CA1165385A - Sintered ethylene vinyl acetate vinyl chloride battery separator - Google Patents
Sintered ethylene vinyl acetate vinyl chloride battery separatorInfo
- Publication number
- CA1165385A CA1165385A CA000392216A CA392216A CA1165385A CA 1165385 A CA1165385 A CA 1165385A CA 000392216 A CA000392216 A CA 000392216A CA 392216 A CA392216 A CA 392216A CA 1165385 A CA1165385 A CA 1165385A
- Authority
- CA
- Canada
- Prior art keywords
- separator
- vinyl acetate
- battery
- terpolymer
- vinyl chloride
- 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
- ZSBRYDJXHOFQMW-UHFFFAOYSA-N chloroethene;ethene;ethenyl acetate Chemical compound C=C.ClC=C.CC(=O)OC=C ZSBRYDJXHOFQMW-UHFFFAOYSA-N 0.000 title abstract 2
- 229920000915 polyvinyl chloride Polymers 0.000 claims abstract description 27
- 239000004800 polyvinyl chloride Substances 0.000 claims abstract description 25
- -1 poly(vinyl chloride) Polymers 0.000 claims abstract description 22
- 239000005038 ethylene vinyl acetate Substances 0.000 claims abstract description 16
- 229920001200 poly(ethylene-vinyl acetate) Polymers 0.000 claims abstract description 16
- 238000003860 storage Methods 0.000 claims abstract description 5
- 229920001897 terpolymer Polymers 0.000 claims description 30
- 239000002245 particle Substances 0.000 claims description 23
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 claims description 10
- 239000005977 Ethylene Substances 0.000 claims description 10
- XTXRWKRVRITETP-UHFFFAOYSA-N Vinyl acetate Chemical compound CC(=O)OC=C XTXRWKRVRITETP-UHFFFAOYSA-N 0.000 claims description 7
- 238000005245 sintering Methods 0.000 claims description 7
- 229920001577 copolymer Polymers 0.000 claims description 6
- DQXBYHZEEUGOBF-UHFFFAOYSA-N but-3-enoic acid;ethene Chemical compound C=C.OC(=O)CC=C DQXBYHZEEUGOBF-UHFFFAOYSA-N 0.000 claims description 5
- 239000003792 electrolyte Substances 0.000 claims description 5
- 229920000642 polymer Polymers 0.000 abstract description 8
- 238000010348 incorporation Methods 0.000 abstract description 2
- 239000000463 material Substances 0.000 description 10
- BZHJMEDXRYGGRV-UHFFFAOYSA-N Vinyl chloride Chemical compound ClC=C BZHJMEDXRYGGRV-UHFFFAOYSA-N 0.000 description 8
- 238000000034 method Methods 0.000 description 7
- 125000000391 vinyl group Chemical group [H]C([*])=C([H])[H] 0.000 description 7
- 229920002554 vinyl polymer Polymers 0.000 description 7
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 6
- 239000000203 mixture Substances 0.000 description 5
- 229920005989 resin Polymers 0.000 description 5
- 239000011347 resin Substances 0.000 description 5
- QTBSBXVTEAMEQO-UHFFFAOYSA-M Acetate Chemical compound CC([O-])=O QTBSBXVTEAMEQO-UHFFFAOYSA-M 0.000 description 4
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 4
- 239000002253 acid Substances 0.000 description 4
- 239000000178 monomer Substances 0.000 description 4
- 238000006116 polymerization reaction Methods 0.000 description 4
- 239000002904 solvent Substances 0.000 description 4
- 238000013461 design Methods 0.000 description 3
- 239000000839 emulsion Substances 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 2
- 239000000470 constituent Substances 0.000 description 2
- 238000005336 cracking Methods 0.000 description 2
- 230000008030 elimination Effects 0.000 description 2
- 238000003379 elimination reaction Methods 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- 239000000843 powder Substances 0.000 description 2
- 238000001694 spray drying Methods 0.000 description 2
- GHPYJLCQYMAXGG-WCCKRBBISA-N (2R)-2-amino-3-(2-boronoethylsulfanyl)propanoic acid hydrochloride Chemical compound Cl.N[C@@H](CSCCB(O)O)C(O)=O GHPYJLCQYMAXGG-WCCKRBBISA-N 0.000 description 1
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 1
- 230000003466 anti-cipated effect Effects 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 229920001519 homopolymer Polymers 0.000 description 1
- 230000001939 inductive effect Effects 0.000 description 1
- 239000003999 initiator Substances 0.000 description 1
- 239000011810 insulating material Substances 0.000 description 1
- 238000002386 leaching Methods 0.000 description 1
- 229940046892 lead acetate Drugs 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 239000002674 ointment Substances 0.000 description 1
- 150000002978 peroxides Chemical class 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 125000006850 spacer group Chemical group 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/24—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by surface fusion and bonding of particles to form voids, e.g. sintering
-
- 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
- H01M50/411—Organic material
- H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
-
- 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
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2351/00—Characterised by the use of graft polymers in which the grafted component is obtained by reactions only involving carbon-to-carbon unsaturated bonds; Derivatives of such polymers
- C08J2351/06—Characterised by the use of graft polymers in which the grafted component is obtained by reactions only involving carbon-to-carbon unsaturated bonds; Derivatives of such polymers grafted on to homopolymers or copolymers of aliphatic hydrocarbons containing only one carbon-to-carbon double bond
-
- 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
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Health & Medical Sciences (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Organic Chemistry (AREA)
- Cell Separators (AREA)
Abstract
SINTERED ETHYLENE VINYL ACETATE
VINYL CHLORIDE BATTERY SEPARATORS
Abstract In accordance with the invention, pliable, sintered, microporous separator sheets are provided for use in electrolytic storage batteries. The separators are made tough and flexible by the incorporation of ter-polymers consisting essentially of linear ethylene vinyl acetate copolymer backbones with pendant grafted segments of poly(vinyl chloride).
