supported on a foraminous material. 9. A VRLA batteiy comprising a case, having alternate negative and positive plates in said case, positive and negative terminals, suitable electrical connections among said plates and said terminals, and separator material between alternate ones of said positive and negative plates that is a multi-layer sheet as claimed in claim 6. 10. A VRLA battery comprising a case, having alternate negative and positive plates in said case, positive and negative terminals, suitable electrical connections among said plates and said terminals, and separator material between alternate ones of said positive and negative plates that is a multi-layer sheet as claimed in claim 6, and has a minimum nitrogen BET surface area of at least 1.1 m'/g. 11. A multi-layer sheet as claimed in claim 6 wherein said first layer has a minimum nitrogen BET surface area of at least 1.6 m2/g. 12. A multi-layer sheet as claimed in claim 6 wherein said second layer contains at least 50% of paniculate silica powder, based upon the weight of libers and silica powder in said second layer. 13. A multi-layer sheet as clauned in claim 6 wherein said second layer contains at least 70% of particulate silica powder , based upon the weight of fibers and silica powder in said second layer. 14. A glass fiber separator material comprising a mass of intermeshed glass fibers substantially all of which have a fiber diameter not greater than about 15 µm, and at least 5 percent w/w of which have a fiber diameter less than 1 µm, and, distributed through the glass fibers, from 0-2 percent w/w to 20 percent w/w of cellulose fibrils from a slurry having a Canadian freeness sufficiendy low that a battery made with the separator has a service life, when cycled, at least 10 percent greater than an otherwise identical separator where glass fibers having an average diameter greater than 1 µm replace the cellulose fibrils, said separator having been produced by suspending glass fibers and from 0.2 percent w/w to 20 percent w/w of cellulose fibrils, based upon the weight of glass fibers and cellulose fibrils, in a gaseous medium, and collecting the suspended glass fibers on a foraminous material, 15. A sealed lead/sulfuric acid recombinant storage battery comprising a plurality' of lead plates in a closed case, a fibrous sheet plate separator as claimed in claim 14 between adjacent ones of said plates, and a body of a sulfuric acid electrolyte absorbed by each of said separators and maintained in contact with each of the adjacent ones of said plates. 16. A glass fiber sepai'ator material which is a mass of intermeshed glass fibers produced by suspending first glass fibers having a given average fiber diameter in a gaseous medium, collecting the suspended first glass fibers on a foraminous material, suspending second glass fibers having an average fiber diameter different from the given average fiber diameter in a gaseous medium, collecting the suspended second glass fibers on the collected first glass fibers, with the proviso that the mass of intermeshed glass fibers has a BET surface area of from 0.2 to 5 m2 per gram. 17. A glass fiber sepai'ator material as claimed in claim 16 wherein the first glass fibers and the second glass fibers have substantially the same chemical composition, 18. In a storage battery as claimed in claim 1, the improvement wherein individual ones of the intermeshed fibers ai'e bonded to adjacent fibers at points of contact by an inorganic binder. 19. In a storage battery as claimed in claim 1, the improvement wherein individual ones of the intermeshed fibers are bonded to adjacent fibers at points of contact by an organic binder. 20. In a storage battery as claimed in claim 1, the improvement wherein said separator sheets consist essentially of intermeshed glass fibers produced by suspending glass fibers of a first group having a given fiber diameter and glass fibers of a second group having a different fiber diameter in a gaseous medium, and collecting the suspended glass fibers on a foraminous material. 21. In a storage battery as claimed in claim 1, the improvement wherein said separator sheets consist essentially of intermeshed glass fibers and organic fibers produced by suspending glass fibers having a given fiber diameter and organic fibers having a different fiber diameter in a gaseous medium, and collecting the suspended glass and organic fibers on a foraminous material. 22. In a storage battery as claimed in claim 1, the improvement wherein at least one of the thickness, tensile strength and stiffness of said separator sheets has been altered, after said sheet was collected, by spraying a liquid thereon and thereafter compressing the sheet. 23. In a storage battery as claimed in claim 1, the improvement wherein the collected fibers were subjected to a cross-lapping process. 24. In a storage battery comprising a plurality of lead plates in a closed case, a fibrous sheet plate separator between adjacent ones of said plates, and a body of a sulfuric acid electrolyte absorbed by each of said separators and maintained in contact with each of the adjacent ones of said plates, the improvement wherein said separator sheets consist essentially of intermeshed glass or organic fibers produced by suspending fibers in a gaseous or liquid medium, and collecting the suspended fibers on a foraminous mateiial in at least four discrete layers, with the proviso that the mass of fibers has a BET surface area of from 0,2 to 5 m2 per gram. 25. In a storage batteiy as claimed in claim 24, the improvement wherein the collected fibers are predominandy glass microfibers. 26. In a storage battery as claimed in claim 24, the improvement wherein the collected fibers are predominantly organic microfibers. 27. In a storage batteiy as claimed in claim 24, the improvement wherein an inorganic particulate material is suspended and collected with the fibers, and the inorganic particulate material constitutes from 5 to 90 percent of the total weight of the fibers and particulate material. 28. In a storage battery as claimed in claim 24, the improvement wherein the fibers are suspended in a liquid medium. 29. In a storage battery as claimed in claim 24, the improvement wherein the fibers arc suspended in a gaseous medium. 30- In a storage battery comprising a plurality of lead plates in a closed case, a fibrous sheet plate separator between adjacent ones of said plates, and a body of a sulfuric acid electrolyte absorbed by each of said separators and maintained in contact with each of the adjacent ones of said plates, the improvement wherein said separator sheets consist essentially of intermeshed glass or organic fibers produced by carding bundled glass or organic fibers, suspending the carded fibers in a gaseous medium, and collecting the suspended fibers on a foraminous material, with the proviso that the mass of fibers has a BET surface area of from 0.2 to 5 m2 per gram. 31. In a storage battery as claimed in claim 30, the improvement wherein the suspended fibers comprise organic fibers. 32. In a storage battery as claimed in claim 31, the improvement wherein the organic fibers are polyolefin. 33. In a storage battery as claimed in claim 32, the improvement wherein the polyolefin fibers are treated to make them hydrophylic. 34. In a storage battery as claimed in claim 31, the improvement wherein the organic fibers are polyester. 35. In a storage battery as claimed in claim 31, the improvement wherein the organic fibers are acrylic. An improved storage battery substantially as herein described with reference to the accompanying drawings.

Full Text

The present invention relates generally to the field of batteries and, more specificali^ to batteries in which separators containing glass fibers are positioned between the positive and negative plates and to a method for producing such separators and batteries. As is subsequently discussed in more detail, separators containing glass fibers are well known. Long before glass fiber separators, however, cedar veneers were used as a separator material, and were replaced by microporous, hard rubbery separators and cellulose sepai'ators impregnated with resins.

