CA1138032A

CA1138032A - Polyolefin battery separator

Info

Publication number: CA1138032A
Application number: CA000334093A
Authority: CA
Inventors: Dennis D. O'rell; Vu Hien Nguyen; Nigel I. Palmer
Original assignee: WR Grace and Co
Current assignee: WR Grace and Co Conn
Priority date: 1978-08-21
Filing date: 1979-08-20
Publication date: 1982-12-21
Also published as: BE878363A; ES483487A1; GB2070092B; FR2435823B1; IT1120533B; SE7906868L; IT7950082A0; AU531071B2; GB2028887B; AU5014079A; JPS5530194A; GB2028887A; GB2070092A; AR227007A1; NL7906296A; FR2435823A1; DE2933103A1; BR7905359A; US4216281A

Abstract

99999999999+6 ABSTRACT
A battery separator is provided that has 30-70% polyolefin synthetic pulp, 15-65% siliceous filler and 1-35% by weight of long fibers having lengths of between 1/4 and 1 inch. The long fibers may be polyester fibers or glass fibers or a mixture. Cellulose may be included in an amount up to about 10%. A process for forming the battery separator is also revealed using standard paper making equipment but employing ionic copolymers contain-ing acrylamide in cationic and anionic combination to give good affinity of the siliceous material and polyolefin. Alum and other processing aids are also included as are other procedural steps such as pressing the web.

Description

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ack~round oE Invention_ Battery separators are porous diaphragms placed between the positive and negative plaLes of a battery so that the batteries eleotrolyte forms the sole internal conductive path between the positive and negative plates. It is generally considered desirable to employ separators which have the smallest pore size since this will retard the rate of active material from the battery plates penetration into and through the separator thereby causing shorting between the positive and negative plates.
Battery separators which are commonly used today in lead acid batteries are commonly composed of phenol-aldehyde impregnated cellulose sheets, sintered polyvinyl chloride or highly filled polyethylene. Separa-tors prepared from phenol-aldehyde impregnated cellulose sheets, as described for example in U.S. Patents 3,272,657 and 3,247,025 have been used extensively in lead acid batteries which had antimony as one component oE the grid alloy. Sintered polyvinyl chloride based separators have also been used extensively in batteries having lead-antimony alloyed grids. The development of maintenance free batteries based on grid alloys which do not contain antimony has required the development of a separator having a small pore structure, good chemical resistance to oxidative a~tack within the battery, good flexibility and capable of being heat sealed. Separators which meet the above criteria are described in U.S. Patents 3,351,495 and 4,024,323. Both of these patents describe battery separators which are composed of an ultra high molecular weight polyolefin, a siliceous filler and a petroleum oil and prepared by extruding the mixture of materials and then extracting most of the petroleum oil. Separators prepared in this fashion have maximum pore sizes of less than 1 micron, are typically 50-55% porous and also exhibit relatively low electrical resistance which is a desirable property. Phenol-aldehyde impregnated cellulosic webs have not been widely used with maintenance free , ~l~3~