VINYL CHLORIDE BATTERY SEPARATORS
Abstract In accordance with the invention, pliable, sintered, microporous separator sheets are provided for use in electrolytic storage batteries. The separators are made tough and flexible by the incorporation of ter-polymers consisting essentially of linear ethylene vinyl acetate copolymer backbones with pendant grafted segments of poly(vinyl chloride).
Description
~ ~53~
D-5,348 C-3313 SINTERED ETHYLENE VINYL ACETATE
INY~ `CHLORIDE:BATTERY SEPARATOR
. .
Background of the InVenti This in~ention rel'ates to tough,' flexible, sintered battery separators based on t~rpolymers having linear ethylene'vinyl acetate'copolymer backbones and pendant gra~ted paly~vinyl chloride~' segments~
Battery separators ~unction to electrically isolate the positive'and negative plates of electrolytic energy ceLls. Most separators for lead-acid, automotive, SIL ~starting-ignition-lighting~ batteries are formed from s~leets of electrolyte-porous insulating materials.
They prevent internal el'ectrical shorts by physically spacing opposite polarity plates apart from one another and by suppressing dendritic crystal growth therebetween (treeing).
Modern SIL battery design seeks to reduce battery sizè'and weight without sacrificing power or life.' Among the` modlfications that ~ay be made'to earlier designs is the elimination o~ mud ribs in the'~ottom of battery : .
cases. This reduces overall case'size and the amount of electrolyte'needed to fill it~ Another is the provision :: `
of thinner battery plates so that a greater number of plates will fit into a smaller case and provide at least as much power as a battery having a larger case which accommodates fewer plates.
The role of the battery separator is critical to the successful implementation of such design modifi-cations. To prevent treeing, which is aggravated by the , 3~
elimination of mud ribs, it is preferre~ to encase every other plate'in a three-sided en~eIope folded arou~d the plate's bottom edge and sealed along its side edges. A
suitable'sheet-type separator material must be flexible enou~'to withstand such'folding, porous enough'to allow ~ree electrolyte ~lo~r and Lough enough to undergo further processing steps in the battery fa~r'ication process without damage.' High quality battery separators ha~e been made lQ by sintering micron size~ poly(vinyl chloride~ (PVC~
particles in accordance with'the'method taught in U.S.
patent 3,551,2,I0, assigned to the assignee of this in-vention. The'patent provides a method of laying d~wn PVC powder and sintering it to form sheet stock at rates of 150 ft. per minute'or better~ It is an ec'onomical ,~ process because PVC resin is relati~ely inexpensive and production rates are highO However, unmodified sintered PVC sheets tend to be'too brittle for use as envelope-type'separators in batteries without mud ribs. Thus, we :
sought a means o~ providing more flexible, tough battery separator sheet material t~at could be made by the ' sintering process. Many different approaches were taken to improve the'flexibility and toughness of sintered PVC
'~ separators, but only those internally plasticized, vinyl - 25 chloride'containing separators described and claimed herein proved successful.
