HK1021591A - Glass fiber separators for batteries - Google Patents

Description

Glass fiber separator for batteries

Background

Technical Field

The present invention relates to the field of batteries, and more particularly to a glass fiber-containing separator disposed between an anode plate and a cathode plate of a battery, and a method of producing such a separator. As discussed in detail below, separators containing glass fibers are well known. But far before the glass fiber separator, the cedar board has been used as a separation material and replaced by a microporous hard rubber separator and a resin-impregnated cellulose separator.

Description of the Prior Art

Valve regulated ("sealed" - "recombinant") lead acid (VRLA) cells are well known, and typically include a plurality of anode and cathode plates (as in prismatic cells), or separator layers and anodes and cathodes wound together (as in "jelly-roll" cells). the arrangement of electrode plates should be alternating, negative-positive-negative, etc., with separator material and paste separating each electrode plate from an adjacent electrode plate. And generates pressure between the electrode plates.

The fiberglass separator material is typically produced using papermaking equipment including fourdrinier machines and rotary formers, inclined fourdrinier machines and extended wire rotary formers. In the production of a separator for a VRLA battery composed of glass fibers, it is preferable that no organic substance is added to the ingredients constituting the separator sheet; entanglement of the fibers is used to hold the separator in a polymeric structure, with water glass sometimes formed on the surface of the fibers being used as a binder. But the organic binder can reduce the ability of the separator to wick acid and reduce the amount of acid the separator can hold. Much work has been done on improving the formulations used to make glass fibers in an effort to improve the performance of the battery and/or reduce the cost of the separator. Some of these incorporate synthetic fibers for various reasons, such as the use of thermoformable plastic fibers to allow the separator to be heat sealed at its edges to encase the electrode plates. Other work that has been done in connection with the field of the present invention involves the use of fillers (e.g., silica) to provide separators that can be compared to all fiberglass separators at a lower cost. It has also been proposed to produce a separator from glass fibers to which cellulose is added and polyolefin fibers to which cellulose is added. Patents in the prior art are discussed below.

U.S. patent 4,465,748(Harris) discloses a sheet of fiberglass material for use as a separator in an electrochemical cell, the material being made from 5 to 33% by weight of fiberglass having a diameter of less than 1 μm; the patent also discloses glass fiber sheets for such applications, comprising fibers having a fiber diameter and length within a continuous range, with most of the fibers having a length not exceeding 5 mm.

U.S. patent 4,216,280(Kono et al) discloses a glass fiber sheet material for use as an electrode plate separator in a battery made from 50-95% by weight of glass fibers having a diameter of less than 1 μm and 50-5% by weight of coarser glass fibers. The reference teaches that the coarser glass fibers have a diameter greater than 5 μm, preferably greater than 10 μm, and most preferably some of the coarse fibers have a diameter of 10-30 μm.

U.S. patent 4,205,122(Minra et al) discloses a battery separator having reduced electrical resistance comprising a self-supporting, non-woven mat consisting essentially of a mixture of olefin resin fibers having a coarseness of 4 to 13decigrex and olefin resin fibers having a coarseness of less than 4decigrex, the latter fibers being present in an amount of not less than 3 parts by weight per 100 parts by weight of the fibers; up to about 600 parts by weight of inert filler may also be used per 100 parts by weight of fiber. A battery separator can be prepared by subjecting a suitable aqueous dispersion to a sheeting operation, drying the resulting wet nonwoven mat, and heat treating the dried mat at a temperature in the range of from 20 deg. below the melting point of the above-described fibers to about 50 deg. above the melting point.

U.S. patent 4,216,281 (O' Rell et al) discloses a separator material made from a furnish containing 30-70% by weight of a polyolefin composite slurry, 15-65% by weight of a siliceous filler and 1-35% by weight of "long" fibers which may be polyester fibers, glass fibers or a mixture of both. Cellulose may also be included as an optional component of the furnish in amounts up to about 10% by weight.

U.S. patent 4,363,856(Waterhouse) discloses a separator material made from a furnish including polyolefin pulp fibers and glass fibers, and suggests that polyester staple (staple) fibers, polyolefin staple fibers, and cellulose pulp fibers may be selected as optional components of the furnish.

Us patent 4,387,144 (mccalum) discloses a battery separator having a low electrical resistance after prolonged use, made by thermally consolidating and hot embossing a synthetic pulp furnish having microwires filled with an inorganic filler to form a paper substrate incorporating a wetting agent, preferably an organic sulfonate and an organic succinate, or an ethoxylated phenol.

U.S. patent 4,373,015(Peters et al) discloses sheets useful as battery separators, and "comprising organic polymer fibers"; both examples in this patent describe the sheet as an "about 0.3mm thick mat of short staple polyester and indicate that the polyester fibers have a diameter in the range of about 1 μm to 6 μm.

In us patent 4,529,677 (Bodendorf); 4,363,856 (Waterhouse); and 4,359,511(Strzempko) disclose sheet separators useful in conventional (not valved) batteries, including glass fibers and organic fibers.

U.S. patent 4,367,271(Hasegawa) discloses a battery separator consisting of up to about 10% by weight acrylic fibers and the balance glass fibers.

The separator material disclosed in Japanese patent document 55/146,872 comprises glass fibers (50-85% by weight) and organic fibers (50-15% by weight).

U.S. patent 4,245,013(Clegg et al) discloses a separator made by laminating a first sheet of fibrous material comprising polyethylene fibers and a second sheet of fibrous material comprising polyethylene fibers, the second sheet having a higher composite pulp content than the first sheet.

The separator disclosed in us patent 4,908,282(Badger) comprises a sheet made of first fibers having an absorbency greater than 90% and second fibers having an absorbency less than 80%, the amounts of the first and second fibers being such that the absorbency of the sheet is 75-95%. The patent discloses that fine glass fibers have a high absorption rate, coarse fibers have a low absorption rate, hydrophobic organic fibers have a very low absorption rate, and when the separator is saturated with electrolyte, unfilled voids are left, allowing gas to migrate from one electrode plate to another for recombination. The disclosure of Badger is incorporated herein by reference.