batteries based on antimony Eree alloys because oE their relatively poor resistance to oxidatlve attack in the battery, their large pore size, their high electrical resistance and the Eact that they cannot be folded around the bottom of the plate and sealed on the sides.
German Offenlegungsschrift 2509823 described a battery separator composed of glass Eiber, thermoplastic polymeric Eibers and silica gell mater-ial which must be heated under specified pressure to yield the desired pro-duct. More specifically, the glass fibers in German Offenlegungsschrift 2509823 must have a diameter in the range of 0.007g" - 0.1S", a length in the range of 0.0039" - 0.160" and have an average length of 0.024"; the thermo-plastic polymeric fiber must have a diameter in the range of 0.20" - 1.18"
and a length in the range of 0.040" - 0.080"; the silica gel material must have a particle size of less than 10 microns and the ratio of glass fiber to polymeric fiber in the product must be in the range of 1:1.5 - 1:2.0 and the ratio of the sum of the fibers to silica gell material must be in the range of 1:0.5 - 1:1. Webs prepared according to such a formula tend to have less tensile strength than those of the present invention due to among other things the absence of fibers having lengths of 0.25" or greater and such prior art webs also tend to have low tear strengths. Webs of such prior art types are typically used in conjunction with stiff glassmats and are in Eact physically glued to the glassmats.
It is an object of the present invention to provide a fibrous battery separator.
It is another obiect of the present invention to provide a battery separator that can be prepared on a typical paper machine which has a significantly smaller maximum pore size than conventional cellulosic fiber based battery separator webs.
It is a further object of the present invention to provide a battery .
. ~ ' ~.~3~ 32 separator which ccm be prepared on a paper machine that has good flexibility so that it can be ~olded around the bottom of a lead battery plate without cracking.
It is yet another object of the present invention to provide a battery separator which can be prepared on a paper machine that can be sealed either by heat or ultrasonic welding.
It is another object of the present invention to provide a battery separator which can be prepared on a paper machine in which the ribs can be thermomolded onto the separator.
It is a further object of the present invention to provide a battery separator which can be prepared on a paper machine which has a tensile strength greater than 8.0 lbs./in. in the machine direction.
It is a further object of the present invention to provide an expedit-ious method for manufacturing the battery separator web of the present inven-tion economically.
According to a broad aspect of the present invention which achieves at least the broad object stated above there is provided a battery separator having a vacuum electrical resistance less than 20 milliohms square inch and comprising about 30 to about 70 weight percent polyolefin synthetic pulp fibers, about 15 to about 65 weight percent siliceous filler and about 1 to about 35 weight percent of long fibers having lengths of at least about 0.1 inch.
Preferably at least 1% of the long fibers are comprised of polyester or acrylic. In one preferred form of the battery separator the long fibers are comprised of 1 to 15% weight percent of polyester fibers and 0 to 35 weight percent of glass fibers. In a preferred form of the battery separator about ~ 3 .. ~ ' 0.5 to about lO weight percent cellulose is included. Preferably the poly-olefin ;s polyethylene and the siliceous filler is comprised of amorphous silica witil a specific surface area of at leas~ 100 m2/g, and the median pore si~e is less -than 10 microns and the maximum pore size is less than 27 microns.
In one preferred form the bat-tery separator contains about 0.02 to about 0.15 weight percent of ~ cationic copolymer containing acrylamide and about 0.02 to about 0.15 weight percent of an anionic copolymer containing acrylamide.
By another aspect of the invention there is provided a process for manufacturing a web comprised of polyolefin fibers and siliceous filler comprising forming an aqueous slurry composition comprising said polyolefin fibers ancl said siliceous filler, sequentially adding a cationic agent and an anionic agent to the slurry composition and then dewatering said composition.
The invention will now be described in greater detail and reference will be made to Figure l which is a schematic view of the laboratory roto-former paper making machine and related equipment used for practicing the process of the present invention.
Preferred Embodiment Unless otherwise stated, percents in this application are by weight based upon 100% end composition weight. Thus 10% by weight means that the component constitutes 10 wt. parts out of every 100 wt. parts of total com-position.
As stated above, the present invention is a battery separator having a vacuum electrical resistance less than 20 milliohms square inch and com-prising about 30 to about 70 weight percent polyolefin synthetic pulp ibers, about 15 to about 65 weight percent siliceous filler and about l to about 35 weight percent of long fibers having lengths of at least about 0.1 inch. '!

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By synthetic pulp it is meant a short polyolefin based predominantly fibro~ls mater:ial having fiber size and shape similar to cellulosic wood pulps. For example the fiber lengths typically average 1 to 4 millimeters for ,~,,. ,y -4a-~.~3~