:
:: ' - 7 ~6~
Oblec~_ of the In~ention It is there~ore an object of this invention to pro~ide an elec~rically insulating r mlcroporous separator ~or use be~ween the'plates of an el'ectrolytic storage battery comprised of sintered particles of a poly(vinyl chloridel' based polymeric materîal which'is both tough and ~lexible.' ~ more particular object îs to provide ba'tter'y separators comprised of sîntered particles con-' taînîng at least a portion of a terpolymer consisting essentîally of a flexible'copolymèr ~ackbone of linearethylene'and vinyl acetate ~EV~l ~hat has ~fted thereto a substantial weight portion of segments o~ poly ~vinyl chloride~. Another objec't of the invention is to provide ~ a f1exible battery separator made from such grafted co-'~ ~ 15 polymer where'the particles before sintering are in the form o~ substantlally smooth'hollow spheroids less than 60 microns in d:lameter so that the'finished product has suitable microporosi~y for free'electrolyte flow without inducing harm~ul dendritic growth.
20;~ ~ more'specific object of the invention is to ; provide'a battery separator made up o~ a portion of sub-stantially pure poly(vinyl chloride) and a portion of a compatible ethylene vlnyl acetate'copolymer having ~rafted ~ poly(vinyl chloride) segments. Another object is to - 25 provide a mixture o~ particles of both resin types and sinter them by known means to create a battery separator which is su~ficiently flexible and tough to withstand 1 ~53~
folding around a ~attery plate'in an envelope configuration and subsequent battery fabrication without damage.
. . .
Brief Summ'ary In accordance with a preferred embodiment of the invention, microporous battery separator sheets are formed ~rom particles of a terpolymer having a backbone of co-polymerized e~hylene'ana ~inyl ace~ate with grafted pen-; dant segments of poly(vinyl chIoride~ ~EVA~g-VC~ or ~
mixture'of the terpolymer and pure poly~vinyl chloride).
The term terpolymer a~ used hexein pertains to copolymers , made up of three'dif~erent kinds of mex units. Preferably, ,'~ the polymer particles are formed by spray drying from a uid polymerization suspension or emulsion so that ~hey have'the'form o~ substantially smooth surfaced hollow spheroids less than 60 microns in diameter~ To form separator shee~' stock, a layer of such particles is deposited onto a smooth'stainless steeI belt and combed into a longitudinally ribbed particle bed of appropriate depth'and width.' The'particles are sintered by kno~n means ~or a time'and at a temperature such that a cohesive yet microporous product results.
The'EVA copolymer backbone portion of the ter-polymer constituent provides the sintered separator material with toughness and flexibility. The graf~ed ~inyl chloride segments add strength and are acid re-sistant. Whether the terpolymer containing particles are sintered alone or in combination with substantially pure 53~
poly(vinyl chloride) resin powaers, the resulting separators are'substantially internally plasticized by the'pres'ence'o~ only a small weight portion o~ EVA. They are'~lexible enough'to be enveIoped around pre~ormed battery plates at room temperature'in automatic folding and heat seal~ng"equiPment withouk deveIoping cracks alon~
the $olded bottom eage or at the'corners. They are ~ough , enough'to tolerate'~urthe'r hattery assembly procedures without damage.
. .
~ 10 Detailed Description of the In~ention , .... _.. .
Our in~ntion ~ill be better understood in view of the following Figures and detailed description~
~ igure'l is a ~iew of a ribbed sheet o~ sintered EVA-g-VC powder prior to folding around a battery plate.
Figure'2 sho~s an expanded lead battery plate , ~ encased by a three-sided' EV~-g-VC enveIope in accordance witb the'in~en~ion. The'separator is ~olded along the , bottom edge'of the plate and heat sealed along the side edges.
Figure 3'is a cross section~l Vie~ alon~ 3;3 o~
Figure'2 sho~ing the battery plate'encased in the ribbed separator envelope.
. .
The subject invention relates to the incor-poration of particles containing EVA-g-VC terpolymer in a microporous sintered battery separator to provide the flexibility and toughness required of an envelope t~pe separator in the manufacture of compact, lead-acid, ~ 1~53~
automotive ~IL ~atteries1 The ~ynthesis of such ter-poly~ers ~or use'in liquid impermeable'coating and molding compositions is wel'l known. -See, e.g~, Gxeat Britain patent No. 1,275,643 A Process ~or -the Production o~
Polymers of ~inyl Chloride filed August 18/ 1964 as a patent of addition to Great Britain patent l,02I,324 dated September 4, 1963.' However, the use'of EVA-g-VC
~erpolymers as flexi~ilizing agents for microporous ~intered ~attery neparators was neither anticipated nor suggested prior to our invention.
