CA1168699A - Acicular mineral material battery separator for lead-acid batteries - Google Patents
Acicular mineral material battery separator for lead-acid batteriesInfo
- Publication number
- CA1168699A CA1168699A CA000376220A CA376220A CA1168699A CA 1168699 A CA1168699 A CA 1168699A CA 000376220 A CA000376220 A CA 000376220A CA 376220 A CA376220 A CA 376220A CA 1168699 A CA1168699 A CA 1168699A
- Authority
- CA
- Canada
- Prior art keywords
- percent
- battery separator
- weight
- web material
- absorption
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/446—Composite material consisting of a mixture of organic and inorganic materials
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2300/00—Electrolytes
- H01M2300/0002—Aqueous electrolytes
- H01M2300/0005—Acid electrolytes
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
Abstract Battery separators are provided for maintenance-free lead-acid batteries. From 10 to 90 percent by weight of the fiber content of the battery separator is comprised of a nometallic acicular mineral, wollastonite, that is substantially less expensive than the microglass fibers used heretofore yet provides comparable, and even superior results with respect to electrolyte absorption and retention characteristics of the battery separator material. The microglass fibers used heretofore also are used in the battery separator of the present invention together with a minor amount, 5 - 15 percent, of snythetic binder fiber.
Description
escriytion _attery Separator for Lead-Acid Ty_e Bat-teries Technical Field .
~he present invention relates to battery separators and is more particularly concerned with a new and improved battery separator material especially designed for use in maintenance-free automotive batteries of the lead-acid type.
Heretofore, battery separators for use in lead-acid storage batteries have consisted of thin fibrous sheets, such as papers, of electrically insulating porous material adapted for prolonged immer-sion in the acidic electrolyte between adjacent plates of the battery. ~bre recently maintenance-free batteries have employed noncellulosic, nonwoven fibrous webs as the electrolyte absorbing and retaining structure.
m e nonwoven materials used in maintenan oe-free batteries have been comprised predominately of glass and~or synthetic FibersO The electrolyte absorbing and retaining separators of such batteries typically absorb the liquid acid electrolyte and distribute it throughout the separator to such an extent that substantially all of the electrolyte is absorbed within the pores of the separator and only a thin film of electrolyte is present on the plates of the battery. The highly retentive and porous flexible separators are typically placed between the plates of opposite polarity which are capable of being stacked and confined within a container exhibiting a variety of configurations and shapes. Such separators ~`
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~he present invention relates to battery separators and is more particularly concerned with a new and improved battery separator material especially designed for use in maintenance-free automotive batteries of the lead-acid type.
Heretofore, battery separators for use in lead-acid storage batteries have consisted of thin fibrous sheets, such as papers, of electrically insulating porous material adapted for prolonged immer-sion in the acidic electrolyte between adjacent plates of the battery. ~bre recently maintenance-free batteries have employed noncellulosic, nonwoven fibrous webs as the electrolyte absorbing and retaining structure.
m e nonwoven materials used in maintenan oe-free batteries have been comprised predominately of glass and~or synthetic FibersO The electrolyte absorbing and retaining separators of such batteries typically absorb the liquid acid electrolyte and distribute it throughout the separator to such an extent that substantially all of the electrolyte is absorbed within the pores of the separator and only a thin film of electrolyte is present on the plates of the battery. The highly retentive and porous flexible separators are typically placed between the plates of opposite polarity which are capable of being stacked and confined within a container exhibiting a variety of configurations and shapes. Such separators ~`
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-2--retain the electrolyte in intimate proximity to the plates regard~
less of the position of the cells.
In the maintenanoe-free battery it is important to control the amDunt of electrolyte placed in the cell~ There must be enou~h so that the hydrogen and sulphate ions together with water are sufficient to support the electrochemical reaction, but there should be little or no exoess or free electrolyte. Substantially all of the electrolyte should be retained within the interstices of the sep æator structure. Thus, the electrolyte content of the battery is in a more or less starved condition. It is important to maintain a starved electrolyte condition in order to max~mize or enhance the reccmbination at the negative plate of oxygen formr ed at the positive plate. In this way gas evolution is reduced and improved electrical performance is obtained over a prolonged period.
A glass sep æ ator material made from microfiber diameter, short staple, glass fibers for use in a st æved electrolyte system is described in GB Patent 1,364,283, In that patent the sheets of glass fibre material have a high surfaoe area with correspondingly small fibre diam~ter and are capable of retaining the electrolyt~
within the separator itself. In order to obtain maximum electro-lyte retention, the separator uses microfine fiber filaments wi-th high surfaoe area per unit of weight. The diameter of the fibers used in these highly flexible materials is in the range of 0.2 to 10 microns and they have a surface area of approximately 0.1 - 20 square meters per gram of silica. m is very high surfaoe area, together with the action by the sulfuric acid of the electrolyte - ' . ' .' : :
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on the glass, is said to result in a separator having a very high volume retentivity of electrolyte per ~it volume of separator.
Examples of synthetic fiber battery separators may be found in GB Patent Applications 2,017,184A and 2,020,086A. In the forNer application, the separators consisted of 70 percent synthet-ic fiber and 30 percent wood fiber, while in ~he latter application a mixture of polyolefin fibers of different coarseness are used, either alone or together with an inert filler.
In accordance with the present invention it has been found that superior acid retention can be achieved together with compar-able electrical properties in a more economical manner. This is accomplished by forming a battery separator from a non oellulosic nonwoven fibrous web material having an acicular mineral material as a significant ccmponent of the fibrous web~ m e separator materi~l also contains microfine glass fibers, perferably in amounts almost equal to the amounts of the acicular mineral mater-ial and utilizes substantially less than 25 percent by weight of a synthetic binder fiber. Advantageously this material exhibits equivalent or superior performan oe characteristics relative to p Aor separators used in maintenan oe-free batteries yet is of significantly lower cost.
Other advantages and feàtures will be in part obvious and in part pointed out more in detail hereinafter~
These and related advantages are obtained by providing an electrolyte absorbing and retaining battery separat~r for lead-acid ~atteries of the starved electrolyte type wherein the separat-or is a noncellulosic nonw~ven fibrous web material comprised of ~ .~
(1) 10-90 percent by weight of an acicular mineral material ex-hibiting a specific gravity substantially greater than 2.46 g/cc, (2) electrolyte resistant microfine fibers, such as glass fibers, having an average fiker diame-ter of less than 10 microns, and
less of the position of the cells.
In the maintenanoe-free battery it is important to control the amDunt of electrolyte placed in the cell~ There must be enou~h so that the hydrogen and sulphate ions together with water are sufficient to support the electrochemical reaction, but there should be little or no exoess or free electrolyte. Substantially all of the electrolyte should be retained within the interstices of the sep æator structure. Thus, the electrolyte content of the battery is in a more or less starved condition. It is important to maintain a starved electrolyte condition in order to max~mize or enhance the reccmbination at the negative plate of oxygen formr ed at the positive plate. In this way gas evolution is reduced and improved electrical performance is obtained over a prolonged period.
A glass sep æ ator material made from microfiber diameter, short staple, glass fibers for use in a st æved electrolyte system is described in GB Patent 1,364,283, In that patent the sheets of glass fibre material have a high surfaoe area with correspondingly small fibre diam~ter and are capable of retaining the electrolyt~
within the separator itself. In order to obtain maximum electro-lyte retention, the separator uses microfine fiber filaments wi-th high surfaoe area per unit of weight. The diameter of the fibers used in these highly flexible materials is in the range of 0.2 to 10 microns and they have a surface area of approximately 0.1 - 20 square meters per gram of silica. m is very high surfaoe area, together with the action by the sulfuric acid of the electrolyte - ' . ' .' : :
. .
on the glass, is said to result in a separator having a very high volume retentivity of electrolyte per ~it volume of separator.