synthetic pulp and 0.5 to 5 mlllimeters for wood pulp. Fiber lengt'ns are measured according to TAPPI standard T232.
The polyolefin synthetic pulp is preEerably a polyethylene or poly-propylene synthetic pulp, more preEerably a polyethylene synthetic pulp.
Such synthetic pulps are described in a number of U.S. Patents lncluding numbers 3,743,272; 3,891,499; 3,902,957; 3,920,508; 3,9379139; 3,997,64~;
~,007,247 and 3,995,001. The preferred polyethy]ene is desirably a low pressure polyethylene having a viscosity average molecular weight range of 20,000 to 2,000,000 as described in U.S. Patent 3,920,508 column 8, lines 21-31 and 39-51. The synthetic pulp fibers may optionally contain a water dispersing agent. It has been found in the present invention, that the most preferred synthetic pulps are those having the highest degree of branching or fibrillation. Polyolefin fibers of the above type are commercial products.
The siliceous filler is preferably an amorphous si]ica having a particle size in the range of about 0.01 microns to about 20 microns, more preferably in the range of about 1 to about 15 microns; a surface area in the range from about 30 to 950 sq. meters per gram and preferably greater than about 100 meters per gram, and a pore volume of greater than about 0.75 cc per gram. Other fillers which meet the above criteria are diatomaceous earths.
The preferred long fibers are polyester, glass and acrylic, more preferably polyester and glass and most preferably polyester with polyethylene terephthalate being preferred.
rne polyester and acrylic fiber are preferably typical paper making staple fiber having a denier ranging from about 1.5 to about 12 and a length ranging from about 0.25 inches -to about 1.0 inch. These fibers tend to be circular in cross sectional shape, and have smooth surfaces in contrast to the polyolefin fibers described earlier which have an irregular cross sectional ~L~3~

shape and have higilly flbrillated surfaces. These fibers mP~y optlonally have on their surface a surfactant to aid their dispersion in water.
The glass Eiber should have good chen~ical resistance in sulfuric acid as evidenced by low weight loss on extended exposure to hot sulfuric acid. Glass which has good chemical resistance will typically lose less than about 2% of its weight after 7 days of exposure to 1.265 sp. gr. sulfuric acid maintained at 180F.
The diameter of the glass fiber may range from about 1 to about 7 microns, but preferably will range from about 5 to about 7 microns and have a length in the range from about 0.1 inch to about 1.0 inch but preferably from about 0.25 inch to about 0.5 inch. The glass may optionally be treated with a surfactant to improve its water dispersability prior to being used in the present invention.
The cellu]osic fibers may be any conventional paper making fibers.
The preferred fibers would be those prepared by conventional chemical pulping procedures.
In the present invention it has been found desirable to emp]oy low levels of alum (aluminum sulfate) to reduce the pH of the water in the hydro-pulper and chest prior to forming the web on the paper machine to improve -the dispersion of the fibers and filler and also to improve the efficiency of the retention aids. Alum is defined here to be any paper making grade of aluminum sulfate which is preferably available in granular form.
In the present invention, it has been found desirable to use reten~
tion aids LO improve the rate at which the siliceous filler is retained in the web during the paper making operation. It has been particularly advantage-ous to use a two component retention aid system, wherein each is added separately and at some distance apart from each other. Retention aids which have been particularly useful in the present invention are those based on ~ 13~ Z