U.S. patent 5,091,275(Brecht et al) discloses that the glass fiber separator swells in the electrolyte. The separator comprises glass fibers impregnated with an aqueous solution of colloidal silica particles and a sulfate. The manufacturing method of the separator comprises the following steps: forming a paper web of glass fibers, impregnating the web with an aqueous mixture of said silica and salt, gently squeezing the web to remove some of the aqueous solution, partially drying the web, squeezing it to a final thickness, and completely drying the web. The thickness of the mesh is preferably extruded to be less than the distance between the electrode plates in a given cell to facilitate insertion of the assembled cell piece into the cell body. When electrolyte is added to the cell body, the salt dissolves in the electrolyte and the separator expands, providing good contact between the electrode plate and the separator. According to the invention, the silica contributes to the reconstitution properties of the battery with the pre-extruded separator. The silica also provides rigidity to the separator sufficient to make the separator rigid.

It is known that the production of battery separators from a furnish of glass fibers and silica powder using paper making techniques creates problems caused by variations in the concentration of silica powder in the furnish. Typical fiberglass formulations have a liquid content in excess of 98% by weight. During the production of the separator sheet, most of the water is removed from the furnish several feet from the beginning of the screen in which the furnish is cast. This water, called white water, circulates and spirals in the headbox of the machine. If the furnish consists only of glass fibers, substantially no fibers pass through the wire screen (wire) and are swirled in the white water. However, formulations comprising glass fibers and silica powder are not as good. Without retention aids, the silica powder in the furnish would be spun in the white water largely through the papermaking wire. Without being limited, this phenomenon can increase the silica concentration in the furnish, causing undesirable changes in the properties of the furnish. Hitherto, it has been the practice to avoid the problem of silica powder or the like passing through the wire of the papermaking by using a binder as a retention aid.

Us patent 2477,000 discloses the production of synthetic fiber paper from fine fibers and fibers made by extruding a fiber solution through very small orifices (spinning orifices) and then coagulating the extruded solution in a precipitation bath or by evaporating the solvent or temperature change to coagulate it (see column 2, line 25 below). The patent teaches that paper can be made using cellulose acetate, cellulose nitrate, cellulose regenerated from viscose, "Vinylite (a synthetic resin polymerized from vinyl compounds), Aralac (a fibrous product made from defatted milk casein) and glass fibers" (length in the range of 1/8 inches to 1 inch, diameter 12 to 80 microns), and fine fibers preferably from flax, Manila hemp, caroa or hemp. At least 90% of the fine fibers should be 0.0015 to 0.0025 inches long and 0.0000027 to 0.0000044 inches thick.

Brief description of the invention

The present invention is based on the discovery that if wood pulp is sufficiently pulped and refined to produce highly fibrillated cellulose fibers, a relatively small amount of wood pulp can be added to a glass fiber furnish suitable for use in the manufacture of battery separator materials, and the addition of a small amount of wood pulp can result in the addition of a relatively small amount of wood pulp

(1) The separator made from the formulation has surprisingly improved certain strength properties,

(2) the cutting resistance of the separator made of the formulation is improved,

(3) has unique characteristics in that the acid added thereto is retained in a large proportion when the separator is subsequently pressed.

In addition, the separator is repulpable, i.e., it can be used as a component of glass fiber in the production of "new" separators; also, a battery made with a glass fiber separator containing a small amount of already well pulped and refined wood pulp has a significantly extended service life as indicated by performance in its cycling test. Typically the slurry should be beaten or refined to a Canadian freeness of no more than about 650 cc. (or equivalent freeness by other measuring techniques), the tensile strength is significantly improved when the slurry is beaten or refined to a Canadian freeness of no greater than about 120cc (or equivalent freeness by other measuring techniques).

Brief description of the drawings

FIG. 1 is a graph of the% by weight of cellulose added to a glass fiber separator of the present invention as a function of the flow of air (liters/second) through the separator under the test conditions described below.

FIG. 2 is a graph of machine direction ("stretch, MD") and cross direction ("stretch, CD") tensile strength as a function of the percent by weight of cellulose incorporated in the glass fiber separator of the present invention.

Fig. 3 is a plot of% initial capacity versus number of test cycles for the cells of the invention and the control cells.

FIGS. 4-9 are thickness versus load (values plotted as 1000 times the thickness (mm) of the separator) and spring back thickness versus load for five fiberglass separator materials of the invention and a control material, wherein the spring back thickness is such that the load is reduced to 0.55 pounds per inch (lb/in) upon loading of the separator²(3.79KPa) 1000 times the thickness (mm) of the back baffle material; the data of fig. 4-9 are for dried separator materials.

Fig. 10-15 are graphs similar to fig. 4-9 showing the thickness versus load and the spring back thickness versus load for five glass fiber separator materials of the present invention and a control material, but prior to testing, each glass fiber separator material was wetted with sulfuric acid (specific gravity 1.286) equal to 7 times its weight.

Fig. 16 and 17 are similar to fig. 4 and 5, except that the former plots interpolated points such that successive points along the X-axis represent equal increases in cellulose content, while the latter plots experimental values, with the result that successive points along the X-axis do not always represent equal increases in cellulose content, as explained later.

Definitions herein, the term "% (volume)" means% by volume; the terms "% (by weight)" and% by symbol mean% by weight; the term "wire", when applied to a papermaking machine, refers to the machine surface on which the furnish is cast during the production of paper, and may be, for example, the screen of a fourdrinier machine or the vacuum drum of a rotary former; the pore diameters reported herein, unless otherwise indicated, are expressed in microns and are determined by first bubble method or liquid porosimeter (Coulter); all temperatures beingIs that; the following abbreviations have the following meanings: μ m = micron; mg = mg; g = gram; kg = kg; l = liter; ml = ml; cc = cm³(ii) a mm = mm; cm = cm; m = m; mil = inch × 10^-3(. times.25.4 converted to mm); KPa = N/m²×10³The pressure of (a); psi = pound/inch²(. times.6.89 conversion to KPa); KN = newton × 10³The force of (c).

