Note: Descriptions are shown in the official language in which they were submitted.
lW;~761
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This invention relates generally to flexibl-,
microporous plastic sheets and, moro particularly, to ~lexi-
ble, microporous plastic sheets usoful as s-parators between
the plates of electrical storage batteries
S As is well approciated in the art, a battery
separator must be porous to allow the passage of ions between
the plates as well as free diffusion of acid In addition,
the battery separator must bo resistant to attack by acids
and electrochemical oxidation as well as being b0th strong
and durable More specifically, it is highly desirable that
the separator be flexible onough to resist cracking during
assembly since even minute cracks, if allowed to propagate
auxing the service life of the battery, could result in
pr~mature batt-ry failure Moroover, the s-parator should
b n~turally hydrophilic since such battery separators do
not r-gulre the addition of a wetting agent,
As disclosed for example, in the U S Patents to
~r Witt (2,772,322) and Selsor et al ~3,696,061), it is well
known in th art to fabric~te battery soparators from compo-
sitions comprising a mixturo of a plastic resin, an inorganic
filler, and a solvent, in such a manner as to produce a
microporous, semi-rigid shoet
Attempts have been made to modi~y such prior art
plastic ~as-d separators to increa~e their flexibility and
2S thus avoid cracking during assem~ly and handling, by adding
plasticizers to the composition being processed
It was found, however, that the mere addition of
pla~ticize~s to these compositions r-sulted in separatoxs
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10~;~761
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possessing significantly inferior physical properties and
particularly inferior electrochemical properties when compar-
ed with non-plasticized separators. Specifically, lt was
observod that when plasticizers were added to such composi-
tions the electrical resistance of the battery separatorincreased although the acid resistanee of the resulting
separator decreased.
Against the foregoing background, it i8 a primary
objective of the present invention to provide a composition
processable into a flexible, plastic-based, microporous
battery separator.
It i8 another object of the present invention to
provide a composition processable into a flexible, plastic-
based, microporous battery separator re6istant to cracking.
It is an additional object of the present invention
to provide a composition processable into a flexible, plastie- s
based, microporous battery separator with good electrical
resistanee properties and whieh is re6istant to attaek by
acid and to oxidation by eleetrochemieals, and, moreover,
one which is normally hydrophilic and wetsoasily without
requiring the addition of a wetting agent.
It is still another object of the pres-nt invention
to provide a composition proeessable into a flexible, plastie-
based, mieroporous battery separator in whieh the plastieizer
is n-lther leached out duri~g proeessing nor during use.
It i8 yet still another objeet of the present
invention to provide a eomposition processable into a flexi-
ble, plastic-based, microporous battery separator whieh is
less subjeet to premature failure than battery separators
heretofore employed.
Aeeording to the present invention there is pro-
vided a proeess for produeing a flexible mieroporous battery
separator from a composition eomprising a thermoplastie
resin binder in an amount between 10% and 16% by weight of
tho total eomposit~on, a plastieizer in an amount between
4~ and 10% by weight of the total eomposition, an inorganie
filler material in an amount between 19% and 23% by weight
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10S';~7~1
of the total composition, a solvent for ~aid thermoplastic
resin binder in an amount between 26% and 32% by weight of
the total composition, and a nonsolvent in an amount between
28% and 34~ by weight of the total composition, said process
including the steps of mixing said thermoplastic resin blnder
together with said plasticizer to form a master batch, add-
ing to said master batch said inorganic filler material,
said solvent, and said nonsolvent and mixing the composition
until the constituents are uniformly dispersed to form an
extrudable mixture, extruding and calendering said extrudable
mixture to form a sheet-like article from said composition,
passing said sheet-like article through an extraction bath
to remove said solvent therefrom, and drying said sheet-
like article to remove said extraction medium and ~aid non-
solvent therefrom.
According to a further aspect of the inventionthere is provided a flexible, microporous, sheet-like article
comprising a plasticized resin matrix and an inorganic fil-
ler material, said article including a plurality of pores
formed within said plasticized resin matrix between said
particles of inorganic filler material and said matrix,
between neighboring particles of said inorganic filler materi-
al and within said matrix itself, said sheet having an
electrical resistance less than 0.070 ohm/in2 and elongation
greater than 40%.
The composition which is herein disclosed and which
may be processed into a flexible, plastic-based, microporous
battery separator, is composed of the following essential
ingredient~:
a) a thermoplastic resin binder;
b) a solvent which serves to solubilize the thermo-
plastic resin binder;
c) an inorganic filler such as silica;
d) a nonsolvent such as water, and
e) a plasticizer.
