RESILIENT MAT; A METHOD OF MAKING THE RESILIENT MAT AND A BATTERY INCLUDING THE RESILIENT MAT

Abstract: A resilient fibrous mat, preferably made of microfibers is especially adapted for use as a battery separator for starved electrolyte batteries. The fibrous mat may be essentially uniform in density throughout its thickness or may include one or two relatively high density, high tensile strength fibrous surface layer(s) and a relatively low density, more resilient fibrous layer integral with and, in one embodiment, intermediate the two surface layers. The fibers in the surface layer(s) are more entangled than the fibers in the resilient layer. The fibrous mat, with one or two surface layers, can be formed from 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(s) relative to the entanglement of the fibers in the resilient fibrous layer. The fibrous mat with a substantially uniform density may be made by flooding the blanket with a liquid and drawing a vacuum through the blanket.

Description: RESILIENT MAT; A METHOD OF MAKING THE RESILIENT MAT AND A BATTERY INCLUDING THE RESILIENT MAT BACKGROUND OF THE INVENTION This application is a continuation of U.S. Serial No. 08/717,144 filed September 20, 1996. The present invention is directed to a resilient mat and a method of making the resilient mat and, in a preferred embodiment, to a resilient mat of microfibers that is especially suited for use as a separator mat in a battery such as a starved electrolyte battery. Rechargeable batteries, such as sealed, starved electrolyte, lead/acid batteries, are commonly used as power sources in vehicles, aircraft, emergency equipment and the like. These batteries, which typically range in size from "D" or "beer can" sized batteries to larger sized batteries, are either single or multi-cell batteries. Currently, each cell of a single cell or multi-cell starved electrolyte, lead/acid battery is defined by a sealed compartment which houses a cell pack that includes at least one porous, positive electrode plate, at least one porous, negative electrode plate, and at least one porous, relatively fragile, microfiber glass mat separator between the electrode plates. A sulfuric acid electrolyte within each cell is absorbed by the porous, microfiber glass mat separator (s) and the porous electrode plates. Thus, the separators used in starved electrolyte, lead/acid batteries are intended to function as both: separators between the positive and negative electrode plates of the cells to maintain the spacings between the positive and negative electrode plates and prevent the formation of short circuits within the cells; and reservoirs for retaining electrolyte within the cells between the positive and negative electrode plates. Short circuits within the cells can occur due to direct contact between the positive and negative electrode plates when the spacing between the electrode plates is not maintained or due to the formation of dendrites or moss shaped particles of the electrode materials between the positive and negative electrode plates. Over the service life of such batteries, the electrode plates repeatedly expand and contract due to changes in active material morphology and density produced by the chemical reactions within the cells producing the electrical energy. Thus, to maintain the spacing between the positive and negative electrode plates over the service life of such a battery and to prolong the service life of such a battery, the electrolyte carrying separators should be resilient to maintain contact with the electrode plates and prevent short circuits through plate to plate contact. In addition, the separators should be free of openings, formed in the separators either during their manufacture or through the handling of the separators and assembly of the battery cells, to prevent or inhibit the formation of short circuiting active material growths, sheddings or dendrites between the electrode plates through such openings over the service life of the batteries. Thus, the separators should be free or essentially free of openings through which active material growths or dendrites could easily form between the electrode plates and should have sufficient integrity to resist tearing, during the handling of the separators and the assembly of separators into the battery cells, which could form openings in the separators through which active material growths or dendrites could easily form between the electrode plates. Since the separators in starved electrolyte batteries, such as starved electrolyte lead/acid batteries, also function as electrolyte reservoirs, the capacity of such batteries is a function of both the porosity and surface areas of the electrode plates and the porosity and surface areas of the separators in contact with the surfaces of the electrode plates. Thus, to maintain the electrolyte between the positive and negative electrode plates and to maintain the major surfaces of the separators in contact with the surfaces of the electrode plates, the separators of such batteries should be resilient so that the separators continue to recover in thickness after the repeated expansion and contraction of the electrode plates over the service life of such batteries. Currently, thin, light weight mats or papers of glass fibers, polymeric fibers and/or other fibers (e.g. mats or papers ranging from about 100 to about 450 grams per square meter, such as glass microfiber separator mats for batteries) are made in various wet laid processes. In these wet laid paper making processes, the fibers are manufactured by various processes and collected in bulk. The glass and/or polymeric fibers are then hydropulped into very short fibers and introduced into and dispersed in a water slurry which is stirred to cause the fibers to become thoroughly and randomly mixed with each other. The fibers are then deposited from the water slurry onto a conventional paper making screen or wire as in a fourdrinier machine or a Rotoformer machine to form a matted paper. When intended for use as a battery separator, the matted paper is then processed through an acid bath to bond the fibers of the matted paper together. After the matted paper is formed and, in the case of battery separators, processed through an acid bath, the matted paper is dried and wound up into a roll or otherwise collected in a conventional manner for further processing, such as being cut into selected sizes for use as a battery separator. These processes for forming thin, light weight matted paper, are costly and result in matted paper products which, at least in part due to the relatively short lengths of the hydropulped fibers, exhibit only limited recovery after compression and low integrity. These matted paper products may also have openings through which active material growths or dendrites can form when these products are used as battery separators. Thus, for many end uses and, especially, for uses as separators for starved electrolyte batteries, such as starved electrolyte lead/acid batteries, the relatively high cost of such matted paper products and the limited recovery after compression, limited integrity and limited ability to prevent the formation of active material growths or dendrites exhibited by such products has resulted in the need for a low cost, resilient mat of relatively high integrity that is free or essentially free of openings through which active material growths or dendrites can easily pass between electrode plates. SUMMARY OP THE INVENTION The present invention is directed to low cost, resilient, fibrous mats of glass, polymeric, cellulose, and/or other fibers which exhibit good integrity and are preferably formed from air laid fibrous blankets or mats which minimize undesirable openings through the layered fibrous mats. While the resilient, fibrous mats of the present invention can be made of larger diameter fibers and of thicknesses greater than those preferred for the present invention, the mats and the method of making the mats of the present invention are