EX 1028
`EX 1028
`
`

`

`United States Patent (19)
`Yu.
`
`54 SHUTDOWN, TRLAYER BATTERY
`SEPARATOR
`
`75) Inventor: Wei-Ching Yu, Charlotte, N.C.
`s
`73 Assignee: Hoechst Celanese Corporation,
`Warren, N.J.
`
`O
`21 Appl. No.: 65
`21 Appl. No.: 650,21
`(22 Filed:
`May 20, 1996
`Related U.S. Application Data
`
`US005691077A
`Patent Number:
`11
`45 Date of Patent:
`
`5,691,077
`NOW... 25, 1997
`s
`
`1/1994 Rein et al. ................................ 429/62
`5,281,491
`1/1995 Higuchi et al. ...
`. 428/316.6
`5,385,777
`5,409,588 4/1995 Mushiake et al. ..
`... 204/252
`5,453,333 9/1995 Takauchi et al. ......................... 429/62
`5,462,777 10/1995 Hayashida et al. .
`428/516X
`5,534,365 7/1996 Gee et al. ................................. 429/62
`FOREIGN PATENT DOCUMENTS
`
`0228757 7/1987 European Pat. Off..
`55/105968 8/1980 Japan.
`55/146873 11/1980 Japan.
`56/147361 11/1981 Japan.
`61/265043 11/1986 Japan.
`O1/319250 12/1989 Japan.
`
`63 Continuation of Ser. No. 359,772, Dec. 20, 1994, aban
`Primary Examiner-Stephen Kalafut
`doned.
`(51
`Int. Cl. is Attorney, Agent, or Firm-Robert H. Hammer, III
`52 U.S. Cl. ........................... 429/62; 429/144; 29/623.3;
`57
`ABSTRACT
`29/623.4; 428/516
`-
`58) Field of Search ................................ 29.6233,634.
`The present invention is directed to a shutdown, trilayer
`428/516; 429/254, 145, 144, 141, 62
`battery separator. The separator has a first and a third
`microporous membranes sandwiching a second microporous
`References Cited
`membrane. The first and the third membranes have a greater
`puncture strength than the second membrane. The second
`U.S. PATENT DOCUMENTS
`membrane has a lower melting temperature than either the
`4,625,395 12/1986 Rowlette ................................
`first or the third membranes.
`4,650,730 3/1987 Lundquist et al.
`... 429/62
`5,240,655 8/1993 Troffkin et al............................ 264/28
`20 Claims, 2 Drawing Sheets
`
`56)
`
`
`
`OO
`
`90
`
`-N Sy 8O
`
`7O
`
`-S
`O
`N-1
`QY 6O
`
`S 5O
`W
`- A
`S 4O
`
`S. NZ 30
`
`2O
`
`O
`
`O
`
`3O
`
`5O
`
`7O
`
`Temperature (C)
`
`90
`
`11O
`
`13O
`
`15O
`
`17O
`
`Ascend Elements EX1028 Page 1
`
`

`

`U.S. Patent
`
`Nov. 25, 1997
`
`Sheet 1 of 2
`
`5,691,077
`
`SSSSs8S
`
`S
`
`S
`
`
`
`S S & 9
`S S S S R
`O
`S O)
`ce
`N to
`Lo
`(sulo) 20ue161622
`
`s
`
`Ascend Elements EX1028 Page 2
`
`

`

`U.S. Patent
`
`Nov. 25, 1997
`
`Sheet 2 of 2
`
`5,691,077
`
`
`
`Ascend Elements EX1028 Page 3
`
`

