U.S. patent application number 13/817322 was filed with the patent office on 2013-06-13 for ion-exchange membrane and process for producing the same.
This patent application is currently assigned to ASAHI KASEI FIBERS CORPORATION. The applicant listed for this patent is Toshio Aritomi, Masayuki Kishino, Tatsuhiko Miya, Ikuo Ueno, Minoru Yoshida, Kiyotaka Yoshie. Invention is credited to Toshio Aritomi, Masayuki Kishino, Tatsuhiko Miya, Ikuo Ueno, Minoru Yoshida, Kiyotaka Yoshie.
Application Number | 20130146450 13/817322 |
Document ID | / |
Family ID | 45605107 |
Filed Date | 2013-06-13 |
United States Patent
Application |
20130146450 |
Kind Code |
A1 |
Kishino; Masayuki ; et
al. |
June 13, 2013 |
ION-EXCHANGE MEMBRANE AND PROCESS FOR PRODUCING THE SAME
Abstract
[Problems] To provide an ion-exchange membrane using an
inexpensive nonwoven fabric sheet as a base sheet, featuring
excellent properties such as strength, dimensional stability and
shape stability, effectively suppressing undulation when it is
brought into contact with the electrolyte, and having a low
membrane resistance and stable properties. [Means for Solution] An
ion-exchange membrane comprising a nonwoven fabric sheet 1 and an
ion-exchange resin coating 3 formed on one surface of the nonwoven
fabric sheet 1, the nonwoven fabric sheet 1 having a fiber layer
structure that includes long filament layers 5 of a fiber diameter
of 8 to 30 .mu.m on both surfaces thereof and an extra-fine
filament layer 7 of a fiber diameter of not more than 5 .mu.m as an
intermediate layer formed by melt-adhesion of fibers between the
long filament layers 5.
Inventors: |
Kishino; Masayuki;
(Shunan-shi, JP) ; Aritomi; Toshio; (Shunan-shi,
JP) ; Yoshie; Kiyotaka; (Shunan-shi, JP) ;
Yoshida; Minoru; (Tokyo, JP) ; Miya; Tatsuhiko;
(Tokyo, JP) ; Ueno; Ikuo; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kishino; Masayuki
Aritomi; Toshio
Yoshie; Kiyotaka
Yoshida; Minoru
Miya; Tatsuhiko
Ueno; Ikuo |
Shunan-shi
Shunan-shi
Shunan-shi
Tokyo
Tokyo
Tokyo |
|
JP
JP
JP
JP
JP
JP |
|
|
Assignee: |
ASAHI KASEI FIBERS
CORPORATION
Osaka-shi, Osaka
JP
ASTOM CORPORATION
Tokyo
JP
|
Family ID: |
45605107 |
Appl. No.: |
13/817322 |
Filed: |
August 8, 2011 |
PCT Filed: |
August 8, 2011 |
PCT NO: |
PCT/JP2011/068020 |
371 Date: |
February 15, 2013 |
Current U.S.
Class: |
204/296 ;
427/402; 442/351 |
Current CPC
Class: |
B01D 69/10 20130101;
B01D 69/12 20130101; B32B 2255/02 20130101; B32B 2262/0238
20130101; B01D 2323/06 20130101; B32B 5/12 20130101; B01D 71/82
20130101; B01D 67/0002 20130101; B32B 2262/0223 20130101; B32B 5/26
20130101; B32B 5/24 20130101; B32B 2262/0284 20130101; C08J 5/22
20130101; B32B 2262/0253 20130101; B32B 2262/0261 20130101; C25B
13/02 20130101; B01J 47/12 20130101; B01D 2325/42 20130101; B32B
2307/726 20130101; B32B 5/022 20130101; B01D 61/44 20130101; Y10T
442/626 20150401 |
Class at
Publication: |
204/296 ;
442/351; 427/402 |
International
Class: |
C25B 13/02 20060101
C25B013/02 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 19, 2010 |
JP |
2010-184132 |
Claims
1. An ion-exchange membrane comprising a nonwoven fabric sheet and
an ion-exchange resin coating formed on one surface of said
nonwoven fabric sheet, said nonwoven fabric sheet having a fiber
layer structure that includes long filament layers of a fiber
diameter of 8 to 30 .mu.m on both surfaces thereof and an
extra-fine filament layer of a fiber diameter of not more than 5
.mu.m as an intermediate layer formed by melt-adhesion of fibers
between said long filament layers.
2. The ion-exchange membrane according to claim 1, wherein said
ion-exchange membrane has a burst strength of not less than 0.1
MPa, an electric resistance (25.degree. C.) of not more than 10
.OMEGA.cm.sup.2, a rate of area change of not more than 2% and a
rate of thickness change of not more than 10% in a dry state of
after it is held in a dry atmosphere of 50.degree. C. for 24 hours
and in a wet state of after it is dipped in pure water of
25.degree. C. for 24 hours, and a surface roughness Ra of not more
than 10 .mu.m on a surface of the ion-exchange resin coating of the
ion-exchange membrane in said wet state.
3. A process for producing an ion-exchange membrane comprising
steps of: providing a nonwoven fabric sheet having a fiber layer
structure that includes long filament layers of a fiber diameter of
8 to 30 .mu.m on both surfaces thereof and an extra-fine filament
layer of a fiber diameter of not more than 5 .mu.m as an
intermediate layer formed by melt-adhesion of fibers between said
long filament layers, a strippable film, and an organic solvent
solution of an ion-exchange resin or an ion-exchange resin
precursor that is capable of introducing ion-exchange groups;
applying said organic solvent solution onto one surface of said
strippable film to form an applied layer of the ion-exchange resin
or the ion-exchange resin precursor; overlapping said nonwoven
fabric sheet on said applied layer; forming a coating of the
ion-exchange resin or the ion-exchange resin precursor by drying
said applied layer in a state where said nonwoven fabric sheet has
been overlapped thereon; and stripping said strippable film.
4. The process for producing the ion-exchange membrane according to
claim 3, wherein when an organic solvent solution of said
ion-exchange resin precursor is used as said organic solvent
solution, provision is, further, made of a step of introducing
ion-exchange groups into said ion-exchange resin precursor after
the coating of the ion-exchange resin precursor has been formed but
before stripping said strippable film.
5. The process for producing the ion-exchange membrane according to
claim 3, wherein said organic solvent solution has a viscosity
(25.degree. C.) in a range of 0.5 to 80 dPas.
6. A nonwoven fabric sheet for use as a base sheet of an
ion-exchange membrane that has a fiber layer structure that
includes long filament layers of a fiber diameter of 8 to 30 .mu.m
on both surfaces thereof and an extra-fine filament layer of a
fiber diameter of not more than 5 .mu.m as an intermediate layer
formed by melt-adhesion of fibers between said long filament
layers.
Description
TECHNICAL FIELD
[0001] This invention relates to an ion-exchange membrane using a
nonwoven fabric sheet as a base sheet and to a process for
producing the same.
BACKGROUND ART
[0002] Ion-exchange membranes have been industrially used as
electrolytic membranes for electrodialysis in the step of desalting
for producing salts and foods, and in the fuel cells. The
ion-exchange membranes have a structure in which a base sheet that
works as a reinforcing material is provided as a core material in
the ion-exchange resin so as to maintain a predetermined membrane
strength.
[0003] There has heretofore been known an ion-exchange membrane
using a porous resin sheet as the base sheet (see, for example,
patent document 1). In the ion-exchange membrane of this form,
voids in the porous resin sheet which is the base material are
filled with the ion-exchange resin offering an advantage of a low
membrane resistance. However, the porous resin sheet is so
expensive that study has been forwarded to use any other
inexpensive material as a base sheet for reinforcement.
[0004] A nonwoven fabric sheet is a representative example of the
inexpensive base sheet, and there has also been known an
ion-exchange membrane using the nonwoven fabric sheet as the base
sheet. Further, to lower the cost of production, there has also
been proposed a method of producing an ion-exchange membrane by
coating a porous base sheet such as of nonwoven fabric with an
organic solvent solution of an ion-exchange resin followed by
drying (see, for example, patent document 2). According to this
method, the organic solvent solution of the ion-exchange resin
permeates into the nonwoven fabric sheet and, therefore, a coating
of the ion-exchange resin is formed in a manner of biting into the
nonwoven fabric, featuring a large strength of adhesion between the
ion-exchange resin layer and the nonwoven fabric sheet and
effectively preventing the two from peeling off.
[0005] Despite of its advantage of low cost, however, the nonwoven
fabric sheet has a small strength, and the ion-exchange membrane
using the nonwoven fabric sheet as the base sheet has such defects
as poor dimensional stability and poor shape stability.
