U.S. patent application number 12/239037 was filed with the patent office on 2009-12-31 for composite membrane and moisture adjustment module using same.
Invention is credited to Thomas Berta, Wiliam B. Johnson, Mahesh Murthy, Keiichi Yamakawa.
Application Number | 20090324929 12/239037 |
Document ID | / |
Family ID | 41447822 |
Filed Date | 2009-12-31 |
United States Patent
Application |
20090324929 |
Kind Code |
A1 |
Yamakawa; Keiichi ; et
al. |
December 31, 2009 |
Composite Membrane and Moisture Adjustment Module Using Same
Abstract
A composite membrane and moisture adjustment module using the
same is disclosed. The composite membrane includes a
moisture-permeable resin layer interposed between porous membranes
that constitute a pair; and the mean thickness of the
moisture-permeable resin layer is 5 .mu.m or less.
Inventors: |
Yamakawa; Keiichi; (Tokyo,
JP) ; Johnson; Wiliam B.; (Newark, DE) ;
Murthy; Mahesh; (Newark, DE) ; Berta; Thomas;
(Wilmington, DE) |
Correspondence
Address: |
GORE ENTERPRISE HOLDINGS, INC.
551 PAPER MILL ROAD, P. O. BOX 9206
NEWARK
DE
19714-9206
US
|
Family ID: |
41447822 |
Appl. No.: |
12/239037 |
Filed: |
September 26, 2008 |
Current U.S.
Class: |
428/315.9 ;
156/229; 156/60; 428/319.3 |
Current CPC
Class: |
B01D 69/10 20130101;
H01M 8/1081 20130101; B01D 67/0013 20130101; B01D 71/38 20130101;
B01D 2325/42 20130101; Y10T 428/249991 20150401; H01M 8/1023
20130101; B01D 2325/04 20130101; B01D 2325/36 20130101; B01D
2325/38 20130101; H01M 8/1018 20130101; H01M 8/04149 20130101; B01D
2325/02 20130101; B01D 71/32 20130101; Y02P 70/50 20151101; Y10T
156/10 20150115; B01D 2313/14 20130101; H01M 8/1053 20130101; H01M
2300/0082 20130101; B01D 2319/06 20130101; Y02E 60/50 20130101;
B01D 2323/08 20130101; H01M 8/1067 20130101; H01M 2008/1095
20130101; Y10T 428/24998 20150401; B01D 2323/30 20130101; H01M
8/1062 20130101; B01D 2325/20 20130101; H01M 8/1039 20130101; B01D
69/12 20130101; H01M 8/106 20130101; B01D 63/082 20130101 |
Class at
Publication: |
428/315.9 ;
428/319.3; 156/229; 156/60 |
International
Class: |
B32B 5/18 20060101
B32B005/18; B32B 38/00 20060101 B32B038/00; B32B 37/02 20060101
B32B037/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 25, 2008 |
JP |
JP2008-166389 |
Claims
1. A composite membrane wherein: a moisture-permeable resin layer
is interposed between porous membranes that constitute a pair; and
the mean thickness of the moisture-permeable resin layer is 5 .mu.m
or less.
2. The composite membrane according to claim 1, wherein said
moisture-permeable resin comprises a water-resistant,
moisture-permeable resin.
3. The composite membrane according to claim 2, wherein the degree
of swelling of said water-resistant, moisture-permeable resin, is
20 times or less.
4. The composite membrane according to claim 2 wherein said
water-resistant, moisture-permeable resin comprises a crosslinked
polyvinyl alcohol.
5. The composite membrane according to claim 2, wherein said
water-resistant, moisture-permeable resin comprises an ion-exchange
fluororesin.
6. The composite membrane according to claim 5, wherein said
water-resistant, moisture-permeable resin comprises a
perfluorosulfonic acid polymer.
7. The composite membrane according to claim 3 wherein said
water-resistant, moisture-permeable resin comprises a crosslinked
polyvinyl alcohol.
8. The composite membrane according to claim 1 wherein at least
part of said moisture-permeable resin is embedded in the porous
membrane.
9. The composite membrane according claim 4 wherein at least part
of said moisture-permeable resin is embedded in the porous
membrane.
10. The composite membrane according claim 6 wherein at least part
of said moisture-permeable resin is embedded in the porous
membrane.
11. The composite membrane according claims 1 wherein: the mean
pore diameter of the said porous membranes is 0.05 .mu.m or
greater; and the maximum pore diameter is 15 .mu.m or less.
12. The composite membrane according claims 4 wherein: the mean
pore diameter of said porous membranes is 0.05 .mu.m or greater;
and the maximum pore diameter is 15 .mu.m or less.
13. The composite membrane according claims 6 wherein: the mean
pore diameter of said porous membranes is 0.05 .mu.m or greater;
and the maximum pore diameter is 15 .mu.m or less.
14. The composite membrane according to claim 1 wherein the void
content of the said porous membranes is 40% or greater.
15. The composite membrane according to claim 4 wherein the void
content of the said porous membranes is 40% or greater.
16. The composite membrane according to claim 6 wherein the void
content of the said porous membranes is 40% or greater.
17. The composite membrane according to claim 1 wherein the mean
thickness of said porous membranes is 1 to 200 .mu.m.
18. The composite membrane according to claim 4 wherein the mean
thickness of said porous membranes is 1 to 200 .mu.m.
19. The composite membrane according to claim 6 wherein the mean
thickness of said porous membranes is 1 to 200 .mu.m.
20. The composite membrane according to any of claims 1 wherein at
least one of said porous membranes comprises a expanded
polytetrafluoroethylene membrane.
21. The composite membrane according to any of claims 4 wherein at
least one of said porous membranes comprises a expanded
polytetrafluoroethylene membrane.
22. The composite membrane according to any of claims 6 wherein at
least one of said porous membranes comprises a expanded
polytetrafluoroethylene membrane.
23. The composite membrane according to claims 1 wherein a
gas-permeable reinforcing element is layered on at least one of the
porous membranes.
24. The composite membrane according to claims 4 wherein a
gas-permeable reinforcing element is layered on at least one of the
porous membranes.
25. The composite membrane according to claims 6 wherein a
gas-permeable reinforcing element is layered on at least one of the
porous membranes.
26. A moisture adjustment module, obtained by superposing the
composite membrane of claims 1 while open spaces are left
therebetween.
27. A moisture adjustment module, obtained by superposing the
composite membrane of claims 4 while open spaces are left
therebetween.
28. A moisture adjustment module, obtained by superposing the
composite membrane of claim 6 while open spaces are left
therebetween.
29. A composite membrane wherein an air-impermeable layer
comprising a perfluorosulfonic acid polymer is interposed between a
first and second micro-porous membrane.
30. A composite membrane of claim 29 wherein at least one of said
first and second micro-porous membranes is hydrophobic.
31. A composite membrane of claim 29 wherein at least one of said
first and second micro-porous membranes is hydrophilic.
32. A composite membrane of claim 29 wherein said perfluorosulfonic
acid polymer further comprises a reinforcement.
33. A composite membrane of claim 29 wherein said air impermeable
layer has a mean thickness less than 20 um.
34. The composite membrane according to claim 29 wherein at least
part of said impermeable layer is embedded in the micro-porous
membrane.
35. The composite membrane according to claim 29 wherein at least
one of said first and second micro-porous layers comprises expanded
polytetrafluoroethylene.
36. A composite membrane of claim 32 wherein said reinforcement
comprises particulates.
37. A composite membrane of claim 32 wherein said reinforcement
comprises a third micro-porous membrane.
38. A composite membrane of claim 37 wherein said third
micro-porous membrane comprises expanded
polytetrafluoroethylene.
39. A composite membrane of claim 29 wherein at least one of said
first and second micro-porous membranes has a reinforcing member
attached to it.
40. A moisture-permselective membrane of claim 39 wherein said
reinforcing member is a non-woven material.
41. A moisture-permselective membrane of claim 39 wherein said
reinforcing member is a woven material.
42. A moisture adjustment module, obtained by superposing the
composite membrane of claims 29 while open spaces are left
therebetween.
43. A moisture adjustment module, obtained by superposing the
composite membrane of claims 32 while open spaces are left
therebetween.
44. A method of preparing a composite membrane comprising the steps
of a. Casting a solution comprising a moisture permselective resin
on a first micro-porous membrane to form a film on the surface of
said micro-porous membrane; b. Stretching a second micro-porous
membrane over said film before it is dry to form a composite
structure; c. Drying said composite structure to remove residual
liquid from said solution.
45. A method of claim 44 wherein said film is between 0.5 and 10 um
thick after step c.
46. A method of claim 44 wherein an additional step of
heat-treating said composite membrane after step (c) is
performed.
47. The method of claim 44 wherein a reinforcing member is
laminated to at least one side of said composite membrane after
step c.
48. A method of claim 46 wherein said heat treatment comprises
holding said composite membrane at a temperature between 100 and
180 C for a period of time between 1 and 15 minutes.
49. A method of preparing a composite membrane comprising the steps
of: a. Preparing a membrane having two sides, said membrane
comprising a moisture permselective resin; b. Laminating one side
of said membrane to a first micro-porous membrane; c. Laminating a
second micro-porous membrane to the second side of said
membrane.
