CA2798928A1

CA2798928A1 - Separating membrane and heat exchanger using same

Info

Publication number: CA2798928A1
Application number: CA2798928A
Authority: CA
Inventors: Kazuhiro Marutani; Takashi Imai
Original assignee: WL Gore and Associates GK
Current assignee: WL Gore and Associates GK
Priority date: 2010-08-05
Filing date: 2011-08-04
Publication date: 2012-02-09
Also published as: WO2012018089A1; CN102933931A; JP2012037120A; AU2011286700A1; KR20130091664A

Abstract

In order to improve diaphragm flame resistance, a diaphragm (12) layers a reinforcing material (40) and a composite film (30) of a porous polytetrafluoroethylene film (10) and a moisture-permeable resin layer (20), the mass per unit area of the porous polytetrafluoroethylene film (10) being 0.5 g/m2 to 7 g/m2 inclusive and the moisture-permeable resin layer (20) containing a moisture-permeable resin and 5 masses to 60 masses inclusive of a fire retardant for every 100 masses of the moisture-permeable resin.

Description

Our Ref.: F11-052PCT
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]

Our Ref: F11-052PCT
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 Our Ref.: F11-052PCT
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 Our Ref: F11-052PCT
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]

Our Ref.: F11-052PCT
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.

Our Ref. F11-052PCT

[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, Our Ref: F11-052PCT
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 Our Ref.: F11-052PCT
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 Our Ref.: F11-052PCT
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]

Our Ref.: F11-052PCT
[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 Our Ref.: F11-052PCT
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 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 Our Ref.: F11-052PCT
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 Our Ref: F11-052PCT
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 Our Ref.: F11-052PCT
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.

=CA 02798928 2012-11-07 Our Ref.. F11-052PCT

[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-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 Our Ref.: F11-052PCT
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

Our Ref.: F11-052PCT
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).

Our Ref: F11-052PCT

[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 Our Ref: F11-052PCT
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]

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 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 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 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 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 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.

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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 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]

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]

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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

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]

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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.

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]

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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 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

Claims

[Claim 1]

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, 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 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.
[Claim 2]

The separating membrane according to claim 1, wherein the reinforcing material is fixed to the moisture-permeable resin layer.
[Claim 3]

The separating membrane according to claim 1 or 2, wherein the moisture-permeable resin is a hydrophilic polyurethane resin.
[Claim 4]

The separating membrane according to any of claims 1 to 3, wherein the reinforcing material is formed of fibers.
[Claim 5]

The separating membrane according to claim 4, wherein the fibers are in the form of a nonwoven fabric.
[Claim 6]

The separating membrane according to any of claims 1 to 5, wherein the reinforcing material contains a frame retardant added thereto.
[Claim 7]

The separating membrane according to any of claims 1 to 6, wherein the porous polytetrafluoroethylene membrane has an average micropore diameter of from 0.07 to 10 µm.
[Claim 8]

The separating membrane according to any of claims 1 to 7, wherein the frame retardant contains an inorganic compound.
[Claim 9]

The separating membrane according to claim 8, wherein the frame retardant contains an antimony compound or a metal hydroxide as the inorganic compound.
[Claim 10]

The separating membrane according to any of claims 1 to 9, wherein the frame retardant comprises a phosphorous type frame retardant.
[Claim 11]

The separating membrane according to any of claims 1 to 10, wherein the reinforcing material contains thermo-fusible resin fibers.
[Claim 12]

The separating membrane according to claim 11, wherein the thermo-fusible resin fibers are polyester type fibers.
[Claim 13]

The separating membrane according to any of claims 1 to 10, wherein the reinforcing material contains thermo-infusible fibers.
[Claim 14]

The separating membrane according to claim 13, wherein the thermo-infusible fibers are carbon fibers.
[Claim 15]

The separating membrane according to claim 13, wherein the thermo-infusible fibers are thermosetting resin fibers.
[Claim 16]

The separating membrane according to claim 15, wherein the thermosetting resin fibers are polyimide fibers.
[Claim 17]

A heat exchanger comprising a separating membrane according to any of claims 1 to 16.