`

`5,691,077
`
`1.
`SHUTDOWN, TRILAYER BATTERY
`SEPARATOR
`
`This is a continuation of application Ser. No. 08/359,772
`filed on Dec. 20, 1994, now abandoned.
`
`FIELD OF THE INVENTION
`The present invention is directed to a shutdown battery
`separator.
`
`10
`
`15
`
`25
`
`35
`
`45
`
`2
`strength is important in battery manufacture, particularly in
`the manufacture of "jelly roll" type batteries because the
`surfaces of the anode and the cathode can be sufficiently
`rough that they can puncture these extremely thin separators
`during manufacture. Good peel strength is important in
`battery manufacture because it prevents delamination of the
`separator. Accordingly, there is a need to produce an
`extremely thin, shutdown battery separator that has a suffi
`cient puncture strength and peel strength to withstand the
`rigors of battery manufacture.
`In the manufacture of secondary lithium batteries good
`puncture strength is of particular importance. The anode and
`cathode used in secondary lithium batteries typically have
`rough surfaces. These rough surfaces present a special
`manufacturing consideration because they can damage the
`thin separators during the battery assembly. Bilayer battery
`separators, that have a shutdown layer and a strength layer,
`are suspectable to damage of the shutdown layer (it is
`weaker than the strength layer) during manufacture, by the
`rough electrode surface. Accordingly, there is a need for a
`battery separator that can withstand, among other things, the
`rough sided electrodes encountered in the manufacture
`batteries, for example, secondary lithium batteries.
`SUMMARY OF THE INVENTION
`The present invention is directed to a shutdown, trilayer
`battery separator. The separator has a first and a third
`microporous membranes sandwiching a second microporous
`membrane. The first and the third membranes have a greater
`puncture strength than the second membrane. The second
`membrane has a lower melting temperature than either the
`first or the third membranes. The first and the third mem
`branes are preferably made from polypropylene. The second
`membrane is preferably made from polyethylene.
`DESCRIPTION OF THE DRAWINGS
`For the purpose of explaining the invention, there is
`shown in the drawings various preferred aspects of the
`invention; it being understood, however, that this invention
`is not limited to the precise arrangements and instrumen
`talities shown.
`FIG. 1 is a graphical representation of a trilayer battery
`separator's ability to shutdown a battery (as measured by
`electrical resistance, in ohms) as a function of temperature
`(in C.).
`FIG.2 is a schematic illustration of a deplying and trilayer
`formation set-up.
`DESCRIPTION OF THE INVENTION
`The present invention shall be described in further detail
`below by way of the following detailed description and the
`non-limiting examples.
`Shutdown battery separator, as used herein, refers to a
`battery separator that has the ability to shutdown ion migra
`tion across the separator in response to aparticular event, for
`example, the rapid evolution of heat. In FIG. 1, a graph
`illustrates the function of a shutdown battery separator.
`Shutdown ability is represented by resistance (in ohms), and
`the evolution of heat is represented by temperature (in C.).
`As the temperature increases over an initial range, resistance
`is little changed. Resistance values spike-up, however, as the
`temperature reaches the melt temperature of the shutdown
`layer. After the resistance spike-up, the resistance values
`plateau until the temperature reaches the melt temperature of
`the strength layers. The data used for plotting the graph of
`
`BACKGROUND OF THE INVENTION
`Shutdown battery separators are known. For example, see
`U.S. Pat. Nos. 4,650,730; 4,731304:5,240,655; 5,281.491;
`and Japanese Kokai No. 6-20671, each of the foregoing is
`incorporated herein by reference.
`In batteries, the anode and cathode are separated from one
`another by a separator. Today, "lithium batteries” are very
`popular because they are able to generate high energy
`outputs. The lithium battery market can be divided into two
`groups, the "primary” lithium battery and the "secondary”
`lithium battery. The primary lithium battery is a disposable
`battery, while the secondary lithium battery is a rechargeable
`battery. A problem associated with secondary lithium bat
`teries is its potential for short circuiting. This short circuit
`may manifest itself with a rapid evolution of heat. This rapid
`evolution of heat can cause the battery to explode.
`Accordingly, the shutdown battery separator was developed.
`The shutdown battery separator generally comprises two
`30
`polymerically dissimilar and juxtaposed microporous mem
`branes. One microporous membrane is chosen for its rela
`tively low melting point and the other for its relative
`strength. For example, the low melting point membrane may
`be a polyethylene material and the strength membrane may
`be a polypropylene material. The polyethylene microporous
`membrane has a melting point of approximately 130°-135°
`C. which is sufficiently low that in the event of a short circuit
`in a lithium battery, the heat generated will melt the poly
`ethylene and shutdown, or fill in the pores of the separator,
`and thereby stop or inhibit the likelihood of a short circuit.
`The polypropylene membrane which has a substantially
`higher melting point, approximately 160° C., provides
`strength to the separator so that it maintains the separator's
`integrity in the event of a short circuit.
`In U.S. Pat. Nos. 4,650,730; 4,731304, 5,240,655; and
`5,281,491, and Japanese Kokai 6-20671, shutdown battery
`separators of the foregoing type are disclosed. In the
`examples of U.S. Pat. Nos. 4,650,730 and 4,731304, bilayer
`separator thicknesses of 3-4 mills are disclosed. In Japanese
`Kokai 6-20671, a shutdown, bilayer battery separator has a
`thickness of about 1 to 2 mills.
`In U.S. Pat. Nos. 5,240,655 and 5,281,491, multi-ply
`separators are disclosed. In Examples 2 and 3 of U.S. Pat.
`No. 5,240,655, a polyethylene-ethylene butene
`copolymer-polyethylene trilayer separator is disclosed. In
`Example 4 of U.S. Pat. No. 5,281.491, a polyethylene
`ethylene butene copolymer polyethylene trilayer separator
`is disclosed. Each of the foregoing separators is made by a
`coextrustion, extraction, stretching process.
`When designing new shutdown battery separators of the
`foregoing type, several factors, in addition to the shutdown
`characteristics, are important. They include: thinness, punc
`ture strength, and peel strength. In the manufacture of
`batteries, it is important to have extremely thin separators, so
`that the electrical resistance across the separator, as well as,
`the size of the battery, may be reduced. Good puncture
`
`50
`
`55
`
`65
`
`Ascend Elements EX1028 Page 4
`
`

