U.S. patent application number 13/044708 was filed with the patent office on 2011-09-15 for biaxially oriented porous membranes, composites, and methods of manufacture and use.
Invention is credited to Michael A. Braswell, Tyrone S. Fields, Charles E. Haire, Karl F. Humiston, Ronald A. Proctor, Gerald P. Rumierz, Xiaomin Zhang.
Application Number | 20110223486 13/044708 |
Document ID | / |
Family ID | 44560305 |
Filed Date | 2011-09-15 |
United States Patent
Application |
20110223486 |
Kind Code |
A1 |
Zhang; Xiaomin ; et
al. |
September 15, 2011 |
BIAXIALLY ORIENTED POROUS MEMBRANES, COMPOSITES, AND METHODS OF
MANUFACTURE AND USE
Abstract
At least a selected microporous membrane is made by a
dry-stretch process and has substantially round shaped pores and a
ratio of machine direction tensile strength to transverse direction
tensile strength in the range of 0.5 to 6.0. The method of making
the foregoing microporous membrane may include the steps of:
extruding a polymer into a nonporous precursor, and biaxially
stretching the nonporous precursor, the biaxial stretching
including a machine direction stretching and a transverse direction
stretching, the transverse direction including a simultaneous
controlled machine direction relax. At least selected embodiments
of the invention may be directed to biaxially oriented porous
membranes, composites including biaxially oriented porous
membranes, biaxially oriented microporous membranes, biaxially
oriented macroporous membranes, battery separators, filtration
media, humidity control media, flat sheet membranes, liquid
retention media, and the like, related methods, methods of
manufacture, methods of use, and the like.
Inventors: |
Zhang; Xiaomin; (Charlotte,
NC) ; Rumierz; Gerald P.; (Fort Mill, SC) ;
Humiston; Karl F.; (Fort Mill, SC) ; Haire; Charles
E.; (Lancaster, SC) ; Fields; Tyrone S.;
(Charlotte, NC) ; Braswell; Michael A.;
(Charlotte, NC) ; Proctor; Ronald A.; (York,
SC) |
Family ID: |
44560305 |
Appl. No.: |
13/044708 |
Filed: |
March 10, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61313152 |
Mar 12, 2010 |
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Current U.S.
Class: |
429/247 ;
210/500.22; 264/46.1; 428/220; 428/315.5; 442/286; 442/304;
442/394; 521/141; 521/143; 521/182; 521/183; 521/186; 521/50 |
Current CPC
Class: |
Y02E 60/10 20130101;
H01M 50/449 20210101; Y10T 442/3854 20150401; H01M 50/403 20210101;
B01D 2325/021 20130101; H01M 50/581 20210101; C08G 69/00 20130101;
Y10T 428/249978 20150401; Y10T 442/40 20150401; H01M 10/0525
20130101; H01M 50/572 20210101; B29L 2031/755 20130101; Y10T
442/674 20150401; H01M 10/0565 20130101; B29C 55/143 20130101; H01M
50/411 20210101; B01D 67/0027 20130101; B01D 2325/02 20130101; B29C
55/16 20130101 |
Class at
Publication: |
429/247 ;
264/46.1; 210/500.22; 428/220; 428/315.5; 442/394; 442/286;
442/304; 521/143; 521/141; 521/182; 521/183; 521/186; 521/50 |
International
Class: |
H01M 2/18 20060101
H01M002/18; B29D 7/01 20060101 B29D007/01; B01D 69/02 20060101
B01D069/02; B01D 71/06 20060101 B01D071/06; B32B 5/18 20060101
B32B005/18; C08F 110/00 20060101 C08F110/00; C08F 116/06 20060101
C08F116/06; C08G 63/00 20060101 C08G063/00; C08G 69/00 20060101
C08G069/00; C08G 4/00 20060101 C08G004/00; C08J 9/00 20060101
C08J009/00 |
Claims
1. A porous membrane comprising: at least one layer of porous
polymer film made by a dry-stretch process including the steps of:
extruding a polymer into at least a single layer nonporous
precursor, and biaxially stretching the nonporous precursor, the
biaxial stretching including a machine direction stretching and a
transverse direction stretching, the transverse direction
stretching including a simultaneous controlled machine direction
relax, and having substantially round shaped pores, a porosity of
about 40% to 90%, a ratio of machine direction tensile strength to
transverse direction tensile strength in the range of about 0.5 to
5.0, a Gurley of less than about 100, a mean flow pore diameter of
at least about 0.04 microns, an Aquapore size of at least about
0.07 microns, and a hydro-head pressure greater than about 140
psi.
2. The membrane according to claim 1, wherein the machine direction
stretching of said biaxially stretching includes the step of
transverse direction stretching with simultaneous machine direction
stretching, and wherein said biaxially stretching further includes
the step of transverse direction relax.
3. The membrane according to claim 2, wherein said biaxially
stretching of said nonporous precursor further includes an
additional step of machine direction stretching.
4. The membrane according to claim 1, wherein said dry-stretch
process further includes the step of: machine direction stretching
to form a porous intermediate prior to said biaxial stretching.
5. The membrane according to claim 1, wherein said biaxially
stretching of said nonporous precursor includes the machine
direction stretching, an additional transverse direction stretching
with simultaneous machine direction stretching, and a transverse
direction relax.
6. The membrane according to claim 1, wherein said dry-stretch
process includes the steps of: machine direction stretching
followed by said biaxial stretching including said transverse
direction stretching with simultaneous controlled machine direction
relax, a second transverse direction stretching with simultaneous
machine direction stretching, followed by transverse direction
relax.
7. The membrane according to claim 1, with said porous polymer film
further having a thickness of at least about 8 microns, a
transverse direction tensile strength of at least about 300
kgf/cm2, a standard deviation of mean flow pore diameter of less
than about 0.025, a water intrusion pressure of at least about 80
psi, and a WVTR of at least about 8,000 g/m.sup.2-day.
8. The membrane according to claim 1, with said porous polymer film
further having a transverse direction shrinkage of less than about
1.0% at 90.degree. C.
9. The membrane according to claim 1, with said porous polymer film
further having a transverse direction shrinkage of less than about
1.5% at 105.degree. C.
10. The membrane according to claim 1, with said porous polymer
film further having a transverse direction shrinkage of less than
about 3.0% at 120.degree. C.
11. The membrane according to claim 1, with said porous polymer
film further having a thickness in a range of about 8 microns to 80
microns.
12. The membrane according to claim 1, wherein said nonporous
precursor is one of a blown film and a slot die film.
13. The membrane according to claim 1, wherein said nonporous
precursor is a single layer precursor formed by at least one of
single layer extrusion and multilayer extrusion.
14. The membrane according to claim 1, wherein said nonporous
precursor is a multilayer precursor formed by at least one of
coextrusion and lamination.
15. The membrane according to claim 1, wherein said porous polymer
film comprises one of polypropylene, polyethylene, blends thereof,
and combinations thereof.
16. The membrane according to claim 1, wherein said precursor is
one of a single layer precursor and a multilayer precursor.
17. The membrane according to claim 1, wherein said membrane
further includes at least one nonwoven, woven, or knit layer bonded
to at least one side of said porous polymer film.
18. The membrane according to claim 1, wherein said membrane has
substantially round shaped pores, a porosity of about 40% to 90%, a
ratio of machine direction tensile strength to transverse direction
tensile strength in the range of about 0.5 to 5.0, a Gurley of less
than about 100, a mean flow pore diameter of at least about 0.04
microns, an Aquapore size of at least about 0.07 microns, and a
hydro-head pressure greater than about 140 psi.
19. The membrane according to claim 1 wherein said polymer being
selected from the group consisting of polyolefins, fluorocarbons,
polyamides, polyesters, polyacetals (or polyoxymethylenes),
polysulfides, polyphenyl sulfide, polyvinyl alcohols, co-polymers
thereof, blends thereof, and combinations thereof.
20. The membrane according to claim 1 with said porous polymer film
further having a porosity of about 65% to 90%, a ratio of machine
direction tensile strength to transverse direction tensile strength
in the range of about 1.0 to 5.0, a Gurley of less than about 20, a
mean flow pore diameter of at least about 0.05 microns, an Aquapore
size of at least about 0.08 microns, and a hydro-head pressure
greater than about 145 psi.
21. The membrane according to claim 1, wherein said substantially
round shaped pores have at least one of an aspect ratio in the
range of about 0.75 to 1.25 and a sphericity factor in the range of
about 0.25 to 8.0.
22. At least one of a filtration membrane, a humidity control
membrane, a gas and/or liquid separation membrane, a selective
passage of humidity and blockage of liquid water membrane, and a
multi-layered membrane structure comprising the membrane of claim
1.
23. The membrane according to claim 1, wherein said biaxially
stretching step of said dry-stretch process includes the
simultaneous biaxial stretching of a plurality of separate,
superimposed, layers or plies of nonporous precursor, wherein none
of the plies are bonded together during the stretching process.
24. The membrane according to claim 1, wherein said biaxially
stretching step of said dry-stretch process includes the
simultaneous biaxial stretching of a plurality of bonded,
superimposed, layers or plies of nonporous precursor, wherein all
of the plies are bonded together during the stretching process.
25. A battery separator comprising: at least one layer of porous
polymer film made by a dry-stretch process including the steps of:
extruding a polymer into at least a single layer nonporous
precursor, and biaxially stretching the nonporous precursor, the
biaxial stretching including a machine direction stretching and a
transverse direction stretching, the transverse direction
stretching including a simultaneous controlled machine direction
relax, and having substantially round shaped pores, a porosity of
about 40% to 70%, a ratio of machine direction tensile strength to
transverse direction tensile strength in the range of about 0.5 to
5.0, a Gurley of less than about 300, a mean flow pore diameter of
at least about 0.01 microns, and an Aquapore size of at least about
0.04 microns.
26. The battery separator according to claim 25, wherein said
substantially round shaped pores have at least one of an aspect
ratio in the range of about 0.75 to 1.25 and a sphericity factor in
the range of about 0.25 to 8.0.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of and priority to
pending U.S. Provisional Patent Application Ser. No. 61/313,152
filed Mar. 12, 2010.
FIELD OF THE INVENTION
[0002] The invention is directed to biaxially oriented porous
membranes, composites including biaxially oriented porous
membranes, biaxially oriented microporous membranes, biaxially
oriented macroporous membranes, battery separators, filtration
media, humidity control media, flat sheet membranes, liquid
retention media, and the like, related methods, methods of
manufacture, methods of use, and the like.
BACKGROUND OF THE INVENTION
[0003] Microporous polymer membranes are known, can be made by
various processes, and the process by which the membrane is made
may have a material impact upon the membrane's physical attributes.
See, for example, Kesting, Robert E., Synthetic Polymeric
Membranes, A Structural Perspective, Second Edition, John Wiley
& Sons, New York, N.Y., (1985). Three different known processes
for making microporous polymer membranes include: the dry-stretch
process (also known as the CELGARD process), the wet process, and
the particle stretch process.
[0004] The dry-stretch process (the CELGARD process) refers to a
process where pore formation results from stretching a nonporous,
semicrystalline, extruded polymer precursor in the machine
direction (MD stretch). See, for example, Kesting, Ibid. pages
290-297, incorporated herein by reference. Such a dry-stretch
process is different from the wet process and the particle stretch
process. Generally, in the wet process, also known as the phase
inversion process, the extraction process, or the TIPS process, the
polymeric raw material is mixed with a processing oil (sometimes
referred to as a plasticizer), this mixture is extruded, and pores
are then formed when the processing oil is removed (these films may
be stretched before or after the removal of the oil). See, for
example, Kesting, Ibid. pages 237-286, incorporated herein by
reference.
[0005] Generally, in the particle stretch process, the polymeric
raw material is mixed with particulate, this mixture is extruded,
and pores are formed during stretching when the interfaces between
the polymer and the particulate fracture due to the stretching
forces. See, for example, U.S. Pat. Nos. 6,057,061 and 6,080,507,
incorporated herein by reference.
[0006] Moreover, the membranes arising from these different
formation processes are usually physically different and the
process by which each is made typically distinguishes one membrane
from the other. For example, dry-stretch process membranes may have
slit shaped pores due to the stretching of the precursor in the
machine direction (the MD)(for example, see FIGS. 1-3). Wet process
membranes tend to have rounder pores and a lacelike appearance due
to the oil or plasticizer and the stretching of the precursor in
the machine direction (MD) and in the transverse machine direction
or transverse direction (the TD)(for example, see FIG. 4). Particle
stretch process membranes, on the other hand, may have oval shaped
pores as the particulate and machine direction stretching (MD
stretch) tend to form the pores (for example, see FIG. 5A).
Accordingly, each membrane may be distinguished from the other by
its method of manufacture.
[0007] While membranes made by the dry-stretch process have met
with excellent commercial success, such as a variety of
CELGARD.RTM. dry-stretch porous membranes sold by Celgard, LLC of
Charlotte, N.C., including flat sheet membranes, battery
separators, hollow fibers, and the like, there is a need to
improve, modify or enhance at least selected physical attributes
thereof, so that they may be used in a wider spectrum of
applications, may perform better for particular purposes, or the
like.
[0008] The use of air-filters to remove or reduce airborne
contaminants such as dust, dust mites, molds, bacteria, dog dander,
odors, and gases is generally known. Conventionally, air-filters
include a filter medium formed from a bat, mat or sheet of porous
material that is pleated and placed in a rectangular frame or
support or folded into a corrugated oval or cylinder to provide a
large filtration area in a relatively small volume.
[0009] While at least certain air filters have met with commercial
success, there is a need for improved filtration media or filters
so that they may be used in a wider spectrum of filtration or
separation applications, may perform better for particular
purposes, or the like.
[0010] The use of porous materials for the selective passage of
gases and blockage of liquids is known. For example, LIQUI-CEL.RTM.
hollow fiber membrane contactors, sold by Membrana-Charlotte a
division of Celgard, LLC of Charlotte, N.C., are used for degassing
or debubbling liquids. More particularly, LIQUI-CEL.RTM. membrane
contactors are used extensively for deaeration of liquids in the
microelectronics, pharmaceutical, power, food, beverage,
industrial, photographic, ink, and analytical markets around the
world.
[0011] The use of porous materials for filtration or separation
processes is known. For example, various flat sheet membranes
marketed or sold by Membrana GmbH of Wuppertal, Germany, or by
Celgard, LLC and Daramic, LLC both of Charlotte, N.C., are used for
filtration or separation processes. More particularly, such flat
sheet membranes have been used to separate solid particles and
liquids, gases from liquids, particles from gases, and the
like.
[0012] While certain such porous materials for filtration or
separation processes have met with commercial success, there is a
need for improved porous materials so that they may be used in a
wider spectrum of applications, may perform better for particular
purposes, or the like.
[0013] The use of porous materials for the selective passage of
humidity (moisture vapor) and blockage of liquid water, liquid
desiccant, or other aqueous solutions may be known. In such
liquid-desiccant systems, temperature and humidity may be
controlled by a salt solution (or desiccant) which absorbs or emits
water vapor.
[0014] The use of porous materials for the selective passage of
water vapor (heat and moisture) and the blockage of gasses (exhaust
and intake gases) may be known in connection with energy recovery
ventilation (ERV) wherein heat and humidity are exchanged between
make-up and exhaust air in a ventilation system.
[0015] The use of porous materials for the selective passage of
pure or fresh water and blockage of salt or salt water is also
known in connection with reverse osmosis desalination wherein a
porous material, such as a reverse osmosis filter (RO filter) which
allows pure water (fresh water) to pass there through but which
restrains salt. With the salt water at a high pressure, fresh water
is forced through the porous material and forms the fresh water
stream.
[0016] The use of porous materials for the selective passage of
water vapor or humidity (moisture vapor) and blockage of liquid
salt water may also be known in connection with steam desalination
wherein a porous material, such as a high charge density membrane
may hold back salt water but pass salt-free water vapor to separate
salt water and fresh water. With the salt water at a high
temperature, fresh water vapor emits from the salt water, may
migrate through the porous material, and condense to form a fresh
water stream.
[0017] The use of porous materials for the selective passage of
gases or humidity (moisture vapor) and blockage of liquids such as
water may be known in connection with fuel cells such as hydrogen
fuel cells having a proton exchange membrane (PEM) that must stay
continually humidified. Waste water in the form of humid vapor may
pass through a porous material and may be collected in a waste
water holding compartment or discharged.
[0018] While possibly certain such porous materials for the
selective passage of gases or humidity (moisture vapor) and
blockage of liquid water or salt water may have met with commercial
success, such as RO membranes sold by Dow Chemical, or expanded
polytetrafluoroethylene (ePTFE) membranes sold by W. L. Gore, BHA,
and others, there is a need for improved porous materials so that
they may be used in a wider spectrum of applications, may perform
better for particular purposes, or the like.
