U.S. patent application number 15/120170 was filed with the patent office on 2017-02-02 for porous support, preparation method therefor, and reinforced membrane containing same.
This patent application is currently assigned to KOLON FASHION MATERIAL. INC.. The applicant listed for this patent is KOLON FASHION MATERIAL. INC.. Invention is credited to Ji Suk BAEK, Jeong Young CHOI, Chul Ki KIM, Sung Jin KIM, Yong Hwan LEE, Heung Ryul OH, Jun Young PARK, Hwan Kwon RHO.
Application Number | 20170030009 15/120170 |
Document ID | / |
Family ID | 54009328 |
Filed Date | 2017-02-02 |
United States Patent
Application |
20170030009 |
Kind Code |
A1 |
KIM; Sung Jin ; et
al. |
February 2, 2017 |
POROUS SUPPORT, PREPARATION METHOD THEREFOR, AND REINFORCED
MEMBRANE CONTAINING SAME
Abstract
The present invention relates to a porous support, a method for
manufacturing the same, and a reinforced membrane comprising the
same, the porous support comprising a nanoweb in which nanofibers
are accumulated in the form of a nonwoven fabric including a
plurality of pores, wherein the nanoweb has a moisture saturation
time of 1 second to 600 seconds. The porous support not only has
excellent durability, heat resistance, and chemical resistance
while exhibiting excellent air permeability and water permeability,
but also has good hydrophilicity.
Inventors: |
KIM; Sung Jin; (Gumi-si,
KR) ; OH; Heung Ryul; (Seoul, KR) ; LEE; Yong
Hwan; (Daegu, KR) ; RHO; Hwan Kwon; (Gumi-si,
KR) ; KIM; Chul Ki; (Gumi-si, KR) ; CHOI;
Jeong Young; (Busan, KR) ; PARK; Jun Young;
(Gumi-si, KR) ; BAEK; Ji Suk; (Gumi-si,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KOLON FASHION MATERIAL. INC. |
|
|
|
|
|
Assignee: |
KOLON FASHION MATERIAL.
INC.
Gwacheon-si, Gyeonggi-do
KR
|
Family ID: |
54009328 |
Appl. No.: |
15/120170 |
Filed: |
February 25, 2015 |
PCT Filed: |
February 25, 2015 |
PCT NO: |
PCT/KR2015/001789 |
371 Date: |
August 19, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D01D 1/02 20130101; D04H
1/728 20130101; D06M 2101/30 20130101; D04H 1/4326 20130101; D01F
1/10 20130101; D04H 1/4382 20130101; D01D 5/003 20130101; D06M
11/00 20130101; D01F 6/74 20130101; D06M 11/46 20130101; D01D 10/06
20130101; D06M 10/025 20130101 |
International
Class: |
D06M 11/46 20060101
D06M011/46; D01D 1/02 20060101 D01D001/02; D01D 5/00 20060101
D01D005/00; D04H 1/4382 20060101 D04H001/4382; D01F 6/74 20060101
D01F006/74; D01D 10/06 20060101 D01D010/06; D04H 1/4326 20060101
D04H001/4326; D06M 10/02 20060101 D06M010/02; D01F 1/10 20060101
D01F001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 25, 2014 |
KR |
10-2014-0021948 |
Claims
1. A porous support comprising a nanoweb in which nanofibers are
integrated in the form of a non-woven fabric including a plurality
of pores, wherein the nanoweb has a moisture content saturation
time of 1 sec to 600 sec.
2. The porous support according to claim 1, wherein the nanoweb has
a moisture regain of 3.0% by weight or more.
3. The porous support according to claim 1, wherein the nanoweb has
wettability in accordance with wicking test, of 2 to 15 cm.
4. The porous support according to claim 1, wherein the nanoweb has
a contact angle of 90.degree. or less.
5. The porous support according to claim 1, wherein the nanofiber
comprises 0.1 to 20 parts by weight of a polymer hydrophilic
additive, with respect to 100 parts by weight of the nanofiber.
6. The porous support according to claim 1, wherein a hydrophilic
additive is impregnated in the pores of the nanoweb.
7. The porous support according to claim 1, wherein a hydrophilic
additive is coated on one or two surfaces of the nanoweb.
8. The porous support according to claim 5, wherein the hydrophilic
additive is selected from the group consisting of TiO.sub.2
anatase, TiO.sub.2 rutile, TiO.sub.2 brookite, tin dioxide (SnO),
zirconium dioxide (ZrO.sub.2), aluminium oxide (Al.sub.2O.sub.3),
oxidized single-walled carbon nanotubes, oxidized multiwalled
carbon nanotubes, graphite oxide, graphene oxide and a combination
thereof.
9. The porous support according to claim 5, wherein the hydrophilic
additive is selected from the group consisting of
polyhydroxyethylmethacrylate, polyvinylacetate, polyurethane,
polydimethylsiloxane, polyimide, polyamide,
polyethyleneterephthalate, polymethylmethacrylate, epoxy and a
combination thereof.
10. The porous support according to claim 5, wherein the
hydrophilic additive has a mean diameter of 0.005 to 1 .mu.m.
11. The porous support according to claim 1, wherein the nanofiber
comprises a polyimide nanofiber.
12. The porous support according to claim 11, wherein the polyimide
has a main chain comprising a substituent selected from the group
consisting of an amine group, a carboxyl group, a hydroxyl group
and a combination thereof.
13. The porous support according to claim 12, wherein the polyimide
is prepared by polymerizing diamine, dianhydride and a comonomer
containing a hydroxyl group to prepare polyamic acid and then
imidizing the polyamic acid.
14. The porous support according to claim 13, wherein the comonomer
containing a hydroxyl group is selected from the group consisting
of dianiline containing a hydroxyl group, diphenyl urea containing
a hydroxyl group, diamine containing a hydroxyl group and a
combination thereof.
15. The porous support according to claim 1, wherein One or two
surfaces of the nanoweb is plasma-treated.
16. The porous support according to claim 1, wherein an inorganic
substance is deposited on one or two surfaces of the nanoweb.
17. The porous support according to claim 16, wherein the inorganic
substance is selected from the group consisting of TiO.sub.2
anatase, TiO.sub.2 rutile, TiO.sub.2 brookite, tin dioxide (SnO),
zirconium dioxide (ZrO.sub.2), aluminium oxide (Al.sub.2O.sub.3),
oxidized single-walled carbon nanotubes, oxidized multiwalled
carbon nanotubes, graphite oxide, graphene oxide and a combination
thereof.
18. A method of producing a porous support comprising: adding
diamine and dianhydride to a solvent to prepare an electrospinning
solution; electrospinning the prepared electrospinning solution to
produce a polyamic acid nanoweb in which nanofibers are integrated
in the form of a non-woven fabric including a plurality of pores;
and imidizing the polyamic acid nanoweb to produce a polyimide
nanoweb, wherein the polyimide nanoweb has a moisture content
saturation time of 1 sec to 600 sec.
19. The method according to claim 18, wherein a comonomer
containing a hydroxyl group is further added to the electrospinning
solution.
20. The method according to claim 18, wherein the nanofibers
present in the polyimide nanoweb have a main chain substituted by a
substituent selected from the group consisting of an amine group, a
carboxyl group, a hydroxyl group and a combination thereof.
21. A method of producing a porous support comprising
electrospinning an electrospinning solution to produce a nanoweb in
which nanofibers are integrated in the form of a non-woven fabric
including a plurality of pores, wherein the nanoweb has a moisture
content saturation time of 1 sec to 600 sec.
22. The method according to claim 21, wherein a hydrophilic
additive is further added to the electrospinning solution.
23. The method according to claim 21, further comprising:
impregnating a hydrophilic additive in pores of the nanoweb.
24. The method according to claim 21, further comprising: coating a
hydrophilic additive on one or two surfaces of the nanoweb.
25. The method according to claim 21, further comprising:
plasma-treating one or two surfaces of the nanoweb.
26. The method according to claim 25, wherein the plasma treatment
is carried out by treating one or two surfaces of the nanoweb with
gas for imparting a hydrophilic group using low-temperature plasma
or radio frequency (RF) plasma.
27. The method according to claim 21, further comprising:
depositing an inorganic substance on one or two surfaces of the
nanoweb.
28. The method according to claim 27, wherein the deposition of the
inorganic substance is carried out by sputtering.
29. A reinforced membrane comprising: the porous support according
to claim 1; and an ion exchange polymer filling pores of the porous
support.
30. The porous support according to claim 6, wherein the
hydrophilic additive is selected from the group consisting of
TiO.sub.2 anatase, TiO.sub.2 rutile, TiO.sub.2 brookite, tin
dioxide (SnO), zirconium dioxide (ZrO.sub.2), aluminium oxide
(Al.sub.2O.sub.3), oxidized single-walled carbon nanotubes,
oxidized multiwalled carbon nanotubes, graphite oxide, graphene
oxide and a combination thereof.
31. The porous support according to claim 6, wherein the
hydrophilic additive is selected from the group consisting of
polyhydroxyethylmethacrylate, polyvinylacetate, polyurethane,
polydimethylsiloxane, polyimide, polyamide,
polyethyleneterephthalate, polymethylmethacrylate, epoxy and a
combination thereof.
32. The porous support according to claim 6, wherein the
hydrophilic additive has a mean diameter of 0.005 to 1 .mu.m.
33. The porous support according to claim 7, wherein the
hydrophilic additive is selected from the group consisting of
TiO.sub.2 anatase, TiO.sub.2 rutile, TiO.sub.2 brookite, tin
dioxide (SnO), zirconium dioxide (ZrO.sub.2), aluminium oxide
(Al.sub.2O.sub.3), oxidized single-walled carbon nanotubes,
oxidized multiwalled carbon nanotubes, graphite oxide, graphene
oxide and a combination thereof.