In a pre~erred practice, a battery separator is prepared by sintexing particles comprised of EV~-g-VÇ
, ~
" terpolymer alone'or a combination of terpolymer and PVC
particles. The'sintering particle mix is prepared so that the finished separator contains from about 2 to 40 percent total resin weight, and preferably 5 to 20 percent, linear ethylene vinyl acetate copolymer. Poly(vinyl chloride) segments are grafted to the vinyl acetate co-polymer backbone so that the total weight pol~(~inyl chloride) is at least 60~ o~ the terpolymer weight. The molecular weight of the terpolymer should be at least about 70,000, the maximum molecular weight being determined b~ the'desired physicaI properties ~or the separator material. The poly(vinyl chloride) portion of the ter-polymer particul~rly pro~ides battery separators withstructure integrity, acid resistance, and strength. The ethylene vinyl acetate copolymer provides increased flexibility and toughness. A high molecular weight EVA-g~VC terpolymer containing a large proportion of grafted ~ inyl chIoride will yieLd a relati~e'stiff but strong material. A low molecular weight terpolymer containing a small proportion of ~rafted PVC will yield a relatively soft, ~lexible materlal. Thus, adjusting the molecular wei`~ht o~ a terpolymer and the proportion of graft PVC
present can modi~y the'polymer's physical properties over a large'ran~e~ T~e mere'formation of a mixture of ethylene vlnyl acetate'and poly(vinyl chloride) by aissolu~ion in a common solvent has been found to improve'neither the strength'nor flexibility of sintered separatorsO Thus, we have found it necess-ary to actually chemically link the polymerlc et'hylene vinyl acetate and PVC constituents in order to make'strong, tough, sintered separator materials. We'belie~e'that a pre~erred ethylene to vinyl ~ce~ate~'ratio in the'copoly~er backbones of the s~lbject terpolymers is about 1:1. Othe'r ratios o~ ethylene to vinyl acetate should also work, althou~h we found ethylene 20; homopolymer with grafted vinyl chIoride segments to be an unsuitable'separator material. However, it is preferred to limit the amount o~ acetate in the terpolymer to less than about 20 weight percent. Leaching of acetate by battery acid may lead to the formation o~ acetic acid in the battery electrolyte. Acetic acid cannot be tolerated because it in turn may form lead acetate which uselessly ties up a battery~s active'lead materials.
~6~
The grafted poly(vinyl chloride~ segments on the ethylene'v~nyl acetate copolymer backbone serve to make the terpolymer compatible with'pure poly(vinyl chloride) resin where'mlxtures of the two are used to ~or~ sintered ~attery separators. In the composltions, the poLy~vinyl chloride~ segments provide the physical pxoperties o~ prior sinte~red PVC separators, particularly, acld resistance,' strength, and processability. The ethylene vinyl acetate portions of the terpolymers pro-vide additional toughness and flexibility.
'~; Whi'le'making the terpolymer is not part of this invention, certain steps should be followed to assure con-sis~ent high quality materials. The terpolymer can be formed by emulsion or solvent polymerization according to well kno~n practices such as those set out in British patent No. 1,275,643'cited above. Terpolymers may also be ormed by dissolving ethylene vinyl acetate copolymar containing the des'ired ratio of ethylene to vinyl acetate in vinyl chloride monomer under heat and pressure in the 2Q presence of a graft initiatox such as a peroxide. The initiator causes the growth of the vinyl chIoride monomers onto the PVC copolymer backbone~ The length of the grafted vinyl chloride segments is determined by the concentration of monomer in the polymerization solution as well as duration, temperature and pressure o~ the reaction.
Another method of making the terpolymer is to dissolve ethylene vinyl acetate copolymer in a solvent and ~ ~$38~
thereafter introduce vinyl chloride monomer under pressure ' until a desired degree of yrafting is obtain~d. Vinyl chloride may also be grafted in this manner beginning with an EVA-water-solvent emulsion.
Past experience'with the'production of poly (vinyl chloride)' battery separators has shown that optimum results are'obtained by spray drying the polymer particles to be'sintered from thei'r solution or emulslon polymeri-zation stocks. This creàtes hollow spheroidal particles less than 60 microns in diame~er. When sintered, these particles yieId battery separators ~ith the~desired degree , of porosity and resistance to treeing.
Figure 1 shows a ribbed sheet of battery ~^~ separator material which could be made by sintering par-~ 15 ticles containing EVA-g-VC terpolymer for flexibility and ; ~toughness. The'separator sheet 2 comprises a web portion 4 and rib portions ~. The thickness of the web portion 4 is generalIy less than about 0.025 inch and preferably about 0.019 inch. The thickness at the rib portions 6 is 20 generally less than a~out 0.05 inch and preferably 0.04 inch. Ribs 6 act primarily as spacers between adjacent plates. Figure 2 shows the separator sheet 2 of Figure 1 folded in an envelope configuration over an expanded metal battery grid 8. It is bottom fold 10 that is most prone to crack in unplasticized sintered PVC separators. The separators o~ this invention~ however, can be severely folded without tearing or cracking. The separator is '~ heat sealed along side'edges 12 of grid 8 so that--it will xemain folded along line 10 and not slip off the grid.