cationically or anioTlically modi~ied high molecular weigl-t polyacrylamides.
Prefcrably the cationic agent is added first. The retention aids are prefer-ably used at levels ranging from about 0.01 weight percent to about 1.0 weight percent based on the weight of the solids in the slurry formed during pro-cessing to form the web. The preferred range i5 O. 0~ to 0.75 weight percent.
Preferably the cationic copolymer is added in an amount ranging from 0.01 to 0.50% and more preferably 0.02 to 0.15%. The anionic copolymer is preferably added at the same rate. The residual ionic agent content in the battery separator is preferably 0.02 to 1.0%, more preferably 0.01 to 0.15% of cationic copolymer containing acry~amide and 0.01 to 0.15% of anionic copolymer containing acrylamide.
Other aids such as wet strength resins and the like are also usable and within the broad purview of the invention.
The battery separator preferably has a median pore size of less than 10 microns and a maximum pore size of less than 27 microns.
The vacuum electrical resistance is less than 20 milliohms . square inch.
The electrical resistance of the battery separator of the present invention may be improved by treatment with surfactants such as bis ~alkyl) sulfoserccinate monovalent salts, aryl nonionic surfactants such as alkylaryl polyethylene glycol, alkyl polyethylene glycol, polyethylene propylene glycols, and other surfactants which have been used by those skilled in lead acid battery development. The level of surfactant employed may range from trace amounts up to about 1% by weight. The specific level used will depend upon the specified surfactant, but is in practice limited to those levels which do not have any adverse effect on battery performance or battery life.
The laboratory rotoformer paper making machine used in the Examples is depicted in Figure 1. A full size scale-up onto a Fourdrinier machine has also been carried out without difficulty in plant trials. ~ne difference in operation in the plant trials is that the siliceous filler was added to the pulper in its shipping bags. This eliminated dust and provided the cellulosic fiber, calculated at about 2% of a final web weight basis.
The paper machine of Figure 1 has a pulper 10, a transfer pump 12 in a transfer line 13 and chest 140 The chest 14 is emptied by transfer line 15 by pump 16. Part of the material in transfer line 15 is recirculated via inlet 17 to chest 14 and the o~her part passes through the metering stuff gate 18 into a dilution box 20. The cationic agen-t metering device 21 is between the stuff gate 18 and the dilution box 20. The anionic agent metering device 22 is about 3 feet downstream in the dilution box 20 which is about 5 feet long. The diluting water is fed into the dilution tank at 23.
The diluted slurry is pumped by pump 24 from the dilution box via transfer line 25 into the head box 26. The rotorformer drum 27 rotates in -the head box picking up the slurry and forming a web. Two vacuum boxes 28 and 29 are present. A lump breaker 30 opposite drum 27 is provided for optional use.
The web is removed from the rotoformer drum 27 and passed over a felt 31. Calendar means 32 and 33 are associated with the felt conveying ~c~,c/5 means for optionally pressing the web. The felt conveying means 31 ~4ed an oven 34 which feeds onto a first heated can 35. There are 7 heated cans 35, 36, 37, 38, 39, 40 and 41 in sequence. An 8th can 42 is not heated. The cans feed to a wind-up station ~3.
Process Turning now to the process for manufacturing the battery separator of the present invention. An aqueous slurry composition comprised of the polyolefin fibers and the s:iliceous filler and an ionic agent is prepared.
The slurry composition preferably is comprised of 30 to 70% of polyolefin fibers as a synthetic pulp and 15 to 65% of a siliceous filler that includes 3~

an amorphous silica. ~n preEerred ~orms glass and cellulosic fibers are added to the aqueous slurry.
The preEerred ionic agent added to the slurry is comprised of a cationic copolymer containing acrylamide and an anionic copolymer containing acrylamide. Preferably the polyolefin fibers and siliceous filler are slurr-ied first followed by the addition of the cationic copolymer which is followed by the addition of anionic copolymer. The cationic copolymer is preferably metered into the slurry on an end product slurry solids weight basis in an amount ranging from 0.01 to 0.50, more preferably 0.02 to 0.15, weight percent and the anionic copolymer is an amount from 0.01 to 0.50, more preferably 0.02 to 0.15 weight percent.
Preferably alum is also added to the aqueous slurry composition in an amount ranging from about 1 to about 5%.
The process also preferably includes pressing the composition to reduce pore size. Preferably the composition is pressed at a temperature of less than 220 F.

A pulp was formed in a pulper by charging 1000 lbs. of water to the pulper followed by 37.6 lbs. of short fibered synthetic polyolefin pulp with average length of 1 mm, cross section area on the order of a few square microns and specific surface area on the order of 10 m /g. polyethylene fibers (tPULPEX A product of Solvay & Cie). This was pulped for about 25 ~ 5 minutes. Then 36 lbs. of siliceous filler, amorphous silica (~i Sil 233 pro-duct of PPG Industries) was added. The filler was wet down before addition to provide dust reduction.
After the silica was added the pulper was operated Eor an additional 5 or 10 minutes to mix well. Then 800 lbs. of additional water was added to aid in more complete mixing and to flush out the pulper.