34. The porous support according to claim 7, wherein the
hydrophilic additive is selected from the group consisting of
polyhydroxyethylmethacrylate, polyvinylacetate, polyurethane,
polydimethylsiloxane, polyimide, polyamide,
polyethyleneterephthalate, polymethylmethacrylate, epoxy and a
combination thereof.
35. The porous support according to claim 7, wherein the
hydrophilic additive has a mean diameter of 0.005 to 1 .mu.m.
Description
TECHNICAL FIELD
[0001] The present invention relates to a porous support, a method
of manufacturing the same, and a reinforced membrane comprising the
same. More particularly, the present invention relates to a porous
support which exhibits superior gas permeability and water
permeability, excellent durability, heat resistance and chemical
resistance, and superior hydrophilicity, a method of manufacturing
the same, and a reinforced membrane comprising the same.
BACKGROUND ART
[0002] Nanofibers are used in a variety of applications such as
filters for water purification, filters for air purification,
composites, membranes for cells and the like, in particular,
reinforced composite membranes for fuel cells for cars, due to wide
surface area and excellent porosity.
[0003] A fuel cell is an electrochemical device which is operated
from hydrogen and oxygen as fuels, which arises as an
environmentally friendly device because its products are pure water
and recyclable heat. In addition, it is widely used as power
sources for household, car and power generation applications and
the like owing to advantages such as easy operation, high output
density and non-noise.
[0004] Depending on the type of electrolyte membrane, the fuel cell
is classified into an alkaline electrolyte fuel cell, a direct
oxidation fuel cell, a polymer electrolyte membrane fuel cell
(PEMFC) and the like. Of these, the polymer electrolyte membrane
fuel cell generates electricity based on transfer of hydrogen ions
(H.sup.+) from an oxidation electrode (anode) to a reduction
electrode (cathode), which can operate at room temperature
(20.degree. C.) and have an advantage of short activation time, as
compared to other fuel cells.
[0005] A polymer electrolyte membrane fuel cell includes an
electricity generator which includes a membrane electrode assembly
(MEA) which is provided with an oxidation electrode and a reduction
electrode which are opposite to each other based on a polymer
electrolyte membrane fuel cell interposed therebetween, and a
separator (also, referred to as a "bipolar plate"), a fuel supply
to supply a fuel to the electricity generator, and an oxidizing
agent supply to supply an oxidizing agent such as oxygen or air to
the electricity generator.
[0006] A polymer electrolyte membrane is a conductor of hydrogen
ions and may be classified into a single membrane including a
polymer such as a fluorine- or hydrocarbon-based polymer and a
composite membrane including a composite of the polymer with an
organic/inorganic substance, a porous support or the like. The most
generally used single membrane is Nafion available from DuPont
which is a perfluorine-based polymer. However, Nafion has drawbacks
of high price, low mechanical and shape stability, and high
membrane resistance due to high thickness.
[0007] In order to solve these drawbacks, a research is underway on
composite membranes with reinforced mechanical and shape stability.
Of composite membranes, a pore-filling membrane including a porous
support impregnated with an ion conductor is actively researched
due to low price as well as excellent performance and mechanical
shape stability.
[0008] The support generally used for pore-filling membranes is
polytetrafluoroethylene (PTFE). However, a PTFE support has
superior chemical resistance, but has a drawback of low porosity of
40 to 60%.
PRIOR ART DOCUMENT
Patent Document
[0009] 1) Korean Patent Laid-open Publication No. 2011-0120185
(published on Nov. 3, 2011)
DISCLOSURE
Technical Problem
[0010] Therefore, it is an object of the present invention to
provide a porous support which exhibits superior gas permeability
and water permeability, excellent durability, heat resistance and
chemical resistance, and superior hydrophilicity.
[0011] It is another object of the present invention to provide a
method of manufacturing the porous support.
[0012] It is another object of the present invention to provide a
reinforced membrane comprising the porous support.
Technical Solution
[0013] In accordance with an aspect of the present invention, the
above and other objects can be accomplished by the provision of a
porous support including a nanoweb in which nanofibers are
integrated in the form of a non-woven fabric including a plurality
of pores, wherein the nanoweb has a moisture content saturation
time of 1 sec to 600 sec.
[0014] The nanoweb may have a moisture regain of 3.0% by weight or
more.
[0015] The nanoweb may have wettability in accordance with wicking
test, of 2 to 15 cm.
[0016] The nanoweb may have a contact angle of 90.degree. or
less.
[0017] The nanofiber may include 0.1 to 20 parts by weight of a
polymer hydrophilic additive, with respect to 100 parts by weight
of the nanofiber.
[0018] A hydrophilic additive may be impregnated in the pores of
the nanoweb.
[0019] A hydrophilic additive may be coated on one or two surfaces
of the nanoweb.
[0020] The hydrophilic additive may be selected from the group
consisting of TiO.sub.2 anatase, TiO.sub.2 rutile, TiO.sub.2
brookite, tin dioxide (SnO), zirconium dioxide (ZrO.sub.2),
aluminium oxide (Al.sub.2O.sub.3), oxidized single-walled carbon
nanotubes, oxidized multiwalled carbon nanotubes, graphite oxide,
graphene oxide and a combination thereof.
[0021] The hydrophilic additive may be selected from the group
consisting of polyhydroxyethylmethacrylate, polyvinylacetate,
polyurethane, polydimethylsiloxane, polyimide, polyamide,
polyethyleneterephthalate, polymethylmethacrylate, epoxy and a
combination thereof.
[0022] The hydrophilic additive may have a mean diameter of 0.005
to 1 .mu.m.
[0023] The nanofiber may include a polyimide nanofiber.
[0024] The polyimide may have a main chain including a substituent
selected from the group consisting of an amine group, a carboxyl
group, a hydroxyl group and a combination thereof.
[0025] The polyimide may be prepared by polymerizing diamine,
dianhydride and a comonomer containing a hydroxyl group to prepare
polyamic acid and then imidizing the polyamic acid.
[0026] The comonomer containing a hydroxyl group may be selected
from the group consisting of dianiline containing a hydroxyl group,
diphenyl urea containing a hydroxyl group, diamine containing a
hydroxyl group and a combination thereof.
[0027] One or two surfaces of the nanoweb may be
plasma-treated.
[0028] An inorganic substance may be deposited on one or two
surfaces of the nanoweb.
[0029] The inorganic substance may be selected from the group
consisting of TiO.sub.2 anatase, TiO.sub.2 rutile, TiO.sub.2
brookite, tin dioxide (SnO), zirconium dioxide (ZrO.sub.2),
aluminium oxide (Al.sub.2O.sub.3), oxidized single-walled carbon
nanotubes, oxidized multiwalled carbon nanotubes, graphite oxide,
graphene oxide and a combination thereof.
[0030] In another aspect of the present invention, provided is a
method of producing a porous support including adding diamine and
dianhydride to a solvent to prepare an electrospinning solution,
electrospinning the prepared electrospinning solution to produce a
polyamic acid nanoweb including nanofibers integrated in the form
of a non-woven fabric including a plurality of pores, and imidizing
the polyamic acid nanoweb to produce a polyimide nanoweb, wherein
the polyimide nanoweb has a moisture content saturation time of 1
sec to 600 sec.
[0031] A comonomer containing a hydroxyl group may be further added
to the electrospinning solution.
[0032] The nanofibers present in the polyimide nanoweb may have a
main chain substituted by a substituent selected from the group
consisting of an amine group, a carboxyl group, a hydroxyl group
and a combination thereof.
[0033] In another aspect of the present invention, provided is a
method of producing a porous support including electrospinning an
electrospinning solution to produce a nanoweb in which nanofibers
are integrated in the form of a non-woven fabric including a
plurality of pores,
[0034] wherein the nanoweb has a moisture content saturation time
of 1 sec to 600 sec.
[0035] A hydrophilic additive may be further added to the
electrospinning solution.
[0036] The method may further include impregnating a hydrophilic
additive in pores of the nanoweb.
[0037] The method may further include coating a hydrophilic
additive on one or two surfaces of the nanoweb.
[0038] The method may further include plasma-treating one or two
surfaces of the nanoweb.
[0039] The plasma treatment may be carried out by treating one or
two surfaces of the nanoweb with gas for imparting a hydrophilic
group using low-temperature plasma or radio frequency (RF)
plasma.
[0040] The method may further include depositing an inorganic
substance on one or two surfaces of the nanoweb.
[0041] The deposition of the inorganic substance may be carried out
by sputtering.
[0042] In another aspect of the present invention, provided is a
reinforced membrane including the porous support and an ion
exchange polymer filling pores of the porous support.
[0043] Other details of embodiments of the present invention are
incorporated in the Detailed Description of the Invention described
below.
Effects of the Invention
[0044] The porous support according to the present invention
exhibits superior gas permeability and water permeability,
excellent durability, heat resistance and chemical resistance, and
superior hydrophilicity.
DESCRIPTION OF DRAWINGS
[0045] The above and other objects, features and other advantages
of the present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
[0046] FIG. 1 is a schematic view illustrating a nozzle-type
electrospinning device.
BEST MODE
[0047] Hereinafter, embodiments of the present invention will be
described in detail. These embodiments are provided only as
examples and should not be construed as limiting the scope and
spirit of the present invention. The present invention is defined
only by the scope of claims given later.
[0048] The terms used herein are used merely to describe specific
embodiments, but are not intended to limit the present invention.
The singular expressions include plural expressions unless
explicitly stated otherwise in the context thereof. It should be
appropriated that in this application, the terms "include(s),"
"comprise(s)", "including" and "comprising" are intended to denote
the presence of the characteristics, numbers, steps, operations,
elements, or components described herein, or combinations thereof,
but do not exclude the probability of presence or addition of one
or more other characteristics, numbers, steps, operations,
elements, components, or combinations thereof.
[0049] As used herein, the term "nano" means a nano-scale and
covers a size of 1 nm or less.