Example 1

The ingredients were deposited on a wire mesh or screen on a laboratory setting, the water of the ingredients was drained, and a hand sheet of glass fiber separator was prepared. The apparatus comprises a tank having a screen at the bottom, a drainage basin under the screen, valves to open and close the drainage basin, and a manual paddle that moves back and forth to simulate the movement of furnish in an industrial papermaking apparatus and establish a "longitudinal direction" parallel to the direction of movement of the paddle. The furnish was prepared by charging acidified water (pH2.7), and solids comprising 74.5% by weight Schuller206 glass fibers (average fiber diameter 0.76 μm), 12.8% by weight Evanite610 glass fibers (nominal fiber diameter 2.6 μm), 12.8% by weight A20-BC-1/2 inch glass fibers (nominal fiber diameter 13 μm) in a tank, agitating for about 1 minute, charging additional kraft pulp in the tank, and agitating for an additional 2 minutes, the kraft pulp having a Canadian freeness of 57cc and a consistency of 1.235%. After addition to the pulp, the composition in the mixer contained 73 weight percent Schuller206 glass fibers, 12.5 weight percent Evanite610 glass fibers, 12.5 weight percent A20-BC-1/2 inch glass fibers, and 2 weight percent pulp fibrils. The furnish and pulp are agitated for about 2 minutes, after which time the valve is opened and water is drained through the screen while the screen is retained on the screen. The furnish contains sufficient glass fibers to produce a 0.15mm thick grammage (gram) of 30g/cm²The separator of (1). The manual pieces of separator were heated to about 150 ℃ for 30 minutes in a drying oven. Two separator sheets made as described above were tested and the data collected are listed below (data is the average after two sheets were tested). Frazier Permeability in L/scc/m in the data below and elsewhere herein²@20mmH₂And O represents. Publication in a method named BCI/RBSM Standard Test MethodsThe tests, instruments and equipment used to determine various properties in example 1 and elsewhere herein are described in (Batter Council International) (the disclosure of which is incorporated herein by reference). Gram number (g/m)²) 36.7 thickness, mm (under 10.34KPa load) 0.15 tensile strength, MD (Newton/m) 363 tensile strength, CD (Newton/m) 275 elongation, MD (percent of total length) 1.3 elongation, CD (percent of total length) 1.4 pore size-first bubble method,. mu.m 30Frazier permeability 98 pore size-liquid porosimeter, Coulter, μm

Minimum 5.1

Maximum 18.5

Average 5.5

The "Frazier permeability values reported herein are" determined using the Frazier permeability tester 91A (TAPPIT 2510M-85).

"capillary suction", reported above and below, was determined using the method described below in U.S. Pat. No. 7, 5,225,298, column 7, line 20, using water instead of the sulfuric acid used in the patent; this test is called the Japanese Industrial Standard method.

The composition of the Schuller206 glass fibers used in example 1 and subsequent examples sometimes varied slightly. The average values (% by weight) of the components calculated from the data provided by Schuller during the performance of the examples were as follows: SiO 2₂ 65.40 Na₂O 16.11A1₂O₃ 2.99 K₂O 0.69CaO 5.88 B₂O₃ 5.31MgO 2.79 F₂ 1.02

Schuller also notes that the glass contains less than 0.1% Fe₂O₃、TiO₂、ZrO₂、Cr₂O₃、SrO、BaO、MnO、ZnO、Li₂O、SO₃And Pb.

The nominal composition of the Evanite610 glass fibers used in example 1 and subsequent examples may vary within the following ranges (% (w/w)): SiO 2₂ 60.0-69.0Al₂O₃ 3.0-6.0CaO 5.0-7.0MgO 2.5-4.5Na₂O 8.0-12.0K₂O 0.5-3.0B₂O₃ ＜0.02F₂ 0.0-1.0ZnO ＜0.04Fe₂O₃ ＜0.02

A20-BC-1/2 inch glass fibers used in the above process and other processes described herein are commercially available from Schuller under the designation.

The glass fiber separator sheet of the present invention was made on a pilot plant paper machine by depositing furnish onto a forward moving wire through which water in the furnish was drained. The furnish was made in a mixer from acidified water (pH2.7) and solids comprising Schuller206 glass fibers, Schuller210X glass fibers (fibers of the same composition as 206 fibers having a nominal diameter of 3.0 μm), and A20-BC-1/2 inch glass fibers. The furnish was stirred in the mixer for about 1 minute, after which kraft pulp having a Canadian freeness of 57cc and a consistency of 1.235% was added to the furnish in the mixer. After the pulp was added, the composition in the mixer contained about 7 parts by weight of Schuller206 glass fibers, about 1 part by weight of each of Schuller210 glass fibers and A20-BC-1/2 inch glass fibers, and about 0.6 parts by weight of pulp fibrils. The furnish and the pulp were stirred for about 2 minutes, after which the furnish containing the pulp was fed into the headbox of the machine of the pilot plant. Then another 0.6 parts by weight of pulp fibrils of red wood pulp beaten to a Canadian freeness of less than 100cc are placed in the stock of the headbox and the resulting furnish is passed onto a forward moving wire to make a thickness of 0.15mm and 30g/m²Grams of separator. Finally the separator was heated to 150 ℃ in a drying oven for 30 minutes. The loss on ignition of the separator was slightly greater than 12% by weight, indicating a total pulp content of about 12% by weight). The method described in this paragraph constitutes the best mode contemplated by the inventors for producing the battery separator material of the present invention.