especially suited for making low cost, relatively thin, resilient, fibrous mats of microfibers which exhibit good integrity and an absence of openings passing directly through the mats between the major surfaces of the mats. In first and second embodiments of the present invention, especially suited for use as a battery separator for starved electrolyte batteries, such as starved electrolyte lead/acid batteries, a resilient fibrous mat of microfibers, includes one or two relatively high density, high tensile strength fibrous surface layer (s) and a relatively low density, more resilient fibrous layer integral with and, in one embodiment, intermediate the two surface layers. Preferably, the mat is binderless and the microfibers in the surface layer (s) of the mat are more entangled than the microfibers in the resilient layer to provide the mat with greater integrity. The resilient, layered fibrous mat of these first and second embodiments of the present invention is preferably formed from a resilient, air laid fibrous blanket by subjecting one or both surfaces of an air laid blanket to hydro entanglement to increase the entanglement of the fibers at and adjacent the major surface (s) of the blanket relative to the entanglement of the fibers in a resilient fibrous layer. The further entanglement of the fibers at and adjacent the major surface (s) increases the tensile strength of the blanket at its surface (s) while retaining the resilience of the resilient fibrous layer so that the resilient, layered fibrous mat so formed has good integrity and retains its resilience after being subjected to repeated compression and expansion cycles, such as when used as an electrode plate separator in a sealed starved electrolyte battery. In a third embodiment of the present invention, especially suited for use as a battery separator for starved electrolyte batteries, such as starved electrolyte lead/acid batteries, the resilient fibrous mat is a resilient air laid felted fibrous mat of randomly oriented fibers, e.g. microfibers, that preferably has a substantially uniform density throughout its thickness. This resilient fibrous mat is made by forming an air laid blanket of randomly oriented fibers; flooding the air laid fibrous blanket with water; drawing a vacuum through the fibrous blanket to remove water from the fibrous blanket and set its thickness; and drying the fibrous blanket to form the resilient fibrous mat. There is no hydropulping of the fibers in this process. The invention is also directed to starved electrolyte batteries, such as starved electrolyte lead/acid batteries, which incorporate the resilient fibrous mats of the present invention in the cells of the batteries as separators between the electrode plates and as electrolyte reservoirs for maintaining electrolyte between the electrode plates. The separator mats are compressed between the major surfaces of the electrode plates and, preferably, extend beyond the perimeters of the electrode plates where they expand due to their resilience to hold additional electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross sectional view through the first embodiment of the resilient fibrous mat of the present invention which has a single surface layer of more entangled fibers. FIG. 2 is a cross sectional view through the second embodiment of the resilient fibrous mat of the present invention which has two surface layer of more entangled fibers. FIG. 3 is a cross sectional view through the third embodiment of the resilient fibrous mat of the present invention which is a felted mat. FIG. 4 is a block flow diagram of a first method of forming the resilient fibrous mat of the present invention. FIG. 5 is a schematic view of a production line for making the resilient fibrous mats of FIGS. 1 and 2. FIG. 6 is a schematic view of a second production line for making the resilient fibrous mats of FIG. 3. FIG. 7 is a schematic of a starved electrolyte battery with a portion broken away to show the resilient fibrous mats of the present invention positioned between the positive and negative electrode plates. FIG. 8 is a schematic of a starved electrolyte battery showing the resilient fibrous mats of the present invention positioned between the positive and negative electrode plates and extending outward beyond the electrode plates. DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2, show first and second embodiments of the resilient fibrous mat 20 of the present invention. These embodiments of the resilient fibrous mat 20 include a resilient layer 22 and one surface layer 24 or two surface layers 24 and 26 which provide the resilient fibrous mat 20 with additional integrity. The fibers in the surface layer 24 or layers 24 and 26 are more entangled than the fibers in the resilient layer 22 and the surface layer 24 or layers 24 and 26 are more compact and have a greater density than the resilient layer 22. The more compact, denser surface layers 24 and 26 increase the tensile strength of the resilient fibrous mat 20 and also increase the tear resistance of one or both surfaces of the resilient fibrous mat 20 while the less entangled fibers of the less compact, less dense, resilient layer 22 provide the resilient fibrous mat with the required resilience. Where the resilient fibrous mat 20 is provided with two surface layers 24 and 26, the degree of fiber entanglement and the density of these two surface layers is normally equal or substantially equal. However, if desired, one surface layer can have greater fiber entanglement; be more compact; and have a greater density than the other surface layer. A resilient fibrous mat with surface layers of different densities may be beneficial for certain applications. For example, it might be beneficial in certain applications to have battery separators wherein the surface layers contacting the electrode plates of one polarity have a greater density than the surface layers contacting the electrode plates of the opposite polarity. The resilient fibrous mat 20 can be made of various fibers or mixtures of fibers, including but not limited to, glass fibers; polyester, polypropylene and other polymeric fibers; and cellulose fibers. However, glass fibers are preferred for certain applications, such as, starved electrolyte lead-acid battery separators. The fiber diameters of the fibers used to form the resilient fibrous mat 20 can also vary. However, for making resilient fibrous mats particularly suited for applications such as battery separators, it is preferred to use microfibers to form the resilient fibrous mat and especially glass microfibers. While the thicknesses and weights of the resilient fibrous mats 20 can vary, for uses such as battery separators, the resilient fibrous mats 20, in an uncompressed state, range in thickness from about 0.01 to about 0.5 inches and preferably, from about 0.05 to about 0.25 inches and weigh between about 50 grams and about 450 grams per square meter. In a preferred embodiment of the present invention, intended for use as a battery separator, the resilient fibrous mat 20 is made of glass microfibers, polymeric microfibers or cellulose fibers or mixtures thereof and most preferably from glass microfibers. In this preferred embodiment, the glass microfibers and the polymeric microfibers of the resilient fibrous mat 20 have mean fiber diameters between about 0.5 and about 3.0 microns; more preferably between about 1.0 and about 2.0 microns; and most preferably between about 1.2 and about 1.7 microns. In this preferred embodiment, the resilient fibrous mats 20 range in weight from about 50 to about 450 grams per square meter; and more preferably from about 75 to about 150 grams per square meter. In this preferred embodiment, the resilient fibrous mat 20 is preferably binderless with the fibers of the resilient fibrous mat 20 being bonded together by means of fiber entanglement. As shown in the block flow diagram of FIG. 4 and the schematic diagram of FIG. 5, one method for forming the resilient fibrous mat 20 of the