[0050] As used herein, the term "diameter" means a length of a
short axis passing through a center of a fiber and the term
"length" means a length of a long axis passing through the center
of the fiber.
[0051] The porous support according to an embodiment of the present
invention includes a nanoweb in which nanofibers are integrated in
the form of a non-woven fabric including a plurality of pores.
[0052] The nanofibers preferably include a hydrocarbon-based
polymer which exhibits superior chemical resistance and
hydrophobicity and is thus free from shape deformation by moisture
under high humidity environments. Specifically, the
hydrocarbon-based polymer may be selected from the group consisting
of nylon, polyimide, polyaramide, polyether imide,
polyacrylonitrile, polyaniline, polyethylene oxide, polyethylene
naphthalate, polybutylene terephthalate, styrene butadiene rubber,
polystyrene, polyvinyl chloride, polyvinyl alcohol, polyvinylidene
fluoride, polyvinyl butylene, polyurethane, polybenzoxazole,
polybenzimidazole, polyamide-imide, polyethylene terephthalate,
polyethylene, polypropylene, a copolymer thereof and a mixture
thereof. Of these, polyimide which exhibits relatively better heat
resistance, chemical resistance and shape stability is preferably
used.
[0053] The porous support includes an assembly of nanofibers, in
which the nanofibers produced by electrospinning are randomly
arranged, that is, a nanoweb. The nanofibers preferably have a mean
diameter of 40 to 5,000 nm, wherein the mean diameter is obtained
as an average of the diameters of 50 nanofibers measured with a
scanning electron microscope (JSM6700F, JEOL) in consideration of
porosity and thickness of the nanoweb. When the mean diameter of
the nanofibers is lower than 40 nm, mechanical strength of the
porous support may be deteriorated and, when the mean diameter of
the nanofibers exceeds 5,000 nm, porosity may be decreased and
thickness may be increased.
[0054] The nanoweb includes the nanofibers described above, thereby
having a porosity of 50% or more. As the porous support has a
porosity of 50% or more, specific surface area of the porous
support increases, thus facilitating impregnation of the ionic
conductor upon application to a separation membrane and, as a
result, improving efficiency of cells. Meanwhile, the nanoweb
preferably has a porosity of 90% or less. When the porosity of the
porous support exceeds 90%, subsequent processes may not be
efficiently performed due to deterioration in shape stability. In
addition, in another example, the porosity is calculated as a ratio
of an air volume with respect to a total volume of the porous
support in accordance with the following Equation 1. In this case,
the total volume is calculated by producing a rectangular porous
support sample and measuring the width, length and thickness of the
sample, and the air volume is obtained by measuring a weight of the
sample and subtracting a polymer volume, calculated back from
polymer density, from the total volume.
Porosity (%)=(Air volume in porous support/Total volume of porous
support).times.100 [Equation 1]
[0055] In addition, the porous support may have a mean thickness of
5 to 40 .mu.m. When the thickness of the porous support is less
than 5 .mu.m, mechanical strength and dimensional stability may be
significantly deteriorated upon application to a separation
membrane and, on the other hand, when the thickness exceeds 40
.mu.m, resistance loss may increase upon application to the
separation membrane and weight reduction and integration may be
deteriorated. More preferably, the nanoweb may have a mean
thickness of 10 to 30 .mu.m.
[0056] In order that the nanoweb includes nanofibers having
superior porosity and an optimal diameter, has a thickness, is
easily produced and exhibits superior tensile strength after
impregnation with an electrolyte, the polymer constituting the
nanoweb preferably has a weight average molecular weight of 30,000
to 500,000 g/mol. When the weight average molecular weight of the
polymer constituting the nanoweb is less than 30,000 g/mol,
porosity and thickness of the nanoweb can be easily controlled, but
porosity and tensile strength after wetting may be deteriorated. On
the other hand, the weight average molecular weight of the polymer
constituting the nanoweb exceeds 500,000 g/mol, heat resistance may
be slightly improved, but the manufacture process does not smoothly
proceed and porosity may be deteriorated.
[0057] In addition, as the nanoweb has a weight average molecular
weight satisfying the range defined above and the polymer precursor
is converted into the polymer under optimal curing conditions, it
has heat resistance of 180.degree. C. or more, preferably
300.degree. C. or more. When the heat resistance of the nanoweb is
less than 180.degree. C., the nanoweb may be readily deformed at a
high temperature due to degraded heat resistance and, as a result,
performance of the electrochemical device produced using the same
may be deteriorated. In addition, when heat resistance of the
nanoweb is degraded, the nanoweb may be deformed by abnormal
heating and performance thereof may be deteriorated, in serious
cases, the nanoweb may be disadvantageously broken and
exploded.
[0058] The nanoweb is insoluble in an organic solvent at room
temperature (at 20.degree. C.) to 100.degree. C. and is thus
chemically stable. The organic solvent may be an ordinary organic
solvent such as NMP, DMF, DMAc, DMSO or THF.
[0059] The nanoweb may have a strain of 10 length % or less,
preferably 5 length % or less. The strain may be obtained by
standing a nanoweb sample with a width 100 mm and a length of 100
mm at 200.degree. C. for 24 hours and calculating an average of
width and length strains before and after standing. When the strain
exceeds 10 length %, dimensional stability of the support may be
deteriorated and shape deformation may occur under high temperature
environments.
[0060] When the nanoweb includes polyimide, the imide conversion
may be 90% or more, preferably 99% or more. The imide conversion
may be measured by measuring an infrared spectrum of the nanoweb
and calculating a ratio of imide C--N absorbance at 1,375 cm.sup.-1
to a p-substituted C--H absorbance at 1,500 cm.sup.-1. When the
imide conversion is less than 90%, physical properties are
deteriorated and shape stability cannot be secured due to
un-reacted substance.
[0061] The nanoweb has air permeability of 50 to 250 .mu.lpm,
preferably 100 to 150 lpm. The air permeability may be measured in
accordance with the method of ISO 9237. When the air permeability
is less than 50 lpm, absorption of electrolyte may be difficult
and, when the air permeability exceeds 250 lpm, the electrolyte may
not be sufficiently incorporated.
[0062] The nanoweb exhibits superior hydrophilicity and thus a
moisture content saturation time of 1 sec to 600 sec, preferably 1
sec to 300 sec, more preferably 1 sec to 180 sec, even more
preferably 1 sec to 60 sec. The moisture content saturation time
may be obtained from a time for which a sample is completely wet
with water which is dropped from a height of 25 mm in accordance
with KS K ISO 9073-6, textile-non-woven test method-Part VI: liquid
absorption measurement method of absorption measurement
standard.
[0063] When the moisture content saturation time is within the
range, in the production of a reinforced membrane by impregnating
an ion exchange polymer in the nanoweb, a great amount of the ion
exchange polymer can be uniformly impregnated throughout pores of
the nanoweb. In addition, as hydrophilicity of the nanoweb
increases, when the reinforced membrane is used as a membrane for
fuel cells, formation of hydrophilic channel is facilitated and ion
conductivity can be thus improved.
[0064] The nanoweb has an electrolyte absorption capacity of to 60%
by weight, preferably 30 to 40% by weight. In accordance with KS K
ISO 9073-6, textile-non-woven test method-Part VI: liquid
absorption measurement method of absorption measurement standard,
the electrolyte absorption capacity may be measured by dropping a
70/30 (v/v) mixture of ethyl methyl carbonate and ethylene
carbonate from a height of 25 mm for 60 sec, vertically draining
the mixture for 120 sec, measuring the weight of the nanoweb and
performing calculation in accordance with the following Equation 2.
When the electrolyte absorption capacity is less than 10% by
weight, performance of cells cannot be sufficiently obtained due to
poor electrolyte absorption and, when the electrolyte absorption
capacity exceeds 60% by weight, physical properties of the support
may be deteriorated.
Electrolyte absorption capacity (%)=(W1-W)/W.times.100 [Equation
2]
[0065] wherein W is weight of nanoweb before absorption of
electrolyte and W1 is weight of nanoweb after absorption of
electrolyte.
[0066] The nanoweb may have a moisture regain of 3.0% by weight or
more, preferably 3.0 to 5.0% by weight, more preferably 3.1 to 5.0%
by weight. The moisture regain may be obtained by measuring, in
accordance with KS K 0221, method of absorbing moisture of textile:
oven balance method, the weight of a sample (O) after the sample
reaches moisture equilibrium for 24 hours under laboratory standard
conditions (KS K 0901), measuring the weight of the dried sample
(D) at 105 to 110.degree. C. for 90 minutes and performing
calculation in accordance with the following Equation 3:
Moisture regain (% by weight)=(O-D)/D.times.100 [Equation 3]
[0067] (O: weight of sample, D: weight of dried sample)
[0068] The nanoweb may have a wettability obtained in accordance
with the wicking test, of 2 to 15 cm, preferably 2.1 to 15 cm, more
preferably 3 to 15 cm. The wicking test may be carried out by
immersing a sample for 30 minutes and then measuring a wicking
maximum distance in accordance with USA AATCC Test Method 197-2011,
Option B, Measure distance at a given time in Vertical Wicking of
Textiles. When the wettability in accordance with the wicking test
is less than 2 cm, a problem in which an ion conductor is detached
from a support occurs under the fuel cell operation environment, or
operation time is delayed or physical shape stability is
deteriorated under the low humidity conditions, and when the
wettability exceeds 15 cm, durability may be deteriorated or the
ion conductor may be detached from the support due to accelerated
swelling of the ion conductor under the fuel cell operation
environment.