The thermoplastic resin binder employed ~hould pre-
ferably be a vinyl chloride resin binder of the "EP" or
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109;~7~;1
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"easing processing" type which are porou~ and highly ab~or-
bent. This thermopla~tic resin binder may be a non-pla~ti-
cized gamma vinyl chloride homopolymer resin or a copolymer
of vinyl chloride admixed with a small amount (less tha~
about 15~) of a monoethylenic monomer such as, for example,
vinyl acetate, vinylidene chloride, propylene or sthylene.
A particularly preferred thermoplastic resin binder i5 the
gamma vinyl chloride homopolymer marke~-~d by Continental
Oil Company under the tradomark Conoco 5385 although good
results have been obta~ned with the gamma vinyl chloride
homopolymers marketed by the B. F, Goodrich Company under
the trademark Geon 103EP and by Solvay & Cie S.A. of Belgium
under the mark Solvic 229. Additionally, other thermoplastic
re~in binders may be used which, when admixed with a solvent,
are converted into a doughy~ mass for oasy processing and
which, upon removal of the solvent, bocome fixed shape.
Moreover, the thermoplastic resin binder selected should
be rho~lly and physically stable under the conditions
under which it is to be used.
The thermoplastic resin binder should comprise
between about 10% and about 16% by weight of the total com-
position with a range between about 11% and about 15% being
preferred. Particularly good results are obtained when the
amount of thermoplastic resin constitutes between about 11%
and 12~ by weight of tho total composition and, as such,
thi~ rango i~ most preferred.
The inoxganic filler material should desirably be
an inorganic ~olid capable of holding at least 30 parts of
water or other volatile matter per lOO parts of filler
material and should be able to release the volatile matter
upon heating to a temperature below the decomposition point
of the thermoplastic resin. While any filler material
capablo of mo-ting these requirement6 may be employed,
silica hydrogel or precipitated hydrated silica are preferred.
Precipitated hydrated silica is particularly preferred and
may bo obtained, for example, from PPG Corporation under the
~rademark Hi Sil 233 or from Chemische Fabrik Hoosch of
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109;~761
Germany under the trademark KS-300.
The inorganic filler material should constitute
between, about 19% and about 23% by weight of the total
composition with 2 range of between about 20% and about
23% by weight of the total composition being preferred.
When the range of inorganic filler material i8 between
about 22% and about 23~, an article with particularly
good physical and electrochemical properties is produced
and, therefore, this range is most preferred.
The solvent employed, preferably an organic 801-
vent, should have a solvating action on the thermoplastic
resinous binder and should be capable of being absorbed
by the filler material. While organic solvents such as,
for example, acetone, ether, dimethyl formamide, orthochloro-
15 benzene, tetrahydrofuran and certain ketones may be employed,
cyclohexanone is preferred since it solubilizes polyvinyl
chloride and is only slightly soluble in water,
The solvent used, preferably cyclohexanone, is
employed in ranges between about 26% and about 32% by weight
20 of the total composition with a range of between about 26%
a~d about 30% being preferred. Pa~ticularly good results
are obtained when the amount of sol~ent constitutes between
about 27% and about 28% by weight of the total composition.
Tho nonsolvent, preferably water, generally con-
2S stitutes between about 28% and about 34% by weight of the
r total composition with a range of between about 29% and
about 33% being preferred. A nonsolvent in an amount rang-
ing betweon about 31~ and about 33% of the total weight o
the composition haæ been found to produce particularly good
30 physical properties and therefore is especially preferred.
The plasticizer selected should be system-compati-
ble and, thus, when admixed with the above mentioned com-
positions, be capable of improving the elongation properties
of the resultant article while not adversely affecting such
35 physical propsrties as electrical resistance and resi~nce to attack by
aci-d or resistance to oxidation by electrochemicals. In
this regard, any monomeric or polymeric plasticizer which
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10~ ~7 ~1
accomplishes theqe goals would be acceptable. ~hi~ would
include both monomeric plasticizers such as, for example,
dioctyl sebacate and polymeric plastiaizers such as, for
example, elastomeric chlorinated polethylene. The use of
a monomeric plasticizer, and particulàrly dioctyl phthalate
and dioctyl adipate i8 preferred. It has been found that
articles fabricated from composition6 containing either of
these two monomeric plastici~ers po~sess ex¢ellent physical
and electrochemical properties.
