JP2003329391A - Porous film for temperature-humidity exchanger and method of manufacture - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a porous film for a temperature-humidity exchanger which performs superior temperature-humidity exchange, while sufficiently reducing gas permeability, and is superior in hydrolysis resistance, and also to provide a method for inexpensively manufacturing this porous film. <P>SOLUTION: This porous film 1 for the temperature-humidity exchanger is arranged between passages of two kinds of gas flows in the temperature-humidity exchanger for performing heat exchange and humidity exchange between the two kinds of gas flows. The porous film 1 is composed of a fiber material, and a surface of the fiber material is coated with a hydrophilic material. This porous film is obtained by refining the surface of the fiber material into a hydrophilic property by coating the surface of the fiber material with metallic oxide deposited from a metallic fluoride containing aqueous solution by soaking the fiber material in the metallic fluoride containing aqueous solution. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous membrane for a temperature / humidity exchanger and a method for producing the same. The present invention relates to a porous membrane for a temperature / humidity exchanger having excellent hydrolyzability and a method for producing the porous membrane at low cost.

[0002]

2. Description of the Related Art A temperature / humidity exchanger for performing heat exchange and humidity exchange between two kinds of gas streams is described in, for example, an air conditioning standard textbook (Ohm Co., Ltd., p157, issued in February 1980). As is well known in the art. FIG. 7 is a diagram for explaining the internal structure of a conventional fixed temperature / humidity exchanger for air conditioning. The temperature / humidity exchanger of FIG. 7 is formed by laminating a moisture permeable film 14 that transmits heat and humidity and a spacing plate 13 of special kraft paper, and between them, the supply gas and the gas to be humidified are orthogonal to each other. Both pass through so that they do not come into contact with each other, and at that time, heat and water contained in the supply gas of high temperature and humidity move to the gas to be humidified through the moisture permeable membrane 14.

Here, in a fuel cell, as is generally well known, a pair of electrodes are brought into contact with each other through an electrolyte membrane, and fuel is supplied to one electrode and an oxidant is supplied to the other electrode. A device that directly converts chemical energy into electrical energy by electrochemically reacting the oxidation of fuel in the cell. There are several types of such fuel cells depending on the type of electrolyte. Recently, a so-called solid polymer type fuel cell using a solid polymer membrane as an electrolyte has been attracting attention as a relatively high performance fuel cell. . For example, in a fuel cell using a proton conductive solid polymer membrane as an electrolyte, a fuel gas (for example, hydrogen gas) is supplied to the anode electrode and an oxidant (for example, air or oxygen gas) is supplied to the cathode electrode. Extract current from the circuit. At this time, the following reactions occur. Cathode reaction: H ₂ → 2H ⁺ + 2e ⁻ (1) Anode reaction: 2H ⁺ + 2e ⁻ + 1 / 2O ₂ → H ₂ O (2)

As described above, hydrogen becomes a proton by the cathode reaction and passes through the solid polymer membrane together with water. The protons then migrate to the anode where they react with oxygen to produce water. At this time, the conductivity of the alternating polymer membrane that conducts hydrogen ions is exhibited by the inclusion of water, so that the solid polymer membrane must be kept wet in order to smoothly cause the above reaction. Therefore, in the operation of the fuel cell as described above, it is necessary to humidify the fuel gas.

Since it is necessary to secure moisture and supply heat to humidify the gas, a method of recovering and using moisture in exhaust gas of a fuel cell by exchanging temperature and humidity is disclosed in, for example, Japanese Patent Publication No. 63-63.
No. 18304. According to this technique, the exhaust gas of the fuel cell, which is still kept at high temperature and humidity, is brought into contact with the fuel gas in the temperature / humidity exchanger, and heat and moisture are transferred to the fuel gas.

[0006]

The polymer electrolyte fuel cell is often operated at a relatively high temperature of 70 ° C. to 80 ° C., and the dew point of the supply gas must be humidified to a high dew point of about 70 ° C. There is. However, for example, in a conventional temperature / humidity exchanger using the above-mentioned kraft paper, the strength of the paper such as kraft paper decreases due to hydrolysis under high temperature and high humidity conditions, and the kraft paper collapses within a few days and is put to practical use. There was a problem that I could not do it.