[0069] The nanoweb may have a contact angle of 90.degree. or less,
preferably 1 to 50.degree., more preferably 5 to 35.degree.. The
contact angle is obtained by charging distilled water in a syringe
while maintaining 30.degree. C. and RH of 40%, dropping a water
drop with a diameter of 3 mm on the nanoweb, allowing the water
drop to spread for 5 minutes and then measuring a contact angle
formed between a separation membrane and the water drop. When the
contact angle is less than 1.degree., wettability of the nanoweb is
excellent, but it may be difficult to produce a nanoweb with high
quality due to excessively high content of additive, and when the
contact angle exceeds 90.degree., it may be difficult for the
nanoweb to exhibit sufficient performance due to deteriorated
wettability when used as a membrane for electrochemical
devices.
[0070] When the nanofiber includes a hydrophobic polymer such as
polyimide, it has advantages of superior heat resistance, chemical
resistance and shape stability, but a great amount of an ion
conducting polymer cannot be uniformly impregnated throughout the
pores of the nanoweb due to lack of hydrophilicity, and ion
conductivity may be deteriorated due to lack of formation of
hydrophilic channel. Accordingly, hydrophilic treatment is required
in order for the nanoweb including a hydrophobic polymer described
above to satisfy the moisture content saturation time, moisture
regain, wettability in accordance with wicking test or contact
angle. Any hydrophilic treatment may be used without particular
limitation in the present invention so long as it is a conventional
method capable of improving hydrophilicity of nanowebs.
[0071] As an example of the hydrophilic treatment of the nanoweb,
the nanoweb may include a hydrophilic additive. That is, the
nanofiber may include the hydrophilic additive therein, the
hydrophilic additive may be impregnated in pores of the nanoweb, or
the hydrophilic additive may be coated on one or both surfaces of
the nanoweb.
[0072] Specifically, when the nanofiber includes the hydrophilic
additive, the nanofiber may include 0.1 to 20 parts by weight,
preferably 0.5 to 20 parts by weight, more preferably 1 to 2 parts
by weight of the hydrophilic additive with respect to 100 parts by
weight of the nanofiber polymer.
[0073] When the content of the hydrophilic additive is less than
0.1 parts by weight, with respect to 100 parts by weight of the
nanofiber polymer, wettability and thus performance of
electrochemical devices are deteriorated due to lack of
hydrophilicity and, when the content exceeds 20 parts by weight,
instability of nanofiber jet during the spinning process is
increased, fibers are non-uniformly collected, and a problem may
occur when applied to a separation membrane for electrochemical
devices.
[0074] When the hydrophilic additive is impregnated in pores of the
nanoweb, or the hydrophilic additive is coated on one or both
surfaces of the nanoweb, the nanoweb may include 0.1 to 20 parts by
weight, preferably 3 to 20 parts by weight, more preferably 5 to 20
parts by weight of the hydrophilic additive with respect to 100
parts by weight of the nanoweb.
[0075] When the content of the hydrophilic additive is less than
0.1 parts by weight, with respect to 100 parts by weight of the
nanoweb, wettability and thus performance of electrochemical
devices are deteriorated due to lack of hydrophilicity, and when
the content exceeds 20 parts by weight, instability of nanofiber
jet during the spinning process is increased, fibers are
non-uniformly collected, and a problem may occur when applied to a
separation membrane for electrochemical devices.
[0076] As the nanoweb includes the hydrophilic additive, it has
superior wettability and excellent wettability to the electrolyte
when used for a separation membrane for electrochemical devices,
thereby improving efficiency of cells. In addition, the porous
support has excellent durability, heat resistance and chemical
resistance, thus maintaining performance of electrochemical devices
even under harsh operation conditions.
[0077] The hydrophilic additive may be an inorganic or organic
hydrophilic additive. Any inorganic hydrophilic additive may be
used without particular limitation so long as it does not cause
oxidation and/or reduction reactions, that is, electrochemical
reactions with an anode or cathode collector within an operation
voltage range (for example, 0 to 5V based on Li/Li.sup.+ in the
case of a lithium secondary battery) of an electrochemical device,
does not impair conductivity and endures the process of producing
nanofibers including the same.
[0078] For example, the inorganic hydrophilic additive may be
selected from the group consisting of TiO.sub.2 anatase, TiO.sub.2
rutile, TiO.sub.2 brookite, tin dioxide (SnO), zirconium dioxide
(ZrO.sub.2) aluminium oxide (Al.sub.2O.sub.3), oxidized
single-walled carbon nanotubes, oxidized multiwalled carbon
nanotubes, graphite oxide, graphene oxide and a combination thereof
and is preferably TiO.sub.2.
[0079] In addition, any organic hydrophilic additive may be used
without particular limitation so long as it does not cause
oxidation and/or reduction reactions, that is, electrochemical
reactions with an anode or cathode collector within an operation
voltage range (for example, 0 to 5V based on Li/Li.sup.+ in the
case of a lithium secondary battery) of an electrochemical device,
does not impair conductivity and endures the process of producing
nanofibers including the same.
[0080] For example, the organic hydrophilic additive is any one
selected from the group consisting of polyhydroxyethylmethacrylate,
polyvinylacetate, polyurethane, polydimethylsiloxane, polyimide,
polyamide, polyethyleneterephthalate, polymethylmethacrylate, epoxy
and a combination thereof.
[0081] The hydrophilic additive may be a nanohydrophilic additive
and has thus a mean diameter of 0.005 to 1 .mu.m, preferably 0.005
to 0.8 .mu.m, more preferably 0.005 to 0.5 .mu.m. When the mean
diameter of the nano hydrophilic additive is less than 0.005 .mu.m,
nano hydrophilic particles are aggregated, thus inhibiting
hydrophilic effect or making it difficult to handle, and when the
mean diameter of the nano hydrophilic additive exceeds 1 .mu.m,
physical tensile strength of the support is deteriorated and
elongation at break is decreased.
[0082] As described above, when the nanofiber includes polyimide as
a hydrophobic polymer, in order to satisfy the moisture content
saturation time, moisture regain, wettability in accordance with
wicking test or contact angle, the main chain of the polyimide may
include any one hydrophilic substituent selected from the group
consisting of an amine group, a carboxyl group, a hydroxyl group
and a combination thereof.
[0083] That is, the polyimide may be prepared by preparing polyamic
acid (PAA) and then conducting imidization during a subsequent
curing process. The polyamic acid may be prepared by an ordinary
preparation method and specifically, by mixing diamine with a
solvent, adding dianhydride thereto and conducting polymerization,
and the diamine is aromatic diamine and the dianhydride is
preferably fully aromatic polyimide prepared from aromatic
dianhydride.
[0084] In this case, in order to incorporate any one substituent
selected from the group consisting of an amine group, a carboxyl
group, a hydroxyl group and a combination thereof into the main
chain of the polyimide, the polyimide or the polyamic acid is
prepared and the main chain of the polyimide or the polyamic acid
is then substituted by the hydrophilic substituent, or the
polyimide is prepared from the diamine and/or the dianhydride
including the hydrophilic substituent, or a comonomer having a
hydroxyl group is incorporated during polymerization, rather than
the diamine and the dianhydride. The comonomer having a hydroxyl
group may be any one selected from the group consisting of
dianiline having a hydroxyl group, diphenyl urea having a hydroxyl
group, diamine having a hydroxyl group and a combination
thereof.
[0085] When the main chain of polyimide includes the hydrophilic
substituent, the hydrophilic substituent may be present in an
amount of 0.01 to 0.1 mol %, preferably 0.01 to 0.08 mol %, more
preferably 0.02 to 0.08 mol % with respect to the total weight of
the polyimide. When the content of the hydrophilic substituent is
less than 0.01 mol %, hydrophilicity may be insufficient due to
reduction of the hydrophilic group in the polyimide main chain, and
when the content exceeds 0.1 mol %, side-reactions may occur and
physical strength and elongation may be deteriorated.
[0086] As described above, when the nanofiber includes a
hydrophobic polymer such as polyimide, one or two surfaces of the
nanoweb may be subjected to plasma treatment in order to satisfy
the moisture content saturation time, moisture regain, wettability
in accordance with wicking test or contact angle. When the nanoweb
is subjected to plasma treatment, the nanoweb surface can be
substituted by any one hydrophilic functional group selected from
the group consisting of a carboxyl group, a hydroxyl group, an
amine group and a combination thereof.
[0087] Specifically, the plasma treatment may be carried out by
treating one or two surfaces of the nanoweb with a gas for
imparting a hydrophilic group using low-temperature plasma or radio
frequency (RF) plasma. The gas for imparting a hydrophilic group
may be any one selected from the group consisting of ammonia gas,
argon gas, oxygen gas and a combination thereof, a flow rate of the
gas for imparting a hydrophilic group may be 10 to 200 sccm, a
power of the plasma is 50 to 200 W, and plasma treatment time may
be 10 sec to 5 min.
[0088] In addition, as described above, when the nanofiber includes
a hydrophobic polymer such as polyimide, an inorganic substance may
be deposited on one or two surfaces of the nanoweb in order to
satisfy the moisture content saturation time, moisture regain,
wettability in accordance with wicking test or contact angle. The
inorganic substance may be any one selected from the group
consisting of TiO.sub.2 anatase, TiO.sub.2 rutile, TiO.sub.2
brookite, tin dioxide (SnO), zirconium dioxide (ZrO.sub.2),
aluminium oxide (Al.sub.2O.sub.3), oxidized single-walled carbon
nanotubes, oxidized multiwalled carbon nanotubes, graphite oxide,
graphene oxide and a combination thereof.
[0089] The porous support has superior gas permeability and water
permeability as well as excellent heat resistance and chemical
resistance, thus being useful for filter materials for gas or
liquid filters, filter materials for dustproof masks, materials for
filters such as vents for cars, vents for cellular phones and vents
for printers, materials for high-quality clothing such as
moisture-permeable waterproof fabrics, polymer electrolytes for
fuel cells, secondary batteries, electrochemical materials such as
separation membranes for electrolysis devices or capacitors, and
medical materials such as dressings for wound treatment, supports
for artificial vessels, bandages, and masks for cosmetics which
require heat resistance and chemical resistance.