50. The method of claim 49 wherein at least one of the first
micro-porous membrane and the second micro-porous membrane comprise
expanded polytetrafluoroethylene.
51. The method of claim 49 wherein said membrane comprising
moisture permselective resin further comprises expanded
polytetrafluoroethylene.
52. The method of claim 49 wherein said membrane comprising
moisture permselective resin comprises a perfluorosulfonic acid
polymer.
53. The method of claim 49 wherein a reinforcing member is
laminated to at least one side of said composite membrane after
step c.
54. The method of claim 49 wherein said membrane comprising
moisture permselective resin in step (a) has a mean thickness of
less than 15 .mu.m.
55. The method of claim 49 wherein said membrane comprising
moisture permselective resin in step (a) has a mean thickness of
less than 6 .mu.m.
56. A composite membrane wherein an air-impermeable layer
comprising an ionomeric polymer is interposed between a first and
second micro-porous membrane.
57. A composite membrane of claim 56 wherein at least one of said
first and second micro-porous membranes is hydrophobic.
58. A composite membrane of claim 56 wherein at least one of said
first and second micro-porous membranes is hydrophilic.
59. A composite membrane of claim 56 wherein said perfluorosulfonic
acid polymer further comprises a reinforcement.
60. A composite membrane of claim 56 wherein said air impermeable
layer has a mean thickness less than 20 um.
61. The composite membrane according to claim 56 wherein at least
part of said impermeable layer is embedded in the micro-porous
membrane.
62. The composite membrane according to claim 56 wherein at least
one of said first and second micro-porous layers comprises expanded
polytetrafluoroethylene.
63. A composite membrane of claim 59 wherein said reinforcement
comprises particulates.
64. A composite membrane of claim 59 wherein said reinforcement
comprises a third micro-porous membrane.
65. A composite membrane of claim 64 wherein said third
micro-porous membrane comprises expanded
polytetrafluoroethylene.
66. A composite membrane of claim 56 wherein at least one of said
first and second micro-porous membranes has a reinforcing member
attached to it.
67. A moisture-permselective membrane of claim 66 wherein said
reinforcing member is a non-woven material.
68. A moisture-permselective membrane of claim 66 wherein said
reinforcing member is a woven material.
69. A moisture adjustment module, obtained by superposing the
composite membrane of claims 56 while open spaces are left
therebetween.
70. A moisture adjustment module, obtained by superposing the
composite membrane of claims 59 while open spaces are left
therebetween.
Description
BACKGROUND OF THE INVENTION
[0001] Conventionally, an olefin-based hollow filament or a hollow
filament obtained using an ion-exchange fluororesin is used to
humidify the gas fed to a fuel electrode or an air electrode of a
fuel cell. However, hollow filaments have high ventilation
resistance and make it difficult to raise the flow rate. Therefore,
a membrane-type moistening module using a vapor-permeable membrane
shows promise.
[0002] A composite membrane 10 having a moisture-permeable resin
layer 30 on both surfaces of a porous polymeric resin article 20 is
disclosed, for example, in Patent Document 1 as a vapor-permeable
membrane, as shown in FIG. 1. However, in many cases, the composite
membrane 10 cannot exhibit sufficient moisture permeability with
one membrane. Therefore, as shown in FIG. 2, a plurality of
composite membranes 10 is superposed while open spaces are left
that can serve as gas channels. Also, spacers 50 are inserted
between the composite membranes 10 in order to form the open
spaces. When the moisture-permeable resin layers 30 are exposed on
the surface of the composite membranes 10, the moisture-permeable
resin layers 30 are damaged by the spacers 50. Furthermore, when
exposed to hot water over a long period of time, the
moisture-permeable resin layers 30 have inadequate durability. The
adhesive strength between the composite membranes 10 and the
spacers 50 is also low.
[0003] Patent Document 2 discloses a composite membrane 10 in
which, in a layered object composed of a porous membrane 20 and a
reinforcing element (nonwoven fabric or the like) 40, a
moisture-permeable resin layer 30 is interposed between the
reinforcing element 40 and the porous membrane 20 along the border
that faces the membrane, as shown in FIG. 3. The risk that the
moisture-permeable resin layer 30 will be damaged by the spacer 50
decreases since the moisture-permeable resin layer 30 is protected
with the reinforcing element 40 and the porous membrane 20. Patent
Document 3 will be described below.
[Patent Document 1] Japanese Laid-Open Patent Publication No.
2006-160966.
[Patent Document 2] Japanese Laid-Open Patent Publication No.
2006-150323.
[0004] [Patent Document 3] U.S. Pat. No. 5,418,054.
[0005] However, according to a study conducted by the inventors,
bringing both the gas barrier properties and moisture permeability
to a higher level was difficult to achieve in the composite
membrane (vapor-permeable membrane) 10 disclosed in Patent Document
2. For example, in the composite membrane 10 disclosed in Patent
Document 2, the moisture permeability deteriorates when the gas
barrier properties are raised, and the gas barrier properties
deteriorate when the moisture permeability is raised.
[0006] The present invention relates to a composite membrane
capable of selectively transmitting water included in gas and
liquid; preferably relates to a composite membrane that can be used
as a dehumidification membrane, moistening membrane, pervaporation
membrane (for example, a membrane for separating water and other
liquids (such ethanol and other alcohols)); and more preferably
relates to a composite membrane that can be used as a separation
membrane to selectively transmit water vapor from a hot and humid
gas (for example, a moistening membrane for using the water vapor
included in the effluent gas (especially effluent gas on the side
of an air electrode) of a fuel cell electrode in the humidification
of the gas fed to a fuel electrode or the air electrode (especially
the fuel electrode)).
[0007] However, according to a study conducted by the inventors,
bringing both the gas barrier properties and moisture permeability
to a higher level was difficult to achieve in the composite
membrane (vapor-permeable membrane) 10 disclosed in Patent Document
2. For example, in the composite membrane 10 disclosed in Patent
Document 2, the moisture permeability deteriorates when the gas
barrier properties are raised, and the gas barrier properties
deteriorate when the moisture permeability is raised.
[0008] The present invention was developed with a focus on
circumstances such as those described above, and an object thereof
is to provide a composite membrane 10 in which the balance between
the gas barrier properties and moisture permeability is further
improved; and to provide a moisture adjustment module using the
composite membrane 10.
[0009] Another object of the present invention is to provide a
composite membrane 10 further having excellent scratch resistance
when brought into contact with a spacer or another external object
50; and to provide a moisture adjustment module using the composite
membrane.
[0010] Yet another object of the present invention is to provide a
composite membrane 10 further having excellent adhesive properties
in relation to an external object (spacer) 50; and to provide a
moisture adjustment module using the composite membrane.
[0011] Yet another object of the present invention is to provide a
less expensive composite membrane 10 that provides very high
moisture vapor transport rates, very low air permeability and
excellent long-term durability while simultaneously utilizing
reduced quantities of a relatively expensive fluoropolymer resin;
and a moisture adjustment module using the composite membrane.
[0012] The present invention was developed with a focus on
circumstances such as those described above, and an object thereof
is to provide a composite membrane 10 in which the balance between
the gas barrier properties and moisture permeability is further
improved; and to provide a moisture adjustment module using the
composite membrane 10.
[0013] Another object of the present invention is to provide a
composite membrane 10 further having excellent scratch resistance
when brought into contact with a spacer or another external object
50; and to provide a moisture adjustment module using the composite
membrane.
[0014] Yet another object of the present invention is to provide a
composite membrane 10 further having excellent adhesive properties
in relation to an external object (spacer) 50; and to provide a
moisture adjustment module using the composite membrane.
[0015] Yet another object of the present invention is to provide a
less expensive composite membrane 10 that provides very high
moisture vapor transport rates, very low air permeability and
excellent long-term durability while simultaneously utilizing
reduced quantities of a relatively expensive fluoropolymer resin;
and a moisture adjustment module using the composite membrane.
SUMMARY OF THE INVENTION
[0016] First embodiments of the invention include a composite
membrane wherein a moisture-permeable resin layer is interposed
between porous membranes that constitute a pair; and the mean
thickness of the moisture-permeable resin layer is 5 .mu.m or less.
The moisture permeable resin can comprise a water-resistance,
moisture permeable resin such that its degree of swelling is 20
times or less. It may also comprise a cross-linked polyvinyl
alcohol, or an ion exchange fluororesin, or a perfluorosulfonic
acid polymer. Additionally, the moisture-permeable resin layer may,
at least in part, be embedded in one or both of the porous
membranes. The porous membranes of these embodiments may have a
mean pore diameter of 0.05 .mu.m or greater; and the maximum pore
diameter of 15 .mu.m or less. Furthermore, the void content of the
porous membranes may be 40% or greater, and their mean thickness
may be between 1 and 200 .mu.m. Additionally, the composite
membrane may have at least one of the porous membranes comprised of
an expanded polytetrafluoroethylene membrane.
[0017] More embodiments of the instant invention include a
composite membrane wherein an air-impermeable layer comprising an
ionomeric polymer is interposed between a first and second
micro-porous membrane. Further, the air-impermeable layer may
comprise a perfluorosulfonic acid polymer. In these embodiments, at
least one of the first or second micro-porous membranes may be
hydrophobic or hydrophilic. The mean thickness of the
air-impermeable layer may be less than 20 um, or less than 6 um.
Further, at least part of the impermeable layer may be embedded in
the micro-porous membrane, and at least one of the first and second
micro-porous layers may comprise expanded polytetrafluoroethylene.
Additionally, the air-impermeable layer may be reinforced, for
example with particulates, a micro-porous membrane, or with
expanded polytetrafluoroethylene.
[0018] In further embodiments, any of the composite membranes
described above may have a gas-permeable reinforcing element
layered on at least one of the porous membranes. The gas-permeable
reinforcing element may be a woven or a non-woven material
comprising a polymer, metal, or ceramic material.
[0019] In yet further embodiments, any of the composite membranes
described above may be used in a moisture adjustment module
obtained by superposing any of the composite membranes described
herein while open spaces are left therebetween.
[0020] More embodiments of the invention include methods of
preparing a composite membrane comprising the steps of (a) casting
a solution comprising a moisture permselective resin on a first
micro-porous membrane to form a film on the surface of the
micro-porous membrane; (b) stretching a second micro-porous
membrane over the film before it is dry to form a composite
structure; and (c) drying the composite structure to remove
residual liquid the solution. The method may also be performed so
that the film is between 0.5 and 10 um thick after step c.
Additionally, an additional step of heat-treating the composite
membrane after step (c) may be performed, and the heat treatment
may comprise holding the composite membrane at a temperature
between 100 and 180 C for a period of time between 1 and 15
minutes. Further embodiments of the method include laminating a
reinforcing member to at least one side of the composite membrane
after step c. The reinforcing member is gas permeable, and may
comprise a woven or non-woven material comprising metal, ceramic or
polymer.
[0021] Yet more embodiments include a method of preparing a
composite membrane comprising the steps of: (a) preparing a
membrane having two sides, the membrane comprising a moisture
permselective resin; (b) laminating one side of the membrane to a
first micro-porous membrane; and (c) laminating a second
micro-porous membrane to the second side of the membrane. As used
herein, lamination may include any combination of heat and/or
pressure required to bond two materials together. The first
micro-porous membrane and the second micro-porous membrane may
comprise expanded polytetrafluoroethylene, or the membrane
comprising the moisture permselective resin may further comprises
expanded polytetrafluoroethylene, or a perfluorosulfonic acid
polymer. Additionally, a reinforcing member may be laminated to at
least one side of the composite membrane after step c. Further, the
membrane comprising the moisture permselective resin in step (a)
may have a mean thickness of less than 15 .mu.m, or less than 6
.mu.m.
DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a schematic cross-sectional view showing an
example of a conventional composite membrane;
[0023] FIG. 2 is a schematic perspective cross-sectional view
showing an example of a moisture adjustment module;
[0024] FIG. 3 is a schematic cross-sectional view showing another
example of the conventional composite membrane;
[0025] FIG. 4 is an expanded schematic cross-sectional view of an
area of the composite membrane in FIG. 3;
[0026] FIG. 5 is a schematic cross-sectional view showing an
example of the composite membrane of the present invention.
[0027] FIG. 6 is an expanded schematic cross-sectional view of an
area of the composite membrane in FIG. 5;
[0028] FIG. 7 is a schematic cross-sectional view showing another
example of the composite membrane of the present invention; and
[0029] FIG. 8 is a schematic cross-sectional view showing another
example of the composite membrane of the present invention.
KEY
[0030] 10: composite membrane [0031] 20: porous membranes [0032]
30: moisture-permeable resin layer [0033] 30: reinforced
moisture-permeable resin layer [0034] 30: moisture-permeable resin
[0035] 30: thin porous membrane [0036] 40: gas-permeable
reinforcing element
DETAILED DESCRIPTION OF THE INVENTION
[0037] Upon repeated intense study aimed at solving the
above-described problems, the inventors of the present invention
discovered that the thickness of a moisture-permeable resin layer
30 becomes non-uniform in cases in which the moisture-permeable
resin layer 30 is formed between a reinforcing element (nonwoven
fabric) 40 and a porous membrane 20 in the manner described with
reference to Patent Document 2. FIG. 4 is a schematic
cross-sectional view showing in enlarged and schematic form areas
in which the nonwoven fabric 40 and the porous membrane 20 are
joined to each other. As shown in the drawing, the fiber 41
constituting the nonwoven fabric 40 is extremely large in
comparison with the surface unevenness (pore diameter) of the
porous membrane 20. Generally, the moisture-permeable resin layer
30 is formed by solidifying a liquid moisture-permeable resin 31.
In cases in which the reinforcing element (nonwoven fabric) 40 and
the porous membrane 20 are layered together, a liquid pool 32
containing the liquid moisture-permeable resin is formed at the
border of the fiber 41 of the nonwoven fabric and the porous
membrane 20, and the thickness of the moisture-permeable resin
layer 30 becomes non-uniform. When the thickness of the
moisture-permeable resin layer 30 becomes non-uniform, the entire
moisture-permeable resin layer 30 must be formed thickly in order
to prevent pinholes from forming in the thin regions and to secure
the desired gas barrier properties, and the moisture permeability
is adversely affected.
[0038] In contrast to this, as shown in FIG. 5, the present
inventors discovered that the moisture-permeable resin layer 30
could be formed thinly and uniformly in cases in which the
moisture-permeable resin layer 30 is formed between two porous
membranes 20 that constitute a pair. FIG. 6 is a schematic
cross-sectional view showing in enlarged and schematic form a joint
between the two porous membranes 20 that constitute a pair. As
shown in the diagram, the surface of the porous membranes 20 is
much smoother than that of the nonwoven fabric 40. Therefore,
liquid pools of the liquid moisture-permeable resin 31 do not form
easily and the moisture-permeable resin layer 30 can be formed
uniformly. If the moisture-permeable resin layer 30 can be formed
uniformly, then the moisture-permeable resin layer 30 can be formed
thinly without producing pinholes, and better moisture permeability
can be obtained without any degradation of the gas barrier
properties. Therefore, it was discovered that the balance between
the gas barrier properties and moisture permeability could be
further improved by forming the moisture-permeable resin layer 30
between the porous membranes 20 that constitute a pair, and the
present invention was perfected.
[0039] Patent Document 3 (U.S. Pat. No. 5,418,054) discloses a
flame-resistant laminate which is waterproof, has moisture
permeability, and includes a first layer of a porous expanded
polytetrafluoroethylene membrane, a second layer of a porous
expanded polytetrafluoroethylene membrane, and a
phosphorus-containing poly(urea/urethane) adhesive layer for
bonding the first and second layers together. However, this
laminate is used for protective clothing, and the
phosphorus-containing poly(urea/urethane) adhesive layer is not
very thin. Rather, when the adhesive layer is made thinner, the
adhesive strength between the layers is reduced by a reduction in
the amount in which the phosphorus-containing poly(urea/urethane)
adhesive is impregnated into the structure of the porous drawn
polytetrafluoroethylene membrane, the layers become detached easily
when washed or subjected to intense movements of the human body,
and the target function cannot be obtained. This is due to the fact
that the phosphorus-containing poly(urea/urethane) adhesive and the
porous drawn polytetrafluoroethylene membranes are bonded to each
other not by chemical bonding but by electrostatic adhesion or the
embedding of the adhesive in the porous structure (anchoring
effect). Also, the document does not mention the pore diameter of
the drawn polytetrafluoroethylene membranes. Normally, the pore
diameter of an expanded polytetrafluoroethylene membrane is small
in protective clothing. Finally, the use of a polymer that is not
cross-linked, i.e., a non-thermosetting polymer, is not disclosed.
For example, the use of a fluororesin layer, for example a layer of
perfluorosulfonic acid polymer, or any ionomeric polymer between
the ePTFE layers was not described. This is an important
distinction because the art to date has demonstrated only the use
of cross-linked polymers because it has been thought that only such
polymers could provide the durability required in applications
where high moisture transport rates were required. The composite
materials of this invention overcome that limitation by protecting
the moisture transport layer with a porous or microporous layer on
both sides the moisture transport layer. This significantly widens
the choice of moisture-permeable resin layers allowing the use of
ionomeric polymers and other non-cross linked polymers.
[0040] Accordingly, the composite membrane according to present
invention has a moisture-permeable resin layer 30 sandwiched
between two porous membranes 20 that constitute a pair, and the
mean thickness of the moisture-permeable resin layer 30 is 5 .mu.m
or less. The moisture-permeable resin is preferably a
water-resistant, moisture-permeable resin. The degree of swelling
of the water-resistant, moisture-permeable resin, as calculated
based on the change in the volume of the resin before and after the
water resistance test described below, is 20 times or less.
Degree of swelling=Volume of resin after water resistance
test/Volume of resin before water resistance test
[0041] Water resistance test: The resin is allowed to stand for 24
hours in an environment having a temperature of 120.degree. C. and
a water vapor pressure of 0.23 MPa, and is subsequently immersed
for 15 minutes in water having a temperature of 25.degree. C.
[0042] The water-resistant, moisture-permeable resin may, for
example, be a crosslinked polyvinyl alcohol, an ion-exchange
fluororesin, or an ionomeric polymer, or the like. As used herein,
an ionomer polymer is an ion-containing copolymer in which up to 15
mol % of the repeat units contain ionic groups. At least part of
the moisture-permeable resin may be embedded in the porous
membrane.
[0043] The porous membrane (expanded polytetrafluoroethylene
membrane or the like) has, for example, a mean pore diameter of
0.05 .mu.m or greater, a maximum pore diameter of 15 .mu.m or less,
a void content of 40% or greater, and a mean thickness of 1 to 200
.mu.m. A gas-permeable reinforcing element may be layered on at
least one of the porous membranes. The present invention includes a
moisture adjustment module obtained by superposing the composite
membranes while open spaces are left therebetween.
[0044] Both the moisture permeability and gas barrier properties of
the composite membrane 10 according to the present invention can be
brought to a higher level because the moisture-permeable resin
layer 30 is formed uniformly and thinly. Furthermore, the
moisture-permeable resin layer 30 is protected with a porous
membrane, and therefore has excellent surface durability when
brought into contact with an external object 50. Furthermore, since
the porous membranes 20 are exposed on the surface, the adhesive
penetrates into the porous membranes 20 and exhibits an anchoring
effect when an external object (especially a spacer) 50 or the like
is attached, and the joint strength can be increased.
[0045] When a water resistant, moisture-permeable resin is used in
the composite membrane 10 of the present invention, durability in
humid and moist conditions (resistance characteristics in a hot and
humid environment) can be improved, and moisture permeability in a
hot and humid environment is improved as well.
[0046] (i) Composite Membrane
[0047] The structure of the composite membrane of the present
invention will be described in detail below with reference to an
illustrated example.
[0048] FIG. 5 is schematic cross-sectional view showing an example
of the composite membrane 10 of the present invention. In the
composite membrane 10 of the present invention, a
moisture-permeable resin layer 30 is sandwiched between two porous
membranes 20 that constitute a pair, as shown in FIG. 5. Therefore,
the moisture-permeable resin layer 30 is protected by the porous
membranes 20 and has excellent surface durability when brought into
contact with an external object 50. Furthermore, since the porous
membranes 20 are exposed on the surface, the adhesive penetrates
into the porous membranes 20 and exhibits an anchoring effect when
an external object (especially a spacer) 50 or the like is
attached, making it possible to increase the joint strength.
Moreover, in cases in which the moisture-permeable resin layer 30
is sandwiched between the two porous membranes 20 that constitute a
pair, the moisture-permeable resin layer 30 can be made thinner
without producing pinholes, unlike in the case of Patent Document
2. Both the moisture permeability and gas barrier properties can be
brought to a higher level by reducing the thickness of the
moisture-permeable resin layer 30.
[0049] The composite membrane 10 can be produced, for example, by
coating a surface of one of the porous membranes 20 with a liquid
that includes a moisture-permeable resin and removing the solvent
from the applied liquid after the coated surface is covered with
the other porous membrane 20. The moisture-permeable resin layer 30
may be formed on that surface without being embedded in the porous
membranes 20. However, normally at least part of the
moisture-permeable resin layer 30 is embedded in the porous
membranes 20. Durability is improved when the moisture-permeable
resin layer 30 is embedded in the porous membranes 20.
[0050] In the composite membrane 10, a gas-permeable reinforcing
element 40 may be layered (bonded) to one of the porous membranes
20, as shown in FIG. 7. The composite membrane 10 can be made
stronger by the layering of the gas-permeable reinforcing element
40. The gas-permeable reinforcing element 40 may be layered on both
of the porous membranes 20.
[0051] The gas-permeable reinforcing element 40 may, for example,
be bonded to the porous membranes 20 by heat fusion or the
like.
[0052] Each of the membranes and layers is described in detail
below.
[0053] (ii) Moisture-Permeable Resin Layer 30
[0054] The mean thickness of moisture-permeable resin layer 30 is 5
.mu.m or less, preferably 3 .mu.m or less, and even more preferably
2 .mu.m or less. The balance between gas barrier properties and air
permeability can be improved by reducing the mean thickness. It is
preferable for the mean thickness to be as small as possible so
long as pinholes do not occur, and the lowest limit allowed may,
for example, be 0.1 .mu.m or greater (particularly, 0.2 .mu.m or
greater).
[0055] The mean thickness t of the moisture-permeable resin layer
30 can be calculated according to the following formula by
observing a section of the composite membrane 10 with a scanning
electron microscope to determine the surface area A of the
moisture-permeable resin layer 30 and the length L of the
moisture-permeable resin layer 30.
Mean thickness t=Surface area A/Length L
[0056] The preferred moisture-permeable resin is a water resistant,
moisture-permeable resin having high water resistance. The high
water resistance allows durability (resistance to high temperature
and humidity) to be improved during service in a hot and humid
environment. In addition, moisture permeability in a hot and humid
environment is improved as well.
[0057] The water resistance of the water
resistant-moisture-permeable resin can be evaluated based on the
degree of swelling determined using the water resistance test
described below. The degree of swelling of the water resistant
moisture-permeable resin is, for example, 20 times or less,
preferably 15 times or less, and even more preferably ten times or
less. The lower limit of the degree of swelling is not particularly
limited and may be two times or greater (particularly five times or
greater).
[0058] Water resistance test: The resin is allowed to stand for 24
hours in an environment having a temperature of 120.degree. C. and
a water vapor pressure of 0.23 MPa, and is subsequently immersed
for 15 minutes in water having a temperature of 25.degree. C. The
change in the volume of the resin is measured before and after the
test, and the degree of swelling is calculated based on the
following formula.
Degree of swelling=Volume of resin after water resistance
test/Volume of resin before water resistance test
[0059] Specific examples of the moisture-permeable resin include
resins (protic hydrophilic resins) having hydrophilic protic groups
in the repeating units thereof, such as polystyrene sulfonic acid,
polyvinyl alcohol, vinyl alcohol copolymers (ethylene/vinyl alcohol
copolymers, tetrafluoroethylene/vinyl alcohol copolymers),
ion-exchange fluororesins ("Nafion (registered trademark)"
manufactured by DuPont, "Flemion (registered trademark)"
manufactured by Asahi Glass Co., Inc., and the like), divinyl
benzene/sulphonic acid copolymers, divinyl benzene/carboxylic acid
copolymers, and other an ion-exchange resins; and resins (aprotic
hydrophilic resins) having aprotic hydrophilic groups in the
repeating units thereof, such as polyethylene oxide, polyvinyl
pyridine, polyvinyl ether, polyvinyl pyrrolidone, and
pyrrolidone.
[0060] Furthermore, the moisture-permeable resin may be formed as a
three dimensional crosslinked structure. Examples of a
three-dimensional crosslinked moisture-permeable resin include
crosslinked protonic hydrophilic resin, crosslinked aprotic
hydrophilic resins, silicone resins, and the like. A
three-dimensional crosslinked moisture-permeable resin has
excellent water resistance.
[0061] The moisture-permeable resin (including the
three-dimensional crosslinked moisture-permeable resin) can be used
individually or as a combination of two or more resins. A preferred
moisture-permeable resin is a crosslinked polyvinyl alcohol (for
example, a crosslinked structure based on a mixture of HCl and
glutaraldehyde, a crosslinked structure based on formaldehyde, a
crosslinked structure based on a blocked isocyanate, or the like)
or an ion-exchange fluororesin. A crosslinked polyvinyl alcohol not
only has excellent water resistance, but can also be applied
readily and can easily produce a thinner moisture-permeable resin
layer 30. Since an ion-exchange fluororesin has excellent heat
resistance and chemical resistance, durability is high in a hot and
humid environment or a system in which an acid, alkali, or the like
is present, and the resin is suitable for use in a severe
environment.
[0062] The moisture-permeable resin layer 30 may also include a
humectant. A humectant-containing moisture-permeable resin layer 30
can retain more moisture, and the moisture permeability can be
further increased. A water-soluble salt can be used as the
humectant. Specifically, a lithium salt, phosphate, or the like can
be used.
[0063] The moisture-permeable resin layer 30 may be reinforced with
a thin porous membrane as long as a predetermined mean thickness
can be maintained. An example of a composite membrane provided with
such a moisture-permeable resin layer is shown in FIG. 8. FIG. 8(a)
is a schematic cross-sectional view of a moisture-permeable resin
layer 35 reinforced with a thin porous membrane 37, and FIG. 8(b)
is a schematic cross-sectional view of a composite membrane 10
provided with the moisture-permeable resin layer 35. The composite
membrane 10 in FIG. 8 can be produced by impregnating the entire
thin porous membranes 37 with a liquid that includes the
moisture-permeable resin 36, then covering both sides of the thin
porous membrane 37 with the porous membranes 20, and subsequently
removing the solvent.
[0064] A membrane similar to the below-described porous membranes
20 can be used as the thin porous membranes 37 within a range in
which the mean thickness of the moisture-permeable resin layer 35
can be maintained.
[0065] (iii) Porous Membranes 20
[0066] As mentioned above, in the present invention, the
moisture-permeable resin layer 30 is made uniformly thinner by
being sandwiched between two porous membranes 20 that constitute a
pair. The surface unevenness (pore diameter) of the porous
membranes 20 is much smaller in comparison with the fiber diameter
of a nonwoven fabric, preventing the liquid moisture-permeable
resin from pooling. Therefore a moisture-permeable resin layer can
be formed uniformly and thinly.
[0067] The maximum pore diameter of the porous membranes 20 is, for
example, 15 .mu.m or less, preferably 5 .mu.m or less, and more
preferably 0.5 .mu.m or less. Making the moisture-permeable resin
layer uniform becomes easier with reduced maximum pore
diameter.
[0068] The maximum pore diameter value can be determined using the
following formula by calculating the bubble point in accordance
with the bubble point method (JIS K3832) using isopropanol.
d=4.gamma..sub.IPA cos .theta..sub.1/P.sub.B
(In the formula, d is the maximum pore diameter, .gamma..sub.IPA is
the surface tension of isopropanol, .theta..sub.1 is the angle of
contact of the porous membranes 20 and isopropanol (cos
.theta..sub.1=1 when the porous membranes 20 are wetted with IPA),
and P.sub.B is the bubble point value.)
[0069] Moisture permeability deteriorates when the pore diameter of
the porous membranes 20 becomes too small. Therefore, the mean pore
diameter of the porous membranes 20 is, for example, 0.05 .mu.m or
greater, preferably 0.1 .mu.m or greater, and more preferably 0.2
.mu.m or greater.
[0070] The mean pore diameter is a value determined based on the
pore distribution (capacity distribution with respect to the pore
diameter). In other words, the pore distribution is measured on the
assumption that all the pores of the porous membranes 20 have a
cylindrical shape, and the pore diameter corresponding to an
intermediate value of the pore capacity is determined as the mean
pore diameter. In the present invention, the mean pore diameter was
determined using a Coulter Porometer manufactured by Coulter
Electronics, Ltd.
[0071] The void content of the porous membranes 20 can be suitably
set in accordance with the pore diameter. The void content is, for
example, 40% or greater (preferably 50% or greater). The void
content is also, for example, about 98% or less (preferably 90% or
less).
[0072] The void content of the porous membranes 20 can be
calculated based on the following formula using the bulk density D
(D=W/V, where the unit of measurement is g/cm.sup.3) and the
density D.sub.standard(2.2 g/cm.sup.3 for a PTFE resin) of a
membrane devoid of any cavities. The densities are determined by
calculating the mass W of the porous membranes 20 and the apparent
volume V that includes cavities. The thickness during calculation
of volume V depends on the mean thickness measured with a dial
thickness gauge (measured using "SM-1201" manufactured by Teclock
Corporation when the only load applied is the main body spring
load).
Void content of the porous membrane
(%)=[1-(D/D.sub.standard)].times.100
[0073] The thickness of porous membranes 20 is not particularly
limited and is, for example, 200 .mu.m or less, preferably 50 .mu.m
or less, and more preferably 40 .mu.m or less. The moisture
transmission rate of the composite membrane 10 deteriorates when
the porous membranes 20 are too thick. Furthermore, the heat
exchange capacity and separation efficiency decrease when the
composite membranes 10 are used as heat exchange membranes or
pervaporation membranes. However, ease of processing is adversely
affected when the porous membranes 20 are too thin. Therefore, it
is recommended that the thickness of the porous membranes 20 be,
for example, 1 .mu.m or greater, preferably 3 .mu.m or greater, and
more preferably 5 .mu.m or greater.
[0074] Various materials can be used for the porous membranes 20.
Examples include polyolefins such as polyethylene, polypropylene,
and the like; polycarbonate; polystyrene; polyvinyl chloride;
polyvinylidene chloride; polyester; and fluororesins such as
polytetrafluoroethylene, tetrafluoroethylene/hexafluoropropylene
copolymers, polyvinyl fluoride, polyvinylidene fluoride, and the
like.
[0075] The preferred porous membranes 20 are fluororesin porous
membranes. Fluororesins have excellent heat resistance and
corrosion resistance. Particularly preferred porous membranes 20
are porous membranes made of expanded polytetrafluoroethylene
(PTFE) (hereinafter occasionally referred to as "ePTFE membrane" or
"drawn porous PTFE membrane"). Extremely fine pores can be formed
in an ePTFE membrane, and the surface smoothness can be increased.
Therefore, the moisture-permeable resin layer 30 can easily be
formed uniformly and thinly.
[0076] An ePTFE membrane can be obtained by a method in which a
paste obtained by mixing a PTFE fine powder with a molding
auxiliary is molded, the molding auxiliary is removed from the
resulting molded article, the article is drawn at a high
temperature and high speed, and the drawn article is baked as
needed. Any process and product known in the art to prepare ePTFE
membranes may be used, for example, materials and processes such as
those described in U.S. patent Nos. U.S. Pat. No. 3,953,566, U.S.
Pat. No. 4,902,423, U.S. Pat. No. 4,985,296, U.S. Pat. No.
5,476,589, U.S. Pat. No. 5,814,405, or U.S. Pat. No. 7,306,729. The
materials disclosed in Japanese Examined Patent Publication No.
S51-18991 are also exemplary. The drawing may be uniaxial or
biaxial. A uniaxially drawn porous PTFE is microscopically
characterized in that thin island-shaped nodes (folding crystals)
are present approximately orthogonal to the drawing direction, and
accordion-shaped fibrils (bundles of linear molecules in which the
folding crystals are melted and extracted by drawing) linking these
nodes are oriented in the drawing direction. On the other hand, a
biaxially drawn porous PTFE is microscopically characterized by
having a cobweb-shaped fiber structure wherein the fibrils spread
radially, and the nodes linking the fibrils are scattered in an
island shape to form numerous spaces partitioned into fibrils and
nodes. A biaxially drawn porous PTFE can be made wider more easily
than a uniaxially drawn porous PTFE, has a better balance of
physical properties in the longitudinal and transverse directions,
and costs less to produce per unit surface area. A biaxially drawn
PTFE is therefore particularly preferred.
[0077] (iv) Gas-Permeable Reinforcing Element 40
[0078] The gas-permeable reinforcing element 40 is usually formed
from a fibrous resin. A reinforcing element 40 having both strength
and air permeability can be produced in a simple manner by using a
fibrous resin. The gas-permeable reinforcing element 40 formed by a
fibrous resin may be any of a woven fabric, a knitted fabric, a
nonwoven fabric (nonwoven fabric formed by a manufacturing method
such as, for example, the thermal bond method or the spun-bond
method), or a net. A particularly preferred gas-permeable
reinforcing element 40 is a nonwoven fabric.
[0079] (v) Use
[0080] The composite membrane 10 of the present invention has
excellent gas barrier properties and high moisture permeability.
The membrane can therefore be appropriately used as a separation
membrane to selectively transmit water contained in a gas or liquid
(a separation membrane for a moisture adjustment module). Examples
of such applications include a dehumidification membrane, a
moistening membrane, a pervaporation membrane (for example, a
membrane for separating water and other liquids (ethanol or another
alcohol or the like)), and the like.
[0081] In the moisture adjustment module, channels are controlled
so that a water-supplying fluid (including a dehydrated fluid) is
fed to one surface of the composite membrane 10, a water-receiving
fluid (including a dehydrating fluid) is fed to the other surface
of the composite membrane 10, and the water-supplying fluid and
water-receiving fluid do not mix with each other. The preferred
moisture adjustment module is a module composed of stacked flat
membranes, and the water-supplying fluid and water-receiving fluid
flow as countercurrents.
[0082] The air permeability of the composite membrane 10 is, for
example, 5,000 seconds or greater, preferably 8,000 seconds or
greater, and more preferably 99,999 seconds or greater using a
standard Gurley test. Composite membranes are considered air
impermeable within this application if they have a Gurley greater
than 5000 s. Furthermore, the moisture permeability of the
composite membrane 10 (JIS L1099, Method A-1) can, for example, be
40 g/m.sup.2/h or greater, preferably 50 g/m.sup.2/h or greater,
and more preferably 60 g/m.sup.2/h or greater. In addition, the
upper limit of moisture permeability is not particularly limited
and may, for example, be 150 g/m.sup.2/h or less (particularly 100
g/m.sup.2/h or less).
[0083] Such composite membranes 10 are superposed with each other
in the moisture adjustment module, and these superposed composite
membranes 10 are spaced apart at predetermined intervals by spacers
50 or the like (for example, cf. FIG. 2). Forming gaps on both
sides of the composite membranes allows the gaps to be used as
fluid channels, and moisture to be adjusted by exchanging moisture
between the fluids on both sides.
[0084] Furthermore, the gas barrier properties and moisture
permeability of the composite membrane 10 of the present invention
can be improved even under conditions of high temperature and high
humidity by using a water-resistant moisture-permeable resin as the
moisture-permeable resin. Therefore, the composite membrane can
also be used as a separation membrane for selectively transmitting
water vapor from a hot and humid gas (for example, as a moistening
membrane for using the water vapor included in the effluent gas
(especially effluent gas on the side of an air electrode) of a fuel
cell electrode in the humidification of the gas fed to a fuel
electrode or the air electrode (especially the fuel
electrode)).
[0085] The following are, for example, the gas barrier properties
and moisture permeability of a composite membrane 10 provided with
improved characteristics under conditions of high temperature and
high humidity. In other words, the air permeability of the
composite membrane 10, after the membrane was introduced into an
autoclave and allowed to stand for 32 hours in an environment
having a temperature of 120.degree. C. and a water vapor pressure
of 0.23 MPa (2.3 kgf/cm.sup.2), may, for example, be 50,000 seconds
or greater, preferably 80,000 seconds or greater, and more
preferably 99,999 seconds or greater. The moisture permeability of
the composite membrane 10 under conditions of high temperature and
high humidity (60.degree. C., wet method, holding time: 5 minutes)
is, for example, 200,000 g/m.sup.2/124 hr or greater, and
preferably 250,000 g/m.sup.2/124 hr or greater. The upper limit of
moisture permeability under conditions of high temperature and high
humidity is not particularly limited and may, for example, be
400,000 g/m.sup.2/124 hr or less (particularly 350,000 g/m.sup.2/24
hr or less).
EXAMPLES
[0086] The present invention will be described in greater detail
below with reference to the following examples. It is apparent,
however, that the present invention is not limited to these
examples and that appropriate modifications can be made within a
scope applicable to the outlines given elsewhere in the document;
all these modifications fall within the technical scope of the
present invention.
[0087] Liquid moisture-permeable resins A and B below were used in
the present examples and comparison examples.
[0088] Liquid Moisture-Permeable Resin A
[0089] An aqueous solution containing the following components 1)
to 4) was prepared in the following concentrations.
[0090] 1) Polyvinyl alcohol
[0091] (PVA217 (product name) manufactured by Kuraray Co., Ltd.):
3% by weight
[0092] 2) Aromatic phosphate flame retardant as a phosphate flame
retardant
[0093] (HF-77 (product name) manufactured by Nicca Chemical Co.,
Ltd.): 3% by weight
[0094] 3) Guanidine phosphate flame retardant
[0095] (P207-S (product name) manufactured by Nicca Chemical Co.,
Ltd.): 10% by weight
[0096] 4) Blocked isocyanate as a cross-linking agent
[0097] ("Meikanate MMF" (product name) manufactured by Meisei
Chemical Works, Ltd.): 3.5% by weight
[0098] Liquid Moisture-Permeable Resin B
[0099] A mixture of the following components 1) to 2) was prepared.
The ratio (former/latter) of the NCO groups in the polyurethane
resin and the OH groups in the ethylene glycol was 1.2/1 (mole
ratio).
[0100] 1) Polyurethane resin
[0101] ("Hipol 2000" (product name) manufactured by the Dow
Chemical Company)
[0102] 2) Ethylene glycol
[0103] Water Resistance
[0104] The water resistance of a moisture-permeable resin layer was
evaluated as described below.
[0105] A liquid moisture-permeable resin was applied to a glass
substrate and processed under suitable conditions depending on the
resin, and a film was obtained. In the case of liquid
moisture-permeable resin A, the solution was applied (amount
applied: 100 g/m.sup.2) and heated at a temperature of 180.degree.
C. for one minute. In the case of liquid moisture-permeable resin
B, the solution was applied (amount applied: 100 g/m.sup.2), dried
at a temperature of 100.degree. C. for 5 minutes, and treated with
moist heat for 60 minutes at a temperature of 100.degree. C. and a
relative humidity of 80% RH.
[0106] The resulting membrane (test substrate) was placed in an
autoclave, allowed to stand for 24 hours in an environment having a
temperature of 120.degree. C. and a water vapor pressure of 0.23
MPa (2.3 kgf/cm.sup.2), and subsequently immersed for 15 minutes in
water having a temperature of 25.degree. C. The degree of swelling
was then calculated based on the following formula.
Degree of swelling=Volume of resin after water resistance
test/Volume of resin before water resistance test
[0107] The results were as follows.
[0108] Liquid moisture-permeable resin A: The degree of swelling
was 8 times.
[0109] Liquid moisture-permeable resin B: It was impossible to
measure the degree of swelling. Most of the moisture-permeable
resin was eluted in water, and the shape of the membrane was unable
to be maintained.
Example 1
[0110] A composite membrane was obtained by a method in which
liquid moisture-permeable resin A was applied (amount applied: 100
g/m.sup.2) to one side of an ePTFE membrane (manufactured by Japan
Gore-Tex Co., Inc.; mean thickness: 20 .mu.m, mean pore diameter:
0.2 .mu.m, maximum pore diameter: 0.4 .mu.m, and void content of
the porous membrane: 85%), an ePTFE membrane (manufactured by Japan
Gore-Tex Co., Inc., mean thickness: 20 .mu.m, mean pore diameter:
0.2 .mu.m, maximum pore diameter: 0.4 .mu.m, void content of the
porous membrane: 85%) was layered on the coated side, and the
membrane was heated for 3 minutes at a temperature of 150.degree.
C.
[0111] Furthermore, a thermal-bond nonwoven fabric (9820F (product
name) manufactured by Shinwa Corp.) obtained using a polyester
fiber ("Melty" (product name), 2.2 dtex, manufactured by Unitika
Fibers, Ltd.) was heat-bonded to one surface (top surface, exposed
surface) of an ePTFE membrane to form a composite membrane with
nonwoven fabric.
[0112] The composite membrane with nonwoven fabric obtained in
Example 1 was cut and the structure of the sectional layer was
confirmed with a scanning electron microscope (SEM). The mean
thickness of the moisture-permeable resin layer was 3 .mu.m.
Furthermore, a portion of the moisture-permeable resin layer was
embedded in the ePTFE membrane.
[0113] An examination was performed to determine the
room-temperature air permeability (using an Oken-type Gurley meter)
and room-temperature moisture permeability (method A-1 of JIS
L1099) of the composite membrane with nonwoven fabric obtained in
Example 1. The air permeability (Gurley number) was 99,999 seconds
or greater, and the moisture permeability was 76 g/m.sup.2/h. The
composite membrane with nonwoven fabric according to Example 1 had
highly balanced moisture permeability and gas barrier
properties.
[0114] The resistance characteristics exhibited in a hot and humid
environment by the composite membrane with nonwoven fabric obtained
in Example 1 were examined as follows. The composite membrane with
nonwoven fabric was placed in an autoclave and allowed to stand for
24 hours in an environment having a temperature of 120.degree. C.
and a water vapor pressure of 0.23 MPa (2.3 kgf/cm.sup.2). The
membrane was then placed in an autoclave and allowed to stand for
32 hours in an environment having a temperature of 120.degree. C.
and a water vapor pressure of 0.23 MPa (2.3 kgf/cm.sup.2). These
conditions were equal to test conditions in which the membrane was
exposed to water vapor for 1,000 hours at temperature of 70.degree.
C. The room-temperature air permeability of the membrane was
examined after the membrane had been allowed to stand in the
conditions described above. As a result, the air permeability
(Gurley number) was 99,999 seconds or greater (for both wet and
dry) and did not decrease at all. The condition of the composite
membrane with nonwoven fabric was visually inspected and no
abnormalities were noted.
[0115] The moisture permeability exhibited in a hot and humid
environment (based on method A-1 of JIS L1099, except that the
measurement temperature was 60.degree. C. and the holding time was
5 minutes) by the composite membrane nonwoven fabric obtained in
Example 1 was examined. The moisture permeability was a high value
of 308,540 g/m.sup.2/124 hr.
[0116] The surface durability of the composite membrane with
nonwoven fabric obtained in Example 1 was examined as follows. A
length of 100 mm or greater of adhesive tape having a width of 50
mm or greater ("Neocraft Tape" (product name) manufactured by
Lintec Corporation) was attached to both sides of the composite
membrane with nonwoven fabric. Subsequently, the adhesive tape that
had been attached was peeled off at a speed of 200 mm/min or less,
surface properties were confirmed by visual inspection, and air
permeability was examined (using an Oken-type Gurley meter). No
defects in the surface of the composite membrane with nonwoven
fabric could be detected by visual inspection after the tape had
been removed. Furthermore, the air permeability (Gurley number) was
99,999 seconds or greater, and the composite membrane with nonwoven
fabric of Example 1 showed excellent surface durability.
Example 2
[0117] An ePTFE membrane (manufactured by Japan Gore-Tex Co., Inc.,
mean thickness: 20 .mu.m, mean pore diameter: 0.2 .mu.m, maximum
pore diameter: 0.4 .mu.m, void content of the porous membrane: 85%)
was impregnated on one side with an ion-exchange fluororesin
("Flemion" (product name) manufactured by Asahi Glass Co., Inc.;
solids content: 17%; ethanol solvent) and dried, whereby the
reinforced moisture-permeable resin layer 35 shown in FIG. 8(a) was
obtained. The reinforced moisture-permeable resin layer was
sandwiched on both sides by two ePTFE membranes (manufactured by
Japan Gore-Tex Co., Inc., mean thickness: 20 .mu.m, mean pore
diameter: 0.2 .mu.m, maximum pore diameter: 0.4 .mu.m, void content
of the porous membrane of 85%) and heated at a temperature of
160.degree. C. for three minutes while a load of 500 kPa was
applied to obtain a composite membrane.
[0118] Furthermore, thermal-bond nonwoven fabric (9820F (product
name) manufactured by Shinwa Corp.) obtained using a polyester
fiber ("Melty" (product name), 2.2 dtex, manufactured by Unitika
Fibers, Ltd.) was fusion-bonded to the surface (top surface,
exposed surface) of the ePTFE membrane to form a composite membrane
with nonwoven fabric.
[0119] The composite membrane with nonwoven fabric obtained in
Example 2 was cut and the structure of the sectional layer was
confirmed with a scanning electron microscope (SEM). The mean
thickness of the moisture-permeable resin layer was 5 .mu.m.
[0120] An examination was conducted to determine the
room-temperature air permeability (using an Oken-type Gurley meter)
and room-temperature moisture permeability (method A-1 of JIS
L1099) of the composite membrane with nonwoven fabric obtained in
Example 2. The air permeability (Gurley number) was 99,999 seconds
or greater, and the moisture permeability was 120 g/m.sup.2/h.
[0121] The resistance characteristics exhibited in a hot and humid
environment by the composite membrane with nonwoven fabric obtained
in Example 2 were examined in the same manner as in Example 1. The
air permeability (Gurley number) was 99,999 seconds or greater (for
both wet and dry), and did not decrease at all. The condition of
the composite membrane nonwoven fabric was visually inspected and
no abnormalities were noted.
Comparison Example 1
[0122] A thermal-bond nonwoven fabric (9820F (product name)
manufactured by Shinwa Corp.) obtained using a polyester fiber
("Melty" (product name), manufactured by Unitika Fibers, Ltd., the
physical properties were the same as those previously described)
was fusion-bonded to one side of an ePTFE membrane (manufactured by
Japan Gore-Tex Co., Inc., mean thickness: 20 .mu.m, mean pore
diameter: 0.2 .mu.m, maximum pore diameter: 0.4 .mu.m, void content
of the porous membrane: 85%). Liquid moisture-permeable resin A was
applied (amount applied: 230 g/m.sup.2) from the nonwoven fabric
side and then heated for 3 minutes at temperature of 150.degree. C.
to obtain the composite membrane.
[0123] The composite membrane obtained in comparison example 1 was
cut and the structure of the sectional layer was confirmed with a
scanning electron microscope (SEM). The moisture-permeable resin
layer was thicker at the interface between the nonwoven fabric and
the ePTFE membrane and was thin elsewhere, resulting in a
moisture-permeable resin layer having a non-uniform thickness.
[0124] The resistance characteristics exhibited in a hot and humid
environment by the composite membrane of comparison example 1 were
examined in the same manner as in Example 1. The air permeability
of the composite membrane according to comparison example 1 (Gurley
number) was 23,600 seconds, the moisture permeability was 35.7
g/m.sup.2/h, and both the gas barrier properties and the moisture
permeability were inadequate.
Comparison Example 2
[0125] Liquid moisture-permeable resin A was applied (amount
applied: 100 g/m.sup.2) to one side of an ePTFE membrane
(manufactured by Japan Gore-Tex Co., Inc., mean thickness: 20
.mu.m, mean pore diameter: 0.2 .mu.m, maximum pore diameter: 0.4
.mu.m, void content of the porous membrane: 85%) and dried for one
minute at a temperature of 180.degree. C. A thermal-bond nonwoven
fabric (9820F (product name) manufactured by Shinwa Corp.) obtained
using a polyester fiber ("Melty" (product name), manufactured by
Unitika Fibers, Ltd., the physical properties were the same as
those previously described) was fusion-bonded to the exposed side
of the ePTFE membrane to obtain a composite membrane.
[0126] The surface durability of the composite membrane of
Comparison Example 2 was examined in the same manner as in Example
1. The resin layer was observed to have peeled on the side of the
moisture-permeable resin layer in the composite membrane following
tape removal. Furthermore, the air permeability (Gurley number) was
20 seconds and the surface durability of the composite membrane of
comparison example 2 was inadequate.
Comparison Example 3
[0127] A composite membrane was obtained by applying (amount
applied: 100 g/m.sup.2) liquid moisture-permeable resin B to one
side of the ePTFE membrane (manufactured by Japan Gore Tex Co.,
Inc., mean thickness: 20 .mu.m, mean pore diameter: 0.2 .mu.m,
maximum pore diameter: 0.4 .mu.m, void content of the porous
membrane: 85%), drying the membrane for 5 minutes at a temperature
of 100.degree. C., and treating the membrane with moist heat for 60
minutes at a temperature of 100.degree. C. and a relative humidity
of 80% RH.
[0128] The resistance characteristics exhibited in a hot and humid
environment by the composite membrane were examined in the same
manner as in reference example 1. The air permeability (Gurley
number) after testing was 99,999 seconds or greater. However, the
surface of the moisture-permeable resin layer was extremely
sticky.
[0129] Furthermore, the moisture permeability exhibited by the
composite membrane of reference example 1 in a hot and humid
environment was examined in the same manner as in Example 1. The
moisture permeability was 198,920 g/m.sup.2/24 hr and had decreased
below that of Example 1.
Examples 3
[0130] A series of examples were made to illustrate various
embodiments of the invention using a fluororesin as an
air-impermeable layer. In this example a perfluorosulfonic acid
(PFSA) polymer solution was prepared as described in paragraph
[113]-[114] of US Patent Publication US2007/0072036 A1. This
solution was cast onto a polyethylene terephthalate (PET) backer
film that had been treated with ethylene tetrafluoroethylene (ETFE)
to improve its release characteristics. The PFSA film was
subsequently dried to remove the liquids, resulting in a
perfluorosulfonic acid membrane with a thickness of .about.4 um.
This film was laminated to an .about.15 cm.times..about.15 cm
micro-porous ePTFE membrane prepared according to the teachings of
U.S. Pat. No. 5,814,405. The ePTFE membrane had a thickness of
about 25 um, a Gurley of about 8.5, a mass per unit area of about
7.5 g/m.sup.2, a longitudinal matrix tensile strength of 267 Mpa
(38,725 psi), a transverse matrix tensile strength of about 282 Mpa
(40,900 psi) and an aspect ratio of about 29. The lamination was
accomplished at 160 C for 3 minutes using a PHI Inc. Model
B-257H-3-MI-X20 hydraulic press with heated platens. A piece of
0.25'' thick GR.RTM. sheet (available from W. L. Gore &
Associates, Inc, Elkton, Md.) was placed between each platen and
films to be laminated. In this example, no pressure was applied in
the press. After the film was laminated to one sheet of ePTFE, the
backer was removed, the product was turned over and laminated under
the same conditions to a second sheet of ePTFE of the same
composition to form the inventive air-impermeable composite
membrane. The moisture vapor transport rate (MVTR) was measured
using a cell and general approach similar to that described by
Gibson [in "Effect of temperature on water vapor transport through
polymer membrane laminates" published in Polymer Testing, Volume
19, Number 6, pages 673-691]. In this test, wet gas with a known
fixed water concentration is passed over one side of a membrane,
and dry gas with a known fixed water concentration is passed over
the other side. The MVTR is measured from either the measured loss
of water between the inlet and outlet of the wet side, or the gain
in water between the inlet and outlet on the dry side of the cell.
Water concentrations in our cell are measured using Vaisala
humidity probes (Vaisala Industrial Instruments, Woburn, Mass.),
and all inlet and outlet lines are heated to at or slightly above
the dew point of the gases to prevent condensation. Humidities and
flows are set using a GlobeTech Inc. fuel cell test stand as
controlled by Scribner and Associates control software. Testing was
performed at a cell temperature of 80.degree. C., which was
maintained by placing the cell in a circulating water bath
(Polysciences, Inc., Warrington, Pa., Model 1167). Testing was
performed using a wet side relative humidity (RH) of 70% and a dry
side humidity of less than 1%. (The specific measured values for
wet side RH for each sample and test are shown below in Table 1).
The MVTR was calculated as described by Gibson using the data from
the change in water concentration on the dry side. The dry side
data was used in preference to the wet side data because it had a
larger signal to noise ratio (i.e., a larger change in the measured
RH between inlet and outlet). The active sample area for our test
apparatus is 3 cm.times.3.5 cm or 10.5 cm.sup.2. In order to
increase the accuracy of the tests, 3 layers of the sample were
layered on top of one another in the test cell. Testing was
performed for each sample with two different flow configurations,
and at four different flow conditions. The flow configurations were
coflow and counterflow, the former having the wet gas and dry gas
passing over the membrane in the same direction, and the latter
having the wet gas and dry gas passing over the membrane in
opposite directions. The two approaches should yield the same
values of and as shown in Table 1, they do within the error of the
measurement. The four flow conditions used were 4 liters per minute
(LPM) on both sides, 2 LPM on both sides, 4 LPM on the wet side
with 2 LPM on the dry side, and finally, 4 LPM on the dry side with
2 LPM on the dry side. The results are tabulated in Table 1 with
the MVTR shown for each configuration as the average obtained with
the four different flow conditions. Also shown is the calculated
value of one standard deviation. Surprisingly, the measured
moisture vapor transport rate (MVTR) was 2.75 times greater than a
typical PFSA membrane (NAFION.RTM. membrane) described below as
Comparison Example 4.
Examples 4
[0131] Example 4 was prepared identically to Example 3 except that
the lamination was performed at 160 degrees C. for 3 minutes under
15 tons of force. The MVTR was 1.5 times that of Comparison Example
4.
Examples 5
[0132] An inventive air-impermeable composite membrane was prepared
as follows: a PFSA polymer solution was prepared as described in
Paragraphs [113]-[114] of U.S. Patent Application 2007/0072036
except the reactants were adjusted during polymerization to produce
a product with an equivalent weight of about 800. The solution was
coated using a #20 Meyer Bar an ETFE treated PET film that was
stretched tight over a glass plate. An ePTFE membrane as described
in Example 3 was then stretched over the wet coating. Then, the
resulting material was dried for 20-60 s with a hair drier and then
heat-treated at 160 C for three minutes. The ePTFE/PFSA film was
removed from the backer and stretched over a second layer of the
same ePTFE membrane described in Example 1 held tight on a glass
dish so the PFSA was in contact with the second layer of ePTFE.
This material was heat treated in a 160.degree. C. air furnace for
three minutes and then removed to cool. The moisture permselective
composite was removed from the glass dish and tested for MVTR as
described in Example 1. The results (Table 1) show The MVTR was
about three times that of Comparison Example 4.
Examples 6
[0133] An inventive moisture permselective composite was prepared
with particulate reinforcement in the PFSA layer as follows: a
platinum/C particulate solution was prepared essentially as
described in Paragraphs [118] of U.S. Patent Application No.
2007/0072036. Three grams of this solution was mixed with 20 grams
of the PFSA solution used in Example 5 plus five grams of deionized
water. This solution was cast using a 6 mil drawdown bar onto the
ePTFE as described in Example 3 that was stretched over an ETFE
coated PET backer. A second ePTFE membrane of the same composition
was stretched over the wet film. The resulting composite was dried,
then annealed in a 160.degree. C. air furnace for three minutes and
then removed to cool. The water permselectivity, tested as
described in Example 1, showed the MVTR was about 3.4 times that of
Comparison Example 4.
Examples 7
[0134] An inventive moisture permselective composite was prepared
to demonstrate that alternate PFSA compositions may be used to
produce high water transport rate materials. A moisture
permselective composite was prepared us ing the same procedure as
described in Example 5 except the PFSA was prepared essentially as
described in Paragraph [116] of U.S. Patent Application No.
2007/0072036. The difference between this Example and Example 5 is
that the PFSA was different, primarily in that in this example the
equivalent weight of the PFSA was about 920 versus the 800
equivalent weight of Example 5. The water permselectivity, tested
as described in Example 1, showed the MVTR of the material of
Example 7 was about 2.8 times that of Comparison Example 4.
Examples 8
[0135] A moisture permselective composite was prepared to
demonstrate that the micro-porous membrane of the inventive
composite may be hydrophilic. A composite was prepared using the
same materials and procedures as Example 5 except the second ePTFE
layer was a water-wettable ePTFE membrane obtained Japan-Gore-Tex,
Inc, Okayama, Japan (product number HSMO 71010). This product is
pre-treated with a thin polyvinyl alcohol (PVA) coating on the
nodes and fibrils of the ePTFE in order to render it hydrophilic
while still maintaining a micro-porous air permeable structure.
This inventive composite had an MVTR (Table 1) of about 2.9 times
that of Comparison Example 4.
Examples 9
[0136] A moisture permselective composite was prepared to
demonstrate that the porous membranes that constitute a pair need
not be identical. A composite was prepared using the same materials
and procedures as Example 5 except the second ePTFE layer was an
ePTFE membrane made using the teachings of U.S. Pat. No. 3,953,566
to Gore with a mass per area of 7.0 g/m.sup.2, a thickness of 20
microns, and porosity of at least 85%, and a longitudinal matrix
tensile strength of about 67 MPa, and a transverse matrix tensile
strength of about 76 MPa. This inventive composite had an MVTR
(Table 1) of about 2.32 times that of Comparison Example 4.
Examples 10
[0137] An inventive moisture perm selective composite was prepared
using the same PFSA polymer as Example 5 and the same procedure as
Example 6. Here, the solution concentrations were adjusted by
adding water so the solids content was .about.15%, and the water
content was about 50%, the balance ethanol. A moisture
permselective composite was then prepared as described in Example 6
using the solution and coating with a #20 Meyer bar. The water
permselectivity, tested as described in Example 1, showed the MVTR
was about 2.4 times that of Comparison Example 4.
Examples 11
[0138] Whereas Example 2 illustrates the inventive composite with a
non-woven gas-permeable reinforcing element attached to one side,
this example illustrates the inventive composite with a woven
polymer attached to both sides of an inventive composite. A woven
carbon filled polyvinylidene fluoride (PVDF) with a fiber diameter
of .about.140 .mu.m (5.5 mils) and 17.times.21 picks/inch
(inLighten.TM. window screen) was obtained from W. L. Gore and
Associates Elkton, Md. Two pieces of .about.14 cm.times.14 cm
pieces of this screen were placed on either side of a slightly
larger piece of the inventive composite of Example 6. A piece of
0.25'' thick GR.RTM. sheet (available from W. L. Gore &
Associates, Inc, Elkton, Md.) was then placed between each screen
and the platens of a PHI Inc. Model B-257H-3-MI-X20 hydraulic press
where the platens were preheated to 160.degree. C. 15-20 tons of
force was applied for 3 minutes, the heaters were turned off and
the part was allowed to cool to room temperature under pressure.
The resulting inventive composite had the woven gas-permeable
reinforcing element firmly attached to both sides of the
composite.
Examples 12
[0139] A composite was prepared using the same procedure as Example
10, except a #9 Meyer bar was used for casting in the first step.
The resulting composite was .about.20 .mu.m thick. The air
permeability of this sample was measured and found to have a Gurley
of >10,000 s.
Examples 13
[0140] A composite moisture permselective composite was prepared
with a micro-porous reinforcement in the ionomeric polymer layer as
follows: A micro-porous ePTFE membrane was prepared according to
the teachings of Bacino, et. al. in U.S. Pat. No. 7,306,729. This
material had properties similar to Example 5 in '729 with a Gurly
of about 7 s and a mass area of 2.4 g/m.sup.2. A membrane was
prepared using this ePTFE using the following process: the PFSA
described in Example 5 was coated onto an ETFE treated PET film
stretched over a glass plate using a #9 Meyer bar. The ePTFE
membrane was then stretched over the wet coating and allowed to
infiltrate. After infiltration, it was dried for 20-60 s with a
hair drier, then annealed at 160.degree. C. for 3 minutes after
removing from the backer and stretching over a glass dish. The
resulting material was sandwiched between two layers of the same
ePTFE used in Example 3, then stretched over the edges of an ETFE
treated PET film held on a glass plate. This was subsequently
annealed at 160.degree. C. for 3 minutes. The sample was removed
from the backer, where it was observed to have formed a composite
where the reinforced ionomer layer was approximately 2 .mu.m
thick.
Comparison Examples 4
[0141] A NAFION.RTM. membrane about 28 .mu.m was prepared by
casting a commercial 5% solution of 1100 equivalent weight
NAFION.RTM. product (available from Ion Power, Inc., New Castle,
Del.) on an ETFE coated PET backer and then drying, followed by
annealing at 160.degree. C. for 3 minute. The MVTR (Table 1) is
dramatically lower than the inventive materials of Examples
3-10.
TABLE-US-00001 TABLE 1 Relative Relative MVTR Co- MVTR MVTR Flow RH
on Wet (Counter- Counterflow Example RH on Wet side MVTR (Coflow)
Std (compared to side (%) Flow) in (compared to Number (%) Co-Flow
in g/m2-s Dev. Comp. Ex. 4) Counter Flow g/m2-s Std Dev. Comp Ex.
4) 3 71% 2.88 .+-.0.36 2.75 70% 3.13 .+-.0.41 2.86 4 70% 1.57
.+-.0.45 1.50 70% 1.84 .+-.0.14 1.68 5 70% 3.24 .+-.0.48 3.08 68%
3.22 .+-.0.45 2.94 6 70% 3.36 .+-.0.42 3.20 70% 3.65 .+-.0.56 3.34
7 71% 2.92 .+-.0.37 2.78 70% 2.99 .+-.0.35 2.73 8 71% 3.05 .+-.0.40
2.90 70% 2.95 .+-.0.38 2.69 9 72% 2.43 .+-.0.25 2.32 72% 2.43
.+-.0.25 2.22 10 70% 2.43 .+-.0.26 2.32 69% 2.66 .+-.0.35 2.42
Comp. Ex 4 72% 1.05 .+-.0.18 1.00 71% 1.10 .+-.0.09 1.00
[0142] While particular embodiments of the present invention have
been illustrated and described herein, the present invention should
not be limited to such illustrations and descriptions. It should be
apparent that changes and modifications may be incorporated and
embodied as part of the present invention within the scope of the
following claims.
* * * * *