The cells of the invention were made using the separator material produced on the paper machine of the pilot plant as described above and life tested in comparison to cells using a conventional all glass separator but otherwise identical. The cell capacity after each cycle (as a percentage of the initial capacity) is listed in table i below (7 cycles after the test of the control cell was finished):

TABLE I

Number of cycles	Capacity,% of initial capacity inventive control
		1	113.5 103.6
2	115.6 93.6
		3	111.9 76.0
4	109.3 53.4
		5	107.4 34.0
6	105.3 25.1
		7	103.6 20.9
8	101.7 ***
		9	100.0 ***
10	98.6 ***
		11	97.2 ***
12	95.5 ***
		13	93.7 ***
14	90.1 ***
		15	87.6 ***
16	86.1 ***
		17	80.0 ***
18	74.9 ***
		19	74.0 ***
20	67.3 ***

The data in Table I is plotted in FIG. 3, which is a computerized plot of the cycle for the cells of the invention and comparative examples 1-7, with the data being entered, but the cycle data for comparative examples 8-20 being zero input.

Examples 2 to 6

Handmade sheets of glass fiber separators were also prepared from other furnishes containing varying amounts of kraft pulp beaten to a consistency of 0.9906% and Canadian freeness 57 cc. The furnish also contained Schuller206, 210X and A20-BC-1/2 inch glass fibers as previously described. Hand pieces can be made on laboratory equipment by depositing the furnish on a wire mesh or screen and draining the furnish. The apparatus comprises a tank with a screen at the bottom, a drainage basin under the screen, a valve to open and close the drainage basin, a manual stirring blade that moves back and forth to simulate the movement of the furnish in an industrial papermaking plant and to establish a "longitudinal direction" parallel to the direction of movement of the stirring blade. The furnish and pulp are agitated for about 2 minutes, after which time the valve is opened and water is drained through the screen while the screen is retained on the screen. The input batch contains enough glass fiber to prepare a 0.15mm thick product with a grammage of 30g/cm²The separator of (1). The manual plates of the separator were heated to about 150 ℃ for 30 minutes in a drying oven. The final composition of each typical formulation and the properties of the hand sheets prepared therefrom are given in Table II below, with the tensile strengths in pounds per inch of separator width (x 0.175 to kilonewtons per meter), the elongations in percent, the stiffness in mg "Gurley stiffness", the pore sizes in μm, and the electrical resistances in ohms/inch, unless otherwise indicated, and are reported in other tables and elsewhere herein²The weight percent loss on ignition of the separator was calculated. The composition of the ingredients is listed in the following table:

ingredient composition	Example 2	Example 3	Example 4	Example 5	Example 6
						210X	79	77	73	70	65
A20-BC1/2 inch fiber	10	10	10	10	10
						206	10	10	10	10	10
Cellulose, process for producing the same, and process for producing the same	1	3	7	10	15

TABLE II

Performance of	Example 2	Example 3	Example 4	Example 5	Example 6
						Gram number, gram/meter2	119.9	121.7	119.3	119.9	119.4
Thickness, mm (10.34KPa) (20KPa)	0.7650.726	0.8500.753	0.6530.644	0.6200.590	0.5910.570
						Tensile Strength, Newton/m MDCD	71.784.7	135.0117.8	135.7108.9	139.2125.4	149.5130.2
Elongation, percent MDCD	1.371.83	2.001.67	1.961.61	2.081.70	2.131.92
						Frazier Permeability	65.7	50.2	13.4	5.9	n.d.
Capillary suction second/10 mm	83	89	104	153	247
						Rigid, mg MDCD	38003100	39003500	52003900	43003500	32003000
Pore size-first bubble method (μm)	16.5	16.0	20.1	21.6	24.0
						Resistance (RC)	0.002	0.003	0.009	0.011	0.014
LOI％	3.3	5.2	9.0	12.5	18.1
						Pore size-liquid porosimeter Coulter, minimum and maximum average of μm	5.57042.248.875	5.38642.248.507	3.73426.075.753	2.62817.804.425	1.69712.433.497

In the above and subsequent tables, the "n.d." listed in the tables means not determined, in examples 6 and 11, because the porosity is too low to determine the Frazier permeability.

In the same manner, hand-made sheets of glass fiber separator were made from a furnish comprising 80 weight percent Schuller210X glass fibers, 10 weight percent A20-BC-1/2 inch glass fibers, and 10 weight percent Schuller206 glass fibers. The average test results for the two pairs of photographs are listed in table iii below:

TABLE III

Gram number, gram/meter2	117.1
		Thickness, mm (10.34KPa) (20KPa)	0.875g/m20.717g/m2
Tensile Strength, Newton/m MDCD	10.811.0
		Elongation, percent MDCD	0.701.21
Frazier Permeability	178.4
		Capillary suction second/10 mm	62
Rigid, mg MDCD	980655
		Pore size-first bubble method, μm	11.0
Pore size-liquid porosimeter Coulter, minimum and maximum average of μm	6.8665.9712.98
		Resistance (RC)	n.d.
LOI％	0.31

The thickness (mm). times.1000 of the hand sheets and the control photographs made in examples 2-6 were measured after production and after wetting with sulfuric acid (specific gravity 1.286) 7 times its dry weight under various loads. All thicknesses reported herein were determined using the method described in U.S. patent 5,336,275. Example numbers are listed in the table in table iv below, when the samples were just produced, under the applied load KPa indicated in the left column, the thicknesses are listed under the heading of an indicated example (the values listed are measured thicknesses (mm) × 1000).

TABLE IV

Applied load, KPa	Comparative example	Example 2	Example 3	Example 4	Example 5	Example 6
							3.79	38	36.5	31	28.5	26	27
6.06	35	30.5	26	25.5	23	22
							9.51	29.5	27.5	23	23.5	21	19.5
13.71	25.5	25.5	21	22.5	20	18.5
							17.57	22	23.5	20	21.5	19	17.5
23.98	20	22.5	18.5	20	19	17
							28.87	19	21.5	17.5	19.5	18	16.5
42.65	16.5	19	16.5	18.5	17	15.5

"rebound" thickness (in mm) x 1000 (thickness after removal of a load exceeding 3.79MPa or more from each "post-production" sample) is listed in table v, the columns indicating the applied load under the head, and the "rebound" of each sample under that load; the values reported are thickness (mm) x 1000 under the load (rebound) indicated in the left column of the table:

TABLE V

Applied load, KPa	Control	Example 2	Example 3	Example 4	Example 5	Example 6
							3.79	36	33.5	28.5	27.5	24.5	26.5
6.06	33.5	30.5	29	26.5	23.5	25.5
							9.51	31.5	29.5	27	25.5	22.5	26
13.71	29.5	28.5	25.5	25.5	22.5	26
							17.57	29.5	28.5	25	25.5	22.5	26
23.98	29	27.5	25	24.5	22.5	25
							28.87	28	27.5	25	24.5	22	23.5
42.65	27	27	24	24.5	22	23

The data in tables IV and V are shown in computer-generated FIGS. 4-9, where the load is expressed in psi and the points are equally spaced along the X-axis, representing 0.55psi (3.79KPa), 0.88psi (6.06KPa), 1.38psi (9.51KPa), 1.99psi (13.71KPa), 2.55psi (17.57KPa), 3.48psi (23.98KPa), 4.19psi (28.87KPa) and 6.19psi (42.65 KPa). Thus, FIGS. 4-9 are non-compliant, e.g., the distance between the first and second points represents a change from 0.55psi (3.79KPa) to 0.88psi (6.06KPa), while the same distance between the last two points represents a change from 4.19psi (28.87KPa) to 6.19psi (42.65 KPa). To represent the data for the photograph and example 2 in a more conventional graph, the thickness and rebound thickness at loads of 0.69psi (4.75KPa), 1.19psi (8.20KPa), 1.69psi (11.64KPa), 2.19psi (15.09KPa), 2.69psi (18.53KPa), 3.19psi (21.98KPa), 3.69psi (25.42KPa), 4.69psi (32.31KPa), 5.19psi (35.76KPa), and 5.69psi (39.20KPa) were calculated by interpolation from the experimental data. These data and test data (mm. times.1000) at 4.19psi (28.86KPa) and 6.19psi (42.65KPa) are set forth in tables VI and VII, respectively:

TABLE VI

Applied load, KPa	Thickness of comparative example	Example 2 thickness	Comparative example rebound	Example 2 rebound
					4.75	36.7	34
8.20	31.6	28.6	34.8	32
					11.64	28.0	26.7	32.3	30
15.09	24.3	24.8	30.5	29.6
					18.53	22.8	23.8	29.5	28.4
21.98	20.6	22.8	29.2	28.4
					25.42	20.3	22.7	28.7	27.5
28.86	30	22.5	28	27.5
					32.31	19.2	21.7	27.8	27.4
35.76	18.3	20.8	27.5	27.3
					39.20	17.4	20.2	27.3	27.2
42.65	16.5	19	27	27

The data of table vi is plotted in fig. 16 and 17, which are computer plots representing load using KPa. It can be seen that the shape of the curves of figures 16 and 17 are similar to the corresponding curves in figures 4 and 5, indicating that valid conclusions can be drawn from the non-compliant curves.

The thickness and rebound thickness were also determined for the separators of examples 2-6 and for the photographs after wetting the material with sulfuric acid of specific gravity 1.286. The applied load (KPa) is listed in the left column of Table VII below, with the thicknesses listed under the heads indicating the samples; the reported thickness is the measured separator thickness (mm) x 1000.

TABLE VII

Applied load, KPa	Comparative example	Example 2	Example 3	Example 4	Example 5	Example 6
							3.79	36	20.5	28	29	27.5	27.5
6.06	31.5	27	26	26	25	24.5
							9.51	28.5	24	23	24	22	22.5
13.91	26.5	22.5	21	22.5	20.5	20.5
							17.57	24	21.5	20	21.7	19.5	19
23.98	20.5	20.5	19	20	19	17.5
							28.87	19	19.5	18	19	18	16.5
42.65	17.5	17.5	16.5	17.5	16.5	15.5

"rebound" thickness (mm) (thickness after removal of a load of 3.79MPa or more from each sulfuric acid-wetted sample) is listed in Table VIII, the adjacent table values in the left hand column given the applied load, the "rebound" of each sample; the reported values are measured thickness (mm). times.1000.

TABLE VIII

Applied load, KPa	Control	Example 2	Example 3	Examples4	Example 5	Example 6
							6.06	32.5	27.5	26.5	27.5	27	25.5
9.51	31	25.5	25.5	26.5	25	24.5
							13.91	29	25.5	25	25	25	23.5
17.57	27.5	25.5	25	25	25	23.5
							23.98	24.5	24.5	24	25	24.5	23.5
28.87	24	24.5	24	25	24	22.5
							42.65	23.5	24.5	24	24.5	24.5	22.5

The data in tables VII and VIII are plotted in FIGS. 10-15, where the load is expressed in KPa. The data in tables IV, V, VII and VIII and FIGS. 4-15 show that the separator materials of examples 2-6 are sufficiently resilient that they can be compressed between the electrode plates of a lead acid battery with sufficient force to press their major surfaces against adjacent electrode plates for satisfactory operation of the battery.

Examples 7 to 11

Also following the procedure described in example 1, glass fiber separators were made from other furnish containing varying amounts of kraft pulp that had been beaten to a consistency of 0.9906% and a Canadian freeness of 57cc, and then soaked in latex (3% (w/w) solids). The final composition (% (w/w)) of the respective formulations is given in Table IX below, and the properties of the separators obtained from these formulations are given in Table X below, the thickness of the separator material being in mm:

TABLE IX

Ingredient composition	Example 7	Example 8	Example 9	Example 10	Example 11
						210X	79	77	73	70	65
A20-BC1/2 inch fiber	10	10	10	10	10
						206	10	10	10	10	10
Cellulose, process for producing the same, and process for producing the same	1	3	7	10	15