SUMMARY OF THE INVENTION
[0019] In accordance with at least selected porous material, film,
layer, membrane, laminate, coextrusion, or composite embodiments of
the present invention, some areas of improvement may include pore
shapes other than slits, round shaped pores, increased transverse
direction tensile strength, a balance of MD and TD physical
properties, high performance related to, for example, moisture
transport and hydrohead pressure, reduced Gurley, high porosity
with balanced physical properties, uniformity of pore structure
including pore size and pore size distribution, enhanced
durability, composites of such membranes with other porous
materials, composites or laminates of such membranes, films or
layers with porous nonwovens, coated membranes, coextruded
membranes, laminated membranes, membranes having desired moisture
transport (or moisture vapor transport), hydrohead performance, and
physical strength properties, usefulness in more physically abusive
environments without loss of desirable membrane features,
combination of membrane moisture transport performance combined
with the macro physical properties, being hydrophobic, highly
permeable, chemically and mechanically stable, having high tensile
strength, combinations thereof, and/or the like.
[0020] While certain membranes made by the dry-stretch process have
met with excellent commercial success, there is a need to improve,
modify or enhance at least selected physical attributes thereof, so
that they may be used in a wider spectrum of applications, perform
better for particular purposes, and/or the like. In accordance with
at least selected embodiments of dry-stretch process membranes of
the present invention, some areas of improvement may include pore
shapes other than slits, round shaped pores, increased transverse
direction tensile strength, a balance of MD and TD physical
properties, uniformity of pore structure including pore size and
pore size distribution, high performance related to, for example,
moisture transport (or moisture vapor transport) and hydrohead
pressure, reduced Gurley, high porosity with balanced physical
properties, enhanced durability, composites of such membranes with
other porous materials, composites or laminates of such membranes
with porous nonwovens, coated membranes, coextruded membranes,
laminated membranes, membranes having desired moisture transport,
hydrohead performance, and physical strength properties, useful in
more physically abusive environments without loss of desirable
membrane features, combination of the membrane moisture transport
performance combined with the macro physical properties,
combinations thereof, and/or the like.
[0021] In accordance with at least selected possibly preferred
embodiments, the porous membrane of the present invention is
possibly preferably a dry-stretch process, porous membrane, film,
layer, or composite that is hydrophobic, highly permeable,
chemically and mechanically stable, has high tensile strength, and
combinations thereof. These properties appear to make it an ideal
membrane or film for the following applications, each of which
(with the exception of air filtration) may involve the selective
passage of moisture vapor (or other gases) and blockage of liquid
water (or other liquids): [0022] 1. HVAC: [0023] a.
Liquid-desiccant (LD) air conditioning (temperature and humidity
control): In a membrane-based LD system, temperature and humidity
may be controlled by a salt solution which absorbs or emits water
vapor through a porous membrane. Heat is the motive force in the
system (not pressure, as in most air conditioning systems). To make
the system work, it may be necessary to have a hydrophobic membrane
(to hold back the liquid) that readily passes water vapor. [0024]
b. Water-based air conditioning (temperature and humidity control):
Evaporative cooling systems or cooling water systems operate on a
somewhat different principle than the LD systems, but would use the
same essential properties of the membrane. [0025] c. Energy
recovery ventilation (ERV): The simplest HVAC application uses the
membrane as a key component of a heat and humidity exchange between
make-up and exhaust air. [0026] 2. Desalination: Steam desalination
applications use the same membrane properties as HVAC. Because the
membrane holds back liquid salt water but passes water vapor, a
system can be constructed which has salt water and fresh water
separated by a membrane. With the salt water at a higher
temperature, fresh water vapor emits from the salt water, migrates
through the membrane, and condenses to form the fresh water stream.
[0027] 3. Fuel cells: In a fuel cell, the proton exchange membrane
(PEM) must stay continually humidified. This can be accomplished
with the use of a membrane-based humidification unit. [0028] 4.
Liquid and/or air filtration: In these embodiments, the porous
membrane may act as a simple filter. As the liquid, vapor, gas, or
air passes through the membrane, particles that are too large to
pass through the pores are blocked at the membrane surface.
Particularly in the cases of liquid and air filtration, the unique
pore structure of at least selected embodiments of the present
invention may provide embodiments, materials or membranes that have
certain specific benefits, such as the benefits of durability, high
efficiency, narrow pore size distribution, and uniform flow
rate.
[0029] In accordance with at least selected porous material or
porous membrane embodiments of the present invention, at least a
selected porous mono-layer polypropylene (monolayer PP) membrane
has excellent balance of MD and TD physical properties while also
being a high performance membrane as measured by the moisture
transport and hydrohead performance. This selected monolayer PP
membrane may also have high porosity (>60%) but still maintain
the balanced physical properties when compared to more traditional
membranes. Also, this selected monolayer PP membrane or film can be
produced in union with or laminated to a porous polypropylene (PP)
nonwoven material (nonwoven PP) on one or both sides thereof. The
resultant composite, membrane or product (monolayer PP/nonwoven PP)
or (nonwoven PP/monolayer PP/nonwoven PP) may preferably retain the
excellent moisture transport and even more improved hydrohead
performance. Also, this resultant composite product (monolayer
PP/nonwoven PP) or (nonwoven PP/monolayer PP/nonwoven PP) may have
physical strength properties that far exceed comparative membranes.
Therefore, this new resultant composite product (monolayer
PP/nonwoven PP) or (nonwoven PP/monolayer PP/nonwoven PP) may have
the added advantage of being useful in more physically abusive
environments without a loss of the highly desirable membrane
features. It is believed that these selected monolayer PP membrane
and composite products (monolayer PP; monolayer PP/nonwoven PP; or,
nonwoven PP/monolayer PP/nonwoven PP) are unique in their
combination of membrane moisture transport performance combined
with their macro physical properties. For example, prior membranes
may have had porosity but not sufficient hydrohead pressure or
performance, other membranes were too fragile, other membranes were
strong but lacked other properties, or the like, while at least
selected embodiments of the present invention may have, for
example, desired porosity, moisture transport, hydrohead pressure,
strength, and the like.
[0030] In accordance with at least selected porous material or
porous membrane embodiments of the present invention, at least a
selected porous multi-layer polypropylene (multilayer PP) membrane
has excellent balance of MD and TD physical properties while also
being a high performance membrane as measured by the moisture
transport and hydrohead performance. This selected multilayer PP
membrane may also have high porosity (>60%) but still maintain
the balanced physical properties when compared to more traditional
membranes. Also, this selected multilayer PP membrane or film can
be produced in union with or laminated to a porous polypropylene
(PP) nonwoven material (nonwoven PP) on one or both sides thereof.
The resultant composite, membrane or product (multilayer
PP/nonwoven PP) or (nonwoven PP/multilayer PP/nonwoven PP) may
preferably retain the excellent moisture transport and even more
improved hydrohead performance. Also, this resultant composite
product (multilayer PP/nonwoven PP) or (nonwoven PP/multilayer
PP/nonwoven PP) may have physical strength properties that far
exceed comparative membranes. Therefore, this new resultant
composite product (multilayer PP/nonwoven PP) or (nonwoven
PP/multilayer PP/nonwoven PP) may have the added advantage of being
useful in more physically abusive environments without a loss of
the highly desirable membrane features. It is believed that these
selected multilayer PP membrane and composite products (multilayer
PP; multilayer PP/nonwoven PP; or, nonwoven PP/multilayer
PP/nonwoven PP) are unique in their combination of membrane
moisture transport performance combined with their macro physical
properties. For example, prior membranes may have had porosity but
not sufficient hydrohead pressure or performance, other membranes
were too fragile, other membranes were strong but lacked other
properties, or the like, while at least selected embodiments of the
present invention may have, for example, desired porosity, moisture
transport, hydrohead pressure, strength, and the like.
[0031] In accordance with at least selected porous material or
porous membrane embodiments of the present invention, at least a
selected porous mono-layer polyethylene (monolayer PE) membrane has
excellent balance of MD and TD physical properties while also being
a high performance membrane as measured by the moisture transport
and hydrohead performance. This selected monolayer PE membrane may
also have high porosity (>60%) but still maintain the balanced
physical properties when compared to more traditional membranes.
Also, this selected monolayer PE membrane or film can be produced
in union with or laminated to a porous polyethylene (PE) nonwoven
material (nonwoven PE) or porous polypropylene (PP) nonwoven
material (nonwoven PP) on one or both sides thereof. The resultant
composite, membrane or product (monolayer PE/nonwoven PE) or
(nonwoven PE/monolayer PE/nonwoven PE) may preferably retain the
excellent moisture transport and even more improved hydrohead
performance. Also, this resultant composite product (monolayer
PE/nonwoven PE) or (nonwoven PE/monolayer PE/nonwoven PE) may have
physical strength properties that far exceed comparative membranes.
Therefore, this new resultant composite product (monolayer
PE/nonwoven PE) or (nonwoven PE/monolayer PE/nonwoven PE) may have
the added advantage of being useful in more physically abusive
environments without a loss of the highly desirable membrane
features. It is believed that these selected monolayer PE membrane
and composite products (monolayer PE; monolayer PE/nonwoven PE; or,
nonwoven PE/monolayer PE/nonwoven PE) are unique in their
combination of membrane moisture transport performance combined
with their macro physical properties. For example, prior membranes
may have had porosity but not sufficient hydrohead pressure or
performance, other membranes were too fragile, other membranes were
strong but lacked other properties, or the like, while at least
selected embodiments of the present invention may have, for
example, desired porosity, moisture transport, hydrohead pressure,
strength, and the like.
[0032] In accordance with at least selected porous material or
porous membrane embodiments of the present invention, at least a
selected porous multi-layer polyethylene (multilayer PE) membrane
has excellent balance of MD and TD physical properties while also
being a high performance membrane as measured by the moisture
transport and hydrohead performance. This selected multilayer PE
membrane may also have high porosity (>60%) but still maintain
the balanced physical properties when compared to more traditional
membranes. Also, this selected multilayer PE membrane or film can
be produced in union with or laminated to a porous polyethylene
(PE) nonwoven material (nonwoven PE) or porous polypropylene (PP)
nonwoven material (nonwoven PP) on one or both sides thereof. The
resultant composite, membrane or product (multilayer PE/nonwoven
PE) or (nonwoven PE/multilayer PE/nonwoven PE) may preferably
retain the excellent moisture transport and even more improved
hydrohead performance. Also, this resultant composite product
(multilayer PE/nonwoven PE) or (nonwoven PE/multilayer PE/nonwoven
PE) may have physical strength properties that far exceed
comparative membranes. Therefore, this new resultant composite
product (multilayer PE/nonwoven PE) or (nonwoven PE/multilayer
PE/nonwoven PE) may have the added advantage of being useful in
more physically abusive environments without a loss of the highly
desirable membrane features. It is believed that these selected
multilayer PE membrane and composite products (multilayer PE;
multilayer PE/nonwoven PE; or, nonwoven PE/multilayer PE/nonwoven
PE) are unique in their combination of membrane moisture transport
performance combined with their macro physical properties. For
example, prior membranes may have had porosity but not sufficient
hydrohead pressure or performance, other membranes were too
fragile, other membranes were strong but lacked other properties,
or the like, while at least selected embodiments of the present
invention may have, for example, desired porosity, moisture
transport, hydrohead pressure, strength, and the like.
[0033] In accordance with at least selected porous material or
porous membrane embodiments of the present invention, at least a
selected porous monolayer polymer membrane, for example, a
monolayer (may have one or more plies) polyolefin (PO) membrane,
such as a polypropylene (PP) and/or polyethylene (PE) (including
PE, PP, or PE+PP blends) monolayer membrane, has excellent balance
of MD and TD physical properties while also being a high
performance membrane as measured by the moisture transport (or
moisture vapor transport) and hydrohead performance. This selected
monolayer PO membrane may also have high porosity (>60%) but
still maintain the balanced physical properties when compared to
more traditional membranes. Also, this selected monolayer PO
membrane or film can be produced in union with or laminated to a
porous nonwoven material, such as a nonwoven polymer material, for
example, a PO nonwoven material (such as a porous polyethylene (PE)
nonwoven material (nonwoven PE) and/or porous polypropylene (PP)
nonwoven material (nonwoven PP) (including PE, PP, or PE+PP
blends)) on one or both sides thereof. The resultant composite,
membrane or product (monolayer PO/nonwoven PO) or (nonwoven
PO/monolayer PO/nonwoven PO) may preferably retain the excellent
moisture transport (or moisture vapor transport) and even more
improved hydrohead performance. Also, this resultant composite
product (monolayer PO/nonwoven PO) or (nonwoven PO/monolayer
PO/nonwoven PO) may have physical strength properties that far
exceed comparative membranes. Therefore, this new resultant
composite product (monolayer PO/nonwoven PO) or (nonwoven
PO/monolayer PO/nonwoven PO) may have the added advantage of being
useful in more physically abusive environments without a loss of
the highly desirable membrane features. It is believed that these
selected monolayer PO membrane and composite products (monolayer
PO; monolayer PO/nonwoven PO; or, nonwoven PO/monolayer PO/nonwoven
PO) are unique in their combination of membrane moisture transport
performance combined with their macro physical properties. For
example, prior membranes may have had porosity but not sufficient
hydrohead pressure or performance, other membranes were too
fragile, other membranes were strong but lacked other properties,
or the like, while at least selected embodiments of the present
invention may have, for example, desired porosity, moisture
transport, moisture vapor transport, hydrohead pressure, strength,
and the like.
[0034] In accordance with at least selected porous material or
porous membrane embodiments of the present invention, at least a
selected porous multi-layer polymer membrane, for example, a
multi-layer (two or more layer) polyolefin (PO) membrane, such as a
polypropylene (PP) and/or polyethylene (PE) (including PE, PP, or
PE+PP blends) multilayer membrane, has excellent balance of MD and
TD physical properties while also being a high performance membrane
as measured by the moisture transport (or moisture vapor transport)
and hydrohead performance. This selected multilayer PO membrane may
also have high porosity (>60%) but still maintain the balanced
physical properties when compared to more traditional membranes.
Also, this selected multilayer PO membrane or film can be produced
in union with or laminated to a porous PO nonwoven material (such
as a porous polyethylene (PE) nonwoven material (nonwoven PE)
and/or porous polypropylene (PP) nonwoven material (nonwoven PP))
on one or both sides thereof. The resultant composite, membrane or
product (multilayer PO/nonwoven PO) or (nonwoven PO/multilayer
PO/nonwoven PO) may preferably retain the excellent moisture
transport and even more improved hydrohead performance. Also, this
resultant composite product (multilayer PO/nonwoven PO) or
(nonwoven PO/multilayer PO/nonwoven PO) may have physical strength
properties that far exceed comparative membranes. Therefore, this
new resultant composite product (multilayer PO/nonwoven PO) or
(nonwoven PO/multilayer PO/nonwoven PO) may have the added
advantage of being useful in more physically abusive environments
without a loss of the highly desirable membrane features. It is
believed that these selected multilayer PO membrane and composite
products (multilayer PO; multilayer PO/nonwoven PO; or, nonwoven
PO/multilayer PO/nonwoven PO) are unique in their combination of
membrane moisture transport performance combined with their macro
physical properties. For example, prior membranes may have had
porosity but not sufficient hydrohead pressure or performance,
other membranes were too fragile, other membranes were strong but
lacked other properties, or the like, while at least selected
embodiments of the present invention may have, for example, desired
porosity, moisture transport, hydrohead pressure, strength, and the
like.
[0035] In accordance with at least selected porous material or
porous membrane embodiments of the present invention, the pores
(openings) have the following pore aspect ratios (based on physical
dimensions of the pore opening in the machine direction
(MD)(length), and transverse machine direction (TD)(width) by
measuring, for example, one or more of the pores (preferably
several of the pores to ascertain an average) in SEMs of the
surface, top or front (A side) of selected membranes or composites,
for example, mono-layer, bi-layer or tri-layer membranes: [0036]
Typical: [0037] MD/TD aspect ratio in range of 0.75 to 1.50 [0038]
Preferred: [0039] MD/TD aspect ratio in range of 0.75 to 1.25
[0040] Most Preferred: [0041] MD/TD aspect ratio in range of 0.85
to 1.25
[0042] In accordance with at least selected porous material or
porous membrane embodiments of the present invention, if the MD/TD
pore aspect ratio were 1.0, then a three-dimensional or 3D pore
sphericity factor or ratio (MD/TD/ND) range could be: 1.0 to 8.0 or
more; possibly preferred 1.0 to 2.5; and, most possibly preferred
1.0 to 2.0 or less (based on physical dimensions of the pore
openings in the machine direction (MD)(length), transverse machine
direction (TD)(width) and thickness direction or cross section
(ND)(thickness); for example, measuring the MD and TD of one or
more pores (preferably several pores to ascertain an average) in
SEMs of the surface, top or front (A side), or the surface, bottom
or back (B side), and measuring the ND of one or more pores
(preferably several pores to ascertain an average) in SEMs of the
cross-section, depth, or height (C side)(either length or width
cross-section or both)(the ND dimension may be of a different pore
than the MD and TD dimension as it may be difficult to measure the
ND, MD and TD dimension of the same pore).