The plasticizer should constitute between about
4% and about 104 by weight of the totàl composition with a
range of between about 4% and about 8~ being preferred.
Particularly good physical properties are observed in the
resultant article when dioctyl phthalate is employed in
amounts between about 6% and about 7~ by weight of the total
composition and, a~ such, when dioctyl phthlate i~ the plasti-
cizer, this range is most preferred. When, however, dioctyl
adipate is the Plasticizer, a range of between 4.5~ and about
5.5~ is most preferred.
In addition to the foregoing ~ngredients, it will
be apparent to those skilled in the art that a variety of
other ingredients may be employed which do not affect the
essential nature of the resultant product. Indeed, many
~uch ingredlent~ may be provided for the purpose of improv-
ing other propertie~ thereof or for the purpose of improving
industrial acceptance. Typical ingredients include, but
are not limited to modifying or stabilizing ingredients such
as, for example, oarbon black and lead stearate.
An important feature of the present invention i8
the manner in whioh the ing~edients are combined to form
the composition capable of fabricating an article such as,
for oxample, a flexible, plastic-based micropoxou~ battery
separator.
In combining the aforementioned ingredients in
the amounts and ra~ges specified, it has been found that
the procedure~ re¢ited in the afor~mentioned U,S. Patent
No. 3,696,061 to Selsor et al. are applicable, with certain
,
.
1092761
modifications. U.S. Patent No. 3,696,061, which i8 a~signed
to the same assignee as the present invention, is also re-
ferred to.
A master batch of the thermoplastic resin binder
S and the plasticizer iB flrst prepared by preferably dry
blending at room temperature the constituent parts in a
low shear solids blender such as, for example, a Patterson-
Kelley high intensity "liquids solids" blender for about
twenty (20) minutes. This is contrasted with the processes
heretofore employed wherein a high shear mixer ~uch as,
for example, a Henschel mixer is used. Additionally, in
the processes heretofore employed, the thermoplastic resin
binder i8 admixed with the plasticizer in the presence of
heat to effect better absorption of the plasticizer into
the thermoplastic resin binder. The Patterson-Kelley high
intensity, "liquid~ solids" blender has a v-shaped cross-
section which is preferred, although it is recognized that
other mixing devices may be employed for this purpose. An
ali~uot of this master batch which is in damp powder form is
then placed in a clean blender and the inorganic filler, in
the prescribed amount, is added, The entire blend, which
then resombles a dry powder, is then admixed until all in-
grodlents are uniformly dispersed.
It is preferred that the prescribed amount of
organlc solvent be then added. The rate at which the sol-
vent i6 added is, however, of some importance 6ince the
maximum absorption rate of the solvent by the inorganic
filler should not be exceeded lest some of the thermoplastic
resin be insolubilized.
The prescribed amount of nonsolvent ~e.g. water)
is then added at a rate less than the maximum absorption
rata of the solvent ladened silica. The resultant compo-
sition is then in the form of a stable, damp, free-flowing
powder.
In order to process this composition into a use-
ful article such as, for example, a flexible, plastic-based,
microporous battery separator, the composition is introduced
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into an extruder, preferably of a vertical screw construction,
wherein the free-flowing powder i8 converted into a doughy
mix, shaped by a sheeting die and calendered into a continu-
ous sheet.
Extrusion temperatures may range from about 80F.
to about 160F. with a narrower range of between about 115F.
and about 130F. being preferred. The temperature of the
die may range between about 80F. and about 160F. The
back-pressure of the extruder may range from between about
200 psig and about 500 psig with a pressure range of between
about 200 psig and about 300 psig being preferred, Other
extruders can, of course, be substituted.
The doughy mass formed within the extruder then
passes through a screen pack of about 40 mesh and a sheet-
ing pipe die before entering a geared down calender which
is maintained at a temperature between about 40F. and about
60F., and preferably between about 40F. and about 45F.
The die is locked i~to the calender to avoid evaporation.
The calender employed i8 a 32" oalender preferably containing
separator patterned rolls.
The composition, now in sheet form iB then sup-
ported on a transport screen and pa~sed through a watçr ex-
traction bath, the temperature of the water being maintained
at between about 120F. and about 200F. although a narrow-
er range of between about 160F. and about 180F. is pre-
ferred. The sheet remains in the bath until the solvent
is removed a~d is then dried by conventional means. The
drying temperature should not exceed about 275F. and a tem-
perature of about 225F. is preferred.