Valve regulated ("sealed" - "recombinant") lead acid (VRLA) batteries are known; they usually comprise a plurality of positive and negative plates, as in a prismatic cell, or layers of separator and positive and negative electrodes wound together, as in a "jelly roll" cell. The plates arc arranged so that they alternate, negative - positive - negative, etc., with separator material separating each plate from adjacent plates. The separator, typically composed of a mat of glass fibers, is an inert material; it stores battery acid, and provides low electric resistance. In addition, in VRLA batteries, the separator material provides innumerable gas channels between the plates through which oxygen can migrate from the positive electrode, when generated there, to the negative electrode where it can be recombined with hydrogen, according to the oxygen cycle. Another important function of a separator is to exert pressure against the plate paste or active material which forces the paste into contact with the plate, and causes a pressure between the plates, ensuring that there is not an interface at which corrosion can occur.
Glass fiber separator material has been produced conmiercially by wet processes on paper making equipment including fourdrinjer macliines and rotoformers, inclined fourdrinier machines and extended wire rotoformers. In the production of separator made of glass fibers for VRLA batteries, it is preferred that to organic bmder be added to a furnish from which separator sheets are made; the entanglement of individual fibers serves to maintain the sheet in a cohesive structure, and water glass or any of various sulfate salts,

which sometimes form on the fiber surfaces, serves as a binder. Organic binders, however, tend to decrcase. the ability of a separator to wick acid, and to decrease the amount of acid a separator can hold. A great deal of work has been dircted to modifying the glass fiber famish from which separators are produced to improve battery performance and/or lower the cost of the separator. Some of the work has entailed the addition of synthetic fibers for various reasons, such as the use of thermoformable plastic fibers so that the separator can be heat sealed on its edges to envelop a plate. Other work, which pertains to the field of this invention, has been directed to the use of filler, e.g., silica, to provide separators which arc comparable to ail glass fiber separators, at a lower cost. Separators made from glass fibers to which cellulose has been added and polyolefm fibers to which cellulose has been added have also been suggested. Prior art patents are discussed below.
US Patent No. 4,465,748 (Harris) discloses glass fiber sheet material for use as a separator in an electrochemical cell, and made from 5 to 35 percent w/w of glass fibers less than 1 µm in diameter; the patent also discloses a glass fiber sheet for such use wherein there are fibers of a continuous range of fiber diameters and lengths, and most of the fibers are not over 5 mm in length.
US patent No- 4,216,280, (Kono et al.), discloses glass fiber sheet material for use as a plate separator in a battery, and made from 50 to 95 percent w/w of glass fibers less than 1 |µm in diameter and 50 to 5 percent w/w of coarser glass fibers. The coarser glass fibers, the reference says, have a fiber diameter larger than 5 µm, preferably larger than 10 µm, and it is advantageous for some of the coarser fibers to have diameters of 10 µm to 30 µm.
US Patent No. 4,205,122 (Minra et al.) discloses a battery separator of reduced electric resistance comprising a self supportmg, non woven mat consisting essentially of a mixture of olefanic resin fibers having a coarseness of from 4 to 13 decigrex and olefinic resin fibers having a coarseness of less than 4 decigrex, the latter fibers being present in an amount of not less than 3 paits by weight per 100 parts by weight of fibers; up to about 600 parts by weight of inert filler materials per 100 parts by weight of fibers can also be used. The battery separator is produced by subjecting a suitable aqueous dispersion to a sheet-forming operadon, drying the resulting wet, non-woven mat, and heat treating the dried mat at a temperature ranging from a point 20°C. lower than the melting point of the aforementioned fibers to a point about 50°C. higher than the melting point.

us Patent No. 4,216,281 (O'Rell et al.) discloses a separator material produced from a furnish containing 30 to 70 percent w/w of polyolefin synthetic pulp, 15 to 65 percent w/w of a siliceous filler and 1 to 35 percent w/w of "long" fibers which can be polyester fibers, glass fibers, or a mixrure of the two. Cellulose in an amount up to about 10 percent w/w is disclosed as an optional ingredient of the furnish.
US Patent No, 4,363,856 (Waterhousc) discloses a separator material made from a furnish composed of polyolefin pulp fibers and glass fibers, and names polyester staple fibers, polyolefin staple fibers and cellulose pulp fibers as alternative constituents of the furnish.
US Patent No. 4,387,144 (McCallum) discloses a battery separator having a low electrical resistance after extended use which is made by therna]lconsolidation and themal embossing of a paper web formed from a furnish containing a synthetic pulp the fibrils of which are filled with an inorganic filler, the web incorporating a wetting agent which is preferably an organic sulphonate, and organic succinate, or phenol ethoxylaie.
US patent No. 4,373,015 (Peters et al.) discloses sheet material for use as a separator in a battery, and "comprising organic polymeric fibers"; boch of the examples of the reference describe the sheet material as "short staple fiber polyester matting about 0.3 mm thick'*, and indicate that the polyester fibers range from about 1 µm to about 6 µm in diameter.
Sheet separators for use in conventional (not valve regulated) batteries and comprising both glass fibers and organic fibers are disclosed in all of the following US patents: No. 4,529,677 (Bodendorf); No. 4,363,856 (Waterhouse); and No. 4,359,511 (Strzempko).
US patent No. 4,367,271, Hasegawa, discloses storage batteiy separators composed of acrylic fibrils in an amount of up to about 10 percent w/w, balance glass fibers.
Japanese patent document 55/146,872 discloses a separator material comprising glass fibers (50-85 percent w/w) and organic fibers (50-15 percent w/w).
US patent No. 4,245,013, Clegg et al,, discloses a separator made by overlaying a first sheet of fibrous material including polyethylene fibers with a second sheet of fibrous material including polyethylene and having a synthetic pulp content higher than the first sheet.
US Patent No. 4,908,282, Badger, discloses a separator comprising a sheet made from first fibers which impart to the sheet an absorbency greater than 90% and second fibers

i
which impart to the sheet an absorbency less than 80% wherein the first and second fibers are present in such proportions thai the sheet has an absorbency of from 75 to 95%. This patent discloses that fine glass fibers have a high absorbency, that coarse glass fibers have a low absorbency, and that hydrophobic organic fibers have an extremely low absorbency, and that, when this separator is saturated with electrolyte, unfilled voids remain so that gas can transfer from plate to plate for recombination. The disclosure of Badger is incorporated herein by reference.
US Patent No. 5,091,275 (Brecht et al.) discloses a glass fiber sepaarator which expands when exposed to electrolyte. The separator comprises glass fibers which are impregnated with an aqueous solution of colloidal silica particles and a sulfate salt. The separator is produced by forming a paper making web of glass fibers, impregnating the web with the aqueous mixture of silica and the salt, lightly compressing the impregnated web to remove some of the aqueous solution, pardally drying the web, compressing the web to a final thickness and completing the drying of the web. The web is preferably compressed to a thickness which is less than the distance between plates in a given cell, so that insertion of an assembled cell stack into a case is facilitated. When electrolyte is added to the case, the salt dissolves in the electrolyte and the separator expands to provide good contact between the plates and the separators. According to the patent, the silica contributes to the recombination performance of cells incorporating the pre-compressed separator. The silica also contributes a great deal of stiffness to the separator, so much so that the separator may be characterised as rigid.
It has been determined that the production of battery separator by paper-making techniques from a furnish of glass fibers and silica powder leads to problems which are caused by variations in the concentration of the silica powder in the furnish. Typical glass fiber furnishes have a liquid content exceeding 98 percent w/w. In the course of making separator sheets, most of the water is removed from the furnish in the first few feet of a screen on which the furnish is cast. The water, known as white water, is recycled and winds up back in the headbox of the machinc. If the furnish is composed exclusively of glass fibers, virtually none of the fibers pass through the wire and wind up in the white water. However, furnishes comprising glass fibers and silica powder do not fare so well In the absence of a retention aid, significant amounts of silica powder from such furnishes do pass through the paper making wire and wind up in the white water. Left unchecked, this phenomenon causes