TABLE X

Performance of	Example 7	Fruit of Chinese wolfberryExample 8	Example 9	Example 10	Example 11
						Gram number, gram/meter2	121.6	121.9	127.5	123.1	122.7
Thickness, mm (10.34KPa) (20KPa)	0.7920.760	0.7780.745	0.7500.720	0.7420.698	0.6030.585
						Tensile Strength, Newton/m MDCD	93.080.6	120.6102.0	139.0122.0	152.3139.2	168.8158.5
Elongation, percent MDCD	1.81.5	2.32.1	1.92.0	2.32.1	1.92.0
						Frazier Permeability	8.97	5.08	1.39	0.918	n.d.
Capillary suction second/10 mm	225	184	253	261	391
						Rigid, mg MDCD	25002200	34002800	43003900	47003900	46003700
Pore size-first bubble method μm	16.8	16.1	19.4	20.5	25.4
						Pore size-liquid porosimeter Coulter, minimum and maximum average of μm	5.28346.549.550	4.72640.897.881	3.42727.525.839	2.28521.734.902	1.09211.882.920
LOI％	6.7	8.4	12.7	17.1	21.3

Examples 12 to 16

Other fiberglass separators were also made from the furnish of examples 7-11, consisting essentially of kraft pulp beaten to a consistency of 1.235% Canadian freeness 57cc, following the procedure described in example 1. The final composition (% (w/w)) of each batch is set forth in Table XI below, and the properties of the separator made from these batches are set forth in Table XII below, with the thickness of the separator material being in millimeters:

table XI

Ingredient composition	Example 12	Example 13	Example 14	Example 15	Example 16
						210X	77	79	791/4	791/2	793/4
A20-BC1/2 inch fiber	10	10	10	10	10
						206	10	10	10	10	10
Cellulose, process for producing the same, and process for producing the same	3	1	3/4	1/2	1/4

Table XII

Performance of	Example 12	Example 13	Example 14	Example 15	Example 16
						Gram number, gram/meter2	118.4	115.6	117.2	116.4	116.3
Thickness, mm (10.34KPa) (20KPa)	0.7570.662	0.7510.694	0.7780.716	0.7740.703	0.7970.722
						Tensile Strength, Newton/m MDCD	49.543.8	25.320.2	23.820.7	20.020.2	18.52.54
Elongation, percent MDCD	8.418.23	5.756.48	6.586.06	6.686.13	7.828.89
						Frazier Permeability	129.6	175.2	175.2	186.4	200.8
Capillary suction second/10 mm	74	76	72	67	62
						Specific surface area	0.6874	0.6114	0.6603	0.6513	0.7030
Corr.	9.9970	9.9962	9.9991	9.9962	9.9970
						Pore size-liquid porosimeter Coulter, minimum and maximum average of μm	6.05044.7110.65	5.94150.4912.04	7.05062.0812.32	6.49670.1312.59	7.58978.2612.17
LOI％	0.46	1.56	1.28	0.89	0.75

In the same manner, a control glass fiber separator was made from a furnish comprising 80 weight percent Schuller210X glass fibers, 10 weight percent A-20-BC-1/2 inch glass fibers, and 10 weight percent Schuller206 glass fibers. The average of the results of the two test specimens is set forth in Table XIII below, in which the thicknesses are expressed in millimeters:

TABLE XIII

Gram number, gram/meter2	113.7
		Thickness, mm (10.34KPa) (20KPa)	0.7420.600
Tensile Strength, Newton/m MDCD	10.111.0
		Elongation, percent MDCD	0.961.27
Frazier Permeability	222.4
		Capillary suction second/10 mm	62

Data for the Frazier permeabilities of tables X (examples 12-16) and XI (corresponding control panels) are plotted in FIG. 1, which is a computer-generated plot of Frazier permeability (referred to as CFM in the figure) versus cellulose content, noting that there are points on the X-axis of FIG. 1 at pulp levels of 1.25, 1.5, 1.75, 2.0, 2.25, 2.5, and 2.75%. Since there is no test data at these points, to enable the plot to show these points, the Frazier permeabilities for these pulp levels can be calculated by interpolating between the 1.0% and 3.0% test values. The experimental and calculated data input to plot fig. 2 are as follows:

percent by weight of cellulose Frazier Permeability

0.0 27.8

0.25 25.05

0.5 23.25

0.75 21.9

1.0 21.85

1.25 (Calculations) 21.14

1.5 (Calculation) 20.44

1.75 (Calculations) 19.73

2.0 (Calculation) 19.03

2.25 (Calculations) 18.32

2.5 (Calcd.) 17.61

2.75 (calculated) 16.91

3.016.2 tables XII and XIII the tensile strength data are plotted in FIG. 2. FIG. 2 is a computer plot of two tensile strengths (pounds per inch), one in the machine direction and the other in the cross direction, as a function of cellulose content. Note that in fig. 2, points with pulp contents of 1.25, 1.5, 1.75, 2.0, 2.25, 2.5, and 2.75% are present on the X-axis. Since there is no test data at these points, to enable the plot to show these points, the tensile strength in both directions for these pulp contents can be calculated by interpolating between the 1.0% and 3.0% test values. The experimental and calculated data input to plot fig. 2 are as follows:

cellulose% weight tensile Strength, MD (pounds per inch)

0.0 1.46

0.25 2.685

0.5 2.90

0.75 2.455

1.0 3.63

1.25 (Calculation) 4.07

1.5 (Calculation) 4.52

1.75 (Calculations) 4.96

2.0 (Calcd.) 5.41

2.25 (Calculation) 5.85

2.5 (Calculation) 6.29

2.75 (Calculation) 6.74

3.0 7.18

Cellulose% by weight tensile Strength, MD (pounds per inch)

0.0 1.55

0.25 2.54

0.5 2.72

0.75 3.005

1.0 2.93

1.25 (Calculation) 3.36

1.5 (Calculations) 3.79

1.75 (Calculation) 4.22

2.0 (Calcd.) 4.65

2.25 (Calculation) 5.07

2.5 (Calculations) 5.50

2.75 (Calcd.) 5.93

3.0 6.36

If the calculated data is not plotted, the computer-generated plot will move the point representing 3.0 wt.% pulp to the left of the point representing 1.25 wt.% causing the curves to sharply increase in tensile strength from 1.93 and 3.63 at 1.0% (w/w) to 6.36 and 7.10 at 3.0% (w/w), but the distance from 1.0-3.0 along the X-axis is the same as the distance from 0.75-1.0.