[0043] In accordance with at least selected porous material or
porous membrane embodiments of the present invention, the pores
(openings) have the following pore aspect ratios (based on physical
dimensions of the pore opening in the machine direction
(MD)(length), and transverse machine direction (TD)(width) based on
measuring the pores in SEMs of the top or front (A side) of
selected mono-layer and tri-layer membranes: Typical numbers for
aspect ratio range of Machine direction MD (length) and Transverse
direction TD (width): MD/TD aspect ratio in range of 0.75 to
1.50
[0044] In accordance with at least selected porous material or
porous membrane embodiments of the present invention, the pores
(openings) have the following three dimensional or 3D pore
sphericity factors or ratios (based on physical dimensions of the
pore openings in the machine direction (MD)(length), transverse
machine direction (TD)(width) and thickness direction or cross
section (ND)(thickness); for example, measuring one or more pores
(preferably several pores to ascertain an average) in SEMs of the
surface, top or front (A side), the surface, bottom or back (B
side), and the cross-section, depth, or height (C side)(either
length or width cross-section or both)(the ND dimension may be of a
different pore than the MD and TD dimension as it may be difficult
to measure the ND, MD and TD dimension of the same pore) of
selected membranes, layers or composites, for example, of selected
mono-layer and tri-layer membranes: [0045] For example: [0046]
Typical: [0047] MD/TD aspect ratio in range of 0.75 to 1.50 [0048]
MD/ND dimension ratio in range of 0.50 to 7.50 [0049] TD/ND
dimension ratio in range of 0.50 to 5.00 [0050] Preferred: [0051]
MD/TD aspect ratio in range of 0.75 to 1.25 [0052] MD/ND dimension
ratio in range of 1.0 to 2.5 [0053] TD/ND dimension ratio in range
of 1.0 to 2.5 [0054] Most Preferred: [0055] MD/TD aspect ratio in
range of 0.85 to 1.25 [0056] MD/ND dimension ratio in range of 1.0
to 2.0 [0057] TD/ND dimension ratio in range of 1.0 to 2.0
[0058] In accordance with at least selected porous material or
porous membrane embodiments of the present invention, the pores
(openings) have the following pore sphericity factors or ratios
(based on physical dimensions of the pore opening in the machine
direction (MD)(length), transverse machine direction (TD)(width)
and thickness direction or cross section (ND)(thickness) based on
measuring the pores in SEMs of the top or front (A side) and the
length and with cross-sections (C side) of selected mono-layer and
tri-layer membranes: [0059] Typical numbers for sphericity factor
or ratio range of Machine direction MD (length), Transverse
direction TD (width), and [0060] Thickness direction ND (vertical
height): [0061] MD/TD aspect ratio in range of 0.75 to 1.50 [0062]
MD/ND dimension ratio in range of 0.50 to 7.50 [0063] TD/ND
dimension ratio in range of 0.50 to 5.00
[0064] In accordance with at least selected embodiments of the
present invention, a microporous membrane is made by a dry-stretch
process and has substantially round shaped pores and a ratio of
machine direction tensile strength to transverse direction tensile
strength in the range of 0.5 to 6.0, preferably 0.5 to 5.0. The
method of making the foregoing microporous membrane includes the
steps of: extruding a polymer into a nonporous precursor, and
biaxially stretching the nonporous precursor, the biaxial
stretching including a machine direction stretching and a
transverse direction stretching, the transverse direction
stretching including a simultaneous controlled machine direction
relax.
[0065] In accordance with at least selected embodiments of the
present invention, a porous membrane is made by a modified
dry-stretch process and has substantially round shaped pores, a
ratio of machine direction tensile strength to transverse direction
tensile strength in the range of 0.5 to 6.0, and has low Gurley as
compared to prior dry-stretch membranes, has larger and more
uniform mean flow pore diameters as compared to prior dry-stretch
membranes, or both low Gurley and larger and more uniform mean flow
pore diameters.
[0066] While certain membranes made by the conventional dry-stretch
process have met with excellent commercial success, in accordance
with at least selected embodiments of the present invention, there
is provided improved, modified or enhanced at least selected
physical attributes thereof, so that they may be used in a wider
spectrum of applications, may perform better for particular
purposes, and/or the like.
[0067] While at least certain air filters have met with commercial
success, in accordance with at least selected embodiments of the
present invention, there is provided improved, modified or enhanced
filtration media so that they may be used in a wider spectrum of
filtration or separation applications, may perform better for
particular purposes, and/or the like.
[0068] While at least certain flat sheet porous materials for
filtration or separation processes have met with commercial
success, in accordance with at least selected embodiments of the
present invention, there is provided improved, modified or enhanced
porous materials so that they may be used in a wider spectrum of
applications, may perform better for particular purposes, and/or
the like.
[0069] While certain porous materials for the selective passage of
gases or humidity (moisture vapor) and blockage of liquid water or
salt water may have met with commercial success, such as RO
membranes sold by Dow Chemical, ePTFE membranes sold by W. L. Gore,
BHA, and others, in accordance with at least selected embodiments
of the present invention, there is provided improved, modified or
enhanced porous materials so that they may be used in a wider
spectrum of applications, may perform better for particular
purposes, and/or the like.
[0070] In accordance with at least selected embodiments of the
present invention, an air-filter cartridge includes at least one
pleated porous membrane such as a microporous membrane.
DESCRIPTION OF THE DRAWINGS
[0071] For the purpose of illustrating the various aspects or
embodiments of the invention, there is shown in the drawings a form
that is presently exemplary; it being understood, however, that the
invention is not limited to the embodiments, precise arrangements
or instrumentalities shown.
[0072] FIG. 1 is a photograph (SEM surface photomicrograph) of a
CELGARD.RTM. monolayer, conventional dry-stretch, polypropylene,
battery separator.
[0073] FIG. 2 is a photograph of a prior art dry-stretched membrane
(single ply membrane).
[0074] FIG. 3 is a photograph of a prior art dry-stretched membrane
(multi-ply membrane, plies laminated then stretched).
[0075] FIG. 4 is a photograph (SEM surface photomicrograph) of a
CELGARD.RTM. monolayer, wet process, polyethylene battery
separator.
[0076] FIG. 5A is a photograph (SEM surface photomicrograph) of a
particle stretch membrane. FIG. 5B is a photograph (SEM
cross-section photomicrograph) of a particle stretch membrane.
[0077] FIG. 6 is a photograph (SEM surface photomicrograph) of a
membrane in accordance with one embodiment of the present invention
(single ply membrane, biaxially oriented process).
[0078] FIG. 7 is a photograph (SEM surface photomicrograph) of a
membrane in accordance with another embodiment of the present
invention (multi-ply membrane, plies laminated together then
stretched, biaxially oriented process).
[0079] FIG. 8 is a photograph (SEM surface photomicrograph) of a
membrane in accordance with yet another embodiment of the instant
invention (multi-ply membrane, plies coextruded then stretched,
biaxially oriented process).
[0080] FIG. 9 is a schematic representation of exemplary TD stretch
processes in accordance with at least one embodiment of the
biaxially oriented membrane manufacturing method of the present
invention.
[0081] FIG. 10 is a photograph (SEM surface photomicrograph) of a
conventional CELGARD.RTM. 2500 membrane (PP monolayer, dry-stretch
process) at 20,000.times. magnification.
[0082] FIG. 11 is a photograph (SEM surface photomicrograph) of the
membrane of FIG. 10 at 5,000.times. magnification.
[0083] FIG. 12 is a photograph (SEM cross section photomicrograph)
of the membrane of FIGS. 10 and 11 at 20,000.times.
magnification.
[0084] FIGS. 13 and 14 are respective photographs (SEM surface A
(top) photomicrographs at 20,000.times. and 5,000.times.
magnification) of a membrane Sample B in accordance with another
membrane embodiment of the instant invention (PP monolayer,
collapsed bubble, biaxially oriented process).
[0085] FIGS. 15 and 16 are respective photographs (SEM surface B
(bottom) photomicrographs at 20,000.times. and 5,000.times.
magnification) of the membrane Sample B of FIGS. 13 and 14.
[0086] FIGS. 17 and 18 are respective photographs (SEM cross
section photomicrographs at 20,000.times. and 5,000.times.
magnification) of the membrane Sample B of FIGS. 13 to 16.
[0087] FIGS. 19, 20 and 21 are respective photographs (SEM surface
A (top) photomicrographs at 20,000.times., 5,000.times. and
1,000.times. magnification) of a membrane Sample C in accordance
with still another membrane or composite embodiment of the instant
invention (PP monolayer [of Sample B]/nonwoven PP, laminated
[heat+pressure]).
[0088] FIGS. 22, 23 and 24 are respective photographs (SEM surface
B (bottom) photomicrographs at 20,000.times., 5,000.times. and
1,000.times. magnification) of the membrane Sample C of FIGS. 19 to
21.
[0089] FIGS. 25 and 26 are respective photographs (SEM cross
section photomicrographs at 20,000.times. and 5,000.times.
magnification) of the membrane Sample C of FIGS. 19 to 24.
[0090] FIG. 27 is a photograph (SEM cross section photomicrograph
at 615.times. magnification) of the membrane Sample C of FIGS. 19
to 26 with the nonwoven PP layer on top (inverted).
[0091] FIG. 27A is a photograph (SEM cross section photomicrograph
at 3,420.times. magnification) of a portion of the monolayer PP
layer of the membrane Sample C of FIG. 27 (note the rectangle in
FIG. 27).
[0092] FIGS. 28 and 29 are respective photographs (SEM surface A
(top) photomicrographs at 20,000.times. and 5,000.times.
magnification) of a membrane Sample A in accordance with yet
another membrane embodiment of the instant invention (monolayer PP,
non-collapse bubble, biaxially oriented process).
[0093] FIGS. 30 and 31 are respective photographs (SEM surface B
(bottom) photomicrographs at 20,000.times. and 5,000.times.
magnification) of the membrane Sample A of FIGS. 28 and 29.
[0094] FIGS. 32, 33 and 34 are respective photographs (SEM surface
A (top) photomicrographs at 20,000.times., 5,000.times. and
1,000.times. magnification) of a membrane or composite Sample G in
accordance with another embodiment of the instant invention (PP
monolayer, non-collapse bubble, biaxially oriented process [of
Sample A]/nonwoven PP, laminated [heat+pressure]).
[0095] FIGS. 35, 36 and 37 are respective photographs (SEM surface
B (bottom) photomicrographs at 20,000.times., 5,000.times. and
1,000.times. magnification) of the membrane Sample G of FIGS. 32 to
34.
[0096] FIGS. 38 and 39 are respective photographs (SEM cross
section photomicrographs at 20,000.times. and 3,420.times.
magnification) of the membrane Sample G of FIGS. 32 to 37.
[0097] FIG. 40 is a photograph (SEM cross section photomicrograph
at 615.times. magnification) of the membrane Sample G of FIGS. 32
to 39 with the nonwoven PP layer on top (inverted).
[0098] FIG. 40A is a photograph (SEM cross section photomicrograph
at 3,420.times. magnification) of a portion of the monolayer PP
layer of the membrane Sample G of FIG. 40 (note the rectangle in
FIG. 40).
[0099] FIGS. 41 and 42 are respective photographs (SEM surface A
(top) photomicrographs at 20,000.times. and 5,000.times.
magnification) of a membrane Sample E in accordance with still
another membrane embodiment of the instant invention (PP monolayer,
collapsed bubble, biaxially oriented process).
[0100] FIGS. 43 and 44 are respective photographs (SEM surface B
(bottom) photomicrographs at 20,000.times. and 5,000.times.
magnification) of the membrane Sample E of FIGS. 41 and 42.
[0101] FIGS. 45 and 46 are respective photographs (SEM cross
section photomicrographs at 20,000.times. and 5,000.times.
magnification) of the membrane Sample E of FIGS. 41 to 44.
[0102] FIGS. 47 and 48 are respective photographs (SEM surface A
(top) photomicrographs at 20,000.times. and 5,000.times.
magnification) of a membrane Sample F in accordance with yet
another membrane embodiment of the instant invention (monolayer PP,
non-collapse bubble, biaxially oriented process).
[0103] FIGS. 49 and 50 are respective photographs (SEM surface B
(bottom) photomicrographs at 20,000.times. and 5,000.times.
magnification) of the membrane Sample F of FIGS. 47 and 48.
[0104] FIGS. 51 and 52 are respective photographs (SEM surface A
(top) photomicrographs at 20,000.times. and 5,000.times.
magnification) of a membrane Sample D in accordance with still yet
another membrane embodiment of the instant invention (coextruded
PP/PE/PP tri-layer, collapsed bubble, biaxially oriented
process).
[0105] FIGS. 53 and 54 are respective photographs (SEM surface B
(bottom) photomicrographs at 20,000.times. and 5,000.times.
magnification) of the membrane Sample D of FIGS. 51 and 52.
DESCRIPTION OF THE INVENTION
[0106] In accordance with at least selected embodiments of the
present invention, a microporous membrane is made by a preferred
modified dry-stretch process (biaxially oriented process) and has
substantially round shaped pores and a ratio of machine direction
tensile strength to transverse direction tensile strength in the
range of 0.5 to 6.0, preferably 0.5 to 5.0, most preferably 0.5 to
4.0. A porous membrane such as a microporous membrane is a thin,
pliable, polymeric sheet, foil, or film having a plurality of pores
therethrough. Such membranes may be single or multiple plies,
single or multiple layers, composites, laminates, or the like and
may be used in a wide variety of applications, including, but not
limited to, mass transfer membranes, pressure regulators,
filtration membranes, medical devices, separators for
electrochemical storage devices, membranes for use in fuel cells,
and/or the like.
[0107] At least selected embodiments of the membrane of the present
invention are made by a modified version of the dry-stretch process
(also known as the CELGARD process). The dry-stretch process refers
to a process where pore formation results from stretching the
nonporous precursor. See, Kesting, R., Synthetic Polymeric
Membranes, A structural perspective, Second Edition, John Wiley
& Sons, New York, N.Y., (1985), pages 290-297, incorporated
herein by reference. The dry-stretch process is distinguished from
the wet process and particle stretch process, as discussed
above.
[0108] At least selected membrane embodiments of the present
invention may be distinguished from prior dry-stretched membranes
in at least two ways: 1) substantially round shape pores, and 2) a
ratio of machine direction tensile strength to transverse direction
tensile strength in the range of 0.5 to 6.0, preferably 0.5 to 5.0,
most preferably 0.5 to 4.0.
[0109] At least selected membrane embodiments of the present
invention may be distinguished from prior dry-stretched membranes
in at least five ways: 1) substantially round shape pores, 2) a
ratio of machine direction tensile strength to transverse direction
tensile strength in the range of 0.5 to 6.0, 3) mean flow pore
diameters in the range of 0.025 to 0.150 um, 4) high gas or
moisture permeability, with JIS Gurley in the range of 0.5 to 200
seconds, and (5) hydrohead pressure higher than 140 psi.
[0110] Regarding the pore shape, the pores are preferably
characterized as substantially round shaped. See, for example,
FIGS. 6-8, 13-16, 19, 20, 22, 23, 28-31, 32, 33, 35, 36, 41-44,
47-50, and 51-54. This pore shape is contrasted with the slit
shaped pores of the prior conventional dry-stretched membranes. See
FIGS. 1-3 and Kesting, Ibid. Further, the pore shape of the instant
membrane may be characterized by an aspect ratio, the ratio of the
length (MD) to the width (TD) of the pore. In one embodiment of the
instant membrane, the aspect ratio ranges from 0.75 to 1.25. This
is contrasted with the aspect ratio of the prior dry-stretched
membranes which are greater than 5.0. See Table I below.
[0111] Regarding the ratio of machine direction (MD) tensile
strength to transverse direction (TD) tensile strength, in one
embodiment, this ratio is between 0.5 to 6.0, preferably 0.5 to
5.0. This ratio is contrasted with the corresponding ratio of the
prior art membranes which is greater than 10.0. See Table I
below.
[0112] U.S. Pat. No. 6,602,593 is directed to a microporous
membrane, made by a dry-stretch process, where the resulting
membrane has a ratio of transverse direction tensile strength to
machine direction tensile strength of 0.12 to 1.2. Therein, the
TD/MD tensile ratio is obtained by a blow-up ratio of at least 1.5
as the precursor is extruded.