It will be appxeciated that the resultant article,
after the solvent and the non-solvent constituents have been
removed during prooessing, comprises a suitably plasticized
thermoplastic resin binder forming a matrix, within and
throughout which are dispersed particles of inorganic filler
material. A network of microvoids or micropores is present
in the article, being formed between neighboring or adjacent
particles of dispersed filler material, between individual
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1092761
particles of filler material and the matrix as well as
withln the matrix it~elf. These microvoids or micorpores
are non-uniform in size, typically ranging between about
0.01 microns and about 100 microns, and have a mean pore
S diameter typically of about 1 micron a6 determined poro-
simetrically by the well-known Mercury Intrusion Method.
The porosity of the resultant article when mea~ured in
alcohol, ranges between about 50% and about 75%.
The resultant article possesses physical properties
making it ideally suited for use as a battery ~eparator.
In particular, the resultant articlo is not only highly
porous, having a total porosity of at least about 50% when
measured in alcohol, but is both strong and flexible, as evi-
denced by its tensile strength which is generally greater
than about 200 psi and its elongation which is generally
greater than about 40%. Moreover, its electrical resistance,
a characteristic of significant importance with respect to
battery separators, is generally no greater than about
0.070 ohms/in2 and normally less than about 0.~40 ohms/in2.
Whon the thickness of the resultant article is reduced to,
for examplo, about Q.025 inchos, olectrical resistance has
been further decreased to about 0.020 ohms/in2.
The following examples serve to illustrate certain
preferred embodiments of the present composition and process
and are not to b0 oo~shuYd as limiting the present invention.
Example I
In order to illustrate the preparation of a com-
position prooessable into a useable arti¢le such as, for
example, a flexible, plastic-based microporous battery se-
parator in accordance with the principles of this invention,a composition was prepared which included a plasticizer as
one of its constit~ent parts in a ratio of 60
parts of plasticizer to 100 parts of thermo-
plastic resin binder. This composition compri~ed the fol-
lowing ingredients with its respective amounts being speci-
fied as a percentage weight of the total weight of the
composition.
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Ingredients Percentage by Weight
Conoco 5385 (a trademark
for a gamma vinyl chlor-
ide homopolymer) 11.17%
5 Dioctyl phthalate 6.67
Hi Sil 233 precipitated
hydrated silica filler 22.20%
Cyclohexanone 27.76%
Water 32.20%
10 Carbon black .001~
The composition was prepared by first dry blend-
ing in a Patter60n-Kelley high inten6ity "liquids solids"
blender the Conoco 5385 with the dioctyl phthalate to form
a master batch and then adding the Hi Sil 233 followed by
the cyclohexanone, water and carbon blac~.
The resultant composition was then introduced
into a vertical Aragon extruder with a stainle6s steel
scrow having a compres6ion ratio of about 1.4/1. The com-
position was extruded at a temperature of about 120F. and
at a pressure of about 250 psig. A 32" calender with a
calender top, pattern separator roll was employed to pro-
duce a separator patterned 6heet approximately 0.100 inches
thick. The resultant sheet was then pa6sed through a water
extraction tank in which the water temperature was maintained
at about 160F. and then dried in an air dryer at an air
temperature of about 225F.
The resultant fabricated article, in this instance,
a flexible, microporous, battery 6eparator, had the follow-
ing physical propertie6:
Tensile Strength 210 p8i
Elongation 65%
Mullen Strength 64 psi
Electrical Re6istance 0.054 Q~in2
Total Porosity (Nercury
, Intru6ion Technique) 1.04 cc/g
Mean Pore Diameter 0.085
~ of Pore6 >20~ 2~5%
109;~761
Of the tests performod, the tensile strength,
elongation, and Mullen ~trength data indicated that the
resultant article was sufficiently strong and flexible to
with~tand any damage inflicted during as~embly and evontual
S use.
The electrical resistance and porosity data indi-
cated a product with a fine pore size which pos~e~sod excel-
lent electrochemical properties. For u~e as a battery
separator, electrical resi~tanc~ ~hould be as low as po~ible,
preferably less than about .070~in2. The re~ultant product's
electrical resistance of .054Qin2 was, therefore, more than
adequate. Additionally, the data with respect to pore ~ize
and total porosity indicated that while the pore size and
distribution was in the microporous range, the resultant
article was highly porous. A mean pore diameter of one
micron or less is preferred. Further, this data indicated
that virtually no plasticizer leached out during processing.
The resultant product was hyarophilic and displayed 9OOa
acid resistance.