`

`5,691,077
`
`10
`
`15
`
`3
`FIG. 1 was obtained from tests on a trilayer shutdown
`battery separator, made according to the instant invention.
`This trilayer separator was constructed from polypropylene
`(PP)-polyethylene (PE)-polypropylene (PP). Further
`information about shutdown battery separators maybe
`obtained from U.S. Pat. Nos. 4,640,730; 4.731,304; 5.2240,
`655; 5.281.491; Japanese Kokai No. 6-20671; U.S. patent
`application No. 08/341.239 filed Nov. 17, 1994, entitled
`"Methods of Making Cross-Ply Microporous Membrane
`Battery Separators, and the Battery Separators Made
`Thereby”; and U.S. patent application No. 08/348,630 filed
`Dec. 2, 1994, entitled "Shutdown, Bilayer Battery
`Separator", each of which is incorporated herein by refer
`CCC.
`The shutdown battery separators according to the instant
`invention has at least three layers. Each of these layers is, of
`course, microporous, and preferably, it is a discrete
`microporous membrane. (For example see Kesting, R.E.,
`Synthetic Polymeric Membranes, 2nd Ed., John Wiley &
`Sons, New York City, N.Y., (1985) at section 8.2 versus
`Ibid, Chapter 7, this reference is incorporated herein by
`reference.) The outermost layers provide the strength, par
`ticularly strength to resist puncture, for example by rough
`electrode surfaces. This strength quality maybe quantified as
`puncture strength (defined hereinbelow). A layer between
`those outermost layers provides the shutdown quality.
`Preferably, the puncture strength of the outermost layers is
`relatively greater than that of the inner shutdown layer, and
`the melting temperature of the inner shutdown layer is
`relatively less than that of the outermost strength layers. In
`the preferred embodiment of the trilayer, shutdown battery
`separator, the outermost strength layers sandwich the inner
`shutdown layer.
`The strength quality of the outermost layers referred to
`above is the principal, but not necessarily the sole, function
`of the layer which is the ability to facilitate the manufacture
`of the battery by providing greater puncture strength to the
`separator, as well as, to maintain the integrity, of the sepa
`rator in the event of a short circuit. Preferably, in lithium
`batteries, the strength capabilities can be provided by a
`material that will melt at a temperature at about or greater
`than the melting temperature of the lowest melting electrode
`(e.g., the lithium material). An example of such amaterial is
`a polyolefin, for example: polypropylene or a blend com
`prising substantially polypropylene or copolymer of
`45
`polypropylene.
`The shutdown quality of the inner layer referred to above
`is the principal, but not necessarily the sole, function of the
`layer which is the ability to close the micropores of the
`separators in the event of a short circuit. This typically
`50
`means that the shutdown layer will melt, at some
`temperature, blind the pores of the separator, and thereby
`terminate the short circuit by prohibiting ion migration
`across the separator. Preferably, in lithium batteries, the
`shutdown capabilities can be provided by a material that will
`melt at a temperature at least 20° C. below the melting
`temperature of the lowest melting electrode (e.g., the lithium
`material, the melting point of lithium is about 180° C.). An
`example of such a material is polyethylene or a blend
`comprising substantially polyethylene or a copolymer com
`prising substantially polyethylene with melting temperature
`greater than 110° C.
`The thickness of these separators is less than 3 mills (about
`75 microns). These separators preferably range in thickness
`between 0.5 mill (about 12 microns) and 1.5 mills (about 38
`microns). Most preferably, the separator has a thickness of