the concentration of silica powder in the furnish to increase, undesirably changing the properties of the furnish. Heretofore, the problem of silica powder and the like passing through a paper making wire has been avoided though the use of binders and retention aids.
US patent No. 2,477,000 discloses a synthetic fiber paper produced from i5brillae and fibers made by methods wherein a solution of the fiber is extruded through very small orifices (spinnerets) and then the extruded solution is allowed to congeal either in a precipitating bath or by evaporation of the solvent or by temperature changes (see column 2, lines 25 and following). The patent says that fibers of cellulose acetate, cellulose nitrate, regenerated cellulose from viscose, "Vinylite (a synthetic resin made by polymerization of vinyl compounds), Araiac (a fibrous product made from skim milk casein), and spun glass" which range in length up to 1 inch and in diameter from 12-80 microns and fibrillae preferably derived from flax, Manila hemp, caroa or hemp can be used to make the paper. At least 90 percent of the fibrillae should be from 0.0015 to 0.0025 inch in length and from 0.0000027 to 0.0000044 inch in width-
WO 98/12759, an International Application published March 26, 1998, discloses "A resilient fibrous mat, preferably made of microfibers is especially adapted for use as a battery separator for starved electrolyte batteries. . . . The fibrous mat, with one or two surface layers, can be formed form an air laid fibrous blanket by subjecting one or both surfaces of the blanket to hydro entanglement to increase the entanglement of the fibers at and adjacent the major surface($) relative to the entanglement of the fibers in the resilient fibrous layer. The fibrous mar with a substantially uniform density may be made by flooding the blanket with a liquid and drawing a vacuum through the blanket."
A publication (apparently, European Patent Application 98-15, Japan Vilene Co.,
Ltd., filed September 29, 1997 as application 97116846) shows the kind of entanglement
disclosed in W098/12759 to produce the material of Figs. 1 and 2 diercof, but applied to
the entire body of the separator material rather than to a region or regions adjacent one or
both major surfaces as in W098/12759.
An English language absti'act of a published Japanese patent application (07147154, published June 6, 1995), entitled SEPARATOR FOR .\LKALINE BATTERY states:
"A fiber having a section form shown in (c) of the drawing, for example, is constituted from 0.04 to 0.12 deniers of circular and petal polypropylene component 2 and 0.12 denier of a polyethylene

component 1. A hundred percent of this dividing composite fiber
with a fineness of 2 deniers and a fiber length of 38mm is opened by
atard machine to laminate unidirectional and cross fiber webs with
METSUKE of 1.3 and 52f/ml This is treated from both surfaces
with a water flow having a water pressure of 130kg/cm2 on a nozzle
plate having a nozzle diameter of 0.13mm and a pitch of 0.6mm. This cloth is dipped in fuming sulfuric acid, sulfonated, and then calendered to provide a separator having a METSUKE of 65g/m2 and a thickness of 0.1 5mm. The same treatment can be performed in constitutions other than (c) in the drawing. Thus, excellent electrolyte resistance, oxidizing property, and liquid holding property are provided, and a battery can be smoothly operated for a long period."
BRIEF DESCRIPTION OF THE INSTANT INVENTION
The instant invendon i.s based upon the discovery that a binderlcss glass fiber mat .suitable for use as a separator for Valve regulated ("sealed" - "recombinant") lead acid (VRLA) batteries can be produced by a dry process by collecting the fibers from fiberizing appai'atus, without subjecting them to a wet paper making or other post forming process. For example, glass fibers produced by the flame blown process, which is subsequendy described in more detail, can be wound on a drum until a mat weighing about 1,000 grams per square meter has been collected; the mat can then be slit transversely, and removed from the drum as sheets weighing about 1,000 grams per square meter, having one dunension which equals the circumference of the drum, and another which equals the width of the drum. This mat wliich, in a typical example, has an average fiber diameter of 0.8 pm, can then be sepai^ated into layers having the weight in grams per square meter desired in a given baaery separator, and the layers can be cut to size and used as separators, as subsequently described in more detail. Web having the targeted grammmage can also be taken direcdy from the drum or glass can be fiberized by another method which is controlled so that a continuous sheet having the targeted grammage is produced.
A glass fiber mat which can be used in practicing the instant invention can also be made by what is called "the rotary process" in glass forming apparatus which includes a glass melting tank, a rapidly rotating centrifugal bushing with small openings in a periphery, at least one high pressure hot gas nozzle from which a high velocity fibcrizing jet is directed across the periphery of the centrifuge, and a collectmg conveyor. Molten glass fed ro the centrifugal bushing is caused by centrifugal force to flow through the peripheral openings of

the bushing mto the fiberizing jet, by which the streams of glass are attenuated and carried onto a collecting conveyor which is pervious to the gas. The mat from this process can also be collected on a drum, slit transversely, and removed from the drum as sheets which, again can weigh about 1,000 grams per square meter and can be composed of fine fibers, average fiber diameter 0,8 µm when the rotary process is that of US patent No. 5,076,826, or can range up to about 3µm when other rotary processes are used. This mat can also be separated into layers having the weight in grams per square meter desired in a given battery separator, and the layers can be cut to size and used as separators, as subsequently described in more detail. This web having the targeted grammage can also be taken directly from the drum.
It has been found by examination, using a scanning electron microscope, of mat produced as described in the two preceding paragraphs and collected on a drum, that the mat is formed in discrete layers, each of which is composed of the fibers deposited during one revolution of the collecting drum, and that there is a fiber diameter gradient within each of the discrete layers, the fibers of the smallest diameter being concentrated adjacent one major surface of each layer, and the fibers of the largest diameter being concentrated adjacent the other major surface. A part of the Increased resilience of battery separator according to the invention is attributed to the observed layering, and another part is attributed to the gradient in fiber diameter within each layer. It will be appreciated that separator material can also be produced by a wet papermaking process where similar layering occurs, for example, by casting a plurality of slurries of glass or other fibers, the first on the screen of paper making apparatus, and the second and subsequent ones on the previously cast fibers, or by assembling a plurality of thin sheets of glass or other fibers made by a wet process to produce a composite separator having the desired thickness and grammage. Accordingly, in one aspect, the invention is a battery separator composed of a plurality of thin sheets of non-woven fabric assembled to constitute the separator, and the thin sheets can be made by an air-laid or wet process.
Thinner sheets of the glass fiber mat can also be produced by either the flame blown process or by the rotary process, includmg that of US patent No. 5,076,826, and enough of the thinner sheets to provide the desired grammage, which usually ranges from about 20 to about 1000 g.m"" can be stacked, and then cat to size. To produce the thinner sheets, glass fibers can be produced from softened glass and collected in a conventional manner, usually on a foraminous conveyor, and the speeds of the fiberizing process and of the conveyor can