Examples of synthetic fiber battery separators may be found in GB Patent Applications 2,017,184A and 2,020,086A. In the forNer application, the separators consisted of 70 percent synthet-ic fiber and 30 percent wood fiber, while in ~he latter application a mixture of polyolefin fibers of different coarseness are used, either alone or together with an inert filler.
In accordance with the present invention it has been found that superior acid retention can be achieved together with compar-able electrical properties in a more economical manner. This is accomplished by forming a battery separator from a non oellulosic nonwoven fibrous web material having an acicular mineral material as a significant ccmponent of the fibrous web~ m e separator materi~l also contains microfine glass fibers, perferably in amounts almost equal to the amounts of the acicular mineral mater-ial and utilizes substantially less than 25 percent by weight of a synthetic binder fiber. Advantageously this material exhibits equivalent or superior performan oe characteristics relative to p Aor separators used in maintenan oe-free batteries yet is of significantly lower cost.
Other advantages and feàtures will be in part obvious and in part pointed out more in detail hereinafter~
These and related advantages are obtained by providing an electrolyte absorbing and retaining battery separat~r for lead-acid ~atteries of the starved electrolyte type wherein the separat-or is a noncellulosic nonw~ven fibrous web material comprised of ~ .~
(1) 10-90 percent by weight of an acicular mineral material ex-hibiting a specific gravity substantially greater than 2.46 g/cc, (2) electrolyte resistant microfine fibers, such as glass fibers, having an average fiker diame-ter of less than 10 microns, and
(3) less than 25 percent by weight of a synthetic binder fiber.
The nonwoven web material exhibits a void volume greater than about 85 percent, an electrolyte absorption of at least about 0.06 g/sq. cm.
and an acid retention of at least about 35 percent of said absorption.
A better understanding of the invention will be obtained from the follcwing detailed description wherein the article of manufac-ture possesses the features/ properties and relation of elements described and exemplified herein.
Description of a Preferred Emb diment As mentioned, battery separators utilized heretofore in mam-tenance-free lead-acid batteries have been made almost entirely from microglass or synthetic fibers. In accordance with the present invention from 10 to 90 percent by weight of the fiber content of the battery separator is comprised of a nonmetallic acicular mineral material that is substantially less expensive than the microglass fibers yet provides comparable, and even superior, results with respect to the electrolyte absorption and retention characteristics of the battery separator material. The microglass fibers used heretofore also are used in the battery separator of the present invention to~èther with a minor amount of synthetic binder fiber In view of the acidic environment of the battery separator during use, it is preferred that the sheet material be non oellul---5--losic and not subject to attack by that environment~ Consequently, one of the preferred major fiber components of the sheet material is the inorganic fiber used heretofore. Although glass fibers æe preferred, other fibers that are resistant to attack by the acid used as the electrolyt , e.g., sulfuric acid, also may be employed.
For example, typical inorganic fibrous materials such as quartz, acid resistant ceramic fibers, and the like may be used, with the preferred fibers being borosilicate glass fibers.
Generally, the inorganic fibers utilized æe of extremely fine diameter, that is, they exhibit a diameter of less than 15 microns and preferably have a diameter on the order of 0~1-10 microns with best results obtained in the range of 0~5-6.0 microns.
Further, since the fibrous web material is produced by a wet papermaking process, it is preferable that the fikers be of a paper-making length and capable of being readily dispersable in water to form a dilute fiber slurry or furnish usable in a papermaking operation. As will be appreciated fibers of different diameter and length may be combined within a single web material and com-binations of different fibers also may be used with good results.
As mentioned it is a feature of the present invention that up to about 90 percent by weight of the total fiber content of the sheet material is an acicular mineral material exhibiting a specif-ic gravity substantially greater than that of the bnrosilicate glass normally used in the manufacture of battery separators Such glass typically has a specific gravity of 2,46g/cc. Ihe preferred mineral is the naturally occurring material known as wollastonite. This material is a nonmetallic calcium metasilicate that typically ~xhibits a very fine diameter size and a length to ¢3~
diameter ratio in the range of from 3:1 to 20:1~ It has an acicular crystalline appearanoe , that is, it is of needle shape, long, slender, and usually pointed at its ends. It ~as a specific gravity of about 2.9 g/cc, well above the 2.46 value for glass.
It exhibits a fiber diameter range of 0.1 to 5.5 microns and an average fiber length in the range of 0.3 to 45 microns with a surface area of approximately 6.3 m2/g.
The preferred acicular material has a length to diameter ratio at the upper end of t~e aforementioned range, i.e., in the range of a~out 10:1 to 20:1 and may be used as mined and separated or may be treated with surface modifyina material to enhan oe its water dispersibility. One of the benefits of this material is that it can be obtained in a relatively pure form as a white, nonmetallic, highly uniform crystalline material. It exhibits exoe llent dielectric properties and exoeptional resistance to moisture absorption as well as resistance to attack by acids such as those used as the electrolyte in lead-acid batteries. A
oommercially available wollastonite found to give good results is the material sold under the trademark "Nyad" by Interpace Corp.
The attrition-milled grade of this material having a typical aspect ratio of 15:1 to 20:1 is preferred.
As mentioned, the acicular calcium metasilicate is used in amounts of from about 10 to 90 percent by weight of the total fiber content and preferably is employed within the range of 40 to 60 percent by ~7eight with the preferred composition heing approximately 50 percent. As can be appreciated many facto~s-must be considered in determining the appropriate amount of the acicular mineral material From a commercial standpoint is has been determined that the more economically desirable calcium metasilicate can be used without sacrifice in ~he necessary physical properties of the battery separator at levels of at least 40 to 60 percent by weight. When levels greater than 60 percent are used, satisfact-ory results are obtained but the performan oe level of the battery separator drops as the amount of glass fiber is reduoed and re-placed with the crystalline calcium metasilicate. Below 40 percent, the economic advantage of the metasilicate over the micro-glass fibers is lessened without a corresponding improvement in the absorption characteristics of the separator material.
In a similar manner, it is necessary to consider the propert-ies of the separator material at various binder levels. Since the binder fiber provides the web material with oertain strength characteristics but at the same time tends to reduce the electro-lyte absorption character of the battery separator material, it is necessary to determine the optimum amount of binder fiber and thereby balance the degree of absorption loss against the amount of strength necessary for the sheet material. Additionally, as will be appreciated, the hydrophobic nature of the binder fiber tends to reduce the wett~bility of the fibrous sheet material and correspondingly decrease the absorption characteristics of that material. Therefore, it is preferred that the lowest possible amount of synthetic binder fib~r be used in order to achieve the desired strength characteristics. In this connection, it has been found that less than 25 percent binder should be used in the fiber .
.. . .
furnish. Although the all-glass sheets used heretofore as battery separators have incorporated binders that were applied as dilute solutions after the web material was formed, it is perferred, in accordance with the present invention, to provide the hinder in the form of fibers which constitute significantly less than 25 percent of the total fiber content of the sheet material~ m e binder fibers typically constitute up to about 15 peroent of the total fiber content and as little as about 2 per oent by weight with preferred amounts keing in the range of abou~ 5 to 10 percent by weight.