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_ 9_ The pulper contents were tra~sferred to the chest of a laboratory rotoformer paper machine. Then 6.4 lbs. of long fibers were added. The long ~ibers were polyethylene terephthalate staple fihers 1.5 denier x ]/4" supplied by Minifibers, Inc. Thereafter about 5500 lbs. of water was added. Next 1.6 lbs. of ground paper makers alum (alum sulfate iron free ground product of DuPont) was added to adjust the pH to 4.5 to 5.5. After thorough mixing and dissolving of the alum the slurry was allowed to stand for about 1 hour. Then the aqueous slurry was transferred from the chest to a dilution box just up-stream of the headbox. The rate of transfer by pumping was set to yield a web having a grammage of 120g/m .
The mix was diluted with water in the dilution box to about .06 weight percent solids. A cationic copolymer containing acrylamide (RETEN
210~ a product of Hercules Inc.) was metered in at the stuff gate9 which is where the chest flurry from the flows into the mixing box, at a concentration of .04% in water at 800 ml/minute. An anionic copolymer containing acrylamide (RETEN 421~ a product of Hercules, Inc.) was metered into the mix box about 3 feet downstream of its 5 foot length at a concentration of .025% in water at 800 ml/minute. The ionic copolymers containing acrylamide functioned as retention aids causing the silica filler to become associated with the synthetic pulp present in the aqueous slurry.
This diluted mix was then transferred to the head box where the web is formed on the rotoformer. While on the rotoformer a lump breaker roll operated at 80 psi to smooth out the top surface of the web. The wire of the rotoformer travelled at a rate of 15 feet/minute.
After leaving the rotoformer and while still resting on a moving belt the web was pressed by opposing hard rolls to reduce the caliper and pore size and increase the strength of the web. The caliper or thickness was reduced to 14 mils.

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The web was then trans~erred from the wire to an open mesh meta]
belt and passed through an oven where it was dried to a water content of about lO lbs. of water for every 10 lbs. of solid web. It was not necessary to heat the oven.
From the oven the web was transferred to steam cans (drums having circumferences of about 12 feet~ operated at surface temperatures of about 270 F and substantially completely dried on the first three cans. The web was then passed over four more cans also operated at surface temperatures of about 270F and the fiber bonding increased. It is believed this bonding is by some melting of the polyolefin fibers at the fiber junctions. Rubbing of the web with the finger nail showed increased web integrity.
The web was then wound up and afterwards cut to desired separator sizes.

The procedure of Example 1 was carried out except as follows: 42 lbs. of the synthetic pulp, 38 lbs. of the filler and 10 lbs. of the long fiber were used. In addition 10 lbs. of cellulose (bleached sulfite pulp with average fiber length of 2.2mm, a product of Rayonier, Inc.) were added with the synthetic pulp and 4 lbs. of wet strength resi~ ymene 557 H, a product of Hercules, Inc.) was added to the chest after the long fibers. The alum and the ionic copolymers containing acrylamide were omitted. The rate of transfer to the dilution box was set to yield a grammage of 115 gr/m . The web was pressPd to a caliper of 12 mils.

The procedure of Example 2 was carried out except as follows: 24 lbs. of the synthetic pulp, 30 lbs. of the filler, 6 lbs. of the long fiber, 3 lbs. of the cellulose and 2.4 lbs. of the web strength resin were used. The rate of transfer to the dilution box was set to yield a grammage of 120 g/m .
~r ~ J~ 1, k ~?~.3~f;g3~2 The web was pressed to a callper of 13 mi]s.

The procedure of Example 3 was carried out except as follows: 90 lbs. of the synthetic pulp, 50 lbs. of filler, 6 lbs. of the long fiber, 24 lbs. of the cellulose, 8 lbs. of the wet strength resin and 4 lbs. of the alum of Example l were used. The filler was composed oE 20 lbs. of the amor-phous silica and 30 lbs. of diatomaceous earch (~Celite 266 a product of Johns-Manville), 30 lbs. of glass fiber ~Tempstran D a product of John-Manville with diameter of 5.1 to 6.4 mlcrons and an average length of l/4 in) was added into the chest right before or after the polyester long fiber. The rate of trans-fer to the dilution box was set to yield a grammage of 185 ~/m2. The wet web was not pressed so as to maintain a higher caliper and hence stiffness. The webs increased thickness imparted by the glass fiber necessitated heating the oven to 400 F to reduce the water content to about 5 lbsOof water for every lO lbSDof solid web.
EX~MPLE 5 The procedure of Example 4 was carried out except as follows:
100 lbs. of synthetic pulp, 55 lbs. of the filler of Example 1, 15 lbs. of the long fiber, 30 lbs. of the glass fiber, 8 lbs. of the wet strength resin and 4 lbs. of the alum were used. The cellulose was omitted. The rate of transfer to the dilution box was set to yield a grammage of 174 g/m .