Examples 17 to 24

Other glass fiber separators were made from a furnish containing 35 parts by weight of 206 glass fibers, 65 parts by weight of 210 glass fibers, and about 1-2 parts by weight of kraft pulp that had been beaten to various Canadian freenesses, according to the method of example 1. The Canadian freeness of the individual formulations and the different properties of the separators produced therefrom are given in Table XIV below, in which the thicknesses are indicated in mm. Because of the small size of the sample and the lack of consistency in the furnish, loss on ignition ("LOI") of the hand sheet is the best indicator of the cellulose content of the furnish from which the sheet is produced. The loss on ignition of the cellulose free hand board was about 1/2%.

TABLE XIV

Performance of	Example 17	Example 18	Example 19	Example 20
					Canadian freeness	660	548	420	225
Gram number, g/m2	147	143	141	143
					Thickness, mm 10KPa20KPa50KPa	0.960.840.79	0.920.810.70	0.880.820.70	0.890.880.68
Average total tension in pounds per inch	1.8	2.3	2.3	1.9
					Average elongation%	2.2	2.4	2.8	2.1
Loss on ignition%	1.6	1.3	2.0	1.7
					Average tensile Strength, g/m2	0.0122	0.0161	0.0163	0.0133

TABLE XIV (continuation)

Performance of	Example 21	Example 22	Example 23	Example 24
					Canadian freeness	120	40	30	20
Gram number, g/m2	143	142	137	146
					Thickness, mm 10KPa20KPa50KPa	0.910.840.73	0.910.800.70	0.940.820.70	0.920.820.72
Average total tension in pounds per inch	2.4	2.5	3.0	4.5
					Average elongation%	2.2	2.3	2.3	2.5
Loss on ignition%	1.8	1.5	1.8	2.6
					Average tensile Strength, g/m2	0.0133	0.0176	0.0219	0.0308

Examples 25 to 32

Other glass fiber separators were made from a furnish containing 35 parts by weight of 206 glass fibers, 65 parts by weight of 210 parts by weight of glass fibers, and 3-5 parts by weight of kraft pulp that had been beaten to various Canadian freenesses, according to the method of example 1. The Canadian freeness of the individual batches and the different properties of the separators produced therefrom are given in Table XV below, in which the thicknesses are indicated in mm.

TABLE XV

Performance of	Example 25	Example 26	Example 27	Example 28
					Canadian freeness	660	548	420	225
Gram number, g/m2	148	144	138	141
					Average total tension in pounds per inch	2.6	3.0	2.7	2.8
Average elongation%	1.9	2.5	3.1	2.2
					Loss on ignition%	3.5	3.7	3.8	4.0
Average tensile Strength, g/m2	0.0176	0.0208	0.0196	0.0199

TABLE XV (continuation)

Performance of	Example 29	Example 30	Example 31	Example 32
					Canadian freeness	120	40	30	20
Gram number, g/m2	141	140	141	141
					Average total tension in pounds per inch	3.5	3.5	5.1	7.0
Average elongation%	1.9	2.0	2.1	2.0
					Loss on ignition%	4.5	3.6	3.6	4.1
Average tensile Strength, g/m2	0.0248	0.0250	0.0362	0.0496

Examples 33 to 40

Other glass fiber separators were made from a furnish containing 35 parts by weight of 206 glass fibers, 65 parts by weight of 210 parts by weight of glass fibers, and 9-11 parts by weight of kraft pulp that had been beaten to various Canadian freenesses, according to the method of example 1. The Canadian freeness of the individual formulations and the different properties of the separators produced therefrom are given in Table XVI below, in which the thicknesses are indicated in mm.

Table XVI

Performance of	Example 33	Example 34	Example 35	Example 36
					Canadian freeness	660	548	420	225
Gram number, g/m2	148	146	140	145
					Average total tension in pounds per inch	2.5	3.8	4.5	5.1
Average elongation%	2.1	2.1	2.1	2.0
					Loss on ignition%	11.3	11.5	8.7	10.0
Average tensile Strength, g/m2	0.0169	0.0261	0.0319	0.0364

Table XVI (continuation)

Performance of	Example 37	Example 38	Example 39	Example 40
					Canadian freeness	120	40	30	20
Gram number, g/m2	138	144	140	150
					Average total tension in pounds per inch	6.9	7.8	9.0	13.3
Average elongation%	2.0	2.3	1.8	2.2
					Loss on ignition%	12.0	10.6	11.5	11.0
Average tensile Strength, g/m2	0.0500	0.0542	0.0643	0.0887

As noted above, when the separator material of the present invention is prepared from pulp that has been beaten or refined to a Canadian freeness of not more than 120cc, the tensile strength is significantly improved. In examples 17 to 40The separator materials of the present invention were prepared from furnishes containing varying amounts of wood pulp refined to several different Canadian freenesses, and this improvement is demonstrated by the tensile strength data of these materials. In terms of average tensile strength in grams/meter²Data relating to Canadian freeness is plotted in the following graphs A, B and C. FIG. A is a graph showing data for examples 17-24; FIG. B is a graph showing data for examples 25-32; FIG. C is a graph showing data of examples 33 to 40.FIG. AFIG. BFIG. C

It has been found that the separator material prepared in each of the foregoing examples can be "repulped" in conventional papermaking equipment, either as the sole source of glass fibers and cellulose fibrils, or supplemented with additional glass fibers and cellulose fibrils, to produce a furnish that can be deposited on the moving wire of the papermaking equipment described above to produce a separator material. Thus, it is not necessary to discard any of the separator materials of the present invention, but rather, these separator materials can be recycled. Moreover, the separator material of the present invention has improved puncture strength (punch strength) over an otherwise identical separator material without cellulose fibrils, thereby improving the yield of acceptable lead acid batteries having expanded metal or continuous cast grids.