As mPntioned, the binder used for the battery separator web material of the present mvention is preferably in the form of binder fibers that can be disbursed with the glass fibers prior to deposition on a paper-forming wire. In this way it is possible to achieve exoellent random distribution of the fibers throughout the sheet material. m e binder fibers found particularly advantageous in this connection are the ployolefin fibers of high molecular weight and low melt index. These ibers are described in greater detail in British patent specification No. 1,386,983. As mentioned in that patent, the essential characteristics of the polyolefin fibers which distinguishes them frcm conventional fibers is their surface area of greater than one square meter per gram and their gxoss morphology, that is, their microfibrillar structure similar to wood pulp, comprising fibrils which in turn are made up of microfibrils. In general, the fibrous polyolefin fibers are such that the polymer cannot be processed into smooth rod-like fibers by the conventional melt spinning technique. These high molecular weight polymeric materials have a melt index of less than about - 1~8t~99 g 0.5 and are not adaptable to conventio.nal processing equipment due to their pcor flcwability charac-teristics under pressure~
These materials preferably have a melt index belcw 0.1 and an average molecular ~eight greater than ~00,000. In general, the polyolefin material should have a viscosity average molecular weight of at least 40,000 and preferably greater than 500,000.
The binder fihers may be formed under conditions of sheer stress in an apparatus such as a disc refiner. The resultant fikers have a typical size and shape co~,parable to the size and shape of wood fibers and are commonly referred to as "synthetic wcod pulp~" mey have an average length of about 1 millimeter, although variations in the manner of their manufacture can result in lengths up to 4 millimeters and more. Of course, shorter fiber lengths are also produced with the loh7er limit of the fiber length being about 0.025 millimeters, ~7ith fibers of the 0.1 to 0.2 millimeters being more commonly observed as the shortest fibers.
Most of the fibers have a length of about 0.2 to 3 millimeters.
These materials have a structure which ccmprises mechanically inter-entangled bundles of fibrils and macro-fibrils, the macrofibrils generally having a width in the range of 1 to 20 microns. In the case of polyethylene, polypropylene and comb.inations thereof, the polym~ric material exhibits an average molecular we.ight between 500,000 and 20,000,000 and a surface area in excess of 1 square meter per gram up to 100 square meters per gram and generally greater than 25 square meters per gram.
~: . ' , ' ' ' -9a-Other synthetic thermDplastic :fibers that could be used for the ~anufacture of the separator according to the present invention include polyamides such as nylon 6.6 and nylon 6 and polyesterS
such as polyethylene terephthalate as well as the polyolefins mentioned hereinbefore, including co-polymers and mixtures thereof.
Ihe preferred fibers have a diameter of S to 30 microns and a length of 1 to 2 microns, although the in~lvidual fibrils are . ~ , 9~
-~10-present in various sizes and various specific surfaces, the shape and size distribution not being unlike that of refined wood pulp.
The sheet material of the present invention generally is made in accordanoe with ccnventional papermaking techniques and pre-ferably takes the form of a nonwoven structure wherein the binderfibers inter-entangle with the nonbindRr fibers and provide suf-ficient structural integrity through simple physical interaction to permit handling of the web material despite a binder fiber content as low as 2-5 percent. As is well known, all of the fibers are mixed and thoroughly disbursed in an aqueous medium, frequently at reduched pH levels by means of a paper mill beater or other mixing devices. The resultant mixture of fiber furnish is then oonveyed to the headbox of a papermaking machine where typically it is further diluted and fed onto the continuous fiber accumwl-ating paper-forming wire, such as a Fourdrinier wire. Where pH
oontrol is required for dispersion of the inorganic or glass fibers, this can be achieved either during the mixing operation or as the fiber furnish is fed to the headbox of the papermaking mach-ine~ Generally, when handling inorganic fibers, the pH control is significant and is adjusted to a neutral of acidic condition prior to the slurry being fed to the headbox.
Although conventional Fourdrinier, cylinder type or other oommercially available papermaking machines may ke employed, the battery separator web material of the present invention is most desirably formed in a papermaking machine utilizing an inclined wire sin oe more dilute dispersions may be used and greater uni-formity with sheet structure can be achieved. In such inclined wire papermaking machines the inorganic fiber dispersion is , generally maintained at a con oentration of about 1 percent by weight and preferably at about 0.1 to 0.3 percent by weight.
Higher concentrations or consistencies may, of course, be applied on cylinder machines and conventional Fourdrinier machines so long as the resultant no~woven web material will exhibit the requisite physical characteristics adapting it for use as a battery separator. A typical exa~ple of the inclined wire papermaking machine can be found in U.S. patent No. 2,045,095 issued to F~ H.
Osborne on June 23, 1936. Nonwoven web materials *ormed on such a machine generally exhibit a desirable three-dimensional network or conf guration with only slight orientation in the machine direction .
The fibrous web material formed in accordance with the present invention is typically dried in a conventional manner and subsequent-ly subjected to temperatures of about 265F and higher so that thebinder fibers approach and preferably exceed their fusion temper-ature thereby imparting greater strength characteristics without interfering with the porosity of the web material~ As will be appreciated, the melting point of the binder fiber will pe~nit the web material to be dried immediately after formation without disadvantageously melting or causing binder buildup on the drier cans of the papermaking machine. The fihrilliform structure of the binder facilitates rapid melting or fusing and at the same time promotes binder adherence to a greater numker of individual glass and wollastonite fibers. m us, as the sheet material is subjected to the elevated fusion temperature for a brief period of time, the binder particles fuse and flow on~o the adjacent fibers in a substantially complete fashion so as to eli~Lnate the fiber structure of the binder. The binder material forms an extremely thin coating, predominately at the cross-over points of the re-maining fibers resulting in an effective fiker diameter of only slightly greater than the diameter of the original fibers them-selves. As will be appreciated, some small globs of binder willbe present at the cross-over or connecting points of the individual inorganic fibers, but in most instances, even these melted and resolidified portions are no larger than the diameter of the fibers constituting the bulk of the sheet material. As will be appreciated, this morphology change of the binder assists in retaining the poro-sity of the fibrous web material while substantially enhancing its tensile strength.
The resultant nonwoven separator web material of the present invention provides improved electrolyte absorption and retentivity which can be attributed at least in part to the high specific gravity of the acicular mineral material relative to the specific gravity of borosilicate glass normally used in the manufacture of nonwoven battery separators. As mentioned, the specific gravity of the acicular crystalline material is about 2.9 g/cc and the average surface area of that material is about 6~3 m /g as contrasted with the surface area of the borosilicate glass of about 3.1 m /g. mese characteristics result in a substantially smaller average pore size in the web material and a substantially larger number of pores thereby providing a greater surfaoe area within the fibrous web material. m ese characteristics, in turn, contri-hute to the Lmproved absorption characteristics of the web material.
There is also a relationship between the void volume of the material and the specific gravity of the fibers. This can be found in the definition of void volume as set forth in the follcwing equation:
V = 100 rl - W
L T(S)~
where V is void volume expressed as a percentage, W is the basis weight of the sheet material, T is the thickness, and S is the specific gravity of the fibers. In accordan oe with the present invention, the utilization of a material which exhibits a sub-stantially higher specific gravity results in a higher void volume and therefore improved absorption characteristics. The void volume, in reality, is a statement of the relationship between the apparent density of the material and the actual density of the fibers used to make the material expressed as a peroe ntage. In this connection, the void volume of the web material is well above the 85 percent level and is typically at or about 90 percent.
The absorption level of the nonw~ven web material prDduced in accordance with the present invention on a weight basis is approximately ten fold and more that of the material itself in a dry condition. Absorption levels of about 0.06 g/sq. cm. are typical with the level seldom dropping below 0.045 g/sq. cm. and extending to and above 0.08 g/sq.cm.
In order to determine the absorption characteristics of the nonwoven web materials the follcwing test procedure is utilized as a screening test. In this prodedure, a small sample of the battery separator material of known dimensional size is weighed in its dry condition and then is allcwed to ahsorb a standardized sulfuric acid solution for a period of 24 hours. me standard ~ ' ~
acid solution is a 43 percent by weight sulfuric acid solution having a specific gîavity of 1.335. Although absorption is essentially instantaneous, the 24 hour absorption period is used to allow for any deterioration or breakdown of the material in the acid and pro~ide a stabilizing effect. After the 24 hour acid absorption period, the saturated sample of battery separator material is weighed to determine the amDunt of acid absorbed by the nonwoven web. As mentioned, the sheet material of the present invention absorbs about ten times and more its own weight.