[0113] At least selected embodiments of the instant membrane may be
further characterized as follows: an average pore size in the range
of 0.03 to 0.30 microns (.mu.m); a porosity in the range of 20-80%;
and/or a transverse direction tensile strength of greater than 250
Kg/cm.sup.2. The foregoing values are exemplary values and are not
intended to be limiting, and accordingly should be viewed as merely
representative of at least selected embodiments of the instant
membrane.
[0114] At least selected embodiments of the instant membrane may be
further characterized as follows: a pore size in the range of 0.30
to 1.0 microns (.mu.m); and an average aspect ratio in the range of
about 1.0 to 1.10. The foregoing values are exemplary values and
are not intended to be limiting, and accordingly should be viewed
as merely representative of at least selected embodiments of the
instant membrane.
[0115] At least selected possibly preferred embodiments of the
instant membrane may be further characterized as follows: an
average aquapore size in the range of 0.05 to 0.50 microns (.mu.m);
a porosity in the range of 40-90%; and/or a transverse direction
tensile strength of greater than 250 Kg/cm.sup.2. The foregoing
values are exemplary values and are not intended to be limiting,
and accordingly should be viewed as merely representative of at
least selected possibly preferred embodiments of the instant
membrane.
[0116] The preferred polymers used in the instant membrane may be
characterized as thermoplastic polymers. These polymers may be
further characterized as semi-crystalline polymers. In one
embodiment, semi-crystalline polymer may be a polymer having a
crystallinity in the range of 20% to 80%. Such polymers may be
selected from the following group: polyolefins, fluorocarbons,
polyamides, polyesters, polyacetals (or polyoxymethylenes),
polysulfides, polyvinyl alcohols, co-polymers thereof, and
combinations thereof. Polyolefins may be preferred and may include
polyethylenes (LDPE, LLDPE, HDPE, UHMWPE), polypropylene,
polybutene, polymethylpentene, co-polymers thereof, and blends
thereof. Fluorocarbons may include polytetrafluoroethylene (PTFE),
polychlorotrifluoroethylene (PCTFE), fluorinated ethylene propylene
(FEP), ethylene chlortrifluoroethylene (ECTFE), ethylene
tetrafluoroethylene (ETFE), polyvinylidene fluoride (PVDF),
polyvinylfluoride (PVF), prefluoroalkoxy (PFA) resin, co-polymers
thereof, and blends thereof. Polyamides may include, but are not
limited to: polyamide 6, polyamide 6/6, Nylon 10/10,
polyphthalamide (PPA), co-polymers thereof, and blends thereof.
Polyesters may include polyester terephthalate (PET), polybutylene
terephthalate (PBT), poly-1-4-cyclohexylenedimethylene
terephthalate (PCT), and liquid crystal polymers (LOP).
Polysulfides include, but are not limited to, polyphenylsulfide,
co-polymers thereof, and blends thereof. Polyvinyl alcohols
include, but are not limited to, ethylene-vinyl alcohol,
co-polymers thereof, and blends thereof.
[0117] At least certain embodiments of the instant membrane may
include other ingredients, as is well known. For example, those
ingredients may include: fillers (inert particulates typically used
to reduce the cost of the membrane, but otherwise having no
significant impact on the manufacture of the membrane), anti-static
agents, anti-blocking agents, anti-oxidants, lubricants (to
facilitate manufacture), colorants, and/or the like.
[0118] Various materials may be added to the polymers to modify or
enhance the properties of the membrane. Such materials include, but
are not limited to: (1) polyolefins or polyolefin oligomers with a
melting temperature less than 130.degree. C.; (2) mineral fillers
include, but are not limited to: calcium carbonate, zinc oxide,
diatomaceous earth, talc, kaolin, synthetic silica, mica, clay,
boron nitride, silicon dioxide, titanium dioxide, barium sulfate,
aluminum hydroxide, magnesium hydroxide, and/or the like, and
blends thereof; (3) elastomers include, but are not limited to:
ethylene-propylene (EPR), ethylene-propylene-diene (EPDM),
styrene-butadiene (SBR), styrene isoprene (SIR), ethylidene
norbornene (ENS), epoxy, and polyurethane, and blends thereof; (4)
wetting agents include, but are not limited to, ethoxylated
alcohols, primary polymeric carboxylic acids, glycols (e.g.,
polypropylene glycol and polyethylene glycols), functionalized
polyolefins, etc; (5) lubricants, for example, silicone,
fluoropolymers, Kemamide.RTM., oleamide, stearamide, erucamide,
calcium stearate, or other metallic stearate; (6) flame retardants
for example, brominated flame retardants, ammonium phosphate,
ammonium hydroxide, alumina trihydrate, and phosphate ester; (7)
cross-linking or coupling agents; (8) polymer processing aids (such
as but not limited plasticizer or processing oil, for example, less
than 10% by weight processing oil); and (9) any types of nucleating
agents including beta-nucleating agents for polypropylene. (At
least the preferred instant membrane, however, specifically
excludes any beta-nucleated polypropylene (BNPP) as disclosed in
U.S. Pat. No. 6,368,742, incorporated herein by reference. A
beta-nucleating agent for polypropylene is a substance that causes
the creation of beta crystals in polypropylene.)
[0119] The instant membrane may be a single ply or multi-ply
membrane. Regarding the multi-ply membrane, the instant biaxially
oriented membrane may be one ply or layer of the multi-ply membrane
or the instant membrane may be all of the plies of the multi-ply
membrane. If the instant membrane is less than all of the plies of
the multi-ply membrane, the multi-ply membrane may be made via a
coating, lamination or bonding process. If the instant membrane is
all plies of the multi-ply membrane, the multi-ply membrane may be
made via a lamination or extrusion process (such as coextrusion).
Further, multi-ply membranes may be made of plies of the same
materials or of differing materials.
[0120] The instant membrane is preferably made by a modified
dry-stretch process where the precursor membrane is biaxially
stretched (i.e., not only stretched in the machine direction, but
also in the transverse machine direction). This process will be
discussed in greater detail below.
[0121] In general, the process for making the foregoing membrane
includes the steps of extruding a nonporous (single or multi-layer)
precursor, and then biaxially stretching the nonporous precursor.
Optionally, the nonporous precursor may be annealed prior to
stretching. In one embodiment, the biaxial stretching includes a
machine direction stretch and a transverse direction stretch with a
simultaneous controlled machine direction relax. The machine
direction stretch and the transverse direction stretch may be
simultaneous or sequential. In one embodiment, the machine
direction stretch is followed by the transverse direction stretch
with the simultaneous machine direction relax. This process is
discussed in greater detail below.
[0122] Extrusion is generally conventional (conventional refers to
conventional for a dry-stretch process). The extruder may have a
slot die (for flat precursor) or an annular die (for parison or
bubble precursor). In the case of the latter, an inflated parison
technique may be employed (e.g., a blow up ratio (BUR) of less than
1.5 as the precursor is extruded). However, the birefringence of
the nonporous precursor does not have to be as high as in the
conventional dry-stretch process. For example, in the conventional
dry-stretch process to produce a membrane with a >35% porosity
from a polypropylene resin with a melt flow index (MFI) <1.0,
the birefringence of the precursor would be >0.0130; while with
the instant process, the birefringence of the PP precursor could be
as low as 0.0100. In another example, a membrane with a >35%
porosity from a polyethylene resin, the birefringence of the
precursor would be >0.0280; while with the instant process, the
birefringence of the PE precursor could be as low as 0.0240.
[0123] Annealing (optional) may be carried out, in one embodiment,
at temperatures between T.sub.m-80.degree. C. and
T.sub.m-10.degree. C. (where T.sub.m is the melt temperature of the
polymer); and in another embodiment, at temperatures between
T.sub.m-50.degree. C. and T.sub.m-15.degree. C. Some materials,
e.g., those with high crystallinity after extrusion, such as
polybutene, may require no annealing. Additional optional steps may
be carried out, for example but not limited to heat set,
extraction, removal, winding, slitting, and/or the like.
[0124] Machine direction stretch may be conducted as a cold stretch
or a hot stretch or both, and as a single step or multiple steps.
In one embodiment, cold stretching may be carried out at
<T.sub.m-50.degree. C., and in another embodiment, at
<T.sub.m-80.degree. C. In one embodiment, hot stretching may be
carried out at <T.sub.m-10.degree. C. In one embodiment, total
machine direction stretching may be in the range of 50-500%, and in
another embodiment, in the range of 100-300%. During machine
direction stretch, the precursor may shrink in the transverse
direction (conventional).
[0125] Transverse direction stretching includes a simultaneous
controlled machine direction relax. This means that as the
precursor is stretched in the transverse direction (TD stretch) the
precursor is simultaneously allowed to contract (i.e., relax), in a
controlled manner, in the machine direction (MD relax). The
transverse direction stretching may be conducted as a cold step, or
a hot step, or a combination of both. In one embodiment, total
transverse direction stretching may be in the range of 100-1200%,
and in another embodiment, in the range of 200-900%. In one
embodiment, the controlled machine direction relax may range from
5-80%, and in another embodiment, in the range of 15-65%. In one
embodiment, transverse stretching may be carried out in multiple
steps. During transverse direction stretching, the precursor may or
may not be allowed to shrink in the machine direction. In an
embodiment of a multi-step transverse direction stretching, the
first transverse direction step may include a transverse stretch
with the controlled machine direction relax, followed by
simultaneous transverse and machine direction stretching, and
followed by transverse direction relax and no machine direction
stretch or relax.
[0126] Optionally, the precursor, after machine direction and
transverse direction stretching may be subjected to a heat setting,
as is well known.
[0127] The foregoing membrane and process embodiments are further
illustrated in the following non-limiting examples.
EXAMPLES
[0128] Unless described otherwise, the test values reported herein,
thickness, porosity, tensile strength, and aspect ratio, were
determined as follows: thickness-ASTM-D374 using the Emveco
Microgage 210-A micrometer; porosity-ASTM D-2873; tensile
strength-ASTM D-882 using an Instron Model 4201; and aspect
ratio-measurements taken from the SEM micrographs.
[0129] The following examples were produced by conventional
dry-stretched techniques, except as noted.
Example 1
[0130] Polypropylene (PP) resin is extruded using a 2.5 inch
extruder. The extruder melt temperature is 221.degree. C. Polymer
melt is fed to a circular die. The die temperature is set at
220.degree. C., polymer melt is cooled by blowing air. Extruded
precursor has a thickness of 27 micrometers (.mu.m) and a
birefringence of 0.0120. The extruded film was then annealed at
150.degree. C. for 2 minutes. The annealed film is then cold
stretched to 20% at room temperature, and then hot stretched to
228% and relaxed to 32% at 140.degree. C. The machine direction
(MD) stretched film has a thickness of 16.4 .mu.m, and porosity of
25%. The MD stretched film is then transverse direction (TD)
stretched 300% at 140.degree. C. with MD relax of 50%. The finished
film has a thickness of 14.1 .mu.m, and porosity of 37%. TD tensile
strength of finished film is 550 Kg/cm.sup.2. See FIG. 6.
Example 2
[0131] Polypropylene (PP) resin is extruded using a 2.5 inch
extruder. The extruder melt temperature is 220.degree. C. Polymer
melt is fed to a circular die. The die temperature is set at
200.degree. C., polymer melt is cooled by blowing air. Extruded
precursor has a thickness of 9.5 .mu.m and a birefringence of
0.0160. HDPE resin is extruded using a 2.5 inch extruder. The
extruder melt temperature is 210.degree. C. Polymer melt is fed to
a circular die. Die temperature is set at 205.degree. C., polymer
melt is cooled by air. Extruded precursor has a thickness of 9.5
.mu.m and a birefringence of 0.0330. Two PP layers and one PE
layers are laminated together to form a PP/PE/PP tri-layer film.
Lamination roll temperature is 150.degree. C. Laminated tri-layer
film is then annealed at 125.degree. C. for 2 minutes. The annealed
film is then cold stretched to 20% at room temperature, and then
hot stretched to 160% and relaxed to 35% at 113.degree. C. The MD
stretched film has a thickness of 25.4 .mu.m, and porosity of 39%.
The MD stretched film is then TD stretched 400% at 115.degree. C.
with MD relax of 30%. The finished film has a thickness of 19.4
.mu.m and porosity of 63%. TD tensile strength of finished film is
350 Kg/cm.sup.2. See FIG. 7.
Example 3
[0132] PP resin and HDPE resin are extruded using a co-extrusion
die to form a PP/PE/PP tri-layer film. Extruder melt temperature
for PP is 243.degree. C., and extruder melt temperature for PE is
214.degree. C. Polymer melt is then fed to a co-extrusion die which
is set at 198.degree. C. Polymer melt is cooled by blowing air. The
extruded film has a thickness of 35.6 .mu.m. The extruded precursor
is then annealed at 125.degree. C. for 2 minutes. The annealed film
is then cold stretched to 45% at room temperature and hot stretched
to 247% and relaxed to 42% at 113.degree. C. The MD stretched film
has a thickness of 21.5 .mu.m and porosity of 29%. The MD stretched
film is then TD stretched 450% at 115.degree. C. with 50% MD relax.
The finished film has a thickness of 16.3 .mu.m and porosity of
59%. TD tensile strength of finished film is 570 Kg/cm.sup.2.
Example 4
[0133] PP resin and HDPE resin are co-extruded and MD stretched the
same way as in Example 3. The MD stretched film is then TD
stretched 800% at 115.degree. C. with 65% MD relax. The finished
film has a thickness of 17.2 .mu.m and porosity of 49%. TD tensile
strength of finished film is 730 Kg/cm.sup.2. See FIG. 8.
Example 5
[0134] PP resin and PB resin are extruded using a co-extrusion die.
Extruder melt temperature for PP is 230.degree. C., and extruder
melt for PB is 206.degree. C. Polymer melt is then fed to a
co-extrusion die which is set at 210.degree. C. Polymer melt is
then cooled by blowing air. The extruded film has a thickness of
36.0 .mu.m. The extruded precursor is then annealed at 105.degree.
C. for 2 minutes. The annealed film is then cold stretched to 20%,
and then hot stretched at 105.degree. C. to 155% and then relaxed
to 35%. The MD stretched film is then TD stretched 140% at
110.degree. C. with 20% MD relax. The finished film has a thickness
of 14.8 .mu.m and porosity of 42%. TD tensile strength of finished
film is 286 Kg/cm.sup.2.
Example 6
[0135] PP resin and PE resin are extruded using a co-extrusion die
to form a PP/PE/PP trilayer film. Extruder melt temperature for PP
is 245.degree. C., and extruder melt temperature for PE is
230.degree. C. Polymer melt is then fed to a co-extrusion die which
is set at 225.degree. C. Polymer melt is cooled by blowing air. The
extruded film has a thickness of 27 .mu.m and a birefringence of
0.0120. The extruded precursor is then annealed at 115.degree. C.
for 2 minutes. The annealed film is then cold stretched to 22% at
room temperature and hot stretched to 254% and relaxed to 25% at
120.degree. C. (total machine direction stretch=251%). The MD
stretched film has a thickness of 15 .mu.m and porosity of 16%. The
MD stretched film is then TD stretched 260% at 130.degree. C. with
50% MD relax, followed by a simultaneous MD and TD stretch of 50%
and 216% in each direction at 130.degree. C., and finally the film
is held fast in the MD (100%) and allowed to relax 57.6% in the TD
at a temperature of 130.degree. C. The finished film has a
thickness of 7.6 .mu.m and porosity of 52%. TD tensile strength of
finished film is 513 Kg/cm.sup.2.
Example 7
[0136] Polypropylene and polyethylene resin(s) are extruded using a
co-extrusion die to form a PP/PE/PP tri-layer film. Extruder melt
temperature for PP is 222.degree. C., and extruder melt temperature
for PE is 225.degree. C. Polymer melt is then fed to a co-extrusion
die which is set at 215.degree. C. Polymer melt is cooled by
blowing air. The extruded film has a thickness of 40 .mu.m and
birefringence of 0.0110. The extruded precursor is then annealed at
105.degree. C. for 2 minutes. The annealed film is then cold
stretched to 36% at room temperature and hot stretched to 264% and
relaxed to 29% at 109.degree. C. (total machine direction stretch
=271%). The MD stretched film has a thickness of 23.8 .mu.m and
porosity of 29.6%. The MD stretched film is then TD stretched 1034%
at 110.degree. C. with 75% MD relax. The finished film has a
thickness of 16.8 .mu.m and porosity of 46%. TD tensile strength of
finished film is 1037 Kg/cm.sup.2.
[0137] In the following Table I the results of the foregoing
examples are summarized and compared to two commercially available
dry-stretched membranes: Com A) CELGARD.RTM. 2400 (single ply
polypropylene membrane), See FIG. 2; and Com B) CELGARD.RTM. 2300
(tri-layer polypropylene/polyethylene/polypropylene), see FIG.
3.