[0090] A method of manufacturing a porous support according to an
embodiment of the present invention includes electrospinning an
electrospinning solution to form a nanoweb in which nanofibers are
integrated in the form of a non-woven fabric including a plurality
of pores.
[0091] For example, when the nanofibers include polyimide as a
hydrophobic polymer, the method of manufacturing a porous support
includes adding diamine and dianhydride to a solvent to prepare an
electrospinning solution, electrospinning the prepared
electrospinning solution to produce a polyamic acid nanoweb
integrated in the form of a non-woven fabric including a plurality
of pores, and imidizing the polyamic acid nanoweb to produce a
polyimide nanoweb.
[0092] Hereinafter, the respective steps will be described. The
electrospinning solution is a solution which contains monomers for
forming the nanofibers, the monomers for forming the nanofibers are
preferably a hydrocarbon-based polymer which exhibits superior
chemical resistance and hydrophobicity and is thus free from shape
deformation by moisture under high humidity environments.
[0093] Specifically, the hydrocarbon-based polymer may be selected
from the group consisting of nylon, polyimide, polyaramide,
polyether imide, polyacrylonitrile, polyaniline, polyethylene
oxide, polyethylene naphthalate, polybutylene terephthalate,
styrene butadiene rubber, polystyrene, polyvinyl chloride,
polyvinyl alcohol, polyvinylidene fluoride, polyvinyl butylene,
polyurethane, polybenzoxazole, polybenzimidazole, polyamide-imide,
polyethylene terephthalate, polyethylene, polypropylene, a
copolymer thereof and a mixture thereof and is preferably polyimide
which exhibits relatively better heat resistance, chemical
resistance and shape stability. Hereinafter, an example in which a
nano-fiber includes polyimide as a hydrophobic polymer will be
described in detail.
[0094] Any monomer for forming the nanofibers may be used without
particular limitation so long as it is capable of forming the
hydrocarbon-based polymer. For example, the nanoweb including
polyimide is prepared by producing a polyamic acid nanoweb using
polyamic acid (PAA) which is a polyimide precursor which is readily
dissolved in an organic solvent and conducting imidization during a
subsequent curing process.
[0095] The polyamic acid nanoweb may be produced by an ordinary
production method, specifically, by mixing diamine with a solvent,
adding dianhydride thereto and then electrospinning the resulting
mixture.
[0096] The dianhydride may be selected from the group consisting of
pyromellitic dianhydride (PMDA),
3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA),
4,4'-oxydiphthalic anhydride (ODPA),
3,4,3',4'-biphenyltetracarboxylic dianhydride (BPDA), and
bis(3,4-dicarboxyphenyl)dimethylsilane dianhydride (SiDA) and
mixtures thereof. In addition, the diamine may be selected from the
group consisting of 4,4'-oxydianiline (ODA),
1,3-bis(4-aminophenoxy)benzene (RODA), p-phenylene diamine (p-PDA),
o-phenylene diamine (o-PDA) and mixtures thereof. The solvent used
for dissolving the poly(amic acid) may be selected from the group
consisting of m-cresol, N-methyl-2-pyrrolidone (NMP),
dimethylformamide (DMF), dimethylacetamide (DMAc),
dimethylsulfoxide (DMSO), acetone, diethyl acetate, tetrahydrofuran
(THF), chloroform, butyrolactone and mixtures thereof.
[0097] The monomers for forming nanofibers is preferably present in
an amount of 5 to 20% by weight with respect to the total weight of
the spinning solution. When the content of the polymer is less than
5% by weight, because spinning cannot smoothly proceed, fibers
cannot be formed or fibers with a uniform diameter cannot be
produced and, on the other hand, when the content of the monomers
exceeds 20% by weight, spinning cannot be conducted or
processability may be deteriorated due to significantly increased
ejection pressure.
[0098] In step 2, the electrospinning solution is spun to produce a
nanoweb precursor, that is, a polyamic acid nanoweb. There is no
particular limitation as to spinning in the present invention, and
the spinning is electrospinning, electro-blown spinning,
centrifugal spinning or melt blowing or the like, preferably,
electrospinning.
[0099] Hereinafter, an example of using electrospinning will be
described in detail.
[0100] FIG. 1 is a schematic view illustrating a nozzle-type
electrospinning device. Referring to FIG. 1, in accordance with
electrospinning, a predetermined amount of the precursor solution
is supplied from a solution tank 1 storing the nanofiber precursor
solution to a nozzle 3 using a volumetric pump 2 and the nanofiber
precursor solution is ejected through the nozzle 3 to form
nanofiber precursors. At this time, the nanofiber precursors are
scattered and, at the same time, coagulated. The coagulated
nanofiber precursors are collected on the collector 4 to produce a
precursor nanofiber of the porous support.
[0101] In this case, the electrospinning may be carried out under
the conditions that a positive charge density near the nozzle is
increased and a negative charge density near the collector is
increased. As a result, when polymer droplets are spun and
scattered, they repel one another, so that they can be
advantageously collected as nanofibers. Near the nozzle or near the
collector may mean an area which is within 10 cm from the surface
of the nozzle or the collector, but the present invention is not
particularly limited thereto.
[0102] Specifically, the positive charge density near the nozzle
can be controlled by installing a high-voltage generator (not
shown) for supplying a positive charge near the nozzle and the
negative charge density near the collector can be controlled by
installing a high-voltage generator (not shown) for supplying a
negative charge near the collector.
[0103] A level of increasing the positive charge density near the
nozzle can be controlled by supplying a positive charge of +10 to
+100 kV near the nozzle, and a level of increasing the negative
charge density near the collector can be controlled by supplying a
negative charge of 0 to -100 kV near the collector. When the amount
of the supplied positive charge is less than +10 kV, spinning
capability may not be sufficient, when the amount exceeds +100 kV,
electrical insulation may be removed and, when the amount of the
supplied negative charge is less than zero, potential difference
may not be sufficient and, when the amount of supplied negative
charge exceeds -100 kV, insulation may be removed.
[0104] In this case, an intensity of electric field between the
nozzle 3 and the collector 4 applied by a high-voltage generator 6
and a voltage transfer road 5 is preferably 850 to 3,500 V/cm. When
the intensity of the electric field is less than 850 V/cm, uniform
thickness of nanofibers cannot be produced because the precursor
solution is not continuously ejected, and production of the nanoweb
may be difficult because the nanofibers formed after spinning
cannot be smoothly collected on the collector and, when the
intensity of electric field exceeds 3,500 V/cm, the nanofibers are
not mounted at a desired position on collector 4, thus making
acquisition of a nanoweb having a normal shape impossible.
[0105] Nanofiber precursors having a uniform fiber diameter,
preferably a mean diameter of 0.01 to 5 .mu.m are produced by the
spinning process, and the nanofiber precursors are arranged in a
predetermined direction or randomly to form a non-woven fabric.
[0106] In step 3, the nanofiber precursor of the nanoweb precursor
is cured.
[0107] In order to convert the nanofiber precursor into the
nanofiber, a curing process which is an additional process
performed on the nanofiber precursor is conducted. For example,
when the nanofiber precursor produced by electrospinning includes
polyamic acid, the nanofiber precursor is converted into polyimide
by imidization during the curing process.
[0108] Accordingly, preferably, the temperature of the curing
process is suitably controlled in consideration of conversion ratio
of the nanofiber precursor. Specifically, the curing process may be
conducted at 80 to 650.degree. C. When the temperature during
curing is lower than 80.degree. C., conversion ratio is decreased
and, as a result, the heat resistance and chemical resistance of
the nanoweb may be deteriorated and, when the curing temperature
exceeds 650.degree. C., physical properties of the nanoweb may be
deteriorated by degradation of the nanofibers.
[0109] Meanwhile, as described above, when the nanofiber includes a
hydrophobic polymer such as polyimide, the nanoweb may include a
hydrophilic additive in order to satisfy the moisture content
saturation time, moisture regain, wettability in accordance with
wicking test or contact angle. That is, the nanofiber may include
the hydrophilic additive therein, the hydrophilic additive may be
impregnated in pores of the nanoweb, or the hydrophilic additive
may be coated on one or both surfaces of the nanoweb.
[0110] Specifically, when the nanofiber includes the hydrophilic
additive, the hydrophilic additive may be further added to the
electrospinning solution and electrospinning may be then conducted.
In this case, the hydrophilic additive may include 0.1 to 20 parts
by weight, preferably 3 to 20 parts by weight, more preferably 5 to
20 parts by weight of the hydrophilic additive, with respect to 100
parts by weight of the monomer for producing the nanofiber.
[0111] When the content of hydrophilic additive is less than 0.1
parts by weight, with respect to 100 parts by weight of the monomer
for producing the nanofiber, wettability and thus performance of
electrochemical devices are deteriorated due to lack of
hydrophilicity and, when the content exceeds 20 parts by weight,
instability of nanofiber jet during the spinning process is
increased, fibers are non-uniformly collected, and a problem may
occur when applied to a separation membrane for electrochemical
devices.
[0112] In addition, spinning of the electrospinning solution can be
carried out under general spinning conditions, but upon spinning of
a precursor solution containing the hydrophilic additive,
nanofibers cannot be uniformly collected on the collector due to
increased instability of spinning jet and nanowebs having high
quality cannot be produced. Accordingly, upon spinning of the
precursor solution including the hydrophilic additive, a cation
blower is installed near a spinning area to improve a cation
density, and a base material for the collector surface is exposed
to an anion blower to improve an anion density of a collector
material. If not, stable spinning jet cannot be obtained and it may
be difficult to produce a uniform and high-quality support.
[0113] When the hydrophilic additive is impregnated in pores of the
nanoweb, or the hydrophilic additive is coated on one or both
surfaces of the nanoweb, the porous support can be produced by
impregnating the nanoweb, through immersion, in a hydrophilic
additive solution prepared by adding the hydrophilic additive to a
solvent, or coating the hydrophilic additive solution on the
surface of the nanoweb.