To deter~ine the degree of electrolyte retention, the saturated sample ob~ained as mentioned a~ove is then lightly blot~
ted on one side with a single dry piece of a battery separator made fro~ glass fibers only and the hlotted sample is reweighed.
The retention values may be reported as the amDunt of acid remaining in the sheet material together with the amDunt originally absorbed, or as a peroentage of the amount oA gi~ally absorbed. In accord-ance with the present invention, it is preferred that the acid retention level as detenmined by this test proce~ure be at least 35 to 40 percent and preferably 50 percent or more of the absorb-tion level at saturation.
It is also desirable that the acid be absorbed within thesheet material as rapidly as possible and that the acid be capable of saturating the entire separator. Ps will be appreciated, the high surface area of the battery se~arator material of the present invention permits extremely rapid saturation of the nonwoven mat-erial by the acid electrolyte. Additionally~ the very small pore size provides for improved retention of the absorbed liquid, there-by providing low resist~n oe to the flow of the electrolyte while .
-15~
at the same time providing improved or enhanced inhibition to the passage or migration of fine active materials formed at one elec-trode and flowing toward the opposite electrode d~lring use. Further, the electrical resistivity of the material is very low. A typical average vdlue is about 1.2 milli-ohms/sq.cm. with the maximum value being 3.0 milli-ohms/sq.cm. and many readings being less than the indicated typical average value.
me following specific examples are given in order that the effectiveness of the present invention may be more fully under-stood. mese examples are set forth for the purpose of illustration only and are not intended in any way to limit the practi oe of the invention. Unless otherwise specified, all parts are given by weight.
EX~IE C~E
Using a commercial papermaking machine, a nonwoven battery separator material was made in accordance with the present invent-ion. About 141 p~unds of wet synthetic pulp polyolefin fibers (56~ pounds on a dry weigh~ ba~is) ~sold under the trademark "PULPEX
E" were added to a beater containing 1800 gallons of water heated to a temperature of 80F. me fiber dispersion was brushed for 20 minutes and 62 pounds of Code 106 glass fibers having a fiber dia-meter of approximately 0.5 - 0.75 microns were added to the beater together with 62 pound~s of ~ inch long, chopped 6 micron diameter glass rovings (Grade DE) and 195 pounds of the acicular calcium metasilicate known as wollastonite (Attrition-millèd grade, sold under the trademark "Nyad-G"). The slurry was defibered for 8 minutes and an additional 600 gallons of water were added thereto~
The fiber furnish was mixed further and fed to the headbax of an inclined wire paperm~king machine where it was deposited on the :
the paper-forming wire at a sufficient concentration to provide a fibrous web having a basis weight of about ao g/m2 The machine was run at a speed of about 120 feet per m m ute and the nonwoven material that was produoe d was dried on can driers heated to a te~perature of akout 300 F. - 325 F.
The resultant web material exhibited a basis weight of 81.42 g/m2, a thickness of 11.0 mils, and a void volume of 90 percent.
A mercury intrusion analysis was conducted both on this material and on a commercial all-glass fiber battery separator material hereinafter referred to as the "control material". The analysis showed that the material of the present invention exhibited a larger total pore area and total pore volume and a smaller average pore diameter than the control material. The total pore volume and total pore area were 3.0728 cc/g and 1.5504 m2/g respectively, for the web material of the presen~ inventiGn as compared with values of 2.9468 cc/g ar.a 0.8354 m2/g for the control material. me average pore diameters for the respective materials were measured as 7.9278 microns and 14.1101 microns.
m e web material produced in accordance with this example was ~also tested or electrolyte absorption and retention using the screening test descriked heretofore. Circular samples of the web material were cut to a size having a diameter of 6.85 cm. Each sample was weighed and plaoe d into a solution of 43 percent by weight sulfuric acid having a specific gravity of 1.335 g/cc. It was visually observed that the sa~ples exhibited verv rapid wett-ability. me samples were covered and allowed to remain in the acid for 24 hours. Each sample was removed from the acid, allcwed to drain for 5 - 10 seconds and then weighed on a preweighed dish to determine the amount of electrolyte absorbed. The a~erage absorption value for four samples of the material of this example ; .
' ~. ' ' ' :
6~
was 0.0531 g/sq.cmu The saturated samples were lightly blotted by placing one side on an all-glass com~ercial grade separator material such as the control material for 5 - 10 seconds. me blotted samples were reweighed to detennine the percent of electrolyte retention~
The average retention value was found to be 61 percent. The retention value for commercial separators using all-glass fibers is between about 56 and 60 percent.
EXPMPLE TW~
Battery separator material was made in the form of continuous webs using the procedure and apparatus of Exa~ple One. The fiber composition ~as changed by reducing the snythetic binder fiber to a 5 percent level and slightly adjusting the remaining co~ponents.
The properties of the resultant material from this exa~ple are compared with those of the material from Example One and the control material in Table I.
TABIE I
Example Exa~ple Fiber Content (%) Control 1 2 . . ~ , , _ Calcium metasilicate - 52 50 Synthetic pulp (Pulpex E) - 15 5 Code 106 glass fi~er - 1~.5 22~5 DE glass rovings - 16.5 22.5 t~" length) ~ ~g/sq.m) 60 81 95 Thickness (mils) 11.8 11 12.7 Void Volume l%) 91 90 90 -Avg. Tensile (g/25mm) 700 11~8 1070 .
c~
TABLE I
Exa~ple Example Fiber Content (~
wi tro~
Absorption (g/sq. cm) .0728 0531 .0742 .
Retention (%) 60 61 70 EXAMPLE THRæE
Hand sheets were prepared from a fiber furnish identical to that used in Example Two. The fiber slurry was prepared in sub-stantially the same m~nner as in Example One. Aftèr mixing the entire furnish, hand sheets were made and the properties thereof measured. ~he average values for the physical praperties of the hand sheets are 6et forth in Table II, which also includes, for comparative purposes, the data associated with an all-glass fiber control material~
EXAMPIE EOUR
The procedure of Example Three was repeated exoept that the amount of synthetic pulp fiber was increased to 10 percent and the amount of glass fiber was reduced so that the fiber furnish con-tained 20 percent of each type of glass fiber. Hand sheets were prepared as in Example Three and the physical data relative thereto is set forth in Table II.
ExpMæLE FIVE
m e procedure of Example Three was repeated agam except that~
the amount of synthetic fiber was increased to 10 percent and the amount of acicular calcium metasilicate was reduced to 45 percent.
Hand sheets ~7ere prepared and the physical data relating to this material is set forth in Table II.
- -- - ~ , :
-- ' ' ' : ' . , : .
~i8~9 TABLE II
Fiber content (%? Control EX. 3 Ex o 4 Ex~ 5 Calcium metasilicate - 50 50 45 Synthetic pulp 5 10 lO
Code 106 glass - 22.5 20 22.5 DE glass rovings ~" - 22.5 20 22.5 Basis Weight (g/m2) 61 72 71 76 m ickness (mils) 12.05 10.2 9.5 9.9 Absor~tion (g/sq.cm.) 0.0610 0.0800 0.0612 0.0736 (corrected to lO mils) Retention (%) 57 59 56 56 EXAMPLE SIX
In this example, the procedure of Exa~iple Three was follcwed but the amount of acicular calcium metasilicate fiber was varied 15 from lO percent to 90 percent using lO percent synthetic pulp fiber in all instances. Hand sheets were prepared from the different fiker furnishes and the form~lations and physical properties relative thereto are set forth in Table III.