`about 1 mill (about 25 microns). The total thickness of the
`
`65
`
`4
`separator is predominantly the sum of the individual layers.
`These individual layers, preferably, have about equal thick
`ness. Measurement details are set forth below,
`The puncture strength should preferably be greater than
`450 grams. Most preferably the puncture strength should be
`greater than 480 grams. These measurements are made at an
`average porosity of 35%. Measurement details are set forth
`below,
`The peel strength should preferably be greater than or
`equal to 4 gramsfinch (1 gram/centimeter). Most preferably,
`the peel strength should be greater than or equal to 6
`gramsfinch (1.5 gram/centimeter). Measurement details are
`set forth below.
`The process, by which the inventive separators are made,
`broadly comprises making a first and third microporous
`membranes, making a second microporous membrane, and
`bonding together the first, second, and third membranes.
`Regarding the preferred method for making the membranes,
`the process requires the following steps: extruding a poly
`mer to form a sheet; annealing the sheet; and stretching the
`annealed sheet. The specific methods for making these
`sheets, particularly polyethylene or polypropylene, will be
`discussed with references to the method of making mem
`branes having a thickness greater than 1 mil. By way of
`non-limiting example, the following references, each of
`which is incorporated herein by reference, illustrate the state
`of the art for making membranes having a thickness greater
`than 1 mil: U.S. Pat. Nos: 3,426,754; 3,558,764; 3,679,538;
`3,801,404; 3,801,692; 3,843,761; 3,853.601; 4,138,459;
`4539.256; 4,726.989; and 4,994,335, each of the foregoing
`is incorporated herein by reference. Knowledge of these
`methods being assumed, the inventive process for making
`thin membranes shall be described below by way of explain
`ing the differences between the prior art methods for making
`standard films (thickness greater than 1 mil) and inventive
`method for making a thin film (thickness less than about a
`mil).
`The differences discussed below regarding extrusion,
`annealing, and stretching are based upon a die configuration
`of a 27" die equipped with a 70 mil mandrel gap. If the die
`configuration changes, then the differences will change. For
`example, if a 6" die is used, the die temperature difference
`between standard film process and thin film process is much
`smaller. Regardless of die configuration, thin films require
`less quench air.
`With regard to extrusion conditions, standard film pro
`cesses typically require stronger quench air conditions and
`lower extrusion temperatures than thin film processes. For
`example, the relevant quench conditions for a standard film
`process include: an air pressure of about 6"HO; an air ring
`gap in the range of 1964 to %4 inches; and an air ring height
`of 1 to 2 inches; on the other hand, the relevant quench
`conditions for a thin film process include: an air pressure of
`about 0.6 to 3.0" H2O; an air ring gap in the range of yes to
`%4 inches; and a ring height of about 1 to 2 inches. The
`relevant extrusion conditions for a standard film process
`(using Exxon's Escorene PP 4292 resin as an example)
`include: a die temperature in the range of 191° to 198° C.
`and a barrel temperature of 200 to 205 C.; on the other
`hand, the relevant extrusion conditions for a thin film
`process (using the same material) include: a die temperature
`in the range of 210°C. (for 0.5 milfinal product) to 224° C.
`(for 0.33 mil final product) and a barrel temperature of 210°
`C.
`With regard to annealing and stretching conditions, the
`inter-ply adhesion (measured as peel strength) must be lower
`
`25
`
`30
`
`35
`
`55
`
`Ascend Elements EX1028 Page 5
`
`