be set so that a mat having the desired grammage is conveyed from the forming operation, and cither rolled for future use, or cut to size, in which case it can be used immediately to produce batteries, or stacked for future use. The continuous sheet can also be collected with a cross-lappcr to hnprove its uniformity.
When a battery is produced, at least one stack of alternating positive and negative plates is assembled, with separator between adjacent plates, and the separator of each stack is compressed so that the stack can be slipped into a pocket which is a part of the case of the battery. It is important that the separator have sufficient resiliency, after such compression, that it exerts the required pressure against the paste or active material on each plate to force the paste into contact with the plate, and to cause a pressure between the plates, ensuring that there is an interface, along the faces of the plates, among the plate paste or active material, the electrolyte and oxygen. A standard test has been developed to measure the resiliency of a separator material. The results of this test, as is subsequently explained in more detail, indicate that separators in batteries according to the invention are significantly more resilient than otherwise identical separators made from different samples of the same glass fibers, but by a conventional wet paper making process, OBJECTS OF THE INVENTION
It is, therefore, an object of the instant invention to provide an improved VRLA or other battery contaning a separator composed, at least predominandy, of glass fibers as collected from a fiber forming process, i.e., without having been subjected to a wet paper making process or to a post fomiing process such as that called an "airlaid" or spunlaced, or to another post forming, secondan' process..
It is another object to provide a method for producing a battery separator composed predominantly of glass fibers.
It is yet another object to provide a glass fiber VRLA separator which has better resiliency than a separator made by the wet paper making process from the same fibers.
It is still another object to provide a glass fiber VRLA battery separator which has greater resiliency, by comparison with previously known separators, and, as a consequence, can be 10 to 50 percent lighter in weight per unit of area (grammage) but still provide the same "BCI" (Battery Council International) thickness as conventional wet laid separator, i.e., 300 grams per square meter for separator having a BCI thickness of 2.13 millimeters.
It is yet another object to provide a VRLA battery separator which has improved

resilience and shock absorbing properties because it is composed of a plurality of separate layers.
It is a further object to provide a glass fiber VRLA separator which has greater absorbency for a battery electrolyte than does a separator made by the wet paper making process from the same fibers.
It is still another object to provide a glass fiber VRLA separator material in which the average fiber length is greater than in a separator made by the wet paper making process from the same fibers because the fiber breakage associated with the paper making or post fonning redispersing and forming processes does not occur.
It is yet another object to provide a separator that is composed of multiple, separately formed layers of glass or other fibers.
Other objects and advantages will be apparent from the description which follows, reference being made to the attached drawings.
DEFINITIONS
As used herein, the term "percent v/v" means percent by volume; the term "percent w/w" and the symbol % mean percent by weight; the term "wire", as applied to a paper making machine, means the surface of the machine on which a furnish is cast in producing paper, and can be, for example, the screen of a Fourdrinier machine or the vacuum drum of a rotoformer machine; pore sizes reported herein, unless otherwise indicated, are in microns, and are determined by the first bubble method or by liquid porosimetry, Coulter; all temperatures are in °C.; and the following abbreviations have the meanings indicated: µm = micron or microns; mg-milligram or milligrams; g=gram or grams; kg-kilogram or kilograms; l=liter or liters; ml=miliiliter or milliliters; cc=cubic centimeter or cubic centimeters; pcf=pound per cubic foot or pounds per cubic foot; m=meter or meters; cm=centimeter or centimeters; mm=millumeter or millimeters; mil=inch x 10-3 or inches x lO-3 (multiply times 25.4 to convert to mm); kPa=ressure in thousands of Newtons per square meter; psi=pounds per square inch (multiply times 6.89 to convert to kPa); and kN=force in thousands of Newtons. BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view with parts broken away to show details of construction of a VRLA battery according to the invention.

Figs. 2 and 2a are vertical sectional views which show different parts of apparatus for producing a glass fiber mat by what is called "the rotary process" that can be used as collected from the fiber forming process, i.e., without having been subjected to a wet paper making process, to produce a battery according to the invention; together, Figs. 2 and 2a constitute a schcmadc representation of the apparatus.
Fig, 3 is a schematic representation similar to a part of the apparatus of Fig. 2a, showing different apparatus which can be used to produce a glass fiber mat by what is called "the flame blown" process; the apparatus of Fig. 3 can be used alone to produce a mat or with the apparatus of Fig. 2 to produce a glass fiber mat that can be used as collected from the fiber forming process to produce a battery according to the invendon.
Fig. 4 is a schematic representation similar to Fig. 3 of still another apparatus which can be used with that of Fig. 2 for producing a glass fiber mat that can be used as collected from the fiber forming process to produce a battery according to the invention.
Fig. 5 and 7 are plots of thickness in mm of separator materials that can be used in batteries according to the invention, when compressed (the compression curve), vs. force in kPa applied to compress the separator to that thickness and of rebound thickness in mm (the rebound curve) vs. force applied before rebound thickness was detennined,
Figs. 6 and 8 are plots of the data represented in Figs* 5 and 7 and, in addition, plots of thickness of a wet-laid glass fiber separator in mm when compressed vs. force in kPa applied to compress the separator to that thickness and of rebound thickness in mm vs. force applied before rebound thickness was determined for commercial separator materials that have been used in batteries.
Fig. 9 is a plot of separator thickness in mm against compression force in kPa for each of two different materials under compression, and rebound thickness for each of the same two materials after they have recovered after being unloaded.
Fig. 10 is a vertical sectional view which shows, schematically, apparatus similar- to that of Fig. 3 for producing a glass fiber mat by what is called "the flame blown method" that can be used as collected from the fiber forming process, i.e., without having been subjected to a wet paper making process, to produce a battery according to the invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS
A single cell batter}' according to the invention with a total of 9 plates is indicated generally at 10 in Fig. 1. Except for the identity of the separator material therein, the battery'

10 is conventional; the separator can be used in other otherwise conventional batteries. The battery 10 comprises four positive plates 11 which are electrically connected to a positive terminal 12 and five negative plates 13 electrically connected to a negative terminal 14. The plates 11 and 13 are housed within a batteiy case 15 which is covered by a top 16. There is an opening through a boss 17 on the top 16 of the battery, Separators 18 are composed of . sheets of separator material wrapped around the bottom and both major faces of each positive plate 11.
In a specific example, five, 8A-U1 batteries similar to the batteries 10, but having four negative and four positive plates were produced from separator material composed of glass fibers collected, as the fibers were formed, into a mat weighing about 310 g.m-2; the fibers had an average diameter of substantially 0.8µm. A control battery was also produced using a separator that is commercially available under the designation BG 30005; this material, which is made by the wet paper making process, weighs 300 +/-15 g.m'-2 This control was made so that assembly and properties of the five 8A-U1 batteries could be compared with the assembly and properties of a control made with separator having the same general target grammage. It was noted that the drylaid separator used to produce the five batteries had a substantially greater thickness and resiliency than the control separator; this confirmed laboratory findings concerning drylaid separator. An assembly of three pairs of positive and negative plates with the drylaid separator had approximately the same thickness as an assembly of five pairs of positive and negative plates with the BG 30005 separator, indicating that drylaid separator for a given battery should have about three fifths the grammage of conventional wetlaid separator for that batteiy.
Difficulties were encountered in the assembly of the batteries from the drylaid separator because of the high resiliency of the airlaid separator. These difficulties arose when attempts were made to cast straps on the assemblies of plates with separators and in inserting assemblies of plates and separators into batteries. The cases of batteries that were made were deformed by forces exerted by the separator. One assembly of plates and drylaid separator was compressed in a press with one ton of force for fifteen minutes; since the plate surfaces were 4.85 inches by 4.85 inches, this amounted to an applied force of about 87 psi. This assembly was then inserted into a battery case, which it did not defoim.