present invention, includes forming a fibrous blanket 28 of randomly oriented, entangled fibers in a blanket forming station or stations 30 by an air laid blanket forming process; needle punching the air laid blanket, if necessary, in a needle punch tacking station 32 to give the air laid blanket greater integrity; passing the air laid blanket through one or two hydro entanglement stations 34 and 36 to further entangle the fibers at and adjacent one or both surfaces of the blanket and form the resilient fibrous mat 20; drying the resulting resilient fibrous mat 20 by passing the resilient fibrous mat 20 through a vacuum extractor and a conventional dryer or oven 38; and collecting the resilient fibrous mat 20 for storage, shipment or further processing in a windup station or the like. It is preferred to use an air laid process for forming the fibrous blanket 28 rather than a wet laid process for several reasons. In air laid processes for forming the fibrous blanket 28, unlike wet laid processes, there is no hydropulping of the fibers. The hydropulping of the fibers in wet laid processes breaks the fibers into shorter lengths thereby reducing the degree of fiber entanglement in the mat, the resilience of the mat and the tensile strength of the mat. In the air laid processes, the fibers can be produced by a fiberizer and collected with the fibers randomly oriented and entangled to form the fibrous blanket 28 without any hydropulping of the fibers. The preferred fibers, for use in forming the fibrous blanket 28 of randomly oriented entangled fibers, are flame attenuated glass fibers. These fibers are formed by drawing continuous primary glass filaments from a conventional feeder or pot of molten glass and introducing these continuous primary glass filaments into the high energy gaseous blast of a flame attenuation burner, e.g. a Selas burner, where the continuous filaments are reheated, attenuated, and formed into fine diameter staple glass fibers of the desired mean diameter. While flame attenuated glass fibers are preferred, other fibers may be used with or instead of the flame attenuated glass fibers to form the fibrous blanket 28, such as but not limited to, glass fibers produced on rotary fiberization processes, and polyester, polypropylene and other polymeric fibers including melt blown polymeric fibers and mixtures of such fibers. It is contemplated that cellulose fibers may also be included in the fibers of the fibrous blanket 28 as part of a mixture of fibers. FIG. 5 shows a partial schematic view which is representative of a production line for making the resilient fibrous mat 20 of the present invention by the method of this invention outlined in the block diagram of FIG. 4. FIG. 5 shows the downstream end of a collection chamber 42 with the fibrous blanket 28 exiting the collection chamber 42 on a collection chain conveyor 44 which can be horizontal, as shown, inclined or vertical. The fibers 46, produced by a flame attenuation process or other process, are drawn to the collection chain conveyor 44 by suction ducts 48 positioned beneath the upper conveyor flight and collected on the upper flight of the collection chain conveyor 44 to form the fibrous blanket 28. As shown, if needed, the fibers can be sprayed with water from a series of spray nozzles 50 extending transversely across the conveyor 44 to enable the vacuum or suction being drawn by the suction ducts to slightly compact the fibrous blanket 28 and provide the fibrous blanket 28 with greater integrity. As shown in the block flow diagram of FIG. 4 , in a preferred method of forming the fibrous blanket 28, the fibrous blanket 28 is formed of between two and six thin fibrous blanket layers which are produced in each of the blanket collection zones or modules 52a - 52f. In this method, a thin fibrous blanket base layer is air laid and collected on a collection conveyor in one of the blanket collection zones 52a through 52e and then one or more additional thin fibrous blanket layers are subsequently and successively collected, in one or more of collection zones 52b through 52f , directly on the previously laid thin fibrous blanket layer or layers to form the fibrous blanket 28. Thus, while the fibrous blanket 28 can be produced in only one collection zone, the fibrous blanket 28 can also be produced in two or more collection zones (preferably up to but not limited to six collection zones) . For example, a blanket weighing 125 grams per square meter can be made in one collection zone or five collection zones with each zone producing a thin fibrous blanket layer weighing about 25 grams per square meter. The suction drawing the fibers 46 toward a collection conveyor draw the fibers more strongly toward areas of the collection conveyor surface with the least amount of fibers thereon. Thus, by forming the fibrous blanket 28 from a series of thin fibrous blanket layers, collected successively one upon the other, the fibers of each successive thin fibrous blanket layer are drawn toward areas of the collection surface least covered by previously collected thin fibrous blanket layers thereby preventing or minimizing the formation of a fibrous blanket 28 with holes passing directly through the blanket from one major surface to the other. Instead, the randomly oriented fibers of the thin fibrous blanket layers forming the fibrous blanket 28 create a tortuous path through the fibrous blanket. Thus, if the resilient fibrous mat 20 made from the blanket 28 is used as a battery separator, clear openings for the formation of active material growths or dendrites between the electrode plates are not present and the formation of active material growths or dendrites between the electrode plates is retarded. In another preferred method for making the blanket 28, a thin fibrous blanket base layer is air laid and collected on a collection conveyor in one of the blanket collection zones 52a through 52e and then one or more additional thin fibrous blanket layers are separately collected on separate collection conveyors in one or more of collection zones 52b through 52f. The thin fibrous blanket layers starting with the base layer are transferred from their separate collection conveyors to a common combining conveyor where the blanket layers from the one or more collection zones 52b through 52f are laid directly on the previously laid thin fibrous blanket layer or layers carried by the combining conveyor to form the fibrous blanket 28. U.S. patent no. 4,120,676, issued October 17, 1978, shows an apparatus of the general type which can be used to form the blanket 28 with individual collection modules where blanket layers are individually collected and then combined on a common conveyor to form a blanket and its disclosure is hereby incorporated by reference. By superimposing the separately formed thin blanket layers to form the fibrous blanket 28, the randomly oriented fibers of the thin fibrous blanket layers forming the fibrous blanket 28 create a tortuous path through the fibrous blanket. Thus, as with the other embodiment of the method of making the fibrous blanket 28 described above, if the resilient fibrous mat 20 made from the blanket 28 is used as a battery separator, clear openings for the formation of active material growths or dendrites between the electrode plates are not present and the formation of active material growths or dendrites between the electrode plates is retarded. As shown in FIG. 5, when forming the resilient fibrous mats 20 of FIGS. 1 and 2, the continuous, fibrous blanket 28 passes from the collection chamber 42 of fiberizing or blanket forming station(s) 30 through the needle punch tacking station 32. When required, the needle punch tacking station 32 is used in the method of the present invention to give the fibrous blanket 28 additional integrity, especially when the fibrous blanket 28 is formed of microfibers. When the needle punch tacking station 32 is used in the manufacturing process, the fibrous blanket 28 is periodically needle punched as the fibrous