Figure 3 sho~s a cross sectional view of the separator envel'oped grid 8. The smooth separator surface 14 lies adiacent expanded portlon 16 of grid 8. The grid retains ,- a leady oxide battery paste'18.
The'subj'ect invention provides for battery separators containing sintered terpolymer particles. The terpolymer has a backbone of ethylene'and vinyl acetate ~, 10 copolymer to which poly(vinyl c~loride) segments are ~ grafted. The EVA ~oughens the'separator and provides it ', with enough flexibility, e.'g., to fold around the bottom of a battery plate'at room temperature without cracking or breaking.
15Whi'le'my invention has been described in terms of specific embodimenks there.of,,other forms may be ; readily adaptable by one'skilled in the art~ Therefore, our invention is only to be'limited by the following claims.
-
D-5,348 C-3313 SINTERED ETHYLENE VINYL ACETATE
INY~ `CHLORIDE:BATTERY SEPARATOR
. .
Background of the InVenti This in~ention rel'ates to tough,' flexible, sintered battery separators based on t~rpolymers having linear ethylene'vinyl acetate'copolymer backbones and pendant gra~ted paly~vinyl chloride~' segments~
Battery separators ~unction to electrically isolate the positive'and negative plates of electrolytic energy ceLls. Most separators for lead-acid, automotive, SIL ~starting-ignition-lighting~ batteries are formed from s~leets of electrolyte-porous insulating materials.
They prevent internal el'ectrical shorts by physically spacing opposite polarity plates apart from one another and by suppressing dendritic crystal growth therebetween (treeing).
Modern SIL battery design seeks to reduce battery sizè'and weight without sacrificing power or life.' Among the` modlfications that ~ay be made'to earlier designs is the elimination o~ mud ribs in the'~ottom of battery : .
cases. This reduces overall case'size and the amount of electrolyte'needed to fill it~ Another is the provision :: `
of thinner battery plates so that a greater number of plates will fit into a smaller case and provide at least as much power as a battery having a larger case which accommodates fewer plates.
The role of the battery separator is critical to the successful implementation of such design modifi-cations. To prevent treeing, which is aggravated by the , 3~
elimination of mud ribs, it is preferre~ to encase every other plate'in a three-sided en~eIope folded arou~d the plate's bottom edge and sealed along its side edges. A
suitable'sheet-type separator material must be flexible enou~'to withstand such'folding, porous enough'to allow ~ree electrolyte ~lo~r and Lough enough to undergo further processing steps in the battery fa~r'ication process without damage.' High quality battery separators ha~e been made lQ by sintering micron size~ poly(vinyl chloride~ (PVC~
particles in accordance with'the'method taught in U.S.
patent 3,551,2,I0, assigned to the assignee of this in-vention. The'patent provides a method of laying d~wn PVC powder and sintering it to form sheet stock at rates of 150 ft. per minute'or better~ It is an ec'onomical ,~ process because PVC resin is relati~ely inexpensive and production rates are highO However, unmodified sintered PVC sheets tend to be'too brittle for use as envelope-type'separators in batteries without mud ribs. Thus, we :
sought a means o~ providing more flexible, tough battery separator sheet material t~at could be made by the ' sintering process. Many different approaches were taken to improve the'flexibility and toughness of sintered PVC
'~ separators, but only those internally plasticized, vinyl - 25 chloride'containing separators described and claimed herein proved successful.
:
:: ' - 7 ~6~
Oblec~_ of the In~ention It is there~ore an object of this invention to pro~ide an elec~rically insulating r mlcroporous separator ~or use be~ween the'plates of an el'ectrolytic storage battery comprised of sintered particles of a poly(vinyl chloridel' based polymeric materîal which'is both tough and ~lexible.' ~ more particular object îs to provide ba'tter'y separators comprised of sîntered particles con-' taînîng at least a portion of a terpolymer consisting essentîally of a flexible'copolymèr ~ackbone of linearethylene'and vinyl acetate ~EV~l ~hat has ~fted thereto a substantial weight portion of segments o~ poly ~vinyl chloride~. Another objec't of the invention is to provide ~ a f1exible battery separator made from such grafted co-'~ ~ 15 polymer where'the particles before sintering are in the form o~ substantlally smooth'hollow spheroids less than 60 microns in d:lameter so that the'finished product has suitable microporosi~y for free'electrolyte flow without inducing harm~ul dendritic growth.