[0006] Further, when the nonwoven fabric sheet is used as a
reinforcing sheet, there often occur such problems that the
resistance of the ion-exchange membrane increases, the ion-exchange
resin layer becomes irregular due to irregularity in the nonwoven
fabric causing the ion-exchange membrane to lose stability in its
properties, and the ion-exchange membrane expands irregularly when
it has swollen giving rise to the occurrence of undulation. That
is, if the ion-exchange membrane is produced by the coating with
the organic solvent solution of the ion-exchange resin as disclosed
in the above patent document 1, the ion-exchange resin solution
permeates into voids in the nonwoven fabric. To form an
ion-exchange resin layer of a predetermined thickness on the
surface of the nonwoven fabric, therefore, it becomes necessary to
apply the organic solvent solution of the ion-exchange resin in
large amounts resulting in a considerable increase in the thickness
of the ion-exchange resin layer formed on the surface of the
nonwoven fabric. Besides, since the ion-exchange resin layer is
formed by applying the organic solvent solution onto the porous
nonwoven fabric, bubbles infiltrate into the ion-exchange resin
layer. Therefore, not only the resistance of the obtained
ion-exchange membrane increases but also the membrane greatly
swells when it comes in contact with the electrolyte giving rise to
the occurrence of undulation. The undulation becomes a cause of
leakage of the electrolyte when electrolysis or electrodialysis is
conducted by using the ion-exchange membrane, and the ion-exchange
membrane fails to effectively exhibit its function.
PRIOR ART DOCUMENTS
Patent Documents
[0007] Patent document 1: JP-A-64-22932 [0008] Patent document 2:
JP-A-2-265929
OUTLINE OF THE INVENTION
Problems that the Invention is to Solve
[0009] It is, therefore, an object of the present invention to
provide an ion-exchange membrane using an inexpensive nonwoven
fabric sheet as a base sheet, featuring excellent properties such
as strength, dimensional stability and shape stability, effectively
suppressing undulation when it is brought into contact with
electrolyte, and having a low membrane resistance and stable
properties, and to provide a method of producing the ion-exchange
membrane.
Means for Solving the Problems
[0010] According to the present invention, there is provided an
ion-exchange membrane comprising a nonwoven fabric sheet and an
ion-exchange resin coating formed on one surface of the nonwoven
fabric sheet, the nonwoven fabric sheet having a fiber layer
structure that includes long filament layers of a fiber diameter of
8 to 30 .mu.m on both surfaces thereof and an extra-fine filament
layer of a fiber diameter of not more than 5 .mu.m as an
intermediate layer formed by melt-adhesion of fibers between the
two long filament layers.
[0011] According to the present invention, it is desired that the
ion-exchange membrane has a burst strength of not less than 0.1
MPa, an electric resistance (25.degree. C.) of not more than 10
.OMEGA.cm.sup.2, a rate of area change of not more than 2% and a
rate of thickness change of not more than 10% in a dry state of
after it is held in a dry atmosphere of 50.degree. C. for 24 hours
and in a wet state of after it is dipped in pure water of
25.degree. C. for 24 hours, and a surface roughness Ra of not more
than 10 .mu.m on the surface of the ion-exchange resin coating of
the ion-exchange membrane in the wet state.
[0012] According to the present invention, further, there is
provided a method of producing an ion-exchange membrane comprising
steps of:
[0013] providing a nonwoven fabric sheet having a fiber layer
structure that includes long filament layers of a fiber diameter of
8 to 30 .mu.m on both surfaces thereof and an extra-fine filament
layer of a fiber diameter of not more than 5 .mu.m as an
intermediate layer formed by the melt-adhesion of fibers between
the two long filament layers, a strippable film, and an organic
solvent solution of an ion-exchange resin or an ion-exchange resin
precursor that is capable of introducing ion-exchange groups;
[0014] applying the organic solvent solution onto one surface of
the strippable film to form an applied layer of the ion-exchange
resin or the ion-exchange resin precursor;
[0015] overlapping the nonwoven fabric sheet on the applied
layer;
[0016] forming a coating of the ion-exchange resin or the
ion-exchange resin precursor by drying the applied layer in a state
where the nonwoven fabric sheet has been overlapped thereon;
and
[0017] stripping the strippable film.
[0018] According to the production method of the present invention,
when an organic solvent solution of the ion-exchange resin
precursor is used as the organic solvent solution, provision is,
further, made of a step of introducing ion-exchange groups into the
ion-exchange resin precursor after the coating of the ion-exchange
resin precursor has been formed but before stripping the strippable
film.
[0019] It is, further, desired that the organic solvent solution
has a viscosity in a range of 0.5 to 80 dPas.
Effects of the Invention
[0020] The ion-exchange membrane of the present invention uses a
nonwoven fabric as a base sheet offering an advantage of a very low
cost. Here, the nonwoven fabric has a fiber layer structure that
includes long filament layers (layers of filaments of a diameter of
8 to 30 .mu.m) on both surfaces thereof, and an extra-fine filament
layer (layer of filament of a diameter of not more than 5 .mu.m) as
an intermediate layer formed by melt-adhesion of fibers between the
two long filament layers, effectively eliminating the defect
specific to the ion-exchange membranes that use the nonwoven fabric
as the base sheet.
[0021] That is, in the nonwoven fabric, in general, the fibers have
not been woven accounting for small strength, i.e., low dimensional
stability and poor shape stability. According to the present
invention, however, the extra-fine filament layer is formed as an
intermediate layer relying on melt-adhesion of fibers. Namely, the
extra-fine filament layer works as a reinforcing layer contributing
to increasing the strength, dimensional stability and shape
stability.
[0022] Besides, formation of the extra-fine filament layer limits
the ion-exchange resin from permeating or biting into voids in the
nonwoven fabric sheet. As a result, the ion-exchange resin coating
is firmly fixed to the nonwoven fabric sheet which is the base
sheet; i.e., the ion-exchange resin coating formed on the surface
of the nonwoven fabric sheet assumes a thin and uniform thickness
exhibiting stable properties without dispersion and exhibiting
decreased membrane resistance.
[0023] According to the production method of the present invention,
further, the nonwoven fabric sheet of the above-mentioned structure
is dried in a state of being overlapped on the layer of the organic
solvent solution of the ion-exchange resin or the precursor thereof
(hereinafter simply referred to as organic solvent solution) that
is applied to thereby form the coating of the ion-exchange resin or
the precursor thereof. Therefore, the organic solvent solution is
limited from permeating into the nonwoven fabric by the
intermediate layer of dense and fine filament in the nonwoven
fabric sheet, making it possible to reliably limit to a
predetermined level the amount of the ion-exchange resin that
permeates into the nonwoven fabric. Besides, bubbles that evolve
due to voids in the nonwoven fabric sheet quickly disperse to the
exterior through the nonwoven fabric sheet, and are effectively
prevented from mixing into the layer that is applied.
[0024] It is, therefore, allowed to form the ion-exchange resin
coating on the surface of the nonwoven fabric sheet using the
organic solvent solution in a decreased amount, the ion-exchange
resin coating assuming a decreased and uniform thickness. Thus, it
is made possible to produce, efficiently and in short periods of
time, the ion-exchange membrane that exhibits stable properties
without dispersion and decreased membrane resistance, swelling
little even when it is brought in contact with the electrolyte and
effectively preventing the occurrence of undulation.
[0025] If, for example, an ordinary nonwoven fabric sheet without
having a dense and fine filament layer as the intermediate layer is
used, the organic solvent solution of the ion-exchange resin or the
precursor thereof cannot be limited from permeating. Therefore, the
organic solvent solution deeply permeates over the whole nonwoven
fabric sheet. In order to form a layer of the ion-exchange resin of
a small thickness on the nonwoven fabric sheet, therefore, the
ion-exchange resin must be used in large amounts resulting in not
only an increase in the membrane resistance but also an increase in
the swelling when the nonwoven fabric sheet is brought into contact
with the electrolyte giving rise to the occurrence of undulation of
the membrane. Besides, the depth to which the organic solvent
solution permeates in the nonwoven fabric does not remain constant
and, therefore, the ion-exchange membrane exhibits dispersing
properties.
[0026] The amount of the organic solvent solution that permeates
into the nonwoven fabric can be minimized by using the organic
solvent solution of a high viscosity. In this case, however, a very
extended period of time is necessary for so permeating the organic
solvent solution into the nonwoven fabric sheet that a large
junction strength is obtained between the nonwoven fabric sheet and
the ion-exchange resin layer, causing a very decrease in the
production efficiency. Besides, the organic solvent solution does
not permeate in a constant amount into the nonwoven fabric but
permeates in unstable amounts still leaving the problem in that the
obtained ion-exchange membrane exhibits dispersing properties.
[0027] Despite of using the nonwoven fabric sheet having a dense
and staple layer as the intermediate layer, further, when the
ion-exchange resin coating is formed on the nonwoven fabric sheet
by applying the organic solvent solution of the ion-exchange resin
or the precursor thereof thereon followed by drying, bubbles evolve
in the layer that is formed by applying the organic solvent
solution onto the porous nonwoven fabric, the bubbles without being
permitted to escape. Accordingly, the ion-exchange resin coating
that is formed contains much bubbles resulting in the formation of
the ion-exchange membrane having a high resistance and exhibiting
unstable properties.
[0028] According to the present invention, on the other hand, use
is made of a nonwoven fabric sheet having a dense and extra-fine
filament layer as the intermediate layer, and the nonwoven fabric
sheet is dried in a state of being overlapped on a layer formed by
applying an organic solvent solution of an ion-exchange resin (or a
precursor thereof) to forma coating of the ion-exchange resin (or
the precursor thereof) solving all of the above-mentioned
problems.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] [FIG. 1] is a sectional view showing the structure of layers
of an ion-exchange membrane of the present invention.