In another example an outer wrap of the separator was removed and batteries similar to the batteries 10, but having 4 positive plates and 4 negative plates were assembled from the rest of the separator, which had a grammage of about 250 g.cm-2. The batteries were found to have cycling characteristics substantially equivalent to those of the control battery. In another specific example, a glass fiber mat was produced which weighed 1000 g-m-2- and was composed of fibers having an average diameter of substantially 0.8 µm; a layer which weighed 318 g.m-2, which was separated from this mat, is the separator in the battery described above m this paragraph. The separator was subjected to "Compression" and "rebound". Compression thicknesses were determined by the method described in U.S, patent No, 5,336,275 under various apphed loads, and after the excess of each applied load above 3.79 kPa was released; the former measurements are the "Compression" thicknesses while the latter are "rebound" thicknesses. The average results arc presented graphically in Fig. 5, which is a plot of the thicknesses of the separator 18 in mm (designated A) at various applied loads in kPa and of the thicknesses in mm (designated B) after the excess above 3.79 kPa of each applied load was released. Each data point for one of the curves of Fig. 5 is indicated by"+' (this is the curve for "rebound" thickness) and each data point for the other curve is indicated by a dot (this is the curve for "Compression" thicknesses). The data plotted in Fig. 5 indicate that the separator is an outstanding material. Compression and rebound thicknesses were determined for a commercially available separator material that is produced by a wet process using paper making equipment. The material tested is available under the trade designadon HOVOSORB BG 30005, grammage318 g.m'-2. The average results of this testing are presented gi'aphically in Fig. 6, which is a plot similar to Fig. 5, showing the data plotted in Fig. 5 and the Compression thicknesses (designated C) of the HOVOSORB BG 30005 separator in mm and the Rebound thicknesses in mm (designated D) against the applied load in kPa.
In yet another specific example, a glass fiber mat was produced which weighed 1000 g.m-2 and was composed of fibers having an average diameter of substantially 0.8 µn; a layer which weighed 130 g.m-2, which was separated from this mat, has been used as the separator in the battery 10. The separator was subjecred to "Compression" and "rebound" testing. The average results are presented graphically in Fig. 7, which is a plot of the Compression thicknesses of the separator in mm (designated E) and of the rebound thicknesses in mm (designated F) against the applied load in kPa. The data points for one of the curves of Fig- 7

are shown by plus marks (these are the data points for the 'Rebound" curve), while those for the other curve are indicated by dots (these are for the "compression" curve). The data plotted in Fig, 7 indicate that the separator is an outstanding material. Compression and rebound thicknesses were determined for a another separator material that is commercially available, this one under the trade designation BGC140, grammage 130 g.m-3. The average results of the BGC140 material are also presented graphicalJy in Fig. 9, which includes a plot of the compression thicknesses of the BGC140 separator in mm (designated G) and of the rebound diicknesses in mm (designated H) against the applied load in kPa. The data points for one of the BGC140 curves are shown by open circles (these are the data points for the "Rebound" curve), while an * indicates each data point for the other BGC140 (these are the "compression" curves).
Compression and rebound testing of otlier separator materials composed of the 608 MP mat which ranged in grammage from 130 to 1151 g-m"", indicated that they arc all outstanding separator materials.
In another example, a glass fiber mat was produced which weighed 258 g.m-2 and was composed of fibers having an average diameter of substantially 0.8 µm This separator was subjected to "Compression" and "rebound" testing. The average results are presented graphically in Fig. 9, which is a plot of the Compression thicknesses of the separator in mm and of the rebound thicknesses in mm against the applied load in kPa. The data points for one of the curves of Fig. 9 (designated I) are the data points for the "Rebound" curve), while those for another cur\'e (designated J arc for the "compression" curve). Compression and rebound thicknesses were also determined for a wetlaid separator material, grammage 244 g.m-2. The average results of the wetlaid separator material are also presented grapliically in Fig, 9, showing the compression thicknesses of the wedaid separator in mm (designated K) and the rebound thicknesses in mm (designated L) against the applied load in kPa.
It has been considered desirable for glass fiber separator material used in VRLA catteries to contain a substantial proportion of fine fibers, e.g., finer than about 5 µm. The separators, if they contain a sufficient proportion of fine fibers, are capable of holding enough of the relatively small amount of electroJyte that is used in such batteries to make :ontact with the plates, and to enable an electric current to flow through the separators. It is usually desirable that the separators also contain a substantial proportion of coarser fibers in order to impart strength and, incidentally, to reduce the cost per pound. The finest presently

known glass fibers have been produced by the flame blown process, for example, that shown in Figs. 2 and 2a, attached, and described herein with reference thereto. This is the method by which the glass fiber mats from which separator material for the battery 10 was separated, as described above. Accordingly, the flame blown process has been used to produce separator material for a battery according to the invention. The flame blown process, as is known, if such variables as the temperature and velocity of the blast of hoc gases that attenuates the glass filaments which are drawn from a melting tank are suitably varied, can also be used to produce fibers that are either coarser or finer than 0.8 \xm in diameter. Apparatus shown in Figs. 3 and 10 also produces glass fibers by the flame blown process, but produces fibers somewhat coarser than that of Figs. 2 and 2a.
Dryland mat produced as described above has been examined under a scanning electron microscope. It was observed that the material which was collected on a drum while that drum rotated more than one revolution was composed of a plurality of discrete layers, one for each rotation of the drum during the collection process and that there was a fiber diameter gradient within each of the discrete layers, the fibers of the smallest diameter being concentrated adjacent one major surface of each layer, and the fibers of the largest diameter being concenti'ated adjacent the other major surface. The tests described above demonstrate that this separator material has improved resilience, by compaiison with wetlaid separator. An experunent that has been performed with plural sheets of wetlaid glass fiber separator demonstrated that the separator composed of discrete layers also has improved shock resistance by comparison with conventional wetlaid separator. The experiment involved compressing a stack of wetlaid sepai'ator sheets using a compression fixmre on a conventional tensile testing machine. Scanning electron microscope examination of the compressed material revealed that substantially all of the defonnation occurred in one of the outside sheets of the stack. This indicates that the layered sepai'ator material would also have improved shock resistance by comparison with material which is substantially uniform throughout its thickness. It will be appreciated that the separator material can also be produced by a wet papermaking process where similar layering occurs, for example, by casting a plurality of slurries of glass or other fibers, the first on the screen of paper making apparatus, and the second and subsequent ones on the previously cast fibers, or by assembling a plurality of thin sheets of glass or other fibers made by a conventional wet process to produce a composite separator having the desired thickness and gramnage.