As explained above, a separator material comprised of first fibers that provide a separator absorption of greater than 90% and second fibers that provide a separator absorption of less than 80%, wherein the first and second fibers are present in a ratio such that the separator absorption is between 75-95%, and wherein when saturated with electrolyte, there are still unfilled voids that allow gas to migrate from one electrode plate to the other for reformation. According to the present invention, a separator material can be produced by adding a slurry of 0.2 to 20% by weight of cellulose fibrils to a slurry containing first fibers at a rate of absorption of the sheet of greater than 90% and second fibers at a rate of absorption of the sheet of less than 80% in a suitable proportion, the cellulose fibril slurry having a Canadian freeness sufficiently low that the separator material made from the resulting slurry has a tensile strength greater than that of an otherwise identical separator material having glass fibers with an average diameter of greater than 1 μm in place of the cellulose fibrils. Fibers that provide separator absorbency less than 80% preferably include relatively coarse glass fibers and hydrophobic organic fibers. Polyethylene, polypropylene, acrylic and polyester fibers are preferred examples of organic hydrophobic organic fibers.

The preferred separator of the present invention having an uptake (as defined by the above-listed Badger patents) of 75-95% and still having unfilled voids when saturated with electrolyte to allow gas to migrate from one electrode plate to another electrode plate for reformation, comprises 33.6 parts by weight Schuller206 glass fibers or equivalent fibers, 50.4 parts by weight Schuller210X glass fibers or equivalent fibers, 11 parts by weight Schuller ra20-BC1/2 inch glass fibers or equivalent fibers, and 5 parts by weight polyethylene fibers, and additionally 0.2-20% by weight cellulose fibrils from a slurry having a Canadian freeness sufficiently low to provide the separator material with a tensile strength greater than an otherwise identical separator having glass fibers with an average diameter greater than 1 μm in place of the cellulose fibrils.

It will be appreciated that various changes and modifications can be made to the invention as described above without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (13)

1. A glass fiber separator material comprising an assemblage of intermeshed glass fibers, substantially all of which have a diameter of no greater than about 20 μm, and at least 5% by weight of which have a diameter of less than 1 μm, and 0.2 to 20% by weight of cellulose fibrils dispersed within the glass fibers, the cellulose 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 having glass fibers with an average diameter greater than 1 μm in place of the cellulose fibrils.

2. A glass fiber separator material as claimed in claim 1 wherein said cellulose fibrils are impregnated with a solidified synthetic resin.

3. A glass fiber separator material as claimed in claim 2 wherein said solidified synthetic resin used to impregnate the cellulose fibrils is a solidified synthetic latex.

4. A glass fiber separator material as claimed in claim 1 wherein said cellulose fibrils are redwood fibrils or cedar fibrils.

5. A glass fiber separator material as claimed in claim 1 wherein said cellulose fibrils are derived from a slurry having a Canadian freeness of no more than 100 cc.

6. A glass fiber separator material as claimed in claim 1 wherein the cellulose fibrils adjacent one of the two opposed major surfaces are impregnated with the cured synthetic resin while the cellulose fibrils adjacent the other major surface are not so impregnated.

7. A glass fiber separator material as claimed in claim 5, wherein the solidified synthetic resin used to impregnate the cellulose fibrils is a solidified synthetic latex.

8. A glass fiber separator material as in claim 1 wherein the glass fiber aggregate further comprises hydrophobic synthetic fibers entangled with and inter-entangled with the glass fibers, the size distribution of the glass fibers and the ratio of glass fibers to synthetic fibers being such that said separator has 75 to 95 volume percent absorption of a sulfuric acid electrolyte.

9. A glass fiber separator material as claimed in claim 8 wherein said hydrophobic synthetic fibers comprise polyethylene fibers, polypropylene fibers, acrylic fibers or polyester fibers.

10. A glass fiber separator material comprising an assemblage of glass fibers intertwined with one another and from 0.2 to 20% by weight of cellulose fibrils dispersed within the glass fibers, substantially all of the glass fibers having a diameter of no more than about 20 μm, at least 5% by weight of the glass fibers having a diameter of less than 1 μm, the cellulose fibrils being derived from a slurry having a Canadian freeness low enough to provide a battery made from the separator which, when cycled, has a useful life at least 10% greater than that of an otherwise identical separator wherein the cellulose fibrils are replaced with glass fibers having an average diameter of greater than 1 μm.

11. A glass fiber separator material as claimed in claim 1 wherein there are also hydrophobic side-by-side or shell-core bicomponent fibers comprising polyethylene, polypropylene, acrylic or polyester materials.

12. A sealed lead/sulfuric acid recombinant battery comprising a plurality of lead electrode plates in a sealed housing, a fibrous sheet separator between adjacent ones of said electrode plates, a sulfuric acid electrolyte absorbed by said separator, the electrolyte remaining in contact with each of said adjacent electrode plates, each of said separator sheets comprising an assemblage of entangled glass fibers, and 0.2 to 20% by weight of cellulose fibrils dispersed in the glass fibers, substantially all of the glass fibers having a diameter of no greater than about 20 μm, at least 5% by weight of the glass fibers having a diameter of less than 1 μm, the cellulose 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 having glass fibers with an average diameter of greater than 1 μm in place of the cellulose fibrils.

13. A sealed lead/sulfuric acid recombinant storage battery comprising a plurality of lead electrode plates in a sealed case, a fibrous sheet separator between adjacent ones of said electrode plates, a sulfuric acid electrolyte absorbed by said separator, the electrolyte remaining in contact with each of said adjacent electrode plates, each of said separator sheets comprising an entangled glass fiber aggregate, and 0.2 to 20 weight percent cellulose fibrils dispersed in the glass fibers, substantially all of the glass fibers having a diameter no greater than about 20 microns and at least 5 weight percent of the glass fibers having a diameter less than 1 micron, the cellulose fibrils being from a slurry having a very low Canadian freeness, the freeness is low enough that a battery made from the separator, when cycled, has a useful life at least 10% longer than an otherwise identical separator having glass fibers with an average diameter greater than 1 μm in place of cellulose fibrils.