[0030] [FIG. 2] is a view illustrating a process for producing the
ion-exchange membrane of the present invention.
MODE FOR CARRYING OUT THE INVENTION
<Structure of the Ion-Exchange Membrane>
[0031] Referring to FIG. 1, the ion-exchange membrane of the
present invention generally designated at 10 includes a nonwoven
fabric sheet 1 as the base sheet, and an ion-exchange resin coating
3 formed on one surface of the nonwoven fabric sheet 1 by a coating
method.
[0032] In the ion-exchange membrane 10 of this structure, the
nonwoven fabric sheet 1 has long filament layers 5 (5a, 5b) on both
surfaces thereof, and an extra-fine filament layer 7 as the
intermediate layer between the long filament layers 5a and 5b, the
extra-fine filament layer 7 firmly holding the long filament layers
5a and 5b relying on the melt-adhesion of fibers and being more
dense than the long filament layers 5a and 5b.
[0033] That is, in the invention, the ion-exchange resin coating 3
is formed on one long filament layer 5a of the nonwoven fabric
sheet 1 of the above structure by applying an organic solvent
solution of an ion-exchange resin or an ion-exchange resin
precursor onto the long filament layer 5a. Therefore, the
ion-exchange resin is permeating into the voids of the long
filament layer 5a and, therefore, the ion-exchange resin coating 3
is firmly fixed to the long filament layer 5a. Besides, the
ion-exchange resin that may deeply permeate is shut off by the
dense and extra-fine filament layer 7 and does not reach the long
filament layer 5b on the opposite side.
[0034] Here, in FIG. 1, the ion-exchange resin that is permeating
into the long filament layer 5a is designated at 3a.
Nonwoven Fabric Sheet 1:
[0035] In the present invention, the long filament layers 5 (5a,
5b) of the nonwoven fabric sheet 1 are formed of fibers of a
thermoplastic resin having a fiber diameter in a range of 8 to 30
.mu.m and, preferably, 10 to 20 .mu.m relying, for example, upon a
spun-bond method. That is, the layers 5 formed by using long
filaments of the above fiber diameters make it possible to form
voids of suitable sizes, to permeate an ion-exchange resin of a
suitable amount into the long filament layer 5a, to firmly hold the
ion-exchange resin coating 3 and to reinforce the ion-exchange
membrane 10. For example, use of the fiber having fiber diameter
larger than the above range impairs the smoothness of the surface
resulting in a decrease in the anchoring effect and, therefore,
making it difficult to firmly hold the ion-exchange resin coating
3. Further, if the fiber diameter is smaller than the above range,
it becomes difficult to form the extra-fine filament layer 7 based
on the melt-adhesion of fibers. Besides, the strength of the
nonwoven fabric sheet 1 decreases, and the ion permeability of the
obtained ion-exchange membrane decreases, too.
[0036] It is, further, desired that the long filament layer 5a is
formed in a weight of 3 to 50 g/m.sup.2. That is, the weight of not
less than 3 g/m.sup.2 is desired since voids become small among the
fibers, the fibers firmly bond to the extra-fine filament layer 7
to reinforce the nonwoven fabric sheet 1, and the anchoring effect
is enhanced to firmly hold the ion-exchange resin coating 3.
[0037] Further, the weight of the long filament layer 5a of not
more than 50 g/m.sup.2 is desired since the amount of the
ion-exchange resin that infiltrates into the layer 5a can be
suppressed when the ion-exchange resin coating 3 is formed, the
ion-exchange resin needs be used in small amounts for forming the
ion-exchange resin coating 3 of a suitable thickness, and the
membrane resistance of the obtained ion-exchange membrane 10 can be
lowered.
[0038] On the other hand, there is no specific limitation on the
weight of the long filament layer 5b on the side where no
ion-exchange resin coating 3 is formed. For example, the weight
thereof may be considerably smaller than that of the long filament
layer 5a but should desirably be nearly the same as that of the
long filament layer 5a. That is, upon selecting the weight to be
nearly the same between the long filament layer 5a on the side
where the ion-exchange resin coating 3 is formed and the long
filament layer 5b on the side where no ion-exchange resin coating 3
is formed, it is allowed to form the ion-exchange resin coating 3
on the long filament layer 5 of either side facilitating the
production of the ion-exchange membrane 10. Further, upon selecting
the thickness of the long filament layer 5b to be nearly the same
as that of the long filament layer 5a, the ion-exchange membrane 10
having an increased strength can be realized without unnecessarily
increasing the thickness thereof.
[0039] The extra-fine filament layer 7 joined to the long filament
layers 5a, 5b based on the melt-adhesion of fibers is formed of a
fiber having a fiber diameter of not more than 5 .mu.m and,
desirably, not more than 3 .mu.m. That is, use of such an
extra-fine filament enables the extra-fine filament layer 7 to be
dense layer as compared to the long filament layers 5. When the
ion-exchange resin coating 3 is formed, therefore, the extra-fine
filament layer 7 shuts off the permeation of the ion-exchange resin
limiting the amount of the ion-exchange resin that permeates and,
as a result, making it possible to avoid an increase in the
membrane resistance as well as to stabilize the membrane
properties. This, further, enables the long filament layers 5 to be
firmly held, and the nonwoven fabric sheet 1 (ion-exchange membrane
10) to possess increased strength, improved dimensional stability
and shape stability, effectively preventing undulation caused by
the swelling of the ion-exchange resin when the ion-exchange
membrane 10 comes in contact with the electrolyte. For example, if
there is used a fiber having a fiber diameter larger than the above
range, the layer 7 does not become dense and the above-mentioned
advantages are not obtained.
[0040] It is desired that the extra-fine filament layer 7 has a
fiber diameter of not less than 0.05 .mu.m and, specifically, not
less than 1 .mu.m. If the fiber diameter is not less than 0.05
.mu.m, the extra-fine filament layer does not easily turn into a
film and the membrane resistance does not easily increase, either,
which is desirable. Namely, the membrane resistance can be lowered
without greatly decreasing the ion permeability of the ion-exchange
membrane 10.
[0041] As the staple layer 7, there is preferably used a fiber
obtained by the melt-blown method. The fiber obtained by the
melt-blown method is lowly crystalline, favorably heat-adheres to
the long filament layers 5, enabling a large strength and
dimensional stability to be easily obtained. It is desired that the
extra-fine filament layer 7 has a weight of not less than 1
g/m.sup.2. That is, if the weight is not less than 1 g/m.sup.2, the
extra-fine filament layer 7 does not become sparse, and the
above-mentioned effect can be exhibited to a sufficient degree.
Further, if the weight so increases that the extra-fine filament
layer 7 becomes unnecessarily thick, then the obtained ion-exchange
membrane 10 may exhibit an increased membrane resistance, a
decreased ion permeability and a decreased strength. It is,
therefore, desired that the extra-fine filament layer 7 has a
thickness in a range of 0.1 to 15 .mu.m and, specifically, 0.5 to
10 .mu.m.
[0042] As the fibers for forming the long filament layers 5 and the
extra-fine filament layer 7, there can be used thermoplastic resin
fibers; i.e., known thermoplastic resin fibers can be used so far
as they have the above-mentioned fiber diameters.
[0043] As the thermoplastic resins for forming such fibers, there
can be exemplified olefin resins which are homopolymers or
copolymers of .alpha.-olefines such as ethylene, propylene,
1-butene, 1-pentene, 1-hexene, 3-methyl-1-butene,
4-methyl-1-pentene and 5-methyl-1-heptene; vinyl chloride resins
such as polyvinyl chloride, vinyl chloride/vinyl acetate copolymer;
vinyl chloride/vinylidene chloride copolymer and
vinylchloride/olefin copolymer; fluorine-contained resins such as
polytetrafluoroethylene, polychlorotrifluoroethylene, vinylidene
polyfluoride, tetrafluoroethylene/hexafluoropropylene copolymer,
tetrafluoroethylene/perfluoroalkylvinyl ether copolymer and
tetrafluoroethylene/ethylene copolymer; polyamide resins such as
nylon 6 and nylon 66; and polyester resins such as polyethylene
terephthalate, polybutylene terephthalate and polytrimethylene
terephthalate.
[0044] In the present invention, it is desired to use the polyester
resin fiber and the olefin resin fiber (specifically, polyethylene
fiber or polypropylene fiber) from the standpoint of membrane
properties (mechanical strength, chemical stability, resistance
against pharmaceuticals) when used as the ion-exchange membrane,
and it is most desired to use the polyethylene fiber from the
standpoint of melt-adhering property.
[0045] The filament layers 5 and the staple layer 7 may be formed
of different fibers. From the standpoint of their melt-adhering
property, however, it is desired that the two are formed of a
thermoplastic resin fiber of the same kind of polymer.
[0046] From the standpoint of preventing the filament layers 5 from
turning into films at the time of melt-adhering the long filament
layers 5 and the extra-fine filament layer 7 together, further,
there can be used a polymer for forming the extra-fine filament
layer 7 having a melting point lower than a melting point of the
polymer for forming the long filament layers 5.
[0047] Here, the nonwoven fabric sheet 1 having the above long
filament layers 5 and the extra-fine filament layer 7 is, usually,
produced in a manner as described below.