It will also be appreciated that dry-laid webs of fibers made by the process described in Chapter 7: Dry-Laid Systems by Albin F, Turbak, Nonwovens: Theory, Process, Performance, and Testing" can also be used as separator material in batteries according to the present invention. This process involves carding bundled fibers that can be purchased from manufacturers, and suspending the carded fibers in air or another gas inside a hood, and usmg vacuum to draw the suspended fibers onto a foramnious conveyor so that they form a web of a desired thickness.
Figs. 2 and 2a show apparatus which can be used to produce battery separator material composed of first glass fibers having a first average fiber diameter and second glass fibers having a second average fiber diameter. The apparatus has two different fiberizeis, one of which is indicated generally at 1.9, and the other of which is indicated generally at 19. The two fiberizers 19 and 19' are identical; each includes a spinner assembly 20,20' carried by a rotatable spindle 21,21' which can be rotated at high speed about its longitudinal axis 22, 22' by a motor (not illustrated) which drives a belt-driven pulley 23,23' that is keyed to the upper end of the spindle 21. 2 1.
Each of the spinner assemblies 20, 20' includes an internal bowl 24,24' wliich rotates with the spindle 21,21'. Each bowl 24,24' has a peripheral wall 25, 25' through which there are several small diameter openings 26,26'.Each spinner assembly 20,20' also has an insulating heat shield 27, 27' which minimizes heat loss from the bowl 24, 24',
As each spinner assembly 20, 20' is rotated, molten glass 28,28' flows from a melting tank (not illustrated) through a mbe 29,29' into one of the bowls 24,24' from which centiifugal force causes streams of the glass to flow through die openings 26, 26'.
An annular nozzle 30, 30' surrounds each of the spinner assemblies 20, 20'. Combustion of a fuel gas in a chamber 31,31' forces a jet of heated gas to flow downwardly through the nozzles 30,30'.
The gas jets flowing from the nozzles 30, 30' attenuate streams of molten glass which flow through the openings 26,26' into fine fibers 32, 32' and direct them downwardly onto a conveyor 33, 33' where they collect as a mat.
Each fiberizer 19 and 19' also includes a riser tube 34, 34' which is connected to a source for compressed air (nor illustrated) and to an end tube 35, 35' which extends vertically upwardly, and teminates just below the heat shields 27, 27'. As is indicated by arrows 36, 36', air flows upwardly through the riser tubes 34, 34' and the end tubes 35, 35'

until it is deflected outwardly by the spinner assembly against the intedor of a veil 37, 37' of fibers.
The fiberizcrs 19 and 19' are disclosed in US patent No. 5,076,826, which explains that the upward flow of air indicated by the arrows 36, 36' prevents a low pressure zone beneath the spinner assemblies 20,20', and, as a consequence, reduces the amount of remelt which forms in the fiber veils 37, 37'. The patent also discloses that the fiberizers, except for the parts thereof which cause the upward flow of air, were prior art.
The apparatus of Figs. 2 and 2a can be operated to produce separator material for use in batteries according to the invention. For example, the fiberizers 19 and 19' can both be operated to produce fibers having an average diameter of 0.8 µm, in which case the speed of the conveyors 33 and 33' can be controlled so that a mat 38 having the desired grammagc is accumulated on the conveyors before it is conveyed from within the housing 39' for delivery to an upwardly inclined conveyor 40 and collection on a take-up roll 4L Ultimately, the mat 38 can be slit to width and used, for example, as described in US patent No. 5,344,466 to produce batteries.
Alternatively, the fiberizer 19 can be operated to produce fibers having an average diameter of 0.8 µm, and the Gberizer 19' can be operated to produce fibers having a larger fiber diameter say 1.5 µm, and the speed of the conveyors 33 and 33' can be controlled to provide mat having a desired grammage and a desired proportion of fibers of the two diameters. Since it is usually desirable that the finest fibers of a separator be adjacent the plates of a banery, two layers of the separator described in this paragraph can be placed on top of one another, with their coarse fiber sides adjacent one another, to provide a particularly advantageous separator material.
Another apparatus (not illustrated) that can also be used to produce separator material composed of two outer layers of fine fibers and a center layer of coarser fibers comprises the apparatus of Figs. 2 and 2a plus a third fiberizer, identical to the fiberizers 19 and 19' which is positioned between the two so that it deposits fibers on a mat that has already been formed in the fiberizer 19 and the fiberizer 19' deposits fibers on the mat discharged by the third fiberizer. In this case, the fiberizers 19 and 19' are preferably operated to produce fine fibers, and the third fiberizer is operated to produce coarser fibers,
Refcrrmg to Fig. 3, still another apparatus that can be used in producing separator material that can be used in a battery according to the invention is indicated generally at 42.

The apparatus 42 comprises a fiber collection zone 43 in which primary filarnents 44 drawn by pull rolls 45 from a fiber forming bushing 46 in a glass melting tank 47 pass over a filament support 48 and into a blast of hot gases from a high pressure hot gas nozzle 49, The blast of hot gas softens the filaments, attenuates them into fine fibers SO, and projects them to the right inside the coUecdon zone 43. As is indicated by arrows 51, atmospheric air can enter the region where the fibers 50 are projected. A glass fiber mat 52, which can be one discharged from the fiberizcr 19 enters the collection zone 43 on a conveyor 53, which passes over a suction box 54, holding the mat 52 in contact with the conveyor 53, and drawing fibers 50 to the bottom of the collecting zone 43 and onto the mat 52 and a mat 55 which forms inside the coilection zone as fibers 50 are deposited, first, onto the mat 52, and then onto fibers 50 that have previously been so deposited.
The mat 55 can be conveyed into the fiberizer 19' for augmentation, or it can be slit, stacked, and used as previously described to produce a battery according to the mvention, or it can be wound on a roll for subsequent processing.
Referring to Fig. 4, still another apparams that can be used in producing separator material that can be used in a battery according to the invention is indicated generally at 56. The apparams 56 comprises a fiber collection zone 57 m which a strand 58 of textile glass fibers is drawn by pull rolls 59 to pull individual fibers 60 fi'om a textile fiber bushing (not illustrated) in a glass melting tank (not illustrated), through a gathering shoe 61 and to second pull rolls 62 by which it is directed into a blast of gases from a high pressure gas nozzle 63, The blast of gas breaks up thr strand 58, and projects the tlbers 60 to the right inside the collection zone 57. A glass fiber mat 63, which can be one discharged from the fiberizer 19 enters the collection zone 57 on a conveyor 64, which passes over a suction box 65, holding the mat 63 in contact with the conveyor 64, and drawing fibers 60 to the bottom of the collecting zone 57 and onto the mat 63 and a mat 66 which forms inside the collection zone as fibers 60 are deposited, first, onto the mat 63, and then onto fibers 60 that have previously been so deposited.
The mat 66 can be conveyed into the fiberizer 19' for augmentation, or it can be slit, stacked, and used as previously described to produce a battery according to the invention, or it can be wound on a roll for subsequent processing.
The appatatus of Figs. 2 and 2a can also be used to produce a multilayer sepai'ator matetial, e.g., by operadng the fiberizing apparatus 19 of Fig. 2 to deposit a mat composed of