blanket moves through the needle punch tacking station from the wire screen conveyor 44 to a wire screen conveyor 54. During each needle punching cycle, barbed needles are passed down through the fibrous blanket 28 and then retrε.cted up through the fibrous blanket 28 to further entangle the fibers, e.g. microfibers, in the blanket 28 and give the fibrous blanket 28 more integrity. The needle punch tacking station 32 has a needle punch 60, such as a Fehrer needle punch, capable of up to 2500 needle punches per minute. The needle punch 60 typically includes a lower, fixed perforated bed plate 62; an upper, vertically adjustable perforated stripper plate 64; and a needle board 66 with barbed needles (preferably 36 gauge star blade needles) depending therefrom, in a preselected pattern, in alignment with the perforations in the upper stripper plate 64 and the lower bed plate 62. In operation, the fibrous blanket 28 slides over the lower, fixed perforated bed plate 62 from conveyor 44 to conveyor 54. The lower, fixed perforated bed plate 62 supports the fibrous blanket 28 during the needle punching operation and the perforations in the bed plate 62 receive the points of the needles when the needles project through the fibrous blanket 28 during the needle punching operation. The upper, vertically adjustable perforated stripper plate 64 is adjusted to a predetermined spacing above the lower bed plate 62, less than the thickness of the blanket 28, and is fixed in that position to maintain the fibrous blanket 28 in a slightly compressed state during the needle punching operation. The needles depending from the needle board 66 pass down and back through the perforations in the stripper plate 64 during the needling or tacking of the fibrous blanket 28. The needle board 66 is driven by a conventional reciprocating drive mechanism which reciprocates the needle board 66 in a vertical direction as shown in FIG. 5. As portions of the fibrous blanket 28 move through the needle punch tacking station, the needle board 66 is moved down passing the barbed needles down through the perforations in the stripper plate 64, the fibrous blanket 28, and into the perforations in the bed plate 62. The needle board 66 is then retracted to its original position drawing the barbed needles back up through the fibrous blanket 28 and the perforated stripper plate 64. The passage of the barbed needles down and back through the fibrous blanket 28 further entangles the fibers of the blanket 28 to give the fibrous blanket 28 greater integrity. From the needle punch tacker station 32, if used, the fibrous blanket 28 passes through two conventional hydro entanglement units 68 and 70 (such as the JET LACE 2000 hydro entanglement units sold by Valmet Honeycomb Corporation) of the hydro entanglement stations 34 and 36. Each of the hydro entanglement units 68 and 70 includes a water jet unit 72, a vacuum suction unit 74, and a carrier screen for carrying the fibrous blanket 28. The vacuum suction units 74 are positioned opposite the water jet units 72 and the fibrous blanket 28 is passed between the water jet unit 72 and the vacuum suction unit 74 of each of the hydro entanglement units 68 and 70. As shown in FIG. 5, the first hydro entanglement unit 68 is positioned to direct water into the fibrous blanket 28 through one major surface 76 of the fibrous blanket and to withdraw water from the fibrous blanket 28 through the other major surface 78 of the fibrous blanket and the second hydro entanglement unit 70 is positioned to direct water into the fibrous blanket 28 through the other major surface 78 of the fibrous blanket and to withdraw water from the fibrous blanket 28 through the major surface 76 of the fibrous blanket. Where the resilient fibrous mat 20 is provided with two surface layers 24 and 26, as shown in FIG. 2, the fibrous blanket 28 is subjected to hydro entanglement by both hydro entanglement units 68 and 70. Where only one major surface of the fibrous blanket 28 is provided with a surface layer, such as layer 24 as shown in FIG. 1, only one of the hydro entanglement units is used. The hydro entanglement units 68 and 70 form the surface layers 24 and/or 26 are by further entangling the fibers of the fibrous blanket at and adjacent the major surfaces 76 and 78 relative to the fiber entanglement of the fibers in the resilient layer 22. After passing through the hydro entanglement stations 34 and 36, the fibrous blanket 28 is dried, preferably by passing the fibrous blanket 28 through a vacuum extractor 80 and an oven 82 to complete the formation of the resilient fibrous mat 20. In a third embodiment of the present invention, shown in FIG. 3 and especially suited for use as a battery separator for starved electrolyte batteries, such as starved electrolyte lead/acid batteries, the resilient microfiber mat is a resilient air laid felted fibrous mat 120 of randomly oriented microfibers. The resilient fibrous mat 120 is uniform or essentially uniform in density throughout its thickness and the fiber entanglement within the resilient fibrous mat is uniform or essentially uniform throughout its thickness. Like the resilient fibrous mat 20, the resilient fibrous mat 120 can be made of various fibers or mixtures of fibers, including but not limited to, glass fibers; polyester, polypropylene and other polymeric fibers; and cellulose fibers. However, glass fibers are preferred for certain applications such as starved electrolyte lead-acid battery separators. The fiber diameters of the fibers used to form the resilient fibrous mat 20 can also vary. However, for making resilient fibrous mats particularly suited for applications such as battery separators, it is preferred to use microfibers to form the resilient fibrous mat and especially glass microfibers. While the thicknesses and weights of the resilient fibrous mats 20 can vary, for uses such as battery separators, the uncompressed resilient fibrous mats 20 range in thickness from about 0.01 to about 0.5 inches and preferably, from about 0.05 to about 0.25 inches and weigh between about 50 grams and about 450 grams per square meter. In a preferred embodiment of the present invention, intended for use as a battery separator, the resilient fibrous mat 120 is made of glass microfibers, polymeric microfibers or cellulose fibers or mixtures thereof and most preferably from glass microfibers. In this preferred embodiment, the glass microfibers and the polymeric microfibers of the resilient fibrous mat 120 have mean fiber diameters between about 0.5 and about 3.0 microns; more preferably between about 1.0 and about 2.0 microns; and most preferably between about 1.2 and about 1.7 microns. In this preferred embodiment, the resilient fibrous mats 120 range in weight from about 50 to about 450 grams per square meter; and more preferably from about 75 to about 150 grams per square meter. In this preferred embodiment, the resilient fibrous mat 120 is preferably binderless with the fibers of the resilient fibrous mat 120 being bonded together by means of fiber entanglement. This resilient microfiber mat 120 is made by forming an air laid blanket 28 of randomly oriented fibers, e.g. microfibers, as described in connection with FIGS. 4 and 5 with regard to the manufacture of the resilient fibrous mats 20 of FIGS. 1 and 2. The fibrous blanket 28 is then passed through a liquid bath 88, e.g. water bath, where it is saturated or flooded with water. The saturated blanket 28 is then passed through a vacuum extractor 80 on a wire screen conveyor. The vacuum extractor 80 draws a vacuum through the fibrous blanket to remove water from the fibrous blanket and set its thickness. The fibrous blanket 28 is then dried in the oven 82 or other conventional dryer means to complete the formation of the resilient fibrous mat 120. There is no hydropulping of the fibers in this process. FIGS. 7 and 8 are schematic figures showing the resilient fibrous mats 20 or 120 of the present invention used as resilient separators and electrolyte reservoirs 96 (hereinafter referred to as "separators") in a starved electrolyte battery 90, such as, a starved electrolyte lead/acid battery. The starved electrolyte battery 90 includes a container (not shown) in which are positioned one or more cells connected m series. Each cell includes one or more positive electrode plates 92 ; one or more negative electrode plates 94; one or more resilient separators 96 interposed between the positive electrode plates 92 and the negative electrode plates 94; an electrolyte absorbed in the positive and the negative electrode plates and the separators 96; a positive electrode lead 98 joining the positive electrode plates 92 to an adjoining cell or the positive battery terminal; and a negative electrode lead 100 joining the negative electrode plates 94 to an adjoining cell or a negative battery terminal. The resilient separators 96 are made from the resilient fibrous mat 20 of FIGS. 1 and 2 or the resilient fibrous mat 120 of FIG. 3, which may be cut to the shape and size of the electrode plates 92 and 94 as shown in FIG. 7 or oversized, as shown in FIG. 8, to extend beyond the electrode plates. Where the separators 96 are made from the resilient fibrous mats 20 each include a resilient layer 22 and either one surface layer 24 or two surface layers 24 and 26 which provide the separators 96 with additional integrity. The fibers in the surface layer 24 or layers 24 and 26 are more entangled than the fibers in the resilient layer 22 and the surface layer 24 or layers 24 and 26 are more compact and have a greater density than the resilient layer 22. The more compact, denser surface layers 24 and 26 increase the tensile strength of the separators 96 and also increase the tear resistance of one or both surfaces of the separators 96 while the less entangled fibers of the less compact, less dense, resilient layer 22 provide the separators 96 with the required resilience and electrolyte retaining capacity. Where the resilient separator 96 is provided with the two surface layers 24 and 26, as shown in FIG. 2, the degree of fiber entanglement and the density of these two surface layers can be equal or one surface layer can have greater fiber entanglement and be more compact and denser than the other surface layer. Where the separators 96 are made from the resilient fibrous mats 120, the separators 96 have one resilient layer which is essentially uniform in density and fiber entanglement throughout its thickness. In one application of the present invention, the resilient separators 96 are made of glass microfibers, polymeric microfibers or cellulose fibers or mixtures thereof and most preferably from glass microfibers. In this application, the glass microfibers and the polymeric microfibers of the resilient separators 96 have mean fiber diameters between about 0.5 and about 3.0 microns; more preferably between about 1.0 and about 2.0 microns; and most preferably between about 1.2 and about 1.7 microns. In this application, the resilient separators 96 range in weight from about 50 to about 450 grams per square meter; and more preferably from about 75 to about 150 grams per square meter. In this application, the resilient separators 96 are preferably binderless with the fibers of the resilient fibrous mat 20 or 120 being bonded together by means of fiber entanglement. In addition, the resilient separators 96 are free of openings passing directly through the resilient separators through which active material growths or dendrites can easily form between the electrode plates. As assembled, the positive electrode plates 92 and the negative electrode plates 94 in the cell or cells of the battery are spaced from each other a selected distance e.g. about 0.1 to about 0.2 inches. Over the service life of the battery, the electrode plates 92 and 94 repeatedly expand when the battery is in use, due to changes in morphology resulting from the chemical reaction producing the electrical energy, and then contract when the battery is recharged. The resilient separators 96, when subjected to a loading normal to their major surfaces of 1.5 pounds per square inch (hereinafter "1.5 psi") , have thicknesses about equal to (100% of the selected distance) or greater than the selected distance between the electrode plates 92 and 94 of the battery cell(s) as assembled; preferably between about 110% and about 250% of the selected distance between the electrode plates 92 and 94 of the battery cell(s) as assembled; and more preferably between about 120% and about 250% of the selected distance between the electrode plates 92 and 94 of the battery cell(s) as assembled. Thus, the resilient separators 96 of starved electrolyte, lead/acid batteries 90 function as both: a) resilient separators between the positive and negative electrode plates 92 and 94 of the cells to maintain the spacings between the positive and negative electrode plates 92 and 94 and prevent the formation of short circuits within the cells; and b) reservoirs for retaining electrolyte within the cells between the positive and negative electrode plates 92 and 94. Where the resilient separators 96 extend beyond the perimeters or peripheries of the electrode plates 92 and 94 and are free to expand as shown in FIG. 8, the resilient separators expand, e.g. to thicknesses equal to 110% or 120% or more of the spacing between the electrode plates as assembled, to form extended reservoirs 100 and thereby increase the electrolyte retaining capacity of the resilient separators 96 and the capacity of the battery. Due to their lack of resilience, the prior art separators made form wet laid mats do not provide this increased electrolyte retaining capacity. Due to their resilience, the resilient separators 96 help prevent short circuits within the cells which can occur due to direct contact between the positive and negative electrode plates when the spacing between the electrode plates is not maintained. Since the resilient separators 96 are free of openings passing directly through the resilient separators between their major surfaces, the resilient separators help to prevent short circuits within the cells due to the formation of active material growths or dendrites of the electrode materials between the positive and negative electrode plates. In the embodiments of the mat shown in FIGS. 1 and 2, the denser surface layer 24 or layers 24 and 26 of the resilient separators 96 provide the resilient separators 96 with sufficient integrity to resist tearing, during the handling of the resilient separators 96 and the assembly of resilient separators 96 into the battery cells, which could form openings in the resilient separators 96 through which active material growths or dendrites between the electrode plates could easily form. As previously discussed, the resilient separators 96, in starved electrolyte batteries, such as starved electrolyte lead/acid batteries, also function as electrolyte reservoirs and the capacity of such batteries is a function of both the surface areas of the electrode plates and the surface areas of the separators in contact with the surfaces of the electrode plates. The resilience of the resilient separators 96 maintains the electrolyte between the positive and negative electrode plates of the batteries and maintain the major surfaces of the resilient separators 96 in contact with the major surfaces of the electrode plates as the resilient separators 96 continue to recover in thickness after the repeated expansion and contraction of the electrode plates over the service life of such batteries. In describing the invention, certain embodiments have been used to illustrate the invention and the practices thereof. However, the invention is not limited to these specific embodiments as other embodiments and modifications within the spirit of the invention will readily occur to those skilled in the art on reading this specification. Thus, the invention is not intended to be limited to the specific embodiments disclosed, but is to be limited only by the claims appended hereto.