`

`5,691,077
`
`5
`than that of the standard process, so that the individual plies
`do not split (i.e. tear apart) when they are deplied. The ability
`to resist splitting is proportional to the ply's thickness. Thus,
`if the plies stick together (due to adhesion) and the stickiness
`is greater than the split resistance, then the piles cannot be
`separated (deplied) without splitting. For example, the adhe
`sion of plies having a thickness of about 1 mill should be less
`than about 15 gramsfinch, whereas for 0.5 mill plies, the
`adhesion should be less than about 8 grams/inch, and for
`0.33 mill plies, less than about 5 grams/inch. To lower the
`adhesion values, the annealing/stretching temperatures for
`the inventive process are less than those for the standard
`process. For example, the annealing/stretching temperatures
`for a polypropylene film would be in the range of 120°-125°
`C. (inventive process) compared to the range of 140°-150°
`C. (standard process), and for a polyethylene film about 110°
`C. (inventive process) compared to about 115° C. (standard
`process).
`To avoid wrinkle formation, trimmed 2-ply films are
`handled until the trilayer separators are formed. The films
`deplying configuration is shown in FIG. 2. In FIG. 2, a deply
`and trilayer formation scheme 10 is shown. Scheme 10
`includes a ground level layout 12 and an elevated layout 14.
`Layouts 12 and 14 are identical, but for elevation (to
`efficiently use space), so only layout 12 will be discussed in
`detail. Layout 12 comprises three unwind stations 16, 18,
`and 20. Stations 16 and 20 support rolls of polypropylene
`microporous membrane (i.e., one roll-2 plies), and station
`18 supports a roll of polyethylene microporous membrane
`30
`(i.e., one roll-2 plies). The membranes (i.e., either the PP
`or PE membranes) in single-ply form are as thin as about/3
`mil. Membranes or films of this thickness are prone to
`wrinkling or creasing. To avoid wrinkling or creasing, these
`membranes are handled (as much as possible), in 2-ply form
`(about 73 mills thick). The polypropylene films 24 and
`polyethylene films 26 are unwound from their rollers,
`deplyed, in some cases with the assistance of guide rollers
`22, and then replied to form trilayer precursors 28. From
`scheme 10, four (4) trilayer precursors 28 are formed. At
`least four trilayer precursors are preferred so to avoid the
`wrinkle problem and to more efficiently use equipment
`(economic reasons). A minimum of at least two trilayer
`precursors is preferred for process economics. The precur
`sors 28 are forwarded to a bonding station 30 (not shown).
`45
`Regarding the preferred methods for bonding the mem
`branes together, several bonding methods are contemplated.
`Broadly, the bonding methods include calendaring, adhering
`with adhesives, and welding. The application of adhesives
`may include: air atomizing; gravure/screen printing; hydrau
`lic spraying; and ultrasonic spraying. The choice of adhesive
`and the rate of adhesive application must be chosen so that
`the separator's porosity is not adversely effected. The weld