Example II
In order to demQnstrato the effects of practicing
the instant invention with a lower ratio of plasticizer to
thermoplastic resin, tho same procedure as set forth in
Example I was repeated with tho following ingredient~ in
tho following percentage~ whorein the ratio of plasticizer
to thermoplastic resin was 50 parts of plasticizer to 100
part~ resin:
Ingreaients Porcentage by Weight
Conoco 5385 ~a trademark for
a gamma vinyl chloride homo-
polymer) lQ.98%
Dioctyl phthalate 5.49%
Hi Sil 233 precipitated
hydrated silica filler 21.97%
35 Cyclohexanone 28.61%
Water 32.95%
Carbon black .001%
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The resultant composition was fabricated into
a useful article such as, for example, a flexible, micro-
porou~ battery separator, in the ~ame manner as in Example
I and the resultant article had the following phy~lcal pro-
5 pertles
Tensile Strength 219 psi
Elongation 54%
Mullen Strength 53 psi
Electrical Resistance 0 041~/in
Total Porosity (Mercury
Intru~ion Te~t) 0 99 cc/g
Mean Pore Diameter 0 095
% of Pores >20~ 2 5%
The results of those physioal tests indicated a
product with properties essontially ~imilar to the composi-
tion in Example I although the elongation figure~ reflected
the fact that the resultant article was somewhat less flexi-
ble than the article in Example I and had a ~lightly higher
electrical resi~tance The re~ultant article, however, was
a commercially accoptable, flexible, pla~tic-based micro-
porous battery separator
Example III
In order to illustrate the preparation of a compo-
sition according to the present invontion wh-rein different
typ-~ of thermoplastic resin and inorganic filler materials
woro mployod although with the ~amo ratio of resin to
plasticizer a~ in Example II, the same procedure as, set
forth in Example I was xepeated with the following ingredi-
ent~ in the following percentages
30 In~redi-nts Peroentage by Weight
Solvic 229 vinyl chloride
homopolymer 14 23~
Dioctyl pbthalate 7 11%
KS 300 precipitated hy-
35 drated sillca filler 19 96%
Cyclohexanone 28 22%
Wator 30 48%
Carbon black 0 001%
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109;~761
The resultant composition was fabricated into a
useful article such as, for example, a flexible microporous
battery eeparator in the same manner as in Example I and
the resultant article had the following phyeical properties:
Tensile Strength 290 p8i
Elongation 57%
Mullen Strength 68 p8i
Electrical Resistance 0.045~/in
Total Porosity (Mercury
Intrusion Test) 0.87 cc/g
Mean Pore Diameter 0.11
% of Pores >201~ 3 5%
In comparing the physical data of this article to
tho article produced in Example I, the tensile strength of
the article was higher than the article of Example I, al-
though its elongation was less, indicating a stronger, but
less flexible product. The electrical resistance of the
article was lower than the electrical resistance of the
article of Example I. Further, the porosity of the article
was loes than ~he porosity of the article of Example I al-
though the pore size was generally greater.
Example IV
In order to illuetrate the preparation of a compo-
sition according to the present invention wherein the type
of plasticizer was changed, the same procedure as set forth
in Example I was r-p-at-d wher-in dioctyl adipate was chosen -
as the plasticizer and used in a ratio of 50 parts of
plasticizer and used in a ratio of 50 parts of plasticiz-r
to 100 parts of resin. Additionally, a diff-rent thermo~
plastic resin was employed. The following percentages were
employ-d:
Ingredients Percentage by Weight
Geon 103EPF 10 thermo-
plastic reein 11.01%
35 Dioctyl adipate 4.96%
~i Sil 233 precipitated
hydrated silica filler 22.03~
Cyclohexanone 29.52%
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1()~;~761
Ingredients Percentage by Weight
Water 32.48~
Carbon blsck 0.001%
The resultant composition was fabricated into a
useful article such as, for example, a flexible, micro-
porous battery separator, in the same manner as in Example
I and the resultant article had the following physical
properties:
Tensile Strength 187 p~i
Elongation 62~
Mullen Strength 60 psi
Electrical Resistance .031~/in
Total Porosity (Mercury
Intrusion Test) 0.07 cc/g
% of Pores >20~ 1.3S
The physical data illustrate that the use of di-
octyl adipate as a plasticizer produced an article with both
physical and electrochemical propertiQs quite similar to the
article of Example I wherein dioctyl phthalate was the
plasticizer employed.
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