Further, when a porous membrane is used as the temperature / humidity exchange membrane in the temperature / humidity exchanger, the air permeability of the porous membrane is generally high, and gas leakage occurs between the supply gas and the humidified gas. There is a drawback that the supply amount of the humidified gas is reduced. As a method for solving such a problem, Japanese Patent Laid-Open No. 7-13
Japanese Patent No. 3994 proposes a method of impregnating a polymer resin porous film with a polymer moisture-permeable resin. However, this method has a drawback that although the moisture permeability of the polymer blocks the pores of the porous membrane, the gas permeability is low, but the moisture permeability is deteriorated. In particular, in a fuel cell in which it is necessary to humidify the fuel gas up to a high dew point, it is not preferable to lower the moisture permeability. In addition, in the operation of a fuel cell in which a gas temperature of 80 ° C. and a dew point of 70 ° C. and a supply of high-humidity fuel gas are required, when an organic substance such as a polymer resin is used for the porous membrane of the temperature / humidity exchanger, Deterioration of the substrate due to decomposition is unavoidable.

Therefore, an object of the present invention is to provide a porous membrane for a temperature / humidity exchanger which is capable of exchanging excellent temperature / humidity while keeping air permeability sufficiently low and is excellent in hydrolysis resistance. Another object of the present invention is to provide a method capable of producing the porous membrane for a temperature / humidity exchanger at low cost.

[0009]

The invention of claim 1 is arranged between flow paths of two kinds of gas flows in a temperature and humidity exchanger for performing heat exchange and humidity exchange between the two kinds of gas flows. A porous membrane for a temperature / humidity exchanger, wherein the porous membrane is made of a fibrous material, and the surface of the fibrous material is coated with a hydrophilic material. . The invention of claim 2 is the porous membrane for a temperature / humidity exchanger according to claim 1, wherein the hydrophilic material is titanium oxide. According to a third aspect of the present invention, the fiber material is immersed in an aqueous solution containing a metal fluoride, the surface of the fiber material is coated with a metal oxide deposited from the aqueous solution containing a metal fluoride, and the surface of the fiber material is made hydrophilic. The method for producing the porous membrane for a temperature / humidity exchanger according to claim 1, which has a step of reforming. The invention of claim 4 is the manufacturing method according to claim 3, wherein the metal oxide is titanium oxide.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1. The temperature-humidity exchanger of the present invention can be used for the purpose of performing heat exchange and humidity exchange between two types of gas streams, as in the conventional case,
A porous membrane is arranged between the flow paths of the two gas flows. The fiber material constituting the porous membrane is not particularly limited, but those having high heat resistance are preferable, for example, polyphenylene sulfide, polyester, vinylon, polypropylene, acrylic, rayon, cellophane, polyvinyl alcohol, polysulfone, polyimide, polycarbonate and the like. Can be mentioned. Further, in the present invention, the fibrous material is coated with the hydrophilic material to increase the corrosion resistance, so that paper (cellulose) having a problem in durability can be used. In the porous membrane 1, it is preferable that the distance between the fibers balances the surface tension of water, that is, the distance between the fibers is such that a so-called wet seal in which voids between the fibers are filled with water is formed. . The porosity of the fiber material is particularly preferably 50 to 80%.

A method of coating a fiber material with a hydrophilic material is a so-called liquid phase deposition method (LPD: Liquid Phase Deposition) in which an oxide thin film is deposited from a metal fluoride aqueous solution.
tion method) is preferred. In this case, a metal oxide is used as the hydrophilic material. Examples of the metal oxide include titanium oxide (TiO ₂ ), aluminum oxide (Al ₂ O ₃ ), silicon dioxide (SiO ₂ ), and the like. Among them, titanium oxide (Ti 2
O ₂ ) is preferred. The hydrophilicity referred to in the present invention is exemplified by a contact angle of 0 to 5 degrees with respect to the solid surface. The liquid phase deposition method is a known method and is disclosed in, for example, JP-A-59-1.
No. 41441, JP-A-1-93443, JP-A-3-285821, JP-A-3-285822, JP-A-4-26516, and JP-B-7-352.
No. 68 publication and the like. Specifically, the liquid phase deposition method is a method of immersing a fiber material in an aqueous solution containing a metal fluoride, for example, an aqueous solution prepared by adding boric acid or aluminum to an aqueous solution of titanium ammonium fluoride or titanium hydrofluoric acid, Is coated with a metal oxide that precipitates from a metal fluoride-containing aqueous solution to make the surface of the fiber material hydrophilic. The liquid phase deposition method is capable of treating a large amount of fiber material at once; even if the fiber material has a complicated shape, it is possible to uniformly coat the inside thereof; Adhesion is relatively good Compared with the CVD method and the PVD method, it is not necessary to use an expensive apparatus, and further, compared to the dip coating method and the spin coating method by the sol-gel method, the fibrous material is simply immersed in the treatment liquid. Is low; the coating can be performed at a temperature close to room temperature, so that less processing energy is required; and the like. When the liquid phase deposition method is adopted, it is preferable to select, as the fiber material, a material that does not easily react with the metal fluoride aqueous solution.

As a further specific example, the liquid phase deposition method in the present embodiment will be described. (NH ₄ ) ₂ TiF
₆ (Ammonium hexafluorotitanate) 0.1mol / l, boric acid
An aqueous solution containing 0.2 mol / l was put in an appropriate container and mixed to obtain a treatment liquid. Vertical, horizontal 20 cm square, thickness 50 μm, porosity 5
A 0% PPS (polyphenylene sulfide) meltblown non-woven fabric was immersed in the treatment solution, defoamed, and then kept at 30 ° C. for 20 hours. After the treatment, wash with pure water, and
It was dried at 0 ° C. to prepare a porous film. FIG. 1 is a microscopic enlarged photograph of fibers of a PPS meltblown nonwoven fabric after being treated by such a liquid phase deposition method. According to FIG. 1, the fiber surface 10 was coated with a titanium oxide thin film and exhibited an interference color due to the titanium oxide layer. In addition, from the weight difference before and after the treatment, the PPS melt blown nonwoven fabric per 1 cm ²
It was found that 1.5 mg of titanium oxide was coated. Approximately 0.38 × 10 ^-3 cm ^{3 when} converted to volume from the specific gravity of titanium oxide
Therefore, the coating did not reduce the pore volume of the PPS meltblown nonwoven fabric. Then unprocessed
PPS melt blown nonwoven fabric and PPS after treated by liquid phase deposition method
The melt blown nonwoven fabric was dipped in pure water for 10 seconds to compare the amount of water absorption by the gravimetric method. The treated PPS melt blown nonwoven fabric is
About 10 times as much water was retained per unit area as compared with the untreated one, and the surface of the treated PPS melt blown nonwoven fabric was uniformly wet-sealed with water.

FIG. 2 is a diagram for explaining an example of the internal structure of the temperature / humidity exchanger using the porous membrane manufactured in this embodiment. In FIG. 2, reference numeral 1 is a porous membrane made of the fiber material produced as described above, and the length and width are 20c.
It is a PPS (polyphenylene sulfide) meltblown nonwoven fabric with m-square, thickness of 50 μm and porosity of 50%. 2 is a separator that supports the upper and lower porous membranes 1 and has a thickness of 250
It is a corrugated PET (polyethylene terephthalate) film of μm. In the present embodiment, ten separators 2 are provided between nine porous membranes 1 and
A laminated body composed of the separator 2 and the separator 2 was formed (note that not all layers are shown in FIG. 2) to provide a temperature / humidity exchanger. In the laminated body, the gas flow path 4 in which the gas flow is in the direction of arrow 21 and the gas flow is in the direction of arrow 22.
The gas flow paths 3 are alternately formed so as to be oriented in the above direction, and are laminated respectively. Then, and the flow of the moist gas is indicated by the arrow 22.
The flow of the dry gas was set so as to be in the direction of arrow 21, and the degree of humidity exchange was examined.
FIG. 3 is a graph showing the relationship between the dew point of the supply gas (wet gas) and the dew point of the humidified gas (dry gas) at the gas outlet of the temperature / humidity exchanger. In the graph of FIG. 3, the solid line shows the result of the temperature / humidity exchanger of the present embodiment. The broken line is an example (comparative example) in which a PPS meltblown nonwoven fabric not coated with titanium oxide was used as a porous membrane. It can be seen that the temperature / humidity exchanger of the present embodiment has a higher dew point of the gas to be humidified than the comparative example, and the humidity exchange efficiency is higher. Therefore, the porous membrane of the present invention,
In particular, it can be used for exhaust gas moisture recovery of a fuel cell that requires a high reaching dew point of the gas to be humidified.

Subsequently, a positive pressure of 0 to 40 kPa is applied to the outlet of the humidified gas of the temperature / humidity exchanger, the amount of gas flowing out from the outlet of the supply gas is measured, and the gas leakage rate in the temperature / humidity exchanger ( The rate of increase in the amount of gas flowing out from the outlet of the supply gas) was measured. FIG. 4 is a graph showing the relationship between the pressure and the leak rate. The temperature-humidity exchanger of the comparative example has 1
It can be seen that the temperature / humidity exchanger according to the present embodiment has a slow increase in the leak rate as compared with the leak rate of 100% at about 0 kPa. According to further experiments by the inventors, the temperature-humidity exchanger according to the present embodiment does not leak between the supply gas and the humidified gas even when a positive pressure of about 200 mmAq is applied to the inside. I found out. It is considered that the reason is that the water content in the supply gas is captured by the porous membrane and a so-called wet seal is formed in which the voids between the fibers of the fibrous material forming the porous membrane are filled with water.

FIG. 5 is a diagram showing the relationship between the fiber material of the porous membrane and the droplets in the supply gas in the temperature and humidity exchangers of this embodiment and the comparative example. In the porous membrane of the temperature / humidity exchanger of the comparative example of FIG. 5 (a), since the surface of the fiber material is not hydrophilic, the droplets 5 are not captured by the fibers 6 and the surface area where the droplets 5 come into contact with gas is It is getting smaller. Also, many voids exist between the fibers 6 to increase the gas leakage rate. Conversely, FIG.
In the porous membrane of the temperature / humidity exchanger of this embodiment of (b), since the surface of the fiber material is hydrophilic, the droplets are captured by the fibers 6 and the surface area where the droplets and the gas come into contact with each other is large. . Further, since the droplets captured by the fibers fill the voids of the fibers and form the wet seal 7, the leak rate becomes small.

Embodiment 2. The porous membrane prepared in Embodiment 1 and the porous membrane of the comparative example were put in an appropriate container,
The sample was immersed in warm water at 0 ° C for 1 month, and the hydrolysis resistance was compared.
The sample after the immersion was cut into a strip of 20 × 100 mm to form a test piece, and a tensile test was performed. FIG. 6 is a graph showing a load curve in a tensile test of a test piece. Figure 6
In the above, it can be seen that the test piece of the present embodiment can withstand the load even when the displacement amount of the test piece length is larger than that of the comparative example, and is excellent in hydrolysis resistance. On the contrary, in the comparative example, it was confirmed that the fibers of the porous membrane were brittle and deteriorated. According to the present embodiment, since the hydrolysis resistance of the porous membrane used in the present invention is remarkably improved, it can be seen that a temperature / humidity exchanger having a long life can be obtained.

Embodiment 3. (NH ₄ ) ₂ TiF ₆ (ammonium hexafluorotitanate) 0.1 mol / l, boric acid 0.2 mol
An aqueous solution containing / l was put in an appropriate container and mixed to obtain a treatment liquid. 50 μm thick PPS melt blown non-woven fabric with 50% porosity and 50 μm thick Japanese paper (cellulose) with 50% porosity
Then, a vinylon film having a thickness of 40 μm and a porosity of 50% was immersed in the treatment solution, defoamed, and then maintained at 30 ° C. for 20 hours. After the treatment, wash with pure water, 60 ℃
Dried in. The treated samples were all coated with a titanium oxide thin film and exhibited an interference color due to the titanium oxide layer. From the weight difference before and after the treatment, 1.5 mg of titanium oxide was added to 1 cm ^{2 of} washi paper per 1 cm ^{2 of} PPS melt blown nonwoven fabric.
So, 1.55 mg of titanium oxide is a vinylon film 1
It was found to be coated with 1.53 mg of titanium oxide per cm ² . Therefore, the coating did not reduce the pore volume of the sample. Also,
PPS melt blown non-woven fabric in the treatment liquid for 10 hours or 3
The one that had been immersed for 0 hours was prepared and compared with the one that had been treated for 20 hours. From the weight difference before and after the treatment, per 1 cm ^{2 of} PPS melt blown nonwoven fabric, 0.8 mg of titanium oxide was treated for 10 hours, and for 20 hours treated.
1.5 mg of titanium oxide is 2.2 after 30 hours treatment
It was found that mg of titanium oxide was coated, and it was found that the coating amount increased in proportion to time. As a result, metal oxide thin films can be formed on various porous membranes, and coatings of any thickness can be made. Therefore, a wide range of choices can be made in selecting the porous membrane material, which is inexpensive and has a long life. The temperature and humidity exchanger has come to be obtained.

[0018]

According to the invention of claim 1, in the temperature and humidity exchanger for performing heat exchange and humidity exchange between two kinds of gas streams,
A porous membrane for temperature-humidity exchanger arranged between the flow paths of seed gas flows, wherein the porous membrane is made of a fiber material, and the surface of the fiber material is coated with a hydrophilic material. Since it is a porous membrane for temperature-humidity exchanger characterized by, the water in the feed gas is trapped in the voids of the fiber material to form a wet seal by water, by which,
For example, compared with a water-repellent fiber material, the surface area of water is large, so that the evaporation rate is high, the air permeability is low, and the moisture permeability is high. Therefore, according to the invention of claim 1, it is possible to provide a favorable temperature / humidity exchange with sufficiently low air permeability, and to provide a porous membrane for a temperature / humidity exchanger having excellent hydrolysis resistance. . The temperature / humidity exchanger provided with such a porous membrane can be suitably used, for example, for humidifying the fuel gas supplied to the fuel cell.

The invention of claim 2 is the porous membrane for a temperature-humidity exchanger according to claim 1, wherein the hydrophilic material is titanium oxide, so that the chemical stability of the porous membrane is very high and the resistance is high. The hydrolyzability is further enhanced. Therefore, the temperature / humidity exchanger provided with such a porous membrane has a long service life.

According to a third aspect of the present invention, the fiber material is immersed in the metal fluoride-containing aqueous solution, the surface of the fiber material is coated with a metal oxide deposited from the metal fluoride-containing aqueous solution, and the surface of the fiber material is coated. The method for producing a porous membrane for a temperature / humidity exchanger according to claim 1, which has a step of modifying to hydrophilicity, so that a metal oxide thin film is formed regardless of the characteristics of the fiber material forming the porous membrane. Since it is possible to form a thin film having an arbitrary thickness, it is possible to select an inexpensive material in selecting the porous film material. Therefore, it is possible to perform favorable temperature / humidity exchange while keeping air permeability sufficiently low, and it is possible to manufacture a porous membrane for a temperature / humidity exchanger excellent in hydrolysis resistance at low cost.

The invention of claim 4 is the production method according to claim 3 in which the metal oxide is titanium oxide, so that the chemical stability of the porous membrane becomes very high and the hydrolysis resistance is further improved. Increase. Therefore, a long-life temperature / humidity exchanger can be provided at low cost.

[Brief description of drawings]

FIG. 1 is a microscopic enlarged photograph of fibers of a PPS meltblown nonwoven fabric after being treated by a liquid phase deposition method.

FIG. 2 is a diagram for explaining an example of an internal structure of a temperature / humidity exchanger using the porous membrane manufactured in the first embodiment.

FIG. 3 is a graph showing the relationship between the dew point of the supply gas (wet gas) and the dew point of the humidified gas (dry gas) at the gas outlet of the temperature / humidity exchanger.

FIG. 4 is a graph showing a relationship between a supply gas pressure and a leak rate.

FIG. 5 is a diagram showing the relationship between the fiber material of the porous membrane and the droplets in the supply gas in the temperature and humidity exchangers of Embodiment 1 and Comparative Example.

FIG. 6 is a graph showing a load curve in a tensile test of a test piece according to the second embodiment.

FIG. 7 is a view for explaining the internal structure of a conventional fixed temperature / humidity exchanger for air conditioning.

[Explanation of symbols]

1 porous membrane, 2 separator, 3, 4 gas flow path, 5
Droplet, 6 fiber, 7 wet seal, 10 fiber surface.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) // C08L 101: 00 C08L 101: 00 (72) Inventor Osamu Hiroi 2-3-2 Marunouchi, Chiyoda-ku, Tokyo No. Sanryo Electric Co., Ltd. F term (reference) 4F074 AA24 AA44 AA46 AA65 AA70 AA74 AA87 AC23 CB03 CB13 CB27 DA49

Claims (4)

[Claims] 1. A porous membrane for a temperature / humidity exchanger, which is disposed between flow paths of the two types of gas streams in a temperature / humidity exchanger that performs heat exchange and humidity exchange between the two types of gas streams, A porous membrane for a temperature-humidity exchanger, wherein the porous membrane is made of a fiber material, and the surface of the fiber material is coated with a hydrophilic material. 2. The hydrophilic material is titanium oxide.
The porous membrane for a temperature / humidity exchanger according to. 3. The surface of the fiber material is modified to be hydrophilic by immersing the fiber material in an aqueous solution containing the metal fluoride and coating the surface of the fiber material with a metal oxide that precipitates from the aqueous solution containing the metal fluoride. The method for producing the porous membrane for a temperature / humidity exchanger according to claim 1, further comprising: 4. The metal oxide is titanium oxide.
The manufacturing method described in.