TABLE-US-00001 TABLE I TD MD MD/ Tensile Tensile TD Thick- Po-
strength strength MD/TD As- TD ness ros- (kg/ (kg/ tensile pect
stretching (.mu.m) ity cm.sup.2) cm.sup.2) ratio ratio Com N/A 25.4
37% 160 1700 10.6 6.10 A Com N/A 25.1 40% 146 1925 13.2 5.50 B Ex 1
300% 14.1 37% 550 1013 1.8 0.90 Ex 2 400% 19.4 63% 350 627 1.8 0.71
Ex 3 450% 16.3 59% 570 754 1.3 -- Ex 4 800% 17.2 49% 730 646 0.9
0.83 Ex 5 140% 14.8 42% 286 1080 3.8 -- Ex 6 418% 7.6 52% 513 1437
2.8 -- Ex 7 1034% 16.8 46% 1037 618 0.6 --
[0138] In accordance with at least selected embodiments of the
membranes of the present invention: [0139] Preferred JIS Gurley
.ltoreq.2.5 to .about.25 for monolayer PP air filtration membrane.
[0140] Preferred JIS Gurley .ltoreq.0.5 to .about.5 for monolayer
PP HEPA/ULPA membrane. [0141] Preferred round pore structure and
highly uniform pore structure across the membrane.
[0142] In accordance with at least selected possibly preferred
embodiments of the present invention, the preferred membranes have
or are:
[0143] Made by dry process, no oil/solvent is added.
[0144] High porosity: 40%-90%.
[0145] Highly hydrophobic.
[0146] Hydro-head pressure >140 psi, water intrusion pressure
>80 psi.
[0147] Unique pore structure as characterized by capillary flow
[0148] Porometry/Aquapore Test/SEM: mean flow pore diameter
measured by capillary flow of at least about 0.04 micron; Uniform,
round or non-slit type of pore structure, with narrow range of pore
diameter. Aquapore size of at least about 0.07 micron
[0149] High Gas/Air/moisture Permeability: JIS Gurley 1.0 to 100;
high flow rate as characterized by capillary flow porometery; WVTR
.gtoreq.8,000 g/m.sup.2-day.
[0150] Balanced MD/TD strength: TD strength (>300 kg/cm2).
[0151] Low TD shrinkage:TD shrinkage at 90 C.ltoreq.2%.
[0152] Preferred PP Polymer: MFI=0.1 to 10.0, polymer's
crystallinity >45%.
[0153] Preferred PE polymer: MFI=0.01 to 5.0, crystallinity >50%
MFI tested with ASTM D-1238 method.
[0154] Below are the testing results for eight membranes (A-G and
M), composites or laminates in accordance with selected embodiments
of the present invention and for a comparative sample Com C:
TABLE-US-00002 TABLE II General Properties Sample ID Unit Com C A B
C D E F G M Sample PP PP PP/PP PP PP/PE/PP PP/PP PP PP PP/PE/PP
Description Mono- Mono- Bonded laminated co- Bonded Mono- laminated
co- layer layer Bi-layer with extruded Bi- layer with extruded
Comparative non- trilayer layer non- trilayer example woven woven
AVG .mu.m 25 18 20 79 21 24 14 77 22 Thickness, Porosity, % 55 73
65 -- 76 80 81 -- 60 Puncture grams 335 226 374 553 256 285 135 358
346 Strength MD kgf/cm2 1055 754 938 -- 500 533 507 -- 862 Tensile
TD Tensile kgf/cm2 135 493 711 -- 450 491 461 -- 473 MD % 5.0 6.1
5.0 1.21 13.8 6.0 6.5 2.29 5.5 shrinkage at 90 C. TD % 0.0 0.4 ~0.0
0.46 1.8 ~0.0 ~0.0 0.19 1.5 shrinkage at 90 C. AVG JIS Sec/100 cc
200 32 60 85 35 26 14 45 65 Gurley, Mean flow .mu.m 0.0365 0.0543
0.0501 0.0468 0.0256 0.0610 0.0737 0.0542 0.250 pore diameter Stdev
of 0.0261 0.0183 0.0187 0.0181 0.0119 0.0190 0.0221 0.0183 0.110
mean flow pore diameter Bubble .mu.m 0.1141 0.0948 0.0892 0.0736
0.0504 0.1078 0.1039 0.0808 0.049 Point Diameter Hydrohead psi 155
149 159 277 364 222 153 206 377 Pressure Water psi >80 >80
>80 >80 >80 >80 >80 >80 >80 Intrusion Pressure
WVTR g/m2 day <6000 29300 178000 8560 29800 >30000 >30000
23000 16500 WVTR testing is based on ASTM F2298-03 using the
moisture gradient method. Test Methods for Water Vapor Diffusion
Resistance and Air Flow Resistance of Clothing Materials Using the
Dynamic Moisture Permeation Cell. Testing condition: Top cell
humidity 95%, bottom cell humidity 5%, Moisture gradient 90%.
Ambient temperatures. Thickness was measured based on ASTM-D374
using Emveco Microgage 210A micrometer. JIS Gurley is gas
permeability test measured by using the OHKEN permeability tester.
JIS Gurley is defined as the time in seconds required for 100 cc of
air to pass through one square inch of film at constant pressure of
4.8 inches of water. Porosity is measured by the method ASTM D2873.
Puncture Strength is measured using Instron Model 4442 based on
ASTM D3763. The measurements were made across the width of the
membrane and the averaged puncture energy (puncture strength) is
defined as the force required to puncture the test sample. Tensile
properties are tested using ASTM-882 standard using an Instron
Model 4201. Shrinkage is measured at 90 C. for 60 minutes using a
modified ASTM-2732-96 procedure. Mean flow pore diameter, bubble
point pore diameter were measured with Capillary Flow analysis
based on ASTM F316-86 standard. Hydrohead pressure was measured
based on ASTM D3393-91. Water Intrusion was tested per ASTM F316-93
(Wetting fluid-water, 68.8 dynes/cm. Gas: air.)
[0155] Although not preferred, a filled, microporous ultra-high
molecular weight polyethylene membrane could be used as a precursor
in the stretching process of the present invention.
[0156] Also, the membrane of the present invention may be laminated
on one or both sides to a non-woven substrate for additional
durability, or it can be coated with a surfactant to make it
hydrophilic.
[0157] In accordance with at least selected embodiments, the
present invention may be directed to: [0158] Biaxially stretching a
blown film with simultaneous stretch and relax to produce a product
useful in applications that require a high level of permeability to
air, moisture vapor, and other gasses, but a high level of
hydrophobicity. Such applications may include membrane-based
humidity and temperature control systems such as liquid desiccant
HVAC systems; membrane desalination; venting; fuel cell moisture
control; liquid filtration; and the like.
[0159] In accordance with at least selected embodiments, the
present invention may be directed to membranes having the following
properties:
TABLE-US-00003 TABLE III Measurement Units Performance Thickness
.mu.m 10-100 JIS Gurley sec (per 1-100 100 ml) MD tensile
kgf/cm.sup.2 500-1500 strength TD tensile kgf/cm.sup.2 350-800
strength Porosity percent 60-90% Mean flow .mu.m 0.04-0.07 pore
diameter Bubble point .mu.m 0.09-0.11 diameter Aquapore .mu.m
0.04-0.12 size Hydrohead psi 149-222 pressure Intrusion Psi >80
pressure Pressure drop psid <3.90 (at 5.3 cm/sec) Particle
percent >99.99% efficiency (at 2.5 cm/sec) Melting point
.degree. C. .gtoreq.165
[0160] In accordance with a possibly preferred embodiment of the
present invention, the membrane is a hydrophobic, highly permeable,
chemically and mechanically stable, high tensile strength membrane.
These properties appear to make it an ideal film for the following
applications, each of which (with the exception of air filtration)
may involve the selective passage of moisture vapor and blockage of
liquid water:
[0161] 1. HVAC
[0162] 2. Liquid-desiccant (LD) air conditioning
[0163] 3. Water-based air conditioning
[0164] 4. Energy recovery ventilation (ERV)
[0165] 5. Desalination
[0166] 6. RD Desalination
[0167] 7. Steam Desalination
[0168] 8. Fuel cells
[0169] 9. Liquid and/or air filtration
Particularly in the case of liquid and air filtration, the unique
pore structure may have some specific benefits.
[0170] In accordance with at least selected embodiments, the
preferred laminated products may have the combination of the
desired membrane moisture transport performance combined with the
desired macro physical properties.
[0171] In accordance with at least selected embodiments, the
preferred monolayer PP products may have excellent balance of MD
and TD physical properties while also being high performance
membranes as measured by the moisture transport (moisture vapor
transport) and hydrohead performance. The membrane may also have
uncharacteristically high porosity (>60%) but still maintains
the balanced physical properties when compared to more traditional
membranes. Also, the membrane can be produced in union with a
laminated PP nonwoven. The resultant laminated product may still
retain the excellent moisture vapor transport and even more
improved hydrohead performance. Also, the resultant product may
have physical strength properties that far exceed comparative
membranes. Therefore, the product may have the added advantage of
being used in more physical abusive environments without a loss of
the highly desirable membrane features.
[0172] In accordance with at least selected embodiments of the
present invention, the membrane may have a unique pore structure
and distribution or properties that may appear to make it an ideal
film for the following applications: [0173] High efficiency air
filtration, [0174] HEPA/ULPA applications, [0175] Near-zero
emissions dust removal applications (cleanroom, vacuum bag,
facemask, surgical suites, dust bag, cartridge), Filtration
applications:
[0176] high efficiency HVAC filter media
[0177] HEPA/ULPA media
[0178] filtration membrane composite [0179] Liquid Filtration,
[0180] Protective Garments, [0181] Functional garments/Performance
sports wear, [0182] Medical fabrics, [0183] and the like.
[0184] In accordance with at least selected porous material, film,
layer, membrane, laminate, coextrusion, or composite embodiments of
the present invention, some areas of improvement may include pore
shapes other than slits, round shaped pores, increased transverse
direction tensile strength, a balance of MD and TD physical
properties, high performance related to, for example, moisture
transport (or moisture vapor transport) and hydrohead pressure,
reduced Gurley, high porosity with balanced physical properties,
uniformity of pore structure including pore size and pore size
distribution, enhanced durability, composites of such membranes
with other porous materials, composites or laminates of such
membranes, films or layers with porous nonwovens, coated membranes,
coextruded membranes, laminated membranes, membranes having desired
moisture transport, hydrohead performance, and physical strength
properties, usefulness in more physically abusive environments
without loss of desirable membrane features, combination of
membrane moisture transport (or moisture vapor transport)
performance combined with the macro physical properties, being
hydrophobic, highly permeable, chemically and mechanically stable,
having high tensile strength, combinations thereof, and/or the
like.
[0185] While certain membranes made by the dry-stretch process have
met with excellent commercial success, there is a need to improve,
modify or enhance at least selected physical attributes thereof, so
that they may be used in a wider spectrum of applications, perform
better for particular purposes, and/or the like. In accordance with
at least selected embodiments of dry-stretch process membranes of
the present invention, some areas of improvement may include pore
shapes other than slits, round shaped pores, increased transverse
direction tensile strength, a balance of MD and TD physical
properties, uniformity of pore structure including pore size and
pore size distribution, high performance related to, for example,
moisture transport (moisture vapor transport) and hydrohead
pressure, reduced Gurley, high porosity with balanced physical
properties, enhanced durability, composites of such membranes with
other porous materials, composites or laminates of such membranes
with porous nonwovens, coated membranes, coextruded membranes,
laminated membranes, membranes having desired moisture transport
(or moisture vapor transport), hydrohead performance, and physical
strength properties, useful in more physically abusive environments
without loss of desirable membrane features, combination of the
membrane moisture transport (moisture vapor transport) performance
combined with the macro physical properties, combinations thereof,
and/or the like.
[0186] In accordance with at least selected possibly preferred
embodiments, the porous membrane of the present invention is
possibly preferably a dry-stretch process, porous membrane, film,
layer, or composite that is hydrophobic, highly permeable,
chemically and mechanically stable, has high tensile strength, and
combinations thereof. These properties appear to make it an ideal
membrane or film for the following applications, each of which
(with the exception of air filtration) may involve the selective
passage of moisture vapor (or other gases) and blockage of liquid
water (or other liquids): [0187] 5. HVAC : [0188] a.
Liquid-desiccant (LD) air conditioning (temperature and humidity
control): In a membrane-based LD system, temperature and humidity
may be controlled by a salt solution which absorbs or emits water
vapor through a porous membrane. Heat is the motive force in the
system (not pressure, as in most air conditioning systems). To make
the system work, it may be necessary to have a hydrophobic membrane
(to hold back the liquid) that readily passes water vapor. [0189]
b. Water-based air conditioning (temperature and humidity control):
Evaporative cooling systems or cooling water systems operate on a
somewhat different principle than the LD systems, but would use the
same essential properties of the membrane. [0190] c. Energy
recovery ventilation (ERV): The simplest HVAC application uses the
membrane as a key component of a heat and humidity exchange between
make-up and exhaust air. [0191] 6. Desalination: Steam desalination
applications use the same membrane properties as HVAC. Because the
membrane holds back liquid salt water but passes water vapor, a
system can be constructed which has salt water and fresh water
separated by a membrane. With the salt water at a higher
temperature, fresh water vapor emits from the salt water, migrates
through the membrane, and condenses to form the fresh water stream.
[0192] 7. Fuel cells: In a fuel cell, the proton exchange membrane
(PEM) must stay continually humidified. This can be accomplished
with the use of a membrane-based humidification unit. [0193] 8.
Liquid and/or air filtration: In these embodiments, the porous
membrane may act as a simple filter. As the liquid, vapor, gas, or
air passes through the membrane, particles that are too large to
pass through the pores are blocked at the membrane surface.
[0194] Particularly in the cases of liquid and air filtration, the
unique pore structure of at least selected embodiments of the
present invention may have certain specific benefits, such as the
benefits of durability, high efficiency, narrow pore size
distribution, and uniform flow rate.
[0195] In accordance with at least selected porous material or
porous membrane embodiments of the present invention, at least a
selected porous mono-layer polypropylene (monolayer PP) membrane
has excellent balance of MD and TD physical properties while also
being a high performance membrane as measured by the moisture
transport and hydrohead performance. This selected monolayer PP
membrane may also have high porosity (>60%) but still maintain
the balanced physical properties when compared to more traditional
membranes. Also, this selected monolayer PP membrane or film can be
produced in union with or laminated to a porous polypropylene (PP)
nonwoven material (nonwoven PP) on one or both sides thereof. The
resultant composite, membrane or product (monolayer PP/nonwoven PP)
or (nonwoven PP/monolayer PP/nonwoven PP) may preferably retain the
excellent moisture transport and even more improved hydrohead
performance. Also, this resultant composite product (monolayer
PP/nonwoven PP) or (nonwoven PP/monolayer PP/nonwoven PP) may have
physical strength properties that far exceed comparative membranes.
Therefore, this new resultant composite product (monolayer
PP/nonwoven PP) or (nonwoven PP/monolayer PP/nonwoven PP) may have
the added advantage of being useful in more physically abusive
environments without a loss of the highly desirable membrane
features. It is believed that these selected monolayer PP membrane
and composite products (monolayer PP; monolayer PP/nonwoven PP; or,
nonwoven PP/monolayer PP/nonwoven PP) are unique in their
combination of membrane moisture transport performance combined
with their macro physical properties. For example, prior membranes
may have had porosity but not sufficient hydrohead pressure or
performance, other membranes were too fragile, other membranes were
strong but lacked other properties, or the like. While at least
selected embodiments of the present invention may have, for
example, desired porosity, moisture transport, hydrohead pressure,
strength, and the like.
[0196] In accordance with at least selected porous material or
porous membrane embodiments of the present invention, at least a
selected porous multi-layer polypropylene (multilayer PP) membrane
has excellent balance of MD and TD physical properties while also
being a high performance membrane as measured by the moisture
transport and hydrohead performance. This selected multilayer PP
membrane may also have high porosity (>60%) but still maintain
the balanced physical properties when compared to more traditional
membranes. Also, this selected multilayer PP membrane or film can
be produced in union with or laminated to a porous polypropylene
(PP) nonwoven material (nonwoven PP) on one or both sides thereof.
The resultant composite, membrane or product (multilayer
PP/nonwoven PP) or (nonwoven PP/multilayer PP/nonwoven PP) may
preferably retain the excellent moisture transport and even more
improved hydrohead performance. Also, this resultant composite
product (multilayer PP/nonwoven PP) or (nonwoven PP/multilayer
PP/nonwoven PP) may have physical strength properties that far
exceed comparative membranes. Therefore, this new resultant
composite product (multilayer PP/nonwoven PP) or (nonwoven
PP/multilayer PP/nonwoven PP) may have the added advantage of being
useful in more physically abusive environments without a loss of
the highly desirable membrane features. It is believed that these
selected multilayer PP membrane and composite products (multilayer
PP; multilayer PP/nonwoven PP; or, nonwoven PP/multilayer
PP/nonwoven PP) are unique in their combination of membrane
moisture transport performance combined with their macro physical
properties. For example, prior membranes may have had porosity but
not sufficient hydrohead pressure or performance, other membranes
were too fragile, other membranes were strong but lacked other
properties, or the like. While at least selected embodiments of the
present invention may have, for example, desired porosity, moisture
transport, hydrohead pressure, strength, and the like.