`ing technique includes thermal welding and ultrasonic weld
`ing. The amount of energy for either welding procedure and
`55
`the pattern of welds should be chosen so that, among other
`things, the separator's porosity is not adversely effected.
`Preferably, bonding is accomplished by calendaring, with
`nips closed, at a temperature ranging from 125° to 130° C.,
`and a residence time attemperature of about 2 to 10 minutes.
`After bonding, the trilayer, shutdown battery separator is
`rewound for use in the manufacture of batteries, particularly
`secondary lithium batteries, as is well known in the art.
`Further information about the foregoing invention may be
`obtained from the following non-limiting examples. The test
`methods referred to herein are set forth below.
`
`50
`
`65
`
`10
`
`15
`
`20
`
`25
`
`35
`
`Gurley
`
`Thickness
`
`Porosity
`Density
`Puncture
`Strength
`
`Peel
`strength
`
`Melt Index
`
`test Methods
`
`ASTM-D726 (B)
`Gurley is a resistance to air flow measured by the
`Gurley densometer (e.g. Model 4120). Gurley is the
`time in seconds required to pass 10 cc of air through
`one square inch of product under a pressure of 12.2
`inches of water.
`Method: T411om-83 developed under the auspices of
`the Technical Association of the Pulp and Paper
`Industry. Thickness is determined using a
`precision micrometer with a $2 inch diameter,
`circular shoe contacting the sample at seven (7)
`PSL. Ten (10) individual micrometer readings
`taken across the width of the sample are averaged.
`ASTMD-2873
`ASTMD-792
`Ten measurements are made across the width of
`the stretched product and averaged. A Mitech
`Stevens LFRA Texture Analyzer is used. The
`needle is 1.65 mm in diameter with 0.5 mm
`radius. The rate of descent is 2 mm/sec and
`the amount of deflection is 6 mm. The film
`is hied tight in the camping device with a
`central hole of 11.3 mm. The displacement
`(in mm) of the film that was pierced by the
`needle was recorded against the resistance
`force (in gram force) developed by the tested
`film. The maximum resistance force is the
`puncture strength.
`Peel strength is measured using a tension and
`compression tester to determine the force in
`grams required to separate two one-inch wide
`sections of bonded membrane. The peel rate
`is 6 inchestminute. Three measurements are
`taken across the web and averaged.
`ASTM D 1238; PE: 190° C.12.16 Kg; PP:
`230° C.12.16 Kg.
`
`EXAMPLE
`
`Shutdown trilayer battery separators, as disclosed above,
`were made in the following manner:
`
`The polypropylene and polyethylene resins used are set
`forth in TABLES 1 & 2:
`
`TABLE 1.
`Polypropylene (PP Monopolymer)
`
`Resin
`
`Density
`(g/cm)
`
`Melt Index
`(g/10 min)
`
`A.
`
`B
`
`Escorene
`PP4292
`Final PP 32.
`
`O90
`
`O905
`
`C
`
`Fina. PP3281
`
`O905
`
`D
`
`E
`
`F
`
`Escoreme
`PP4292
`(nucleated)
`Escorene
`PP4372 -
`Escorene
`PP3182
`
`0.90
`
`0.90
`
`O90
`
`*contains an antiblocking agent
`
`14
`
`1.5
`
`1.1
`
`1.4
`
`.4
`
`3.0
`
`Supplier
`
`Exxon
`Chemical
`Fina Oil
`&
`Chemical
`Final Oil
`&
`Chemical
`Exxon
`Chemical
`
`Exxon
`Chemical
`Exxon
`Chemical
`
`Ascend Elements EX1028 Page 6
`
`