20;~ ~ more'specific object of the invention is to ; provide'a battery separator made up o~ a portion of sub-stantially pure poly(vinyl chloride) and a portion of a compatible ethylene vlnyl acetate'copolymer having ~rafted ~ poly(vinyl chloride) segments. Another object is to - 25 provide a mixture o~ particles of both resin types and sinter them by known means to create a battery separator which is su~ficiently flexible and tough to withstand 1 ~53~
folding around a ~attery plate'in an envelope configuration and subsequent battery fabrication without damage.
. . .
Brief Summ'ary In accordance with a preferred embodiment of the invention, microporous battery separator sheets are formed ~rom particles of a terpolymer having a backbone of co-polymerized e~hylene'ana ~inyl ace~ate with grafted pen-; dant segments of poly(vinyl chIoride~ ~EVA~g-VC~ or ~
mixture'of the terpolymer and pure poly~vinyl chloride).
The term terpolymer a~ used hexein pertains to copolymers , made up of three'dif~erent kinds of mex units. Preferably, ,'~ the polymer particles are formed by spray drying from a uid polymerization suspension or emulsion so that ~hey have'the'form o~ substantially smooth surfaced hollow spheroids less than 60 microns in diameter~ To form separator shee~' stock, a layer of such particles is deposited onto a smooth'stainless steeI belt and combed into a longitudinally ribbed particle bed of appropriate depth'and width.' The'particles are sintered by kno~n means ~or a time'and at a temperature such that a cohesive yet microporous product results.
The'EVA copolymer backbone portion of the ter-polymer constituent provides the sintered separator material with toughness and flexibility. The graf~ed ~inyl chloride segments add strength and are acid re-sistant. Whether the terpolymer containing particles are sintered alone or in combination with substantially pure 53~
poly(vinyl chloride) resin powaers, the resulting separators are'substantially internally plasticized by the'pres'ence'o~ only a small weight portion o~ EVA. They are'~lexible enough'to be enveIoped around pre~ormed battery plates at room temperature'in automatic folding and heat seal~ng"equiPment withouk deveIoping cracks alon~
the $olded bottom eage or at the'corners. They are ~ough , enough'to tolerate'~urthe'r hattery assembly procedures without damage.
. .
~ 10 Detailed Description of the In~ention , .... _.. .
Our in~ntion ~ill be better understood in view of the following Figures and detailed description~
~ igure'l is a ~iew of a ribbed sheet o~ sintered EVA-g-VC powder prior to folding around a battery plate.
Figure'2 sho~s an expanded lead battery plate , ~ encased by a three-sided' EV~-g-VC enveIope in accordance witb the'in~en~ion. The'separator is ~olded along the , bottom edge'of the plate and heat sealed along the side edges.
Figure 3'is a cross section~l Vie~ alon~ 3;3 o~
Figure'2 sho~ing the battery plate'encased in the ribbed separator envelope.
. .
The subject invention relates to the incor-poration of particles containing EVA-g-VC terpolymer in a microporous sintered battery separator to provide the flexibility and toughness required of an envelope t~pe separator in the manufacture of compact, lead-acid, ~ 1~53~
automotive ~IL ~atteries1 The ~ynthesis of such ter-poly~ers ~or use'in liquid impermeable'coating and molding compositions is wel'l known. -See, e.g~, Gxeat Britain patent No. 1,275,643 A Process ~or -the Production o~
Polymers of ~inyl Chloride filed August 18/ 1964 as a patent of addition to Great Britain patent l,02I,324 dated September 4, 1963.' However, the use'of EVA-g-VC
~erpolymers as flexi~ilizing agents for microporous ~intered ~attery neparators was neither anticipated nor suggested prior to our invention.
In a pre~erred practice, a battery separator is prepared by sintexing particles comprised of EV~-g-VÇ
, ~
" terpolymer alone'or a combination of terpolymer and PVC
particles. The'sintering particle mix is prepared so that the finished separator contains from about 2 to 40 percent total resin weight, and preferably 5 to 20 percent, linear ethylene vinyl acetate copolymer. Poly(vinyl chloride) segments are grafted to the vinyl acetate co-polymer backbone so that the total weight pol~(~inyl chloride) is at least 60~ o~ the terpolymer weight. The molecular weight of the terpolymer should be at least about 70,000, the maximum molecular weight being determined b~ the'desired physicaI properties ~or the separator material. The poly(vinyl chloride) portion of the ter-polymer particul~rly pro~ides battery separators withstructure integrity, acid resistance, and strength. The ethylene vinyl acetate copolymer provides increased flexibility and toughness. A high molecular weight EVA-g~VC terpolymer containing a large proportion of grafted ~ inyl chIoride will yieLd a relati~e'stiff but strong material. A low molecular weight terpolymer containing a small proportion of ~rafted PVC will yield a relatively soft, ~lexible materlal. Thus, adjusting the molecular wei`~ht o~ a terpolymer and the proportion of graft PVC
present can modi~y the'polymer's physical properties over a large'ran~e~ T~e mere'formation of a mixture of ethylene vlnyl acetate'and poly(vinyl chloride) by aissolu~ion in a common solvent has been found to improve'neither the strength'nor flexibility of sintered separatorsO Thus, we have found it necess-ary to actually chemically link the polymerlc et'hylene vinyl acetate and PVC constituents in order to make'strong, tough, sintered separator materials. We'belie~e'that a pre~erred ethylene to vinyl ~ce~ate~'ratio in the'copoly~er backbones of the s~lbject terpolymers is about 1:1. Othe'r ratios o~ ethylene to vinyl acetate should also work, althou~h we found ethylene 20; homopolymer with grafted vinyl chIoride segments to be an unsuitable'separator material. However, it is preferred to limit the amount o~ acetate in the terpolymer to less than about 20 weight percent. Leaching of acetate by battery acid may lead to the formation o~ acetic acid in the battery electrolyte. Acetic acid cannot be tolerated because it in turn may form lead acetate which uselessly ties up a battery~s active'lead materials.