[0197] In accordance with at least selected porous material or
porous membrane embodiments of the present invention, at least a
selected porous mono-layer polyethylene (monolayer PE) membrane has
excellent balance of MD and TD physical properties while also being
a high performance membrane as measured by the moisture transport
and hydrohead performance. This selected monolayer PE membrane may
also have high porosity (>60%) but still maintain the balanced
physical properties when compared to more traditional membranes.
Also, this selected monolayer PE membrane or film can be produced
in union with or laminated to a porous polyethylene (PE) nonwoven
material (nonwoven PE) or porous polypropylene (PP) nonwoven
material (nonwoven PP) on one or both sides thereof. The resultant
composite, membrane or product (monolayer PE/nonwoven PE) or
(nonwoven PE/monolayer PE/nonwoven PE) may preferably retain the
excellent moisture transport and even more improved hydrohead
performance. Also, this resultant composite product (monolayer
PE/nonwoven PE) or (nonwoven PE/monolayer PE/nonwoven PE) may have
physical strength properties that far exceed comparative membranes.
Therefore, this new resultant composite product (monolayer
PE/nonwoven PE) or (nonwoven PE/monolayer PE/nonwoven PE) may have
the added advantage of being useful in more physically abusive
environments without a loss of the highly desirable membrane
features. It is believed that these selected monolayer PE membrane
and composite products (monolayer PE; monolayer PE/nonwoven PE; or,
nonwoven PE/monolayer PE/nonwoven PE) are unique in their
combination of membrane moisture transport performance combined
with their macro physical properties. For example, prior membranes
may have had porosity but not sufficient hydrohead pressure or
performance, other membranes were too fragile, other membranes were
strong but lacked other properties, or the like. While at least
selected embodiments of the present invention may have, for
example, desired porosity, moisture transport, hydrohead pressure,
strength, and the like.
[0198] In accordance with at least selected porous material or
porous membrane embodiments of the present invention, at least a
selected porous multi-layer polyethylene (multilayer PE) membrane
has excellent balance of MD and TD physical properties while also
being a high performance membrane as measured by the moisture
transport and hydrohead performance. This selected multilayer PE
membrane may also have high porosity (>60%) but still maintain
the balanced physical properties when compared to more traditional
membranes. Also, this selected multilayer PE membrane or film can
be produced in union with or laminated to a porous polyethylene
(PE) nonwoven material (nonwoven PE) or porous polypropylene (PP)
nonwoven material (nonwoven PP) on one or both sides thereof. The
resultant composite, membrane or product (multilayer PE/nonwoven
PE) or (nonwoven PE/multilayer PE/nonwoven PE) may preferably
retain the excellent moisture transport and even more improved
hydrohead performance. Also, this resultant composite product
(multilayer PE/nonwoven PE) or (nonwoven PE/multilayer PE/nonwoven
PE) may have physical strength properties that far exceed
comparative membranes. Therefore, this new resultant composite
product (multilayer PE/nonwoven PE) or (nonwoven PE/multilayer
PE/nonwoven PE) may have the added advantage of being useful in
more physically abusive environments without a loss of the highly
desirable membrane features. It is believed that these selected
multilayer PE membrane and composite products (multilayer PE;
multilayer PE/nonwoven PE; or, nonwoven PE/multilayer PE/nonwoven
PE) are unique in their combination of membrane moisture transport
performance combined with their macro physical properties. For
example, prior membranes may have had porosity but not sufficient
hydrohead pressure or performance, other membranes were too
fragile, other membranes were strong but lacked other properties,
or the like. While at least selected embodiments of the present
invention may have, for example, desired porosity, moisture
transport, hydrohead pressure, strength, and the like.
[0199] In accordance with at least selected porous material or
porous membrane embodiments of the present invention, at least a
selected porous monolayer polymer membrane, for example, a
monolayer (may have one or more plies) polyolefin (PO) membrane,
such as a polypropylene (PP) and/or polyethylene (PE) (including
PE, PP, or PE+PP blends) monolayer membrane, has excellent balance
of MD and TD physical properties while also being a high
performance membrane as measured by the moisture transport (or
moisture vapor transport) and hydrohead performance. This selected
monolayer PO membrane may also have high porosity (>60%) but
still maintain the balanced physical properties when compared to
more traditional membranes. Also, this selected monolayer PO
membrane or film can be produced in union with or laminated to a
porous nonwoven material, such as a nonwoven polymer material, for
example, a PO nonwoven material (such as a porous polyethylene (PE)
nonwoven material (nonwoven PE) and/or porous polypropylene (PP)
nonwoven material (nonwoven PP) (including PE, PP, or PE +PP
blends)) on one or both sides thereof. The resultant composite,
membrane or product (monolayer PO/nonwoven PO) or (nonwoven
PO/monolayer PO/nonwoven PO) may preferably retain the excellent
moisture transport (or moisture vapor transport) and even more
improved hydrohead performance. Also, this resultant composite
product (monolayer PO/nonwoven PO) or (nonwoven PO/monolayer
PO/nonwoven PO) may have physical strength properties that far
exceed comparative membranes. Therefore, this new resultant
composite product (monolayer PO/nonwoven PO) or (nonwoven
PO/monolayer PO/nonwoven PO) may have the added advantage of being
useful in more physically abusive environments without a loss of
the highly desirable membrane features. It is believed that these
selected monolayer PO membrane and composite products (monolayer
PO; monolayer PO/nonwoven PO; or, nonwoven PO/monolayer PO/nonwoven
PO) are unique in their combination of membrane moisture transport
performance combined with their macro physical properties. For
example, prior membranes may have had porosity but not sufficient
hydrohead pressure or performance, other membranes were too
fragile, other membranes were strong but lacked other properties,
or the like, while at least selected embodiments of the present
invention may have, for example, desired porosity, moisture
transport, moisture vapor transport, hydrohead pressure, strength,
and the like.
[0200] In accordance with at least selected porous material or
porous membrane embodiments of the present invention, at least a
selected porous multi-layer polymer membrane, for example, a
multi-layer (two or more layer) polyolefin (PO) membrane, such as a
polypropylene (PP) and/or polyethylene (PE) (including PE, PP, or
PE+PP blends) multilayer membrane, has excellent balance of MD and
TD physical properties while also being a high performance membrane
as measured by the moisture transport (or moisture vapor transport)
and hydrohead performance. This selected multilayer PO membrane may
also have high porosity (>60%) but still maintain the balanced
physical properties when compared to more traditional membranes.
Also, this selected multilayer PO membrane or film can be produced
in union with or laminated to a porous PO nonwoven material (such
as a porous polyethylene (PE) nonwoven material (nonwoven PE)
and/or porous polypropylene (PP) nonwoven material (nonwoven PP))
on one or both sides thereof. The resultant composite, membrane or
product (multilayer PO/nonwoven PO) or (nonwoven PO/multilayer
PO/nonwoven PO) may preferably retain the excellent moisture
transport and even more improved hydrohead performance. Also, this
resultant composite product (multilayer PO/nonwoven PO) or
(nonwoven PO/multilayer PO/nonwoven PO) may have physical strength
properties that far exceed comparative membranes. Therefore, this
new resultant composite product (multilayer PO/nonwoven PO) or
(nonwoven PO/multilayer PO/nonwoven PO) may have the added
advantage of being useful in more physically abusive environments
without a loss of the highly desirable membrane features. It is
believed that these selected multilayer PO membrane and composite
products (multilayer PO; multilayer PO/nonwoven PO; or, nonwoven
PO/multilayer PO/nonwoven PO) are unique in their combination of
membrane moisture transport performance combined with their macro
physical properties. For example, prior membranes may have had
porosity but not sufficient hydrohead pressure or performance,
other membranes were too fragile, other membranes were strong but
lacked other properties, or the like, while at least selected
embodiments of the present invention may have, for example, desired
porosity, moisture transport, hydrohead pressure, strength, and the
like.
[0201] In accordance with at least selected porous material or
porous membrane embodiments of the present invention, the pores
(openings) have the following pore aspect ratios (based on physical
dimensions of the pore opening in the machine direction
(MD)(length), and transverse machine direction (TD)(width) by
measuring, for example, one or more of the pores (preferably
several of the pores to ascertain an average) in SEMs of the
surface, top or front (A side) of selected membranes or composites,
for example, mono-layer, bi-layer or tri-layer membranes: [0202]
Typical: [0203] MD/TD aspect ratio in range of 0.75 to 1.50 [0204]
Preferred: [0205] MD/TD aspect ratio in range of 0.75 to 1.25
[0206] Most Preferred: [0207] MD/TD aspect ratio in range of 0.85
to 1.25
[0208] In accordance with at least selected porous material or
porous membrane embodiments of the present invention, if the MD/TD
pore aspect ratio were 1.0, then a three-dimensional or 3D pore
sphericity factor or ratio (MD/TD/ND) range could be: 1.0 to 8.0 or
more; possibly preferred 1.0 to 2.5; and, most possibly preferred
1.0 to 2.0 or less (based on physical dimensions of the pore
openings in the machine direction (MD)(length), transverse machine
direction (TD)(width) and thickness direction or cross section
(ND)(thickness); for example, measuring the MD and TD of one or
more pores (preferably several pores to ascertain an average) in
SEMs of the surface, top or front (A side), or the surface, bottom
or back (B side), and measuring the ND of one or more pores
(preferably several pores to ascertain an average) in SEMs of the
cross-section, depth, or height (C side)(either length or width
cross-section or both)(the ND dimension may be of a different pore
than the MD and TD dimension as it may be difficult to measure the
ND, MD and TD dimension of the same pore).
[0209] In accordance with at least selected porous material or
porous membrane embodiments of the present invention, the
three-dimensional or 3D MD/TD/ND pore sphericity factor or ratio
range could be: 0.25 to 8.0 or more ; possibly preferred 0.50 to
4.0 ; and, most possibly preferred 1.0 to 2.0 or less.
[0210] In accordance with at least selected porous material or
porous membrane embodiments of the present invention, the pores
(openings) have the following pore aspect ratios (based on physical
dimensions of the pore opening in the machine direction
(MD)(length), and transverse machine direction (TD)(width) based on
measuring the pores in SEMs of the top or front (A side) of
selected mono-layer and tri-layer membranes: Here are the typical
numbers for aspect ratio range of Machine direction MD (length) and
Transverse direction TD (width): MD/TD aspect ratio in range of
0.75 to 1.50
[0211] In accordance with at least selected porous material or
porous membrane embodiments of the present invention, the pores
(openings) have the following three dimensional or 3D pore
sphericity factors or ratios (based on physical dimensions of the
pore openings in the machine direction (MD)(length), transverse
machine direction (TD)(width) and thickness direction or cross
section (ND)(thickness); for example, measuring one or more pores
(preferably several pores to ascertain an average) in SEMs of the
surface, top or front (A side), the surface, bottom or back (B
side), and the cross-section, depth, or height (C side)(either
length or width cross-section or both)(the ND dimension may be of a
different pore than the MD and TD dimension as it may be difficult
to measure the ND, MD and TD dimension of the same pore) of
selected membranes, layers or composites, for example, of selected
mono-layer and tri-layer membranes: [0212] For example: [0213]
Typical: [0214] MD/TD aspect ratio in range of 0.75 to 1.50 [0215]
MD/ND dimension ratio in range of 0.50 to 7.50 [0216] TD/ND
dimension ratio in range of 0.50 to 5.00 [0217] Preferred: [0218]
MD/TD aspect ratio in range of 0.75 to 1.25 [0219] MD/ND dimension
ratio in range of 1.0 to 2.5 [0220] TD/ND dimension ratio in range
of 1.0 to 2.5 [0221] Most Preferred: [0222] MD/TD aspect ratio in
range of 0.85 to 1.25 [0223] MD/ND dimension ratio in range of 1.0
to 2.0 [0224] TD/ND dimension ratio in range of 1.0 to 2.0
[0225] In accordance with at least selected porous material or
porous membrane embodiments of the present invention, the pores
(openings) have the following pore sphericity factors or ratios
(based on physical dimensions of the pore opening in the machine
direction (MD)(length), transverse machine direction (TD)(width)
and thickness direction or cross section (ND)(thickness) based on
measuring the pores in SEMs of the top or front (A side) and the
length and with cross-sections (C side) of selected mono-layer and
tri-layer membranes: [0226] Here are the typical numbers for
sphericity factor or ratio range of Machine direction MD (length),
Transverse direction TD (width), and Thickness direction ND
(vertical height): [0227] MD/TD aspect ratio in range of 0.75 to
1.50 [0228] MD/ND dimension ratio in range of 0.50 to 7.50 [0229]
TD/ND dimension ratio in range of 0.50 to 5.00
[0230] In accordance with at least selected embodiments of the
present invention, a microporous membrane is made by a dry-stretch
process and has substantially round shaped pores and a ratio of
machine direction tensile strength to transverse direction tensile
strength in the range of 0.5 to 6.0, preferably 0.5 to 5.0. The
method of making the foregoing microporous membrane includes the
steps of: extruding a polymer into a nonporous precursor, and
biaxially stretching the nonporous precursor, the biaxial
stretching including a machine direction stretching and a
transverse direction stretching, the transverse direction
stretching including a simultaneous controlled machine direction
relax.
[0231] In accordance with at least selected embodiments of the
present invention, a porous membrane is made by a modified
dry-stretch process and has substantially round shaped pores, a
ratio of machine direction tensile strength to transverse direction
tensile strength in the range of 0.5 to 6.0, and has low Gurley as
compared to prior dry-stretch membranes, has larger and more
uniform mean flow pore diameters as compared to prior dry-stretch
membranes, or both low Gurley and larger and more uniform mean flow
pore diameters.
[0232] While membranes made by the conventional dry-stretch process
have met with excellent commercial success, in accordance with at
least selected embodiments of the present invention, there is
provided improved, modified or enhanced at least selected physical
attributes thereof, so that they may be used in a wider spectrum of
applications, may perform better for particular purposes, and/or
the like.
[0233] While at least certain air filters have met with commercial
success, in accordance with at least selected embodiments of the
present invention, there is provided improved, modified or enhanced
filtration media so that they may be used in a wider spectrum of
filtration or separation applications, may perform better for
particular purposes, and/or the like.
[0234] While certain such flat sheet porous materials for
filtration or separation processes have met with commercial
success, in accordance with at least selected embodiments of the
present invention, there is provided improved, modified or enhanced
porous materials so that they may be used in a wider spectrum of
applications, may perform better for particular purposes, and/or
the like.
[0235] While porous materials for the selective passage of gases or
humidity (moisture vapor) and blockage of liquid water or salt
water may have met with commercial success, such as RO membranes
sold by Dow Chemical, ePTFE membranes sold by W. L. Gore, BHA, and
others, in accordance with at least selected embodiments of the
present invention, there is provided improved, modified or enhanced
porous materials so that they may be used in a wider spectrum of
applications, may perform better for particular purposes, and/or
the like.
[0236] In accordance with at least selected embodiments of the
present invention, an air-filter includes at least one porous
membrane such as a microporous membrane.
[0237] In accordance with at least selected embodiments of the
present invention, a microporous membrane is made by a dry-stretch
process and has substantially round shaped pores and a ratio of
machine direction tensile strength to transverse direction tensile
strength in the range of 0.5 to 5.0. The method of making the
foregoing microporous membrane includes the steps of: extruding a
polymer into a nonporous precursor, and biaxially stretching the
nonporous precursor, the biaxial stretching including a machine
direction stretching and a transverse direction stretching, the
transverse direction stretching including a simultaneous controlled
machine direction relax.
[0238] In accordance with at least selected embodiments of the
present invention, a porous membrane is made by a modified
dry-stretch process and has substantially round shaped pores, a
ratio of machine direction tensile strength to transverse direction
tensile strength in the range of 0.5 to 6.0, and has low Gurley as
compared to prior dry-stretch membranes, has larger and more
uniform mean flow pore diameters as compared to prior dry-stretch
membranes, or both low Gurley and larger and more uniform mean flow
pore diameters.
[0239] An air-filter cartridge according to the instant invention
may include at least one pleated microporous membrane, a plurality
of microporous membranes, and it may further include end-plates,
spacers, or the like.