Claims: What is claimed is: 1. A resilient fibrous mat, comprising: a fibrous mat of microfibers having first and second major surfaces; said fibrous mat having a first fibrous layer, said first fibrous layer having a density, a tensile strength and a resilience; said fibrous mat having a second fibrous layer; said second fibrous layer having a density, a tensile strength and a resilience; said first major surface of said fibrous mat being an outer surface of said first fibrous layer; said density and said tensile strength of said first fibrous layer being greater than said density and said tensile strength of said second fibrous layer; said resilience of said second fibrous layer being greater than said resilience of said first fibrous layer; and said first and said second fibrous layers being integral. 2. The resilient fibrous mat according to claims 1, including: a third fibrous layer; said second major surface of said fibrous mat being an outer surface of said third fibrous layer; said third fibrous layer having a density and a tensile strength greater than said density and said tensile strength of said second fibrous layer; said resilience of said second fibrous layer being greater than a resilience of said third fibrous layer; said second fibrous layer being intermediate said first and said third fibrous layers; and said third fibrous layer being integral with said first and said second fibrous layers. 3. The resilient fibrous mat according to claim 2, wherein: microfibers in said first and said third fibrous layers are more entangled than microfibers in said second fibrous layer. 4. The resilient fibrous mat according to claim 3, wherein: said microfibers are glass microfibers. 5. The resilient fibrous mat according to claim 4, wherein: said fibrous mat is binderless. 6. The resilient fibrous mat according to claim 4, wherein: said fibrous mat weighs between about 50 and 450 grams per square meter. 7. The resilient fibrous mat according to claim 4, wherein: said microfibers of said fibrous mat have a mean diameter between about 0.5 and about 3 microns. 8. The resilient fibrous mat according to claim 3, wherein: said microfibers comprise glass microfibers and cellulose fibers. 9. The resilient fibrous mat according to claim 3, wherein: said microfibers comprise glass and polymeric microfibers. 10. The resilient fibrous mat according to claim 5, wherein: said fibrous mat weighs between about 75 and about 150 grams per square meter; and said microfibers have a mean diameter between about 0.5 and about 3 microns . 11. The resilient fibrous mat according to claim 5, wherein: said fibrous mat weighs between about 75 and about 150 grams per square meter; and said microfibers have a mean diameter between about 1 and about 2 microns. 12. The resilient fibrous mat according to claim 5, wherein: said fibrous mat weighs between about 75 and about 150 grams per square meter; and said microfibers have a mean diameter between about 1.2 and about 1.7 microns. 13. The resilient fibrous mat according to claim 2, wherein: said density of said first fibrous layer is greater than said density of said third fibrous layer. 14. The resilient fibrous mat according to claim 2, wherein: said fibrous mat comprises air laid microfibers and is a battery separator. 15. A method of making a resilient fibrous mat comprising: forming a fibrous blanket of entangled fibers; said fibrous blanket having a weight per unit of surface area, a density, a resilience and a tensile strength; said fibrous blanket having first and second major surfaces; passing said fibrous blanket between a first water jet and a first suction unit, opposite said first water jet, of a first water jet hydro entanglement apparatus; spraying water from said water jet into said first major surface of said blanket and simultaneously withdrawing water from said fibrous blanket with said suction unit through said second major surface of said blanket to further entangle said fibers at and adjacent said first major surface and form a first fibrous layer at said first major surface and a second fibrous layer integral with said first fibrous layer; said fibers in said first fibrous layer being more entangled than said fibers in said second fibrous layer; said first fibrous layer having a density and tensile strength greater than a density and tensile strength of said second fibrous layer; and said second fibrous layer having a resilience greater than a resilience of said first fibrous layer. 16. The method of making a resilient fibrous mat according to claim 15, including: passing said fibrous blanket between a second water jet and a second suction unit, opposite said second water jet, of a second water jet hydro entanglement apparatus; spraying water into said second major surface of said blanket with said second water jet and simultaneously withdrawing water from said fibrous blanket with said second suction unit through said first major surface of said blanket to further entangle said fibers at and adjacent said first major surface and form a third fibrous layer at said second major surface integral with said first and said second fibrous layers; said fibers in said third fibrous layer being more entangled than said fibers in said second fibrous layer; said third fibrous layer having a density and tensile strength greater than said density and tensile strength of said second fibrous layer; and said resilience of said second fibrous layer being greater than a resilience of said third fibrous layer. 17. The method of making a resilient fibrous mat according o claim 16, wherein: said density of said first fibrous layer s greater than said density of said third fibrous layer. 18. The method of making a resilient fibrous mat according o claim 16, including: needle punching said fibrous blanket prior to passing said fibrous blanket through said first water jet hydro entanglement apparatus to further entangle said fibers in said fibrous blanket and increase said tensile strength of said fibrous blanket. 19. The method of making a resilient fibrous mat according to claim 18, wherein: said density, resilience and tensile strength of said second fibrous layer are substantially equal to said density, resilience and tensile strength of a portion of said needle punched fibrous blanket made into said second fibrous layer. 20. The method of making a resilient fibrous mat according to claim 16, wherein: said fibrous blanket is formed by air laying microfibers to form said fibrous blanket. 21. The method of making a resilient fibrous mat according to claim 16, wherein: said fibrous blanket is formed by air laying a thin fibrous blanket layer and subsequently, successively air laying between one and five additional thin fibrous blanket layers directly on previously air laid thin fibrous blanket layers of said thin fibrous blanket layers. 22. The method of making a resilient fibrous mat according to claim 15, including: needle punching said fibrous blanket prior to passing said fibrous blanket through said first water jet hydro entanglement unit to further entangle said microfibers in said fibrous blanket and increase said tensile strength of said fibrous blanket. 23. The method of making a resilient fibrous mat according to claim 15, wherein: said fibers are microfibers and said fibrous blanket is formed by air laying said microfibers of said fibrous blanket. 24. The method of making a resilient fibrous mat according to claim 15, wherein: said fibrous blanket is formed by air laying a thin fibrous blanket layer and subsequently, successively air laying between one and five additional thin fibrous blanket layers directly on previously air laid thin fibrous blanket layers of said thin fibrous blanket layers. 