[0114] The impregnation of the nanoweb in the hydrophilic additive
solution may be carried out by immersing the nanoweb in the
hydrophilic additive solution at room temperature (20.degree. C.)
for 5 to 30 minutes, then drying the same at 50 to 100.degree. C.
in an air oven for 3 hours or longer and repeating the immersing
and drying operations two or five times.
[0115] In addition, the coating of the hydrophilic additive
solution on the surface of the nanoweb may be carried out using a
variety of methods well-known in the art such as a laminating,
spraying, screen printing or doctor blade process.
[0116] The hydrophilic additive solution may be preparing by adding
an inorganic hydrophilic additive selected from the group
consisting of TiO.sub.2 anatase, TiO.sub.2 rutile, TiO.sub.2
brookite, tin dioxide (SnO), zirconium dioxide (ZrO.sub.2),
aluminium oxide (Al.sub.2O.sub.3), oxidized single-walled carbon
nanotubes, oxidized multiwalled carbon nanotubes, graphite oxide,
graphene oxide and a combination thereof, or any one organic
hydrophilic additive selected from the group consisting of
polyhydroxyethylmethacrylate, polyvinylacetate, polyurethane,
polydimethylsiloxane, polyimide, polyamide,
polyethyleneterephthalate, polymethylmethacrylate, epoxy and a
combination thereof to any one solvent selected from the group
consisting of N-methyl-2-pyrrolidine (NMP), dimethylformamide
(DMF), dimethylacetamide (DMA), dimethylsulfoxide (DMSO) and a
combination thereof, followed by mixing.
[0117] As described above, when the produced nanoweb includes
polyimide as a hydrophobic polymer, the main chain of polyimide may
include any one hydrophilic substituent selected from the group
consisting of an amine group, a carboxyl group, a hydroxyl group
and a combination thereof in order to satisfy the moisture content
saturation time, moisture regain, wettability in accordance with
wicking test or contact angle.
[0118] That is, in order to produce a nanoweb including polyimide
including the hydrophilic substituent in a main chain, the porous
support can be produced by preparing the polyimide or the polyamic
acid and then substituting the main chain of the polyimide or the
polyamic acid by the hydrophilic substituent, or preparing the
polyimide from the diamine and/or the dianhydride including the
hydrophilic substituent, or incorporating the comonomer having a
hydroxyl group during polymerization, in addition to the diamine
and the dianhydride.
[0119] The substitution of the main chain of the polyimide or the
polyamic acid by the hydrophilic substituent may be carried out by
substituting a part of the main chain by a carboxyl group and an
amine group by treatment with an alkaline aqueous solution such as
KOH or NaOH.
[0120] In addition, any one may be used as the comonomer having a
hydroxyl group so long as it includes the hydrophilic substituent
and can be polymerized with the diamine and/or the dianhydride. For
example, the comonomer having a hydroxyl group may be any one
selected from the group consisting of dianiline having a hydroxyl
group, diphenyl urea having a hydroxyl group, diamine having a
hydroxyl group and a combination thereof.
[0121] As described above, when the nanofiber includes a
hydrophobic polymer such as polyimide, one or two surfaces of the
nanoweb may be subjected to plasma treatment in order to satisfy
the moisture content saturation time, moisture regain, wettability
in accordance with wicking test or contact angle. When the nanoweb
is subjected to plasma treatment, the nanoweb surface can be
substituted by any one hydrophilic functional group selected from
the group consisting of a carboxyl group, a hydroxyl group, an
amine group and a combination thereof.
[0122] Specifically, the plasma treatment may be carried out by
treating one or two surfaces of the nanoweb with a gas for
imparting a hydrophilic group using low-temperature plasma or radio
frequency (RF) plasma. The gas for imparting a hydrophilic group
may be any one selected from the group consisting of ammonia gas,
argon gas, oxygen gas and a combination thereof, a flow rate of the
gas for imparting a hydrophilic group may be 10 to 200 sccm, a
power of the plasma is 50 to 200 W, and plasma treatment time may
be 10 sec to 5 min.
[0123] As described above, when the nanofiber includes a
hydrophobic polymer such as polyimide, an inorganic substance may
be deposited on one or two surfaces of the nanoweb in order to
satisfy the moisture content saturation time, moisture regain,
wettability in accordance with wicking test or contact angle.
[0124] The deposited inorganic substance layer can be formed by
depositing any one precursor selected from the group consisting of
TiO.sub.2 anatase, TiO.sub.2 rutile, TiO.sub.2 brookite, tin
dioxide (SnO), zirconium dioxide (ZrO.sub.2), aluminium oxide
(Al.sub.2O.sub.3), oxidized single-walled carbon nanotubes,
oxidized multiwalled carbon nanotubes, graphite oxide, graphene
oxide and a combination thereof, by chemical vapor deposition (CVD)
or physical vapor deposition (PVD) including sputtering. The
deposition may be carried out by disposing a target for imparting a
hydrophilic group on the surface using an RF sputter or depositor
and treating at a temperature of 50 to 300.degree. C. for 1 to 60
minutes.
[0125] In accordance with another embodiment of the present
invention, provided is a reinforced membrane which includes the
porous support and an ion exchange polymer filling pores of the
porous support.
[0126] A method of filling an ion exchange polymer in pores of the
porous support is for example impregnation. The impregnation may be
carried out by dipping the porous support in a solution containing
an ion exchange polymer. In addition, the ion exchange polymer may
be formed by dipping an associated monomer or low molecular weight
oligomer in the porous support and polymerizing in-situ the same in
the porous support.
[0127] The impregnation temperature and time may be affected by
various parameters. For example, the impregnation temperature and
time may be affected by the thickness of the nanoweb, concentration
of the ion exchange polymer, the type of solvent, concentration of
ion exchange polymer to be impregnated in the porous support and
the like. The impregnation process may be carried out at a
temperature of not less than a freezing point of the solvent and
not higher than 100.degree. C., more typically at room temperature
(20.degree. C.) to a temperature of 70.degree. C. or lower. The
temperature cannot be a melting point or higher of the
nanofibers.
[0128] The ion exchange polymer may be a cation exchange polymer
having a cation exchange group such as a proton, or an anion
exchange polymer having an anion exchange group such as a hydroxyl,
carbonate or bicarbonate ion.
[0129] The cation exchange group may be any one selected from the
group consisting of a sulfonic acid group, a carboxyl group, a
boronic acid group, a phosphoric acid group, an imide group, a
sulfonimide group, a sulfonamide group and a combination thereof
and is generally a sulfonic acid group or a carboxyl group.
[0130] The cation exchange polymer includes the cation exchange
group and examples thereof include fluoro-based polymers containing
fluorine in a main chain; hydrocarbon-based polymers such as
benzimidazole, polyamide, polyamideimide, polyimide, polyacetal,
polyethylene, polypropylene, acrylic resins, polyester,
polysulfone, polyether, polyetherimide, polyester,
polyethersulfone, polyetherimide, polycarbonate, polystyrene,
polyphenylenesulfide, polyetheretherketone, polyetherketone,
polyarylethersulfone, polyphosphazene or polyphenylquinoxaline;
partially fluorinated polymers such as
polystyrene-graft-ethylenetetrafluoroethylene copolymers or
polystyrene-graft-polytetrafluoroethylene copolymers; and sulfone
imide.
[0131] More specifically, when the cation exchange polymer is a
hydrogen ion cation exchange polymer, the polymers may include, in
a side chain, a cation exchange group selected from the group
consisting of a sulfonic acid group, a carboxylic acid group, a
phosphoric acid group, a phosphonic acid group and a derivative
thereof, and examples thereof include, but are not limited to, a
fluoro-based polymer including poly(perfluorosulfonic acid),
poly(perfluorocarboxylic acid) including a sulfonic acid group, a
copolymer of tetrafluoroethylene including a sulfonic acid group
with fluorovinylether, defluorinated sulfide polyetherketone or a
mixture thereof; and a hydrocarbon-based polymer including
sulfonated polyimide (S-PI), sulfonated polyarylethersulfone
(S-PAES), sulfonated polyetheretherketone (SPEEK), sulfonated
polybenzimidazole (SPBI), sulfonated polysulfone (S-PSU),
sulfonated polystyrene (S-PS), sulfonated polyphosphazene and a
mixture thereof.
[0132] The anion exchange polymer is a polymer which is capable of
transferring an anion such as a hydroxyl, carbonate or bicarbonate
ion, commercially available anion exchange polymers are hydroxides
or halides (generally, chloride), and the anion exchange polymer
may be used for industrial water purifications, metal separation or
catalyst process and the like.
[0133] The anion exchange polymer is generally a metal
hydroxide-doped polymer and specifically, is metal hydroxide-doped
poly(ethersulfone), polystyrene, vinyl-based polymers, poly(vinyl
chloride), poly(vinylidene fluoride), poly(tetrafluoroethylene),
poly(benzimidazole) or poly(ethyleneglycol) or the like.
[0134] The ion exchange polymer may be present in an amount of 50
to 99% by weight with respect to the total weight of the reinforced
membrane. When the content of the ion exchange polymer is less than
50% by weight, ion conductivity of the reinforced membrane may be
deteriorated and, when the content of the ion exchange polymer
exceeds 99% by weight, the mechanical strength and dimensional
stability of the reinforced membrane may be deteriorated.
[0135] When the ion exchange polymers are filled in pores of the
porous support, a coating layer may be formed on one or two
surfaces of the porous support during the production process. The
thickness of the coating layer of the ion exchange polymer is
preferably controlled to 30 .mu.m or less. When the coating layer
of the ion exchange polymer is formed to a thickness of higher than
30 .mu.m on the surface of the porous support, the mechanical
strength of the reinforced membrane may be deteriorated, the total
thickness of the reinforced membrane is increased and resistance
loss is thus increased.