[0240] An air-filter cartridge, as used herein, refers to a
cartridge that may either be used in an air-filter or an
air-purifier. The instant application describes the instant
invention in terms of an air-filter cartridge; however, the instant
invention is not limited so, and it may include air-purifier
cartridges as well. Also, the membrane may be pleated to provide a
large filtration area in a relatively small volume. In the
alternative, the membrane may have a sinusoidal pattern to provide
a large filtration area in a relatively small volume.
[0241] Further, the membrane may have any configuration; for
example, it may have a configuration selected from the group
consisting of pleated cylinder configuration, pleated flat sheet
configuration, and spiral wound configuration.
[0242] In an example manufacturing process, at least one flat sheet
microporous membrane is constructed and then, the membrane is
folded into a pleated or an accordion folded shape thereby
increasing the filtration area. Subsequently, the pleated membrane
may be wound into a cylinder, and sealed via end-plates thereby
forming an air-filter cartridge. The air-filter cartridge may be
inserted into a housing, and sealed via end caps.
[0243] In accordance with at least selected embodiments, which may
be well suited as battery separators, the possibly preferred
membrane is preferably made of one or more polyolefins and may be
further characterized by one or more of the following parameters:
thickness, porosity, average pore size, puncture strength, JIS
Gurley Number, and shutdown temperature.
[0244] The thickness of the membrane may be less than 6.0 mils (150
microns). In another embodiment, the thickness may range from 10
microns to 150 microns. In yet another embodiment, the thickness
may range from 10 microns to 50 microns.
[0245] The porosity of the membrane may be between 40 and 90%. In
one embodiment, porosity ranges from 60-90%. In yet another
embodiment, porosity ranges from 65-80%.
[0246] The average Aquapore size of the membrane may be between
0.04-0.20 microns. In one embodiment, the average pore size ranges
from 0.04-0.120 microns. In yet another embodiment, the average
pore size ranges from 0.07-0.12 microns.
[0247] The puncture strength may be greater than or equal to 300
gr-force/mil. Puncture strength is determined by averaging 10
measurements across the width of the final product using a Midtech
Stevens LFRA texture analyzer and a needle with a 1.65 mm diameter
and a 0.5 mm radius recording data at a rate of 2 mm/sec with a
maximum amount of deflection of 6 mm.
[0248] The JIS Gurley Number (normalized to one mil thickness) may
be less than 100 sec/100 cc/mil thickness. In one embodiment, the
JIS Gurley number ranges from 12 to 80 sec/10 cc/mil.
[0249] In accordance with certain embodiments, the intrinsic
viscosity (IV) of the membrane may be greater than or equal to 1.0
dl/g. In another embodiment, the IV may be greater than or equal to
5.0 dl/g. In another embodiment, the IV may preferably be greater
than or equal to 3.0 dl/g. The IV of the film is not the weighted
average of the pre-extruded resins composing the membrane because
during extrusion the polymers undergo chain scission and the
molecular weight is thereby lowered. Intrinsic viscosity, as used
herein, refers to the measure of the capability of a polymer in
solution to enhance the viscosity of the solution. The intrinsic
viscosity number is defined as the limiting value of the specific
viscosity/concentration ratio at zero concentration. Thus, it
becomes necessary to find the viscosity at different
concentrations, and then extrapolate to zero concentration. The
variation of the viscosity number with concentration depends on the
type of molecule as well as the solvent. In general, the intrinsic
viscosity of linear macromolecular substances is related to the
weight average molecular weight or degree of polymerization. With
linear macromolecules, viscosity number measurements can provide a
method for the rapid determination of molecular weight when the
relationship between viscosity and molecular weight has been
established. IV is measured by first dissolving 0.02 g of the
membrane in 100 ml of decalin at 150.degree. C. for one hour, and
then, determining its intrinsic viscosity at 135.degree. C. via an
Ubbelohd viscometer. This is according to ASTM D4020 (RSV values
reported herein).
[0250] The shutdown temperature may be less than 260.degree. C.
(260 degrees Centigrade or Celsius). In one embodiment, the
shutdown temperature may be less than 190.degree. C. In yet another
embodiment, the shutdown temperature may be less than 140.degree.
C. In still another embodiment, the shutdown temperature may be
less than 130.degree. C. In yet still another embodiment, the
shutdown temperature may be less than 120.degree. C.
[0251] The membrane of the present invention may be made of a
single polymer or a blend of polymers or of layers of the same or
different polymers or of layers of different materials bonded,
laminated or coextruded together. The possibly preferred polymers
are polyolefins, such as polypropylene (PP) and/or polyethylene
(PE). For example, the membrane may be made of one or more layers
of PP and/or PE. In one particular example, the membrane is a
porous PP film or sheet. In another particular example, the
membrane is a porous PE film or sheet. In yet another particular
example, the membrane is a tri-layer membrane made of two exterior
PP layers and an intermediate or center PE layer. In another
particular example, the membrane is a bi-layer membrane made of two
PP layers, two PE layers, or one PP and one PE layer bonded
together, laminated together, or coextruded together. In still yet
another particular example, the membrane is a composite of a porous
PP film or sheet and a porous material such as nonwoven glass or PP
material. In still another particular example, the membrane is a
porous film or sheet made of a blend of polyolefins having
differing molecular weights.
[0252] In accordance with at least selected embodiments, a gas
filtration media comprises a microporous membrane. A gas filtration
media, as used herein refers to a filtration media for removal of
particulates from a gas, e.g., air.
[0253] The gas filter media of the present invention may include an
ultrahigh molecular weight polyethylene and an inorganic material.
The gas filter media may further include a processing oil (i.e.,
oil remains in the media after extraction). The gas filter media
may further include a thermoplastic polyolefin, conventional
additives, such as stabilizers and antioxidants, and the like as is
well known in the art.
[0254] The gas filter media may be used as a filter media for any
end-use applications. For example, the gas filter media may be used
as a filter media for an end-use application selected from the
group consisting of particulate removal from gases, air-filtration
application, elevated temperature application, baghouse
application, particulate filtration in food and pharmaceuticals,
particulate filtration in combustion process, particulate
filtration in metals, and particulate filtration in cements.
Particulate removal from gases includes industries such as HVAC,
HEPA and ULPA clean rooms, vacuum cleaning, respirators, cement,
metals, food, pharmaceuticals, processed fluids, and combustion
processes.
[0255] The gas filter media may stand alone as a filter media; or
in the alternative, it may be joined with (e.g., laminated to or
bonded to) a support material, for example, a non-woven material or
a fabric. Exemplary lamination or bonding techniques include such
conventional methods as, but not limited to, adhesives, welding
(heat/ultrasonics) and the like. Furthermore, the gas filter media
may be flat or formed into pleats or shapes.
[0256] There is a need to have a more dimensionally stable (or high
temperature melt integrity) separator for larger cells, because if
short-circuiting occurs, the rupture of the cell could be more
significant because of the greater mass of lithium material
contained in the larger cell. Thus, in accordance with at least
certain embodiments, a battery separator is made from a nonwoven
flat sheet material having high temperature melt integrity, a
microporous membrane having low temperature shutdown properties,
and an optional adhesive bonding the nonwoven flat sheet to the
microporous membrane and being adapted for swelling when contacted
by an electrolyte.
[0257] The high temperature melt integrity separator may comprise a
microporous membrane and a nonwoven flat sheet that are bonded
together with or without an adhesive or polymer therebetween.
Nonwoven flat sheet may refer to a plurality of fibers held
together by various methods, e.g., thermal fusion, resin, solvent
bonding, or mechanical interlocking of fibers, sometimes
concurrently with their extrusion. Nonwoven flat sheet includes
fibrous structures made by such processes as dry, wet, or air
laying, needlepunching, spunbonding, or melt blowing processes, and
hydroentanglement. The fibers may be directionally or randomly
oriented. While nonwoven typically does not include paper, for this
application, papers are included. The fibers may be made of
thermoplastic polymers, cellulosic, and/or ceramics. Thermoplastic
polymers include, but are not limited to, polystyrenes, polyvinyl
chlorides, polyacrylics, polyacetals, polyamides, polycarbonates,
polyesters, polyetherimides, polyimides, polyketones, polyphenylene
ethers, polyphenylene sulfides, polysulfones. Cellulosics include,
but are not limited to, cellulose (e.g., cotton or other naturally
occurring sources), regenerated cellulose (e.g., rayon), and
cellulose acetate (e.g., cellulose acetate and cellulose
triacetate). Ceramics include, but are not limited to, glass of all
types and alumina, silica, and zirconia compounds (e.g., aluminum
silicate).
[0258] Additionally, the nonwoven or the fibers of the nonwoven may
be coated or surface treated to improve the functionality of the
nonwoven. For example, the coating or surface treatment may be to
improve the adhesiveness of the nonwoven or its fibers, to improve
the high temperature melt integrity of the nonwoven, and/or to
improve the wettability of the nonwoven. With regard to improving
the high temperature melt integrity, the nonwoven and/or its fibers
may be coated or surface treated with a ceramic material. Such
ceramic materials include, but are not limited to, alumina, silica,
and zirconia compounds, and combinations thereof.
[0259] In accordance with at least selected embodiments, bonding of
the microporous membrane to the nonwoven flat sheet should maintain
a high discharge rate which may require that there will be free
mobility of the ionic species of the electrolyte between the anode
and the cathode. The mobility of the ionic species is typically
measured as electrical resistance (ER) or MacMullen number (the
ratio of electrical resistance of an electrolyte-saturated porous
medium to the electrical resistance of an equivalent volume of
electrolyte [See: U.S. Pat. No. 4,464,238, incorporated herein by
reference]). Accordingly, there may be a need for adhering the
sheet to the membrane with a material that does not decrease ion
mobility (or increase the electrical resistance) across the
separator.
[0260] The adhesive may be selected from, but is not limited to,
polyvinylidene fluoride (PVDF); polyurethane; polyethylene oxide
(PEO); polyacrylonitrile (PAN); polymethylacrylate (PMA);
poly(methylmethacrylate) (PMMA); polyacrylamide; polyvinyl acetate;
polyvinylpyrrolidone; polytetraethylene glycol diacrylate;
copolymers of any the foregoing and combinations thereof. One
criterion for comonomer selection is the comonomer's ability to
modify the surface energy of the homopolymer. Surface energy
impacts, at least: the solubility of the copolymer, thereby
affecting coating the copolymer onto the membrane; the adhesion of
the copolymer to the membrane, thereby affecting battery
manufacture and subsequent performance; and the wettability of the
coating, thereby affecting absorption of liquid electrolyte into
the separator. Suitable comonomers include, but are not limited to,
hexafluoropropylene, octofluoro-1-butene, octofluoroisobutene, and
tetrafluoroethylene. The comonomer content preferably ranges from 3
to 20% by weight, and most preferably, 7 to 15%. Preferably, the
adhesive or swellable polymer is a copolymer of polyvinylidene
fluoride. Preferably, the PVDF copolymer is a copolymer of
polyvinylidene fluoride and hexafluoropropylene (PVDF:HFP), and,
most preferably, the PVDF:HFP ratio is 91:9. The PVDF copolymers
are commercially available from Elf Atochem, Philadelphia, Pa.,
USA; Solvay SA, Brussels, Belgium; and Kureha Chemical Industries,
LTD, Ibaraki, Japan. A preferred PVDF:HFP copolymer is KYNAR 2800
from Elf Atochem.
[0261] The wetting agent may be selected from materials that are
compatible with (i.e., miscible with or will not phase separate
from) the swellable polymer, that, in trace amounts (e.g., 10 20%
of the swellable polymer), will not have a detrimental effect upon
the battery chemistry (such as wetting agents that contain
sulfones, sulphates, and nitrogen), and that are fluid at room
temperature or have a Tg (glass transition temperature)
<50.degree. C. The wetting agent may be selected from, but is
not limited to, phthalate-based esters, cyclic carbonates,
polymeric carbonates, and mixtures thereof. Phthalate-based esters
are selected from, but are not limited to, dibutyl phthalate (DBP).
Cyclic carbonates are selected from ethylene carbonate (EC),
propylene carbonate (PC), butylene carbonate (BC), and mixtures
thereof. Polymeric carbonates are selected from, but are not
limited to; polyvinylene carbonate, and linear propylene
carbonates.
[0262] At least selected embodiments of the present invention may
provide a microporous battery separator having two portions bonded
together. Each portion may consist of a co-extruded or
non-coextruded layer and may be made of the same or different
materials. To obtain greater puncture strength, certain embodiments
may bond together two portions that are sized, when combined, to
have the desired total thickness of the separator. Selected
embodiments may, preferably, be made by a collapsed bubble
technique; i.e. a blown film technique in which a single molten
polymer (or blend of polymers) is extruded through an annular die,
the bubble which issues from the die has a first portion and a
second portion (each portion representing roughly one-half of the
circumference of the bubble), and then the bubble is collapsed onto
itself and bonded prior to micropore formation (preferably by
annealing and stretching). When the bubble issues from the die, it
is substantially oriented in the machine direction. Thus, when the
bubble is collapsed onto itself and bonded, the first portion and
the second portion may be oriented in substantially the same
direction (angular bias between oriented portions being less
than)15.degree.. Collapsing and bonding are performed in the same
step by allowing the molten (or near molten) polymer of the bubble
to knit together. By collapsing the bubble onto itself and bonding
same, increased puncture strength is obtained at thicknesses which
may be equivalent to other separators. The first portion and the
second portion, which when bonded provide the precursor for the
micropore formation process (e.g. an anneal and stretch operation),
may be made of materials such as polyolefins, preferably
polyethylene or polypropylene, copolymers thereof, and mixtures
thereof, and most preferably polyethylene and polypropylene.
[0263] A trilayer, shutdown battery separator may refer to a porous
film for use in electrochemical cells, e.g., batteries,
particularly secondary (or rechargeable) batteries, such as lithium
batteries. This trilayer separator may have a
polypropylene-polyethylene-polypropylene construction. The
separator may have a thickness of less than 3 mils (about 75
microns). The separator's thickness preferably ranges between 0.5
mils (about 12 microns) and 1.5 mils (about 38 microns). Most
preferably, the separator's thickness is about 1 mil (about 25
microns). Preferably, the separator has a permeability, as measured
by JIS Gurley, of less than 300 sec. Preferably, the separator has
a puncture strength of at least 300 grams. Preferably, the
separator has porosity in the range of 40% to 70%.
[0264] One method of making the trilayer, shutdown battery
separator generally comprises the steps of: extruding non-porous
polypropylene precursors; extruding a non-porous polyethylene
precursor; forming a non-porous trilayer precursor where the
polyethylene precursor is sandwiched between the polypropylene
precursors; bonding the trilayer precursor; annealing the trilayer
precursor; and stretching the bonded and annealed, non-porous
trilayer precursor to form the porous battery separator.
[0265] In at least one embodiment, the membrane may be a
microporous sheet made from a blend of at least two ultra high
molecular weight polyolefins having differing molecular weights. In
one embodiment, these ultra high molecular weight polyolefins may
be ultra high molecular weight polyethylene (UHMWPE). In another
embodiment, the membrane is a blend of a first ultra high molecular
weight polyethylene having a first molecular weight and a second
ultra high molecular weight polyethylene having a second molecular
weight, the first molecular weight and the second molecular weight
being greater than 1 million and being different from one another.
In another embodiment, the membrane is a blend of a first ultra
high molecular weight polyethylene having a first molecular weight,
a second ultra high molecular weight polyethylene having a second
molecular weight, the first molecular weight and the second
molecular weight being greater than 1 million and being different
from one another, and a third polyolefin having a third molecular
weight, the third molecular weight being less than 1 million. In
yet another embodiment, the membrane may have an IV greater than or
equal to 6.3 dl/g. In another embodiment, the membrane may have an
IV greater than or equal to 7.7 dl/g.
[0266] In at least selected embodiments, the invention is directed
to biaxially oriented porous membranes, composites including
biaxially oriented porous membranes, biaxially oriented microporous
membranes, biaxially oriented macroporous membranes, battery
separators, filtration media, humidity control media, flat sheet
membranes, liquid retention media, and the like, related methods,
methods of manufacture, methods of use, and the like.
[0267] In accordance with at least selected embodiments, a
laminated material or fabric may incorporate a composite membrane
made according to the present invention and that is wind and liquid
penetration resistant, moisture vapor transmissive and air
permeable. The laminated fabric may also include one or more layers
of textile base or shell fabric material that are laminated to the
membrane by any suitable process. The shell fabric may be made from
any suitable material that meets performance and other criteria
established for a given application.
[0268] "Moisture vapor transmissive" is used to describe an article
that permits the passage of water vapor through the article, such
as the laminated fabric or composite membrane. The term "resistant
to liquid penetration" is used to describe an article that is not
"wet" or "wet out" by a challenge liquid, such as water, and
prevents the penetration of liquid through the membrane under
ambient conditions of relatively low pressure. The term "resistant
to wind penetration" describes the ability of an article to prevent
air penetration above more than about three (3) CFM per square foot
at a pressure differential across the article of 0.5'' of
water.