25. The method of making a resilient fibrous mat according to claim 15, wherein: said density, resilience and tensile strength of said second fibrous layer are substantially equal to said density, resilience and tensile strength of a portion of said fibrous blanket made into said second fibrous layer. 26. The method of making a resilient fibrous mat according to claim 15, wherein: said fibers are glass microfibers. 27. The method of making a resilient fibrous mat according to claim 15, wherein: said fibrous blanket is binderless. 28. The method of making a resilient fibrous mat according to claim 15, wherein: said fibrous mat formed weighs between about 50 and 450 grams per square meter. 29. The method of making a resilient fibrous mat according to claim 15, wherein: said fibers of said fibrous mat formed have a mean diameter between about 0.5 and about 3 microns. 30. The method of making a resilient fibrous mat according to claim 15, wherein: said fibers comprise glass microfibers and cellulose fibers. 31. The method of making a resilient fibrous mat according to claim 15, wherein: said fibers comprise glass microfibers and polymeric microfibers. 32. The method of making a resilient fibrous mat according to claim 15, wherein: said fibrous mat formed weighs between about 75 and about 150 grams per square meter; and said fibers have a mean diameter between about 0.5 and about 3 microns. 33. The method of making a resilient fibrous mat according to claim 15, wherein: said fibrous mat formed weighs between about 75 and about 150 grams per square meter; and said fibers have a mean diameter between about l and about 2 microns. 34. The method of making a resilient fibrous mat according to claim 15, wherein: said fibrous mat formed weighs between about 75 and about 150 grams per square meter; and said fibers have a mean diameter between about 1.2 and about 1.7 microns. 35. In a starved electrolyte battery including a container in which is positioned at least one positive electrode plate; a least one negative electrode plate; a separator interposed between said positive and said negative electrode plates; an electrolyte absorbed in said positive and said negative electrode plates and said separator; a positive electrode lead joining said at least one positive electrode plate to a positive battery terminal; a negative electrode lead joining said at least one negative electrode plate to a negative battery terminal; the improvement comprising: said separator being a fibrous sheet of microfibers having first and second major surfaces; said fibrous sheet having a first fibrous layer; said first fibrous layer having a density, a tensile strength and a resilience; said fibrous sheet having a second fibrous layer; said second fibrous layer having a density, a tensile strength and a resilience; said first major surface of said fibrous sheet being an outer surface of said first fibrous layer; said density and said tensile strength of said first fibrous layer being greater than said density and said tensile strength of said second fibrous layer; said resilience of said second fibrous layer being greater than said resilience of said first fibrous layer; and said first and said second fibrous layers being integral whereby said density and said tensile strength of said first layer provide said separator with integrity and said resilience of said second fibrous layer allows said separator to undergo repeated compression and expansion, in a direction perpendicular to its major surfaces, when said electrode plates expand and contract during usage of said battery. 36. The starved electrolyte battery according to claims 35, wherein: said separator includes a third fibrous layer; said second major surface of said fibrous sheet being an outer surface of said third fibrous layer; said third fibrous layer having a density and a tensile strength greater than said density and said tensile strength of said second fibrous layer to provide said separator with additional integrity; said resilience of said second fibrous layer being greater than a resilience of said third fibrous layer; said second fibrous layer being intermediate said first and said third fibrous layers; and said third fibrous layer being integral with said first and said second fibrous layers. 37. The starved electrolyte battery according to claim 36, wherein: microfibers in said first and said third fibrous layers are more entangled than microfibers in said second fibrous layer. 38. The starved electrolyte battery according to claim 36, wherein: said microfibers are glass fibers. 39. The starved electrolyte battery according to claim 36, wherein: said fibrous sheet is binderless. 40. The starved electrolyte battery according to claim 36, wherein: said fibrous sheet weighs between about 50 and 450 grams per square meter . 41. The starved electrolyte battery according to claim 36, wherein: said microfibers of said fibrous sheet have a mean diameter between about 0.5 and about 3 microns. 42. The starved electrolyte battery according to claim 36, wherein: said microfibers comprise glass microfibers and cellulose fibers. 43. The starved electrolyte battery according to claim 36, wherein: said microfibers comprise glass microfibers and polymeric microfibers. 44. The starved electrolyte battery according to claim 36, wherein: said fibrous sheet weighs between about 75 and about 150 grams per square meter; and said microfibers have a mean diameter between about 0.5 and about 3 microns. 45. The sta- ved electrolyte battery according to claim 36, wherein: said fibrous sheet weighs between about 75 and about 150 grams per square meter; and said microfibers have a mean diameter between about 1 and about 2 microns. 46. The starved electrolyte battery according to claim 36, wherein: said fibrous sheet weighs between about 75 and about 150 grams per square meter; and said microfibers have a mean diameter between about 1.2 and about 1.7 microns. 47. The starved electrolyte battery according to claim 36, wherein: said density of said first fibrous layer is greater than said density of said third fibrous layer. 48. The starved electrolyte battery according to claim 35, wherein: said positive electrode plate and said negative electrode plate have opposing, spaced apart surfaces which are spaced a selected distance in said battery as assembled; and said separator having a thickness, when said separator is subjected to a loading of 1.5 psi, between about 110% and about 250% of said selected distance. 49. The starved electrolyte battery according to claim 35, wherein: said positive electrode plate and said negative electrode plate have opposing, spaced apart surfaces which are spaced a selected distance in said battery as assembled; and said separator having a thickness, when said separator is subjected to a loading of 1.5 psi, between about 120% and about 250% of said selected distance. 50. The starved electrolyte battery according to claim 35, wherein: said positive electrode plate and said negative electrode plate have opposing, spaced apart surfaces which are spaced a selected distance in said battery as assembled; and said separator having a thickness, when subjected to a loading of 1.5 psi, about equal to or greater than said selected distance. 51. The starved electrolyte battery according to claim 36, wherein: said positive electrode plate and said negative electrode plate have opposing, spaced apart surfaces which are spaced a selected distance in said battery as assembled; and said separator having a thickness when subjected to a loading of 1.5 psi, between about 110% and about 250% of said selected distance. 