[0048] Onto a web (corresponds to the long filament layer 5) of
filaments having a predetermined fiber diameter formed by, for
example, the spun-bond method, the extra-fine filament layer 7 is
formed by the melt-blown method and, next, the same filaments as
those described above are blown onto the extra-fine filament layer
7. The thus obtained sheet of laminated fiber layers is adhered
together by the application of heat and pressure to thereby obtain
the desired nonwoven fabric sheet 1. The adhesion by the
application of heat and pressure is, desirably, conducted through a
calender treatment by using flat rolls, the temperature of the
calender treatment being, desirably, not lower than a glass
transition point of the melt-blown fiber but lower than a melting
point thereof and, more desirably, being lower by 10 to 100.degree.
C. than the melting point of the filaments. This makes it possible
to effectively prevent the long filament layers 5 and the
extra-fine filament layers 7 from turning into films.
[0049] The fiber diameters and weight can be adjusted by known
means.
Ion-Exchange Resin Coating 3:
[0050] In the present invention, the ion-exchange resin coating 3
is formed on the long filament layer 5 (5a) of the nonwoven fabric
sheet 1, and comprises an ion-exchange resin that can be applied by
being dissolved in an organic solvent. Namely, the ion-exchange
resin coating 3 has a structure in which an ion-exchange group that
exhibits ion-exchange capacity or, concretely, a cation-exchange
group or an anion-exchange group is introduced into a hydrocarbon
resin such as a polymer obtained by polymerizing a monomer having
an ethylenically unsaturated double bond, such as vinyl, styrene or
acrylics, or a polymer that includes an aromatic ring in the main
chain thereof, such as polysulfone, polyphenylene sulfide,
polyether ketone, polyetherether ketone, polyetherimide,
polyphenylene oxide, polyethersulfone, or polybenzimidazole.
[0051] Further, the ion-exchange group is a functional group that
could become a negative or positive electric charge in an aqueous
solution, and may be a sulfonic acid group, a carboxylic acid group
or a phosphonic acid group in the case of the cation-exchange group
and is, usually and desirably, the sulfonic acid group which is a
strong acid group. In the case of the anion-exchange group, it may
be primary to tertiary amino group, quaternary ammonium group,
pyridyl group, imidazole group or quaternary pyridinium group and
is, usually and desirably, the quaternary ammonium group or the
quaternary pyridinium group which is strongly basic.
[0052] As the cation-exchange resin, there can be exemplified
monomers of the type of sulfonic acid such as .alpha.-halogenated
vinylsulfonic acid, styrenesulfonic acid and vinylsulfonic acid,
monomers of the type of carboxylic acid such as methacrylic acid,
acrylic acid and maleic anhydride, monomers of the type of
phosphonic acid such as vinylphosphoric acid, and polymers obtained
by polymerizing the salts thereof and esters thereof.
[0053] As the anion-exchange resin, there can be exemplified
amine-type monomers such as vinylbenzyltrimethylamine and
vinylbenzyltriethylamine, nitrogen-containing heterocyclic monomers
such as vinylpyridine and vinylimidazole, and polymers obtained by
polymerizing the salts thereof and esters thereof.
[0054] The ion-exchange resins may have a crosslinked structure so
far as they can be dissolved in an organic solvent to prepare a
solution thereof. The ion-exchange resins may have been crosslinked
with a polyfunctional monomer as represented by a divinyl compound
such as divinylbenzene, divinylsulfone, butadiene, chloroprene,
divinylbiphenyl, trivinylbenzenes, divinylnaphthaline, diallylamine
or divinylpyridine. Or the ion-exchange resins may be copolymers
obtained by copolymerizing other monomers such as styrene,
acrylonitrile, methylstyrene, acrolein, methylvinylketone and
vinylbiphenyl.
[0055] It is desired that the ion-exchange resins have ion-exchange
capacities in a range of 0.5 to 3.0 meq/g and, specifically, 0.8 to
2.0 meq/g. With the ion-exchange capacity being not less than 0.8
meq/g, the membrane resistance becomes sufficiently low and high
membrane properties are obtained. With the ion-exchange capacity
being not more than 2.0 meq/g, the ion-exchange resin is suppressed
from dissolving in the electrolyte and is, further, suppressed from
swelling too much. Therefore, the shape changes little and the
membrane little undergoes the stripping. It is, therefore, desired
to so introduce the cation-exchange groups or the anion-exchange
groups that the ion-exchange capacity is realized as described
above.
[0056] The ion-exchange resin coating 3 that comprises the above
ion-exchange resin is formed on the surface layer 5a of long
filaments. Here, the ion-exchange resin forming the coating 3 is
biting into the interior (voids) of the surface layer 5a. Though
the whole thickness cannot be strictly specified, it is desired
that the thickness d of the portion present on the surface layer 5a
is in a range of, for example, about 1 to about 50 .mu.m so that
the ion-exchange capacity of the obtained ion-exchange membrane 10
is about 0.05 to about 2 meq/g and, specifically, about 0.1 to
about 1 meq/g. Namely, with the thickness being not less than 1
.mu.m, the ion-exchange resin coating 3 assumes a uniform thickness
suppressing dispersion in the membrane properties and stabilizing
membrane properties. With the thickness being not more than 50
.mu.m, further, swelling does not occur despite of an increase in
the ion-exchange capacity and the shape of the membrane does not
vary suppressing a decrease in the membrane properties.
[0057] In the ion-exchange membrane 10 of the invention having the
structure as described above, the ion-exchange resin coating is
formed on the surface of the highly strong nonwoven fabric sheet 1
that has the dense and extra-fine filament layer 7 as an
intermediate layer between the long filament layers 5a and 5b.
Therefore, the strength is so large that the burst strength is not
less than 0.1 MPa featuring excellent dimensional stability and
shape stability. Being coated with the ion-exchange resin, further,
the ion-exchange membrane 10 of the present invention suppresses
the permeation of water; i.e., the amount of water permeation
therethrough is measured to be not more than 100 ml/m.sup.2h and,
specifically, not more than 50 ml/m.sup.2h.
[0058] Further, since the ion-exchange resin is suitably limited
from permeating into the nonwoven fabric sheet 1, there is no
dispersion in the membrane properties; i.e., stable properties are
exhibited and, besides, the membrane resistance is very small.
Specifically, the ion-exchange membrane 10 of the present invention
produced by the following method effectively suppresses the bubbles
from being mixed into the ion-exchange resin coating 3 and,
therefore, has an electric resistance (25.degree. C.) of not more
than 10 .OMEGA.cm.sup.2 and, particularly, not more than 5
.OMEGA.cm.sup.2.
<Production of the Ion-Exchange Membrane 10>
[0059] The ion-exchange membrane 10 of the above structure is
produced by forming the ion-exchange resin layer (ion-exchange
resin coating 3) on the surface of the above nonwoven fabric sheet
1 (long filament layer 5a) by the coating method.
[0060] The above-mentioned organic solvent solution of the
ion-exchange resin is used for forming the ion-exchange resin
coating 3 by the coating method. It is also allowable to use the
organic solvent solution of the ion-exchange resin precursor in its
place.
[0061] The ion-exchange resin precursor is a polymer having a
functional group capable of introducing an ion-exchange group. As
the polymer having a functional group capable of introducing a
cation-exchange group, there can be exemplified those polymers
obtained by polymerizing such monomers as styrene, vinyltoluene,
vinylxylene, .alpha.-methylstyrene, vinylnaphthalene and
.alpha.-halogenated styrenes. As the polymer having a functional
group capable of introducing an anion-exchange group, there can be
exemplified those polymers obtained by polymerizing such monomers
as styrene, vinyltoluene, chloromethylstyrene, vinylpyridine,
vinylimidasole, .alpha.-methylstyrene and vinylnaphthalene.
[0062] The ion-exchange resin precursors may be those into which
the crosslinked structure has been introduced by the
copolymerization of a polyfunctional monomer such as the
above-mentioned divinyl compound and the like so far as they can be
dissolved in the organic solvent, and may be, further,
copolymerized with other monomers, as required.
[0063] When the organic solvent solution of the ion-exchange resin
precursor is used, it becomes necessary to introduce the
ion-exchange groups in the final step.
[0064] As the organic solvent used for preparing the organic
solvent solution of the ion-exchange resin or the ion-exchange
resin precursor, there can be used any organic solvent without
limitation provided it is capable of dissolving the above polymers.
From the standpoint of easy removal by drying, however, there can
be used ethylene chloride, chloroform, tetrahydrofurane,
dimethylformamide, N-methylpyrrolidone and methyl alcohol in one
kind or in the form of a mixed solvent of two or more kinds
thereof.
[0065] The organic solvent should be used in an amount that is
suited for being applied by means that will be described later and
should be used, for example, in such an amount that the organic
solvent solution assumes a viscosity (25.degree. C.) in a range of
0.5 to 80 dPas and, specifically, 1.0 to 60 dPas. If the viscosity
is too high, the permeation becomes slow when it is applied onto
the nonwoven fabric consuming an extended period of time for
obtaining a sufficiently large adhesiveness and lowering the
productivity. If the viscosity is too low, on the other hand, the
resin solution permeates into the nonwoven fabric as well as into
the intermediate layer making it difficult to form a coating of the
ion-exchange resin on the surface. From the standpoint of
productivity, not less than 0.5 m/min and, specifically, not less
than 1 m/min is preferred.