The procedure of Example 3 was carried out except as follows: 4~
lbs. of synthetic pulp, and 42 lbs. of the filler, lO lbs. of the long fiber, 4 lbs. of the wet strength resin and 2 lbs. of the alum of Example l were used. The cellulose was omitted. The rate of transfer to the dilution box was set to yield a web with a grammage of 126 g/m2. The web was pressed to a caliper of 14 mils.
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EXA~LE 7 The procedure of Example 4 was carried ou~ except as follows: 30 lbs. of the synthetic pulp, 15 lbs. of the diatomaceous earth of Example 4 and 15 lbs. of the cellulose were used. The polyester long fiber and the glass long fiber arld the wet strength resin and alum were omitted. The rate of transfer to the dilution box was set to yield a web with a grammage of 144 g/m .

The procedure oE Example 4 was carried out except as follows: 50 lbs. of synthetic pulp, 20 lbs. of the filler of Example 7, 15 lbs. of the cellulose, and 5 lbs. of glass fiber were used. The synthetic pulp was S ~ grade R-790 a product of Crown-Zellerbach Corporation, the average fiber length was 1.6 mm. The polyester fiber and the wet strength resin and alum were omitted. The rate of transfer to the dilution box was set to yield a grammage of 145 g/m .

The procedure of Example 4 was carried out except as follows: 36 lbs. of the synthetic pulp, 9 lbs. of the filler and 15 lbs. of the cellulose were used. The polyester long fiber, the glass fiDer and the wet strength resin and alum were omitted. The rate of transfer was set to yield a grammage of 145 g/m .
E ~PLE lO
The procedure of Example 4 was carried out except as follows: 30 lbs. of the synthetic pulp, 7.5 lbs. of the silica of Example 1, 11.25 lbs.
of the diatomaceous earth of Example 4, 1 lb. of cellulose, 3 lbs. of the wet strength resin and l 1/2 lbs. of alum were used. The rate of transfer was set to yield a grammage of 167 g/m .
The battery separator produced by the above methods were tested and 3~1.3~332 the results are tabulated in Table 1. The percentages of the constituents listed in the fumish equal 100% and ignore the small, several percent, of residual processing aids and the like added during processing.
The testing used in establishing the value in Table 1 was carried out as follows:
Tensile - A Scott Tester using a sample width of l inch and a 2 inch jaw separation, and a cross head speed of 12"/min.
Puncture - Standard battery industry testing procedure.
Stiffness - Gurley stiffness tester.
Tear - Elmendorf tear tester.
Densometer - Gurley Densometer.
Maximum Pore Size - Bubble test ASTM F316-70.
Acid wt. loss - a piece of web was weighed and then placed in 1.265 specific gravity sulfonic acid and boiled for 3 hours and then weighed again.

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Table 1 illustrates a number of points among them:
1) Any formulatiGns with cellulosic contents exceeding 10% would have an acid weight loss greater than 10% which is no~ desirable.

2) In cases where there is no long fiber in the formulation e.g.
polyester or glass fiber, such as in Example 7, the tear strength was low.

3) For the same grammage, formulations wlth higher silica levels have lower electrical resistances.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A battery separator having a vacuum electrical resistance less than 20 milliohms square inch and comprising about 30 to about 70 weight percent polyoelfin synthetic pulp fibers, about 15 to about 65 weight percent siliceous filler and about 1 to about 35 weight percent of long fibers having lengths of at least about 0.1 inch.

2. The battery separator of claim 1 wherein at least 1 weight % of said long fibers are comprised of polyester or acrylic.

3. The battery separator of claim 1 wherein said long fibers are comprised of 1 to 15 weight percent of polyester fibers and 0 to 35 weight percent of glass fibers.