`

`7
`
`TABLE 2
`Polyethylene (HDPE)
`
`Resin
`
`G
`
`H
`
`Fina
`HDPEGF7750
`Escorene
`HDZO7
`
`Density
`(gicm)
`
`Melt Index
`(g/10 min)
`
`O958
`
`O.964
`
`OTO
`
`0.30
`
`Supplier
`
`Fina Oil &
`Chemical
`Exxon
`Chemical
`
`The extruder equipment was configured, as set forth in
`TABLE 3:
`
`TABLE 3
`
`Extruder
`
`LD Barrel Die
`Ratio
`Size Size
`
`Die
`Opening
`
`Land
`Length
`
`Blow-up
`Ratio
`
`E.
`
`E2
`E3
`
`24
`
`24
`3O
`
`2.5" 12. d
`
`3.5" i. o
`1.25" 7.
`
`70 mil
`
`70 mil
`7O mil
`
`3"
`
`3"
`3"
`
`1.
`
`The resins were extruded as set forth in TABLE 4 to form a
`tubular precursor films (parison), as set forth in TABLE 4:
`
`TABLE 4
`
`Extrusion Condition
`
`5,691,077
`
`8
`8-ply film. The annealing conditions are set forth below in
`TABLE 5:
`
`TABLE 5
`
`Annealing Conditions
`
`Product
`(see Table 4)
`
`O
`
`Annealing Temp., C,
`
`Annealing
`Time, Min
`
`Peel
`strength
`(gramlinch)
`
`P1
`P2
`P3
`P4, P5
`P6
`E1
`E2
`
`136
`140
`120
`120
`135
`110
`115
`
`more
`
`2
`O
`
`16
`16
`16
`16
`16
`19
`19
`
`The annealed precursor films are stretched to form
`microporous membranes. The annealed precursor films were
`stretched as 16-ply films (8 rolls of 2 ply films from an
`extruded tubular precursor). Alternatively, the annealed pre
`cursor films maybe stretched as an 8-ply film or 24-ply film.
`The stretching conditions are set forth in TABLE 6:
`
`25
`
`Extruderd
`Resin
`Die Size
`(See
`(see
`Tables
`Product 1 & 2) Table 3)
`P
`A.
`E3f6"
`P2
`C
`E316"
`P3
`C
`E227"
`P4
`A.
`E22"
`P5
`A.
`E212"
`P6
`B
`E227"
`E1
`G
`E1127"
`E2
`H
`E1.12"
`
`Air
`Ring
`Extruder Melt Die
`Temp Temp Temp Height
`(C.)
`(°C.) (°C.)
`(inch)
`200
`2O5
`205
`1"
`205
`215
`215
`1"
`230
`243
`243.
`1"
`210
`224,
`224.
`1"
`220
`224,
`224.
`1"
`210
`22a:
`224
`"
`200
`220 200
`1"
`18O
`199
`85
`125"
`
`Quenching
`Air Press Air Ring Thick-
`(inches
`Opening
`SS
`HO)
`(inches)
`(mil)
`15"
`0.08"
`0.38
`15"
`0.08"
`0.38
`12"
`0.018"
`O.38
`2"
`0.078"
`0.38
`12"
`OOI8"
`0.38
`12"
`0.078"
`0.38
`10"
`O.O78'
`0.38
`10."
`0.094."
`O.59
`
`Line
`Speed
`(filmin)
`42
`42
`47
`50
`50
`50
`60
`60
`
`The precursor films were annealed in an 8-ply film. This
`means that since the precursor films are extruded as inflated
`tubes, when they are collapsed, they created a 2-ply film.
`Four of these 2-ply films are wound up together to make the
`
`45
`
`TABLE 6
`Stretching Conditions
`
`Product
`(see
`CABLE
`5)
`P4, P5
`P6
`E1.
`E2
`
`Hot
`Hot
`Relax
`Stretch
`Cold
`Temp
`Hot
`Temp
`Cold
`Stretch,
`(C.)
`(C.) Stretch
`Temp (°C.) Stretch
`120° C.
`120° C. 115%.
`ambient
`25%.
`135° C. 11.5%. 135° C.
`ambient
`25%.
`ambiet
`40% 19 C.
`10%. 110 C,
`ambient
`45%. 15° C. 105%.
`115° C.
`
`Hot
`Relax",
`40%
`40%
`50%
`40%
`
`Thick
`ness
`(mil)
`0.33
`0.33
`0.33
`0.5
`
`Gurley
`(sec)
`12
`O
`8
`
`*The percentage of the stretching/relaxing was based on the original length before cold stretching
`'The relax step indicates that the stretched film is allowed to shrink back,
`
`Ascend Elements EX1028 Page 7
`
`