a thill layer of fine fibers on the conveyor 33, advancing this thin layer of mat into the fiberlzing apparatus of Fig. 2a and depositing additional fibers and silica on top of the thin layer of mat. The fibers can be deposited in the apparatus of Fig. 2a as previously described, and an aqueous slurry of the silica can be fed at a suitable rate to a rotating dish 67 with veins 68 so that the slurry is thrown outwai'dly by centrifugal force in the dish 67 aud then projected radially outwardly by the veins 68 into the veil 37. Any of the slurry that falls onto the thin layer of the mat on the conveyor 33' is merely collected there, becoming a part of the separator material just like that which impinges on the veil 37.
Similaily, the apparatus of Figs. 2 and 2a can be used to produce still another multilayer separator material, e.g., by operating the fiberizing apparatus 19 of Fig. 2 to deposit a mat composed of fine fibers on the conveyor 33, advancing this layer of mat into the fiberizing apparatus of Fig. 2a and depositing additional fibers and a concentrated slurry of extremely fine cellulose fibrils on top of the layer of mat. The fibers can be deposited in the apparams of Fig. 2a as previously described, and an aqueous sluny of the cellulose fibrils can be fed at a suitable rate to a rotating dish 67 with veins 68 so that the sluny is thrown outwai'dly by centrifugal force in the dish 67 and then projected radially outwardly (as indicated at 70) by the veins 68 into the veil 37. Any of the slurry that falls onto the thin layer of the mat on the conveyor 33' is merely collected there, becoming a part of the separator material just like that which impinges on the veil 37. There can also be a dish 67 (not illustrated) in [he fiberizer 19 of Fig. 2, which can be operated as just described to introduce cellulose fibrils into the fibers formed in the fiberizer 19.
Referring now to Fig. 10, apparatus indicated generally at 69 is sumilar' to that of Fig. 3, except that a drum collector 70 has been substituted for the conveyor 53 of the Fig, 3 apparatus. The apparatus 69 comprises a fiber collecdon zone 71 in which primary filaments 44 drawn by pull rolls 45 from a fiber forming bushing 46 in a glass melting tank 47 pass over a filament support 48 and into a blast of hot gases from a high pressure hot gas nozzle 49. The blast of hot gas softens the filaments, attenuates them into fine fibers 50, and projects them to the right inside the collection zone 43. As is indicated by arrows 51, atmospheric air can enter the region where the fibers 50 are projected. A mat 72 which is collected on a foraminous surface 73 of the drum 70 is removed from the drum by a roll 74 from which it is delivered to a collection zone, not shown.

It will be appreciated that the intant invention, as described above, may be subjected 10 various modifications without departing from the spirit of the invention disclosed and claimed herein. For example, separator according to the invention and comprised of a plurality of sheets or layers may be needled or sewn together to provide added physical integrity for the separator. Additionally or alternatively, layers of material can be cross-lapped. In addition, additives which do not affect the essential characteristics of the separator may be incorporated.

I claim:
1. In a storage battery comprising a plurality of lead plares in a closed case, a fibrous
sheer plate separator between adjacent ones of said plates, and a body of a sulfuric acid
electrolyte absorbed by each of said separators and maintained in contact with each of the
adjacent ones of said plates, the improvement wherein said separator sheets consist essentially of intermeshed glass fibers produced by suspending glass fibers in a gaseous medium, and collecting the suspended glass fibers on a foraminous material, with the proviso that the mass of fibers has a BET surface area of from 0.2 to 5 m2 per gram.
2. A glass fiber separator material which is a mass of intermeshed glass fibers
produced by suspending glass fibers in a gaseous medium, spraying an aqueous slurry
containing from 0.2 percent w/w to 20 percent w/w of cellulose fibrils, based upon the
weight of glass fibers and cellulose fibrils, into contact with the suspended glass fibers, said
fibrils being from a slurry having a Canadian freeness sufficiently low that the separator
material has a tensile strength greater than an otherwise identical separator where glass fibers
having an average diameter greater than I µm replace the cellulose fibrils, and collecting the
suspended glass fibers and the cellulose fibrils on a foraminous material, with the proviso
that the mass of glass fibers suspended and collected has a BET surface area of horn 0.2 lo 5
m2 per gram.
3. A glass fiber separator material as claimed in claim 2 wherein the cellulose fibrils are impregnated with a solidified, synthedc latex.
4. A glass fiber scparator material as claimed in claim 2 wherein the cellulose fibrils are from a slurry which has a Canadian freeness not greater than 100 cc.
5. A glass fiber separator material as claimed in claim 2 wherem the cellulose fibrils adjacent one of the two opposed major surfaces are impregnated with a solidified, synthetic latex, while the cellulose fibrils adjacent the other of the two opposed major surfaces are not so impregnated.
6. A multi-layer sheet useful as a separator in a valve regulated lead acid battery, said sheet comprising at least a first layer and a second layer, said sheet being produced by the method consisting of the steps of

forming said first layer by suspending glass fibers in a gaseous medium, collecting a mat of the glass fibers on a foraminous material, and
forming said second layer by suspending glass fibers and a powder that is inert to battery reactions in a gaseous medium, collecting the glass fibers and the powder on said first layer, said powder having a mean particle size ranging from 0.001 µm to 20 µm,
said first layer having a sufficiently small pore size that substandally all of the powder is collected on said fh'st layer and is retained in the multi-layer sheet,
with the proviso that the BET surface area of the fibers in the multi-layer sheet is from 0.2 to 5 m' per gram.
7. A multi-layer sheet as claimed in claim 6 wherein said first layer has a grammage less than 50 g/m2,
8. A multi-layer sheet as claimed in claim 6 which additionally includes a third layer, and wherein said third layer was formed by suspending glass fibers in a gaseous medium, and collecting the suspended glass fibers as said third layer on said first and second layers while they are supported on a foraminous material.
9. A VRLA batteiy comprising a case, having alternate negative and positive plates in said case, positive and negative terminals, suitable electrical connections among said plates and said terminals, and separator material between alternate ones of said positive and negative plates that is a multi-layer sheet as claimed in claim 6.

10. A VRLA battery comprising a case, having alternate negative and positive plates in said case, positive and negative terminals, suitable electrical connections among said plates and said terminals, and separator material between alternate ones of said positive and negative plates that is a multi-layer sheet as claimed in claim 6, and has a minimum nitrogen BET surface area of at least 1.1 m'/g.
11. A multi-layer sheet as claimed in claim 6 wherein said first layer has a minimum nitrogen BET surface area of at least 1.6 m2/g.