[0136] The reinforced membrane has a structure in which the ion
exchange polymer is filled in pores of the porous support, thus
exhibiting superior mechanical strength of 40 MPa or more. As such,
as mechanical strength increases, the total thickness of the
reinforced membrane can be reduced to 80 .mu.m or less and, as a
result, material costs are reduced, ion conduction speed is
increased and resistance loss is reduced.
[0137] In addition, the reinforced membrane includes a porous
support having superior durability and superior binding capability
between nanofibers and the ion exchange polymer constituting the
porous support, thereby preventing three-dimensional expansion of
the reinforced membrane resulting from moisture and reducing length
and thickness increase fractions. Specifically, the reinforced
membrane has superior dimensional stability of 5% or less when
swollen in water. The dimensional stability is a physical property
which is evaluated in accordance with the following Equation 4 from
variation in length before and after swelling of the reinforced
membrane.
Dimensional stability=[(length after swelling-length before
swelling)/length before swelling].times.100 [Equation 4]
[0138] The reinforced membrane has superior dimensional stability
and ion conductivity, thus being preferably useful for polymer
electrolyte membranes for fuel cells or membranes for reverse
osmosis filters.
MODE FOR INVENTION
[0139] Hereinafter, embodiments according to the present invention
will be described in detail to such an extent that a person having
ordinary knowledge in the art field to which the invention pertains
can easily carry out the invention. However, the present invention
can be realized in various forms and is not limited to embodiments
stated herein.
PRODUCTION EXAMPLE
Production of Porous Support
Example 1-1
[0140] 100 parts by weight of PMDA, ODA and PDA monomers, and parts
by weight of nano TiO.sub.2 anatase as a hydrophilic additive were
dissolved in a dimethylformamide solvent to prepare 5 L of a
spinning solution having a solid content of 12.5% by weight and a
viscosity of 620 poise. The prepared spinning solution was
transferred to a solution tank, fed by a volumetric gear pump to a
spinning chamber having 26 nozzles and to which a high voltage of
49 kV was applied, and then spun to produce a polyamic acid
nanoweb. At this time, the amount of supplied solution was 1.0
ml/min. In addition, a cation blower and an anion blower were
installed on a spinning chamber and a collector material,
respectively, to improve cation density based on the spinning
environment and anion density based on the collector material.
[0141] Subsequently, the polyamic acid nanoweb was transferred by a
roll-to-roll method and heat-cured in a continuous curing furnace
at a temperature of 420.degree. C. for 10 minutes to produce a
porous support including a polyimide nanoweb.
Example 1-2
[0142] A porous support was produced in the same manner as in
Example 1-1 except that 0.1 parts by weight of nano TiO.sub.2
anatase was used as the hydrophilic additive.
Example 1-3
[0143] A porous support was produced in the same manner as in
Example 1-1 except that 20 parts by weight of nano TiO.sub.2
anatase was used as the hydrophilic additive.
Comparative Example 1-1
[0144] 100 parts by weight of PMDA, ODA and PDA monomers, and 5
parts by weight of nano TiO.sub.2 anatase as a hydrophilic additive
were dissolved in a dimethylformamide solution to prepare 5 L of a
spinning solution having a solid content of 12.5% by weight and a
viscosity of 620 poise. The prepared spinning solution was
transferred to a solution tank, fed by a volumetric gear pump to a
spinning chamber having 26 nozzles and to which a high voltage of
49 kV was applied, and then spun to produce a polyamic acid
nanoweb. At this time, the amount of supplied solution was 1.0
ml/min.
[0145] Subsequently, the polyamic acid nanoweb was heat-cured in a
continuous curing furnace at a temperature of 420.degree. C. for
minutes to produce a porous support including a polyimide
nanoweb.
Test Example 1
Measurement of Properties of Porous Support
[0146] The moisture content saturation time, moisture regain,
wettability and contact angle of the porous supports produced in
Examples and Comparative Examples were measured and results are
summarized in the following Table 1.
TABLE-US-00001 TABLE 1 Comparative Example Example Example Example
1-1 1-2 1-3 1-1 Moisture 200 600 60 3600 content saturation
time.sup.1) Moisture 3.5 3.0 5.0 2.5 regain.sup.2)
Wettability.sup.3) 3 2 7 0 contact 45 80 25 113 angle.sup.4)
.sup.1)Moisture content saturation time (sec): the moisture content
saturation time was obtained from a time for which a sample was
completely wet with water which was dropped from a height of 25 mm
in accordance with KS K ISO 9073-6, textile-non-woven test
method-Part VI: liquid absorption measurement method of absorption
measurement standard. .sup.2)Moisture regain (% by weight): was
obtained by measuring, in accordance with KS K 0221, method of
absorbing moisture of textile: oven balance method, the weight of a
sample (O) after the sample reaches moisture equilibrium for 24
hours under laboratory standard conditions (KS K 0901), measuring
the weight of the dried sample (D) at 105 to 110 C..degree. for 90
minutes and then calculating a weight variation .sup.3)Wettability
(cm): was measured by immersing a sample for 30 minutes and then
measuring a wicking maximum distance in accordance with USA AATCC
Test Method 197-2011, Option B, Measure distance at a given time in
Vertical Wicking of Textiles. .sup.4)Contact angle (.degree.): was
measured by charging distilled water in a syringe while maintaining
30.degree. C. and RH of 40%, dropping a water drop with a diameter
of 3 mm on the nanoweb, allowing the water drop to spread for 5
minutes and then measuring a contact angle formed between a
separation membrane and the water drop.
[0147] As can be seen from Table 1, the porous membrane produced in
Example has superior hydrophilicity as compared to the porous
membrane produced in Comparative Example.
Production Example 2
Production of Porous Support
Example 2-1
[0148] PMDA, ODA and PDA monomers were dissolved in a
dimethylformamide solvent to prepare 5 L of a spinning solution
having a solid content of 12.5% by weight and a viscosity of 620
poise. The prepared spinning solution was transferred to a solution
tank, fed by a volumetric gear pump to a spinning chamber having 26
nozzles and to which a high voltage of 49 kV was applied, and then
spun to produce a polyamic acid nanoweb. At this time, the amount
of supplied solution was 1.0 ml/min.
[0149] Subsequently, the polyamic acid nanoweb was heat-cured in a
continuous curing furnace maintained at a temperature of
420.degree. C. for 10 minutes to produce a polyimide nanoweb.
[0150] Meanwhile, nano TiO.sub.2 anatase as a hydrophilic additive
was dissolved in a dimethylformamide solvent and stirred to prepare
a hydrophilic additive solution. The produced nanoweb was immersed
in the prepared hydrophilic additive solution at room temperature
(20.degree. C.) for 5 to 30 minutes, was dried at 50 to 100.degree.
C. in an air oven for 3 hours or longer and the immersing and
drying operations were repeated two or five times to impregnate the
hydrophilic additive in the nanoweb.
Example 2-2
[0151] A porous support was produced in the same manner as in
Example 2-1 except that coating the hydrophilic additive solution
on two surfaces of the nanoweb by spraying and then drying the same
were repeated.
Example 2-3
[0152] PMDA, ODA and PDA monomers were dissolved in a
dimethylformamide solvent to prepare 5 L of a spinning solution
having a solid content of 12.5% by weight and a viscosity of 620
poise. The prepared spinning solution was transferred to a solution
tank, fed by a volumetric gear pump to a spinning chamber having 26
nozzles and to which a high voltage of 49 kV was applied, and then
spun to produce a polyamic acid nanoweb. At this time, the amount
of supplied solution was 1.0 ml/min.
[0153] Subsequently, the polyamic acid nanoweb was heat-cured in a
continuous curing furnace maintained at a temperature of
420.degree. C. for 10 minutes to produce a polyimide nanoweb. The
two surfaces of the produced polyimide nanoweb were fed into a
plasma treatment chamber, oxygen gas was fed thereto at a flow rate
of 150 sccm using low-temperature plasma and plasma treatment was
conducted at 20 W for 5 minutes.
Example 2-4
[0154] PMDA, ODA and PDA monomers were dissolved in a
dimethylformamide solvent to prepare 5 L of a spinning solution
having a solid content of 12.5% by weight of and a viscosity of 620
poise. The prepared spinning solution was transferred to a solution
tank, fed by a volumetric gear pump to a spinning chamber having 26
nozzles and to which a high voltage of 49 kV was applied, and then
spun to produce a polyamic acid nanoweb. At this time, the amount
of supplied solution was 1.0 ml/min.
[0155] Subsequently, the polyamic acid nanoweb was heat-cured in a
continuous curing furnace maintained at a temperature of
420.degree. C. for 6 minutes to produce a polyimide nanoweb. The
two surfaces of the produced polyimide nanoweb was sputtered at a
constant deposition power of 150 W and a constant sample
temperature of 200.degree. C. using an RF sputter for 10 minutes to
form a TiO.sub.2 inorganic substance layer.
Test Example 2
Measurement of Properties of Porous Support
[0156] The moisture content saturation time, moisture regain,
wettability and contact angle of the porous supports produced in
Examples and Comparative Examples were measured and results are
summarized in the following Table 2.
TABLE-US-00002 TABLE 2 Exam- Comparative Example Example Example
ple Example 2-1 2-2 2-3 2-4 1-1 Moisture 250 280 10 300 3600
content saturation time.sup.1) Moisture 3.3 3.6 5.0 3.8 2.5
regain.sup.2) Wettability.sup.3) 4 4.5 15 6 0 Contact 38 43 10 30
113 angle.sup.4) .sup.1)Moisture content saturation time (sec): the
moisture content saturation time was obtained from a time for which
a sample was completely wet with water which was dropped from a
height of 25 mm in accordance with KS K ISO 9073-6,
textile-non-woven test method-Part VI: liquid absorption
measurement method of absorption measurement standard.
.sup.2)Moisture regain (% by weight): was obtained by measuring, in
accordance with KS K 0221, method of absorbing moisture of textile:
oven balance method, the weight of a sample (O) after the sample
reaches moisture equilibrium for 24 hours under laboratory standard
conditions (KS K 0901), measuring the weight of the dried sample
(D) at 105 to 110.degree. C. for 90 minutes and then calculating a
weight variation .sup.3)Wettability (cm): was measured by immersing
a sample for 30 minutes and then measuring a wicking maximum
distance in accordance with USA AATCC Test Method 197-2011, Option
B, Measure distance at a given time in Vertical Wicking of
Textiles. .sup.4)Contact angle (.degree.): was measured by charging
distilled water in a syringe while maintaining 30.degree. C. and RH
of 40%, dropping a water drop with a diameter of 3 mm on the
nanoweb, allowing the water drop to spread for 5 minutes and then
measuring a contact angle formed between a separation membrane and
the water drop.
[0157] As can be seen from Table 2, the porous membrane produced in
Example has superior hydrophilicity as compared to the porous
membrane produced in Comparative Example.
Production Example 3
Production of Porous Support
Example 3-1
[0158] PMDA, ODA and PDA, and a hydroxyl group-containing diphenyl
urea monomer were dissolved at a ratio of 50:45:5 in a
dimethylformamide solvent to prepare 5 L of a spinning solution
having a solid content of 12.5% by weight and a viscosity of 620
poise.
[0159] The prepared spinning solution was transferred to a solution
tank, fed by a volumetric gear pump to a spinning chamber having 26
nozzles and to which a high voltage of 49 kV was applied, and then
spun to produce a polyamic acid nanoweb. At this time, the amount
of supplied solution was 1.0 ml/min.
[0160] Subsequently, the polyamic acid nanoweb was heat-cured in a
continuous curing furnace maintained at a temperature of
420.degree. C. for 10 minutes to produce a polyimide nanoweb.
Example 3-2
[0161] PMDA, ODA and PDA monomers were dissolved in a
dimethylformamide solvent to prepare 5 L of a spinning solution
having a solid content of 12.5% by weight and a viscosity of 620
poise. The prepared spinning solution was transferred to a solution
tank, fed by a volumetric gear pump to a spinning chamber having 26
nozzles and to which a high voltage of 49 kV was applied, and then
spun to produce a polyamic acid nanoweb. At this time, the amount
of supplied solution was 1.0 ml/min.
[0162] Subsequently, the polyamic acid nanoweb was heat-cured in a
continuous curing furnace maintained at a temperature of
420.degree. C. for 10 minutes to produce a polyimide nanoweb.
[0163] A 0.1N KOH solution was sprayed on the surface of the
produced polyimide nanoweb using a spray for one second and then
dried to substitute a main chain of the polyimide by a carboxyl
group in 0.02 mol %.
Example 3-3
[0164] PMDA, ODA and PDA monomers were dissolved in a
dimethylformamide solvent to prepare 5 L of a spinning solution
having a solid content of 12.5% by weight and a viscosity of 620
poise. The prepared spinning solution was transferred to a solution
tank, fed by a volumetric gear pump to a spinning chamber having 26
nozzles and to which a high voltage of 49 kV was applied, and then
spun to produce a polyamic acid nanoweb. At this time, the amount
of supplied solution was 1.0 ml/min.
[0165] Subsequently, the polyamic acid nanoweb was heat-cured in a
continuous curing furnace maintained at a temperature of
420.degree. C. for 10 minutes to produce a polyimide nanoweb.
[0166] A 0.1N KOH solution was sprayed on the surface of the
produced polyimide nanoweb using a spray for one second and then
dried to substitute a main chain of the polyimide by a carboxyl
group in 0.01 mol %.
Test Example 3
Measurement of Properties of Porous Support
[0167] The moisture content saturation time, moisture regain,
wettability and contact angle of the porous supports produced in
Examples and Comparative Examples were measured and results are
summarized in the following Table 3.
TABLE-US-00003 TABLE 3 Example Comparative Example 3-1 Example 3-2
3-3 Example 1-1 Moisture content 500 580 600 3600 saturation
time.sup.1) Moisture regain.sup.2) 3.1 3.3 3.2 2.5
Wettability.sup.3) 2.5 2.9 2.8 0 Contact angle.sup.4) 48 42 44 113
.sup.1)Moisture content saturation time (sec): the moisture content
saturation time was obtained from a time for which a sample was
completely wet with water which was dropped from a height of 25 mm
in accordance with KS K ISO 9073-6, textile-non-woven test
method-Part VI: liquid absorption measurement method of absorption
measurement standard. .sup.2)Moisture regain (% by weight): was
obtained by measuring, in accordance with KS K 0221, method of
absorbing moisture of textile: oven balance method, the weight of a
sample (O) after the sample reaches moisture equilibrium for 24
hours under laboratory standard conditions (KS K 0901), measuring
the weight of the dried sample (D) at 105 to 110.degree. C. for 90
minutes and then calculating a weight variation .sup.3)Wettability
(cm): was measured by immersing a sample for 30 minutes and then
measuring a wicking maximum distance in accordance with USA AATCC
Test Method 197-2011, Option B, Measure distance at a given time in
Vertical Wicking of Textiles. .sup.4)Contact angle (.degree.): was
measured by charging distilled water in a syringe while maintaining
30.degree. C. and RH of 40%, dropping a water drop with a diameter
of 3 mm on the nanoweb, allowing the water drop to spread for 5
minutes and then measuring a contact angle formed between a
separation membrane and the water drop.
[0168] As can be seen from Table 3, the porous membrane produced in
Example has superior hydrophilicity as compared to the porous
membrane produced in Comparative Example.
Production Example 4
Production of Reinforced Membrane
[0169] The porous supports produced in Production Examples 1 to 3
and 5% by weight of a Nafion solution were fed onto a petri dish
such that 0.06 g of Nafion was impregnated per a unit area
(cm.sup.2) of the web and was then dried at 60.degree. C. in an
oven for 4 hours or longer to produce a reinforced membrane.
Test Example 4
[0170] The reinforced membrane produced in Production Example 4 was
immersed in a 1M sulfuric acid solution for 3 hours to sufficiently
activate the hydrophilic group and the surface thereof was washed
with ultrapure water to prepare a sample for measurement of
conductivity, and ion conductivity was measured at a humidity of
90% and at 25.degree. C. and 80.degree. C. by a 4-electrode
method.
[0171] In addition, the reinforced membrane produced in Production
Example 4 was dried at 60.degree. C. in an oven for 6 hours or
longer and then stored in 80.degree. C. hot water for 2 hours, the
drying and storing operations were repeated 5 times, tensile
strength of the reinforced membrane was measured with UTM-3365
equipment and whether or not detachment occurred was observed.
[0172] In addition, in order to evaluate shape stability of the
reinforced membrane produced in Production Example 4, the
reinforced membrane was dried in a hot air oven at a temperature of
50.degree. C. for 6 hours and immersed in ultrapure water for 24
hours and dimensional variation of the reinforced membrane was
measured.
[0173] Measurement results are shown in the following Table 4.
TABLE-US-00004 TABLE 4 Tensile strength Ionic (MPa) Dimensional
conductivity After variation (Scm.sup.-1) Before measurement 5 (%)
25.degree. C. 80.degree. C. evaluation times Detachment X Y Example
0.07 0.08 47 45 Detachment X 1 1 1-1 Example 0.06 0.07 40 33
Detachment X 0.5 0.5 1-2 Example 0.09 0.10 49 49 Detachment X 0.1
0.1 1-3 Example 0.07 0.08 46 43 Detachment X 0.5 0.5 2-1 Example
0.07 0.08 46 43 Detachment X 0.5 0.5 2-2 Example 0.08 0.09 40 35
Detachment X 1.0 1.0 2-3 Example 0.07 0.08 43 43 Detachment X 0.5
0.5 2-4 Example 0.07 0.08 41 40 Detachment X 0.5 0.5 3-1 Example
0.07 0.08 40 35 Detachment X 0.5 0.5 3-2 Example 0.07 0.08 40 35
Detachment X 0.5 0.5 3-3 Comparative 0.06 0.07 40 30 Detachment 1.0
1.0 Example 1-1 Comparative 0.09 0.10 36 26 Detachment 10.0 10.0
Example.sup.1) .sup.1)Control Example: polymer electrolyte membrane
prepared by immersing the Nafion 117 membrane available from DuPont
in ultrapure water for 3 hours such that water was sufficiently
present in the membrane.
[0174] As can be seen from Table 4 above, the reinforced membranes
of Examples and the reinforced membranes of Comparative Examples
exhibited similar or identical hydrogen ionic conductivity at
25.degree. C., as compared to the fluoro-based reinforced membrane
of Control Example known to exhibit superior hydrogen ionic
conductivity. However, at a high temperature of 80.degree. C., the
reinforced membrane of Example exhibited similar or identical
hydrogen ion conductivity to the fluoro-based reinforced membrane
of Comparative Example, whereas the reinforced membrane of
Comparative Example exhibited significantly deteriorated ion
conductivity, as compared to the fluoro-based reinforced membrane
of Control Example.
[0175] In addition, the reinforced membrane of Example exhibited
significantly improved shape stability, as compared to the
fluoro-based reinforced membrane of Control Example known to
exhibit superior hydrogen ion conductivity.
[0176] Although the preferred embodiments of the present invention
have been disclosed for illustrative purposes, those skilled in the
art will appropriate that various modifications, additions and
substitutions are possible, without departing from the scope and
spirit of the invention as disclosed in the accompanying
claims.
INDUSTRIAL APPLICABILITY
[0177] The porous support according to the present invention has
wide surface area and excellent porosity, thus being useful for a
variety of applications such as filters for water purification,
filters for air purification, composites, membranes for cells and
the like, in particular, being useful for reinforced composite
membranes for fuel cells for cars.
* * * * *