4. The battery separator of claim 3 wherein about 0.5 to about 10 weight percent cellulose is included.

5. The battery separator of claim 3 wherein said polyolefin is comprised of polyethylene.

6. The battery separator of claim 1 wherein said siliceous filler is comprised of amorphous silica with a specific surface area of at least 100 m2/g.

7. The battery separator of claim 1 wherein the median pore size is less than 10 microns.

8. The battery separator of claim 1 wherein the maximum pore size is less than 27 microns.

9. The battery separator of claim 1 comprising about 0.01 to about 1 weight percent ionic agent and about l to about 5 weight percent alum.

10. The battery separator of claim l wherein the long fibers include 3 to 10 weight percent of polyester fibers with deniers of about 1.5 to about 6.0 and lengths of about 0.25 to about 1 inch and 0 to 35 weight percent of glass fibers, 1 to 5 weight percent cellulose, the siliceous filler comprises silica having particle sizes of about 1 to about 15 microns and a surface area of at least 100 m2/g, the median pore size is less than 10 microns and the polyolefin fibers are at least partially melt bonded.

11. The battery separator of claim 10 comprising about 0.02 to about 0.15 weight percent of a cationic copolymer containing acrylamide and about 0.02 to about 0.15 weight percent of an anionic copolymer containing acrylamide.

12. The battery separator of claim 10 wherein said polyester fibers have lengths of 0.25 to 0.5 inch.

13. A lead acid battery separator having a vacuum electrical resistance less than 20 milliohms square inch and comprising about 30 to about 70 weight percent of a fiberous polyolefin synthetic pulp, about 15 to about 65 weight percent of a particulate siliceous filler having a particle size of about 0.01 to about 20 microns and about 1 to about 35 weight percent of long paper making staple fiber having a length of at least about 0.25 inch, a denier of about 1.5 to about 12 and chosen from the group consisting of polyethylene terephthalate polyester fibers, acrylic fibers and mixtures thereof.

14. The lead acid battery separator of claim 13 wherein said polyolefin is polyethylene and at least some of the fibers or the polyethylene synthetic pulp are at least partially melt bonded and said long fibers include glass fibers having a diameter of about 1 to about 7 microns with a combined long fiber upper limit in said battery separator of about 35 weight percent.

15. The lead acid battery separator of claim 14 comprising about 0.5 to about 10 weight percent cellulosic fiber and wherein at least 1 weight percent of said long paper making staple fiber is comprised of polyethylene tereph-thalate polyester and said synthetic pulp has an average fiber length of about 1 to about 4 millimeters.

16. A process for manufacturing a web comprised of polyolefin fibers and siliceous filler comprising forming an aqueous slurry composition comprising said polyolefin fibers and said siliceous filler, sequentially adding a cationic agent and an anionic agent to the slurry composition and then de-watering said composition.

17. The process of claim 16 wherein said slurry composition on a solids weight basis includes about 30 to about 70 weight percent of said polyolefin fibers as a synthetic pulp and about 15 to about 65 weight percent of said siliceous filler, which filler includes amorphous silica.

18. The process of claim 16 wherein said cationic agent is a cationic copolymer containing acrylamide, and said anionic agent is an anionic copoly-mer containing acrylamide.

19. The process of claim 18 wherein on a solids weight basis said cationic copolymer is added in an amount ranging from about 0.01 to about 0-50 weight percent and said anionic copolymer is added in an amount ranging from about 0.01 to about 0.50 weight percent.

20. The process of claim 18 wherein on a solids weight basis said cationic copolymer is added in an amount ranging from about 0.02 to about 0.15 weight percent and said anionic copolymer is added in an amount ranging from about 0.02 to about 0.15 weight percent.

21. The process of claim 16 wherein on a total composition solids weight basis alum is added to said aqueous slurry composition in an amount ranging from about 1 to about 5 weight percent.

22. The process of claim 16 comprising drying the dewatered composition and then heating said dried composition sufficiently to at least partially heat bond said polyolefin fibers.

23. The process of claim 16 wherein said composition is pressed to reduce the pore size.

24. The process of claim 23 wherein said composition is pressed at a temperature of less than 220°F and glass fibers and cellulosic fibers are added to the aqueous slurry.