TAEiLE III
Fiber Conte~t (%) Calcium metasilicate lO.0 25.0 75.0 90.0 Synthetic fiber (Pulpex E) 10.0 10.0 10.0 10.0 Oode 106 glass 40.0 32.5 7.5 0 DE glass 40~0 32.5 7.5 0 Basis Weight (g/m ) 56 63 81 100 Thickness (nils) 9. 68 9.98 9.45 10.18 (g/sq.om.) 0.0650 0.0659 0.0506 0.0506 (corrected to 10 mils) Retention (~) 48 52 49 60 .
As will be apparent to persons skilled in the artl various modifications, adaptations, and variations of the foreg~ing specific disclosure can be made without departing from the teachings of the present invention.
The nonwoven web material exhibits a void volume greater than about 85 percent, an electrolyte absorption of at least about 0.06 g/sq. cm.
and an acid retention of at least about 35 percent of said absorption.
A better understanding of the invention will be obtained from the follcwing detailed description wherein the article of manufac-ture possesses the features/ properties and relation of elements described and exemplified herein.
Description of a Preferred Emb diment As mentioned, battery separators utilized heretofore in mam-tenance-free lead-acid batteries have been made almost entirely from microglass or synthetic fibers. In accordance with the present invention from 10 to 90 percent by weight of the fiber content of the battery separator is comprised of a nonmetallic acicular mineral material that is substantially less expensive than the microglass fibers yet provides comparable, and even superior, results with respect to the electrolyte absorption and retention characteristics of the battery separator material. The microglass fibers used heretofore also are used in the battery separator of the present invention to~èther with a minor amount of synthetic binder fiber In view of the acidic environment of the battery separator during use, it is preferred that the sheet material be non oellul---5--losic and not subject to attack by that environment~ Consequently, one of the preferred major fiber components of the sheet material is the inorganic fiber used heretofore. Although glass fibers æe preferred, other fibers that are resistant to attack by the acid used as the electrolyt , e.g., sulfuric acid, also may be employed.
For example, typical inorganic fibrous materials such as quartz, acid resistant ceramic fibers, and the like may be used, with the preferred fibers being borosilicate glass fibers.
Generally, the inorganic fibers utilized æe of extremely fine diameter, that is, they exhibit a diameter of less than 15 microns and preferably have a diameter on the order of 0~1-10 microns with best results obtained in the range of 0~5-6.0 microns.
Further, since the fibrous web material is produced by a wet papermaking process, it is preferable that the fikers be of a paper-making length and capable of being readily dispersable in water to form a dilute fiber slurry or furnish usable in a papermaking operation. As will be appreciated fibers of different diameter and length may be combined within a single web material and com-binations of different fibers also may be used with good results.
As mentioned it is a feature of the present invention that up to about 90 percent by weight of the total fiber content of the sheet material is an acicular mineral material exhibiting a specif-ic gravity substantially greater than that of the bnrosilicate glass normally used in the manufacture of battery separators Such glass typically has a specific gravity of 2,46g/cc. Ihe preferred mineral is the naturally occurring material known as wollastonite. This material is a nonmetallic calcium metasilicate that typically ~xhibits a very fine diameter size and a length to ¢3~
diameter ratio in the range of from 3:1 to 20:1~ It has an acicular crystalline appearanoe , that is, it is of needle shape, long, slender, and usually pointed at its ends. It ~as a specific gravity of about 2.9 g/cc, well above the 2.46 value for glass.
It exhibits a fiber diameter range of 0.1 to 5.5 microns and an average fiber length in the range of 0.3 to 45 microns with a surface area of approximately 6.3 m2/g.
The preferred acicular material has a length to diameter ratio at the upper end of t~e aforementioned range, i.e., in the range of a~out 10:1 to 20:1 and may be used as mined and separated or may be treated with surface modifyina material to enhan oe its water dispersibility. One of the benefits of this material is that it can be obtained in a relatively pure form as a white, nonmetallic, highly uniform crystalline material. It exhibits exoe llent dielectric properties and exoeptional resistance to moisture absorption as well as resistance to attack by acids such as those used as the electrolyte in lead-acid batteries. A
oommercially available wollastonite found to give good results is the material sold under the trademark "Nyad" by Interpace Corp.
The attrition-milled grade of this material having a typical aspect ratio of 15:1 to 20:1 is preferred.
As mentioned, the acicular calcium metasilicate is used in amounts of from about 10 to 90 percent by weight of the total fiber content and preferably is employed within the range of 40 to 60 percent by ~7eight with the preferred composition heing approximately 50 percent. As can be appreciated many facto~s-must be considered in determining the appropriate amount of the acicular mineral material From a commercial standpoint is has been determined that the more economically desirable calcium metasilicate can be used without sacrifice in ~he necessary physical properties of the battery separator at levels of at least 40 to 60 percent by weight. When levels greater than 60 percent are used, satisfact-ory results are obtained but the performan oe level of the battery separator drops as the amount of glass fiber is reduoed and re-placed with the crystalline calcium metasilicate. Below 40 percent, the economic advantage of the metasilicate over the micro-glass fibers is lessened without a corresponding improvement in the absorption characteristics of the separator material.
In a similar manner, it is necessary to consider the propert-ies of the separator material at various binder levels. Since the binder fiber provides the web material with oertain strength characteristics but at the same time tends to reduce the electro-lyte absorption character of the battery separator material, it is necessary to determine the optimum amount of binder fiber and thereby balance the degree of absorption loss against the amount of strength necessary for the sheet material. Additionally, as will be appreciated, the hydrophobic nature of the binder fiber tends to reduce the wett~bility of the fibrous sheet material and correspondingly decrease the absorption characteristics of that material. Therefore, it is preferred that the lowest possible amount of synthetic binder fib~r be used in order to achieve the desired strength characteristics. In this connection, it has been found that less than 25 percent binder should be used in the fiber .
.. . .
furnish. Although the all-glass sheets used heretofore as battery separators have incorporated binders that were applied as dilute solutions after the web material was formed, it is perferred, in accordance with the present invention, to provide the hinder in the form of fibers which constitute significantly less than 25 percent of the total fiber content of the sheet material~ m e binder fibers typically constitute up to about 15 peroent of the total fiber content and as little as about 2 per oent by weight with preferred amounts keing in the range of abou~ 5 to 10 percent by weight.
As mPntioned, the binder used for the battery separator web material of the present mvention is preferably in the form of binder fibers that can be disbursed with the glass fibers prior to deposition on a paper-forming wire. In this way it is possible to achieve exoellent random distribution of the fibers throughout the sheet material. m e binder fibers found particularly advantageous in this connection are the ployolefin fibers of high molecular weight and low melt index. These ibers are described in greater detail in British patent specification No. 1,386,983. As mentioned in that patent, the essential characteristics of the polyolefin fibers which distinguishes them frcm conventional fibers is their surface area of greater than one square meter per gram and their gxoss morphology, that is, their microfibrillar structure similar to wood pulp, comprising fibrils which in turn are made up of microfibrils. In general, the fibrous polyolefin fibers are such that the polymer cannot be processed into smooth rod-like fibers by the conventional melt spinning technique. These high molecular weight polymeric materials have a melt index of less than about - 1~8t~99 g 0.5 and are not adaptable to conventio.nal processing equipment due to their pcor flcwability charac-teristics under pressure~
These materials preferably have a melt index belcw 0.1 and an average molecular ~eight greater than ~00,000. In general, the polyolefin material should have a viscosity average molecular weight of at least 40,000 and preferably greater than 500,000.
The binder fihers may be formed under conditions of sheer stress in an apparatus such as a disc refiner. The resultant fikers have a typical size and shape co~,parable to the size and shape of wood fibers and are commonly referred to as "synthetic wcod pulp~" mey have an average length of about 1 millimeter, although variations in the manner of their manufacture can result in lengths up to 4 millimeters and more. Of course, shorter fiber lengths are also produced with the loh7er limit of the fiber length being about 0.025 millimeters, ~7ith fibers of the 0.1 to 0.2 millimeters being more commonly observed as the shortest fibers.