12. A multi-layer sheet as claimed in claim 6 wherein said second layer contains at least 50% of paniculate silica powder, based upon the weight of libers and silica powder in said second layer.
13. A multi-layer sheet as clauned in claim 6 wherein said second layer contains at least 70% of particulate silica powder , based upon the weight of fibers and silica powder in said second layer.

14. A glass fiber separator material comprising a mass of intermeshed glass fibers substantially all of which have a fiber diameter not greater than about 15 µm, and at least 5 percent w/w of which have a fiber diameter less than 1 µm, and, distributed through the glass fibers, from 0-2 percent w/w to 20 percent w/w of cellulose fibrils from a slurry having a Canadian freeness sufficiendy low that a battery made with the separator has a service life, when cycled, at least 10 percent greater than an otherwise identical separator where glass fibers having an average diameter greater than 1 µm replace the cellulose fibrils, said separator having been produced by suspending glass fibers and from 0.2 percent w/w to 20 percent w/w of cellulose fibrils, based upon the weight of glass fibers and cellulose fibrils, in a gaseous medium, and collecting the suspended glass fibers on a foraminous material,
15. A sealed lead/sulfuric acid recombinant storage battery comprising a plurality' of lead plates in a closed case, a fibrous sheet plate separator as claimed in claim 14 between adjacent ones of said plates, and a body of a sulfuric acid electrolyte absorbed by each of said separators and maintained in contact with each of the adjacent ones of said plates.
16. A glass fiber sepai'ator material which is a mass of intermeshed glass fibers produced by suspending first glass fibers having a given average fiber diameter in a gaseous medium, collecting the suspended first glass fibers on a foraminous material, suspending second glass fibers having an average fiber diameter different from the given average fiber diameter in a gaseous medium, collecting the suspended second glass fibers on the collected first glass fibers, with the proviso that the mass of intermeshed glass fibers has a BET surface area of from 0.2 to 5 m2 per gram.
17. A glass fiber sepai'ator material as claimed in claim 16 wherein the first glass fibers and the second glass fibers have substantially the same chemical composition,
18. In a storage battery as claimed in claim 1, the improvement wherein individual ones of the intermeshed fibers ai'e bonded to adjacent fibers at points of contact by an inorganic binder.
19. In a storage battery as claimed in claim 1, the improvement wherein individual ones of the intermeshed fibers are bonded to adjacent fibers at points of contact by an organic binder.
20. In a storage battery as claimed in claim 1, the improvement wherein said separator sheets consist essentially of intermeshed glass fibers produced by suspending glass fibers of a first group having a given fiber diameter and glass fibers of a second group having

a different fiber diameter in a gaseous medium, and collecting the suspended glass fibers on a foraminous material.
21. In a storage battery as claimed in claim 1, the improvement wherein said
separator sheets consist essentially of intermeshed glass fibers and organic fibers produced
by suspending glass fibers having a given fiber diameter and organic fibers having a different
fiber diameter in a gaseous medium, and collecting the suspended glass and organic fibers on
a foraminous material.
22. In a storage battery as claimed in claim 1, the improvement wherein at least one of the thickness, tensile strength and stiffness of said separator sheets has been altered, after said sheet was collected, by spraying a liquid thereon and thereafter compressing the sheet.
23. In a storage battery as claimed in claim 1, the improvement wherein the collected fibers were subjected to a cross-lapping process.
24. In a storage battery comprising a plurality of lead plates in a closed case, a fibrous sheet plate separator between adjacent ones of said plates, and a body of a sulfuric acid electrolyte absorbed by each of said separators and maintained in contact with each of the adjacent ones of said plates, the improvement wherein said separator sheets consist essentially of intermeshed glass or organic fibers produced by suspending fibers in a gaseous or liquid medium, and collecting the suspended fibers on a foraminous mateiial in at least four discrete layers, with the proviso that the mass of fibers has a BET surface area of from 0,2 to 5 m2 per gram.
25. In a storage batteiy as claimed in claim 24, the improvement wherein the collected fibers are predominandy glass microfibers.
26. In a storage battery as claimed in claim 24, the improvement wherein the collected fibers are predominantly organic microfibers.
27. In a storage batteiy as claimed in claim 24, the improvement wherein an inorganic particulate material is suspended and collected with the fibers, and the inorganic particulate material constitutes from 5 to 90 percent of the total weight of the fibers and particulate material.
28. In a storage battery as claimed in claim 24, the improvement wherein the fibers are suspended in a liquid medium.
29. In a storage battery as claimed in claim 24, the improvement wherein the fibers arc suspended in a gaseous medium.

30- In a storage battery comprising a plurality of lead plates in a closed case, a fibrous sheet plate separator between adjacent ones of said plates, and a body of a sulfuric acid electrolyte absorbed by each of said separators and maintained in contact with each of the adjacent ones of said plates, the improvement wherein said separator sheets consist essentially of intermeshed glass or organic fibers produced by carding bundled glass or organic fibers, suspending the carded fibers in a gaseous medium, and collecting the suspended fibers on a foraminous material, with the proviso that the mass of fibers has a BET surface area of from 0.2 to 5 m2 per gram.
31. In a storage battery as claimed in claim 30, the improvement wherein the
suspended fibers comprise organic fibers.
32. In a storage battery as claimed in claim 31, the improvement wherein the organic
fibers are polyolefin.
33. In a storage battery as claimed in claim 32, the improvement wherein the
polyolefin fibers are treated to make them hydrophylic.
34. In a storage battery as claimed in claim 31, the improvement wherein the organic
fibers are polyester.
35. In a storage battery as claimed in claim 31, the improvement wherein the organic
fibers are acrylic.
An improved storage battery substantially as herein described with reference to the accompanying drawings.

Documents:

1981-mas-1998-abstract.pdf

1981-mas-1998-claims filed.pdf

1981-mas-1998-claims granted.pdf

1981-mas-1998-correspondnece-others.pdf

1981-mas-1998-correspondnece-po.pdf

1981-mas-1998-description(complete)filed.pdf

1981-mas-1998-description(complete)granted.pdf

1981-mas-1998-drawings.pdf

1981-mas-1998-form 1.pdf

1981-mas-1998-form 26.pdf

1981-mas-1998-form 3.pdf

1981-mas-1998-form 5.pdf

1981-mas-1998-other documents.pdf

abs-1981-mas-1998.jpg

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Patent Number

212437

Indian Patent Application Number

1981/MAS/1998

PG Journal Number

07/2008

Publication Date

15-Feb-2008

Grant Date

03-Dec-2007

Date of Filing

02-Sep-1998

Name of Patentee

M/S. KVG TECHNOLOGIES, INC

Applicant Address

STATE OF DELAWARE, 112 WASHINGTON STREET, EAST WALPOLE, MASSACHUSETTS 02032,

Inventors:

#	Inventor's Name	Inventor's Address
1	GEORGE C ZGURIS	6 NEW ROAD, CANTERBURY, NEW HAMPSHIRE 03224,

PCT International Classification Number

H 01 M 002/16

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	08/923,876	1997-09-02	U.S.A.