52. The starved electrolyte battery according to claim 36, wherein: said positive electrode plate and said negative electrode plate have opposing, spaced apart surfaces which are spaced a selected distance in said battery as assembled; and said separator having a thickness when subjected to a loading of 1.5 psi, between about 120% and about 250% of said selected distance. 53. The starved electrolyte battery according to claim 36, wherein: said positive electrode plate and said negative electrode plate have opposing, spaced apart surfaces which are spaced a selected distance in said battery as assembled; and said separator having a thickness when subjected to a loading of 1.5 psi, about equal to or greater than said selected distance. 54. The starved electrolyte battery according to claim 48, wherein: said separator extends beyond a periphery of said positive and negative electrode plates to form an extended electrolyte reservoir. 55. The starved electrolyte battery according to claim 51, wherein: said separator extends beyond a periphery of said positive and negative electrode plates to form an extended electrolyte reservoir. 56. In a starved electrolyte battery including a container in which is positioned at least one positive electrode plate; a least one negative electrode plate; a separator interposed between said positive and said negative electrode plates; an electrolyte absorbed in said positive and said negative electrode plates and said separator; a positive electrode lead joining said at least one positive electrode plate to a positive battery terminal; a negative electrode lead joining said at least one negative electrode plate to a negative battery terminal; the improvement comprising: said separator being a fibrous sheet of microfibers having first and second major surfaces in contact with said electrode plates and a resilience which allows said separator to maintain contact with said electrode plates while undergoing repeated compressions and expansions, in a direction perpendicular to its major surfaces, when said electrode plates expand and contract during usage of said battery. 57. The starved electrolyte battery according to claim 56, wherein: said positive electrode plate and said negative electrode plate have opposing, spaced apart surfaces which are spaced a selected distance in said battery as assembled; and said separator having a thickness when subjected to a loading of 1.5 psi, between about 110% and about 250% of said selected distance. 58. The starved electrolyte battery according to claim 57, wherein: said separator extends beyond a periphery of said positive and negative electrode plates to form an extended electrolyte reservoir. 59. The starved electrolyte battery according to claim 56, wherein: said positive electrode plate and said negative electrode plate have opposing, spaced apart surfaces which are spaced a selected distance in said battery as assembled; and said separator having a thickness when subjected to a loading of 1.5 psi, between about 120% and about 250% of said selected distance. 60. The starved electrolyte battery according to claim 48, wherein: said separator extends beyond a periphery of said positive and negative electrode plates to form an extended electrolyte reservoir. 61. The starved electrolyte battery according to claim 56, wherein: said fibrous sheet weighs between about 50 and 450 grams per square meter . 62. The starved electrolyte battery according to claim 56, wherein: said fibers of said fibrous sheet have a mean diameter between about 0.5 and about 3 microns. 63. The starved electrolyte battery according to claim 56, wherein: said fibers comprise glass microfibers and cellulose fibers. 64. The starved electrolyte battery according to claim 56, wherein: said fibers comprise glass microfibers and polymeric microfibers . 65. The starved electrolyte battery according to claim 56, wherein: said fibrous sheet weighs between about 75 and about 150 grams per square meter; and said fibers have a mean diameter between about 0.5 and about 3 microns. 66. The starved electrolyte battery according to claim 56, wherein: said fibrous sheet weighs between about 75 and about 150 grams per square meter; and said fibers have a mean diameter between about 1 and about 2 microns. 67. The star-zed electrolyte battery according to claim 56, wherein: said fibrous sheet weighs between about 75 and about 150 grams per square meter; and said fibers have a mean diameter between about 1.2 and about 1.7 microns. 68. A battery separator comprising: a fibrous air laid sheet of microfibers having first and second major surfaces for contacting major surfaces of electrode plates of a battery and a resilience which allows said separator to maintain contact with said electrode plates while undergoing repeated compressions and expansions, in a direction perpendicular to said major surfaces of said sheet, when said electrode plates expand and contrast during usage of said battery; said sheet having a thickness when subjected to a loading of 1.5 psi at least equal to a spacing between said electrode plates of said battery as assembled; and said sheet having a substantially uniform density across said thickness of said sheet. 69. The battery separator according to claim 68, wherein: said thickness of said sheet, when subjected to a loading of 1.5 psi, is between about 110% and about 250% of said spacing between said electrode plates. 70. The battery separator according to claim 68, wherein: said thickness of said sheet, when subjected to a loading of 1.5 psi, is between about 120% and about 250% of said spacing between said electrode plates. 71. The battery separator according to claim 68, wherein: said microfibers are glass microfibers. 72. The battery separator according to claim 68, wherein: said sheet is binderless. 73. The battery separator according to claim 68, wherein: said sheet weighs between about 50 and 450 grams per square meter; and said microfibers of said sheet have a mean diameter between about 0.5 and about 3 microns . 74. The battery separator according to claim 68, wherein: said microfibers comprise glass microfibers and cellulose fibers. 75. The battery separator according to claim 68, wherein: said microfibers comprise glass and polymeric microfibers. 76. The battery separator according to claim 68, wherein: said sheet weighs between about 75 and about 150 grams per square meter; and said microfibers have a mean diameter between about 1.2 and about 1.7 microns . 77. The battery separator according to claim 68, wherein: said microfibers are polymeric microfibers. 78. The resilient fibrous mat according to claim 3, wherein: said microfibers are polymeric microfibers. 79. The starved electrolyte battery according to claim 36, wherein: said microfibers are polymeric microfibers. 80. The starved electrolyte battery according to claim 56, wherein: said microfibers are polymeric microfibers.

Inventors: CUSICK MICHAEL JOHN, FORTE DON AUGUST, MARTIN PHILLIP CHARLES, RUMIESZ JOSEPH JR, CUSICK, MICHAEL, JOHN, FORTE, DON, AUGUST, MARTIN, PHILLIP, CHARLES, RUMIESZ, JOSEPH, JR.
Applicants: CUSICK MICHAEL JOHN, FORTE DON AUGUST, JOHNS MANVILLE INT INC, MARTIN PHILLIP CHARLES, RUMIESZ JOSEPH JR, CUSICK, MICHAEL, JOHN, FORTE, DON, AUGUST, JOHNS MANVILLE INTERNATIONAL, INC., MARTIN, PHILLIP, CHARLES, RUMIESZ, JOSEPH, JR.
Application year: 1997
Main classification: H01M2
IPC codes: D04H1, D04H3, D04H13, H01M2