~6~
The grafted poly(vinyl chloride~ segments on the ethylene'v~nyl acetate copolymer backbone serve to make the terpolymer compatible with'pure poly(vinyl chloride) resin where'mlxtures of the two are used to ~or~ sintered ~attery separators. In the composltions, the poLy~vinyl chloride~ segments provide the physical pxoperties o~ prior sinte~red PVC separators, particularly, acld resistance,' strength, and processability. The ethylene vinyl acetate portions of the terpolymers pro-vide additional toughness and flexibility.
'~; Whi'le'making the terpolymer is not part of this invention, certain steps should be followed to assure con-sis~ent high quality materials. The terpolymer can be formed by emulsion or solvent polymerization according to well kno~n practices such as those set out in British patent No. 1,275,643'cited above. Terpolymers may also be ormed by dissolving ethylene vinyl acetate copolymar containing the des'ired ratio of ethylene to vinyl acetate in vinyl chloride monomer under heat and pressure in the 2Q presence of a graft initiatox such as a peroxide. The initiator causes the growth of the vinyl chIoride monomers onto the PVC copolymer backbone~ The length of the grafted vinyl chloride segments is determined by the concentration of monomer in the polymerization solution as well as duration, temperature and pressure o~ the reaction.
Another method of making the terpolymer is to dissolve ethylene vinyl acetate copolymer in a solvent and ~ ~$38~
thereafter introduce vinyl chloride monomer under pressure ' until a desired degree of yrafting is obtain~d. Vinyl chloride may also be grafted in this manner beginning with an EVA-water-solvent emulsion.
Past experience'with the'production of poly (vinyl chloride)' battery separators has shown that optimum results are'obtained by spray drying the polymer particles to be'sintered from thei'r solution or emulslon polymeri-zation stocks. This creàtes hollow spheroidal particles less than 60 microns in diame~er. When sintered, these particles yieId battery separators ~ith the~desired degree , of porosity and resistance to treeing.
Figure 1 shows a ribbed sheet of battery ~^~ separator material which could be made by sintering par-~ 15 ticles containing EVA-g-VC terpolymer for flexibility and ; ~toughness. The'separator sheet 2 comprises a web portion 4 and rib portions ~. The thickness of the web portion 4 is generalIy less than about 0.025 inch and preferably about 0.019 inch. The thickness at the rib portions 6 is 20 generally less than a~out 0.05 inch and preferably 0.04 inch. Ribs 6 act primarily as spacers between adjacent plates. Figure 2 shows the separator sheet 2 of Figure 1 folded in an envelope configuration over an expanded metal battery grid 8. It is bottom fold 10 that is most prone to crack in unplasticized sintered PVC separators. The separators o~ this invention~ however, can be severely folded without tearing or cracking. The separator is '~ heat sealed along side'edges 12 of grid 8 so that--it will xemain folded along line 10 and not slip off the grid.
Figure 3 sho~s a cross sectional view of the separator envel'oped grid 8. The smooth separator surface 14 lies adiacent expanded portlon 16 of grid 8. The grid retains ,- a leady oxide battery paste'18.
The'subj'ect invention provides for battery separators containing sintered terpolymer particles. The terpolymer has a backbone of ethylene'and vinyl acetate ~, 10 copolymer to which poly(vinyl c~loride) segments are ~ grafted. The EVA ~oughens the'separator and provides it ', with enough flexibility, e.'g., to fold around the bottom of a battery plate'at room temperature without cracking or breaking.