Most of the fibers have a length of about 0.2 to 3 millimeters.
These materials have a structure which ccmprises mechanically inter-entangled bundles of fibrils and macro-fibrils, the macrofibrils generally having a width in the range of 1 to 20 microns. In the case of polyethylene, polypropylene and comb.inations thereof, the polym~ric material exhibits an average molecular we.ight between 500,000 and 20,000,000 and a surface area in excess of 1 square meter per gram up to 100 square meters per gram and generally greater than 25 square meters per gram.
~: . ' , ' ' ' -9a-Other synthetic thermDplastic :fibers that could be used for the ~anufacture of the separator according to the present invention include polyamides such as nylon 6.6 and nylon 6 and polyesterS
such as polyethylene terephthalate as well as the polyolefins mentioned hereinbefore, including co-polymers and mixtures thereof.
Ihe preferred fibers have a diameter of S to 30 microns and a length of 1 to 2 microns, although the in~lvidual fibrils are . ~ , 9~
-~10-present in various sizes and various specific surfaces, the shape and size distribution not being unlike that of refined wood pulp.
The sheet material of the present invention generally is made in accordanoe with ccnventional papermaking techniques and pre-ferably takes the form of a nonwoven structure wherein the binderfibers inter-entangle with the nonbindRr fibers and provide suf-ficient structural integrity through simple physical interaction to permit handling of the web material despite a binder fiber content as low as 2-5 percent. As is well known, all of the fibers are mixed and thoroughly disbursed in an aqueous medium, frequently at reduched pH levels by means of a paper mill beater or other mixing devices. The resultant mixture of fiber furnish is then oonveyed to the headbox of a papermaking machine where typically it is further diluted and fed onto the continuous fiber accumwl-ating paper-forming wire, such as a Fourdrinier wire. Where pH
oontrol is required for dispersion of the inorganic or glass fibers, this can be achieved either during the mixing operation or as the fiber furnish is fed to the headbox of the papermaking mach-ine~ Generally, when handling inorganic fibers, the pH control is significant and is adjusted to a neutral of acidic condition prior to the slurry being fed to the headbox.
Although conventional Fourdrinier, cylinder type or other oommercially available papermaking machines may ke employed, the battery separator web material of the present invention is most desirably formed in a papermaking machine utilizing an inclined wire sin oe more dilute dispersions may be used and greater uni-formity with sheet structure can be achieved. In such inclined wire papermaking machines the inorganic fiber dispersion is , generally maintained at a con oentration of about 1 percent by weight and preferably at about 0.1 to 0.3 percent by weight.
Higher concentrations or consistencies may, of course, be applied on cylinder machines and conventional Fourdrinier machines so long as the resultant no~woven web material will exhibit the requisite physical characteristics adapting it for use as a battery separator. A typical exa~ple of the inclined wire papermaking machine can be found in U.S. patent No. 2,045,095 issued to F~ H.
Osborne on June 23, 1936. Nonwoven web materials *ormed on such a machine generally exhibit a desirable three-dimensional network or conf guration with only slight orientation in the machine direction .
The fibrous web material formed in accordance with the present invention is typically dried in a conventional manner and subsequent-ly subjected to temperatures of about 265F and higher so that thebinder fibers approach and preferably exceed their fusion temper-ature thereby imparting greater strength characteristics without interfering with the porosity of the web material~ As will be appreciated, the melting point of the binder fiber will pe~nit the web material to be dried immediately after formation without disadvantageously melting or causing binder buildup on the drier cans of the papermaking machine. The fihrilliform structure of the binder facilitates rapid melting or fusing and at the same time promotes binder adherence to a greater numker of individual glass and wollastonite fibers. m us, as the sheet material is subjected to the elevated fusion temperature for a brief period of time, the binder particles fuse and flow on~o the adjacent fibers in a substantially complete fashion so as to eli~Lnate the fiber structure of the binder. The binder material forms an extremely thin coating, predominately at the cross-over points of the re-maining fibers resulting in an effective fiker diameter of only slightly greater than the diameter of the original fibers them-selves. As will be appreciated, some small globs of binder willbe present at the cross-over or connecting points of the individual inorganic fibers, but in most instances, even these melted and resolidified portions are no larger than the diameter of the fibers constituting the bulk of the sheet material. As will be appreciated, this morphology change of the binder assists in retaining the poro-sity of the fibrous web material while substantially enhancing its tensile strength.
The resultant nonwoven separator web material of the present invention provides improved electrolyte absorption and retentivity which can be attributed at least in part to the high specific gravity of the acicular mineral material relative to the specific gravity of borosilicate glass normally used in the manufacture of nonwoven battery separators. As mentioned, the specific gravity of the acicular crystalline material is about 2.9 g/cc and the average surface area of that material is about 6~3 m /g as contrasted with the surface area of the borosilicate glass of about 3.1 m /g. mese characteristics result in a substantially smaller average pore size in the web material and a substantially larger number of pores thereby providing a greater surfaoe area within the fibrous web material. m ese characteristics, in turn, contri-hute to the Lmproved absorption characteristics of the web material.
There is also a relationship between the void volume of the material and the specific gravity of the fibers. This can be found in the definition of void volume as set forth in the follcwing equation:
V = 100 rl - W
L T(S)~
where V is void volume expressed as a percentage, W is the basis weight of the sheet material, T is the thickness, and S is the specific gravity of the fibers. In accordan oe with the present invention, the utilization of a material which exhibits a sub-stantially higher specific gravity results in a higher void volume and therefore improved absorption characteristics. The void volume, in reality, is a statement of the relationship between the apparent density of the material and the actual density of the fibers used to make the material expressed as a peroe ntage. In this connection, the void volume of the web material is well above the 85 percent level and is typically at or about 90 percent.
The absorption level of the nonw~ven web material prDduced in accordance with the present invention on a weight basis is approximately ten fold and more that of the material itself in a dry condition. Absorption levels of about 0.06 g/sq. cm. are typical with the level seldom dropping below 0.045 g/sq. cm. and extending to and above 0.08 g/sq.cm.
In order to determine the absorption characteristics of the nonwoven web materials the follcwing test procedure is utilized as a screening test. In this prodedure, a small sample of the battery separator material of known dimensional size is weighed in its dry condition and then is allcwed to ahsorb a standardized sulfuric acid solution for a period of 24 hours. me standard ~ ' ~
acid solution is a 43 percent by weight sulfuric acid solution having a specific gîavity of 1.335. Although absorption is essentially instantaneous, the 24 hour absorption period is used to allow for any deterioration or breakdown of the material in the acid and pro~ide a stabilizing effect. After the 24 hour acid absorption period, the saturated sample of battery separator material is weighed to determine the amDunt of acid absorbed by the nonwoven web. As mentioned, the sheet material of the present invention absorbs about ten times and more its own weight.
To deter~ine the degree of electrolyte retention, the saturated sample ob~ained as mentioned a~ove is then lightly blot~
ted on one side with a single dry piece of a battery separator made fro~ glass fibers only and the hlotted sample is reweighed.
The retention values may be reported as the amDunt of acid remaining in the sheet material together with the amDunt originally absorbed, or as a peroentage of the amount oA gi~ally absorbed. In accord-ance with the present invention, it is preferred that the acid retention level as detenmined by this test proce~ure be at least 35 to 40 percent and preferably 50 percent or more of the absorb-tion level at saturation.