[0066] Referring to FIG. 2, the ion-exchange resin coating 3 is
formed on the nonwoven fabric sheet 1 by using the ion-exchange
resin prepared as described above or by using the organic solvent
solution of the ion-exchange resin.
[0067] First, a strippable film 20 is provided and on which the
organic solvent solution for forming a coating prepared above is
applied to thereby form a layer 23 of the organic solvent solution
(see FIG. 2(a)). The layer 23 applied here will be transferred onto
the surface on one side of the nonwoven fabric sheet 1 to form the
ion-exchange resin coating 3.
[0068] The strippable film 20 is the one that does not adhere to
the ion-exchange resin coating 3 that is formed last, and may be of
any kind and may have any thickness provided it does not dissolve
in the organic solvent in the layer 23 and easily peels off at the
final step. Usually, however, a polyester film such as of
polyethylene terephthalate is desirably used from the standpoint of
excellent durability, mechanical strength and repetitive use.
[0069] The organic solvent solution can be applied by known means
such as doctor-blade coating, knife coating, roll coating or bar
coating. The thickness of application thereof when dried is about
the thickness consisting of the thickness d of the desired
ion-exchange resin coating 3 and the thickness of the long filament
layer 5a in the nonwoven fabric sheet 1.
[0070] After the layer 23 of the organic solvent solution is formed
as described above, the nonwoven fabric sheet 1 is overlapped and
is held thereon prior to drying the layer 23 (see FIG. 2(b)). In
this case, the nonwoven fabric sheet 1 is so overlapped that the
filament layer 5a of the nonwoven fabric sheet 1 faces the layer
23. If the filament layers 5a and 5b have been formed having the
same thickness, then either side thereof may be overlapped to face
the layer 23.
[0071] At the time of overlapping, the layer 23 is in a wet state
of not being dried. Therefore, the organic solvent solution forming
the layer 23 gradually permeates into voids in the long filament
layer 5a in the nonwoven fabric sheet 1. The permeation, however,
is shut off by the dense and extra-fine filament layer 7 and does
not reach the interior of the long filament layer 5b on the
opposite side. Further, bubbles mix as the organic solvent solution
permeates into the long filament layer 5a. However, since the upper
side is the fiber layer which is an open system, the bubbles
quickly escape from the upper side; i.e., it is allowed to
effectively prevent the bubbles from mixing into the ion-exchange
resin coating 3 that is finally formed.
[0072] The overlapping is suitably conducted under the application
of pressure accelerating the permeation of the organic solvent
solution into the filament layer 5a of the nonwoven fabric sheet 1.
The pressure can be applied relying on, for example, the roller
press and is, usually, set to lie in a range in which the layer 23
that is applied will not be excessively compressed.
[0073] In the present invention, the viscosity of the organic
solvent solution is set to lie in the above-mentioned range
enabling the step of overlapping to be conducted in a short period
of time, enabling the nonwoven fabric sheet to be laminated by
overlapping at an increased rate and, therefore, the productivity
is improved.
[0074] The nonwoven fabric sheet 1 is overlapped as described above
so that the upper part of the layer 23 infiltrates into the
filament layer 5a of the nonwoven fabric sheet 1. Thereafter, the
layer 23 is dried to remove the organic solvent; i.e., the wet
layer 23 is solidified to thereby form the ion-exchange resin
coating 3. The drying will be in the form of drying with heating,
drying in a reduced pressure or drying by blowing the air and at
such a temperature that the nonwoven fabric sheet 1 will not be
melted to turn into a film.
[0075] When the layer 23 is formed by using the organic solvent
solution of the ion-exchange resin precursor, the layer obtained by
the above drying is a layer of the ion-exchange resin precursor. It
is, therefore, necessary to conduct the treatment to introduce the
ion-exchange groups after the drying.
[0076] The ion-exchange groups are introduced by a known method
such as sulfonation, phosphoniation or hydrolysis when, for
example, a cation-exchange membrane is to be produced, or amination
or alkylation when an anion-exchange membrane is to be produced.
That is, a solution of a treating agent for conducting the above
treatment is brought into contact with the coating of the
ion-exchange resin precursor that is obtained by drying to conduct
the reaction for introducing the exchange groups followed by
washing and drying to form the ion-exchange resin coating 3.
[0077] After the ion-exchange resin coating 3 is formed as
described above, the stripping film 20 is stripped to obtain the
desired ion-exchange membrane 10 (FIG. 2(c)).
[0078] In the embodiment shown in FIG. 1, the ion-exchange resin 3a
is permeating up to the interface between the long filament layer
5a and the extra-fine filament layer 7. So far as the anchoring
effect is obtained to a sufficient degree and the desired strength
as well as dimensional stability are assured, however, the
ion-exchange resin 3a does not have to be reaching the interface
between the long filament layer 5a and the extra-fine filament
layer 7.
[0079] The ion-exchange membrane 10 of the invention thus formed
uses the nonwoven fabric sheet 1 as the base sheet, and is very
inexpensive improving the strength which is a defect of when the
nonwoven fabric sheet is used as the base sheet, having a very
large strength (e.g., burst strength of not less than 0.1 MPa as
described earlier), and featuring excellent dimensional stability
and shape stability. Specifically, since the ion-exchange resin is
effectively limited from permeating into the nonwoven fabric sheet
1, the ion-exchange resin coating 3 has a small and uniform
thickness without dispersion in the membrane properties such as
membrane resistance, being suppressed from excessively swelling
when it is brought into contact with the electrolyte, effectively
preventing the undulation that stems from the swelling, effectively
preventing the bubbles from mixing into the ion-exchange resin
coating and, therefore, featuring a small membrane resistance.
[0080] Besides, the ion-exchange membrane can be favorably
mass-produced, and is industrially very useful, such as being used
as a membrane for electrodialysis for producing water and salts, as
a membrane for diffuse dialysis, as a diaphragm for cells and as a
pressure filter.
EXAMPLES
[0081] The invention will now be described in further detail by way
of Examples.
[0082] Properties of the ion-exchange membranes in Examples and
Comparative Examples were found by the measurements described
below.
(Measuring the Electric Resistance)
[0083] The ion-exchange membranes produced in Examples and
Comparative Examples were held in a two-chamber cell having
platinum black electrode plates, a sodium chloride aqueous solution
of 0.5 mols/l was filled on both sides of the ion-exchange
membranes, a resistance across the electrodes at 25.degree. C. was
measured relying on an AC bridge (at a frequency of 1000
cycles/sec.), and a difference between the resistance across the
electrodes at this moment and the resistance across the electrodes
measured without installing the ion-exchange membrane was recorded
as a membrane resistance.
[0084] The ion-exchange membrane used for the above measurement was
the one that had been put to be in an equilibrium state in the
sodium chloride aqueous solution of 0.5 mols/l.
(Measuring the Burst Strength)
[0085] The ion-exchange membranes in the wet state obtained at the
time of measuring the rate of area change and the rate of thickness
change that will be described later, were measured for their burst
strengths by using the Mullen burst strength tester (manufactured
by Toyo Seiki Seisakusho Co.).
(Measuring the Viscosity)
[0086] The viscosity of the organic solvent solution (polymer
solution) of the ion-exchange resin or the ion-exchange resin
precursor was measured by using a rotary cylindrical viscometer,
Visco Tester VT-04F (manufactured by Rion Co.).
(Measuring the Rate of Area Change and the Rate of Thickness
Change)
[0087] The ion-exchange membrane was cut into 50 mm.times.50 mm,
and was left to stand in a drier maintained at 50.degree. C. for 24
hours so as to be dried to a sufficient degree. The area of the
ion-exchange membrane in the dry state was regarded to be Si and
the thickness thereof to be T1. The sample in this dry state was
dipped in pure water maintained at 25.degree. C..+-.2.degree. C.
for 24 hours so as to be wet. The area of the ion-exchange membrane
in the wet state was regarded to be S2 and the thickness thereof to
be T2. From these values, the rate of area change and the rate of
thickness change were calculated in compliance with the following
formulas.
[0088] Rate of area change=(S2-S1).times.100/S1
[0089] Rate of thickness change=(T2-T1).times.100/T1
(Measuring the Surface Roughness)
[0090] The arithmetic mean roughness (Ra) of the surface of the
ion-exchange membrane was a value found by the following method. By
using a color 3D laser microscope, VK-8700 (manufactured by Keyence
Co.), the surfaces of the membrane samples were observed through a
ten-power objective lens. Suitable places free of impurities were
selected in the visual field, and an arithmetic mean roughness Ra
was found from the following numerical formula (1). This operation
was repeated several times, and an average value thereof was
regarded to be Ra.
Ra = 1 N n = 1 N Rn [ Numerical 1 ] ##EQU00001##
(Measuring the Amount of Water Permeation)
[0091] The ion-exchange membrane was set in a cylindrical pressure
filter container (effective filtering area of 10.9 cm.sup.2) pure
water was pressurized with 0.1 MPa, and the amount of water that
permeated per hour was measured.