15Whi'le'my invention has been described in terms of specific embodimenks there.of,,other forms may be ; readily adaptable by one'skilled in the art~ Therefore, our invention is only to be'limited by the following claims.
-
Claims (3)
1. A pliable microporous battery separator sheet for use between the plates of an electrolytic storage battery comprising sintered particles of a terpolymer consisting essentially of a linear ethylene vinyl acetate copolymer backbone and grafted thereto segments of poly-(vinyl chloride) in an amount of at least about 60% of the terpolymer weight, the ethylene vinyl acetate portion of the terpolymer providing the separator with toughness and flexibility.
2. A microporous separator sheet for use between the plates of an electrolytic storage battery comprising sintered particles of a terpolymer consisting essentially of a copolymer backbone of ethylene and vinyl acetate having grafted thereto segments of poly(vinyl chloride), said particles before sintering being in the form of sub-stantially smooth surfaced hollow spheroids less than 30 microns in diameter wherein said separator may be bent around a battery plate at room temperature and heat sealed in an envelope configuration without damage.
3. A tough, crack resistant separator for use between plates of an electrolytic storage battery which separator is electrically insulating and through-porous to battery electrolyte consisting essentially of sintered polymeric particles comprising of a terpolymer having a linear ethylene vinyl acetate copolymer backbone and pendant poly(vinyl chloride), segments grafted thereto, about 2-40 weight percent of said terpolymer consisting essentially of said ethylene vinyl acetate copolymer and the balance said poly(vinyl chloride), said ethylene vinyl acetate providing said separator with flexibility and toughness so that it can be folded around a battery plate at room temperature and heat sealed at the plate edges without damage.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US25995281A | 1981-05-04 | 1981-05-04 | |
| US259,952 | 1981-05-04 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1165385A true CA1165385A (en) | 1984-04-10 |
Family
ID=22987158
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000392216A Expired CA1165385A (en) | 1981-05-04 | 1981-12-14 | Sintered ethylene vinyl acetate vinyl chloride battery separator |
Country Status (4)
| Country | Link |
|---|---|
| CA (1) | CA1165385A (en) |
| DE (1) | DE3215659A1 (en) |
| FR (1) | FR2505095A1 (en) |
| GB (1) | GB2098129B (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4490447A (en) * | 1984-04-06 | 1984-12-25 | Usm Corporation | Battery separators |
| DE3426929A1 (en) * | 1984-07-21 | 1986-01-23 | Hoechst Ag, 6230 Frankfurt | SINTERABLE, FINE-PARTED MOLDING DIMENSIONS BASED ON VINYL CHLORIDE POLYMERISAT |
| AT383815B (en) * | 1984-09-26 | 1987-08-25 | Rappold Helmuth F | MICROPOROESE SINTER MATERIAL, METHOD FOR THE PRODUCTION AND USE THEREOF |
| DE3622492C2 (en) * | 1986-07-02 | 1996-07-18 | Hagen Batterie Ag | Lead accumulator, the positive electrode plates of which are pocketed in separator pockets that are open at the top |
| US4699857A (en) * | 1986-10-15 | 1987-10-13 | W. R. Grace & Co. | Battery separator |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB848539A (en) * | 1958-07-21 | 1960-09-21 | Thomas Jerome Masse | Method and apparatus for making battery separators |
| NL297480A (en) * | 1962-09-04 | |||
| CH451523A (en) * | 1963-01-31 | 1968-05-15 | Dynamit Nobel Ag | Process for the production of impact-resistant polymers |
| JPS4911259B1 (en) * | 1970-06-04 | 1974-03-15 | ||
| FR2393815A1 (en) * | 1977-06-07 | 1979-01-05 | Solvay | PROCESS FOR THE AQUEOUS SUSPENSION POLYMERIZATION OF VINYL CHLORIDE |
| US4210998A (en) * | 1978-12-04 | 1980-07-08 | General Motors Corporation | Toughening of PVC-separator-enveloped battery plates |
| DE3018922A1 (en) * | 1980-05-17 | 1981-12-03 | Hoechst Ag, 6000 Frankfurt | SINTERABLE, FINE-PIECE POLYVINYL CHLORIDE MOLDING |
-
1981
- 1981-12-14 CA CA000392216A patent/CA1165385A/en not_active Expired
-
1982
- 1982-04-15 GB GB8210951A patent/GB2098129B/en not_active Expired
- 1982-04-27 DE DE19823215659 patent/DE3215659A1/en not_active Withdrawn
- 1982-04-30 FR FR8207575A patent/FR2505095A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| GB2098129B (en) | 1984-09-05 |
| FR2505095A1 (en) | 1982-11-05 |
| DE3215659A1 (en) | 1982-11-18 |
| GB2098129A (en) | 1982-11-17 |
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