It is also desirable that the acid be absorbed within thesheet material as rapidly as possible and that the acid be capable of saturating the entire separator. Ps will be appreciated, the high surface area of the battery se~arator material of the present invention permits extremely rapid saturation of the nonwoven mat-erial by the acid electrolyte. Additionally~ the very small pore size provides for improved retention of the absorbed liquid, there-by providing low resist~n oe to the flow of the electrolyte while .
-15~
at the same time providing improved or enhanced inhibition to the passage or migration of fine active materials formed at one elec-trode and flowing toward the opposite electrode d~lring use. Further, the electrical resistivity of the material is very low. A typical average vdlue is about 1.2 milli-ohms/sq.cm. with the maximum value being 3.0 milli-ohms/sq.cm. and many readings being less than the indicated typical average value.
me following specific examples are given in order that the effectiveness of the present invention may be more fully under-stood. mese examples are set forth for the purpose of illustration only and are not intended in any way to limit the practi oe of the invention. Unless otherwise specified, all parts are given by weight.
EX~IE C~E
Using a commercial papermaking machine, a nonwoven battery separator material was made in accordance with the present invent-ion. About 141 p~unds of wet synthetic pulp polyolefin fibers (56~ pounds on a dry weigh~ ba~is) ~sold under the trademark "PULPEX
E" were added to a beater containing 1800 gallons of water heated to a temperature of 80F. me fiber dispersion was brushed for 20 minutes and 62 pounds of Code 106 glass fibers having a fiber dia-meter of approximately 0.5 - 0.75 microns were added to the beater together with 62 pound~s of ~ inch long, chopped 6 micron diameter glass rovings (Grade DE) and 195 pounds of the acicular calcium metasilicate known as wollastonite (Attrition-millèd grade, sold under the trademark "Nyad-G"). The slurry was defibered for 8 minutes and an additional 600 gallons of water were added thereto~
The fiber furnish was mixed further and fed to the headbax of an inclined wire paperm~king machine where it was deposited on the :
the paper-forming wire at a sufficient concentration to provide a fibrous web having a basis weight of about ao g/m2 The machine was run at a speed of about 120 feet per m m ute and the nonwoven material that was produoe d was dried on can driers heated to a te~perature of akout 300 F. - 325 F.
The resultant web material exhibited a basis weight of 81.42 g/m2, a thickness of 11.0 mils, and a void volume of 90 percent.
A mercury intrusion analysis was conducted both on this material and on a commercial all-glass fiber battery separator material hereinafter referred to as the "control material". The analysis showed that the material of the present invention exhibited a larger total pore area and total pore volume and a smaller average pore diameter than the control material. The total pore volume and total pore area were 3.0728 cc/g and 1.5504 m2/g respectively, for the web material of the presen~ inventiGn as compared with values of 2.9468 cc/g ar.a 0.8354 m2/g for the control material. me average pore diameters for the respective materials were measured as 7.9278 microns and 14.1101 microns.
m e web material produced in accordance with this example was ~also tested or electrolyte absorption and retention using the screening test descriked heretofore. Circular samples of the web material were cut to a size having a diameter of 6.85 cm. Each sample was weighed and plaoe d into a solution of 43 percent by weight sulfuric acid having a specific gravity of 1.335 g/cc. It was visually observed that the sa~ples exhibited verv rapid wett-ability. me samples were covered and allowed to remain in the acid for 24 hours. Each sample was removed from the acid, allcwed to drain for 5 - 10 seconds and then weighed on a preweighed dish to determine the amount of electrolyte absorbed. The a~erage absorption value for four samples of the material of this example ; .
' ~. ' ' ' :
6~
was 0.0531 g/sq.cmu The saturated samples were lightly blotted by placing one side on an all-glass com~ercial grade separator material such as the control material for 5 - 10 seconds. me blotted samples were reweighed to detennine the percent of electrolyte retention~
The average retention value was found to be 61 percent. The retention value for commercial separators using all-glass fibers is between about 56 and 60 percent.
EXPMPLE TW~
Battery separator material was made in the form of continuous webs using the procedure and apparatus of Exa~ple One. The fiber composition ~as changed by reducing the snythetic binder fiber to a 5 percent level and slightly adjusting the remaining co~ponents.
The properties of the resultant material from this exa~ple are compared with those of the material from Example One and the control material in Table I.
TABIE I
Example Exa~ple Fiber Content (%) Control 1 2 . . ~ , , _ Calcium metasilicate - 52 50 Synthetic pulp (Pulpex E) - 15 5 Code 106 glass fi~er - 1~.5 22~5 DE glass rovings - 16.5 22.5 t~" length) ~ ~g/sq.m) 60 81 95 Thickness (mils) 11.8 11 12.7 Void Volume l%) 91 90 90 -Avg. Tensile (g/25mm) 700 11~8 1070 .
c~
TABLE I
Exa~ple Example Fiber Content (~
wi tro~
Absorption (g/sq. cm) .0728 0531 .0742 .
Retention (%) 60 61 70 EXAMPLE THRæE
Hand sheets were prepared from a fiber furnish identical to that used in Example Two. The fiber slurry was prepared in sub-stantially the same m~nner as in Example One. Aftèr mixing the entire furnish, hand sheets were made and the properties thereof measured. ~he average values for the physical praperties of the hand sheets are 6et forth in Table II, which also includes, for comparative purposes, the data associated with an all-glass fiber control material~
EXAMPIE EOUR
The procedure of Example Three was repeated exoept that the amount of synthetic pulp fiber was increased to 10 percent and the amount of glass fiber was reduced so that the fiber furnish con-tained 20 percent of each type of glass fiber. Hand sheets were prepared as in Example Three and the physical data relative thereto is set forth in Table II.
ExpMæLE FIVE
m e procedure of Example Three was repeated agam except that~
the amount of synthetic fiber was increased to 10 percent and the amount of acicular calcium metasilicate was reduced to 45 percent.
Hand sheets ~7ere prepared and the physical data relating to this material is set forth in Table II.
- -- - ~ , :
-- ' ' ' : ' . , : .
~i8~9 TABLE II
Fiber content (%? Control EX. 3 Ex o 4 Ex~ 5 Calcium metasilicate - 50 50 45 Synthetic pulp 5 10 lO
Code 106 glass - 22.5 20 22.5 DE glass rovings ~" - 22.5 20 22.5 Basis Weight (g/m2) 61 72 71 76 m ickness (mils) 12.05 10.2 9.5 9.9 Absor~tion (g/sq.cm.) 0.0610 0.0800 0.0612 0.0736 (corrected to lO mils) Retention (%) 57 59 56 56 EXAMPLE SIX
In this example, the procedure of Exa~iple Three was follcwed but the amount of acicular calcium metasilicate fiber was varied 15 from lO percent to 90 percent using lO percent synthetic pulp fiber in all instances. Hand sheets were prepared from the different fiker furnishes and the form~lations and physical properties relative thereto are set forth in Table III.
TAEiLE III
Fiber Conte~t (%) Calcium metasilicate lO.0 25.0 75.0 90.0 Synthetic fiber (Pulpex E) 10.0 10.0 10.0 10.0 Oode 106 glass 40.0 32.5 7.5 0 DE glass 40~0 32.5 7.5 0 Basis Weight (g/m ) 56 63 81 100 Thickness (nils) 9. 68 9.98 9.45 10.18 (g/sq.om.) 0.0650 0.0659 0.0506 0.0506 (corrected to 10 mils) Retention (~) 48 52 49 60 .
As will be apparent to persons skilled in the artl various modifications, adaptations, and variations of the foreg~ing specific disclosure can be made without departing from the teachings of the present invention.