`

`5,691,077
`
`9
`The microporous membranes, as the 16-ply films, are
`deplied to 2-ply films. The edge portions of the 2-ply films
`are trimmed, thereby separating the 2-ply film into
`individual, detached plies. The PP plies are trimmed 0.5
`inches wider than the PE plies.
`The trilayer precursor were bonded together by calendar
`ing at 128°C., a line speed of 25feet/minute, and a residence
`time at the bonding temperature of about 5-10 minutes.
`The trilayer separator, made according to the foregoing
`example, have the properties set forth in TABLE 7:
`
`TABLE 7
`Trilayer Separator Properties
`
`PP/PE/PP
`(see
`Product Table 6)
`T
`P2E1/P2
`T2
`P4P5/E11
`P4P5
`P6/ElP6
`P4P5E21
`P4P5
`
`T3
`T4
`
`Thickness
`(mil)
`102
`1.01
`
`Gurley
`(sec)
`20
`29
`
`Puncture
`Strength.
`(g)
`480
`480
`
`Adhesion
`(g/cm)
`4.3
`-
`
`1.01
`1.15
`
`22
`30
`
`483
`500
`
`-
`6.5
`
`10
`
`15
`
`20
`
`10
`6. The battery separator of claims 1 further comprising a
`peel strength of greater than or equal to 4 grams per inch.
`7. The battery separator of claim 6 wherein said peel
`strength is greater than or equal to 6 grams per inch.
`8. A battery comprising the separator of claim 1.
`9. A shutdown battery separator comprising a first and a
`third microporous polypropylene membranes sandwiching a
`microporous polyethylene membrane, said separator having:
`a thickness in the range of about 0.5 mils to about 1.5 mils;
`a puncture strength greater than or equal to about 450 grams;
`and a peel strength of greater than 4 grams per inch.
`10. The shutdown separator according to claim.9 wherein
`said thickness is about 1 mil.
`11. The shutdown separator according to claim 9 wherein
`said puncture strength is greater than or equal to about 480
`grams.
`12. The shutdown separator according to claim.9 wherein
`said peel strength is greater than or equal to about 6 grams
`per inch.
`13. A battery comprising the separator of claim 9.
`14. A method for making a microporous membrane hav
`ing a thickness less than about 0.5 mills comprises the steps
`of:
`extruding a parison;
`collapsing the parison onto itself to form a flat sheet
`comprising two plies;
`annealing the flat sheet;
`stretching the flat sheet; and
`winding up the flat sheet, an adhesion force between the
`two plies being less than 8 grams per inch.
`15. The method according to claim 14 for making a
`microporous membrane having a thickness less than or equal
`to about 0.33 mils wherein the adhesion force is less than 5
`grams per inch.
`16. The method according to claim 14 further comprising
`the step of quenching the extruded parison with a gas having
`an air pressure ranging from 0.6 to 3.0 inches of water.
`17. A method of making a trilayer shutdown battery
`separator comprising the steps of:
`providing a first and third flat sheet comprising two plies
`of microporous polypropylene membranes and a sec
`ond flat sheet comprising two plies of a microporous
`polyethylene membrane made according to the method
`of claim 14;
`deplying the first and third flat sheets of microporous
`polypropylene membranes;
`deplying the second flat sheet of polyethylene
`microporous membranes;
`replying the individual plies to form a polypropylene
`polyethylene-polypropylene structure;
`bonding the structure to form a trilayer separator; and
`winding-up the separator.
`18. The method according to claim 17 wherein bonding
`comprises calendaring or adhering with adhesives or weld
`ing.
`19. A shutdown, trilayer battery separator comprising a
`first and a third microporous polypropylene membrane sand
`wiching a microporous polyethylene membrane and having
`a thickness of less than 3 mills.
`20. A battery separator comprising a first and a third
`microporous polypropylene membrane sandwiching a
`microporous polyethylene membrane and having athickness
`of less than 3 mils.
`
`The properties of a trilayer battery separator are compared
`to other battery separators (Celgard(E)-type single-ply PP;
`Celgard®-type single-ply PE; bilayer PP/PE(see U.S. patent
`application Ser. No. 08/348,630 filed Dec. 2, 1994); and
`cross-ply PE (see U.S. patent application Ser. No. 08/341,
`239 filed Nov. 11, 1994) in TABLE 8:
`
`25
`
`TABLE 8
`Comparison of trilayer (PPPEPP) with other battery separators
`single-
`single-
`bilayer
`crossply
`trilayer
`ply PP ply PE
`PPIPE
`PEPE
`PP/PE/PP
`
`Property
`
`thickness
`(mil)
`Porosity
`(%)
`Gurley
`(sec)
`Shutdown
`temp (C.)
`Shutdown
`temp
`range
`(°C)
`puncture
`strength
`(g)
`
`10
`
`10
`
`38
`
`25
`
`38
`
`25
`
`165
`
`132
`
`-
`
`20
`
`1.0
`
`38
`
`25
`
`32
`
`35
`
`1.0
`
`38
`
`25
`
`132
`
`20
`
`10
`
`38
`
`25
`
`132
`
`35
`
`380
`
`290
`
`490 (PP)
`300 (PE)
`
`490
`
`480
`
`35
`
`45
`
`The present invention maybe embodied in other specific
`forms without departing from the spirit or essential attributes
`thereof, and, accordingly, reference should be made to the
`appended claims, rather than to the foregoing specification
`as indicating the scope of the invention.
`I claim:
`1. Ashutdown, trilayer battery separator comprising a first
`and a third microporous polypropylene membranes sand
`wiching a microporous polyethylene membrane.
`2. The battery separator of claim 1 further comprising a
`thickness ranging from about 0.5 to about 1.5 mils.
`3. The battery separator of claim 2 further comprising a
`thickness of about 1 mill.
`4. The battery separator of claim 1 wherein said puncture
`strength is greater than or equal to about 450 grams.
`5. The battery separator of claim 4 wherein said puncture
`strength is greater than or equal to about 480 grams.
`
`50
`
`55
`
`65
`
`Ascend Elements EX1028 Page 8
`
`