Example 1
Preparation of a Polymer Solution:
[0092] A polyphenylene oxide was dissolved in chloroform, reacted
with a chlorosulfonic acid, neutralized with a sodium hydroxide,
and from which the solvent was removed to obtain a sulfonated
polyphenelene oxide (cation-exchange resin) having an ion-exchange
capacity of 1.6 meq/g.
[0093] Next, the sulfonated polyphenelene oxide was dissolved in an
N,N-dimethylformamide to prepare a sulfonated polyphenylene oxide
solution having a viscosity of 11 dPas.
Nonwoven Fabric Sheet:
[0094] A group of filaments obtained from a general-purpose PET by
the spun-bond method was extrusion-spun onto the surface of a
moving trap net to form a filament web that served as a back
surface layer. Onto the above web, a fiber spun by the melt-blown
method was directly blown to prepare a laminated web comprising an
extra-fine filament layer formed on the filament web. Further, a
spun-bond web same as that of the back surface layer was formed on
the extra-fine filament layer of the laminated web, followed by the
treatment through a flat calender to thereby obtain a nonwoven
fabric sheet of a three-layer structure described below having a
weight of 70 g/m.sup.2 and a thickness of 90 .mu.m, which was then
used as a base sheet. Filament layer on the back surface:
[0095] Fiber material: Polyethylene terephthalate (m.p.,
260.degree. C.)
[0096] Fiber diameter: 13 .mu.m
[0097] Weight: 31 g/m.sup.2
Intermediate Layer (Extra-Fine Filament Layer):
[0098] Fiber material: Polyethylene terephthalate (m.p.,
260.degree. C.)
[0099] Fiber diameter: 1.7 .mu.m
[0100] Weight: 8 g/m.sup.2
Filament Layer on the Front Surface:
[0101] Fiber material: Polyethylene terephthalate (m.p.,
260.degree. C.)
[0102] Fiber diameter: 12 .mu.m
[0103] Weight: 31 g/m.sup.2
Preparation of an Ion-Exchange Membrane:
[0104] By using a bar coater, the polymer solution prepared above
was applied onto a PET film so as to possess a liquid thickness of
100 .mu.m to thereby form an applied layer (cast layer).
[0105] Next, by using the PET film forming the cast layer, an
ion-exchange resin coating was formed on one surface of the
nonwoven fabric sheet. That is, the nonwoven fabric sheet was
overlapped on the cast layer and was laminated thereon by being
pressed by a roller. This method was regarded as the method A. The
rate of lamination at this moment was set to be 10 m/min (when the
rate of laminating the nonwoven fabric sheet was set to be larger
than the above rate, the polymer solution permeated insufficiently
and the nonwoven fabric sheet has peeled off).
[0106] Next, the cast layer was dried and solidified by being
heated at 60.degree. C. and, thereafter, the PET film was stripped
to obtain a cation-exchange membrane.
[0107] The ion-exchange resin coating on the surface of the
nonwoven fabric sheet of the obtained cation-exchange membrane
possessed a thickness d of 18 .mu.m, and exhibited a burst strength
of 0.6 MPa, an electric resistance of 2.4 .OMEGA.cm.sup.2, an
exchange capacity of 0.44 meq/g, a rate of area change of 0.8%, a
rate of thickness change of 5.0%, a surface roughness of 1.1 .mu.m
and an amount of water permeation of 0 ml/m.sup.2h.
Example 2
[0108] A cation-exchange membrane was obtained in the same manner
as in Example 1 but changing the viscosity of the polymer solution
(sulfonated polyphenylene oxide solution) to 50 dPas and changing
the thickness of the cast layer to a liquid thickness of 50 .mu.m.
The rate of laminating the nonwoven fabric sheet was set to be 5
m/min.
[0109] The ion-exchange resin coating on the surface of the
nonwoven fabric sheet of the obtained cation-exchange membrane
possessed a thickness d of 11 .mu.m, and exhibited a burst strength
of 0.6 MPa, an electric resistance of 2.2 .OMEGA.cm.sup.2, an
exchange capacity of 0.28 meq/g, a rate of area change of 0.4%, a
rate of thickness change of 3.2%, a surface roughness of 1.5 .mu.m
and an amount of water permeation of 0 ml/m.sup.2h.
[0110] When the rate of laminating the nonwoven fabric sheet was
set to be larger than the above rate, the polymer solution
permeated insufficiently and the nonwoven fabric sheet has peeled
off.
Example 3
[0111] A cation-exchange membrane was obtained in the same manner
as in Example 2 but changing the viscosity of the polymer solution
(sulfonated polyphenylene oxide solution) to 75 dPas. The rate of
laminating the nonwoven fabric sheet was set to be 2.5 m/min.
[0112] The ion-exchange resin coating on the surface of the
nonwoven fabric sheet of the obtained cation-exchange membrane
possessed a thickness d of 13 .mu.m, and exhibited a burst strength
of 0.6 MPa, an electric resistance of 2.1 .OMEGA.cm.sup.2, an
exchange capacity of 0.30 meq/g, a ratio of area change of 0.6%, a
ratio of thickness change of 3.8%, a surface roughness of 1.2 .mu.m
and an amount of water permeation of 0 ml/m.sup.2h.
[0113] When the rate of laminating the nonwoven fabric sheet was
set to be larger than the above rate, the polymer solution
permeated insufficiently and the nonwoven fabric sheet has peeled
off.
Example 4
[0114] A cation-exchange membrane was obtained in the same manner
as in Example 2 but changing the viscosity of the polymer solution
(sulfonated polyphenylene oxide solution) to 32 dPas. The rate of
laminating the nonwoven fabric sheet was set to be 7.0 m/min.
[0115] The ion-exchange resin coating on the surface of the
nonwoven fabric sheet of the obtained cation-exchange membrane
possessed a thickness d of 10 .mu.m, and exhibited a burst strength
of 0.6 MPa, an electric resistance of 2.3 .OMEGA.cm.sup.2, an
exchange capacity of 0.26 meq/g, a ratio of area change of 0.2%, a
ratio of thickness change of 2.4%, a surface roughness of 1.6 .mu.m
and an amount of water permeation of 0 ml/m.sup.2h.
[0116] When the rate of laminating the nonwoven fabric sheet was
set to be larger than the above rate, the polymer solution
permeated insufficiently and the nonwoven fabric sheet has peeled
off.
Example 5
[0117] A cation-exchange membrane was obtained in the same manner
as in Example 1 but changing the viscosity of the polymer solution
(sulfonated polyphenylene oxide solution) to 5 dPas. The rate of
laminating the nonwoven fabric sheet was set to be 20.0 m/min.
[0118] The ion-exchange resin coating on the surface of the
nonwoven fabric sheet of the obtained cation-exchange membrane
possessed a thickness d of 13 .mu.m, and exhibited a burst strength
of 0.6 MPa, an electric resistance of 3.2 .OMEGA.cm.sup.2, an
exchange capacity of 0.36 meq/g, a ratio of area change of 0.6%, a
ratio of thickness change of 3.9%, a surface roughness of 1.2 .mu.m
and an amount of water permeation of 0 ml/m.sup.2h.
[0119] When the rate of laminating the nonwoven fabric sheet was
set to be larger than the above rate, the polymer solution
permeated insufficiently and the nonwoven fabric sheet has peeled
off.
Example 6
[0120] A nonwoven fabric sheet having the following three-layer
structure was prepared in the same manner as in Example 1. Filament
layers on the front and back surfaces:
[0121] Fiber material: Polyethylene terephthalate (m/p.,
260.degree. C.)
[0122] Fiber diameter: 12 .mu.m
[0123] Weight: 12 g/m.sup.2
Intermediate Layer (Extra-Fine Filament Layer):
[0124] Fiber material: Polyethylene terephthalate (m/p.,
260.degree. C.)
[0125] Fiber diameter: 5 .mu.m
[0126] Weight: 15 g/m.sup.2
[0127] A cation-exchange membrane was obtained in the same manner
as in Example 1 but using the above nonwoven fabric sheet. The rate
of laminating the nonwoven fabric sheet was set to be 10 m/min.
[0128] The ion-exchange resin coating on the surface of the
nonwoven fabric sheet of the obtained cation-exchange membrane
possessed a thickness d of 21 .mu.m, and exhibited a burst strength
of 0.4 MPa, an electric resistance of 1.8 .OMEGA.cm.sup.2, an
exchange capacity of 0.42 meq/g, a ratio of area change of 0.8%, a
ratio of thickness change of 7.8%, a surface roughness of 1.0 .mu.m
and an amount of water permeation of 0 ml/m.sup.2h.
[0129] When the rate of laminating the nonwoven fabric sheet was
set to be larger than the above rate, the polymer solution
permeated insufficiently and the nonwoven fabric sheet has peeled
off.
Example 7
[0130] A polysulfone was chloromethylated and was, next,
transformed into a quaternary base thereof with the trimethylamine
to prepare an aminated polysulfone which was an anion-exchange
resin (ion-exchange capacity of quaternary base, 1.3 meq/g).
[0131] The aminated polysulfone was dissolved in a mixed solvent of
methanol and chloroform (volume ratio of 1:1) to prepare an
aminated polysulfone solution of a viscosity of 14 dPas.
Preparation of an Ion-Exchange Membrane:
[0132] By using a bar coater, the polymer solution prepared above
was applied onto a PET film so as to possess a liquid thickness of
100 .mu.m to thereby form a cast layer.
[0133] The nonwoven fabric sheet used in Example 1 was overlapped
on the cast layer and was laminated thereon. The rate of laminating
the nonwoven fabric sheet was set to be 8 m/min.
[0134] Next, the cast layer was dried and solidified by being
heated at 60.degree. C. and, thereafter, the PET film was stripped
to obtain an anion-exchange membrane.
[0135] The ion-exchange resin coating on the surface of the
nonwoven fabric sheet of the obtained anion-exchange membrane
possessed a thickness d of 7 .mu.m, and exhibited a burst strength
of 0.6 MPa, an electric resistance of 2.5 .OMEGA.cm.sup.2, an
exchange capacity of 0.16 meq/g, a rate of area change of 0.2%, a
rate of thickness change of 1.4%, a surface roughness of 1.6 .mu.m
and an amount of water permeation of 0 ml/m.sup.2h.
[0136] When the rate of laminating the nonwoven fabric sheet was
set to be larger than the above rate, the polymer solution
permeated insufficiently and the nonwoven fabric sheet has peeled
off.
Example 8
Preparation of a Polymer Solution:
[0137] A chloromethylated polystyrene was transformed into a
quaternary base thereof with the trimethylamine to prepare an
aminated polystyrene which was an anion-exchange resin
(ion-exchange capacity of quaternary base, 2.0 meq/g).
[0138] The polymer solution was dissolved in chloroform to prepare
an aminated polystyrene solution of a viscosity of 1.2 dPas.
Preparation of an Ion-Exchange Membrane:
[0139] By using a bar coater, the polymer solution prepared above
was applied onto a PET film so as to possess a liquid thickness of
100 .mu.m to thereby form a cast layer.
[0140] The nonwoven fabric sheet used in Example 1 was overlapped
on the cast layer and was laminated thereon. The rate of laminating
the nonwoven fabric sheet was set to be 40 m/min.
[0141] Next, the cast layer was dried and solidified by being
heated at 60.degree. C. and, thereafter, the PET film was stripped
to obtain an anion-exchange membrane.
[0142] The ion-exchange resin coating on the surface of the
nonwoven fabric sheet of the obtained anion-exchange membrane
possessed a thickness d of 5 .mu.m, and exhibited a burst strength
of 0.6 MPa, an electric resistance of 1.8 .OMEGA.cm.sup.2, an
exchange capacity of 0.25 meq/g, a rate of area change of 0.1%, a
rate of thickness change of 1.6%, a surface roughness of 1.7 .mu.m
and an amount of water permeation of 0 ml/m.sup.2h.
[0143] When the rate of laminating the nonwoven fabric sheet was
set to be larger than the above rate, the polymer solution
permeated insufficiently and the nonwoven fabric sheet has peeled
off.
Example 9
[0144] A nonwoven fabric sheet having the following three-layer
structure was prepared in the same manner as in Example 1. Filament
layers on the front and back surfaces:
[0145] Fiber material: Polyethylene terephthalate (m/p.,
260.degree. C.)
[0146] Fiber diameter: 20 .mu.m
[0147] Weight: 20 g/m.sup.2
Intermediate Layer (Extra-Fine Filament Layer):
[0148] Fiber material: Polyethylene terephthalate (m/p.,
260.degree. C.)
[0149] Fiber diameter: 1.0 .mu.m
[0150] Weight: 10 g/m.sup.2
[0151] An anion-exchange membrane was obtained in the same manner
as in Example 7 but using the above nonwoven fabric sheet. The rate
of laminating the nonwoven fabric sheet was set to be 8 m/min.
[0152] The ion-exchange resin coating on the surface of the
nonwoven fabric sheet of the obtained anion-exchange membrane
possessed a thickness d of 3 .mu.m, and exhibited a burst strength
of 0.7 MPa, an electric resistance of 3.2 .OMEGA.cm.sup.2, an
exchange capacity of 0.22 meq/g, a rate of area change of 0.1%, a
rate of thickness change of 0.6%, a surface roughness of 1.9 .mu.m
and an amount of water permeation of 0 ml/m.sup.2h.
[0153] When the rate of laminating the nonwoven fabric sheet was
set to be larger than the above rate, the polymer solution
permeated insufficiently and the nonwoven fabric sheet has peeled
off.
Comparative Example 1
[0154] A nonwoven fabric sheet of only one layer was prepared by
the spun-bond method. The nonwoven fabric sheet possessed the
following specifications.
[0155] Fiber material: Polyethylene terephthalate (m/p.,
260.degree. C.)
[0156] Fiber diameter: 15 .mu.m
[0157] Weight: 50 g/m.sup.2
[0158] A cation-exchange membrane was obtained in the same manner
as in Example 1 but using the above nonwoven fabric sheet. The rate
of laminating the nonwoven fabric sheet was set to be 10 m/min.
[0159] The ion-exchange resin coating on the surface of the
nonwoven fabric sheet of the obtained cation-exchange membrane
possessed a thickness d of 2 .mu.m, and exhibited a burst strength
of 0.1 MPa, an electric resistance of 1.0 .OMEGA.cm.sup.2, an
exchange capacity of 0.53 meq/g, a rate of area change of 6%, a
rate of thickness change of 12.1% and a surface roughness of 15.0
.mu.m. The nonwoven fabric consisted of only one layer without
staple layer and, therefore, the ion-exchange resin solution has
permeated into the whole nonwoven fabric without forming surface
coating and permitting water to permeate in an amount of not less
than 20,000 ml/m.sup.2h.
[0160] When the rate of laminating the nonwoven fabric sheet was
set to be larger than the above rate, the polymer solution
permeated insufficiently and the nonwoven fabric sheet has peeled
off.
Comparative Example 2
[0161] A nonwoven fabric sheet of only one layer was prepared by
the spun-bond method in the same manner as in Comparative Example
1. The nonwoven fabric sheet possessed the following
specifications.
[0162] Fiber material: Polyethylene terephthalate (m/p.,
260.degree. C.)
[0163] Fiber diameter: 13 .mu.m
[0164] Weight: 20 g/m.sup.2
[0165] A cation-exchange membrane was obtained in the same manner
as in Example 1 but using the above nonwoven fabric sheet. The rate
of laminating the nonwoven fabric sheet was set to be 10 m/min.
[0166] The ion-exchange resin coating on the surface of the
nonwoven fabric sheet of the obtained cation-exchange membrane
possessed a thickness d of 7 .mu.m, and exhibited a burst strength
of 0.08 MPa, an electric resistance of 0.8 .OMEGA.cm.sup.2, an
exchange capacity of 0.89 meq/g, a rate of area change of 21%, a
rate of thickness change of 42.3%, a surface roughness of 20.0
.mu.m and an amount of water permeation of not less than 20, 000
ml/m.sup.2h. Due to its low strength, the nonwoven fabric exhibited
a large rate of area change and a large rate of thickness change
and, further, appeared to be curled and undulated to a large
degree.
[0167] When the rate of laminating the nonwoven fabric sheet was
set to be larger than the above rate, the polymer solution
permeated insufficiently and the nonwoven fabric sheet has peeled
off.
Comparative Example 3
[0168] A cation-exchange membrane was obtained in the same manner
as in Example 1 but directly coating the nonwoven fabric with the
polymer solution. The method of directly coating the nonwoven
fabric was regarded as the method B. The rate of coating was set to
be 10.0 m/min.
[0169] The ion-exchange resin coating on the surface of the
nonwoven fabric sheet of the obtained cation-exchange membrane
possessed a thickness d of 10 .mu.m, and exhibited a burst strength
of 0.6 MPa, an electric resistance of 8.2 .OMEGA.cm.sup.2, an
exchange capacity of 0.44 meq/g, a rate of area change of 0.8%, a
rate of thickness change of 3.0%, a surface roughness of 11.2 .mu.m
and an amount of water permeation of not less than 20,000
ml/m.sup.2h. Since the nonwoven fabric was directly coated, the
ion-exchange resin permeated into the nonwoven fabric, and the
surface layer was not uniformly formed permitting the surface to
become very rough and water to permeate through much.
Comparative Example 4
[0170] A cation-exchange membrane was obtained in the same manner
as in Example 3 but changing the coating thickness to 200 .mu.m of
liquid thickness. The rate of coating was set to be 10.0 m/min.
[0171] The ion-exchange resin coating on the surface of the
nonwoven fabric sheet of the obtained cation-exchange membrane
possessed a thickness d of 25 .mu.m, and exhibited a burst strength
of 0.6 MPa, an electric resistance of 10.6 .OMEGA.cm.sup.2, an
exchange capacity of 0.67 meq/g, a rate of area change of 1.1%, a
rate of thickness change of 7.8%, a surface roughness of 9.6 .mu.m
and an amount of water permeation of 0 ml/m.sup.2h. Since the
nonwoven fabric was directly coated, the ion-exchange resin
permeated into the nonwoven fabric, and the electric resistance was
large.
Comparative Example 5
[0172] A cation-exchange membrane was obtained in the same manner
as in Example 1 but changing the viscosity of the polymer solution
(sulfonated polyphenylene oxide solution) to 100 dPas. The rate of
lamination was set to be as very low as 0.1 m/min, and the
productivity was poor.
[0173] The ion-exchange resin coating on the surface of the
nonwoven fabric sheet of the obtained cation-exchange membrane
possessed a thickness d of 28 .mu.m, and exhibited a burst strength
of 0.6 MPa, an electric resistance of 3.9 .OMEGA.cm.sup.2, an
exchange capacity of 0.53 meq/g, a rate of area change of 1.6%, a
rate of thickness change of 7.1%, a surface roughness of 0.9 .mu.m
and an amount of water permeation of 0 ml/m.sup.2h.
[0174] When the rate of laminating the nonwoven fabric sheet was
set to be larger than the above rate, the polymer solution
permeated insufficiently and the nonwoven fabric sheet has peeled
off.
Comparative Example 6
[0175] A cation-exchange membrane was obtained in the same manner
as in Example 1 but changing the viscosity of the polymer solution
(sulfonated polyphenylene oxide solution) to 0.2 dPas. The rate of
laminating the nonwoven fabric sheet was set to be as 50 m/min.
When the rate was set to be larger than the above rate, the polymer
solution permeated insufficiently and the nonwoven fabric sheet has
peeled off.
[0176] The obtained cation-exchange membrane exhibited a burst
strength of 0.6 MPa, an electric resistance of 1.5 .OMEGA.cm.sup.2,
an exchange capacity of 0.11 meq/g, a rate of area change of 0.1%,
a rate of thickness change of 0.5%, and was favorable. However,
since the viscosity of the polymer solution was low, the thickness
of the ion-exchange resin coating was irregular on the surface of
the nonwoven fabric sheet, pinholes were observed, and the amount
of water permeation was not less than 20,000 ml/m.sup.2h. Further,
since the coating was not sufficiently formed, the surface
roughness was as large as 18 .mu.m.
Comparative Example 7
[0177] A nonwoven fabric sheet having the following three-layer
structure was prepared in the same manner as in Example 1. Filament
layers on the front and back surfaces:
[0178] Fiber material: Polyethylene terephthalate (m/p.,
260.degree. C.)
[0179] Fiber diameter: 20 .mu.m
[0180] Weight: 20 g/m.sup.2
Intermediate Layer (Extra-Fine Filament Layer):
[0181] Fiber material: Polyethylene terephthalate (m/p.,
260.degree. C.)
[0182] Fiber diameter: 10 .mu.m
[0183] Weight: 25 g/m.sup.2
[0184] A cation-exchange membrane was obtained in the same manner
as in Example 1 but using the above nonwoven fabric sheet. The rate
of laminating the nonwoven fabric sheet was set to be 15 m/min.
[0185] In the thus obtained cation-exchange membrane, the staple
layer in the nonwoven fabric sheet was not working for shutting off
the permeation of the polymer solution. Therefore, there was formed
no ion-exchange resin coating having a uniform thickness on the
surface of the nonwoven fabric sheet, and pinholes were observed.
The obtained membrane exhibited a burst strength of 0.3 MPa, an
exchange capacity of 0.44 meq/g and a rate of thickness change of
2.5%. However, since the cation-exchange resin has permeated too
much into the nonwoven fabric sheet, the electric resistance was as
high as 7.6 .OMEGA.cm.sup.2. Besides, since the strength of the
nonwoven fabric sheet was small, the rate of area change was as
high as 3.0% and the coating had not been formed to a sufficient
degree permitting water to permeate in an amount of not less than
20,000 ml/m.sup.2h. The surface roughness was 5.2 .mu.m.
Comparative Example 8
[0186] A nonwoven fabric sheet having the following three-layer
structure was prepared in the same manner as in Example 1. Filament
layers on the front and back surfaces:
[0187] Fiber material: Polyethylene terephthalate (m/p.,
260.degree. C.)
[0188] Fiber diameter: 6 .mu.m
[0189] Weight: 6 g/m.sup.2
Intermediate Layer (Staple Layer):
[0190] Fiber material: Polyethylene terephthalate (m/p.,
260.degree. C.)
[0191] Fiber diameter: 2 .mu.m
[0192] Weight: 10 g/m.sup.2
[0193] It was attempted to produce a cation-exchange membrane in
the same manner as in Example 1 but using the above nonwoven fabric
sheet. However, the nonwoven fabric sheet and the ion-exchange
resin coating could not be joined together, the resin layer has
peeled off, and the ion-exchange membrane could not be
obtained.
[0194] Table 1 shows the conditions of experiments in the above
Examples and Comparative Examples, and Table 2 shows the results of
experiments.
[0195] In Table 2, the rate of laminating the nonwoven fabric sheet
was shown as productivity.
TABLE-US-00001 TABLE 1 Viscosity of Exchange polymer Thickness of
Kind of Coating capacity solution cast liquid Example resin method
meq/g dPa s .mu.m 1 *1 A 1.6 11 100 2 *1 A 1.6 50 50 3 *1 A 1.6 75
50 4 *1 A 1.6 32 50 5 *1 A 1.6 5 100 6 *1 A 1.6 11 100 7 *2 A 1.3
14 100 8 *3 A 2 1.2 100 9 *2 A 1.3 14 100 Comp. Ex. 1 *1 A 1.6 11
100 Comp. Ex. 2 *1 A 1.6 11 100 Comp. Ex. 3 *1 B 1.6 11 100 Comp.
Ex. 4 *1 B 1.6 11 200 Comp. Ex. 5 *1 A 1.6 100 200 Comp. Ex. 6 *1 A
1.6 0.2 100 Comp. Ex. 7 *1 A 1.6 11 100 Comp. Ex. 8 *1 A 1.6 11 100
Coating method A: A cast layer is formed on a PET film and is
overlapped on the nonwoven fabric. B: The nonwoven fabric is
directly coated. *1: sulfonated polyphenylene oxide, *2: aminated
polysulfone, *3: aminated polystyrene Nonwoven base sheet Front
filament Intermediate layer layer Back filament layer *3 *4 *3 *4
*3 *4 Example .mu.m g/m.sup.2 .mu.m g/m.sup.2 .mu.m g/m.sup.2 1 12
31 1.7 8 13 31 2 12 31 1.7 8 13 31 3 12 31 1.7 8 13 31 4 12 31 1.7
8 13 31 5 12 31 1.7 8 13 31 6 12 12 5.0 15 12 12 7 12 31 1.7 8 13
31 8 12 31 1.7 8 13 31 9 20 20 1.0 10 20 20 Comp. Ex. 1 15 50 -- --
-- -- Comp. Ex. 2 13 20 -- -- -- -- Comp. Ex. 3 12 31 1.7 8 13 31
Comp. Ex. 4 12 31 1.7 8 13 31 Comp. Ex. 5 12 31 1.7 8 13 31 Comp.
Ex. 6 12 31 1.7 8 13 31 Comp. Ex. 7 20 20 10.0 25 20 20 Comp. Ex. 8
6 6 2.0 10 6 6 *3: Fiber diameter, *4: Weight
TABLE-US-00002 TABLE 2 Properties of ion-exchange membrane
Productivity *1 *2 *3 *4 *5 *6 *7 *8 Example m/min Mpa
.OMEGA.cm.sup.2 meq/g .mu.m % % .mu.m ml/m.sup.2h 1 10 0.6 2.4 0.44
18 0.8 5.0 1.1 0 2 5 0.6 2.2 0.28 11 0.4 3.2 1.5 0 3 2.5 0.6 2.1
0.30 13 0.6 3.8 1.2 0 4 7 0.6 2.3 0.26 8 0.2 2.4 1.6 0 5 20 0.6 3.2
0.36 13 0.6 3.9 1.2 0 6 10 0.4 1.8 0.42 21 0.8 7.8 1.0 0 7 8 0.6
2.5 0.16 7 0.2 1.4 1.6 0 8 40 0.6 1.8 0.25 5 0.1 1.6 1.7 0 9 8 0.7
3.2 0.22 3 0.1 0.6 1.9 0 Comp. Ex. 1 10 0.1 1.0 0.53 2 6.0 12.1
15.0 >20000 Comp. Ex. 2 10 0.08 0.8 0.89 7 21.0 42.3 20.0
>20000 Comp. Ex. 3 10 0.6 8.2 0.44 10 0.8 3.0 11.2 >20000
Comp. Ex. 4 10 0.6 10.6 0.67 25 1.1 7.8 9.6 0 Comp. Ex. 5 0.1 0.6
3.9 0.53 28 1.6 7.1 0.9 0 Comp. Ex. 6 50 0.6 1.5 0.11 -- 0.1 0.5
18.0 >20000 Comp. Ex. 7 15 0.3 7.6 0.44 -- 3.0 2.5 5.2 >20000
Comp. Ex. 8 -- -- -- -- -- -- -- -- -- *1: Bursting strength, *2:
Electric resistance, *3: Exchange capacity, *4: Surface layer
thickness d, *5: Area change, *6: Thickness change, *7: Surface
roughness, *8: Water permeation
DESCRIPTION OF REFERENCE NUMERALS
[0196] 1: Nonwoven fabric sheet [0197] 3: Ion-exchange resin
coating [0198] 5: Long filament layers [0199] 7: Extra-fine
filament layer
* * * * *