Claims (9)
1. An electrolyte absorbing and retaining battery separator for lead-acid batteries of the starved electrolyte type comprising a nonwoven fibrous web material comprising from about 10 to about 90 percent by weight of an acicular mineral material exhibiting a specific gravity substantially greater than 2.4 g/cc, an inorganic electrolyte-resistant fibrous material and less than 25 percent by weight of a synthetic binder, said nonwoven web material having a void volume greater than about 85 percent, an acid absorption of at least about 0.04 g/sq.cm.
and an acid retention of at least about 35 percent of said absorption.
and an acid retention of at least about 35 percent of said absorption.
2. The battery separator of claim 1 wherein the acicular mineral material is a nonmetallic, highly uniform, crystalline mater-ial having a length to diameter ratio of about 3:1 to 20:1 and the inorganic fibrous material includes glass fibers having an average fiber diameter of 0.1 - 10 microns.
3. The battery separator of claim 1 wherein the fibrous web material is noncellulosic, the inorganic fibrous material including glass fibers having an average fiber diameter of less than about 10 microns and there being about 2 - 15 percent by weight of a snythetic binder consisting essentially of thermo-plastic synthetic pulp, the web material exhibiting a smaller pore size and larger pore surface area than all-glass fiber separator material.
4, The battery separator of claims 1, 2, or 3 whewein the acicular mineral material is naturally occurring calcium metasilicate having an average fiber diameter of 0.1 - 5.5 microns, a length of 3 - 45 microns and a length to diameter ratio of from 3:1 to 20:1,
5. m e battery separator of claim 1 wherein the acicular mineral material is calcium metasilicate having a length to diameter ratio of 10:1 to 20:1 and a specific gravity of 2.9 g/cc; the inorganic fibrous material includes glass fibers having an average fiber diameter of 0.5 - 6.0 microns; the synthetic bin-der consists essentially of thermoplastic synthetic pulp in amounts of 5 - 15 percent by weight and the web material exhib-its an electrolyte absorption of about 0.06 g/sq.cm. and more and a retention level of 50 percent and more of the absorption.
6. me battery separator of claim 1 wherein the fibrous web material comprises 40 - 60 percent by weight of wollastonite having a length to diameter ratio of 15:1 to 20:1 and a specific gravity of 2.9 g/cc; 55 percent by weight and less of glass fibers having an average fiber diameter of 0.5 - 6.0 microns;
the synthetic binder consists essentially of thermoplastic poly-olefin synthetic pulp in amounts of 5 - 10 percent by weight, and the web material exhibits a smaller pore size and larger pore surface area than all-glass fiber separator material and an electrolyte absorption of at least about 0.06 g/sq.em.
and a retention level of 50 percent and more of the absorption.
the synthetic binder consists essentially of thermoplastic poly-olefin synthetic pulp in amounts of 5 - 10 percent by weight, and the web material exhibits a smaller pore size and larger pore surface area than all-glass fiber separator material and an electrolyte absorption of at least about 0.06 g/sq.em.
and a retention level of 50 percent and more of the absorption.
7. The battery separator of claim 1 wherein the acicular mineral material is a naturally occurring material, the synthetic bind-er consists essentially of thermoplastic synthetic pulp in amounts of 2 - 15 percent by weight and the web material exhibits a smaller pore size and larger pore surface area than all-glass fiber separator materials.
8. The battery separator of claim 1 wherein the snythetic binder consists essentially of thermoplastic polyolefin synthetic pulp in amounts of 5 - 15 percent by weight and the web material exhibits a void volume of about 90 percent.
9. The battery separator of claim 1 wherein the fibrous web material is noncellulosic and caprices highly uniform, crystalline wollastonite having an average fiber diameter of 0,1 - 5.5 microns and a length to diameter ratio of 15:1 to 20:1, the synthetic binder is a thermoplastic polyolefin synthetic pulp in amounts of 2 - 15 percent by weight, and the web material exhibits an electrolyte absorption of about 0.06 g/sq. cm. and a retention level of 50 percent and more of the absorption
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| PCT/US1980/000591 WO1981003397A1 (en) | 1980-05-12 | 1980-05-12 | Battery separator for lead-acid type batteries |
| US80/00591 | 1980-05-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1168699A true CA1168699A (en) | 1984-06-05 |
Family
ID=22154355
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000376220A Expired CA1168699A (en) | 1980-05-12 | 1981-04-24 | Acicular mineral material battery separator for lead-acid batteries |
Country Status (9)
| Country | Link |
|---|---|
| EP (1) | EP0051599A4 (en) |
| JP (1) | JPS57500627A (en) |
| AU (1) | AU536383B2 (en) |
| BE (1) | BE888774A (en) |
| BR (1) | BR8009065A (en) |
| CA (1) | CA1168699A (en) |
| DK (1) | DK8382A (en) |
| IL (1) | IL62829A0 (en) |
| WO (1) | WO1981003397A1 (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3302535C2 (en) * | 1982-02-02 | 1996-10-31 | Emhart Ind | Battery separator, method for its manufacture and its use in a battery |
| ATE24343T1 (en) * | 1982-12-30 | 1987-01-15 | Bern Luechtrath | PAPER, CARDBOARD OR PAPER-LIKE MATERIAL. |
| DE3306528A1 (en) * | 1982-12-30 | 1984-07-05 | Lüchtrath, Bern, 8700 Würzburg | PAPER, CARDBOARD AND PAPER-LIKE MATERIAL |
| EP0145339B1 (en) * | 1983-11-25 | 1988-05-25 | Vitek Inc. | Acetabular prosthesis |
| AR243297A1 (en) * | 1986-11-12 | 1993-07-30 | Hollingsworth & Vose | Recombinant battery and plate separator therefor |
| JP4659762B2 (en) * | 2004-11-24 | 2011-03-30 | 日本板硝子株式会社 | Inorganic fiber paper |
| WO2014208596A1 (en) * | 2013-06-25 | 2014-12-31 | 日立化成株式会社 | Separator for electrochemical elements and lithium ion secondary battery |
| CN112018308B (en) * | 2019-05-29 | 2023-01-31 | 中国科学院宁波材料技术与工程研究所 | Preparation method and application of aluminum silicate ceramic fiber diaphragm of lithium air battery |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA1009301A (en) * | 1970-08-03 | 1977-04-26 | John L. Devitt | Maintenance-free lead-acid sealed electrochemical cell with gas recombination |
| US4216281A (en) * | 1978-08-21 | 1980-08-05 | W. R. Grace & Co. | Battery separator |
| US4224393A (en) * | 1979-05-10 | 1980-09-23 | W. R. Grace & Co. | Battery separator |
-
1980
- 1980-05-12 JP JP81500796A patent/JPS57500627A/ja active Pending
- 1980-05-12 AU AU67847/81A patent/AU536383B2/en not_active Expired - Fee Related
- 1980-05-12 BR BR8009065A patent/BR8009065A/en unknown
- 1980-05-12 WO PCT/US1980/000591 patent/WO1981003397A1/en not_active Application Discontinuation
- 1980-05-12 EP EP19810900533 patent/EP0051599A4/en not_active Withdrawn
-
1981
- 1981-04-24 CA CA000376220A patent/CA1168699A/en not_active Expired
- 1981-05-10 IL IL62829A patent/IL62829A0/en unknown
- 1981-05-12 BE BE0/204767A patent/BE888774A/en not_active IP Right Cessation
-
1982
- 1982-01-11 DK DK8382A patent/DK8382A/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| EP0051599A1 (en) | 1982-05-19 |
| IL62829A0 (en) | 1981-07-31 |
| JPS57500627A (en) | 1982-04-08 |
| AU6784781A (en) | 1981-12-07 |
| EP0051599A4 (en) | 1982-09-03 |
| BR8009065A (en) | 1982-04-06 |
| AU536383B2 (en) | 1984-05-03 |
| BE888774A (en) | 1981-11-12 |
| DK8382A (en) | 1982-01-11 |
| WO1981003397A1 (en) | 1981-11-26 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |