Note: Descriptions are shown in the official language in which they were submitted.
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DESCRIPTION
Title of Invention: SEPARATING MEMBRANE AND HEAT EXCHANGER USING
SAME
Technical Field
[0001]
The present invention relates to a separating membrane and a heat exchanger
using the same, in which the separating membrane is useful as a heat (total
heat)
exchange membrane, a humidification membrane, a dehumidification membrane, a
pervaporation membrane (i.e., a membrane for separating, for example, water
and
another liquid (e.g., ethanol) from each other), and the like.
Background Art
[0002]
As a conventional total heat exchange membrane, there has been used a
separating membrane made of paper and impregnated with a hydrophilic flame
retardant. The separating membrane made of paper, however, has low water
resistance. For example, dew condensation water may be attached to the
separating
membrane, depending on the use conditions of a heat exchanger. If the dew
condensation water is frozen, the separating membrane may be broken. Further,
the
dew condensation water may cause the elution of the flame retardant contained
in the
separating membrane, and therefore, the flame retardancy or the latent heat
exchange
performance of the separating membrane may be decreased.
[0003]
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Patent Documents I and 2 describe using a layered product obtained by
forming a continuous layer of a moisture-permeable resin on the surface of a
porous
fluororesin membrane for the purpose of preventing a separating membrane from
being broken by dew condensation water. The layered product is usually
reinforced
by a nonwoven fabric or the like. Patent Document 2 further describes allowing
the
moisture-permeable resin layer to contain a flame retardant in order to
improve the
flame retardancy of the layered product.
[0004]
Meanwhile, Patent Document 3 describes a dust removal filter formed of an
electret filter and a flame-retarded nonwoven fabric, and further describes
blending a
flame retardant also into an adhesive for attaching the electret filter to the
flame-
retarded nonwoven fabric.
Prior Art Documents
Patent Documents
[0005]
Patent Document 1: Japanese Patent Laid-open Publication No. 7-133994
Patent Document 2: Japanese Patent Laid-open Publication No. 2006-150323
Patent Document 3: Japanese Patent Laid-open Publication No. 2002-292214
Disclosure of the Invention
Problems to be Solved by the Invention
[0006]
As described above, separating membranes used in various fields have
improved flameproofness by the use of a flame retardant in order to minimize
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damage in the unlikely event of a fire. Techniques using a flame retardant,
however,
have entered a somewhat mature stage, and therefore, in order to further
improve
flameproofness, it is also necessary to take a technical approach other than
the sole
use of a flame retardant. At the present time, however, effective measures
have not
yet been found.
[0007]
The present invention has been completed by specialization in a separating
membrane using a porous polytetrafluoroethylene membrane, and more
specifically,
the present invention is an improvement in the flameproofness of a separating
membrane comprising: a composite membrane formed of a porous
polytetrafluoroethylene membrane and a moisture-permeable resin layer; and a
reinforcing material, in which the composite membrane and the reinforcing
material
are layered with each other. In the present invention, it is an object to
improve the
flameproofness of an entire separating membrane more than ever before by,
while
using a flame retardant in the moisture-permeable resin layer, using another
solving
means in combination therewith.
Means of Solving the Problems
[0008]
The separating membrane of the present invention, which can solve the above
problem, is a separating membrane comprising: a composite membrane formed of a
porous polytetrafluoroethylene membrane and a moisture-permeable resin layer;
and
a reinforcing material, in which the composite membrane and the reinforcing
layer
are layered with each other, wherein the porous polytetrafluoroethylene
membrane
has a mass per unit area of not smaller than 0.5 g/m2 and not greater than 7
g/m2, and
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the moisture-permeable resin layer contains a moisture-permeable resin and a
frame
retardant, in which the amount of the frame retardant to be contained is not
smaller
than 5 parts by mass and not greater than 60 parts by mass, relative to 100
parts by
mass of the moisture-permeable resin. In particular, since the mass per unit
area of
the porous polytetrafluoroethylene membrane is adjusted to not grater than 7
g/m2,
the separating membrane can have a shorter fire spread distance until fire
extinction
even if part of the separating membrane catches fire. More specifically, it
can be
verified by the test method in the JIS-Z-2150-A method described below.
[0009]
In the above separating membrane, a preferred embodiment may be such that
the reinforcing material is fixed to the moisture-permeable resin layer in the
composite membrane.
[0010]
In the above separating membrane, a hydrophilic polyurethane resin may
preferably be used as the moisture-permeable resin.
[0011]
In the above separating membrane, a preferred embodiment may be such that
the reinforcing material is formed of fibers.
[0012]
In the above separating membrane, the fibers may preferably be in the form of
a nonwoven fabric.
[0013]
In the above separating membrane, a frame retardant may more preferably be
added also to the reinforcing material.
[0014]
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In the above separating membrane, the porous polytetrafluoroethylene
membrane may preferably have an average micropore diameter of from 0.07 to 10
gm.
[0015]
In the above separating membrane, a preferred embodiment may be such that
an inorganic compound is contained in the frame retardant.
[0016]
In the above separating membrane, a preferred embodiment may be such that
an antimony compound or a metal hydroxide compound is contained as the
inorganic
compound.
[0017]
In the above separating membrane, a preferred embodiment may be such that
a phosphorous type frame retardant is included in the frame retardant.
[0018]
In the above separating membrane, a preferred embodiment may be such that
the reinforcing material contains thermo-fusible resin fibers.
[0019]
In the above separating membrane, polyester type fibers may preferably be
used as the thermo-fusible resin fibers.
[0020]
In the above separating membrane, a preferred embodiment may be such that
the reinforcing material contains thermo-infusible fibers.
[0021]
In the above separating membrane, carbon fibers may preferably be used as
the thermo-infusible fibers.
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[0022]
In the above separating membrane, thermosetting resin fibers may preferably
be used as the thermo-infusible fibers.
[0023]
In the above separating membrane, the thermosetting resin fibers may
preferably be formed of polyimide fibers.
[0024]
The use of the above separating membrane in a heat exchanger makes it
possible to provide a heat exchanger having improved flameproofness.
[0025]
Meanwhile, both the terms "layer" and "membrane" as used herein are not
intended to distinguish their thicknesses from each other.
Effects of the Invention
[0026]
In the present invention, a separating membrane comprises a porous
polytetrafluoroethylene membrane and a moisture-permeable resin layer, in
which
the porous polytetrafluoroethylene membrane and the moisture-permeable resin
layer
are layered with each other; the mass per unit area of the porous
polytetrafluoroethylene membrane is adjusted to not smaller than 0.5 g/m2 and
not
greater than 7 g/m2; the moisture-permeable resin layer is allowed to contain
a flame
retardant at an amount of not smaller than 5 parts by mass and not greater
than 60
parts by mass, relative to 100 parts by mass of the moisture-permeable resin;
and the
separating membrane further comprises a reinforcing material, in which the
composite membrane and the reinforcing material are layered with each other.
Thus,
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the flameproofness of an entire separating membrane can be improved more than
ever before.
Brief Description of the Drawings
[0027]
[FIG. 1] This is a cross-sectional view of one separating membrane in an
embodiment of the present invention.
[FIG. 2] This is a cross-sectional view of another separating membrane in an
embodiment of the present invention.
[FIG. 3] This shows one example of a heat exchange using separating
membranes.
[FIG. 4] This is a graph showing the relationship between the mass per unit
area and the flameproofness of each of the porous PTFE membranes in Example 1.
[FIG. 5] This is a graph showing the relationship between the mass per unit
area and the flameproofness of each of the porous PTFE membranes in Example 2.
Mode for Carrying out the Invention
[0028]
The following will describe a separating membrane according to an
embodiment of the present invention. FIG. I is a cross-sectional view of the
separating membrane according to the embodiment of the present invention. As
shown in FIG. 1, a separating membrane 12 according to the embodiment of the
present invention comprises: a composite membrane 30 formed of a porous
polytetrafluoroethylene membrane 10 and a moisture-permeable resin layer 20;
and a
reinforcing material 40, in which the composite membrane 30 and the
reinforcing
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material 40 are layered with each other. As another embodiment of the present
invention, there can also similarly be put into practice a layered product
comprising,
as shown in FIG. 2, a composite membrane 30 and a reinforcing material 40, in
which the composite membrane 30 and the reinforcing material 40 are layered
with
each other, and the layering order of a porous polytetrafluoroethylene
membrane 10
and a moisture-permeable resin layer 20 in the composite membrane 30 is
opposite
to that in the example of FIG 1.
[0029]
In order that the separating membrane 12 satisfies certain flameproof
performance, the moisture-permeable resin layer 20 contains a flame retardant
in
addition to the moisture-permeable resin. Although described below in detail,
the
amount of the flame retardant to be contained may be not smaller than 5 parts
by
mass and not greater than 60 parts by mass, relative to 100 parts by mass of
the
moisture-permeable resin.
[0030]
The present inventors have advanced a study to improve the flameproofness
of the separating membrane 12 on the premise that a specific material, i.e.,
porous
polytetrafluoroethylene, is used as a component (the membrane 10) of the
separating
membrane 12. As a result, the present inventors have found that when the
porous
polytetrafluoroethylene membrane 10 has a mass per unit area of not greater
than 7
g/m2, the separating membrane 12 can have extremely-improved flameproofness.
In
the past, the improvement of flameproofness has depended solely on the
blending of
a flame retardant. In the present invention, however, the flameproofness of an
entire
separating membrane can be improved more than ever before by allowing the
porous
polytetrafluoroethylene membrane 10 to have a mass per unit area in a specific
range
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while using a flame retardant in the moisture-permeable resin layer. The
flameproofness is an indicator based on the JIS-Z-2150-A method (i.e., a test
method
for the flameproofness of thin materials (the 45 Meckel burner method)), and
it is
determined on the basis of char length, afterflame, and afterglow observed
when a
test material (i.e., the separating membrane 12 in the present invention) has
been
brought close to a flame. The test results are classified into the first-grade
flame
retardancy, the second-grade flame retardancy, and the third-grade flame
retardancy,
in which the first-grade flame retardancy indicates the highest
flameproofness.
[0031]
In the present invention, in order to improve the flameproofness of the
separating membrane 12 with increased certainty, it is desirable that the
porous
polytetrafluoroethylene membrane 10 may preferably be allowed to have a mass
per
unit area of not greater than 6 g/m2, more preferably not greater than 5 g/m2,
and still
more preferably not greater than 4 g/m2. Meanwhile, in respect of
flameproofness,
the lower limit of the mass per unit area is not particularly limited. In
order to
prevent the porous polytetrafluoroethylene membrane 10 from being broken,
however, the mass per unit area is adjusted to be not smaller than 0.5 g/m2.
It is
desirable that the mass per unit area may preferably be adjusted to be not
smaller
than 0.7 g/m2, more preferably not smaller than 1.0 g/m2, and still more
preferably
not smaller than 1.5 g/m2.
[0032]
The following will describe more specifically the basic components of the
separating membrane 12, i.e., the porous polytetrafluoroethylene membrane 10,
the
moisture-permeable resin layer 20, and the reinforcing material 40.
[0033]
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[Porous Polytetrafluoroethylene membrane 10]
Porous polytetrafluoroethylene is a polytetrafluoroethylene (PTFE) material
made porous by expanding. The porous polytetrafluoroethylene membrane 10 can
be
allowed to have high porosity. The porous polytetrafluoroethylene membrane 10
can
also be allowed to have very minute pores formed therein.
[0034]
The porous polytetrafluoroethylene membrane 10 is obtained by mixing
PTFE fine powder with a molding aid to form a paste; molding the paste to form
a
molded product; removing the molding aid from the molded product; subsequently
expanding the molded product at a high temperature and at a high speed; and if
necessary, baking the expanded molded product. The details thereof are
described
in, for example, Japanese Patent Publication No. 51-18991. In this regard,
however,
expanding may be either uniaxially expanding or biaxially expanding. The
porous
polytetrafluoroethylene membrane 10 that has uniaxially been expanded is
microscopically characterized in that it has nodes (folded crystals) arranged
approximately orthogonal to the expanding direction in a thin island manner,
and
fibrils (linear molecule bundles in which folded crystals have been unraveled
and
pulled out by the expanding) oriented in the expanding direction in a reed-
screen
manner so as to connect the nodes. In contrast, the porous
polytetrafluoroethylene
membrane 10 that has biaxially been expanded is microscopically characterized
in
that it has fibrils extending in a radial manner and this leads to a spider's-
web-like
fibrous structure in which nodes connecting fibrils are interspersed in an
island
manner so that there are many spaces defined by the fibrils and the nodes. In
particular, the porous polytetrafluoroethylene membrane 10 that has biaxially
been
expanded may preferably be used, because it is easier to increase its width
than that
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of the porous polytetrafluoroethylene membrane 10 that has uniaxially been
expanded, and further, the porous polytetrafluoroethylene membrane 10 that has
biaxially been expanded has an excellent balance between the physical
properties
both in the machine direction and in the traverse direction, and therefore,
the
production cost per unit area can be reduced.
[0035]
The porous polytetrafluoroethylene membrane 10 may have an average
micropore diameter of, for example, about from 0.07 to 10 m. If the average
micropore diameter is too small, the porous polytetrafluoroethylene membrane
10
may have decreased moisture permeability, so that the moisture permeation
performance of the separating membrane 12 is decreased, and therefore, the
heat
exchange performance of the separating membrane 12 is decreased when used as a
heat exchange membrane. The average micropore diameter may more preferably be
not smaller than 0.09 m. In contrast, if the average micropore diameter is
too great,
the moisture-permeable resin layer 20 may easily enter into the micropores of
the
porous polytetrafluoroethylene membrane 10. This results in an increase in the
substantial thickness of the moisture-permeable resin (which is equal to the
thickness
of the moisture-permeable resin portion plus the thickness of the moisture-
permeable
resin portion in the porous polytetrafluoroethylene membrane), so that the
traveling
time of moisture is increased, and therefore, moisture permeability is
decreased. The
average micropore diameter may more preferably be not greater than 5 m.
[0036]
In this connection, the average micropore diameter of the porous
polytetrafluoroethylene membrane 10 means the average value of the pore
diameters
measured using a Coulter Porometer of Coulter Electronics Ltd. The average
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micropore diameter of the porous polytetrafluoroethylene membrane 10 can
appropriately be controlled by expansion ratio or other factors.
[0037]
The porosity of the porous polytetrafluoroethylene membrane 10 can
appropriately be adjusted depending on the average micropore diameter
described
above, and it is recommended that the porosity may be, for example, not
smaller than
50% (preferably not smaller than 60%) and not greater than 98% (preferably not
greater than 90%).
[0038]
The porosity of the porous polytetrafluoroethylene membrane 10 can be
calculated on the basis of the following formula, using a bulk density D
obtained by
measuring a mass W and an apparent volume V including pore portions, of the
porous polytetrafluoroethylene membrane 10 (i.e., D = W/V in units of g/cm3);
and a
density Dstandard when no pores are formed (e.g., 2.2 g/cm3 in the case of a
PTFE
resin). In this connection, the thickness used to calculate the volume V is
obtained
on the basis of an average thickness when measured with a dial thickness gauge
(when measured using "SM-1201" available from Teclock Corporation, in the
state
where no load was applied other than the spring load of the gauge body).
Porosity (%) = [1 - (D/Dstandard)] X 100
[0039]
The porous polytetrafluoroethylene membrane 10 has an air permeability of,
for example, not greater than 500 seconds, preferably not greater than 10
seconds. If
the value of the air permeability is too great, the membrane may have
decreased
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moisture permeability, and therefore, the separating membrane 12 obtained may
have
insufficient moisture permeability. Further, when the separating membrane 12
is
used as a heat exchange membrane or a pervaporation membrane, there occurs a
decrease in heat exchange performance and a decrease in separation efficiency.
The
method of measuring air permeability will be described below.
[0040]
[Moisture-Permeable Resin Layer 20]
The moisture-permeable resin layer 20 is a nonporous membrane-shaped
layer made of a moisture-permeable resin, and is a portion that exhibits the
functions
as a separating membrane by allowing heat and moisture (water vapor) to pass
therethrough but not allowing air to pass therethrough. As the moisture-
permeable
resin, there may be used a water-insoluble resin. The separating membrane 12
of the
present invention, however, has improved resistance to dew condensation, and
therefore, a water-soluble resin may also be used by making it poorly soluble
in
water. As the method of making a water-soluble resin poorly soluble in water,
there
may be a method by the combined use of heat treatment and addition of a cross-
linking agent.
[0041]
As the moisture-permeable resin, hydrophilic polyurethane can be mentioned.
Besides, polyvinyl alcohol, polyethylene oxide, or polyacrylic acid can be
used.
[0042]
The thickness of the moisture-permeable resin layer 20 is not particularly
limited so long as the moisture-permeable resin layer 20 can exhibit the above
functions. The thickness of the moisture-permeable resin layer 20 may be, for
example, about from 0.01 m to 100 m, preferably about from 0.1 to 50 gm, and
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more preferably about from 0.1 to 10 gm. If the moisture-permeable resin layer
20 is
too thin, there is the possibility that coating may become uneven and pinholes
may
be formed. On the other hand, if the moisture-permeable resin layer 20 is too
thick,
the moisture-permeable resin layer 20 may have decreased moisture
permeability.
[0043]
The moisture-permeable resin layer 20 contains a flame retardant. The
containing of a flame retardant improves the flame retardancy (flameproofness)
of
the moisture-permeable resin layer 20. This results in that the flame
retardancy of
the entire separating membrane 12 can be ensured at or above a certain level.
The
amount of the flame retardant to be contained is not smaller than 5 parts by
mass and
not greater than 60 parts by mass, relative to 100 parts by mass of the
moisture-
permeable resin. The lower limit of the amount of the flame retardant to be
contained is set to be 5 parts by mass in view of securing the effectiveness
of flame
retardancy. The lower limit of the amount of the flame retardant to be
contained may
more preferably be set to be 8 parts by mass, still more preferably 10 parts
by mass.
On the other hand, if the flame retardant is contained at an amount of greater
than 60
parts by mass, the amount of the moisture-permeable resin to be contained may
become relatively small, so that the functions of the moisture-permeable resin
layer
cannot be exhibited. For this reason, the upper limit of the amount of the
flame
20 retardant to be contained is set to be 60 parts by mass. The upper limit of
the content
of the flame retardant to be contained may more preferably be set to be 50
parts by
mass, still more preferably 40 parts by mass. As the method of adding the
flame
retardant to the moisture-permeable resin layer 20, the flame retardant may be
added
to a raw material of the moisture-permeable resin, and these may be mixed
together
by a synthetic resin mixing machine or other means.
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[0044]
The kind of flame retardant is not particularly limited, and can appropriately
be determined depending on the required grade of flame retardancy. Taking into
consideration an influence on the environment, it is desirable to use a non-
halogen
type flame retardant. More specifically, there can be used any of non-halogen
type
flame retardants such as aromatic phosphate type flame retardants, guanidine
phosphate type flame retardants, and alicyclic phosphate type flame
retardants.
Aromatic phosphate type flame retardants are water-insoluble, and, when heated
to a
temperature equal to or higher than the glass transition temperature of a
fibrous resin
forming the reinforcing material 40, the aromatic phosphate type flame
retardants are
absorbed into the fibers. Thus, the aromatic phosphate type flame retardants
do not
melt out even when brought in contact with dew condensation water or the like,
and
therefore, can be expected to exhibit the stable effect of flame retardancy.
Guanidine
phosphate type flame retardants and alicyclic phosphate type flame retardants
have
water absorption properties, and therefore, can be expected to exhibit the
effect of
moisture absorption. Meanwhile, as the flame retardant, there can also be used
an
inorganic compound. Some of antimony compounds and metal hydroxides can be
used as the inorganic compound.
[0045]
It is desirable that the entire separating membrane 12 may satisfy flame
retardancy at a level of the third-grade flame retardancy defined in the JIS-Z-
2150-A
method or flame retardancy at a level of VTM-2 defined in UL94.
[0046]
The moisture-permeable resin layer 20 may further contain a moisture
absorbent. The containing of a moisture absorbent increases the water holding
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capacity of the moisture-permeable resin layer 20. This makes it possible to
further
increase moisture permeability. As the moisture absorbent, there can be used
any of
water-soluble salts. More specifically, lithium salts, phosphoric salts, or
other salts
can be used.
[0047]
The separating membrane 12 of the present invention has an air permeability
of, for example, not smaller than 3,000 seconds. If the air permeability is
too small,
the fluids separated by the separating membrane may be mixed with each other.
In
this connection, the upper limit of the air permeability is not particularly
limited, and
there may be even no need for ventilation at all. Meanwhile, the air
permeability
means the Gurley number. The Gurley number is defined as the time (in seconds)
required for 100 cm3 of air to flow through an area per square inch (6.45 cm2)
under
a pressure of 1.23 kPa (JIS-P-8117).
[0048]
In addition, the separating membrane 12 of the present invention has a
moisture permeability of, for example, not smaller than 3,000 g/m2/24 hours.
If the
moisture permeability is too low, the transmission of water vapor becomes
insufficient, so that moisture may be condensed on the surfaces of the
separating
membrane 12, and therefore, dew condensation may occur, thereby causing a
deterioration of the separating membrane. The separating membrane 12 may
preferably have a moisture permeability of not smaller than 6,000 g/m2/24
hours,
more preferably not smaller than 10,000 g/m2/24 hours. The separating membrane
12 having higher moisture permeability may be considered more excellent. Thus,
the
upper limit of the moisture permeability is not limited. Meanwhile, the
moisture
permeability is defined as the value measured on the basis of JIS-L-1099 (the
B-I
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method).
[0049]
[Reinforcing Material 40]
The reinforcing material 40 can reinforce the composite membrane 30, and
has such spaces (air permeability) as not to block a fluid to be processed
(e.g.,
outside air to be subjected to heat exchange and moisture exchange) and the
composite membrane 30. The porosity of the reinforcing material 40 may be, for
example, about from 30% to 95%.
[0050]
The reinforcing material 40 is usually formed of a fibrous resin. The use of a
fibrous resin makes it possible to easily produce the reinforcing material 40
having a
prescribed porosity. The reinforcing material 40 formed of a fibrous resin may
be
any of woven fabrics, knitted fabrics, nonwoven fabrics, and nets. A
particularly
preferred fibrous reinforcing material 40 is a nonwoven fabric. A nonwoven
fabric
has minute space portions formed of numerous fibers (i.e., the spaces between
the
fibers), and therefore, can exhibit moisture permeability.
[0051]
As the nonwoven fabric, there may preferably be used a nonwoven fabric
having a small mass per unit area. Any of nonwoven fabrics can be used,
including
spunbonded nonwoven fabrics, thermally bonded nonwoven fabrics, wet nonwoven
fabrics, and nonwoven fabrics formed by needle punching and other methods such
as
spunlacing and melt blowing, in which none of these nonwoven fabrics contains
a
flame retardant. The nonwoven fabrics may be those using fusible resins as
their
materials, such as polyester type resins, olefin type resins, styrene type
resins,
aramid type resins, and polyphenylene sulfide (PPS).
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[0052]
In addition, in order to further improve the flame retardancy of the
separating
membrane 12, there can also be used, as the material of the reinforcing
material 40,
flame-retarded nonwoven fabrics obtained by kneading a flame retardant into
their
fibers. Examples of the flame-retarded nonwoven fabrics may include HEIM
(registered trademark) available from Toyobo Co., Ltd., and Eltas FR
(registered
trademark) available from Asahi Kasei Fibers Corporation. In the same manner,
there can also be used flame-retarded nonwoven fabrics using raw material
fibers
used in the above flame-retarded nonwoven fabrics. Further, it is also
possible to use
nonwoven fabrics using nylon fibers, acrylic fibers, carbon fibers, or other
fibers, all
of which do not cause fusion.
[0053]
For the attachment of the composite membrane 30 to the reinforcing material
40, for example, a method with an adhesive can be used. As the adhesive,
general-
purpose adhesives can be used, but the use of a moisture-permeable resin may
be
preferred. This is in order to maintain the moisture permeability of the
entire
separating membrane 12. Examples of the moisture-permeable resin material may
include hydrophilic polyurethane, as described above, and in addition to this,
polyvinyl alcohol, polyethylene oxide, or polyacrylic acid can be used. As the
method of applying such an adhesive, it is also possible to apply a moisture-
permeable resin to the composite membrane 30, and, immediately thereafter,
attach
the reinforcing material 40 to the composite membrane 30 before the moisture-
permeable resin is cured.
[0054]
The use of a thermo-fusible resin as the fiber material of the reinforcing
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material 40 makes it possible to employ a method using thermal fusion bonding
to
attach the composite membrane 30 to the reinforcing material 40. In this case,
the
production process of the separating membrane 12 can be simplified as compared
to
the case where an adhesive is applied.
[0055]
For example, when the reinforcing material (resin) 40 and the porous
polytetrafluoroethylene membrane 10 are attached to each other as shown in
FIG. 2
described above, the fixation between the porous polytetrafluoroethylene
membrane
and the reinforcing material 40 can significantly be improved. This is because
10 part of the reinforcing material 40 enters the micropores of the porous
polytetrafluoroethylene membrane 10.
[0056]
As the fiber forming the reinforcing material 40, a thermo-fusible resin and a
thermo-infusible resin can also be used in combination. If a thermo-fusible
resin is
used solely, the resin may be fused excessively to form a dense membrane,
possibly
resulting in the reduction of moisture permeability or in the occurrence of
wrinkles.
The combination of a thermo-fusible resin with a thermo-infusible resin can
prevent
the formation of a dense membrane. Further, when the separating membrane 12 is
subjected to deformation processing such as corrugation processing in order to
increase the surface area of the separating membrane 12, the reinforcing
material 40
formed of a thermo-fusible resin and a thermo-infusible resin facilitates the
provision
of a shape due to the action of the thermo-fusible resin at the time of
deformation
processing, and also facilitates the maintenance of the shape due to the
action of the
thermo-infusible resin.
[0057]
19
CA 02798928 2012-11-07
Our Ref: F11-052PCT
When a thermo-fusible resin and a thermo-infusible resin are used in
combination, a mixed fiber may be used, which is obtained by mixing the thermo-
fusible resin with the thermo-infusible resin. For example, a mixed fiber may
be
used, which has a splittable structure where the thermo-fusible resin covers
around
the thermo-infusible resin. Alternatively, a fiber may be used, which is
integrally
formed of both the thermo-fusible resin and the thermo-infusible resin.
Examples of
such an integrally-formed fiber may include a fiber having a core-clad
structure
where the thermo-fusible resin covers around the thermo-infusible resin.
[0058]
In addition, besides the above fibers, a fiber can also be used, which is
formed of resins different in melting point and in material to have a core-
clad
structure. Alternatively, as the reinforcing material 40, a nonwoven fabric
can also
be used, which is obtained by combining fibers formed of a thermo-infusible
resin
using a thermo-fusible resin as a binder.
[0059]
As a resin used for the fiber forming the reinforcing material 40, a resin
having low moisture absorption properties is recommended. The use of a resin
having higher moisture absorption properties may cause a decrease in strength
when
dew condensation occurs, resulting in that the separating membrane 12 becomes
likely to be deformed or broken. Examples of the resin having low moisture
absorption properties may include acrylic type resins, nylon type resins,
polyester
type resins, polylactic type resins, and polyolefin type resins. A reinforcing
material
having high moisture absorption and desorption properties is also recommended
because it increases the moisture permeation performance. Examples of the
resin
having high moisture absorption properties may include vinylon and urethane.
In
CA 02798928 2012-11-07
Our Ref.: F11-052PCT
this connection, when a flame retardant is used, a high surface energy of a
polyolefin
type resin makes it difficult to fix the flame retardant. Thus, when a flame
retardant
is used, there can preferably be used any of resins other than polyolefin type
resins
(e.g., any of acrylic type resins, nylon type resins, vinylon type resins,
polyester type
resins, and polylactic type resins).
[0060]
The reinforcing material 40 may desirably be allowed to have a mass per unit
area of from 2 to 100 g/m2, preferably from 3 to 50 g/m2, and more preferably
from 5
to 40 g/m2. This is because if the mass per unit area is too small, an
effective
reinforcement cannot be achieved; on the other hand, if the mass per unit area
is too
great, the total heat exchange efficiency may become decreased. If the mass
per unit
area of the reinforcing material 40 is too great, the separating membrane 12
may
have decreased moisture permeation performance. Further, this leads to an
increase
in the size of an apparatus using the separating membrane 12 (e.g., any of
heat
exchangers, humidifiers, and dehumidifiers). In addition, when the separating
membrane 12 is used as a heat exchange membrane, the heat exchange performance
is decreased. On the other hand, if the mass per unit area of the reinforcing
material
40 is too small, the workability of the separating membrane 12 may be
deteriorated.
[0061]
The thickness of the reinforcing material 40 is not particularly limited, but
it
may be, for example, about not smaller than 5 gm (preferably not smaller than
10
gm) and about not greater than 1,000 gm (preferably not greater than 500 m).
[0062]
[Heat Exchanger]
As an application of the separating membrane 12 described above, the
21
CA 02798928 2012-11-07
Our Ref.: F11-052PCT
following will describe a heat exchanger using the separating membranes 12.
FIG. 3
shows one example of the heat exchanger using the separating membranes 12.
[0063]
In FIG. 3, the numeral "1" indicates separators; "12" indicates separating
membranes used as heat exchange membranes; "3" indicates the flow of exhaust
air;
and "4" indicates the flow of intake air. The separators I are corrugated, and
are
layered alternately with the separating membranes 12. In this case, the
separators I
are placed such that the direction of the corrugation of each separator I is
orthogonal
to the direction of the corrugation of another separator I adjacent thereto,
so as to
form the flow paths of the exhaust air and the intake air.
[0064]
For example, in the case where the exhaust air 3 is warm humidified air in a
heated room and the intake air 4 is cold dry air outside the room, heat and
moisture
are exchanged via the separating membranes 12 when the exhaust air 3 and the
intake air 4 pass through the corresponding flow paths formed by the
separators I
and the separating membranes 12. As a result, the intake air 4 is warmed and
then
taken in a humidified state into the heated room. This makes it possible to
increase
the heating efficiency in the heated room, and also to control the humidity of
the air
in the room.
Examples
[0065]
The present invention will be described below more specifically by way of
Examples, but the present invention is not limited to the following Examples.
The
present invention can be put into practice after appropriate modifications or
22
CA 02798928 2012-11-07
Our Ref.: F11-052PCT
variations within a range meeting the gists described above and below, all of
which
are included in the technical scope of the present invention.
[0066]
(Example 1)
Five kinds of separating membrane samples (sample numbers 1A to 5A)
different in the masses per unit area of porous polytetrafluoroethylene
membranes
(porous PTFE membranes) were prepared, and tests were performed to confirm the
flameproofness and other physical properties of each sample. The porous PTFE
membranes had a mass per unit area of 3 g/m2, 6 g/m2, 9 g/m2, 12 g/m2, and 20
g/m2,
respectively.
[0067]
Using a hydrophilic polyurethane resin ("HYPOL 2000" available from the
Dow Chemical Company) as a moisture-permeable resin material, each porous PTFE
membrane was coated, in a proportion of about 10 g/m2, with a product obtained
by
mixing 40 parts by mass of a phosphorus type flame retardant available from
Nicca
Chemical Co., Ltd. (product name "NICCA FI-NONE") with 100 parts by mass of
the hydrophilic polyurethane resin, thereby obtaining a composite membrane
formed
of a porous PTFE membrane and a moisture-permeable resin layer.
[0068]
As a reinforcing material, there was used a spunbonded nonwoven fabric
(HEIM (registered trademark) H3201 available from Toyobo Co., Ltd. (having a
mass per unit area of 20 g/m2 and a thickness of 0.15 mm)), in which the
spunbonded
nonwoven fabric was made of polyester fibers copolymerized with a phosphorus
type
flame retardant. A separating membrane was obtained by attaching each
composite
membrane to the reinforcing material before the hydrophilic polyurethane resin
was
23
CA 02798928 2012-11-07
Our Ref.: F11-052PCT
cured.
[0069]
Table 1 shows the specifications and the test results of each sample. FIG. 4
is
a graph showing the relationship between the mass per unit area and the
flameproofness, shown in Table 1, of each porous PTFE membrane.
24
CA 02798928 2012-11-07
h Cr
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CA 02798928 2012-11-07
Your Ref.: JGP-565/PCT
Our Ref.: F11-052PCT
[0071]
From Table I and FIG. 4, sample 5A in which the porous PTFE membrane
had a mass per unit area of 20 g/m 2 was not accepted for flameproofness
because the
char length of the separating membrane was 17 cm. In contrast, samples 3A and
4A
in which the porous PTFE membranes had a mass per unit area of 9 g/m2 and 12
g/m2, respectively, was accepted as showing the third-grade flame retardancy
because the char lengths of the separating membranes were from 14 to 15 cm.
Then,
surprisingly, samples in which the porous PTFE membranes had a mass per unit
area
of 3 g/m2 and 6 g/m2, respectively, were even accepted as showing the first-
grade
flame retardancy because the char lengths of the separating membranes were
decreased considerably to 4 cm. Further, their flame retardant durabilities
(i.e.,
flameproofness after immersion in warm water, which will be described below in
detail) were not decreased. From these results, it can be said that when the
porous
PTFE membrane has a mass per unit area of not greater than 7 g/m2 (preferably
not
greater than 6 g/m2), the porous PTFE membrane has considerably excellent
flameproofness.
[0072]
(Example 2)
Six kinds of separating membrane samples (sample numbers lB to 6B)
different in the masses per unit area of porous PTFE membranes and in the
kinds of
reinforcing materials were prepared, and tests were performed to confirm the
flameproofness and other physical properties of each sample. The porous PTFE
membranes had a mass per unit area of 3 g/m2, 3 g/m2, 6 g/m2, 9 g/m2, 12 g/m2,
and
12 g/m2, respectively.
[0073]
26
CA 02798928 2012-11-07
Your Ref.: JGP-565/PCT
Our Ref: F11-052PCT
Using a hydrophilic polyurethane resin ("HYPOL 2000" available from the
Dow Chemical Company) as a moisture-permeable resin material, each porous PTFE
membrane was coated, in a proportion of about 10 g/m2, with a product obtained
by
mixing 40 parts by mass of a phosphorus type flame retardant available from
Nicca
Chemical Co., Ltd. (product name "NICCA FI-NONE") with 100 parts by mass of
the hydrophilic polyurethane resin, thereby obtaining a composite membrane
formed
of a porous PTFE membrane and a moisture-permeable resin layer.
[0074]
As a reinforcing material, there was used a spunbonded nonwoven fabric
(ECULE (registered trademark) available from Toyobo Co., Ltd.; product number
3151A (having a mass per unit area of 15 g/m2 and a thickness of 0.12 mm) or
product number 320 IA (having a mass per unit area of 20 g/m2 and a thickness
of
0.15 mm), in which the spunbonded nonwoven fabric was made of polyester fibers
containing no flame retardant. A separating membrane was obtained by attaching
each composite membrane to the reinforcing material before the hydrophilic
polyurethane resin was cured.
[0075]
Table 2 shows the specifications and the test results of each sample. FIG. 5
is
a graph showing the relationship between the mass per unit area and the
flameproofness, shown in Table 2, of each porous PTFE membrane in samples (1
B,
3B, 4B, and 513) using product number 3151A (having a mass per unit area of 15
g/m2)
[0076]
27
CA 02798928 2012-11-07
U N N a y
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CA 02798928 2012-11-07
Your Ref: JGP-565/PCT
Our Ref: F11-052PCT
[0077]
From Table 2, samples 4B to 6B in which the porous PTFE membranes had
masses per unit area of from 9 to 12 g/m 2 were not accepted for
flameproofness
because the char lengths of the separating membranes were from 16 to 18 cm. In
contrast, samples I B to 3B in which the porous PTFE membranes had masses per
unit area of from 3 to 6 g/m2 were accepted as showing the first-grade flame
retardancy because the char lengths of the separating membranes were decreased
considerably to from 4 to 5 cm in the same manner as described in Example 1.
Further, their flame retardant durabilities were not decreased.
[0078]
Despite the use of fibers containing no flame retardant as the reinforcing
material, in Example 2, as can be seen from Table 2 and FIG. 5, when the
porous
PTFE membrane has a mass per unit area of not greater than 7 g/m2 (preferably
not
greater than 6 g/m2), the porous PTFE membrane has considerably excellent
flameproofness in the same manner as described in Example 1.
[0079]
(Example 3)
Five kinds of separating membrane samples (sample numbers IC to 5C)
different in the masses per unit area of porous PTFE membranes were prepared,
and
tests were performed to confirm the flameproofness and other physical
properties of
each sample. The porous PTFE membranes had a mass per unit area of 3 g/m2, 6
g/m2, 9 g/m2, 12 g/m2, and 20 g/m2, respectively.
[0080]
Using a hydrophilic polyurethane resin ("HYPOL 2000" available from the
Dow Chemical Company) as a moisture-permeable resin material, each porous PTFE
29
CA 02798928 2012-11-07
Your Ref: JGP-565/PCT
Our Ref.: F11-052PCT
membrane was coated, in a proportion of about 10 g/m2, with the hydrophilic
polyurethane resin, thereby obtaining a composite membrane formed of a porous
PTFE membrane and a moisture-permeable resin layer. In Example 3, a flame
retardant was not mixed in the moisture-permeable resin membrane.
[0081]
As a reinforcing material, there was used a spunbonded nonwoven fabric
(HEIM (registered trademark) H3201 available from Toyobo Co., Ltd. (having a
mass per unit area of 20 g/m2 and a thickness of 0.18 mm)), in which the
spunbonded
nonwoven fabric was made of polyester fibers copolymerized with a phosphorus
type
flame retardant. A separating membrane was obtained by attaching each
composite
membrane to the reinforcing material before the hydrophilic polyurethane resin
was
cured. Table 3 shows the specifications and the test results of each sample.
[0082]
CA 02798928 2012-11-07
h h
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CA 02798928 2012-11-07
Your Ref: JGP-565/PCT
Our Ref . F11-052PCT
[0083]
From Table 3, all the samples were not accepted for flameproofness, despite
large or small values of the masses per unit area of the expanded porous PTFE
membranes. Thus, it was confirmed that the moisture-permeable resin layer
forming
part of each separating membrane needs to contain a flame retardant.
[0084]
(Example 4)
Three kinds of separating membrane samples (sample numbers ID to 3D)
different in the blending ratios of flame retardants mixed in the moisture-
permeable
resin membranes were prepared, and tests were performed to confirm the
flameproofness and other physical properties of each sample. The mass per unit
area
of a porous PTFE membrane was 3 g/m2.
[0085]
Using a hydrophilic polyurethane resin ("HYPOL 2000" available from the
Dow Chemical Company) as a moisture-permeable resin material, the porous PTFE
membrane was coated, in a proportion of about 10 g/m2, with any of the
following
three kinds of products: a product obtained by mixing 20 parts by mass of a
phosphorus type flame retardant available from Nicca Chemical Co., Ltd.
(product
name "NICCA FI-NONE") with 100 parts by mass of the hydrophilic polyurethane
resin (sample 2D); a product obtained by mixing 40 parts by mass of the
phosphorus
type flame retardant with 100 parts by mass of the hydrophilic polyurethane
resin
(sample 3D); and a product obtained by not mixing the phosphorus type flame
retardant with 100 parts by mass of the hydrophilic polyurethane resin at all
(sample
I D), thereby obtaining a composite membrane formed of a porous PTFE membrane
and a moisture-permeable resin layer.
32
CA 02798928 2012-11-07
Your Ref: JGP-565/PCT
Our Ref: F11-052PCT
[0086]
As a reinforcing material, there was used a spunbonded nonwoven fabric
(HEIM (registered trademark) H3201 available from Toyobo Co., Ltd. (having a
mass per unit area of 20 g/m2 and a thickness of 0.15 mm)), in which the
spunbonded
nonwoven fabric was made of polyester fibers copolymerized with a phosphorus
type
flame retardant. A separating membrane was obtained by attaching each
composite
membrane to the reinforcing material before the hydrophilic polyurethane resin
was
cured. Table 4 shows the specifications and the test results of each sample.
[0087]
33
CA 02798928 2012-11-07
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CA 02798928 2012-11-07
Your Ref: JGP-565/PCT
Our Ref.: F11-052PCT
[0088]
From Table 4, with respect to samples 2D and 3D in which the moisture-
permeable resin membranes contained flame retardants, the first-grade flame
retardancy was obtained. It was confirmed that the moisture-permeable resin
layer
needs to contain a flame retardant in the same manner as described in Example
3.
[0089]
All the separating membranes obtained in the above experimental examples
had air permeabilities of not smaller than 10,000 seconds. Further, other
physical
properties of the separating membranes were evaluated as follows.
[0090]
(1) Flameproofness
The separating membranes were examined for flameproofness in accordance
with the JIS-Z-2150-A method (in which the heating time was 10 seconds). The
moisture-permeable separating membrane materials after the test were examined
for
char length and evaluated on the following criteria.
Accepted (the first-grade flame retardancy): the char length is not longer
than
50 mm;
Accepted (the second-grade flame retardancy): the char length is longer than
50 mm and not longer than 100 mm;
Accepted (the third-grade flame retardancy): the char length is longer than
100 mm and not longer than 150 mm; and
Not accepted: the char length is longer than 150 mm.
[0091]
(2) Flame Retardant Durability
The flame retardant durability refers to the flameproofness of a separating
CA 02798928 2012-11-07
Your Ref.: JGP-565/PCT
Our Ref.: F11-052PCT
membrane that has been immersed in warm water at 50 C for 5 hours and dried,
after
which the separating membrane has been subjected to a test in accordance with
the
J1S-Z-2150-A method. The reason why a test was carried out again on the
flameproofness after immersion in warm water was in order to examine the
presence
or absence of performance degradation due to the flowing out of a flame
retardant,
assuming dew condensation or the like.
Industrial Applicability
[0092]
The separating membrane of the present invention can be used for all the
applications required to have flameproofness, such as heat exchangers,
humidifiers,
dehumidifiers, and separation devices using pervaporation membranes. In
addition,
the separating membrane of the present invention can also be used for
applications
including building materials, vehicle materials, and flameproof garments such
as
firefighter uniforms and combat uniforms.
Explanation of Numerals
[0093]
10 Porous polytetrafluoroethylene membrane
20 Moisture-permeable resin layer
Composite membrane
Reinfircing meterial
12 Separating membrane
36