[0269] By way of example, jackets, coats, or other garments or
finished products incorporating the laminated fabric may permit
moisture vapor transmission through the garment. Moisture vapor may
result from perspiration of the user, and the garment or finished
product preferably permits moisture vapor transmission at a rate
sufficient for the user to remain dry and comfortable during use in
typical conditions. The laminated fabric is also preferably
resistant to liquid and wind penetration, while being air
permeable.
[0270] In accordance with at least selected embodiments of the
present invention, an air-filter cartridge includes at least one
pleated microporous membrane.
[0271] At least a selected microporous membrane is made by a
dry-stretch process and has substantially round shaped pores and a
ratio of machine direction tensile strength to transverse direction
tensile strength in the range of 0.5 to 6.0. The method of making
the foregoing microporous membrane may include the steps of:
extruding a polymer into a nonporous precursor, and biaxially
stretching the nonporous precursor, the biaxial stretching
including a machine direction stretching and a transverse direction
stretching, the transverse direction including a simultaneous
controlled machine direction relax.
[0272] At least selected embodiments of the invention may be
directed to biaxially oriented porous membranes, composites
including biaxially oriented porous membranes, biaxially oriented
microporous membranes, biaxially oriented macroporous membranes,
battery separators, filtration media, humidity control media, flat
sheet membranes, liquid retention media, and the like, related
methods, methods of manufacture, methods of use, and the like.
[0273] In accordance with at least selected embodiments of the
present invention, there is provided at least one of:
[0274] A membrane comprising: [0275] at least one layer of porous
polymer film made by a dry-stretch process including the steps of:
[0276] extruding a polymer into at least a single layer nonporous
precursor, and [0277] biaxially stretching the nonporous precursor,
the biaxial stretching including a machine direction stretching and
a transverse direction stretching, the transverse direction
stretching including a simultaneous controlled machine direction
relax,
[0278] and having substantially round shaped pores, a porosity of
about 40% to 90%, a ratio of machine direction tensile strength to
transverse direction tensile strength in the range of about 0.5 to
5.0, a Gurley of less than about 100, a mean flow pore diameter of
at least about 0.04 microns, an Aquapore size of at least about
0.07 microns, and a hydro-head pressure greater than about 140
psi.
[0279] The above membrane, wherein the machine direction stretching
of said biaxially stretching includes the step of transverse
direction stretching with simultaneous machine direction
stretching, and wherein said biaxially stretching further includes
the step of transverse direction relax.
[0280] The above membrane, wherein said biaxially stretching of
said nonporous precursor further includes an additional step of
machine direction stretching.
[0281] The above membrane, wherein said dry-stretch process further
includes the step of: [0282] machine direction stretching to form a
porous intermediate prior to said biaxial stretching.
[0283] The above membrane, wherein said biaxially stretching of
said nonporous precursor includes the machine direction stretching,
an additional transverse direction stretching with simultaneous
machine direction stretching, and a transverse direction relax.
[0284] The above membrane, wherein said dry-stretch process
includes the steps of: [0285] machine direction stretching followed
by said biaxial stretching including said transverse direction
stretching with simultaneous controlled machine direction relax, a
second transverse direction stretching with simultaneous machine
direction stretching, followed by transverse direction relax.
[0286] The above membrane, with said porous polymer film further
having a thickness of at least about 8 microns, a transverse
direction tensile strength of at least about 300 kgf/cm2, a
standard deviation of mean flow pore diameter of less than about
0.025, a water intrusion pressure of at least about 80 psi, and a
WVTR of at least about 8,000 g/m.sup.2-day.
[0287] The above membrane, with said porous polymer film further
having a transverse direction shrinkage of less than about 1.0% at
90.degree. C.
[0288] The above membrane, with said porous polymer film further
having a transverse direction shrinkage of less than about 1.5% at
105.degree. C.
[0289] The above membrane, with said porous polymer film further
having a transverse direction shrinkage of less than about 3.0% at
120.degree. C.
[0290] The above membrane, with said porous polymer film further
having a machine direction shrinkage of less than about 10% at
90.degree. C.
[0291] The above membrane, with said porous polymer film further
having a machine direction shrinkage of less than about 20% at
105.degree. C.
[0292] The above membrane, with said porous polymer film further
having a machine direction shrinkage of less than about 30% at
120.degree. C.
[0293] The above membrane, with said porous polymer film further
having a thickness in a range of about 8 microns to 80 microns.
[0294] The above membrane, wherein said nonporous precursor is one
of a blown film and a slot die film.
[0295] The above membrane, wherein said nonporous precursor is a
single layer precursor formed by at least one of single layer
extrusion and multilayer extrusion.
[0296] The above membrane, wherein said nonporous precursor is a
multilayer precursor formed by at least one of coextrusion and
lamination.
[0297] The above membrane, wherein said porous polymer film
comprises one of polypropylene, polyethylene, blends thereof, and
combinations thereof.
[0298] The above membrane, wherein said porous polymer film uses
polyolefin resins which have a melt flow index (MFI) of about 0.01
to 10.0 and a polymer crystallinity of at least about 45%.
[0299] The above membrane, wherein said precursor is one of a
single layer precursor and a multilayer precursor.
[0300] The above membrane, wherein said membrane further includes
at least one nonwoven, woven, or knit layer bonded to at least one
side of said porous polymer film.
[0301] The above membrane, wherein said membrane is made up of a
plurality of said porous polymer films.
[0302] The above membrane, wherein said porous polymer film is made
up of at least two layers.
[0303] The above membrane, wherein said membrane has substantially
round shaped pores, a porosity of about 40% to 90%, a ratio of
machine direction tensile strength to transverse direction tensile
strength in the range of about 0.5 to 5.0, a Gurley of less than
about 100, a mean flow pore diameter of at least about 0.04
microns, an Aquapore size of at least about 0.07 microns, and a
hydro-head pressure greater than about 140 psi.
[0304] The above membrane, wherein said polymer being a
semi-crystalline polymer.
[0305] The above membrane, wherein said polymer being selected from
the group consisting of polyolefins, fluorocarbons, polyamides,
polyesters, polyacetals (or polyoxymethylenes), polysulfides,
polyphenyl sulfide, polyvinyl alcohols, co-polymers thereof, blends
thereof, and combinations thereof.
[0306] The above membrane, with said porous polymer film further
having a porosity of about 65% to 90%, a ratio of machine direction
tensile strength to transverse direction tensile strength in the
range of about 1.0 to 5.0, a Gurley of less than about 20, a mean
flow pore diameter of at least about 0.05 microns, an Aquapore size
of at least about 0.08 microns, and a hydro-head pressure greater
than about 145 psi.
[0307] The above membrane, wherein said substantially round shaped
pores have at least one of an aspect ratio in the range of about
0.75 to 1.25 and a sphericity factor in the range of about 0.25 to
8.0.
[0308] At least one of a filtration membrane, a humidity control
membrane, a gas and/or liquid separation membrane, a selective
passage of humidity and blockage of liquid water membrane, and a
multi-layered membrane structure comprising the above membrane.
[0309] The above membrane, wherein said biaxially stretching step
of said dry-stretch process includes the simultaneous biaxial
stretching of a plurality of separate, superimposed, layers or
plies of nonporous precursor, wherein none of the plies are bonded
together during the stretching process.
[0310] The above membrane, wherein said biaxially stretching step
of said dry-stretch process includes the simultaneous biaxial
stretching of at least three separate, superimposed, layers of
nonporous precursor.
[0311] The above membrane, wherein said biaxially stretching step
of said dry-stretch process includes the simultaneous biaxial
stretching of at least eight separate, superimposed, layers of
nonporous precursor.
[0312] The above membrane, wherein said biaxially stretching step
of said dry-stretch process includes the simultaneous biaxial
stretching of at least sixteen separate, superimposed, layers of
nonporous precursor.
[0313] The above membrane, wherein said biaxially stretching step
of said dry-stretch process includes the simultaneous biaxial
stretching of a plurality of bonded, superimposed, layers or plies
of nonporous precursor, wherein all of the plies are bonded
together during the stretching process.
[0314] The above membrane, wherein said biaxially stretching step
of said dry-stretch process includes the simultaneous biaxial
stretching of a plurality of separate, superimposed, layers or
plies of nonporous precursor, and a plurality of bonded,
superimposed, layers or plies of nonporous precursor, wherein some
of the plies are bonded together during the stretching process.
[0315] The above membrane, wherein said extruding step is a dry
extrusion process, using an extruder having at least one of a slot
die and an annular die.
[0316] A battery separator comprising: [0317] at least one layer of
porous polymer film made by a dry-stretch process including the
steps of: [0318] extruding a polymer into at least a single layer
nonporous precursor, and [0319] biaxially stretching the nonporous
precursor, the biaxial stretching including a machine direction
stretching and a transverse direction stretching, the transverse
direction stretching including a simultaneous controlled machine
direction relax,
[0320] and having substantially round shaped pores, a porosity of
about 40% to 70%, a ratio of machine direction tensile strength to
transverse direction tensile strength in the range of about 0.5 to
5.0, a Gurley of less than about 300, a mean flow pore diameter of
at least about 0.01 microns, and an Aquapore size of at least about
0.04 microns.
[0321] The above battery separator, wherein said at least one layer
of porous polymer film further having a thickness of at least about
8 microns, a transverse direction tensile strength of at least
about 300 kgf/cm2, a standard deviation of mean flow pore diameter
of less than about 0.025.
[0322] The above battery separator, wherein said at least one layer
of porous polymer film further having a transverse direction
shrinkage of less than about 2% at 90.degree. C.
[0323] The above battery, wherein said at least one layer of porous
polymer film further having a machine direction shrinkage of less
than about 6% at 90.degree. C.
[0324] The above battery separator, wherein said nonporous
precursor is formed by at least one of single layer extrusion and
multilayer extrusion.
[0325] The above battery separator, wherein said nonporous
precursor is a multilayer precursor formed by at least one of
coextrusion and lamination.
[0326] The above battery separator, wherein said separator is made
up of a plurality of said porous polymer films.
[0327] The above battery separator, wherein said polymer being
selected from the group consisting of polyolefins, fluorocarbons,
polyamides, polyesters, polyacetals (or polyoxymethylenes),
polysulfides, polyphenyl sulfide, polyvinyl alcohols, co-polymers
thereof, blends thereof, and combinations thereof.
[0328] The above battery separator, wherein said substantially
round shaped pores have at least one of an aspect ratio in the
range of about 0.75 to 1.25 and a sphericity factor in the range of
about 0.25 to 8.0.
[0329] A porous membrane comprising: [0330] at least one layer of
porous polymer film made by a stretch process process including the
steps of: [0331] extruding a polymer into at least a single layer
nonporous precursor, and [0332] biaxially stretching the nonporous
precursor, the biaxial stretching including a machine direction
stretching and a transverse direction stretching, the transverse
direction stretching including a simultaneous controlled machine
direction relax,
[0333] and having substantially round shaped pores, a porosity of
at least about 40%, a ratio of machine direction tensile strength
to transverse direction tensile strength in the range of about 0.5
to 5.0, a Gurley of less than about 300, a mean flow pore diameter
of at least about 0.01 microns, and an Aquapore size of at least
about 0.04 microns.
[0334] At least one of a battery separator, a filtration membrane,
a humidity control membrane, a gas and/or liquid separation
membrane, a selective passage of humidity and blockage of liquid
water membrane, and a multi-layered membrane structure comprising
the above membrane.
[0335] In a device requiring humidity control, the improvement
comprising the above membrane.
[0336] In a filtration device, the improvement comprising the above
membrane.
[0337] In a temperature affecting device, the improvement
comprising the above membrane.
[0338] A method of making a microporous membrane comprising the
steps of: [0339] extruding a polymer into a nonporous precursor,
and [0340] biaxially stretching the nonporous precursor, the
biaxial stretching including a machine direction stretching and a
transverse direction stretching, the transverse direction including
a simultaneous controlled machine direction relax.
[0341] The above method, wherein the polymer excludes any oils for
subsequent removal to form pores or any pore-forming materials to
facilitate pore formation.
[0342] The above method, wherein the polymer being a
semi-crystalline polymer.
[0343] The above method, wherein the polymer being selected from
the group consisting of polyolefins, fluorocarbons, polyamides,
polyesters, polyacetals (or polyoxymethylenes), polysulfides,
polyvinyl alcohols, co-polymers thereof, and combinations
thereof.
[0344] The above method, further comprising the step of: [0345]
annealing the non-porous precursor after extruding and before
biaxially stretching.
[0346] The above method, wherein annealing being conducted at a
temperature in the range of T.sub.m-80.degree. C. to
T.sub.m-10.degree. C.
[0347] The above method, wherein biaxially stretching comprising
the steps of: [0348] machine direction stretching, and [0349]
thereafter transverse direction stretching including a simultaneous
machine direction relax.
[0350] The above method, wherein machine direction stretching being
conducted either hot or cold or both.
[0351] The above method, wherein cold machine direction stretching
being conducted at a temperature <T.sub.m-50.degree. C.
[0352] The above method, wherein hot machine direction stretching
being conducted at a temperature <T.sub.m-10.degree. C.
[0353] The above method, wherein the total machine direction
stretch being in the range of 50-500%.
[0354] The above method, wherein the total transverse direction
stretch being in the range of 100-1200%.
[0355] The above method, wherein the machine direction relax being
in the range of 5-80%.
[0356] A membrane comprising: [0357] a microporous polymer film
made by a dry-stretch process and having substantially round shaped
pore and a ratio of machine direction tensile strength to
transverse direction tensile strength in the range of 0.5 to
6.0.
[0358] The above membrane, wherein an average pore size of said
microporous polymer film being in the range of 0.03 to 0.30
microns.
[0359] The above membrane, wherein said microporous polymer film
having a porosity in the range of 20-80%.
[0360] The above membrane, wherein said substantially round shaped
pores having at one of an aspect ratio in the range of about 0.75
to 1.25 and a sphericity factor in the range of about 0.25 to
8.0.
[0361] The above membrane, wherein said transverse tensile strength
being .gtoreq.250 Kg/cm.sup.2.
[0362] A battery separator comprising the above membrane.
[0363] A multi-layered membrane structure comprising the above
membrane.
[0364] An air-filter cartridge comprising the above membrane.
[0365] In a method of filtering particulates from a gas, the
improvement comprising the above membrane.
[0366] A gas filtration media comprising the above membrane.
[0367] A battery separator comprising: a nonwoven flat sheet having
a high temperature melt integrity; and the above membrane.
[0368] A battery made with the above separator.
[0369] In a porous membrane, the improvement comprising at least
one of: pore shapes other than slits, round shaped pores, pores
like those shown in one of FIGS. 6-8 and 13-54, pores like those
shown in one of FIGS. 13-50, pores like those shown in one of FIGS.
6-8 and 13-50, the properties shown in one of Tables I, II or III,
increased transverse direction tensile strength, a balance of MD
and TD physical properties, high performance related to moisture
transport and hydrohead pressure, reduced Gurley, high porosity
with balanced physical properties, uniformity of pore structure
including pore size and pore size distribution, enhanced
durability, composites of such membranes with other porous
materials, composites or laminates of such membranes, films or
layers with porous nonwovens, coated membranes, coextruded
membranes, laminated membranes, membranes having desired moisture
transport or moisture vapor transport, hydrohead performance, and
physical strength properties, usefulness in more physically abusive
environments without loss of desirable membrane features, a
combination of membrane moisture transport performance combined
with the macro physical properties, being hydrophobic, highly
permeable, chemically and mechanically stable, having high tensile
strength, and combinations thereof.
[0370] At least a selected microporous membrane is made by a
dry-stretch process and has substantially round shaped pores and a
ratio of machine direction tensile strength to transverse direction
tensile strength in the range of 0.5 to 6.0. The method of making
the foregoing microporous membrane may include the steps of:
extruding a polymer into a nonporous precursor, and biaxially
stretching the nonporous precursor, the biaxial stretching
including a machine direction stretching and a transverse direction
stretching, the transverse direction including a simultaneous
controlled machine direction relax. At least selected embodiments
of the invention may be directed to biaxially oriented porous
membranes, composites including biaxially oriented porous
membranes, biaxially oriented microporous membranes, biaxially
oriented macroporous membranes, battery separators, filtration
media, humidity control media, flat sheet membranes, liquid
retention media, and the like, related methods, methods of
manufacture, methods of use, and the like.
[0371] The present invention may be embodied in other forms without
departing from the spirit and the essential attributes thereof,
and, accordingly, reference should be made to the appended claims,
rather than to the foregoing specification, as indicated the scope
of the invention. Further, all numerical ranges set forth herein
should be considered as approximate ranges and not necessarily as
absolute ranges.
* * * * *